A comparison of fibre size, fibre type constitution and spatial fibre type distribution in normal human muscle and in muscle from cases of spinal muscular atrophy and from other neuromuscular disorders

Comparison of onset of neuromuscular blockade with electromyographic and acceleromyographic monitoring: a prospective clinical trial

BACKGROUND

Reliable devices that quantitatively monitor the level of neuromuscular blockade after neuromuscular blocking agents' administration are crucial. Electromyography and acceleromyography are two monitoring modalities commonly used in clinical practice. The primary outcome of this study is to compare the onset of neuromuscular blockade, defined as a Train-Of-Four Count (TOFC) equal to 0, as measured by an electromyography-based device (TetraGraph) and an acceleromyography-based device (TOFscan). The secondary outcome was to compare intubating conditions when one of these two devices reached a TOFC equal to 0.

METHODS

One hundred adult patients scheduled for elective surgery requiring neuromuscular blockade were enrolled. Prior to induction of anesthesia, TetraGraph electrodes were placed over the forearm of patients' dominant/non-dominant hand based on randomization and TOFscan electrodes placed on the contralateral forearm. Intraoperative neuromuscular blocking agent dose was standardized to 0.5 mg.kg-1 of rocuronium. After baseline values were obtained, objective measurements were recorded every 20 seconds and intubation was performed using video laryngoscopy once either device displayed a TOFC = 0. The anesthesia provider was then surveyed about intubating conditions.

RESULTS

Baseline TetraGraph train-of-four ratios were higher than those obtained with TOFscan (Median: 1.02 [0.88, 1.20] vs. 1.00 [0.64, 1.01], respectively, p < 0.001). The time to reach a TOFC = 0 was significantly longer when measured with TetraGraph compared to TOFscan (Median: 160 [40, 900] vs. 120 [60, 300] seconds, respectively, p < 0.001). There was no significant difference in intubating conditions when either device was used to determine the timing of endotracheal intubation.

CONCLUSIONS

The onset of neuromuscular blockade was longer when measured with TetraGraph than TOFscan, and a train-of-four count of zero in either device was a useful indicator for adequate intubating conditions.

CLINICAL TRIAL NUMBER AND REGISTRY

URL NCT05120999, https://clinicaltrials.gov/ct2/show/NCT05120999.

Diffusion-tensor magnetic resonance imaging captures increased skeletal muscle fibre diameters in Becker muscular dystrophy

BACKGROUND

Becker muscular dystrophy (BMD) is an X-linked disorder characterized by slow, progressive muscle damage and muscle weakness. Hallmarks include fibre-size variation and replacement of skeletal muscle with fibrous and adipose tissues, after repeated cycles of regeneration. Muscle histology can detect these features, but the required biopsies are invasive, are difficult to repeat and capture only small muscle volumes. Diffusion-tensor magnetic resonance imaging (DT-MRI) is a potential non-invasive alternative that can calculate muscle fibre diameters when applied with the novel random permeable barrier model (RPBM). In this study, we assessed muscle fibre diameters using DT-MRI in BMD patients and healthy controls and compared these with histology.

METHODS

We included 13 BMD patients and 9 age-matched controls, who underwent water-fat MRI and DT-MRI at multiple diffusion times, allowing RPBM parameter estimation in the lower leg muscles. Tibialis anterior muscle biopsies were taken from the contralateral leg in 6 BMD patients who underwent DT-MRI and from an additional 32 BMD patients and 15 healthy controls. Laminin and Sirius-red stainings were performed to evaluate muscle fibre morphology and fibrosis. Twelve ambulant patients from the MRI cohort underwent the North Star ambulatory assessment, and 6-min walk, rise-from-floor and 10-m run/walk functional tests.

RESULTS

RPBM fibre diameter was significantly larger in BMD patients (P = 0.015): mean (SD) = 68.0 (25.3) μm versus 59.4 (19.2) μm in controls. Inter-muscle differences were also observed (P ≤ 0.002). Both inter- and intra-individual RPBM fibre diameter variability were similar between groups. Laminin staining agreed with the RPBM, showing larger median fibre diameters in patients than in controls: 72.5 (7.9) versus 63.2 (6.9) μm, P = 0.006. However, despite showing similar inter-individual variation, patients showed more intra-individual fibre diameter variability than controls-mean variance (SD) = 34.2 (7.9) versus 21.4 (6.9) μm, P < 0.001-and larger fibrosis areas: median (interquartile range) = 21.7 (5.6)% versus 14.9 (3.4)%, P < 0.001. Despite good overall agreement of RPBM and laminin fibre diameters, they were not associated in patients who underwent DT-MRI and muscle biopsy, perhaps due to lack of colocalization of DT-MRI with biopsy samples.

CONCLUSIONS

DT-MRI RPBM metrics agree with histology and can quantify changes in muscle fibre size that are associated with regeneration without the need for biopsies. They therefore show promise as imaging biomarkers for muscular dystrophies.

Differential activation of the plantar flexor muscles in balance control across different feet orientations on the ground

The ankle plantar flexor muscles act synergistically to control quiet and dynamic body balance. Previous research has shown that the medial (MG) and lateral (LG) gastrocnemii, and soleus (SOL) are differentially activated as a function of motor task requirements. In the present investigation, we evaluated modulation of the plantar flexors' activation from feet orientation on the ground in an upright stance and the ensuing reactive response to a perturbation. A single group of young participants (n = 24) was evaluated in a task requiring initial stabilization of body balance against a backward pulling load (5% or 10% of body weight) attached to their trunk, and then the balance was suddenly perturbed, releasing the load. Four feet orientations were compared: parallel (0°), outward orientation at 15° and 30°, and the preferred orientation (M = 10.5°). Results revealed a higher activation magnitude of SOL compared to MG-LG when sustaining quiet balance against the 10% load. In the generation of reactive responses, MG was characterized by earlier, steeper, and proportionally higher activation than LG-SOL. Feet orientation at 30° led to higher muscular activation than the other orientations, while the activation relationship across muscles was unaffected by feet orientation. Our results support the conclusion of task-specific differential modulation of the plantar flexor muscles for balance control.

Effect of gender, muscle type and skinfold thickness on myometric parameters in young people

Background

The aim of the study was to compare the mechanical properties of three human skeletal muscles: biceps brachii (BB), rectus femoris (RF), and tibialis anterior (TA) at rest measured by myoton device in males (n = 16, mean age 21.2 ± 0.6 years) and females (n = 16; 21.2 ± 0.9 years) and to investigate the influence of skin and subcutaneous tissue thickness (skinfold thickness, SFT) and gender on myometric parameters of the three skeletal muscles.

