4 Hormones and Their Impact on Your Training Regimen


Aggressive young man in glasses screaming and tearing off his shirt over blackboard background

1. Testosterone

Testosterone is an androgen hormone produced in both males and females, although the amount is 15-20 times greater in men. Testosterone interacts with muscle tissue, primarily affecting muscular size. This is why it is much easier for men to grow larger muscles than women. Testosterone affects muscle size directly by promoting protein synthesis—the process of building new muscular tissue. It affects muscle size indirectly by increasing growth hormone production, and potentially negating the catabolic (tissue breakdown) effects of cortisol. Additionally, testosterone levels tend to decline with age, but consistent resistance training has been shown to combat this decline and improve testosterone levels in aging populations.

What you need to know to improve your training:

Testosterone levels increase as a result of resistance training in both men and women, although, as mentioned earlier, this increase is much smaller in women. More specifically, performing large, compound movements (such as deadlifts and squats) at roughly 85-95% of one’s single-rep maximum (1RM) has been shown to have the greatest effect on post-workout testosterone levels. Additionally, workouts containing moderate to heavy volume (multiple sets) and short rest intervals (30 seconds-1 minute) also lead to greater increases in testosterone levels compared to single-set workouts or workouts containing longer rest periods. Therefore, if your goal is to build muscle, your workouts should contain multiple sets of heavy compound movements with short breaks between sets. Additionally, because of their lower testosterone production, women do not need to worry about building bulky muscles, even if they follow an intensive weight lifting routine.

Thyroxine molecule, chemical structure. Thyroid gland hormone that plays a role in energy metabolism regulation. It is a iodine containing derivative of thyrosine. Atoms are represented as spheres with conventional color coding: hydrogen (white), carbon (grey), oxygen (red), nitrogen (blue), iodine (purple).

2. Growth Hormone

Growth hormone is produced by the pituitary gland, and promotes protein synthesis leading to increased muscular size of type I and II muscle fibers (slow- and fast-twitch muscle fibers, respectively) while also aiding in tissue repair and recovery. Additional effects of growth hormone include an increase in fat breakdown, stimulation of cartilage growth, and enhanced immune cell function. Growth hormone plays a vital role in the normal development of children, but also plays a role in stress adaptations. Outside of exercise-related factors, variables such as age, gender, nutrition, sleep, and alcohol consumption affect growth hormone release. Additionally, resting growth hormone levels of women vary depending on their menstrual cycle.

What you need to know to improve your training:

Greater growth hormone levels have been measured with resistance training containing short rest periods using moderately heavy loads. If increasing muscular size is your primary goal (as opposed to maximal strength-related goals), you can maximize growth hormone secretion by keeping your rest intervals below one minute, and completing multiple sets of at least ten repetitions (using a weight that you couldn’t lift for an 11th rep).

Illustration showing insulin and glucose in bloodstream

3. Insulin-Like Growth Factor

There are two different types of insulin-like growth factor (IGF): IGF-I and IGF-II, both of which are stimulated by growth hormone, thyroid hormones, and testosterone. They act very similarly to insulin. The process of IGF-I synthesis (most commonly studied) can take anywhere from 8-29 hours following the release of growth hormone and is believed to positively affect protein synthesis. Although the exact mechanism for this benefit is still unclear, it is believed to support the functioning of growth hormone. While IGF is stimulated by the interplay of other hormones, nutrition plays an important role in the amount of IGF released. In one study, participants had higher levels of IGF post-workout when they consumed a carbohydrate/protein supplement pre- and post-workout.

What you need to know to improve your training:

Although IGF is believed to support the functioning of growth hormone in producing increased muscular size, studies have shown that the effect of exercise on IGF levels is not definitive. IGF levels post-workout seem to be more dependent on pre-workout levels of IGF— with an increase in IGF post-workout with low levels pre-workout, and no change when IGF levels are already high pre-workout. In other words, IGF seems to maintain an equilibrium point and acts in a supporting role to support the functioning of other hormones. Additionally, IGF seems to support the release of Brain-Derived Neurotrophic Factor (BDNF), which supports improved cognitive function as a result of exercise. Lastly, while levels of IGF seem to maintain a point of equilibrium, consuming a pre- and post-workout meal consisting of carbohydrates and protein may help elevate levels of IGF.

Hormone glucagon written on notebook. Test tubes and hormones li

4. Glucagon

Glucagon is a hormone secreted by the pancreas. Its main purpose is to work in tandem with insulin to regulate blood sugar. While insulin helps the body utilize sugar in the blood for energy, glucagon helps ensure that blood sugar levels never drop too low, preventing hypoglycemia. When there is not enough sugar in the bloodstream, negative side effects such as dizziness or fainting can occur. Glucagon combats these side effects by producing glucose (sugar) via glycogenolysis, the process of converting glycogen (stored sugar in the liver and muscles) into glucose, and gluconeogenesis, the process of converting protein into glucose to be used for energy. In other words, glucagon acts to create energy when there is a shortage of circulating nutrients.

What you need to know to improve your training:

Since glucagon is responsible for creating available energy when there is a lack in nutrients, it makes sense that glucagon levels are higher during prolonged endurance exercise. However, because glucagon converts this energy from protein (muscle) it can disrupt protein synthesis and lead to potential muscle wasting (burning away muscle). To prevent losing potential muscular gains, or even losing muscle you already have, make sure you have a plan for proper nutrient intake to replenish blood sugar, particularly during prolonged, endurance-type exercise (i.e. long-distance running).

Now that we’ve covered the full spectrum of hormones that are affected by exercise, you are in a better position to maximize the benefit each can provide you by manipulating your training sessions accordingly. Each hormone—insulin, cortisol, epinephrine, BDNF, testosterone, growth hormone, IGF, and glucagon—plays an important role in creating adaptation in the body as a result of the stress created by exercise. Having a basic understanding of each will help you better understand the role of your workouts, and how they can get you closer to your goals.


About Alex McBrairty

Alex McBrairty is a personal trainer based in Ann Arbor, MI. He educates his clients in exercise, nutrition, and behavior change to help them develop new habits and reach their goals. Alex also teaches, writes, and speaks about fitness motivation and behavior change.