Department of Kinesiology, Applied Physiology Laboratory, Health Promotion and Recreation, University of North Texas, Denton, Texas, USA.
J Strength Cond Res. 2012 Mar;26(3):641-7. doi: 10.1519/JSC.0b013e318245c0b1.
Bench press throws are commonly used in the assessment of upper-body power and are often performed on a Smith machine that uses a counterbalance weight to reduce the net load on the barbell. The use of a counterbalanced Smith machine was recently shown to reduce performance measures, but the mechanisms for this reduction have not been established. The purpose of this study was to determine the underlying physiological and biomechanical causes of the reduced performance measures found when using a counterbalanced Smith machine. Twenty-four men (mean ± SE: age, 23 ± 1 years; weight, 91.0 ± 3.5 kg; height, 178.9 ± 1.2 cm) performed Smith machine bench press throws at 30% of 1-repetition maximum under 4 conditions: (a) rebound movement and counterbalance, (b) rebound movement and no counterbalance, (c) concentric-only movement and counterbalance, and (d) concentric-only movement and no counterbalance. Peak power, peak force, and peak concentric and eccentric velocities were measured using a linear accelerometer, and peak ground reaction force was measured using a force plate. The counterbalance condition produced significantly (p < 0.05) lower peak accelerometer-based force (-21.2 and -17.0% for rebound and concentric-only bench press throws, respectively) but increased peak ground reaction force (5.3 and 3.2%). The discrepancy between changes in peak accelerometer-based force and peak ground reaction force suggests that an increase in net external load occurred during the movement. For performance testing of explosive movements, the use of a counterbalance system results in an underestimation of performance capability, likely because of an increase in the net external load during the concentric phase. Therefore, a counterbalance system should not be used for explosive movement performance testing.
卧推挺举常用于评估上半身力量，通常在史密斯机上进行，史密斯机使用平衡重量来减少杠铃的净负荷。最近的研究表明，使用平衡重的史密斯机可以降低运动表现的衡量标准，但这种降低的机制尚未确定。本研究的目的是确定使用平衡重的史密斯机时发现的运动表现衡量标准降低的潜在生理和生物力学原因。24 名男性（平均值±SE：年龄 23±1 岁；体重 91.0±3.5kg；身高 178.9±1.2cm）在 4 种条件下以 30%的 1 次重复最大力量进行史密斯机卧推挺举：（a）反弹运动和平衡重，（b）反弹运动和无平衡重，（c）向心-离心运动和平衡重，以及（d）向心-离心运动和无平衡重。线性加速度计测量峰值功率、峰值力以及峰值向心和离心速度，力板测量峰值地面反作用力。平衡重条件产生了显著的（p<0.05）较低的峰值加速度计测量力（反弹和向心-离心卧推挺举分别为-21.2%和-17.0%），但增加了峰值地面反作用力（5.3%和 3.2%）。峰值加速度计测量力和峰值地面反作用力变化之间的差异表明，在运动过程中净外部负荷增加。对于爆发力运动的性能测试，使用平衡系统会导致性能能力的低估，可能是因为在向心阶段净外部负荷增加。因此，平衡系统不应用于爆发力运动性能测试。
