Dech Silas, Bittmann Frank N, Schaefer Laura V
Department of Sport and Health Sciences, Regulative Physiology and Prevention, Human Science Faculty, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14479, Potsdam, Germany.
BMC Sports Sci Med Rehabil. 2022 Mar 30;14(1):55. doi: 10.1186/s13102-022-00447-9.
Isometric muscle actions can be performed either by initiating the action, e.g., pulling on an immovable resistance (PIMA), or by reacting to an external load, e.g., holding a weight (HIMA). In the present study, it was mainly examined if these modalities could be differentiated by oxygenation variables as well as by time to task failure (TTF). Furthermore, it was analyzed if variables are changed by intermittent voluntary muscle twitches during weight holding (Twitch). It was assumed that twitches during a weight holding task change the character of the isometric muscle action from reacting (≙ HIMA) to acting (≙ PIMA).
Twelve subjects (two drop outs) randomly performed two tasks (HIMA vs. PIMA or HIMA vs. Twitch, n = 5 each) with the elbow flexors at 60% of maximal torque maintained until muscle failure with each arm. Local capillary venous oxygen saturation (SvO) and relative hemoglobin amount (rHb) were measured by light spectrometry.
Within subjects, no significant differences were found between tasks regarding the behavior of SvO and rHb, the slope and extent of deoxygenation (max. SvO decrease), SvO level at global rHb minimum, and time to SvO steady states. The TTF was significantly longer during Twitch and PIMA (incl. Twitch) compared to HIMA (p = 0.043 and 0.047, respectively). There was no substantial correlation between TTF and maximal deoxygenation independently of the task (r = - 0.13).
HIMA and PIMA seem to have a similar microvascular oxygen and blood supply. The supply might be sufficient, which is expressed by homeostatic steady states of SvO in all trials and increases in rHb in most of the trials. Intermittent voluntary muscle twitches might not serve as a further support but extend the TTF. A changed neuromuscular control is discussed as possible explanation.
等长肌肉动作可以通过启动动作来执行，例如拉动固定阻力（PIMA），或者通过对外部负荷做出反应来执行，例如握住重物（HIMA）。在本研究中，主要研究了这些方式是否可以通过氧合变量以及任务失败时间（TTF）来区分。此外，分析了在握重过程中间歇性自愿肌肉抽搐（Twitch）是否会改变变量。假设在握重任务期间的抽搐会将等长肌肉动作的性质从反应性（≙HIMA）转变为主动性（≙PIMA）。
12名受试者（2名退出）随机进行两项任务（HIMA对PIMA或HIMA对Twitch，每组n = 5），使用肘部屈肌以最大扭矩的60%进行，每只手臂保持到肌肉疲劳。通过光谱法测量局部毛细血管静脉血氧饱和度（SvO）和相对血红蛋白量（rHb）。
在受试者内部，在SvO和rHb的行为、脱氧斜率和程度（最大SvO降低）、全局rHb最低时的SvO水平以及SvO达到稳态的时间方面，任务之间未发现显著差异。与HIMA相比，Twitch和PIMA（包括Twitch）期间的TTF显著更长（分别为p = 0.043和0.047）。无论任务如何，TTF与最大脱氧之间均无显著相关性（r = -0.13）。
HIMA和PIMA似乎具有相似的微血管氧和血液供应。这种供应可能是充足的，这在所有试验中SvO的稳态以及大多数试验中rHb的增加中得到体现。间歇性自愿肌肉抽搐可能不会提供进一步的支持，但会延长TTF。讨论了神经肌肉控制的改变作为可能的解释。
