Effect of trunk inclination on isometric extensor and flexor torque of healthy adult males: biokinetics practice and sport injuries

The aim of the study was to establish a viable method of measuring the maximal trunk flexion and extension isometric strength in healthy South African adult males. Ten active, but untrained, males (four whites, six blacks; 28.6 ± 5.8 y) participated in the study. A Cybex 6000, dynamometer Trunk extension / flexion unit was used to measure maximal voluntary isometric strength of the lumbar flexor and extensor muscles at 0, 23, 46, 69 and 92 degrees of trunk flexion. ANOVA with post-hoc testing was applied to the flexion and extension data. Alpha was set at p < 0.05. Significant interaction effects were found at 23 (p < 0.05) and 92 (p < 0.001) degrees of trunk flexion with the peak isometric torque significantly higher for extension than flexion. Significant differences (p < 0.0001) were found between the mean peak isometric flexion torques at 0, 23, 46, 69 degrees compared to 92 degrees. There were significant differences (p < 0.0001) between the extension/flexion ratios at 0, 23, 46 and 69 degrees compared to 92 degrees. Any angle between 0 - 69 degrees of flexion may be used to assess peak isometric flexion torques, while any trunk flexion angle between 0 - 92 degrees may be used to measure isometric extension peak torques. The present methodology can be used as a reference base for future research efforts with implications for rehabilitation, performance and industry.