The technique of multi-fiber muscle velocity recovery cycle recordings was developed as a diagnostic tool to assess muscle membrane potential changes and ion channel function in vivo. This study was undertaken to assess the impact of intermittent high frequency stimulation on muscle velocity recovery cycle components, and to study whether the changes can be modified by endurance training. We recorded muscle velocity recovery cycles with 1 and 2 conditioning stimuli in the left tibialis anterior muscle in 15 healthy subjects during intermittent 37 Hz stimulation and analyzed its effects on the different phases of supernormality. Recordings were conducted before and after two weeks endurance training. Training effect was assessed by measuring the difference in endurance time, peak force and limb circumference. Muscle velocity recovery cycle recordings during intermittent high frequency stimulation were successfully recorded in 12 subjects. Supernormality for interstimulus intervals shorter than 15 ms (early supernormality) was maximally reduced at the beginning of repetitive stimulation and recovered during stimulation. Supernormality for interstimulus intervals between 50 and 150 ms (late supernormality) showed a delayed decrease and stayed significantly reduced after high frequency stimulation. Training had no significant effect on any of the measured parameters, but we found that training induced changes in peak force correlated positively with baseline changes of early supernormality. Our results support the hypothesis that early supernormality represents membrane potential, which depolarizes in the beginning of high frequency stimulation. Late supernormality probably reflects transverse tubular function and shows progressive changes during high frequency stimulation with delayed normalization.

中文翻译：

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间歇性高频刺激对肌肉速度恢复周期记录的影响

多纤维肌肉速度恢复循环记录技术被开发为一种诊断工具，用于评估体内肌肉膜电位变化和离子通道功能。本研究旨在评估间歇性高频刺激对肌肉速度恢复周期成分的影响，并研究是否可以通过耐力训练来改变这些变化。我们在间歇性 37 Hz 刺激期间记录了 15 名健康受试者左侧胫骨前肌中 1 次和 2 次调理刺激的肌肉速度恢复周期，并分析了其对不同阶段超常状态的影响。在两周耐力训练之前和之后进行记录。通过测量耐力时间、峰值力量和肢体周长的差异来评估训练效果。12 名受试者成功记录了间歇性高频刺激期间的肌肉速度恢复周期记录。短于 15 ms 的刺激间隔的超常性（早期超常性）在重复刺激开始时最大程度地减少，并在刺激期间恢复。50 到 150 ms 之间的刺激间隔的超常性（晚期超常性）显示出延迟降低，并在高频刺激后保持显着降低。训练对任何测量参数都没有显着影响，但我们发现训练引起的峰值力量变化与早期超常态的基线变化呈正相关。我们的结果支持早期超正常代表膜电位的假设，膜电位在高频刺激开始时去极化。