Training in Heat: Pacing, Fatigue, and Cooling

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.

Keep the conditions with the workout

TandemFit can save a weather snapshot with a completed workout when location and weather data are available. You can look back at the recorded temperature, humidity, wind, and conditions alongside your session. If your usual pace felt harder on a hot day, that context makes it easier to compare the day with a cooler workout and decide what to watch for next time.

The snapshot describes conditions near the recorded location; it is not a continuous measurement of what your body experienced. Compare it with your pace and how the session felt, while remembering that terrain, sleep, and other factors may also differ. A weather record can help you ask a better question about your training, not prove what caused a change in performance.