Bone-On-Bone Axial Forces During Dance Landings

Abstract

Clinical evidence of joint degeneration in dancers by ages 25 to 37 years (1) would suggest that repetitive loading contributes to excessive joint wear. Therefore, the purpose of the study was to investigate the effect of landing distance on lower extremity axial forces (AF) during the landing phase of a leap. Six female dancers performed 45 dance leaps at distances ranging from 30% to 100% maximum jump distance aD). A sagittal view of the dancer landing onto the force platform (500 Hz) with the right leg was filmed (100 fps). A Newtonian model was used to generate the individual axial force components. Based on within-subject analyses (p < .05), subjects increased the magnitude and velocity of knee flexion at greater JD. Increased peak magnitudes and rates of loading (dFmax/dt) for AF variables were demonstrated except for peak gastroc-soleus AF, knee gastroc AF and total ankle AF, which displayed mixed responses among the subjects. For most variables, the corresponding times to the peak magnitudes decreased. Gastroc-soleus AF for the maximum magnitude and dFmax/dt were highly associated with the total ankle AF (R2 = .923 and .873, respectively). Maximum quad AF was the most important determinant (R2 = .957 and .911, respectively) of peak total knee AF and dFmax/dt. Kinematic variables were not associated with total joint AF. Although the joint reaction AF contributed significantly to the total joint AF, the muscle AF were a greater influence. Individual differences in maximum gastroc-soleus AF reflect diverse landing strategies for jumping at greater JD. The sizable magnitudes and high interrelationship of quad AF to the total knee AF indicates that quad. AFs are very important in controlling the reduction of vertical momentum during landing. In conclusion, although subjects used greater and more rapid knee flexion during landing, the eccentric knee extensor action required during the later portion of the landing phase significantly increased the compressive knee joint forces and dFmax/dt at greater JD. 1. McLain, D. Clinics in Sports Med., 563-570,1983. Supported by a grant from the Univ. of Georgia Research Foundation