Where do Your Strength Gains Come From? Muscle Activity > Hypertrophy > Initial Strength - 3/5 Candidates Matter

Find out what's taking you from PR to PR, is it an increase in muscle size or activation on how important is how strong you already are?

Have you ever asked yourselves why you've been adding 20lbs of weight to your squat and your legs still don't look any bigger? If you're a man you're probably not happy about that. I am not sure if the insights into Balshaw et al.'s recent study provide into the mechanism behind the resistance-training-induced strength gains will help you will make you happy/-ier, but certainly smarter ;-)

The British scientists got to the bottom of your gains by assessing the individual and combined contribution of the adaptations in neural (agonist quadriceps EMG, antagonist hamstring EMG) and morphological (quadriceps muscle volume and θp, the fascicle pennation angle) variables.

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Based on the data from their 12-week study in twenty-eight healthy young men, who had not completed lower body RT for >18 months and were not involved in systematic physical training, the scientists were able to calculate the individual contribution of the previously named variables and the trainees' baseline strength on the effect of the following workout:

"After a brief warm-up of submaximum contractions of both legs, participants completed four sets of ten unilat eral isometric knee extensor contractions of each leg; with sets alternating between dominant and non-dominant legs. Each set took 60 s with 2 min between successive sets on the same leg" (Balshaw 2017). 

To differentiate potential interference with explosive vs. sustained contractions, the participants were further randomized to two groups:

• the explosive contraction group completed short, explosive contractions with participants instructed to perform each contraction “as fast and hard as possible” up to ≥80% MVT for ~1 s, and then relax for 5 s between repetitions.
• the sustained contraction group completed prolonged contractions at 75% MVT, with 2-s rest between contractions. 

For both groups, the scientists provided a computer monitor that displayed the rate of torque development (10-ms time epoch) and a target torque trace 2 s before every contraction, in the explosive and sustained contraction group, respectively.

Without a follow-up study in trained individuals, we have to speculate to which extent increases in muscle activity, hypertrophy, and the pre-training strength explain the variability of strength gains in trained individuals. The above is my estimate - just an educated guess.

What does the study tell us about better-trained individuals? If we compare the results of the study at hand to related study, it may be possible to make predictions about the driving forces of muscle growth in better-trained individuals, eventually, though, the study would have to be repeated with a different subject group to tell for sure.

As Balshaw et al. point out, their results are in line with other EMG studies assessing the effect of training on the lower extremities. What is interesting, however, is that they conflict with a study by Erskine et al. (2014) who found only a marginal correlation between improved activity patterns and strength gains for the biceps a muscle with an already high level of activation even in untrained individuals.

This result is important for our prediction because it suggests that a higher baseline activation level will reduce the contribution of improvements in agonist neural drive to the strength gains. This, in turn, obviously suggests that, in trained individuals who have already undergone significant improvements in neural drive, muscle activity will contribute significantly less to the strength gains than it does in untrained individuals. An equivalent to Figure 3 for well-trained athletes may thus look as I have sketched it in the figure on the left-hand side: Hypertrophy could make the largest, while improved muscle activation, only a marginal contribution to strength gains - but keep in mind: that's just an educated guess that is based on the assumption that the relative contribution of hypertrophy will increase as the relative contribution of improvements in muscle activation patterns will decrease over time (Note: Whether the three variables will then still explain 60% of the variation appears questionable, though; thus the 10% reduction in total predictive power in the figure above).

Each subject performed the above isometric knee extensor RT thrice a week (3/week). Before and after isometric maximum voluntary torque (MVT) as well as the neural drive to the agonist (QEMGMVT) and antagonist (HEMGANTAG) were assessed simultaneously. In addition, QUADSVOL was determined with MRI and QUADSθp with B-mode ultrasound.

