Variability of histochemical and morphometric data from needle biopsy specimens of human quadriceps femoris muscle

Stiffness of elastic cuffs affects physiological and perceptual responses but not motor performance fatigue during low external load resistance exercise with practical blood flow restriction

Practical blood flow restriction (pBFR), using non-pneumatic elastic cuffs, is a feasible and cost-effective alternative to pneumatic systems. There is evidence that cuff stiffness influences haemodynamic and perceptual responses in the upper body during rest. However, the impact of cuff stiffness during exercise is still unknown. Therefore, this study investigated the influence of cuff stiffness on physiological, perceptual, and performance changes during exercise. In a randomized and counterbalanced order, ten recreationally active males performed four sets of unilateral elbow flexions at 20% of individuals' one-repetition-maximum with two elastic cuffs of different stiffness (low stiffness cuff [LS] and high stiffness cuff [HS]) each applied with two different overlaps (10% and 20% overlap in relation to the limb circumference) as well as a control condition without pBFR. Before and after exercise, maximal voluntary isometric contraction torque was measured to assess motor performance fatigue. During exercise, muscle oxygen saturation of the biceps brachii as well as effort and exercise-induced muscle pain perception were recorded. Statistical analysis revealed that motor performance fatigue was not different between conditions (BF10 = 0.289). The decline in muscle oxygen saturation (BF10 = 8.508 and BF10 = 1039.543) as well as effort (BF10 = 2646.104 and BF10 = 2.773∙106) and exercise-induced muscle pain perception (BF10 = 14087.983 and BF10 = 7.306∙109) were higher when using the stiffer cuff at 10% and 20% overlap, respectively. Conclusively, physiological and perceptual responses but not motor performance fatigue were affected by cuff stiffness when equal relative overlaps were applied.

The W' Balance Model: Mathematical and Methodological Considerations

Since its publication in 2012, the W' balance model has become an important tool in the scientific armamentarium for understanding and predicting human physiology and performance during high-intensity intermittent exercise. Indeed, publications featuring the model are accumulating, and it has been adapted for popular use both in desktop computer software and on wrist-worn devices. Despite the model's intuitive appeal, it has achieved mixed results thus far, in part due to a lack of clarity in its basis and calculation. Purpose: This review examines the theoretical basis, assumptions, calculation methods, and the strengths and limitations of the integral and differential forms of the W' balance model. In particular, the authors emphasize that the formulations are based on distinct assumptions about the depletion and reconstitution of W' during intermittent exercise; understanding the distinctions between the 2 forms will enable practitioners to correctly implement the models and interpret their results. The authors then discuss foundational issues affecting the validity and utility of the model, followed by evaluating potential modifications and suggesting avenues for further research. Conclusions: The W' balance model has served as a valuable conceptual and computational tool. Improved versions may better predict performance and further advance the physiology of high-intensity intermittent exercise.

Variability in vastus lateralis fiber type distribution, fiber size, and myonuclear content along and between the legs

Human skeletal muscle characteristics such as fiber type composition, fiber size, and myonuclear content are widely studied in clinical and sports-related contexts. Being aware of the methodological and biological variability of the characteristics is a critical aspect in study design and outcome interpretation, but comprehensive data on the variability of morphological features in human skeletal muscle are currently limited. Accordingly, in the present study, m. vastus lateralis biopsies (10 per subject) from young and healthy individuals, collected in a systematic manner, were analyzed for various characteristics using immunohistochemistry (n = 7) and SDS-PAGE (n = 25). None of the analyzed parameters, fiber type % (FT%), type I and II fiber cross-sectional area (fCSA), percentage fiber type area (fCSA%), myosin heavy chain composition (MyHC%), type IIX content, myonuclear content, or myonuclear domain, varied in a systematic manner longitudinally along the muscle or between the two legs. The average within-subject coefficient of variation for FT%, fCSA, fCSA%, and MyHC% ranged between 13% and 18% but was only 5% for fiber-specific myonuclear content, which reduced the variability for myonuclear domain size to 11%-12%. Pure type IIX fibers and type IIX MyHC were randomly distributed and present in <24% of the analyzed samples, with the average content being 0.1% and 1.1%, respectively. In conclusion, leg or longitudinal orientation does not seem to be an important aspect to consider when investigating human vastus lateralis characteristics. However, single muscle biopsies should preferably not be used when studying fiber type- and fiber size-related aspects, given the notable sample-to-sample variability.NEW & NOTEWORTHY This study provides a comprehensive analysis of the variability of key human skeletal muscle fiber characteristics in multiple sites along and between the m. vastus lateralis of healthy and active individuals. We found a notable but nonsystematic variability in fiber type and size, whereas myonuclear content was distinctively less variable, and the prevalence of type IIX fibers was random and very low. These data are important to consider when designing and interpreting studies including m. vastus lateralis biopsies.

Variability in skeletal muscle fibre characteristics during repeated muscle biopsy sampling in human vastus lateralis

The percutaneous muscle biopsy procedure is an invaluable tool for characterizing skeletal muscle and capillarization. Little is known about methodological or biological variation stemming from the technique in heterogeneous muscle. Five muscle biopsies were taken from the vastus lateralis of a group of young men (n = 29, 22 ± 1 years) over a 96-h period. We investigated the repeatability of fibre distribution, indices of muscle capillarization and perfusion, and myofibre characteristics. No differences between the biopsies were reported in myofibre type distribution, cross-sectional area (CSA), and perimeter. Capillary-to-fibre perimeter exchange index and individual capillary-fibre contacts were unchanged with respect to the location of the muscle biopsy and index of capillarization. The variability in the sampling distribution of fibre type specific muscle CSA increased when fewer than 150 muscle fibres were quantified. Variability in fibre type distribution increased when fewer than 150 muscle fibres were quantified. Myofibre characteristics and indices of capillarization are largely consistent throughout the vastus lateralis when assessed via the skeletal muscle biopsy technique. Novelty Markers of muscle capillarization and perfusion were unchanged across multiple sites of the human vastus lateralis. Myofibre characteristics such as muscle cross-sectional area, perimeter, and fibre type distribution were also unchanged. Variation of muscle CSA was higher when fewer than 150 muscle fibres were quantified.

