The Relationship Between Achilles Tendon Moment Arm Length and Vertical Jump Performance

Abstract

Vertical jump testing is widely used across sports to assess lower-body explosiveness, and previous research in explosive tasks such as sprinting has associated a shorter Achilles tendon moment arm (ATMA) with faster sprint times, raising the question of whether a shorter moment arm may be advantageous to jumping in a similar manner. The purpose of this study was to determine whether ATMA length had a relationship with vertical jump performance in recreationally active adult males. The secondary analysis was an examination of the relationship between Achilles tendon stiffness and vertical jump height. Twenty-two recreationally active men completed countermovement jump (CMJ), squat jump (SJ), standing vertical jump (VJ), and single-leg approach jump (AJ) trials. ATMA was measured using a hybrid ultrasound and motion-capture method at neutral, plantarflexed, and dorsiflexed ankle positions. Achilles tendon stiffness was assessed at a neutral ankle position using shear wave elastography. Contrary to the hypothesis that a shorter ATMA would predict greater jump performance, there were no significant relationships found between ATMA and any of the vertical jump heights. There was, however, a trend in the opposite direction than our hypothesis for ATMA and CMJ, VJ, and AJ, suggesting that athletes with longer ATMA produced greater jump heights. In contrast, Achilles tendon stiffness demonstrated the strongest correlation with jump performance, maintaining significant associations with both CMJ and SJ height even after statistically controlling for plantarflexor strength. These findings suggest that the performance advantages of a shorter ATMA identified in sprinting research do not directly transfer to vertical jumping. Tendon stiffness being a modifiable property may represent a more actionable target than ATMA for practitioners seeking to improve jump performance, and future work should compare elite and recreational jumpers to test this further.