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Surface electromyographic amplitude-to-work ratios during isokinetic and isotonic muscle actions.

CONTEXT: Isokinetic and isotonic resistance training exercises are commonly used to increase strength during musculoskeletal rehabilitation programs. Our study was designed to examine the efficacy of isokinetic and isotonic muscle actions using surface electromyographic (EMG) amplitude-to-work ratios (EMG/WK) and to extend previous findings to include a range of isokinetic velocities and isotonic loads. OBJECTIVE: To examine work (WK), surface EMG amplitude, and EMG/WK during concentric-only maximal isokinetic muscle actions at 60, 120, 180, 240, and 300 degrees /s and isotonic muscle actions at 10%, 20%, 30%, 40%, and 50% of the maximal voluntary isometric contraction (MVIC) torque during leg extension exercises. DESIGN: A randomized, counterbalanced, cross-sectional, repeated-measures design. SETTING: A university-based human muscle physiology research laboratory. PATIENTS OR OTHER PARTICIPANTS: Ten women (mean age = 22.0 +/- 2.6 years) and 10 men (mean age = 20.8 +/- 1.7 years) who were apparently healthy and recreationally active. INTERVENTION(S): Using the dominant leg, each participant performed 5 maximal voluntary concentric isokinetic leg extension exercises at randomly ordered angular velocities of 60, 120, 180, 240, and 300 degrees /s and 5 concentric isotonic leg extension exercises at randomly ordered loads of 10%, 20%, 30%, 40%, and 50% of the isometric MVIC. MAIN OUTCOME MEASURE(S): Work was recorded by a Biodex System 3 dynamometer, and surface EMG was recorded from the superficial quadriceps femoris muscles (vastus lateralis, rectus femoris, and vastus medialis) during the testing and was normalized to the MVIC. The EMG/WK ratios were calculated as the quotient of EMG amplitude (muVrms) and WK (J) during the concentric phase of each exercise. RESULTS: Isotonic EMG/WK remained unchanged ( P > .05) from 10% to 50% MVIC, but isokinetic EMG/WK increased ( P < .05) from 60 to 300 degrees /s. Isotonic EMG/WK was greater ( P < .05) than isokinetic EMG/WK for 50% MVIC versus 60 degrees /s, 40% MVIC versus 120 degrees /s, and 30% MVIC versus 180 degrees /s; however, no differences were noted ( P > .05) between 20% MVIC versus 240 degrees /s or 10% MVIC versus 300 degrees /s. An 18% decrease in active range of motion was seen for the isotonic muscle actions, from 10% to 50% MVIC, and a 3% increase in range of motion for the isokinetic muscle actions from 60 to 300 degrees /s was also observed. Furthermore, the peak angular velocities for the isotonic muscle actions ranged from 272.9 to 483.0 degrees /s for 50% and 10% MVIC, respectively. CONCLUSIONS: When considering EMG/WK, peak angular velocity, and range of motion together, our data indicate that maximal isokinetic muscle actions at 240 degrees /s or controlled-velocity isotonic muscle actions at 10%, 20%, or 30% MVIC may maximize the amount of muscle activation per unit of WK done during the early stages of musculoskeletal rehabilitation. These results may be useful to allied health professionals who incorporate open-chain resistance training exercises during the early phases of rehabilitation and researchers who use isotonic or isokinetic modes of resistance exercise to examine muscle function.

Journal Article↗

Assessment of isokinetic and hand-held dynamometer measures of shoulder rotator strength among individuals with spinal cord injury.

