Forearm Muscle Cross-sectional Area Research Articles

The Impact of Disuse and High-Fat Overfeeding on Forearm Muscle Amino Acid Metabolism in Humans.

Anabolic resistance is mechanistically implicated in muscle disuse atrophy. The objective of this study is to assess whether anabolic resistance is associated with reduced postprandial amino acid uptake or exacerbated by excess lipid availability. Twenty men underwent 7 days of forearm immobilization while consuming a eucaloric (CON; n = 11) or high-fat overfeeding (HFD; n = 9; 50% excess energy as fat) diet (parallel design) within our Nutritional Physiology Research Unit. Preimmobilization and postimmobilization we measured forearm muscle cross-sectional area (aCSA), and postabsorptive and postprandial (3-hour postingestion of a liquid, protein-rich, mixed meal) forearm amino acid metabolism using the arterialized venous-deep venous balance method and infusions of L-[ring-2H5]phenylalanine and L-[1-13C]leucine. Immobilization did not affect forearm muscle aCSA in either group, but tended to reduce postabsorptive phenylalanine (P = .07) and leucine (P = .05) net balances equivalently in CON and HFD. Mixed-meal ingestion switched phenylalanine and leucine net balances from negative to positive (P < .05), an effect blunted by immobilization (P < .05) and to a greater extent in HFD than CON (P < .05). Preimmobilization, meal ingestion increased leucine rates of disappearance (Rd; P < .05), with values peaking at 191% (from 87 ± 38 to 254 ± 60 µmol·min-1·100 mL forearm volume-1) and 183% (from 141 ± 24 to 339 ± 51 µmol·min-1·100 mL-1) above postabsorptive rates in CON and HFD, respectively, with meal-induced increases not evident postimmobilization in either group (P > .05). Disuse impairs the ability of a protein-rich meal to promote positive muscle amino acid balance, which is aggravated by dietary lipid oversupply. Moreover, disuse reduced postprandial forearm amino acid uptake; however, this is not worsened under high-fat conditions.

Metabolic Syndrome and Its Associations with Components of Sarcopenia in Overweight and Obese Older Adults.

Ageing, obesity and the metabolic syndrome (MetS) may all contribute to poor muscle health (sarcopenia). This study aimed to determine the cross-sectional associations between MetS (International Diabetes Federation classification) and sarcopenia (revised European Working Group on Sarcopenia in Older People definition) in 84 overweight and obese older adults. Components of sarcopenia included muscle strength (hand grip and leg extension), physical performance (stair climb test and short physical performance battery (SPPB), including gait speed and repeated chair stands time), muscle mass (appendicular lean mass (ALM), dual-energy X-ray absorptiometry), muscle size (peripheral quantitative computed tomography-determined calf and forearm cross-sectional area (CSA)) and muscle quality (muscle density and strength normalised to lean mass). Waist circumference was associated with greater muscle size, but poorer leg extension strength, chair stands and stair climb time, gait speed, SPPB scores and muscle quality measures (all p < 0.05). MetS was positively associated with ALM and forearm muscle CSA, and negatively associated with muscle quality measures and chair stands time (all p < 0.05). MetS is associated with larger muscle size, yet poorer muscle quality in overweight and obese older adults. Assessments of muscle function and quality should be considered for obese older adults and those with MetS.

Unilateral strength training leads to muscle-specific sparing effects during opposite homologous limb immobilization.

