Muscle volume reconstruction from several short magnetic resonance imaging sequences

The gold standard to determine muscle morphological parameters is magnetic resonance imaging (MRI). To measure large muscles like the vastus lateralis (VL) in one sequence, scanners with a large field of view (FOV) and a high flux density are needed. However, large scanners are expensive and not always available. The purpose of the current study was to develop a marker-based approach to reconstruct the VL from several separate MRI sequences, acquired with a low-field MRI scanner. The VL muscle of 21 volunteers was marked at one-third and two-third of thigh length using fish oil capsules. Three consecutive MRI sequences (i.e. proximal, medial and distal part) of the thigh were captured between the markers and the muscle insertion and origin. After a manual segmentation of the VL the muscle was reconstructed using the developed approach. The muscle volume, maximal anatomical cross-sectional area and length were 715.1 ± 93.4 cm³, 34.0 ± 4.0 cm² and 34.4 ± 2.2 cm respectively. The procedure showed an average error between 0.9% and 2.2% for the reconstructed muscle volume, the averaged RMSD between the cross-sectional areas of two overlapping sequences were between 0.80 ± 0.71 cm² and 0.88 ± 0.78 cm². The proposed approach provides an appropriate accuracy for muscle volume assessment, as the estimated error for muscle volume calculation was quite small. The reconstruction quality depends mainly on the proper marker attachment and identification, as well as the spatial resolution of the image sequences. We are confident that the presented method can be used in most investigations regarding muscle morphology.     

Alterations of treatment-naïve pelvis and thigh muscle morphology in children with cerebral palsy

Lower limb (LL) muscle morphology and growth are altered in children with cerebral palsy (CP). Muscle alterations differ with age and with severity of motor impairment, classified according to the gross motor classification system (GMFCS). Muscle alterations differ also with orthopedic intervention, frequently performed at the level of the shank muscles since an early age, such as the gastrocnemius. The aim was to investigate the alterations of treatment-naïve pelvis and thigh muscle lengths and volumes in children with GMFCS levels I and II, of varying ages.17 children with CP (GMFCS I: N = 9, II: N = 8, age: 11.7 ± 4 years), age-matched to 17 typically developing (TD) children, underwent MRI of the LL. Three-dimensional reconstructions of the muscles were performed bilaterally. Muscle volumes and lengths were calculated in 3D and compared between groups. Linear regression between muscle volumes and age were computed.Adductor-brevis and gracilis lengths, as well as rectus-femoris volume, were decreased in GMFCS I compared to TD (p < 0.05). Almost all the reconstructed muscle volumes and lengths were found to be altered in GMFCS II compared to TD and GMFCS I. All muscle volumes showed significant increase with age in TD and GMFCS I (R² range: 0.3–0.9, p < 0.05). Rectus-femoris, hamstrings and adductor-longus showed reduced increase in the muscle volume with age in GMFCS II when compared to TD and GMFCS I.Alterations of treatment-naïve pelvis and thigh muscle volumes and lengths, as well as muscle growth, seem to increase with the severity of motor impairment in ambulant children with CP.     

In vivo pediatric shoulder muscle volumes and their relationship to 3D strength

In the pediatric shoulder, injury and pathology can disrupt the muscle force balance, resulting in severe functional losses. As little data exists pertaining to in vivo pediatric shoulder muscle function, musculoskeletal data are crucially needed to advance the treatment of pediatric shoulder pathology/injury. Therefore, the purpose of this study was to develop a pediatric database of in vivo volumes for the major shoulder muscles and correlate these volumes with maximum isometric flexion/extension, internal/external rotation, and abduction/adduction joint moments. A methodology was developed to derive 3D shoulder muscle volumes and to divide the deltoid into sub-units with unique torque producing capabilities, based on segmentation of three-dimensional magnetic resonance images. Eleven typically developing children/adolescents (4F/7M, 12.0±3.2 years, 150.8±16.7 cm, 49.2±16.4 kg) participated. Correlation and regression analyses were used to evaluate the relationship between volume and maximum, voluntary, isometric joint torques. The deltoid demonstrated the largest (30.4±1.2%) and the supraspinatus the smallest (4.8±0.5%) percent of the total summed volume of all six muscles evaluated. The anterior and posterior deltoid sections were 43.4±3.9% and 56.6±3.9% of the total deltoid volume. The percent volumes were highly consistent across subjects. Individual muscle volumes demonstrated moderate-high correlations with torque values (0.70–0.94, p<0.001). This study presents a comprehensive database documenting normative pediatric shoulder muscle volume. Using these data a clear relationship between shoulder volume and the torques they produce was established in all three rotational degrees-of-freedom. This study furthers the understanding of shoulder muscle function and serves as a foundation for evaluating shoulder injury/pathology in the pediatric/adolescent population.     

