Indoor Running Training Guide

When the days shorten and ice coats our favourite paths, many runners find themselves on an indoor treadmill. Those indoor runners face a major challenge – underperformance caused by overheating.

Outdoors, many runners enjoy workouts in the cool of evening or early morning, boosted by a refreshing breeze to evaporate sweat. But indoors, many runners are faced with room temperatures over 20° C/ 68° F. Coupled with maybe a small fan to recirculate stale air, they quickly find themselves too hot. Their heart rate goes up, speed goes down, and they remember why the treadmill is often known as the “dreadmill”.

Thankfully, there’s a better way.


Heat training is the solution

That feeling of treadmill misery is caused by the runner’s inability to cope with a quickly rising core body temperature. Blood is diverted from the muscles to the skin, meaning there’s less oxygen going to the muscles. In an non-heat-adapted individual, that process is very inefficient. But heat training teaches the body to cool efficiently.

Simple heat training accomplishes two things:

  1. it keeps the core body temp lower for longer; and,
  2. once core temp does rises, heat training maintains significant blood flow to the muscles.

These improvements occur primarily through the generation of more blood plasma. The result is that faster paces can be maintained in both hot and cool ambient temperatures.

CORE has an excellent guide to heat training, which is a great resource to learn the basics. What follows here is an overview of how runners can heat train on the treadmill.

Identifying and using your heat training zone

Heat training starts by identifying your heat training zone. This is done through a heat ramp test for the treadmill.

Once you know your ideal heat training zone, doing heat training a minimum of 2 or 3 times a week will adapt your body to the heat. During each session, maintain your core body temperature in your heat training zone for approximately 45 to 75 minutes (consult your coach for your individual needs). Note that each training session will be longer than that, as it will take some time to elevate your core temp into your heat training zone.

Reaching optimal temperature

Let's say you've identified your optimal heat training zone as between 38.4° C and 38.6° C (101.1° F and 101.5° F) You can reach that core body temperature in a number of ways – a warm room, extra clothes, a faster pace, or a greater treadmill slope (or any combination of the four). Do not use fans – they simply prolong the time it takes to reach the heat training zone.

Note that core body temperature is a slow-moving number. Its rise will lag behind an increased heart rate, and lag even further behind an increase in speed. You'll quickly learn how to “ease into” your heat training zone and stabilize your core temperature with small adjustments to pace and heart rate.

Most runners are accustomed to varying intensity to reach the heart rate or pacing targets for the workout. However, during heat training, you will vary intensity to maintain a targeted core body temperature. Staying in your heat training zone is the primary goal, and heart rate and pace are secondary.

At first, you will notice that your pace is much slower than typical for a given heart rate. This is to be expected, as your body is diverting blood from muscles to cool itself. After just a few days of heat training, you will start to see your pace quicken again. This is the result of your body adapting to the heat training.

Sample training sessions

Easy run

Set-up: long sleeve shirt, running tights, warm room, no fan

Warm-up at moderate intensity until your core body temp is close to your heat training zone. If it's difficult to reach the heat training zone at the desired intensity, add clothes or warm up the room. If you’re in a cool room, you may need to wear more clothes than you ever do while running outside, even during the winter.

Pick a heart rate and pace that lets you ease into the heat training zone. Keep your core body temp in that zone for 45 to 75 minutes. Adjust heart rate and pace as needed to stabilize your core temperature.

Optionally, after the workout is completed, go into the sauna or hot bath to maintain your core body temperature in the heat training zone. This “time in zone” counts toward the time needed to adapt to heat (please note that the CORE sensor is not validated as accurate in the sauna, and the plastic will begin to melt above 80° C/ 176° F).

Intervals run

Set-up: short sleeve shirt and shorts, normal room temperature, fan available (but begin with it off)

  1. Do the intervals portion of your workout as normal while monitoring your core body temperature. If necessary, use the fan or other cooling measures to ensure you stay below the heat training zone.
  2. After finishing intervals, turn off the fan. Run at an intensity that will keep your core temp in the heat training zone. Add clothes if you’d prefer to run slower.
  3. End the workout after you have accumulated 45 to 75 minutes total in the heat training zone.
  4. Optionally, after the workout is completed, go into the sauna or hot bath to maintain your core body temperature in the heat training zone.

Strength training day

Set-up: shorts, cool room, fan

  1. Strength training is best done with a core body temp below the heat training zone. In other words, do not use strength training to accumulate heat training time.
  2. Monitor core body temp throughout the workout.
  3. For maximal effect, cool off between sets to stay below heat training zone.

Stay cool for maximum performance

After a couple of weeks of heat training, your core temp should rise more slowly and you should experience less speed loss when your core temp is high. This means you can better perform your speed intervals indoors. The goal of speed intervals is to build VO2 max and lactate threshold. High intensity work is needed for this, and it shouldn’t be impeded by an elevated core temp.

This means that once you’ve adapted to the heat, you should run your intervals staying as cool as possible. The secrets to doing thi are cool room temperatures, lots of air flow, and evaporating water from the skin. Creative solutions abound, but here are some proven measures for cool indoor racing:

  • bring in more and bigger fans
  • cool the room before starting
  • open windows to allow air exchange with the outdoors. Fans are not as effective if they're simply recirculating warm air.
  • strategically place cold, wet towels on your body
  • regularly mist water onto your body with a spray bottle
  • pre-chill your drinks
  • use an ice vest to pre-cool your core temp before the workout
  • and did we mention more fans?

Maintaining heat adaption

Once you’ve attained heat adaption, you’ll need to maintain those blood plasma gains. Most people can do this with 2 or 3 heat sessions per week, with 45 to 75 minutes in the heat training zone each time. Most runners choose to do their heat-training maintenance during their easy runs or toward the end of a long run.