Training Volume, Intensity, and Your Libido - How Bad is It? Who Read the Study Knows: It's not Just About Cardio ... !

Both, the male and female libido are at risk by overtraining. So don't continue your daily 1h stairmaster sessions, ladies!

You may have seen this study elsewhere on Facebook before... and I have to apologize that I am late to the party, but it disappeared in the "to write about" pile on my virtual desktop and resurfaced only today when I didn't find another recent study worth writing about.

Enough of the excuses, though. After all, the SuppVersity is the place to get all the study details - including an assessment of its practical relevance and a brief glimpse at relevant related research. What? No, I bet you didn't get that in one of the reposts to the abstract on PubMed, did you? Or did you understand what a low, medium or high "total intensity" was when you read those copy and paste jobs? It's not simply the VO2max. If you thought so, you probably misunderstood the study.

Overly frequent use of intensity techniques will also put you at higher risk of libido loss:

What's the Latest on Failure?

Drop-Sets: Vol-ume ↑, Gains ↕

Pre-Exhaustion = Growth!?

Full ROM ➯ Full Size Gains!

Super-Setting - Yes, but How?

Eccentrics For Excellent Gains?

Now, without further delay, let's take a look at what the study actually did. To study the associations between aspects of endurance exercise training and the sexual libido in healthy men using a cross-sectional online survey was conducted. Since this is the first study of its kind, a new online survey questionnaire had to be developed. As the scientists explain, ...

"[t]he questionnaire was based upon pre-existing validated questionnaires and use to assess elements of physical characteristics, exercise traininghabits and libido of participants (n=1077). Three evidence-based categories were created for the primary outcome of total libido score and low, normal, and high response categories set. The high and normal categories were combined to form a high/normal score group and the low category formed a low score group" (Hackney 2017). 

The fact that it "was based on pre-existing validated questionnaires", namely the ADAM, the SDI-2 and the AMS questionnaire for the libido-, and the IPAQ and the Baecke questionnaire for the physical activity, i  quite important. Even though this gives it an air of authority, we have to keep in mind that questionnaires can be pretty misleading (de Yébenes Prous 2009; Rosen 2004) and eventually the one at hand is non-validated - regardless of the excellent Cronbach's alpha of 0.70 to 0.96 (Tavakol 2011) and thus a high internal consistency of the individual constituents.

Table 1: The physical and exercise training characteristics of the participants (Hackney 2017).

If we assume that there were no built-in problems with the questionnaire, and appreciate that the scientists recruitment via sports clubs, national sports organizations, university athletic departments, and sporting magazines was decently successful (N = 1077 participants filled out the questionnaires | see Table 1 for participant data | mind the age groups: 1: < 18 years = not included in analysis; 2: 18-25; 3: 26-40; 4: 41-55; 5: ≥ 56), I guess we can live pretty well with the correlations the scientists calculated between their three evidence-based categories: duration, intensity of the workouts, age and total libido score (all featuring low, normal, and high response category sets).

Update on the significance of the results for women:On Facebook, Lillian rightly asked how I could claim that women would have to avoid hours of medium-to-high intensity cardio based on a study in men. Here's a brief reminder of what I've discussed in other articles about overtraining and the (female) athlete triad. There's very good evidence that - unlike resistance training - high(er) intensity long-duration "cardio" messes with the female reproductive system and female libido (Boyden 1983; Warren 1992 & 2001). Later this week I will discuss a recent study showing that this is not the case for frequent intense resistance training, though.

The fact that all participants were men, by the way, reduces the significance of the absolute results (i.e. the hours of exercise per week and the so-called "total intensity", but the general trend(s) should be similar for women). Unlike men, however, women will yet not just lose their libido (early phase), but also notice concurrent irregularities in their menstrual cycle (later phase | see red box above).

Table 2: Part of the dataset the scientists generated - I will dissect and discuss the relevant parts below (Hackney 2017).

A problem that we cannot ignore, though, is that the high and normal categories were combined to form a high/normal score group, while the low category formed a low score group before the odds ratios (OR = how likely is it that...) - to identify what "promotes" your libido is thus not possible. What we can tell, is what will keep you in either the normal or the high libido zone and that's:

• low "chronic duration" (1-16h per week; 4-fold more likely) and medium "chronic duration" (20-40h per week; 2.5-fold more likely) compared to high "chronic duration" training (50 – 100h per week for years)
• training at low "total intensity" (0-1100 VO2max x hours per week; 6.9-fold more likely) and medium intensities (1140-2480 VO2max x hours per week; 2.8-fold more likely) compared to subjects with a high "total intensity (2500-1000 VO2max x hours per week).

So what do you make of the results? Well, the total intensity was a computed variable representative of a number of training sessions at a low, moderate, hard intensity times the hours of each per week using the well-known VO2 cutoffs of low ≤35% of VO2max, moderate ~50% of VO2max, and high ≥70% of VO2max. 

Figure 1: Odds ratio of having a normal or high libido with low and medium duration, intensity, and age (Hackney 2017).

This is an important insight, after all, it goes against the notion that "steady state cardio [even walking on the treadmill as a cool-down] is generally bad" that many people who shared this post online evoked (deliberately or not) - a HIIT session of only 10 minutes at 95% of VO2max would, after all, generate a higher "total intensity" than a steady state session of walking at 30% of your VO2max on the treadmill if both had been done five times a week in the past five years which was the median value. 

Figure 2: Intensity and duration for different types of training done five times per week for five years plotted alongside the calculated "total intensity" values and information about the risk of libido loss (Hackney 2017).

In general, however, there's no debating, the highest "total intensity" levels are probably going to be generated by the typical "fat burning workouts" I have been criticizing for years, i.e. the 45-90 minutes on the treadmill at ~70% of your VO2max, in the alleged "fat burning zone". An even higher value would be observed for the Crossfit addict doing 5x60 min workouts powering the weights up and down at 80% of his/her VO2max per week (see Figure 2 for a comparison of the different exercise modes and the corresponding "calculated intensity").

Much easier to understand than the total intensity is the "chronic duration". Being computed as the arithmetic product of the time you spend in the gym or elsewhere doing any sports it is a simple proxy of your total training volume irrespective of the form and intensity of your training that - and this is important - does not involve the number of years you've been following this approach already (for me that is a questionable methodological choice the scientists made with the previously discussed "total intensity"). The unmistakable message here is: the more you work out on a weekly basis (or the less you recover per workout hour?), the higher your risk will be.