Methods

We measured the following mechanical and viscoelastic muscle properties using MyotonPRO^®: frequency (F [Hz]), decrement (D [log]), stiffness (S [N/m]), relaxation time (R [ms]) and creepability (C [De]). The values of SFT for all selected muscles were assessed by caliper. A mixed-design analysis of variance with gender as between subject comparison was used for assessing the differences between gender and muscles in SFT and each of the myometric parameters separately (F, D, S, R and C). Pearson correlation coefficient or Spearman’s rank correlation coefficient between SFT and myometric parameters was conducted for males, females and males and females together. The level of statistical significance was set at α ≤ 0.05 with Bonferroni correction for multiple comparisons.

Results

The SFT over the RF, TA, and BB muscles in women was statistically significantly larger compared with that of males. In females and males, the SFT over the RF was larger than over the TA and BB, and the SFT over the TA was larger compared with over the BB. The values of F and S recorded for the TA muscle were the highest among the three muscles, while D, C, and R were lowest in TA but highest in the RF muscle in men and women. The values of F and S were smaller in females than in males. Gender comparison of D, C, and R values showed that only D for the RF was significantly lower in females than in males, and C for the RF and TA was significantly larger in females than in males. Some correlation between SFT and myometric parameters were different between males and females. For example, there was a significant, negative correlation between SFT and F for all muscles in females, and a significant, positive correlation between these parameters for BB and TA (not for RF) in males. For pooled data (males and females together), a negative significant correlation between SFT and F was observed for RF and TA (not significant for BB muscle).

Discussion

It is concluded that the TA compared with the BB and RF has significantly greater F and S but the smallest D and C and the shortest R. Gender and muscle differences in the SFT may affect the measurements of muscle properties using MyotonPRO^®. The relationship between SFT and myometric parameters is different in males and females in the RF, TA, and BB muscles. Therefore, the myometric data should be analyzed in males and females separately.

Association between the Range of Motion and Passive Property of the Gastrocnemius Muscle-Tendon Unit in Older Population

Range of motion has been widely known to decrease with age; however, factors associated with its decrease in the elderly population and especially its gender difference have been unclear. Therefore, this study aimed to investigate the factors associated with ankle dorsiflexion range of motion in the older population. Both male (n = 17, mean ± SD; 70.5 ± 4.2 years; 165.4 ± 5.3 cm; 63.8 ± 7.7 kg) and female (n = 25, 74.0 ± 4.0 years; 151.2 ± 4.9 cm; 50.1 ± 5.6 kg) community-dwelling older adults participated in this study. The ankle dorsiflexion and passive torque of both legs were measured using a dynamometer, and shear elastic modulus of the medial gastrocnemius muscle at 0° ankle angle was measured using ultrasonic shear wave elastography. In this study, we defined the passive torque at dorsiflexion range of motion (DF ROM) as the index of stretch tolerance, and shear elastic modulus as the index of passive muscle stiffness. The partial correlation coefficient adjusted by age, height, weight, and side (dominant or nondominant side) was used to analyze the relationship between DF ROM and passive torque at DF ROM or shear elastic modulus of MG in each male and female participant, respectively. Our results revealed that dorsiflexion range of motion was significantly associated with passive torque at dorsiflexion range of motion in both male (r = 0.455, p = 0.012) and female (r = 0.486, p < 0.01), but not with shear elastic modulus in both male (r = -0.123, p = 0.519) and female (r = 0.019, p = 0.898). Our results suggested that the ankle dorsiflexion range of motion could be related to the stretch tolerance, but not to passive muscle stiffness in community-dwelling elderly population regardless of gender.

Associations between Range of Motion and Tissue Stiffness in Young and Older People

Supplemental digital content is available in the text.

Purpose

The purpose of this study was to investigate differences in the associations between passive ankle dorsiflexion range of motion (ROM) and stiffness of the triceps surae, sciatic nerve, and deep fascia located in the posterior leg between young and older people.

Methods

Twenty young and twenty older males were recruited and were placed in a prone position with their hip and knee fully extended. Passive ankle dorsiflexion ROM was determined based on the onset of pain during passive dorsiflexion at 1°·s⁻¹ using an isokinetic dynamometer. Shear wave speeds (as a stiffness index) of the triceps surae, the sciatic nerve, and the deep fascia in the posterior leg were evaluated by ultrasound shear wave elastography.

Results

The shear wave speeds of the medial and lateral gastrocnemius measured at 15° dorsiflexion correlated negatively with passive ROM in young but not in older participants. The shear wave speed of the sciatic nerve measured at 15° dorsiflexion correlated negatively with passive ROM only in older participants. No association was observed between passive ROM and shear wave speed of the deep fascia in the posterior leg. For data measured at maximal dorsiflexion angle (as an index of stretch tolerance), shear wave speeds of the triceps surae and passive joint torque correlated positively with passive ROM in both groups.

Conclusion

These results suggest that the tissues limiting passive ankle dorsiflexion ROM are muscle and nerve for young and older people, respectively, whereas stretch tolerance influences passive ROM for both groups. This implies that the relative contribution of nonmuscular tissues to joint flexibility become stronger than that of muscles with age.

Neuroanatomical Models of Muscle Strength and Relationship to Ambulatory Function in Spinal Muscular Atrophy

BACKGROUND

Individuals with spinal muscular atrophy (SMA) III walk independently, but experience muscle weakness, gait impairments, and fatigue. Although SMA affects proximal more than distal muscles, the characteristic pattern of selective muscle weakness has not been explained. Two theories have been proposed: 1) location of spinal motor neurons; and 2) differences in segmental innervation.

OBJECTIVE

To identify neuroanatomical models that explain the selective muscle weakness in individuals with SMA and assess the relationship of these models to ambulatory function.

METHODS

Data from 23 ambulatory SMA participants (78.2% male), ages 10-56 years, enrolled in two clinical studies (NCT01166022, NCT02895789) were included. Strength was assessed using the Medical Research Council (MRC) score; ambulatory function was measured by distance walked on the 6-minute walk test (6 MWT). Three models were identified, and relationships assessed using Pearson correlation coefficients and linear regression.

RESULTS

All models demonstrated a positive association between strength and function, (p < 0.02). Linear regression revealed that Model 3B, consisting of muscles innervated by lower lumbar and sacral segments, explained 67% of the variability observed in 6 MWT performance (β= 0.670, p = 0.003).

CONCLUSIONS

Muscles innervated by lower lumbar and sacral segments, i.e. hip extensors, hip abductors, knee flexors and ankle dorsiflexors, correlated with and predicted greater ambulatory function. The neuroanatomical patterns of muscle weakness may contribute to a better understanding of disease mechanisms and enable delivery of targeted therapies.

