Endocrine system and resistance training

The endocrine system is responsible for the release and regulation of hormones during exercise that are responsible for the anabolic and catabolic processes in the body. Hormones have the potential for increase neural excitability, glucose utilization, protein synthesis and overall body repair after exercise and during sleep. The interaction between hormones regulates the physiological functions which if working optimally would lead to great sport performance adaptation. However, if hormones present disequilibrium, this could lead to stress, aging, loss of body mass, illness and eventually injury (Demling, 2005).

Testosterone – Physiologically, testosterone (T) plays a double role in the human body. The first one is the androgenic effects responsible for reproduction and male characteristics. The second is the anabolic effects, which is related to muscle building, stimulating protein synthesis and inhibiting protein degradation (Vingren et al., 2010). Testosterone is secreted by the testes in male and by the ovaries in females, and in turn is converted by 5α-reductase which is found in skeletal muscle (Tortora, 2012).  The production oftestosterone is also known to indirectly stimulate the production of Growth Hormone and Insulin like growth factor (Anabolic hormones) and suppress cortisol (catabolic hormones) (Komi.2003). Testosterone is known to increase during and post exercise, and the amount of T released is dependent on the type of exercise. Usually, high metabolic, high load and high volume are known to increase T levels (Kraemer & Ratamess, 2005) .

Cortisol - Commonly referred to as a glucocorticoid hormone, cortisol (C) is produced by the zona fasciculata of the adrenal cortex in the adrenal gland and its main physiological role is related to control glucose metabolism. Cortisol increases during stress such as the fight or flight response and during exercise the cortisol level rises correspondingly to exercise intensity (Hackney, Battaglini, & Evans, 2008). Cortisol is also known to be a powerful anti-inflammatory and immunosuppressive. However, a high concentration of C is related to the inhibition of bone formation, muscle weakness, risk of infection, suppression of calcium absorption and psycho-neurological detriments. This hormone stimulates a number of processes related to blood glucose, such as:

Synthesis of glucose from non-carbohydrate substrates such as amino acids and glycerol from triglyceride breakdown.

Mobilization of amino-acids and lipid metabolism.

Stimulation of Beta-Oxidization which helps during hydrolyses of triglycerides as a spare source of energy.

Improving gluconeogenesis and glycogenolysis via glycogen.

Enhancing the expression of enzymes involved in the gluconeogenesis pathways. This is a key metabolic function of glucocorticoids (Crewther, Cook, Cardinale, & Weatherby, 2011)

Growth Hormone - Growth Hormone (GH) is released by the anterior pituitary gland, it is secreted during sleep and exercise and it has been is suggested to be responsive by the elevation in catecholamines mediated by exercise (Godfrey & Blazevich, 2004). GH is responsible for bone growth, stimulates insulin like growth factor (IGF-1), protein synthesis and influences metabolism. It works synergistically with IGF-1, increasing protein synthesis by facilitation of amino-acids transport. It is also a powerful lipolytic compound responsible for fat breakdown and inhibiting fat storage enzymes and facilitates carbohydrates metabolism utilization (Kraemer et al., 2010) 

Insulin like growth factor – IGF-1 is secreted by the liver and presents a structure similar to insulin. It is known to work synergistically with GH which in turn increases protein synthesis in cells and enhances hypertrophy (Kraemer & Ratamess, 2005). 

Insulin - Insulin is secreted by the pancreas and it is greatly affected by blood glucose concentrations. It is responsible for glycogen storage, promoting glucose into the cells and is involved in protein synthesis (Bachaele et al., 2008).

Hormonal response to exercise

Individual levels of T are related to factors such as training experience, total muscle recruitment, and exercise selection(Crewther et al, 2011). Multi-joint exercises elicit greater levels of T and exercises such as squats and Olympic lift produce the largest spike in T. In addition, intensity and volume need to be high enough to evoke hormonal adaptations, as a low volume of training is correlated to a low level of T (Cadore et al., 2008). Also, short rest intervals during exercises are known to raise T, GH and IGF-1 levels (Kraemer et al., 2010).

Hormonal response to a bout of resistance training appears to be dependent on the type of training modality. Hypertrophy workouts present the greatest concentration of T (West & Phillips, 2010) However, the training should be changed periodically to enhance anabolic response and adapt to individual responses (Buresh, Berg, & French, 2009). Nonetheless, the volume has to be tailored accordingly, too much  volume for untrained athletes might lead to greater cortisol response anda high volume for and an advance athlete might be needed to elicit hormonal responses (Cadore et al., 2008).  On the other hand endurance athletes such as runners present lower level of T compared to strength athletes.

Strength Training – Lower repetitions and longer resting intervals are characteristics of strength training. However, despite the fact that there is an increase in T & C levels from this type of training, T & C concentrations during strength training it is not as significant as hypertrophy training (Crewther, Cronin, Keogh & Cook, 2008). Also, senior athletes have shown an increase in overall T levels while engaging in a long term a strength training program (Kraemer et al., 1999).

Power Training – According to Fry and Lohnes (2010), high power exercises produce elevation on T/C levels and apparently are due to the hypertrophy characteristic presented by power athletes.  Crewther et al (2006), states that the adaptations to power is related to a combination of physiologic factors such as hormonal, neural and mechanic.

The combination of heavy training and power training (complex training) has shown a greater T response. This type of training has shown to be superior that training power alone and should be considerate during a training program (Beaven, Nicholas, Ingram, &, & Hopkins, 2011).

 Below is a comparison of a variety of studies and acute T response in men.

(Komi, 2003)

A – Bench press – 1 set at 70% RM max effort

B- Bench press - 6Sets/8Reps at 70%

C – Olympic lift exercises

D- Full Olympic exercises workout

E – 3Sets/4 exercise at 80% RM

F – Deadlifts - 5Sets/5RM – beginner athlete

G – Deadlifts - 5Sets/5RM - advanced athlete

H – Squats - 4 Sets/6Reps at 90%-95%

I & J– 8 exercises – 3Sets/ at 10RM – 1 minute rest interval

K – Bench press & Leg press – 5 sets at 10RM with 3 minute rest interval


Bottom line:

Hypertrophy training appears to elicit the greatest peak of hormone concentrations.

Although strength and power training elevates T as well as GH and IGF-1, it appears not to be enough to increase muscle cross sectional area. Therefore, strength athletes that are concerned in keep the weight should adopt this type of training.

Multi-joint exercises provoke superior T response and the intensity should be individually tailored to elicit the physiological adaptations.

It has been suggested that a greater production of lactic acid is related to higher GH serum concentrations (Komi, 2003).

Cortisol is fundamental during exercise; however it is also related to increase catabolic effects. Ingestion of carbohydrates during exercise decreases catabolic hormones and positively enhances the immune system (Gleeson & Bishop, 2000).


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