Exercise Tolerance: New Insights From Single-leg Cycling Exercise

Abstract

The biological factors determining the maximal exercise capacity are typically assessed during whole-body exercise (e.g. double-leg cycling), implicitly assuming that limbs contribute homogeneously to exercise tolerance. However, given the presence of limb dominance, it is possible that the dominant leg may achieve greater peak O2 uptake (V̇O2peak) and be able to sustain greater power outputs during prolonged dynamic exercise compared to the non-dominant leg. PURPOSE: To investigate peak power output (PPO), V̇O2peak, and maximal lactate steady-state (MLSS) during double-leg as well as during dominant and non-dominant and counter-weighted single-leg cycling exercise performed with the dominant and non-dominant legs. METHODS: Twelve men (30 ± 5 yrs) during 12 to 14 lab visits performed: (i) a ramp-incremental test to determine PPO, V̇O2peak, and maximal O2 extraction; and (ii) 30-min constant-load tests to determine MLSS. These tests were performed using both legs (DBL), the dominant leg only (SLd), and the non-dominant leg only (SLnd). Gas exchange variables were measured with a metabolic cart; local de-oxygenation ([HHb]) of the vastus lateralis (VL) was measured using a frequency-domain NIRS; capillary blood samples were analysed for lactate concentration ([Lac-]b). RESULTS: PPO for DBL, SLd, and SLnd was different in each condition: 329 ± 38, 181 ± 30, 168 ± 27 W, respectively (p < 0.05). V̇O2peak for DBL, SLd, and SLnd was different in each condition: 3.43 ± 0.34, 2.92 ± 0.42, 2.74 ± 0.38 L·min-1, respectively (p < 0.05). The [HHb] amplitude of the VL was greater in the dominant compared to the non-dominant leg during both DBL (18.6 ± 8.5 vs 15.4 ± 9.5 mMol) and SL (15.4 ± 9.5 vs 11.6 ± 7.7 mMol) ramp-exercise (p < 0.05). These amplitudes were highly correlated with the V̇O2peak values observed during DBL dominant and non-dominant (r = 0.86 and r=0.91, respectively), SLd (r=0.79), and SLnd (r=0.71) RI tests (p < 0.05). The PO at MLSS for DBL, SLd, and SLnd was different in each condition: 183 ± 32, 119 ± 25, and 111 ± 24 W, respectively (p < 0.05). The V̇O2, [Lac-]b, and RPE values during SLnd and SLd were similar (p > 0.05) despite this lower PO. CONCLUSIONS: These data indicate a heterogeneous exercise capacity of the exercising limbs that should be considered when evaluating exercise tolerance during double-leg exercise.