Is inflammatory signaling involved in disease-related muscle wasting? Evidence from osteoarthritis, chronic obstructive pulmonary disease and type II diabetes

Muscle loss is an important feature that occurs in multiple pathologies including osteoarthritis (OA), chronic obstructive pulmonary disease (COPD) and type II diabetes (T2D). Despite differences in pathogenesis and disease-related complications, there are reasons to believe that some fundamental underlying mechanisms are inherent to the muscle wasting process, irrespective of the pathology. Recent evidence shows that inflammation, either local or systemic, contributes to the modulation of muscle mass and/or muscle strength, via an altered molecular profile in muscle tissue. However, it remains ambiguous to which extent and via which mechanisms inflammatory signaling affects muscle mass in disease. Therefore, the objective of the present review is to discuss the role of inflammation on skeletal muscle anabolism, catabolism and functionality in three pathologies that are characterized by an eventual loss in muscle mass (and muscle strength), i.e. OA, COPD and T2D. In OA and COPD, most rodent models confirmed that systemic (COPD) or muscle (OA) inflammation directly induces muscle loss or muscle dysfunctionality. However, in a patient population, the association between inflammation and muscular maladaptations are more ambiguous. For example, in T2D patients, systemic inflammation is associated with muscle loss whereas in OA patients this link has not consistently been established. T2D rodent models revealed that increased levels of advanced glycation end-products (AGEs) and a decreased mTORC1 activation play a key role in muscle atrophy, but it remains to be elucidated whether AGEs and mTORC1 are interconnected and contribute to muscle loss in T2D patients. Generally, if any, associations between inflammation and muscle are mainly based on observational and cross-sectional data. There is definitely a need for longitudinal evidence through well-powered randomized control trials that take into account confounders such as age, disease-phenotypes, comorbidities, physical (in) activity etc. This will allow to improve our understanding of the complex interaction between inflammatory signaling and muscle mass loss and hence contribute to the development of therapeutic strategies to combat muscle wasting in these diseases.

Autopsy of a child with Spinal muscular atrophy Type I (Werdnig-Hoffmann disease)

Spinal muscular atrophy (SMA) is a heritable neuromuscular disorder which encompasses a large group of genetic disorders characterized by slowly progressive degeneration of lower motor neurons. The mutation is seen in the SMN1 gene mapped on chromosome 5. Depending on the age of the onset and the degree of severity, SMA has three subtypes. We discuss the autopsy findings in a case of Type 1 SMA also known by the name Werdnig-Hoffmann disease, to highlight the primary changes in the spinal cord, and skeletal muscle with association changes in the liver and terminal respiratory complications.

Muscle contractility dysfunction precedes loss of motor unit connectivity in SOD1(G93A) mice

INTRODUCTION

Electrophysiological measurements are used in longitudinal clinical studies to provide insight into the progression of amyotrophic lateral sclerosis (ALS) and the relationship between muscle weakness and motor unit (MU) degeneration. Here, we used a similar longitudinal approach in the Cu/Zn superoxide dismutase (SOD1[G93A]) mouse model of ALS.

METHODS

In vivo muscle contractility and MU connectivity assays were assessed longitudinally in SOD1(G93A) and wild type mice from postnatal days 35 to 119.

RESULTS

In SOD1(G93A) males, muscle contractility was reduced by day 35 and preceded MU loss. Muscle contractility and motor unit reduction were delayed in SOD1(G93A) females compared with males, but, just as with males, muscle contractility reduction preceded MU loss.

DISCUSSION

The longitudinal contractility and connectivity paradigm employed here provides additional insight into the SOD1(G93A) mouse model and suggests that loss of muscle contractility is an early finding that may precede loss of MUs and motor neuron death. Muscle Nerve 59:254-262, 2019.

Age- and Sex-Related Differences in Motor Performance During Sustained Maximal Voluntary Contraction of the First Dorsal Interosseous

Age and sex affect the neuromuscular system including performance fatigability. Data on performance fatigability and underlying mechanisms in hand muscles are scarce. Therefore, we determined the effects of age and sex on force decline, and the mechanisms contributing to force decline, during a sustained isometric maximal voluntary contraction (MVC) with the index finger abductor (first dorsal interosseous, FDI). Subjects (n = 51, age range: 19–77 years, 25 females) performed brief and a 2-min sustained MVC with the right FDI. Abduction force and root mean squared electromyographic activity (rms-EMG) were recorded in both hands. Double-pulse stimulation was applied to the ulnar nerve during (superimposed twitch) and after (doublet-force) the brief and sustained MVCs. Compared to females, males were stronger (134%, p < 0.001) and exhibited a greater decline in voluntary (difference: 8%, p = 0.010) and evoked (doublet) force (difference: 12%, p = 0.010) during and after the sustained MVC. Age did not affect MVC, force decline and superimposed twitch. The ratio between the doublet- and MVC-force was greater in females (0.33, p = 0.007) and in older (0.38, p = 0.06) individuals than in males (0.30) and younger (0.30) individuals; after the sustained MVC this ratio increased with age and the increase was larger for females compared to males (p = 0.04). The inadvertent contralateral, left force and rms-EMG activity increased over time (2.7–13.6% MVC and 5.4–17.7% MVC, respectively). Males had higher contralateral forces than females (p = 0.012) and contralateral force was higher at the start of the contralateral contraction in older compared with young subjects (difference: 29%, p = 0.008). In conclusion, our results suggest that the observed sex-differences in performance fatigability were mainly due to differences in peripheral muscle properties. Yet the reduced amount of contralateral activity and the larger difference in evoked versus voluntary force in female subjects indicate that sex-differences in voluntary activation should not be overlooked. These data obtained in neurological healthy adults provides a framework and help the interpretation and referencing of neurophysiological measures in patients suffering from neuromuscular diseases, who often present with symptoms of performance fatigability.

Myoeletric indices of fatigue adopting different rest intervals during leg press sets

INTRODUCTION

The purpose of this study was to examine the acute effect of different rest intervals between multiple sets of the 45° angled leg press exercise (LP45) on surface electromyographic (SEMG) spectral and amplitude indices of fatigue.

METHODS

Fifteen recreationally trained females performed three protocols in a randomized crossover design; each consisting of four sets of 10 repetitions with 1 (P1), 3 (P3), or 5 (P5) minute rest intervals between sets. Each set was performed with 70% of the LP45 ten-repetition maximum load. The SEMG data for biceps femoris (BF), vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles was then evaluated.

RESULTS

The SEMG amplitude change in the time coefficient (CRMS) and spectral fatigue index (Cf5) indicated higher levels of fatigue for all muscles evaluated during the P3 protocol versus the P1 and P5 protocols (p ≤ 0.05), respectively. The RF and VL muscles showed greater fatigue levels by the second and third sets; whereas, greater fatigue was shown in the VM and BF muscles by the fourth set (p ≤ 0.05).

CONCLUSIONS

A three-minute rest interval between sets might represent a neuromuscular window between a fatigue stated and fully recovered state in the context of neural activation. Moreover, a three minute rest interval between sets might allow for consistent recruitment of high threshold motor units over multiple sets, and thus promote a more effective stimulus for strength gains.

