For many guys, it’s natural to experience a sense of accomplishment following an intense workout. But when you get obsessed with training Cardiello explains, it's easy to fall into the trap of thinking that "more is better." That has two dangerous effects: Overtraining and lowered self-esteem. Cardiello explains this feeling is related to the body's nervous system, since overtraining “affects an athlete’s level of ‘happiness’ to train, depression, insomnia, and irritability.” He also cautions overtraining can be heightened by such things as “lack of proper nutrition (hydration), proper sleep, and personal/work stressors.”
ATHLETES: Overtraining can seriously affect performance. Researchers have identified several short term key markers that result from overtraining, including "impaired anaerobic lactic acid perforance and a reduced time to exhaustion". [ 7 ] The same study discusses many other soon-to-follow issues including problems with uric acid levels, ammonia, creatine kinase, free testosterone/cortisol, growth hormone and so on. More subjective issues include excessively sore muscles and sleep and mood disorders. Again, overtraining is real and leads to real physiological issues.