Biomechanical Markers of Lower Extremity Fatigue: A Literature Review




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Purpose: Lower-extremity (LE) muscular fatigue plays a pivotal role in injury occurrence across various domains, including sports, occupational settings, and daily activities. This is partly because fatigued muscles can absorb less energy before reaching the degree of stretch that causes injury. This review explores the significance of employing measurable biomechanical markers to assess lower extremity fatigue. Some studies have shown significant changes in post-fatigue functional tasks (vertical jump height), acceleration/velocity, postural stability (center of pressure), spatio-temporal gait metrics, and pressure distribution, but few reviews have compared these factors to identify the best predictors of fatigue. With the prevalence of musculoskeletal injuries, understanding the biomechanical changes associated with fatigue becomes imperative for predicting and preventing injury.

Methods: PubMed, Google Scholar, and Scopus were searched using 20 distinct queries, which yielded 3,068 articles. The inclusion criteria used were: An experimental pre/post-test design, fatiguing protocol targeting lower extremities, recent studies after 2010, greater than 10 participants, data recorded via force plates or IMU, and a healthy adult population. In total, 44 articles met the inclusion criteria.

Results: Of the included studies, CoP changes were dependent on the protocol used. High-intensity fatigue protocols were associated with significant increases in postural instability, measured by CoP displacement, velocity, and variability in both sagittal and coronal planes, but CoP measures were inconclusive in low-moderate intensity fatiguing protocols. When observing Spatio-Temporal gait metrics, the literature showed a strong positive correlation between increased ground contact time and fatigue. Stride length was negatively correlated with fatigue. Step width variability and single stance time were increased following fatigue. In terms of pressure distributions, increasing muscle fatigue was correlated with increases in plantar pressure. Peak pressure and force of metatarsals I - V were inconclusive, attributable to varying rear versus forefoot strike patterns, however, medial and lateral heel peak pressures consistently increased with muscle fatigue. In line with these findings, various studies demonstrated that increasing fatigue correlated with kinetic parameters such as increased stride cadence and, consequently, increased tibial acceleration. Prolonged or repetitive exposure to elevated tibial acceleration levels may be associated with greater impact forces and loading on the lower extremities, potentially contributing to muscle fatigue and elevating the risk of overuse injuries. Functional tests, such as jump height, showed a significant negative relationship with fatigue regardless of protocol intensity. A study comparing different jump height modalities and fatigue showed the highest repeatability and immediate/prolonged fatigue produced changes with CMJ, supported by its widespread use as an indicator for fatigue.

Conclusions: We consistently found significant increases in sagittal plane CoP velocity, ground contact time, heel loading, and tibial acceleration with a significant decrease in CMJ height following LE fatigue. Limitations included variability in the fatigue protocols used and limited research that met inclusion criteria. In the future, these results can have implications for the development of wearables to track fatigue in athletes to decrease the incidence of injury.