In vivo examination of the dynamic properties of the human heel pad.

The shock-absorbing characteristics of the heel pad in vivo were examined in adults (N = 16) and 7-year-old children (N = 5) using a drop-impact tester (wt = 5 kg). Impact velocities were 0.72 m/s and 0.93 m/s. It was found that in adults the average peak deceleration was 11.6 G at an impact velocity of 0.93 m/s. The maximum deformation of the heel pad was 11.3 mm, and the computed energy absorption during impact amounted to 79% (range = 75%-89%). These mechanical characteristics remained nearly the same even after 6 min of repeated impacts by the impact tester and even after a 10 km run. The children had larger values of peak deceleration and maximum deformation and smaller energy loss than the adults. It was concluded that the heel pad was a fairly effective shock attenuator and high energy absorber, and that these characteristics remain nearly unchanged even after a relatively long period of repeated impacts. It was also concluded that the mechanical properties of the children's heel pads were different from those of the adults.