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Understanding your body during exercise

7 Oct 2020

Working to heart rate (HR)
It is important to understand what’s happening to your body when you exercise and to be able to measure your effort levels.
As you exercise, the blood in your body moves towards the muscles that you are using. This is why it is said don’t train just after a meal. When you eat, blood goes into your stomach to aid digestion. If you exercise just after a meal, the blood leaves your stomach and redirects to your muscles, leaving the job half done, which gives you indigestion.

Muscles need oxygen to produce the energy required for exercise. The harder you work out, the more oxygen your muscles need. Your heart beats more quickly to transport the blood, and your breathing rate increases. The heart is a muscle. As you get fitter, your heart gets stronger. If you train too hard, you will put a strain on your heart as it can’t cope with the demand. Likewise, if you train too little, you will not challenge your body and your fitness will not improve.

It is all about balance: knowing your body’s strengths and also its limitations. Recognising when to stop is just as important as knowing when to push. Listen to your body. When your heart starts beating rapidly and you can feel your chest tightening as your breathing increases, you are training too hard. If you feel like you could do the exercise all day and your breathing hasn’t changed much, then step it up until it does. This is where working to heart rate comes into play. It’s the perfect way to understand your effort levels in a safe and accurate way.

There are plenty of devices now that will monitor your heart rate, unlike the old-fashioned way where you had to stop training, measure your pulse for 30 seconds and multiply the reading by two. Now all you have to do is glance at your wrist. When you work to heart rate you never want to exceed your maximum heart rate (MHR). Working any higher will put unnecessary stress on your heart.

Your MHR is calculated by deducting your age from 220. So, if you are 70 years old, your MHR is 150 beats per minute (bpm). When exercising, your target heart rate zone is 50–85% of MHR. A 70-year-old person should therefore have a heart rate of 75–128 beats per minute when exercising.

One thing to mention that often gets overlooked is medication and heart rate. Some medications have side effects that will lower your resting heart rate. An example of this is blood pressure pills. You may find your resting heart rate is 60 bpm or lower. If this is the case, talk to a health professional. You may have to recalculate the heart rate figures for these circumstances. If you are targeting a working heart rate of 120 bpm but your natural heart rate has been lowered by medication, you can easily blow a gasket trying to get there, so you will need to reduce the figures to accommodate this change.

Rate of perceived exertion (RPE)
The rate of perceived exertion is a way of measuring exercise intensity that gives you awareness of effort. Usually, trainers will
ask you to imagine a scale between zero and 10, zero being no effort and 10 being very, very hard. They will then ask where your effort level is on that scale. It is a way of looking at our effort levels without the need for a heart rate monitor. I have modified the scale to show what I expect of you whilst exercising. Try to keep your effort in between 4 and 7 on the scale, which is the equivalent of working to 50–85% of MHR.

  1. Not even trying
  2. I’m trying a little, but if I’m honest, not much
  3. There might be some effort involved
  4. Well, I’m getting warmer
  5. Something’s happening
  6. I can feel my muscles and my body is letting me know
  7. I’m starting to sweat but am still talking and breathing
  8. ’Ave it! I can really feel this now
  9. Breathing is getting difficult, and I’m not sure how long I will last
  10. Crikey, I hope my affairs are in order

If you haven’t got a device to measure your heart rate and you can’t be bothered with the faff of counting your pulse, then the RPE is the next best thing to monitor your effort levels.

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