Cross education (CE) occurs after unilateral training whereby performance of the untrained contralateral limb is enhanced. A few studies have shown that CE can preserve or "spare" strength and size of an opposite immobilized limb, but the specificity (i.e., trained homologous muscle and contraction type) of these effects is unknown. The purpose was to investigate specificity of CE "sparing" effects with immobilization. The nondominant forearm of 16 participants was immobilized with a cast, and participants were randomly assigned to a resistance training (eccentric wrist flexion, 3 times/week) or control group for 4 weeks. Pre- and posttesting involved wrist flexors and extensors eccentric, concentric and isometric maximal voluntary contractions (via dynamometer), muscle thickness (via ultrasound), and forearm muscle cross-sectional area (MCSA; via peripheral quantitative computed tomography). Only the training group showed strength preservation across all contractions in the wrist flexors of the immobilized limb (training: -2.4% vs. control: -21.6%; P = 0.04), and increased wrist flexors strength of the nonimmobilized limb (training: 30.8% vs. control: -7.4%; P = 0.04). Immobilized arm MCSA was preserved for the training group only (training: 1.3% vs. control: -2.3%; P = 0.01). Muscle thickness differed between groups for the immobilized (training: 2.8% vs. control: -3.2%; P = 0.01) and nonimmobilized wrist flexors (training: 7.1% vs. control: -3.7%; P = 0.02). Strength preservation was nonspecific to contraction type ( P = 0.69, [Formula: see text] = 0.03) yet specific to the trained flexors muscle. These findings suggest that eccentric training of the nonimmobilized limb can preserve size of the immobilized contralateral homologous muscle and strength across multiple contraction types. NEW & NOTEWORTHY Unilateral strength training preserves strength, muscle thickness, and muscle cross-sectional area in an opposite immobilized limb. The preservation of size and strength was confined to the trained homologous muscle group. However, strength was preserved across multiple contraction types.

Skeletal Characteristics of Competitive Female Rowers

Weight-supported activities, such as rowing, are not commonly prescribed for fracture prevention. However, rowing requires large magnitudes of internal loading, thus it has potential to induce positive skeletal adaptations, especially in the hip and radius, two common fracture sites. PURPOSE: To examine skeletal health and body composition in college aged competitive female rowers. METHODS: In this cross-sectional study, 24 rowers and 24 age and body mass (±2yrs and 5lbs) matched physically active controls were compared. DXA was used to measure body composition and areal BMD (aBMD) of the total body, lumbar spine, hips and forearms, and hip structural analysis variables. pQCT was used to assess bone characteristics and bone strength of the tibiae (4%, 38%, 66%) and radii (4%, 66%) sites. RESULTS: Age- and height-adjusted aBMDs were not significantly different between groups (p>0.05), but rowers had greater hip cross-sectional moment of inertia (p≤0.05). Rowers had greater tibiae 4% total area, trabecular area, and periosteal circumference (PeriC) (p≤0.05). Also, total bone content and area, cortical area, PeriC, iPolar and SSI were greater at the tibiae 38% and 66% sites for rowers (p≤0.05). Controls had significantly greater 38% tibiae cortical density than rowers (p≤0.05). Rowers had significantly greater forearm muscle cross sectional area (p≤0.01) at the 66% radial site, and greater PeriC at the 4% radial site (p≤0.05). CONCLUSIONS: Rowers had greater tibiae bone area and strength compared to controls, but there were no group differences in aBMD or most radial bone variables. Our findings suggest that competitive rowing has osteogenic potential and may be particularly beneficial for improving bone quality at the tibiae even when compared to physically active controls.Table 1: Group comparisons of mean bilateral skeletal characteristics (means±SE)

Mechanical loading with or without weight-bearing activity: influence on bone strength index in elite female adolescent athletes engaged in water polo, gymnastics, and track-and-field

Bone health is considered not to benefit from water-based sports because of their weight-supported nature, but available evidence primarily relies on DXA technology. Our purpose was to investigate musculoskeletal health in the upper and lower body in well-trained adolescent female athletes using pQCT and compare these athletes with less-active, age- and sex-matched peers. Bone mineral content, volumetric cortical and trabecular BMD, total and cortical area, and bone strength index were assessed at the distal and proximal tibia and radius in four groups of adolescent females (mean age, 14.9years) including water polo players (n=30), gymnasts (n=25), track-and-field athletes (n=34), and nonactive controls (n=28). Water polo players did not show any benefit in bone strength index or muscle size in the lower leg when compared with controls. In contrast, gymnasts showed 60.1% and 53.4% greater bone strength index at the distal and proximal tibia, respectively, than nonactive females (p<0.05). Similarly, track-and-field athletes displayed 33.9% and 14.7% greater bone strength index at the distal and proximal tibia, respectively, compared with controls (p<0.05). In the upper body, water polo players had 31.9% greater bone strength index at the distal radius, but not the radial shaft, and 15.2% larger forearm muscle cross-sectional area than controls (p<0.05). The greatest musculoskeletal benefits in the upper body were found in gymnasts. In conclusion, despite training at an elite level, female water polo players did not show any benefits in musculoskeletal health in the lower leg and only limited benefits in the upper body when compared with nonactive girls.

