Peak torque-to-body weight ratios in the trunk: a critical analysis

The purpose of this study was to document the relationships between body weight and isokinetic extension and flexion peak torque produced by the trunk musculature. Using a dynamometer, we collected isokinetic measurements during trunk flexion and extension at speeds of 60 degrees and 120 degrees/sec on 61 healthy subjects (29 men, 32 women; 20-60 years old) while standing. Extension and flexion peak torque measurements were calculated for each subject at each speed. Male and female subjects' data were analyzed separately. Each subject's body weight was paired with peak torque at each speed, and Pearson product-moment correlation coefficients (r) were calculated. The correlation coefficients ranged from .27 to .39 for extension and from .66 to .70 for flexion, establishing a positive linear relationship between body weight and each of the isokinetic measurements. Body weight accounted for very small proportions of the variance (as low as 7%-15% in extension isokinetic measurements). In attempting to use a client's body weight to predict isokinetic peak torque measurements, the clinician should be aware that a great deal of unaccounted for variance exists. We recommend that clinicians use other variables (eg, activity level, age) in addition to body weight to control for individual differences among healthy subjects when measuring isokinetic trunk extension muscle performance.