Isometric Knee Extension Strength Research Articles

Force control of quadriceps muscle is bilaterally impaired in subacute stroke

We tested the hypothesis that force variability and error during maintenance of submaximal isometric knee extension are greater in subacute stroke patients than in controls and are related to motor impairments. Contralesional (more-affected) and ipsilesional (less-affected) legs of 33 stroke patients with sufficiently high motor abilities (62 ± 13 yr, 16 ± 2 days postinjury) and the dominant leg of 20 controls (62 ± 10 yr) were tested in sitting position. After peak knee extension torque [maximum voluntary contraction (MVC)] was established, subjects maintained 10, 20, 30, and 50% of MVC as steady and accurate as possible for 10 s by matching voluntary force to the target level displayed on a monitor. Coefficient of variation (CV) and root-mean-square error (RMSE) were used to quantify force variability and error, respectively. The MVC was significantly smaller in the more-affected than less-affected leg, and both were significantly lower than in controls. The CV was significantly larger in the more-affected than less-affected leg at 20 and 50% MVC, whereas both were significantly larger compared with controls across all force levels. Both more-affected and less-affected legs of patients showed significantly greater RMSE than controls at 30 and 50% MVC. The CV and RMSE were not related to the Fugl-Meyer motor score or to the Rivermead Mobility Index. The CV negatively correlated with MVC in controls but only in the less-affected leg of patients. It is concluded that isometric knee extension strength and force control are bilaterally impaired soon after stroke but more so in the more-affected leg. Future studies should examine possible mechanisms and the evolution of these changes.

Testing of knee extension muscle strength: A comparison of two portable alternatives for the NIH toolbox study

Given the functional and epidemiological significance of lower extremity strength, portable, low-cost measures of lower extremity strength with robust psychometric properties are needed for clinical practice and research. The purpose of this study was to compare measures of isometric knee extension strength obtained with portable devices with criterion measures obtained with a Biodex dynamometer. Sixty-eight healthy adults from Illinois and Connecticut participated in this study. Each participant's isometric knee extension strength was tested in random order using: 1) an integrated tension load cell device (ITLCD), 2) a belt stabilized hand held dynamometer (BSHHD) and 3) a Biodex System 3 isokinetic dynamometer. Equivalence of the 3 measures was evaluated using repeated measures analysis of variance (ANOVA), Pearson correlations (r), and intraclass correlation coefficients (ICCs). Results supported good agreement between measures obtained with the ITLCD, BSHHD and Biodex ( r> 0.90, ICCs > 0.79). The ANOVA results demonstrated that measures obtained with the ITLCD and the BSHHD did not differ significantly. On average, the maximum isometric knee extension torque was underestimated by 27 N-m and 32 N-m by the ITLCD and BSHHD, respectively. Because The ITLCD was slightly better at approximating Biodex torque scores and does not depend on skills of the examiner, the ITLCD was recommended for inclusion in the motor battery of the NIH Toolbox.

The Effect of Pomegranate Juice Supplementation on Strength and Soreness after Eccentric Exercise

The purpose of this study was to determine if pomegranate juice supplementation improved the recovery of skeletal muscle strength after eccentric exercise in subjects who routinely performed resistance training. Resistance trained men (n = 17) were randomized into a crossover design with either pomegranate juice or placebo. To produce delayed onset muscle soreness, the subjects performed 3 sets of 20 unilateral eccentric elbow flexion and 6 sets of 10 unilateral eccentric knee extension exercises. Maximal isometric elbow flexion and knee extension strength and muscle soreness measurements were made at baseline and 2, 24, 48, 72, 96, and 168 hours postexercise. Elbow flexion strength was significantly higher during the 2- to 168-hour period postexercise with pomegranate juice compared with that of placebo (main treatment effect; p = 0.031). Elbow flexor muscle soreness was also significantly reduced with pomegranate juice compared with that of placebo (main treatment effect; p = 0.006) and at 48 and 72 hours postexercise (p = 0.003 and p = 0.038, respectively). Isometric strength and muscle soreness in the knee extensors were not significantly different with pomegranate juice compared with those using placebo. Supplementation with pomegranate juice attenuates weakness and reduces soreness of the elbow flexor but not of knee extensor muscles. These results indicate a mild, acute ergogenic effect of pomegranate juice in the elbow flexor muscles of resistance trained individuals after eccentric exercise.

