The paper for this journal club was:
What was the aim of the paper?
The aim of the paper was to look at whether thermal strain that is associated with prolonged self-paced exercise in the heat contributed to increased cardiovascular strain and therefore limited performance. The researchers hypothesised that thermal strain would increase cardiovascular strain (increase heart rate, reduce stroke volume, cardiac output and mean arterial pressure). The research was carried out by researchers at the University of Sydney and Australian Catholic University. It was supported by the University of Sydney Faculty of Health Sciences.
What did the study involve?
This was a laboratory study that used eight male endurance trained cyclists. Prior to the main experimental trials, the researchers measured maximal oxygen uptake of the cyclists on a cycle ergometer. The subjects then attended the laboratory on two occasions and were randomly assigned to either hot (35°C 60% RH) or thermoneutral (20°C 40% RH) conditions. The participants completed a 40 km time trial and the researchers measured oxygen uptake every 10 minutes during the trial and during the final km. Cardiac output and stroke volume were calculated and heart rate was monitored continuously. Core temperature and skin temperature were taken at 1 minute intervals and blood glucose and lactate measured were taken at rest, 10, 30, 45 minutes and upon completion of the time trial. Ratings of perceived exertion and thermal comfort were taken at 10 minute intervals and at the end of the time trial.
What were the main results?
Time to completion was lower in the thermoneutral condition (59.8 min) than the hot condition (64.3 min). Power output was lower from 20 minutes onwards in the heat, compared with the thermoneutral condition (P= ˂0.05). From 5 minutes onwards core temperature increased significantly in the heat and skin temperature remained significantly higher throughout the hot trial.Oxygen uptake was significantly higher in the thermoneutral condition and heart rate was higher in the hot trial. Stroke volume, cardiac output and mean arterial pressure were signficantly lower compared with the thermoneutral condition. There were no differences in rating of perceived exertion between the two trials (the authors do not mention this in the abstract).
What can we take from it?
The methodology in this study seemed well thought through and was relevant for the specific research question, for example the choice of ergometer for the time trial was relevant as the participants were cyclists and the researchers used an area weighted mean to measure skin temperature and calibrated the loggers before and after the study. The authors also took extra measurements that are not usually taken in similar studies, such as intravenous blood sampling and using a skin blood flow laser sensor. However, it also feels like the authors left out some important details of the study, for example they didn’t explain how the participants were randomly assigned to each condition.
The research question was focused, but as Ben and Chris mention the study did not add anything to what we already know about this subject. The paper is one of many studies that have looked at exercise performance and thermal strain during exercise in the heat.
As with the last journal club, the researchers studied only well-trained athletes and did not look at different ages, sex or ethnic groups. Therefore the results may not apply to other groups of people.
The following points from the journal club comments are really interesting and sum up the research really well.
- I am unsure that the data specifically supports the conclusions made.
- It would also be interesting to see whether the initial resting period within the climate lab has an impact on the perception of thermal comfort and sensation.
- Clearly you can’t blind participants or researchers to this intervention, so did the performance look they way it did because participants just expected to perform at a lower level during the hot trial.
- I’m not sure if the authors fitted a story a bit more to what they expected to happen then what the data warrants. To a large extent I think the arguments presented are logical, and quite possibly correct, I’d just like to see other research before I’m convinced.
- Self-paced exercise, particularly in hot environments, requires familiarised participants. The variability increases the less familiar the participant is with the testing modality and/or environmental conditions.
Overall, although the research area is interesting, this study doesn’t add anything to what we already know.