Section of Movement Sciences, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Via Casorati 43, 37131, Verona, Italy.
Eur J Appl Physiol. 2024 Mar;124(3):861-872. doi: 10.1007/s00421-023-05315-z. Epub 2023 Sep 29.
When exercising above the lactic threshold (LT), the slow component of oxygen uptake ([Formula: see text]) appears, mainly ascribed to the progressive recruitment of Type II fibers. However, also the progressive decay of the economy of contraction may contribute to it. We investigated oxygen uptake ([Formula: see text]) during isometric contractions clamping torque (T) or muscular activation to quantify the contributions of the two mechanisms.
We assessed for 7 min T of the leg extensors, net oxygen uptake ([Formula: see text]) and root mean square (RMS) from vastus lateralis (VL) in 11 volunteers (21 ± 2 yy; 1.73 ± 0.11 m; 67 ± 14 kg) during cyclic isometric contractions (contraction/relaxation 5 s/5 s): (i) at 65% of maximal voluntary contraction (MVC) (FB-Torque) and; (ii) keeping the level of RMS equal to that at 65% of MVC (FB-EMG).
[Formula: see text] after the third minute in FB-Torque increased with time ([Formula: see text] = 94 × t + 564; R = 0.99; P = 0.001), but not during FB-EMG. [Formula: see text]/T increased only during FB-Torque ([Formula: see text]/T = 1.10 × t + 0.57; R = 0.99; P = 0.001). RMS was larger in FB-Torque than in FB-EMG and significantly increased in the first three minutes of exercise to stabilize till the end of the trial, indicating that the pool of recruited MUs remained constant despite [Formula: see text].
The analysis of the RMS, [Formula: see text] and T during FB-Torque suggests that the intrinsic mechanism attributable to the decay of contraction efficiency was responsible for an increase of [Formula: see text] equal to 18% of the total [Formula: see text].
在乳酸阈（LT）以上进行运动时，会出现氧气摄取的缓慢成分（[Formula: see text]），主要归因于 II 型纤维的逐渐募集。然而，收缩经济性的逐渐衰减也可能对此有贡献。我们通过等长收缩来研究氧气摄取（[Formula: see text]），即通过钳制扭矩（T）或肌肉激活来量化这两个机制的贡献。
我们评估了 11 名志愿者（21 ± 2 岁；1.73 ± 0.11 m；67 ± 14 kg）的腿部伸肌在 7 分钟内的 T，在循环等长收缩（收缩/放松 5 s/5 s）期间，获得了股外侧肌（VL）的净氧气摄取（[Formula: see text]）和均方根（RMS）：（i）在最大自主收缩（MVC）的 65%（FB-Torque）下；（ii）保持 RMS 等于 MVC 的 65%（FB-EMG）。
在 FB-Torque 中，[Formula: see text]在第三分钟后随时间增加（[Formula: see text] = 94 × t + 564；R = 0.99；P = 0.001），但在 FB-EMG 中没有增加。只有在 FB-Torque 中，[Formula: see text]/T 才增加（[Formula: see text]/T = 1.10 × t + 0.57；R = 0.99；P = 0.001）。在 FB-Torque 中，RMS 大于 FB-EMG，在运动的前三分钟内显著增加，直到试验结束时稳定，表明尽管 [Formula: see text]增加，但募集的 MU 池保持不变。
通过分析 FB-Torque 期间的 RMS、[Formula: see text]和 T，表明归因于收缩效率衰减的内在机制负责增加[Formula: see text]，占总[Formula: see text]的 18%。