OBJECTIVE: To determine the intrarater reliability of the hand-held dynamometer (HHD) for the measurement of shoulder rotation and to examine the relationship between the peak force values of the HHD and the isokinetic dynamometer. PARTICIPANTS: Twenty-five spinal cord injured individuals, 12 persons with paraplegia and 13 persons with tetraplegia between the ages of 18 and 42 years, were recruited from the community. SETTING: Private practice clinic. PROCEDURES: All participants were tested with the HHD by one examiner to determine reliability. On the same day, these participants underwent isokinetic testing to determine the relationship of the HHD and Cybex dynamometer measurements. RESULTS: The intraclass correlation coefficients for the intrarater reliability ranged from .89 to .96. The Pearson product moment correlation was used to analyze the relationship between the two devices. All coefficients (.52 to .88) were statistically significant (p < .01); however, separate analyses for the persons with paraplegia and tetraplegia differed considerably. There was substantial variability of the isokinetic strength values at the lower levels of isometric strength. CONCLUSIONS: The HHD can be used reliably to measure shoulder rotation in paraplegic and tetraplegic spinal cord injured individuals. Although it appears that the relationship between HHD and isokinetic measurement is poor for the participants with tetraplegia, the variability of the isokinetic scores indicates that this observation may be a function of the method of isokinetic measurements. Further study with a modified isokinetic testing protocol is needed to clarify the results of the participants with tetraplegia.

Adolescent↗

A standard method of shoulder strength measurement for the Constant score with a spring balance.

The strength component of the Constant score has been criticized for its lack of a precisely defined measurement method. A series of experiments was performed to compare three different methods in normal and pathologic shoulders with the use of a standard test position. These were (1) the Isobex isometric dynamometer, (2) Constant's unsecured spring balance, and (3) a new modification in which the spring balance is fixed at one end and the reading is taken after 5 seconds of maximum effort. The results suggest that this simple modification with a low-cost spring balance can give similar values to those from the Isobex. The need for precision of terms and a definition of the method is discussed, and recommendations for the standardization of the many variables in making this measurement are made.

Adult↗

Isokinetic arm and leg strength of adults with Down syndrome: a comparative study.

This study compared isokinetic arm (elbow flexion and extension) and leg (knee flexion and extension) strength of individuals with Down syndrome (DS), with mental retardation without DS (NDS), and sedentary young adults with no mental retardation (NMR). Eighteen individuals with DS, NDS, and NMR (11 men and seven women in each group) performed strength tests on a Cybex 340 isokinetic dynamometer. Parameters measured were peak torque (ft/lb), peak torque percent body weight (%BW), average power (watts), and average power %BW. Subjects with mental retardation (ie, DS and NDS groups) performed the test on two separate days with best test results chosen for statistical comparisons. The NMR group performed the test once. In all isokinetic strength parameters measured for arm strength, the NMR group demonstrated significantly higher scores than subjects with DS and NDS. Subjects with DS and NDS displayed similar test results. Similarly, for all the isokinetic strength parameters measured for leg strength, NMR demonstrated significantly higher scores than subjects with DS and NDS. Subjects with NDS, however, averaged significantly higher test results than subjects with DS for leg strength. The results of this study indicate that both subject populations who were mentally retarded exhibited lower arm and leg strength than the NMR subjects. Additionally, subjects with DS demonstrated inferior leg strength when compared to their peers with NDS.

Adult↗

Age specific isokinetic glenohumeral internal and external rotation strength in elite junior tennis players.

The high incidence of overuse shoulder injuries in elite junior tennis players is often attributed to both the high repetitive stresses inherent in the game, as well as muscular imbalances in the humeral rotators. The purpose of this study was to isokinetically measure concentric glenohumeral joint internal and external rotation strength, to develop a bilateral descriptive profile in elite junior tennis players across two age ranges. One hundred forty seven elite junior players between the ages of 12 and 21 were bilaterally tested on a Cybex isokinetic dynamometer with 90 degrees of abduction. Players were analysed in two groups (12-17 and 18-21 years of age), using isokinetic variables of peak torque and work relative to body weight. Data analysis consisted of ANOVAs, with dependent t-tests used for post-hoc testing where main effect differences were identified. Results indicated no significant main effect difference in the isokinetic relative parameters between the two age groups (p > .01). Significantly greater (p < .001) dominant arm internal rotation was measured in both groups for both males and females, with no significant difference in external rotation strength measured between extremities in either age group. These data show specific adaptations in shoulder strength and identify a relative muscular imbalance between the internal and external rotators on the dominant arm of elite junior tennis players. Normative data presented in this study can assist clinicians and researchers in interpreting isokinetic test results in elite junior tennis players.

Adolescent↗

Is grip strength associated with health-related quality of life? Findings from the Hertfordshire Cohort Study.

