Overtraining trigger Cortisol, the hormone made in Adrenals, which break muscles into small pieces of carbon. Then another hormone, Insulin, made in Pancreas, change those pieces to glucose for additional energy, and all exercise effort is gone. Cortisol also relieves pain. When muscles are in pain cortisol is released to mitigate pain so damage to muscles is doubled.
Don’t try to exercise when your muscles are sore. U can make even more damage and definitely u don’t achieve desirable muscle growth or fat loss if u are after 40.