Elbow Flexion Force Research Articles

The Possibility and Potential Feasibility of Putting an Extra Functioning Free Muscle Transplant onto a Normal Limb

Functioning free muscle transplantation is currently and popularly used clinically to restore motor deficit caused by traumatic muscle loss or chronic muscle denervation. However, no one uses functioning free muscle transplantation in a normal subject who has no motor deficit. This study was designed to investigate the possible and potential feasibility of transferring an extra free muscle transplant onto a normal limb. A chimeric flap including biceps muscle with its neurovascular pedicles and a skin perforator flap was designed, harvested, and transferred from a Lewis inbred rat to the other rat overlying the original biceps following neurovascular repair where the ulnar nerve was chosen as the neurotizer. Sixteen rats were operated on and evaluated 6 months after surgery. Outcome measurements included arm circumferences, electrophysiologic studies, elbow flexion force, and muscle mass. The contralateral normal biceps was used as the control. All outcome measurements revealed that the extra muscle transfer resulted in significant increases in size and function of the operative limb without interfering with the original biceps function. The authors' study demonstrates the possible and potential application of using extra free muscle transplantation for functional and aesthetic augmentation purposes in a normal subject.

Acceleration and Force Reveal Different Mechanisms of Electromechanical Delay

Electromechanical delay (EMD) represents a series of complex processes of converting an electrical stimulus to a mechanical response. To quantify the contribution of electrochemical and mechanical processes of EMD in the human biceps brachii muscle over a wide range of elbow joint angles, we determined the onset of muscle contraction and the beginning of force development by recording acceleration of skin surface over the muscle and elbow flexion force, respectively. Ten healthy male volunteers underwent two experimental sessions, in which submaximal paired-pulse stimuli were applied percutaneously to the resting biceps brachii muscle at 10 different elbow joint angles from 40° to 130° (0° represents full extension). The electrical stimulation induced repeatable contractions, in which the test-retest reliability of time parameters was sufficiently high (intraclass correlation coefficient=0.84-0.88). The time for electrochemical process ranged between 3.1±0.8 and 3.6±0.9 ms and was independent of elbow joint angle (P=0.64). The time for mechanical process and the total duration of EMD, however, were significantly greater at elbow flexion positions than at 40°, the most extended position in this study (P<0.05). Regression analysis revealed that at elbow flexion positions, the time for mechanical process increased significantly with decreasing the muscle-tendon length of the biceps brachii calculated from a musculoskeletal model (R=0.54, P<0.001). These results suggest that, in the human biceps brachii muscle, the prolongation of EMD at short muscle-tendon length is not attributed to the impairment of the electrochemical process of muscle contraction but to the increased slack within the muscle-tendon unit.

Effects of monopolar and bipolar electrode configurations on surface EMG spike analysis

This study compared the effects of monopolar and bipolar electrode configurations on interference pattern analysis of the surface electromyographic (sEMG). Twenty-four college-aged male participants performed isometric actions of the elbow flexors at 40, 60, 80, and 100 percent of maximal voluntary contraction (MVC). Separate (Ag/AgCl) electrodes were used for both configurations. There were five measures associated with “spike shape” analysis: mean spike amplitude (MSA), mean spike frequency (MSF), mean spike slope (MSS), mean spike duration (MSD) and mean number of peaks per spike (MNPPS). A load-cell and wrist-cuff assembly was used to record isometric elbow flexion forces. Both electrode configurations resulted in the same trends force changes in spike shape measures across force levels: there was a linear increase in MSA, MSS, and a quadratic decrease in MSF and the MNPPS ( p's < 0.05). The MSD underwent a quadratic increase ( p < 0.05). The spike shape measures had greater mean magnitudes and exhibited greater rates of changes across force levels for the monopolar electrode configuration ( p's < 0.05). The monopolar electrode configuration was therefore more sensitive to changes in muscle activity with increases in isometric force. This is an important consideration because the rate at which muscle electrical activity develops into a full interference pattern is an important qualitative and quantitative diagnostic measure.

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.

