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Understanding Heart Rate Zones and Energy Systems

When it comes to exercise and training, heart rate zones and energy systems play a crucial role in determining the intensity, duration, and specific benefits of your workouts.

By understanding these concepts, you can optimize your training and achieve your fitness goals more effectively. (or you can just leave it to your personal trainer 😅). Let's dive into the different heart rate zones and energy systems to unravel the mysteries of how our bodies produce energy during exercise.

Heart Rate Zones:

Zone 1 - Active Recovery (50-60% of MHR):

This zone is characterized by very light activity and is ideal for warm-ups, cool-downs, and active recovery. It promotes blood flow, aids in recovery, and prepares the body for more intense exercise.

Zone 2 - Aerobic Endurance (60-70% of MHR):

Zone 2 is the sweet spot for fat-burning and improving aerobic capacity. It allows for sustainable exercise duration, enhances cardiovascular fitness, and trains the body to utilize fat as a primary energy source. Think about a slow jog or a brisk jog for 20-40 mins.

Zone 3 - Tempo Training (70-80% of MHR):

This zone focuses on moderate to high-intensity exercise and helps improve the lactate threshold. It enhances endurance, promotes the utilization of carbohydrates for fuel, and increases overall cardiovascular fitness.

Zone 4 - Threshold Training (80-90% of MHR):

Zone 4 pushes the limits of your aerobic capacity and trains your body to work at higher intensities for extended periods. It improves anaerobic threshold, enhances speed, and increases the body's ability to sustain high-intensity efforts.

Zone 5 - Maximum Effort (90-100% of MHR):

Zone 5 represents maximum effort and is reserved for short bursts of intense exercise. It primarily targets anaerobic energy systems, enhances power, speed, and performance, and is typically used for interval training or high-intensity interval training (HIIT).

At Portside, our trainers like to use a combination of these zones to get a range of benefits through the session. We use various different exercises, movement patterns and intensities to work your whole body through a spectrum of intensity levels.

Energy Systems:

Aerobic Energy System:

The aerobic energy system utilizes oxygen to convert carbohydrates and fats into ATP (adenosine triphosphate), the body's primary source of energy. This system is primarily used during low to moderate-intensity exercises, such as Zone 2 training, where oxygen supply meets the energy demands of the activity. In basic terms, your body uses the carbohydrate and oxygen available without needing any extra input.

Anaerobic Energy Systems

1. Alactic System (ATP-PCr System)

This system provides rapid bursts of energy for short-duration, high-intensity activities, such as explosive weightlifting or sprinting. It relies on stored ATP and phosphocreatine (PCr) within the muscles and does not require oxygen.

2. Lactic System (Glycolytic System)

The glycolytic system provides energy for high-intensity activities lasting longer than a few seconds. It breaks down stored glycogen (carbohydrates) into ATP, generating lactic acid as a byproduct. This system is involved in activities like weightlifting, sprinting, and intense interval training. This is why we feel that build up of lactic acid in the muscles after a prolonged period of relatively intense exercise.

By understanding the interplay between heart rate zones and energy systems, you can tailor your workouts to specific goals:

  • To improve aerobic endurance and fat burning, focus on Zone 2 training, which engages the aerobic energy system.

  • To enhance speed, power, and anaerobic capacity, incorporate higher intensity workouts in Zones 3, 4, and 5, tapping into anaerobic energy systems.

  • By combining different zones and energy systems in your training regimen, you can achieve a well-rounded and balanced approach to fitness.

Remember, individual fitness levels, goals, and preferences should guide your training. Our trainers look to incorporate all these energy systems and heart rate zones, with more emphasis on the ones which correlate to your specific goals to provide a well rounded, yet focussed programme.

Tips for Effective Training

Determine Your Maximum Heart Rate (MHR):

To accurately establish your heart rate zones, it's essential to know your MHR.

To get a rough estimate of your MHR you can use the formula 220-age. You can then multiply that by particular percentage ranges to see what your HR would be in the different HR zones.

Use Heart Rate Monitoring

Invest in a reliable heart rate monitor or use fitness tracking apps and devices that can accurately monitor your heart rate during workouts. This real-time feedback will help you stay within your desired heart rate zones and ensure you're training at the appropriate intensity.

Gradually Increase Intensity

If you're new to heart rate zone training, start by building a strong aerobic foundation in Zone 2 before progressing to higher intensity zones. Gradually increase the duration and intensity of your workouts to avoid overexertion and minimize the risk of injury.

Mix Up Your Training

To experience well-rounded fitness benefits, incorporate a variety of training modalities. Include endurance activities like running or cycling for Zone 2 training, interval training for Zones 3 and 4, and explosive movements or high-intensity intervals for Zone 5 workouts. This variety challenges your body in different ways, promoting overall fitness and preventing monotony.

Listen to Your Body

While heart rate zones provide valuable guidance, it's essential to listen to your body's signals during exercise. Factors such as fatigue, stress, illness, and recovery levels can influence your heart rate response. If you're feeling excessively fatigued or experiencing unusual discomfort, adjust your intensity accordingly and prioritize rest and recovery.

Combine with Strength Training

While heart rate zone training is effective for cardiovascular fitness and fat loss, don't neglect the benefits of strength training. Incorporate resistance exercises to build lean muscle mass, increase metabolism, and improve overall body composition. A balanced approach combining cardiovascular training and strength training will yield optimal results.


Heart rate zones and energy systems are invaluable tools that empower you to optimize your training and achieve specific fitness goals. By understanding the different heart rate zones and energy systems at play, you can design workouts that target fat burning, improve endurance, boost anaerobic capacity, and enhance overall fitness.

Remember, training should be individualized based on your fitness level, goals, and preferences. Embrace the power of heart rate zone training and energy systems, and embark on a journey of transformative fitness, vitality, and wellbeing.

If you'd like more help with your training or understanding your particular heart rate zones then don't hesitate to get in touch for a free personal training consultation to discuss your goals and the best ways for you to reach them!

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