Key takeaways
- During intense exercise your heart rate rises, your blood vessels widen and your cardiac output can rise from about 5 litres a minute at rest to as much as 30 litres a minute.
- Intense exercise triggers the same “fight or flight” response as emotional stress, so it needs to be balanced with recovery.
- How quickly your heart rate returns to normal after exercise (heart rate recovery) is a useful marker of cardiovascular fitness.
- Zone 2 training, at around 60 to 70% of your maximum heart rate, strengthens your heart without excessive strain.
Whether you’re lacing up for a hard run, hitting a HIIT session or training for a Hyrox competition, intense exercise is one of the most demanding stressors for your heart.
What happens to your heart during intense exercise?
Your heart rate rises rapidly, your blood vessels widen and the amount of blood your heart pumps every minute (your cardiac output) increases, so more oxygen-rich blood reaches your muscles. This is normal, and it’s how your heart gets stronger.
Exercise is one of the fundamentals of a healthy heart, but high-intensity exercise places a lot of demand on it. During intense exercise your body activates the sympathetic nervous system: the same “fight or flight” pathway that’s triggered by emotional stress, poor sleep and everyday pressures such as work deadlines. When you exercise, this response is temporary, but it needs to be paired with recovery so your heart doesn’t stay under strain.
30 litres a minute. At rest, your cardiac output is around 5 litres a minute. During exercise it can soar to as much as 30 litres a minute, as both your heart rate and your stroke volume (the amount of blood pumped out with every beat) increase.
Why is heart rate recovery important?
How quickly your heart rate returns to its baseline after exercise is an important marker of cardiovascular fitness. Faster recovery is usually associated with a higher level of fitness, and it shows how well your body moves from a state of stress back to rest.
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How can you improve your recovery?
Improving your recovery needn’t be complicated:
- Prioritise good-quality sleep.
- Stay hydrated.
- Eat enough nutrient-dense food to support your training.
- Avoid back-to-back intense sessions, and give some days to gentle movement instead.
What is Zone 2 training?
Not all heart training needs to leave you breathless. Much of the most effective heart development happens at lower intensities, known as Zone 2 training, where your heart rate stays at around 60 to 70% of your maximum heart rate.
To estimate your maximum heart rate, subtract your age from 220. If you don’t track your heart rate while you exercise, aim for a chatty run, a brisk walk or a steady bike ride: if you can hold a conversation fairly comfortably, you’re likely to be in Zone 2. This strengthens your heart without excessive strain.
A Tomorrow Health Check includes a heart and lung exercise test with a stress ECG, which shows how your heart responds to exercise and how quickly it recovers.
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Photo: Miguel A Amutio on Unsplash.
Frequently asked questions
How do I work out my Zone 2 heart rate?
Estimate your maximum heart rate by subtracting your age from 220, then aim for 60 to 70% of that number. Without a heart rate monitor, a pace at which you can still hold a conversation is usually Zone 2.
What is a good heart rate recovery after exercise?
The faster your heart rate returns to its resting level after exercise, the fitter your cardiovascular system usually is. A slower-than-normal recovery can mean your heart is under strain or needs more rest.
Is high-intensity exercise bad for your heart?
No, exercise is one of the fundamentals of a healthy heart. But intense exercise is a significant stressor, so balance it with recovery: sleep well, stay hydrated, eat well and avoid back-to-back hard sessions.