Flood Andrew, Waddington Gordon, Keegan Richard J, Thompson Kevin G, Cathcart Stuart
Research Institute for Sport & Exercise, University of Canberra, Bruce, Australian Capital Territory, Australia; Centre for Applied Psychology, University of Canberra, Bruce, Australian Capital Territory, Australia.
Research Institute for Sport & Exercise, University of Canberra , Bruce , Australian Capital Territory , Australia.
PeerJ. 2017 Mar 2;5:e3028. doi: 10.7717/peerj.3028. eCollection 2017.
The ergogenic effects of analgesic substances suggest that pain perception is an important regulator of work-rate during fatiguing exercise. Recent research has shown that endogenous inhibitory responses, which act to attenuate nociceptive input and reduce perceived pain, can be increased following transcranial direct current stimulation of the hand motor cortex. Using high-definition transcranial direct current stimulation (HD-tDCS; 2 mA, 20 min), the current study aimed to examine the effects of elevated pain inhibitory capacity on endurance exercise performance. It was hypothesised that HD-tDCS would enhance the efficiency of the endogenous pain inhibitory response and improve endurance exercise performance.
Twelve healthy males between 18 and 40 years of age ( = 24.42 ± 3.85) were recruited for participation. Endogenous pain inhibitory capacity and exercise performance were assessed before and after both active and sham (placebo) stimulation. The conditioned pain modulation protocol was used for the measurement of pain inhibition. Exercise performance assessment consisted of both maximal voluntary contraction (MVC) and submaximal muscular endurance performance trials using isometric contractions of the non-dominant leg extensors.
Active HD-tDCS (pre-tDCS, -.32 ± 1.33 kg; post-tDCS, -1.23 ± 1.21 kg) significantly increased pain inhibitory responses relative to the effects of sham HD-tDCS (pre-tDCS, -.91 ± .92 kg; post-tDCS, -.26 ± .92 kg; = .046). Irrespective of condition, peak MVC force and muscular endurance was reduced from pre- to post-stimulation. HD-tDCS did not significantly influence this reduction in maximal force (active: pre-tDCS, 264.89 ± 66.87 Nm; post-tDCS, 236.33 ± 66.51 Nm; sham: pre-tDCS, 249.25 ± 88.56 Nm; post-tDCS, 239.63 ± 67.53 Nm) or muscular endurance (active: pre-tDCS, 104.65 ± 42.36 s; post-tDCS, 93.07 ± 33.73 s; sham: pre-tDCS, 123.42 ± 72.48 s; post-tDCS, 100.27 ± 44.25 s).
Despite increasing pain inhibitory capacity relative to sham stimulation, active HD-tDCS did not significantly elevate maximal force production or muscular endurance. These findings question the role of endogenous pain inhibitory networks in the regulation of exercise performance.
止痛物质的促力效应表明，疼痛感知是疲劳运动期间工作率的重要调节因素。最近的研究表明，经颅直流电刺激手部运动皮层后，可增强内源性抑制反应，这种反应可减弱伤害性输入并减轻疼痛感知。本研究使用高清经颅直流电刺激（HD-tDCS；2毫安，20分钟），旨在检验疼痛抑制能力增强对耐力运动表现的影响。研究假设为，HD-tDCS将提高内源性疼痛抑制反应的效率并改善耐力运动表现。
招募了12名年龄在18至40岁之间的健康男性（平均年龄=24.42±3.85岁）参与研究。在主动和假刺激（安慰剂）前后，对内源性疼痛抑制能力和运动表现进行评估。使用条件性疼痛调制方案测量疼痛抑制。运动表现评估包括最大自主收缩（MVC）和使用非优势腿伸肌等长收缩的次最大肌肉耐力表现试验。
相对于假HD-tDCS的效果，主动HD-tDCS（刺激前，-.32±1.33千克；刺激后，-1.23±1.21千克）显著增加了疼痛抑制反应（假HD-tDCS：刺激前，-.91±.92千克；刺激后，-.26±.92千克；P=0.046）。无论刺激条件如何，从刺激前到刺激后，峰值MVC力量和肌肉耐力均降低。HD-tDCS对最大力量的降低没有显著影响（主动：刺激前，264.89±66.87牛米；刺激后，236.33±66.51牛米；假刺激：刺激前，249.25±88.56牛米；刺激后，239.63±67.53牛米）或肌肉耐力（主动：刺激前，104.65±42.36秒；刺激后，93.07±33.73秒；假刺激：刺激前，123.42±72.48秒；刺激后，100.27±44.25秒）。
尽管相对于假刺激，主动HD-tDCS增加了疼痛抑制能力，但并未显著提高最大力量产生或肌肉耐力。这些发现质疑了内源性疼痛抑制网络在运动表现调节中的作用。
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