https://www.sciencedaily.com/releases/2 ... 091652.htm
Over the past few years, researchers have found evidence that lifting more repetitions of lighter weight can build muscle mass just as well as fewer reps of heavier weight. Even so, those who train with heavier weight still see greater gains in strength than those who lift lighter loads.
But if strength differs even when muscle mass does not, what explains the disparity?
Nathaniel Jenkins and his colleagues may have uncovered some answers by measuring how the brain and motor neurons -- cells that send electrical signals to muscle -- adapt to high- vs. low-load weight training. Their study suggests that high-load training better conditions the nervous system to transmit electrical signals from the brain to muscles, increasing the force those muscles can produce to a greater extent than does low-load training.
Muscles contract when they receive electrical signals that originate in the brain's neuron-rich motor cortex. Those signals descend from the cortex to the spinal tract, speeding through the spine while jumping to other motor neurons that then excite muscle fibers.
Jenkins found evidence that the nervous system activates more of those motor neurons -- or excites them more frequently -- when subjected to high-load training. That increased excitation could account for the greater strength gains despite comparable growth in muscle mass.
"If we see a decrease in voluntary activation at these sub-maximal force levels, that suggests that these guys are more efficient," Jenkins said. "They are able to produce the same force, but they activate fewer motor units to do it."
Placing electrodes on the participants to record the electrical signatures of their quadriceps reinforced those results. High-load training led to a substantially larger drop in electrical activity after six weeks, the study reported, and that activity was lower across most levels of exertion.