DeMont R G, Lephart S M
Neuromuscular Research Laboratory, University of Pittsburgh, Pittsburgh, PA, USA.
Br J Sports Med. 2004 Apr;38(2):120-4. doi: 10.1136/bjsm.2002.000195.
The reason for the higher incidence of anterior cruciate ligament injury from non-contact mechanisms in female athletes is not known. Stability of the joint from dynamic restraints occurs through proprioceptive and kinaesthetic mechanisms providing a flexion moment. Reflexive muscle activation is different between the sexes, but it is unclear if sex differences exist in the ability to dynamically stabilise joints through a neuromuscular feed forward process as measured by preactivation of the muscles.
To determine if the level of preactivation of the gastrocnemius and hamstring muscles during dynamic activity is affected by sex.
Thirty four healthy active subjects, evenly grouped by sex, participated in the study. Maximum voluntary contraction normalised electromyographic (EMG) activity of the quadriceps, hamstrings, and gastrocnemius muscles was recorded during downhill walking (0.92 m/s) and running (2.08 m/s) on a 15 degrees declined treadmill. Preactivation of the EMG signal was calculated by setting a mark 150 milliseconds before foot strike, as indicated by a footswitch. Multiple t tests for sex differences of preactivity mean percentage (M-EMG%) during the downhill activities were performed.
The female subjects had a higher M-EMG% for the medial hamstrings than the male subjects (31.73 (9.89) and 23.04 (8.59) respectively; t((2,32)) = 2.732, p = 0.01) during walking. No other muscles exhibited a sex difference in M-EMG% during either activity.
The female subjects in this study showed higher medial hamstring preactivation. However, this may be because they were not injured, indicating their propensity for joint stabilisation. A long term prospective study is required to eliminate this potential explanation. No sex difference in gastrocnemius preactivation was seen, adding to the controversy about whether this muscle contributes to feed forward joint stability. Further research of preactivation of the musculature of the leg is required.
女性运动员非接触性机制导致前交叉韧带损伤发生率较高的原因尚不清楚。关节的动态稳定性通过本体感觉和动觉机制产生屈曲力矩来实现。反射性肌肉激活在性别之间存在差异，但尚不清楚在通过肌肉预激活测量的神经肌肉前馈过程中，两性在动态稳定关节的能力上是否存在性别差异。
确定动态活动期间腓肠肌和腘绳肌的预激活水平是否受性别影响。
34名健康的活跃受试者按性别平均分组，参与本研究。在15度倾斜的跑步机上进行下坡行走（0.92米/秒）和跑步（2.08米/秒）时，记录股四头肌、腘绳肌和腓肠肌的最大自主收缩标准化肌电图（EMG）活动。如脚踏开关所示，通过在足跟着地前150毫秒设置一个标记来计算EMG信号的预激活。对下坡活动期间预激活平均百分比（M-EMG%）的性别差异进行多次t检验。
行走过程中，女性受试者腘绳肌内侧的M-EMG%高于男性受试者（分别为31.73（9.89）和23.04（8.59）；t（（2,32））=2.732，p = 0.01）。在任何一项活动中，其他肌肉的M-EMG%均未表现出性别差异。
本研究中的女性受试者表现出较高的腘绳肌内侧预激活。然而，这可能是因为她们未受伤，表明她们具有稳定关节的倾向。需要进行长期前瞻性研究以排除这种潜在解释。未观察到腓肠肌预激活的性别差异，这增加了关于该肌肉是否有助于前馈关节稳定性的争议。需要对腿部肌肉组织的预激活进行进一步研究。