Differential Effect of Aging on Acute Hormonal Response to Low-Volume Resistance Exercise

Age associated decrease in skeletal muscle mass and function (sarcopenia) leads to an increased risk of fall, fracture, and bedridden. Resistance exercise has been shown to be a useful intervention to increase skeletal muscle mass and strength; however, aging seems to blunt the acute hormonal response to high-intensity, high-volume resistance exercise. PURPOSE: To investigate the acute effect of a traditional resistance exercise protocol (i.e. low-volume and high-intensity) on hormonal responses in healthy young and older men. METHODS: Fourteen old men (68 ± 6.8 yrs, 64 ± 4kg) and eight young men (23 ± 1.3 yrs, 68 ± 8kg) were recruited for the study. Before the study, all subjects were assessed for muscle cross sectional area at mid-thigh, maximal knee extension and flexion strength. After taking a baseline blood sample, each subject performed a bout of resistance exercise consisting of bilateral knee extension and flexion at 70% 1-RM (3 sets of 10 reps, 3 min rest between sets). Blood samples were drawn immediately after and following exercise up to 3 hours. Blood samples were analyzed for metabolites and hormones. RESULTS: Although muscle CSA of knee extensor and flexor muscles as well as maximal isometric knee extension and flexion strength were significantly higher in young men as compared to older men(P<0.05), no significant difference in specific strength was observed between young and older subjects (3.24 ± 0.14 and 3.09 ± 0.15 Nm/cm2, P>0.1). In response to a bout of resistance exercise, GH increased significantly in young men, whereas no significant change was observed for older men (11.4 ± 6.0 and 1.7 ± 0.6 ng/ml for young and old; P<0.05). Although no significant change in testosterone or cortisol concentration was observed in either group in response to resistance exercise (P>0.1), hormonal concentrations were significantly suppressed in older men throughout the experiment (P<0.05). CONCLUSION: Although specific strength was well matched, hormonal responses to conventional low-volume, high-intensity resistance exercise protocol were significantly suppressed in older men as compared to those of young men. Further training study is warranted to investigate the relationship between age associated decline in hormonal response and capacity of muscle hypertrophy in older individuals.

Quality of Life and Functional Status After Revascularization or Conservative Treatment in Patients With Intermittent Claudication

Revascularization of patients with intermittent claudication (IC) is recommended only for selected patients who have chronic pain or disabling disease. However, improvement in the quality of life (QoL) could justify more widespread use. To determine the effect of conservative treatment and revascularization on the QoL and physical performance of selected patients with IC. This nonrandomized, parallel group, follow-up study included 83 patients with IC at Fontaine stage II. On the basis of interventional opportunities and the risks and benefits, combined with the preference of the patient, 47 patients were treated conservatively and 41 were revascularized. The patients were examined at inclusion and 3 months later. The evaluations included the QoL measure Short Form 36 (SF-36), the Walking Impairment Questionnaire (WIQ), pain-free and maximal walking distance (treadmill at 3 km/h, no incline), maximal isometric knee-extension strength and endurance, and ankle-brachial blood pressure index (ABI). At baseline, the SF-36 and WIQ scores and the ABI were significantly lower in the patients selected for revascularization. After revascularization, all dimensions of QoL and functional status increased significantly in the patients who underwent revascularisation compared with the patients treated conservatively. The difference in the change in the physical component summary of SF-36 was 29.4% (P < .001), in the total WIQ 63.6% (P = .0002), and in the pain-free and maximal walking distances 313% (P < .001) and 135% (P < .001), respectively. After adjustment for age, smoking, ABI, body mass index (BMI), and baseline values, the differences remained statistically significant. Revascularization above the knee increased QoL, functional status, and walking distance significantly in patients with moderate IC.

