Heart Rate Reserve (HHR): Understanding, Calculation, and Training Application

What is HHR in exercise?

In exercise science, HHR stands for Heart Rate Reserve, a crucial metric used to precisely determine an individual's effective training intensity by considering both their maximum and resting heart rates.

Understanding Heart Rate Zones

To fully grasp Heart Rate Reserve (HHR), it's essential to first understand the two foundational components of an individual's heart rate range:

• Maximum Heart Rate (MHR): This is the highest number of beats your heart can achieve per minute during maximal exertion. While MHR can be precisely determined through a graded exercise test under medical supervision, it is often estimated using formulas. The most common and widely accepted general estimation is the "220 minus age" formula (e.g., a 40-year-old would have an estimated MHR of 180 bpm). However, it's important to note that this is a population average and individual variations can be significant. More refined estimations like the Tanaka formula (208 – (0.7 x age)) or the Gellish formula (207 – (0.7 x age)) may offer slight improvements but are still estimations.
• Resting Heart Rate (RHR): This is the number of times your heart beats per minute while at complete rest, typically measured first thing in the morning before any physical activity or caffeine intake. A lower RHR generally indicates better cardiovascular fitness, as the heart is more efficient at pumping blood.

What is Heart Rate Reserve (HHR)?

Heart Rate Reserve (HHR) represents the difference between your Maximum Heart Rate (MHR) and your Resting Heart Rate (RHR). It is calculated simply as:

HHR = MHR - RHR

This value signifies the total range of heartbeats available to you for exercise. Unlike simply using a percentage of Maximum Heart Rate, HHR accounts for an individual's unique physiological fitness level as indicated by their resting heart rate. For instance, a highly conditioned athlete with a low RHR will have a larger HHR compared to a deconditioned individual of the same age with a higher RHR. This larger range means the athlete has a greater capacity for increasing their heart rate during exercise, reflecting their superior cardiovascular efficiency.

The Karvonen Formula: Utilizing HHR for Training

The HHR is primarily utilized in the Karvonen Formula, a highly regarded method for calculating target heart rate training zones. This formula provides a more personalized and accurate approach to exercise intensity prescription compared to simpler percentage-of-MHR methods.

The Karvonen Formula is as follows:

Target Heart Rate = [(MHR - RHR) x % Intensity] + RHR

Let's break down each component:

• (MHR - RHR): This is your Heart Rate Reserve (HHR), the total range of heartbeats available for work.
• % Intensity: This is your desired training intensity, expressed as a decimal (e.g., 70% intensity would be 0.70). This percentage is applied to your HHR, not your MHR.
• + RHR: After calculating the percentage of your HHR, your Resting Heart Rate is added back in. This crucial step ensures that the target heart rate reflects the full range from rest to the desired intensity, providing a more physiologically relevant target.

By integrating both MHR and RHR, the Karvonen Formula tailors the training zones to an individual's specific fitness level, making it a gold standard for precise cardiovascular training.

Benefits of Training with HHR (Karvonen Method)

Utilizing HHR through the Karvonen Formula offers several significant advantages for exercise prescription and training effectiveness:

• Personalized Intensity: It accounts for individual differences in fitness levels, as reflected by varying resting heart rates. This means two individuals of the same age might have different target heart rates for the same perceived exertion, accurately reflecting their physiological state.
• Improved Training Specificity: It allows for more precise targeting of specific physiological adaptations. For example, training at 60-70% HHR might be ideal for improving aerobic base, while 80-90% HHR targets anaerobic threshold improvements.
• Enhanced Safety and Effectiveness: By providing more accurate intensity guidelines, it helps prevent overtraining in less conditioned individuals and ensures sufficient stimulus for more conditioned athletes, optimizing both safety and results.
• Better Reflection of Physiological Stress: Training based on HHR better reflects the actual physiological stress placed on the cardiovascular system during exercise, as it considers the heart's working capacity above its resting state.

Calculating Your HHR and Target Heart Rate Zones

Here's a step-by-step guide to calculating your HHR and applying it to determine personalized training zones:

1. Determine Your Resting Heart Rate (RHR):

   • Measure your pulse for one full minute immediately upon waking, before getting out of bed. Repeat for several days and take an average.
   • Example: Let's assume RHR = 60 bpm.

2. Estimate Your Maximum Heart Rate (MHR):

   • Use the "220 - age" formula or a more refined one.
   • Example: For a 30-year-old: MHR = 220 - 30 = 190 bpm.

3. Calculate Your Heart Rate Reserve (HHR):

   • HHR = MHR - RHR
   • Example: HHR = 190 bpm - 60 bpm = 130 bpm.

4. Apply the Karvonen Formula for Target Heart Rate Zones:

   • Choose your desired intensity percentage. Common zones include:

     • Very Light (50-60% HHR): Recovery, warm-up, cool-down.
     • Light/Aerobic Base (60-70% HHR): Improves endurance, fat burning.
     • Moderate/Aerobic Fitness (70-80% HHR): Improves cardiovascular fitness, stamina.
     • Vigorous/Anaerobic Threshold (80-90% HHR): Improves speed, power, lactate threshold.
     • Maximum (90-100% HHR): Short bursts, high-intensity interval training (HIIT).

   • Example Calculation (for 70% intensity):

     • Target HR = [(190 - 60) x 0.70] + 60
     • Target HR = [130 x 0.70] + 60
     • Target HR = 91 + 60
     • Target HR = 151 bpm

   • This means for a 30-year-old with an RHR of 60 bpm, a moderate intensity workout at 70% HHR would target a heart rate of 151 bpm.

Practical Application and Considerations

• Monitoring During Exercise: To effectively train within your HHR zones, you'll need to monitor your heart rate during exercise. This can be done using wearable devices (fitness trackers, smartwatches, chest strap monitors) or by manually checking your pulse at your wrist or neck.
• Factors Influencing Heart Rate: Be aware that various factors can influence your heart rate beyond exercise intensity, including stress, fatigue, illness, medication, hydration status, environmental temperature, and even caffeine intake. These can cause your heart rate to deviate from expected values.
• Limitations of Estimations: While the formulas for MHR are widely used, they are estimations. For the most accurate MHR, a maximal exercise test overseen by a healthcare professional is recommended, especially for individuals with underlying health conditions or those beginning a rigorous exercise program.
• Consult a Professional: Always consult with a healthcare provider or a certified exercise professional before starting a new exercise program, particularly if you have any pre-existing health conditions or concerns. They can help you determine appropriate intensity levels and ensure your exercise plan is safe and effective for your individual needs.

Conclusion: The Precision of HHR Training

Heart Rate Reserve (HHR) is a sophisticated and highly effective metric that moves beyond generalized heart rate predictions to offer a truly personalized approach to exercise intensity. By integrating an individual's maximum and resting heart rates, HHR, particularly when applied through the Karvonen Formula, allows for the precise targeting of training zones. This precision optimizes physiological adaptations, enhances safety, and ultimately empowers individuals and fitness professionals to design exercise programs that are both highly effective and uniquely tailored to the individual's cardiovascular capacity.