Forearm muscle size, strength, force, and power in relation to pQCT-derived bone strength at the radius in adults

We aimed to examine the relationship between forearm muscle cross-sectional area (MCSA), muscle force, or rate of torque development (RTD) and 2 estimated radius bone strength indices - compressive bone strength index (BSI) at the wrist and strength strain index in torsion (SSI(p)) at the shaft - in healthy middle-aged males and females. Distal (4%) and shaft (65%) sites of nondominant forearms were scanned using peripheral quantitative computed tomography (pQCT) in a sample of 48 adults (mean age ± SD, 49.4 ± 2.4y) to obtain estimated bone strength indices and MCSA. Muscle force, measured by grip dynamometry and wrist flexion RTD, was obtained using an isokinetic dynamometer. Hierarchical linear regressions, adjusted for weight, explained 27% and 36% of the BSI variance at the 4% site in males and premenopausal females, respectively (p< 0.05). At the radius shaft, weight explained 26% (p< 0.05) and 83% (p< 0.01) of SSI(p) variance. The unique variance of BSI explained by MCSA was 16% in males (p< 0.05) and 31% in females (p< 0.01). Grip force predicted variance in SSI(p) in males (p< 0.01) and BSI in females (p< 0.05). RTD did not explain any variance in BSI or SSI(p). Body weight was the only significant predictor (p< 0.05) of SSI(p) in females. Although forearm muscle size and grip strength are associated with estimates of radius bone strength at midlife, this relationship appears to be sex dependent. The differences observed between muscle size and strength properties and bone strength at distal and shaft sites of the radius suggest a property-, sex-, and site-specific relationship between muscle and bone in the forearm.

WISE-2005: Bed-rest induced changes in bone mineral density in women during 60 days simulated microgravity

To better understand the effects of prolonged bed-rest in women, 24 healthy women aged 25 to 40 years participated in 60-days of strict 6° head-down tilt bed-rest (WISE-2005). Subjects were assigned to either a control group (CON, n=8) which performed no countermeasure, an exercise group (EXE, n=8) undertaking a combination of resistive and endurance training or a nutrition group (NUT, n=8), which received a high protein diet. Using peripheral quantitative computed tomography (pQCT) and dual X-ray absorptiometry (DXA), bone mineral density (BMD) changes at various sites, body-composition and lower-leg and forearm muscle cross-sectional area were measured up to 1-year after bed-rest. Bone loss was greatest at the distal tibia and proximal femur, though losses in trabecular density at the distal radius were also seen. Some of these bone losses remained statistically significant one-year after bed-rest. There was no statistically significant impediment of bone loss by either countermeasure in comparison to the control-group. The exercise countermeasure did, however, reduce muscle cross-sectional area and lean mass loss in the lower-limb and also resulted in a greater loss of fat mass whereas the nutrition countermeasure had no impact on these parameters. The findings suggest that regional differences in bone loss occur in women during prolonged bed-rest with incomplete recovery of this loss one-year after bed-rest. The countermeasures as implemented were not optimal in preventing bone loss during bed-rest and further development is required.

Abnormal bone geometry at the metacarpal bone shaft of rheumatoid arthritis patients with maintained muscle–bone relationship

Metacarpal juxtaarticular bone is altered in rheumatoid arthritis (RA). However, a detailed analysis of disease-related geometric adaptations of the metacarpal shaft is missing. The aim of the present study was to assess the role of RA disease, forearm muscle cross-sectional area (CSA), age, and sex on bone geometry at the metacarpal shaft. In 64 RA patients and 128 control subjects, geometric properties of the third metacarpal bone midshaft and forearm muscle CSA were measured by peripheral quantitative computed tomography (QCT). Linear models were performed for cortical CSA, total bone CSA, polar stress-strain index (SSI; a surrogate for a bone's resistance to bending and torsion), cortical thickness, and the metacarpal index (MI; cortical CSA/total CSA), with the explanatory variables muscle CSA, age, RA status, and sex. Forearm muscle CSA was associated with cortical and total metacarpal CSA and polar SSI. RA group status was associated with all bone parameters except cortical CSA. There was a significant interaction between RA status and age, indicating that the RA group had a greater age-related decrease in cortical CSA, cortical thickness, and the MI. Bone geometry of the metacarpal shaft is altered in RA patients compared to healthy controls. Whereas bone mass of the metacarpal shaft is adapted to forearm muscle mass, cortical thickness and the MI are reduced, but outer bone shaft circumference and the polar SSI increased in RA patients. These adaptations correspond to an enhanced aging pattern in RA patients.

