An analysis of injuries resulting from professional horse racing in France during 1991-2001: a comparison with injuries resulting from professional horse racing in Great Britain during 1992-2001.

BACKGROUND: It has been previously shown that professional jockeys suffer high rates of fatal and non-fatal injuries in the pursuit of their occupation. Little is known, however, about differences in injury rates between countries. AIM: To determine the rate of fatal and non-fatal injuries in flat and jump jockeys in France and to compare the injury rates with those in Great Britain and Ireland Method: Prospectively collected injury data on professional jockeys were used as the basis of the analysis. RESULTS: Limb fractures occur four times more often in both flat and jump racing in France than in Great Britain. Similarly dislocations are diagnosed 20 times more often in flat and three times more often in jump racing. This difference is surprising given that French jockeys have fewer falls per ride than their British counterparts in flat racing, although they do have more falls than the British in jump racing. Similarly concussion rates seem to be higher in French jockeys, although there may be a difference in the diagnostic methods used in the different countries. By contrast, soft tissue injuries account for a far smaller percentage of injuries than in Great Britain. CONCLUSION: There are striking differences in injury rates between countries which may be explained in part by a difference in track conditions-for example, harder tracks in France-or different styles of racing--for example, larger fields of horses per race in France.

Wintertime vitamin D deficiency in male adolescents: effect on parathyroid function and response to vitamin D3 supplements.

The first part of this study consisted of an 18 month follow-up of the vitamin D status and parathyroid function in a group of 54 French male adolescents, aged from 13 to 16 years old and all pupils of a jockey training school. During the 18 month period four samplings were made, one every 6 months. The first was during September of the first year, the second and third during March and October of the second year, and the last in March of the third year. Therefore we had two main periods: summer and winter. The summer 25-hydroxyvitamin D (25(OH)D) concentrations were higher (71.6 +/- 19.9 and 52.4 +/- 16.5 nmol/l) than the winter ones (20.4 +/- 6.9 and 21.4 +/- 6.1 nmol/l). Conversely, the winter intact parathyroid hormone (iPTH) serum levels (4.18 +/- 1.18 and 4.11 +/- 1.35 pmol/l) were higher than the summer ones (2.44 +/- 0.82 and 2.71 +/- 0.71 pmol/l). At the two winter time points the 25(OH)D concentrations were lower than 25 nmol/l (10 ng/ml) in 72% (2nd year) and 68% (3rd year) of the adolescents. In the second part of the study we tried a vitamin D3 supplementation procedure designed to maintain the 25(OH)D and iPTH postsummer serum levels throughout the winter. Pairs of male adolescents matched for height, weight and Tanner pubertal stage were randomly assigned to either vitamin D3 supplementation (2.5 mg, i.e., 100,000 IU) administered orally at three specific periods (end of September, November and January) or no vitamin D3 treatment (control subjects). Blood was collected just before the first intake of vitamin D3 and 2 months after the last intake (March). The control subjects had blood drawn at the same time points. In the vitamin D3-treated subjects, the concentrations of 25 (OH)D (55.3 +/- 11.5 nmol/l) and of iPTH (3.09 +/- 1.16 pmol/l) in March and September (53.8 +/- 12.3 nmol/l and 2.75 +/- 1.26 pmol/l) were not significantly different. In the control subjects, March 25(OH)D levels (21.0 +/- nmol/l were low, with values below 25 nmol/l in 78% of subjects, and iPTH concentrations (3.97 +/- 1.08 pmol/l) were significantly (p<0.001) higher than in September (2.91 +/- 0.81 pmol/l). The constant vitamin D wintertime deficiency and wintertime rise in iPTH in adolescent French males throughout puberty has been demonstrated. In adolescents with low dairy calcium intakes, the vitamin D3 treatment was sufficient to maintain 25(OH)D concentrations at their summer levels throughout winter and to prevent an excessive wintertime rise in iPTH levels.

Vitamin D status during puberty in French healthy male adolescents.

