David M. Carpenter

Effect of training frequency and specificity on isometric lumbar extension strength

To investigate the effects of training frequency and specificity of training on isolated lumbar extension strength, 72 men (age = 31 +/- 9 years) and 42 women (age = 28 +/- 9 years) were tested before and after 12 weeks of training. Each test involved the measurement of maximum voluntary isometric torque at 72 degrees, 60 degrees, 48 degrees, 36 degrees, 24 degrees, 12 degrees, and 0 degrees of lumbar flexion. After the pretraining tests, subjects were randomly stratified to groups that trained with variable resistance dynamic exercise every other week (1X/2 weeks, n = 19), once per week (1X/week, n = 22), twice per week (2X/week, n = 23) or three times per week (3X/week, n = 21); a group that trained isometrically once per week (n = 14); or a control group that did not train (n = 15). Analysis of covariance showed that all training groups improved their ability to generate isometric torque at each angle measured when compared with controls (P less than 0.05). There was no statistical difference in adjusted posttraining isometric torques among the groups that trained (P greater than 0.05), but dynamic training weight increased to a lesser extent (P less than 0.08) for the 1X/2 weeks group (26.6%) than for the groups that trained 1X/week, 2X/week, and 3X/week (37.2 to 41.4%). These data indicate that a training frequency as low as 1X/week provides an effective training stimulus for the development of lumbar extension strength. Improvements in strength noted after isometric training suggest that isometric exercise provides an effective alternative for developing lumbar strength.

Quantitative assessment of full range-of-motion isometric lumbar extension strength.

The purpose of this study was to evaluate the reliability and variability of repeated measurements of isometric (IM)lumbar extension (LB EXT) strength made at differnt joint angles. Fifty-six men (age, 29.4 ± 10.7 years) and 80 women (age, 24.3 ± 9.1 years) completed IM LB EXT strength tests on 3 separate days (D1, D2, and D3). On D1 and D2, subjects completed two tests (T1 and T2) separated by a 20-to 30-minute rest interval. For each test, IM LB EXT strenth was measured at 72, 60, 48, 36, 24, 12, and 0° of lumbar extension. Mean IM strength values, within-day reliability coefficients, and test variability over the seven angles improved from D1 to D2 (D1: mean, 160.0 to 304.1 N · m, r=0.78 to 0.96, SEE = 37.6 to 46.9 N · m; D2: mean, 176.3 to 329.1 N · m, r = 0.94 to 0.98, SEE = 29.0 to 34.4 N · m). Mean strength values leveled off by D3 (174.5 to 317.0 N · m). The most reliable test results showed that the IM LB EXT strength curves were linear and descending from flexion to extension and ranged from 235.8 ± 85.2 to 464.9 ± 150.7 N · m for men (extension to flexion) and from 134.6 ± 53.2 to 237.3 ± 71.9 N. m for women. Lumbar extension strength was clearly greatest in full flexion, which is in contrat to previously reported results. One practice test was required to attain the most accurate and reliable results. These data indicate that repeated measures of IM LB EXT strength are highly reliable and can be used for the quantification of IM LB EXT strength through a range of motion.

Low back strengthening for the prevention and treatment of low back pain.

PURPOSE Chronic low back pain (CLBP) remains one of the most difficult and costly medical problems in the industrialized world. A review of nineteenth and early twentieth century spine rehabilitation shows that back disorders were commonly treated with aggressive and specific progressive resistance exercise (PRE). Despite a lack of scientific evidence to support their efficacy, therapeutic approaches to back rehabilitation over the past 30 yr have focused primarily upon passive care for symptom relief. Recent spine rehabilitation programs have returned to active reconditioning PRE centered around low back strengthening to restore normal musculoskeletal function. Research has shown that lumbar extension exercise using PRE significantly increases strength and decreases pain in CLBP patients. It appears that isolated lumbar extension exercise with the pelvis stabilized using specialized equipment elicits the most favorable improvements in low back strength, muscle cross-sectional area, and vertebral bone mineral density (BMD). These improvements occur with a low training volume of 1 set of 8 to 15 repetitions performed to volitional fatigue one time per week. CLBP patients participating in isolated lumbar extension PRE programs demonstrate significant reductions in pain and symptoms associated with improved muscle strength, endurance, and joint mobility. Improvements occur independent of diagnosis, are long-lasting, and appear to result in less re-utilization of the health care system than other more passive treatments. Low back strengthening shows promise for the reduction of industrial back injuries and associated costs.

