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NUMBER OF TRIALS NECESSARY TO ACHIEVE PERFORMANCE STABILITY OF SELECTED
GROUND REACTION FORCE VARIABLES DURING LANDING
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C.
Roger James1 ,
Joseph A. Herman2, Janet S. Dufek3 and Barry
T. Bates4 |
1Center for Rehabilitation Research, Texas Tech University Health Sciences
Center, Lubbock, Texas, USA
2Department of Health, Exercise, and Sport Sciences, Texas Tech University,
Lubbock, Texas, USA
3Department of Kinesiology, University of Nevada, Las Vegas, Las Vegas,
Nevada, USA
4Human Performance & Wellness, Inc., Henderson, Nevada, USA
| Received |
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23 August 2006 |
| Accepted |
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26
January 2007 |
| Published |
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01
March 2007 |
©
Journal of Sports Science and Medicine (2007) 6, 126 - 134
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| ABSTRACT |
| The objectives were to determine the number of trials necessary
to achieve performance stability of selected ground reaction force
(GRF) variables during landing and to compare two methods of determining
stability. Ten subjects divided into two groups each completed a minimum
of 20 drop or step-off landings from 0.60 or 0.61 m onto a force platform
(1000 Hz). Five vertical GRF variables (first and second peaks, average
loading rates to these peaks, and impulse) were quantified during
the initial 100 ms post-contact period. Test-retest reliability (stability)
was determined using two methods: (1) intra-class correlation coefficient
(ICC) analysis, and (2) sequential averaging analysis. Results of
the ICC analysis indicated that an average of four trials (mean 3.8
± 2.7 Group 1; 3.6 ± 1.7 Group 2) were necessary to achieve maximum
ICC values. Maximum ICC values ranged from 0.55 to 0.99 and all were
significantly (p < 0. 05) different from zero. Results of the sequential
averaging analysis revealed that an average of 12 trials (mean 11.7
± 3.1 Group 1; 11.5 ± 4.5 Group 2) were necessary to achieve performance
stability using criteria previously reported in the literature. Using
10 reference trials, the sequential averaging technique required standard
deviation criterion values of 0.60 and 0.49 for Groups 1 and 2, respectively,
in order to approximate the ICC results. The results of the study
suggest that the ICC might be a less conservative, but more objective
method for determining stability, especially when compared to previous
applications of the sequential averaging technique. Moreover, criteria
for implementing the sequential averaging technique can be adjusted
so that results closely approximate the results from ICC. In conclusion,
subjects in landing experiments should perform a minimum of four and
possibly as many as eight trials to achieve performance stability
of selected GRF variables. Researchers should use this information
to plan future studies and to report the stability of GRF data in
landing experiments.
KEY
WORDS: Reliability, variability, sequential averaging, intra-class
correlation coefficient.
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