Resistance Arm Training in Patients With COPD: A Randomized Controlled Trial

The study aimed to evaluate the effect of upper extremity resistance training for patients with COPD on dyspnea during activity of daily living (ADL), arm function, arm exercise capacity, muscle strength, and health-related quality of life (HRQL).Patients were randomly assigned to an intervention or control group. The intervention group underwent arm resistance training. The control group performed a sham. Both groups exercised three times a week for 6 weeks. Dyspnea during ADL and HRQL were measured using the Chronic Respiratory Disease Questionnaire (CRDQ). Arm function and exercise capacity were measured using the 6-min pegboard and ring test (6PBRT) and the unsupported upper limb exercise test (UULEX), respectively. Muscle strength for the biceps, triceps, and anterior and middle deltoids was obtained using an isometric dynamometer.Thirty-six patients with COPD (66 ± 9 years) participated in the study. Compared with the control group, the magnitude of change in the intervention group was greater for the 6PBRT (P = .03), UULEX (P = .01), elbow flexion force (P = .01), elbow extension force (P = .02), shoulder flexion force (P = .029), and shoulder abduction force (P = .01). There was no between-group difference in dyspnea during ADL, HRQL, or symptoms during the 6PBRT or UULEX (all P values > .08).Resistance-based arm training improved arm function, arm exercise capacity, and muscle strength in patients with COPD. No improvement in dyspnea during ADL, HRQL, or symptoms was demonstrated.

Feasibility of using an artificial neural network model to estimate the elbow flexion force from mechanomyography

The goal of this study was to demonstrate the feasibility of using artificial neural network (ANN) models to estimate the elbow flexion forces from mechanomyography (MMG) under isometric muscle contraction and compare the performance of the ANN models with the performance from multiple linear regression (MLR) models. Five participants (mean±SD age=25.4±2.96 yrs) performed ten predefined and ten randomly ordered elbow flexions from 0% to 80% maximal voluntary contractions (MVCs). The MMG signals were recorded from the biceps brachii (BR) and brachioradialis (BRD), both of which contribute to elbow flexion. Inputs into the model included the root-mean-square (RMS), a temporal characterization feature, which resulted in a slightly higher signal-to-noise ratio (SNR) than when using the mean absolute value (MAV), and the zero-crossing (ZC) as spectral characterization features. Additionally, how the RMS and the ZC as model inputs affected the estimation accuracy was investigated. A cross-subject validation test was performed to determine if the established model of one subject could be applied to another subject. It was observed that the ANN model provided a more accurate estimation based on the values of the normalized root mean square error (NRMSE=0.141±0.023) and the cross-correlation coefficient (CORR=0.883±0.030) than the estimations from the MLR model (NRMSE=0.164±0.030, CORR=0.846±0.033). The estimation results from the same-subject validation test were significantly better than those of the cross-subject validation test. Thus, using an ANN model on a subject-by-subject basis to quantify and track changes in the temporal and spectral responses of MMG signals to estimate the elbow flexion force is a reliable method.

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

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

A Comparison of Intercostal and Partial Ulnar Nerve Transfers in Restoring Elbow Flexion Following Upper Brachial Plexus Injury (C5-C6±C7)

Restoring active elbow flexion is essential in the surgical management of C5-C6 +/- C7 brachial plexus palsies. This study compares the clinical results of 2 techniques to restore elbow flexion: the partial ulnar nerve transfer and the intercostal nerve transfer. Partial ulnar nerve transfer was performed in 23 patients, and intercostal nerve transfer was performed in 17 patients. For both techniques, the transfer to the musculocutaneous nerve was made at the same anatomical point. Age and preoperative delay were comparable between groups of patients. Biceps reinnervation time was significantly earlier (p = .001) in the ulnar nerve technique (mean, 5.1 mo) than the intercostal nerve technique (mean 9.9 mo). Ten of 17 patients recovered useful elbow flexion force (British Medical Research Council grade >M3) in the intercostal nerve transfer group, compared with 20 of 23 patients in the ulnar nerve transfer group. No patient who had surgery more than 6 months after the injury recovered useful elbow flexion force in the intercostal nerve transfer. Elbow flexion strength was better in patients less than 30 years old in the intercostal nerve group. No complications were observed in either group. This study shows that transferring fascicles of the ulnar nerve yields better results than intercostals nerve transfer for restoring elbow flexion. Moreover, preoperative delay and age are important preoperative prognostic factors for the intercostal nerves transfers. Therapeutic III.

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.

Cancer-Related Fatigue: Central or Peripheral?

