Normalizing Foot Moment Arm Lengths in Men and Women

Abstract

Foot anthropometric dimensions may influence moment arm lengths and respective moments of force resisted by skeletal muscles. Depending upon circumstances, absolute or normalized expressions of these measures may have greater utility. PURPOSE: To determine the stability reliability and precision of two absolute and normalized moment arm lengths of the foot. METHODS: Longitudinal foot dimensions were obtained in 27 men and 27 women including the anterior-posterior distance between the posterior calcaneus and: 1) talocrural (TALO) and 2) metatarsophalangeal (META) joints. Bilateral measurements of seated subjects were performed using a digital sliding caliper. Absolute dimensions were normalized to height and lower-limb length (LLL, greater trochanter to lateral malleolus). Measures were obtained twice, separated by either 24 or 48 hours. Stability reliability was determined using intraclass correlation coefficient (ICC), and precision using standard error of measurement (SEM). RESULTS: The scatter of points around the trend lines for all 54 subjects combined appear to be uniform and the separate SEMs for men and women are similar. Assuming homoscedasticity, data are reported for the combined groups. For the 3 bilateral expressions of the 2 foot dimensions (12 measures), the low and high means (standard deviation) are reported for each session as well as the ICC and SEM for the pair of sessions. For TALO, means were 5.1 (0.4) and 5.2 (0.5) cm, ICCs were 0.79 and 0.82, and SEMs were 0.2 and 0.2. When normalized to height, means were 0.030 (0.002) and 0.030 (0.002) cm/cm height, ICCs were 0.65 and 0.75, and SEMs were 0.001 and 0.001. When normalized to LLL, means were 0.062 (0.005) and 0.063 (0.005) cm/cm LLL, ICCs were 0.69 and 0.73, and SEMs were 0.003 and 0.003. For META, means were 17.0 (1.2) and 17.1 (1.1) cm, ICCs were 0.97 and 0.98, and SEMs were 0.2 and 0.2. When normalized to height, means were 0.098 (0.002) and 0.100 (0.002) cm/cm height, ICCs were 0.92 and 0.94, and SEMs were 0.001 and 0.001. When normalized to LLL, means were 0.205 (0.010) and 0.208 (0.011) cm/cm LLL, ICCs were 0.92 and 0.92, and SEMs were 0.003 and 0.003. CONCLUSIONS: Surface landmarks and digital calipers can be used to precisely measure the 2 foot dimensions in question, whether or not they are normalized. Reliability is high for the META dimension, and lower for the TALO dimension. Meticulous data acquisition protocols are required to acquire potentially useful data.