In vivo measurement of membrane permeability and myofiber size in human muscle using time-dependent diffusion tensor imaging and the random permeable barrier model

The time dependence of the diffusion coefficient is a hallmark of tissue complexity at the micrometer level. Here we demonstrate how biophysical modeling, combined with a specifically tailored diffusion MRI acquisition performing diffusion tensor imaging (DTI) for varying diffusion times, can be used to determine fiber size and membrane permeability of muscle fibers in vivo. We describe the random permeable barrier model (RPBM) and its assumptions, as well as the details of stimulated echo DTI acquisition, signal processing steps, and potential pitfalls. We illustrate the RPBM method on a few pilot examples involving human subjects (previously published as well as new), such as revealing myofiber size derived from RPBM increase after training in a calf muscle, and size decrease with atrophy in shoulder rotator cuff muscle. Finally, we comment on the potential clinical relevance of our results. Copyright © 2016 John Wiley & Sons, Ltd.

A nontargeted study of muscle proteome in severely obese women with androgen excess compared with severely obese men and nonhyperandrogenic women

OBJECTIVE

Androgen excess in women is frequently associated with muscle insulin resistance, especially in obese women with polycystic ovary syndrome. However, whether this is a primary event or the result of indirect mechanisms is currently debated.

DESIGN

This is an observational study.

METHODS

We obtained skeletal muscle biopsies during bariatric surgery from severely obese men (n=6) and women with (n=5) or without (n=5) androgen excess. We used two-dimensional differential gel electrophoresis and matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight mass spectrometry to identify muscle proteins showing differences in abundance between the groups of obese subjects.

RESULTS

Women with hyperandrogenism presented the lowest abundances of glycogen phosphorylase, pyruvate kinase, β-enolase, glycerol-3-phosphate dehydrogenase, creatine kinase M-type, and desmin, whereas the abundances of these molecules were similar in control women and men.

CONCLUSION

According to our nontargeted proteomic approach, women with hyperandrogenism show a specific alteration of the skeletal muscle proteome that could contribute to their insulin resistance. Because men do not show similar results, this alteration does not appear to be the direct effect on muscle of androgen excess, but rather the consequence of indirect mechanisms that merit further studies.

Histological characterization and biochemical analysis of paraspinal muscles in neuromuscularly healthy subjects

INTRODUCTION

There are no generally accepted histopathological reference values in paraspinal skeletal muscle biopsies.

METHODS

We examined multifidii muscle biopsies from 20 neuromuscularly healthy subjects using routine histological stains and biochemical analyses of respiratory chain enzymes.

RESULTS

Staining showed incomplete myopathic features, such as increased variability in fiber size, type 1 hypertrophy, rounded fiber shape, endomysial fibrosis, and replacement by adipose tissue. Acid phosphatase reaction was positive in up to 35% of the selected muscle fibers. Mitochondrial changes were obvious but revealed no selective age dependence. Reduced complex I, cytochrome c oxidase (COX), and citrate synthase (CS) could be observed.

CONCLUSIONS

Because the increased variability in morphological details can easily be misinterpreted as myopathic changes, analysis of paraspinal muscles should take into consideration that incomplete myopathic features and reduced oxidative enzyme activities for complex I, COX, and CS are normal variations at this location.

Muscle force, work and cost: a novel technique to revisit the Fenn effect

Muscle produces force by forming cross-bridges, using energy released from ATP. While the magnitude and duration of force production primarily determine the energy requirement, nearly a century ago Fenn observed that muscle shortening or lengthening influenced energetic cost of contraction. When work is done by the muscle, the energy cost is increased and when work is done on the muscle the energy cost is reduced. However, the magnitude of the 'Fenn effect' and its mirror ('negative Fenn effect') have not been quantitatively resolved. We describe a new technique coupling magnetic resonance spectroscopy with an in vivo force clamp that can directly quantify the Fenn effect [E=I+W, energy liberated (E) equals the energy cost of isometric force production (I) plus the work done (W)] and the negative Fenn effect (E=I-W) for one muscle, the first dorsal interosseous (FDI). ATP cost was measured during a series of contractions, each of which occurred at a constant force and for a constant duration, thus constant force-time integral (FTI). In all subjects, as the FTI increased with load, there was a proportional linear increase in energy cost. In addition, the cost of producing force greatly increased when the muscle shortened, and was slightly reduced during lengthening contraction. These results, though limited to a single muscle, contraction velocity and muscle length change, do quantitatively support the Fenn effect. We speculate that they also suggest that an elastic element within the FDI muscle functions to preserve the force generated within the cross-bridges.

Evaluation of central and peripheral fatigue in the quadriceps using fractal dimension and conduction velocity in young females

PURPOSE

Over the past decade, linear and non-linear surface electromyography descriptors for central and peripheral components of fatigue have been developed. In the current study, we tested fractal dimension (FD) and conduction velocity (CV) as myoelectric descriptors of central and peripheral fatigue, respectively. To this aim, we analyzed FD and CV slopes during sustained fatiguing contractions of the quadriceps femoris in healthy humans.

METHODS

A total of 29 recreationally active women (mean age±standard deviation: 24±4 years) and two female elite athletes (one power athlete, age 24 and one endurance athlete, age 30 years) performed two knee extensions: (1) at 20% maximal voluntary contraction (MVC) for 30 s, and (2) at 60% MVC held until exhaustion. Surface EMG signals were detected from the vastus lateralis and vastus medialis using bidimensional arrays.

RESULTS

Central and peripheral fatigue were described as decreases in FD and CV, respectively. A positive correlation between FD and CV (R=0.51, p<0.01) was found during the sustained 60% MVC, probably as a result of simultaneous motor unit synchronization and a decrease in muscle fiber CV during the fatiguing task.

CONCLUSIONS

Central and peripheral fatigue can be described as changes in FD and CV, at least in young, healthy women. The significant correlation between FD and CV observed at 60% MVC suggests that a mutual interaction between central and peripheral fatigue can arise during submaximal isometric contractions.

Is spinal excitability of the triceps surae mainly affected by muscle activity or body position?

The aim of this study was to determine how muscle activity and body orientation contribute to the triceps surae spinal transmission modulation, when moving from a sitting to a standing position. Maximal Hoffmann-reflex (Hmax) and motor potential (Mmax) were evoked in the soleus (SOL), medial and lateral gastrocnemius in 10 male subjects and in three conditions, passive sitting, active sitting and upright standing, with the same SOL activity in active sitting and upright standing. Moreover volitional wave (V) was evoked in the two active conditions (i.e., active sitting and upright standing). The results showed that SOL Hmax/Mmax was lower in active sitting than in passive sitting, while for the gastrocnemii it was not significantly altered. For the three plantar flexors, Hmax/Mmax was lower in upright standing than in active sitting, whereas V/Mmax was not modulated. SOL H-reflex is therefore affected by the increase in muscle activity and change in body orientation, while, in the gastrocnemii, it was only affected by a change in posture. In conclusion, passing from a sitting to a standing position affects the Hmax/Mmax of the whole triceps surae, but the mechanisms responsible for this change differ among the synergist muscles. The V/Mmax does not change when upright stance is assumed. This means that the increased inhibitory activity in orthostatic position is compensated by an increased excitatory inflow to the α-motoneurons of central and/or peripheral origin.

