Chimpanzee hind limb muscle electromyographic activity patterns during locomotion.

Variation in myology of the hind limb among salamanders has been poorly characterized. Nineteen major hind limb muscles of Ambystoma tigrinum (Ambystomatidae) and Dicamptodon tenebrosus (Dicamptodontidae) were studied to provide baseline descriptive data on hind limb myology in salamanders and to generate hypotheses of hind limb muscle function. Most superficial muscles of the hind limbs span multiple joints, including a unique three-joint muscle, the ischioflexorius, that extends from the pelvic girdle to the plantar fascia. The deeper hind limb muscles spen single joints. No myological diffrences were observed between the hind limbs of A. tigrinum larvae and individuals that had just metamorphosed. Fully adult tiger salamanders that had been housed in terraria for many years had hypertrophied femorofibularis and ischiofemoralis muscles, a condition similar to that reported in Paramesotriton and Taricha, which engage in terrestrial locomotion. In contrast, adults of D. tenebrosus, which are also good walkers, possess a hypertrophied ischioflexorius muscle and a reduced femorofibularis. These regular myological diffences, and those described by previous workers for different salamnder taxa, may be associated with differences in life-history traits, and in the case of A. tigrinum, with patterns of muscle use.

The synaptic connections among the cells of the vertebrate nervous system undergo extensive rearrangements early in development. During their initial growth, neurones apparently form synaptic connections with an excessive number of targets, later retracting a portion of these synapses in establishing the adult neural circuits. Because of the profound effects which experience has upon the developing nervous system, a question of considerable interest has been the role which the functional use of these developing synapses might play in determining the final pattern of connectivity. At the neuromuscular junction the early changes in synaptic connections are well documented, and here questions about the importance of function can be relatively easily addressed. Mammalian skeletal muscle fibres experience a perinatal period of synapse elimination so that all but one of several synapses formed on each muscle fibre are lost. This synapse elimination is sensitive to alterations of neuromuscular use or activity. Reduction of muscle use by tenotomy or by paralysis of the muscle with drugs blocking nerve impulse conduction or neuromuscular transmission delays or even prevents synapse loss, while increased use produced by stimulation of the muscle nerve apparently accelerates the rate at which synapses are lost. I report here a further examination of the role of neuromuscular activity in synapse elimination. I show that chronic neuromuscular stimulation accelerates synapse elimination but that this acceleration is dependent on the temporal pattern in which the stimuli are presented: brief stimulus trains containing 100 Hz bursts of stimuli produce this acceleration whereas the same number of stimuli presented continuously at 1 Hz do not. Furthermore, the 100 Hz activity pattern which is effective in altering synapse elimination also alters two other muscle properties: the sensitivity of the muscle fibers to acetylcholine and the 'speed' of muscle contractions. These findings suggest that the ability of muscle fibres to maintain more than one nerve terminal, like other muscle properties, is sensitive to the pattern of muscle use rather than just the total amount of use.

All mammalian infants suckle, a fundamentally different process than drinking in adults. Infant mammal oropharyngeal anatomy is also anteroposteriorly compressed and becomes more elongate postnatally. While suckling and drinking require different patterns of muscle use and kinematics, little insight exists into how the neuromotor and anatomical systems change through the time that infants suckle. We measured the orientation, activity and contractile patterns of five muscles active during infant feeding from early infancy until weaning using a pig model. Muscles not aligned with the long axis of the body became less mediolaterally orientated with age. However, the timing of activation and the contractile patterns of those muscles exhibited little change, although variation was larger in younger infants than older infants. At both ages, there were differences in contractile patterns within muscles active during both sucking and swallowing, as well as variation among muscles during swallowing. The changes in anatomy, coupled with less variation closer to weaning and little change in muscle firing and shortening patterns suggest that the neuromotor system may be optimized to transition to solid foods. The lesser consequences of aspiration during feeding on an all-liquid diet may not necessitate the evolution of variation in neuromotor function through infancy.

