Heart Rate 101

It's a twee Valentine's card marketing slogan, but the saying 'Listen to your heart' is also useful advice for runners. Here are some Q&As explaining why.

What does my heart rate tell me?

With each beat, the heart pumps blood-borne oxygen molecules out to working muscles. The harder a run, the more oxygen muscles need, so the quicker the heart beats. This makes heart rate a useful measure of physical exertion, helping you avoid the most common training mistake of all - going too fast during long, slow runs.

How do I work out the stats?

First, work out your maximum heart rate (HR max) using a heart rate monitor. Run easy for 15 minutes, hard for five, then as hard as possible for another minute. The highest number your monitor records is your maximum heart rate. Now use this figure to calculate your three basic training zones:

Low Intensity 60-70% of max

This zone encompasses recovery and steady runs and should feel fairly easy. It encourages fat burning and a strong cardiovascular system. New runners should spend 90 per cent of their overall training time in this zone to keep their enthusiasm in check and help build time on their feet. More advanced runners should aim for 70-80 per cent.

Moderate Intensity 70-80% of max

This zone includes faster steady runs and marathon pace runs for more experienced runners. Spend 10-25 per cent of your training time here.

High Intensity 80-95% of max


The lower end (80-85 per cent) of this zone encompasses tempo (or lactate threshold) runs - a 'comfortably hard' intensity that can be sustained for a few miles, but isn't all-out. Running at this intensity burns more stored carbohydrate (glycogen), rather than fat.

The higher end of the zone (85-95 per cent) includes speedwork reps. These develop speed and improve VO2 max, but can only be maintained for a few minutes at a time.

Heart rate tends to lag behind effort, so most runners prefer to look over heart rate data after high-intensity sessions. Once you reach a good level of conditioning, spend five to 10 per cent of training here.

What else should I know?

Over time you'll run faster at the same heart rate. Let the monitor be your guide, not your taskmaster: don't slow to a crawl when running uphill just because the monitor tells you to. Just aim to stay within the zone most of the time.

Also, research has shown that dehydration, heat, altitude, time of day and natural variation between individuals can all influence heart rate by up to 20 per cent.

Dehydration in particular can lead to 'cardiac drift', when your heart rate increases during a session even when you're holding a constant pace. It happens because the volume of blood in your system drops if fluid lost in sweat isn't replaced.

Denser blood means more work for the heart, hence a gradually rising heart rate for the same level of exertion. It's not a cause for concern, but if it happens, up your fluid intake and perhaps slow down.


Invest Wisely

Take the following into account before buying a heart rate monitor, says Fox

  • Ideally you want an alarm to alert you when you stray into a different  heart rate zone.
  •  A lap counter helps when sessions involve training in two or more zones, such as in an out-and-back run.
  •  It's useful to be able to download  data after your workout to computer software that helps you analyse and track your progress.
  •  GPS-enabled devices provide a sophisticated way to analyse training as they can also record pace, routes and gradient, using satellites.