Boynton Alicia M, Carrier David R
Division of Biological Science, University of Utah, Salt Lake City, Utah 84112, USA.
Integr Org Biol. 2022 Jun 2;4(1):obac021. doi: 10.1093/iob/obac021. eCollection 2022.
During locomotion, cervical muscles must be active to stabilize the head as the body accelerates and decelerates. We hypothesized that cervical muscles are also part of the linked chain of axial muscles that provide core stabilization against torques applied to the hip joint by the extrinsic muscles of the legs. To test whether specific cervical muscles play a role in postural stabilization of the head and/or core stabilization of the pelvic girdle, we used surface electromyography to measure changes in muscle activity in response to force manipulations during constant speed running and maximum effort counter-movement jumps. We found that doubling the mass of the head during both running and maximum effort jumping had little or no effect on (1) acceleration of the body and (2) cervical muscle activity. Application of horizontal forward and rearward directed forces at the pelvis during running tripled mean fore and aft accelerations, thereby increasing both the pitching moments on the head and flexion and extension torques applied to the hip. These manipulations primarily resulted in increases in cervical muscle activity that is appropriate for core stabilization of the pelvis. Additionally, when subjects jumped maximally with an applied downward directed force that reduced acceleration and therefore need for cervical muscles to stabilize the head, cervical muscle activity did not decrease. These results suggest that during locomotion, rather than acting to stabilize the head against the effects of inertia, the superficial muscles of the neck monitored in this study help to stabilize the pelvis against torques imposed by the extrinsic muscles of the legs at the hip joint. We suggest that a division of labor may exist between deep cervical muscles that presumably provide postural stabilization of the head versus superficial cervical muscles that provide core stabilization against torques applied to the pelvic and pectoral girdles by the extrinsic appendicular muscles.
在运动过程中，当身体加速和减速时，颈部肌肉必须保持活跃以稳定头部。我们推测，颈部肌肉也是轴向肌肉连锁的一部分，这些轴向肌肉可提供核心稳定性，以抵抗腿部外在肌肉施加于髋关节的扭矩。为了测试特定的颈部肌肉是否在头部的姿势稳定和/或骨盆带的核心稳定中发挥作用，我们使用表面肌电图来测量在恒速跑步和最大努力反向运动跳跃期间，肌肉活动对力操作的反应变化。我们发现，在跑步和最大努力跳跃过程中，将头部质量加倍对（1）身体加速度和（2）颈部肌肉活动几乎没有影响。在跑步过程中，在骨盆处施加水平向前和向后的力，使平均前后加速度增加了两倍，从而增加了头部的俯仰力矩以及施加于髋关节的屈伸扭矩。这些操作主要导致颈部肌肉活动增加，这对于骨盆的核心稳定是合适的。此外，当受试者在施加向下的力的情况下进行最大跳跃时，该力降低了加速度，因此需要颈部肌肉来稳定头部，但颈部肌肉活动并未减少。这些结果表明，在运动过程中，本研究中监测的颈部表层肌肉并非是为了抵抗惯性作用来稳定头部，而是有助于稳定骨盆，以抵抗腿部外在肌肉在髋关节处施加的扭矩。我们认为，在可能提供头部姿势稳定的深层颈部肌肉与提供核心稳定以抵抗附肢外在肌肉施加于骨盆和胸带的扭矩的表层颈部肌肉之间，可能存在分工。