The development of skeletal muscle hypertrophy through resistance training: the role of muscle damage and muscle protein synthesis

Resistance training (RT)-induced skeletal muscle hypertrophy is a highly intricate process. Despite substantial advances, we are far from understanding exactly how muscle hypertrophy develops during RT. The aim of the present review is to discuss new insights related to the role of skeletal muscle damage and muscle protein synthesis (MPS) in mediating RT-induced hypertrophy. Specifically, the thesis that in the early phase of RT (≤ 4 previous RT sessions) increases in muscle cross-sectional area are mostly attributable to muscle damage-induced muscle swelling; then (after ~ 10 sessions), a modest magnitude of muscle hypertrophy ensues; but only during a latter phase of RT (after ~ 18 sessions) is true muscle hypertrophy observed. We argue that the initial increases in MPS post-RT are likely directed to muscle repair and remodelling due to damage, and do not correlate with eventual muscle hypertrophy induced by several RT weeks. Increases in MPS post-RT session only contribute to muscle hypertrophy after a progressive attenuation of muscle damage, and even more significantly when damage is minimal. Furthermore, RT protocols that do not promote significant muscle damage still induce similar muscle hypertrophy and strength gains compared to conditions that do promote initial muscle damage. Thus, we conclude that muscle damage is not the process that mediates or potentiates RT-induced muscle hypertrophy.

Intramuscular determinants of the ability to recover work capacity above critical power

PURPOSE

The primary purpose of this investigation was to compare the recovery of the W' to the recovery of intramuscular substrates and metabolites using (31)P- and (1)H-magnetic resonance spectroscopy.

METHODS

Ten healthy recreationally trained subjects were tested to determine critical power (CP) and W' for single-leg-extensor exercise. They subsequently exercised in the bore of a 1.5-T MRI scanner at a supra-CP work rate. Following exhaustion, the subjects rested in place for 1, 2, 5 or 7 min, and then repeated the effort. The temporal course of W' recovery was estimated, which was then compared to the recovery of creatine phosphate [PCr], pH, carnosine content, and to the output of a novel derivation of the W' BAL model.

RESULTS

W' recovery closely correlated with the predictions of the novel model (r = 0.97, p = 0.03). [PCr] recovered faster [Formula: see text] than W' [Formula: see text] The W' available for the second exercise bout was directly correlated with the difference between [PCr] at the beginning of the work bout and [PCr] at exhaustion (r = 0.99, p = 0.005). Nonlinear regression revealed an inverse curvilinear relationship between carnosine concentration and the W' t 1/2 (r (2) = 0.55).

CONCLUSION

The kinetics of W' recovery in single-leg-extensor exercise is comparable to that observed in whole-body exercise, suggesting a conserved mechanism. The extent to which the recovery of the W' can be directly attributed to the recovery of [PCr] is unclear. The relationship of the W' to muscle carnosine content suggests novel future avenues of investigation.

Characterization of fiber types in different muscles of the hindlimb in female weanling and adult Wistar rats

We analyzed lesser diameter and distribution of fiber types in different skeletal muscles from female Wistar rats using a histoenzymology Myofibrillar Adenosine Tri-phosphatase (mATPase) method. Fragments from muscles were frozen and processed by mATPase in different pH. Adult and weanling rat soleus muscles presented a predominance of type I fibers and larger fiber diameters. In the plantar muscle in adult rats, the type IIB fibers demonstrated greater lesser diameter while in the weanling animals, types I and IIB fibers were larger. The plantar muscle of animals of both ages was composed predominantly of the type IID fibers. The type IID fibers were observed in similar amounts in the lateral gastrocnemius and the medial gastrocnemius muscles. Type IIB fibers showed predominance and presented higher size in comparison with other types in the EDL muscle. The present study shows that data on fiber type distribution and fiber lesser diameter obtained in adult animals cannot always be applied to weanling animals of the same species. Using the mATPase, despite the difficult handling, is an important tool to determine the different characteristics of the specific fibers in the skeletal muscle tissue.

Fibre type composition of the human psoas major muscle with regard to the level of its origin

The aim of our study was to explore the fibre type composition of the human psoas major muscle at different levels of its origin, from the first lumbar to the fourth lumbar vertebra, and to compare the muscle fibre size and distribution of different fibre types between levels with respect to its complex postural and dynamic function. Muscle samples were collected from 15 young males (younger than 35 years). Serial transverse sections (5 microm) of the samples were cut by cryomicrotome. Type I, IIA and IIX muscle fibres were typed using myosin heavy chain identification. The serial sections were analysed using a light microscope with a magnitude of 100x. The differences between measurements were evaluated using a repeated-measures anova and Scheffé test for post-hoc analysis. Our study showed that the human psoas major muscle was composed of type I, IIA and IIX muscle fibres. It had a predominance of type IIA muscle fibres, whereas type I muscle fibres had the largest cross-sectional area. Type IIX muscle fibres were present as a far smaller percentage and had the smallest cross-sectional area. Moreover, the fibre type composition of the psoas major muscle was different between levels of its origin starting from the first lumbar to the fourth lumbar vertebra. We conclude that the fibre type composition of the psoas major muscle indicated its dynamic and postural functions, which supports the fact that it is the main flexor of the hip joint (dynamic function) and stabilizer of the lumbar spine, sacroiliac and hip joints (postural function). The cranial part of the psoas major muscle has a primarily postural role, whereas the caudal part of the muscle has a dynamic role.

