Changes in Lifting Ability After a Training Program to Increase Knee Extensor Strength

Article type: Research Article

Authors: Harris, Scott^{a; *} | Takiguchi, Dean^{a; **} | Byl, Nancy^{a; ***; ****}

Affiliations: [a] University of California/San Francisco State University, San Francisco, California

Note: [*] Student in the University of California/San Francisco State University Graduate Program in Physical Therapy, University of California, San Francisco, CA. This study was carried out in partial fulfillment of the degree requirements for the Masters in Physical Therapy.

Note: [**] Student in the University of California/San Francisco State University Graduate Program in Physical Therapy, University of California, San Francisco, CA. This study was carried out in partial fulfillment of the degree requirements for the Masters in Physical Therapy.

Note: [***] Associate Professor, Director of Graduate Program in Physical Therapy, University of California, San Francisco, CA.

Note: [****] Address reprint requests to Nancy Byl, PhD, PT, Associate Professor, Graduate Program in Physical Therapy, University of California, School of Medicine, Box 0736, 374 Parnassus, San Francisco, CA 94122.

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.

Keywords: Back lifting ability, knee extensor strength, isokinetic assessment

DOI: 10.3233/IES-1993-3402

Journal: Isokinetics and Exercise Science, vol. 3, no. 4, pp. 181-187, 1993