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PubMed2003

Assessment and interpretation of isokinetic muscle strength during growth and maturation.

The majority of strength studies examining changes during growth and maturation have investigated isometric actions, which tell us little about the muscle under dynamic conditions. There are numerous methodological issues in the isokinetic testing of paediatric populations that require further investigation. However, several studies have indicated that children can be reliably assessed isokinetically using both concentric and eccentric actions. Most paediatric studies have examined the knee joint and more data are needed to elucidate the reliability of upper body isokinetic strength testing. The age- and sex-associated development of isokinetic strength is less well understood. Studies have indicated that isokinetic strength increases with age but the mechanisms associated with this increase require further investigation. Current data are also conflicting regarding the age at which sex differences become apparent in isokinetic strength. More work is needed to examine the influence of maturation on isokinetic strength development, but available data suggest that maturation is a non-significant contributory factor once stature and body mass are accounted for. Most studies have demonstrated a significant relationship between stature, body mass and isokinetic strength during growth and maturation. The importance that changes in body composition during growth have on isokinetic strength has been investigated using fat-free mass and muscle cross-sectional area. Data have shown that although fat-free mass and muscle cross-sectional area are important contributors to isokinetic strength, other unexplained factors also influence isokinetic strength development. Additional work needs to investigate possible qualitative changes in muscle during growth and maturation. More work is also needed to examine changes in eccentric strength with age and to investigate sex differences in upper body isokinetic strength. Future studies should preferably be longitudinal in nature and examine known covariates simultaneously using appropriate statistical techniques.

Biomechanical Phenomena↗
PubMed2003

Non-volitional assessment of skeletal muscle strength in patients with chronic obstructive pulmonary disease.

BACKGROUND: Although quadriceps weakness is well recognised in chronic obstructive pulmonary disease (COPD), the aetiology remains unknown. In disabled patients the quadriceps is a particularly underused muscle and may not reflect skeletal muscle function as a whole. Loss of muscle function is likely to be equally distributed if the underlying pathology is a systemic abnormality. Conversely, if deconditioning and disuse are the principal aetiological factors, weakness would be most marked in the lower limb muscles. METHODS: The non-volitional technique of supramaximal magnetic stimulation was used to assess twitch tensions of the adductor pollicis, quadriceps, and diaphragm muscles (TwAP, TwQ, and TwPdi) in 22 stable non-weight losing COPD patients and 18 elderly controls. RESULTS: Mean (SD) TwQ tension was reduced in the COPD patients (7.1 (2.2) kg v 10.0 (2.7) kg; 95% confidence intervals (CI) -4.4 to -1.4; p<0.001). Neither TwAP nor TwPdi (when corrected for lung volume) differed significantly between patients and controls (mean (SD) TwAP 6.52 (1.90) N for COPD patients and 6.80 (1.99) N for controls (95% CI -1.5 to 0.97, p=0.65; TwPdi 23.0 (5.6) cm H(2)O for COPD patients and 23.5 (5.2) cm H(2)O for controls (95% CI -4.5 to 3.5, p=0.81). CONCLUSIONS: The strength of the adductor pollicis muscle (and the diaphragm) is normal in patients with stable COPD whereas quadriceps strength is substantially reduced. Disuse may be the principal factor in the development of skeletal muscle weakness in COPD, but a systemic process preferentially affecting the proximal muscles cannot be excluded.

Aged↗
PubMed1989

Effect of low frequency fatigue on human muscle strength and fatigability during subsequent stimulated activity.

Fatiguing contractions of the adductor pollicis muscle were produced by intermittent supramaximal stimulation of the ulnar nerve in a set frequency pattern, in six normal subjects. At the end of an initial fatiguing contraction series, low frequency fatigue (LFF) had been induced and persisted at 15 min of recovery. Stimulated fatiguing activity was then repeated in an identical fashion to the initial series. At high frequencies, declines in force were similar for both series. At low frequencies, declines in force were greater during the second series despite similar changes in compound muscle action potential amplitude. This confirmation that LFF persists during subsequent stimulated activity, and reduces low but not high frequency fatigue resistance, suggests that the impaired endurance of fatigued muscle during voluntary activity primarily results from peripheral changes at low frequency. These findings also have implications for therapeutic electrical stimulation of muscle.