Electromyographic, but not mechanomyographic amplitude-force relationships, distinguished differences in voluntary activation capabilities between individuals

The purpose of the present study was to examine the influence of activation capabilities on the electromyography (EMGRMS) and mechanomyography amplitude (MMGRMS)-force relationships of the vastus lateralis (VL) and rectus femoris (RF). Thirteen men (mean±SD; age=22±3 year) performed nine submaximal contractions (10-90% maximal voluntary contraction [MVC]) with the interpolated twitch technique performed during a separate contraction at 90% MVC to calculate percent voluntary activation (%VA). Nine participants with >90% VA were categorized into the high-activated group with the remaining categorized into the moderate-activated group. Slopes (b terms) were calculated from the log-transformed EMGRMS and MMGRMS-force relationships. The b terms (collapsed across the VL and RF) for the EMGRMS-force relationships were greater for the high- (1.29±0.31) than the moderate-activated (1.10±0.20) group. In contrast, there were no differences in the b terms for the MMGRMS-force relationships between the high- and moderate-activated groups. For the EMGRMS and MMGRMS-force relationships, the b terms were greater for the RF (1.38±0.30, 0.81±0.20) than the VL (1.08±0.19, 0.60±0.13) collapsed across groups. The b terms from the EMGRMS-force relationships, but not the MMGRMS-force relationships, reflected differences in %VA.

Quadriceps and ankle dorsiflexor strength in chronic obstructive pulmonary disease

INTRODUCTION

Quadriceps strength and size are commonly reduced in chronic obstructive pulmonary disease (COPD). We wished to assess volitional and nonvolitional ankle dorsiflexor strength in COPD.

METHODS

Quadriceps and ankle dorsiflexor strength were measured by maximum voluntary contraction (MVC) and by twitch responses to supramaximal femoral and fibular nerve stimulation. Cross-sectional areas of the tibialis anterior (TA(CSA)) and rectus femoris muscles (RF(CSA)) were measured by ultrasound.

RESULTS

Eighteen elderly subjects and 20 COPD patients [mean(SD) %predictedFEV(1) 50(20)%] participated. No significant difference in fat-free mass index, ankle dorsiflexor strength, or TA(CSA) were observed in the presence of reduced quadriceps strength and size in COPD [mean MVC difference: -10.9 kg (95% confidence interval {CI}: -17.1 kg to -4.8 kg, P < 0.01; mean RF(CSA) difference -119 mm(2), 95% CI: -180 mm(2) to -58 mm(2), P < 0.01)].

CONCLUSIONS

Ankle dorsiflexor strength is less attenuated than quadriceps strength in COPD patients with moderate airflow obstruction. Direct quadriceps assessment may be more relevant than measurement of lower limb fat-free mass.

Determinação da carga de treino nos exercícios supino e rosca bíceps em mulheres jovens

O objetivo deste estudo foi avaliar a força máxima dinâmica (1RM) nos exercícios supino e rosca scott, e relacioná-la com a massa corporal total (MCT) e com a massa corporal magra (MCM), bem como avaliar o número máximo de repetições em diferentes percentuais de 1RM. Onze mulheres (24 ± 1,4 anos) foram submetidas à avaliação da composição corporal, testes de 1RM e testes de repetições máximas em 50, 60, 70 e 80% de 1RM. No tratamento dos dados, foram utilizados a regressão linear múltipla, a ANOVA para medidas repetidas e o teste t pareado. A MCM é a variável que melhor explica a variância de 1RM, podendo ser utilizada para a determinação de um coeficiente para a estimativa da carga de treino. Houve diferenças significativas entre os números de repetições em todos os percentuais e em ambos os exercícios [(supino (p=0,000) e rosca scott (p=0,000)], sendo esses números progressivamente menores com o incremento da carga.

Hoffmann reflex is increased after 14 days of daily repeated Achilles tendon vibration for the soleus but not for the gastrocnemii muscles

In a previous study, Achilles tendon vibrations were enough to improve the triceps surae (TS) activation capacities and also to slightly increase TS Hoffmann reflex (H-reflex) obtained by summing up soleus (Sol) and gastrocnemii (GM and GL) EMGs. The purpose of the present study was to analyze separately Sol and GM or GL reflexes to account for different effects of the vibrations on the reflex excitability of the slow soleus and of the gastrocnemii muscles. A control group (n = 13) and a vibration group (n = 16) were tested in pre-test and post-test conditions. The Achilles tendon vibration program consisted of 1 h of daily vibration (frequency: 50 Hz) applied during 14 days. Maximal Sol, GM and GL H-reflexes, and M-waves were recorded, and their H(max)/M(max) ratios gave the index of reflex excitability. After the vibration protocol, only Sol H(max)/M(max) was enhanced (p < 0.001). The enhanced Sol reflex excitability after vibration is in favor of a decrease in the pre-synaptic inhibition due to the repeated vibrations and the high solicitation of the reflex pathway. Those results of a short period of vibration applied at rest may be limited to the soleus because of its high density in muscle spindles and slow motor units, both structures being very sensitive to vibrations.

Human myotubes from myoblast cultures undergoing senescence exhibit defects in glucose and lipid metabolism

Adult stem cells are known to have a finite replication potential. Muscle biopsy-derived human satellite cells (SCs) were grown at different passages and differentiated to human myotubes in culture to analyze the functional state of various carbohydrate and lipid metabolic pathways. As the proliferative potential of myoblasts decreased dramatically with passage number, a number of cellular functions were altered: the capacity of myoblasts to fuse and differentiate into myotubes was reduced, and metabolic processes in myotubes such as glucose uptake, glycogen synthesis, glucose oxidation and fatty acid β-oxidation became gradually impaired. Upon insulin stimulation, glucose uptake and glycogen synthesis increased but as the cellular proliferative capacity became gradually exhausted, the response dropped concomitantly. Palmitic acid incorporation into lipids in myotubes decreased with passage number and could be explained by reduced incorporation into diacyl- and triacylglycerols. The levels of long-chain acyl-CoA esters decreased with increased passage number. Late-passage, non-proliferating, myoblast cultures showed strong senescence-associated β-galactosidase activity indicating that the observed metabolic defects accompany the induction of a senescent state. The main function of SCs is regeneration and skeletal muscle-build up. Thus, the metabolic defects observed during aging of SC-derived myotubes could have a role in sarcopenia, the gradual age-related loss of muscle mass and strength.

Assessment of impulse duration thresholds for electrical stimulation of muscles (chronaxy) in dogs

OBJECTIVE

To determine the electrical impulse duration thresholds (chronaxy) for maximal motor contraction of various muscles without stimulation of pain fibers in dogs.

ANIMALS

10 healthy adult Beagles.

