Elbow Flexor Strength, Muscle Size, and Moment Arms in Prepubertal Boys and Girls

The aim of this study was to examine elbow flexion torque, muscle cross-sectional area (CSA), and leverage in boys and girls. Thirty-eight prepubertal children (9.6 ± 0.3 years) volunteered to participate. All performed isometric flexion actions at 10°, 50°, and 90° of elbow flexion. Magnetic resonance imaging was used to assess elbow flexor (EF) muscle CSA and brachialis moment arm lengths. No significant gender differences were observed for any of the variables studied. EF CSA was directly proportional to isometric torque at 50° and 90°. CSA explained between 47% and 57% of torque variance. Moment arm estimates explained 19% of the variance in isometric torque at 90°. These baseline data contribute to our understanding of factors influencing strength variation during childhood.

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Muscle fiber number in biceps brachii in bodybuilders and control subjects

Journal of Applied Physiology ◽

10.1152/jappl.1984.57.5.1399 ◽

1984 ◽

Vol 57 (5) ◽

pp. 1399-1403 ◽

Cited By ~ 52

Author(s):

J. D. MacDougall ◽

D. G. Sale ◽

S. E. Alway ◽

J. R. Sutton

Keyword(s):

Muscle Fiber ◽

Biceps Brachii ◽

Cross Sectional Area ◽

Muscle Size ◽

Sectional Area ◽

Cross Sectional ◽

Trained Subjects ◽

Fiber Area ◽

Muscle Cross Sectional Area

Muscle fiber numbers were estimated in vivo in biceps brachii in 5 elite male bodybuilders, 7 intermediate caliber bodybuilders, and 13 age-matched controls. Mean fiber area and collagen volume density were calculated from needle biopsies and muscle cross-sectional area by computerized tomographic scanning. Contralateral measurements in a subsample of seven subjects indicated the method for estimation of fiber numbers to have adequate reliability. There was a wide interindividual range for fiber numbers in biceps (172,085–418,884), but despite large differences in muscle size both bodybuilder groups possessed the same number of muscle fibers as the group of untrained controls. Although there was a high correlation between average cross-sectional fiber area and total muscle cross-sectional area within each group, many of the subjects with the largest muscles also tended to have a large number of fibers. Since there were equally well-trained subjects with fewer than normal fiber numbers, we interpret this finding to be due to genetic endowment rather than to training-induced hyperplasia. The proportion of muscle comprised of connective and other noncontractile tissue was the same for all subjects (approximately 13%), thus indicating greater absolute amounts of connective tissue in the trained subjects. We conclude that in humans, heavy resistance training directed toward achieving maximum size in skeletal muscle does not result in an increase in fiber numbers.

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Muscle Strengths and Musculoskeletal Geometry of the Upper Limb

Engineering in Medicine ◽

10.1243/emed_jour_1979_008_010_02 ◽

1979 ◽

Vol 8 (1) ◽

pp. 41-48 ◽

Cited By ~ 137

Author(s):

A A Amis ◽

D Dowson ◽

V Wright

Keyword(s):

Upper Limb ◽

Cross Sections ◽

Wrist Joint ◽

Elbow Flexion ◽

Reliable Data ◽

Moment Arm ◽

Joint Replacements ◽

Moment Arms ◽

Joint Forces

A survey of past literature has shown that there is a lack of reliable data for use in prediction of joint forces in the upper limb although this is desirable when developing joint replacements. Upper limb geometry has been analysed, leading to muscle moment arm data at the wrist and elbow. The variation of these moment arms during elbow flexion has also been examined. Analysis of the dimensions of muscles has enabled their relative strengths to be predicted, based on their ‘physiological cross-sections’. When used in conjuction with published emg data, this information will enable elbow and wrist joint forces to be estimated more realistically than has previously been possible.