Could something as simple as a saliva test tell you if you or your clients are overtraining? I mean, common sense would dictate that cortisol, free T and IL-6 should tell us something. Learn more in my 2016 article "Overtrained or in the Zone? Tests & Analyses of Samples of Athletes' Saliva Shall Help Determine Objective Criteria" | more

So, you better limit your weekly sports activity to 16h total!? True, that's the message the non-exercise and non-intensity specific "chronic duration" data sends. If you train more than 50hrs per week your risk of suffering from a low libido is maximal. On the other hand, people who train only 20-40h per week and 1-16h per week are 4x and 2.5x more likely to have either normal or even high libido ratings on the subjective tests that were used in the test at hand.

The "total intensity" data, on the other hand, is hard to interpret. It mixes training volume, intensity, and number of the years of sticking to this madness. So, don't remember the actual figures, but rather the following interpretation: the higher your intensity, the lower your training frequency, training time and the time you stick to this intensity withing your year-long periodization regimen should be.

Practically speaking this means: Yes, you can CrossFit or do the classic 1h cardio regimen five days a week for some time, but you should know that after months and years this is going to crush your libido, while 5x20 minutes walking or doing 5x10 minute of HIIT at 95% of your VO2max are not that likely to induce the same libido reduction | Comment!

References:

• Boyden, Thomas W., et al. "Sex steroids and endurance running in women." Fertility and sterility 39.5 (1983): 629-632.
• de Yébenes Prous, M. Jesús García, Francisco Rodríguez Salvanés, and Loreto Carmona Ortells. "Validation of questionnaires." Reumatología Clínica (English Edition) 5.4 (2009): 171-177.
• Hackney, Anthony C., et al. "Endurance Exercise Training and Male Sexual Libido." Medicine and science in sports and exercise (2017).
• Rosen, Raymond C., et al. "Male Sexual Health Questionnaire (MSHQ): scale development and psychometric validation." Urology 64.4 (2004): 777-782.
• Tavakol, Mohsen, and Reg Dennick. "Making sense of Cronbach's alpha." International journal of medical education 2 (2011): 53.
• Warren, MICHELLE P. "Clinical review 40: Amenorrhea in endurance runners." The Journal of Clinical Endocrinology & Metabolism 75.6 (1992): 1393-1397.
• Warren, M. P., and N. E. Perlroth. "The effects of intense exercise on the female reproductive system." Journal of Endocrinology 170.1 (2001): 3-11.

Each +30 Min/d of Physical Activity Reduce HbA1c by 11%, Protein + CHO Maintain Bone Mass, Overlooked Benefits of BFR, New Marker of Overtraining - Jan '17 Science Update

  This is what the Jan '17 Science Update has to offer? -11% HbA1c reduction per 30 minutes activity, new benefits of blood flow restricted tr., the bone protective effect of immediate post-workout whey plus carb ingestion, and a new overtraining gauge...

It's almost, February... almost and that's why today's SuppVersity article still qualifies as a January '17 research update. One that is based on the latest (ahead of print) papers from the peer-reviewed journal "Medicine & Science in Sports & Exercise" - papers about the large impact of short bouts of moderate-to-vigorous physical activity (MVPA) on the messed up glucose management of people with an increased T2DM risk, the bone-preserving effects of a mix of whey and dextrose and how this effect depends on timing, the belated and thus overlooked beneficial effects of blood flow restriction on muscular rapid force development and, last but not least, a potential new marker of overreaching and -training that could also explain the dichotomous role of IL-6 in the adaptive and maladaptive response to exercise.

Learn more about blood flow restriction at the SuppVersity

BFR for VO2 & Strength Gains

Using BFR in Periodization

BFR Precondi-tioning = Useless

Benefits of Cuffs After sets?!

No Extra-Gains W/ BFR vs. HIT

Hormonal Re-sponse to BFR

• Scientists find new marker of overreaching and potentially -training: You know that exercise will increase the levels of the allegedly "bad" cytokine IL-6. Now, as a SuppVersity reader, you will yet also know that this "cytokine" is, in fact, a "myokine" if it is released in response to muscle contractions and that it appears to figure in the hormetic response to exercise stress... or, in other words, without it, you're not going to get the adaptational response in form of strength and size gains you're training for. With that being said, studies also show that significantly elevated levels of IL-6 can also occur with overtraining and are - in this situation - a sign of dysfunctional adaptation.
  
  Recent research does now suggest that the "dichotomous nature of IL-6 signalling appears to be determined by the respective concentration of its receptors (both membrane-bound (IL-6R) and soluble (sIL-6R) forms)" (Cullen. 2017) - measuring these concentrations could thus provide important information about whether the circulating IL-6 is going to trigger a hormetic response or not. Accordingly, Cullen et al. conducted a study that investigated the response of sIL-6R to long-term training, and the relationship between sIL-6R, self-reported measures of wellbeing, and upper respiratory illness symptoms (URS) in highly-trained endurance athletes.
  

  

  Figure 1: Unlike cortisol, which has a long history as a suspected, but rarely useful overtraining gauge, sIL-6R doesn't have a circadian rhythm (see explanation in green box). This doesn't mean it's an accurate marker of overtraining, but it does mean that it is less complicated and more convenient to use, because with overtraining the circadian rhythm can be so messed up that simply measuring at the same time won't suffice to get comparable and thus useful results to gauge your training status.

  Their results are quite conclusive: Firstly, they confirmed that sIL-6R is responsive to prolonged periods of exercise training. And second- and more importantly, the subjects' sIL-6R levels varied according to the individual training volume and could be linked to common symptoms of overreaching such as high levels of stress, and/or depressed mood.
  
  This is obviously not enough to use sIL-6R as an overtraining gauge. With future studies that determine the level of sIL-6R in overreaching and overtraining athletes, it may thus be possible to distinguish between these states (and regular training) and to use this information to optimize athletes and gymrats workout routines. 
• Rapid Force Capacity (RFC) increases sign. with blood flow restriction, but study shows: Adaptation takes time: This observation Nielsen, et al. (2017) made in their recent study is an important one, because it implies that previous studies on the effects of blood flow restriction + low-intensity training may simply have missed the beneficial effects when they measured (just as Nielsen, et al. did it, too), the adaptational response only 5 days after having subjects participate in a series of standardized workouts.
  
  In the study at hand, this series constituted of twenty-three training sessions which were performed within 19 days. In all 10 male subjects (22.8+/-2.3 years) who performed four sets of knee extensor exercise (20%1RM) to concentric failure during concurrent BFR of the thigh (100mmHg), and the eight work-matched controls (21.9+/-3.0 years) who trained without BFR (CON), the scientists tested the maximal slow and fast knee joint velocity muscle strength and rapid force capacity (e.g. RTD) as well as evoked twitch contractile parameters before and after the study.
  