Protein-containing nutrient supplementation following strength training enhances the effect on muscle mass, strength, and bone formation in postmenopausal women

We evaluated the response of various muscle and bone adaptation parameters with 24 wk of strength training in healthy, early postmenopausal women when a nutrient supplement (protein, carbohydrate, calcium, and vitamin D) or a placebo supplement (a minimum of energy) was ingested immediately following each training session. At inclusion, each woman was randomly and double-blindedly assigned to a nutrient group or a placebo (control) group. Muscle hypertrophy was evaluated from biopsies, MRI, and dual-energy X-ray absorptiometry (DEXA) scans, and muscle strength was determined in a dynamometer. Bone mineral density (BMD) was measured using DEXA scans, and bone turnover was determined from serum osteocalcin and collagen type I cross-linked carboxyl terminal peptide. The nutrient group improved concentric and isokinetic (60°/s) muscle strength from 6 to 24 wk by 9 ± 3% ( P < 0.01), whereas controls showed no change (1 ± 2%, P > 0.05). Only the nutrient group improved lean body mass ( P < 0.05) over the 24 wk. BMD responded similarly at the lumbar spine but changed differently in the two groups at the femoral neck ( P < 0.05) [control: 0.943 ± 0.028 to 0.930 ± 0.024 g/mm3 (−1.0 ± 1.4%); nutrient group: 0.953 ± 0.051 to 0.978 ± 0.043 g/mm3 (3.8 ± 3.4%)] when adjusted for age, body mass index, and BMD at inclusion. Bone formation displayed an interaction ( P < 0.05), mainly caused by increased osteocalcin at 24 wk in the nutrient group. In conclusion, we report that nutrient supplementation results in superior improvements in muscle mass, muscle strength, femoral neck BMD, and bone formation during 24 wk of strength training. The observed differences following such a short intervention emphasize the significance of postexercise nutrient supply on musculoskeletal maintenance.

Exercise training with dietary counselling increases mitochondrial chaperone expression in middle-aged subjects with impaired glucose tolerance

BACKGROUND

Insulin resistance and diabetes are associated with increased oxidative stress and impairment of cellular defence systems. Our purpose was to investigate the interaction between glucose metabolism, antioxidative capacity and heat shock protein (HSP) defence in different skeletal muscle phenotypes among middle-aged obese subjects during a long-term exercise and dietary intervention. As a sub-study of the Finnish Diabetes Prevention Study (DPS), 22 persons with impaired glucose tolerance (IGT) taking part in the intervention volunteered to give samples from the vastus lateralis muscle. Subjects were divided into two sub-groups (IGTslow and IGTfast) on the basis of their baseline myosin heavy chain profile. Glucose metabolism, oxidative stress and HSP expressions were measured before and after the 2-year intervention.

RESULTS

Exercise training, combined with dietary counselling, increased the expression of mitochondrial chaperones HSP60 and glucose-regulated protein 75 (GRP75) in the vastus lateralis muscle in the IGTslow group and that of HSP60 in the IGTfast group. In cytoplasmic chaperones HSP72 or HSP90 no changes took place. In the IGTslow group, a significant positive correlation between the increased muscle content of HSP60 and the oxygen radical absorbing capacity values and, in the IGTfast group, between the improved VO2max value and the increased protein expression of GRP75 were found. Serum uric acid concentrations decreased in both sub-groups and serum protein carbonyl concentrations decreased in the IGTfast group.

CONCLUSION

The 2-year intervention up-regulated mitochondrial HSP expressions in middle-aged subjects with impaired glucose tolerance. These improvements, however, were not correlated directly with enhanced glucose tolerance.

Molecular biomarkers monitoring human skeletal muscle fibres and microvasculature following long-term bed rest with and without countermeasures

The cellular mechanisms of human skeletal muscle adaptation to disuse are largely unknown. The aim of this study was to determine the morphological and biochemical changes of the lower limb soleus and vastus lateralis muscles following 60 days of head-down tilt bed rest in women with and without exercise countermeasure using molecular biomarkers monitoring functional cell compartments. Muscle biopsies were taken before (pre) and after bed rest (post) from a bed rest-only and a bed rest exercise group (n = 8, each). NOS1 and NOS3/PECAM, markers of myofibre 'activity' and capillary density, and MuRF1 (E3 ubiquitin-ligase), a marker of proteolysis, were documented by confocal immunofluorescence and immunoblot analyses. Morphometrical parameters (myofibre cross-sectional area, type I/II distribution) were largely preserved in muscles from the exercise group with a robust trend for type II hypertrophy in vastus lateralis. In the bed rest-only group, the relative NOS1 immunostaining intensity was decreased at type I and II myofibre membranes, while the bed rest plus exercise group compensated for this loss particularly in soleus. In the microvascular network, NOS3 expression and the capillary-to-fibre ratio were both increased in the exercise group. Elevated MuRF1 immunosignals found in subgroups of atrophic myofibres probably reflected accelerated proteolysis. Immunoblots revealed overexpression of the MuRF1 protein in the soleus of the bed rest-only group (> 35% vs. pre). We conclude that exercise countermeasure during bed rest affected both NOS/NO signalling and proteolysis in female skeletal muscle. Maintenance of NO signalling mechanisms and normal protein turnover by exercise countermeasure may be crucial steps to attenuate human skeletal muscle atrophy and to maintain cell function following chronic disuse.

The Adaptations to Strength Training

High-resistance strength training (HRST) is one of the most widely practiced forms of physical activity, which is used to enhance athletic performance, augment musculo-skeletal health and alter body aesthetics. Chronic exposure to this type of activity produces marked increases in muscular strength, which are attributed to a range of neurological and morphological adaptations. This review assesses the evidence for these adaptations, their interplay and contribution to enhanced strength and the methodologies employed. The primary morphological adaptations involve an increase in the cross-sectional area of the whole muscle and individual muscle fibres, which is due to an increase in myofibrillar size and number. Satellite cells are activated in the very early stages of training; their proliferation and later fusion with existing fibres appears to be intimately involved in the hypertrophy response. Other possible morphological adaptations include hyperplasia, changes in fibre type, muscle architecture, myofilament density and the structure of connective tissue and tendons. Indirect evidence for neurological adaptations, which encompasses learning and coordination, comes from the specificity of the training adaptation, transfer of unilateral training to the contralateral limb and imagined contractions. The apparent rise in whole-muscle specific tension has been primarily used as evidence for neurological adaptations; however, morphological factors (e.g. preferential hypertrophy of type 2 fibres, increased angle of fibre pennation, increase in radiological density) are also likely to contribute to this phenomenon. Changes in inter-muscular coordination appear critical. Adaptations in agonist muscle activation, as assessed by electromyography, tetanic stimulation and the twitch interpolation technique, suggest small, but significant increases. Enhanced firing frequency and spinal reflexes most likely explain this improvement, although there is contrary evidence suggesting no change in cortical or corticospinal excitability. The gains in strength with HRST are undoubtedly due to a wide combination of neurological and morphological factors. Whilst the neurological factors may make their greatest contribution during the early stages of a training programme, hypertrophic processes also commence at the onset of training.