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The Biomechanics of Multi-articular Muscle–Tendon Systems in Snakes

Integrative and Comparative Biology ◽

10.1093/icb/icaa012 ◽

2020 ◽

Vol 60 (1) ◽

pp. 140-155 ◽

Cited By ~ 1

Author(s):

Henry C Astley

Keyword(s):

Musculoskeletal System ◽

Previous Analysis ◽

Metabolic Cost ◽

Cross Sectional ◽

Performance Loss ◽

Moment Arms ◽

Gap Bridging ◽

Static Systems ◽

Muscle Cross Sectional Area ◽

Snake Robots

Synopsis The geometry of the musculoskeletal system, such as moment arms and linkages, determines the link between muscular functions and external mechanical results, but as the geometry becomes more complex, this link becomes less clear. The musculoskeletal system of snakes is extremely complex, with several muscles that span dozens of vertebrae, ranging from 10 to 45 vertebrae in the snake semispinalis-spinalis muscle (a dorsiflexor). Furthermore, this span correlates with habitat in Caenophidians, with burrowing and aquatic species showing shorter spans while arboreal species show longer spans. Similar multi-articular spans are present in the prehensile tails of primates, the necks of birds, and our own digits. However, no previous analysis has adequately explained the mechanical consequences of these multi-articular spans. This paper uses techniques from the analysis of static systems in engineering to analyze the consequences of multiarticular muscle configurations in cantilevered gap bridging and compares these outcomes to a hypothetical mono-articular system. Multi-articular muscle spans dramatically reduce the forces needed in each muscle, but the consequent partitioning of muscle cross-sectional area between numerous muscles results in a small net performance loss. However, when a substantial fraction of this span is tendinous, performance increases dramatically. Similarly, metabolic cost is increased for purely muscular multi-articular spans, but decreases rapidly with increasing tendon ratio. However, highly tendinous spans require increased muscle strain to achieve the same motion, while purely muscular systems are unaffected. These results correspond well with comparative data from snakes and offer the potential to dramatically improve the mechanics of biomimetic snake robots.

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Implementing Eccentric Resistance Training—Part 1: A Brief Review of Existing Methods

Journal of Functional Morphology and Kinesiology ◽

10.3390/jfmk4020038 ◽

2019 ◽

Vol 4 (2) ◽

pp. 38 ◽

Cited By ~ 17

Author(s):

Timothy J. Suchomel ◽

John P. Wagle ◽

Jamie Douglas ◽

Christopher B. Taber ◽

Mellissa Harden ◽

...

Keyword(s):

Resistance Training ◽

Marked Effect ◽

Muscle Size ◽

Training Methods ◽

Eccentric Training ◽

Plyometric Training ◽

Force Output ◽

Cross Sectional ◽

Muscle Cross Sectional Area ◽

Production Characteristics

The purpose of this review was to provide a physiological rationale for the use of eccentric resistance training and to provide an overview of the most commonly prescribed eccentric training methods. Based on the existing literature, there is a strong physiological rationale for the incorporation of eccentric training into a training program for an individual seeking to maximize muscle size, strength, and power. Specific adaptations may include an increase in muscle cross-sectional area, force output, and fiber shortening velocities, all of which have the potential to benefit power production characteristics. Tempo eccentric training, flywheel inertial training, accentuated eccentric loading, and plyometric training are commonly implemented in applied contexts. These methods tend to involve different force absorption characteristics and thus, overload the muscle or musculotendinous unit in different ways during lengthening actions. For this reason, they may produce different magnitudes of improvement in hypertrophy, strength, and power. The constraints to which they are implemented can have a marked effect on the characteristics of force absorption and therefore, could affect the nature of the adaptive response. However, the versatility of the constraints when prescribing these methods mean that they can be effectively implemented to induce these adaptations within a variety of populations.

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Plantar flexor moment arm and muscle volume predict torque-generating capacity in young men

Journal of Applied Physiology ◽

10.1152/japplphysiol.01140.2013 ◽

2014 ◽

Vol 116 (5) ◽

pp. 538-544 ◽

Cited By ~ 37

Author(s):

Josh R. Baxter ◽

Stephen J. Piazza

Keyword(s):

Plantar Flexion ◽

Young Men ◽

Knee Extensor ◽

Muscle Volume ◽

Joint Torque ◽

Muscle Size ◽

Plantar Flexor ◽

Moment Arm ◽

Joint Rotation ◽

Moment Arms

Muscle volume is known to correlate with maximal joint torque in humans, but the role of muscle moment arm in determining maximal torque is less clear. Moderate correlations have been reported between maximal isometric knee extensor torque and knee extensor moment arm, but no such observations have been made for the ankle joint. It has been suggested that smaller muscle moment arms may enhance force generation at high rates of joint rotation, but this has not yet been observed for ankle muscles in vivo. The purpose of the present study was to correlate plantar flexor moment arm and plantar flexor muscle volume with maximal plantar flexor torque measured at different rates of plantar flexion. Magnetic resonance imaging was used to quantify the plantar flexor moment arm and muscle volume of the posterior compartment in 20 healthy young men. Maximal plantar flexor torque was measured isometrically and at three plantar flexion speeds using an isokinetic dynamometer. Plantar flexor torque was significantly correlated with muscle volume (0.222 < R2 < 0.322) and with muscle moment arm at each speed (0.323 < R2 < 0.494). While muscle volume was strongly correlated with body mass and stature, moment arm was not. The slope of the torque-moment arm regression line decreased as the rate of joint rotation increased, indicating that subjects with small moment arms experienced smaller reductions in torque at high speeds. The findings of this study suggest that plantar flexor moment arm is a determinant of joint strength that is at least as important as muscle size.

