A test of the hypothesis of abdominal pressure as a disc load-reducing mechanism: A study using quantitative electromyography

Effects of a new industrial lifting belt on back muscular activity, hand force, and body stability during symmetric lifting

This work investigated how wearing a new design of back belt affects erector spinae activity, hand force, and body stability. The belt was first tested with static holding tasks and found to significantly decrease the back muscle activity. Actual lifting tasks were further carried out to test the effect of the belt. Ten male subjects performed a symmetric lifting task of low-lying loads (11 and 16 kg) at natural toting velocity, using either a squat or stoop lifting posture, both with and without a belt. The study measured various independent variables using electromyography (EMG), load cells, and motion capture device. The results demonstrated that the belt reduced the load on the erector spinae, as well as the triceps brachii and biceps brachii. The overall mean values of the peak (hand) force did not appear significantly affected while wearing the belt, but the force peaks appeared postponed. The belt did not alter body stability while lifting. From the present findings, the belt effectively changed the force distribution during lifting, at least reducing the muscle load on the back. The belt may be a potentially useful device for symmetric industrial lifting tasks.

Intra-abdominal pressure mechanism for stabilizing the lumbar spine

Currently, intra-abdominal pressure (IAP) is thought to provide stability to the lumbar spine but the exact principles have yet to be specified. A simplified physical model was constructed and theoretical calculations performed to illustrate a possible intra-abdominal pressure mechanism for stabilizing the spine. The model consisted of an inverted pendulum with linear springs representing abdominal and erector spinae muscle groups. The IAP force was simulated with a pneumatic piston activated with compressed air. The critical load of the model was calculated theoretically based on the minimum potential energy principle and obtained experimentally by increasing weight on the model until the point of buckling. Two distinct mechanisms were simulated separately and in combination. One was antagonistic flexor extensor muscle coactivation and the second was abdominal muscle activation along with generation of IAP. Both mechanisms were effective in stabilizing the model of a lumbar spine. The critical load and therefore the stability of the spine model increased with either increased antagonistic muscle coactivation forces or increased IAP along with increased abdominal spring force. Both mechanisms were also effective in providing mechanical stability to the spine model when activated simultaneously. Theoretical calculation of the critical load agreed very well with experimental results (95.5% average error). The IAP mechanism for stabilizing the lumbar spine appears preferable in tasks that demand trunk extensor moment such as lifting or jumping. This mechanism can increase spine stability without the additional coactivation of erector spinae muscles.

The effect of sustained spinal load on intra-abdominal pressure and EMG characteristics of trunk muscles

Fourteen young male students (mean age 21 years, mean weight 69.4 kg, and mean height 175.4 cm) and 12 young female students (mean age 22.2 years, mean weight 60.6 kg, and mean height 169.3 cm) held 9.07 kg and 6.8 kg, respectively, at their three-quarters horizontal reach distance in upright and stooping postures for a period of 5 min. During these periods the external torque on the lumbosacral disc, intra-abdominal pressure, and electromyographic signals from erectores spinae at T12 and L3 levels, latissimus dorsi and external obliques were recorded at 1 kHz for 2.1 s every 15 s for a period of 5 min. The EMGs were processed in magnitude and time domains to determine muscle fatigue. Through the data obtained it was seen that the intra-abdominal pressure did not follow or reflect either the spinal load or the muscle activity. Based on the arguments presented, it was concluded that the intra-abdominal pressure does not appear to have a role of relieving the spine of some of its load. Instead, it is suggested that it is a dependent variable manifesting itself when mechanisms for spinal stability are evoked to overcome large voluntary and inertial loads.