Paradoxical variation of strength determinants with different rotation axes in trunk flexion and extension strength tests

Isometric Trunk Strength Assessment of Athletes: Effects of Sex, Sport, and Low Back Pain History

CONTEXT

The importance of isometric trunk strength (ITS) among sport science professionals is higher than its actual reported effect size on either performance or low back pain (LBP) occurrence.

OBJECTIVE

To provide normative values of ITS and strength ratios, and to evaluate the effect of sex, sports discipline, and LBP status.

DESIGN

Crossover study.

SETTING

University research laboratory.

PARTICIPANTS

Five hundred and sixty-seven elite athletes (186 females) with and without a history of LBP from different sports.

MAIN OUTCOME MEASURE

Participants underwent ITS testing for trunk flexors, extensors, and lateral flexors. Normalized maximal strength (in newton meter per kilogram) and strength ratios were calculated. Differences between sex, LBP, and sport disciplines were assessed with 3-way analysis of variance (sex × LBP status × 7 sport categories) and partial eta-squared (ηp2) effect size. The predictive validity of ITS for LBP was checked with receiver operating characteristics (area under the curve).

RESULTS

The authors found significant differences in extensor and flexor ITS in favor of male athletes (medium ηp2, P < .05), while sex differences in lateral flexion ITS had a low size effect (P < .05). A low size effect was also observed for the differences in strength ratios extensors/flexors (mean 1.47; 95% confidence interval, 1.45-1.50) and left flexors/right flexors (mean 0.99; 95% confidence interval, 0.98-1.01) among sexes. The sport discipline-related differences generally had a low size effect. No significant differences in ITS were found between LBP and LBP-free athletes. Only 50% to 58% of athletes (area under the curve, 0.501-0.582) were correctly classified as LBP or LBP-free using different ITS and strength ratio variables.

CONCLUSIONS

ITS and strength ratios have low predictive validity for LBP history but may discriminate between sex and sport disciplines. Our data are a useful reference point for meaningful individual results interpretation when athletes are evaluated during training or rehabilitation.

Cross-sectional area of the paraspinal muscles and its association with muscle strength among fighter pilots: a 5-year follow-up

Background

A small cross sectional area (CSA) of the paraspinal muscles may be related to low back pain among military aviators but previous studies have mainly concentrated on spinal disc degeneration. Therefore, the primary aim of the study was to investigate the changes in muscle CSA and composition of the psoas and paraspinal muscles during a 5-year follow up among Finnish Air Force (FINAF) fighter pilots.

Methods

Study population consisted of 26 volunteered FINAF male fighter pilots (age: 20.6 (±0.6) at the baseline). The magnetic resonance imaging (MRI) examinations were collected at baseline and after 5 years of follow-up. CSA and composition of the paraspinal and psoas muscles were obtained at the levels of 3–4 and 4–5 lumbar spine. Maximal isometric strength tests were only performed on one occasion at baseline.

Results

The follow-up comparisons indicated that the mean CSA of the paraspinal muscles increased (p < 0.01) by 8% at L3–4 level and 7% at L4–5 level during the 5-year period. There was no change in muscle composition during the follow-up period. The paraspinal and psoas muscles’ CSA was positively related to overall maximal isometric strength at the baseline. However, there was no association between LBP and muscle composition or CSA.

Conclusions

The paraspinal muscles’ CSA increased among FINAF fighter pilots during the first 5 years of service. This might be explained by physically demanding work and regular physical activity. However, no associations between muscle composition or CSA and low back pain (LBP) experienced were observed after the five-year follow-up.

Randomized controlled trial of postoperative exercise rehabilitation program after lumbar spine fusion: study protocol

Background

Lumbar spine fusion (LSF) effectively decreases pain and disability in specific spinal disorders; however, the disability rate following surgery remains high. This, combined with the fact that in Western countries the number of LSF surgeries is increasing rapidly it is important to develop rehabilitation interventions that improve outcomes.

