Caffeine and Hypoxia During Exercise in Males and Females

NCT ID: NCT05764018

Last Updated: 2024-08-12

Basic Information

• Recruitment Status: COMPLETED
• Clinical Phase: NA
• Total Enrollment: 29 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2023-03-06
• Study Completion Date: 2024-03-19

Brief Summary

Several high-altitude destinations recommend their visitors to avoid caffeine, theoretically due to the associated diuresis which could contribute to acute mountain sickness. There is however no direct evidence for this association. In fact, caffeine ingestion is known to improve exercise performance at sea level, and may therefore help mountaineers during expeditions.

Sport science research is largely conducted in male participants, and the findings from these studies are assumed to apply to the female population. Given the known sex differences in body composition, hormones, and other physiological factors, this may not be appropriate. It is therefore important to conduct research in women, to allow for female-specific recommendations.

Detailed Description

As a result of transportation modernisation and tourism development, an increasing number of individuals are visiting high-altitude destinations for work and leisure purposes. The resulting exposure to (hypobaric) hypoxia is known to reduce exercise capacity due to a reduction in maximal oxygen uptake induced by lower oxygen pressure throughout the oxygen cascade. Several high-altitude destinations recommend their visitors to reduce or completely avoid caffeine intake during their stay. This recommendation is often based on the diuretic effects of caffeine, as the increased fluid loss through urine could accentuate dehydration, potentially contributing to feelings of acute mountain sickness. However, there is currently no scientific evidence to substantiate this recommendation. In fact, caffeine is known to be a particularly effective stimulant to improve exercise performance at sea level. Caffeine could therefore help mountaineers who engage in relatively intense physical activity during expeditions at altitude. The mechanisms underlying the ergogenic effects of caffeine are believed to originate centrally and peripherally. Of particular interest is the potential for caffeine to increase ventilation at submaximal and maximal exercise intensities. In a high-altitude environment, this could help to offset exercise- and hypoxia-induced hypoxemia, thereby enhancing exercise capacity.

Some studies have indeed provided evidence for the notion that caffeine could enhance exercise capabilities in hypoxia. Caffeine doses of 4.0 - 6.0 mg/kg body mass have been assessed, in (simulated and terrestrial) altitude environments equating to 2000 - 4300 m. In each case, it appeared that exercise performance and/or capacity at altitude could indeed be enhanced by caffeine ingestion. However, further mechanistic work is required, particularly in the assessment of the physiological effects of caffeine beyond typical exercise performance (time trial) and exercise capacity (peak power output, maximal oxygen uptake) outcomes. An enhanced holistic understanding of respiratory, cardiovascular, muscular and metabolic responses to exercise, caffeine and hypoxia is necessary to understand if caffeine ingestion at altitude is advisable.

Sport science research is largely conducted in male participants, and the findings from these studies are assumed to also apply to the female population. However, given the known sex differences in body composition, hormones, and other physiological factors, these assumptions may not be appropriate. It is therefore important to conduct research in women, to allow female-specific recommendations to be applied to athletes and to the general population.

As these are important considerations, the aim of this project is to investigate the effects of caffeine supplementation on exercise in hypoxia, and to determine whether these effects are influenced by sex differences.

24 healthy adult participants (12 male, 12 female) will be recruited to take part in the project. A preliminary testing session will be used to determine the maximal oxygen uptake of the participants in normoxia, and to familiarise them with the main trial protocol. A second preliminary laboratory visit will be used to measure the resting metabolic rate of the participants.

The main phase of the experiment will be a four-trial randomised crossover study; normoxia (ambient) vs. hypoxia (fraction of inspired oxygen = 0.13) and placebo (20 g maltodextrin) vs. caffeine (20 g maltodextrin + 6 mg/kg body mass caffeine). Participants will avoid caffeine, alcohol and intense exercise for 24 h prior to each laboratory visit. They will also replicate their diet for 24 h before each main trial. Each main trial will involve a 20-minute moderate-intensity cycling period, immediately followed by an incremental exercise test to exhaustion. Participants will be blinded to the environmental condition and the contents of the test drink. Outcome measures will include gas exchange variables, blood glucose/lactate concentration, muscle and brain oxygenation, blood oxygen saturation, heart rate and rating of perceived exertion. These measurements will provide a holistic overview of the broad physiological response to exercise, hypoxia and caffeine.