Figure 1: Relationships of percentage change (∆) in knee extension may. voluntary torque (MVT) and ∆ quadriceps muscle volume (QUADSVOL; r = 0.461, P = 0.014), b ∆ quadriceps muscle fascicle pennation angle (QUADSθp; r = −0.207, P = 0.291), after 12 wks of resistance training. Solid and dashed lines indicate the trend of the relationship between variables and 95% confidence intervals, respectively. Black triangles denote sustained-contraction resistance training participants (n = 15); white circles denote explosive-contraction resistance training participants (n = 13 | Balshaw 2017)

I have to say that the way the scientists plotted the data is a bit odd - with the strength gains being the actual outcome variable of interest, I would expect it to be placed on the vertical, not the horizontal axis... but anyway. Figures 1-2 tell you that...

• hypertrophy contributes quasi-linearly to the gains (Figure 1 A) - I would estimate the reciprocal of the slope of the linear regression line to be ~2.5, meaning for each 1 % increase in muscle volume there was a 2.5% increase in maximal voluntary torque;
• agonist activity changes contribute quasi-linearly to the gains (Figure 2 A) - I would estimate the reciprocal of the slope of the linear regression line to be "only" ~0.8, meaning for each 1% increase in muscle activity there was a 0.8% increase in maximal voluntary torque;
• pre-training strength negatively predicts the strength gains (Figure 2 C) - What may sound odd, initially, is actually only logical. The stronger you are at baseline, the lower your strength gains are going to be. For this relationship, I would estimate the slope of the linear regression analysis to be approx. -1.5, which means that for each extra Newton-metre (nM) of pre-training maximal voluntary torque, the increase in response to training will be reduced by 1.5%;
• pennation angle and antagonist activity changes do not contribute clearly to the strength gains (Figure 1 B, Figure 2 B) - you know that because there was no clear correlation between the corresponding variables in the regression analysis the scientists did

So, there's clear evidence that size gains (hypertrophy), muscular activation (EMG) and, of course, the baseline strength determine the strength gains in resistance training rookies.

Figure 2: The relationships between the percentage change (∆) in knee extension maximum voluntary torque (MVT) and: (A) ∆ quadriceps EMG at knee extension MVT (QEMGMVT; r = 0.576, P = 0.001); (B) ∆ antagonist hamstrings EMG during knee extension MVT (HEMGANTAG; r = 0.298, P = 0.123) and (C) pre-training knee extension MVT (r = −0.429, P = 0.023), after 12 weeks of resistance training (Balshaw 2017).

The pennation angle, and antagonist activity (here the hamstring) on the other hand appear to contribute only marginally to the increase in strength gains the previously untrained subjects saw over the course of the 12-week study.

Figure 3: The scientists' multiple regression analysis reveals the strength of the contribution of each variable the scientists assessed in their study (Balshaw 2017).

So, what's the most important contributor? That's difficult to tell. With the individual correlations being relatively weak, one cannot rely on the previously calculated slopes. Those give you an idea of what the real-world contribution would be if there was a perfect correlation between the individual variables.

To answer the above question, we will thus have to turn to the subsequent multiple regression analysis of which the scientists highlight that it "found for the first time that these three variables simultaneously contributed to the total explained variance in strength" (Balshaw 2017).

Even if you take the  size gains (hypertrophy), muscular activation (EMG) and, of course, the baseline strength them into account, these variables explain only 60% of the total variance in strength gains - with the individual contributions (see Figure 3) being agonist neural drive, aka the muscle activation (EMG) explaining 30.6%, the size gains 18.7% and the pre-training strength 10.6% of the strength gains the rookies made over the course of the 12-week study... which leads me to an inevitable question: What about experienced strength trainees? I knew you'd be asking that and have addressed this question in the red box above Figure 1, so read it before you ask about the implications for trained individuals on Facebook!

References:

• Balshaw, Thomas G., et al. "Changes in agonist neural drive, hypertrophy and pre-training strength all contribute to the individual strength gains after resistance training." European Journal of Applied Physiology (2017): 1-10.
• Erskine, Robert M., Gareth Fletcher, and Jonathan P. Folland. "The contribution of muscle hypertrophy to strength changes following resistance training." European journal of applied physiology 114.6 (2014): 1239-1249.

