Methods for investigating the sensitivity of joint resultants to body segment parameter variations

Two methods are presented for determining the sensitivity of joint resultants to variations in body segment parameters (BSPs) when solving inverse dynamics problems: the exact sampling method (ESM), and the approximate variational method (AVM). These methods are illustrated by applying them to a single segment in fixed-axis rotation. The results indicate that (a) the AVM provides first-order (linear) approximations to the total variations in joint resultants obtained when using the ESM, (b) the ESM should be used when BSP variations become large and higher-order terms in these variations can no longer be ignored as negligible in the BSP-dependent expansions for the joint resultants, (c) small percent variations in BSPs can propagate into considerably larger percent variations in the joint resultants obtained when solving inverse dynamics problems, and (d) if BSP variations are sufficiently small to allow nonlinear terms in these variations to be ignored as negligible, the AVM is much simpler and easier to use than the ESM.