The effect of protein and carbohydrate supplementation on strength training outcome of rehabilitation in ACL patients

Patients with anterior cruciate ligament (ACL) injury experience atrophy and weakening of the extensor as well as the hamstrings muscles at the injured leg. Especially, the weakness of the quadriceps muscle has been ascribed to hamper daily physical tasks. The purpose of the present study was therefore to investigate if nutrient supplementation during 12 weeks of conservative rehabilitation strength training could enhance hypertrophy and strength of the quadriceps muscle in ACL-injured patients. Twenty-six ACL-injured men and women were included and randomly distributed into three supplementation groups: Protein+Carbohydrate (PC), Isocaloric-Carbohydrate (IC), or Placebo (PL), ingesting the supplementation immediately after each of 36 training sessions. Determined from images of thigh cross-sections (magnetic resonance imaging) the hypertrophy of the quadriceps muscle differed significantly between groups at the distal part, with the PC group demonstrating the largest hypertrophy. Peak torque of the quadriceps muscle at constant velocity 60 degrees.s-1 was significantly elevated in the PC group only, and the time to reach peak torque tended to decrease as well only in the PC group. The results from this study demonstrate that restoration of the distal vasti muscle mass and knee extension muscle strength with resistance training is promoted further by protein-containing nutrient supplementation immediately after single exercise sessions. Thus, exercise-related protein supplementation may seem important for surgery-related rehabilitation of skeletal muscle.

Skeletal muscle fiber composition of the English sparrow (Passer domesticus)

Substrate utilization by English sparrow skeletal muscle has been extensively studied in our lab. However, there are few published studies on the muscle fiber composition of English sparrow wing and gastrocnemius muscles. The objective of the present study was to examine the fiber type composition of a variety of muscles in the English sparrow. The classification of a muscle fiber as fast glycolytic, slow oxidative, or fast oxidative glycolytic provides insight into the physiological function of muscles. Therefore, we completed mATPase and NADH stains on four muscles of the sparrow wing, as well as the gastrocnemius muscle, to characterize these muscle fiber types. Results show that the fibers of extensor digitorum communis, extensor metacarpi ulnaris, and extensor metacarpi radialis are homogeneous fast oxidative. The fibers of the supinator are homogeneous fast oxidative in 62.5% of samples, and heterogeneous (45.2% fast oxidative, 54.8% fast nonoxidative) in 37.5% of samples. Whereas the gastrocnemius muscle fibers are heterogeneous (10% fast oxidative, 64% fast nonoxidative, 26% slow oxidative) in all muscles examined.

Role of skeletal muscle-fibre type in regulation of glucose metabolism in middle-aged subjects with impaired glucose tolerance during a long-term exercise and dietary intervention

AIM

The aim of this study was to investigate the role of skeletal muscle fibre type in the regulation of glucose metabolism in middle-aged obese subjects with impaired glucose tolerance (IGT) during a 2-year exercise and dietary intervention.

METHODS

Muscle biopsies (musculus vastus lateralis) were taken from 22 subjects belonging to the intervention group of the Finnish Diabetes Prevention Study [1]. According to their myosin heavy chain (MHC) profile at the baseline, the subjects were divided into two groups: IGT(slow) (n=10) with a high proportion of MHC I isoforms and IGT(fast) (n=12) with a high proportion of MHC II isoforms in the vastus lateralis muscle. The intervention consisted of dietary counselling, strength and power training and/or aerobic exercise. The amount of exercise was the same in both groups; the exercise frequency was 5.1+/-2.7 h/week in the IGT(slow) and 5.1+/-2.8 h/week in the IGT(fast) group.

RESULTS

Fasting glucose (p<0.05), 2-h glucose (p<0.05), fasting insulin (p<0.05), haemoglobin A1c (HbA(1c)) (p<0.01) and insulin resistance (p<0.05) [homeostasis model assessment for insulin resistance (HOMA-IR)] decreased in the IGT(fast) group, whereas only the 2-h glucose and HbA(1c) concentrations decreased in the IGT(slow) group. The amount of the glycogen synthase kinase-3-alphabeta (GSK-3-alphabeta) decreased in the IGT(fast) group (p<0.05). Exercise training increased the lactate dehydrogenase (LDH) (p<0.01), LDH-1 (p<0.05) and citrate synthase (CS) (p<0.05) activities in the vastus lateralis muscle in the IGT(slow) group, but only the CS activity (p<0.05) in the IGT(fast) group.

CONCLUSIONS

The glucose metabolism improved both in the IGT(slow) and IGT(fast) group during the 2-year exercise and dietary intervention. The change was more prominent in the IGT(fast) group than in the IGT(slow) group, associated with the decrease of the GSK-alphabeta protein expression in skeletal muscle. The exercise training improved both glycolytic and oxidative capacity in the vastus lateralis muscle. The glycolytic capacity improved in the IGT(slow) group and the oxidative capacity in both groups.

The effects of aging on biceps brachii muscle fibers: a morphometrical study from biopsies and autopsies

OBJECTIVES: In order to study the morphology and size of muscle fibers, cross sections of biceps brachii samples from autopsies, up to 9 hours after death, and biopsies of 72 subjects were compared. The subjects aged 13 to 84 years in both sexes. METHODS: The samples obtained from autopsies (n=47) were from subjects with sudden death, or who died after acute disease without evidence of neuromuscular involvement. The biopsies (n=25) were from patients with symptoms suggestive of inflammatory or metabolic myopathy, not confirmed morphologically. The lesser diameter of muscle fibers was measured using the ATPase reaction. RESULTS: Morphological analysis showed that aging changes were present from the sixth decade in autopsies, and consisted of atrophy and/or type-grouping. The statistical models adjusted for females in both autopsies and biopsies were linear straight with no variation in fiber size with increasing age. The models adjusted for males in both groups were quadratic, indicating that age influenced the size of different type fibers. In males type 2 were larger than type 1 fibers, and than fibers in females. CONCLUSIONS: These values might be useful as controls, helping interpretation of changes in fiber size in samples obtained from biopsies and autopsies.

