Abstract
Many workers have jobs that require the physical capacity to lift on a regular basis. When preparing for these jobs or retraining for these jobs after a back injury, the question is whether it is necessary to retrain the knee extensors, the trunk, or both. The purpose of this study was to determine whether an 8-wk isotonic training program designed to increase knee extensor strength could result in increased lifting ability. Fifteen physical therapy students, ranging in age from 23 to 28 years, volunteered for the study and were randomly assigned to either a treatment or a control group. Both groups were pretested for strength using the Cybex 340 (Cybex Inc., Ronkonkoma, NY) extremity unit to test concentric knee extensor torque (at 60, 90, and 120 deg/sec), the Cybex Liftask to measure isometric and concentric isokinetic lifting (18 inches/sec), and a modified milk crate to measure maximal functional lifting. The treatment group participated in an 8-week strength and flexibility training program, whereas the control group participated in only the flexibility program. At the end of 8 wk all subjects were retested. At baseline, no significant correlations were found between knee extensor peak torque production and isometric or isokinetic lifting ability for either group. The treatment group showed a significant increase in knee extensor peak torque production at 60 deg/sec (p < 0.01), 90 deg/sec (p < 0.01), and 120 deg/sec (p < 0.02). However, a significant correlation was found between the change in knee extensor peak torque production at 60 deg/sec and the change in functional lifting ability for the treatment group (r = 0.5125, p < 0.05). These results suggest that it may be helpful to increase functional lifting ability by isotonically training the knee extensors.