Effects of reducing resistance, repetitions, and frequency of back-strengthening exercise in healthy young women: a pilot study

OBJECTIVE: To determine the effects of reducing intensity or frequency of back-strengthening exercise on back extensor strength. DESIGN: Randomized controlled trial. SETTING: Exercises were performed in participants' homes. Instruction and measurements were performed at the rehabilitation center in the hospital. PARTICIPANTS: Fifty-eight healthy female volunteers (mean age, 20 y). INTERVENTIONS: Participants were assigned to 1 of 5 exercise intervention groups: control; standard protocol (STD) that has been shown to increase back extensor strength; weight reduction (WRD); repetition reduction (RRD); and frequency reduction (FRD). Back exercises involved lifting a weighted backpack while in a prone position. The study period was 12 weeks. MAIN OUTCOME MEASURE: Isometric back extensor strength. RESULTS: Back extensor strength increased significantly in all groups except the control group. The maximum increase was achieved by the STD group (39%), followed by the FRD (25%), WRD (22%), RRD (20%), and control (5%) groups. Percentage change in back extensor strength was significantly greater in the STD group than in all other groups except the FRD group. CONCLUSIONS: Back extensor strength in the WRD, RRD, and FRD groups was significantly higher at 12 weeks compared with baseline. Reductions in intensity and frequency resulted in similar effects on increases in back extensor strength.