Isometric Elbow Flexion Force Research Articles

Estimation of the muscle force by perineural intramuscular electrical stimulation in healthy volunteers.

The present study aimed to evaluate the elbow flexor force induced by perineural intramuscular stimulation compared with surface electrical stimulation (ES) and maximal voluntary contraction. Thirty nondominant arms of healthy volunteers were evaluated. Isometric elbow flexion force was evaluated using a surface electrode stimulation at the biceps brachii muscle, a perineural intramuscular stimulation around the musculocutaneous nerve, and maximum voluntary contraction. The elbow flexion force was measured at the wrist volar area in a 90° elbow flexion posture, fixed with a rigid elbow orthosis. Pain and discomfort associated with ES were evaluated using a numeric rating scale. The mean maximum elbow flexion force was 16.6 ± 4.1 kgf via voluntary contraction. The mean elbow flexion force by ES was 2.9 ± 2.0 kgf, stimulation intensity was 24.8 ± 5.5 mA, and the numeric rating scale was 5.0 ± 2.5 via surface electrode stimulation and 3.1 ± 2.0 kgf, 5.0 mA, and 3.8 ± 1.9 via perineural stimulation, respectively. ES provides 16% to 18% of the maximal voluntary contraction force in elbow flexion, which corresponds to a fair grade of muscle force. Perineural intramuscular stimulation can generate an equivocal contraction force with less discomfort in elbow flexion than surface electrode stimulation.

The Impact Of Increasing Blood Flow Restriction Pressure During Already Occlusive Contractions.

Restricting blood flow during resistance exercise reduces the number of repetitions required to see adaptations, with higher blood flow restriction pressures resulting in greater muscle fatigue when sub-occlusive pressures are applied. The augmented fatigue is thought to be related to alterations in blood flow, but the impact of increasing the restriction pressure during completely occlusive contractions remains unknown and may provide information on alternative mechanisms responsible for fatigue. PURPOSE: To determine whether increasing the blood flow restriction pressure reduces local muscular endurance and increases discomfort when the contractions are already occlusive. We also the examined potential changes in force steadiness. METHODS: Twenty-two individuals performed a contraction at 30% of maximal isometric elbow flexion force for as long as possible. One arm completed the contraction with 100% of arterial occlusion pressure applied, while the other arm had 150% of arterial occlusion pressure applied. At the end of the protocol individuals were asked to rate their perceived discomfort. A Bayesian paired samples t-test was used to compare differences in time to task failure, average force output, and force steadiness and a Wilcoxon signed rank test was performed to compare differences in discomfort between high and low pressure conditions. RESULTS: Individuals had a longer time to task failure when performing the 100% arterial occlusion condition as compared to the 150% arterial occlusion pressure condition (time to task failure = 82.4 vs. 70.8 seconds; BF10 = 5.77). There were no differences in discomfort between the 100% and 150% conditions (median discomfort = 5.5 vs. 6; p = 0.243) nor were there differences in force steadiness (standard deviation of force output 1.09 vs. 1.06 %; BF10 = 0.29). CONCLUSIONS: The results of the present study suggest that, even when contractions are already occlusive, increasing the restriction pressure reduces local muscle endurance but does not impact discomfort or force steadiness. This provides an indication that mechanisms other than the direct alteration of blood flow are contributing to the increased fatigue with added restrictive pressure. Future studies are needed to examine neural mechanisms that may explain this finding.

Force-velocity relationship profile of elbow flexors in male gymnasts.