Methods/design

In the present RCT-study we aim to assess the effectiveness of a combined back-specific and aerobic exercise intervention for patients after LSF surgery. One hundred patients will be randomly allocated to a 12-month exercise intervention arm or a usual care arm. The exercise intervention will start three months after surgery and consist of six individual guidance sessions with a physiotherapist and a home-based exercise program. The primary outcome measures are low back pain, lower extremity pain, disability and quality of life. Secondary outcomes are back function and kinesiophobia. Exercise adherence will also be evaluated. The outcome measurements will be assessed at baseline (3 months postoperatively), at the end of the exercise intervention period (15 months postoperatively), and after a 1-year follow-up.

Discussion

The present RCT will evaluate the effectiveness of a long-term rehabilitation program after LSF. To our knowledge this will be the first study to evaluate a combination of strength training, control of the neutral lumbar spine position and aerobic training principles in rehabilitation after LSF.

Trial registration

ClinicalTrials.gov Identifier NCT00834015

The early changes in trunk muscle strength and disability following lumbar spine fusion

PURPOSE

To analyze trunk muscle function pre- and postoperatively in patients undergoing lumbar spine fusion. Associations between changes in trunk muscle strength and disability were also studied.

METHOD

A total of 114 patients undergoing lumbar spine fusion participated in the study. The flexion and extension strength of the trunk was measured preoperatively and 3 months after surgery using a strain-gauge dynamometer. Disability and pain during the past week was evaluated with the Oswestry disability index (ODI) and visual analog scale (VAS), respectively.

RESULTS

Preoperative trunk extension and flexion strength levels were 319 N and 436 N in males, respectively, and 160 N and 214 N in females, respectively. In females 3 months postoperatively, the trunk extension strength increased by 39 N (p < 0.001) and flexion by 38N (p < 0.001), whereas it remained unchanged in males. The preoperative extension/flexion strength ratio was 0.79 in females and 0.76 in males. Three months postoperatively, the strength ratio decreased to 0.66 in males (p = 0.02). The mean ODI improved by 47% and back pain decreased by 65% (both p < 0.001). The changes in the ODI correlated with changes in trunk extension (r = -0.38) and flexion (r = -0.43) strength.

CONCLUSIONS

Patients undergoing lumbar spine fusion had low trunk muscle strength and strength imbalance. Back fusion surgery leads to considerable relief of pain and disability, but patients still have low trunk extension and flexion strength levels 3 months postoperatively. Therefore, there is need for a proper progressive strength training protocols to normalize back function.

Effect of a specific exercise program on the strength and resistance levels of lumbar muscles in warehouse workers

OBJECTIVE

The aim of this study was to verify the influence of a specific exercise program on the strength and resistance levels of lumbar flexors and extensors in warehouse workers.

MATERIALS AND METHODS

The population used in this randomized controlled trial included 557 warehouse male workers from a food distribution company in Oporto/Portugal. Upon the application of the selection criteria, 98 workers deemed eligible were randomized in two groups: 57 were assigned to the intervention group and 41 to the control group. The intervention included 9 easily-executed exercises to promote stretching and strengthening of the lumbar region, to be executed daily, at the beginning of the working time, at the company facilities and lasting 8'. Trunk muscles' voluntary strength and resistance were measured using an isometric electronic dynamometer (Globus Ergometer, Globus, Codigné, Italy) at baseline and eleven months after implementing the exercise program. The data was analyzed using SPSS®, version 17.0.

RESULTS

After implementation of the exercise program, in the intervention group, all variables increased, significant differences were observed as for the muscle strength and resistance values (p = 0.014 and p = 0.006, respectively), as well as in the ratio extensors/flexors (p = 0.037). In the control group, all variables decreased, with a statistically significant decrease of the trunk flexors strength level (p = 0.009).

CONCLUSION

The results of this study suggest that a specific exercise intervention program can increase trunk extensors strength and resistance.

Neuromuscular function and balance of prepubertal and pubertal blind and sighted boys

AIM

To compare the neuromuscular function and balance of blind prepuberty- and puberty-aged boys to those with normal sight.

METHODS

Thirty-three prepubertal (aged 9-13 y) and pubertal (aged 15-18 y) blind and sighted boys were tested for muscle mass thickness, electromyography and maximal isometric strength, dynamic explosive actions, and balance.