  

  Figure 2: Changes in rate of force development (left) and mean muscle fibre area (right | Nielsen. 2017).

  Now, that's nothing new. What was new, however, is that they tested before (Pre) and 5 and 12 days after training (Post5, Post12). In conjunction with the data from the biopsies, Nielsen et al. were thus able to detect the improved rate of torque development for the first time. The sign. difference in muscle fiber area (Figure 2, right), on the other hand, is - interesting as it may be - no news: after all, we're comparing light load with BFR to light load w/out BFR and not, as many other studies did, light load BFR to regular high load training, where time and again the regular training group saw the greater muscle increases.
• Each extra 30 minutes of daily moderate to vigorous physical activity improve HbA1c of subjects at increased T2DM risk by 11%: MVPA aka "moderate to vigorous physical activity" is the buzzword of the fitness tracker generation. Now, a three-year study confirms what the medals your fitness tracker software will award to you already suggested: each minute spend moving at moderate to vigorous intensity is an investment into your health and well-being.
  
  

  

  How Accurate Are Activity Trackers? EE Data From Omron, Fitbit, Jawbone & Other Devices Reveals 10% Error & More | read the full SV article

  The above is the result of a recent study that correlated longitudinal (three-year follow-up) activity tracker data with changes of the long-term glucose marker HbA1c in a sample of 489 men and women at high risk of developing type II diabetes, participants (mean age 64.2 +/- 7.3 years, BMI 31.7 +/- 5.1, 63.4% male). And it's a result based on which the authors, Mathew McCarthy, and colleagues, rightly conclude that "[i]ncreases in MVPA and body weight were associated with a reduction and increase in HbA1c respectively, particularly in those with dysglycemia" (McCarthy. 2017).
• Immediate Protein + CHO post-workout nutrition protect your bone from the bone resorption in the hours after exhaustive running: Next to its important result, there are two things which make a recent study by Rebecca Townsend et al. particularly interesting. Firstly: The subjects were young, healthy men, not post-menopausal women as in so many other bone health studies; and second- and not less importantly, the study tested both the efficacy of a mix of 1.5g/kg dextrose + 0.5g/kg whey as a means to reduce bone resorption (=calcium leeching) markers and the effects of timing.
  

  

  Figure 3: Overview of the study design, note that active treatment or PLA were administered at three different time points with two servings of placebo ensuring that the subjects could not differentiate between the immediate supplementation, the 2h-post and 4h-post supplementation trial (Townsend. 2017).

  And guess what. The study, in the course of which the dextrose + whey drinks were administered either before or after a placebo drink immediately or 2h after the run (see Figure 3) did not just confirm that the nutrient mix can ameliorate and shorten the exercise-induced (75% VO2Max run to exhaustion) increase in the bone resorption markers β-CTX and P1NP, it also found that this effect is time-dependent with the administration of the dextrose + whey mix right after the workout having more beneficial effects than taking it 2h post. With the immediate consumption reducing the levels below pre-exercise levels (-22% to -61%) within 1h, while it remained elevated with the placebo drink and/or in the DF group in which the supplement was consumed 2h after the workout. Now all that could well be a mere time-shift in the bone anabolic response. The scientists' observation that "[t]he overall β-CTX response was significantly lower in the IF trial than the DF trial (P=0.019, d=0.37) and the PLA trial (P≤0.001, d=0.84)" (Townsend. 2017) does however clearly suggest a definite benefit of immediate (IF) vs. postponed (DF and PLA) nutrient consumption after exhaustive workouts.
  
  In this context, however, it is important to realize that that, eventually, i.e. 3-4h after the run, the level of β-CTX decreased to similar below pre-test levels in all groups. Practically speaking this means that the net effect of a single session of exhaustive exercise on the young men's bone was almost certainly positive, irrespective of whether and when they ingested the supplement.

What's the take away of the studies in this Science Update: For me personally, the most important lesson comes from the MVPA study by McCarthy et al. (2017). A mere 30 minutes of "exercise" (even fast walking would qualify) is after all an easily manageable workload of that will contribute to statistically and, more importantly, clinically significant improvements in blood glucose management.

Drop the weights, grab the shake! Timing matters for advanced trainees.

Sort of surprising was the time-dependence of the beneficial effects of a dextrose + whey mix on bone resorption after exhaustive running in young male subjects. As I hinted at in the discussion of the study, however, we got to be careful not to mistake a timeshift in the response for an actual improvement.

Imho, future (best longitudinal studies) should investigate the net effect on bone mass to avoid a similar confusion as we've had them for protein supplements of which the majority of studies refutes that their ingestion in the immediate vicinity of the workout would improve your gains.

Last but not least, there's Nielsen's BFR study, which doesn't just prove another hitherto overlooked benefit of blood flow restricted low-intensity training, but also constitutes a lesson in study design, which reminds us that the timing of a retest will often determine if you find an effect or not. Apropos timing, while the latter may matter less for sIL-6R data than it does for cortisol, there's still a lot of research necessary to confirm the validity of this new marker of overreaching and -training and develop reliable tests for athletes and gymrats | Comment on Facebook!

References:

• Cullen, Tom; Thomas, Andrew W.; Webb, Richard; Phillips, Thom; Hughes, Michael G. "sIL-6R Is Related to Weekly Training Mileage and Psychological Well-being in Athletes." Medicine & Science in Sports & Exercise: Post Acceptance: January 24, 2017.
• McCarthy, Matthew; Edwardson, Charlotte L; Davies, Melanie J; Henson, Joseph; Gray, Laura; Khunti, Kamlesh; Yates, Thomas. "Change in Sedentary Time, Physical Activity, Bodyweight, and Hba1c in High-Risk Adults." Medicine & Science in Sports & Exercise: Post Acceptance: January 24, 2017.
• Nielsen, Jakob Lindberg; Frandsen, Ulrik; Prokhorova, Tatyana; Bech, Rune Dueholm; Nygaard, Tobias; Suetta, Charlotte; Aagaard, Per. "Delayed Effect of Blood-Flow-Restricted Resistance Training on Rapid Force Capacity." Medicine & Science in Sports & Exercise: Post Acceptance: January 23, 2017. 
• Townsend, Rebecca; Elliott-Sale, Kirsty J.; Currell, Kevin; Tang, Jonathan; Fraser, William D.; Sale, Craig. "The Effect of Postexercise Carbohydrate and Protein Ingestion on Bone Metabolism." Medicine & Science in Sports & Exercise: Post Acceptance: January 24, 2017.

