The effect of leg preference on mechanical efficiency during single-leg extension exercise

To investigate how leg preference affects net efficiency (η_net), we examined central and peripheral hemodynamics, muscle fiber type, activation and force of preferred (PL) and nonpreferred (NPL) leg. Our hypothesis was that PL greater efficiency could be explained by adaptations and interactions between central, peripheral factors, and force. Fifteen young participants performed single-leg extension exercise at absolute (35 W) and relative [50% peak power-output (W_peak)] workloads with PL and NPL. Oxygen uptake, photoplethysmography, Doppler ultrasound, near-infrared-spectroscopy deoxyhemoglobin [HHb], integrated electromyography (iEMG), maximal isometric force (MVC), rate of force development (RFD_50-100), and muscle biopsies of both vastus lateralis were studied to assess central and peripheral determinants of η_net. During exercise executed at 35 W, η_net was 17.5 ± 5.1% and 11.9 ± 2.1% (P < 0.01) in PL and NPL respectively, whereas during exercise at the 50% of W_peak was in PL = 18.1 ± 5.1% and in NPL = 12.5 ± 1.9 (P < 0.01). The only parameter correlated with η_net was iEMG, which showed an inverse correlation for absolute (r = -0.83 and -0.69 for PL and NPL) and relative workloads (r = -0.92 and -0.79 for PL and NPL). MVC and RFD_50-100 were higher in PL than in NPL but not correlated to η_net. This study identified a critical role of leg preference in the efficiency during single-leg extension exercise. The whole spectrum of the central and peripheral, circulatory, and muscular determinants of η_net did not explain the difference between PL and NPL efficiency. Therefore, the lower muscle activation exhibited by the PL is likely the primary determinant of this physiological phenomenon.NEW & NOTEWORTHY This study examined the impact of leg preference on efficiency during single-leg exercise. The results revealed lower efficiency of the nonpreferred leg during exercises performed at absolute and relative workloads. Central (cardiac output) and peripheral (fiber typing) determinants of efficiency did not explain the difference between the legs. However, the lower muscle activation of the preferred leg that was inversely correlated with efficiency is likely the primary determinant of this physiological feature.