Romer Lee M, Lovering Andrew T, Haverkamp Hans C, Pegelow David F, Dempsey Jerome A
John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, Medical Sciences Center, University of Wisconsin, Madison 53706, USA.
J Physiol. 2006 Mar 1;571(Pt 2):425-39. doi: 10.1113/jphysiol.2005.099697. Epub 2005 Dec 22.
The work of breathing required during maximal exercise compromises blood flow to limb locomotor muscles and reduces exercise performance. We asked if force output of the inspiratory muscles affected exercise-induced peripheral fatigue of locomotor muscles. Eight male cyclists exercised at > or = 90% peak O2 uptake to exhaustion (CTRL). On a separate occasion, subjects exercised for the same duration and power output as CTRL (13.2 +/- 0.9 min, 292 W), but force output of the inspiratory muscles was reduced (-56% versus CTRL) using a proportional assist ventilator (PAV). Subjects also exercised to exhaustion (7.9 +/- 0.6 min, 292 W) while force output of the inspiratory muscles was increased (+80%versus CTRL) via inspiratory resistive loads (IRLs), and again for the same duration and power output with breathing unimpeded (IRL-CTRL). Quadriceps twitch force (Q(tw)), in response to supramaximal paired magnetic stimuli of the femoral nerve (1-100 Hz), was assessed pre- and at 2.5 through to 70 min postexercise. Immediately after CTRL exercise, Q(tw) was reduced -28 +/- 5% below pre-exercise baseline and this reduction was attenuated following PAV exercise (-20 +/- 5%; P < 0.05). Conversely, increasing the force output of the inspiratory muscles (IRL) exacerbated exercise-induced quadriceps muscle fatigue (Q(tw) = -12 +/- 8% IRL-CTRL versus-20 +/- 7% IRL; P < 0.05). Repeat studies between days showed that the effects of exercise per se, and of superimposed inspiratory muscle loading on quadriceps fatigue were highly reproducible. In conclusion, peripheral fatigue of locomotor muscles resulting from high-intensity sustained exercise is, in part, due to the accompanying high levels of respiratory muscle work.
最大运动强度时所需的呼吸功会影响肢体运动肌肉的血流，并降低运动表现。我们研究了吸气肌的力量输出是否会影响运动诱发的运动肌肉外周疲劳。八名男性自行车运动员以≥90%的峰值摄氧量进行运动直至力竭（对照组）。在另一次实验中，受试者以与对照组相同的持续时间和功率输出（13.2±0.9分钟，292瓦）进行运动，但使用比例辅助通气器（PAV）使吸气肌的力量输出降低（与对照组相比降低56%）。受试者还在吸气肌力量输出通过吸气阻力负荷（IRL）增加（与对照组相比增加80%）的情况下运动至力竭（7.9±0.6分钟，292瓦），并再次在相同持续时间和功率输出且呼吸不受阻碍的情况下运动（IRL-对照组）。在运动前以及运动后2.5分钟至70分钟，评估股四头肌对股神经超最大成对磁刺激（1 - 100赫兹）的抽搐力（Q(tw)）。对照组运动后即刻，Q(tw)比运动前基线降低了28±5%，而在PAV运动后这种降低有所减轻（-20±5%；P<0.05）。相反，增加吸气肌的力量输出（IRL）会加剧运动诱发的股四头肌肌肉疲劳（Q(tw)= -12±8% IRL-对照组对比-20±7% IRL；P<0.05）。不同日期的重复研究表明，运动本身以及叠加的吸气肌负荷对股四头肌疲劳的影响具有高度可重复性。总之，高强度持续运动导致的运动肌肉外周疲劳部分归因于伴随的高水平呼吸肌工作。