Variability in human quadriceps muscles: quantitative study and review of clinical literature

Knowledge of variations in normal human thigh musculature is important for the interpretation of various clinical and biomedical investigations. In this study, cross-sections from whole thighs of 34 cadavers were analyzed qualitatively and morphometrically. Sections were cut from right and left limbs at three levels in the region often used for muscle biopsy. Measurements were made of limb circumferences and cross-sectional areas of the three vasti and of the femur, and of the extent of overlap and fusion between the vasti on the lateral aspect of the thigh. Limb circumference proved to be a good predictor of total cross-sectional area of the quadriceps muscle. Large individual variations were found for most measurements but especially for the amount of fusion between the muscle bellies of vastus lateralis and vastus intermedius. Significant differences were found for most variables between the three levels, but there were few differences between sides except for the cross-sectional area of vastus lateralis which was greater on the right at the most distal level. These variations in size and form of thigh musculature should be considered when interpreting data obtained from muscle biopsy, imaging, biomechanical, electromyographic, and functional studies of the human thigh. Review of the literature on variability of quadriceps muscle and its clinical relevance showed a diversity of approaches but insufficient definitive data suitable for interpreting functional outcomes in response to exercise or following surgery. Further work is suggested combining current anatomical datasets with advanced imaging techniques capable of determining muscle fiber orientation and fiber type composition, and including 3D reconstruction.

Fiber type composition of the vastus lateralis muscle of young men and women

This study presents data collected over the past 10 years on the muscle fiber type composition of the vastus lateralis muscle of young men and women. Biopsies were taken from the vastus lateralis muscle of 55 women (21.2+/-2.2 yr) and 95 men (21.5+/-2.4 yr) who had volunteered to participate in various research projects. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were classified using mATPase histochemistry, and cross-sectional area was measured for the major fiber types (I, IIA, and IIB). Myosin heavy chain (MHC) content was determined electrophoretically on all of the samples from the men and on 26 samples from the women. With the exception of fiber Type IC, no significant differences were found between men and women for muscle fiber type distribution. The vastus lateralis muscle of both the men and women contained approximately 41% I, 1% IC, 1% IIC, 31% IIA, 6% IIAB, and 20% IIB. However, the cross-sectional area of all three major fiber types was larger for the men compared to the women. In addition, the Type IIA fibers were the largest for the men, whereas the Type I fibers tended to be the largest for the women. Therefore, gender differences were found with regard to the area occupied by each specific fiber type: IIA>I>IIB for the men and I>IIA>IIB for the women. These data establish normative values for the mATPase-based fiber type distribution and sizes in untrained young men and women.

Muscle fibre type and dimension in genetically obese and lean Zucker rats

Skeletal muscle structure and morphology may be altered in obesity. To study this further, muscles from six genetically obese (fa/fa) and six normal male rats were examined at 15 weeks of age. The gluteus medius, vastus lateralis and rectus abdominis muscles were dissected out and stained for histochemical fibre typing. In addition the fibre cross-sectional area was measured on a graphic tablet. The proportion of fast-twitch fibres was larger in the vastus lateralis and rectus abdominis muscles of the obese rats (P < 0.01); no difference was seen for the gluteus medius muscle. For the normal rats the cross-sectional area of the fast-twitch fibres was 2-3 times larger than the area of slow-twitch fibres in the same muscle. The cross-sectional area of the fast-twitch fibres in the obese rats was 40-47% less than in the control animals (P < 0.003), while no difference between the two groups was found for the slow-twitch fibre area. The data thus suggest that in the genetically obese rats the development of fast-twitch fibres was primarily affected. Moreover, in these animals some muscles may be more affected than others.

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.

Comparison of the histochemical and contractile properties of human triceps surae

The purpose of the study was to compare the contractile properties determined from an electrically stimulated twitch with histochemically determined fibre type parameters of the human triceps surae. Muscle samples were obtained from the medial head of the gastrocnemius of ten male athletes. Ages ranged from 20 to 29 years. Muscle samples from the belly of the medial gastrocnemius muscle were obtained using the needle biopsy technique. The samples were treated histochemically for myosin ATPase to classify the fibres as either slow twitch (ST) or fast twitch (FT) and to determine fibre areas. Surface electrical stimulation was used to determine muscle twitch parameters. The contractile variables of the muscle twitch were latency (L), time to peak force (TPF), peak force (PF), half-contraction time (1/2 CT) and half-relaxation time (1/2 RT). Backward elimination procedures for dependent variables were used to determine which contractile properties best represented the histochemical profile of the muscles. Prediction formulas were developed for FT and ST percentages (R2 = 0.98, p < 0.001), relative area percentage (R2 = 0.87, p < 0.001), and ST area (R2 = 0.85, p < 0.01). It was concluded that the use of the electrotensiometer (ETM) protocol was a valid testing procedure when studying physiological relationships of histochemical properties in intact human skeletal muscle.

Alterations of skeletal muscle in chronic heart failure

BACKGROUND

The present study was designed to define the prevalence and characteristics of skeletal muscle alterations in patients with chronic heart failure (CHF) and their relation to exercise capacity.

