We have all experienced fatigue due to stress from training. It may be because we worked out too hard or for too long without giving our body time to recover. But what we do not understand is how this happens and how we can manipulate our training to help optimize our performance and prevent overtraining and unscheduled overreaching.
Our endocrine system helps us get back to a homeostatic function to help respond to external stimulus. It tells our body to make certain changes to help support the demands of exercise and recovery. This system is important because it can help proper periodization for individuals.
Resistance training stimulates multiple hormones like testosterone, growth hormone, insulin-like growth factor, cortisol and multiple cathecholamines. To have proper training adaptation and continued progress optimization of these hormones may help boost training progressions.
Testosterone is the primary androgen hormone interacting with skeletal muscles. There is an indirect marker of motor unit activation and metabolic demands when there is an increase in testosterone concentration. The importance of circulating testosterone concentration for anabolic signal is the binding to its receptor which is key to stimulating anabolic function.
This hormone is responsible for GH responses that leads to synthesis of new proteins and an increase in strength and size. For this to happen high bound testosterone are needed in the blood to increase the potential for higher levels of free testosterone. For testosterone to interact with target tissues there must be free testosterone in the blood.
In women, they have significantly less testosterone compared to men, around 20 times less. Increase in testosterone post workout have not been seen but researches suggest that if there are some changes they are very little. But women who train with heavy resistance does increase but not as much as men. This can also vary per person as some women may secrete more testosterone compared to others.
How does testosterone affect training and performance?
It has been shown that a high intensity training with one to two reps at a lower volume may not change concentration of testosterone but can increase binding sites to testosterone and the number of receptors. On the other hand, an increase in catabolic tissue response can increase in testosterone during high-intensity aerobic endurance exercise. Although aerobic endurance can increase testosterone concentration, it can decrease muscle fiber size.
An increase in testosterone occurs in response of an exercise protocol. The cells then increase binding sites for testosterone to be utilized or due to the lack of need for testosterone use the binding sites to not increase testosterone utilization.
To increase concentration of testosterone in the blood, training and experience may be an important factor to alter testosterone concentration. Testosterone also influenced the nervous system through neural adaptations for strength gain in highly trained strength and power athletes.
Growth Hormone is a vital role in adaptation to the stress of resistance training. It directly responds to target tissues like bone, fat cells, skeletal muscle, immune cells and liver tissue.
The main physiological roles of growth hormone are:
-Decrease glucose utilization (does not turn into glycogen)
-Decrease glycogen synthesis (glucose does not turn into glycogen to be stored in the body)
-Increase amino acid transport (provides amino acid for protein synthesis)
-Increase protein synthesis (creating new protein)
-Increase utilization of fatty acids (More FA to target tissues to make ATP and create protein)
-Increase lipolysis (breakdown of fat, increase availability of nutrients in the blood -fatty acids-)
-Increase availability of glucose and amino acids (increase number of glucose transporters in the membrane to uptake more glucose it can then increase protein synthesis in the skeletal muscle)
-Stimulate cartilage growth (Helps bone grow in length)
How does growth hormone affect training and performance?
Growth hormones responds to the stress of exercise. Although a threshold must be reached to elicit GH response to resistance training especially with resting time under 3 minutes. Growth hormones stimulates insulin-like growth factor 1 (IGF-1) from the liver, protein synthesis, growth and metabolism.
An increase in GH is sensitive to the volume of exercise, the amount of rest and the resistance used. For example, a training day of 10 RM for 3 sets (that equals to 60,00 Joules) and short rest (<1min). Short rest results in higher serum concentrations vs long rest.
Although there it has been observed that there is little change in measurement of resting GH concentrating in elite lifters.
Insulin-Like Growth Factor (IGF)
Insulin-like growth factor (IGF) is secreted by the liver after GH stimulates the cells to start synthesizing IGF. IGF secretes its own binding proteins within the muscle to modulate the responsiveness of the cells to IGF. For IGF to be viable for a longer period that can reduce IGF degradation, binding proteins must be released. Small changes in nitrogen balance, protein intake and nutrition status affect a variety of mechanism.
