Low‐volume resistance exercise attenuates the decline in strength and muscle mass associated with immobilization

We determined the effectiveness of low‐volume resistance exercise (EX) for the attenuation of loss of muscle mass and strength during leg immobilization. Men (N = 5) and women (N = 12, age 24 ± 5 years, body mass index 25.4 ± 3.6 kg/m²) were divided into two groups: exercise (EX; n = 12) and control (CON; n = 5). Subjects wore a knee brace on one leg that prevented weight bearing for 14 days. Resistance exercise (EX; 80% of maximal) was performed by the immobilized limb every other day. Immobilization induced a significant reduction (P < 0.05) in muscle fiber and thigh cross‐sectional area (CSA), isometric knee extensor, and plantarflexor strength in the CON (P < 0.01) but not in the EX group. There were significant losses in triceps surae CSA in the CON and EX groups (P < 0.05), but the losses were greater in CON subjects (P < 0.01). A minimal volume (140 contractions in 14 days) of resistive exercise is an effective countermeasure against immobilization‐induced atrophy of the quadriceps femoris but is only partially effective for the triceps surae. Muscle Nerve, 2010     

The effect of magnification on sonographically measured nerve cross‐sectional area

Introduction: The primary aim of this investigation was to determine whether use of write‐zoom magnification affects sonographically determined cross‐sectional area (CSA) of peripheral nerves. Methods: CSAs of the median (MN) and posterior interosseous (PIN) nerves were measured in 22 limbs from 11 asymptomatic volunteers using both standard imaging and write‐zoom magnification. CSA measurements were repeated on the same images 1 week later. Results: The average CSA of write‐zoomed images for the MN was significantly larger at both measurement sessions (week 1: 11.1 mm² write‐zoom vs. 10.0 mm² standard, P = 0.019; week 2: 11.8 mm² vs. 10.4 mm², P = 0.023). Similar differences were noted for the PIN (week 1: 2.3 mm² vs. 1.9 mm², P = 0.002; week 2: 2.5 mm² vs. 1.9 mm², P = 0.001). Conclusions: Write‐zoom magnification may significantly increase the measured CSA of peripheral nerves. These changes appear to be more substantial when smaller nerves are measured. Muscle Nerve 51 : 30–34, 2015     

Sonographic median nerve change after steroid injection for carpal tunnel syndrome

Introduction: The sonographic changes of the median nerve after steroid injection for carpal tunnel syndrome (CTS) still require investigation. Methods: Sixty‐two patients with CTS were included. The Boston Carpal Tunnel Questionnaire was administered, and ultrasonographic examinations were performed before and at 2, 6, and 12 weeks after steroid injection. At 12 weeks, general improvement was scored on a 6‐point Likert scale. Results: After treatment, the cross‐sectional area (CSA) of the median nerve was significantly reduced at 2‐, 6‐, and 12‐week follow‐ups (for each, P < 0.001, analysis of variance). The “significant improvement” group (n = 39) had a significantly greater reduction in the CSA at the carpal tunnel inlet (P = 0.014) and CSA in the proximal carpal tunnel (P = 0.003) compared with the “little/no improvement” group (n = 23). Discussion: Sonographic measurement of CSA may be considered complementary to the standard clinical evaluation in monitoring of treatment response in patients with CTS. Muscle Nerve 58 : 402–406, 2018     

Effects of neuromuscular fatigue on electromechanical delay of the leg extensors and flexors in young men and women

Introduction: We examined the effects of neuromuscular fatigue on volitional electromechanical delay (EMD) of leg extensors and flexors between genders. Methods: Twenty‐one men and 20 women performed 2 maximal voluntary contractions (MVCs), followed by intermittent isometric contractions of leg extensors and flexors using a 0.6 duty cycle (6‐s contraction, 4‐s relaxation) at 50% of MVC until volitional fatigue was achieved. MVCs were again performed at 0, 7, 15, and 30 min post‐fatigue. Results: EMD was greater compared with baseline at all post‐fatigue time phases for the leg flexors (P = 0.001–0.007), while EMD was greater at Post0, Post15 and Post30 (P = 0.001–0.023) for the leg extensors. EMD was also greater for leg extensors compared with leg flexors only at Post0. Conclusion: No differential gender‐related fatigue effects on EMD were shown. There were different fatigue‐induced responses between leg extensors and flexors, with leg extensors exhibiting higher EMD immediately post‐fatigue. Muscle Nerve 52 : 844–851, 2015     

Functional implications of impaired control of submaximal hip flexion following stroke