At birth, synaptic sites in developing rodent muscles are innervated by numerous motor axons. During subsequent weeks, this multiple innervation disappears as one terminal strengthens, and all the others are eliminated. Experimental perturbations that alter neuromuscular activity affect the rate of synaptic refinement, with more activity accelerating the time to single innervation and neuromuscular blockade retarding it. However, it remains unclear whether patterns of muscle use (driven by endogenous neuronal activity) contribute to the rate of synapse elimination. For this reason we examined the timing of supernumerary nerve terminal elimination at synapses in extraocular muscles (EOMs), a specialized set of muscles controlling eye movements. On the basis of their exceptionally high patterns of activity, we hypothesized that synaptic refinement would be greatly accelerated at these synapses. We found, however, that rates of synaptic refinement were only modestly accelerated in rectus and oblique EOMs compared with synapses in somite‐derived skeletal muscle. In contrast to these results, we observed a dramatic delay in the elimination of supernumerary nerve terminals from synapses in the levator palpebrae superioris (LPS) muscle, a specialized EOM that initiates and maintains eyelid elevation. In mice, natural eye opening occurs at the end of the second postnatal week of development. Thus, although synapse elimination is occurring in most EOMs and somite‐derived skeletal muscles, it appears to be dramatically delayed in a set of specialized eyelid muscles that remain immobile during early postnatal development. J. Comp. Neurol. 519:2907‐2921, 2011. � 2011 Wiley‐Liss, Inc.

At birth, synaptic sites in developing rodent muscles are innervated by numerous motor axons. During subsequent weeks, this multiple innervation disappears as one terminal strengthens, and all the others are eliminated. Experimental perturbations that alter neuromuscular activity affect the rate of synaptic refinement, with more activity accelerating the time to single innervation and neuromuscular blockade retarding it. However, it remains unclear whether patterns of muscle use (driven by endogenous neuronal activity) contribute to the rate of synapse elimination. For this reason we examined the timing of supernumerary nerve terminal elimination at synapses in extraocular muscles (EOMs), a specialized set of muscles controlling eye movements. On the basis of their exceptionally high patterns of activity, we hypothesized that synaptic refinement would be greatly accelerated at these synapses. We found, however, that rates of synaptic refinement were only modestly accelerated in rectus and oblique EOMs compared with synapses in somite-derived skeletal muscle. In contrast to these results, we observed a dramatic delay in the elimination of supernumerary nerve terminals from synapses in the levator palpebrae superioris (LPS) muscle, a specialized EOM that initiates and maintains eyelid elevation. In mice, natural eye opening occurs at the end of the second postnatal week of development. Thus, although synapse elimination is occurring in most EOMs and somite-derived skeletal muscles, it appears to be dramatically delayed in a set of specialized eyelid muscles that remain immobile during early postnatal development.

Physical symptoms present in a large percentage of instrumental musicians at all levels of expertise, yet the impact of these symptoms on patterns of muscle use and perceived exertion during performance is still unclear. Quantify the effects of physical symptoms on muscle activity and perceived exertion in skilled violinists during a range of bowing actions. Fifty-five professional or university (undergraduate or postgraduate) violinists performed 5 randomly ordered 45-second musical excerpts designed to elicit a range of right arm bowing actions. Surface electromyography data were obtained from 16 muscles of the trunk, shoulder, and right arm during each excerpt performance. Sites of current physical symptoms were reported using a pre-test questionnaire. Average rating of perceived exertion (RPE) for the excerpt performances was obtained immediately after the final excerpt performance. Right upper trapezius muscle activity levels were significantly reduced in participants reporting right shoulder symptoms (p<0.05). Violinists with right wrist symptoms displayed global increases in average muscle activity across all investigated muscles (p<0.03). RPE did not differ significantly between any groups of symptomatic and asymptomatic participants. Differential muscle activity patterns appear between right shoulder symptomatic, right wrist symptomatic, and asymptomatic violinists, presenting the possibility of altered biomechanical responses to physical symptoms that vary with symptom location.

