Smith Ian C, Onasch Franziska, Kryściak Katarzyna, Celichowski Jan, Herzog Walter
Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, 2500 University Drive NW Calgary, Alberta, T2N 1N4, Canada.
Department of Neurobiology, Poznan University of Physical Education, 27/39 Królowej Jadwigi Street, 61-871, Poznań, Poland.
Eur J Appl Physiol. 2021 Feb;121(2):645-658. doi: 10.1007/s00421-020-04561-9. Epub 2020 Nov 22.
A period of extra-efficient force production ("boost") followed by a decline in force ("sag") is often observed at the onset of unfused tetanic contractions. We tested the hypothesis that in human muscle boost and sag are diminished in repeated contractions separated by short rest periods and are re-established or enhanced following long rest periods.
Two sets of 3 unfused tetanic contractions were evoked in the right quadriceps muscle group of 29 participants via percutaneous stimulation of the femoral nerve. Contractions consisted of 20 pulses evoked at inter-pulse intervals of 1.25 × twitch time to peak torque. Contractions were evoked 5 s apart and sets were evoked 5 min apart.
The ratio of the angular impulse of pulses 1-10 to the angular impulse of pulses 11-20 was used as the boost indicator. By this metric, boost was higher (P < 0.05) in the first relative to the second and third contractions within a set, but did not differ between sets (Set 1: 1.31 ± 0.15, 1.18 ± 0.12, 1.14 ± 0.12 vs Set 2: 1.34 ± 0.17, 1.17 ± 0.13, 1.14 ± 0.13). Sag (the percent decline in torque within each contraction) was also higher (P < 0.05) in the first relative to the second and third contractions within a set, but did not differ between sets (Set 1: 40.8 ± 7.5%, 35.4 ± 6.8%, 33.2 ± 7.8% vs Set 2: 42.1 ± 8.0%, 35.5 ± 6.8%, 33.9 ± 7.2%). Participants' sex and resistance training background did not influence boost or sag.
Boost and sag are sensitive to contractile history in whole human quadriceps. Optimizing boost may have application in strength and power sports.
在非融合强直收缩开始时，常观察到一段超高效力产生期（“增强”），随后是力的下降（“松弛”）。我们检验了这样一个假设，即在短休息期隔开的重复收缩中，人体肌肉的增强和松弛会减弱，而在长休息期后会重新建立或增强。
通过经皮刺激股神经，在29名参与者的右股四头肌群中诱发两组3次非融合强直收缩。收缩由20个脉冲组成，脉冲间隔为1.25×达到峰值扭矩的单收缩时间。收缩间隔5秒诱发，两组收缩间隔5分钟诱发。
将第1 - 10个脉冲的角冲量与第11 - 20个脉冲的角冲量之比用作增强指标。根据这个指标，一组内第一次收缩相对于第二次和第三次收缩的增强更高（P < 0.05），但两组之间没有差异（第1组：1.31±0.15、1.18±0.12、1.14±0.12，第2组：1.34±0.17、1.17±0.13、1.14±0.13）。松弛（每次收缩中扭矩下降的百分比）在一组内第一次收缩相对于第二次和第三次收缩时也更高（P < 0.05） , 但两组之间没有差异（第1组：40.8±7.5%、35.4±6.8%、33.2±7.8%，第2组：42.1±8.0%、35.5±6.8%、33.9±7.2%）。参与者的性别和抗阻训练背景不影响增强或松弛。
增强和松弛对整个人体股四头肌的收缩历史敏感。优化增强可能在力量和体能运动中有应用价值。
