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This study was the first to explore the potential role of the myostatin (GDF8) pathway in relation to muscle strength and estimated muscle cross-sectional area in humans using linkage analysis with a candidate gene approach. In young male sibs (n = 329) 11 polymorphic markers in or near 10 candidate genes from the myostatin pathway were genotyped. Muscle mass was estimated by anthropometric measurements, and maximal knee strength was evaluated using isokinetic dynamometers (Cybex NORM). Single-point nonparametric variance components and linear quantitative trait locus regression linkage analysis methods were used. Linkage patterns were observed between knee extension and flexion peak torque with markers D2S118 (GDF8), D6S1051 (CDKN1A), and D11S4138 (MYOD1), and a maximum LOD score of 2.63 (P = 0.0002) was observed with D2S118. The ratios of peak torque over muscle and bone area of the midthigh of the lower contraction velocity (60 degrees/s) showed more frequently significant LOD scores than the torques at high velocity (240 degrees/s). Although myostatin is physiologically more related to muscle mass through possible effects of hyperplasia and hypertrophy than it is to strength, only two estimated muscle cross-sectional areas were marginally linked (LOD 1.06 and 1.07, P = 0.01) with marker D2S118 near GDF8 (2q32.2). The present results gave suggestive evidence that the myostatin pathway might be important for strength phenotypes, and GDF8, CDKN1A, and MYOD1 are potential candidate regions for a further and denser mapping with respect to these phenotypes.

Growth in peak VO2 exhibits a clear growth spurt in both sexes during adolescence. The growth spurt occurs earlier in females but is of greater magnitude in males.

The purpose of this study was to estimate the genetic and environmental contribution to variation in skeletal muscle mass and strength. In addition, important determinants were analyzed by stepwise multiple regression. In a large (N = 748) sibling pair sample of young brothers, ages 24.3 +/- 4.5 years, upper-limit heritabilities (t2) were estimated as a proportion of genetic and shared environmental variability over total phenotypic variability by the variance components method in QTDT. Maximal isometric strength measures of knee, trunk, and elbow had higher t2 (82 to 96%) than concentric strength (63 to 87%) on Cybex isokinetic dynamometers. Indicators of muscle mass revealed very high transmissions (>90%) whereas t2 was lower for adiposity (<70%). Stepwise regression showed that fat-free mass was the primary determinant in knee and trunk strength (partial explained variance, R2 = 33-45%), but a local muscularity estimate (forearm circumference) was the main covariable for elbow strength (partial R2 = 18-39%). In this sample neither age nor physical activity, measured by the sport index of Baecke, appeared to be an important determinant of muscle mass or strength. These results show that maximal muscle strength and mass are highly transmissible and that muscle mass is the primary determinant of muscle strength.

No abstract

Postnatal weight gain from birth, rather than birth weight, was associated with childhood risk markers for adult metabolic disease. Childhood weight gain was highly heritable, and genetic factors associated with postnatal weight gain are likely to also contribute to risks for adult disease.

This study reports the results of a multipoint linkage study that aims to unravel the genetic basis of muscle strength and muscle mass in humans. Myostatin (GDF8) is known to be a strong inhibitor of muscle growth in animals. However, studies examining human myostatin polymorphisms are rare and are limited to the GDF8 gene itself. Here, the contribution to isometric and concentric knee strength of nine key proteins involved in the myostatin pathway is studied in a nonparametric multipoint linkage analysis by means of a variance components and regression method. A sample of 367 healthy young male siblings was phenotyped on an isokinetic dynamometer and genotyped for markers of the myostatin pathway genes. Three of the loci were found significantly linked with a quantitative trait locus (QTL) for knee muscle strength. First, D13S1303 showed replication of an explorative single-point linkage study with a maximum LOD score of 2.7 (P = 0.0002). Second, maximum LOD scores of 3.4 (P = 0.00004) and 3.3 (P = 0.00005) were observed for markers D12S1042 and D12S85, respectively, at 12q12-14. Finally, marker D12S78 showed an LOD score of 2.7 at 12q22-23. We conclude that several genes involved in the myostatin pathway, but not the myostatin gene itself, are important QTLs for human muscle strength. An additional set of valuable candidate genes that were not part of the myostatin pathway was found in the chromosome 12 and 13 genomic regions.

The present paper will use fat mass percentage (FM%) obtained via BOD POD w air-displacement plethysmography (FM ADP %) to examine the relative validity of (1) anthropometric measurements/indices and (2) of FM% assessed with equations (FM eq %) based on skinfold thickness and bioelectrical impedance (BIA). In 480 Belgian children (aged 5 -11 years) weight, height, skinfold thickness (triceps and subscapular), body circumferences (mid-upper arm, waist and hip), foot-to-foot BIA (Tanita w ) and FM ADP % were measured. Anthropometric measurements and calculated indices were compared with FM ADP %. Next, published equations were used to calculate FM eq % using impedance (equations of Tanita w , Tyrrell, Shaefer and Deurenberg) or skinfold thickness (equations of Slaughter, Goran, Dezenberg and Deurenberg). Both indices and equations performed better in girls than in boys. For both sexes, the sum of skinfold thicknesses resulted in the highest correlation with FM ADP %, followed by triceps skinfold, arm fat area and subscapular skinfold. In general, comparing FM eq % with FM ADP % indicated mostly an age and sex effect, and an increasing underestimation but less dispersion with increasing FM%. The Tanita w impedance equation and the Deurenberg skinfold equation performed the best, although none of the used equations were interchangeable with FM ADP %. In conclusion, the sum of triceps and subscapular skinfold thickness is recommended as marker of FM% in the absence of specialised technologies. Nevertheless, the higher workload, cost and survey management of an immobile device like the BOD POD w remains justified.Key words: Air-displacement plethysmography: Anthropometry: Bioelectrical impedance: Children: Skinfold thickness Air-displacement plethysmography (ADP), integrated in the commercially available system BOD POD w , is a validated technique to assess body composition (1) . It has the advantage over the four-compartment model of including a quick, comfortable, automated, non-invasive and safe measurement process, making it feasible for children. As the best performing two-compartment model, ADP is more reliable for body composition than routine anthropometric measurements (2) . Nevertheless, the conversion from body density obtained by ADP measurement to fat mass percentage (FM ADP %) needs * Corresponding author: N. Michels, fax þ32 9 332 49 94, email nathalie.michels@ugent.be Abbreviations: ADP, air-displacement plethysmography; AFA, arm fat area; BIA, bioelectrical impedance; ConI, conicity index; FM%, fat mass percentage; FM ADP %, fat mass percentage with air-displacement plethysmography; FM eq %, fat mass percentage assessed with equations; LOA, limits of agreement; MUAC, mid-upper arm circumference; SEE, standard error of the estimate; SSF, subscapular skinfold; TSF, triceps skinfold; WHR, waist:hip ratio; WHtR, waist:height ratio.