Changes in balance, functional performance and fall risk following whole body vibration training and vitamin D supplementation in institutionalized elderly women. A 6 month randomized controlled trial

Falls in the elderly consitute a growing public health problem. This randomized controlled trial investigated the potential benefit of 6 months of whole body vibration (WBV) training and/or vitamin D supplementation on balance, functionality and estimated fall risk in institutionalized elderly women. A total of 113 women (mean age: 79.6) were randomly assigned to either a WBV or a no-training group, receiving either a conventional dose (880 IU/d) or a high dose (1600 IU/d) of vitamin D3. The WBV group performed exercises on a vibration platform 3×/week. Balance was evaluated by computerized posturography. Functionality was assessed by 10 m walk test, Timed up and Go (TUG) performance and endurance capacity (Shuttle Walk). Fall risk was determined with the Physiological Profile Assessment. Performance on the 10 m walk test and on TUG improved over time in all groups. For none of the parameters, high-dose vitamin D resulted in a better performance than conventional dosing. The improvements in the WBV group in endurance capacity, walking at preferred speed, and TUG were significantly larger than the changes with supplementation alone. No additional benefit of WBV training could be detected on fall risk and postural control, although sway velocity and maximal isometric knee extension strength improved only in the WBV group. This trial showed that a high-dose vitamin D supplementation is not more efficient than conventional dosing in improving functionality in institutionalized elderly. WBV training on top of vitamin D supplementation provided an added benefit with regard to walking, TUG performance, and endurance capacity.

Sit-to-stand test: Performance and determinants across the age-span.

Although the validity of the sit-to-stand (STS) test as a measure of lower limb strength has been questioned, it is widely used as such among older adults. The purposes of this study were: 1) to describe five-repetition STS test (FRSTST) performance (time) by adolescents and adults and 2) to determine the relationship of isometric knee extension strength (force and torque), age, gender, weight, and stature with that performance. Participants were 111 female and 70 male (14-85 years) community-dwelling enrollees in the NIH Toolbox Assessment of Neurological and Behavioral Function. The FRSTST was conducted using a standard armless chair. Knee extension force was measured using a belt-stabilized hand-held dynamometer; knee extension torque was measured using a Biodex dynamometer. The mean times for the FRSTST ranged from 6.0 sec (20-29 years) to 10.8 sec (80-85 years). For both the entire sample and a sub-sample of participants 50-85 years, knee extension strength (r = -0.388 to -0.634), age (r = 0.561 and 0.466), and gender (r = 0.182 and 0.276) were correlated significantly with FRSTST times. In all multiple regression models, knee extension strength provided the best explanation of FRSTST performance, but age contributed as well. Bodyweight and stature were less consistent in explaining FRSTST performance. Gender did not add to the explanation of FRSTST performance. Our findings suggest, therefore, that FRSTST time reflects lower limb strength, but that performance should be interpreted in light of age and other factors.

Randomized double-blind placebo-controlled crossover study of caffeine in patients with intermittent claudication

Intermittent claudication is a disabling symptom of peripheral arterial disease for which few medical treatments are available. This study investigated the effect of caffeine on physical capacity in patients with intermittent claudication. This randomized double-blind placebo-controlled crossover study included 88 patients recruited by surgeons from outpatient clinics. The participants abstained from caffeine for 48 h before each test and then received either a placebo or oral caffeine (6 mg/kg). After 75 min, pain-free and maximal walking distance on a treadmill, perceived pain, reaction times, postural stability, maximal isometric knee extension strength, submaximal knee extension endurance and cognitive function were measured. The analysis was by intention to treat. Caffeine increased the pain-free walking distance by 20.0 (95 per cent confidence interval 3.7 to 38.8) per cent (P = 0.014), maximal walking distance by 26.6 (12.1 to 43.0) per cent (P < 0.001), muscle strength by 9.8 (3.0 to 17.0) per cent (P = 0.005) and endurance by 21.4 (1.2 to 45.7) per cent (P = 0.004). However, postural stability was reduced significantly, by 22.1 (11.7 to 33.4) per cent with eyes open (P < 0.001) and by 21.8 (7.6 to 37.8) per cent with eyes closed (P = 0.002). Neither reaction time nor cognition was affected. In patients with moderate intermittent claudication, caffeine increased walking distance, maximal strength and endurance, but affected balance adversely.

