Distance running over the long term : observations on bone mineral density and testosterone in men

• Main Author: Mackelvie, Kerry
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/8253

In recent years, physical activity has become an important focus in the prevention of osteoporosis. Mechanical usage of bone through vigorous physical activity can increase the bone modeling and remodeling processes which evoke architectural adaptations and/or increase bone mass. Much of the research in this area has focused on women due to the higher incidence of osteoporotic fractures in this population. However, men sustain one-third of hip fractures worldwide, and are more likely than women to die within one year of the injury (Seeman, 1995). Although physical activity is advocated to increase bone mineral density (BMD) of the hip area and decrease the risk of fracture in old age, the optimal 'osteogenic' exercise program remains undefined. Running is a weight bearing activity which loads the lower extremity. However, the magnitude of bone strains at the hip and spine associated with long distance running are lower than those associated with high impact sports and weight lifting (Frost 1997). Conflicting results have emerged from various studies of BMD in male runners, as both higher and lower proximal femur and lumbar spine BMDs were noted in male distance runners when compared to less active controls (Bilanen et al, 1989; MacDougall et al, 1992; Hetland et al, 1993; Bennell et al, 1997; Lane et al, 1998.). Both training and absolute age, as well as training volume are important factors that have not been controlled in previous studies. In situations of chronic, high volume endurance training in men, alterations in the regulation of the anabolic sex hormone, testosterone, have been observed (Wheeler et al, 1984, Ayers et al, 1985; Arce et a;. 1993). Clinically low levels of testosterone are associated with low BMD (Jackson et al, 1990). This study was designed to examine the effects of long term distance running in men over the age of 40 (range = 40 - 55), in terms of BMD measured by DXA (g/cm²), total testosterone (TT nmol/L), and free testosterone (FT pmol/L) levels. Two groups of men, distance runners (DR) training at a minimum weekly volume of 64 km per week for over 20 years (n=12), and agematched, normally active, healthy controls (C) (n=12), were compared using the student's t-test. Body weight and BMI were not significantly different between groups. As a secondary comparison, the distance runners were divided into moderate (64 to 90 km/week, n=7) and high (95 + km/week, n=5) volume training groups (MV and HV), and compared to C, using single factor ANOVA and Tukey's HSD to compare means. BMD of the femoral neck (FN) (0.86 +/- 0.14 vs. 0.78 +/- 0.071), trochanteric region (T) (0.81 +/- 0.13 vs. 0.73 +/- 0.053) and total proximal femur (PF) (1.04 +/- 0.15 vs. 0.94 +/- 0.056) were significantly greater (p<0.05) in DR when compared to C. Lumbar Spine (LS) BMD was not significantly different between DR and C (0.98 +/- 0.15 vs. 0.92 +/- 0.095). M V had significantly higher BMD at FN (0.91 +/- 0.16), T (0.85 +/- 0.14), and TPF (1.09 +/- 0.17) than C. All other BMD comparisons between MV, HV, and C were not significant. HV had the lowest mean for TT (33.7 % lower than M V and 16.8 % lower than C) and FT (21.2 % lower than MV, and 26.2 % lower than C). These differences in TT and FT were not significantly different between groups. TT and training volume for DR were significantly negatively correlated (r=-0.73, p<0.005), as was FT and training volume (r=-0.79, p<0.002). BMD and TT/FT were not significantly correlated (TT vs. FN: r= 0.12 (p=0.56); TT vs. T: r=0.12 (p= 0.58); TT vs. TPF: r= 0.03 (p=0.88); TT vs. LS: r=0.13 (p= 0.55); FT vs. FN: r= 0.05 (p=0.82); FT vs. T: r=0.16 (p=0.45), FT vs. TPF: r= 0.13 (p=0.55); FT vs. LS: r= 0.19 (p=0.37)). In summary, our results from a small, cross-sectional sample of distance runners suggest that lifetime distance running in men had a positive effect on BMD of the proximal femur, when training volumes did not exceed 90 km/week. BMD was not maintained at a higher level in distance runners training more than 95 km/week when compared to moderately active men. There was an association between training volume and testosterone levels, although the relationship between testosterone and BMD at high levels of training needs to be more clearly defined. === Education, Faculty of === Kinesiology, School of === Graduate