You may feel warm during and after exercising. However, exercise is not a problem when using Natural Cycles since you measure your temperature with a basal thermometer first thing in the morning —before sitting up, getting out of bed, or doing anything else— or your temperature is synced from your wearable device after you sleep.
If you use a wearable device, even if you sync your data after getting up or exercising, the temperature shown on your Add Data page is calculated from your night of sleep. Wearable devices can distinguish between sleep and wake periods, ensuring the correct temperature is used.
If you exercise during the day, you can log your temperature the next morning as usual. For more information about when to exclude a temperature, please read this article When and how should I exclude my temperature?
It's important to be aware that a significant increase in exercise, similar to any major lifestyle change, has the potential to affect your cycle. Tracking your cycle with Natural Cycles will allow you to quickly spot any changes specific to your body.