Assessment of Leg Muscle Power Using a Low Step Height Stair Test

A stair-climbing power test using an ordinary stair is an inexpensive, practical test that is simple to perform. An individual's lower extremity power is a critical element associated with both mobility and the activities of daily living, while it is also a key determinant of independence for elderly people. However, no report has so far described the efficacy of lower height step stairs to assess the leg muscle power. PURPOSE: To determine the usefulness of the low step height stair-climbing power (LSSCP) test by comparing the results obtained from the LSSCP test with those from a leg power test in young people. METHODS: The subjects of this study included healthy young males (N=17, 20.8±2.9 yrs) and females (N=19, 20.5±2.6 yrs). The LSSCP was measured using lower height step stairs (9 cm step height, 10-stair flights, 72 cm total height). The time spent in stair climbing was measured by a contact mat connected with an electronic timer. The circuit is automatically opened at take off and closed when the subject touches the mat. The subjects were instructed to ascend the stairs as fast as they could. The stair-climbing power was then calculated with the body mass, the time spent in stair climbing, the vertical height travelled, and the gravitational acceleration. The bilateral leg extensor power (LEP) was measured using an isotonic leg power system in a sitting position. The isometric knee extension strength (KES) was measured on each side of the knee using a specially designed dynamometer. Test-test reliability was determined from participants, with the use of the intraclass correlation coefficient (ICC) model. RESULTS: The LSSCP was 338.7±48.3 watts (mean ± SD) for males and 246.1±43.0 watts for females. The LEP was 1411.7±448.7 watts (mean ± SD) for males and 718.5 ± 203.2 watts for females. The LSSCP significantly correlated with both the LEP (both p<0.05) and the KES (both p<0.05) in males and females, respectively. The ICC value of LSSCP was 0.81 for males and 0.95 for females, indicating excellent reliability. CONCLUSIONS: From a practical viewpoint as a field test, the LSSCP test was therefore found to be useful for accurately assessing the functional leg power levels.

Low-intensity Walk Training With Blood-Flow Reduction Concurrently Improved VO2peak and Muscular Function In Elderly Women

Low-intensity walk training with leg blood flow reduction (BFR-walk) has been shown to elicit a significant increase in skeletal muscle size and strength, and may also improve in aerobic capacity in young subjects. However, it is unknown if BFR-walk training would improve muscular function/ hypertrophy and aerobic capacity in older subjects. PURPOSE: To investigate the effects of BFR-walk training on MRI-measured muscle size and function as well as peak oxygen uptake (VO2peak) in the elderly women. METHODS: 18 elderly women (age, 65.7±4.3 yrs; BMI, 22.8±2.8 kg/m2) were divided into two walk training groups: BFR-walk (n=10) and control walk (n=8, CON-walk). Both groups performed 20 min treadmill walking at an exercise intensity of 45% of heart rate reserve, 4 days per week for 10 weeks. The BFR-walk group wore pressure cuff belts (5 cm wide) on the proximal part of both upper legs during training (external compression: 160-200 mmHg). MRI-measured mid-thigh muscle cross-sectional area (CSA), and also maximal isometric and isokinetic (30 and 180 deg/sec) knee extension and flexion strength (Biodex system-3) were measured before and after training. VO2peak was estimated by fitting age-predicted maximum heart rate (HRmax) value into a linear regression equation computed from the individual VO2 and HR values obtained during a graded cycle exercise test (until ∼80% HRmax). Functional ability was assessed by the Timed Up and Go test (time to walk both ways from the chair to 2.4m marker, UG-Test) and the Chair Stand test (repeated chair stand in 30 seconds, CS-Test). RESULTS: Maximum isometric (6%) and isokinetic (3∼22%) strength and thigh muscle CSA (3.3%) increased in the BFR-walk group, but not in the CON-walk group. VO2peak also increased (P<0.05), but only in the BFR-walk group (pre, 25.0±4.0; post, 27.5±5.2 ml/kg/min), however, there was a trend for improvement in the CON-walk group (pre, 26.3±3.1; post, 29.1±3.9 ml/kg/min). Similarly, functional ability improved (P<0.01) only in the BFR-walk group (10.7% for UG-Test, 20.5% for CS-Test). CONCLUSION: Our results suggest that 40-50% intensity BFR-walk training improves both muscle hypertrophy and aerobic capacity concurrently in the elderly. The improvements of functional ability were probably due in part to the increases in muscular function.

