Relaxed Biceps Research Articles

UBC-Nepal Expedition: Motor Unit Characteristics in Lowlanders Acclimatized to High Altitude and Sherpa.

With acclimatization to high altitude (HA), adaptations occur throughout the nervous system and at the level of the muscle, which may affect motor unit (MU) characteristics. However, despite the importance of MUs as the final common pathway for the control of voluntary movement, little is known about their adaptations with acclimatization. Ten lowlanders and Sherpa participated in this study 7 to 14 d after arrival at HA (5050 m), with seven lowlanders repeating the experiment at sea level (SL), 6 months after the expedition. The maximal compound muscle action potential (M max ) was recorded from relaxed biceps brachii. During isometric elbow flexions at 10% of maximal torque, a needle electrode recorded the MU discharge rate (MUDR) and MU potential (MUP) characteristics of single biceps brachii MUs. Compared with SL, acclimatized lowlanders had ~10% greater MUDR, ~11% longer MUP duration, as well as ~18% lower amplitude and ~6% greater duration of the first phase of the M max (all P < 0.05). No differences were noted between SL and HA for variables related to MUP shape (e.g., jitter, jiggle; P > 0.08). Apart from lower near-fiber MUP area for Sherpa than acclimatized lowlanders ( P < 0.05), no M max or MU data were different between groups ( P > 0.10). Like other components of the body, MUs in lowlanders adapt with acclimatization to HA. The absence of differences between acclimatized lowlanders and Sherpa suggests that evolutionary adaptations to HA are smaller for MUs than components of the cardiovascular or respiratory systems.

Effects of acute isometric resistance exercise on cervicomedullary motor evoked potentials.

Cervicomedullary motor evoked potentials (CMEPs) in relaxed biceps brachii have been reported to facilitate after acute isometric exercise of the elbow flexors. This facilitation, which reflects either enhanced corticospinal transmission or increased motoneurone excitability, has only been documented in the limb posture used during exercise. In Experiment 1, we tested if these spinal changes "transfer" to a second posture. Fourteen individuals completed 12 sets of high-force isometric contractions of the elbow flexors with the forearm pronated. Before and after exercise, biceps CMEPs were acquired with the forearm either pronated or supinated. CMEPs in pronation and supination were facilitated after exercise, indicating transfer (57.5±55.5% and 53.9±54.9%, respectively; mean±SD). In Experiment 2, we examined if exercise posture influences the effect that exercise has on CMEPs. A different sample of 14 individuals performed isometric exercise in 2 sessions. In one, exercise was performed in supination. In the other, exercise was performed in pronation. Exercise intensity and volume were the same as in Experiment 1, as were participant characteristics. CMEPs were unchanged after exercise in supination (13.6±31.2%) and pronation (7.7±41.5%). The absence of an effect differs from the finding of Experiment 1. Thus, effects of acute isometric resistance exercise on corticospinal transmission and/or motoneurone excitability are not as consistent as previously thought. When exercise induces this spinal change, the effect is not specific to the posture used for exercise. However, the change does not always occur, and the reasons for this remain unknown.

Spike shape analysis of electromyography for parkinsonian tremor evaluation.

Standard electromyography (EMG) parameters have limited utility for evaluation of Parkinson disease (PD) tremor. Spike shape analysis (SSA) EMG parameters are more sensitive than standard EMG parameters for studying motor control mechanisms in healthy subjects. SSA of EMG has not been used to assess parkinsonian tremor. This study assessed the utility of SSA and standard time and frequency analysis for electromyographic evaluation of PD-related resting tremor. We analyzed 1-s periods of EMG recordings to detect nontremor and tremor signals in relaxed biceps brachii muscle of seven mild to moderate PD patients. SSA revealed higher mean spike amplitude, duration, and slope and lower mean spike frequency in tremor signals than in nontremor signals. Standard EMG parameters (root mean square, median, and mean frequency) did not show differences between the tremor and nontremor signals. SSA of EMG data is a sensitive method for parkinsonian tremor evaluation.

Interval training-induced alleviation of rigidity and hypertonia in patients with Parkinson's disease is accompanied by increased basal serum brain-derived neurotrophic factor.

