From the Center for Exercise Science, College of Medicine, and the College of Health and Human Performance, University of Florida, Gainesville, Florida.

4. Abstract
Development of a new testing machine, which stabilized the pelvis, allowed us to evaluate the lumbar extensor muscles before and after training. Fifteen healthy subjects (29.1 ± 8 years of age) trained 1 day per week for 10 weeks and 10 healthy subjects (33.7 ± 16 years of age) acted as controls. Training consisted of 6 to 15 repetitions of full range of motion variable resistance lumbar extension exercise to volitional fatigue and periodic maximal isometric contractions taken at seven angles through a full range of motion. Before and after the 10 week training period, subjects completed a maximum isometric strength test at seven angles through a 72° range of motion (0°, 12°, 24°, 36°, 48°, 60°, and 72° of lumbar flexion). The training group significantly improved in lumbar extension strength at all angles (r £ 0.01). The results at 0° (full extension) showed an increase from 180.0 ± 25 Nm to 364.1 ± 43 Nm (+102%) and at 72° (full flexion) from 427.4 ± 44.1 to 607.4 ± 68 (+42%) Nm. Results form the control group showed no change (r ©¯ 0.05). The magnitude of gain showed by the training group reflects the low initial trained state of the lumbar extensor muscles. These data indicate that when the lumbar area is isolated through pelvic stabilization, the isolated lumbar extensor muscles show an abnormally large potential for strength increase.