Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Chatham, Kent, ME4 4AG, UK.
School of Sport, Rehabilitation and Exercise Sciences, University of Essex, Wivenhoe Park, Colchester, UK.
Eur J Appl Physiol. 2020 Sep;120(9):2047-2058. doi: 10.1007/s00421-020-04425-2. Epub 2020 Jun 29.
Increased nociceptive activity and the experience of exercise-induced pain (EIP) may contribute to fatigue during endurance exercise. To investigate this, a pain model that produces pain similar to EIP and decouples its relationship to exercise intensity is required. This study (1) compared the quality of pain caused by a hypertonic saline injection into the vastus lateralis in resting and exercise conditions, and (2) investigated whether this pain contributes to changes in time to task failure.
On separate days, 18 participants completed a time to task failure at 20% maximal voluntary torque (MVT), a resting hypertonic saline intramuscular injection, and in a further three visits a time to task failure at 10% MVT following injection of isotonic saline, hypertonic saline or a control (no injection).
In a subset of eligible participants (n = 12), the hypertonic saline combined with 10% MVT produced a qualitative experience of pain (assessed by the McGill Pain Questionnaire) that felt similar to EIP. 10% MVT with hypertonic saline significantly elevated pain intensity in the first 20% of the time to task failure and caused a significantly (P < 0.05) shorter time to task failure (448 ± 240 s) compared with the isotonic saline (605 ± 285 s) and control (514 ± 197 s) conditions.
These findings demonstrate that hypertonic saline increases the intensity of pain during exercise, which results in a faster occurrence of exercise-induced fatigue. These results provide important evidence supporting pain as a limiting factor in endurance performance.
痛觉活动增加和运动引起的疼痛（EIP）体验可能导致耐力运动时疲劳。为了研究这一点，需要一种产生类似于 EIP 的疼痛的疼痛模型，并使其与运动强度的关系脱钩。本研究（1）比较了在休息和运动条件下大腿外侧注射高渗盐水引起的疼痛质量，（2）研究了这种疼痛是否会导致任务失败时间的变化。
在不同的日子里，18 名参与者在 20%最大自主扭矩（MVT）下完成了任务失败时间，在休息时接受高渗盐水肌内注射，在另外三次访问中，在注射等渗盐水、高渗盐水或对照（无注射）后，在 10%MVT 下完成任务失败时间。
在合格参与者的一部分（n = 12）中，高渗盐水与 10%MVT 联合产生了一种与 EIP 感觉相似的疼痛定性体验（通过 McGill 疼痛问卷评估）。10%MVT 与高渗盐水联合使用会显著增加任务失败前 20%时间内的疼痛强度，并导致任务失败时间明显缩短（448 ± 240 s），与等渗盐水（605 ± 285 s）和对照（514 ± 197 s）条件相比。
这些发现表明，高渗盐水会增加运动时的疼痛强度，从而导致运动引起的疲劳更快发生。这些结果为疼痛作为耐力表现的限制因素提供了重要证据。