The vitamin D status was determined on one to four occasions either after summer (September-October) or after winter (March-April) in 175 male adolescents (13-17 years), resulting in 394 measurements of serum 25-hydroxyvitamin D (25(OH)D) and intact parathyroid hormone (iPTH). The subjects lived in a rural area to the north of Paris (49 degrees N). After summer the 25(OH)D concentration was 58.5 +/- 18.0 nmol/l (mean +/- SD), while after winter it had fallen to 20.6 +/-6.0 nmol/l (p = 0.0001). Meanwhile the iPTH concentration was 2.76 +/- 0.97 pmol/l (mean +/- SD) after summer and increased to 4.20 +/- 1.21 pmol/l after winter (p = 0. 0001). All the results were pooled and a nonlinear population model with random parameters was used to describe the relationship between serum iPTH and 25(OH)D. When the concentration of 25(OH)D was higher than 83 nmol/l, an iPTH mean 'plateau' level at 2.48 pmol/l was reached. When 25(OH)D concentrations fell below 83 nmol/l, the increase in iPTH concentration accelerates, and when the mean 25(OH)D concentration was equal to or lower than 10 nmol/l the mean iPTH level (4.97 pmol/l) was twice as high as the 'plateau' value.

[Vitamin D status in the adolescent: seasonal variations and effects of winter supplementation with vitamin D3]. / Statut vitaminique D de l'adolescent: variations saisonnières et effets d'une supplémentation hivernale par la vitamine D3.

BACKGROUND: Recently, 25 hydroxyvitamin D (25 OHD) blood concentrations measured in adolescents during or at the end of winter were found very low. A concomitant stimulation of parathyroid function was observed. The aim of the present study was to test the biological effects of a treatment with vitamin D3 during winter. POPULATIONS AND METHODS: The effects of vitamin D3 supplementation (100,000 IU, twice, at the end of November and of January) were assessed in 24 male Caucasian adolescents (mean age +/- SD: 14 y 6 m +/- 9 m). They were pupils in a lad-jockeys training center located in the countryside near Chantilly (49 degrees northern latitude). Blood concentrations of 25 OHD, calcium and intact parathormone (PTH) were measured three times: before each oral intake of vitamin D3 and 2 months after the last intake (March). A group of 32 male adolescents (mean age +/- SD: 14 y 9 m +/- 6 m), pupils in the same center, receiving no vitamin D and sampled in November and in March, served as controls. RESULTS: In March, mean concentrations of 25 OHD (8.36 +/- 2.73 micrograms/L) were very low in vitamin D-not supplemented adolescents since 34% had levels less than 6 micrograms/L. In March, PTH concentrations (40.5 +/- 12.2 ng/L) were significantly (P = 0.0001) higher than in November (28.8 +/- 9.9 ng/L). In boys receiving vitamin D3 25 OHD serum concentrations measured in January (17.5 +/- 3.2 micrograms/L) and in March (18.7 +/- 4.0 micrograms/L) remained at a level not very different from that measured in November (16.6 +/- 3.8 micrograms/L). During the same period, calcium and PTH concentrations (32.2 +/- 11.7 ng/L in November; 32.4 +/- 14.3 in January and 32.9 +/- 13.5 ng/L in March) remained at their basal level as well. CONCLUSIONS: The observation that, after winter, a relatively large number of adolescents presented low concentrations of 25 OHD suggests that, during winter, usual dietary intakes and/or vitamin D stores are not sufficient to provide for their needs. Administration of two oral doses of 100,000 IU of vitamin D3 could maintain the vitamin D status at its initial level. The efficiency of such a prophylactic treatment is also assessed by its effect on parathyroid function.

Vitamin D-dependent seasonal variation of PTH in growing male adolescents.

