John P. Obusek

How do load carriage and walking speed influence trunk coordination and stride parameters

To determine the effects of load carriage and walking speed on stride parameters and the coordination of trunk movements, 12 subjects walked on a treadmill at a range of walking speeds (0.6-1.6 m s(-1)) with and without a backpack containing 40% of their body mass. It was hypothesized that compared to unloaded walking, load carriage decreases transverse pelvic and thoracic rotation, the mean relative phase between pelvic and thoracic rotations, and increases hip excursion. In addition, it was hypothesized that these changes would coincide with a decreased stride length and increased stride frequency. The findings supported the hypotheses. Dimensionless analyses indicated that there was a significantly larger contribution of hip excursion and smaller contribution of transverse plane pelvic rotation to increases in stride length during load carriage. In addition, there was a significant effect of load carriage on the amplitudes of transverse pelvic and thoracic rotation and the relative phase of pelvic and thoracic rotation. It was concluded that the shorter stride length and higher stride frequency observed when carrying a backpack is the result of decreased pelvic rotation. During unloaded walking, increases in pelvic rotation contribute to increases in stride length with increasing walking speed. The decreased pelvic rotation during load carriage requires an increased hip excursion to compensate. However, the increase in hip excursion is insufficient to fully compensate for the observed decrease in pelvis rotation, requiring an increase in stride frequency during load carriage to maintain a constant walking speed.

Increased musculoskeletal stiffness during load carriage at increasing walking speeds maintains constant vertical excursion of the body center of mass.

The primary objective of this research was to determine changes in body and joint stiffness parameters and kinematics of the knee and body center of mass (COM), that result from wearing a backpack (BP) with a 40% body weight load at increasing speeds of walking. It was hypothesized that there would be speed and load-related increases in stiffness that would prevent significant deviations in the COM trajectory and in lower-extremity joint angles. Three independent biomechanical models employing kinematic data were used to estimate global lower-extremity stiffness, vertical stiffness and knee joint rotational stiffness in the sagittal plane during walking on a treadmill at speeds of 0.6-1.6 ms(-1) in 0.2 ms(-1) increments in BP and no backpack conditions. Kinematic data were collected using an Optotrak, three-dimensional motion analysis system. Knee angles and vertical excursion of the COM during the compression (loading phase) increased as a function of speed but not load. All three estimates of stiffness showed significant increases as a function of both speed and load. Significant interaction effects indicated a convergence of load-related stiffness values at lower speeds. Results suggested that increases in muscle-mediated stiffness are used to maintain a constant vertical excursion of the COM under load across the speeds tested, and thereby limit increases in metabolic cost that would occur if the COM would travel through greater vertical range of motion.

Transverse plane kinetics during treadmill walking with and without a load

OBJECTIVE The purpose of this experiment was to determine the effects of wearing a backpack on transverse plane upper and lower body torque. BACKGROUND During unloaded walking the upper and lower body counter-rotate to reduce the net angular momentum of the body. There is less counter-rotation while carrying a load, suggesting a more rigid link between the upper and lower body. We predicted that load carriage would result in an increase in upper body torque. Because the upper and lower body may be more rigidly linked during load carriage, we also predicted an increase in lower body torque. METHODS Twelve subjects (5 male, 7 female, mean age=26) walked with and without a backpack containing 40% of their body mass on a treadmill at speeds from 0.6 to 1.6 ms(-1). Kinematic data were sampled for 30 s at each speed, upper and lower body torque were calculated from angular acceleration and moment of inertia. RESULTS Higher levels of upper and lower body torque were observed during load carriage than during unloaded walking. However, the increase in upper body torque was 225%, while upper body moment of inertia increased by 400%. CONCLUSIONS The differences in torque between loaded and unloaded walking suggest that a goal of loaded walking is to minimize upper body torque, which may reduce the likelihood of injury. RELEVANCE Knowledge of the effects of load carriage on upper and lower body torque, and related changes in coordination may provide insight into injury reduction mechanisms during load carriage.

The effects of a lower body exoskeleton load carriage assistive device on limits of stability and postural sway

The study investigated the effects of using a lower body prototype exoskeleton (EXO) on static limits of stability and postural sway. Measurements were taken with participants, 10 US Army enlisted men, standing on a force platform. The men were tested with and without the EXO (15 kg) while carrying military loads of 20, 40 and 55 kg. Body lean to the left and right was significantly less and postural sway excursions and maximal range of movement were significantly reduced when the EXO was used. Hurst values indicated that body sway was less random over short-term time intervals and more random over long-term intervals with the EXO than without it. Feedback to the users balance control mechanisms most likely was changed with the EXO. The reduced sway and relatively small changes in sway with increasing load weights suggest that the EXO structure may have functioned to provide a bracing effect on the body.