To examine the effects of cycloergometric interval training on parkinsonian rigidity, relaxed biceps brachii muscle tone in affected upper extremities, and serum level of brain-derived neurotrophic factor. Case series, repeated-measures design, pilot study. Eleven patients with mild-to-moderate Parkinson's disease (Hoehn & Yahr scale 2.3 ± 0.72), recruited from a neurological clinic, underwent cycle training and were tested along with non-trained, healthy control subjects (n = 11) in a motor control laboratory. Patients underwent 8 weeks of interval training (3 × 1-h sessions weekly, consisting of a 10-min warm-up, 40 min of interval exercise, and 10-min cool-down) on a stationary cycloergometer. Parkinsonian rigidity (Unified Parkinson's Disease-Rating-Scale) in the upper extremity, resting biceps brachii muscle tone (myometric stiffness and frequency), and brain-derived neurotrophic factor level were measured 1-3 days before interval training cycle started and 6-10 days after the last training session. Training resulted in a decrease in rigidity (p = 0.048) and biceps brachii myometric muscle stiffness (p = 0.030) and frequency (p = 0.006), and an increase in the level of brain-derived neurotrophic factor (p = 0.035) relative to pre-training values. The increase in brain-derived neurotrophic factor level correlated with improvements in parkinsonian rigidity (p = 0.025), biceps brachii myometric stiffness (p = 0.001) and frequency (p = 0.002). Training-induced alleviation of parkinsonian rigidity and muscle tone decrease may be associated with neuroplastic changes caused by a training-induced increase in the level of brain-derived neurotrophic factor.

Physical countermeasures to increase orthostatic tolerance

Keywords: blood pressure, cardiac output, muscle pump, orthostatic hypotension, syncope, venous return.IntroductionStanding upright challenges the cardiovascularsystem as the pull of gravity displaces about 70%of the circulating blood volume to below heart level,much of it to the compliant veins of the dependentlimbs and the pelvic organs. In patients withautonomic failure due to neurodegenerative dis-eases, the normal cardiovascular adjustments tothis challenge are impaired, and symptomaticorthostatic hypotension becomes a common riskon standing or even sitting quietly. These patientslearn to sway and shift, so that the pumping actionof the muscles can be utilized to counter gravita-tional displacement of blood by squeezing venousblood from the legs upward. Augmentation ofvenous return in the upright posture can also beachieved by deliberate tensing of lower limb andabdominal muscles [1, 2], as depicted in Fig. 1.These clinical observations were the basis forphysical countermeasures, which are taught topatients with autonomic failure to combat symp-tomatic orthostatic hypotension [3–5]. Physicalcounterpressure manoeuvres specifically generatea counterpressure to oppose gravitational venouspooling (e.g. a single bout of lower-body musclecontraction to translocate blood centrally andsustained tensing of the same muscles to preventsubsequent peripheral pooling in the legs andabdomen). More recently, it has been shown thatphysical counterpressure manoeuvres are alsoeffective interventions in otherwise healthy sub-jects with episodic orthostatic syncope due toneurally mediated (i.e. vasovagal reactions) [6, 7]or postexercise syncope [8].In this narrative review, we will primarily considerthese physical counterpressure manoeuvres. Sec-ondarily, we will describe the broader category ofphysical countermeasures that include breathingmanoeuvres and other physical methods, tooppose orthostasis. Existing external devices,which operate through some of the same physio-logical principles as these manoeuvres, will only bediscussed for proof of principle.The defining characteristic of the manoeuvresdescribed in this review is the fact that they canbe employed by patients when a faint is imminent.This is in contrast to devices such as bandages andabdominal belts, which require ongoing use to beeffective. We will discuss both early studies inpatient with primary autonomic failure due toneurodegenerative diseases, as well as more recentexperience obtained in patients with neurally med-iated syncope. The physiology and pathophysiologyof orthostatic blood pressure control and perfusionof the brain are key factors in understanding howphysical countermeasures work. These topics havebeen reviewed extensively [2, 9–12] and will only bediscussed here briefly.Physical counterpressure manoeuvresMuscle tensingIt has been reported that intramuscular pressure isrelated to orthostatic tolerance [2]. Hendersonet al. demonstrated that intramuscular pressuremeasured in the relaxed biceps muscle wasdecreased after prolonged bed rest (38%), followingsurgery (35%), during voluntary hyperventilation(28%) and in the absence of air movement over theskin (31%) [13, 14]. These conditions are stronglyassociated with decreased orthostatic toleranceand a tendency to faint [2, 15]. In addition,intramuscular calf pressure has been shown tobe 15–24 and 6–9 mmHg, respectively, in thosewithout and with a tendency to faint during thehead-up tilt test using a tilt table with a saddle andsuspended legs (Fig. 1) [16].Although these interesting results from studiesperformed in the 1930s and early 1940s have

