Bent Postures Research Articles

Muscular strains in different modes of load handling

The influence of posture on the ability of a person to hold loads was evaluated from a study on six healthy, young males. The muscle activities in terms of isometric strength and electromyographic (EMG) characteristics of the trunk and lower limb were determined in ten load-holding postures. The postures were comprised of trunk, knee and elbow in different straight and bent positions to include load heights (LH) of 32, 44, 85 and 125cm from the ground and subject-load distance (SLD) of 12 and 32cm. The pull-up maximum voluntary contraction (MVC) was significantly influenced by the SLD. The MVC values were consistently high with the increase in LH, when the SLD was 12 cm but the opposite was the case for SLD of 32 cm. The trunk-bent/knee-straight postures had higher MVC values (31 ± 8 to 34 ± 2·5 kgf) than those in knee-bent/trunk-straight postures (21 ± 3 to 28 ± 5 kgf). The trunk muscles behaved differently in trunk-straight and in bent postures. The hamstrings and quadriceps were counter-balanced in sharing loads during knee-bent or straight postures. It was observed that the load-holding operations were performed better in trunk-bent/knee-straight postures, and when the load was closer to the body at heights ranging from 32 to 44 cm. Whereas, in trunk and knee-straight postures, the pulling of the load was more convenient from waist height.

Male and Female Responses to Stoopwalking Tasks

This study was performed to evaluate the changes in physiological responses to task performance in trained male and female subjects while stoopwalking in increasingly bent postures. Following a 10-day training program, 5 male and 5 female subjects stoopwalked at heights corresponding to 100, 90, 80, and 70 percent of each subjects normal upright stature at speeds of 1.5, 2.0, 2.5, 3.0, and 3.5 miles per hour. Physiological variables were equilibrium heart rate, ventilation volume, weight adjusted oxygen uptake, and the percentage of work capacity required for task performance. A MANOVA analysis of the dependent variables showed there to be a significant sex difference in the composite response to task performance. Univariate ANOVA and discrimate analyses performed on the dependent variables showed that this difference was due to females experiencing significantly greater heart rates than the males, and greater, but not significantly so, percentages of work capacity to perform the same task loadings as the males.