Longitudinal changes in bone mineral density in male master cyclists and nonathletes

Journal Title (Medline/Pubmed accepted abbreviation): J Strength Cond Res
Year: 2011
Volume: 25
Page numbers: 2-11
doi: 10.1519/JSC.0b013e3181c6a116

Summary of Background and Research Design

Background: Impact exercise such as running and weight training have known benefits for bone health. Little is known, however, about the effect of low-impact sports on bone mineral density (BMD). Previous research has reported lower regional BMD in cyclists compared with both running counterparts and non-athletes.

Hypothesis/purpose of study: To compare total and regional changes in BMD between highly trained male cyclists and age-matched control nonathletes over 7 years.

Subjects: Twenty-seven (27) competitive cyclists (age, 40 to 60 yr; training ≥ 10 hr/wk for ≥ 10 yr) and 24 nonathletic but active male controls were included in the initial study in 2001. Nineteen cyclists and 18 controls were followed during the 7-year follow-up reported here. Subjects were matched for age, height, weight, and body mass index (BMI); however, the cyclist population had lower body fat and higher lean tissue mass than the control groups.

Experimental design: Observational

Treatments and protocol: Subjects completed health/exercise questionnaires and were screened for conditions that could affect bone density at baseline. Food intake, in particular calcium intake, and exercise patterns were tracked and evaluated as independent factors. Subjects’ BMD was tested by dual-energy X-ray absorptiometry of the total body, the lumbar spine (L1 to L4), total hip, and the proximal femur at baseline and 7 years. Osteopenia was a T-score between –1 and –2.5 at the spine, femoral neck, or total hip. Osteoporosis was a T-score ≤ –2.5.

Summary of research findings:
  • The master cyclists had lower BMD both at baseline and after the 7-year follow-up than the nonathlete group at all measured bone sites (P < .05 for total hip and femoral neck).
  • There was a greater decline in BMD in the master cyclist group vs the nonathlete group
    -   –2.1% vs –0.2%, respectively, for total body
  • Participants who had increased weight training or other impact activity since the initial study findings in 2001 had lost less BMD at the spine and femoral neck (P < .05).
  • Significantly more cyclists had osteopenia or osteoporosis at baseline (84.2% cyclists vs 50% nonathletes, P = .026) and after 7 years (89.5% cyclists vs 61.1% nonathletes, P = .034).
  • The dietary calcium intake of the master cyclists was significantly higher than that of the nonathletes at both baseline (1,557 ? 775 vs 933 ? 524 mg/day, P < .005) and at 7 years (1,156 ? 530 vs 687 ? 261 mg/day, P < .005).

Interpretation of findings/Key practice applications:

The lower BMD in male cyclists is potentially concerning, especially given the high risk of falls and fractures that are inherent to the sport. It is believed that many cyclists actually avoid heavy impact exercise to recover more quickly from a heavy cycling training program. These athletes should be encouraged to participate in activities that improve bone density, such as weight training or plyometrics to minimize bone loss. In addition, these athletes should be regularly screened for bone health and educated in minimizing additional modifiable risk factors. However, further studies are required to determine if the lower BMD observed is actually associated with increased fracture risk in an athletic population such as cyclists. One potentially interesting finding was that the calcium intake of the master cyclists was higher than for the nonathletes, both at baseline and at 7 years, despite the lower BMD that was observed in the cyclists. However, it should be noted that 3-day food records were used for the baseline measures, whereas food frequency questionnaires were used at the 7-year point.

Although several confounding factors, such as smoking or medications affecting bone mass, were controlled in this study, it has a few limitations. The small study size limited the statistical power to detect small differences, and testosterone levels, which affect bone mass and may be suppressed in endurance athletes, were not assessed.

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