OBJECTIVE: to investigate the relationship between grip strength and health-related quality of life (HRQoL). DESIGN: cross-sectional survey within a cohort study design. SETTING: the county of Hertfordshire in the UK. PARTICIPANTS: a total of 2,987 community-dwelling men and women aged 59-73 years of age. MEASUREMENTS: grip strength was used as a marker of sarcopaenia and measured using a Jamar dynamometer. HRQoL was assessed using the eight domain scores of the Short Form-36 (SF-36) questionnaire, and subjects in the lowest sex-specific fifth of the distribution were classified as having 'poor' status for each domain. RESULTS: men and women with lower grip strength were significantly more likely to report a poor as opposed to excellent to fair overall opinion of their general health (GH) [odds ratio (OR) per kilogram decrease in grip strength = 1.13, 95% CI = 1.06-1.19, P < 0.001 in men, 1.13, 95% CI = 1.07-1.20, P < 0.001 in women]. Among men, after adjustment for age, size, physical activity and known co-morbidity, decreased grip strength was associated with increased prevalence of poor SF-36 scores for the physical functioning (PF) (OR per kilogram decrease in grip strength = 1.03, 95% CI = 1.01-1.06, P = 0.007) and GH domains (OR = 1.03, 95% CI = 1.01-1.05, P = 0.01). Similar associations were seen in women. CONCLUSIONS: our findings suggest that lower grip strength is associated with reduced HRQoL in older men and women. This does not appear to be explained by age, size, physical activity or co-morbidity and may reflect the link between sarcopaenia and generalised frailty. Individuals with sarcopaenia may benefit from interventions to improve muscle mass and strength before the onset of chronic disorders usually associated with impaired HRQoL.

Accidental Falls↗

Mechanomyographic and electromyographic responses to unilateral isometric training.

The purpose of this investigation was to examine the effects of unilateral, isometric training of the forearm flexors on strength and the mechanomyographic (MMG) and electromyographic (EMG) responses of the biceps brachii in the trained and untrained limb at three joint angles. Seventeen adult females (mean age +/- SD = 21 +/- 2 years) were randomly assigned to a control (CTL; N=7) or a training (TRN; N=10) group. The TRN group performed isometric training of the non-dominant forearm flexors on a Cybex II Dynamometer at a joint angle such that the Cybex lever arm was positioned 60 degrees above the horizontal plane. The training consisted of 3 to 5 sets of 8, 6-second repetitions at 80% of maximal voluntary contraction 3 times per week for 8 weeks. The results indicated a significant increase in flexed arm circumference as well as isometric strength in the trained limb at all three joint angles. There were, however, no changes in MMG or EMG amplitude in the trained or untrained limb and no cross-training effect for strength or flexed arm circumference. These findings suggested that the increased strength may have been due to factors associated with hypertrophy, independent of neural adaptations in the biceps brachii. Furthermore, hypertrophy may have had counteractive effects on the MMG signal that could be responsible for the lack of a training-induced change in the MMG amplitude.

Adult↗

Electrical stimulation and swimming performance.

The purpose of the study was to examine the influence of a 3-wk period of electrostimulation training on the strength of the latissimus dorsi m. and the swimming performances of 14 competitive swimmers divided into 7 electrostimulated (EG) and 7 control swimmers (CG). The peak torques registered during the flexion-extension of the arm was determined with the help of an isokinetic dynamometer at different velocities (from -60 degrees.s(-1) to 360 degrees.s(-1)). Performances were measured over a 25-m pull buoy and a 50-m freestyle swim. For EG, a significant increase of the peak torques was measured in isometric, eccentric, and concentric conditions (P < 0.5). The swimming times declined significantly (P < 0.01) by 0.19 +/- 0.14 s, for the 25-m pull-buoy, and by 0.38 +/- 0.24 s, for the 50-m freestyle. For CG, no significant difference was found for any of the tests. For the whole group, the variations of the peak torques, measured in eccentric condition (-60 degrees.s(-1)) were related to the variations of the performances (r = 0.77; P < 0.01). These results showed that an electrostimulation program of the latissimus dorsi increased the strength and swimming performances of a group of competitive swimmers.

Adult↗

[The assessment of functional capacity in workers with the thoracic outlet syndrome. A pilot study].

