Integrated Neuromuscular Physiology Laboratory, Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia , Kelowna, British Columbia , Canada.
J Appl Physiol (1985). 2019 May 1;126(5):1352-1359. doi: 10.1152/japplphysiol.00840.2018. Epub 2019 Mar 14.
Prolonged low-frequency force depression (PLFFD) after damaging eccentric exercise may last for several days. Historically, PLFFD has been calculated from the tetanic force responses to trains of supramaximal stimuli. More recently, for methodological reasons, stimulation has been reduced to two pulses. However, it is unknown whether doublet responses provide a valid measure of PLFFD in the days after eccentric exercise. In 12 participants, doublets and tetani were elicited at 10 and 100 Hz before and after (2, 3, 5 min, 48 and 96 h) 200 eccentric maximal voluntary contractions of the dorsiflexors. Doublet and tetanic torque responses at 10 Hz were similarly depressed throughout recovery ( > 0.05; e.g., 2 min: 58.9 ± 12.8% vs. 57.1 ± 14.5% baseline; 96 h: 85.6 ± 11.04% vs. 85.1 ± 10.8% baseline). At 100 Hz, doublet torque was impaired more than tetanic torque at all time points ( < 0.05; e.g., 2 min: 70.5 ± 14.2% vs. 88.1 ± 11.7% baseline; 96 h: 83.0 ± 14.2% vs. 98.7 ± 9.5% baseline). As a result, the postfatigue reduction of the 10 Hz-to-100 Hz ratio (PLFFD) was markedly greater for tetani than for doublets ( < 0.05; e.g., 2 min: 64.3 ± 15.1% vs. 83.0 ± 5.8% baseline). In addition, the doublet ratio recovered by 48 h (99.2 ± 5.0% baseline), whereas the tetanic ratio was still impaired at 96 h (88.2 ± 9.7% baseline). Our results indicate that doublets are not a valid measure of PLFFD in the minutes and days after eccentric exercise. If study design favors the use of paired stimuli, it should be acknowledged that the true magnitude and duration of PLFFD are likely underestimated. Prolonged low-frequency force depression (PLFFD) will result from damaging exercise and may last for several days. After 200 eccentric maximal dorsiflexor contractions, we compared the gold-standard measure of PLFFD (calculated using trains of supramaximal stimulation) to the value obtained from an alternative technique that is becoming increasingly common (paired supramaximal stimuli). Doublets underestimated the magnitude and duration of PLFFD compared with tetani, so caution must be used when reporting PLFFD derived from paired stimuli.
在损伤性离心运动后，低频力抑制（PLFFD）可能会持续数天。历史上，PLFFD 是通过对超最大刺激的串刺激的强直力反应来计算的。最近，出于方法学原因，刺激减少到两个脉冲。然而，在离心运动后几天，双脉冲反应是否能提供 PLFFD 的有效测量值尚不清楚。在 12 名参与者中，在进行 200 次最大主动背屈离心收缩之前和之后（2、3、5 分钟、48 和 96 小时），在 10 和 100 Hz 下引出双脉冲和强直。在恢复过程中，10 Hz 时的双脉冲和强直扭矩反应均受到类似的抑制（> 0.05；例如，2 分钟：58.9 ± 12.8%比基线 57.1 ± 14.5%；96 小时：85.6 ± 11.04%比基线 85.1 ± 10.8%）。在 100 Hz 时，在所有时间点，双脉冲扭矩的损伤程度均大于强直扭矩（< 0.05；例如，2 分钟：70.5 ± 14.2%比基线 88.1 ± 11.7%；96 小时：83.0 ± 14.2%比基线 98.7 ± 9.5%）。因此，与双脉冲相比，强直的 10 Hz 到 100 Hz 比值（PLFFD）在疲劳后明显降低（< 0.05；例如，2 分钟：64.3 ± 15.1%比基线 83.0 ± 5.8%）。此外，双脉冲比值在 48 小时恢复（99.2 ± 5.0%基线），而强直比值在 96 小时仍受损（88.2 ± 9.7%基线）。我们的结果表明，在离心运动后的几分钟和几天内，双脉冲不是 PLFFD 的有效测量方法。如果研究设计有利于使用成对刺激，则应该承认，PLFFD 的真实幅度和持续时间可能被低估了。在损伤性运动后，低频力抑制（PLFFD）将持续存在，可能会持续数天。在进行 200 次离心最大背屈收缩后，我们比较了 PLFFD 的金标准测量方法（使用超最大刺激的串刺激计算）与一种越来越常见的替代技术（成对超最大刺激）的测量值。与强直相比，双脉冲低估了 PLFFD 的幅度和持续时间，因此在报告源自成对刺激的 PLFFD 时必须小心。
