Locomotor performance in highly-trained young soccer players: does body size always matter?

To examine the effects of body size on locomotor performance, 807 15-year-old French and 64 Qatari soccer players participated in the present study. They performed a 40-m sprint and an incremental running test to assess maximal sprinting (MSS) and aerobic speeds, respectively. French players were advanced in maturity, taller, heavier, faster and fitter than their Qatari counterparts (e.g., Cohen's d=+1.3 and + 0.5 for body mass and MSS). However, when adjusted for body mass (BM), Qatari players had possibly greater MSS than French players (d=+0.2). A relative age effect was observed within both countries, with the players born in the first quarter of the year being taller, heavier and faster that those born during the fourth quarter (e.g., d=+0.2 for MSS in French players). When directly adjusted for BM, these MSS differences remained (d=+0.2). Finally, in both countries, players selected in National teams were taller, heavier, faster and fitter than their non-selected counterparts (e.g., d=+0.6 for MSS in French players), even after adjustments for body size (d=+0.5). Differences in locomotor performances between players with different phenotypes are likely mediated by differences in body size. However, when considering more homogeneous player groups, body dimensions are unlikely to substantially explain the superior locomotor performances of older and/or international players.

Relationship between dyspnea increase and ventilatory gas exchange thresholds during exercise in children with surgically corrected heart impairment.

To study the relationship between the onset of an increase in dyspnea and ventilatory threshold (VT) in children with congenital heart impairment, sixteen young subjects underwent a cardiopulmonary exercise test with dyspnea perception and ventilatory gas exchange assessments. Dyspnea score was measured from a visual analogical scale at rest and during each step of an incremental exercise test. Dyspnea score was plotted against oxygen uptake and the onset of an increase in dyspnea (DT) was determined when a brutal disruption occurs on the dyspnea score-oxygen uptake curve. VT was defined from gas exchange according to Beaver's method. The first breakdown point in the oxygen uptake-carbon dioxide production relationship locates VT. Oxygen uptake (V(.-)O (2)), pulmonary ventilation (V(.-)E), heart rate (HR), oxygen pulse (O (2) pulse = V(.-)O (2)/HR), carbon dioxide production (V(.-)CO (2)) and power output (P) were measured both at VT and DT effort level. Results pointed out that there was no significant difference between the cardiorespiratory variables measured respectively at VT and DT: V(.-)O (2) (VTV(.-)O (2) = 16.71 +/- 2.65 vs. DTV(.-)O (2) = 18.34 +/- 5.74 ml x kg (-1) x min (-1)), V(.-)E (VTV(.-)E = 24.33 +/- 6.86 vs. DTV(.-)E = 26.82 +/- 9.59 l x min (-1)), (VTV(.-)CO (2) = 789.31 +/- 165.17 vs. DTV(.-)CO (2) = 924.02 +/- 342.28 ml x min (-1)), HR (VTHR = 116 +/- 10 vs. DTHR = 123 +/- 20 beat x min (-1)), O (2) pulse (VT O (2) pulse = 7.83 +/- 2.00 vs. DT O (2) pulse = 8.01 +/- 2.13 ml x kg (-1) x beat (-1)), and P (VTP = 43 +/- 16 vs. DTP = 52 +/- 27 W). Moreover, the cardiorespiratory variables measured at DT and VT were closely related: V(.-)O (2) (r = 0.64, p < 0.01), V(.-)E (r = 0.51, p < 0.01), HR (r = 0.75, p < 0.02), O (2) pulse (r = 0.90, p < 0.001), and P (r = 0.80, p < 0.01). In addition, according to Bland and Altman's procedure, the onset of dyspnea increase and ventilatory threshold were shown in close agreement for the cardiorespiratory variables measured at these effort levels. The standard errors of the estimates were low. It was concluded that dyspnea and ventilatory gas exchange thresholds occur concomitantly and were strongly correlated in children with congenital heart impairment. The use of the onset of dyspnea increase for aerobic capacity assessment may be a good alternative to ventilatory gas exchange threshold measurement.

Genotypic variation of quantitative trait loci controlling in vitro androgenesis in maize.

A quantitative trait loci (QTL) analysis for androgenetic capability has been conducted on three different crosses in maize, including very high and nonresponding lines for androgenesis. The doubled haploid lines derived by anther culture from the crosses DH5 x DH7, A188 x DH7, and R6 x DH99 showed a range of 0-70%, 0-40%, and 0-50% androgenetic responding anthers, respectively. The genotypic heritability of means for this trait is close to 0.90 for A188 x DH7 and 0.78 for R6 x DH99. The QTL analysis involved in each population the mapping of more than 100 loci covering a large part of the genome with reasonably spaced markers averaging 12 cM. Different measurements describing the androgenetic process were studied: AC, percentage of responding anthers; ELS, number of androgenetic embryos produced per 100 plated anthers; PLE, number of plantlets regenerated per 100 embryos; PLA, number of plantlets per 100 plated anthers. In each cross, three to four QTLs were found for AC, explaining 30-40% of the phenotypic variation. The QTL detected for PLA was also strong QTL for AC or ELS. This agrees with the observation that these last two traits are good predictors for final plantlet yield. The QTLs found were specific, although the same line DH7 was used in two crosses and DH99 derived from DH5 and DH7 in the third cross. These results suggest that the transfer of the androgenetic capabilities in elite germplasm will still involve a phenotypic evaluation of the androgenetic performances. A backcross-assisted selection based only on the genotype at the QTL is probably possible but only within the crosses used for this QTL analysis.

Aerobic capacity of competitive ice hockey players 10-15 years old.

Oxygen uptakes (VO2) recorded at anaerobic threshold and at the end of a maximal exercise (VO2 max) and their relation to left ventricular function were analyzed in 11 young ice hockey players during an incremental exercise on a bicycle ergometer. The children, highly trained, participated annually during 6 years (from the age of 10-15 years) in laboratory tests. The maturative status of the subjects was evaluated from peak height velocity (PHV). Heart rate was recorded by electrocardiogram. Oxygen uptake, CO2 production, respiratory frequency, pulmonary ventilation (VE) were recorded at rest and every 30 s during exercise through a Rudolph valve connected to a calibrated oxycon gas analyser. The anaerobic threshold was determined by a non-invasive method from pulmonary ventilation curves. Left ventricular volumes at end-systole and end-diastole were obtained, at rest, by M mode echocardiography. Results showed that both VO2 at anaerobic threshold and VO2max were positively correlated with body mass or with age of PHV. The increments were constant from year to year. At anaerobic threshold, the ratio VO2/VO2max was independent of maturative age. Similar findings were observed when considering VE except after the years of PHV where there was a remarkable increase in pulmonary ventilation. The results indicate that the growth of each cardiorespiratory component is optimalized with body size increase in order to keep constant the aerobic response to exercise. As judged by the explained variance of the different linear regression analyses between resting left ventricular dimensions and VO2, cardiac volume was of minimal importance in determining VO2. In the postpubertal period, stroke volume accounted for 26.7% of VO2 at anaerobic threshold and 30.0% of VO2max. This suggests that local changes occurring at muscular level are of paramount importance in determining the aerobic capacity of highly trained boys.