Dalton Benjamin, Hester Garrett, Alesi Michaela, McDougle Jacob, Cooper Michael, VanDusseldorp Trisha, Buresh Robert, Feito Yuri
Wellstar College of Health and Human Services, Kennesaw State University, Kennesaw, GA, United States.
Bonafide Health, LLC, JDS Therapeutics, Harrison, NY, United States.
Front Physiol. 2024 Aug 20;15:1434473. doi: 10.3389/fphys.2024.1434473. eCollection 2024.
Maximal voluntary isometric contractions (MVICs) as a fatiguing modality have been widely studied, but little attention has been given to the influence of the rate of torque development. Given the established differences in motor command and neuromuscular activation between ramp and rapid MIVCs, it is likely performance fatigue differs as well as the underlying physiological mechanisms.
To compare responses for rapid and maximal torque following ramp and rapid MVICs, and the corresponding neuromuscular and corticospinal alterations.
On separate visits, twelve healthy males (22.8 ± 2.5 years) performed fatiguing intermittent MVICs of the knee extensors with either 2 s (RAMP) or explosive (RAPID) ramp-ups until a 50% reduction in peak torque was achieved. Before and after each condition, maximal and rapid torque measures were determined from an MVIC. Additionally, peripheral (twitch parameters) and central (voluntary activation) fatigue, as well as rapid muscle activation, and cortical-evoked twitch and electromyographic responses were recorded.
Maximal and late-phase rapid torque measures ( ≤ 0.001; = 0.635-0.904) were reduced similarly, but early rapid torque capacity (0-50 ms) ( = 0.003; = 1.11 vs. = 0.054; = 0.62) and rapid muscle activation ( = 0.008; = 1.07 vs. = 0.875; = 0.06) decreased more after RAMP. Changes in peripheral fatigue, as indicated by singlet and doublet contractile parameters ( < 0.001 for all; = 0.752-0.859), and nerve-evoked voluntary activation ( < 0.001; 0.660) were similar between conditions. Corticospinal inhibition (via silent period) was only increased after RAPID ( = 0.007; = 0.94 vs. = 0.753; = 0.09), whereas corticospinal voluntary activation and excitability were unchanged.
Ramp, fatiguing MVICs impaired early rapid torque capacity more than rapid MVICs, and this was accompanied by decrements in rapid muscle activation. Responses for peripheral and central fatigue (nerve and cortical stimulation) were largely similar between conditions, except that rapid MVICs increased corticospinal inhibition.
最大自主等长收缩（MVICs）作为一种疲劳方式已得到广泛研究，但扭矩发展速率的影响却很少受到关注。鉴于斜坡式和快速MVICs在运动指令和神经肌肉激活方面已确定的差异，运动表现疲劳以及潜在的生理机制可能也有所不同。
比较斜坡式和快速MVICs后快速和最大扭矩的反应，以及相应的神经肌肉和皮质脊髓改变。
在不同的访视中，12名健康男性（22.8±2.5岁）对膝关节伸肌进行疲劳性间歇性MVICs，斜坡上升时间为2秒（RAMP）或爆发式（RAPID），直到峰值扭矩降低50%。在每种情况之前和之后，通过MVIC确定最大和快速扭矩测量值。此外，记录外周（抽搐参数）和中枢（自主激活）疲劳，以及快速肌肉激活、皮质诱发抽搐和肌电图反应。
最大扭矩和晚期快速扭矩测量值（≤0.001；=0.635 - 0.904）的降低相似，但早期快速扭矩能力（0 - 50毫秒）（=0.003；=1.11对=0.054；=0.62）和快速肌肉激活（=0.008；=1.07对=0.875；=0.06）在RAMP后下降更多。单收缩和双收缩收缩参数表明的外周疲劳变化（所有<0.001；=0.752 - 0.859）以及神经诱发的自主激活（<0.001；0.660）在不同条件下相似。皮质脊髓抑制（通过静息期）仅在RAPID后增加（=0.007；=0.94对=0.753；=0.09），而皮质脊髓自主激活和兴奋性未改变。
斜坡式疲劳性MVICs比快速MVICs更损害早期快速扭矩能力，并且这伴随着快速肌肉激活的下降。外周和中枢疲劳（神经和皮质刺激）的反应在不同条件下基本相似，除了快速MVICs增加了皮质脊髓抑制。
