Distance runners have long treated heat training and altitude training as roughly interchangeable ways to force an adaptation, but a growing body of research is making the case that the two stresses work through genuinely different physiological pathways and should be thought about separately rather than as substitutes for one another. Heat exposure drives its benefits primarily through plasma volume expansion, increasing the fluid component of blood and, with it, cardiac output — the heart pumps more blood per beat, delivering oxygen more efficiently even back at normal temperatures.
Altitude works through a different mechanism entirely: hypoxic exposure, or reduced oxygen availability, triggers adaptations including increased red blood cell production over time and changes to how muscles extract and use the oxygen that is delivered. Because the two stimuli operate on largely separate systems, researchers say there is a physiological case for combining both rather than treating a training camp as either "heat" or "altitude," although logistics — access to genuine elevation versus a heat chamber or sauna — usually force athletes to pick one.
New guidance drawn from recent training-camp research suggests teams and individual athletes preparing to compete at high elevation may be better served basing at a moderate altitude of roughly 950 to 1,700 metres than staying at sea level and flying in late. Elite runners in controlled studies have shown measurable improvements in running economy and VO2 max after around 20 days of simulated moderate-altitude exposure, adaptations that do not reliably show up from heat training alone, reinforcing that altitude's benefits are not simply a slower version of what heat produces.
That does not make heat training a lesser option for runners without access to elevation. Heat protocols — whether structured hot-room sessions, sauna use after easy runs, or simply training through summer heat with intent — remain one of the most time-efficient ways to chase some of the cardiovascular gains associated with altitude, particularly plasma volume expansion, without the cost and logistics of a training camp. For an athlete preparing for a hot-weather race specifically, heat acclimation also has the advantage of training the exact stress they will face on race day, something altitude training does not replicate.
The practical takeaway emerging from this research is less about choosing a single superior method and more about matching the tool to the goal: heat for plasma volume and race-day heat tolerance, altitude for oxygen-carrying capacity and running economy, and — where logistics allow — a combination of both for athletes able to build a camp around genuine elevation with warm daytime conditions. For the large majority of recreational runners without access to either extreme, researchers note the more modest but still real gains from consistent heat exposure during summer training remain the most accessible entry point.