Action Potentials↗
PubMed2006

Reliability of pelvic floor muscle strength assessment using different test positions and tools.

AIMS: The aims of this study were to determine the intra-therapist reliability for digital muscle testing and vaginal manometry on maximum voluntary contraction strength and endurance. In addition, we assessed how reliability varied with different tools and different testing positions. METHODS: Subjects included 20 female physiotherapists. The modified Oxford scale was used for the digital muscle testing, and the Peritron perineometer was used for the vaginal resting pressure and vaginal squeeze pressure assessments. Strength and endurance testing were performed. The highest of the maximum voluntary contraction scores was used in strength analysis, and a fatigue index value was calculated from the endurance repetitions. Bent-knee lying, supine, sitting, and standing positions were used. The time interval for between-session reliability was 2-6 weeks. RESULTS: Kappa values for the between-session reliability of digital muscle testing were 0.69, 0.69, 0.86, and 0.79 for the four test positions, respectively. Intra-class correlation coefficient (ICC) values for squeeze pressure readings for the four positions were 0.95, 0.91, 0.96, and 0.92 for maximum voluntary contraction, and 0.05, 0.42, 0.13, and 0.35 for endurance testing. ICC values for resting pressure were 0.74, 0.77, 0.47, and 0.29. CONCLUSIONS: Reliability of digital muscle testing was very good in sitting and good in the other three positions. vaginal resting pressure demonstrated very good reliability in all four positions for maximum voluntary contraction, but was unreliable for endurance testing. Vaginal resting pressure was not reliable in upright positions. Both measurement tools are reliable in certain positions, with manometry demonstrating higher reliability coefficients.

Adult↗
PubMed2000

Validity and reliability of two muscle strength scores commonly used as endpoints in assessing treatment of myasthenia gravis.

Valid and reliable measurements of muscle impairment are needed to assess therapeutic efficacy in patients with generalized myasthenia gravis (MG). In 22 patients we compared the validity and interobserver reliability of two scoring methods commonly used as main endpoints in clinical trials, i.e., the Myasthenic Muscle Score (MMS) ranging from 0 to 100 (normal) and the Quantified Myasthenia Gravis Strength Score (QMGSS) ranging from 0 (normal) to 39. Each score is correlated more with functional scale and less with the patient's self-evaluation. Using intraclass correlation we found strong agreement between observers for both the MMS (r = 0.906) and the QMGSS (r = 0.905). The correlation between MMS and QGMSS was high (r = 0.87). The reliability of neither score depended on any specific item, since the removal of individual items did not significantly alter the intraclass correlation coefficient (ranging from 0.86 to 0.93).

Adult↗
PubMed1985

The effects of age on muscle strength and anthropometric indices within a group of elderly men and women.

Within a group of 184 subjects (100 females) aged 65-90 years living independently, age was found to have a significant negative correlation with strength of triceps surae in the calf and biceps brachii in the arm. Muscle area in the limbs also declined significantly with age in males. Weight and strength per cross-sectional area in the calves declined significantly with age in females. Superficial fat did not change with age; height declined, perhaps due to kyphosis. The strength of the calf compared to body weight also declined significantly with age in both sexes. Multiple regression analysis has been used to describe the effects of sex, age and weight on muscle variables.

Age Factors↗
PubMed2002

Mice lacking skeletal muscle actin show reduced muscle strength and growth deficits and die during the neonatal period.

All four of the muscle actins (skeletal, cardiac, vascular, and enteric) in higher vertebrates show distinct expression patterns and display highly conserved amino acid sequences. While it is hypothesized that each of the muscle isoactins is specifically adapted to its respective tissue and that the minor variations among them have developmental and/or physiological relevance, the exact functional and developmental significance of these proteins remains largely unknown. In order to begin to assess these issues, we disrupted the skeletal actin gene by homologous recombination. All mice lacking skeletal actin die in the early neonatal period (day 1 to 9). These null animals appear normal at birth and can breathe, walk, and suckle, but within 4 days, they show a markedly lower body weight than normal littermates and many develop scoliosis. Null mice show a loss of glycogen and reduced brown fat that is consistent with malnutrition leading to death. Newborn skeletal muscles from null mice are similar to those of wild-type mice in size, fiber type, and ultrastructural organization. At birth, both hemizygous and homozygous null animals show an increase in cardiac and vascular actin mRNA in skeletal muscle, with no skeletal actin mRNA present in null mice. Adult hemizygous animals show an increased level of skeletal actin mRNA in hind limb muscle but no overt phenotype. Extensor digitorum longus (EDL) muscle isolated from skeletal-actin-deficient mice at day 2 to 3 showed a marked reduction in force production compared to that of control littermates, and EDL muscle from hemizygous animals displayed an intermediate force generation. Thus, while increases in cardiac and vascular smooth-muscle actin can partially compensate for the lack of skeletal actin in null mice, this is not sufficient to support adequate skeletal muscle growth and/or function.

