The use of acoustic myography to assess changes in muscle control with ageing in healthy subjects ranging 20 to 79 years.

In some neurological conditions, like Parkinson’s disease (PD) and Cerebral Palsy (CP), as well as with ageing, muscle spindles have been mentioned as participating in the pathological response of observed muscles. The aim of this review has therefore been to examine what is known about muscle spindle receptors, their function and how they are involved in regulating precise muscle movement in relation to these two conditions. Data from acoustic myography (AMG) studies with healthy controls (HC), CP and PD subjects have been re-examined with a view to identifying possible effects of changes in muscle movement which could be related to muscle spindle receptor function. Studies of muscle spindles have shown that during shortening and lengthening contractions the fusimotor system is activated differently with different discharge frequencies and sensitivities. With increasing age comes a loss of precise proprioception, something that coincides with a change in the AMG E-score towards lower values, indicating a reduced level of coordination and efficiency of muscle use. With PD and CP there is likewise a documented decrease in proprioception, also showing lower E-values than age-matched HC subjects. We conclude that the decrease in proprioception observed in these subjects must be partly due to a change in the muscle spindle / C-centre feedback system.

Acoustic myography (AMG) is a non-invasive method to assess muscle function during daily activities. AMG has great scope for assessment of musculoskeletal problems. The aim of this study was to create an AMG data set for general clinical use and relate these findings to age and gender. 10 healthy subjects (5 men/5 women), in each decade from 20 to 69 years of age (n = 50), were assessed. Their clinical health was tested. AMG measurements were carried out on muscles involved in defined movements of the upper and lower extremities. Muscle performance was measured using efficiency (E-score) and fibre recruitment (temporal (T-score) and spatial (S-score) summation). AMG-measurements showed good reproducibility. In each age group, it was found that for all those daily living skills measured, there was no gender difference. A walking and stair climbing test revealed that both legs are used equally and in a balanced way in healthy subjects. Moreover, there was no change in this function with increasing age up to 69 years. However, a cycling test with loading revealed that in elderly subjects the coordination of muscle use is impaired compared to that of the younger adults. Finally, a flexion test of the arm revealed an age-related decrease in the efficiency/coordination of m.Biceps alone, and a keyboard writing test suggests no effect on m.Trapezius. This reference data set now illustrates the reproducibility and ease of use of acoustic myography in the clinic and provides a means of assessing individuals with musculoskeletal problems.

An Investigation Into the Short-Term Effects of Photobiomodulation on the Mechanical Nociceptive Thresholds of M. Longissimus and M. Gluteus Medius, in Relation to Muscle Firing Rate in Horses at Three Different Gaits

The evidence for neural mechanisms underpinning rapid strength increases has been investigated and discussed for over 30 years using indirect methods, such as surface electromyography, with inferences made toward the nervous system. Alternatively, electrical stimulation techniques such as the Hoffman reflex, volitional wave, and maximal wave have provided evidence of central nervous system changes at the spinal level. For 25 years, the technique of transcranial magnetic stimulation (TMS) has allowed for noninvasive supraspinal measurement of the human nervous system in a number of areas such as fatigue, skill acquisition, clinical neurophysiology, and neurology. However, it has only been within the last decade that this technique has been used to assess neural changes after strength training. The aim of this brief review is to provide an overview of TMS, discuss specific strength training studies that have investigated changes, after short-term strength training in healthy populations in upper and lower limbs, and conclude with further research suggestions and the application of this knowledge for the strength and conditioning coach.

The effects of subablative Q-switched Nd-YAG laser irradiation on the nerve fiber population of the sciatic nerve in rat were estimated using a quantitative method. The acute and cumulative effects were evaluated separately. When 5-minute laser irradiation was applied to the sciatic nerve, there was a differential decrease in the number of active fibers in slow and fast fiber classes. Fast fibers were insensitive to the radiation as the number of fibers was not altered significantly except at high radiating energies. The amount of decrease in each fiber class was not strictly proportional to the radiating laser energy. The cumulative effects show an exponential decay in fiber number after radiation sequence of gradually incremented laser pulse energy. Similarly, the impairment of fast fiber classes was less significant than slow fiber classes. At high cumulative optical energy, the number of fibers in fast fiber classes started decreasing whereas fiber population in slow fiber classes increased. We postulate that the impairment of the node of Ranvier was the dominant mechanism at lowenergy radiation, whereas the change in the cable properties of internodes resulted in the shift of fast fibers to slower fiber classes.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electromyography (EMG) and acoustic myography (AMG) play crucial roles in assessing muscle function, providing valuable insights into neural control, muscle activation, and fatigue levels. However, the current landscape reveals a gap in dual‐modal stretchable sensing patches, highlighting the need for comfortable and wearable solutions in the field of in situ monitoring of synchronous EMG and AMG sensing. In this work, a dual‐modal stretchable patch (DMSP) is developed that fully integrates a multi‐channel EMG electrode with AMG sensors. It possesses stable electromechanical properties even at strains exceeding 200%. With an overall modulus of under 40 kPa and a skin adhesion force surpassing 30 N m−1, the DMSP exhibits exceptional durability, enduring 1000 stretching cycles. The DMSP enables in situ simultaneous monitoring of EMG and AMG signals from sternocleidomastoid muscle during neck rotation where the mechanical strain reaches up to 30%. The DMSP proves instrumental in characterizing muscle activity, facilitating in‐depth research on muscle movement, and thus enhancing clinical outcomes in rehabilitation medicine and physical therapy.