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Muscle Strength and Contractile Kinetics of Isometric Elbow Flexion in Girls and Women

Pediatric Exercise Science ◽

10.1123/pes.21.3.354 ◽

2009 ◽

Vol 21 (3) ◽

pp. 354-364 ◽

Cited By ~ 13

Author(s):

Bareket Falk ◽

Laura Brunton ◽

Raffy Dotan ◽

Charlotte Usselman ◽

Panagiota Klentrou ◽

...

Keyword(s):

Statistical Significance ◽

Elbow Flexion ◽

Peak Torque ◽

Muscle Size ◽

Cross Sectional ◽

Time To Peak ◽

Peak Rate ◽

Rate Of Torque Development ◽

Age Related ◽

Torque Development

Ten prepubertal girls and 15 young women were tested for maximal torque, peak rate of torque development, electro-mechanical delay (EMD), and time to peak rate of torque development during isometric elbow flexion. Absolute peak torque (17.0 ± 7.7 vs. 40.5 ± 8.3 Nm) and peak rate of torque development (105.9 ± 58.6 vs. 297.2 ± 113.0 Nm·s−1) were lower in the girls (p < .05). Normalized to muscle cross sectional area, torque was similar (8.27 ± 2.74 vs. 8.44 ± 1.65 Nm·cm−2), as was peak rate of torque development, normalized to peak torque (6.21 ± 1.94 vs. 7.30 ± 2.26 Nm·s−1/Nm). Both, time to peak rate of torque development (123.8 ± 36.0 vs. 110.5 ± 52.6 ms) and EMD (73.2 ± 28.6 vs. 51.9 ± 25.6 ms), were longer in the girls, although EMD’s difference only approached statistical significance (p = .06). Age-related isometric strength differences in females appear to be mainly muscle-size dependent. However, the time to peak torque and EMD findings suggest differential motor-unit activation which may functionally manifest itself in fast dynamic contractions.

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Relationship Between Calf Muscle Size and Strength after Achilles Rupture Repair

Foot & Ankle International ◽

10.1177/107110070002100410 ◽

2000 ◽

Vol 21 (4) ◽

pp. 330-335 ◽

Cited By ~ 35

Author(s):

J. Leppilahti ◽

S. Lähde ◽

K. Forsman ◽

J. Kangas ◽

K. Kauranen ◽

...

Keyword(s):

Plantar Flexion ◽

Achilles Tendon Rupture ◽

Peak Torque ◽

Cross Sectional Area ◽

Calf Muscle ◽

Muscle Size ◽

Sectional Area ◽

Unaffected Side ◽

Cross Sectional ◽

Muscle Cross Sectional Area

The object was to study the relationships between calf muscle size and strength in 85 patients an average of 3.1 years after repair of achilles tendon rupture. The isokinetic calf muscle strength results were excellent or good for 73 % of the patients, whereas calf muscle size was normal in only 30 %. The average plantar flexion peak torque per unit muscle cross-sectional area was higher on the injured side than on the uninjured side. The average calf muscle cross-sectional area deficit was 15±9% (p<0.001) of that on the unaffected side, while the average plantar flexion peak torque deficit was speed-dependent, being 9±18%, 10±18 and 2±13% of that on the unaffected side at 30, 90, and 2407sec (p<0.001). The correlation between cross-sectional area and peak torque varied in the range 0.52–0.61 at 30, 90 and 2407sec (p<0.001).

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ACTN3 genotype is associated with increases in muscle strength in response to resistance training in women

Journal of Applied Physiology ◽

10.1152/japplphysiol.01139.2004 ◽

2005 ◽

Vol 99 (1) ◽

pp. 154-163 ◽

Cited By ~ 174

Author(s):

Priscilla M. Clarkson ◽

Joseph M. Devaney ◽

Heather Gordish-Dressman ◽

Paul D. Thompson ◽

Monica J. Hubal ◽

...

