Muscle fibers have 2 recruitment patterns:
- Innervate units that recruit the same fibers, but do so at different times, so that some can rest while others work.
- Fibers that are more fatigue-resistant are recruited before fibers that are rapidly fatigued.
Time-under-tension is a well-known tool, which is known to encourage growth. The longer the muscle is under tension the more micro trauma is incurred, which causes a growth stimulus. But when it comes to the nervous system – both central and peripheral nervous system – training to failure is not a great stimulus for growth. As the muscle fibers exhaust, failure becomes imminent, and the nervous system recruits all available motor units and fires them as much as possible; however, as maximum contraction continues, this frequency of firing decreases.
What does this mean?
The nervous system controls the muscles through electrical impulses. Over trained or recently trained muscles require larger signal to actually complete contractions of the same magnitude as a fresh, rested muscle. By training intuitively, one can still cause sufficient micro trauma to the muscle fibers to encourage growth and that too without continually draining the nervous system. Training to a stage just before the failure will still create gains and help to lower body fat.
This relates to the peripheral nervous system, so what about the central nervous system?
The CNS functions by sending electrical impulses through the nerves to the designated motor unit. This signal is not sustained for prolonged periods of time with the speed and power for optimum frequency. Eventually, a state of break point is reached to prevent itself from further stimuli. This is the point when one seems to lose all strength and drop the weight in pure exhaustion.
So what does this mean?
By training to failure each time one trains, it will set the nerve cells into a constant state of inhibition, causing to tax the CNS too much through the increased output of the electrical impulses. It also means that it’s not always a muscular failure that is occurring; it is more a central nervous system failure, which means that the muscles are not being worked anyway, so stimulus for growth is not being achieved every time you train.
So, in conclusion to this, muscular failure, even if it’s concentric, eccentric or isometric, is not necessary to provide a growth stimulus. Important factors are good form, continuous training, and the buildup of fatigue products, and good diet and resting patterns.