Sport-Specific Physiological Adaptations in Highly Trained Endurance Athletes

Purpose: This study aims to compare maximal oxygen uptake (VO_2max), blood volume (BV), hemoglobin mass (Hb_mass), and brachial endothelial function, measured as flow-mediated dilatation (FMD), in international-level endurance athletes primarily exercising with the whole body (cross-country skiing), lower body (orienteering), or upper body (flatwater kayak). 

Methods: Seventeen cross-country skiers, 15 orienteers, and 11 flatwater kayakers were tested for VO_2max, BV, Hb_mass, and FMD. Additionally, body composition and annual training (type, volume, and intensity of training) were analyzed. 

Results: Absolute and body-mass-normalized VO_2max values were 11.3% and 9.9% higher, respectively, in skiers (5.83 ± 0.60 L·min^-1 and 77.9 ± 4.2 mL·min^-1·kg^-1) compared to orienteers (5.24 ± 0.45 L·min^-1 and 70.9 ± 3.5 mL·min^-1·kg^-1) (P < 0.01), whereas kayakers (5.78 ± 0.56 L·min^-1 and 73.7 ± 6.3 mL·min^-1·kg^-1) did not differ from skiers. BV was 9.9%-11.8% higher in skiers and orienteers compared to kayakers when normalized for total body mass and fat-free mass, and skiers had 9.2% and 9.9% higher Hb_mass normalized for total body mass and fat-free mass compared to kayakers (all P < 0.05). Arterial diameter was 11.8%-15.0% larger in kayakers (4.38 ± 0.63 mm) and skiers (4.22 ± 0.36 mm) compared to orienteers (3.81 ± 0.32 mm) (P < 0.05), whereas FMD did not differ between groups. 

Conclusions: This study indicates that higher VO_2max in cross-country skiers and greater arterial diameters in the arms of skiers and kayakers are sport-specific physiological adaptations to chronic endurance training in whole-body and upper-body exercise modes. However, variations in these variables are not associated with BV or Hb_mass.