Exploring the effect of repeated-day familiarization on the ability to generate reliable maximum voluntary muscle activation

Maximum voluntary isometric contractions (MVCs) are commonly used to normalize electromyography (EMG) data and must be reliable even if the individual has no prior experience performing MVCs. This study explored the effect of familiarization over three testing sessions on MVC performance and reliability by comparing muscle activation during standardized maximal and sub-maximal muscle contractions. Participants were recruited into two groups: (1) individuals who regularly engaged in upper body resistance training; (2) individuals with little or no prior experience in upper body resistance training. EMG was collected from two pairs of muscles; biceps brachii and triceps brachii from the arm, and erector spinae and external oblique from the trunk. The trunk muscles were chosen as muscles that are less frequently activated in isolation in day-to-day life. It was found that there were no significant improvements in MVC performance or within-day reliability over the three testing sessions for both resistance trained and non-resistance trained groups. Resistance-trained individuals showed a trend to be more reliable within-day than non-resistance trained participants. Day-to-day MVC reliability, particularly of the erector spinae muscle, was limited in some participants. This suggests that further efforts are needed to improve our capability of reliably eliciting muscle activation MVCs for EMG normalization, especially for muscles that are less frequently activated in isolation.