PROCEDURES

The dogs were used to assess the minimal intensity (rheobase) required to elicit motor contraction of 11 muscles (5 in the forelimb [supraspinatus, infraspinatus, deltoideus, lateral head of the triceps brachii, and extensor carpi radialis], 5 in the hind limb [gluteus medius, biceps femoris, semitendinosus, vastus lateralis, and tibialis cranialis], and the erector spinae). The rheobase was used to determine the chronaxy for each of the 11 muscles in the 10 dogs; chronaxy values were compared with those reported for the corresponding muscles in humans.

RESULTS

Compared with values in humans, chronaxy values for stimulation of AA motor fibers in the biceps femoris and semitendinosus muscles and muscles of the more distal portions of limbs were lower in dogs. For the other muscles evaluated, chronaxy values did not differ between dogs and humans.

CONCLUSIONS AND CLINICAL RELEVANCE

Application of the dog-specific chronaxy values when performing electrical stimulation for strengthening muscles or providing pain relief is likely to minimize the pain perceived during treatment in dogs.

An X-linked myopathy with postural muscle atrophy and generalized hypertrophy, termed XMPMA, is caused by mutations in FHL1

We have identified a large multigenerational Austrian family displaying a novel form of X-linked recessive myopathy. Affected individuals develop an adult-onset scapulo-axio-peroneal myopathy with bent-spine syndrome characterized by specific atrophy of postural muscles along with pseudoathleticism or hypertrophy and cardiac involvement. Known X-linked myopathies were excluded by simple-tandem-repeat polymorphism (STRP) and single-nucleotide polymorphism (SNP) analysis, direct gene sequencing, and immunohistochemical analysis. STRP analysis revealed significant linkage at Xq25-q27.1. Haplotype analysis based on SNP microarray data from selected family members confirmed this linkage region on the distal arm of the X chromosome, thereby narrowing down the critical interval to 12 Mb. Sequencing of functional candidate genes led to the identification of a missense mutation within the four and a half LIM domain 1 gene (FHL1), which putatively disrupts the fourth LIM domain of the protein. Mutation screening of FHL1 in a myopathy family from the UK exhibiting an almost identical phenotype revealed a 3 bp insertion mutation within the second LIM domain. FHL1 on Xq26.3 is highly expressed in skeletal and cardiac muscles. Western-blot analysis of muscle biopsies showed a marked decrease in protein expression of FHL1 in patients, in concordance with the genetic data. In summary, we have to our knowledge characterized a new disorder, X-linked myopathy with postural muscle atrophy (XMPMA), and identified FHL1 as the causative gene. This is the first FHL protein to be identified in conjunction with a human genetic disorder and further supports the role of FHL proteins in the development and maintenance of muscle tissue. Mutation screening of FHL1 should be considered for patients with uncharacterized myopathies and cardiomyopathies.

Predictive model of muscle fatigue after spinal cord injury in humans

The fatigability of paralyzed muscle limits its ability to deliver physiological loads to paralyzed extremities during repetitive electrical stimulation. The purposes of this study were to determine the reliability of measuring paralyzed muscle fatigue and to develop a model to predict the temporal changes in muscle fatigue that occur after spinal cord injury (SCI). Thirty-four subjects underwent soleus fatigue testing with a modified Burke electrical stimulation fatigue protocol. The between-day reliability of this protocol was high (intraclass correlation, 0.96). We fit the fatigue index (FI) data to a quadratic-linear segmental polynomial model. FI declined rapidly (0.3854 per year) for the first 1.7 years, and more slowly (0.01 per year) thereafter. The rapid decline of FI immediately after SCI implies that a "window of opportunity" exists for the clinician if the goal is to prevent these changes. Understanding the timing of change in muscle endurance properties (and, therefore, load-generating capacity) after SCI may assist clinicians when developing therapeutic interventions to maintain musculoskeletal integrity.

Postfatigue potentiation of the paralyzed soleus muscle: evidence for adaptation with long-term electrical stimulation training

Understanding the torque output behavior of paralyzed muscle has important implications for the use of functional neuromuscular electrical stimulation systems. Postfatigue potentiation is an augmentation of peak muscle torque during repetitive activation after a fatigue protocol. The purposes of this study were 1) to quantify postfatigue potentiation in the acutely and chronically paralyzed soleus and 2) to determine the effect of long-term soleus electrical stimulation training on the potentiation characteristics of recently paralyzed soleus muscle. Five subjects with chronic paralysis (>2 yr) demonstrated significant postfatigue potentiation during a repetitive soleus activation protocol that induced low-frequency fatigue. Ten subjects with acute paralysis (<6 mo) demonstrated no torque potentiation in response to repetitive stimulation. Seven of these acute subjects completed 2 yr of home-based isometric soleus electrical stimulation training of one limb (compliance = 83%; 8,300 contractions/wk). With the early implementation of electrically stimulated training, potentiation characteristics of trained soleus muscles were preserved as in the acute postinjury state. In contrast, untrained limbs showed marked postfatigue potentiation at 2 yr after spinal cord injury (SCI). A single acute SCI subject who was followed longitudinally developed potentiation characteristics very similar to the untrained limbs of the training subjects. The results of the present investigation support that postfatigue potentiation is a characteristic of fast-fatigable muscle and can be prevented by timely neuromuscular electrical stimulation training. Potentiation is an important consideration in the design of functional electrical stimulation control systems for people with SCI.

Oxidative stress and the pathogenesis of muscular dystrophies

The muscular dystrophies represent a diverse group of diseases differing in underlying genetic basis, age of onset, mode of inheritance, and severity of progression, but they share certain common pathologic features. Most prominent among these features is the necrotic degeneration of muscle fibers. Although the genetic basis of many of the dystrophies has been known for over a decade and new disease genes continue to be discovered, the pathogenetic mechanisms leading to muscle cell death in the dystrophies remain a mystery. This review focuses on the oxidative stress theory, which states that the final common pathway of muscle cell death in these diseases involves oxidative damage.

Ultrastructural changes in paravertebral muscles associated with degenerative spondylolisthesis

STUDY DESIGN

The paravertebral muscle of 30 patients with spondylolisthesis and 30 control patients were investigated histologically.

OBJECTIVE

To propose myopathologic paravertebral muscle changes in cases of degenerative lumbar spondylolisthesis.

SUMMARY OF BACKGROUND DATA

The stability of the vertebral column is based on both active and passive systems. The passive system is composed of the vertebrae, the intervertebral discs, and the ligaments. Surrounding muscles and tendons constitute the active system. The autochthonous back muscles take over support functions if the passive system is ineffective. In some cases, muscles are overstrained for a long period, ultimately leading to muscular changes. This study was performed to determine the histopathologic correlates of this permanent strain.

METHODS

Between July 1998 and July 1999, paravertebral muscle biopsies were performed for 30 patients with monosegmental degenerative spondylolisthesis undergoing posterior lumbar interbody fusion. The tissue samples were submitted to histologic analysis including immune and enzyme histochemistry and electron microscopy. In addition, the muscle fibers were submitted to morphometry.

