Department of Human Health and Nutritional Sciences, University of Guelph , Guelph, Ontario , Canada.
Toronto General Research Institute, Toronto General Hospital , Toronto, Ontario , Canada.
J Appl Physiol (1985). 2019 Feb 1;126(2):278-285. doi: 10.1152/japplphysiol.00601.2018. Epub 2018 Nov 1.
The present study investigated the effects of prior lengthening or shortening contractions on cardiovascular responses during isometric exercise. We utilized the history dependence of skeletal muscle, where active 2-s lengthening or shortening before an isometric contraction can increase [residual force enhancement (RFE)] or decrease [force depression (FD)] force production. Matching torque output between RFE and FD conditions yields lower and higher electromyography (EMG) values, respectively. In study 1, heart rate and perceived exertion (PE; Borg10) were measured in 20 participants during 20-s isometric plantar flexion contractions at low (16 ± 4% MVC)-, moderate (50 ± 5% MVC)-, and high (88 ± 7% MVC)-intensity. In study 2, heart rate and blood pressure were measured in 14 participants during 2-min isometric plantar flexion contractions (40% MVC). In both studies, torque output was held constant between FD and RFE conditions resulting in differences in soleus EMG activity ( P < 0.05). In study 1, PE was lower during the RFE condition ( P < 0.01), while increases in heart rate were similar between FD and RFE at low (∆2 ± 8 vs. 3 ± 6 beats/min, P > 0.99) and moderate (∆14 ± 9 vs. 14 ± 9 beats/min, P > 0.99) intensity but smaller during RFE at high intensity (∆35 ± 13 vs. 29 ± 13 beats/min, P = 0.004). In study 2, heart rate responses were smaller in the RFE condition following the initial 20-s period; diastolic blood pressure responses were smaller during the last 80 s. A 2-s active change in muscle length before an isometric contraction can influence heart rate and blood pressure responses; however, these differences appear to be modulated by both intensity and duration of the contraction. NEW & NOTEWORTHY Using the history dependence of isometric force to alter maximal torque production and motor unit activation between residual force enhancement and force depression conditions, we observed that heart rate responses were different between conditions during a subsequent 20-s high-, but not low- or moderate-, intensity isometric contraction. A 2-min moderate-intensity contraction revealed time-dependent effects on heart rate and diastolic blood pressure. Active 2-s shortening and lengthening before an isometric contraction can influence the cardiovascular responses.
本研究探讨了等长运动期间先拉长或缩短收缩对心血管反应的影响。我们利用骨骼肌的历史依赖性，即在等长收缩前进行 2 秒主动拉长或缩短，可以增加[剩余力增强（RFE）]或减少[力抑制（FD）]力的产生。在 RFE 和 FD 条件下匹配扭矩输出会导致 EMG 值分别降低和升高。在研究 1 中，20 名参与者在低强度（16±4%MVC）、中强度（50±5%MVC）和高强度（88±7%MVC）下进行 20 秒足底屈肌等长收缩时，测量心率和感觉用力（Borg10）。在研究 2 中，14 名参与者在 2 分钟的等长足底屈肌收缩（40%MVC）期间测量心率和血压。在两项研究中，FD 和 RFE 条件下的扭矩输出保持恒定，导致比目鱼肌 EMG 活动的差异（P<0.05）。在研究 1 中，RFE 条件下感觉用力较低（P<0.01），而在低强度（Δ2±8 与 3±6 次/分钟，P>0.99）和中强度（Δ14±9 与 14±9 次/分钟，P>0.99）时，FD 和 RFE 之间的心率增加相似，但在高强度时 RFE 时较小（Δ35±13 与 29±13 次/分钟，P=0.004）。在研究 2 中，在最初的 20 秒后，RFE 条件下的心率反应较小；在最后 80 秒期间，舒张压反应较小。在等长收缩前进行 2 秒的肌肉长度主动变化可以影响心率和血压反应；然而，这些差异似乎受到收缩强度和持续时间的调节。 使用等长力的历史依赖性来改变剩余力增强和力抑制条件之间的最大扭矩产生和运动单位激活，我们观察到在随后的 20 秒高强度但不是低强度或中强度等长收缩期间，两种条件之间的心率反应不同。2 分钟的中强度收缩对心率和舒张压显示出时间依赖性影响。在等长收缩前进行 2 秒的主动缩短和拉长可以影响心血管反应。
