Patellofemoral Joint and Achilles Tendon Loads During Overground and Treadmill Running

STUDY DESIGN: Level 4, controlled laboratory study. BACKGROUND: Little is known regarding how the potential differences between treadmill and overground running may affect patellofemoral joint and Achilles tendon loading characteristics. OBJECTIVES: To compare measures of loading of the patellofemoral joint and Achilles tendon across treadmill and overground running in healthy, uninjured runners. METHODS: Eighteen healthy runners ran at their self-selected speed on an instrumented treadmill and overground, while 3-D running mechanics were sampled. A musculoskeletal model derived peak load, rate of loading, and estimated cumulative load per 1 km of continuous running for the patellofemoral joint and Achilles tendon for each condition. Data were analyzed via paired t tests and Pearson correlations to detect differences and assess relationships, respectively, between the 2 running mediums. RESULTS: No differences (P > .05) were found between treadmill and overground running for peak load, rate of loading, or estimated cumulative patellofemoral joint stress per 1 km of continuous running. However, treadmill running resulted in 12.5% greater peak Achilles tendon force (P < .001), 15.6% greater loading rate of Achilles tendon force (P < .001), and 14.2% greater estimated cumulative Achilles tendon force per 1 km of continuous running (P < .001) compared with overground running. There were strong (r > 0.70) and moderate agreements (r > 0.50) for most patellofemoral joint and Achilles measures, respectively, between treadmill and overground running. CONCLUSION: No differences were observed in loading characteristics to the patellofemoral joint between running mediums; however, treadmill running resulted in greater Achilles tendon loading compared with overground running. Future investigations should examine whether sudden bouts of treadmill running may increase the risk of mechanical overload of the Achilles tendon in runners who habitually train overground.