Cavagna G A, Legramandi M A, Peyré-Tartaruga L A
Istituto di Fisiologia Umana, Università degli Studi di Milano, Via Mangiagalli 32, 20133 Milan, Italy.
Proc Biol Sci. 2008 Feb 22;275(1633):411-8. doi: 10.1098/rspb.2007.1288.
It is known that muscular force is reduced in old age. We investigate what are the effects of this phenomenon on the mechanics of running. We hypothesized that the deficit in force would result in a lower push, causing reduced amplitude of the vertical oscillation, with smaller elastic energy storage and increased step frequency. To test this hypothesis, we measured the mechanical energy of the centre of mass of the body during running in old and young subjects. The amplitude of the oscillation is indeed reduced in the old subjects, resulting in an approximately 20% smaller elastic recovery and a greater step frequency (3.7 versus 2.8 Hz, p=1.9x10(-5), at 15-17 km h(-1)). Interestingly, the greater step frequency is due to a lower aerial time, and not to a greater natural frequency of the system, which is similar in old and young subjects (3.6 versus 3.4 Hz, p=0.2). Moreover, we find that in the old subjects, the step frequency is always similar to the natural frequency, even at the highest speeds. This is at variance with young subjects who adopt a step frequency lower than the natural frequency at high speeds, to contain the aerobic energy expenditure. Finally, the external work to maintain the motion of the centre of mass is reduced in the old subjects (0.9 versus 1.2 J kg(-1) m(-1), p=5.1x10(-6)) due to the lower work done against gravity, but the higher step frequency involves a greater internal work to reset the limbs at each step. The net result is that the total work increases with speed more steeply in the old subjects than in young subjects.
众所周知，老年时肌肉力量会下降。我们研究了这种现象对跑步力学有哪些影响。我们假设力量不足会导致蹬地力度降低，从而使垂直振荡幅度减小，弹性储能减少且步频增加。为了验证这一假设，我们测量了老年和年轻受试者跑步时身体重心的机械能。老年受试者的振荡幅度确实减小了，导致弹性恢复减少约20%，步频更高（在15 - 17 km h⁻¹时，步频为3.7对2.8 Hz，p = 1.9×10⁻⁵）。有趣的是，步频更高是由于腾空时间缩短，而不是系统固有频率更高，老年和年轻受试者的固有频率相似（3.6对3.4 Hz，p = 0.2）。此外，我们发现老年受试者即使在最高速度下，步频也总是与固有频率相似。这与年轻受试者不同，年轻受试者在高速时采用低于固有频率的步频，以控制有氧能量消耗。最后，由于对抗重力所做的功较低，老年受试者维持身体重心运动的外部功减少（0.9对1.2 J kg⁻¹ m⁻¹，p = 5.1×10⁻⁶），但更高的步频意味着在每一步重置肢体需要更大的内部功。最终结果是，老年受试者的总功随速度增加的幅度比年轻受试者更陡。