Twenty-eight young male adolescents (age from 13 years 6 months to 15 years 9 months) from a horseback-riding school were studied. They were studied at the end of summer (September of 1993) and, six months later, at the end of winter (March of 1994). At each timepoint their height and weight were measured and their pubertal status determined. Blood was collected and 25-hydroxyvitamin D [25(OH)D], intact parathyroid hormone (PTH1-84), and 1,25-dihydroxy-vitamin D [1,25(OH)2D] were measured. After winter, weight and height had increased by a mean of 2.9 +/- 1.3 kg and of 3.3 +/- 1.2 cm, respectively. 25(OH)D concentrations which were 29.96 +/- 7.46 micrograms/L in September had significantly (p = 0.0001) fallen by a mean of 23.31 +/- 6.6 micrograms/L in March (6.61 +/- 2.04 micrograms/L). March and September concentrations of 25(OH)D were significantly correlated (r = 0.536, p = 0.0039). March values were negatively correlated with the pubertal status (r = 0.41; p = 0.03). In the meantime, PTH had significantly (p = 0.0001) increased by a mean of 8.59 +/- 8.53 ng/L (22.8 +/- 7.44 ng/L in September vs. 30.33 +/- 8.05 ng/L in March). A statistically significant correlation between PTH and 25(OH)D concentrations (r = 0.493; p = 0.0001) was obtained. Serum 1,25(OH)2D concentrations measured in September (37.7 +/- 12.94 ng/L) and in March (38.2 +/- 7.8 ng/L) were not different. March values were positively correlated with pubertal status (r = 0.49; p = 0.008). Modulation of PTH secretion by vitamin D appears to be a physiological mechanism occurring during adolescence. In spite of a marked depletion of vitamin D stores after winter, PTH values remained within normal range. Nevertheless, we cannot exclude that a more prolonged vitamin D deficiency could adversely affect bone metabolism during this critical period of life characterized by an increased need of vitamin D.

Influence of cycle ergometer characteristics on the adolescents' anaerobic abilities testing.

The present study examined whether the reported lower values of anaerobic abilities in children and adolescents, both in absolute and related to bodyweight values, as compared to adults can be explained, partially at least, by a non-optimal testing apparatus. So, they cannot express their anaerobic abilities. Specifically, we examined the force-velocity (F-V) relationship on a mechanical cycle ergometer, in 23 adolescents and 11 adults, with two wheels of very different weights: 6.3 kg (Wh6) and 18 kg (Wh18). A higher wheel inertia might explain a late reach or no reach of the true peak velocity and the maximal anaerobic power (PmaxAn). The adolescent group showed higher Vo (V for zero braking force) values with Wh6 (238 +/- 14 vs 223 +/- 16 rpm) (P < 0.001) than with Wh18. The absolute or relative PmaxAn values for this group were slightly higher, but not significantly, with Wh6 (10.6 +/- 2.2 vs 10.2 +/- 1.9 W/kg). The delay to reach peak velocity was higher with Wh18 than with Wh6 (P < 0.001) in the two groups. In addition, the delay was always higher (P < 0.001) in the adolescent group compared to the adult group for both wheels. This suggests that the fatigue related to the observed late reach and the rapid decrease of power over time could lead to an underestimation of the PmaxAn peak in children.

Changes in the characteristics of anaerobic exercise in the upper limb during puberty in boys.

The aim of this study was to examine the relationships between the characteristics of anaerobic exercise in the upper limb and important indicators of growth and developmental age such as height (h), body mass (mb), skeletal age (SA), plasma testosterone (T) and pubertal stage (PS). We used the force-velocity (F-v) relationship test in a population of 66 healthy adolescent male junior jockeys, with considerable variation in these indicators but of the same physical fitness level (training effect). The mean values of the maximal anaerobic power (Wan,max) were 391 (SD 93) W. The values of the variables in the F-v relationship for the upper limb were only slightly or uncorrelated with the chronological age, but highly correlated with h, mb and SA (P < 0.001). The correlation with T was less significant. Using ANOVA a highly significant effect of PS on the variables in the F-v relationship was found (P < 0.001). The absolute or relative (normalized to mb) increase in Wan,max during puberty was greater from PS P2 and P3 than at other stages. Therefore PS would appear to be a significant factor for developmental changes in anaerobic characteristics during puberty in the adolescent. The PS P3 determined only by public hair might be an easy and accurate indicator for sports category classification of adolescents during puberty.