Low-Back Biomechanics and Static Stability During Isometric Pushing

Abstract

Pushing and pulling tasks are increasingly prevalent in industrial workplaces. Few studies have investigated low-back biomechanical risk factors associated with pushing, and we are aware of none that has quantified spinal stability during pushing exertions. Data recorded from 11 healthy participants performing isometric pushing exertions demonstrated that trunk posture, vector force direction of the applied load, and trunk moment were influenced (p < .01) by exertion level, elevation of the handle for the pushing task, and foot position. A biomechanical model was used to analyze the posture and hand force data gathered from the pushing exertions. Model results indicate that pushing exertions provide significantly (p < .01) less stability than lifting when antagonistic cocontraction is ignored. However, stability can be augmented by recruitment of muscle cocontraction. Results suggest that cocontraction may be recruited to compensate for the fact that equilibrium mechanics provide little intrinsic trunk stiffness and stability during pushing exertions. If one maintains stability by means of cocontraction, additional spinal load is thereby created, increasing the risk of overload injury. Thus it is important to consider muscle cocontraction when evaluating the biomechanics of pushing exertions. Potential applications of this research include improved assessment of biomechanical risk factors for the design of industrial pushing tasks.

The effect of bracing availability on one-hand isometric force exertion capability

“…Importantly, both nominal on-axis and off-axis forces were found to change with task handle location and varying levels of bracing availability. The results of this study are generally consistent with other research on force exertions in unconstrained environments (de Looze et al 2000;Granata and Bennett 2005;Boocock et al 2006;Hoffman, Reed, and Chaffin 2011). Differences in the off-axis force that were observed from the interaction effects of task handle location, bracing availability and nominal force generation in the presence of a kinematic obstruction were congruent with the body of literature derived from unconstrained conditions.…”

“…de Looze et al (2000) showed that as handle height and force exertion increase, the deviation of the push forward direction increased with respect to the expected or nominal horizontal direction, while the pull force direction transitioned from pulling upwards with a substantial vertical component with low handles, to the desired nominal horizontal force with higher handles. Likewise, Granata and Bennett (2005) found a consistent and significant trend of greater upward pushing force for greater exertion levels and handle heights in nominally horizontal pushes. Okunribido and Haslegrave (2008) quantified significant off-axis forces, with the resulting force in the requested direction averaging between 77% and 95% of the total force exerted in various experimental configurations.…”

“…Previous studies of push and pull tasks performed in unconstrained environments where bracing is not available have documented the effect of variables such as body weight, height of force application, distance between body and point of force application, coefficient of friction (CoF) between floor and footwear, and volitional postures on the mechanical loading of the low back and shoulders (Grieve and Pheasant 1981;Pheasant et al 1982;Chaffin, Andres, and Garg 1983;de Looze et al 2000;Hoozemans et al 2004;Granata and Bennett 2005;Boocock et al 2006). Numerous studies have also found that the exertion handle location at which push -pull forces were applied has a significant effect on maximum hand force capability (Martin and Chaffin 1972;Ayoub and McDaniel 1974;Chaffin, Andres, and Garg 1983;Kumar 1991;Gagnon, Beaugrand, and Authier 1992).…”

EMG in rotation–flexion of the torso

“…Kumar et al (1996Kumar et al ( , 2002a concluded that the axial rotation is achieved by activities of the contralateral external obliques and ipsilateral latissimus dorsi constituting a force couple with spine acting as a fulcrum. The erectors spinae, however, increased their activity only modestly with increasing magnitude of contraction contributing to spinal stability through this contraction (Granata and Bennett, 2005;Granata and Wilson, 2001;Lavender et al, 1993 andPerez andNussbaum, 2002). The trunk returned to the neutral position after rotational displacement due to elastic recoil controlled by the same agonistic muscles .…”

Effects of selected wheel and caster fixture design on the push force: the case of four-wheeled industrial carts

“…The National Institute of Occupational Safety and Health (NIOSH) first published their Lifting Guide in 1981 [1]. Since that time, industry has responded by working to reduce the amount of manual lifting, lowering, and carrying found in workplaces, often replacing those tasks with pushing and pulling [2]. In certain industries, pushing and pulling maneuvers can account for an estimated 50% of the manual material tasks [3].…”