INTRODUCTION

Heart rate training is one of the most effective ways to monitor and improve athletic performance. By tracking how hard your heart is working during exercise, coaches and athletes can ensure every workout has a purpose — whether that is building endurance, improving fitness, or pushing peak performance. This guide explains the key concepts behind the metrics in SquadHR and TeamHR.


WHAT IS HEART RATE TRAINING?

Heart rate training is the method of tracking your heart rate to optimize your workout. Heart rate (HR) is the number of times your heart beats per minute (bpm) as it pumps blood through your body. HR shares a direct relationship with exercise intensity — the more intense the exercise, the higher the heart rate. This makes HR one of the best indicators of how hard your body is working during a workout.

As aerobic fitness develops, your muscles become more efficient at using oxygen, and your heart rate decreases at any given level of effort. In general, a drop in exercise heart rate over time is a good indicator of improving fitness.

HR and physical characteristics such as body weight, age, and gender are also used to estimate energy expenditure, exercise intensity, and aerobic fitness.


HEART RATE TRAINING ZONES

Heart rate zones are ranges of heart rate that correspond to different exercise intensities and training benefits. There are five zones, each defined as a percentage of your maximum heart rate (MHR).

Zone 1 — Very Light (50–60% MHR)
Used for warm-ups, cool-downs, and active recovery. Helps promote blood flow and prepares the body for more intense work.

Zone 2 — Light (60–70% MHR)
The endurance zone. Builds aerobic base, improves fat utilisation, and can be sustained for long periods. An essential part of any training program.

Zone 3 — Moderate (70–80% MHR)
Improves cardiovascular efficiency and overall conditioning. Moderate effort — you can speak a few words but not full sentences.

Zone 4 — Hard (80–90% MHR)
Improves performance and aerobic capacity. Breathing is laboured and sustained effort is difficult. Used for interval training and threshold sessions.

Zone 5 — Maximum (90–100% MHR)
Used for short, maximum effort bursts such as sprints or HIIT. Improves speed and power. Cannot be sustained for long periods.

An effective training program includes sessions across multiple zones, with the majority of time spent in the lower zones to build a solid aerobic base.


MAXIMUM HEART RATE

Maximum heart rate (MHR) is the highest number of beats per minute your heart can pump under maximum effort. It is used to calculate your heart rate training zones.

MHR can be estimated using the formula: 220 minus age. However, this formula is not perfectly accurate, particularly for people who have been fit for many years or for older individuals. A more accurate method is to warm up properly and perform a series of high-intensity intervals to maximum effort, such as hill climbs or inclined treadmill running, while wearing a heart rate sensor.

For safety reasons, people aged over 35, those who are overweight, in poor physical condition, have been sedentary for several years, or have a family history of heart disease, should have their max heart rate clinically measured by a cardiologist or exercise physiologist.


ACTIVE ENERGY

Active energy or energy expenditure (Cal/kJ) is estimated using an equation developed in a study published in the Journal of Sports Sciences in 2005 and funded by Polar Electro Oy. In the study, participants completed multiple steady-state exercises at varying intensities. The researchers demonstrated that energy expenditure can be estimated with good accuracy using heart rate, age, weight, and gender.


AFTERBURN ENERGY

The afterburn effect, also known as Excess Post-exercise Oxygen Consumption (EPOC), occurs when your body continues to burn calories after exercise to replenish oxygen stores during recovery.

Afterburn energy is estimated using an equation derived from a 2011 study published in Medicine and Science in Sports and Exercise. In the study, ten men performed a vigorous 45-minute workout on a stationary bike. The results showed an additional 37% post-exercise energy expenditure to the net energy expended during the session, persisting for up to 14 hours.

Based on these results, the app calculates 37% of the net energy expended above a vigorous training threshold of 70% maximum heart rate to estimate a conservative value for afterburn.


TRAINING SCORE

Training Score (or Training IMPulse, TRIMP) is a measure of cumulative exercise intensity from a single workout, used to quantify training load. The app uses Edwards' summated heart rate zones method.

Training score is calculated as the cumulated duration (in minutes) in each of five heart rate zones, multiplied by a zone coefficient:

90–100% MHR = 5 points per minute
80–90% MHR = 4 points per minute
70–80% MHR = 3 points per minute
60–70% MHR = 2 points per minute
50–60% MHR = 1 point per minute
Below 50% = 0 points

The score is then mapped as a percentage of the maximum possible score for that session duration. For example, a score of 100 over 45 minutes equals 44% of the maximum score, classified as Moderate intensity. The same score over 30 minutes equals 67%, classified as Hard intensity.

Higher training scores are achieved with longer duration and/or more vigorous workouts.


HEART RATE VARIABILITY

Heart rate variability (HRV) is the difference in time between consecutive heartbeats, measured in milliseconds. The app calculates HRV using the standard deviation (SDNN) of beat-to-beat measurements captured by the heart rate sensor.

HRV is useful for evaluating fitness and determining exercise readiness. In general, higher HRV is a sign of better fitness. HRV is a highly personal metric that varies between individuals, and is affected by age, gender, fitness level, lifestyle, environment, and genetics.

HRV can only be calculated with HRV-enabled heart rate sensors, such as the Polar H9 or H10.


CARDIO RECOVERY

Cardio recovery refers to how quickly your heart rate returns to normal after exercise. The fitter you are, the faster your heart rate falls during the first minute after peak exertion.

According to the National Academy of Sports Medicine (NASM), the average recovery rate is a drop of 15 to 25 beats per minute. General guidelines are:

Excellent: more than 25 beats
Good: 18–25 beats
Fair: 12–17 beats
Poor: fewer than 12 beats

A recovery drop of fewer than 12 beats has been linked to an increased risk of cardiac events. Recovery is influenced by age, fitness level, hydration, medications such as beta-blockers, and overall health. Tracking recovery over time can help monitor improvements in cardiovascular fitness.


RECOVERY DROP

Recovery drop is measured by subtracting your heart rate one minute after exercise from your peak heart rate during the session. For example, if your peak heart rate is 160 bpm and it drops to 135 bpm after one minute of rest, your recovery drop is 25 beats.


HEART RATE SENSORS

SquadHR and TeamHR work with all iPhone-compatible Bluetooth heart rate sensors. For best results, a chest strap sensor is recommended, as chest straps measure the electrical signals of the heart directly and are more accurate than wrist-based optical sensors, particularly during high-intensity exercise and activities with significant arm movement.

The Polar H10 is our recommended sensor for accuracy and reliability.


NEED HELP?

Visit our Frequently Asked Questions page or contact us at info@trackteam.net.