Repeatability of Static and Isokinetic Maximum Voluntary Back Strength Exertions.
Ch in "Trends in Ergonomics/human Factors V" 1988 :779-785
This Bureau of Mines paper describes tests in which 12 subjects (mean age 36 +- 8 sd) performed static and dynamic back strength exertions in standing and kneeling postures using an isokinetic dynamometer. A test-retest criterion was employed that required two maximum voluntary contractions (mvc's) to be within 10 pct of one another for each of 12 experimental conditions. The higher of these two values was accepted as the true maximum exertion. Data were analyzed to determine (1) the number of trials required to satisfy the test-retest criterion and (2) at which trial the mvc occurred for each experimental condition. An analysis of variance with repeated measurements demonstrated that dynamic back strength measurements required significantly more trials to satisfy the test- retest criterion (f1.11=5.837,P<0.05) Than did the static exertions. The average trial upon which the true maximum was obsreved was lower for static (2.39 Trials) tests than dynamic (2.82 Trials) tests; however, this difference was not significant (f1,11 = 4.199,P = 0.065). The results of this study indicate that fast isokinetic contractions are not as easily repeatable as slower isokinetic or static contractions. This may be due to the effects of rapid acceleration and perhaps an increased potential for a variable jerking motion during the strength measurement. The results of this study indicate that the use of a test-retest criterion may provide better estimates of both isometric and isokinetic strength.
Ch. in "Trends in Ergonomics/human Factors V" 1988, PP. 779-785