Moran Kieran A, Marshall Brendan M
Biomechanics Research Centre, School of Health and Human Performance, Faculty of Science and Health, Dublin City University, Dublin, Ireland.
Med Sci Sports Exerc. 2006 Oct;38(10):1836-42. doi: 10.1249/01.mss.0000229567.09661.20.
The principle of specificity suggests that it may be beneficial to undertake plyometric drop-jump training when fatigued. However, this may increase peak-impact accelerations and therefore increase the risk of injury. The aims of the study were to determine if whole-body fatigue (i) increased peak-impact acceleration on the proximal tibia during plyometric drop jumps and (ii) produced associated changes in knee-joint kinematics during landing.
Fifteen physically active male subjects performed drop jumps (30 and 50 cm) when nonfatigued and when fatigued. Whole-body fatigue was induced using a treadmill running protocol that incrementally increased effort. Peak-impact acceleration was measured with an accelerometer attached to the proximal tibia. Knee-joint kinematics were assessed during the eccentric phase: angle at initial touch down, maximum angle of flexion, range of motion, and peak angular velocity.
Fatigue caused a significant increase in tibial impact acceleration and peak angular velocity in drop jumps from 30 cm (154.9 +/- 93.8 vs 192.6 +/- 103.9 m x s(-2): 24%; 675.3 +/- 60.7 vs 811.4 +/- 68.9 degrees x s(-1): 20%), but not from 50 cm (222.4 +/- 74.9 vs 234.1 +/- 83.9 m x s(-2): 5%; 962.0 +/- 189.0 vs 984.4 +/- 189.3 degrees x s(-1): 2.6%), with no associated change in the knee-joint angles assessed. It was argued, however, that rather than the neuromuscular system being selectively affected by fatigue at 30 cm and not 50 cm, drop jumps from 50 cm resulted in larger-impact accelerations with the neuromuscular system having only a limited ability to attenuate them per se, whether fatigued or nonfatigued.
Care should be taken when performing drop jumps from a height of 30 cm in a fatigued state because of the reduced capacity to attenuate impact accelerations at the tibia, which may be associated with an increased risk of injury.
特异性原则表明，疲劳时进行增强式跳深训练可能有益。然而，这可能会增加峰值冲击加速度，从而增加受伤风险。本研究的目的是确定全身疲劳是否会（i）在增强式跳深过程中增加胫骨近端的峰值冲击加速度，以及（ii）在着陆过程中使膝关节运动学产生相关变化。
15名身体活跃的男性受试者在非疲劳和疲劳状态下进行跳深（30厘米和50厘米）。使用递增努力的跑步机跑步方案诱导全身疲劳。用附着在胫骨近端的加速度计测量峰值冲击加速度。在离心阶段评估膝关节运动学：初始触地角度、最大屈曲角度、运动范围和峰值角速度。
疲劳导致从30厘米进行跳深时胫骨冲击加速度和峰值角速度显著增加（154.9±93.8对192.6±103.9米×秒⁻²：24%；675.3±60.7对811.4±68.9度×秒⁻¹：20%），但从50厘米进行跳深时未出现这种情况（222.4±74.9对234.1±83.9米×秒⁻²：5%；962.0±189.0对984.4±189.3度×秒⁻¹：2.6%），且所评估的膝关节角度没有相关变化。然而，有人认为，不是神经肌肉系统在30厘米跳深时被疲劳选择性影响而在50厘米跳深时未受影响，而是从50厘米进行跳深会产生更大的冲击加速度，无论疲劳与否，神经肌肉系统本身衰减这些加速度的能力有限。
在疲劳状态下从30厘米高度进行跳深时应谨慎，因为胫骨衰减冲击加速度的能力降低，这可能与受伤风险增加有关。
