title: Influence of angular velocity and movement frequency on development of fatigue in repeated isokinetic knee extensions.
abstract: Six sedentary students, six orienteers, and six soccer players were each subjected to 15 tests, comprising 120 s of repeated, maximal isokinetic knee extensions. The tests differed with respect to movement velocity (30 degrees.s-1, 120 degrees.s-1, and 300 degrees.s-1), and movement frequency (5 at each velocity). At a certain velocity, a rectilinear relationship was found between muscular performance intensity (expressed either as average power output or as exercise time ratio) and development of fatigue (expressed either as an absolute or as a fractional decline in work output). Significant inter-velocity differences existed between the slopes of these lines at some combinations of performance and fatigue expressions. Only tendencies towards a difference in x-intercept values were found. This x-intercept value can be taken as a measure of the greatest attainable intensity level of performance without the development of fatigue. This suggestion is valuable both in basic physiological research, and as a possible criterion for optimization of muscular performance. At a given exercise time ratio, increasing movement velocity produced increasing fatigue. However, at a given muscular power output--above 15 W approximately--fatigue developed to a greater extent at the low velocity than at the two higher ones, which did not differ significantly. Substantial individual variation was seen in the positions of the low-, medium-, and high-velocity lines. These variations did not depend on the training background. This implies that the validity of using single-velocity, single-frequency tests in determining isokinetic endurance is doubtful.
authors.affiliation: National Institute of Occupational Health, Department of Physiology, Solna, Sweden.
authors.forename: S E
authors.initials: SE
authors.lastname: Mathiassen
mesh_terms: D000328:Adult; D005221:Fatigue / Q000209:etiology* / Q000503:physiopathology; D006801:Humans; D007717:Knee / Q000033:anatomy & histology / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D009132:Muscles / Q000502:physiology; D010806:Physical Education and Training