Author(s): HALLÉN, J., LUND-HANSEN, M., Institution: NORWEGIAN SCHOOL OF SPORT SCIENCES, Country: NORWAY, Abstract-ID: 2492

INTRODUCTION:
Endurance-trained (ET) individuals have higher maximal oxygen uptake (VO2max), blood volume (BV) and haemoglobin mass (Hb-mass) compared with non-endurance-trained (non-ET) individuals and endurance training has been found to increase these variables. Most studies comparing VO2max, BV, and Hb-mass between ET and non-ET individuals, as well as males and females, typically adjust for differences in body mass (BM). However, Hb-mass and BV are strongly associated with fat-free mass (FFM) and VO2max are associated with Hb-mass. Since ET individuals tend to have lower body fat percentages than non-ET individuals, some of the differences in VO2max, Hb-mass and BV are attributed to differences in body composition. This study aimed to investigate the impact of body fat percentage on the difference in BV, Hb-mass and VO2max between ET and non-ET individuals.
METHODS:
Forty-seven international and national level endurance athletes (ETA; 33 males; age 24.0±5.0 yrs; VO2max 73 and 65 mL/kg/min for males and females) and 34 controls (CTR; 22 males; age 27.9±4.8yrs; VO2max 54 and 48 mL/kg/min for males and females) were tested for VO2max, Hb-mass (CO-rebreathing), BV and anthropometrics (DXA). The ETA engaged in endurance training 8-12 times a week using running, skiing, and biking throughout the year. The CTR mostly did not train endurance, and those who did, trained less than once a week. Differences between groups were tested with Students t-Test and values are mean±SD.
RESULTS:
Fat percentages were 12.9±3.6 and 20.2±7.2 for male ETA and CTR, and 20.3±3.9 and 28.5±6.7 for female ETA and CTR. The differences in VO2max between ETA and CTR were ~35% relative to BM and ~25% relative to FFM, similar for males and females. Importantly, the difference in VO2max between males and females was reduced in ETA from 16% (p<0.001) to 5% (p=0.035) and in CTR from 13% (p=0.015) to 3% (p=ns). Female ETA had 17.0% and male ETA 17.9% higher Hb-mass relative to BM than CTR (females 11.0±1.2 vs 9.4±1.1 g/kg, p=0.001; males 13.5±1.1 vs 11.5±1.1 g/kg, p<0.001). Relative to FFM, female ETA had 6.3% and male ETA 8.1% higher Hb-mass than CTR (females 13.6±1.1 vs 12.8±1.0 g/kg, p=0.067; males 15.2±1.0 vs 14.1±1.0 g/kg, p<0.001). The same picture is true for BV with the differences between ETA and CTR reduced by approximately 50% when expressed relative to FFM compared to relative to BM.
CONCLUSION:
The difference in fat percentage explains the entire difference in VO2max between non-ET males and females and about 66% of the difference in VO2max between ET males and females. Also, 30% of the difference in VO2max between ET and non-ET individuals is explained by the difference in fat percentage. Similarly, more than 50% of the differences in Hb-mass and BV between ET and non-ET individuals are explained by the differences in fat percentage. Hence, when comparing VO2max and intravascular volumes between groups (i.e. trained vs untrained and males vs females) these variables should be related to FFM rather than BM.