In vertebrates ageing is characterized by reduced viscoelasticity of the ligamentous and tendineous structures and fibre changes in muscle. Also, some vertebral joint degeneration develops with ageing. The aim of this study was to apply dynamic time warping to compare the temporal characteristics of the surface electromyography (sEMG) data and to illustrate the differences in the pattern of muscle use during tasks of daily life in old and mature horses. In vivo kinematics (24 skin markers) and sEMG measurements of neck extensors and flexors were taken in five mature horses (age 10 ± 2 years, half of mean life expectancy) and five old horses (age 25 ± 5 years, older than the mean life expectancy). All horses had the same level of activity in the 12 months prior to the measurement. Tasks measured were neck flexion and neck extension as well as neutral neck position. Muscle activation, minimum and maximum muscle activation were collected. Quartiles of muscle activity based on the maximum observed activity of each muscle were calculated to document the relative increase of activity level during the task. Kinematics as well as overall muscle activity patterns were similar across horses and age groups. However, in the neutral position old horses showed increased extensor activity compared to mature horses, indicating that old equine muscle requires more activity to counteract gravity. Dynamic time warping specified optimal temporal alignments of time series, and different temporal performances were identified. The age groups differed during the flexion task, while extension and neutral were more similar. The results of this study show that even in the second half of life and in the absence of muscle disuse the muscular strategy employed by horses continues to be adapted.

The aim of this mini-review is to describe the present state of knowledge regarding the effects of chronic changes in the patterns of muscle use (defined as changes lasting >1 wk), including muscle stretching, strengthening, and others, on the passive mechanical properties of healthy human skeletal muscles. Various forms of muscle stretch training and some forms of strength training (especially eccentric training) are known to strongly impact the maximum elongation capacity of muscles in vivo (i.e., maximum joint range of motion), largely by increasing our ability to tolerate higher stretch loads. However, only small effects are observed in the passive stiffness of the muscle-tendon unit (MTU) or the muscle itself, although a reduction in muscle stiffness has been observed in the plantar flexors after both stretching and eccentric exercise interventions. No changes have yet been observed in viscoelastic properties such as the MTU stress-relaxation response, although a minimum of evidence indicates that hysteresis during passive stretch-relaxation cycles may be reduced by muscle stretching training. Importantly, data exist for relatively few muscle groups, and little is known about the effects of age and sex on the adaptive process of passive mechanical properties. Despite the significant research effort afforded to understanding the effects of altered physical activity patterns on the maximum range of motion at some joints, further information is needed before it will be possible to develop targeted physical activity interventions with the aim of evoking specific changes in passive mechanical properties in individuals or in specific muscles and muscle groups.

Recent studies on the restoration of locomotion after spinal cord injury have employed robotic means of positioning rats above a treadmill such that the animals are held in an upright posture and engage in bipedal locomotor activity. However, the impact of the upright posture alone, which alters hindlimb loading, an important variable in locomotor control, has not been examined. Here we compared the locomotor capabilities of chronic spinal rats when placed in the horizontal and upright postures. Hindlimb locomotor movements induced by exteroceptive stimulation (tail pinching) were monitored with video and EMG recordings. We found that the upright posture alone significantly improved plantar stepping. Locomotor trials using anaesthesia of the paws and air stepping demonstrated that the cutaneous receptors of the paws are responsible for the improved plantar stepping observed when the animals are placed in the upright posture.We also tested the effectiveness of serotonergic drugs that facilitate locomotor activity in spinal rats in both the horizontal and upright postures. Quipazine and (±)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) improved locomotion in the horizontal posture but in the upright posture either interfered with or had no effect on plantar walking. Combined treatment with quipazine and 8-OH-DPAT at lower doses dramatically improved locomotor activity in both postures and mitigated the need to activate the locomotor CPG with exteroceptive stimulation. Our results suggest that afferent input from the paw facilitates the spinal CPG for locomotion. These potent effects of afferent input from the paw should be taken into account when interpreting the results obtained with rats in an upright posture and when designing interventions for restoration of locomotion after spinal cord injury.