Actins↗
PubMed2005

Back muscle strength and fatigue in healthy and chronic low back pain subjects: a comparative study of 3 assessment protocols.

OBJECTIVE: To compare the sensitivity of 3 different back test protocols in measuring differences in strength and fatigue between subjects with and without chronic low back pain (CLBP). DESIGN: Descriptive study using a repeated-measures design. SETTING: A research laboratory within a rehabilitation center. PARTICIPANTS: Eighteen healthy subjects and 13 subjects with CLBP were assessed in a single session to compare the 3 protocols. The protocols were an upright position test (UPP), a semicrouched lifting test (LIF), and the Sorensen fatigue test. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Moments of force and surface electromyography were recorded bilaterally from 4 homologous back muscles while the subjects performed static trunk extension efforts for each protocol. Fatigue was quantified by the slopes of the linear regression of electromyography time-series. RESULTS: The back muscle fatigue and strength scores did not differ significantly for the 2 subject groups for any of the 3 protocols. The electromyography fatigue indices revealed that the Sorensen fatigue test and UPP produced more fatigue in the back muscles than the LIF. CONCLUSIONS: It was impossible to specify which protocol is more sensitive to low back status because no between-group difference was observed for any of the 3 tests.

Adult↗
PubMed1994

The impact of a repeated bout of eccentric exercise on muscular strength, muscle soreness and creatine kinase.

The purpose of this study was to determine if there were any beneficial or detrimental effects regarding delayed onset muscle soreness (DOMS), serum creatine kinase (CK), and maximum concentric strength at 80% of 1-RMconc, if a bout of eccentric exercise was repeated at 48 h after an initial bout. A secondary purpose was to determine whether unaccustomed eccentrics might affect plasma cholesterol (TC). Twenty-six men were randomly assigned to a control (Group 1) or experimental group (Group 2). Both groups performed three sets (12 repetitions per set) of the eccentric phase of a chest press, at 80% of one repetition maximum (1-RMconc); Group 2 repeated this exercise 48 h later. DOMS and CK were measured before, and every 24 h for 8 days after; TC was measured before, and every 24 h for 4 days. Maximum strength during the concentric phase of a chest press (1-RMconc) was measured before and at 48-h intervals after. A repeated measures analysis of variance revealed a significant time effect (P < 0.05) for DOMS, CK and strength, but no significant difference between groups (P < 0.05). An interesting finding was the significant (P < 0.05) reduction in TC at 24, 48 and 72 h, after exercise in both groups, which we hypothesized was associated with cellular repair. From these results we concluded that when a bout of eccentrics is repeated 48 h after an initial bout, there is no change in the characteristic time-course and/or intensity of DOMS, CK or 1-RMconc.

Adult↗
PubMedDate not supplied

The therapeutic effects of alfacalcidol on bone strength, muscle metabolism and prevention of falls and fractures.