Bench Press - The Truth About the Effects of Bench Angle on Pec Activity Varies Depending on the Phase of the Lift

The bench press, in one form or another, is part of almost everyone's workout, but what's the best way to do it?

You may have seen Brad Schoenfeld's post about the just accepted study of his that confirms the well-known link between muscle activity and poundage (higher weight = higher activity | see EMG Series). Well, another recent study provides additional intricate insights into the link between muscle activity and the way you perform the bench press.

Just like Schoenfeld et al.'s study, the study compared the muscular activation during bench presses - albeit in this case that of the pectoralis major, anterior deltoid and triceps brachii during a freeweight barbell bench press performed at different angles: 0°, 30°, 45° & -15° angles, to be specific.

Want to become stronger, bigger, faster and leaner? Periodize appropriately!

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As the authors from the Department of Kinesiology, Cardiopulmonary and Metabolic Research Laboratory at the University of Toledo point out, this is not as "boring" as you may think it is,, as previous investigations may have systematically examined muscle activation during various bench press conditions only throughout the complete lift. Needless to say that "[d]uring any resistance exercise a complete ROM is important", but Jakob D. Lauver et al. are right to point out that there may be potentially relevant differences in the level of muscle activation over the course of the full range of motion (ROM). The latter could be significant enough to...

"[...] have the potential to attenuate any difference in muscle activation observed during the complete lift between bench angle conditions as differences in activation may have been evident throughout different time points of contractions" (Lauver. 2016). 

Accordingly, the primary purpose of the present investigation was, as Lauver et al write "to compare the changes in muscle activation at various time points across contraction phases (concentric, eccentric) during free-weight barbell bench press at varying bench angles (–15°, 0°, 30°, 45°) while maintaining the same absolute resistance load" (Lauver. 2016). The scientists hoped that the results of their study would lead to a better understanding of the effect of bench angle on muscle activation during bench press exercise and "aid in selection of variations in bench press exercise to develop upper extremity strength and musculature" (Lauver. 2016).

So, 80% = maximum activity - Why did the scientists use 65% 1RM? If Schoenfeld et al. found that you need 80% of the 1RM it may initially appear to be a methodological shortcoming to use only 65% of the 1RM. On the other hand, the fact that high loads, alone, maximize the muscle activity may nullify the significance of angle- or phase dependent differences... I cannot tell you, however, whether that's what the scientists had in mind when they decided to go for "only" 65% of the 1RM or whether they simply wanted to avoid fatigue having an effect on subsequent sets.

For their study, Lauver et al. recruited 14 healthy resistance trained men (age 21.4 ± 0.4 years) who performed one set of six repetitions for each bench press conditions at 65% one repetition maximum. As in previous studies, Lauver et al. used surface electromyography (sEMG) to quantify the muscular contraction. In contrast to previous studies, however, they analyzed the corresponding data during four parts of the lift individually - not just for the whole lift.

Figure 1: Upper and lower (U- / L-) pectoralis major activity during eccentric (UA / LA) and concentric (UB / LB) quarts of the bench press at different angles (-15°, 0°, 30° and 45° | Lauver. 2016).

This is important, because their data showed no difference during any of the bench conditions, when the scientists examining the complete contraction and/or only the concentric part (pushing the bar up) of the contraction. A different picture emerged, however, when Lauver et al. analyzed the four phases of the eccentric and concentric phase individually:

• Differences were found for 26–50% contraction for both the 30° [122.5 ± 10.1% maximal voluntary isometric contraction (MVIC)] and for 45° (124 ± 9.1% MVIC) bench condition, resulting in greater sEMG compared to horizontal (98.2 ± 5.4% MVIC) and –15 (96.1 ± 5.5% MVIC). 
• The sEMG of lower pectoralis was greater during –15° (100.4 ± 5.7% MVIC), 30° (86.6 ± 4.8% MVIC) and horizontal (100.1 ± 5.2% MVIC) bench conditions compared to the 45° (71.9 ± 4.5% MVIC) for the whole concentric contraction. 

