Mazara Nicole, Hess Adam J, Chen Jackey, Power Geoffrey A
Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
J Sport Health Sci. 2018 Jul;7(3):310-317. doi: 10.1016/j.jshs.2018.05.001. Epub 2018 May 16.
The isometric steady-state following active lengthening is associated with greater torque production and lower activation, as measured by electromyographic activity (EMG), in comparison with a purely isometric contraction (ISO) at the same joint angle. This phenomenon is termed residual force enhancement (RFE). While there has been a great deal of research investigating the basic mechanisms of RFE, little work has been performed to understand the everyday relevance of RFE. The purpose of this study was to investigate whether neuromuscular control strategies differ between ISO and RFE by measuring torque steadiness of the human ankle plantar flexors.
Following ISO maximal voluntary contractions in 12 males (25 ± 4 years), an active lengthening contraction was performed at 15°/s over a 30° ankle excursion, ending at the same joint angle as ISO (5° dorsiflexion; RFE). Surface EMG of the tibialis anterior and soleus muscles was recorded during all tasks. Torque steadiness was determined as the standard deviation (SD) and coefficient of variation (CV) of the torque trace in the ISO and RFE condition during activation-matching (20% and 60% integrated EMG) and torque-matching (20% and 60% maximal voluntary contraction) experiments. Two-tailed, paired tests were used, within subjects, to determine the presence of RFE/activation reduction (AR) and whether there was a difference in torque steadiness between ISO and RFE conditions.
During the maximal and submaximal conditions, there was 5%-9% RFE with a 9%-11% AR ( < 0.05), respectively, with no difference in antagonist coactivation between RFE and ISO ( > 0.05). There were no differences in SD and CV of the torque trace for the 20% and 60% activation-matching or the 60% and maximal torque-matching trials in either the RFE or ISO condition ( > 0.05). During the 20% torque-matching trial, there were ∼37% higher values for SD and CV in the RFE as compared with the ISO condition ( < 0.05). A significant moderate-to-strong negative relationship was identified between the reduction in torque steadiness following active lengthening and the accompanying AR ( < 0.05).
It appears that while the RFE-associated AR provides some improved neuromuscular economy, this comes at the cost of increased torque fluctuations in the isometric steady-state following active lengthening during submaximal contractions.
与在相同关节角度下的纯等长收缩（ISO）相比，主动拉长后的等长稳态与更大的扭矩产生以及更低的激活程度相关，激活程度通过肌电图活动（EMG）来衡量。这种现象被称为残余力增强（RFE）。虽然已经有大量研究探讨了RFE的基本机制，但对于RFE在日常中的相关性却鲜有研究。本研究的目的是通过测量人类踝关节跖屈肌的扭矩稳定性，来探究ISO和RFE之间神经肌肉控制策略是否存在差异。
在12名男性（25±4岁）进行ISO最大自主收缩后，以15°/秒的速度在30°的踝关节活动范围内进行主动拉长收缩，结束时的关节角度与ISO相同（背屈5°；RFE）。在所有任务过程中记录胫骨前肌和比目鱼肌的表面肌电图。在激活匹配（20%和60%积分肌电图）和扭矩匹配（20%和60%最大自主收缩）实验中，将扭矩稳定性确定为ISO和RFE条件下扭矩轨迹的标准差（SD）和变异系数（CV）。在受试者内部使用双尾配对检验来确定RFE/激活减少（AR）的存在，以及ISO和RFE条件之间扭矩稳定性是否存在差异。
在最大和次最大条件下，分别存在5%-9%的RFE和9%-11%的AR（P<0.05），RFE和ISO之间的拮抗肌共同激活没有差异（P>0.05）。在RFE或ISO条件下，20%和60%激活匹配试验以及60%和最大扭矩匹配试验中，扭矩轨迹的SD和CV没有差异（P>0.05）。在20%扭矩匹配试验中，与ISO条件相比，RFE条件下的SD和CV值高约37%（P<0.05）。在主动拉长后扭矩稳定性的降低与伴随的AR之间发现了显著的中度至强负相关（P<0.05）。
似乎虽然与RFE相关的AR提供了一些改善的神经肌肉经济性，但这是以次最大收缩期间主动拉长后的等长稳态中扭矩波动增加为代价的。