Increased corticospinal excitability prior to arm cycling is due to enhanced supraspinal but not spinal motoneurone excitability

Human studies have not assessed supraspinal or spinal motoneurone excitability in the quiescent state prior to a rhythmic and alternating cyclical motor output. The purpose of the current study was to determine whether supraspinal and (or) spinal motoneurone excitability was modulated in humans prior to arm cycling when compared with rest with no intention to move. We hypothesized that corticospinal excitability would be enhanced prior to arm cycling due, in part, to increased spinal motoneurone excitability. Supraspinal and spinal motoneurone excitability were assessed via transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid stimulation of the corticospinal tract, respectively. Surface electromyography recordings of TMS motor evoked potentials (MEPs) and cervicomedullary MEPs (CMEPs) were made from the relaxed biceps brachii muscle prior to rhythmic arm cycling and at rest with no intention to move. The amplitude of the MEPs was greater (mean increase: +9.8% of maximal M wave; p = 0.006) and their onset latencies were shorter (mean decrease: -1.5 ms; p < 0.05) prior to cycling when compared with rest. The amplitudes of the CMEPs at any of 3 stimulation intensities were not different between conditions. We conclude that premovement enhancement of corticospinal excitability is greater prior to arm cycling than at rest because of increases in supraspinal but not spinal motoneurone excitability.

Quantitative Mechanical Properties of the Relaxed Biceps and Triceps Brachii Muscles in Patients with Subacute Stroke: A Reliability Study of the Myoton-3 Myometer

Objective. Test-retest reliability of the myotonometer was investigated in patients with subacute stroke. Methods. Twelve patients with substroke (3 to 9 months poststroke) were examined in standardized testing position twice, 60 minutes apart, with the Myoton-3 myometer to measure tone, elasticity, and stiffness of relaxed bilateral biceps and triceps brachii muscles. Intrarater reliability of muscle properties was determined using intraclass correlation coefficient (ICC), the standard error of measurement (SEM), and the minimal detectable change (MDC). Results. Intrarater reliability of muscle properties of bilateral biceps and triceps brachii muscles were good (ICCs = 0.79–0.96) except for unaffected biceps tone (ICC = 0.72). The SEM and MDC of bilateral biceps and triceps brachii muscles indicated small measurement error (SEM% <10%, MDC% <25%). Conclusion. The Myoton-3 myometer is a reliable tool for quantifying muscle tone, elasticity, and stiffness of the biceps and triceps brachii in patients with subacute stroke.

Increased muscle belly and tendon stiffness in patients with Parkinson's disease, as measured by myotonometry

Based on Davis's law, greater tonus of the muscle belly in individuals with Parkinson's disease can create greater tension in the tendon, leading to structural adjustment and an increase in tendon stiffness. Our study aimed to separately assess passive stiffness in the muscle belly and tendon in medicated patients with Parkinson's disease, using myotonometry. We tested 12 patients with Parkinson's disease and 12 healthy matched controls. Passive stiffness of muscle belly and tendon was estimated by myotonometry, electromyography, and mechanomyography in relaxed biceps and triceps brachii muscles. Compared with controls, patients with Parkinson's disease had higher stiffness in the muscle belly and tendon of the biceps brachii and in the tendon of the triceps brachii. In patients with Parkinson's disease, there was a positive correlation between muscle belly stiffness and parkinsonian rigidity in the biceps brachii. Patients with Parkinson's disease have higher passive stiffness of the muscle belly and tendon than healthy matched controls.