Purpose To determine which potential contributing factors are associated with upper limb associated reaction (AR) expression in individuals with acquired brain injury (ABI). Methods Forty-two participants underwent three-dimensional motion analysis at self-selected walking speed to generate the AR outcome measure, quantifying their upper limb kinematic deviation compared to healthy controls. Clinical assessment included: upper and lower limb hypertonicity, spasticity and strength, balance, dynamic walking stability, arm and leg function, anxiety, arm pain/discomfort, and fear of falling. Results Significant, moderate-to-strong correlations (r = 0.42–0.74, p < 0.05) existed between upper limb ARs and both hypertonicity and spasticity of the upper limb muscles and the knee extensors. Significant, moderate correlations to ARs (r = 0.42–0.59, p < 0.05) existed for balance, dynamic stability, upper limb strength, and arm function. The severity of AR was significantly different between those with and without hypertonicity of the four tested upper limb muscles, elbow and long finger flexor spasticity, knee extensor spasticity, and reduced dynamic stability (p < 0.05; effect sizes ≥0.80). However, these contributing factors were not present in all participants. Conclusions Associated reactions are complex and multi-factorial. There were several significant correlations indicating that factors may influence AR severity. While positive upper motor neuron syndrome features should be prioritised for clinical assessment, these factors are not prerequisites for ARs. IMPLICATIONS FOR REHABILITATION Upper limb associated reactions are a complex and multi-factorial phenomenon. Upper limb muscle hypertonicity and spasticity should be prioritised for assessment; however, they are not prerequisites for associated reactions. Hypertonicity and spasticity should be differentiated as they may have differing relationships to associated reactions. Knee extensor hypertonicity and spasticity, postural stability, upper limb strength, and arm function may also be contributing factors to consider.

Effects of upper limb unilateral isometric efforts on postural stabilization in subjects with hemiparesis

The reticulospinal (RS) system is a fundamental descending pathway involved in human movement control. However, the relative strength of RS projections across different muscles and its specific contributions to distinct movements are poorly understood. We systematically mapped the RS drive across a broad range of muscles in the upper and lower extremities. The RS drive was assessed in 14 muscles of 29 healthy participants using the StartReact paradigm, characterized by shortened premotor reaction times when movement initiation is paired with a loud versus moderate acoustic stimulus. Reaction times were assessed by surface EMG. RS drive was compared as follows: (1) across individual muscles; (2) between proximal and distal muscles; and (3) between flexor and extensor muscles. The RS drive was lowest in the finger abductor, with significantly reduced values in comparison to those in the shoulder flexor and extensor, the elbow flexor, hip and knee extensors, and the ankle plantar flexor. A proximal‐to‐distal gradient in RS drive was observed only in the upper extremities, mainly attributable to the low RS drive to the finger abductor. Additionally, the RS drive was greater to flexors than to extensors in the upper extremities. Conversely, the RS drive was enhanced to extensors versus flexors in the lower extremities. Our findings emphasize the presence of RS drive in all examined muscles, with no distinctive proximal‐to‐distal gradient in RS motor control. Notably, a reversed flexor–extensor bias in RS control was evident between the upper and lower extremities. These findings advance our understanding of RS motor control and might inform the development of targeted neurorehabilitation strategies.