Overall, the study results obviously still confirm what you've read previously at the SuppVersity: "[T]he use of a horizontal bench to achieve muscular activation of both the upper and lower heads of the pectoralis" (Lauver. 2016).

This doesn't mean that adding an incline press to your regimen would be useless. As Lauver et al. point out, there's still use for the incline bench press - specifically at 30°!, because it "resulted in greater muscular activation during certain time points", so that the overall results of the study suggest "that it is important to consider how muscular activation is affected at various time points when selecting bench press exercises" (Lauver. 2016).

Shoulder Presses Ain't for Delts, Only! Standing, Seated w/ BB or DB, They Also Hammer the Core, Biceps & Triceps. That's at least what a previously discussed study shows | learn more

Bottom line: The implications of the study are not 100% straight forward. But overall it appears as if there were two take home messages: (1) If you're doing just one exercise, you should stick to the flat bench (or vary cyclically). (2) If there's room for another bench press you should favor the 30° over the 45° degree bench press, because it achieves the same upper pectoralis activation as the 45° incline bench press, but a great lower pectoralis activation.

What is a bit surprising, but may be due to the differences in methodology compared to the previously cited study in the SuppVersity EMG Series is that there were no measurable advantages of the decline bench press, which may have benefited from the subjects' ability to lift more weight in previous studies. If that's the same for you, I personally wouldn't discount the decline press yet - you will, after all, probably not lift with 65% of your 1RM, right? | Comment!

References:

• Lauver, Jakob D., Trent E. Cayot, and Barry W. Scheuermann. "Influence of bench angle on upper extremity muscular activation during bench press exercise." European journal of sport science (2015): 1-8.
• Schoenfeld, Brad J; Contreras, Bret, Vigotsky, Andrew D.; et al. "Upper body muscle activation during low- versus high-load resistance exercise in the bench press." Not yet published; private communication on Facebook (2016).

Training to Failure and Modifying Rest Times: Two Ways to Maximize Muscle Activity? Two Studies, Similar Implications

This is what science looks like... Well, at least in the Hiscock study, where the subjects, 10 young men with at leas 12 months of training experience did regular and hammer dumbbell curls on the preacher bench - (photo | Hiscock. 2015).

In today's SuppVersity feature article, I am going to address not one, but two potentially highly relevant articles from the Journal of Strength and Conditioning Research (Looney. 2015) and the European Journal of Sport Science (Hiscock. 2015). What makes these papers interesting is the fact that both investigated the effect of commonly prescribed remedies to "bust a plateau" by providing novel growth triggers: (a) Training to failure and (b) modifying rep schemes and whether you fail or don't fail on every set.

If you believe in what you can read in many articles on strength training, both, training to failure and decreasing rest times / drop sets should significantly increase the muscle activity and thus - this is the most important thing - the number of motor units that are recruited during the exercises.

Want to become stronger, bigger, faster and leaner? Periodize appropriately!

30% More on the Big Three: Squat, DL, BP!

Block Periodization Done Right

Linear vs. Undulating Periodizationt

12% Body Fat in 12 Weeks W/ Periodizatoin

Detraining + Periodization - How to?

Tapering 101 - Learn How It's Done!

But is this actually true? I mean, is there a link between EMG activity, the number of motor units that are firing and the way you train? I guess, it would be wise to take a brief look at the pertinent research before we get to design and results of the individual studies. So, what do we have? As Looney et al. point out, motor unit activity can be measured through electromyography (EMG) which is commonly considered to reflect the neural drive to the muscle. Since the electrical impulse should be proportional to the number of motor units that are firing and in view of the fact that the latter determines the acute force output, it should be obvious that increasing force demands result in higher EMG amplitude due to the greater recruitment of motor units and faster firing rates necessary to increase the contractile force.

