The focus of this study was to examine the role of walking velocity in stability during normal gait. Local dynamic stability was quantified through the use of maximum finite-time Lyapunov exponents, λ Max . These quantify the rate of attenuation of kinematic variability of joint angle data recorded as subjects walked on a motorized treadmill at 20%, 40%, 60%, and 80% of the Froude velocity. A monotonic trend between λ Max and walking velocity was observed with smaller λ Max at slower walking velocities. Smaller λ Max indicates more stable walking dynamics. This trend was evident whether stride duration variability remained or was removed by time normalizing the data. This suggests that slower walking velocities lead to increases in stability. These results may reveal more detailed information on the behavior of the neuro-controller than variability-based analyses alone.

Nonlinear dynamic systems analyses were successfully applied to empirically measured data, which were used to characterize the neuromuscular control of stability during repetitive dynamic trunk movements. Movement pace and movement direction influenced the control of spinal stability. These stability assessment techniques are recommended for improved workplace design and the clinical assessment of spinal stability in patients with low back pain.

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The objective of this project was to develop a comprehensive methodology to assess the suit fit and performance differences between a nominally sized extravehicular mobility unit (EMU) spacesuit and a nominal +1 (plus) sized EMU. Method: This study considered a multitude of evaluation metrics including 3D clearances and pressure point mapping to quantify potential issues associated with using offnominal suit sizes. Results: There were minimal differences with using a plus suit size. Discussion: Analysis of the results indicates that future suit size evaluations should consider this ergonomic approach to understand and mitigate potential suit fit and performance issues.

Spinal stability has been characterized in static but not in dynamic movements. The goal of this study was to determine whether movement pace and direction of dynamic trunk flexion influence the control of spinal stability. Twenty healthy subjects performed dynamic lifting movements at 20 and 40 cycles per minute. Lyapunov exponents were calculated from the measured trunk kinematics to estimate stability. Complexity of torso dynamics required at least five embedded dimensions thereby indicating that torso dynamics requires more than the 3-dimensions of movement for sufficient characterization. Dynamic stability is was greater in slow lifting movement than in fast movements. Asymmetric movements demonstrated greater multi-dimensional kinematic divergence than asymmetric movements. This indicates that the sagittal plane of movement may not be a principle dynamic axis of torso movement. Results provide biomechanical insight regarding the role of workplace design and risk of musculoskeletal instability in dynamic lifting tasks.