Eccentric Quasi-Isometric vs. Isotonic Resistance Exercise of the Elbow Flexors
Acute Neuromuscular, Set, and Sex-Differences in Untrained Individuals When Using a Unilateral Model
DOI:
https://doi.org/10.51224/SRXIV.508Keywords:
Muscle, Fatigue, weight trainingAbstract
Traditional isotonic resistance exercise (TRD-RE) improves muscle mass, strength, and overall health. However, TRD-RE may be impractical or unfeasible in injury or sport specific situations. Compared to TRD-RE, eccentric quasi-isometric resistance exercise (EQI-RE) is a low-velocity resistance exercise modality suggested to acutely produce similar and/or greater time under tension, motor unit recruitment, and antagonist co-activation. With limited investigations or comparisons to other forms of resistance exercise, however, evidence is lacking. As differences between males and females exist in time under tension and motor unit behaviour in other resistance exercise contexts, the current study explored sex-differences in time under tension and surface electromyography (sEMG) across 2 sets of TRD-RE and EQI-RE. Twenty-seven (n = 13 females) participants performed unilateral TRD-RE and EQI-RE of the elbow flexors while sEMG was collected from the biceps and triceps brachii. Several main and interaction effects of resistance exercise type, set, and sex were present for time under tension, linear envelope peak (LEpeak), absolute (iEMGabs) and relative (iEMG%) integrated sEMG, with set 1 typically having higher sEMG values than set 2, and EQI-RE having greater time under tension than TRD-RE. Notably, females produced significantly more time under tension, iEMGabs, iEMG%, and co-activation than males during EQI-RE, while males experienced a more significant set-to-set reduction in time under tension and LEpeak during TRD-RE. Overall, TRD-RE may result in quicker voluntary excitation and subsequent fatigue of motor units compared to EQI-RE, while females may accrue more resistance exercise volume than males when performing EQI-RE. Theoretically, these effects could lead to long-term sex-differences in strength and hypertrophy outcomes between males and females, TRD-RE and EQI-RE.
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