RESULTS

There was no difference in the muscle mass thickness, maximal strength or vertical jump between the blind and sighted boys. However, fitness-ball throwing and five-jump distances were significantly shorter in both blind groups compared to the sighted groups. One-leg stance of the prepuberty-aged sighted boys was 109 (67) s and in blind boys 32 (12) s, and in the puberty-aged boys 120 (57) s and 31 (8) s, respectively. When vision was blocked in the sighted boys, differences between the blind and sighted boys disappeared.

CONCLUSION

The results showed comparable performance between prepubertal and pubertal blind and sighted boys in the static physical fitness tests. However, balance and performance in dynamic multi-joint tests did not improve similarly in the blind groups compared to sighted groups, indicating that maturation, learning and experience by themselves cannot compensate for the loss of sight.

Effects of home strength training and stretching versus stretching alone after lumbar disk surgery: a randomized study with a 1-year follow-up

OBJECTIVE

To assess the adherence to and effects of a 12-month combined strength and stretching home exercise regimen versus stretching alone, on patient outcome after lumbar disk surgery.

DESIGN

Randomized controlled trial.

SETTING

Departments of physical medicine and rehabilitation and orthopedics at a Finnish hospital.

PARTICIPANTS

Patients (N=126) were randomized into either a combined strength training and stretching group (STG, n=65) or a control group (CG, n=61).

INTERVENTION

The STG was instructed to perform strength training and both the STG and CG were instructed in the same stretching and stabilization exercises for 12 months.

MAIN OUTCOME MEASURES

Pain on the visual analog scale (VAS), the Oswestry and the Million disability indexes, isometric and dynamic trunk muscle strength, mobility in the lumbar spine, and straight-leg raising were measured.

RESULTS

The trial was completed by 71% and 77% of the patients from the STG and the CG, respectively. The mean strength training frequency decreased from 1.5 to 0.6 times a week in the STG during the intervention. The mean stretching frequency decreased from 3.7 to 1.6 times a week in both groups. Median back and leg pain varied between 17 and 23 mm (VAS), and the Million and Oswestry indices varied between 14 and 23 points 2 months postoperatively. No statistically significant changes took place in these outcome measures during the 12-month follow-up in both groups. The changes in isometric trunk extension favored the STG ( P =.016) during the first 2 months. However, during the whole 12-month training period, both dynamic and isometric back extension and flexion strength, as well as mobility of the spine and repetitive squat-test results, improved significantly in both groups, and no differences were found in any of the physical function parameters between the STG and CG.

CONCLUSIONS

At the 12-month follow-up, no statistically significant changes were found in the physical function, pain, or disability measures between the groups. In the STG, training adherence with regard to training frequency and intensity remained too low to lead to specific training-induced adaptations in the neuromuscular system. Progressive loading, supervision of training, and psychosocial support is needed in long-term rehabilitation programs to maintain patient motivation.

Muscle strength, pain, and disease activity explain individual subdimensions of the Health Assessment Questionnaire disability index, especially in women with rheumatoid arthritis

OBJECTIVE

To study the extent to which muscle strength and performance, pain, and disease activity are associated with the total Health Assessment Questionnaire (HAQ) disability index and its subdimensions in male and female patients with rheumatoid arthritis.

METHODS

HAQ for functional capacity was completed by 135 patients with rheumatoid arthritis referred for orthopaedic surgery (74% women; mean (SD) age 62 (10) years; disease duration 19 (13) years, 70% positive for rheumatoid factor). Knee extension, trunk extension and flexion, grip strength, walking speed, and sit-to-stand test were measured to mirror physical function. Radiographs of hands and feet, pain, and the modified 28 joint disease activity score (DAS28) were also assessed.

RESULTS

Mean total HAQ was 1.08 (0.68) in women and 0.67 (0.70) in men (p = 0.0031). Women had greater disability than men in five of the eight subdimensions of the HAQ. Grip strength was 48%, knee extension strength 46%, trunk extension strength 54%, and trunk flexion strength 43% lower in women than in men. Knee extension strength was inversely correlated with walking time (r = -0.63 (95% confidence interval, -0.73 to -0.51)) and with sit-to-stand test (r = -0.47 (-0.60 to -0.31)). In an ordered logistic regression analysis in female rheumatoid patients, DAS28, pain, knee extension strength, and grip strength were associated with the total HAQ disability index.