BackgroundThe theoretical maximum force (F0), velocity (V0), and power (Pmax) of athletes calculated from the relationship between force and velocity (F-V relationship) and the slope of the F-V relationship, reflect their competitive and training activity profiles. Evaluating the F-V relationship of athletes facilitates categorizing the profiles of dynamic muscle functions in relation to long-term sport-specific training. For gymnastics, however, no studies have tried to examine the profiles of F-V relation and power output for upper limb muscles in relation to the muscularity, while the use of the upper extremities in this sport is very unique as described earlier.PurposeIt was hypothesized that the F-V relationship of the elbow flexion in gymnasts might be characterized by low capacity for generating explosive force, notably in terms of the force normalized to muscle size.MethodsThe F0, V0, and Pmax derived from the force-velocity relationship during explosive elbow flexion against six different loads (unloaded condition, 15, 30, 45, 60, and 75% of maximal voluntary isometric elbow flexion force (MVFEF)) for 16 gymnasts (GYM) and 22 judo athletes (JD). F0 and Pmax were expressed as values relative to the cross-sectional area index (CSAindex) of elbow flexors (F0/CSAindex and Pmax/CSAindex, respectively), which was calculated from muscle thickness in the anterior upper arm. The electromyogram (EMG) activities of the biceps brachii (BB) during the maximal isometric and dynamic tasks were also determined.ResultsThere were no significant differences in CSAindex of elbow flexors between GYM and JD. MVFEF/CSAindex for GYM was significantly lower than that for JD. Force was linearly associated with velocity in the dynamic elbow flexion for all the participants (r = − 0.997 to −0.905 for GYM, r = − 0.998 to −0.840 for JD). F0, F0/ CSAindex, V0, Pmax, Pmax/CSAindex, and MVFEF were significantly lower in GYM than in JD. The activity levels of BB during the dynamic tasks tended to be lower in GYM than in JD at load of <45%MVC.ConclusionGymnasts cannot generate explosive elbow flexion force corresponding to their muscle size. This may be due to low neuromuscular activities during the maximal dynamic tasks against relatively low loads.

Effects of Aerobic and Resistance Exercise in Older Adults With Rheumatoid Arthritis: A Randomized Controlled Trial.

ObjectiveTo evaluate the effect of a moderate‐to‐high–intensity, aerobic and resistance exercise with person‐centered guidance in older adults with rheumatoid arthritis (RA), through a randomized controlled multicenter trial.MethodsOlder adults (ages 65–75 years) with RA (n = 74) were randomized to either a 20‐week exercise intervention at a gym (n = 36) or to home‐based exercise of light intensity (n = 38). Assessments were performed at baseline, at 20 weeks, and at 12 months. The primary outcome was the difference in the Health Assessment Questionnaire disability index (HAQ DI) score, and the secondary outcomes were the differences in physical fitness assessed by a cardiopulmonary exercise test, an endurance test, the timed up and go test, the sit to stand test, and an isometric elbow flexion force measurement.ResultsNo significant differences between the groups were found for the primary outcome, HAQ DI score. Within the intervention group there was a significant improvement in the HAQ DI score when compared to baseline (P = 0.022). Aerobic capacity (P < 0.001) and 3 of 4 additional performance‐based tests of endurance and strength significantly improved (P < 0.05) in the intervention group when compared to the control group. In the intervention group, 71% of patients rated their health as much or very much improved compared to 24% of patients in the control group (P < 0.001). At the 12‐month follow‐up, there were no significant differences in change between the 2 groups on the HAQ DI score. A significant between‐group difference was found for change in an endurance test (P = 0.022).ConclusionAerobic and resistance exercise with person‐centered guidance improved physical fitness in terms of aerobic capacity, endurance, and strength in older adults with RA.

Controlled, cross-sectional, multi-center study of physical capacity and associated factors in women with fibromyalgia