Higher Muscle Passive Stiffness in Parkinson's Disease Patients Than in Controls Measured by Myotonometry

Marusiak J, Kisiel-Sajewicz K, Jaskólska A, Jaskólski A. Higher muscle passive stiffness in Parkinson's disease patients than in controls measured by myotonometry. Objective To assess muscle passive stiffness in medicated Parkinson's disease patients using myotonometry. Design Case-control study. Setting Kinesiology laboratory. Participants Women with Parkinson's disease (PD) (n=8) and healthy matched elderly women (controls) (n=10) (mean age: PD, 77±3y; controls, 77±4y). Interventions Not applicable. Main Outcome Measures Passive stiffness of relaxed biceps brachii (BB) muscle was measured using myotonometry. Additionally, surface electromyographic and mechanomyographic signals were recorded from the muscle at rest, and amplitude of those signals was analyzed offline. Results The values of BB muscle passive stiffness were significantly ( P=.004) higher in PD than in the controls, with a statistically significant influence of parkinsonian rigidity score (Unified Parkinson's Disease Rating Scale) on intergroup differences ( P<.001). The Spearman correlation coefficient ρ value showed a significant ( P=.005) positive relationship (ρ=.866) between the parkinsonian rigidity score and passive stiffness values of BB in PD. The groups did not differ significantly in the electromyogram amplitude ( P=.631) and mechanomyogram amplitude ( P=.593) of the BB muscle, and values of these parameters did not correlate significantly with rigidity score ( P=.555, P=.745, respectively) in the patients. Conclusions Myotonometer is a sensitive enough tool to show that PD patients have higher muscle passive stiffness than healthy controls.

Exhaustive intermittent leg press influences intracortical inhibition and facilitation in proximal and distal muscles of the relaxed upper limb

There are many reports of the effects of fatiguing muscle contraction on corticospinal and intracortical excitability of the projection to the exercised muscle. In contrast, very few reports deal with how exercise of one muscle group influences excitability in projections to non-exercised muscles. Here we examine the effects of leg muscle fatigue on MEPs and intracortical inhibition (SICI) and facilitation (ICF) in relaxed biceps and first dorsal interosseous (FDI) muscles of the right arm.

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.

BODY COMPOSITION IN 181 POSTMENOPAUSAL WOMEN CLASSIFIED AS NORMAL, OSTEOPENIC, OR OSTOEPOROTIC

512 This study assessed body composition among 3 groups of postmenopausal women classified by femoral bone density as normal (n=28), osteopenic (n=101), or osteoporotic (n=52) according to WHO standards. Ss were volunteers and at least 5 yrs past menopause. Standing height and body weight were measured on Detecto Scales. Sitting height was measured with the subjects seated on a stool and a tape secured to the wall behind them. Eight skinfolds (triceps, chest, midaxillary, abdomen, subscapular, suprallium. calf, & thigh) were assessed with Harpendon Calipers according to the procedures of Jackson (1980) and 8 muscle circumferences (contracted forearm, contracted biceps, relaxed biceps, chest, waist, thigh, gluteal, & calf) were measured with a Gulick Tape according to the procedures of Lohman (1991). Percent Body Fat (%BF) was obtained with DEXA using the Hologic QDR-2000. Results of one-way ANOVAs with Newman-Keuls Multiple Comparison Tests, used to assess group differences, revealed: 1) Osteopenic and osteoporotic groups significantly (p<.05) shorter in sitting height than the normals (84. 16±3.99 and 85.49±2.83 to 86.81±3.25cm, respectively), 2) Body weight significantly decreased between groups (normals=75.82±14.76kg, osteopenics=67.61±12.02kg, and osteoporotics=60.88±7.97kg), 3) Normal group had significantly more%BF by DEXA than the osteopenic and osteoporotic groups (44.50±6.45% to 41.76±7.72% and 39.46±7.83%, respectively). 4) Normals had larger sum of 8 skinfolds and body girths than other two groups. It was concluded that body composition varied significantly between the 3 groups and may have been a contributing factor to bone density.