Overtrained or in the Zone? Tests & Analyses of Samples of Athletes' Saliva Shall Help Determine Objective Criteria

Could something as simple as a saliva test tell you if you or your clients are overtraining? I mean, common sense would dictate that cortisol, free T and IL-6 should tell us something.

Salivary testosterone, cortisol, and interleukin-6, those are the three parameters Travis Anderson and colleagues had on their list of candidates when they conducted their latest study at the University of North Carolina (Anderson. 2016).

As you will remember from previous articles I wrote about overtraining. The only decently reliable method of seeing it coming is to assess you heart rate variability. On the other hand, athletes who are complaining of general fatigue and decreasing performances in the latter phase of their overtraining, when the symptoms become often almost unbearable, will also show high cortisol, low free testosterone and increased IL-6 levels.

If you want to mess with your cortisol rhythm overtraining is exactly what you "need"!

Heart Rate Variability (HRV)

ABEL Sports Test + More

Overtraining & Undereating

Calculate your Energy Intake!

Overtraining W/ Only 25min/day?

Reinvent Your Training!

It is thus only logical that the scientists assumed that it would be possible to evaluate the (overtraining) response of 20 moderate-to-highly trained young men to a standardized 6-week pre-season workout by the means of the said three parameters.

For this purpose, each subject was assessed at six separate sessions, next to their body composition, the scientists also measured the subjects' individual Recovery-Stress by the means of the standardized Recovery-Stress Questionnaire. In conjunction with the orally administered hormone / cytokine tests (always at 15:00-17:00 h) and the independently recorded training intensities and volumes (that was done by the researchers, not the subjects) on the bench, the back squat and the Olympic-style clean (+ auxiliary movements, see Table 1 | total session length including warm-up 45-60 minutes) these measurements were the basis for the scientists analysis.

Table 1: Overview of the primary and auxiliary exercises in the std. RT protocol (Anderson. 2016).

To make the subjects more overtraining-prone, the scientists kept gradually increasing the training load and began adding in conditioning runs to the workouts from week two on. The latter were done immediately after the RT workouts and consisted of 100 or 300m runs, of which the latter were replaced in week five with a speed/agility circuit that lasted another whopping 45 minutes.

Figure 1: Cortisol, IL-6 and free testosterone (left axes) and body weight (blue, right axis) development (Anderson. 2016).

As you may see with some surprise, the subjects' weight knew only one direction. Unfortunately, the body fat and lean muscle data was either only measured at baseline or simply omitted from the respective table, which holds nothing but the weight information.

Since the subjects' performance on all the prime movers increased significantly, though, we can assume that at least some of these gains were muscle - and that in spite of the significant reduction of the free testosterone / cortisol ratio and the skyrocketing IL-6 levels.

Table 2: REST-Q score by affective category (Anderson. 2016); * denotes sign. difference from baseline (p < 0.05); values for the score range from 1 = low anger, depression, etc. to 5 = high anger, depression, etc.

For the latter, it is, by the way, easy to see that the thing that "hurt" the trainees the most was the late addition of the agility work (another 45 minutes of intense aerobic workouts | -20% free T, +110% cortisol, +600% IL-6 |  note: this is in line with previous studies showing that aerobic exercise is more likely to result in overtraining than anaerobic training). Strength training alone (week 1) and combined with the sprints (weeks 2-4), on the other hand, didn't affect the alleged anabolism gauge, the testosterone / cortisol ratio, significantly.

Based on both the accepted physiological (weight, performance) and psychological (REST-Q) the subjects were, as the authors rightly point out "not symptomatic of overtraining". A conclusion that leaves us with the question...

No overtraining and still sign. markers of overtraining in the saliva? As the authors point out, there's little doubt (based on previous studies) that their workout routines should have brought the subjects - even though they were experienced weight with the performance of elite American Football athletes - to the verge of overtraining. Moreover, the hormonal changes and sign. cytokine increases in weeks 5-6, clearly indicate that the exercise regimen was taxing.

Hormonal Response to Exercise, Revisited: A Consequence, not a Determinant of Your Mood, Effort & Performance | more

The fact that the typical signs of overtraining still didn't occur (unless you count the psychological effects, which appear to be generally emotionally suppressive as signi-ficant symptoms of overtraining), is difficult to interpret. Anderson et al., however, still believe that they were on the right track. At least with IL-6, of which previous studies such as Robson-Ansley (2007) indicate(d) that it, or rather, the overall cytokine response will be sign. elevated in overtrained athletes, the scientists still believe that they've backed the right horse - albeit without knowing the magic numbers, i.e. how much does IL-6 end up over baseline to serve as a viable predictor of overtraining. Testosterone and cortisol, on the other hand, turn out to be rather useless alleged markers of anabolism and I would love if the bros would finally acknowledge that | Comment!

References:

• Anderson, Travis, Et Al. "Changes in Resting Salivary Testosterone, Cortisol and Interleukin-6 as Biomarkers of Overtraining." Sport And Health (2016): 2.
• Robson-Ansley, Paula J., Andrew Blannin, and Michael Gleeson. "Elevated plasma interleukin-6 levels in trained male triathletes following an acute period of intense interval training." European journal of applied physiology 99.4 (2007): 353-360.

Take Control of Your Cortisol Levels - Use These 5x Stress-Modulating Diet, Lifestyle & Supplementation Rules Wisely

Always remember: You want to control cortisol, not eradicate it if you want to melt away your belly fat, beat your personal bests and feel just great!

As a SuppVersity reader, you belong to the chosen few who know that cortisol is not the villain as which it is stigmatized in the fitness industry (obviously to sell supplements | learn more). Rather than being "bad" or "good", cortisol, a glucocorticoid, i.e. a hormone that keeps your blood glucose stable, and potent anti-inflammatory agent, is more vital than any "vitamin" - in spite of not having the magic "vita" in its name.

Whether the effects of this vital adrenal hormone are going to be "bad" or "good" for you, depends mostly on whether it rises and falls according to its natural 24-h rhythm or is chronically low (often labeled adrenal insufficiency) or chronically high.

If you want to mess with your cortisol rhythm overtraining is exactly what you "need"!

Heart Rate Variablity (HRV)

ABEL Sports Test + More

Overtraining & Undereating

Calculate your Energy Intake!

Overtraining W/ Only 25min/day?

Reinvent Your Training!