Introduction: We quantified submaximal torque regulation during low to moderate intensity isometric hip flexion contractions in individuals with stroke and the associations with leg function. Methods: Ten participants with chronic stroke and 10 controls performed isometric hip flexion contractions at 5%, 10%, 15%, 20%, and 40% of maximal voluntary contraction (MVC) in paretic, nonparetic, and control legs. Results: Participants with stroke had larger torque fluctuations (coefficient of variation, CV), for both the paretic and nonparetic legs, than controls (P < 0.05) with the largest CV at 5% MVC in the paretic leg (P < 0.05). The paretic CV correlated with walking speed (r² = 0.54) and Berg Balance Score (r² = 0.40). At 5% MVC, there were larger torque fluctuations in the contralateral leg during paretic contractions compared with the control leg. Conclusions: Impaired low‐force regulation of paretic leg hip flexion can be functionally relevant and related to control versus strength deficits poststroke. Muscle Nerve 49 : 225–232, 2014     

Normal values of median nerve cross‐sectional area obtained by ultrasound along its course in the arm with electrophysiological correlations,in 100 Asian subjects

Introduction: The objective of this study is to obtain normative cross‐sectional area (CSA) values for median nerve by ultrasound at predetermined sites and correlate them with electrophysiological variables in healthy Asian subjects. Methods: The median nerve was examined ultrasonographically in 100 healthy volunteers, mean age 39 years (range, 18–75 years). CSA of the median nerve was measured at wrist, mid‐forearm, mid‐arm, and axilla. All subjects underwent simultaneous standardized nerve conduction studies. Results: The mean median nerve CSAs ± SD at the distal wrist crease was 7.2 ± 1 mm²; mid‐forearm 4.8 ± 0.9 mm²; mid‐arm 6.1 ± 1 mm²; axilla 5.9 ± 0.9 mm². The CSA at the wrist was the largest compared with other levels (P < 0.001), and it increased with advancing age (P < 0.002). Conclusions: These normative data show that median nerve CSA is not uniform along its length. There are differences between gender, and values increase with advancing age. Muscle Nerve 49 : 284–286, 2014     

Neck Vessel Cross‐Sectional Area Measured with MRI: Scan‐Rescan Reproducibility for Longitudinal Evaluations

BACKGROUND AND PURPOSE

The cross‐sectional area (CSA) of common carotid arteries‐internal carotid arteries (CCA‐ICAs), vertebral arteries (VAs), and internal jugular veins (IJVs) is influenced by aging. However, the neck vessel CSA can be affected by other factors as well, including subject positioning, hydration, and respiration, especially in longitudinal studies. This study aimed to assess scan‐rescan reproducibility of CCA‐ICAs, VAs, and IJVs CSA measurements in order to evaluate their feasibility for longitudinal CSA assessments, and to apply the segmentation method on a longitudinal pilot dataset.

METHODS

Two set of 2‐dimensional neck magnetic resonance angiography (MRA) images were acquired on a 3‐T scanner from two separate datasets: 9 healthy individuals (HIs) were scanned 5 days apart (scan‐rescan dataset) and 12 HIs were acquired 5 years apart (baseline‐follow‐up dataset). CCA‐ICAs, VAs, and IJVs were segmented along the whole vessel length between C3 and C7 intervertebral spaces. Repeated measure analysis of covariance, adjusted for cervical level and sample, and Wilcoxon signed‐rank sum test were used to assess the scan‐rescan and baseline‐follow‐up CSA differences. Intraclass correlation coefficient (ICC) was also computed to evaluate scan‐rescan reliability.

RESULTS

No significant CSA differences were found for the scan‐rescan and baseline‐follow‐up CSA comparisons, using the whole vessel length or single cervical level measurements. ICC analysis showed good degree of scan‐rescan reproducibility (considering whole vessel measures: ICC > .9, P‐value < .001 for CCA‐ICAs, ICC > .6, P‐value < .001 for VAs, and ICC > .7, P‐value < .001 for IJVs).

CONCLUSIONS

Scan‐rescan reproducibility of CCA‐ICAs, VAs, and IJVs CSA measurements is high, making longitudinal studies feasible.     

