Higher legs muscle mass reduces gross mechanical efficiency during moderate intensity cycling in young healthy men

Twelve healthy untrained men (age 22 ± 1 years; body mass (BM) 76.8 ± 14.4 kg; height 180 ± 8 cm, (mean ± SD)), participated in this study. The subjects performed an incremental exercise test on a cycloergometer with an increase of power output (PO) by 30 W every 3 min - until exhaustion. Gross mechanical efficiency (GE) and delta efficiency (DE) during exercise of moderate-intensity (below lactate threshold - < LT) was calculated. Both legs muscle mass (LMM) (determined using 3T MRI) amounted to 14.1 ± 2.1 kg (i.e., 18.6% of body mass). Pulmonary oxygen consumption (V̇O₂) at rest (sitting position) was 391 ± 42 mL min^-1. The slope of the V̇O₂(PO) relationship (at the PO's < LT) amounted to 10.25 ± 0.99 mL O₂ min^-1 W^-1 and the intercept 501 ± 130 mL min^-1. Pulmonary maximal oxygen uptake (V̇O_2max) was 3198 ± 458 mL O₂ min^-1, 42.2 ± 5.7 mL O₂ min^-1 kg^-1 BM and 187 ± 30 mL O₂ min^-1 kg^-1 of LMM. The LMM was positively correlated with the V̇O₂ at rest (p = 0.01). No relation between the LMM and the DE was found, whereas GE at the PO of 30-90 W was negatively correlated with the LMM (p ≤ 0.05). We concluded that greater muscle mass is not favorable when performing moderate-intensity cycling, since it results in poorer gross muscle mechanical efficiency.