A recent New Scientist feature focused on electrical-stimulation techniques used to treat disorders such as depression and anxiety. This clinical procedure of days gone by, portrayed so starkly in One Flew Over the Cuckoo’s Nest, is being resurrected in the rapidly evolving field of neuroscience. And if it can be shown to work for the brain (which, though an organ, acts like a muscle – in other words, it can be trained to improve), it could also boost the credibility of neuromuscular electrostimulation systems that claim to improve sporting performance. A recent paper in the journal, Frontiers in Physiology looked at the evidence.
A team of researchers led by Professor Menno Veldman of the Centre for Human Movement Sciences in the Netherlands waded through years of research and journals, and came to two key conclusions. First, neuromuscular electrical stimulation (NMES) increases muscular strength by increasing muscular tension, and second, though evidence remains equivocal, NMES also elevates endurance performance.
So what mechanisms are at play? It seems the neurological process that increases strength involves electrical stimulation (from devices such as those produced by Compex) depolarising the motor neurons of the nervous system. High-frequency electrical pulses (around 50Hz) from electrodes planted on the skin, for instance, triggers muscle contraction up to 60% of maximum.
However, several studies suggested that high-frequency NMES training has a negligible effect on endurance performance – a conclusion disputed by the new paper’s authors. Why? First, they argued, a session of high-frequency NMES induces an exaggerated metabolic and cardiovascular stress, primarily due to increased motor-unit recruitment.
“Secondly, high-frequency NMES results in a fast-to-slow shift in fibre type distribution together with increased oxidative capacity and capillarisation of the stimulated muscles,” the researchers stated, highlighting that these are key attributes of a highly endurance-trained individual.
Still, the technique’s physiological impact on boosting strength and endurance at the same time is disputed; further research should be encouraged, say the authors, to prove whether or not such training delivers benefits.
The authors also examined the impact of low-frequency NMES on muscle and functional endurance. Though noting the scarcity of research in this area, they discovered three studies that pointed to improved work capacity and oxygen consumption at the anaerobic threshold – both positive traits in triathlon.
Is this relevant to the active triathlete, you might ask? Yes, respond the researchers. Not only is NMES useful when recovering from injury if weight-bearing exercise is curtailed, it’s also of benefit when time is short and you want a brief ‘sedentary’ workout.
High-frequency NMES training is purportedly beneficial for strength, with a frequency up to 50Hz applied intermittently.
Low-frequency NMES (10Hz and under) could boost endurance. Apply continuously rather than in intervals.
New to NMES? Start at a low frequency. In rare cases, users have reported nausea.
Research shows that ‘less-fit’ individuals benefit more from NMES training than unfit ones.