Influence of repeated measurements on isokinetic lifting strength

Abstract

The aim of the study was to evaluate the effect of repeated measurements on isokinetic lifting strength in a smaple of patients with low back pain. The measures were performed in series of five consecutive lifts on two occasions 1–13 days apart, and the patients continued their normal living during this period. A group of healthy subjects was used as a control. The hypothesis was that a mere repetition of the lifting procedure would increase the performance, and that the increase would be bigger in the patient group that in the non-patient group. In addition, grip strength was measured on both occasions. It was supposed that grip strength would not change from trial 1 to trial 2. The results showed an increase in lifting strength from first to second trial in the patient group by an average of 28%, and in the control group by an average of 16%. Grip strength did not increase in either group. The last of five consecutive lifts was the best one in a majority of the cases in both trials. Neither five consecutive lifts nor measurements on two different occassions seem enough to define a reliable baseline for maximal lifting capacity. Other factors than an increase in muscle strength influence the performance, one being a repetition of the lifting procedure. This must be accounted for when defining a baseline for isokinetic lifting capacity.