METHODS AND RESULTS

The ultrastructure of skeletal muscle was analyzed by ultrastructural morphometry in 57 patients with CHF and 18 healthy controls. The volume density of mitochondria (Vvm) and the surface density (Svmc) of mitochondrial cristae were evaluated as a structural correlate of oxidative capacity of skeletal muscle. Vvm and Svmc were reduced by approximately 20% in patients with severe CHF irrespective of age and etiology. The cytochrome oxidase activity in mitochondria as determined by cytochemistry and subsequent morphometry in a subset of patients (n = 10) was significantly decreased in heart failure (p less than 0.01). The capillary length density of skeletal muscle was reduced in CHF (n = 12, p less than 0.05), and the fiber type distribution was shifted to type II fibers (n = 15, p less than 0.05). Vvm and Svmc were significantly related to peak exercise VO2 (r = 0.56, p less than 0.001, n = 60) and to VO2 at anaerobic threshold (r = 0.535, p less than 0.0001, n = 60). In 16 patients with severe heart failure, Vvm was inversely related to the duration of heart failure (r = 0.545, p less than 0.03). In 11 patients who underwent repeat biopsies after 4 months, a correlation was observed between the change in Vvm and the change in peak exercise VO2 (r = 0.89, p less than 0.001).

CONCLUSIONS

These findings indicate that patients with CHF develop significant ultrastructural abnormalities of skeletal muscle reflecting a depressed oxidative capacity of working muscle. It appears that these alterations of skeletal muscle contribute to the decreased exercise capacity of these patients but are, in principle, reversible by an effective treatment regimen.

Type 2 fiber predominance in Lambert-Eaton myasthenic syndrome

Serial muscle biopsies in a noncarcinomatous case of Lambert-Eaton myasthenic syndrome (LEMS) have shown progressive atrophy and loss of type 1 fibers, resulting in overwhelming type 2 predominance. A similar abnormality was found in a single biopsy from a second case of LEMS without associated carcinoma. Review of the literature suggests that type 2 fiber predominance has been observed in at least one other biopsied case. Interference with transmitter release caused by anti-voltage-gated calcium channel antibodies may deprive type 1 muscle fibers of the low frequency discharge necessary to maintain their metabolic properties.

A morphometrical comparison of right and left whole human vastus lateralis muscle: how to reduce sampling errors in biopsy techniques

In studies of the effects of different training programmes, one muscle--most commonly the vastus lateralis--is used for the experiment while the contralateral muscle serves as a control, at the same time as muscle biopsies are taken from both sides. In order to increase the reliability of such studies, the sources and the magnitude of the sampling errors in the biopsy techniques need to be assessed in detail. In this study, cross-sections of whole right and left vastus lateralis muscle from six young sedentary right-handed men were prepared, and the total number and size of fibres and the proportion of the different fibre types were calculated. A significant difference (P less than 0.05-P less than 0.001) between the right and the left muscle was found for at least one of the three variables in each of the six men, but there was no systematic difference and, therefore, no significant right-left difference for the whole group. The maximum difference between the right and the left side for the mean fibre size was 25% and for the fibre type proportion 5%; these differences are much smaller than the known variation within individual muscles. In conclusion, any study involving biopsies from both the right and the left vastus lateralis may use either muscle for the experiment while the contralateral muscle serves as a control without leading to systematic sampling error, whereas the errors involved in taking small samples from each muscle are much more important to control and to reduce.

Comparison of the histochemical and contractile properties of human gastrocnemius muscle

Contractile and histochemical properties of the human gastrocnemius muscle were compared in 21 male athletes ranging from 20 to 29 years of age. Surface electrical stimulation was used to determine muscle twitch parameters. The contractile variables of the muscle twitch were: latency (L), time to peak force (TPF1 and TPF2), peak force (Pf1 and Pf2), half-contraction time (1/2 CT), and half-relaxation time (1/2 RT). Muscle samples from the belly of the medial gastrocnemius muscle were obtained using the needle biopsy technique. The samples were treated histochemically for myosin ATPase in order to classify the fibers as slow twitch (ST) or fast twitch (FT) and to determine fiber areas. Multiple correlations were performed between the contractile and histochemical variables. The results demonstrated significant (p < 0.05) positive relationships between the calculated twitch recordings and percentage of FT fibers (R = 0.85), percentage of ST fibers (R = 0.85), relative percent area of FT fibers (R = 0.84), and relative percent area of ST fibers (R = 0.84). The results suggest that fiber type percentage and relative percent area determined using myosin ATPase are related to electrically stimulated isometric contractile properties. J Orthop Sports Phys Ther 1991;13(6):322-328.

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.

Muscle hypertrophy and fast fiber type conversions in heavy resistance-trained women

Twenty-four women completed a 20-week heavy-resistance weight training program for the lower extremity. Workouts were twice a week and consisted of warm-up exercises followed by three sets each of full squats, vertical leg presses, leg extensions, and leg curls. All exercises were performed to failure using 6-8 RM (repetition maximum). Weight training caused a significant increase in maximal isotonic strength (1 RM) for each exercise. After training, there was a decrease in body fat percentage (p less than 0.05), and an increase in lean body mass (p less than 0.05) with no overall change in thigh girth. Biopsies were obtained before and after training from the superficial portion of the vastus lateralis muscle. Sections were prepared for histological and histochemical examination. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were distinguished following routine myofibrillar adenosine triphosphatase histochemistry. Areas were determined for fiber types I, IIA, and IIAB + IIB. The heavy-resistance training resulted in significant hypertrophy of all three groups: I (15%), IIA (45%), and IIAB + IIB (57%). These data are similar to those in men and suggest considerable hypertrophy of all major fiber types is also possible in women if exercise intensity and duration are sufficient. In addition, the training resulted in a significant decrease in the percentage of IIB with a concomitant increase in IIA fibers, suggesting that strength training may lead to fiber conversions.

Variability in muscle fibre areas in whole human quadriceps muscle. How much and why?