BackgroundHealth and physical capacity are commonly associated with disease, age, and socioeconomic factors. The primary objective of this study was to investigate the degree to which physical capacity, defined as muscle strength and walking ability, is decreased in women with fibromyalgia (FM), as compared to healthy women, who are matched for age and level of education. The secondary aim was to investigate whether muscle strength and walking ability are associated with age, symptom duration, activity limitations and, Body Mass Index (BMI) in women with FM and control subjects.MethodsThis controlled, cross-sectional, multi-center study comprised 118 women with FM and 93 age- and education-level-matched healthy women. The outcome measures were isometric knee-extension force, isometric elbow-flexion force, isometric hand-grip force, and walking ability. Differences between the groups were calculated, and for the women with FM analyses of correlations between the measures of physical capacity and variables were performed.ResultsThe women with FM showed 20% (p < 0.001) lower isometric knee-extension force, 36% (p < 0.001) lower isometric elbow-flexion force, 34% (p < 0.001) lower isometric hand-grip force, and 16% lower walking ability (p < 0.001), as compared to the healthy controls. All measures of muscle strength in women with FM showed significant weak to moderate relationship to symptom duration (rs = − 0.23–0.32) and walking ability (rs = 0.25–0.36). Isometric knee-extension force correlated with activity limitations, as measured using the SF-36 Physical function subscale (rs=0.23, p = 0.011).ConclusionsPhysical capacity was considerably decreased in the women with FM, as compared to the age- and education-level-matched control group. All measures of physical capacity showed a significant association with symptom duration. Knee-extension force and walking ability were significantly associated with activity limitations, age, and BMI. It seems important to address this problem and to target interventions to prevent decline in muscle strength. Assessments of muscle strength and walking ability are easy to administer and should be routinely carried out in the clinical setting for women with FM.Trial registrationClinicalTrials.gov identification number: NCT01226784, Oct 21, 2010.

Variability, frequency composition, and temporal regularity of submaximal isometric elbow flexion force in subacute stroke.

We compared variability, frequency composition, and temporal regularity of submaximal isometric elbow flexion force at 10, 20, 35, and 50% of peak torque between 34 stroke subjects (5-48days post-onset, both arms) and 24 age-matched controls (dominant arm), and related the findings in the paretic arm to motor impairment. Force variability was quantified by the coefficient of variation (CV), frequency composition by the median frequency and relative power in 0-3-, 4-6-, and 8-12-Hz bands, and regularity by the sample entropy (SampEn). The paretic elbow flexors showed significantly increased CV and relative power in 0-3-Hz band, decreased power in 4-6- and 8-12-Hz bands, and decreased SampEn compared to both the non-paretic and control elbow flexors (P≤0.0002), with no differences between the latter two (P≥0.012). With increasing contraction intensity, the relative power in different frequency bands was insufficiently modulated and SampEn excessively decreased in the paretic elbow flexors. Also, CV in the paretic elbow flexors was non-linearly related to the relative power in different frequency bands and SampEn across contraction intensities (rectangular hyperbolic fit, 0.21≤R 2≤0.55, P≤0.006), whereas no force parameter correlated with arm motor impairment. These results largely extend our previous findings in the paretic knee extensors to the elbow flexors in subacute stroke, except that here force variability was increased only in the paretic elbow flexors and modulation of force regularity with increasing contraction intensity showed the opposite, decreasing pattern, which was considerably exaggerated in the paretic muscles.

Effects of mate tea consumption on muscle strength and oxidative stress markers after eccentric exercise

Dietary phytochemical supplementation may improve muscle recovery from exercise. In this study, we investigated the effect of mate tea (MT) consumption - a phenol-rich beverage - on muscle strength and oxidative stress biomarkers after eccentric exercise. In a randomised, cross-over design, twelve men were assigned to drink either MT or water (control; CON) for 11 d. On the 8th day, subjects performed three sets of twenty maximal eccentric elbow flexion exercises. Maximal isometric elbow flexion force was measured before and at 0, 24, 48 and 72 h after exercise. Blood samples were obtained before and at 24, 48 and 72 h after exercise and analysed for total phenolics, GSH, GSSG, GSH:GSSG ratio and lipid hydroperoxides (LOOH). After eccentric exercise, muscle strength was significantly reduced over time, regardless of treatments. However, MT improved the rate of strength recovery by 8·6 % on the 1st day after exercise (P<0·05). Plasma concentration of total phenolic compounds was higher in MT than in CON at all time points (P<0·05) but decreased significantly at 72 h after exercise in both trials (P<0·05). Blood levels of GSH were significantly decreased at 48 and 72 h after exercise in CON (P<0·05) but did not change over time in MT. No significant changes were observed for GSSG, GSH:GSSG ratio and LOOH levels. MT intake did not influence muscle strength at all time points assessed but hastened the strength recovery over 24 h after exercise. MT also favoured the concentration of blood antioxidant compounds.

