@Article{Kowalski2026,
journal="Biology of Sport",
issn="0860-021X",
volume="43",
number="1",
year="2026",
title="Physiological and performance parameters associated with critical 
power decline in hypoxia among highly-trained endurance athletes",
abstract="We sought to investigate whether the magnitude of differences in cycling critical power between normoxia and hypoxia (∆CP) is associated with fitness level or haematological status in highly trained endurance athletes. Thirty-three triathletes and longtrack speed skaters (11 females) completed two 3-minute CP cycling tests: one in normoxia (F i O 2  = 20.8%) and the other in normobaric hypoxia (F i O 2  = 14.2%). This cross-sectional study analysed ∆CP regarding performance, physiological, and haematological indices using correlation and regression analyses. Significant correlations were found between ∆CP and baseline CP in normoxia ( r  = -0.366,  p  = 0.047), V̇ O 2max  ( r  = -0.437,  p  = 0.018), and MCH ( r  = 0.487,  p  = 0.012). Only a few significant associations were found between the indices obtained from venous blood sampling and ∆CP, different for females and males. In females, ∆CP was correlated with Hbmass ( r  = -0.761,  p  = 0.017), erythrocyte volume ( r  = -0.783,  p  = 0.013), plasma volume ( r  = -0.745,  p  = 0.021), and blood volume ( r  = -0.870,  p  = 0.002), all established with the CO rebreathing method. The best-performing regression model (R 2  = 0.501, RMSE = 0.033,  p  = 0.002, Cohen’s F 2  = 1.004) included MCH, V̇ O 2max , and Hb mass . A higher fitness level is associated with a greater CP decrease in hypoxia among the homogeneous cohort of highly trained endurance athletes. Haematological status plays a more prominent role in females, and the CO rebreathing method should be considered a preferred approach for assessing haematological status in highly trained athletes.",
author="Kowalski, Tomasz
and Wilk, Adrian
and Rębiś, Kinga
and Malczewska-Lenczowska, Jadwiga
and Klusiewicz, Andrzej
and Debevec, Tadej
and Faiss, Raphael",
pages="257--265",
doi="10.5114/biolsport.2026.153530",
url="http://dx.doi.org/10.5114/biolsport.2026.153530"
}