Your Heart Knows How to Get Fit

In the interest of understanding the benefit and effectiveness of High Intensity Interval Training (HIIT) the concept of heart rate zones should be revisited.

The reason why it is important to know your heart rate while exercising is that it indicates your current effort level and available work capacity, and it provides information about how close you are working to your aerobic and anaerobic thresholds.


The main heart rate zones include the 50-60% of maximum heart rate (Whats your MHR – MHR is roughly calculated with the following equation: 220 – age = MHR), which is suitable for performing light cardio to improve blood flow and circulation. It is therefore ideal of warming up and cooling down and is the base zone used to target fat stores for use as a main source of energy.


Working out in the 60-70% of MHR range is ideal for developing general fitness and is the ideal range for utilising fat stores as an energy source, as it engages more of the cardiovascular and respiratory systems due to the increasing load.


The 70-80% of MHR range is the aerobic zone, and is ideal for developing endurance and improve lactate thresholds. Due to the energy demands in this zone your body will rely more on stored glycogen and digested carbs for energy, but around half of your energy will still be supplied from fat stores.


The 80-90% of MHR zone is the anaerobic threshold limit, where your body is producing massive amounts of lactic acid and is only able to maintain this level for a short period of time. This is the best zone to increase your VO2 max to improve your body’s ability to utilise oxygen. This heart rate zone relies on predominantly on your ATP-PC system for energy, with some reliance on glycogen.


The 90-100% of MHR zone is the upper limits of your physical capacity, and should only ever be reached during HIIT for a short period of time, if at all.

Knowing and understanding these zones will ensure that you work at the right level to achieve your goals, and it will make your training more accurate. As such, you will notice there are a number of zones that preferentially use fat as an energy source, namely the 50-75% of MHR zone. You could therefore be forgiven for thinking that this was the best way to go about losing weight…

However, the reality is that the best way to lose weight, and keep it off, is to burn as many calories as possible during your workout. The best way to achieve this is to use HIIT combined with high intensity weight training because working at higher intensities burns a greater number of calories, which is what you should be concerned with when trying to lose weight, not losing fat. Once you reach your ideal weight, muscle development and tone you can start using more targeted fat loss heart rate zones to ‘sculpt’ your physique.

H.I.I.T. guidelines:

  • Use major muscle groups when doing HIIT
  • Warm up and cool down properly
  • Train for 15 to 20 minutes
  • Slowly progress by increasing multiple variables (speed, duration or difficulty level)
  • Train with accuracy by using a heart rate monitor
  • Do not do HIIT on consecutive days (take 24 to 48 hours to recover)
  • Only engage in HIIT if you already have a suitable level of conditioning and fitness
  • Eat properly
  • Do not engage in HIIT if you have any injuries. Check with your medical professional before starting any similar programme.
Training type Exertion interval Rest interval No of intervals Total time
Intensity Duration Intensity Duration
Beginner: Stationary cycling 70% MHR 30 sec 50% MHR 60 sec 10 each 15 min
Intermediate: Elliptical runner 75% MHR 45 sec 55% MHR 90 sec 8 each 18 min
Advanced: Treadmill running 75-85% MHR 60 sec 55-60% 120 sec 6 each 18min

Author: Tanja Schmitz

Co-Publisher at Maverick Media and until recently, Fitness Magazine editor. Tanja now manages multiple digital platforms, consults and create exciting campaigns and opportunities in the fitness industry. You’ll find her behind her computer or on her bike, dreaming up new ways to improve or create content for you.

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