Mits de oefening juist wordt uitgevoerd, neem ik aan.
Dat geldt natuurlijk voor alle leeftijden.
Entrez PubMed
Exercise training, menstrual irregularities and bone development in children and adolescents.
* Eliakim A,
* Beyth Y.
Child Health & Sports Center, Pediatric Department, Meir General Hospital, Sackler School of Medicine, Tel-Aviv University, Israel.
Weight bearing physical activity plays an important role in bone development. This is particularly important in children and adolescents since bone mineral density reaches about 90% of its peak by the end of the second decade, and because about one quarter of adult bone is accumulated during the two years surrounding the peak bone growth velocity.
Recent studies suggested that the exercise-induced increase in bone mineralization is maturity dependent, and that there is a "window of opportunity" and a critical period for bone response to weight bearing exercise during early puberty and premenarchal years. This supports the idea that increase in physical activity during childhood and adolescence can prevent bone disorders (like osteoporosis) later in life. In contrast, strenuous physical activity may affect the female reproductive system and lead to "athletic amenorrhea". The prevalence of "athletic amenorrhea" is 4-20 times higher than the general population. As a consequence, bone demineralization may develop with increased risk of skeletal fragility, fractures, vertebral instability, and curvature. Menstrual abnormalities in the female athlete result from hypothalamic suppression of the spontaneous pulsatile secretion of gonadotropin releasing hormone. Recent studies suggested that reduced energy availability (
increased energy expenditure with inadequate caloric intake) is the main cause of the central suppression of the hypothalamic pituitary-gonadal axis. Therefore, effort should be made to optimize the nutritional state of female athletes, and if not successful, to reduce the training load in order to prevent menstrual abnormalities, and deleterious bone effects in particular during the critical period of rapid bone growth.
PMID: 14550383 [PubMed - indexed for MEDLINE]
verder is dit nog wel interessant om er bij te vermelden, gezien het belang van goede voeding voor vrouwen in de pubertijd dat blijkt uit bovengaande:
Entrez PubMed
Dose-response relationships between energy availability and bone turnover in young exercising women.
* Ihle R,
* Loucks AB.
Department of Biological Sciences, Ohio University, Athens, Ohio 45701, USA.
To help refine nutritional guidelines for military servicewomen, we assessed bone turnover after manipulating the energy availability of 29 young women. Bone formation was impaired by less severe restrictions than that which increased bone resorption. Military servicewomen and others may need to improve their nutrition to avoid these effects. INTRODUCTION: We determined the dose-response relationship between energy availability (defined as dietary energy intake minus exercise energy expenditure) and selected markers of bone turnover in 29 regularly menstruating, habitually sedentary, young women of normal body composition. MATERIALS AND METHODS: For 5 days in the early follicular phase of two menstrual cycles separated by at least 2 months, subjects expended 15 kcal/kgLBM/day in supervised exercise at 70% of aerobic capacity and consumed controlled amounts of a clinical dietary product in balanced (45 kcal/kgLBM/day) and one of three restricted (either 10, 20, or 30 kcal/kgLBM/day) energy availability treatments in random order. Blood was sampled at 10-minute intervals, and urine was collected for 24 h. Samples were assayed for plasma osteocalcin (OC), serum type I procollagen carboxy-terminal propeptide (PICP), and urinary N-telopeptide (NTX). RESULTS: NTX concentrations (p < 0.01) and indices of bone resorption/formation uncoupling (Z(NTX-OC) and Z(NTX-PICP); both p < 10(-4)) were increased by the 10 kcal/kgLBM/day treatment. OC and PICP concentrations were suppressed by all restricted energy availability treatments (all p < 0.05). PICP declined linearly (p < 10(-6)) with energy availability, whereas most of the suppression of OC occurred abruptly between 20 and 30 kcal/kgLBM/day (p < 0.05). CONCLUSIONS: These dose-response relationships closely resembled those of particular reproductive and metabolic hormones found in the same experiment and reported previously: similar relationships were observed for NTX and estradiol; for PICP and insulin; and for OC, triiodothyronine (T3), and insulin-like growth factor (IGF)-I.
The uncoupling of bone resorption and formation by severely restricted energy availability, if left to continue, may lead to irreversible reductions in BMD, and the suppression of bone formation by less severe restrictions may prevent young women from achieving their genetic potential for peak bone mass. More prolonged experiments are needed to determine the dose-response relationships between chronic restrictions of energy availability and bone turnover.
PMID: 15231009 [PubMed - indexed for MEDLINE]
hola eentje vergeten
Physical activity and strength of the femoral neck during the adolescent growth spurt: a longitudinal analysis.
* Forwood MR,
* Baxter-Jones AD,
* Beck TJ,
* Mirwald RL,
* Howard A,
* Bailey DA.
School of Biomedical Sciences, Department of Anatomy and Developmental Biology, The University of Queensland, Brisbane, Queensland 4072, Australia.
m.forwood@uq.edu.au
Loading of the femoral neck (FN) is dominated by bending and compressive stresses. We hypothesize that adaptation of the FN to physical activity would be manifested in the cross-sectional area (CSA) and section modulus (Z) of bone, indices of axial and bending strength, respectively. We investigated the influence of physical activity on bone strength during adolescence using 7 years of longitudinal data from 109 boys and 121 girls from the Saskatchewan Paediatric Bone and Mineral Accrual Study (PBMAS). Physical activity data (PAC-Q physical activity inventory) and anthropometric measurements were taken every 6 months and DXA bone scans were measured annually (Hologic QDR2000, array mode). We applied hip structural analysis to derive strength and geometric indices of the femoral neck using DXA scans. To control for maturation, we determined a biological maturity age defined as years from age at peak height velocity (APHV). To account for the repeated measures within individual nature of longitudinal data, multilevel random effects regression analyses were used to analyze the data. When biological maturity age and body size (height and weight) were controlled, in both boys and girls, physical activity was a significant positive independent predictor of CSA and Z of the narrow region of the femoral neck (P < 0.05). There was no independent effect of physical activity on the subperiosteal width of the femoral neck. When leg length and leg lean mass were introduced into the random effects models to control for size and muscle mass of the leg (instead of height and weight), all significant effects of physical activity disappeared. Even among adolescents engaged in normal levels of physical activity, the statistically significant relationship between physical activity and indices of bone strength demonstrate that modifiable lifestyle factors like exercise play an important role in optimizing bone strength during the growing years. Physical activity differences were explained by the interdependence between activity and lean mass considerations. Physical activity is important for optimal development of bone strength.
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