Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, OK, USA.
Department of Health and Human Physiology, University of Iowa, Iowa City, IA, USA.
Eur J Sport Sci. 2021 Oct;21(10):1403-1413. doi: 10.1080/17461391.2020.1836262. Epub 2020 Nov 10.
We examined the motor unit action potential amplitude versus recruitment threshold relationship (MUAP-RT) as an indicator of MU-specific hypertrophy following high-intensity exercise training in females. Participants were assigned to either a high-intensity exercise (EX, = 9) or control (CON, = 18) condition and completed pre- (PRE) and post-testing (POST) during which maximal voluntary isometric leg extension strength (MVIT), (VL) muscle cross sectional area (mCSA), whole leg skeletal muscle mass (SMM), and high-density surface EMG (HD-sEMG) signals were recorded from the VL during an isometric ramp contraction at 70% MVIT. The HD-sEMG signals were decomposed and yielded a MUAP and an absolute (ABS; Nm) and normalized (NORM; %MVIC) RT for each MU. Individual MUAP-RT slopes and intercepts were calculated for each subject. Changes in the pooled MUAP-RT relationships for each group were also examined. Finally, relationships among individual changes in slopes of MUAP-RT and individual changes in mCSA and SMM were examined. Training elicited increases in MVIT (+18%), mCSA (+12%), and mean and pooled slopes of MUAP-RT. The individual changes in slopes of both the MUAP-RT relationships were moderately to strongly ( = 0.48-0.68) related to changes in mCSA and SMM. Eight-weeks of high-intensity exercise elicited increases in MUAP-RT slope in females. Further, the observed change in slope was related to both VL mCSA and SMM of the tested leg. However, changes in slope for the MUAP-RT relationship were more subdued when MUAP was expressed relative to the absolute versus relative RT.
我们研究了运动单位动作电位幅度与募集阈值关系（MUAP-RT），作为高强度运动训练后 MU 特异性肥大的指标。参与者被分配到高强度运动（EX，n=9）或对照组（CON，n=18），并在预测试（PRE）和后测试（POST）期间完成测试，在此期间，通过等长 ramp 收缩从 VL 记录最大自愿等长腿伸肌力量（MVIT）、（VL）肌肉横截面积（mCSA）、整条腿骨骼肌质量（SMM）和高密度表面肌电图（HD-sEMG）信号，收缩强度为 70%MVIT。HD-sEMG 信号被分解，得到每个 MU 的 MUAP 和绝对（ABS；Nm）和归一化（NORM；%MVIC）RT。为每个受试者计算了单个 MUAP-RT 斜率和截距。还检查了每个组中 MUAP-RT 关系的变化。最后，还检查了单个 MUAP-RT 斜率变化与单个 mCSA 和 SMM 变化之间的关系。训练引起 MVIT（增加 18%）、mCSA（增加 12%）和 MUAP-RT 平均和聚合斜率的增加。MUAP-RT 关系中斜率的个体变化与 mCSA 和 SMM 的个体变化中度至强烈相关（ = 0.48-0.68）。八周的高强度运动引起女性 MUAP-RT 斜率的增加。此外，观察到的斜率变化与测试腿的 VL mCSA 和 SMM 均有关。然而，当 MUAP 相对于绝对 RT 而不是相对 RT 表达时，MUAP-RT 关系的斜率变化较为温和。
