The effects of both jump/land phases and direction on Achilles tendon loading

Athletes in jumping and running sports have a high incidence of Achilles tendon (AT) injuries. We compared AT loading during jumping and landing phases in anteroposterior (AP) and mediolateral (ML) directions.

Sixteen males (age: 21.6±1.8 years, height: 178.4±6.4 cm, weight: 76.4±11.2 kg) performed single leg AP and ML jump-landings during both propulsive (jump) and braking (land) phases. Inverse dynamics and static optimization were used to determine muscle forces. AT cross sectional area was measured with ultrasound. AT force was divided by cross sectional area to determine stress while strain was determined from previous data. Two-way repeated measures analysis of variance (α=0.05) compared several variables (vertical ground reaction force (VGRF), ankle and knee angle, ankle joint muscle moment arm, external ankle moment arm, AT tendon force, stress, and strain) between movements (jump-landings) and directions (AP/ML).

AT loading was higher during jump than land in the ML compared to AP direction. VGRF was higher during land versus jump with no direction effect (AP/ML). An interaction showed a higher VGRF during the AP land and ML jump. The ankle joint moment arm was lower in jump and AP direction at peak tendon stress. External ankle moment arm at peak tendon stress was higher in jump and ML direction with an interaction. A larger external ankle moment arm occurred in ML but the change was less in the jump.

Higher tendon loading occurred during the jump and ML direction. This may provide insight into both injuries and rehabilitation efforts.