LOADS ON THE LUMBAR SPINE DURING BUNGEE JUMPING

Abstract

INTRODUCTION: The purpose of this study was to quantify the load that occurs on the lumbar spine during bungee jumping and to compare these results with loads that occur during trampoline and vertical jumps. METHODS: For each of ten bungee jumpers representing two weight classes, three dimensional acceleration measurements were recorded by an accelerometer attached to their skin at the iliac spine. Similarly, two dimensional (vertical and sagittal) acceleration measurements were recorded for trampoline and vertical jumps of subjects representing different heights and landing performances. The following loading parameters were analyzed:maximum vertical acceleration, maximum sagittal acceleration, calculated vertical forces on the lumbar vertebral bodies in relation to the tensile strength for bungee jumping, calculated vertical forces on the lumbar vertebral bodies in relation to the compresive strength for trampoline and vertical jumps, relative vertical forces on the lumbar intervertebral discs. In addition, for bungee jumping, the differences between the two weight classes and the influence of body weight on vertical acceleration were examined. RESULTS: 1. During bungee jumping the vertical acceleration maxima and the relative vertical forces of vertebral bodies and intervertebral discs were significantly or high significantly greater in the lower weight class (50 - 80 kg) compared to the higher weight class (80-110 kg). 2. During bungee jumping, in both groups, the correlation between body weight and vertical acceleration maximum was negative; in the lower weight class, there was a high correlation (r = -0.995; p < 0.01) between these parameters. 3. The mean of the vertical acceleration maxima for bungee jumping (2.7 g) was lower than the corresponding means in trampoline (5.8 – 8.7 g), and the hard (3.7 – 11.1 g) and most of the soft vertical jump landings (3.3 – 7.3 g). 4. The mean of the maximal sagittal acceleration for bungee jumping (2.5 g) was higher than one group in trampoline (1.5 g), most of the soft (1 – 2.2 g) and two of the hard vertical juimp landing performances (1.1 – 1.9 g). 5. The mean of the relative vertical forces on the lumbar vertebral bodies for bungee jumping (30.3 %) was lower than in trampoline (38.3 – 59.2 %), in most of the hard vertical landing performances (34.5 – 67.3 %) and lower in the soft landing performances from 1.1 m to 1.5 m (33.2 – 44.4 %). 6. The mean of the relative vertical forces on the lumbar intervertebral discs during bungee jumping (34 %) was higher than the corresponding means in trampoline (17.1 – 27.0 %), and hard (10.0 – 29.9 %) and soft (6.5 – 19.6 %) vertical landing performances.