It is not clear if fat oxidation is attenuated at higher exercise intensities, when exercising with a small muscle mass, and therefore, we studied leg fat oxidation during graded one‐leg exercise. Ten males (age: 27 ± 2 years, body mass: 82 ± 3 kg, BMI: 24 ± 1 kg m−2, V̇O2max: 49 ± 2 mL min−1 kg−1) performed one‐leg exercise at 25% of maximal workload (Wmax) for 30 min, followed by 120‐min exercise at 55% Wmax with the contralateral leg, and finally 30‐min exercise at 85% Wmax with the first leg. Blood was sampled from an artery and both femoral veins, and blood flow was determined using Doppler ultrasound. Muscle biopsies were obtained before and after 30 min at each workload. One‐way RM ANOVA was applied to determine the impact of exercise intensity. Data are expressed as mean ± SEM. From rest through exercise average blood flow (0.4 ± 0.1, 2.1 ± 0.1, 2.6 ± 0.2, 3.7 ± 0.2 L min−1) and oxygen uptake across the leg (0.03 ± 0.01, 0.23 ± 0.02, 0.35 ± 0.03, 0.53 ± 0.04 L min−1) increased with exercise intensity (p < 0.001). Leg RQ (0.76 ± 0.04, 0.86 ± 0.02,0.87 ± 0.01, 0.92 ± 0.01, p < 0.001), leg plasma FA uptake (2 ± 2, 46 ± 8,83 ± 9, 114 ± 16 μmol min−1; p < 0.001) and rate of leg fat oxidation (0.016 ± 0.005, 0.062 ± 0.012, 0.075 ± 0.011, 0.084 ± 0.018 g min−1, p < 0.007) increased with exercise intensity. Muscle‐free carnitine content was unchanged from rest at 25% Wmax and decreased after 30 min exercise at 55% and 85% Wmax (17.4 ± 1.6, 16.6 ± 0.7, 14.5 ± 1.2, 10.5 ± 1.0 mmol/kg dry muscle, respectively; p < 0.006). During incremental one‐leg exercise, the rate of leg fat oxidation was not attenuated with increasing exercise intensity, probably due to an insufficient muscle metabolic stress response.

中文翻译：

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在增量强度单腿伸膝运动中，腿部脂肪氧化率没有减弱


目前尚不清楚在小肌肉量运动时，较高运动强度下脂肪氧化是否会减弱，因此，我们研究了分级单腿运动期间的腿部脂肪氧化。 10 名男性（年龄：27 ± 2 岁，体重：82 ± 3 kg，BMI：24 ± 1 kg m−2，V̇O2max：49 ± 2 mL min−1 kg−1）以 25% 的强度进行单腿运动最大负荷 (Wmax) 30 分钟，然后用对侧腿以 55% Wmax 进行 120 分钟锻炼，最后用第一条腿以 85% Wmax 进行 30 分钟锻炼。从动脉和两条股静脉采集血液样本，并使用多普勒超声确定血流量。在每个工作负荷前和 30 分钟后进行肌肉活检。应用单向 RM 方差分析来确定运动强度的影响。数据表示为平均值±SEM。从休息到运动，腿部平均血流量（0.4 ± 0.1、2.1 ± 0.1、2.6 ± 0.2、3.7 ± 0.2 L min−1）和摄氧量（0.03 ± 0.01、0.23 ± 0.02、0.35 ± 0.03、0.53 ± 0.04 L min−1) 随着运动强度的增加而增加 (p < 0.001)。腿部 RQ（0.76 ± 0.04、0.86 ± 0.02、0.87 ± 0.01、0.92 ± 0.01、p < 0.001），腿部血浆 FA 摄取量（2 ± 2、46 ± 8,83 ± 9、114 ± 16 μmol min−1； p < 0.001) 和腿部脂肪氧化率 (0.016 ± 0.005, 0.062 ± 0.012, 0.075 ± 0.011, 0.084 ± 0.018 g min−1, p < 0.007) 随着运动强度的增加而增加。在 25% Wmax 时，无肌肉碱含量与休息时相比没有变化，在 55% 和 85% Wmax 运动 30 分钟后下降（分别为 17.4 ± 1.6、16.6 ± 0.7、14.5 ± 1.2、10.5 ± 1.0 mmol/kg 干肌肉； p< 0.006)。在增量单腿运动过程中，腿部脂肪氧化率并没有随着运动强度的增加而减弱，这可能是由于肌肉代谢应激反应不足所致。