Abstract:

PURPOSE: The hip extensors (gluteus maximus [GMax] and hamstrings) and knee flexors (hamstrings) play an important role in enhancing performance and reducing injury risk, during numerous athletic tasks. Additionally, the erector spinae (ES) muscles contribute to stabilization of the spine and therefore transference of forces from the lower to the upper body. Appropriate exercise selection and programming is, therefore, important for strengthening such muscles. It is important, therefore, to accurately determine the level of activation of these muscles, via electromyography (EMG), to permit effective comparisons between exercises. Interestingly, while researchers have reported very high EMG values (100-200% of maximum voluntary isometric contraction (MVIC)) for the hamstrings during the razor curl, these values were likely elevated due to suboptimal normalization techniques. Currently, no comparisons in peak EMG between the Russian curl and razor curl appear to have been published, which formed the aim of this investigation. METHODS: Subjects (n = 10; age = 23±4 years, height = 175.9±6.9 cm; mass = 75.2±9.7 kg) had EMG electrodes placed on GMax, biceps femoris (BF), and ES in accordance with SENIAM guidelines. Subjects performed 3 MVIC trials during hip extension, knee flexion and lumbar extension using an isokinetic dynamometer to normalize peak EMG. Subjects then performed 3 repetitions of both the Russian curl and the razor curl, in a randomized order. EMG data were analyzed in Microsoft Excel, identifying the start of the extension phase of the exercises based on thresholds of >2 standard deviations + mean EMG during periods of residual EMG, with the start of the flexion phase identified via a manual trigger during a pause between phases. Reliability between trials was assessed using intraclass correlation coefficients (ICC) and coefficient of variation (CV). Peak EMG data were compared between exercises, for both phases, using paired samples t-tests or Wilcoxon’s tests, based on the normality of data. Hedges g effect sizes were also calculated to determine the magnitude of differences in peak EMG between exercises. An a priori alpha level was set at p < 0.05. RESULTS: High reliability (ICC >0.80) was observed for all EMG data, with low variability (CV < 10%) for all muscles, other than the GMax during both phases of the razor curl. During the extension phase, greater peak EMG was observed in the BF and ES during the razor curl compared to the Russian curl, but not for the GMax. In contrast, during the flexion phase, peak EMG was greater for the BF and ES during the Russian curl compared to the razor curl, although not for the GMax (Table 1). PRACTICAL APPLICATIONS: The Russian curl is likely a more effective exercise for strengthening the BF and ES muscles compared to the razor curl, based on the EMG during flexion phase.

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