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Abstract

The present thesis considers the premise that breath-holding in aquatic sports, primarily
swimming, in order to enhance performance, can potentially cause adaptation to tissue
hypoxia. To investigate this theory, a series of studies needed to be performed:
I. Analysis of variability in individuals’ responses to hypoxia, to evaluate the range of
degrees acclimation to the stimulus. Data from three bed rest projects (LunHab
project: 10-d bedrest; FemHab project: 10-d bed rest; PlanHab project: 21-d bed rest)
were combined for a total of 31 participants that completed two bed rest
experimental conditions in each project: i) normoxic bed rest (NBR), and ii) hypoxic
bed rest (HBR).
II. Introduction and establishment of a carbon monoxide rebreathing technique in our
laboratory to assess the total haemoglobin mass (Hbmass). 22 participants were
tested for Hbmass from both the antecubital vein and fingertip for measures of
validity. 13 participants returned for a second identical visit where reliability was
assessed.
III. Assessment of markers of hypoxic adaptation in a group of swimmers against full
controls, terrestrial exercise controls (cross-country skiers), and breath-holding nonexercise
controls (apnoea divers). Participants were evaluated for differences in blood
oxygen-carrying capacity (aerobic capacity and Hbmass) and chemosensitivity
(hypoxic and hypercapnic ventilatory response).
IV. Longitudinal analysis of swimmers and control participants over the course of a
swimming season to assess seasonal variation. Of Study III’s participants, 5 control
participants and 4 swimmers returned for two further bouts of testing during the
2021/22 swimming season.
The results of the above studies were as follows:
I. Sex had an impact on the erythropoietin (EPO) response in NBR and HBR, whereas
bed rest duration had no effect. Relative EPO responses are not sufficient indicators
of the resultant increased production of reticulocytes and red blood cells.
II. Fingertip capillary blood sampling was an acceptable alternative to venous blood for
the calculation of Hbmass and blood volumes in terms of validity, but not reliability.
III. Despite differences in aerobic capacity between all athletic groups and the control
group, no differences were found in the haematological values or chemosensitivity to
hypoxia and hypercapnia
IV. The seasonal variation seen in controls and swimmers was similar, suggesting that
training load changes over the course of a season have no effect on the values
measured and are more likely due to typical seasonal lifestyle changes, measurement
and/or biological error, and biological variation.
From these results, it was concluded that the swimmers in the present study were not
exposed to a hypoxic stimulus of sufficient intensity to invoke hypoxic adaptation. This is
observed also when comparing their values to both full and terrestrial exercise controls.
The present thesis has also elucidated the importance of reporting individual values as well
as means and standard deviations in physiological research.