Capillarization,mitochondrial densities,oxygen diffusion distances and innervation of red and white muscle of the lizard Dipsosaurus dorsalis

Summary The white and red regions of the iliofibularis muscle of the lizard Dipsosaurus dorsalis were analyzed using histologic and morphometric analysis. These regions are composed of fast glycolytic (FG) and both fast oxidative, glycolytic (FOG) and tonic fibers, respectively. Endplate morphology and number of endplates per fiber were estimated from fibers from both areas. Capillary volume densities of the red and white regions were quantified from transverse sections. Mitochondrial volume of fibers from the red and white regions were estimated from electron micrographs.All fibers from the white region of the iliofibularis possessed a single, well defined endplate, as did most red region fibers. The remaining red fibers (28±5%) possessed an average of 14.7±3 endplates each, distributed along the entire length of the fiber at intervals of approximately 1124 m.Red fibers possessed twice the mitochondrial volume of white fibers (7.6±0.4%, red; 3.8±0.3%, white). Mitochondria were distributed uniformly through the fibers from both regions. Capillary anisotropy was low ( = 1.018) in both regions. Capillary densities of the red region (629±35 mm^-2) were much greater than those of the corresponding White region (73±8 mm^-2).The data indicate that capillary densities, mitochondrial volumes and theoretical diffusion distances correlate well with the oxidative capacity of lizard muscle fibers. Tonic fibrs of this species appear oxidative and therefore metabolically capable of functioning during locomotion. The similar mitochondrial volumes and capillary densities of reptilian and mammalian muscles suggest that the greater oxidative capacity of mammalian muscle is due in part to possession of more oxidatively active mitochondria rather than to possession of more mitochondria per se.     

Validation of a simplified method for muscle volume assessment

The present study investigated the validity of a simplified muscle volume assessment that uses only the maximum anatomical cross-sectional area (ACSA_max), the muscle length (L_M) and a muscle-specific shape factor for muscle volume calculation ( Albracht et al., 2008, J Biomech 41, 2211–2218). The validation on the example of the triceps surae (TS) muscles was conducted in two steps. First L_M, ACSA_max, muscle volume and shape factor were calculated from magnet resonance image muscle reconstructions of the soleus (SO), gastrocnemius medialis (GM) and lateralis (GL) of a group of untrained individuals (n=13), endurance (n=9) and strength trained (n=10) athletes. Though there were significant differences in the muscle dimensions, the shape factors were similar across groups and were in average 0.497±0.026, 0.596±0.030, and 0.556±0.041 for the SO, GM and GL respectively. In a second step, the shape factors were applied to an independent recreationally active group (n=21) to compare the muscle volume assessed by the simplified method to the results from whole muscle reconstructions. There were no significant differences between the volumes assessed by the two methods. In conclusion, assessing TS muscle volume on the basis of the reported shape factors is valid across populations and the root mean square differences to whole muscle reconstruction of 7.9%, 4.8% and 8.3% for SO, GM and GL show that the simplified method is sensitive enough to detect changes in muscle volume in the context of degeneration, atrophy or hypertrophy.     

Oxygen consumption and the composition of skeletal muscle tissue after training and inactivation in the European woodmouse (Apodemus sylvaticus)

Summary In European woodmice the amount and intensity of daily activity was compared to oxygen uptake and to the potential for oxidative metabolism of heart and skeletal muscle. One group of animals was inactivated by exposition to light during night time; another group of animals was trained by enforced running on a treadmill. The oxidative potential of the muscle tissue was assessed by morphometry of capillaries and mitochondria. A novel sampling technique was used which allowed us to obtain morphological data related to single muscles, to muscle groups, and finally to whole body muscle mass.Reducing the spontaneous activity by ten fold had no effect on oxygen uptake nor on capillaries or mitochondria in locomotory muscles. Mitochondrial volume was reduced, however, in heart and diaphragm. Enforced running increased the weight specific maximal oxygen uptake significantly. It also increased the mitochondrial volume in heart and diaphragm as well as in M. tibialis anterior. Capillary densities were neither affected by training nor by inactivation. A significant correlation was found between the capillary density and the volume density of mitochondria in all muscles analysed morphometrically. For the whole skeletal muscle mass of a European woodmouse the inner mitochondrial membranes were estimated to cover 30 m². The oxygen consumption per unit time and per unit volume of muscle mitochondrion was found to be identical in all groups of animals (4.9 ml O₂ min^–1 cm^–3).Symbols S _v (im,m) surface area of inner mitochondrial membranes per unit mitochondrial volume - V _v (mt, f) volume density of mitochondria (mitochondrial volume per fiber volume) - V (mt) total mitochondrial volume - V (f) muscle volume - N _A (c, f) capillary density - (f) mean fiber cross-sectional area     

Tumor necrosis factor-α in macrophages of heart,liver, kidney,and in the pituitary gland

The relationship between myonuclear number, cellular size, succinate dehydrogenase activity, and myosin type was examined in single fiber segments (n=54; 9±3 mm long) mechanically dissected from soleus and plantaris muscles of adult rats. One end of each fiber segment was stained for DNA before quantitative photometric analysis of succinate dehydrogenase activity; the other end was double immunolabelled with fast and slow myosin heavy chain monoclonal antibodies. Mean±S.D. cytoplasmic volume/myonucleus ratio was higher in fast and slow plantaris fibers (112±69 vs. 34±21x10³ m³) than fast and slow soleus fibers (40±20 vs. 30±14x10³ m³), respectively. Slow fibers always had small volumes/myonucleus, regardless of fiber diameter, succinate dehydrogenase activity, or muscle of origin. In contrast, smaller diameter (<70 m) fast soleus and plantaris fibers with high succinate dehydrogenase activity appeared to have low volumes/myonucleus while larger diameter (>70 m) fast fibers with low succinate dehydrogenase activity always had large volume/myonucleus. Slow soleus fibers had significantly greater numbers of myonuclei/mm than did either fast soleus or fast plantaris fibers (116±51 vs. 55±22 and 44±23), respectively. These data suggest that the myonuclear domain is more limited in slow than fast fibers and in the fibers with a high, compared to a low, oxidative metabolic capability.     

Magnetic resonance tomography measurement of the thigh adipose tissue volume in men

The volume of the thigh adipose tissue was estimated using magnetic resonance tomography (MRT) and anthropometric measurements. Eighty-seven physically well-developed men aged 18–45 years participated in the experiment. The MRT estimate of the thigh fat volume was 2206 ± 882 cm³. The results were used to derive two multiple linear regression equations for calculating the thigh adipose tissue volume from anthropometric parameters. The correlation coefficient between the thigh adipose tissue volumes calculated from the equation and measured by MRT was r = 0.97.     

Suboccipital muscles in the cat neck: Morphometry and histochemistry of the rectus capitis muscle complex

The morphometry, histochemistry, and biomechanical relationships of rectus capitis muscles were examined in adult cats. This family of muscles contained six members on the dorsal, ventral, and lateral aspects of the upper cervical vertebral column. Three dorsal muscles (rectus capitis posterior major, medius, and minor) formed a layered complex spanning from C1 and C2 to the skull. Rectus capitis posterior major was composed predominantly of fast fibers, but the other two deeper muscles contained progressively higher proportions of slow fibers. One ventral muscle, rectus capitis anterior major, was architecturally complex. It originated from several cervical vertebrae and appeared to be divided into two different heads. In contrast, rectus capitis anterior minor and rectus capitis lateralis were short, parallel-fibered muscles spanning between the skull and C1. The ventral muscles all had nonuniform distributions of muscle-fiber types in which fast fibers predominated. Dorsal and ventral muscle groupings usually had cross-sectional areas of 0.5 cm² or more, reflecting a potential capacity to generate maximal tetanic force in excess of 9 N. Biomechanical analyses suggested that one muscle, rectus capitis lateralis, had its largest moment in lateral flexion, whereas the other muscles had large, posturally dependent moment arms appropriate for actions in flexion-extension. The observation that most rectus muscles have relatively large cross-sectional areas and high fast-fiber proportions suggests that the muscles may have important phasic as well as postural roles during head movement. © 1993 Wiley-Liss, Inc.     

Stereological estimation of the surface area and oxygen diffusing capacity of the respiratory stomach of the air‐breathing armored catfish Pterygoplichthys anisitsi (Teleostei: Loricariidae)

The stomach of Pterygoplichthys anisitsi has a thin, translucent wall and a simple squamous epithelium with an underlying dense capillary network. In the cardiac and pyloric regions, most cells have short microvilli distributed throughout the cell surface and their edges are characterized by short, densely packed microvilli. The mucosal layer of the stomach has two types of pavement epithelial cells that are similar to those in the aerial respiratory organs. Type 1 pavement epithelial cells, resembling the Type I pneumocyte in mammal lungs, are flat, with a large nucleus, and extend a thin sheet of cytoplasm on the underlying capillary. Type 2 cells, resembling the Type II pneumocyte, possess numerous mitochondria, a well‐developed Golgi complex, rough endoplasmic reticulum, and numerous lamellar bodies in different stages of maturation. The gastric glands, distributed throughout the mucosal layer, also have several cells with many lamellar bodies. The total volume (air + tissue), tissue, and air capacity of the stomach when inflated, increase along with body mass. The surface‐to‐tissue‐volume ratio of stomach varies from 108 cm^?1 in the smallest fish (0.084 kg) to 59 cm^?1 in the largest fish (0.60 kg). The total stomach surface area shows a low correlation to body mass. Nevertheless, the body‐mass‐specific surface area varied from 281.40 cm² kg^?1 in the smallest fish to 68.08 cm² kg^?1 in the largest fish, indicating a negative correlation to body mass (b = ?0.76). The arithmetic mean barrier thickness between air and blood was 1.52 ± 0.07 μm, whereas the harmonic mean thickness (τ_h) of the diffusion barrier ranged from 0.40 to 0.74 μm. The anatomical diffusion factor (ADF = cm² μm^?1 kg^?1) and the morphological O₂ diffusion capacity (D_morpholO₂ = cm³ min^?1 mmHg^?1 kg^?1) are higher in the smallest specimen and lower in the largest one. In conclusion, the structure and morphometric data of P. anisitsi stomach indicate that this organ is adapted for oxygen uptake from air. J. Morphol. 2009. © 2008 Wiley‐Liss, Inc.     

High content of polyunsaturated fatty acids in muscle phospholipids of a fast runner,the European brown hare (Lepus europaeus)

To investigate both seasonal changes and possible intracorporal gradients of phospholipid fatty acid composition, skeletal muscles (n=124), hearts (n=27), and livers (n=34) from free-living brown hares (Lepus europaeus) were analyzed. Phospholipids from both skeletal muscles and heart had a high degree of unsaturation with 66.8±0.63% and 65.7±0.5% polyunsaturated fatty acids, respectively. This is the highest proportion of polyunsaturated fatty acids reported in any mammalian tissue. Polyunsaturated fatty acid content in skeletal muscles was 2.3% greater in winter compared to summer (F_1,106=17.7; P=0.0001), which may reflect thermoregulatory adjustments. Arachidonate (C20:4n-6) showed the greatest seasonal increase (+2.5%; F=7.95; P=0.0057). However, there were no pronounced differences in polyunsaturated fatty acid content between skeletal muscles from different locations in the body (m. iliopsoas, m. longissimus dorsi and m. vastus). Total muscle phospholipid polyunsaturated fatty acid content was correlated with polyunsaturated fatty acid content in triacyglycerols from perirenal white adipose tissue depots (r²=0.61; P=0.004). Polyunsaturated fatty acids were enriched in muscle phospholipids (56.8–73.6%), compared to white adipose tissue lipids (20.9–61.2%), and liver phospholipids (25.1–54.2%). We suggest that the high degree of muscle membrane unsaturation is related to hare-specific traits, such as a high maximum running speed.Abbreviations BMR basal metabolic rate - DPA docosapentaenoic acid - DHA docosahexaenoic acid - FA fatty acid - MUFA monounsaturated fatty acid - PC principal component - PUFA polyunsaturated fatty acid - SFA saturated fatty acid - UI unsaturation index - WAT white adipose tissueCommunicated by: G. Heldmaier     

Osmotic water movement across the sarcolemma of frog skeletal muscle fibers

Summary The permeability coefficient for osmotically induced water flux across the sarcolemma of frog skeletal muscle fibers was determined. A new method for measuring the fiber volume change was applied, based on the fact that the resting tension of a slightly stretched muscle fiber depends on the bathing solution tonicity. Thus, after a quick change in tonicity, the volume change can be derived from the simultaneously occurring tension change. Fitting a theoretical curve to the experimentally obtained values yielded a filtration permeability coefficient for water of 0.54±0.12 cm⁴/osmol sec (mean ±sd, n=12). Doubling the driving force did not alter the productP _Wx membrane area. TheP _W value found in the present work is compared with that for muscle fibers and other cells given previously.     

Effects of elevated cytosolic calcium on ACh-induced swine tracheal smooth muscle contraction

Increased intracellular calcium concentration ([Ca²⁺]_i) is required for smooth muscle contraction. In tracheal and other tonic smooth muscles, contraction and elevated [Ca²⁺]_i are maintained as long as an agonist is present. To evaluate the physiological role of steady-state increases in Ca²⁺ on tension maintenance, [Ca²⁺]_i was elevated using ionomycin, a Ca²⁺ ionophore or charybdotoxin, a large-conductance calcium-activated potassium channel (K_Ca) blocker prior to or during exposure of tracheal smooth muscle strips to Ach (10^–9 to 10^–4 M). Ionomycin (5 µM) in resting muscles induced increases in [Ca²⁺]_i to 500±230 nM and small increases in force of 2.6±2.3 N/cm². This tension is only 10% of the maximal tension induced by ACh. Charybdotoxin had no effect on [Ca²⁺]_i or tension in resting muscle. After pretreatment of muscle with ionomycin, the concentration-response relationship for ACh-induced changes in tension shifted to the left (EC₅₀=0.07±0.05 µM ionomycin; 0.17±0.07 µM, control, p<0.05). When applied to the muscles during steady-state responses to submaximal concentrations of ACh, both ionomycin and charybdotoxin induced further increases in tension. The same magnitude increase in tension occurs after ionomycin and charybdotoxin treatment, even though the increase in [Ca²⁺]_i induced by charybdotoxin is much smaller than that induced by ionomycin. We conclude that the resting muscle is much less sensitive to elevation of [Ca²⁺]_i when compared to muscles stimulated with ACh. Steady-state [Ca²⁺]_i limits tension development induced by submaximal concentrations of ACh. The activity of K_Ca moderates the response of the muscle to ACh at concentrations less than 1 µM.     

Threshold for shivering in aerobic and anaerobic muscles in bantam cocks and incubating hens

Summary Electromyographic activity (EMG) from the musculus pectoralis (breast muscle), m. iliotibialis (thigh muscle) and m. gastrocnemius (leg muscle), cloacal temperature (Tb) and O₂ consumption were measured in bantam cocks (Gallus domesticus) exposed to different ambient temperatures (Ta). The same parameters were measured in bantam hens incubating eggs artificially thermoregulated to 40° and 25°C (Te).EMG activity appeared in thigh and leg muscles at Ta below 32°C (Tsh). This temperature probably represents the thermoneutral temperature (TNT) of the cock. EMG activity in breast muscles appeared at Ta below 20°C, or 4°C below the lower critical temperature (Tc).All muscles were quiet when the hen incubated 40°C egg at Ta=Tsh. When Te was abruptly changed to 25°C, EMG activity in the iliotibialis muscle appared 3 min before the activity in the pectoralis muscle. Tb dropped from 41.2° to 40.6°C in 14 min. When Te was returned to 40°C, the EMG activity in the pectoralis muscle disappeared almost at once, while the iliotibialis muscle was active until Tb returned to normal.Aerobic muscles seem to be responsible for shivering thermogenesis between Tc and Tsh, while anaerobic muscles are recruited at lower Ta or when the heat loss during incubation becomes severe.Abbreviations EMG electromyography - Ta ambient temperature - Tb cloacal temperature - Tc lower critical temperature - Te egg temperature - TNT thermoneutral temperature - Tsh shivering threshold temperature     

Relationships of 35 lower limb muscles to height and body mass quantified using MRI

Skeletal muscle is the most abundant tissue in the body and serves various physiological functions including the generation of movement and support. Whole body motor function requires adequate quantity, geometry, and distribution of muscle. This raises the question: how do muscles scale with subject size in order to achieve similar function across humans? While much of the current knowledge of human muscle architecture is based on cadaver dissection, modern medical imaging avoids limitations of old age, poor health, and limited subject pool, allowing for muscle architecture data to be obtained in vivo from healthy subjects ranging in size. The purpose of this study was to use novel fast-acquisition MRI to quantify volumes and lengths of 35 major lower limb muscles in 24 young, healthy subjects and to determine if muscle size correlates with bone geometry and subject parameters of mass and height. It was found that total lower limb muscle volume scales with mass (R²=0.85) and with the height–mass product (R²=0.92). Furthermore, individual muscle volumes scale with total muscle volume (median R²=0.66), with the height–mass product (median R²=0.61), and with mass (median R²=0.52). Muscle volume scales with bone volume (R²=0.75), and muscle length relative to bone length is conserved (median s.d.=2.1% of limb length). These relationships allow for an arbitrary subject's individual muscle volumes to be estimated from mass or mass and height while muscle lengths may be estimated from limb length. The dataset presented here can further be used as a normative standard to compare populations with musculoskeletal pathologies.     

Sex differences in the cross-sectional areas of psoas major and thigh muscles in high school track and field athletes and nonathletes

The present study aimed to examine the sex differences in the cross-sectional areas of the psoas major, quadriceps femoris, hamstrings, and adductors in high school track and field athletes and nonathletes. The cross-sectional areas of the psoas major at L4-L5 and three thigh muscles at the mid-thigh were determined in the right side of the body using magnetic resonance imaging in 61 sprinters (29 boys and 32 girls), 50 jumpers (28 boys and 22 girls), 33 throwers (18 boys and 15 girls), and 40 nonathletes (20 boys and 20 girls), aged from 16 to 18 yrs. On the whole, the cross-sectional area for every muscle group was greater in the athletes than in the nonathletes and in the boys than in the girls. The average value of the cross-sectional area for the girls as a percentage of that for the boys in every subject group was lower in the psoas major (57.6-64.7%) than in the thigh muscles (67.8-82.9%). Among the thigh muscles, the muscle group which showed significant sex differences in the ratio of cross-sectional area to the two-third power of lean body mass was limited to the quadriceps femoris in the sprinters and nonathletes and hamstrings in the throwers. However, the ratio for the psoas major was significantly higher in the boys than in the girls in all subject groups. The current results indicate that, although regular participation in sports training during adolescence promotes hypertrophy in the psoas major and thigh muscles in not only boys but also girls, a greater sex difference exists in the muscularity of the psoas major than of the thigh muscles, in athletes and nonathletes.     

Volume flows and pressure changes during an action potential in cells ofChara australis

Summary Methods have been used for monitoring either volume flows or pressure changes, simultaneously with membrane potentials, in giant algal cells ofChara australis during an action potential. The volume flows were measured from the movement of a mercury bead in a capillary tube recorded by a photo-transducer. The pressure changes were measured by monitoring the deflection of a thin wedge, resting transversely across a cell, and using the same photo-transducer, the deflection of the wedge being directly related to the cell's turgor pressure. The average maximum rate of volume flow per unit area during an action potential was 0.88±0.11 nliter·sec^–1·cm^–2 in the direction of an outflow from the cell (total volume outflow being about 3 nliter·cm^–2 per action potential). Similarly, the maximum rate of change of pressure was 19.6±3.8×10^–3 atm·sec^–1 (peak change being 19.3±2.9×10^–3 atm equivalent to 14.7±2.2 mm Hg). The volume flow and pressure changes followed the vacuolar potential quite closely, the peak rate of volume flow lagging behind the peak of the action potential by 0.17±0.08 sec and the peak rate of pressure change leading it by 0.09±0.07 sec.     