Figure 1: Previous studies show that the motor unit recruited (or at least it's indicator, the mean EMG values) increases over the duration of sustained or repeated muscle actions at a constant force level (Masuda. 1999 - l; Mottram. 2005 - r)

Unfortunately, more does not necessarily help more. If you take a closer look at the existing research you have to realize you cannot stretch this proven increase of the EMG amplitude (Carpentier. 2001; Fuglevand. 1993; Lind. 1979; Masuda. 1999; Mottram. 2005; Petrofsky. 1982) infinitely. Over prolonged exercise / contraction times, the initially increasing firing rates will eventually decrease. That this is the case is interpreted by many scientists as evidence of the the fact that the initial rise in EMG amplitude is just a compensatory mechanism for sustaining contractile force as fatigue accumulates (when the individual fibers fatigue, more are recruited to sustain the same force). This hypothesis appears to be confirmed by numerous investigations that have demonstrated that EMG amplitude increases during dynamic exercise as the extent of the effort, or number of repetitions performed, increases (Hasani. 2006; Spreuwenberg. 2006; etc.).

Why is it even important that all muscle fibers contract? The reason should be obvious, but I am happy to explain it once more. It is the contraction that's responsible for the exercise induced increase in GLUT-4 receptor expression and mTOR phosphorylation. In view of the fact that the latter determine the increase in glucose uptake and protein synthesis after a workout, you obviously want as many muscle fibers to contract as possible. Or, to put it differently: If you don't use it you won't grow it, bro... well, at least not to the same / optimal extent.

This is where the "train to failure to maximize motor unit recruitment"-theory comes from. After all, this observation indicates that usually inactive motor units are going to fire only during prolonged training at high intensities (best to failure). As usual, though, there are problems with this theory:

"While the increase in EMG amplitude observed during repeated muscle actions has been explained by increased central drive necessary to sustain force as fatigue accumulates, it is inconclusive whether fatigue derived from earlier performed exercise induces greater EMG amplitude during subsequent exercise. Previous studies have shown EMG amplitude diminishes after strenuous resistance exercise protocols. In contrast, Smilios et al. demonstrated progressive increases in EMG amplitude over a series of 20-repetition sets with gradually decreasing resistance interspaced with 2-minute rest periods. Further uncertainly exists pertaining to consecutive maximal effort sets with progressively lighter resistance performed without allotted rest periods. This frequently incorporated training technique, commonly known as a “drop set”, has remained relatively uninvestigated" (Looney. 2015).

Needless to say that we all expect that lighter weights can stimulate greater motor unit recruitment, if you use them in dropsets, but as Looney et al. say, the science that would conclusively confirm that is simply not there (yet). The goals of Looney's study were thus as follows:

• Firstly, confirm / refute the assumption that EMG amplitude would be significantly greater in light resistance exercise (50% 1RM) performed in rested conditions to a maximal number of repetitions than to a submaximal number of repetitions. 
• Secondly, assess whether the EMG amplitude would be significantly lower in maximal repetition sets performed in rested conditions with 50% 1RM resistance than with heavy resistance (90% 1RM). 
• Thirdly, test whether the EMG amplitude would be greater in maximal repetition 50% 1RM resistance sets performed in pre-fatigued conditions (no prior rest period) than in rested conditions. 

As the authors rightly point out, the "findings of this investigation would provide critical information on understanding the changes in neuromuscular physiology during dynamic exercise related to variable levels of target repetitions, resistance, and fatigue" (Looney. 2015) and may thus be of great value to scientists (initially, because the would have to still check the practical consequences of any increases in motor recruitment) and coaches + athletes (later). What the Hiscock study in which the researchers evaluated the rate of perceived exertion (RPE) and its correlation with muscle activation and lactate levels can add to the table is information on the effect of another parameter: Different rest times.

If you don't do them as an intensity add-on / finisher don't do partial reps at all - "Full Rom, Full Gains" | more

Don't forget that form, time under tension and the range of motion matter, as well. In 2013, for example, I discussed the results of a study by McMahon et al. that leaves little doubt that the increased mechanical stress and workload (remember work is the product of force x time) from doing exercises over the full range of motion will trigger greater morphological and architectural adaptations in response to resistance training than doing the same exercises over only a partial range of motion. Unfortunately, the evidence in favor of the significance of optimal form (beyond going over the full range) and the time under tension for optimal gains is less convincing and in parts contradictory.

