You trained all winter at 40°F. Your PT test is in July at 92°F. Your target time feels impossibly hard. It should — because it is. Not because you lost fitness, but because heat fundamentally changes the physiological cost of running.
How Heat Affects Performance
When you run in heat, your body diverts blood from working muscles to the skin for cooling. This reduces oxygen delivery to muscles, increases heart rate, and raises the perceived effort of any given pace. The same 8:00/mile that felt like RPE 5 in cool weather now feels like RPE 7.
The primary factor isn’t air temperature — it’s dew point, which measures the moisture content of the air. High humidity impairs your body’s primary cooling mechanism (evaporative sweating). Dry heat is manageable. Humid heat is brutal.
The Numbers
Pacewright uses dew point to calculate pace adjustments:
| Dew Point | Pace Adjustment |
|---|---|
| Below 55°F | 0% — optimal conditions |
| 55-60°F | +1% slower |
| 60-65°F | +2.5% slower |
| 65-70°F | +4.5% slower |
| 70-75°F | +6.5% slower |
| Above 75°F | +9% slower |
What this means for a PT test: If your goal time for a 1.5-mile test is 12:00 (8:00/mile) and the dew point is 72°F, you should expect approximately 12:47 at the same effort level — nearly a minute slower from heat alone.
For comparison, altitude also matters: approximately 1.5% slower per 1,000 feet above 3,000 feet. If you’re testing at Fort Huachuca (4,600 feet) in August, both adjustments apply.
What This Means for Your Test
Your fitness didn’t change. A slower time in heat doesn’t mean you lost fitness. It means the same fitness produces a different pace in different conditions. Most PT test scoring rubrics don’t adjust for weather — which means you may need to be fitter than the scoring table implies if you’re testing in summer.
Adjust your pacing plan. If you trained your pacing strategy for a 12:00 target, your heat-adjusted target might be 12:30-12:45. Start at the adjusted pace, not the cool-weather pace. Going out at your cool-weather goal pace in heat guarantees a dramatic second-half fade.
The strength events are less affected. Push-ups and sit-ups are short-duration events that don’t generate the same thermoregulatory challenge as sustained running. You may feel warmer and sweat more, but the performance impact on 2 minutes of push-ups is minimal compared to the impact on a timed run.
Heat Acclimatization
If you know your test will be in hot conditions, 10-14 days of heat exposure significantly improves your body’s cooling efficiency:
- Sweating starts earlier and increases in volume
- Heart rate at a given pace decreases
- Core temperature stabilizes at a lower point
- Perceived effort at a given pace drops
You don’t need to train hard in the heat — just run in it. Easy runs in hot conditions for 10-14 days produce most of the acclimatization benefit. Hard sessions can still be done in cooler conditions (morning, treadmill) to protect workout quality.
Race-Day Heat Strategy
Hydrate the day before. Good hydration starts 24 hours before the test, not 30 minutes before. Drinking too much water right before running causes sloshing and discomfort.
Pre-cool if possible. A cold towel on the neck, a cold drink, or time in air conditioning before the warmup lowers your starting core temperature, buying you a few extra minutes before heat becomes performance-limiting.
Adjust warmup length. In hot conditions, shorten the warmup to 5-10 minutes instead of 15. The purpose of warming up is to elevate core temperature and prepare muscles — in 90°F heat, you’re already warm. An extended warmup just starts the heat stress early.
Accept the adjusted time. This is the hardest part. The clock doesn’t know it’s hot. But your body does. Running 30-60 seconds slower than your cool-weather time in extreme heat isn’t failure — it’s physics.