Weight training provides the stimulus for muscle growth, but behind the scenes, a bevy of hormones play a prominent role in supporting muscle hypertrophy. These hormones are known as anabolic hormones because they boost muscle protein synthesis and reduce muscle breakdown, so the muscle has the opportunity to grow. Your body produces these hormones even if you don’t strength train, but strength training itself may stimulate greater production of these hormones for a short time after a workout. Sometimes, bodybuilders use supplements to maximize the potential of these hormones.
It is not clear whether the additional anabolic hormones released after a resistance workout impact muscle gains. However, these hormones are still important for muscle growth and maintenance of muscle tissue. Some studies show that high-resistance strength training that emphasizes large muscle groups, high volume training, and short rest periods between sets favors the release of anabolic hormones that support muscle growth.
What are these hormones and how do they impact your ability to build strength and muscle size?
Testosterone
You might think of testosterone as being a male hormone, but women have low levels of testosterone as well. In fact, women have 10 to 20 times lower levels of circulating testosterone relative to men. In men, the testes produce testosterone, but in women, it’s the adrenal glands that release this anabolic hormone.
Testosterone impacts muscle growth in several ways. It can directly stimulate muscle tissue to grow. It also enhances the activity of another anabolic hormone that aids in strength gains, growth hormone. Finally, it can interact with nerve cells in the brain and affect the release of neurotransmitters, although this doesn’t directly impact muscle growth, it likely plays a role in the nervous system adaptations to strength training
Studies show a rise in circulating testosterone in men after heavy resistance training as well as after high-intensity aerobic workouts. It’s less clear whether women get a rise in testosterone after exercise, although some studies show a small bump up after heavy resistance training. In one study, researchers asked 60 healthy, young women to do six sets of 10RM squats. Afterward, the women showed a small but significant rise in circulating testosterone.
The best way to maximize the post-exercise rise in testosterone is to lift heavy (75–95% of one-rep max), focus on large muscle groups, perform mostly compound exercises, use short rest intervals (1 minute) and do multiple sets. (at least 3) The best exercises for maximizing testosterone release are deadlifts, squats, and bench press. One study also found that regular, high volume exercise in females (10 hours weekly) boosted testosterone and helped lower body mass index.
Growth Hormone
The very name, growth hormone, shows how anabolic this hormone is. Produced by the pituitary gland in the brain, growth hormone helps muscle cells take up the amino acids they need to grow and repair. Growth hormone also boosts muscle protein synthesis itself. That’s the secret to getting your muscles to grow! Growth hormone plays another role in body composition–it promotes fat breakdown to aid in fat loss. It also supports and stimulates the synthesis of cartilage and bone.
Your body releases most of the growth hormone it produces over a 24- hour period during deep sleep. This makes sense as growth hormone also helps your body repair and heal damaged tissue. No wonder sleep is so important for body composition! Other factors that impact the release of growth hormone include sleep habits, nutrition, gender, and age.
Growth hormone release decreases with age and the elderly don’t get the same boost in growth hormone that younger people do after a workout. According to one study, growth hormone release in older individuals was 4.7-fold less than in younger individuals. Research also shows that before menopause, women have higher levels of growth hormone relative to men with the amount varying with the menstrual cycle. Women also release more growth hormone after aerobic exercise relative to men.
Like testosterone, working large muscle groups with compound exercises and minimizing rest periods stimulates the greatest release. In one study where participants used a light resistance (28% of 7RM), there was no rise in growth hormone. So, there’s likely a threshold level below which resistance training doesn’t boost the release of growth hormone. So, focusing on compound exercises that work the large muscle groups in the lower body maximizes the post-workout release of growth hormone. Think squats and deadlifts!
IGF-1
IGF-1 is another name for insulin-like growth factor. IGF-1 is like a worker employed by growth hormone to help out. The liver produces IGF-1 under the direction of growth hormone. Insulin and nutritional factors also influence how much IGF-1 the liver produces. Low levels of insulin and decreased calorie intake reduce the liver’s output of IGF-1. Once released by the liver, IGF-1 circulates in the bloodstream freely or bound to binding proteins.
Research shows IGF-1 has an anabolic effect on skeletal muscle tissue. Along with insulin, IGF-1 turns on the mTOR pathway, the most important metabolic pathway for turning on muscle protein synthesis. Some research suggests that muscles damage boosts the release of IGF-1, so lifting heavier and emphasizing the eccentric portion of muscle contractions may be of benefit for boosting IGF-1. Eccentric contractions elicit more damage and disruption of muscle fibers. Protein increases IGF-1, especially animal protein.
The Bottom Line
It’s not clear how much a single exercise session boosts the release of anabolic hormones, but the literature suggests that lifting heavier and working large muscle groups via compound exercises maximizes the potential.
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