Dorsiflexion Capacity Affects Achilles Tendon Loading during Drop Landings
John W. Whitting, Julie R. Steele, Deirdre E. Mcghee, and Bridget J. Munro. Medicine and Science in Sports and Exercise. 2011; 43(4): 706-713
During dynamic activities, the ability to absorb and dissipate force is critical to preventing injuries. During highly demanding movements, such as jumping and landing in sports activity, large forces are created in the plantarflexors and transmitted through the Achilles tendon. It has been suggested that athletes with reduced ankle range of motion may be at higher risk for ACL injury because these individuals are not able to sufficiently flex the knee during landings (see previous post on this topic: Improving ankle range of motion may be a key factor in reducing ACL injuries). In addition to the potential risk for knee injury, athletes with reduced dorsiflexion range of motion and plantarflexor tightness may also develop greater forces in the Achilles tendon, putting them at greater risk for tendon rupture or other ankle injury. To examine this relationship, the authors evaluated joint kinematics, kinetics, and shank EMG from a group of individuals with varying degree of dorsiflexion ROM.
The dorsiflexion ROM from 48 physically-active men was measured using a standing lunge test. The subjects were then ranked according to ROM and the middle 15 subjects were removed, leaving two distinct groups – a high ROM group and a low ROM group. EMG was recorded from the Tibialis Anterior, Soleus, Medial Gastrocnemius and Lateral Gastrocnemius. Three dimensional joint kinematics and kinetics, as well as ground reaction force, were recorded during a drop jump of 2 different velocities (2.25 and 3.21 ms-1). The authors found that there was no difference in EMG onset and offset between groups, although the onset of some muscles occurred earlier at the higher velocity drop jump. For the majority of the kinematic and kinetic variables at the ankle, there was no difference between groups. However, the lower ROM group demonstrated a significantly greater amount of eversion during the activity. Also, as may be expected, the individuals in the lower ROM group used a greater percentage of their available ROM.
Contradictory to the article title, there was no direct measure of tendon loading and calculated Achilles tendon force was not different between groups. However, several important conclusions can be drawn from the results of this study. It is generally believed that performing activities at the extreme ends of an individual’s motion may predispose them to injury. Although there was no difference in the absolute magnitude in ROM between these two groups, there was a difference in the percentage of total motion, with the individuals with lower ROM using a greater percentage. It would be interesting to prospectively follow a group of individuals with low ROM to determine if these individuals have greater proclivity for ankle injury. Additionally, the individuals in the lower ROM group had significantly greater eversion during the activity. This may be a compensatory motion to absorb the large forces that cannot be sufficiently dissipated at the ankle joint during demanding activities. It is possible that this could predispose these individuals for injury.  Future research, including prospective clinical studies, is needed to determine the clinical impact of the preliminary findings discussed in this article.
Written by Joseph Zeni, Jr
Reviewed by Jeffrey Driban