Assessment of musculo‐articular and muscle stiffness in young and older men

Introduction: The aim of this cross‐sectional study was to concurrently assess musculo‐articular stiffness (MAS) and muscle stiffness (MS) of the knee extensors in younger and older individuals. Methods: Fourteen young (22.1 ± 3.0 years old) and 12 older (65.4 ± 5.7 years old) men were tested for maximal voluntary contraction (MVC), rate of torque development (RTD), muscle thickness, MAS, and MS of knee extensors. Results: MVC, RTD, and muscle thickness were higher in the younger group (288.6 vs. 194.3 Nm, 1319.5 vs. 787.0 Nm s^?1, 23.1 vs. 17.7 mm, respectively, P < 0.05). MAS normalized to the load supported (30% of MVC) was not different between groups (87.9 vs. 88.5 Nm^?1kg^?1), whereas the older group exhibited a higher level of normalized MS (23.2 vs. 18.6 Nm^?1kg^?1, P < 0.05). Conclusions: Determinants of MS have been highlighted along with their role in elevated MS. The unaltered level of MAS, which is functionally important in an aging population, might be achieved through a decrease in tendon stiffness. Muscle Nerve 46: 559–565, 2012     

Variability and distribution of muscle strength and its determinants in humans

Introduction: Inter‐individual variability in measurements of muscle strength and its determinants was identified to: (1) produce a normative data set describing the normal range and (2) determine whether some measurements are more informative than others when evaluating inter‐individual differences. Methods: Functional and morphological characteristics of the vastus lateralis were measured in 73 healthy, untrained adult men. Results: Inter‐individual variability (coefficient of variation) was greater for isometric maximal voluntary contraction (MVC) torque (18.9%) compared with fascicle force (14.6%; P = 0.025) and physiological cross‐sectional area (PCSA; 17.2%) compared with anatomical cross‐sectional area (ACSA, 13.0%; P < 0.0005). The relationship between ACSA and isometric MVC torque (r² = 0.56) was weaker than that between PCSA and fascicle force (r² = 0.68). Conclusions: These results provide a normative data set on inter‐individual variability in a variety of muscle strength‐related measurements and illustrate the benefit of using more stringent measures of muscle properties. Muscle Nerve 49 : 879–886, 2014     

Effects of microgravity on the mouse triceps brachii muscle

Introduction: In this study we investigated the effects of microgravity on the fiber properties of the mouse triceps brachii, a forelimb muscle that has no antigravity function. Methods: Mice (n = 7) were exposed to microgravity for 13 days on the space shuttle Atlantis (Space Transportation System‐135). The fiber cross‐sectional area (CSA) and succinate dehydrogenase (SDH) staining intensity of the triceps brachii muscle were compared with those of controls (n = 7). SDH activity in this muscle was also estimated. Results: Microgravity did not affect the body weight, muscle weight, or fiber CSA, but there was reduced SDH staining intensity of all types of fibers, irrespective of the muscle region (P < 0.05). Microgravity also reduced muscle SDH activity (P < 0.05). Conclusions: Short‐term exposure to microgravity induced a decrease in oxidative capacity, but not atrophy, in the triceps brachii muscle of mice. Muscle Nerve 52 : 63–68, 2015     

Post‐activation potentiation: The neural effects of post—activation depression

Introduction: Our knowledge of the neurophysiology of post‐activation potentiation (PAP) is limited. The purpose of this study was to examine the effect of PAP on twitch torque and H‐reflex amplitude after a 10‐s maximal voluntary contraction (MVC). Methods: PAP measurements were assessed with the plantarflexors in a relaxed state and during a tonic contraction at 10% MVC. Results: The H‐reflex/maximum M‐wave ratio (H/M) decreased significantly (P < 0.05) and returned to baseline levels after 1 min. The decrement in H/M was depressed when the plantarflexors were active at 10% MVC, and the depression was more obvious in the lateral gastrocnemius than in the soleus muscle. Conclusions: The inhibition induced immediately after contraction could be attributed to post‐activation depression. We conclude that PAP after a 10‐s MVC cannot be attributed to increased motor neuron excitability through the reflex pathway as assessed by the H‐reflex technique. Muscle Nerve 52 : 252–259, 2015     

Muscle function in monozygotic female twin pairs discordant for hormone replacement therapy

