Seven Things We Know About How Hormones Affect Muscle & Strength Development

Strength training builds muscle. Lifting heavy stuff makes you stronger. By training with a certain volume and intensity, you can produce a significant release of the hormones, growth hormone (GH), testosterone, and insulin-like growth factor (IGF-1). It’s been widely accepted that this hormone response promotes muscle building. Recent evidence shows it may not be so!

A close look at research from the past five years shows that even though there are numerous associations between these hormones and hypertrophy, contradictions abound. For example, a series of studies from a Canadian research group have found that although testosterone, GH, and IGF-1 promote growth in certain situations, the post-exercise hormone response does not influence protein synthesis or hypertrophy.

Still, the “hormone hypothesis” that acute post-workout increases in hormone levels play a primary role in building muscle and strength persists. Here’s what we do know:

1) Resistance training can result in a post-workout increase in the hormones, testosterone, GH, and IGF-1. However, these hormones are not necessary for building muscle or gaining strength, and it’s possible that the exercise-induced response has no effect on muscle development.

The research group from Canada did a 15-week study in which they had young men train their biceps under two separate hormone conditions:

A Low Hormone condition in which one arm performed biceps curls only (4 x 10 at 95 percent of the 10RM) twice a week and a High Hormone condition where they trained the contralateral arm with the same exercises followed immediately by a bout of leg exercises (5 x 10 leg presses, and 3 x 12 of leg extension/leg curl supersets). The High Hormone condition produced a significant elevation in testosterone, GH, and IGF-1, and the Low Hormone condition did not.

Results showed that there were no differences in protein synthesis rates, muscle growth, or strength gains between the two conditions. Researchers suggest that the post-exercise hormone response has no effect on hypertrophy. As seen in the Low Hormone condition, hypertrophy and strength development occur in the absence of a post-exercise hormone response.

Take Away: There is a hormone response to certain training protocols. Is it relevant to muscle building? Maybe not. Hypertrophy and strength development occur to a similar degree whether the “anabolic” hormones are present or not.

2) A recent study from Norway found contradictory results to the Canadian study. Researchers used the same within subject design but had trainees lift legs before the biceps workout in the High Hormone condition. They also trained greater volume: The Low Hormone condition performed two sets of biceps curls, hammer curls, and pronated biceps curls. The High Hormone condition did 3 sets of leg press, knee extension, and knee flexion followed by the same arm workout.

Results showed that the High Hormone group gained significantly more strength and more muscle than the Low Hormone group. The High Hormone group increased cross-sectional area of the biceps more than the Low Hormone group.

Researchers suggest the elevated hormones are responsible for the superior muscle and strength gains. This study has been criticized because training loads were not different between the two conditions, but final 1RMs were. In addition, the increase in muscle CSA only occurred at two out of four measured sites.

One review of this study suggests that if post-exercise hormone response affects muscle development, the magnitude of the effect is fairly modest. Of course, even a modest increase in hypertrophy could be relevant for elite athletes or body builders.

Take Away

Considering the conflicting evidence on hormones, hypertrophy, and strength development, we can’t make definitive conclusions about the role of GH, IGF-1, and T. If an effect exists, it is fairly small. This may be relevant to elite athletes or body builders, particularly when considering the long-term development of strength and muscle over a lifetime.

3) Testosterone has a general anabolic effect. However, this does not mean that the post-workout increase in testosterone affects muscle development because the elevation simply does not last long enough to significantly influence protein synthesis. For example, the Canadian study discussed in #1 showed nearly a 2.5-fold increase in free T in the High Hormone condition, but this did not lead to greater protein synthesis, muscle growth, or strength.

Take Away

Post-exercise testosterone elevations are NOT required for muscle growth.

4) Having an optimal resting level of testosterone is extremely important for male health and body composition. Higher resting levels of T are associated with greater muscle mass, less body fat, better bone strength, and less risk of all-cause mortality as men age.

In addition, it’s been shown that suppressing T in young men who are resistance training leads to less muscle and strength development. The same thing happens to older women with low resting T levels.

Supraphysiolgical doses via T supplementation, which are much greater than the amount seen post-workout, lead to significant muscle and strength gains. In addition, pre-competition testosterone levels have been shown to correlate with performance in athletes.

Take Away: Although the post-workout T response isn’t necessary to build strength or muscle, it is still extremely important and relevant for health and athletics. Supporting the body’s ability to produce T with diet and lifestyle may be most important.

5) Growth hormone can enhance fat metabolism and it stimulates cellular uptake into various proteins, including muscle. It’s suggested that GH’s primary role in building muscle is via its ability to enhance the action of IGF-1, rather than to control protein synthesis.

Similar to the situation with T, it’s unclear if the exercise-induced increase in GH increases the hypertrophic response to training. Surely, hypertrophy can occur in the absence of GH release as seen in the Canadian study.

It’s possible GH may be most relevant for fat loss. Some researchers have suggested that the purpose of growth hormone release during training is to mobilize fuel stores in the body during intense exercise.

Take Away

It’s unlikely that the exercise-induced increase in GH significantly influences muscle development. However, GH has generally been shown to mobilize fat burning, have an anti-catabolic effect, and improve protein synthesis, conveying relevance to this hormone for body composition.

6) IGF-1 isn’t necessary to build muscle for the average person—studies show a working IGF-1 receptor is not needed for muscle growth from resistance training—but it may lead to greater gains for the more advanced trainees. For example, in a study of trained men who did near maximal bench press training, expression of IGF-1 and the related hormone, Mechno Growth Factor (MGF) were increased dramatically, which may have “kick started” dormant satellite cells—muscle cells that won’t grow unless activated.

Researchers suggest that for long-term gains in muscle mass, as in body builders or advanced athletes, IGF-1 and MGF may be most relevant because of the effect on satellite cells. For example, one research analysis showed there were extreme hypertrophy responders, moderate responders, and non-responders in a 16-week training study. Mechano Growth Factor was 126 percent greater in the extreme responders compared to the non-responders.

Take Away

Greater IGF-1 and MGF response to training appears to enhance hypertrophy for more advanced trainees. The ability to elevate these hormones and activate satellite cells is critical for maximal muscle growth and likely plays a role in strength development.

7) Given the inconsistencies in the research, it is premature to draw definitive conclusions about the role of exercise-induced hormones on hypertrophy. Nonetheless, the effect of appropriate training overload is still muscle development, and the training parameters known to promote hypertrophy are effective. They just happen to be effective due to enhanced protein synthesis that is not thought to be a direct result of hormone response.

Instead, two key factors are proposed as critical for hypertrophy:

• The activation of gene signaling pathways due to time under tension.
• Optimal nutrition in the form of whey protein intake, and specific amino acids (leucine) during the immediate and extended post-workout period.

In addition, it’s possible genetic factors influence a person’s response to post-exercise hormonal increases. Also, there is a major lack of research on trained individuals. Research shows that hormonal levels following training have been shown to be much greater in strength athletes than endurance athletes or sedentary people. This suggests that hormone response may play a role in hypertrophy and strength development in the long term.

Take Away

Proper training and nutrition are critical for muscle building. The most important factor at a given time will be unique to the individual. The hormone response to training may influence hypertrophy in trained individuals over the long-term.