To determine the variability in fibre areas in the human vastus lateralis muscle, cross-sections (15 microns) of whole autopsied muscles from eight young men have been prepared, and the cross-sectional area (CSA) of 375 type 1 and 375 type 2 fibres has been measured in five different regions throughout each muscle. The CSA of both fibre types varied significantly within all muscle cross-sections. Fibres in the deep parts of the muscle were larger than superficially. There was a significant correlation between the CSA of the two fibre types within each region: if a fibre of a given type was small, or large, the other fibre type was also small, or large. The CSA of type 2 fibres was larger than the CSA of type 1 fibres in 26 of the 40 regions: regions with type 1 fibres larger than type 2 fibres were mostly (71%) found deep in the muscle. The standard deviation of the CSA of type 1 fibres was significantly larger than for type 2 fibres in 35 of the 40 regions. In conclusion, the CSA of the different fibre types in the vastus lateralis of young men varies non-randomly. The pattern of variation, both throughout the muscle and in small sample regions, supports the general opinion that the functional demands placed on the fibre population are an important factor in the development of the fibre properties.

Aerobic fitness and running performance of male and female recreational runners

The purpose of the present study was to assess fitness and running performance in a group of recreational runners (men, n = 18; women, n = 13). 'Fitness' was determined on the basis of their physiological and metabolic responses during maximal and submaximal exercise. There were strong correlations between VO2 max and treadmill running speeds equivalent to blood lactate concentrations of 2 mmol l-1 (V-2 mM) or 4 mmol l-1 (V-4 mM), 'relative running economy' and 5 km times (r = -0.84), but modest and non-significant correlations between muscle fibre composition and running performance. The results of the submaximal exercise tests suggested that the female runners were as well trained as the male runners. However, the men still recorded faster 5 km times (19.20 +/- 1.97 min vs 20.97 +/- 1.70 min; P less than 0.05). Therefore the of the present study suggest that the faster performance times recorded by the men were best explained by their higher VO2 max values, rather than their training status per se.

An unusual familial muscle disorder

Autosomal dominant inheritance of an unusual muscle disease is reported in a family. The pathological appearance, of regularly arranged markedly atrophic muscle fibres without other evidence of disturbed innervation, are similar in each case. However, the onset of the disease, its distribution and its progression has varied within the family.

Sequential studies of a childhood myopathy: a clinical, histochemical and morphometric investigation

An unusual inherited progressive distal myopathy of early childhood onset is described in two sisters from a consanguineous Asian family. Motor milestones were normal but gait deteriorated slowly thereafter with development of generalized hypotonia and muscle weakness particularly in the wrist extensors and hand muscles. Muscle biopsies obtained at the ages of 6 and 10 years respectively (Case 1) showed significant differences. At 6 years muscle morphology and histochemical appearance were normal although type I fibres predominated (79%) and a substantial pool of 'undifferentiated' fibres (12%) was present. By 10 years there was a significant reduction in type I fibres (-13%) and in 'undifferentiated' fibres (-10%) with a concomitant increase in type II fibres (+23%). Fibre size and shape were normal at the age of 6 years but no further fibre growth was evident 4 years later. The older sister (Case 2, age 13 years) was similarly affected. The possibility of this progressive myopathy being caused by loss of neural control at two separate stages of development is discussed. The importance of performing sequential morphometric studies of muscle biopsies from patients with unusual childhood myopathies is emphasized.

Familial myopathy associated with thrombocytopenia: a clinical and histomorphometric study

We describe an unusual vacuolar myopathy with tubular aggregates in a mother and son from a family presenting with a slowly progressive, predominantly limb girdle, weakness and distal upper limb weakness in association with reduced blood clotting ability. To our knowledge this is the first report of a familial clinical defect of both muscle and platelets in the same individuals. The possibility that the primary defect may be due to an abnormality of the tubular intramembranous systems in muscle cells and platelet precursors is discussed.

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.

Comparison of the histochemical and contractile properties of human triceps surae

Contractile and histochemical properties of the triceps surae were compared in 16 males and 4 females aged 20 to 49 years. Surface electrical stimulation was used to determine twitch, tetanic and fatigue parameters. From these tests, twitch tension (Pt), time to peak tension (TPT), half relaxation time (1/2 RT), tetanic tensions at 10, 20 and 50 Hz and an index of fatigue (FI) were calculated. A maximal voluntary contraction (MVC) was also performed. Muscle samples from the belly of the lateral gastrocnemius were obtained using the needle biopsy technique. The samples were treated histochemically for myosin ATPase and NADH-tetrazolium reductase in order to classify the fibres as either Type I, slow twitch (ST) or Type II, fast twitch (FT) and to determine fibre areas. Correlations were performed between the grouped male and female contractile and histochemical variables. The results demonstrated significant positive relationships demonstrated significant positive relationships between percentage of ST fibres (%ST) and TPT (r = 0.49), and %ST and the ratio of tetanic forces at 10 Hz to 50 Hz (Po10/Po50) (r = 0.55). No significant relationships were obtained for Pt, 1/2 RT, MVC or FI with any histochemical parameter. The results suggest that fibre type distribution determined using myosin ATPase is related to electrically stimulated isometric contractile speeds and not to voluntary force generation (MVC) or electrically induced fatigue.

Additional biochemical criteria in the differential diagnosis of myositis

Thirty-six biopsy specimens of human biceps and vastus lateralis muscles were examined by histometric analysis and determination of enzyme activities (phosphorylase, triosephosphate dehydrogenase, 3-hydroxacyl-CoA-dehydrogenase, lactate dehydrogenase, hexose isomerase, citrate synthetase, 6-phosphogluconate dehydrogenase). The series included 13 specimens from patients suffering from a benign form of muscular dystrophy (limb girdle and Becker type of muscular dystrophy) and 12 specimens from patients with an acute (n = 5) or chronic (n = 7) form of myositis. Muscle fibres were atrophic in myositis and hypertrophic (with an increased variation of fibre diameters) in muscular dystrophies, as has been shown previously. When myositis samples were compared with either normal or dystrophic muscles, a highly significant lowering of glycolytic enzyme activity was found in chronic myositis, while the activity of 6-phosphogluconate dehydrogenase was elevated to highly significant levels. Measurements of the latter enzyme's activity might be of additional value in differentiating chronic forms of myositis from benign muscular dystrophies.

