Specificity of Individual Differences in Arm Movement Fatigue within Two Levels of Work Load

Abstract Fifty subjects were given fatiguing tests at two work loads on a horizontal arm-crank friction ergometer.2 The initial speed was 120 rpm; the test continued for 10 min. Both fatigue curves were S-shaped—the rate of work dropped off slowly at first, then went through a rapid drop-off phase followed by a slow drop-off phase that approached an asymptotic steady state. The mathematical form was a two-component exponential equation which fitted the observed data very closely. Using a 2-k. work load, there was 22 percent decrement at the end of the test. Using a 3.45-k. work load (1 week later), the decrement was 48 percent. Test-retest reliability of individual differences in drop-off was moderately high (r = .86 and .85 for the two work loads). However, the correlation between drop-offs for the two work loads was only r = .61 and even after correction for attenuation was only .71. Thus only 50 percent of the individual difference variance in fatigability was common to the two work loads, while 50 per...