Training in Heat: Pacing, Fatigue, and Cooling
Training through hot weather? Explore how heat affects a workout and what pacing and cooling research can help you consider.
A familiar pace can feel much harder in hot weather. Studies of running and cooling help explain some of that change, but they do not provide a guarantee that matching perceived effort makes all temperatures equally demanding or safe.
Slower running, similar results on one fatigue test
A 2023 crossover trial had 13 recreational distance runners from a tropical region complete self-paced, as-fast-as-possible 10-kilometre treadmill runs at 25°C and 35°C. The group included 11 men and two women.
At 35°C, they took about 14 minutes longer on average, reported greater effort, and had transiently higher core temperatures. Jump height measured one hour afterward fell by about 7%, with no effect of temperature on that reduction.
That is a finding about a particular neuromuscular test after one running protocol. It does not demonstrate identical muscle damage, total fatigue, or heat-illness risk. The authors suggested that the faster external workload in the cooler condition helped explain the similar jump response. Their interpretation should not become a promise that slowing down equalizes every physiological strain.
Cooling results depend on the protocol
A field study of eight highly trained tennis players compared 30-minute conditioning sessions at 35°C and 55% relative humidity. Before one session, players used an ice vest and cold towels, then warmed up in a cold compression garment.
Perceived effort and thermal stress were lower with cooling. The study did not find significant differences in performance, the rise in core temperature, or lower-body peak power. It did find a smaller change in body mass after cooling. With a small sample and nonsignificant trends for some outcomes, the study cannot establish that cooling has no physiological benefit or is purely psychological.
Indeed, a consensus statement on exercise in the heat includes cooling strategies among options to facilitate heat loss or increase heat-storage capacity. One limited field protocol does not negate that broader guidance.
Preparation goes beyond changing pace
The consensus recommends repeated exercise-heat exposures over one to two weeks for acclimatization, beginning exercise adequately hydrated, and minimizing dehydration. It also discusses shade, cooling, and additional recovery opportunities at hot-weather events.
These recommendations support planning for the conditions rather than forcing a usual pace. The one-to-two-week period is a preparation framework, not a date after which heat ceases to pose a risk. Pacing, environmental conditions, hydration, cooling access, and individual response all remain relevant. Neither a comfortable sensation after cooling nor an acceptable effort rating proves that heat strain has been eliminated.