Keyword(s):

Resistance Training ◽

Body Mass ◽

Biceps Brachii ◽

Elbow Flexor ◽

Muscle Performance ◽

Muscle Size ◽

P Value ◽

Ratio Test ◽

Cross Sectional ◽

Resistance Training Program

The α-actinin 3 (ACTN3) gene encodes a protein of the Z disk of myofibers, and a polymorphism of ACTN3 results in complete loss of the protein. The ACTN3 genotype (R577X) has been found to be associated with performance in Australian elite athletes (Yang N, MacArthur DG, Gulbin JP, Hahn AG, Beggs AH, Easteal S, and North K. Am J Hum Genet 73: 627–631, 2003). We studied associations between ACTN3 genotype and muscle size [cross-sectional area of the biceps brachii via magnetic resonance imaging (MRI)] and elbow flexor isometric (MVC) and dynamic [1-repetition maximum (1-RM)] strength in a large group of men ( N = 247) and women ( N = 355) enrolled in a 12-wk standardized elbow flexor/extensor resistance training program of the nondominant arm at one of eight study centers. We found no association between ACTN3 R577X genotype and muscle phenotype in men. However, women homozygous for the ACTN3 577X allele (XX) had lower baseline MVC compared with heterozygotes ( P < 0.05) when adjusted for body mass and age. Women homozygous for the mutant allele (577X) demonstrated greater absolute and relative 1-RM gains compared with the homozygous wild type (RR) after resistance training when adjusted for body mass and age ( P < 0.05). There was a trend for a dose-response with genotype such that gains were greatest for XX and least for RR. Significant associations were validated in at least one ethnic subpopulation (Caucasians, Asians) and were independent of training volume. About 2% of baseline MVC and of 1-RM strength gain after training were attributable to ACTN3 genotype (likelihood-ratio test P value, P = 0.01), suggesting that ACTN3 is one of many genes contributing to genetic variation in muscle performance and adaptation to exercise.

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Specific force of the vastus lateralis in adults with achondroplasia

Journal of Applied Physiology ◽

10.1152/japplphysiol.00638.2017 ◽

2018 ◽

Vol 124 (3) ◽

pp. 696-703 ◽

Cited By ~ 7

Author(s):

David T. Sims ◽

Gladys L. Onambélé-Pearson ◽

Adrian Burden ◽

Carl Payton ◽

Christopher I. Morse

Keyword(s):

Vastus Lateralis ◽

Force Production ◽

Limb Length ◽

Muscle Size ◽

Knee Extensors ◽

Specific Force ◽

Moment Arm ◽

Cross Sectional ◽

Volume Activation

Achondroplasia is a clinical condition defined by shorter stature and disproportionate limb length. Force production in able-bodied individuals (controls) is proportional to muscle size, but given the disproportionate nature of achondroplasia, normalizing to anatomical cross-sectional area (ACSA) is inappropriate. The aim of this study was to assess specific force of the vastus lateralis (VL) in 10 adults with achondroplasia (22 ± 3 yr) and 18 sex-matched controls (22 ± 2 yr). Isometric torque (iMVCτ) of the dominant knee extensors (KE) and in vivo measures of VL muscle architecture, volume, activation, and patella tendon moment arm were used to calculate VL physiological CSA (PCSA), fascicle force, and specific force in both groups. Achondroplasic muscle volume was 53% smaller than controls (284 ± 36 vs. 604 ± 102 cm3, P < 0.001). KE iMVCτ was 63% lower in achondroplasia compared with controls (95 ± 24 vs. 256 ± 47 N⋅m, P < 0.001). Activation and moment arm length were similar between groups ( P > 0.05), but coactivation of bicep femoris of achondroplasic subjects was 70% more than controls (43 ± 20 vs. 13 ± 5%, P < 0.001). Achondroplasic subjects had 58% less PCSA (43 ± 10 vs. 74.7 ± 14 cm2, P < 0.001), 29% lower fascicle force (702 ± 235 vs. 1704 ± 303 N, P < 0.001), and 29% lower specific force than control subjects (17 ± 6 vs. 24 ± 6 N⋅cm−2, P = 0.012). The smaller VL specific force in achondroplasia may be attributed to infiltration of fat and connective tissue, rather than to any difference in myofilament function. NEW & NOTEWORTHY The novel observation of this study was the measurement of normalized force production in a group of individuals with disproportionate limb length-to-torso ratios.

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