INFLUENCE OF CONTRACTILE TENSION DEVELOPMENT ON DYNAMIC STRENGTH MEASUREMENTS OF THE PLANTARFLEXORS IN MAN

The influence of the contractile tension rise time on isokinetic force-angle records has been inferred from static force-time curves but has not been experimentally determined. The purpose of this study is thus to describe the influence of the contractile rise time on the force-angle curves produced during maximal voluntary, acceleration controlled, isokinetic plantarflexions at 30'/s. Since we could not measure directly the period of force development unbiased by changes in muscle length during the movements, we devised an experimental strategy which allowed the computation of the dynamic force-time curve. Thus in five normal men, we first recorded force-angle curves produced during maximal voluntary plantarflexion movements preceded by maximal static pre-loading (D: - 10 degree Max) in order to eliminate the period of tension development from the force-angle record. Next, we recorded force-angle curves produced during maximal voluntary contractions initiated from two different starting angles without pre-loading (D: - 10 degree Min and D: 0 degree Min) to include the period of tension rise. The dynamic force-time curve was computed by correcting these force-angle curves (D: - 10 degree Min and D: 0 degree Min) for the hypothetical loss in force due to muscle shortening. We compared the relative (to remove the effects of force magnitude) computed dynamic force-time curves with relative static force-time curves measured at three different angles.