Target heights alter the energetics of drop jumps when drop height is held constant.

Plyometrics are a popular form of training the stretch-shortening cycle in competitive athletes and recreational athletes. One method of controlling intensity is to vary the dropping height during the training session. It may be possible to alter the intensity by creating a target height to jump over when holding the dropping height constant. Fifteen college recreational athletes performed 15 trials of 60-cm depth jumps over 3 different target heights (40, 60, and 80 cm). One-way repeated measures analysis of variance was used to identify significant differences in kinematic and kinetic variables for both the concentric and eccentric phases. There were no significant differences in eccentric work found between the 3 conditions. Significant differences were found in the total work performed during the concentric portion of the jumps between the 40- and 60-cm trials but not between the 60- and 80-cm trials. These results were found to be different at each joint of the lower extremity as compared with past research. Power analysis showed no significant differences between target heights, which may suggest that higher target heights may not be necessary to achieve the same ground contact parameters. Overall analysis of the variables suggests that 60 cm is an adequate target height when dropping from 60 cm.

Effect of competitiveness on forty-yard dash performance in college men and women.

The objective of this study was to determine performance differences between individual and competitive trials of the 40-yard dash. Physically active college men (n = 25) and women (n = 29) performed an individual 40-yard dash, followed by completion of the Sports Competition Trait Inventory (SCTI) before performing a paired 40-yard dash against a time-matched competitor. All sprints were performed on an indoor rubberized track using photoelectric gates to start and stop a digital timer. In addition, 3 timers used hand-held stopwatches to record the individual sprint time. There was no significant difference (p = 0.10) between men (120.3 +/- 16.6) and women (111.7 +/- 20.3) on the SCTI. There was no significant difference between individual and competitive 40-yard dash times for either men (5.21 +/- 0.24 and 5.19 +/- 0.23 seconds, respectively) or women (6.12 +/- 0.31 and 6.11 +/- 0.32 seconds, respectively). The correlation between SCTI and both individual and competitive 40-yard dashes was significant (p < 0.05) for women (r = -0.45 and -0.44, respectively) but not for men (r = -0.10 and 0.10, respectively). Electronic times (5.70 +/- 0.54 seconds) were not significantly different from 1 hand-timer (5.71 +/- 0.56 seconds) but were significantly faster than the other 2 timers (5.80 +/- 0.58 and 5.82 +/- 0.57 seconds). Averaging the 3 hand times (5.78 +/- 0.56 seconds) for comparison with the electronic timing (5.70 +/- 0.54 seconds) produced a high correlation (r = 0.96) but a significantly slower time (p < 0.05). A competitive environment does not appear to improve short sprint times in either men or women. In addition, hand timing may not always produce faster times compared to electronic timing.