Greater electromyographic responses do not imply greater motor unit recruitment and 'hypertrophic potential' cannot be inferred.

2 3 4 We read with interest the study by Looney et al. (13), investigating the effects of load on 5 electromyography (EMG) amplitude and rating of perceived exertion (RPE) during squats taken 6 to muscular failure. There are numerous interesting takeaways from this study, including the 7 similar RPE outcomes of different loads when sets are taken to failure; however, we demur with 8 the authors' interpretation of the findings. 9 10 In the title and the body of the article, the term motor unit (MU) recruitment is used 11 synonymously with EMG amplitude. This is an incorrect assumption, but regrettably a common 12 mistake in sports and exercise science. We find this mistake being made especially when dealing 13 with fatiguing and dynamic conditions, such as those investigated by Looney et al. (13). In fact, 14 Enoka and Duchateau (7) recently described how numerous studies have misinterpreted surface 15 EMG signals by inferring specific MU recruitment. More than two decades previously, De Luca 16 (4) stated, " To its detriment, electromyography is too easy to use and consequently too easy to 17 abuse. " Looney et al. (13) state that MU firing rate decreases with fatigue (10, 15) and 18 consequently that the increase in EMG amplitude is caused by increased MU recruitment (19-21) 19 and have applied that same logic to the subsequent interpretation of the findings, as the authors 20 repeatedly state that the greater EMG amplitude observed in the heavier conditions is indicative 21 of greater MU recruitment. Regrettably, the interpretation of EMG is not so straightforward. 22 Moreover, different quadriceps muscles may utilize different neural strategies to maintain force 23