Now your diet alone will probably not suffice to induce one or the other state of chronically messed up cortisol (unless you eat (a) almost nothing while training like a maniac for weeks ⇉ low cortisol; or (b) too much of a typically Western diet ⇉ high cortisol). And yet, it is still a good idea to know more about the diet ⇆ cortisol interaction(s) to be able to maintain hormonal homeostasis, and the SuppVersity is obviously the right place to learn all about it.

Figure 1: Overview of the three areas of your physiology that are directly affected by the levels and rhythm of cortisol.

With the ever-increasing number of "functional" foods boasting of being able to modify health-relevant parameters, including your cortisol level and thus your ability to, through its
multipronged action, stabilize or mess with your blood levels of glucose, to stimulate your tissue's
regenerative processes and to inhibit inflammation in each and every organ of your body.

Figure 2: This is how cortisol is "made" in your body (Stachowicz. 2016). In theory, you can influence its concentration by modifying this cascade at any point.

As Stachowicz, et al. point out in a recent review of the literature they published in the peer-reviewed journal Eur Food Res Technol (Stachowicz. 2016), diet is obviously not the only factor that influences our cortisol levels. Of at least as much importance are "[f]actors like stressful work, personal problems, [and] intensive training" , which "can lead to long-term sustained, excessive concentration of this hormone, affecting formation of metabolic disorders such as insulin resistance, increased blood pressure, abnormal bone regeneration and collagen synthesis or calcium deficiency in the organism" (ibid.). Against that background, it is hardly surprising that various groups of the society try to modulate their cortisol levels in ways they consider healthy (again: low is not healthy!) by supplementing or eating / avoiding certain foods that contain nutrients which regulate steroid hormones homeostasis.

In the short term, e.g. strategic overreaching, your body can cope with the exercise induced release of cortisol, but when over-reaching becomes over-training you run the risk of plumetting into the deep dark valley of unsurmountable fatigue.

Excursion - Exercise and cortisol: Athletes experience substantial increases of cortisol and adrenaline during intense workouts. That's normal and even necessary to (a) keep your blood glucose levels stable and (b) train at high(est) intensities. In fact, studies have shown that in athletes with higher motivation and orientation on the success, levels of these hormones were higher than those of other players. As Stachowicz, et al. point out "[t]hey also generally achieve better results" (Obmiński. 2009). On the other hand, studies show that people who experience mental fatigue experience limited activity of pituitary gland and sympathetic nervous system - in other words low cortisol levels (or rather the absence of appropriate spikes in response to e.g. exercise and other stressors).

And that rightly so! After all, Stachowicz et al. (2016) rightly point out, a "balanced diet with optional supplementation is one of the important factors determining the high physical and mental capacity of organism" (ibid) - and this goes for everyone from the frail elderly over the hobby- and pro-athletes to the stressed manager or teacher, who are all "particularly exposed to abnormal secretion, metabolism and transport of hormones, including cortisol" (ibid.) - people who will probably know about the effects of chronic stress:

"It was shown that in stressful situations appetite for sweet and fat meals rises, probably because of their high rewarding character (Zellner. 2005). Consumption of meals induces [an] increase in cortisol level. This response is strongly marked in men than in women. Influence of kind of macronutrients in taken food on cortisol concentration was investigated in many [types of research], but the results are not clear" (Stachowicz. 2016). 

One of the best known (and most logical) effectors of cortisol production is the content and type of carbohydrates in your diet - especially if you're not a sedentary slob; after all, cortisol's main function as a glucocorticoid is to counter hypoglycemia.

• Rule #1 (esp. for easily fatigued athletes) - Eat enough (or no) carbs: Eat either no carbs at all (ketogenic diet) or enough carbs before, during and after training to prevent hypoglycemic conditions (click here to learn why this will also help to stay lean) and thus an abnormally high intra- and post-workout spike of hydrocortisone in blood while the consumption of liquids (studies show that this takes some carbs, i.e. 7% vs. just 1.5% in the intra-workout beverage | cf. Ihalainen, 2014 vs. Caris, 2014).
• Rule #2 - Don't believe everything the supplement industry claims: As Stachowicz et al. rightly point out, the impact of around training protein, glutamine, arginine or branched-chain amino acids (BCAA), on the other hand, "is not clear and requires testing on large groups of athletes of various disciplines" (Stachowicz. 2016).
  
  What has been shown to work is tryptophan, which is a precursor of serotonin, that will effectively ameliorate the cortisol level increase, during and after workouts, but its potential side effects (esp. performance decrements) have not been well-studied, yet. The same must be said of phosphatidylserine and phosphatidic acid, which have been shown to (a) normalize the stress reactivity of hypothalamus-pituaryadrenal-axis in chronically stressed men and to reduce the cortisol response to exercise in a sponsored trial in which it was administered at dosages of 400 mg/day for 6 weeks - the total number of studies to support PS as a useful supplement for anyone from manager to athlete and from elderly to toddler, however is low; oftentimes, there's sponsorship involved and long-term studies or studies that would evaluate the effect of cortisol control on the adaptational response to exercise are missing.
• Rule #3 - Don't overrate its benefits but get enough protein (1.6-2.2 g/kg per day): As explained in rule #2, there's no evidence that simply adding more protein to your diet is going to help you control cortisol. In fact, eating too much protein and too little fat and carbs may chronically elevate the glucocorticoid, because it has to keep the production of glucose from amino acids in the liver, i.e. gluconeogenesis, working. That adequate protein intakes are necessary, on the other hand, is a logical consequence of the role of serine, taurine, and other amino acids play in the control of the balance and optimal function of your hypothalamus-pituitary-adrenal-axis.
• Rule #4 - Optimize your sleep by sleep hygiene and (optional) supplements: By optimizing your sleep you can restore a normal and healthy circadian rhythm and thus battle what makes cortisol a problem for so many in our society directly. How's that? Well, as previously highlighted, it's not the cortisol spikes you experience in the AM and during and after workouts, but chronically elevated (or depleted) levels of cortisol and spikes that occur untimely (e.g. the "2AM wake-up call", when your cortisol rises way too early and you cannot sleep longer than until 1-3 AM).
  

  

  Figure 3: Optimal sleep, melatonin and cortisol patterns are mutually dependent in health and disease - if you mess up one with the way you behave / live and/or supplements you mess up all (Glickman. 2010).