To evaluate cancer-related fatigue (CRF) by objective measurements to determine if CRF is a more centrally or peripherally mediated disorder, cancer patients and matched noncancer controls completed a Brief Fatigue Inventory (BFI) and underwent neuromuscular testing. Cancer patients had fatigue measured by the BFI, were off chemotherapy and radiation (for more than four weeks), had a hemoglobin level higher than 10 g/dL, and were neither receiving antidepressants nor were depressed on a screening question. The controls were screened for depression and matched by age, gender, and body mass index. Neuromuscular testing involved a sustained submaximal elbow flexion contraction (SC) at 30% maximal level (30% maximum elbow flexion force). Endurance time (ET) was measured from the beginning of the SC to the time when participants could not maintain the SC. Evoked twitch force (TF), a measure of muscle fatigue, and compound action potential (M-wave), an assessment of neuromuscular-junction transmission were performed during the SC. Compared with controls, the CRF group had a higher BFI score ( P < 0.001), a shorter ET ( P < 0.001), and a greater TF with the SC (CRF > controls, P < 0.05). This indicated less muscle fatigue. There was a greater TF ( P < 0.05) at the end of the SC, indicating greater central fatigue, in the CRF group, which failed to recruit muscle (to continue the SC), as well as the controls. M-Wave amplitude was lower in the CRF group than in the controls ( P < 0.01), indicating impaired neuromuscular junction conduction with CRF unrelated to central fatigue (M-wave amplitude did not change with SC). These data demonstrate that CRF patients exhibited greater central fatigue, indicated by shorter ET and less voluntary muscle recruitment during an SC relative to controls.

An Inverted Seated Posture Decreases Elbow Flexion Force and Muscle Activation

An Inverted Seated Posture Decreases Elbow Flexion Force and Muscle Activation

Pronation–supination torque and associated electromyographic activity varies during a sustained elbow flexor contraction but does not influence the time to task failure

In this study we measured the pronation-supination torque, flexion force, and electromyographic activity in elbow flexor muscles during an isometric contraction in which a submaximal elbow flexion force was kept constant for as long as possible. Ten subjects performed the contraction at 20% of maximal voluntary contraction (MVC) torque until failure. Electromyographic (EMG) activity of the long and short heads of biceps brachii, brachialis, brachioradialis, and triceps brachii was recorded with surface and intramuscular electrodes. The mean time to failure was 8.2 +/- 6.2 min. The fluctuations in flexion force and pronation-supination torque were correlated (r range = 0.68-0.92), and subjects exhibited a range of pronation-torque profiles that were not associated with the time to failure. Knowing the influence of concurrent actions about the pronation-supination axis during a submaximal fatiguing contraction with the elbow flexor muscles has implications for the design of workstations in ergonomic settings and in the prescription of activities for rehabilitation programs. Muscle Nerve 40: 231-239, 2009.

An inverted seated posture decreases elbow flexion force and muscle activation

The purpose of this study was to determine if discrepancies exist between upright and inverted seated positions in isometric maximal voluntary contraction (MVC) elbow flexor force, MVC force produced in the first 100 ms (F100), MVC rate of force development, electromyographic (EMG) activity of the biceps and triceps as well as heart rate and blood pressure. The results showed significantly (p < 0.01) higher MVC force (543.6 +/- 29.6 vs. 486.5 +/- 23.0 N), F100 (328.3 +/- 94.5 vs. 274.6 +/- 101.8 N), rate of force development (p = 0.003) (1,851.9 +/- 742.2 vs. 1,591.0 +/- 719.6 N s(-1)) and biceps brachii EMG activity (48%, p < 0.01) in the upright versus inverted condition. There were relatively greater co-contractions with the inverted position (p < 0.01) due to the lack of change in triceps' EMG and the substantial decrease in biceps' EMG. There were no significant changes in trunk EMG activity. With inversion, there were significant decreases in heart rate (16.8%), systolic (11.6%) and diastolic (12.1%) blood pressures (p < 0.0001). These results illustrate decrements in neuromuscular performance with an inverted seated posture which may be related to an altered sympathetic response.

Counterpoint: Sympathetic nerve activity does not influence cerebral blood flow

It is intuitively clear that the cerebral circulation cannot take part in general cardiovascular regulation. During states of shock, where the sympathetic nervous system is activated, leading to a decrease in the perfusion of kidneys and mesenteric vascular bed, the cerebral circulation is kept

The Role of the Musculocutaneous and Radial Nerves in Elbow Flexion and Forearm Supination: A Biomechanical Study

The intention of this prospective study was to evaluate the role of the musculocutaneous and radial nerves in elbow flexion and forearm supination. The study included 29 patients having loco-regional anaesthesia for minor hand surgery. Elbow flexion and forearm supination forces were evaluated before and after an isolated musculocutaneous nerve block in one group and an isolated radial nerve block in another group. The results showed that the biceps tendon is responsible for 47% of the forearm supination force and the combination of brachioradialis and the supinator for 64% of this force. It showed also that the musculocutaneous and radial nerves contribute by 42% and 27.5%, respectively, to the flexion force of the elbow. These results are intended to help surgeons in decision making when treating chronic biceps tendon rupture, in repair of traumatic brachial plexus neuropathy and in using tendon transfers, such as the Steindler transfer, around the elbow.

