Motor unit behaviour during resistance exercise

The Challenge

Blood flow restriction training (BFR) is a safe and novel adjunct that aims to partially occlude arterial inflow and fully restrict venous outflow in active muscles during exercise to enhance hypertrophic change. BFR is utilised during training and rehabilitation as it enhances hypertrophy at relatively low loads of resistance. Exercising during BFR restricts oxygenation, reducing efficiency of exercising muscle fibres resulting in the recruitment of additional fibres to sustain activity, thus increasing the potential for muscle hypertrophy. Both BFR and non-BFR high-intensity resistance exercise are hypothesised to be equally effective in increasing the recruitment of high threshold motors units, however, the potential for BFR resistance exercise to do this using low-intensities is particularly attractive. Until recently, research comparing BFR and non-BFR workouts has only utilised surface electromyography (EMG) which lacks the ability to uncover specific aspects of individual motor unit behaviour. As such, research is needed to better understand the mechanisms underpinning BFR training so that resistance exercise using this novel adjunct can be utilised to its full potential.

The approach

Recent advances in technology now enable the decomposition of surface EMG signals to reveal important details regarding individual motor unit behaviour (e.g., recruitment, firing rate, recruitment thresholds). The utilisation of this non-invasive technique will enable the acute responses to BFR and non-BFR training to be compared so the underlying mechanisms can be elucidated. Furthermore, consideration will be given to the effect of different arterial occlusion pressures on the motor unit responses to BFR which has not yet been considered.

The impact

By better understanding the motor unit responses to BFR and the influence of arterial occlusion pressure, the application of this technique in clinical practice can be optimised. This will have important considerations for populations in which the recruitment of high-threshold motor units may be advantageous at low resistance training intensities. This may benefit healthy individuals seeking to slow-down age-related decline but may also positively influence patients undergoing rehabilitation.