Effect of reduced frequency of training and detraining on lumbar extension strength

To investigate the effect of reduced frequency of training and detraining on lumbar extension strength, 50 subjects (34 men, aged 34 ± 11yrs; and 16 women, aged 33 ± 11yrs) were recruited from ongoing strength training programs. Initial training consisted of 10 or 12 weeks of variable resistance lumbar extension strength exercise to volitional fatigue 1, 2 or 3 times a week. After the initial training, subjects reduced the frequency of training to once every 2 weeks (n = 18) or once every 4 weeks (n = 22) for 12 weeks. Only the frequency of training was changed; the mode, volume, and intensity of exercise remained constant for both reduced frequency of training groups. An additional ten subjects terminated training and acted as controls (detraining group). Isometric lumbar extension strength was evaluated at seven angles through a 72 degree range-of-motion before training, after training, and after reduced frequency of training or detraining. Analysis of variance with repeated measures indicated that lumbar extension strength improved P ≤ 0.05) for all groups after the initial to or 12 weeks of training. After 12 weeks of training, the once every 2 weeks and once every 4 weeks groups showed no significant reduction in lumbar extension strength at any angle tested, whereas the detraining group demonstrated an average 55% reduction in strength. These findings indicate that isometric lumbar extension strength can be maintained for up to 12 weeks with a reduced frequency of training as low as once ovary 4 weeks when the intensity and the volume of exercise are maintained.

Frequency and volume of resistance training : effect on cervical extension strength

Quantification of cervical extension (CERV EXT) strength is complicated by the inability to stabilize the torso and isolate the CERV EXT muscles. A newly developed machine designed to stabilize the torso and isolate the CERV EXT muscles was used to evaluate the effect of frequency and volume of resistance training on CERV EXT strength. Fifty men (age, 26 +/- 9 years; height, 174 +/- 16 cm; weight, 74 +/- 9 kg) and 28 women (age, 30 +/- 9 years; height, 152 +/- 32 cm; weight, 62 +/- 7 kg) volunteered to participate. Subjects were randomly stratified to one of four training groups or a control group (CONT, n = 19) that did not train. Each training group exercised for 12 weeks as follows; once per week using one set of dynamic exercise (DYN 1x/wk, n = 14), once per week using one set of DYN and one set of maximal isometric (IM) exercise at eight angles through a 126 degrees-range of CERV EXT (DYN-IM 1x/wk, n = 16), DYN 2x/wk (n = 19), or DYN-IM 2x/wk (n = 10). Maximal IM torque was measured at eight angles initially and after 12 weeks of training. All training groups improved CERV EXT strength (p < or = 0.05) at all angles tested compared to the CONT except for DYN once per week at 0 degree of CERV flexion. A greater increase in strength was found when the groups that trained two times a week were compared to those that trained once per week.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative assessment and training of isometric cervical extension strength

The purpose of this study was to evaluate the reliability and variability of repeated measurements of isometric cervical extension strength and determine the effect of 10 weeks of dynamic variable resistance cervical ex tension training on isometric cervical extension strength. Seventy-three subjects (age, 29 ± 12 years [mean ± SD]) completed isometric cervical extension strength tests on 4 separate days (D1, D2, D3, and D4). For each test, isometric cervical strength was measured at 126°, 108°, 90°, 72°, 54°, 36°, 18°, and 0° of cervical flexion. Between-day correlation coeffi cients over the eight angles of cervical flexion were high for D2 versus D3 (r = 0.90 to 0.96). Test variability (standard error of estimate) between D2 versus D3 was low (7.4% to 10.2% of mean) through the entire range of motion. Regression analysis showed that the iso metric cervical extension strength curve is linear and descending from flexion to extension. In a second study, 14 subjects (age, 25 ± 3 years) trained the cervical extensor muscles for 10 weeks while 10 sub jects (age, 23 ± 3 years) served as controls. Training included 8 to 12 cervical extensions to volitional fatigue, 1 day per week. The training group improved isometric cervical extension strength at six of eight angles before to after training (P ≤ 0.05). During the same time period the control group did not change. These data indicate that repeated measures of isometric cervical extension strength are highly reliable and can be used for the quantification of isometric cervical extension strength through a 126° range of motion. Also, training the cervical extensors 1 day per week can significantly increase isometric cervical extension strength through most of the range of motion.

