Department of Physical Performance, Norwegian School of Sport Sciences, Oslo, NORWAY.
Med Sci Sports Exerc. 2022 Jun 1;54(6):974-983. doi: 10.1249/MSS.0000000000002864. Epub 2022 Jan 25.
Skeletal muscle perfusion and oxygen (O2) delivery are restricted during whole-body exercise because of a limited cardiac output (Q˙). This study investigated the role of reducing central limitations to exercise on the maximal fat oxidation rate (MFO) by comparing mass-specific MFO (per kilogram of active lean mass) during one-legged (1L) and two-legged (2L) cycling. We hypothesized that the mass-specific MFO would be higher during 1L than 2L cycling.
Twelve male subjects (V̇O2peak, 59.3 ± 8.4 mL·kg-1·min-1; mean ± SD) performed step-incremental 2L- (30%-80% of V̇O2peak) and 1L (50% of 2L power output, i.e., equal power output per leg) cycling (counterbalanced) while steady-state pulmonary gas exchanges, Q˙ (pulse-contour analysis), and skeletal muscle (vastus lateralis) oxygenation (near-infrared spectroscopy) were determined. MFO and the associated power output (FatMax) were calculated from pulmonary gas exchanges and stoichiometric equations. A counterweight (10.9 kg) was added to the contralateral pedal arm during 1L cycling. Leg lean mass was determined by DEXA.
The absolute MFO was 24% lower (0.31 ± 0.12 vs 0.44 ± 0.20 g·min-1, P = 0.018), whereas mass-specific MFO was 52% higher (28 ± 11 vs 20 ± 10 mg·min-1·kg-1, P = 0.009) during 1L than 2L cycling. FatMax was similar expressed as power output per leg (60 ± 28 vs 58 ± 22 W, P = 0.649). Q˙ increased more from rest to exercise during 1L than 2L cycling when expressed per active leg (ANOVA main effect: P = 0.003). Tissue oxygenation index and Δ[deoxy(Hb + Mb)] were not different between exercise modes (ANOVA main effects: P ≥ 0.587), indicating similar skeletal muscle fractional O2 extraction.
Mass-specific MFO is increased by exercising a small muscle mass, potentially explained by increased perfusion and more favorable conditions for O2 delivery than during whole-body exercise.
由于心输出量（Q˙）有限，全身运动期间骨骼肌灌注和氧气（O2）输送受到限制。本研究通过比较单腿（1L）和双腿（2L）骑行时每公斤活瘦体重的最大脂肪氧化率（MFO），来研究减少中枢运动限制对最大脂肪氧化率的作用。我们假设在 1L 比 2L 骑行时，MFO 会更高。
12 名男性受试者（峰值摄氧量，59.3 ± 8.4 mL·kg-1·min-1；平均值 ± 标准差）进行了递增式 2L-（30%-80% 的峰值摄氧量）和 1L（2L 功率输出的 50%，即每条腿的功率输出相等）骑行（平衡），同时稳定状态下的肺气体交换、Q˙（脉搏轮廓分析）和骨骼肌（股外侧肌）氧合（近红外光谱）被确定。从肺气体交换和化学计量方程中计算 MFO 和相关的功率输出（FatMax）。在 1L 骑行时，在对侧脚踏臂上添加了一个 10.9 公斤的砝码。腿部瘦体重通过 DEXA 确定。
绝对 MFO 降低了 24%（0.31 ± 0.12 比 0.44 ± 0.20 g·min-1，P = 0.018），而每公斤体重的 MFO 增加了 52%（28 ± 11 比 20 ± 10 mg·min-1·kg-1，P = 0.009）。当以每条腿的功率输出表示时，FatMax 相似（60 ± 28 比 58 ± 22 W，P = 0.649）。当按活跃腿表示时，1L 比 2L 骑行时，Q˙在休息到运动期间的增加更大（ANOVA 主要效应：P = 0.003）。运动模式之间组织氧指数和 Δ[脱氧（Hb + Mb）]没有差异（ANOVA 主要效应：P ≥ 0.587），表明骨骼肌的氧提取分数相似。
通过锻炼小肌肉群，每公斤体重的最大脂肪氧化率增加，这可能是由于灌注增加和 O2 输送的条件更有利，而不是在全身运动期间。