  Next to using earplugs, a blindfold (or curtains to make sure light doesn't disturb your sleep), reducing your (blue) light exposure in the evening, and using a non-stressing alarm to tell you that it's time to go to bed, a sleep tracker to access whether your intervention is successful, your circadian rhythm restoration program may involve: (1) no caffeine, coffee, or other stimulants in the 6h window before bed (some people will have to extend this window even further); (2) GABA at doses of 100-500mg before bed (don't take more or you may faint); if you cannot tolerate GABA, try taurine, instead, it will also enter the brain and act on the GABA receptor (Song. 2003); (3) melatonin at dosages you will have to figure out yourself (start with 1-3mg and ramp up until you sleep well and wake up refreshed, not groggy, which is usually a side effect of taking (a) too much or (b) the by no means recommendable time-released melatonin preparations).  
• Rule #5 - Strategically supplement with... In contrast to the previous rules, rule #5 is "optional" or facilitative. There's mixed evidence for some vitamins, namely vitamin C (500-1000 mg), vitamin E (400 IU+), vitamin D (>2,000 IU), as well as high doses of vitamin B1, B2, and niacin, which are involved in metabolism and production of cortisol, can lower the glucocorticoid response to exercise. 

  

  Figure 4: Sign. associations between PWO hormone levels and lean mass, as well as fiber size, increases (West. 2012) - they exist, but the largest and best study to investigate them clearly shows: It's cortisol that predicts lean mass gains (left) and GH that predicts the growth of individual fibers. High post-workout testosterone, however, predicts ... nothing (learn more) .

  At least for the former (vitamin C and vitamin E), however, it has also been shown that it will impair the exercise-induced adaptational processes, i.e. improved conditioning, muscle strength, and size when taken chronically. No wonder, if you think about the previously outlined beneficial effects of your body's most potent anti-inflammatory homrone, cortisol, (see Figure 4, too) on the regenerative process after workouts.
  
  The beneficial effects of a natural (controlled) cortisol response to exercise are something you should also keep in mind when using magnesium supplements which have been shown to blunt the cortisol increase to physical exercise in Golf et al. (1984) 32 years ago. Since newer studies were not generally able to confirm Golf's findings, though, I wouldn't be too afraid of (or rely too much on) magnesium's ability to lower your cortisol levels in non-(mg)-deficiency situations. That's particularly true in view of the fact that Cinar et al. saw a sign. increase in cortisol in response to a similar combination of magnesium supplementation (10 mg/kg b.w.) and physical activity in 2008. Stachowicz, et al. are thus right to point out that "[t]he impact of magnesium supplementation on cortisol levels in athletes is not clear and needs further investigation" (Stachowicz. 2016).
  

  

  Figure 5: While we do have evidence that boron will have opposing effects (vs. magnesium or the previously mentioned vitamins on cortisol), the existing evidence is far from being conclusive (Naghii. 2011).

  The same must be said of the cortisol modulating effects of a former star on the bodybuilding supplement sky that has been largely forgotten today: boron. While Naghii et al. (2011) confirmed relatively recently that a daily morning use of preparation containing 11.6 mg of boron, just after 1 week, results in increase in cortisol and free testosterone, dihydrotestosterone (DHT) and vitamin D while decreasing estradiol levels, we are far from being able to call boron a proven ergogenic - also because its long-term benefits appeared to be zero in most exercise-related long-term studies with relevant outcome parameters (not hormones, but gainz in performance, size or strength). The same must be said of fish oil, which has been shown to reduce perceived stress, green tea (EGCG), which is supposed to inhibit the activity of 11β-hydroxysteroid dehydrogenase type 1 that converts cortisone to cortisol, and betaine with one study backing its anti-cortisol effect in trained individuals (Apicella. 2013).
  
  Long-term data assessing its safety, and potential detrimental effects on testosterone is also lacking on the effectiveness of licorice, one of the few supplements of which we have reliable evidence that it affects (increases) cortisol. 

Cardio - Only significantly "too much" can hurt your circadian cortisol rhythm, but if it does, it trigger muscle loss, fatique and (in a caloric surplus) even fat gain | learn more.

So what's the verdict? Get your ducks in a row by following rules #1-4. If you still feel (or even better have evidence from multiple cortisol swap tests in 24h) that you cortisol rhythm is messed up (see Figure 3 for what you should look out), try using supplements like magnesium, green tea or b-vitamins to lower and boron or licorice to increase it strategically.

Needless to say that the latter will require proper timing with the supplements that lower cortisol being taken at times when you want cortisol to decrease (PM) and supplements that increase the glucocorticoid being taken at times when you want it to increase.

Why the timing? If you'd read the whole article and not just the bottom line you wouldn't be asking that, because you'd should know by now that you want a natural cycle of peaks and troughs, not chronically high or low levels (don't use supplements that block your body's ability to activate / deactivate cortisone <> cortisol completely, unless you've good medical reasons, to) of this important adrenal glucoregulatory + anti-inflammatory hormone  | Comment!

References:

• Caris, Aline V., et al. "Carbohydrate and glutamine supplementation modulates the Th1/Th2 balance after exercise performed at a simulated altitude of 4500 m." Nutrition 30.11 (2014): 1331-1336.
• Cinar, Vedat, et al. "Adrenocorticotropic hormone and cortisol levels in athletes and sedentary subjects at rest and exhaustion: effects of magnesium supplementation." Biological trace element research 121.3 (2008): 215-220.
• Glickman, Gena. "Circadian rhythms and sleep in children with autism." Neuroscience & Biobehavioral Reviews 34.5 (2010): 755-768.
• Golf, S. W., et al. "Plasma aldosterone, cortisol and electrolyte concentrations in physical exercise after magnesium supplementation." Clinical Chemistry and Laboratory Medicine 22.11 (1984): 717-722.
• Hellhammer, Juliane, et al. "A soy-based phosphatidylserine/phosphatidic acid complex (PAS) normalizes the stress reactivity of hypothalamus-pituitary-adrenal-axis in chronically stressed male subjects: a randomized, placebo-controlled study." Lipids in health and disease 13.1 (2014): 1.
• Ihalainen, Johanna K., et al. "Effects of Carbohydrate Ingestion on Acute Leukocyte, Cortisol, and Interleukin-6 Response in High-Intensity Long-Distance Running." The Journal of Strength & Conditioning Research 28.10 (2014): 2786-2792.
• Naghii, Mohammad Reza, et al. "Comparative effects of daily and weekly boron supplementation on plasma steroid hormones and proinflammatory cytokines." Journal of Trace Elements in Medicine and Biology 25.1 (2011): 54-58.
• Obmiński, Zbigniew. "Pre-And Post-Start Hormone Levels In Blood As An Indicator Of Psycho-Physiological Load With Junior Judo Competitors." Polish Journal of Sport & Tourism 16.3 (2009).
• Stachowicz, Marta, and Anna Lebiedzińska. "The effect of diet components on the level of cortisol." European Food Research and Technology (2016): 1-9.
• Song, Zhilin, and Glenn I. Hatton. "Taurine and the control of basal hormone release from rat neurohypophysis." Experimental neurology 183.2 (2003): 330-337.
• Zellner, Debra A., et al. "Food selection changes under stress." Physiology & Behavior 87.4 (2006): 789-793.

