Comparison of haemoglobin mass across elite endurance sports and within-subject reliability using the optimised CO...

Total haemoglobin mass (tHb_mass) is a critical factor in endurance performance. The aim of this study was to compare tHb_mass between elite endurance athletes of different sports and assess the reliability of the optimised carbon monoxide rebreathing (oCOR) method in elite endurance athletes.

A retrospective analysis was conducted on 99 male and 75 female elite endurance athletes from athletics_long (22 males/22 females), athletics_middle (33 males/24 females), swimming (28 males/17 females), and triathlon (16 males/12 females).

Linear regression modelling revealed that tHb_mass was positively associated with age, body mass and sex (p < 0.001). After adjusting for age, body mass, and sex, athletics_long and triathlon exhibited greater tHb_mass than swimming (+9.5%, 3.8-15.4%; +9.1%, 3.8-15.0%) and athletics_middle (+6.1%, 2.1-11.9%; +5.7%, 1.4-11.5%) respectively. No difference was observed between athletics_long and triathlon (0.4%, -4.1-5.8%) or between athletics_middle and swimming (3.1%, -1.3%-8.8%) (values represent % difference with 95% confidence intervals). Analysis of within-subject reliability for tHb_mass measurements showed homoscedastic error and a standard error of measurement of 23 ± 3 g, indicating that measurement error represents a larger proportion of smaller tHb_mass values than of larger ones.

These findings demonstrate that elite athletes from distinct endurance disciplines can exhibit sport-specific haematological adaptations. In addition, this study provides reliability data that can assist practitioners working in elite sport to identify the minimum detectable difference and inform the optimal number of replicate measurements using the oCOR method.