Richardson Michael S, Cramer Joel T, Bemben Debra A, Shehab Randa L, Glover John, Bemben Michael G
University of Oklahoma, Department of Health and Exercise Science, Neuromuscular Research Laboratory, 401 Asp Avenue, Norman, OK 73019, USA.
J Geriatr Phys Ther. 2006;29(1):28-34.
Both aging and anterior cruciate ligament (ACL) reconstruction are associated with strength deficits, which can in turn influence performance of activities of daily living. Thus it is informative to understand mechanisms underlying strength deficits. Age-related declines in strength follow reductions in muscle fiber numbers and size, whereas strength deficits following ACL reconstruction may be caused by the loss of intraligamentous mechanoreceptors. A common link between these conditions is the gamma spindle system, or the gamma loop. Appropriately applied vibration can affect the gamma loop by causing disruption of afferent feedback to a muscle and result in decreased force capabilities. We investigated the effect of age and ACL reconstruction on gamma loop function.
Maximal isometric strength (MVC) and electromyography (EMG) of the quadriceps were quantified before and after vibration stimulation of the infrapatellar tendon of 3 groups: young healthy (n=4; mean age=23.8 yrs), young ACL reconstructed (n=7; mean age=22.4 yrs), and older healthy (n=4; mean age=66.1 yrs) individuals.
The quadriceps MVC, vastus lateralis EMG, vastus medialis EMG, and rectus femoris EMG declined significantly in the young healthy group following vibration stimulation to the infrapatellar tendon, which indicated an intact gamma loop. There were no changes in these variables for the old healthy and ACL reconstructed groups.
Gamma loop function was impaired in both the older and ACL reconstructed groups possibly due to either decreased muscle spindle sensitivity or the loss of mechanoreceptors.
衰老和前交叉韧带（ACL）重建均与力量不足相关，而这反过来又会影响日常生活活动的表现。因此，了解力量不足背后的机制很有意义。与年龄相关的力量下降是随着肌纤维数量和大小的减少而发生的，而ACL重建后的力量不足可能是由韧带内机械感受器的丧失引起的。这些情况之间的一个共同联系是γ纺锤体系统，即γ环。适当施加振动可通过破坏肌肉的传入反馈来影响γ环，并导致力量能力下降。我们研究了年龄和ACL重建对γ环功能的影响。
对3组人群的髌腱进行振动刺激前后，对股四头肌的最大等长力量（MVC）和肌电图（EMG）进行量化：年轻健康者（n = 4；平均年龄 = 23.8岁）、年轻ACL重建者（n = 7；平均年龄 = 22.4岁）和老年健康者（n = 4；平均年龄 = 66.1岁）。
对年轻健康组的髌腱进行振动刺激后，股四头肌MVC、股外侧肌EMG、股内侧肌EMG和股直肌EMG均显著下降，这表明γ环完整。老年健康组和ACL重建组的这些变量没有变化。
老年组和ACL重建组的γ环功能均受损，可能是由于肌梭敏感性降低或机械感受器丧失。
