An alternative to the Iterative Newton-Euler or linked segment model was developed to compute lower extremity joint moments using the mechanics of the double pendulum. The double pendulum model equations were applied to both the swing and stance phases of locomotion. Both the Iterative Newton-Euler and double pendulum models computed virtually identical joint moment data over the entire stride cycle. The double pendulum equations, however, also included terms for other mechanical factors acting on limb segments, namely hip acceleration and segment angular velocities and accelerations Thus, the exact manners in which the lower extremity segments interacted with each other could be quantified throughout the gait cycle. The linear acceleration of the hip and the angular acceleration of the thigh played comparable roles to muscular actions during both swing and stance.
Saunders N. Whittlesey and Joseph Hamill
Saunders N. Whittlesey, Richard E.A. van Emmerik and Joseph Hamill
Many studies have assumed that the swing phase of human walking at preferred velocity is largely passive and thus highly analogous to the swing of an unforced pendulum. In other words, while swing-phase joint moments are generally nonzero during swing, it was assumed that they were either zero or at least negligibly small compared to gravity. While neglect of joint moments does not invalidate a study by default, it remains that the limitations of such an assumption have not been explored thoroughly. This paper makes five arguments that the swing phase cannot be passive, using both original data and the literature: (1) Computer simulations of the swing phase require muscular control to be accurate. (2) Swing-phase joint moments, while smaller than those during stance, are still greater than those due to gravity. (3) Gravity accounts for a minority of the total kinetics of a swing phase. (4) The kinetics due to gravity do not have the pattern needed to develop a normal swing phase. (5) There is no correlation between pendular swing times and human walking periods in overground walking. The conclusion of this paper is that the swing phase must be an actively controlled process, and should be assumed to be passive only when a study does not require a quantitative result. This conclusion has significant implications for many areas of gait research, including clinical study, control theory, and mechanical modeling.
Edward C. Frederick, Jeremy J. Determan, Saunders N. Whittlesey and Joseph Hamill
Seven top amateur or professional skateboarders (BW = 713 N ± 83 N) performed Ollie maneuvers onto and off an elevated wooden platform (45.7 cm high). We recorded ground reaction force (GRF) data for three Ollie Up (OU) and Ollie Down (OD) trials per participant. The vertical GRF (VGRF) during the OU has a characteristic propulsive peak (M = 2.22 body weight [BW] ± 0.22) resulting from rapidly rotating the tail of the board into the ground to propel the skater and board up and forward. The anterior-posterior (A-P) GRF also shows a pronounced peak (M = 0.05 ± 0.01 BW) corresponding with this propulsive VGRF peak. The initial phase of landing in the OD shows an impact peak in VGRF rising during the first 30 to 80 ms to a mean of 4.74 ± 0.46 BW. These impact peaks are higher than expected given the relatively short drop of 45.7 cm and crouched body position. But we observed that our participants intentionally affected a firm landing to stabilize the landing position; and the Ollie off the platform raised the center of mass, also contributing to higher forces.