In order to avoid any confusion, though, let's initially look at the Looney study in isolation. In said study ten resistance trained men (age, 23±3 yr; height, 187±7 cm; body mass, 91.5±6.9 kg; squat 1RM, 141±28 kg) had EMG electrodes attached to their vastus lateralis and vastus medialis muscles on two occasions:

• A drop set day, on which he subjects performed three consecutive maximal repetition sets at 90%, 70%, and 50% 1RM to failure with no rest periods in between. 
• A single set day, on which the subjects performed a maximal repetition set at 50% 1RM to failure (no "dropping" involved). 

The analysis of the EMG data yielded overall unambiguous results: The maximal repetition sets to failure at 50% and 70% 1RM resulted in higher peak EMG amplitude than during submaximal repetition sets with the same resistance. In view of the fact that the peak EMG amplitude was significantly (P ≤ 0.05) greater in the maximal 90% 1RM set than on any of the other sets the subjects performed, the classic drop set with 90%, 70% and 50% 1RM should thus still have an edge over any regular "low intensity + high rep to failure" single set training. The question remains, however, whether it will also have the edge over conventional training?

Figure 2: Very general summary of the research interests and designs of the two studies discussed in today's SuppVersity article by Looney et al. (2015) and Hiscock et al. (2015)

We will get back to that question in the bottom line. In the mean time, let's briefly take a look at another, quite surprising result, one that will also lead us to the results of the previously mentioned study by Hiscock et al. (2015): The lack of association between the ratings of perceived exertion (CR-10). In contrast to what most of you certainly expected, the fatigue levels did not differ over the intensity range of loads and did not reflect the degree motor unit recruitment in any way (see Figure 3). You as an individual without the necessary technical equipment are thus probably unable to tell hor many motor units you've actually recruitment in a workout; and - even more importantly - the mere fact that you have to crawl instead of walk out of the gym is not a sign of a productive workout.

Figure 4: Mean number of repetitions (left, top), rate of perceived exertion (RPE | left, bottom), and peak EMG amplitude as a measure of motor recruitment (Looney. 2015).

You don't want to believe that? Well, bad luck for you: This result appears to be confirmed by Hiscock's study, in which 10 recreationally trained (>12 months of previous resistance training) did DB Curls and DB Hammer Curls on the preacher bench for three sets with their preferred arm at a constant load of 70% of their individual 1-RM over 4 trials:

1. 3 sets × 8 repetitions × 120 s recovery between sets; 
2. 3 sets × 8 repetitions × 240 s recovery; 
3. 3 sets × maximum number of repetitions (MNR) × 120 s recovery; 
4. 3 sets × MNR × 240 s recovery.

After each of the exercises the participants rated their overall and active arm muscle rate of perceived exertion (RPE-O and RPE-AM) and the data was correlated with the biceps brachii and brachioradialis muscle EMG activity during each set for each trial.

Figure 5: Despite sign. higher volumes (see boxes) and a 100% increase in rate of perceived local muscular exertion there was no significant increase in muscle activity with lifting 70% of the 1RM for 8 vs. to failure (Hiscock. 2015).

Just like in the Looney study, the measured rates of perceived exertion in the Hiscock study had did not correlate with with either the muscle activation or the lactate accumulation in the biceps. Rather than that, it appears as if the subjects' bicepses didn't even care about rep schemes and failure. While the RPE increased significantly, when the subjects trained to failure, the mean and peak EMG activity levels in Figure 5 are more or less identical for all rep x intensity (+/- failure) schemes.

So what's the significance of the results, then? If you put some faith into Looney's conclusion, it is that the results of his (and I may add Hiscock's study, too) confirm "previous recommendations for the use of heavier loads during resistance training programs to stimulate the maximal development of strength and hypertrophy" (Looney. 2015).