Hereditary sensory and autonomic neuropathy type III (HSAN III), also known as familial dysautonomia or Riley–Day syndrome, results from an autosomal recessive genetic mutation that causes a selective loss of specific sensory neurones, leading to greatly elevated pain and temperature thresholds, poor proprioception, marked ataxia and disturbances in blood pressure control. Stretch reflexes are absent throughout the body, which can be explained by the absence of functional muscle spindle afferents – assessed by intraneural microelectrodes inserted into peripheral nerves in the upper and lower limbs. This also explains the greatly compromised proprioception at the knee joint, as assessed by passive joint‐angle matching. Moreover, there is a tight correlation between loss of proprioceptive acuity at the knee and the severity of gait impairment. Surprisingly, proprioception is normal at the elbow, suggesting that participants are relying more on sensory cues from the overlying skin; microelectrode recordings have shown that myelinated tactile afferents in the upper and lower limbs appear to be normal. Nevertheless, the lack of muscle spindles does affect sensorimotor control in the upper limb: in addition to poor performance in the finger‐to‐nose test, manual performance in the Purdue pegboard task is much worse than in age‐matched healthy controls. Unlike those rare individuals with large‐fibre sensory neuropathy, in which both muscle spindle and cutaneous afferents are absent, those with HSAN III present as a means of assessing sensorimotor control following the selective loss of muscle spindle afferents.

Invited Commentary on: ‘Advances in neuromuscular electrical stimulation for the upper limb post stroke’, Hayward et al. Hayward et al.’s review paper summarizes the current applications of neuromuscular electrical stimulation (NMES) and the treatment effects of different types of NMES in the impairment, activity, and participation domains of International Classification of Functioning, Disability and Health model for stroke patients. In addition, they suggested future research directions for NMES research. We would like to remind readers that there is another important question for future research, i.e. the influence of NMES parameters (stimulation time, intensity, treatment duration, and target muscles) on affected upper limb recovery post-stroke. It has been suggested that parameters of electrical stimulation are likely to be crucial factors related to treatment effect. Owing to the heterogeneity of NMES parameters adopted in the articles reviewed in the current study, the readers must be cautious while applying the results from this study to their individual patients. According to motor learning theories, repetition is important for improving movement performance. Hence, it is reasonable to assume that there might be a positive relationship between number of practice trials and motor performance improvement. Previous studies have demonstrated that increasing exercise time led to better functional outcomes. Can we apply this principle for NMES treatment? Will higher doses of NMES lead to better arm function recovery than lower doses of NMES? What is the optimal treatment dose for selected NMES to improve impairment or function of the upper limb after stroke? The answers to these questions remain ambiguous because the stimulation doses of NMES ranged widely from as little as a total of 6 hours to more than 200 hours among studies. The minimal effective dose for improving upper limb function from our own study was 10 hours. Our study revealed that dosage of NMES was a significant predictor for upper limb function improvement and increasing the stimulation dose of NMES led to greater improvement in the action research arm test score at follow-up. Another important issue in NMES application is the influence of selection of target muscles. de Kroon et al.’s study showed that there was no significant difference between alternating stimulation of the hand extensor and flexor muscles or stimulation hand extensors only. Our study found that patients who received stimulation of both hand flexor and extensor muscles showed greater improvement as compared with those receiving stimulation of extensor muscles. Furthermore, de Kroon et al.’s review paper reported an increased likelihood of a positive outcome if elbow and shoulder muscles were stimulated in addition to wrist and/or finger extensors. The relationship between stimulated target muscles and arm function remains unclear based on current available evidences. Hayward et al. suggested that more studies are needed to investigate effects of NMES on patients with severe paresis or paralysis in acute stage. This could provide more information for clinicians regarding which stroke patients will benefit from NMES intervention or is suitable for which types of NMES. Some studies supported the treatment effect of NMES in the acute phase; however, few studies have applied NMES in patients with severe paresis. Our own experience indicated that cyclic NMES can be applied to patients in the acute flaccid stage or to patients with severe arm weakness with satisfactory results on both the impairment and the function levels. NMES is a useful adjunct therapy for stroke rehabilitation during both acute and chronic stages. The current review paper provided an overview of current and emerging NMES applications. It offers a good overview for clinicians to select appropriate NMES techniques for improving either the impairment or function of upper limb after stroke. For future studies, we hope that more information on the influence of NMES parameters on affected upper limb recovery can be provided.

BackgroundMagnetic resonance imaging (MRI) features are typical findings in Hirayama disease (HD) and are useful diagnostic entities but may not be present in all patients.Case presentationWe present the case of a 22-year-old Nepalese man who presented with insidious onset of weakness of his right upper limb of more than 5 years duration. His weakness was progressive for the first 3 years, and then remained static. On examination, weakness of the interossei, thenar, hypothenar, flexor, and extensor muscles were present in his right upper limb, power was normal in his left upper and bilateral lower limbs. Minipolymyoclonus was present in both upper limbs, less prominent on the left side. Electrophysiological findings showed motor axonal neuropathy in his right upper limb, neurogenic discharges and fibrillations, and fasciculations in both upper limbs. Contrast magnetic resonance imaging (MRI) of his cervical spine in flexion was normal. Our patient was diagnosed with HD based on clinical and electrophysiological findings. Our patient was advised to use a cervical collar and regular physiotherapy and was found to have subjective benefit.ConclusionA normal cervical MRI does not rule out HD and the diagnosis can also be made based on clinical and electrophysiological studies. Progressive distal upper limb weakness or tremor in young patients should be evaluated for HD, because early diagnosis and intervention might halt the progression.

