Bone mineral density of female long distance runners in Nelson Mandela Bay

Abstract

Long distance running may present positive and negative effects on the bone mineral density (BMD) of such participants. The advantage of high impact loads placed on the body of these runners may be neutralised or reversed, as too high a load may cause a decreased BMD. Furthermore, competitive female runners are generally considered to be leaner than their peers due to the nature of the sport. Therefore, it is expected that the majority of these runners would have a low body fat percentage (BF%) and body mass index (BMI) which may negatively affect the BMD, resulting in impaired bone quality. Due to the general inaccessibility of BMD assessments because of the cost involved, the incidence of risk for lowered BMD among long distance runners and particularly female runners are not readily known. The primary aim of the present study was therefore to determine the BMD rating and its association with body composition (BF% and BMI) and other selected factors among female long distance runners in Nelson Mandela Bay (NMB). The study utilized a quantitative approach and was exploratory, descriptive and non-experimental in nature. Non-probability, convenience sampling was implemented. A total of 40 female long distance runners between the age of 25 and 68 years (with a mean age of 43.6 ± 9.67 years) who have completed at least two marathon events were included in the study. The study utilized a questionnaire to collect demographic and other relevant information from the participants; a stadiometer and an electronic scale to measure height and weight and ultimately calculate BMI; and a bone densitometer with Dual-Energy X-ray Absorptiometry (DXA) (Hologic Discovery W) to determine the various BMD variables required as well as the BF%. Three densitometry scans were performed by a qualified radiographer which presented four analyses namely that of the relevant BMD variables for the hip, lumbar spine and total body, respectively, as well as of the BF% for the total body. The results of the study in respect of the overall BMD profile of the female long distance runners was considered to be normal except for the lumbar spine, found to be osteopenic when considering the mean T-score for this region of those 50 years and older. Overall the participants had an ‘average’ BF% (26.71 ± 6.33%) classification according to the ACSM classification rating system and were classified as ‘normal’ (22.80 ± 2.58 kg/m²) in respect of the BMI category rating. Significant correlations (r ≥ 0.312) were found between BMI and BMD related Z-scores for the hip, lumbar spine and total body, respectively. When considering the effect of selected variables on the various BMD variables, BF% and BMI, respectively, the following significant (p 0.2) results were found: (1) BMD (one or more rating and or Z-score) was positively influenced (had higher ratings) in runners who were overweight, consumed alcoholic beverages of five or less per week and who ran less than 51 km/week, respectively; (2) BMD (one or more rating and or Z-score) was negatively influenced (had lower ratings) in runners who had more full-term pregnancies and among those who were menopausal, respectively; (3) BF% and BMI were both found to be lower in runners who: were not menopausal, competed in six or more ultra-marathon events, completed marathons in less than or equal to three hours and 50 minutes, had an incidence of breaking a bone due to a traumatic event, and engaged in an average weekly running distance of more than 50 km/week, respectively