Objective. The purpose of this study was to determine whether race day cortisol was related to bone mineral density (BMD) in competitive male cyclists. A secondary purpose was to determine additional factors associated with BMD in competitive male cyclists. Methods. Measurements of lumbar spine and hip BMD were performed in 35 male competitors in a state championship cycling time trial event. Salivary cortisol was measured 10 minutes prior to the start of the race and 5 minutes after race finished. Participants reported daily calcium intake, age, years of bike training, races per season, and average weekly minutes spent riding a bike, weight training, and running on a survey. Results. Cortisol level increased significantly from pre- to postcompetition but was not significantly associated with BMD. Increased weekly minutes of weight training was associated with higher BMD of the lumbar spine and the hip. The increased number of years of cycling experience was associated with lower BMD of the femoral neck. Increased daily calcium intake was associated with higher BMD of the lumbar spine and femoral neck. Conclusions. Findings indicate that cyclists should participate in weight training and increase calcium intake in order to increase or maintain BMD of the lumbar spine and hip. 1. Introduction Interest in bone health among endurance athletes is growing. Studies showing low bone mineral density (BMD) in male cyclists are numerous [1–5], and osteopenia is prevalent in this population [4, 6]. Reports of lower BMD in competitive cyclists compared to age-matched controls are found in adult male cyclists [7], male master (over 30 years of age) cyclists [3], and in male postpubertal cyclists [8, 9]. Although not well documented, orthopedic injuries occur due to falls during cycling training and competition [10] making the occurrence of low BMD even more concerning. The etiology of low BMD in cyclists is multifactorial and may be partially due to an imbalance in hormones, such as cortisol [11, 12]. Cortisol triggers bone mineral resorption (removal) to free amino acids for use as an energy source through gluconeogenesis. Cortisol indirectly acts on bone by blocking calcium absorption which decreases bone cell growth [12]. The disruption to serum calcium homeostasis increases bone resorption [13] and ultimately reduces BMD [14]. Even a short bout of elevated cortisol secretion may cause a decrease in BMD [11, 12]. Excessive elevation of cortisol levels, such as in hypercortisolism or Cushing’s syndrome, is linked to a high prevalence of osteoporosis and may be
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