Established osteoporosis in older patients of both sexes is characterized by decoupled bone remodelling induced by sex hormone deficits and by somatopause, but also by lack of vitamin D and reduced synthesis of the D-Hormone (calcitriol; 1.25 (OH)2D) in the kidneys and bone, as well as from lack of receptors and/or receptor affinity for D-Hormone in the target organs. Parallel to the decreased bone strength a loss of muscle power occurs, together with an increase in balance disorders and an increasing risk of "intrinsic", nonsyncopal locomotoric falls. In alfacalcidol therapy, D-Hormone is provided to the body in circumvention of its own regulation, by means of which higher hormone concentrations can be achieved in the target tissues than by administration of plain vitamin D. In vitro and in vivo experiments have provided growing evidence that D-Hormone analogs tend to normalize PTH, lead to an increase in the number and activity of osteoblasts, reduce the activity of osteoclasts, and might thus normalize the "high bone turnover" in elderly osteoporotic patients ("supercoupling"). In addition, it has been shown that D-Hormone analogs are able to increase muscle power and walking distance in elderly D-Hormone deficient patients. Besides the known effect on the vertebral fracture rate, new clinical data confirm that D-Hormone analogs might reduce peripheral fractures by reducing falls. The expanded understanding of the pathogenesis of glucocorticoid- induced osteoporosis with its disturbed calcium homeostasis and the pharmacological effects of alfacalcidol, which counteract such iatrogenic bone loss, contribute to the understanding of its clinical efficacy in this most frequent form of secondary osteoporosis. Due to its recently discovered immunomodulating properties, alfacalcidol might find a slot in the management of bone loss caused by chronic inflammatory diseases or by organ transplantations. Alfacalcidol has multifactorial effects, among which the best known are its anti-bone loss and anti-fracture efficacies in postmenopausal osteoporosis. This demonstrated efficacy is related to its involvement in bone remodelling, leading to an improved bone strength. Its mode of action on muscle power, which reduces falls, is unique, differentiating this form of therapy from all other anti-osteoporotic drugs, none having demonstrated any influence on falls.

Accidental Falls↗
PubMed1998

Correlation between the M and F wave characteristics and the innervated muscle strength in spinal muscular atrophy.

The purpose of this study is to elucidate the interrelation between the M and F wave characteristics of the median nerve and the grip power in patients with spinal muscular atrophy (SMA). The SMA patients showed decreased amplitudes of the M and F waves, decreased frequency of the F wave, and an increase of the F/M ratio as compared with the normative values. The F wave frequency and the amplitudes of M and F waves, which showed a significant linear correlation with each other, became lower in accordance with the decrease of grip power. The properties of M and F waves strongly correlated with the number of surviving motor neurons which would be fewer in those severely affected by SMA.

Adolescent↗
PubMed2000

Hand-grip muscle strength, lean body mass, and plasma proteins as markers of nutritional status in patients with chronic renal failure close to start of dialysis therapy.

We studied 115 patients (69 men, 46 women) with chronic renal failure (CRF) aged younger than 70 years close to the start of dialysis therapy to assess the prevalence of malnutrition and study the relationship between various nutritional parameters in these patients. Nutritional status was classified by means of subjective global assessment. Anthropometric measurements (AMs) were performed, and hand-grip strength (HGS) was measured using the Harpenden dynamometer. Body composition, including lean body mass (LBM), was evaluated by dual-energy x-ray absorptiometry (DXA), and LBM was also estimated by means of AMs and creatinine kinetics (CK). The mean age of the patients was 52 +/- 12 years, and creatinine clearance was 9 +/- 3 mL/min. Malnutrition was seen in 53 patients (48%). As expected, malnourished patients differed in several aspects from well-nourished patients. LBM (estimated by all methods), fat mass (FM), HGS, creatinine clearance, and transthyretin and vitamin A levels were less in malnourished patients, whereas serum albumin levels did not differ. Estimates of LBM by means of DXA, AMs, and CK correlated well with each other. Although DXA and AMs gave similar mean values, LBM was an average of 8 kg less estimated by means of CK, and Bland-Altman plots showed the best agreement between AMs and DXA. HGS showed a strong correlation to LBM (regardless of method) in both men and women. Serum albumin level was not related to HGS or LBM, whereas significant correlations were found between serum albumin level and albumin losses in urine, C-reactive protein (CRP) level, and creatinine clearance. Multiple logistic regression showed that low HGS, low percentage of FM, female sex, and high serum CRP levels were independent factors associated with malnutrition, whereas serum albumin level and percentage of LBM did not reach statistical significance. In conclusion, the present study shows a high prevalence of malnutrition in predialysis patients with CRF and suggests that HGS is a reliable, inexpensive, and easy-to-perform nutritional parameter in patients with CRF. Conversely, serum albumin level seems to be a poor nutritional marker in patients with advanced CRF.

Blood Proteins↗