Workouts stimulate the release of cortisol, or the "stress hormone," in your body. Your ancestors needed that boost of energy to chase after dinner or protect their family from marauders in the old days. Proper amounts of stress and cortisol trigger growth and increased capability in terms of cardiovascular health, muscle strength and general awareness. That growth occurs during the rest and recovery period, not during the exercise itself. It is during the rest period after exercise that endorphins and growth hormone are released. Endorphins and growth hormone flush cortisol out of your body.
While exercise results in endorphin release and can relieve stress, extended workouts stress the body and increase cortisol levels in a cumulative way. Aerobic workouts that last longer than 45 minutes and strength training that goes on for longer than an hour can cause cortisol levels to rise in a way that has negative health effects on the body rather than positive ones.
Cortisol and Stress
Cortisol is involved in the fight-or-flight reaction to stress. This steroid hormone alters your metabolism to provide immediate energy to deal with the stress. Chronic and prolonged stress elevates cortisol levels and triggers an emergency situation in the body. Fat is preserved, and muscle mass is broken down. The immune system is weakened, and heart rate and blood pressure are affected.
Physiological Effects of Extended Workouts
Extended workouts can lead to overtraining syndrome, a neuroendocrine disorder. High cortisol levels lead to altered sleep patterns, decreased performance and reduced testosterone levels. Fatigue is the most common result of overtraining and often is accompanied by depression, irritability or loss of enthusiasm for exercise. Physical symptoms include loss of appetite, muscle soreness and increases in injuries and viral illnesses.
The Importance of Rest
Improving fitness requires more than working out; adequate rest allows your body to respond to cortisol levels and stress in positive ways. During recovery, cardiovascular and muscular systems compensate for the stress levels you've imposed, improving in anticipation of such stress in the future. Human growth hormone rises during rest and expels cortisol from the body. Without rest and recovery, growth and regeneration cannot occur, and the effect becomes cumulative with chronic overtraining. A long break from workouts is necessary to overcome overtraining syndrome, and the duration of this break depends upon how long the extended workouts have gone on.
Interval Training
Interval training is a useful alternative to extended workouts. Short bursts of intense activity with rest periods in between can knock out stress and prevent high cortisol levels. The recovery periods allow the release of human growth hormone and endorphins, relieving muscular tension and replacing muscle mass. Alternating aerobic exercise with strength training is another way to maximize your workouts.