Resistance exercise improves muscle strength, health status and pain intensity in fibromyalgia--a randomized controlled trial.

IntroductionFibromyalgia (FM) is characterized by persistent widespread pain, increased pain sensitivity and tenderness. Muscle strength in women with FM is reduced compared to healthy women. The aim of this study was to examine the effects of a progressive resistance exercise program on muscle strength, health status, and current pain intensity in women with FM.MethodsA total of 130 women with FM (age 22–64 years, symptom duration 0–35 years) were included in this assessor-blinded randomized controlled multi-center trial examining the effects of progressive resistance group exercise compared with an active control group. A person-centred model of exercise was used to support the participants’ self-confidence for management of exercise because of known risks of activity-induced pain in FM. The intervention was performed twice a week for 15 weeks and was supervised by experienced physiotherapists. Primary outcome measure was isometric knee-extension force (Steve Strong®), secondary outcome measures were health status (FIQ total score), current pain intensity (VAS), 6MWT, isometric elbow-flexion force, hand-grip force, health related quality of life, pain disability, pain acceptance, fear avoidance beliefs, and patient global impression of change (PGIC). Outcomes were assessed at baseline and immediately after the intervention. Long-term follow up comprised the self-reported questionnaires only and was conducted after 13–18 months. Between-group and within-group differences were calculated using non-parametric statistics.ResultsSignificant improvements were found for isometric knee-extension force (p = 0.010), health status (p = 0.038), current pain intensity (p = 0.033), 6MWT (p = 0.003), isometric elbow flexion force (p = 0.02), pain disability (p = 0.005), and pain acceptance (p = 0.043) in the resistance exercise group (n = 56) when compared to the control group (n = 49). PGIC differed significantly (p = 0.001) in favor of the resistance exercise group at post-treatment examinations. No significant differences between the resistance exercise group and the active control group were found regarding change in self-reported questionnaires from baseline to 13–18 months.ConclusionsPerson-centered progressive resistance exercise was found to be a feasible mode of exercise for women with FM, improving muscle strength, health status, and current pain intensity when assessed immediately after the intervention.Trial registrationClinicalTrials.gov identification number: NCT01226784, Oct 21, 2010.

Spasticity, weakness, force variability, and sustained spontaneous motor unit discharges of resting spastic–paretic biceps brachii muscles in chronic stroke

The purpose of our study was to examine relations among spasticity, weakness, force variability, and sustained spontaneous motor unit discharges in spastic-paretic biceps brachii muscles in chronic stroke. Ten chronic stroke subjects produced submaximal isometric elbow flexion force on impaired and non-impaired sides. Intramuscular EMG (iEMG) was recorded from biceps and triceps brachii muscles. We observed sustained spontaneous motor unit discharges in resting biceps on iEMG. Spontaneous discharges increased after voluntary activation only on the impaired side. The impaired side had greater matching errors and greater fluctuations in isometric force. Spontaneous discharges were not related functionally to spasticity, force variability, or weakness. However, greater strength on the impaired side correlated with less force variability. Weakness rather than spasticity is a main factor interfering with voluntary force control in paretic-spastic biceps brachii muscles in chronic stroke.

Muscle Stiffness Quantification With Novel Ultrasound Elastography Imaging During Fatiguing Contraction