CONCLUSIONS

Women reported greater disability than men both in the total HAQ and in the majority of its eight subdimensions. In addition to disease activity and pain, muscle strength has a major impact on disability especially in female rheumatoid patients.

Sustained maintenance of exercise induced muscle strength gains and normal bone mineral density in patients with early rheumatoid arthritis: a 5 year follow up

OBJECTIVE

To investigate at 5 years whether an initial 2 year home based strength training period imposes sustained effects on muscle strength, bone mineral density (BMD), structural joint damage, and on disease activity in patients with early rheumatoid arthritis (RA).

METHODS

Seventy patients were randomised either to perform home based strength training with loads of 50-70% of repetition maximum (EG) or range of motion exercises (CG). Both groups were encouraged to take part in aerobic activities 2-3 times a week. Maximal muscle strength of different muscle groups was measured by dynamometers, and BMD at the femoral neck and lumbar spine by dual x ray densitometry. Disease activity was assessed by the 28 joint disease activity score, and joint damage by x ray findings.

RESULTS

62 patients completed 2 years' training and 59 patients attended check up at 5 years. Mean (SD) maximum muscle strength indices increased from baseline to 2 years-in EG from 212 (78) kg by a mean (95% CI) of 68 (55 to 80) and in CG from 195 (72) kg by 35 (13 to 60) kg-and remained at that level for the next 3 years. Development of BMD in EG tended to be more favourable than that in CG. Muscle strength training was not detrimental to joint structures or disease activity.

CONCLUSION

The patients' exercise induced muscle strength gains during a 2 year training period were maintained throughout a subsequent self monitored training period of 3 years. Despite substantial training effects in muscle strength, BMD values remained relatively constant. Radiographic damage remained low even at 5 years.

A home-based two-year strength training period in early rheumatoid arthritis led to good long-term compliance: a five-year followup

OBJECTIVE

To evaluate the impact of a 2-year home-based strength-training program on physical function in patients with early rheumatoid arthritis (RA) after a subsequent 3-year followup.

METHODS

Seventy patients with early RA were randomized to perform either strength training (experimental group [EG]) or range-of-motion exercises (control group [CG]). Maximal strength values were recorded by dynamometers. The Modified Disease Activity Score (DAS28), pain, Health Assessment Questionnaire (HAQ), walking speed, and stair-climbing speed were also measured.

RESULTS

The maximum strength of assessed muscle groups increased by 19-59% in the EG during the training period and remained at the reached level throughout the subsequent 3 years. Muscle strength improved in the CG by 1-31%, but less compared with the EG. During the 2-year training period, DAS28 decreased by 50% and 45% and pain by 67% and 39% in the EG and CG, respectively. The differences in muscle strength, DAS28, and HAQ were significantly in favor of the EG both at the 2-year and 5-year followup assessments.

CONCLUSIONS

The improvements achieved during the 2-year strength-training period were sustained for 3 years in patients with early RA.

Effects of concurrent strength and endurance training in women with early or longstanding rheumatoid arthritis: Comparison with healthy subjects

OBJECTIVE

To investigate the effects of a 21-week concurrent strength and endurance training protocol on physical fitness profile in women with early or longstanding rheumatoid arthritis (RA) compared with healthy subjects.

METHODS

Twenty-three female patients with RA volunteered for the study. Twelve had early RA and eleven had longstanding RA. Twelve healthy women served as controls. Maximal strength of different muscle groups was measured by dynamometers, walking speed with light cells, and vertical squat jump on the force platform to mirror explosive force. Maximal oxygen uptake was measured by gas analyzer. Six training sessions (3 strength training and 3 endurance training) were carried out in a 2-week period for 21 weeks.

RESULTS

The training led to large gains in maximal strength both in women with RA and in healthy women (P < 0.043-0.001). The strength gains were accompanied by increases in walking speed (P < 0.034-0.001) and vertical squat jump (P < 0.034-0.001). Significant improvements also occurred in maximal aerobic capacity in all groups (P < 0.023-0.014).

