Maganaris C N, Baltzopoulos V, Sargeant A J
Biomechanics and Neuromuscular Biology Research Groups, Manchester Metropolitan University, Alsager ST7 2HL, UK.
Exp Physiol. 1998 Nov;83(6):843-55. doi: 10.1113/expphysiol.1998.sp004164.
The present study examined the hypothesis that the antagonistic ankle dorsiflexor coactivation level during maximum isometric voluntary plantarflexion (MVC) is a function of ankle angle. Six male subjects generated plantarflexion and dorsiflexion MVC trials at ankle angles of -15 deg (dorsiflexed direction), 0 deg (neutral position), +15 deg (plantarflexed direction) and +30 deg having the knee flexed at an angle of 90 deg. In all contractions surface EMG measurements were taken from tibialis anterior and soleus which were considered representative muscles of all dorsiflexors and plantarflexors, respectively. Antagonistic dorsiflexor coactivation was expressed as normalized EMG and moment. Calculations of the antagonistic dorsiflexor moment were based on the tibialis anterior EMG-dorsiflexor moment relationship from contractions at 50, 40, 30, 20 and 10 % of the dorsiflexion MVC moment. In both legs dorsiflexor coactivation level followed an open U-shaped pattern as a function of ankle angle. Differences of 9 and 14 % (P < 0.05) were found in the measured net plantarflexion MVC moment between legs at ankle angles of -15 and +30 deg, respectively. No difference (P > 0.05) was found in the calf circumference between legs. Differences were found in the antagonistic dorsiflexor coactivation between legs at ankle angles of -15 and +30 deg. In the weaker leg the antagonistic EMG measurements were higher by 100 and 45 % (P < 0.01) and the estimated antagonistic moments were higher by 70 and 43 % (P < 0.01) compared with the weaker leg at -15 and +30 deg, respectively. This finding was associated with a decreased range of motion (ROM) in the weaker leg (14 %, P < 0.01), such that no difference (P > 0.05) was found in dorsiflexor antagonistic coactivation between legs at end-range ankle angles. The findings of the study (i) have to be taken into consideration when estimating musculoskeletal loads in the lower extremity, (ii) imply that stretching training can result in a stronger plantarflexion at end-range ankle angles through inhibition of the dorsiflexors, and (iii) imply a neural drive inadequacy during a plantarflexion MVC at end-range angles.
在最大等长自主跖屈（MVC）过程中，拮抗肌踝背屈协同激活水平是踝关节角度的函数。六名男性受试者在膝关节屈曲90度的情况下，于踝关节角度为-15度（背屈方向）、0度（中立位）、+15度（跖屈方向）和+30度时进行了跖屈和背屈MVC试验。在所有收缩过程中，分别从胫骨前肌和比目鱼肌进行表面肌电图测量，这两块肌肉分别被视为所有背屈肌和跖屈肌的代表性肌肉。拮抗肌背屈协同激活以标准化肌电图和力矩表示。拮抗肌背屈力矩的计算基于在背屈MVC力矩的50%、40%、30%、20%和10%收缩时胫骨前肌肌电图与背屈力矩的关系。在双腿中，背屈肌协同激活水平随踝关节角度呈开放U形模式。在踝关节角度为-15度和+30度时，测量的净跖屈MVC力矩在双腿之间分别存在9%和14%的差异（P<0.05）。双腿小腿周长无差异（P>0.05）。在踝关节角度为-15度和+30度时，双腿之间的拮抗肌背屈协同激活存在差异。与较弱腿在-15度和+30度时相比，在较弱腿中，拮抗肌肌电图测量值分别高出100%和45%（P<0.01），估计的拮抗肌力矩分别高出70%和43%（P<0.01）。这一发现与较弱腿的运动范围（ROM）减小（14%，P<0.01）相关，因此在踝关节终末角度时，双腿之间的背屈肌拮抗协同激活无差异（P>0.05）。本研究结果：（i）在估计下肢肌肉骨骼负荷时必须予以考虑；（ii）意味着拉伸训练可通过抑制背屈肌在踝关节终末角度产生更强的跖屈；（iii）意味着在踝关节终末角度的跖屈MVC过程中存在神经驱动不足。