Introduction: Postmenopausal monozygotic twin pairs discordant for hormone replacement therapy (HRT) provide an advantageous study design controlling for genetic background for elucidating the relationships between aging, sex hormone levels, muscle strength, contractile capacity, and fatigability. Methods: Thirteen postmenopausal monozygotic twin pairs discordant for HRT were measured for maximal voluntary torque (MVC) and twitch characteristics using electrical stimulation before and after intermittent dynamic plantarflexor exercise until exhaustion. Results: Peak twitch torque was 32% higher in HRT users than in their non‐HRT, genetically identical sisters (P = 0.002), but MVC did not differ. There were no differences in the activation level or twitch time characteristics between the co‐twins. Fatigue caused decreases in MVC (P = 0.001), twitch torque (P = 0.001), time to peak (P = 0.013), and half‐relaxation time (P = 0.001) similarly in HRT users and non–HRT users. Conclusion: In early postmenopausal women, involuntary but not voluntary force‐generating mechanisms of the plantarflexors are augmented by the use of HRT. Muscle Nerve, 2011     

Ultrasonographic cross‐sectional area normal values of the ulnar nerve along its course in the arm with electrophysiological correlations in 100 asian subjects

Introduction: Normative cross‐sectional areas (CSAs) have been obtained for the Western population. We obtained CSAs of normal ulnar nerves at predetermined sites and correlate them with electrophysiological variables in Asian subjects. Methods: One hundred healthy volunteers, mean age 39 ± 14 years (range, 18–75 years), were recruited for the study after obtaining informed consent. The ulnar nerve was examined ultrasonographically from wrist to axilla, and CSA was measured at predetermined sites. All subjects underwent a simultaneous standardized nerve conduction study. Results: Men had larger CSAs, and CSAs increased with advancing age. There was a statistically significant correlation between CSA at the wrist and distal ulnar motor latency (P = 0.005). Conclusions: Ulnar CSA correlated with age, gender, and distal motor latency. No correlations were observed with height, weight, or body mass index. Muscle Nerve 47: 673–676, 2013     

Nerve enlargement after cold exposure: A pilot study with ultrasound imaging

Introduction: Changes of electrophysiogical parameters with regard to cold have been studied intensively but not the morphology of nerves. We explored the effects of cold exposure on median nerve morphology. Methods: Cross‐sectional area (CSA) and depth of the right median nerve were assessed at the carpal tunnel and mid‐forearm levels before and after 15 min ice‐pack application in 34 healthy volunteers. Results: After cooling, mean CSA measurements increased at the carpal tunnel and mid‐forearm levels (from 8.00 to 8.85 and 6.64 to 7.55, respectively, P < 0.05); however, the depth values were similar. Conclusions: These preliminary results revealed that cold exposure may cause acute nerve swelling. Further studies with larger samples will be necessary to confirm our findings, to correlate them with electrophysiological data, and to explore when/how the nerve edema resolves. Muscle Nerve 49:502–505, 2014     

Reference values for ultrasonograpy of peripheral nerves

Introduction: High‐resolution ultrasonography (HRU) is a novel method that provides morphological information about peripheral nerves. We aimed to determine reference values for nerve cross‐sectional area (CSA) on HRU. Methods: One hundred healthy volunteers had HRU of median, radial, ulnar, fibular, tibial, sural, and superficial fibular nerves at defined sites. The CSA was measured and the effects of age, gender, and body mass index (BMI) were evaluated. Results: CSA values in healthy subjects are described. CSA is larger in lower limb motor nerves than in sensory nerves at similar sites, and the CSA tends to be symmetrical. The strongest effect on CSA was for age, although gender and BMI had some effects. Conclusions: This study provides normative values for HRU, and it suggests that further research with age‐ and gender‐specific distributions must be a key priority in the development of HRU for use as a diagnostic test for peripheral nerve diseases. Muscle Nerve 53 : 538–544, 2016     

Increased voluntary drive is associated with changes in common oscillations from 13 to 60 Hz of interference but not rectified electromyography

The purpose of this study was to compare the capability of interference and rectified electromyography (EMG) to detect changes in the beta (13–30‐HZ ) and Piper (30–60‐HZ ) bands when voluntary force is increased. Twenty adults exerted a constant force abduction of the index finger at 15% and 50% of maximum. The common oscillations at various frequency bands (0–500 HZ ) were estimated from the first dorsal interosseous muscle using cross wavelets of interference and rectified EMG. For the interference EMG signals, normalized power significantly (P < 0.01) increased with force in the beta (9.0 ± 0.9 vs. 15.5 ± 2.1%) and Piper (13.6 ± 0.9 vs. 21 ± 1.7%) bands. For rectified EMG signals, however, the beta and Piper bands remained unchanged (P > 0.4). Although rectified EMG is used in many clinical studies to identify changes in the oscillatory drive to the muscle, our findings suggest that only interference EMG can accurately capture the increase in oscillatory drive from 13 to 60 HZ with voluntary force. Muscle Nerve, 2010     