CONCLUSIONS

Both early and longstanding RA patients with stable disease can safely improve all characteristics of their physical fitness profile using a progressive concurrent strength and endurance training protocol.

Trunk muscle strength in flexion, extension, and axial rotation in patients managed with lumbar disc herniation surgery and in healthy control subjects

STUDY DESIGN

A cross-sectional study was conducted.

OBJECTIVE

To compare maximal flexion, extension, and rotation strength as well as force-time characteristics of trunk muscles in patients who undergo lumbar disc herniation with those in healthy control subjects 2 months after surgery.

SUMMARY OF BACKGROUND DATA

Insufficient attention has been paid to muscle strength characteristics after lumbar disc herniation surgery.

METHODS

For this study, 30 postoperative patients with lumbar disc herniation and 30 healthy control subjects volunteered to participate. Isometric trunk flexion, extension in the standing position, and seated rotation strength were tested bilaterally in a neutral posture and at 30 degrees axial prerotation. The area under the curve was calculated to analyze explosive force capacity. Dynamic endurance strength was measured by calculating the repetition maximum. Pain during the strength measurements was assessed by a visual analog scale.

RESULTS

The healthy control subjects showed 44% and 36% higher isometric trunk flexion (P < 0.001) and extension (P < 0.001) forces, respectively, than the patients. The respective values for the area under the curve were 41% and 37% higher for the trunk flexors (P < 0.001) and extensors (P < 0.001) in the healthy control subjects than in the patients. The differences in trunk rotation force between the groups were statistically significant when the lower body was rotated 30 degrees to the right (P = 0.023) or to the left (P = 0.043) and the upper body was rotated in the opposite direction. Furthermore, in the dynamic endurance strength test, the healthy control subjects performed 70% more repetitions both for trunk flexors and extensors than did the patients. Some of the patients reported mild pain during the strength measurements, but the level of pain did not correlate with the strength values.

CONCLUSIONS

The recovery of maximal endurance and explosive type strength characteristics is incomplete in patients with lumbar disc herniation 2 months after surgery. Active strength training is recommended to restore muscle function in these patients.

Effects of dynamic strength training on physical function, Valpar 9 work sample test, and working capacity in patients with recent-onset rheumatoid arthritis

OBJECTIVE

To study the impact of 24 months of strength training on the physical function of patients with early rheumatoid arthritis (RA).

METHODS

Seventy patients were assigned to either the strength training (experimental) group (n = 35) or the control group (n = 35). Patients in the experimental group performed strength training for 24 months, and control patients were instructed to perform range of motion exercises. Maximal strength of the knee extensors, trunk flexors, and extensors, as well as grip strength were recorded with dynamometers. Disease activity was assessed by the erythrocyte sedimentation rate and Ritchie's articular index, joint damage was determined by the Larsen x-ray index, and functional capacity was assessed using the Valpar 9 test and the Stanford Health Assessment Questionnaire (HAQ). The employment status of each patient was recorded.

RESULTS

In the experimental group, strength training led to significant increases (19-59%) in maximal strength of the trained muscles. Such increases in the control group varied from 1% to 31%. There was a clear training effect on muscular strength in favor of the experimental group, but significant improvements in the HAQ indices as well as in the Valpar 9 test were seen also in control patients. Results of the Valpar 9 and the HAQ were statistically significantly better in patients who remained gainfully employed compared with patients who retired preterm during followup. However, compared with patients who remained in the work force, patients who retired were older, and their work was physically more demanding.

CONCLUSION

As expected, strength training led to increased muscle strength, but this increase did not correlate with improved physical function as assessed by the Valpar 9 work sample test. The increased muscle performance did not prevent a substantial proportion of patients from retiring preterm. The 2 items from the Valpar 9 test that were applied were not sensitive enough to differentiate the patients according to their working status.

Determination of functional rotation axes during elevation of the shoulder complex

STUDY DESIGN

A cross-sectional, descriptive study of shoulder movements conducted on nonimpaired subjects.

OBJECTIVE

To investigate whether a single functional rotation axis about the shoulder complex can be determined during elevation in the coronal or sagittal planes, and to identify their location.

