Objective: To examine training frequency's effect on torso rotation muscle strength. Design: The study followed a pretest-posttest randomized-group design. Setting: University laboratory. Patients: Subjects, 33 men (age 30 +/- 11 yr) and 25 women (age 28 +/- 10 yr) with no history of low back pain, volunteered to participate in the study and were tested for isometric (IM) torso rotation strength before (T1) and after (T2) 12 weeks of training. Measurements of maximal voluntary LM torso rotation torque (N . m) were made through a 108 degrees range of motion (54 degrees, 36 degrees, 18 degrees, 0 degrees, -18 degrees, -36 degrees, -54 degrees). Subjects were stratified by peak torque at T1, and randomized to a nonexercising control group (C, n = 10), or groups that trained once a week (1 x/wk, n = 16), twice a week (2 x/wk, n = 17), or three times a week (3 x/wk, n = 15); and all groups were similar in strength. Interventions: Training consisted of 8 to 12 repetitions of full range dynamic variable resistance exercise to volitional fatigue, for both left and right rotation. Main Outcome: To determine the best training frequency for the development of torso rotation strength. Results: Relative improvements (average increase in strength gained at each angle) for the training groups were 4.9%, 16.3%, and 11.9% for the 1, 2, and 3 x/wk groups, respectively. The 1 x/wk group did not increase in IM torso rotation strength compared to the control group at any angle. Both the 2 and 3 x/wk groups increased their IM torso rotation strength compared to the control group at all but one angle. There were no significant differences in IM torso rotation strength between the groups that trained 2 or 3 x/wk. During the training period, the 2 and 3 x/wk groups increased their dynamic training load significantly more than the 1 x/wk group. Conclusions: Posttraining dynamic strength was not different between training frequencies of 2 and 3 x/wk. Therefore, training the rotary torso muscles 2 x/wk is recommended. (C) 1997 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehnbilitation
