Performance under pressure: Physiological and Cognitive responses to hyperoxic Exercise in SCUBA-diving

Introduction:
Hyperoxia reduces minute ventilation (V̇E), heart rate (HR), and blood lactate ([Lac-]) during exercise in normobaric settings1,2. In addition, hyperoxia and exercise are known to positively affect executive functions (EF) of cognition3,4. However, little is known about applied sports activities underwater, like SCUBA-diving, where the practical relevance is emphasized by elevated inspiratory oxygen pressures (PIO2) from water depth and used gas mixtures. Here, environmental factors, the sport-specific exercise modality of underwater fin-swimming (UFS), and breathing resistance from diving equipment might alter previous results. We hypothesized that the combined increase in exercise intensity and PIO2 would (I) reduce V̇E and (II) amplify a positive interaction between exercise intensity and EF performance.
Methods:
Based on a priori power analysis (f=0.5; Power 1-β=0.9), 15 experienced SCUBA-divers (age: 28±6.2; 5 female) performed 3×8min of UFS at individual exercise intensities of 25% (LOW), 45% (MOD), and 75% (vIG) heart rate reserve. This scenario was repeated on three separate days with altered oxygen fractions in the breathing gas, resulting in 29, 56, and 140kPa PIO2 at 4m water depth (double-blind). HR and V̇E were measured continuously. Post-exercise, an EF task on inhibitory control was conducted (100 stimuli), capillary blood taken, and breathing gas analysis performed. Two-way ANOVAs with repeated measures on the factor INTENSITY and GAS investigated differences in V̇E, [Lac-], end-tidal pressure of carbon dioxide PetCO2, and incompatible reaction times (RT) and accuracy (ACC) for EF.
Results:
V̇E was significantly lower during 140kPa PIO2 compared to 29kPa at MOD (p=0.006, d=0.437) and VIG (p=0.006, d=0.405), and during 56kPa compared to 29kPa at VIG (p=0.002, d=0.525) compared to air (GAS: p=0.004, η2P=0.356). [Lac-] and PetCO2 showed no effects. RTs, not ACC, was significantly faster after vIG compared to REST, LOW, and MOD (all p≤0.022), without effects for GAS.
Discussion and Conclusion:
V̇E was reduced by 8-10 % during MOD to VIG exercise only, while a ceiling can be assumed between 56 and 140kPa PIO2. Based on similar post-exercise [Lac-] and PetCO2 values (all p>0.669), but in contrast to studies with submerged bicycle exercise (-15% V̇E5), dampened chemoreceptor control rather than metabolic changes was suspected as a possible cause. Superior EF performance corresponds to elevated [Lac-]- levels6 and maintained cerebral oxygenation during severe exercise7. Findings emphasize sport-specific influence from exercise modality and capacity, affecting safety, planning, and training for underwater activities like SCUBA diving.

1Stellingwerff et al. (2006) 10.1152/ajpendo.00499.2005
2Ulrich et al. (2017) 10.1159/000453620
3Pontifex et al. (2009) 10.1016/j.psychsport.2018.08.015
4Damato et al. (2020) 10.1113/JP280326
5Peacher et al. (2010) 10.1152/japplphysiol.01431.200
6Hashimoto et al. (2010) 10.1096/fj.201700381RR
7Tempest et al. (2017) 10.1016/j.bandc.2017.02.001