Excessive Cardio & Testosterone: The free T / Cortisol Ratio Revisited | Plus: Why Even a 72% Decrease in fT/C May be Less Significant for Your Gains Than You Thought It'd Be

Cardio - Only "too much" can hurt you.

Let me get this straight: this is not an anti-cardio article. There's not just little, there's rather absolutely no doubt that a sane amount of endurance training is nothing but healthy for us, but done in excess, especially "running has been demonstrated to provide a large physiological stress to the body, resulting in large neuroendocrine system responses" (Anderson. 2016) - more specifically, running to exhaustion will have the hypothalamic–pituitary–adrenal (HPA) axis overproduce the glucocorticoid hormone, cortisol, which in turn appears to suppress the production of testosterone.

Now, cortisol - you've learned that in previous articles - is not the villain as which it is portrait by companies that are trying to sell you useless and potentially counter-productive "cortisol blockers". Rather than ruining your results, normal amount of cortisol will aid in substrate mobilization (including the use of body fat during your workouts) and can even improve your running performance.

You can learn more about overtraining and checking your training status at the SuppVersity

Heart Rate Variablity (HRV)

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Overtraining & Undereating

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Surprised? Well, I guess you will be likewise surprised to hear that the well-established connection between high cortisol and low testosterone levels that are characteristic of overtraining is likewise not as black-and-white as you may have heard. In 2005, for example, Brownlee et al. were able to show that the significant decline in total testosterone in response to exercise goes hand in hand with a disassociation of testosterone and its binding globulin SHBG that triggers an increase in free and thus bio-active testosterone levels - an increase that correlates with the exercise-induced increase in cortisol (as Brownlee et al. point out this is probably due to "an adrenal cortex contribution of fT or disassociation of fT from sex hormone binding globulin" | Brownlee. 2005).

Figure 1: Free testosterone and cortisol in young mend during recovery from 60-90min intense exercise (Brownlee. 2005).

In that, it is important to acknowledge that this finding of which the scientists rightly say that it "would seem to support the notion that the observed testosterone reductions following certain forms of physical exercise could be related to cortisol elevations in response to that exercise" does not "indicate a cause and effect relationship" (Brownlee. 2005).

What are the limitations of the study at hand? Next to a too limited (to fully grasp the time-course of the fT / cortisol response after exercise) number of blood draws and the small sample size that did not suffice to confirm the significance of the 24- and 24-h post hormonal changes (this would have required N = 16 subjects), the study at hand shares a general limitation with other studies: it fails to expand its analysis beyond the regular fT : cortisol ratio and into the realm of additional neuroendocrine biomarkers (e.g., prolactin, growth hormone, catecholamines), of which Anderson et al. (2016) rightly point out that they me of particularly importance in women and could vary and eventually determine the fitness-related differences in the hormone response we see in trained vs. untrained athletes.

What it does do, however, is tell us that we cannot restrict post-workout hormone essays to cortisol and total testosterone - unfortunately, the many currently available studies do just that... and what's more: they also fail to "assess the time course required for the neuroendocrine system to return to a resting homeostatic state" (Anderson. 2016) - even though

"[s]uch information is potentially vital to the coach and athlete in establishing timeline guidance forthe number of rest days necessary after strenuous exercise, such as might occur in a competition" (Anderson. 2016).

It is thus only logical that Travis Anderson and colleagues conducted a study to assess
the dynamics (!) of cortisol and testosterone concentration during recovery, following an exhaustive exercise bout. A study the results of which gain significance to the researchers' choice of subjects.

Table 1: Subject characteristics - Certainly not a bad thing to use elite athletes instead of noobs (Anderson. 2016).

12 elite endurance runners who reported to the laboratory on seven separate occasions each time being required to adhere to the preassessment guidelines, which included being 2.5 h fasted, abstaining from strenuous activity, alcohol and sexual activity for 24 h, and abstaining from caffeine consumption for 12 h.

Table 2: Exhaustive exercise session (X ± SD) | VO 2 oxygen uptake, HR heart rate, RPE rate of perceived exertion, VT ventilatory threshold (Anderson. 2016).

Following a 7-day wash-out period, participants took part in a standardized exhaustive exercise test -- a prolonged exercise run on the treadmill until volitional fatigue, running at 100 % +/-3% (see Table 3) of their pre-determined ventilatory threshold (VT | ventilatory threshold refers to the point during exercise at which ventilation starts to increase at a faster rate than VO2, the VT thus reflects the levels of anaerobiosis and lactate accumulation).

Complete exhaustion is key to the ill effects of "cardio"
.
To ensure "a truly fatiguing exercise session", strong "verbal encouragement" was given to subjects towards the end of the exercise session (the RPE levels in Table 2 indicate that this worked - the subjects, elite athletes or not, were truly exhausted) after which the subjects completed a ~5 min cool down, prior to a post-exercise blood sample being taken (+0 h).

Figure 2: Free testosterone (left, top), cortisol (left, bottom) and fT:cortisol ratio (right | Anderson. 2016).

Subjects reported back to the laboratory at the same time of day 24 (+24 h), 48 (+48 h), and 72 (+72 h) hours after the exhaustive exercise bout, where blood samples were again drawn. Subjects
were asked to maintain a similar diet and activity level compared to the pre-EES period during this 72 h of recovery, and the latter involved only activities of daily living and no exercise training. The analysis of these samples revealed the following results:

• free testosterone - as far as fT is concerned the researchers observed a significant decrease in fT following EES compared to pre-EES time points (−48 to 0 h; p = 0.053 to p = 0.001) that persisted for up to +48 h into recovery, before returning to baseline (pre-EES) levels at +72 h,
• cortisol - the scientists' REPANOVA and post hoc analysis revealed increases and decreases in C following EES compared to pre-EES. At +0 h, C was increased (p < 0.001) and decreased at +24 h (p < 0.002) before returning to baseline (pre-EES) levels,
• free testosterone : cortisol ratio - the analysis of the ratio of the two measured hormones revealed significant differences with post hoc analysis showing fT:C was significantly decreased at +0 h (0.167 ± 0.084) relative to all other time points (p < 0.005), interestingly enough, it took only 24h for the fT:C to return to pre-EES, with no significant differences between +48 h or +72 h compared to any pre-EES values,

With the increase in cortisol being - as preciously hinted at and discussed at length in "All About Cortisol" | read it) - indicative of an increased use of alternative (=non-glucose) substrates, it is not surprising that the intense exercise session, despite being conducted out of the "fat burning zone", did not affect the subjects' glucose concentrations at any measurement time. How's that significant? Well, previously, scientists have speculated that the reduction in testosterone and increase in cortisol could be a stress response to hypoglycemia (=low blood glucose levels). With the study at hand demonstrating stable blood glucose levels, this hypothesis must be refuted. 