Muscle morphometry in motor neuron disease

It has previously been suggested that the pathological abnormalities seen in muscle biopsies from patients with motor neuron disease (MND) are of predictive value in relation to the rate of progression of the disease. In this study, quadriceps muscle biopsies from 19 patients with MND and 20 age matched controls were prepared for histochemistry and analysed morphometrically. Pathological features of denervation and reinnervation were observed in all MND patients although considerable variation between patients was noted. Motor neuron disease biopsies also showed increased connective tissue, an increased variation in fibre size, and a random fibre type distribution. Several of these abnormalities were more severe in female patients. Many of these 'abnormalities' were also frequent, albeit to a milder degree, in control biopsies and emphasize the need for age matched controls. The morphometric data was not related to the age of the patient, disease duration, type of MND or muscle strength, thus suggesting that the progression and severity of MND and its prognosis cannot be judged on the basis of quadriceps muscle pathology alone.

Skeletal muscle capillary density and fiber type are possible determinants of in vivo insulin resistance in man

We have compared the capillary density and muscle fiber type of musculus vastus lateralis with in vivo insulin action determined by the euglycemic clamp (M value) in 23 Caucasians and 41 Pima Indian nondiabetic men. M value was significantly correlated with capillary density (r = 0.63; P less than or equal to 0.0001), percent type I fibers (r = 0.29; P less than 0.02), and percent type 2B fibers (r = -0.38; P less than 0.003). Fasting plasma glucose and insulin concentrations were significantly negatively correlated with capillary density (r = -0.46, P less than or equal to 0.0001; r = -0.47, P less than or equal to 0.0001, respectively). Waist circumference/thigh circumference ratio was correlated with percent type 1 fibers (r = -0.39; P less than 0.002). These results suggest that diffusion distance from capillary to muscle cells or some associated biochemical change, and fiber type, could play a role in determining in vivo insulin action. The association of muscle fiber type with body fat distribution may indicate that central obesity is only one aspect of a more generalized metabolic syndrome. The data may provide at least a partial explanation for the insulin resistance associated with obesity and for the altered kinetics of insulin action in the obese.

Effect of testosterone on muscle protein synthesis in myotonic dystrophy

Muscle wasting in myotonic dystrophy may result from decreased muscle anabolic processes rather than from increased catabolism. Male patients with myotonic dystrophy often have low levels of circulating androgens, and androgen administration has been shown to increase their muscle mass. We have studied the effect of testosterone enanthate administration (3 mg/kg weekly for 3 months) on muscle and whole body protein synthesis in 6 male patients with myotonic dystrophy. Muscle protein synthesis was estimated from the rate of isotope incorporation into muscle protein obtained by quadriceps muscle biopsy during a primed continuous infusion of L-[1-13C]leucine. Testosterone administration resulted in a significant increase in muscle protein synthesis in all patients. Whole body protein synthesis did not increase, indicating that protein synthesis in other tissues may have declined. Muscle ribonucleic acid content rose significantly in response to testosterone administration, suggesting that testosterone initiated its effect by hormone receptor interaction with muscle nuclei.

Repeatability of fibre type and enzyme activity measurements in human skeletal muscle

In order to assess the variability in repeated determination of human muscle fibre type distribution, fibre area and enzyme activity measurements, two biopsies were taken within 10 days in the same vastus lateralis for 12 females and 13 males, and in the right and in the left muscles for 25 other subjects (13 females and 12 males). Within muscle, intraclass reliability coefficients were 0.88, 0.82 and 0.56 for type I, IIa and IIb per cent fibres, respectively, and ranged from 0.74 to 0.82 for fibre areas and from 0.71 to 0.90 for enzyme markers of different metabolic pathways. Correlations between right and left muscle measurements were also high for fibre areas (from 0.85 to 0.91) and enzyme activities (from 0.71 to 0.87), except for phosphofructokinase (r = 0.63). In contrast, the right and left thigh muscle correlation reached 0.67, 0.40 and 0.64 for type I, IIa and IIb fibre distribution, respectively. Thus, the variation in muscle sampling and technical procedures reached about 15% of the total variation (i.e. total differences between subjects) for the proportion of fibre type I and IIa and about 20-25% for fibre areas and enzyme activities. On the other hand, the technical error for the proportion of fibre type I and IIa is about 6-7%. This implies that differences brought about by any experimental treatment on these skeletal muscle characteristics in human studies have to be of a relatively large magnitude before being detectable. On the other hand, fibre areas and enzyme activities measured in single needle biopsy sample, from one of the vastus lateralis muscles, are quite representative of the other vastus lateralis. Similarity in fibre type proportion between right and left vastus lateralis cannot be postulated, however, without investigating both muscles.

Human skeletal muscle fiber type alteration with high-intensity intermittent training

The response of muscle fiber type proportions and fiber areas to 15 weeks of strenuous high-intensity intermittent training was investigated in twenty-four carefully ascertained sedentary (14 women and 10 men) and 10 control (4 women and 6 men) subjects. The supervised training program consisted mainly of series of supramaximal exercise lasting 15 s to 90 s on a cycle ergometer. Proportions of muscle fiber type and areas of the fibers were determined from a biopsy of the vastus lateralis before and after the training program. No significant change was observed for any of the histochemical characteristics in the control group. Training significantly increased the proportion of type I and decreased type IIb fibers, the proportion of type IIa remained unchanged. Areas of type I and IIb fibers increased significantly with training. These results suggest that high-intensity intermittent training in humans may alter the proportion of type I and the area of type I and IIb fibers and in consequence that fiber type composition in human vastus lateralis muscle is not determined solely by genetic factors.

Needle muscle biopsy: will it make open biopsy obsolete?

Seventy-five needle muscle biopsies have been performed in this department over the past two years. Adequate biopsies were obtained in 69 cases. In 40 cases a variety of neuromuscular conditions was seen, broadly categorised as necrotizing myopathy (10), neurogenic atrophy (7), metabolic myopathy (5), vasculitis (2), normal muscle (7), and non-specific changes (9). Twenty-nine cases were for muscular dystrophy carrier detection. There were no complications associated with the procedure. The technique is simple and quick, and can be performed on outpatients or in the ward. Needle biopsy is the method of choice for sampling skeletal muscle in most patients, although open biopsy is still indicated for certain conditions.

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.