Plantarflexor fiber and tendon slack length are strong determinates of simulated single-leg heel raise height

• Published in: Journal of biomechanics Vol. 86; pp. 27 - 33
• Main Authors: Baxter, Josh R., Farber, Daniel C., Hast, Michael W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 27.03.2019; Elsevier Limited
• Subjects: Achilles tendon; Achilles Tendon - anatomy & histology; Achilles Tendon - physiology; Achilles tendon rupture; Adult; Ankle; Ankle - physiopathology; Ankle Joint - physiology; Computer Simulation; Conflicts of interest; Correlation analysis; Elongation; Female; Force; Heel - physiology; Humans; Leg; Male; Muscle, Skeletal - physiology; Muscle-tendon unit; Muscles; Musculoskeletal model; Musculoskeletal Physiological Phenomena; Musculoskeletal system; Parameters; Patient function; Patients; Rupture - physiopathology; Rupture - rehabilitation; Simulation; Structure-function relationships; Tendon Injuries - rehabilitation; Tendons; Muscle-tendon unit; Musculoskeletal model; Simulation; Patient function; Achilles tendon rupture
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2019.01.035

Achilles tendon ruptures have been linked with detrimental changes in muscle-tendon structure, which may help explain long-term functional deficits. However, the causal effects of muscle-tendon structure on joint function have not been tested in a controlled setting. Therefore, the purpose of this study was to test the implications of muscle-tendon unit parameters on simulated single-leg heel raise height. We hypothesized that muscle fiber length and resting ankle angle – a clinical surrogate measure of tendon slack length – would predict single-leg heel raise height more strongly than other parameters. To test this hypothesis, we developed a two-part simulation paradigm that recreated clinically relevant muscle-tendon scenarios and then tested these parameters on single-leg heel raise height. We found that longer muscle fibers had the greatest positive effect on single-leg heel raise height. However, tendon slack length, determined by simulating resting ankle angles in a secondary analysis, revealed a stronger negative correlation with heel raise height. Our findings support previous clinical observations that both muscle fascicle length and resting tendon length are important muscle-tendon parameters for patient function. In addition to minimizing tendon elongation following rupture, treatment plans should focus on preserving plantarflexor muscle structure to mitigate functional loses following Achilles tendon ruptures.