Simple SummaryWhole-Body Vibration (WBV) on vibrating platforms has been used as an alternative method of physiotherapy and rehabilitation for musculoskeletal, neurological or metabolic conditions in humans. However, in dogs, the use of WBV as a physical therapeutic modality has not been well established. This pilot study used several parameters to evaluate the long-term effects of WBV in lame dogs with borderline-to-severe hip dysplasia diagnosed radiographically. Although these results were preliminary, WBV significantly increased the size of both hind limb quadriceps femoris muscles and the left gluteal muscle. The owner’s perception was that, during the trial period, their dog’s pain decreased. However, no significant changes in the gait pattern or lameness score were found. Further studies evaluating the use of WBV for canine hip dysplasia appear to be justified.This pilot study aimed to evaluate the long-term effects of Whole-Body Vibration (WBV) on hind limb muscles, gait and pain in lame dogs with borderline-to-severe hip dysplasia. Ten lame client-owned dogs with borderline-to-severe hip dysplasia, aged from 1.5 to 9.0 years and weighing 14.5 to 53.0 kg, were enrolled. The WBV training program consisted of 15 min sessions three times weekly for 16 weeks. Muscles of the hind limbs were evaluated using measurements of thigh circumference, the cross-sectional thickness of selected hind limb muscles by ultrasound assessment, and vastus lateralis muscle activity determined by surface electromyography (EMG). Lameness and clinical signs of pain were assessed by visual lameness scoring, orthopedic examination and an owner-based questionnaire. Kinetic analysis was performed by using a pressure-sensitive walkway. Manual thigh circumference measurements of both hind limbs showed significant increases over the trial period with a greater degree of change observed after week 8. Ultrasound measurements of the left gluteal muscles and the quadriceps femoris muscles of both hind limbs showed significant increases in the cross-section thickness post WBV. Owner’s perception of pain also showed a decrease in signs of pain at week 12 and week 16 compared to baseline. Based on graphs of the EMG activity patterns of the vastus lateralis muscle, 65% of the hind limbs had an improvement after 48 WBV sessions when compared to pre-session patterns. However, no significant differences were observed in visual lameness evaluation and kinetic analysis. Therefore, further studies will help to better clarify the role of WBV in canine rehabilitation protocols.

Following spinal cord injury (SCI) reduced limb usage typically results in muscle atrophy. While robotic locomotor training has been shown to improve several aspects of stepping ability following SCI, little is known regarding the effects of automated training on the preservation of muscle function. The purpose of this study was to evaluate the effects of two robotic locomotor training algorithms on hindlimb strength and muscle mass in a rat model of SCI. Eighteen Sprague-Dawley rats received a mid-thoracic spinal cord transection at 5 days of age, and were randomly assigned to one of three groups: control (no training), standard robotic training, and robotic training with a downward force applied to the shank during the stance phase of gait. Training occurred 5 days/week for 5 min/day, and animals received 90% body weight support for all sessions. Following 4 weeks of training, vertical and propulsive ground reaction force during stepping and en vitro mass of two plantarflexor muscles were significantly increased for all of the trained animals when compared to the untrained control group. Post hoc analysis revealed that standard robotic training did not appear to increase ground reaction force and muscle mass to the same extent as the loaded condition. These results indicate that automated robotic training helps to preserve hindlimb muscle function in rats following SCI. Further, the addition of a plantarflexion stance load appears to promote greater increases in muscle mass and stepping kinetics.

Mallard ducks are capable of performing a wide range of behaviors including nearly vertical takeoffs from both terrestrial and aquatic habitats. The hindlimb plays a key role during takeoffs from both media. However, because force generation differs in water versus on land, hindlimb kinematics and muscle function are likely modulated between these environments. Specifically, we hypothesize that hindlimb joint motion and muscle shortening are faster during aquatic takeoffs, but greater hindlimb muscle forces are generated during terrestrial takeoffs. In this study, we examined the hindlimb kinematics and in vivo contractile function of the lateral gastrocnemius (LG), a major ankle extensor and knee flexor, during takeoffs from water versus land in mallard ducks. In contrast to our hypothesis, we observed no change in ankle angular velocity between media. However, the hip and metatarsophalangeal joints underwent large excursions during terrestrial takeoffs but exhibited almost no motion during aquatic takeoffs. The knee extended during terrestrial takeoffs but flexed during aquatic takeoffs. Correspondingly, LG fascicle shortening strain, shortening velocity and pennation angle change were greater during aquatic takeoffs than during terrestrial takeoffs because of the differences in knee motion. Nevertheless, we observed no significant differences in LG stress or work, but did see an increase in muscle power output during aquatic takeoffs. Because differences in the physical properties of aquatic and terrestrial media require differing hindlimb kinematics and muscle function, animals such as mallards may be challenged to tune their muscle properties for movement across differing environments.