Occupational specialists are well aware of the lack of objective measurements for the diagnosis and the functional evaluation of workers affected by thoracic outlet syndrome (TOS). Subjects affected by TOS refer pain, sensation of fatigue in the arm frequently aggravated by overhead work. A "stick-up" position tends to close the costoclavicular space and tense the neck and shoulder muscles to bring into play the abnormal compression mechanism that may affect the brachial plexus nerves and the subclavian vessels. In a previous study, we demonstrated the reliability of an isokinetic hand grip endurance test. In this pilot study we asked 7 industrial workers affected by TOS to perform a 30-second isokinetic endurance test for hand gripping with a Lido WorkSET dynamometer. Tests were performed in two positions (resting and "stick-up" position) before and after a 3-week intensive rehabilitation program. In addition, the subjects performed daily aerobic exercise with an arm crank ergometer. Objective indexes of posttreatment improvement were found. Subjects were able to generate higher grip forces during the isokinetic hand grip endurance test and to sustain higher mechanical workload with the arm ergometer at the same intensity level for longer duration after completion of the rehabilitation program.

Adult↗

[Validation of the EK functional motor scale in the Portuguese language].

OBJECTIVE: To validate a Portuguese version of the EK scale (Egen Klassifikation), that was developed in Denmark for patients with Duchenne muscular dystrophy, and spinal muscular atrophy. METHODS: An English version of the EK scale was translated into the Portuguese language as spoken in Brazil. This scale was applied to 26 male patients (mean age = 12.7 +/- 4.0 years) with Duchenne muscular dystrophy. Patients also answered questions of a Portuguese version of the Barthel index questionnaire, and had their right and left hand grip forces measured with a dynamometer. RESULTS: The mean total EK scale score was 8.1 +/- 7.3 and the Barthel index 54.0 +/- 26.2. The mean hand grip force was 12.7 +/- 17.2 % predicted for the right hand, and 14.6 +/- 19.8 % predicted for the left hand. The EK scale scores showed highly significant statistical correlations with age (r= 0.596, p= 0.0013), right hand grip force (r= -0.556, p= 0.0032), left hand grip force (r= -0.623, p=0.0007), and Barthel index (r= -0.928, p < 0.0001). CONCLUSION: This translated Portuguese version of the EK scale is an adequate tool to be used for Brazilian Duchenne muscular dystrophy patients.

Adolescent↗

Grip and pinch strength variations in different types of workers.

We measured grip and pinch strengths in non-manual, light manual and heavy manual workers using a Jamar dynamometer and a pinch measuring device. Heavy manual workers had the strongest grips with the least difference between sides. Office workers had the weakest grips and the greatest difference between sides. Light manual workers were between these two groups. Consequently, the occupation of the patient must be taken into account when using grip and pinch strength measurements to assess the need for rehabilitation and in medicolegal reports.

Adult↗

The abdominal linea alba: an anatomo-radiologic and biomechanical study.

Traditionally, the linea alba represents the principal route of approach in abdominal surgery and in consequence it is the commonest site of incisional hernia. The aim of this study was to review its morphology and to study its mechanical parameters of resistance, deformation and elasticity in order to compare these with the prosthetic materials most often used in the treatment of incisional hernia. Forty fresh cadavers were dissected and tests with a dynamometer and "bursting strength tester" were performed on samples taken from the linea alba at three levels: supra-umbilical, subumbilical and umbilical. Forty abdomino-pelvic scans were analysed. The morphologic results allowed definition of diastasis of the rectus mm. in terms of subject age: below 45 years of age diastasis was considered as a separation of the two rectus mm. exceeding 10 mm above the umbilicus, 27 mm at the umbilical ring and 9 mm below the umbilicus; above 45 years of age the corresponding values were 15 mm, 27 mm and 14 mm respectively. In the biomechanical study the subumbilical region exhibited a coefficient of elasticity greater than that of the supra-umbilical portion, but no significant difference in resistance was found between the different parts studied. The biomechanical results are compared with the corresponding data for prosthetic materials.

Abdominal Muscles↗

Association between polymorphisms of vitamin D receptor gene ApaI, BsmI and TaqI and muscular strength in young Chinese women.