Association of body composition and muscle function with hip geometry and BMD in premenopausal women

Background: Muscle mass and function are related to bone mineral density (BMD) but associations with bone geometry and BMD at differently loaded hip regions are less well-known.Aim: To examine associations of muscle strength, maximal impact forces and body composition with hip bone density and geometry.Subjects and methods: In 88 sedentary, premenopausal women (32.6 ± 8.5 years), fat-free mass (FFM), isometric knee extension strength (IKES), and peak landing ground reaction force (GRF) were measured. BMD at the proximal femur and sub-regions, section modulus (Z), and cross-sectional area (CSA) were estimated using dual X-ray absorptiometry.Results: BMD at hip sites was significantly associated with body mass, IKES, GRF and FFM (r = 0.31–0.50) whilst Z and CSA were correlated with FFM (r = 0.67 and 0.62, respectively). In multivariate models, variables explaining most variance were body mass for lower neck and shaft BMD (25% and 17%, respectively), IKES for upper neck BMD (21%), GRF for trochanter (19%) and total hip BMD (18%) and FFM for femoral neck Z, CSA and BMD (54%, 38% and 20%, respectively).Conclusion: BMD at superolateral hip sites was most strongly related to muscle function and maximal impact forces, BMD at inferiomedial hip sites to body mass, and hip geometry to FFM.

Mobility performance and its sensory, psychomotor and musculoskeletal determinants from age 75 to age 80

Prospective studies on the simultaneous effects of multiple determinants on objectively assessed mobility are few. The aim of this study was to analyse mobility performance, its stability and sensory, psychomotor and musculoskeletal determinants in an older population from age 75 to age 80. Sixty-three men and 121 women aged 75 participated at baseline and, five years later, in the follow-up phase of this population-based prospective study. Maximal walking speed and step-mounting height were assessed at baseline and follow-up. Maximal isometric knee extension strength, standing balance on force platform, reaction time, visual acuity and limitations in range of motion (ROM) of hips and knees were assessed at baseline. Structural equation modeling was used to analyse the associations. The stability of mobility performance from baseline to the five-year follow- up was high (coefficient 0.80 in men, 0.78 in women). In men, knee extension strength, standing balance, ROM limitations and visual acuity explained 69% of the variation in mobility performance at baseline and, indirectly, 59% of that variation at follow-up. Among women, knee extension strength, standing balance, visual acuity and reaction time explained 52% of the variation of mobility performance at baseline and, indirectly, 30% at the five-year follow-up. Results indicate that the predictive effects of sensory, psychomotor and musculoskeletal functions on mobility performance extend over five years in older people. In seeking to prevent mobility limitations, vision, reaction time and lower extremity ROM need to be targeted, in addition to muscle strength and balance.

An Examination of the Relationships Among Myosin Heavy Chain Isoform Content, Isometric Strength, and Mechanomyographic Median Frequency

The purpose of the present study was to determine if the combination of isometric knee extension strength and mechanomyographic (MMG) median frequency (MDF) could be used to estimate the percent (%) myosin heavy chain (MHC) Type II isoform content of the vastus lateralis. Five resistance-trained (mean +/- SD age = 23.2 +/- 3.7 years) and 5 aerobically trained (mean +/- SD age = 32.6 +/- 5.2 years) men volunteered to perform a 6-second isometric maximum voluntary contraction (MVC) of the dominant knee extensors at a joint angle of 90 degrees between the thigh and leg. During the isometric MVC, the surface MMG signal was detected from the vastus lateralis, and the MDF was calculated with the discrete Fourier transform. Following the isometric MVC and MMG measurements, muscle biopsies were taken from the vastus lateralis and analyzed for % MHC Type II isoform content. The results showed that neither isometric knee extension strength nor MMG MDF alone was significantly correlated with the % MHC Type II isoform content. The combination of isometric knee extension strength and MMG MDF, however, explained a significant proportion (i.e., 59.8%) of the variance in % MHC Type II isoform content, with a multiple correlation of R = 0.773 and a standard error of the estimate (SEE) of 15.4%. These findings indicated that a simple, time-efficient, and noninvasive test that simultaneously measures isometric strength and MMG MDF could be useful for estimating the % MHC Type II isoform content in well-trained men.