Isometric torso rotation strength: Effect of training frequency on its development

OBJECTIVE To examine training frequencys 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 +/- 11yr) and 25 women (age 28 +/- 10yr) 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 IM torso rotation torque (N.m) were made through a 108 degrees range of motion (54 degrees, 36 degrees, 18 degrees, 0 degree, -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 (1x/wk, n = 16), twice a week (2x/wk, n = 17), or three times a week (3x/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 3x/wk groups, respectively. The 1x/wk group did not increase in IM torso rotation strength compared to the control group at any angle. Both the 2 and 3x/ 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 3x/wk. During the training period, the 2 and 3x/wk groups increased their dynamic training load significantly more than the 1x/wk group. CONCLUSIONS Posttraining dynamic strength was not different between training frequencies of 2 and 3x/wk. Therefore, training the rotary torso muscles 2x/wk is recommended.

Limited range-of-motion lumbar extension strength training

The purpose of this study was to evaluate the effect of limited range-of-motion (ROM) resistance training on the development of lumbar extension strength through a 72 degrees ROM. Thirty-three men and 25 women (age = 30 +/- 11 yr) were randomly assigned to one of three training groups or a control group (C; n = 10) that did not train. Training was conducted once per week for 12 wk and consisted of one set of 8-12 repetitions of variable resistance lumbar extensions until volitional fatigue. Group A (n = 18) trained from 72 degrees to 36 degrees of lumbar flexion; group B (n = 14) from 36 degrees to 0 degree of lumbar flexion; and group AB (n = 16) from 72 degrees to 0 degree of lumbar flexion. Prior to and after training, isometric lumbar extension torque was assessed at 72 degrees, 60 degrees, 48 degrees, 36 degrees, 24 degrees, 12 degrees, and 0 degree of lumbar flexion. Analysis of covariance showed that groups A, B, and AB increased lumbar extension torque (P less than or equal to 0.05) at all angles measured when compared with C. The greatest gains in torque were noted for groups A and B in their respective ranges of training but A and B did not differ from AB (P greater than 0.05) at any angle. These data indicate that limited ROM lumbar extension training through a 36 degrees ROM is effective for developing strength through 72 degrees of lumbar extension.

Constant vs variable resistance knee extension training.

To compare the effect of constant resistance (CR) and variable resistance (VR) training on full range-of-motion (ROM) strength development, 22 men and 27 women (age = 26 +/- 5 yr) were randomly assigned to either a CR training group (N = 17), a VR training group (N = 17), or a control group (N = 15) that did not train. The CR and VR groups trained 2 to 3 d.wk-1 for 10 wk. Subjects completed one set of full ROM (120 to 0 degrees of flexion) bilateral knee extensions with an amount of weight that allowed 8 to 12 repetitions during each training session. For the VR group, resistance was varied with a cam supplied by the manufacturer (Nautilus). For the CR group, the cam was removed and replaced with a round sprocket. Prior to and after training, maximal voluntary isometric torque was measured at 9, 20, 35, 50, 65, 80, 95, and 110 degrees of knee flexion. Analysis of covariance indicated that the VR and CR groups gained strength at all angles (P less than or equal to 0.05) when compared to the control. [table: see text] There was no difference (P greater than 0.05) between the CR and VR groups at any angle, and the magnitude of strength gained was similar (P greater than 0.05) among angles for both groups. These data indicate that both CR and VR knee extension training elicit full ROM strength development.