I would say that a high percentage of folks who exercise are overtraining. It is important to keep the nervous system healthy and working efficiently. Performing too many reps, sets, and using an intensity greater than threshold repeatedly will result in poor synaptic transmission.
When the action potential fires from the nervous system to the muscle the muscle contracts. The more action potentials the weaker the synaptic transmission becomes. What this means is that the intensity of the stimulation to make the muscle contract becomes less. This is why during the normal lifting sequence we get fatigued on the last set and can't perform as many reps. The synaptic transmission has been depleted. So, if you continue to work the muscle and nervous system beyond the effective limit you will produce an overtraining effect.
You don't have to work a muscle at 100% intensity. This will cause a loss of anabolic hormone and cause cortisol to release. Working at 100% overstimulates the motor units. Whenever the motor units are overstimulated the natural secretion of anabolic hormone is not released. Our nervous system is very sensitive to any kind of external and internal stimulation. Working beyond threshold will weaken the nervous system.
I suggest that you use a weight that is 65-85% of your maximum. Workout with the higher end percentage at the beginning of the week, and the lower end percentage at the end of the week. The reason for this is because your nervous system will be able to handle the heavier load at the beginning of the week because you are coming off a rest from the weekend. As the week progresses the nervous system becomes weaker, due to physical and mental stress (from work, family, etc).
For some reason we were taught at an early age that more is better and that the heavier the weigh the better. But this is not true. The more is better philosophy will only hurt you in the long run. It is better to train smarter than to over train.
Bottom line: Your nervous system is very sensitive. It is the gateway to muscular contractions. When it becomes weak, muscle contractions become weak. Poor muscle contractions = no gains!
tags: Vince Gironda, Daryl Conant, Ron Kosloff, human cell, human cell human cell, human cell