Isokinetic trunk extension discriminates uninjured subjects from subjects with previous low back pain

This investigation compared the ability of a previously defined, non-standard isokinetic variable set to that of standard isokinetic variables to discriminate trunk extension performance of control subjects from subjects with a history of low back pain. Ten male subjects with history of low back pain, asymptomatic at the time of the test, and nine subjects without history of low back pain participated in a single session, test-retest protocol. The test and retest each consisted of five maximum effort isokinetic trunk extension-flexion repetitions at 60, 120, and 180 deg s(-1). At each isokinetic speed, eight isokinetic trunk extension performance variables were extracted and the mean value for each calculated from Trials 2, 3, and 4. The set of 48 variables was reduced to seven, demonstrating intergroup differences at the selected criterion probability level (P<0.025). These variables were submitted to a stepwise discriminant analysis that eliminated one variable, generated a significant discriminant function (P = 0.005), and correctly categorized 100% of the control and low back pain patients. The variables satisfying the entry criterion into the discriminant analysis were from the 120 and 180 deg s(-1) conditions, suggesting that residual functional deficits related to trunk extensor muscular power generation are associated with low back pain. For comparison purposes, secondary discriminant analyses using standard isokinetic variables were conducted but the results were statistically and clinically inferior to those of the initial discriminant function. The results of this study imply that rehabilitation from low back dysfunction should include a component of muscular power restoration. The present results can offer no resolution to the clinical question related to the cause of the power deficit. This type of inquiry will require the use of additional technologies such as electromyography that can lend insight into agonist-antagonist relationships.