Baseline Lower Extremity Strength and Subsequent Decline in Functional Performance at 6‐Year Follow‐Up in Persons with Lower Extremity Peripheral Arterial Disease

To evaluate associations between baseline lower extremity strength and decline in functional performance over 6 years of follow-up in men and women with lower extremity peripheral arterial disease (PAD). Prospective observational study. Three Chicago-area hospitals. Three hundred seventy-four men and women with PAD. Baseline isometric hip extension, hip flexion, knee flexion, and knee extension strength were measured using a musculoskeletal fitness evaluation chair. Usual and fastest-paced 4-m walking speed, 6-minute walk, and Short Physical Performance Battery (SPPB) were assessed at baseline and annually thereafter. Analyses were adjusted for age, sex, race, ankle-brachial index (ABI), comorbidities, and other confounders. In women with PAD, weaker baseline hip and knee flexion strength were associated with faster average annual decline in usual-pace 4-m walking speed (P trend <.001 and .02, respectively) and SPPB (P trend=.02 and .01, respectively). In women, weaker hip extension strength was associated with faster decline in usual-pace 4-m walking speed and SPPB (P trend=.01 and <.01, respectively). There were no significant associations between baseline strength and decline in 6-minute walk in women. There were no significant associations between any baseline strength measure and functional decline in men. Weaker baseline leg strength is associated with faster functional decline in nonendurance measures of functional performance in women with PAD but not in men with PAD.

Raloxifene and body composition and muscle strength in postmenopausal women: a randomized, double-blind, placebo-controlled trial

To compare the effects of raloxifene and placebo on body composition and muscle strength. Randomized, double-blind, placebo-controlled trial involving 198 healthy women aged 70 years or older conducted between July 2003 and January 2008 at the University Medical Centre, Utrecht, The Netherlands. Participants were randomly assigned to receive raloxifene 60 mg or placebo daily for 12 months. Measurements were taken at baseline, 3, 6, and 12 months, and change from baseline was calculated. Main outcome measures were body composition (bioelectrical impedance analysis), muscle strength, and muscle power (maximum voluntary isometric knee extension strength, explosive leg extensor power, and handgrip strength). At 12 months, the body composition of women taking raloxifene was significantly different from that of women taking placebo: fat-free mass (FFM) had increased by a mean of 0.83 (2.4) kg in the raloxifene group versus 0.03 (1.5) kg in the placebo group (P=0.05), and total body water had increased by a mean of 0.6 (1.8) litres in the raloxifene group versus a decrease of 0.06 (1.1) litres in the placebo group (P=0.02). Muscle strength and power were not significantly different. Raloxifene significantly changed body composition (increased FFM; increased water content) compared with placebo in postmenopausal women.

Comparing Eccentric Resistance Exercise in Prostate Cancer Survivors On and Off Hormone Therapy: A Pilot Study

