Attenuation of spinal transients at heel strike using viscoelastic heel insoles: An in vivo study

Background. The transients introduced at heel strikes were linked with increased risk for low back pain. The present study was designed to monitor the transients acting on the spinal column at gait, and to find out whether said transients are attenuated by interposition of a viscoelastic heel insoles. Methods. A lightweight (2 g) accelerometer was held against the forehead with an elastic strap. The subject was instructed to walk naturally along an 8-m rigid walkway with a built-in, high-frequency (<500 Hz) response Kistler force plate. Seven subjects, shoed in leather-soled shoes, were studied sequentially without and with viscoelastic heel insoles (Viscoheel, Bauerfeind). Ground reaction force and vertical acceleration were simultaneously recorded. The data were analog-stored and analyzed with respect to time and frequency domains. Results. Under the aforementioned conditions, the heel strike introduced a transient that averaged 60% of body weight and lasted for up to 5 ms. Maximal deceleration was recorded in the order of 5G, with a frequency spectrum of 100 Hz. Interposition of silicone heel insoles attenuated the ground reaction force by one third and deceleration by two thirds, the highest frequency components having been eliminated. Conclusion. Viscoelastic heel insoles significantly attenuate the strain on the spinal column that is caused by walking.