Science has shown in recent years that high intensity interval training involving short bursts of intense exercise is a great way to build strength, muscle mass and increase cardiovascular endurance. Now, research finds that the reason why high intensity exercise is so effective comes from better conditioning of the brain to do its part in the heavy lifting.
The interconnections between the brain, the nervous system and the development of muscle strength and power are continually being explored in new ways. In one direction and particularly with reference to the aging brain, research has uncovered how important exercise and keeping up muscle mass can be to staying mentally fit. A University of British Columbia study involving women with mild cognitive impairment found, for instance, that regular exercise classes can lead to cognitive and memory improvements, offering promise to slowing the progression of dementia.
Now, researchers at the University of Nebraska-Lincoln have found that the brain’s role in creating muscle strength and power may be even greater than previously thought. The study involved 26 men who trained for six weeks on a leg-extension machine, three times a week, with some assigned to exercise at 80 per cent of their maximum weight capacity and others at just 30 per cent, in both cases lifting until they couldn’t complete any more repetitions.
As in previous studies, the results showed similar growth in muscle mass for the two groups but a higher increase in strength — about ten pounds’ worth — in the high-load group. The researchers further tested what is known as voluntary muscle activation in the two groups, finding that the low-load group increased voluntary activation from 90.07 to 90.22 per cent whereas the high-load group’s percentage went from 90.94 to 93.29, a difference that the researchers saw as evidence that the brains and nervous systems of the participants in the high intensity group were employing more motor neurons in the physical action than those in the low-intensity group.
“During a maximal contraction, it would be advantageous if we are activating – or more fully activating – more motor units,” said Nathaniel Jenkins of the University of Nebraska Lincoln’s Department of Nutrition and Health Sciences and study co-author in a statement. “The result of that should be greater voluntary force production – an increase in strength. That’s consistent with what we’re seeing.”
Jenkins and colleagues hooked up participants to electrodes to measure electrical signals at their quadriceps and found that after six weeks of training, those in the high-load group had a higher drop in the electrical activity than the lower-load group, meaning that they were able to produce the same amount of force in a more efficient manner.
“From a practical standpoint, that should make the activities of daily living easier,” Jenkins said. “If I’m lifting sub-maximal loads, I should be able to do more repetitions with fewer motor units active, so maybe I fatigue a little bit slower.”
The role of brain power and strong neural networks in muscle development was further tested in a 2015 study at Ohio University, where participants had their arms voluntarily placed in casts for four weeks. Some were asked to perform mental imagery exercises five times a week where participants imagined themselves flexing and resting their immobilized wrists. After four weeks, those who did the mental exercises had lost 25 per cent of their arm strength while those who did not had lost 45 per cent.