| Summary: | 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
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