Ultrasonography in severe carpal tunnel syndrome

Introduction: In up to 30% of patients with carpal tunnel syndrome (CTS), the cross‐sectional area (CSA) of the median nerve may not be enlarged. We hypothesize that this could be the result of secondary atrophy of the nerve in severe CTS. The aim of this study was to measure the ultrasonographic CSA of the median nerve at the wrist in patients with severe CTS. Methods: In 14 consecutive patients with clinically and electrophysiologically defined severe CTS, the CSA of the median nerve was measured and compared with that of control subjects. Results: CSA of the median nerve exceeded the upper limit of normal in the majority of patients with severe CTS. Conclusions: Atrophy of the median nerve in severe CTS does not explain negative ultrasonographic test results. Instead, the CSA of the median nerve is enlarged in most patients with severe CTS. Muscle Nerve, 2012     

Spinal and supraspinal mechanisms affecting torque development at different joint angles

Introduction: We examined the neural mechanisms responsible for plantar flexion torque changes at different joint positions. Methods: Nine subjects performed maximal voluntary contractions (MVC) at 6 ankle–knee angle combinations [3 ankle angles (dorsiflexion, anatomic position, plantar flexion) and 2 knee angles (flexion, full extension)]. Neural mechanisms were determined by V‐wave, H‐reflex (at rest and during MVC), and electromyography during MVC (RMS), normalized to the muscle compound action potential (V/M_sup, H_max/M_max, H_sup/M_sup and RMS/M_sup) and voluntary activation (VA), while muscle function was assessed by doublet amplitude. Results: MVC and doublet amplitude were significantly lower at plantar flexion (P < 0.01), while VA was significantly lower at dorsiflexion and full knee extension (P < 0.05). V/M_sup and RMS/M_sup were significantly lower at knee extension (P < 0.01), while H_sup/M_sup was not affected by joint angle. Conclusions: These results indicate that joint positions leading to muscle lengthening produce reduced neural drive, due mainly to supraspinal mechanisms. Muscle Nerve 53 : 626–632, 2016     

Neuromuscular fatigue of the knee extensors during repeated maximal intensity intermittent‐sprints on a cycle ergometer

Introduction: We studied the time course of neuromuscular fatigue during maximal intensity intermittent‐sprint cycling. Methods: Eight participants completed 10, 10‐s sprints interspersed with 180 s of recovery. The power outputs were recorded for each sprint. Knee extensor maximum voluntary contraction (MVC) force, voluntary activation, and evoked contractile properties were recorded presprint, postsprint 5, and postsprint 10. Results: Total work over the 10 sprints decreased significantly (P < 0.05) and could be described by 2 linear relationships from sprints 1–5 compared with sprints 6–10. Participants had significantly (P < 0.05) lower MVC and twitch forces postsprint 5 compared with presprint. MVC, voluntary activation, and twitch force were decreased (P < 0.05) postsprint 10 compared with postsprint 5. Conclusions: The maximal intermittent sprints induced neuromuscular fatigue. Neuromuscular fatigue in the first 5 sprints was mainly peripheral, whereas in the last 5 sprints it was both peripheral and central. Muscle Nerve 51: 569–579, 2015     

Age‐ and gender‐related regional variations of human brain cortical thickness,complexity, and gradient in the third decade

Brain functional and cytoarchitectural maturation continue until adulthood, but little is known about the evolution of the regional pattern of cortical thickness (CT), complexity (CC), and intensity or gradient (CG) in young adults. We attempted to detect global and regional age‐ and gender‐related variations of brain CT, CC, and CG, in 28 healthy young adults (19–33 years) using a three‐dimensional T₁‐weighted magnetic resonance imaging sequence and surface‐based methods. Whole brain interindividual variations of CT and CG were similar to that in the literature. As a new finding, age‐ and gender‐related variations significantly affected brain complexity (P < 0.01) on posterior cingulate and middle temporal cortices (age), and the fronto‐orbital cortex (gender), all in the right hemisphere. Regions of interest analyses showed age and gender significant interaction (P < 0.05) on the temporopolar, inferior, and middle temporal‐entorrhinal cortices bilaterally, as well as left inferior parietal. In addition, we found significant inverse correlations between CT and CC and between CT and CG over the whole brain and markedly in precentral and occipital areas. Our findings differ in details from previous reports and may correlate with late brain maturation and learning plasticity in young adults' brain in the third decade. Hum Brain Mapp 35:2817–2835, 2014. © 2013 Wiley Periodicals, Inc.