Bone mineral density in female swimmers

It is well establsihed that skeletal development is influenced by mulitple factors including, genetics, physical activity, nutrition and hormones (Dlugolecka, Czeczelewski & Raczynska, 2011). The human skeletal system provides support for the body and is a place for muscle attachment, protection for all internal organs, and a store of calcium, phosphorous and magnesium. The human skeleton, depending on age, is subject to constant changes in bone mass, phases of growth, consolidation (mending of bone) and involution (decline in) of bone tissue. During childhood and puberty there is a significant impact one bone mineral content, with 90 to 95 percent of bone mass being formed by age 20 (Dlugolecka, Czeczelewski & Raczynska, 2011). Girls attain approximately 80 percent of their peak bone mass before their first menstruation (Dlugolecka, Czeczelewski & Raczynska, 2011). However, 40 percent of peak bone mass is achieved between 10 and 12 years of age, with the remainder accumulating at a rapid pace during puberty. After puberty this process slows down.

The factors necessary to attain optimal peak bone mass include, a diet containing adequate amounts of calcium (with an appropriate ratio of calcium), vitamin D and protein, exercise that is appropriate to biological age and proper synthesis of oestradial in girls and testosterone in boys. Moreover, it is important to eliminate factors that will disrupt optimal bone development such as chronic use of medication, poor nutrition, insufficient exercise or excessive physical activity. It is suggested that the population most vulnerable to the negative impact of diet and hormone disorders are girls who are actively involved in competitive sport, due to the physical stress placed on the body and nonweight bearing activity (Dlugolecka, Czeczelewski & Raczynska, 2011). This being so, peak bone mass coincides with excessive physical burden, which can compromise how bone tissue is metabolised.

In a recent study, researchers from The Jazef Pilsudski University of Physical Education, assessed the bone mineral density (matter per area of bone) and bone mineral content in girls practising swimming in the period of peak bone mass in comparison to girls at the same age who are not actively involved in sport (Dlugolecka, Czeczelewski & Raczynska, 2011). This study involved 86 girls aged between 11 and 15 years, including 41 athletes from sporting schools involved in swimming, who represented their school at a national level. The average length of training for swimmers was 2.4 years, swimming 12 hours per week (70 percent aquatic training, 30 percent dry land training). Individual analysis of bone density confirmed that 14.6 percent of girls from the swimming group showed a low bone density in relation to their chronological age. Results indicated that intake of protein and phosphorous in the group of girls practising swimming as well as girls who were not involved in sport exceeded the average recommended daily intake. However, average calcium consumption was reported at 49 percent of recommended daily intake for both groups. Nevertheless, retrospective data confirmed that 25 percent of girls not involved in sports frequently consume 2-3 serves of calicum daily, whereas only 15 percent of girls in the swimming group consumed 2-3 serves daily. Although the results of this study suggest that female swimmers are not at increased risk of developing osteopenia (below average bone mineral density), a numer of clinical studies have indicated that girls actively involved in sport may be one of the groups affected by increased risk of reduced bone mass (Bianchi, M.L, 2007; Btaszczyk & Chlebna-Sokot, 2003; Heer, 2004; Heinrich & Going, 1990).

Bianchi, M.L. 2007. Osteoporosis in childrend and adolescents. Bone, 41, 486-495.

Btaszczyk, A & Chlebna-Sokot, D. 2003. Dietary factors and the condition of bone mineral content in school aged children. Osteoathralgia, 1, 45-85.

Dlugolecka, B., Czeczelewski, J & Raczynska, B. 2011. Bone mineral content and bone mineral density in female swimmers during the time of peak bone mass attainment. Biology of Sport, 28, 1, 69-74.

Heer, M. 2004. Bone turnover during inpatient nutritional therapy and outpatient follow up in patients with anorexia nervousa compared with healthy control subjects. American Journal of Clinical Nutrition, 3, 774-781.

Heinrich, C.H & Going, S.B. 1990. Bone mineral content of cyclically menstruating, female resistance and endurance trained athletes. Medical Science of Sports Exercise, 22, 558-563.

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