It is unknown how muscle stiffness changes during muscle fatigue with sustained contraction. Recent development of novel ultrasound elastography has opened the possibility for objectively quantifying muscle stiffness by imaging the internal propagation of muscle vibration with ultrafast ultrasound technology (Shinohara et al. Muscle & Nerve, 2010). PURPOSE: To examine the changes in muscle stiffness during sustained fatiguing contractions with the novel ultrasound elastography. METHODS: To induce fatigue in the biceps brachii muscle, six healthy young adults sustained isometric elbow flexion force corresponding to 30% of maximal voluntary contraction until they can no longer maintain it. The elbow joint angle was fixed at 90 degrees and the wrist was in the neutral position. Ultrasound elastography images of the biceps brachii muscle were obtained during the task. The alignment of ultrasound probe was alternated between longitudinal and transverse to the biceps brachii muscle. From these images, muscle stiffness in the biceps brachii was quantified in the units of kPa. Measurements in the longitudinal direction were used to assess changes in muscle stiffness due to fatigue of the muscle contractile elements whereas those in the transverse direction were used to assess changes in muscle stiffness due to factors that were not directly related to muscle contractile elements, such as a potential increase in muscle temperature. RESULTS: Subjects sustained the contraction for 11.0 ± 9.4 min. Muscle stiffness measured in the longitudinal alignment was 110.2 ± 11.4 kPa at the onset of contraction. It started to decrease at the 20% of the total duration and the steady decline continued until the 40% of the total duration. The average reduction in muscle stiffness was more rapid between 60% and 80% of the total duration. At the 80% of the total duration, muscle stiffness declined by > 30% to 75.0 ± 26.5 kPa (P < 0.05) compared with the onset. There were minimal changes in muscle stiffness with the transverse direction of the ultrasound probe. CONCLUSIONS: Muscle stiffness during muscle fatigue with sustained submaximal contraction showed a progressive decrease, most likely due to alterations in mechanical properties of the contractile elements, as quantified with the novel ultrasound elastography imaging.

Estimation of elbow flexion force during isometric muscle contraction from mechanomyography and electromyography

Mechanomyography (MMG) is the muscle surface oscillations that are generated by the dimensional change of the contracting muscle fibers. Because MMG reflects the number of recruited motor units and their firing rates, just as electromyography (EMG) is influenced by these two factors, it can be used to estimate the force exerted by skeletal muscles. The aim of this study was to demonstrate the feasibility of MMG for estimating the elbow flexion force at the wrist under an isometric contraction by using an artificial neural network in comparison with EMG. We performed experiments with five subjects, and the force at the wrist and the MMG from the contributing muscles were recorded. It was found that MMG could be utilized to accurately estimate the isometric elbow flexion force based on the values of the normalized root mean square error (NRMSE = 0.131 ± 0.018) and the cross-correlation coefficient (CORR = 0.892 ± 0.033). Although MMG can be influenced by the physical milieu/morphology of the muscle and EMG performed better than MMG, these experimental results suggest that MMG has the potential to estimate muscle forces. These experimental results also demonstrated that MMG in combination with EMG resulted in better performance estimation in comparison with EMG or MMG alone, indicating that a combination of MMG and EMG signals could be used to provide complimentary information on muscle contraction.

Interaction interference between arm and leg: Division of attention through muscle force regulation

The first purpose of this study was to examine whether decreases in muscle force similar to the bilateral deficit occur during simultaneous use of arm and leg. The second purpose was to examine the effect on the muscle force of one leg by a division of attention through the regulation of the muscle force in the arm. Six participants completed each of the following three tasks in a random order: (1) maximal unilateral flexion of the right or left elbow, (2) maximal unilateral extension of the left knee, and (3) multilimb effort (a maximal contraction of the muscles in the leg while maintaining a constant submaximal isometric elbow flexion force at 25%, 50%, 75%, or 100% MVC). The results showed that muscle force was lower during simultaneous exertion of arm and leg than during exertion of one limb alone. The maximal knee extension force was significantly ( p < .05) lower, by as much as 40% or so, during regulation at 25% MVC. The division of attention is also thought to be involved in task execution and may thus explain the test results. A decrease in the muscle force of the leg due to the level of regulation of the muscle force of the arm indicates that the regulation of the muscle force affects the division of attention, and the finer level of muscle force regulation is a task that requires greater attention. When the muscle force is precisely controlled, a more accurate and more appropriate adjustment is required to focus attention.