SuppVersity Suggested Topical Article: "Failure, a Necessary Prerequisite for Max. Muscle Growth & Strength Gains? Another Study Says 'No Need to Fail, Bro!'" | read more

Reducing the load and training to failure (Looney's "single set" day) or reducing the rest times and or switching from a set rep number to training to failure (Hiscock's groups A-D), on the other hand, has no effect on motor recruitment and could, in view of potentially increased recovery times due to higher rates of perceived exertion w/ training to failure, rather hinder than facilitate rapid strength and size gains. Whether the same is the case for the drop-set, though, is not 100% clear. With the peak muscle activity occurring in the first set, you cannot argue that the stimulus was weakened. On the other hand, there's a proven reduction in total volume (reps x weight | Melibeu Bentes. 2012) of which long-term studies would have to investigate whether the can impair your strength and size gains.

Overall, there is still little doubt that the results of the two studies I discussed today support the notion that "going heavy" is still the way to activate a maximal number of muscle fibers. Whether this does also mean that it is necessarily the best way to make those fibers grow and or increase their glucose uptake, however, is still not fully proven. The same goes for the usefulness of training to failure, of which some studies suggest that failure does not matter, while others appear to indicate that "failing" is almost necessary to maximize your gains - as usual, I've written about both of them and will continue to do so in the future, so stay tuned if you want to be among the first to learn what works best for strength and hypertrophy training ;-) | Comment on Facebook!

References:

• Carpentier, Alain, Jacques Duchateau, and Karl Hainaut. "Motor unit behaviour and contractile changes during fatigue in the human first dorsal interosseus." The Journal of physiology 534.3 (2001): 903-912.
• Fuglevand, A. J., et al. "Impairment of neuromuscular propagation during human fatiguing contractions at submaximal forces." The Journal of physiology 460.1 (1993): 549-572.
• Gibson, A. St Clair, E. J. Schabort, and T. D. Noakes. "Reduced neuromuscular activity and force generation during prolonged cycling." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 281.1 (2001): R187-R196.
• Hassani, A., et al. "Agonist and antagonist muscle activation during maximal and submaximal isokinetic fatigue tests of the knee extensors." Journal of Electromyography and Kinesiology 16.6 (2006): 661-668.
• Hiscock, Daniel J., et al. "Muscle activation, blood lactate, and perceived exertion responses to changing resistance training programming variables." European Journal of Sport Science ahead-of-print (2015): 1-9.
• Lind, Alexander R., and Jerrold S. Petrofsky. "Amplitude of the surface electromyogram during fatiguing isometric contractions." Muscle & nerve 2.4 (1979): 257-264.
• Looney, David P., et al. "Electromyographical and Perceptual Responses to Different Resistance Intensities in a Squat Protocol: Does Performing Sets to Failure With Light Loads Recruit More Motor Units?." The Journal of Strength & Conditioning Research (2015).
• Masuda, Kazumi, et al. "Changes in surface EMG parameters during static and dynamic fatiguing contractions." Journal of Electromyography and Kinesiology 9.1 (1999): 39-46.
• McMahon, Gerard E., et al. "Impact of range of motion during ecologically valid resistance training protocols on muscle size, subcutaneous fat, and strength." The Journal of Strength & Conditioning Research 28.1 (2014): 245-255.
• Mottram, Carol J., et al. "Motor-unit activity differs with load type during a fatiguing contraction." Journal of neurophysiology 93.3 (2005): 1381-1392.
• Petrofsky, Jerrold Scott, et al. "Evaluation of the amplitude and frequency components of the surface EMG as an index of muscle fatigue." Ergonomics 25.3 (1982): 213-223.
• Smilios, Ilias, Keijo Häkkinen, and Savvas P. Tokmakidis. "Power output and electromyographic activity during and after a moderate load muscular endurance session." The Journal of Strength & Conditioning Research 24.8 (2010): 2122-2131.
• Spreuwenberg, Luuk PB, et al. "Influence of exercise order in a resistance-training exercise session." The Journal of Strength & Conditioning Research 20.1 (2006): 141-144.