Abstract
Passive stiffness (Nm/°) of the plantar flexors was measured during a passive stretch into dorsiflexion (DF) in 18 healthy female subjects(range 18–60 years old) using an isokinetic dynamometer. Passive stiffness of the ankle joint was measured at a short range of motion (from 10° of plantar flexion (PF) to 10° of DF), and at a full range of motion (from 10° PF to maximal DF for each individual) with a neutral EMG from a subset of four legs. The purpose of the study was to assess the variances in the measurements of passive stiffness of the calf muscle and to correlate passive stiffness to age and jumping ability. There was a significant correlation (r=0.76) between the FRS and FRS test-retest. The methodological error for duplicate determinations was 7.7% for the SRS and 5.5% for the FRS. There was a significant correlation between age and the (FRS) full-range stiffness (r=0.83). There was a significant negative correlation between age and jumping (r=−0.54). We conclude that the test model of passive stiffness used in the present study is a useful method with good reliability. The passive elastic properties of muscles and tendons might explain part of the muscle performance in functional tests with ageing. However, other qualities may influence performance as well.