To determine the feasibility of an eccentric resistance exercise training protocol in men with prostate cancer and to assess whether men with prostate cancer who are receiving androgen deprivation therapy (ADT) have a blunted effect from the training as compared with prostate cancer survivors not receiving ADT. Prospective pilot study. Academic medical center. Sixteen men with prostate cancer (Gleason scores 3+3 to 4+4) were initially enrolled. Ten men (mean age 66, range 48-86) completed the study, 5 were currently receiving ADT. Analysis was performed on these 10 men. Subjects were evaluated at baseline. All men underwent a 12-week resistance exercise training protocol using a recumbent, high-force eccentric, leg cycle ergometer 3 times per week at a "somewhat hard" perceived exertion for 12 to 15 minutes. Preexercise and postexercise training changes were examined within and between groups. Quadriceps muscle volume (magnetic resonance imaging), isometric knee extension strength, functional mobility (Timed Up and Go Test [TUG] and 6-minute walk [6MW]), health-related quality of life (FACT-P), and fatigue (FACIT-fatigue scale). The ADT group demonstrated significant within-group improvements in the 6MW (P = .01) and isometric knee extension strength (P = .03). This group also demonstrated a clinically relevant change in the FACT-P; however, this did not meet statistical significance. The non-ADT group demonstrated significant within-group improvements in the physical subscale of the FACT-P (P = .03) and an increase in muscle volume (P = .04). Their improvements in the TUG approached significance (P = .08). No between-group differences existed. Eccentric resistance exercise was well tolerated, and both groups derived some benefits in strength and functional mobility. Men receiving ADT did not appear to have a blunted response to the exercise as compared with prostate cancer survivors not receiving ADT.

Knee Extension and Flexion Weakness in People With Knee Osteoarthritis: Is Antagonist Cocontraction a Factor?

Controlled laboratory study, cross-sectional data. To investigate isometric knee flexion and extension strength, failure of voluntary muscle activation, and antagonist cocontraction of subjects with knee osteoarthritis (OA) compared with age-matched asymptomatic control subjects. Quadriceps weakness is a common impairment in individuals with knee OA. Disuse atrophy, failure of voluntary muscle activation, and antagonist muscle cocontraction are thought to be possible mechanisms underlying this weakness; but antagonist cocontraction has not been examined during testing requiring maximum voluntary isometric contraction. Fifty-four subjects with knee OA (mean +/- SD age, 65.6 +/- 7.6 years) and 27 similarly aged control subjects (age, 64.2 +/- 5.1 years) were recruited for this study. Isometric knee flexion and extension strength were measured, and electromyographic data were recorded, from 7 muscles crossing the knee and used to calculate cocontraction ratios during maximal effort knee flexion and extension trials. The burst superimposition technique was used to measure failure of voluntary activation. Knee extension strength of subjects with knee OA (mean +/- SD, 115.9 +/- 6.7 Nm) was significantly lower than for those in the control group (152.3 +/- 9.6 Nm). No significant between-group difference was found for failure of voluntary muscle activation, or the cocontraction ratios during maximum effort knee flexion or extension. These results demonstrate that the reduction in isometric extension strength, measured with a 90 degrees knee flexion angle, in subjects with knee OA is not associated with increased antagonist cocontraction.

Assessment Of Leg Muscle Power Using A Stair-climbing Power Test In Community-dwelling Elderly People

A stair-climbing power test (SCPT) is an inexpensive, practical test that is simple to perform. An individual's lower extremity power is a critical element regarding both mobility and the activities of daily living, while it is also a key determinant of independence for elderly people. PURPOSE: To determine the usefulness of the SCPT, a modification of the Margaria stair-climbing power test, by comparing the results obtained from the SCPT with those from a leg power test in community-dwelling elderly people. METHODS: The subjects of this study consisted of physically-independent elderly men (N=19, aged 75+/-6 yrs) and women (N=18, aged 77+/-6 yrs). The stair-climbing power was measured using ordinary stairs (17.5cm step height, 6-stair flights, 105 cm total height). The time spent in stair climbing was measured by a stopwatch. The subjects were instructed to ascend the stairs as fast as they could. The stair-climbing power was then calculated with the body mass, the time spent in stair climbing, the vertical height travelled, and the gravitational acceleration. The bilateral leg extensor power (LEP) was measured using an isotonic leg power system (Combi, Anaero Press 3500, Japan) in a sitting position. The isometric knee extension strength was measured on each side of the knee using a specially designed dynamometer (Yagami, Japan). RESULTS: The stair-climbing power was 297.6+/-60.3 watts (mean +/- SD) for men and 199.1 +/-60.6 watts for women. LEP was 768.2+/-324.6 watts for men and 361.6+/-152.8 watts for women. The knee extension strength was 39.4 +/-9.2 kg for men and 24.0 +/-6.8 kg for women. The stair-climbing power correlated closely with both the leg extensor power (r=0.557, p<0.05 in men and r=0.541, p<0.05 in women) and with the knee extension strength (r=0.566, p<0.05 in men and r=0.657, p<0.05 in women). CONCLUSIONS: From a practical viewpoint as a field test, the SCPT was found to be useful for assessing the functional leg power levels in physically-independent, ambulatory elderly people.

