Contribution of Age and Muscle Strength of Lower Limbs to Steadiness and Stability in Standing Posture

Abstract

The purposes of this study were to show changes with aging in steadiness and stability of standing posture, and to show the relationships between the steadiness and stability on one hand and the isometric strength of ankle dorsal flexion (ADF), ankle planter flexion (APF), or hallucial flexion (HF) on the other.The steadiness was evaluated by the length (L) of trace of the center of foot pressure (CEP) while maintaining the following postures for 20 seconds: (1) quiet standing posture (QSP), (2) backward leaning posture (BLP) with CFP at 25% from the heel regarding the foot length as 100%, and (3) forward leaning posture (FLP) with CFP at 65%. The stability was evaluated in terms of the CFP in extreme backward and forward leaning postures maintained for 10 seconds. These measurements were obtained while the subjects were standing on a Gravicorder (Anima K. K. ) with the eyes opened and the stance closed. The isometric strength was measured by a strain gage dynamometer in sitting position with the knee extended. The angle of the ankle was fixed at 90 degrees in APF and HF, and at 105 degrees in ADF. The age of subjects, 99 males and 140 females, ranged from 20 to 79 years. The results obtained were as follows:(1) The steadiness reduced in both sexes with increase of age after fifties in QSP and FLP, and after twenties in BLP.(2) The forward limits (FL) of the stability area shifted backward with age after fifties in both sexes, while the backward limits (BL) of the stability area shifted forward after twenties in both sexes.(3) The isometric strength of APF and HF decreased with age after forties in both sexes, while that of ADF decreased with age after twenties in female and after thirties in male. These changes in the muscle strength corresponded with the changes in the steadiness and stability described above.(4) No significant correlations (partial correlation holding the age constant) were shown between the L value in QSP and the isometric strength of APF, ADF and HF. Significant correlations (partial correlation holding the age constant) were shown between the L value in FLP and the APF strength, the BL and the ADF strength, and the FL and the APF as well as the HF strength, respectively.