Determinants of bone size and strength in 13-year-old South African children: The influence of ethnicity, sex and pubertal maturation

We have previously shown ethnic differences in bone mass between pre-pubertal black and white children using DXA. To investigate these ethnic differences further, using pQCT, and to determine the influence of sex and pubertal development, we measured appendicular bone variables in 13-year-old children using pQCT.We collected pQCT data on a cohort of 471 black and white children at age 13years. Black boys and girls were shorter and had less lean mass than their white peers, and black boys were lighter than white boys at an earlier stage of pubertal development. Metaphyseal (4%) radial trabecular density was greater in the black girls than their white peers (239.5±49.5 vs. 222.7±34.2mg/cm3; p<0.05). Bone strength index was not different between the ethnic groups. All metaphyseal measures were 3–41% greater in boys than girls, after adjusting for height where appropriate. Diaphyseal (38%) tibial values, including total area, endosteal diameter, tibial diameter, periosteal circumference and polar strength-strain index were 4–22% greater in the black than white children and in boys than in girls. Cortical density was greater in black than white boys (1079.0±39.4 vs. 1058.7±34.5mg/mm3; p<0.001) and greater in the girls than boys (black: 1129.3±33.7 vs. 1079.0±39.4mg/mm3; p<0.001; white: 1126.8±28.3 vs. 1058.7±34.5mg/mm3; p<0.001). Cortical thickness was less in the black groups. Lower leg muscle cross-sectional area (MCSA) was higher in white than black children, and forearm MCSA was higher in white than black boys. There was no difference in fat cross-sectional area between the ethnic groups. In conclusion, ethnic and sex differences in both metaphyseal and diaphyseal bone parameters exist during puberty, which are not accounted for by differences in body size or skeletal maturity. South African black children have wider diaphyseal regions of appendicular bones with greater measures of bone strength.

Comparisons of Bone Mineral Density and Bone Quality in Adult Rock Climbers, Resistance-Trained Men, and Untrained Men

The nature of muscular contractions and episodes of impact loading during technical rock climbing are often varied and complex, and the resulting effects on bone health are unclear. The purpose of this study was to compare total body, lumbar spine, proximal femur, and forearm areal bone mineral density (aBMD) and tibia and forearm bone quality in male rock climbers (RC) (n = 15), resistance trained men (RT) (n = 16), and untrained male controls (CTR) (n = 16). Total body, anteroposterior (AP) lumbar spine, proximal femur, and forearm aBMD and body composition were measured using dual-energy X-ray absorptiometry (DXA) (Lunar Prodigy, v. 10.50.086; GE Healthcare, Waukesha, Wisconsin, U.S.A.). Volumetric BMD (vBMD), bone content, bone area, and muscle cross-sectional area (MCSA) of the tibia and forearm were measured using pQCT (peripheral quantitative computed tomography; Stratec XCT 3000, Pforzheim, Germany). No significant group differences were seen in bone-free lean body mass. CTR had significantly (p < 0.05) greater body fat % than RC and RT and significantly (p < 0.05) greater fat mass than RC. Lumbar spine and femoral neck aBMD were significantly (p < 0.05) greater in RT compared to both RC and CTR. RC had significantly (p < 0.05) lower aBMD at the 33% radius site than CTR. Forearm MCSA was significantly (p < 0.05) lower in CTR than in the other groups. No significant differences were seen between groups for vBMD or bone area of the tibia and forearm. In conclusion, resistance-trained men had higher bone density at the central skeletal sites than rock climbers; however, bone quality variables of the peripheral limbs were similar in rock climber and resistance-trained groups.