Maximal Voluntary Isometric Elbow Flexion Force during Unilateral versus Bilateral Contractions in Individuals with Chronic Stroke

The purpose of this study was to determine whether the phenomenon of bilateral deficit in muscular force production observed in healthy subjects and mildly impaired stroke patients also exists in patients with more chronic and greater levels of stroke impairment. Ten patients with chronic hemiparesis resulting from stroke performed unilateral and bilateral maximal voluntary isometric contractions of the elbow flexors. When the total force produced by both arms was compared, 12% less force was produced in the bilateral compared with unilateral condition (p=0.01). However, studying the effect of task conditions on each arm separately revealed a significant decline in nonparetic (p=0.01) but not paretic elbow flexor force in the bilateral compared with unilateral condition. Results suggest that a significant bilateral force deficit exists in the nonparetic but not the paretic arm in individuals with chronic stroke. Bilateral task conditions do not seem to benefit or impair paretic arm maximal isometric force production in individuals with moderate-severity chronic stroke.

Effect of Induced Functional Asymmetry on the Bilateral Deficit

Asymmetrical force production in homologous limbs may affect the magnitude of the bilateral deficit, but this influence is not well understood. PURPOSE: To determine the effect of an induced functional asymmetry on the bilateral deficit. METHODS: Twenty participants (age 28.4 ± 11.7 years) completed unilateral and bilateral isometric elbow flexion trials at 100% and 50% of maximal effort with the forearms supinated and pronated. Eight subjects' ability to produce maximal isometric elbow flexion force was impaired when the forearm was pronated. For these subjects, unilateral maximum isometric elbow flexion force was reduced by 10.0 ± 6.8% in the dominant arm and 13.0 ± 6.3% in the non-dominant arm when pronated. Bilateral indices for these subjects were calculated for each bilateral condition at both intensities. The indices were compared using a 2 × 4 (intensity × condition) repeated measures ANOVA. RESULTS: Maximal and submaximal effort bilateral indices were significantly less than zero (p<0.05) for all conditions, indicating the presence of bilateral deficits (Table 1), but none were significantly different from each other. Pronating the dominant arm increased the bilateral deficit by 5.5% (ES = .60) at maximal effort and 5.7% (ES = .47) at submaximal effort while pronating the non-dominant arm increased the deficit by 9.3% (ES = .56) only for the submaximal effort.Table 1: Bilateral indices for symmetrical and asymmetrical isometric elbow flexion trials.CONCLUSION: Compromising one limb's ability to produce force increases the size of the bilateral deficit at maximal and submaximal intensities.

Contractile Properties, Fatigue and Recovery are not Influenced by Short‐Term Creatine Supplementation in Human Muscle

There have been several studies on the effect of short-term creatine (Cr) supplementation on exercise performance, but none have investigated both voluntary and stimulated muscle contractions in the same experiment. Fourteen moderately active young men (19-28 years) were randomly assigned, in a double blind manner, to either a creatine (Cr) or placebo (P) group. The subjects supplemented their regular diet 4 times a day for 5 days with either 5 g Cr + 5 g maltodextrin (Cr group), or 5 g maltodextrin (P group). Isometric maximal voluntary contraction (MVC), muscle activation, as assessed using the modified twitch interpolation technique, electrically stimulated contractile properties, electromyography (EMG), endurance time and recovery from fatigue were measured in the elbow flexors. The fatigue protocol involved both voluntary and stimulated contractions. Following supplementation there was a significant weight gain in the Cr group (1.0 kg), whereas the P group did not change. For each group, pre-supplementation measures were not significantly different from post-supplementation for MVC, twitch and tetanic tensions at rest, time to peak tension, half-relaxation time and contraction duration. Prior to Cr supplementation time to fatigue was 10 +/- 4 min (mean +/- S.E.M.) for both groups, and following supplementation there was a non-significant increase of 1 min in each group. MVC force, muscle activation, EMG, stimulated tensions and durations were similar for the Cr and P groups over the course of the fatigue protocol and did not change after supplementation. Furthermore, recovery of MVC, stimulated tensions and contractile speeds did not differ as a result of Cr supplementation. These results indicate that short-term Cr supplementation does not influence isometric elbow flexion force, muscle activation, stimulated contractile properties, or delay time to fatigue or improve recovery.