The purpose of this study was to examine the effects of mild, artificially-induced, LLI on running mechanics, including lower-limb joint kinematics, ground reaction forces, and lower-limb muscle activity.
Approval for this study was obtained by an Institutional Review Board prior to subject recruitment. 20 subjects in good-to-excellent health, recruited in series from December 2021 - March 2023, participated in this study (53% female, mean age ~23 years, mean height ~ 1.72 meters, and mean weight ~81 Kg); subjects were excluded if they reported any active pathology, bodily pain, or were unable to complete the testing protocol. Peak tibialis anterior and medial gastrocnemius muscle activity, peak ground reaction force (pGRF); maximal trunk, hip, knee, and ankle joint range-of-motion; and spatiotemporal parameters of gait and running were measured while walking 5.15 km/h and running 8.05 km/h with an artificially-induced LLI, using one and two 12.7 mm polyethylene shims on a treadmill instrumented with a single markerless 3D kinematic camera system (Microsoft Kinect/Walkerview 3.0).
Artificially-induced LLI was associated with significant differences in pGRF; hip, knee, and ankle range-of-motion; and both stride-length and stance-time (p 0.03) between the longer and shorter sides while running, but no changes in medial head of gastrocnemius (p > 0.09) or tibialis anterior (p > 0.35) muscle activity were found between sides. Greater pGRF were found while running compared to walking (p = 0.00) and were greater on the relatively shorter limb (p = 0.00). Hip and knee flexion were found to be greater on the longer side (p 0.002) while running. Stride-length was found to be greater (p 0.01 ) and stance-time was lesser (p = 0.00) on the shorter side while running.
Biomechanical changes do occur while running with a mild, artificially-induced LLI, the changes appear to be distinct compared to gait, and the changes appear to have a positive linear relationship with the magnitude of the LLI. In contrast to previous work, greater pGRF were found on the relatively shorter limb, indicating some musculoskeletal pathologies may be more likely to manifest on the shorter limb. Future research should investigate the effects of long-standing LLI on running mechanics using valid and reliable instruments, including a more comprehensive assessment of lower-limb muscle activity in both a controlled laboratory and overground outdoor environments.
Clinicians should include LLI assessment as part of a comprehensive physical examination among running athletes and consider implementing strategies to promote balanced lower-limb loading while running. Theoretically, this may reduce the risk of running-related injuries among this population.
leg-length inequality
biomechanics
