Achilles Tendon Loading during Running Estimated via Shear Wave Tensiometry: A Step Towards Wearable Kinetic Analysis

ABSTRACT Purpose Understanding muscle-tendon forces (e.g., triceps surae and Achilles tendon) during locomotion may aid in the assessment of human performance, injury risk, and rehabilitation progress. Shear wave tensiometry is a noninvasive technique for assessing in vivo tendon forces that has been recently adapted to a wearable technology. However, previous lab-based and outdoor tensiometry studies have not evaluated running. This study was undertaken to assess the capacity for shear wave tensiometry to produce valid measures of Achilles tendon loading during running at a range of speeds. Methods Participants walked (1.34 m/s) and ran (2.68, 3.35, and 4.47 m/s) on an instrumented treadmill while shear wave tensiometers recorded Achilles tendon wave speeds simultaneously with whole body kinematic and ground reaction force data. A simple isometric task allowed for the participant-specific conversion of Achilles tendon wave speeds to forces. Achilles tendon forces were compared to ankle torque measures obtained independently via inverse dynamics analyses. Differences in Achilles tendon wave speed, Achilles tendon force, and ankle torque across walking and running speeds were analyzed with linear mixed-effects models. Results Achilles tendon wave speed, Achilles tendon force, and ankle torque exhibited similar temporal patterns across the stance phase of walking and running. Significant monotonic increases in peak Achilles tendon wave speed (56.0-83.8 m/s), Achilles tendon force (44.0-98.7 N/kg), and ankle torque (1.72-3.68 N-m/kg) were observed with increasing locomotion speed (1.34-4.47 m/s). Tensiometry estimates of peak Achilles tendon force during running (8.2-10.1 body weights) were within the range of those estimated previously via indirect methods. Conclusions These results set the stage for using tensiometry to evaluate Achilles tendon loading during unobstructed athletic movements, such as running, performed in the field.