Group III and IV muscle afferents differentially affect the motor cortex and motoneurones in humans

The influence of group III and IV muscle afferents on human motor pathways is poorly understood. We used experimental muscle pain to investigate their effects at cortical and spinal levels. In two studies, electromyographic (EMG) responses in elbow flexors and extensors to stimulation of the motor cortex (MEPs) and corticospinal tract (CMEPs) were evoked before, during, and after infusion of hypertonic saline into biceps brachii to evoke deep pain. In study 1, MEPs and CMEPs were evoked in relaxed muscles and during contractions to a constant elbow flexion force. In study 2, responses were evoked during elbow flexion and extension to a constant level of biceps or triceps brachii EMG, respectively. During pain, the size of CMEPs in relaxed biceps and triceps increased (by approximately 47% and approximately 56%, respectively; P < 0.05). MEPs did not change with pain, but relative to CMEPs, they decreased in biceps (by approximately 34%) and triceps (by approximately 43%; P < 0.05). During flexion with constant force, ongoing background EMG and MEPs decreased for biceps during pain (by approximately 14% and 15%; P < 0.05). During flexion with a constant EMG level, CMEPs in biceps and triceps increased during pain (by approximately 30% and approximately 26%, respectively; P < 0.05) and relative to CMEPs, MEPs decreased for both muscles (by approximately 20% and approximately 17%; P < 0.05). For extension, CMEPs in triceps increased during pain (by approximately 22%) whereas MEPs decreased (by approximately 15%; P < 0.05). Activity in group III and IV muscle afferents produced by hypertonic saline facilitates motoneurones innervating elbow flexor and extensor muscles but depresses motor cortical cells projecting to these muscles.

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.

Identifying the Source of Radial Nerve Afferents that Inhibit Biceps Brachii

Electrical stimulation of the brachioradialis branch of the radial nerve inhibits the discharge of motor units in biceps brachii. Because the distal portion of brachialis is also innervated by a branch of the radial nerve, however, there is uncertainty over the origin of the inhibitory projection to the motor units in biceps brachii. PURPOSE: To determine the extent to which inhibition of the biceps brachii motor neuron pool with radial nerve stimulation is mediated by afferent projections from the brachioradialis or brachialis. METHODS: Stimulating electrode location was optimized for both the brachioradialis and brachialis branches of the radial nerve by observing the electrically evoked motor responses from the interference electromyogram of both muscles. Six male subjects produced low elbow flexion forces (2.8 ± 1.6 %MVC) to maintain the discharge of a biceps brachii motor unit at 11.1 ±0.8 pps. Stimulation was applied every 2 – 3 s with a 30-ms delay after the discharge of the motor unit. Stimulus intensity was 0.9x motor threshold (MT). Pre- and post-stimulus time histograms were constructed from the 108 ±12 stimuli that occurred during the discharge of the motor units. The influence of the two stimulus locations was assessed on the same biceps brachii motor unit. Inhibition was quantified as the percent change from the pre- to post-stimulus interspike intervals. RESULTS: Seven motor units were recorded for each stimulation location. To determine the selectivity of stimulation, motor thresholds were identified for both muscles at each stimulation site. There was a limited capacity to selectively stimulate either nerve branch; the stimulus intensity (0.9x MT) for each muscle corresponded to ∼0.73x MT for the other muscle. Despite this limited selectivity, the magnitude of inhibition on biceps brachii motor units was significantly less (P <0.05) when stimulation was optimized for the brachialis branch of the radial nerve (3.4 %) than the brachioradialis branch (6.5 %). CONCLUSION: These data suggest that either there are fewer inhibitory afferent projections from radial nerve-innervated brachialis than from brachioradialis or that brachialis afferents do not inhibit biceps brachii motor units and the observed inhibition was due to activation of brachioradialis afferents at a lower stimulus intensity. Inhibition of biceps brachii motor units with radial nerve stimulation appears to be primarily mediated by afferents from the brachioradialis muscle. Supported by NINDS R01 NS43275.