UNLABELLED: The association between the polymorphisms of vitamin D receptor gene ApaI, BsmI and TaqI and isokinetic muscular strength was examined in 109 healthy, young Chinese women. METHODS: Genomic DNA was extracted from mouthwash samples and vitamin D receptor genotypes were determined with the established methods. The peak torque of the dominant limb in concentric and eccentric knee extensors and flexors and elbow extensors and flexors was measured using Cybex-Norm-770 isokinetic dynamometer at slow and fast velocities. The distribution frequency of vitamin D receptor gene alleles was analyzed by chi-square test. The difference in muscular strength between VDR genotype groups was analyzed using one-way ANOVA. The ApaI, BsmI and TaqI alleles and genotype frequencies appeared to be in a Hardy-Weinberg equilibrium. Subjects with the vitamin D receptor ApaI null (A allele) mutation (AA) exhibited significantly lower knee and elbow concentric or eccentric peak torque than those with aa homozygous or Aa heterozygous. The BB & Bb group showed significantly higher peak torque in concentric knee flexors than bb group. No association was found between vitamin D receptor gene TaqI and muscular strength. The data indicated that vitamin D receptor gene ApaI and BsmI polymorphisms rather than TaqI polymorphism might be associated with muscular strength.

Adult↗

Reliability of a new instrument for measuring maximum rising strength.

OBJECTIVE: To assess the intrarater test-retest reliability of a newly developed instrument for measuring maximum rising strength (MRS) in comparison with that of maximum knee extension strength (KES). DESIGN: Three replications of isometric MRS and KES were measured on three test occasions separated by 1 wk in 97 healthy men and women aged 23-90. MRS was measured in seated subjects using a dynamometer fixed on the ground and connected by an adjustable nonelastic cord to a padded belt. RESULTS: The intraclass coefficients (ICCs) of MRS were 0.92 and 0.93 at 60 and 70 degrees of knee flexion, respectively, and 0.98 when the mean of three highest peak values of MRS at 60 degrees and the three highest peak values at 70 degrees knee flexion on each session were considered vs. 0.95 for KES. A significant increase in MRS and KES strength was found between the first and the third sessions (+7 to 8%)(P < 0.001). No side effects of strength measurements were noticed. CONCLUSION: Despite a significant learning effect, MRS measurement is reliable in men and women of a wide range of ages. Whether this instrument will be useful for targeting individuals with early sit-to-stand difficulties requires further investigation.

Adult↗

Physical activity and the changes in maximal isometric strength in men and women from the age of 75 to 80 years.

OBJECTIVE: To research the natural changes in maximal isometric strength, over a period of 5 years, in men and women aged 75 at baseline, and to study the effect of everyday physical activity on strength alterations. DESIGN: A 5-year longitudinal study. SETTING: Exercise laboratory. PARTICIPANTS: The target group in 1989 was the total 75-year-old population of Jyväskylä. One hundred one men (81%) and 186 women (75%) participated in baseline strength tests, and after 5 years, 55 men and 111 women (70% and 72% of the survivors) took part in the follow-up measurements. METHODS: Maximal isometric hand grip, arm flexion, knee extension, trunk flexion, and trunk extension forces were measured using dynamometers. Self-rated physical activity was recorded using a scale by Grimby (1986). Strength changes were compared between groups based on the amount of everyday physical activity: (1) remained active (AA, 24 men, 24 women); (2) remained sedentary (SS, 11 men, 43 women); (3) decreased activity (AS, 11 women); and (4) increased activity (SA, 32 women). AS and SA could be formed for women only because of the small number of men. All analyses were stratified by gender. MAIN RESULTS: The average percentage change in strength over 5 years among survivors varied from a 4% increase in knee extension strength observed in men and women to a 16% decrease in grip strength in women. The grip strength decrease was greater in women than men. The AA men maintained their trunk extension strength at a higher level than the SS men. Time by group interactions in men were not significant. In women, the rate of decline in AS was 32% in grip and 27% in elbow flexion strength, which was greater than in the other activity groups. The AA women retained their knee extension strength at a higher level than the other groups. Those who died before follow-up tests exhibited poorer strength test results at baseline. Physical activity decreased over follow-up. CONCLUSIONS: Strength alterations with age differed between muscle groups. Undertaking everyday physical activities such as household work, walking, and gardening, which are also the most common physically demanding activities of older people, may play an important role in maintaining strength at an adequate level for independent living.