BACKGROUND

Accurate measurement of isokinetic torques about a joint requires alignment of the dynamometer axis with an assumed rotation axis of the joint. To assess shoulder function on a dynamometer, the location of a single rotation axis is not evident because the shoulder joint motion is based on several anatomical joints. Therefore, the rotation axis where humerothoracic movements occur should be judged as a functional rotation axis.

METHODS AND MEASURES

During slow elevation movements in the sagittal and coronal plane, the position of the epicondyle and acromion were recorded with a motion analysis system. The motion trajectory of the elbow coordinates was fitted to a circle and considered an estimate of the functional shoulder joint rotation axis in the specified plane.

RESULTS

The fitted trajectory appeared to be very accurate (root-mean-square error < 2%; N = 7). In the sagittal plane, the estimated functional rotation axis was found at the humeral head; in the coronal plane, it was located about 13 centimeters medial relative to the acromion.

CONCLUSION

The shoulder complex of nonimpaired subjects can act as a hinge joint of the upper arm relative to the thorax during elevation in each measured plane.

A randomized two-year study of the effects of dynamic strength training on muscle strength, disease activity, functional capacity, and bone mineral density in early rheumatoid arthritis

OBJECTIVE

To evaluate the impact of a 2-year program of strength training on muscle strength, bone mineral density (BMD), physical function, joint damage, and disease activity in patients with recent-onset (<2 years) rheumatoid arthritis (RA).

METHODS

In this prospective trial, 70 RA patients were randomly assigned to perform either strength training (all major muscle groups of the lower and upper extremities and trunk, with loads of 50-70% of repetition maximum) or range of motion exercises (without resistance) twice a week; all were encouraged to engage in recreational activities 2-3 times a week. All patients completed training diaries (evaluated bi-monthly) and were examined at 6-month intervals. All were treated with medications to achieve disease remission. Maximum strength of the knee extensors, trunk flexors and extensors, and grip strength was measured with dynamometers. BMD was measured at the femoral neck and lumbar spine by dual x-ray densitometry. Disease activity was determined by the Disease Activity Score, the extent of joint damage by the Larsen score, and functional capacity by the Health Assessment Questionnaire (HAQ); walking speed was also measured.

RESULTS

Sixty-two patients (31 per group) completed the study. Strength training compliance averaged 1.4-1.5 times/week. The maximum strength of all muscle groups examined increased significantly (19-59%) in the strength-training group, with statistically significant improvements in clinical disease activity parameters, HAQ scores, and walking speed. While muscle strength, disease activity parameters, and physical function also improved significantly in the control group, the changes were not as great as those in the strength-training group. BMD in the femoral neck and spine increased by a mean +/- SD of 0.51 +/- 1.64% and by 1.17 +/- 5.34%, respectively, in the strength-training group, but decreased by 0.70 +/- 2.25% and 0.91 +/- 4.07% in the controls. Femoral neck BMD in the 17 patients with high initial disease activity (and subsequent use of oral glucocorticoids) remained constantly at a statistically significantly lower level than that in the other 45 patients.

CONCLUSION

Regular dynamic strength training combined with endurance-type physical activities improves muscle strength and physical function, but not BMD, in patients with early RA, without detrimental effects on disease activity.

Optimal sagittal motion axis for trunk extension and flexion tests in chronic low back trouble

OBJECTIVE

To find the optimal height for sagittal motion axis for trunk strength test in chronic low back trouble.

DESIGN

Cross-sectional study.

BACKGROUND

The strength of trunk muscles of low back pain patients is decreased. The measured strength depends on the height of the sagittal motion axis but the differences between patients and controls are not known.

METHODS

114 (67 female) patients with chronic low back trouble are classified according to Quebec Task Force, 50 (31 female) patients with rheumatic disorder, but without low back trouble, and 33 (22 female) healthy controls, no appreciable physical differences but clear differences in Oswestry score. Isometric trunk extension-flexion test with different heights for the pelvic fulcrum.

