Electrically evoked isometric and isokinetic properties of the triceps surae in young male subjects

Summary

The relationship between electrically evoked isometric and isokinetic properties of the triceps surae have been studied in 11 healthy male subjects. The results showed that the time to peak tension (TPT) and half relaxation time (1/2 RT) of the maximal twitch were 110±11 ms and 82±11 ms respectively, and the peak rates of rise of contraction (ΔP ₅₀, ΔP ₂₀₀) and relaxation (ΔP _R50, ΔP _R200) at 50 and 200 Hz were 0.36±0.07, 0.48±0.08 and 1.27±0.33, 1.25±0.27% Po ms⁻¹ respectively. The decline in force during a fatigue test was significantly (P<0.02) associated with the decrease in maximal relaxation rate (r=0.79). The TPT was significantly (P<0.05) and inversely related to ΔP ₅₀ and ΔP ₂₀₀. The mean angle specific torque-velocity relationship for the 11 subjects was adequately described by the empirical exponential equation of the form: V=16.5 (e ^−p/30.8−e ^−84.3/30.8) where V=velocity (rads s⁻¹) P=torque (Nm). The only significant association found between the isometric and isokinetic properties of the muscle was between ΔP _R200 and the torque expressed at a given velocity of 4 rads s⁻¹. This lack of association between the two variables is difficult to explain with certainty but it is suggested that it may be due to the differential effects of Ca²⁺ release and uptake and cross-bridge turnover rate in the two situations.