PURPOSE: Accurate measurements of bench press throw performance (power, force, velocity of movement) can be obtained using free weights equipment. Due to the risk of injury and the curvilinear bar path involved in free weight bench press throws, smith machines that allow for only vertical movement are commonly used when assessing bench press throw performance. Smith machines often utilize a counter-balance weight to reduce the load of the bar; however, to our knowledge it has not been demonstrated if the use of a counter-balance weight affects measurements of performance. Therefore, the purpose of this study was to determine the effect of using a counter-balance weight on measurements of bench press throw performance. METHODS: Twenty-four men and women (mean +/- standard deviation: 24.7 +/- 3.9 years, 173 +/- 10 cm, 77.7 +/- 18.3 kg) completed three maximal rebound bench press throws on a smith machine for each of four different conditions: with or without a counter-balance weight and using either a light (48 +/- 13 % 1-repetition maximum [1-RM]) or a moderate (61 +/- 13 % 1-RM) load. For the counter-balance condition, a weight equal to that of the counter-balance weight (13.6 kg) was added to the bar. Peak power, peak force, and peak velocity for each throw were measured using an accelerometer attached to the bar. The best of the three throws for each condition was used for further analysis. For each load condition, the differences between measurements obtained with and without the use of the counter-balance weight were calculated. RESULTS: With the light load, the use of a counter-balance resulted in significant (p<0.001) reductions in measurements of peak power (-221 +/- 215 W; -29 %), peak force (-112 +/- 99 N; -18 %), and peak velocity (-48 +/- 48 m[middle dot]s-1; -26 %). Similarly, with moderate load, the use of a counter-balance resulted in significant reductions in measurements of peak power (-143 +/- 139 W; -21 %), peak force (-140 +/- 115 N; -19 %), and peak velocity (-33 +/- 37 m[middle dot]s-1; -23 %). There were no differences in the reductions for any variable between the two load conditions. CONCLUSIONS: Use of equipment with a counter-balance weight (i.e., counter-balanced smith machine) caused constant underestimation peak power, peak force, and peak velocity of movement in the bench press throw at light (48 +/- 13 % 1-RM) and moderate (61 +/- 13 % 1-RM) loads. Practical Applications: When measuring peak power, peak force, and peak velocity of movement for a resistance exercise, counter-balanced equipment should not be used as this will lead to an underestimation of the magnitude of each these variables.
(C) 2011 National Strength and Conditioning Association