Stability and consistency is a critical aspect in joint kinetic measurements. By applying a statistical technique, called sequential estimation procedure, the aim of this work was to determine the minimum number of trials required to obtain a stable mean for peak hip, knee, and ankle moments and powers during vertical jump. Nine competitive track and field sprinters (21.7 ± 3.5 yrs, 177.6 ± 4.3 cm, 70.8 ± 3.6 kg) performed 5 series of 5 double-legged maximum-height countermovement vertical jumps. From force platform and kinematic data, moment and power output were calculated for hip, knee, and ankle joints. The sequential estimation procedure applied to these data revealed that at least a 12-trial protocol is needed to establish a true measure for all the selected parameters. The mean number of trials for each variable was greater than 8 and less than 13. When hip moments were excluded from the analysis, a 10-trial protocol could be sufficient to reach a stable mean. In conclusion. the results of this study gave statistical evidence for the need to adopt multiple-trial protocols in order to obtain a stable mean for joint kinetic data.
The authors are with the Bioengineering Center, Polytechnic of Milan (Don Gnocchi Foundation, I.R.C.C.S. Milan), Via Capecelatro 66, 20148 Milan, Italy.