Terrestrial animals increase their walking speed by increasing the activity of the extensor muscles. However, the mechanism underlying how this speed-dependent amplitude modulation is achieved remains obscure. Previous studies have shown that group Ib afferent feedback from Golgi tendon organs that signal force is one of the major regulators of the strength of muscle activity during walking in cats and humans. In contrast, the contribution of group Ia/II afferent feedback from muscle spindle stretch receptors that signal angular displacement of leg joints is unclear. Some studies indicate that group II afferent feedback may be important for amplitude regulation in humans, but the role of muscle spindle feedback in regulation of muscle activity strength in quadrupedal animals is very poorly understood. To examine the role of feedback from muscle spindles, we combined in vivo electrophysiology and motion analysis with mouse genetics and gene delivery with adeno-associated virus. We provide evidence that proprioceptive sensory feedback from muscle spindles is important for the regulation of the muscle activity strength and speed-dependent amplitude modulation. Furthermore, our data suggest that feedback from the muscle spindles of the ankle extensor muscles, the triceps surae, is the main source for this mechanism. In contrast, muscle spindle feedback from the knee extensor muscles, the quadriceps femoris, has no influence on speed-dependent amplitude modulation. We provide evidence that proprioceptive feedback from ankle extensor muscles is critical for regulating muscle activity strength as gait speed increases. NEW & NOTEWORTHY Animals upregulate the activity of extensor muscles to increase their walking speed, but the mechanism behind this is not known. We show that this speed-dependent amplitude modulation requires proprioceptive sensory feedback from muscle spindles of ankle extensor muscle. In the absence of muscle spindle feedback, animals cannot walk at higher speeds as they can when muscle spindle feedback is present.

The present study investigated potential age-related changes in human muscle spindles with respect to the intrafusal fiber-type content and myosin heavy chain (MyHC) composition in biceps brachii muscle. The total number of intrafusal fibers per spindle decreased significantly with aging, due to a significant reduction in the number of nuclear chain fibers. Nuclear chain fibers in old spindles were short and some showed novel expression of MyHC alpha-cardiac. The expression of MyHC alpha-cardiac in bag1 and bag2 fibers was greatly decreased in the A region. The expression of slow MyHC was increased in nuclear bag1 fibers and that of fetal MyHC decreased in bag2 fibers whereas the patterns of distribution of the remaining MyHC isoforms were generally not affected by aging. We conclude that aging appears to have an important impact on muscle spindle composition. These changes in muscle spindle phenotype may reflect an age-related deterioration in sensory and motor innervation and are likely to have an impact in motor control in the elderly.

Individuals with hereditary sensory and autonomic neuropathy type III (HSAN III), also known as Riley-Day syndrome or familial dysautonomia, do not have functional muscle spindle afferents but do have essentially normal cutaneous mechanoreceptors. Lack of muscle spindle feedback from the legs may account for the poor proprioception at the knee and the ataxic gait typical of HSAN III. Given that functional muscle spindle afferents are also absent in the upper limb, we assessed whether proprioception at the elbow was likewise compromised. Passive joint angle matching showed that proprioception was normal at the elbow, suggesting that individuals with HSAN III rely more on cutaneous afferents around the elbow. Hereditary sensory and autonomic neuropathy type III (HSAN III) is a rare neurological condition that features a marked ataxic gait that progressively worsens over time. We have shown that functional muscle spindle afferents are absent in the upper and lower limbs in HSAN III, and we have argued that this may account for the ataxia. We recently used passive joint angle matching to demonstrate that proprioception of the knee joint is very poor in HSAN III but can be improved towards normal by application of elastic kinesiology tape across the knee joints, which we attribute to the presence of intact cutaneous mechanoreceptors. Here we assessed whether proprioception was equally compromised at the elbow joint, and whether it could be improved through taping. Proprioception at the elbow joint was assessed using passive joint angle matching in 12 HSAN III patients and 12 age-matched controls. There was no difference in absolute error, gradient or correlation coefficient of the relationship between joint angles of the reference and indicator arms. Unlike at the knee, taping did not improve elbow proprioception in either group. Clearly, the lack of muscle spindles compromised proprioception at the knee but not at the elbow, and we suggest that the HSAN III patients rely more on proprioceptive signals from the skin around the elbow.