IGF increase glucose and amino acid uptake in the target cells to provide energy for cell function. This then signals the pancreas to secrete insulin to direct muscles and fat cells to increase glucose uptake. When glucose is not used it is converted into glycogen and stored.
How does Insulin-Like Growth Factor affect training and performance?
Insulin-Like Growth Factor was responsive to exercise but with the increase in growth hormone, there were no increase in IGF. IGF is more sensitive to caloric loads with supplementation of carbs and protein before and after a workout
Cortisol is a primary signal for the metabolism of carbohydrates and glycogen stores despite it being viewed as a catabolic hormone in skeletal muscle. When glycogen stores are depleted, the body catabolizes protein to produce energy to support blood glucose concentration maintenance.
It stimulates amino acid conversion to carbs and increases enzymes that breakdown protein and inhibits protein synthesis (Proteolytic Enzymes). It effects Type II fibers more than Type I fibers due to Type II fibers having more protein.
Cortisol’s catabolic effects are countered by the anabolic effects of testosterone and insulin. When testosterone receptors increase it blocks cortisol and its receptor inhibiting cortisol to bind and conserving and enhancing protein. On the other hand, when there is an increase in cortisol receptor protein is lost and degraded.
How does cortisol affect training and performance?
High volume utilizing large muscle groups and short rest periods increases cortisol values. A chronic high concentration of cortisol may have catabolic effects, an acute increase can help muscle tissue remodeling and blood glucose maintenance. But for overtraining problems to happen cortisol concentration levels may need to be greater than 800 mmol/L.
The primary catecholamine is epinephrine (adrenaline), but there is also norepinephrine (noradrenaline) and dopamine which are secreted in the adrenal medulla. These catecholamines are important in short expressions of strength and power.
Their roles are:
-Increase the production of force and metabolic enzyme activity
-Increase the rate at which muscle contracts
-Increase blood pressure
-Increase available energy
-Increase muscle blood flow
-Change the secretion rate of other hormones like testosterone
How does cortisol affect training and performance?
For an athlete to increase their ability to release huge amounts of epinephrine, they must train at with heavy resistance which will increase epinephrine secretion during maximal exercise.
Also training variability is important to prevent the adrenal gland from continued production of catecholamines and delay recovery due to cortisol’s negative effects on the immune system cells and protein structure.
How can you change training programs to enhance endocrine system response?
Testosterone: train in the 85%-95% of 1RM with short rest intervals, higher exercise volume and train larger muscle groups. Two years or more of resistance training can also help with increasing testosterone concentration.
Growth Hormone: 10RM at high intensity, 1 minute or less rest periods and 3 sets of every exercise. While supplementing with carbs and protein before and after training.
Adrenal Hormone Response (Cortisol & Catecholamines): Variation in training, high volume, short rest periods while training large muscle groups.
How different training modes affect production and secretion of hormones.
Testosterone secretion increases as a response to exercise and can vary based on training and experience. By secreting testosterone, it increases its binding sites to cells which reduces cortisol’s catabolic effects. Testosterone secretion then stimulates the release of growth hormone to help with protein synthesis and improve strength and size of a muscle.
With the secretion of growth hormone to the target cells (liver, skeletal muscle, bones and a fat cells), there is an increase in protein synthesis due to the increase in availability of amino acid in the blood. Glucose, fatty acid and amino acid uptake increases in the target muscles to use for energy and protein synthesis. Lastly when glucose is used there is decrease in glycogen being stored.
The Secretion of growth hormone in the liver signals insulin-like growth factor to be released and increase glucose and amino acid uptake in the target cells. It also signals the secretion of insulin in the pancreas to tell the muscles and fat cells to increase glucose uptake.
During heavy resistance training, catecholamines are secreted to help with acute strength and power output. Without variability, adrenal fatigue may occur.
Vingren, Jakob L., and Barry A. Spiering. “Endocrine Responses to Resistance Exercise.” Essentials of Strength Training and Conditioning, by William J. Kraemer, 5th ed., Human Kinetics, 2016, pp. 65–86.