Aged↗

Maximal voluntary contraction as a functional indicator of adult chronic undernutrition.

Maximal voluntary contraction (MVC) using a handgrip dynamometer was assessed in seventy-two young adult males. The subjects were divided into two groups on the basis of a BMI of 18.5 kg/m2. The subjects with a BMI < 18.5 kg/m2 (n 38) were further divided into an underweight (UW; n 20) group and a chronically energy-deficient (CED; n 18) group. The CED subjects had significantly lower MVC (30.1, SD 5.9 kg) than either the well-nourished controls (BMI > 18.5 kg/m2: 39.8, SD 5.8 kg) or the underweight group (37.6, SD 4.9 kg). The differences between the CED and UW groups persisted even after the MVC were corrected for forearm muscle area and stature. The results suggest that MVC may be a useful functional indicator of nutritional status particularly in differentiating subjects with chronic undernutrition from individuals who are underweight and not undernourished but have similar BMI.

Adolescent↗

Isokinetic strength of collegiate baseball pitchers during a season.

Pitching is suggested to expose the arm to physical stress that may lead to a decrease in strength. The purpose of this study was to examine the isokinetic internal and external rotational shoulder strength of Division II pitchers preseason, midseason, and postseason. The 9 pitchers were 23 +/- 0.67 years of age and weighed 91.2 +/- 3.14 kg. Each subject was evaluated utilizing a Biodex Isokinetic Dynamometer. Isokinetic internal and external concentric strength was assessed at 90 degrees of shoulder abduction and 90 degrees of elbow flexion at 300 and 450 degrees .s(-1) at each time point. A repeated-measures analysis of variance statistical analysis was performed using SPSS software. All data are reported as mean +/- SEM. Mean internal peak torques at 300 and 450 degrees .s(-1) preseason, midseason, and postseason were 50.66 +/- 2.27, 49.70 +/- 2.54, and 51.70 +/- 2.94 N.m and 37.14 +/- 2.54, 37.36 +/- 2.74, and 38.26 +/- 2.50 N.m, respectively. Mean external peak torques at 300 and 450 degrees .s(-1) preseason, midseason, and postseason were 30.16 +/- 1.69, 29.50 +/- 2.22, and 29.79 +/- 2.08 N.m and 17.68 +/- 2.15, 16.89 +/- 2.46, and 18.20 +/- 2.35 N.m, respectively. There were no differences in isokinetic internal or external concentric shoulder rotational mean peak torque of Division II pitchers at any speed tested or time point examined.

Adult↗

Weakness is the primary contributor to finger impairment in chronic stroke.

OBJECTIVE: To assess the relative contributions of several neurologic and biomechanic impairment mechanisms to overall finger and hand impairment in chronic hemiparetic stroke survivors. DESIGN: Repeated-measures design. SETTING: Clinical research laboratory. PARTICIPANTS: Thirty stroke survivors with chronic hemiparesis. Fifteen subjects had severe hand motor impairment and 15 had moderate impairment, as measured with the Chedoke-McMaster Stroke Assessment. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The biomechanic factors stiffness and resting flexion torque, together with the neurologic factors spasticity, strength, and coactivation, were quantified by using a custom hand manipulator, a dynamometer, and electromyographic recordings. Both passive and active rotations of the metacarpophalangeal joints of the fingers were examined. RESULTS: Although subjects in the severely impaired group exhibited statistically greater passive stiffness and resting flexion torque than their moderately impaired counterparts (P<.05), the overall effect of these biomechanic changes appeared small in relation to the deficits attributable to neurologic changes such as spasticity and, especially, weakness. In fact, weakness in grip strength and isometric extension accounted for the greatest portion of the variance between the 2 groups (eta(2)=.40 and eta(2)=.23, respectively). CONCLUSIONS: Thus, deficits in hand motor control after stroke seem to derive mainly from weakness, which may be attributable to the loss of descending corticospinal pathway activation of motoneurons.

Biomechanical Phenomena↗