RESULTS

Severe pathologic alterations were found. The findings showed that 22 patients (73.3%) had ragged red fibers with evident ultrastructural mitochondrial anomalies. The cristae appeared irregular in 12 patients (40%) Type 1 paracrystalline inclusions were detected in five samples (16.6%) and dense bodies in eight (26.6%). Fibers with ubiquitin-positive inclusions were detected by immunohistochemistry in 13 patients (43.3%). As shown by the electron microscope, these corresponded to granulofilamentous inclusions and polyglucosan bodies. The samples were submitted to genetical analysis because biochemical studies showed reduced activity of the respiratory chain enzymes. Normal mitochondrial deoxyribonucleic acids of unchanged length were detected.

CONCLUSIONS

Apart from nonspecific myopathic changes such as those observed in rimmed vacuoles and rods, increased numbers of polyglucosan bodies were detected. This increase in polyglucosan bodies currently has not been described in patients with otherwise normal muscles.

Fibre size, atrophy, and hypertrophy factors in vastus lateralis muscle from 18- to 29-year-old men

In order to study the size of muscle fibres, cross-sections of autopsied vastus lateralis muscle from 8 healthy men, aged 18 to 29 years, who have died suddenly were prepared and analyzed. Data were obtained on cross-sectional area, on lesser diameter, and on atrophy and hypertrophy factors of type 1 and type 2 fibres, subdivided into 2a, 2b, and 2c fibres. The difference in mean fibre size between type 1 and 2 fibres was not significant, whereas the differences between type 1 and 2b, type 1 and 2a, and type 2a and 2b fibres were significant. In the whole material type 2a fibres were the largest and type 2b fibres the smallest. There were considerable differences between post-mortem subjects. Because of these differences and the variability of all fibre types in respect of size in a sample the normal ranges of fibre size were large. The normal ranges and a continuous scale of weights were used to determine the atrophy and hypertrophy factors in each sample, and the upper limits of these factors accepted as being normal. The estimates of the limits of normality of the area, diameter, atrophy and hypertrophy factors of type 1, 2, 2a and 2b fibres reflect the situation in the vastus lateralis muscle of healthy young men. These values might be useful in studying physiological and pathological conditions influencing the size of different fibre types.

Histomorphometric and histopathological study of the human cricopharyngeus muscle: in health and in motor neuron disease

Abnormalities in muscle histology have been reported frequently for the cricopharyngeus muscle of patients with oculopharyngeal muscular dystrophy, motor neuron disease and other neurological disorders in which dysphagia is a common clinical sign. However, there are few detailed reports of the normal structure of this muscle nor quantitative baseline data with which to compare the diseased state. In this study, cricopharyngeus muscles from 21 healthy individuals and four patients with motor neuron disease underwent quantitative histological and histochemical examination. In addition to the extensive connective tissue content (40%), comprising abundant elastic fibres, cricopharyngeus muscles from normal individuals possessed small calibre striated muscle fibres (mean narrow diameter 30 microns) of widely varying size (coefficient of variation 41%). The majority of fibres were histochemically type I (82%) and highly oxidative. All muscles comprised numerous muscle fibres with aberrant histological and histochemical features (internalized nuclei, 'ragged red' crescents, splits, degenerating fibres, 'moth-eaten' fibres, or nemaline rods.) The histomorphometric and histopathological features were similar in males and females and some showed a correlation with age. There were increases in fibre size and roundedness and decreases in the numerical density and percentage of type I and split fibres in the specimens from older individuals. Cricopharyngeus muscles from patients with motor neuron disease were not significantly different from the controls for most parameters. It is therefore suggested that previous descriptions of specific cricopharyngeal pathology accompanying neuromuscular disease or dysphagia be interpreted with caution. The importance of obtaining normal structural, morphometric and histopathological data from muscles other than the usually biopsied limb muscles, is emphasized.

Genetics of congenital nemaline myopathy: a study of 10 families

In order to investigate the inheritance in congenital nemaline myopathy (CNM), we studied the family histories and pedigrees of 13 patients with CNM from 10 families, and the 20 patients, by physical examination, single fibre electromyography, ultrasonography of muscles, measurement of serum creatine kinase, muscle biopsy, and electrophoresis of muscle proteins. None of the parents was affected. In three families there were two affected children. Of the parents, 15 showed deficiency of type 2B muscle fibres, and all except one father showed some other minor neuromuscular abnormality. These may represent heterozygous manifestations of recessive gene. Most of the ancestors came from sparsely populated rural communities in the west of Finland. We conclude that in the Finnish CNM patients, the mode of inheritance appears to be recessive. Apart from a few instances of dominant inheritance, most cases published also seem compatible with recessive inheritance.

A test to detect clustering applied to muscle fibres

The random arrangement of a chosen uncommon element type within a mosaic has been assessed by the new statistics, 'Number of Clusters' and 'Mean Cluster Size'. Their distributions were obtained by simulation assuming the mosaic has a hexagonal arrangement. When this assumption was relaxed to allow mosaics nearer to those observed in nature, the results were little changed. This method was then applied to a set of muscle fibre data to test hypotheses about the likely targets in inflammatory muscle disorders.

Pathology of congenital nemaline myopathy. A follow-up study

This study was undertaken to review the development over 5-18 years of pathologic changes in 13 patients (4 male and 9 female) with congenital nemaline myopathy. Follow-up biopsies were compared with earlier biopsies and with published normal values as to quantity and location of nemaline bodies, secondary signs of myopathy, and in 6 patients as to muscle fiber type and size. Biopsy findings were correlated with the mobility and muscle power of the patient. The main differences in myofiber maturation in the patients as compared with normal myofiber maturation were: (1) deficient differentiation of type 2 fibers, (2) further increase of variation in fiber size with age, and (3) skewing in early adulthood of fiber size distribution curves toward the atrophic end. In ambulant patients, this skew seemed to be compensated with a population of hypertrophic fibers. The nemaline bodies tended to be located beneath the sarcolemma in the younger patients and inside the muscle fibers in the older patients. The quantity of nemaline bodies seemed to have increased with age. The clinical deterioration and the defective myofiber maturation in the patients together with an increase in internal nuclei and endomysial fat or fibrosis indicate an active disease process. This speaks against the generally held view that congenital nemaline myopathy is static.

A general, computer-based method for study of the spatial distribution of muscle fiber types in skeletal muscle

The present method provides detailed quantitative information on the spatial distribution of the muscle fiber types in skeletal muscle. This is accomplished by comparing the measured spatial distribution of the fiber types with a computer-simulated random pattern. The method is based on a registration of the absolute frequency for six principal categories of fiber contacts (I-I, I-IIA, I-IIB, IIA-IIA, IIA-IIB, IIB-IIB). A computer program was designed to simulate a random pattern of fibers. The simulations were performed with high accuracy with regard to fiber type proportion and the number of neighbouring fibers. The computer then calculated the frequency for each of the different categories of fiber contacts in the simulated random pattern. The measured distribution of fiber contacts could thus be compared to the simulated random pattern. In three bovine muscles studied, the spatial distribution of the muscle fiber types showed a similar pattern. The muscle fibers had a distinct tendency to be surrounded by fibers of a different type. In all three muscles the difference between the measured and the simulated random pattern was statistically significant (p less than 10(-3).