RESULTS

Force decreased in extension, increased in flexion, and torque increased both in flexion and extension in every group (P<0.001) as the fulcrum was moved caudally. The male controls were stronger than patients with low back trouble (P<0.01). The female controls were stronger only if the fulcrum was set at the hip joint level (P<0.05). There were no differences between patients with rheumatic disorder and low back trouble, except in extension if the fulcrum was at the hip joint level (P<0.02).

CONCLUSIONS

The rotation axis in trunk extension-flexion strength test should be set at the level of the hip joint.

RELEVANCE

Trunk muscle weakness is a common sign of different rheumatic disorders. Proper setting of sagittal motion axis and concomitant measurement of trunk and hip extensor or flexor muscles increases the specificity of the strength test for low back trouble.

Back and hip extensor muscle function during therapeutic exercises

BACKGROUND

Therapeutic exercises are widely used in the treatment of low back problems. Clinical knowledge about targeting the load in these exercises, however, is insufficient. This study assessed the L2 and L5 level paraspinal and gluteus maximus muscle activities in different therapeutic exercises. Intramuscular and surface electromyography (EMG) measurements were obtained to study whether surface EMG measurements can be used in the assessment of multifidus muscle function.

METHODS

Eleven healthy subjects (5 men, 6 women) 21 to 38 years of age volunteered for the study. The subjects performed 18 different therapeutic exercises. During the exercises paraspinal EMG was recorded using fine wire and surface electrodes. The normalized peak and average muscle EMG activities (percentage of amplitude in maximal voluntary contraction [MVC]) during each task were determined.

RESULTS

The correlations between the average intramuscular and surface activities of the normalized EMG (% of MVC) at the L2 and L5 levels were .928 and .950, respectively. The peak and average EMG amplitudes of the exercises were below 50% and 25% of MVC, respectively. At the L5 level, the multifidus peak and average EMG amplitudes (% MVC) were higher in women than in men, whereas no significant difference was found at the L2 level. In women, the normalized multifidus EMG amplitude was higher at the L5 level than at the L2 level, whereas no significant difference was found in men. In both sexes, the normalized EMG amplitude was higher in the multifidus than in the longissimus muscle.

CONCLUSION

Surface EMG measurements may be used in the assessment of multifidus muscle function. Simple therapeutic exercises are effective in activating the lumbar paraspinal muscles.

Trunk extensor and flexor strength measured by the Cybex 6000 dynamometer. Assessment of short-term and long-term reproducibility of several strength variables

STUDY DESIGN

Isokinetic trunk extensor and flexor strength (peak torque, total work, power acceleration time, and torque acceleration energy) at 30 degrees/sec, 120 degrees/sec, and 180 degrees/sec and isometric extensor and flexor peak torque were measured in 24 healthy women. Measurements were performed in three separate sessions at the same time of day and by the same experienced examiner. The number of days between Session 1 and Session 2 and between Session 1 and Session 3 ranged from 1 to 7 (median, 2 days) and from 23 to 48 (median, 32 days), respectively. The test results were not revealed before all sessions were completed.

OBJECTIVES

To determine the intrasession, short-term, and long-term reproducibility of several trunk strength variables measured by the Cybex 6000 isokinetic dynamometer (Lumex, Inc., Ronkonkoma, NY).

SUMMARY OF BACKGROUND DATA

Only few and insufficient data regarding the reproducibility of trunk strength measurements exist. Previous studies have focused on coefficients of correlation to express reproducibility. Correlations, however, are misleading and inappropriate for this purpose. The critical difference is the difference between two results that would be statistically significant when applied to a reference group in steady state. The critical difference in percentage is calculated as 2.77 X coefficient of variation (%).

METHODS

Isokinetic dynamometry (Cybex 6000). Reproducibility was expressed as pooled coefficients of variation, individual coefficients of variation, and critical differences.

RESULTS

Substantial between-subject variation of coefficients of variation was found for all strength variables; for example, the 80% central range for individual coefficients of variation for long-term reproducibility of extensor strength measurements at 30 degrees/sec ranged from 2.5% to 19.5%. Critical differences calculated using the pooled variances for long-term reproducibility were higher than 20% for all measures, mounting to 80% for acceleration time.

CONCLUSIONS

Strength testing is of limited value in the individual subject because of considerable day-to-day variability. This finding has important clinical implications.