Is Resistance Training in the PM More Anabolic Than in the AM? Time of the Workout Doesn't Influence Acute Hormonal Response or Circadian Pattern of Testosterone Production

The sun is setting and you're still working out. Could this disrupt your circadian testosterone rhythm? Or is it maybe even beneficial? I mean, you could compensate the natural nadir in testosterone in the PM, right?
Testosterone, much like any other hormone, is subject to a circadian rhythm. This means that there are spikes and troughs at certain time points in the day. Now, we all know that a bout of resistance training will also have an effect on testosterone, i.e. it will lead to a measurable increase in the post-workout period, and could thus (a) amplify natural spikes and / or (b) fill natural troughs.

Against that background, it appears to be a warranted question, whether one would want to do (a) or (b), i.e. amplify a natural spike as it occur in the morning and head to the gym at 8:00AM, or whether it would make more sense to wait a until the late afternoon / evening to hit the gym at 8:00PM, when the testosterone levels are at a nadir?
You can learn more about sleep and the circadian rhythm at the SuppVersity

Sunlight, Bluelight, Backlight and Your Clock

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Breaking the Fast to Synchronize the Clock

Fasting (Re-)Sets the Peripheral Clock

Vitamin A & Caffeine Set the Clock

Pre-Workout Supps Could Ruin Your Sleep
The practical question thus is: "Are athletes better off undertaking their resistance exercise in the  morning  or  afternoon?" A question, Ardalan Shariat, Mehdi Kargarfard, Mahmoud Danaee, and Shamsul Bahri Mohd Tamrin tried to answer by determining, whether there were any significant  differences  in  hormonal response to a standardized high intensity resistance training regimen when it was performed once in the AM, once in the PM.

The natural ups and downs get lost, when a man goes through andropause (Bremner, 1983)
To this ends, the scientists recruited 20 healthy young male recreational lifters  (age 18.0± 1.3) with two years of experience in weightlifting. The subjects were randomized to to either the resistance exercise group (n=10), who completed a series of resistance exercise (3 times a week, in the afternoon, 6-7 repetitions, at 85% of 1RM for 3 weeks), or a control group (n=10), who did not exercise during the 3 weeks. The control group was installed to eliminate other effects, such as the circannial fluctuactions in testosterone levels as they were described, for example, by Reinberg et al. in 1978.

The workout was a classic full-body workout with a focus on exercises that work: Hang pulls, bench press, leg press, sated row, leg curl, shoulder press, lat pulls, knee extensions, arm curls each à 3 sets of 7 reps and sit-ups with 3 sets of 20 reps.
This is not an acute, only study! The good thing about the study at hand is that it's not testing the acute effects, but the chronic effects of resistance training on the circadian rhythm of testosterone. That's much different from the acute studies we know and of which we currently believe that they don't provide relevant information about the potential long-term effects of resistance training. This would obviously be different for a chronic change in the circadian testosterone profile - an upward shift, for example, could be anabolic, a crash, on the other hand, would almost certainly impair the strength and mass gains.
In contrast to a previous study by Kramer et al. which also lacked a control group, Shariat et al. moved the workout to the afternoon hours to mirror the training practices of the majority of trainees.
Figure 1: Circadian testosterone rhythm in response to resistance training in the PM (left; Shariat. 2014) and AM (right; Kraemer. 2001); mind the units (!) - pmol/mL on the left, pg/mL on the right!
In additon, the researchers chose a lower number of reps and correspondingly higher workout weight to "voke a larger effect on hormonal responses in comparison with Kraemer’s 2001 study."
If you look at the data in Figure 1, you will still see that the results Shariat et al. produced (left) are quite similar to those from Kraemer's 2001 study (right): 
"The main finding of the present study was that an intense period of intensive resistance-oriented sport activities provides a nominal temporary effect upon the testosterone circadian rhythm that diminishes an hour after the workout, after which testosterone levels return to normal." (Shariat. 2014)
The findings obtained through both resistance exercise and control groups obviously manifest a circadian pattern in which there is a presence of higher concentrations during the morning and lower concentrations during the evening and it is under circadian patterns.
So, when do I train, now? The answer to this question is easy: Whenever you have time and feel that it works for you. There is no "best time to train" for everyone and if you have to work at 9am, what would be the use of a (if anything marginally) increased anabolism from working out at 8am if you have to stress yourself like crazy to arrive at your working place in time?
Bottom line: Overall, the study at hand confirms the results Kraemer et al. presented in their paper in the European Journal of Applied Physiology in 2001, already. As Shariat et al. point out, neither AM nor PM training will have lasting effects on the circadian rhythm of testosterone concentrations.

In view of the fact that the acute effects remain acute (at least as long as you are not overtraining, there are no chronic effects on T-levels or their rhythm) the results of the cited studies leave us with the previously mentioned insight that the interaction between exercise and free testosterone could be less important for the anabolic cascade that's triggered in response to a workout than broscience would tell us.
  • Bremner, William J., Michael V. Vitiello, and Patricia N. Prinz. "Loss of Circadian Rhythmicity in Blood Testosterone Levels with Aging in Normal Men*." The Journal of Clinical Endocrinology & Metabolism 56.6 (1983): 1278-1281.
  • Kraemer, William J., et al. "The effect of heavy resistance exercise on the circadian rhythm of salivary testosterone in men." European journal of applied physiology 84.1-2 (2001): 13-18.
  • Reinberg, Alain, et al. "Circadian and circannual rhythms in plasma hormones and other variables of five healthy young human males." Acta endocrinologica 88.3 (1978): 417-427.
  • Shariat, Ardalan. Intensive Resistance Exercise and Circadian Salivary Testosterone Concentrations among Young Male Recreational lifters. Diss. Islamic Azad University, Roudehen, Iran. 4, 2014.
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