Muscle Size, Strength, and Bone Geometry in the Upper Limbs of Young and Old Men

Bone loss in old men is associated with a decrease in muscle mass and strength. However, the influence of muscle size and strength on age-related changes in bone geometry has not been comprehensively described. Methods. Men in their third (group I, 23 +/- 3 y, n = 20), eighth (group II, 77 +/- 1 y, n = 10), and ninth (group III, 86 +/- 4 y, n = 13) decades of age were studied. The cross-sectional area (CSA) of the elbow flexors, elbow extensors, and forearm muscles, the total area (TA), cortical area (CA), and medullary area (MA) of the midhumerus, and distal third of the radius and ulna (n = 7 group II; n = 6 group III) were measured with magnetic resonance imaging. The maximal isometric strength (MVC) of the elbow flexors and elbow extensors was also determined. The CSA and MVC of the arm muscles (elbow flexors plus elbow extensors) were less in group II (-17% and -22%) and III (-32% and -39%), respectively, compared to group I. However, forearm CSA was less (-21%) in group III only. The TA and MA of all bones were greater in the older groups. The CA of the humerus (-14%) and ulna (-10%), but not the radius, was less in group III compared to group I, whereas CA was unchanged in group II. Stepwise multiple linear regression determined that arm muscle CSA (r = 0.52, p <.01) and forearm muscle CSA (r = 0.41, p <.05) provided the best prediction of CA in the humerus and forearm, respectively. Muscle size and strength are important determinants of CA in the humerus and forearm. The lower CA in the ninth decade may be explained, in part, by reduced bone strains due to a smaller muscle mass.

Bone mineral content per muscle cross-sectional area as an index of the functional muscle-bone unit.

Bone densitometric data often are difficult to interpret in children and adolescents because of large inter- and intraindividual variations in bone size. Here, we propose a functional approach to bone densitometry that addresses two questions: Is bone strength normally adapted to the largest physiological loads, that is, muscle force? Is muscle force adequate for body size? To implement this approach, forearm muscle cross-sectional area (CSA) and bone mineral content (BMC) of the radial diaphysis were measured in 349 healthy subjects from 6 to 19 years of age (183 girls), using peripheral quantitative computed tomography (pQCT). Reference data were established for height-dependent muscle CSA and for the variation with age in the BMC/muscle CSA ratio. These reference data were used to evaluate results from three pediatric patient groups: children who had sustained multiple fractures without adequate trauma (n = 11), children with preterminal chronic renal failure (n = 11), and renal transplant recipients (n = 15). In all three groups mean height, muscle CSA, and BMC were low for age, but muscle CSA was normal for height. In the multiple fracture group and in renal transplant recipients the BMC/muscle CSA ratio was decreased (p <. 0.05), suggesting that bone strength was not adapted adequately to muscle force. In contrast, chronic renal failure patients had a normal BMC/muscle CSA ratio, suggesting that their musculoskeletal system was adapted normally to their (decreased) body size. This functional approach to pediatric bone densitometric data should be adaptable to a variety of densitometric techniques.

Musculoskeletal Analyses of the Forearm in Young Women with Turner Syndrome: A Study Using Peripheral Quantitative Computed Tomography

Turner syndrome (TS) is associated with multiple skeletal abnormalities. Fracture incidence appears to be increased, but the reasons for this are not entirely clear. In the present study, we used peripheral quantitative computed tomography to evaluate bone mass, density, geometry, and strength of the radial metaphysis and diaphysis as well as maximum forearm muscle cross-sectional area (CSA) in a group of 21 TS patients. These individuals were 19.5 ± 2.3 yr of age (mean ± sd; range, 16.2–25.4 yr) and had completed growth after having received GH therapy; all but one were receiving estrogen supplementation. Despite short stature, cross-sectional bone size was normal compared with age-matched healthy controls. However, bone mineral content was decreased, resulting in a low total volumetric bone mineral density. This was due to decreased cortical thickness at both sites of measurement, whereas trabecular volumetric bone mineral density of the metaphysis was normal. Muscular CSA was normal. The relationship between muscle CSA and external bone size was similar between TS patients and healthy young women. However, TS patients had less bone mineral content and cortical CSA relative to muscle CSA than healthy young women, but similar muscle-bone relationships as healthy prepubertal girls. These findings are compatible with a normal adaptation of external bone size to the mechanical loads imposed by the muscle system and a lack of pubertal effect on the endocortical bone surface, despite estrogen supplementation. Bone strength may not be adequate for the relatively high body weight of TS patients (+0.8 sd score), which could contribute to an increased propensity for fractures.

