Thelen D G, Schultz A B, Alexander N B, Ashton-Miller J A
Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor, USA.
J Gerontol A Biol Sci Med Sci. 1996 Sep;51(5):M226-32. doi: 10.1093/gerona/51a.5.m226.
When balance is disturbed, often only fractions of a second are available in which to make the initial responses needed for its restoration. Abilities to develop joint torques rapidly may be critical to such responses. We undertook this study to quantify age effects among healthy adults in abilities to develop ankle joint torques rapidly.
Ankle dorsiflexion (DF) and plantarflexion (PF) torque development during rapid isometric and during isokinetic (30, 60, 120, 180, and 240 deg/sec) exertions was assessed in 24 healthy young (mean age 23 years) and 24 healthy old adults (mean age 72 years). The effects of age, gender, and torque direction on the times needed to reach given torque magnitudes, maximum rates of isometric torque development (MRTD), and maximum isokinetic torques were examined.
The old adults required substantially more time to reach given torque magnitudes than the young adults. For example, the young and old females needed approximately 236 and 337 msec to develop 15 Nm of DF torque, of which 141 and 164 msec were reaction times. Isometric MRTD were 25 to 36% lower in the old than in the young adults. The age declines in isometric torque development time were associated with losses in maximum isometric strength. Maximum isokinetic torques developed by the old were 20 to 40% lower than those of young adults. The percent losses in isokinetic torques with age were independent of joint angular velocity for PF, but increased with velocity for DF.
We found substantial age declines in abilities of healthy old adults to rapidly develop ankle joint torques. The capacities of even healthy old adults to recover balance or to carry out other time-critical actions that require moderate-to-substantial strengths may be considerably degraded by these declines.
当平衡受到干扰时，通常只有短短几分之一秒的时间来做出恢复平衡所需的初始反应。快速产生关节扭矩的能力对于此类反应可能至关重要。我们进行这项研究以量化健康成年人在快速产生踝关节扭矩能力方面的年龄差异。
对24名健康年轻人（平均年龄23岁）和24名健康老年人（平均年龄72岁）在快速等长收缩和等速收缩（30、60、120、180和240度/秒）过程中踝关节背屈（DF）和跖屈（PF）扭矩的产生情况进行了评估。研究了年龄、性别和扭矩方向对达到给定扭矩大小所需时间、等长扭矩最大发展速率（MRTD）和最大等速扭矩的影响。
老年人达到给定扭矩大小所需的时间比年轻人长得多。例如，年轻和老年女性产生15牛米的DF扭矩分别需要约236和337毫秒，其中反应时间分别为141和164毫秒。老年人的等长MRTD比年轻人低25%至36%。等长扭矩发展时间的年龄下降与最大等长力量的损失有关。老年人产生的最大等速扭矩比年轻人低20%至40%。等速扭矩随年龄的损失百分比对于PF来说与关节角速度无关，但对于DF来说随速度增加。
我们发现健康老年人快速产生踝关节扭矩的能力随年龄大幅下降。即使是健康的老年人，其恢复平衡或进行其他需要中等至较大力量的对时间要求较高的动作的能力，可能会因这些下降而受到显著影响。