Effects of 8-week in-season upper and lower limb heavy resistance training on the peak power, throwing velocity, and sprint performance of elite male handball players

The aims of this study were to test the potential of in-season heavy upper and lower limb strength training to enhance peak power output (Wpeak), vertical jump, and handball related field performance in elite male handball players who were apparently already well trained, and to assess any adverse effects on sprint velocity. Twenty-four competitors were divided randomly between a heavy resistance (HR) group (age 20 ± 0.7 years) and a control group (C; age 20 ± 0.1 years). Resistance training sessions were performed twice a week for 8 weeks. Performance was assessed before and after conditioning. Peak power (W(peak)) was determined by cycle ergometer; vertical squat jump (SJ) and countermovement jump (CMJ); video analyses assessed velocities during the first step (V(1S)), the first 5 m (V(5m)), and between 25 and 30 m (V(peak)) of a 30-m sprint. Upper limb bench press and pull-over exercises and lower limb back half squats were performed to 1-repetition maximum (1RM). Upper limb, leg, and thigh muscle volumes and mean thigh cross-sectional area (CSA) were assessed by anthropometry. W(peak) (W) for both limbs (p < 0.001), vertical jump height (p < 0.01 for both SJ and CMJ), 1RM (p < 0.001 for both upper and lower limbs) and sprint velocities (p < 0.01 for V(1S) and V(5m); p < 0.001 for V(peak)) improved in the HR group. Upper body, leg, and thigh muscle volumes and thigh CSA also increased significantly after strength training. We conclude that in-season biweekly heavy back half-squat, pull-over, and bench-press exercises can be commended to elite male handball players as improving many measures of handball-related performance without adverse effects upon speed of movement.     

Architecture of the hind limb muscles of cats: Functional significance

Force, velocity, and displacement properties of a muscle are determined in large part by its architectural design. The relative effect of muscle architecture on these physiological variables was studied by determining muscle weight, fiber length, average sarcomere length, and approximate angle of pinnation for 24 cat hind limb muscles. Muscle lengths ranged from 28.3 to 144 mm, whereas fiber lengths ranged from 8.4 to 105.5 mm. Generally, fiber to muscle length ratios were similar throughout a muscle. Estimated angles of pinnation of muscle fibers varied from 0 to 21° with most having an angle of less than 10°. The cross-sectional area of the knee extensors was similar to the knee flexors (16.43 vs. 16.83 cm²) whereas the cross-sectional area of the ankle extensors was more than six times greater than the ankle flexors (18.59 vs. 2.83 cm²). There was a 6.7-fold difference in the maximal force between muscles, when normalized to a constant weight, that could be attributed to architectural features. Rations of wet weight to predicted maximal tetanic tension for each muscle and group were calculated to compare the relative priority of muscle force versus muscle length-velocity for a given mass of muscle. These ratios varied from 0.4 to 4.84. The ratios suggest that velocity and/or displacement is a priority for the hamstrings, whereas force is a priority for the quadriceps and lower leg muscles. As much as a 12.6-fold difference in maximal velocity between muscles can be attributed to differences in fiber lengths. This can be compared to approximately a 2.5-fold difference in maximal velocity reported to occur as a result of biochemical (intrinsic) differences.     

Effects of chronic low-frequency electrical stimulation of human knee extensor muscles exposed to static passive stretching

The study investigated the effects of chronic low-frequency electrical stimulation (CLFES) of the stretched knee extensor muscles versus CLFES without a resistance load. A total of 19 male volunteers were randomized into two groups with similar aerobic and force-velocity properties. In group 1, anterior thigh muscles (the knee extensors) of both legs were exposed to CLFES (15 Hz). In group 2, the CLFES of the knee extensors was combined with stretching. The stimulated subjects demonstrated a marked tendency towards increasing endurance and a significant increase (by 10%) in both succinate dehydrogenase activity and the percentage of muscle fibers containing slow myosin heavy chain (MHC) isoforms. At the same time, the proportion of fibers reacting with the antibody against fast MHC isoforms decreased by 12%. In group 1, the maximum voluntary force (MVF) significantly decreased, the volume of m. quadriceps femoris (as measured by magnetic resonance imaging) remained unchanged, and the size of the fast fibers slightly decreased (by 11%). In group 2, no significant decrease in the MVF was observed, while there was a significant increase in muscle volume and the cross-sectional area of muscle fibers.