Most runners have heard of the 80/20 principle where the majority of training is low intensity with 20% high intensity. Many cardio machines in the gym have training zone guidelines for fat loss. Sports watches will programme your training based upon heart rate zones. So what is the science behind it and is it helpful to measure your heart rate during training?
The above image is a commonly used guideline , it claims to show the benefits of working at each training zone.
LOSE WEIGHT
Firstly I have to stress that you can lose weight without any exercise or by exercising in any of the training zones. Body weight is a function of calories in vs calories out. NOTHING ELSE MATTERS. Of course a healthier diet is preferable but the body is amazing at making what it needs so if you don't eat any fat, but eat a lot of carbohydrates your body will make fat.
FOR RUNNING
As previously mentioned the 80/20 idea is based upon good science, lower intensity running does provide a stimulus to improve aerobic fitness which improves the speed at which you can run by improving the efficiency of heart and lung functions, and creating positive adaptations within the working muscles. When hitting that 20% you can provide a stimulus to improve your anaerobic fitness which occurs when the aerobic systems are already maxed out and you still need a little bit more. This will improve your ability to work under fatigue and will also often provide more stress to your muscles and joints by nature of running faster therefore having to produce more force in a shorter time frame.
SHOULD I FOCUS ON HEART RATE?
Heart rate is a guide, it can help you to measure the level of intensity of your training. The issue is when people treat it as an exact science. Training zones are based upon a percentage of your maximum heart rate, the issue is what is your max heart rate? This will vary massively from person to person. 220-age is often used but I have seem people in the lab achieve above 210 BPM and still have some room to go. I've also seen people who struggle to achieve 140. My fancy smart watch updates my training zones after almost every run. Which suggests that either my heart changes every day or that the previous estimates were wrong. On 2 consecutive days my training threshold was 154 and 168.
TAKE HOME MESSAGE
So by all means use your heart rate as a guide but although its widely used by gym goers and recreational athletes its use in performance sport is much more limited. Learn to feel your way through training, if your legs are burning and you are struggling to breathe then you are above your aerobic threshold, if you could hold a conversation you are below. For my clients I monitor pace, distance, heart rate, RPE along with data from the route and my testing. For my professional athletes we use GPS data to monitor distances covered at five different speed thresholds along with accelerations and decelerations and meters per minute.
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