School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, 1151 Richmond Street, London, ON, N63K7, Canada.
Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, ON, N63K7, Canada.
Exp Brain Res. 2019 Sep;237(9):2345-2352. doi: 10.1007/s00221-019-05570-7. Epub 2019 Jul 10.
Gastrocnemii muscle fibers shorten when the knee joint is in a flexed compared to an extended position. This leads to inhibition of medial gastrocnemius (MG) motor units, however, it is unclear whether this affects motor unit properties of the lateral gastrocnemius (LG) or soleus (SOL). We recorded 171 motor units from the MG (61), LG (39) and SOL (71) at an extended (160°) and flexed (100°) knee joint position with the ankle and hip joints at 90°. Subjects performed isometric ramp plantar flexion contractions at 25, 50 and 100% of the maximal voluntary contraction. MG (p = 0.0002) and LG (p = 0.02) motor unit recruitment thresholds (RT) were higher, whereas only MG motor unit firing rates (FR) were lower (p = 0.008) in the flexed compared to the extended knee joint position. SOL motor unit RT (p = 0.66) and FR (p = 0.08) were not statistically different between positions. When comparing properties of the same motor unit followed during contractions at both knee joint positions, RT of ten gastrocnemii motor units were higher (p = 0.0008) and FR were lower (p = 0.01) when the knee was flexed. Additionally, in six SOL motor units, RT (p = 0.42) and FR (p = 0.96) were not different between the two positions. Thus, MG and LG activation is similarly inhibited during plantar flexion contractions in a flexed compared to an extended knee joint position. Furthermore, our findings indicate that knee joint position changes have no effect on SOL excitability.
当膝关节处于弯曲状态而不是伸展状态时，比目鱼肌纤维会缩短。这会抑制内侧比目鱼肌（MG）运动单位，但尚不清楚这是否会影响外侧比目鱼肌（LG）或跟腱（SOL）的运动单位特性。我们在膝关节伸展（160°）和弯曲（100°）位置下，在踝关节和髋关节呈 90°角时，从 MG（61）、LG（39）和 SOL（71）中记录了 171 个运动单位。在 25%、50%和 100%最大随意收缩的情况下，进行等长斜坡跖屈收缩。MG（p=0.0002）和 LG（p=0.02）运动单位募集阈值（RT）更高，而只有 MG 运动单位放电频率（FR）更低（p=0.008）在弯曲的膝关节位置比伸展的膝关节位置。SOL 运动单位 RT（p=0.66）和 FR（p=0.08）在两个位置之间没有统计学差异。当比较在两个膝关节位置下进行收缩时相同运动单位的特性时，十个比目鱼肌运动单位的 RT 更高（p=0.0008），而 FR 更低（p=0.01）当膝关节弯曲时。此外，在六个 SOL 运动单位中，RT（p=0.42）和 FR（p=0.96）在两个位置之间没有差异。因此，与伸展的膝关节位置相比，在弯曲的膝关节位置下进行跖屈收缩时，MG 和 LG 的激活受到类似的抑制。此外，我们的研究结果表明，膝关节位置变化对 SOL 兴奋性没有影响。
