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Background and aim: Spinal injury especially during occupational lifting is one of the most common neuromuscular disorders in the general population of the world. Asymmetric motions of trunk frequent bending and twisting, lifting and forceful activities contribute to spine disorders. Sport as a comprehensive activity might be able to cause less force to the spine and decrease spinal injuries. The purpose of present study was to determine the effect of lifting on motor control pattern during combined symmetric and asymmetric trunk motions on athlete and non-athlete subjects.
Materials and Methods: Seventeen non-athlete female subjects and seventeen athlete female subjects performed to lift four loads ( 5,7,9 ,12 kilogram ) at symmetric and asymmetric conditions. Under each condition temporal parameters of motor control were measured on flexor and extensor of trunk muscles.
Result: In two groups of athletes and non-athletes with increasing load , muscles begin their activity faster ( P<0.05 ). No significant change was found at asymmetric condition. Also, in athletes premotor time of muscles during lifting was less than non-athletes.
Conclusion: With increasing load, according to the feed forward control mechanism and awareness of subjects from amount of loads, muscles quickly prepared to contract for starting the movement. It seems that the response of movement on the neuromotor system of athletes is preprogrammed and automatic due to sport experience. Actually muscles have anticipation activity.

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Abstract

Background and Aim: Nowadays personal lifting assistive devices, in order to reduce the load applied from the lifted weight to muscles - in particular lower back muscles, become more widely used. The objective of our study is to analyze an empirical model of a Weight Lifting Aid Vest (WLAV) during anterior flexion (anteflexion) and studying its effects on reduction of loads on the muscles in particular back muscles. To analyze this, the intensity of signals captured from involved muscles, during the lifting in two case of with and without WLAV, was studied by the use of electromyography amplifier.

Materials and Methods: In this process, 20 subjects who lifted 10-kilogram loads in semi-squatting position were participated. With the use of a tensile-compressive spring, embedded at the back of WLAV, the amount of body stretch and deflection of their hip and knees were measured. The influence of the WLAV on satisfaction during the lifting was studied.

Results: Data were collected from electromyography findings from eight involved muscles in back, stomach and feet. The results depicted that there are a overall reduction of 25.12-percent in activation of all the muscles and particularly a reduction of 57%, 28% and 26.5% in activation of external oblique, lateral hamstring, and erector spine, respectively. In contrast, there is 11% increase in activation of Gluteus Maximus in the case of usage of WLAV.

Conclusion: WLAV can significantly mitigate the activation of back muscles and rate of load insertion on muscles) P<0.005). It also clarified the tendency of the subjects towards users WLAV) P<0.005).

Keywords: Electromyography, Load measurement, Root mean square, Weight lifting aid vest (WLAV), Muscular demand