Conditions

Caffeine; Hypoxia

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: CROSSOVER
• Primary Study Purpose: OTHER
• Blinding Strategy: TRIPLE

Study Groups

Normoxia-Placebo

Participants will be breathing room air, and ingest a flavoured drink containing only a trivial amount of maltodextrin.

Group Type: PLACEBO_COMPARATOR

Placebo

Intervention Type: OTHER

Negligible amount of maltodextrin in flavoured drink solution provided 45 minutes before exercise.

Normoxia

Intervention Type: OTHER

Participants will be breathing from ambient air (\~21% O2) for the duration of the exercise bout. This will provide no hypoxic stimulus as the laboratory is located relatively near sea level (295 m)

Normoxia-Caffeine

Participants will be breathing room air, and ingest a flavoured drink containing a trivial amount of maltodextrin and 6 mg/kg body mass caffeine.

Group Type: EXPERIMENTAL

Caffeine

Intervention Type: DIETARY_SUPPLEMENT

Negligible amount of maltodextrin in flavoured drink solution containing 6 mg/kg body mass caffeine provided 45 minutes before exercise

Normoxia

Intervention Type: OTHER

Participants will be breathing from ambient air (\~21% O2) for the duration of the exercise bout. This will provide no hypoxic stimulus as the laboratory is located relatively near sea level (295 m)

Hypoxia-Placebo

Participants will be breathing a 13% oxygen gas mixture, and ingest a flavoured drink containing only a trivial amount of maltodextrin.

Group Type: PLACEBO_COMPARATOR

Hypoxia

Intervention Type: OTHER

Participants will be breathing from a hypoxic gas mixture (13% O2) for the duration of the exercise bout. This will simulate an altitude of approximately 3500 m.

Placebo

Intervention Type: OTHER

Negligible amount of maltodextrin in flavoured drink solution provided 45 minutes before exercise.

Hypoxia-Caffeine

Participants will be breathing a 13% oxygen gas mixture, and ingest a flavoured drink containing a trivial amount of maltodextrin and 6 mg/kg body mass caffeine.

Group Type: EXPERIMENTAL

Caffeine

Intervention Type: DIETARY_SUPPLEMENT

Negligible amount of maltodextrin in flavoured drink solution containing 6 mg/kg body mass caffeine provided 45 minutes before exercise

Hypoxia

Intervention Type: OTHER

Participants will be breathing from a hypoxic gas mixture (13% O2) for the duration of the exercise bout. This will simulate an altitude of approximately 3500 m.

Interventions

Caffeine

Negligible amount of maltodextrin in flavoured drink solution containing 6 mg/kg body mass caffeine provided 45 minutes before exercise

Intervention Type: DIETARY_SUPPLEMENT

Hypoxia

Participants will be breathing from a hypoxic gas mixture (13% O2) for the duration of the exercise bout. This will simulate an altitude of approximately 3500 m.

Intervention Type: OTHER

Placebo

Negligible amount of maltodextrin in flavoured drink solution provided 45 minutes before exercise.

Intervention Type: OTHER

Normoxia

Participants will be breathing from ambient air (\~21% O2) for the duration of the exercise bout. This will provide no hypoxic stimulus as the laboratory is located relatively near sea level (295 m)

Intervention Type: OTHER

Other Intervention Names

Simulated altitude; No caffeine; Sea level

Eligibility Criteria

Inclusion Criteria

• Regularly physically active (at least 30 mins of structured exercise 5 times per week).
• Sea-level natives.

Exclusion Criteria

• presence of any medical risk factors to exercise and/or exposure to altitude
• presence of any medical condition that would make the protocol unreasonably hazardous for the participant
• smokers
• exposure to altitude above 2000 m in the last 2 months

• Minimum Eligible Age: 18 Years
• Maximum Eligible Age: 30 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: Yes

Sponsors

Jozef Stefan Institute

OTHER

Sponsor Role: lead

Responsible Party

Tadej Debevec

Principal Investigator

Responsibility Role: PRINCIPAL_INVESTIGATOR

Principal Investigators

Tadej Debevec, PhD

Role: PRINCIPAL_INVESTIGATOR

University of Ljubljana

Locations

University of Ljubljana

Ljubljana, , Slovenia

Countries

Slovenia

Other Identifiers

HypoCaff

Identifier Type: -

Identifier Source: org_study_id