Bone Mineral Density in Cystic Fibrosis: Benefit of Exercise Capacity

The aim of this study was to evaluate the association between bone mineral density (BMD) and objective maximal exercise measurements in adults with cystic fibrosis (CF). Twenty-five CF patients (19 males, 6 females, mean age 25.5 yr, range: 17-52) underwent BMD assessment and maximal-cycle ergometer exercise testing. We examined the relationship between gas exchange (% peak-predicted O2 uptake, CO2 output, O2 saturation), exercise performance (maximum power, exercise duration), and respiratory mechanics (tidal volume, rate) with lumbar spine and total proximal femur BMD. The strongest clinical correlate with BMD was forced expiratory volume at 1 s (lumbar spine Z-score, r = 0.36; total proximal femur Z-score, r = 0.68, p < 0.01). The strongest exercise correlate was % peak-predicted O2 uptake (lumbar spine Z-score, r = 0.44, p < 0.01; total proximal femur Z-score, r = 0.59, p < 0.01). There was a closer association between exercise parameters and total proximal femur BMD (r = 0.43-0.60) than with lumbar spine BMD (r = 0.04-0.45). Multiple regression analysis revealed VO2 to be the strongest independent predictor of BMD (R2 = 0.86, p < 0.001) followed by petCO2 and body mass index (R2 = 0.7 and 0.5, respectively, p < 0.01). Exercise appears to influence total proximal femur BMD more than lumbar spine BMD in CF. Exercise rehabilitation programs focusing on peripheral strength training may benefit those CF patients with low total proximal femur BMD.