Creatine supplementation enhances muscle force recovery after eccentrically-induced muscle damage in healthy individuals

BackgroundEccentric exercise-induced damage leads to reductions in muscle force, increased soreness, and impaired muscle function. Creatine monohydrate's (Cr) ergogenic potential is well established; however few studies have directly examined the effects of Cr supplementation on recovery after damage. We examined the effects of Cr supplementation on muscle proteins and force recovery after eccentrically-induced muscle damage in healthy individuals.MethodsFourteen untrained male participants (22.1 ± 2.3 yrs, 173 ± 7.7 cm, 76.2 ± 9.3 kg) were randomly separated into 2 supplement groups: i) Cr and carbohydrate (Cr-CHO; n = 7); or ii) carbohydrate (CHO; n = 7). Participants consumed their supplement for a period of 5 days prior to, and 14 days following a resistance exercise session. Participants performed 4 sets of 10 eccentric-only repetitions at 120% of their maximum concentric 1-RM on the leg press, leg extension and leg flexion exercise machine. Plasma creatine kinase (CK) and lactate dehydrogenase (LDH) activity were assessed as relevant blood markers of muscle damage. Muscle strength was examined by voluntary isokinetic knee extension using a Cybex dynamometer. Data were analyzed using repeated measures ANOVA with an alpha of 0.05.ResultsThe Cr-supplemented group had significantly greater isokinetic (10% higher) and isometric (21% higher) knee extension strength during recovery from exercise-induced muscle damage. Furthermore, plasma CK activity was significantly lower (by an average of 84%) after 48 hrs (P < 0.01), 72 hrs (P < 0.001), 96 hrs (P < 0.0001), and 7 days (P < 0.001) recovery in the Cr-supplemented group.ConclusionThe major finding of this investigation was a significant improvement in the rate of recovery of knee extensor muscle function after Cr supplementation following injury.

Skeletal muscle size and strength are increased following walk training with restricted leg muscle blood flow: implications for training duration and frequency

The purpose of this study was to investigate once-daily walk training with restricted leg blood flow (KAATSU) on thigh muscle size and strength. Twelve young men performed walk training: KAATSU-walk training (n=6) and control (no KAATSU-walk; n=6). Training was conducted once daily, 6 days per week, for 3 weeks. Treadmill walking (50 m/min) was performed for 5 sets of 2-min bouts interspersed with 1-min rest periods. The KAATSU-walk group wore pressure cuff belts (5 cm wide) on both legs during training, with incremental increases in external compression starting at 160 mmHg and ending at 230 mmHg. Thigh muscle volume and isometric and 1-repetition maximal (1-RM) strength were measured before and after training. In the KAATSU-walk group, quadriceps and hamstrings muscle volume increased 1.7 and 2.4% (both P<0.05), respectively, following training. One-RM leg press and leg curl increased 7.3 and 8.6% (both P<0.05), respectively, following KAATSU-walk training. Also, isometric knee extension strength (4.4%; P<0.01), but not knee flexion strength (1.7%), increased following KAATSU-walk training. There were no changes in muscle volume or strength in the control-walk group. These results confirm previous work showing that the combination of slow walk training and leg muscle blood flow restriction induces muscle hypertrophy and strength gains. However, the magnitude of change in muscle mass and strength following once-daily KAATSU-walk training was approximately one-half that reported for twice-daily KAATSU-walk training over a 3-week period. These results in combination with previous observations lead to the conclusion that the impact of KAATSU-walk training on muscle size and strength is related to an ability to accomplish a high number of training bouts within a compressed training duration. Second, frequency-dependent muscle enlargement appears to be associated with KAATSU-walk training.