Figure 3: Changes in testosterone (top) and T/C values (bottom) of Rugby players during the rest day (black bars), during the competition day (grey bars) and during the postcompetitive recovery period at 8 am and 8 pm (white bars | Elloumi. 2003)

Could HIIT actually increase your testosterone levels in the long(er) run? One interesting artifact the researchers found when reviewing the existing literature on the effects of exercise on (free) testosterone was the sign. increase in testosterone Elloumi et al. observed in the 6 days after an intense rugby match. What speaks against this theory, however, is the fact that Morville et al. have observed a similar increase in T in response to a 100km run in a 1979 study.

Against that background, Anderson's assumption that high-intensity, intermittent nature exercise would elevate, not lower the levels of testosterone during recovery, despite being in line with research in Wrestlers (Passelergue. 1999), appears to be questionable and I would recommend not to try to use high intensity interval (HIIT) training (of all) as a means of increasing your testosterone levels.

As Anderson et al. point out, the results of the study at hand also conflict with previous research suggesting significantly shorter recovery times for the fT:cortisol ratio, namely 38 h and 24h in Rugby and soccer players (after matches | Cunniffe et al. 2010; Ispirlidis et al. 2008).

Eventually, the study at hand therefore supports the previously voiced hypothesis that there may be a mechanistic link between increased cortisol and decreased testosterone levels - a mechanism that has been confirmed for orally ingested cortisol, which resulted in testosterone suppression without changes in follicle-stimulating hormone or luteinizing hormone as early as in 1976 (Doerr. 1976).
Overall, the existing evidence can thus be said to suggests that glucocorticoids will directly suppress steroidogenesis at the level of the Leydig cells, where LH and will no longer do its testosterone production triggering magic when your testes are bathing in cortisol - how the previously discussed increases in free testosterone fit in here, however, requires further research.

One important last finding I would like to discuss before wrapping it up is the (also previously observed | Kraemer. 2009) time-lag between the decline in cortisol and the recovery of testosterone levels. In fact, previous studies in athletes indicate that cortisol will be depressed during recovery. Now, acutely, this may be considered what Cunnife et al. (2010) call a "rebound anabolic stimulus" stimulus during recovery - in the long run, however, a suppressed diurnal cortisol rhythm is one of the hallmark features of overtraining that contributes to its ill effects on both overall well-being and physical performance.

Bottom line: No, cardio is not the devil and cortisol is not always bad for you. In fact, the almost oscillating nature of the individual hormone recovery dynamics in the 48 h postexercise, prior to returning to pre-exercise values clearly supports "the hypothesis that a negative relationship only exists between these hormones when cortisol is significantly elevated (>160 % of baseline values) | Brownlee et al. 2005)" (Anderson. 2016) - with the rapid clearance of cortisol from the bloodstream during the recovery period rendering its effects void within only 24 h of recovery from an exhaustive exercise bout.

Figure 4: Correlations between acute GH, free testosterone, IGF-1 and cortisol responses (area under the curve—AUC) and gains in lean body mass (n = 56). Cortisol AUC was correlated with LBM (r = 0.29, P = 0.03 | West. 2010).

Furthermore, we should not forget that the assumption that the fT or total T to cortisol ratio was a reliable marker of anabolic / catabolic state in the hours and days after a workout is, much in contrast to what the average bro-article on bodybuilding websites would suggest, not backed by science. Rather than that, studies such as may favorite large-scale + long-term resistance training study by West et al. (2009 / 2012) indicate that (a) the transient increases in endogenous purportedly anabolic hormones do not enhance fed-state anabolic signalling or MPS following resistance exercise (West. 2009) and (b) the post-exercise increase in the allegedly catabolic hormone cortisol even correlates with the extent of the 12-week skeletal muscle hypertrophy response to resistance training in 56 young men.

It should be obvious that this does not mean that you should aim to chronically elevate your cortisol levels, but I'd hope that the profound decline in testosterone in response to exhaustive (cardio) exercise is not the only information you take away from today's SuppVersity article. After all, the full recovery of fT within only 24h is of equal if not greater importance when it comes to the allegedly negative effects of sane amounts of cardio training on hormonal parameters of which we assume, but don't know that they determine our training success | Comment!

References:

• Anderson, Travis, Amy R. Lane, and Anthony C. Hackney. "Cortisol and testosterone dynamics following exhaustive endurance exercise." European journal of applied physiology (2016): 1-7.
• Cunniffe, Brian, et al. "Time course of changes in immuneoendocrine markers following an international rugby game." European Journal of Applied Physiology 108.1 (2010): 113-122.
• Doerr, P., and K. M. Pirke. "Cortisol-induced suppression of plasma testosterone in normal adult males." Acta Endocrinologica 80.1 Suppla (1975): S55-S55.
• Elloumi, M., et al. "Behaviour of saliva cortisol [C], testosterone [T] and the T/C ratio during a rugby match and during the post-competition recovery days." European journal of applied physiology 90.1-2 (2003): 23-28.
• Ispirlidis, Ioannis, et al. "Time-course of changes in inflammatory and performance responses following a soccer game." Clinical Journal of Sport Medicine 18.5 (2008): 423-431.
• Kraemer, William J., et al. "Recovery from a national collegiate athletic association division I football game: muscle damage and hormonal status." The Journal of Strength & Conditioning Research 23.1 (2009): 2-10.
• Passelergue, P., and G. Lac. "Saliva cortisol, testosterone and T/C ratio variations during a wrestling competition and during the post-competitive recovery period." International Journal of Sports Medicine 20.02 (1999): 109-113.
• West, Daniel WD, et al. "Resistance exercise‐induced increases in putative anabolic hormones do not enhance muscle protein synthesis or intracellular signalling in young men." The Journal of physiology 587.21 (2009): 5239-5247.
• West, Daniel WD, and Stuart M. Phillips. "Associations of exercise-induced hormone profiles and gains in strength and hypertrophy in a large cohort after weight training." European journal of applied physiology 112.7 (2012): 2693-2702.