After each series of kettlebell drops and scissors movement, balls were fired at the free-hanging racquet to measure rebound speed, spin, and angle. The goal was to observe any change in performance characteristics due to repeated impacts. Because the speed, spin, and angle of balls fired from a ball machine vary slightly from shot to shot, these input parameters were normalized (procedure described in the article "Spin and Material" ) to be the same for a given racquet. Each racquet was normalized separately since what interests us are the performance changes for a given racquet, not between racquets. About 15 balls were fired and measured after each series of kettlebell drops. Table 2 shows the average results.