Running at Self-selected Speed Can Prevent Step Length Asymmetry
April 06, 2018
Dynamic elastic response prostheses are designed to absorb and return strain energy in running. While past research has focused on running prostheses with a single toe spring designed for high speeds, researchers at the University of Roehampton, Whitelands College, London, England, wanted to determine how runners with transtibial amputations controlled the ground reaction force of each limb while running at different speeds while using a general-purpose dynamic prosthesis with a heel spring.
Overground running data was collected from 16 recreational runners (eight runners with a transtibial amputation who used their own Endolite BladeXT prosthesis and eight control participants). Researchers used Vicon Nexus Motion Capture Software V.2.5 with Kistler force plates for data collection. The participants ran at a self-selected running pace, and 70 percent and 130 percent of that pace. Runners were analyzed for vertical, braking, propulsion peak ground reaction forces and impulses, and for vertical loading and decay rates between limbs at each speed, and their association with speed was assessed.
The data, published online in the May issue of Gait & Posture, showed that the vertical, braking forces and impulses and propulsive force were significantly less on the prosthetic limb than controls at the faster speed. Researchers found, however, that there appeared to be no difference in the propulsive impulse. The intact limb did not show increased vertical force at any speed, but experienced increased braking compared to both prosthetic limb and controls at the slower speed. For all limbs, braking and propulsive peak forces, decay rate, step length, and step frequency were strongly and significantly associated with speed. On the prosthetic limb, vertical impulse was strongly and significantly negatively associated with speed and control's braking impulse was associated with speed.
Researchers determined that a leg-specific response was found at different speeds. On the prosthetic side, the technique was to brake less, not propel more, at higher speeds with reduced vertical drive. The data suggests that running at a self-selected speed could be beneficial for fitness without inducing detrimental ground reaction forces on the intact limb or evoking asymmetry in step length and frequency, according to the study's authors.