Dorsiflexion Capacity Affects Achilles Tendon Loading during Drop Landings

WHITTING, J. W., J. R. STEELE, D. E. MCGHEE, and B. J. MUNRO. Dorsiflexion Capacity Affects Achilles Tendon Loading during Drop Landings. Med. Sci. Sports Exerc., Vol. 43, No. 4, pp. 706-713, 2011. Purpose: Evidence suggests a link between decreased dorsiflexion range of motion (DROM) and injury risk during landings. The purpose of this study was to determine the effect of weight-bearing DROM on ankle mechanics during drop landings. Methods: Forty-eight men (mean +/- SD = 22.5 +/- 4.7 yr) were measured for DROM. Participants performed drop landings onto a force platform at two vertical descent velocities (2.25 +/- 0.15 and 3.21 +/- 0.17 m.s(-1)), while EMG activity of four shank muscles and three-dimensional ankle joint kinematics were recorded. Participants were classified into low (37.7 degrees +/- 2.5 degrees) and high (48.4 degrees +/- 2.5 degrees) DROM groups. Results: Ground reaction force, EMG, dorsiflexion angle, plantarflexion moment, and Achilles tendon force outcome variables were all equivalent for the two DROM groups during each landing condition. However, the low DROM group performed each landing condition at a significantly greater percentage of their DROM and displayed significantly more ankle eversion throughout most of the movement. The low and high DROM groups displayed DROM percentages of 27 perpendicular to 11 and 10 perpendicular to 11 (P = 0.013), 32 perpendicular to 9 and 23 perpendicular to 9 (P = 0.056), 60 perpendicular to 13 and 46 perpendicular to 13 (P = 0.004), and 66 perpendicular to 16 and 54 perpendicular to 9 (P = 0.003) when they encountered the peak plantarflexion moments, Achilles tendon force, eversion angles, and dorsiflexion angles, respectively. Conclusion: Participants with a low DROM absorbed the landing impact forces with their plantarflexor muscle-tendon units in a more lengthened and everted position. Athletes with a low DROM may be more likely to regularly overload their plantarflexor muscle-tendon units, thereby potentially exposing themselves to a higher likelihood of incurring injuries such as Achilles tendinopathy.