De Ruiter Cornelis J, Hamacher Philipp, Wolfs Bart G A
Research Institute MOVE, Vrije Universiteit Amsterdam, THE NETHERLANDS.
Med Sci Sports Exerc. 2016 May;48(5):913-9. doi: 10.1249/MSS.0000000000000832.
Recently, a fatigue threshold obtained during submaximal repetitive isometric knee extensor contractions was related to V˙O2max measured during cycling and to exercise endurance. However, test duration is quite long (20-30 min in young people) to be of practical and possibly clinical use. The purpose of the present study was to test the day-to-day reliability of a newly developed short test that assessed the fatigue threshold during a submaximal test with the knee extensors.
Fifteen healthy young males were tested three times, once using the original long protocol (5-min blocks of repetitive unilateral isometric knee extensor contractions with stepwise (5% MVC) increases of force) and twice using a new shorter protocol. In the latter, force increased by 2% MVC every 30 s, starting at 15% MVC (all contractions were 3 s on, 2 s off). The fatigue threshold was defined as the force where the EMG/force ratio started to increase and, compared with the force, at which deoxygenated hemoglobin concentration ([HHb]) increased steeply (HHb threshold).
The EMG/force threshold during the short trials was reached after 3.9 ± 1.5 min of submaximal exercise and similar (P > 0.05) between days. The EMG/force threshold showed good reliability (intraclass correlation coefficient = 0.87, SEM = 2.2%) and did not differ between (P > 0.05) the short (31.1% ± 7.6% MVC) and long tests (30.5% ± 6.2% MVC), with a significant relation (r = 0.71) between both tests. Similar results (P > 0.05) were found for the HHb threshold.
In young healthy men, a fatigue threshold can be detected during repetitive isometric knee extensor contractions using a short submaximal test, which may be suitable for untrained or frail people and patients.
最近，在次最大重复等长膝关节伸展收缩过程中获得的疲劳阈值与骑行时测得的最大摄氧量（V˙O2max）以及运动耐力相关。然而，测试持续时间相当长（年轻人为20 - 30分钟），难以实际应用，也不太可能用于临床。本研究的目的是测试一种新开发的短测试的日常可靠性，该测试用于评估在次最大测试中膝关节伸肌的疲劳阈值。
15名健康年轻男性接受了三次测试，一次使用原始的长方案（5分钟的重复单侧等长膝关节伸展收缩，力量逐步增加（5%最大自主收缩量（MVC））），两次使用新的较短方案。在后者中，力量从15%MVC开始，每30秒增加2%MVC（所有收缩为3秒收缩、2秒放松）。疲劳阈值定义为肌电图/力量比值开始增加时的力量，并与该力量相比，此时脱氧血红蛋白浓度（[HHb]）急剧增加（HHb阈值）。
短测试中，在次最大运动3.9±1.5分钟后达到肌电图/力量阈值，且不同日期之间相似（P>0.05）。肌电图/力量阈值显示出良好的可靠性（组内相关系数=0.87，标准误=2.2%），短测试（31.1%±7.6%MVC）和长测试（30.5%±6.2%MVC）之间无差异（P>0.05），两次测试之间存在显著相关性（r = 0.71）。HHb阈值也得到了相似的结果（P>0.05）。
在年轻健康男性中，使用短次最大测试可在重复等长膝关节伸展收缩过程中检测到疲劳阈值，该测试可能适用于未经训练或体弱的人群及患者。