Musculoskeletal analyses of the forearm in young women with Turner syndrome: a study using peripheral quantitative computed tomography.

Turner syndrome (TS) is associated with multiple skeletal abnormalities. Fracture incidence appears to be increased, but the reasons for this are not entirely clear. In the present study, we used peripheral quantitative computed tomography to evaluate bone mass, density, geometry, and strength of the radial metaphysis and diaphysis as well as maximum forearm muscle cross-sectional area (CSA) in a group of 21 TS patients. These individuals were 19.5 +/- 2.3 yr of age (mean +/- SD; range, 16.2-25.4 yr) and had completed growth after having received GH therapy; all but one were receiving estrogen supplementation. Despite short stature, cross-sectional bone size was normal compared with age-matched healthy controls. However, bone mineral content was decreased, resulting in a low total volumetric bone mineral density. This was due to decreased cortical thickness at both sites of measurement, whereas trabecular volumetric bone mineral density of the metaphysis was normal. Muscular CSA was normal. The relationship between muscle CSA and external bone size was similar between TS patients and healthy young women. However, TS patients had less bone mineral content and cortical CSA relative to muscle CSA than healthy young women, but similar muscle-bone relationships as healthy prepubertal girls. These findings are compatible with a normal adaptation of external bone size to the mechanical loads imposed by the muscle system and a lack of pubertal effect on the endocortical bone surface, despite estrogen supplementation. Bone strength may not be adequate for the relatively high body weight of TS patients (+0.8 SD score), which could contribute to an increased propensity for fractures.

The Contribution of Different Tissues to Stiffness of the Wrist Joint

Passive articular stiffness is not only a function of articular tissues, but also tissues associated with movement, such as muscles and tendons. Allowance has been made for the relative contribution of these extra-articular tissues in comparing the resting stiffness of normal subjects and patients with rheumatoid arthritis. In addition, the stiffness of the muscle-joint complex with agonist/antagonist muscles co-contracting has been measured. Significant muscle wasting was found in rheumatoid arthritis (forearm muscle cross-sectional area for normals: 30.9 cm2, for rheumatoid arthritis: 22.7 cm2, p = 0.002). Allowing for this, there was a significant difference in resting stiffness between normals and rheumatoid arthritis subjects (adjusted resting stiffness normals: 90.8 × 10-3 Nm/deg, rheumatoid arthritis: 120.3 × 10-3 Nm/deg, p = 0.015). There was no difference between the groups in terms of the relationship between stiffness and grip at different levels of muscle co-contraction, suggesting the muscles are qualitatively normal in rheumatoid arthritis.

Muscle function at the wrist following 9 d of immobilization and suspension

The purpose of this study was to evaluate the effects of 9 d of immobilization and partial suspension on muscle function at the wrist. Twelve female subjects (19-27 yr) wore a cast suspended from the neck by a sling that immobilized muscles acting on the wrist. Atrophy, muscle damage indicators, isometric and isokinetic strength, reaction time, speed of movement, and fatigability were assessed. Forearm muscle cross-sectional area decreased by 4.1% following immobilization and suspension. There was no indication that significant muscle degeneration occurred during immobilization or when muscles resumed normal function. Isometric strength for flexion and extension decreased by 29.3 and 32.5%, respectively. Concentric strength decrements for flexion, extension, pronation, and supination ranged from 8.9-21.7% at 2.11 and 3.16 rad.s-1. Eccentric strength decrements at 2.11 rad.s-1 for the same movements ranged from 12.5-18.5%. Fatigability was unaffected. Greater relative strength losses compared to decreased muscle cross-sectional area may be the result of a decrease in contractile protein density or unidentified neural factors following immobilization and partial suspension. However, neuromuscular control of reaction time was not affected.