2009 March | Female Athlete Triad Coalition

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Bone metabolism in adolescent athletes with amenorrhea, athletes with eumenorrhea, and control subjects

By Christo K, Prabhakaran R, Lamparello B, Cord J, Miller KK, Goldstein MA, Gupta N, Herzog DB, Klibanski A, Misra M (2008) in Pediatrics 121:1127-1136

Studies investigating the impact of amenorrhea on adolescent athletes’ bone health are scarce. Most studies have been performed in adults. This study compared dual energy x-ray absorptiometry (DXA)-derived areal bone mineral density (aBMD) and bone turnover markers between adolescent endurance athletes with amenorrhea (n=21), athletes with eumenorrhea (n=18), and control subjects (n=18), aged 12-18 years. Results are presented as Z-scores. The Z-score is a statistical measure of the distance (in standard deviations, SD) of an individual from the population mean of the same age (in contrast to the T-score, which is a comparison of an individual with the mean in young adults). For example, a Z-score of +1SD for aBMD means that the participant’s aBMD is 1 SD higher than the mean for his/her age. The study showed that aBMD and bone mineral apparent density (BMAD; an estimate of volumetric density) at the lumbar spine were lower in amenorrheic than eumenorrheic athletes and controls, with 38 % of amenorrheic athletes being osteopenic (Z-score<-1 SD). Hip aBMD Z-scores were also lower in amenorrheic athletes than eumenorrheic counterparts. Body mass index Z-scores, lean mass, IGF-I and menstrual status were independent predictors of Z-scores in aBMD. The authors also reported that levels of bone turnover markers (P1NP for bone formation and NTx for bone resorption) were lower in athletes with amenorrhea than in control subjects. The study confirmed that athletes with primary or secondary amenorrhea have lower aBMD than eumenorrheic athletes. At the spine, the amenorrheic athletes even had lower values than the control athletes. These findings suggest that the spine, which is rich in trabecular bone, is more sensitive to hypoestrogenism and/or benefits less from repetitive loading than the hip. Findings in bone turnover markers must still be considered with caution in adolescents, particularly in cross-sectional studies, as markers were shown to depend on sex, Tanner stage, height velocity, as well as skeletal mass and rate of bone mineral accrual. The study indicates that negative impact of amenorrhea on bone health can already be detected during adolescence, which is a crucial period for bone mass accrual and the attainment of peak bone mass in young adulthood.

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Vitamin D status and muscle function in post-menarchal adolescent girls

By Ward KA, Das G, Berry JL, Roberts SA, Rawer R, Adams JE, Mughal Z (2009) in J Clin Endocrinol Metab94:559-563

Vitamin D status was shown to influence muscle function, and therefore the risk of falls and osteoporotic fractures, in the elderly. In addition, myopathy is an important clinical symptom of vitamin D deficiency in children. This study investigated the influence of vitamin D status on muscle function in 99 healthy post-menarcheal girls. It was conducted based on previous investigations by this research group showing that more than 70% of school girls in that area (Manchester, UK) had low 25(OH)D levels (<37.5 nmol/L). Muscle power and force was measured by jumping mechanography. Participants were asked to perform countermovement jumps on a force platform and different parameters such as jump height, vertical velocity, and power per kg body weight (Esslinger Fitness Index) were calculated. Median serum 25(OH)D levels was 21.3 nmol/L (range 2.5-88.5 nmol/L). Current recommended levels are ≥50 nmol/L, indicating lower than normal serum 25(OH)D levels. After correction for weight using a quadratic function, there was a positive relationship between 25(OH)D and jump velocity, jump height, power, Esslinger Fitness Index, and force. Although these girls were asymptomatic, muscle function seemed to be affected by vitamin D status. Importantly, 68% of the sample was of South Asian origin (Indian Pakistani and Bangladeshi) and a resurgence of vitamin D deficiency in this population had been observed in the UK. The study did not mention when the measurements took place (winter or another season). Seasonal variations of vitamin D status have long been documented, since the major source of vitamin D (~90%) comes from sun exposure. In addition to its direct role in bone metabolism (mainly facilitating calcium absorption), vitamin D may also influence bone health through its effects on muscle function. Muscle forces are indeed the major forces applied onto the bones, contributing to bone mineral accrual during growth.

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Section modulus is the optimum geometric predictor for stress fractures and medial tibial stress syndrome in both male and female athletes

By Franklyn M, Oakes BW, Field B, Wells P, D. M. (2008) in Am J Sports Med 36:1179-1189

Areal bone mineral density (aBMD) as measured by dual energy x-ray absorptiometry (DXA) is not a good predictor of stress fracture risk. Previous studies have shown that aBMD can be higher, similar or lower in fractured athletes as compared to non-fractured peers. Investigations by x-ray and computed tomography (CT) suggested that geometrical parameters (e.g. bone diameter, cortical cross-sectional area), could better discriminate athletes with and without stress fracture. This study examined tibial bone geometry in 88 subjects (43 men) including sedentary controls, active controls, athletes with stress fracture and athletes with medial tibial stress syndrome (MTTS, commonly known as shin splints). Using x-ray and CT, athletes with stress fracture were found to have a lower section modulus than uninjured counterparts (without stress fracture). Section modulus reflects the distribution of bone mass away from the maximum principal axis of the bone’s cross-section, normalised by bone size. A small section modulus means that the most extreme point on the cross-section (the furthest from the centroid) is submitted to the highest stress under bending. The authors also found that subjects with MTSS had smaller tibial cross-sectional dimensions than did uninjured athletes. Most studies on stress fracture risk have been performed in military recruits, who are not necessarily very active prior to basic training, which partly explains the high incidence of stress fractures in this population. The present study indicates that stress fracture risk in athletes also seems associated with bone geometry. The major limitation of the study is the sample size, with only 5 men and 6 women with stress fractures. There were more participants with MTTS, based on the consideration by some clinicians that MTSS represents the early stage of stress fracture. The strengths of this study were the bone imaging techniques that were used (x-ray and CT), the depth of the biomechanical analysis, the quality of the recruitment (only subjects with stress fracture at the junction between mid-third and distal third of the tibia were included), the documentation of stress fracture and MTTS diagnosis, and the adjustment of the data to account for body size.