Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Finland.
J Exp Biol. 2010 Apr;213(Pt 8):1259-65. doi: 10.1242/jeb.033514.
Stiffness of the human Achilles tendon (AT) was determined in vivo before and after a single bout of hopping exercise. It was hypothesized, based on published data using in vitro specimens, that a reduction in AT stiffness may occur after just 1000 loading cycles at physiological stress levels. Ten healthy subjects performed two-legged hopping exercise consisting of 1150-2600 high impacts. Tendon stiffness was determined in several isometric ramp contractions [20%, 40%, 60%, 80% and 100% maximum voluntary contraction (MVC)] during which tendon elongation was measured using ultrasonography and two cameras. Tendon force was calculated by dividing measured ankle torque by magnetic resonance imaging-derived AT lever arm length. Tendon stiffness remained unchanged, being 430+/-200 N mm(-1) before and 390+/-190 N mm(-1) after the exercise [not significant (n.s.)]. Despite the lack of changes in stiffness, maximum tendon force during MVC was reduced from 3.5+/-0.6 kN to 2.8+/-0.7 kN (P<0.01). As the proposed decline in stiffness was not observed, it is concluded that mechanical fatigue did not take place in the AT of healthy individuals after a single bout of high-impact exercise performed until exhaustion.
本研究旨在活体条件下，单次跳跃运动后即刻测量跟腱（Achilles tendon，AT）僵硬度，以验证根据体外标本得出的研究结果，即：在生理负荷水平下，仅 1000 次循环加载后 AT 僵硬度可能会降低。10 名健康受试者进行双腿跳跃运动，包括 1150-2600 次高冲击。在 20%、40%、60%、80%和 100%最大自主收缩（maximal voluntary contraction，MVC）等几个等长斜坡收缩期间，采用超声和两台摄像机测量跟腱伸长，确定跟腱僵硬度。通过将测量的踝关节扭矩除以磁共振成像（magnetic resonance imaging，MRI）得出的跟腱杠杆臂长度，计算跟腱力。跳跃运动前后，跟腱僵硬度无明显变化，分别为 430+/-200 N mm(-1)和 390+/-190 N mm(-1)（无统计学差异，n.s.）。尽管僵硬度没有变化，但 MVC 时最大跟腱力从 3.5+/-0.6 kN 降至 2.8+/-0.7 kN（P<0.01）。由于未观察到僵硬度的预期降低，因此，单次高冲击运动直至力竭后，健康个体的跟腱并未发生机械性疲劳。
