Trunk extensor muscle function in young and old women: A pilot study 1

Abstract

The purpose of this study was to document age-related alterations in trunk extensor strength and to compare these to changes in knee extensor strength over varying angles of muscle contraction. A secondary purpose was to compare age-related changes in trunk extensor endurance while statistically correcting for torso mass differences. Eighteen older (70 ± 7.3 years) and fifteen younger (22.1 ± 4.6 years) women volunteered for the study. Torso mass and trunk extension endurance (Modified-Sørenson test) were also evaluated. The results suggested that age-related torque production was both angle and muscle group dependent. Younger adults were 29% stronger in the knee and 23% stronger in the trunk extensors. Furthermore, the difference between age groups in knee extensor strength was 2.30 Nm/kg at 78°, but only 0.47 Nm/kg at 6° of knee flexion. This angle discrepancy was not evident in the trunk extensors. Following torso mass correction, trunk extension endurance time did not differ between ages (Young: 160.4 ± 65.8 vs. Old: 159.5 ± 71.9 sec, $p =$ 0.99). Our study suggests that the elderly should focus on improving trunk extension strength rather than endurance. Also, knee extensor strength exercises should be emphasized between 60° and 108° of knee flexion in the elderly to combat the age-related loss of lower extremity strength.