IntroductionImpaired muscle function is a frequent consequence of musculoskeletal disorders in dogs. Musculoskeletal disorders, especially stifle joint diseases, are common in dogs and assessment of muscle function in dogs is clinically relevant. Acoustic myography (AMG) is a non-invasive method to assess muscle activity. Quantifying muscle function in normal dogs could help identify clinically relevant changes in dogs with orthopaedic disease and allow targeted interventions to improve recovery in these. The objectives of the study were to characterize hindlimb muscle function in healthy dogs using AMG and to investigate the repeatability and reproducibility of AMG in dogs. MethodsHealthy dogs (15–40 kg) without musculoskeletal disorders were recruited and screened for eligibility to participate in the study. The muscle activity in four hindlimb muscles related to the stifle was assessed using AMG. The degree of symmetry between the hindlimbs in these dogs was investigated and the reliability of AMG was evaluated. Results and conclusionsThe study population comprised 21 dogs. Reference intervals and symmetry indices for AMG scores of the hindlimb muscles were identified, with highest variability for the E-scores. For all AMG-scores, same-day variation was lower than between days variation, and both were lowest for S- and T-scores. Further investigation is needed to establish if AMG can enable discrimination between dogs with altered muscle function and healthy dogs.

The Quarter Horse (bred for acceleration) and the Arab (bred for endurance) are situated at either end of the equine athletic spectrum. Studies into the form and function of the leg muscles in human sprint and endurance runners have demonstrated that differences exist in their muscle architecture. It is not known whether similar differences exist in the horse. Six Quarter Horse and six Arab fresh hind limb cadavers were dissected to gain information on the muscle mass and architecture of the following muscles: gluteus medius; biceps femoris; semitendinosus; vastus lateralis; gastrocnemius; tibialis cranialis and extensor digitorum longus. Specifically, muscle mass, fascicle length and pennation angle were quantified and physiological cross-sectional area (PCSA) and maximum isometric force were estimated. The hind limb muscles of the Quarter Horse were of a significantly greater mass, but had similar fascicle lengths and pennation angles when compared with those of the Arab; this resulted in the Quarter Horse hind limb muscles having greater PCSAs and hence greater isometric force potential. This study suggests that Quarter Horses as a breed inherently possess large strong hind limb muscles, with the potential to accelerate their body mass more rapidly than those of the Arab.

Alterations in signaling pathway activity have been implicated in the pathogenesis of Duchenne muscular dystrophy, a degenerative muscle disease caused by a deficiency in the costameric protein dystrophin. Accordingly, the notion of the dystrophin-glycoprotein complex, and by extension the costamere, as harboring signaling components has received increased attention in recent years. The localization of most, if not all, signaling enzymes to this subcellular region relies on interactions with scaffolding proteins directly or indirectly associated with the dystrophin-glycoprotein complex. One of these scaffolds is myospryn, a large, muscle-specific protein kinase A (PKA) anchoring protein or AKAP. Previous studies have demonstrated a dysregulation of myospryn expression in human Duchenne muscular dystrophy, suggesting a connection to the pathophysiology of the disorder. Here we report that dystrophic muscle exhibits reduced PKA activity resulting, in part, from severely mislocalized myospryn and the type II regulatory subunit (RIIalpha) of PKA. Furthermore, we show that myospryn and dystrophin coimmunoprecipitate in native muscle extracts and directly interact in vitro. Our findings reveal for the first time abnormalities in the PKA signal transduction pathway and myospryn regulation in dystrophin deficiency.