Fiber-type composition of selected hindlimb muscles of a primate (cynomolgus monkey)

The distribution of fiber types in selected leg and thigh muscles of three male Cynomolgus monkeys were determined. Almost all fibers could be classified as fast-glycolytic (FG), fast-oxidative glycolytic (FOG), or slow-oxidative (SO) according to the qualitative histochemical staining scheme described by Peter et al. (1972). Most muscles showed regional variations in fiber-type distributions, i.e., the percent SO was higher and the percent FG was lower in the deep, compared to the superficial, regions of the muscle. Exceptions were the soleus and plantaris muscles, which contained similar distributions of fiber types throughout their cross sections. In the extensor compartment of the leg, a layering of fiber types from deep to superficial were evident in the triceps surae and plantaris complex with the deepest muscle, the soleus, having primarily SO fibers. A similar layering arrangement was observed in the extensor compartment of the thigh, with the deepest muscle, the vastus intermedius, having a much larger proportion of SO fibers than the other muscles in the quadriceps complex. These results indicate that Cynomolgus monkey hindlimb muscles, unlike human leg muscles (Saltin and Gollnick: Handbook of Physiology, L.D. Peachey, ed. American Physiological Society, MD, pp. 55-631, 1983) have a regional distribution of fiber types similar to that observed in many subprimate mammals. Further, the presence of compartmentalization of fiber types within the cross section of several of the muscles studied is suggestive of structure-function interrelationships related to motor control.

Morphological detection of neurogenic muscle disorders: how can statistical methods aid diagnosis?

The light microscopical observation of groups of histochemically similar muscle fibres, referred to as fibre-type grouping, is commonly considered to be evidence of a denervation and reinnervation process affecting the spinal motor neurons or the peripheral nerves. It can be difficult to assess whether such groups have occurred by chance or are due to a slowly progressive pathological process in an early stage of development. Consequently, there is a need for one or more objective methods for assessing the fibre-type arrangement in healthy and diseased human muscles. The purposes here are to review the methods for the detection of fibre-type grouping that have been published in the last two decades, to describe some unsolved problems, and to indicate some likely lines of development.

A simple test for the random arrangement of muscle fibres

The random arrangement of a given muscle fibre class has been assessed by estimating 'mean cluster size' in transverse sections of skeletal muscle. The method was found to be useful when the proportion of the fibre class of interest was low. The statistical distribution of this measure was investigated by computer simulation using a hexagonal lattice model of muscle fibre arrangement. An approximate significance test was developed by considering the extreme points of the distribution. Minor changes to the hexagonal lattice model were incorporated to give a more realistic representation of fibre arrangement and these were found to give very similar results to the simpler model.

Quantitative analysis of quadriceps muscle biopsy. Results in 30 healthy females

Open biopsy was performed in right quadriceps muscle (vastus lateralis) in 30 healthy female volunteers between 20 and 50 years of age. Histometric analysis was carried out on ATPase stained sections preincubated at pH 4.5. Type 1, 2a, 2b, and 2 fibres were quantified taking into account the following parameters: percentage of fibre types, mean diameter, atrophy and hypertrophy factor, variability coefficient of mean diameter and mean diameter ratio of type 1: type 2 fibres. Results showed that there is a large variation in fibre type percentage, mean diameter and hypertrophy factor, and consequently ranges of normal values are wider than those previously reported. Atrophy factor and variability coefficient are the least variable parameters. The importance of normal controls is stressed to avoid false positives in histometric evaluation of muscle biopsy with minimal changes.

Abnormalities of muscle metabolism and histology in malnourished patients awaiting surgery: effects of a course of intravenous nutrition

Malnourished surgical patients have metabolic and functional abnormalities of skeletal muscle and it has been suggested that these are due to reduced activities of glycolytic enzymes associated with abnormalities of muscle fibres. We have measured the activities of four key enzymes of glucose utilization and the size and distribution of muscle fibre types in vastus lateralis biopsies from 14 undernourished patients awaiting surgery (mean weight loss 24 +/- 10 per cent). These results were compared with those from 14 normally nourished controls, comparable in age, sex, race and habitual activity. Fructose bisphosphatase activity was reduced in undernourished patients by 44 per cent (P less than 0.01), phosphofructokinase by 40 per cent (P = 0.005) and hexokinase by 37 per cent (P less than 0.001). Both fibre types were smaller in patients than controls (area I, 41.4 micron2 X 10(-2) +/- 0.4 vs. 73.3 micron2 X 10(-2) +/- 0.6, less than 0.001; area II, 27.7 micron2 X 10(-2) +/- 0.4 vs. 72.5 micron2 X 10(-2) +/- 0.5, P less than 0.001), and there was a smaller proportional number of type II fibres in patients (35 per cent vs. 65 per cent, P less than 0.01). This loss of type II fibre numbers and preferential type II atrophy may account for the enzyme depression associated with it and could produce the syndrome of impaired glucose tolerance, muscle weakness and fatigue seen in undernourished patients. In a subgroup of 11 patients, biopsy was repeated after 14 days of intravenous nutrition. Only phosphofructokinase activity rose significantly (19.62 +/- 1.85 to 30.74 +/- 2.99 mumol min-1 g-1, P less than 0.01) and both type II fibre size (40.6 +/- 18.5 to 47.4 micron2 +/- 20.3 X 10(-2), P less than 0.05) and number (42 per cent +/- 6 to 56 per cent +/- 5, P less than 0.05) also rose. Intravenous nutrition may therefore increase maximum glycolytic rate and improve muscle function in undernourished surgical patients.

Single fiber electromyography in the differential diagnosis of myopathic limb girdle syndromes and chronic spinal muscular atrophy

Single fiber electromyography ( SFEMG ) of the extensor digitorum communis muscle was performed on 20 patients with either myopathic limb girdle syndromes ( LGS ) or chronic spinal muscular atrophy ( CSMA ) to assess its value in the differential diagnosis of these disorders. Neurologic examinations (muscle biopsies, standard electromyography, or both) were reviewed in 16 patients and resulted in diagnosing LGS in 11 patients and CSMA in 5 patients. In four patients, discordance between EMG and biopsy, or mixed features of myopathy and neuropathy in either test, resulted in an indeterminate diagnosis. Two groups were discerned from SFEMG , one with higher fiber density, jitter, and percentage of abnormal pairs consistent with neuropathy and another with lower values consistent with myopathy. In all 16 patients, SFEMG confirmed the initial diagnosis, and in the four patients with indeterminate diagnoses, SFEMG suggested diagnoses of LGS in two patients and CSMA in two patients. Single fiber electromyography may be a useful diagnostic aid in the differential diagnosis of myopathic LGS and CSMA .