by Davide DeRemigis, Precor Master Coach and Professional Trainer in Milan, Italy

Heart rate (HR) and exercise go hand in hand in goal achievement. This is especially true when preparing for an endurance event, as heart rate monitors are an important tool to keep track of performance changes. For example, applying HR to interval training is a very trackable way to measure a client’s stress response and progress over time. With HR monitoring we have better physiological and reliable information to optimize work and rest periods.

In order to use a heart monitor effectively, we need to know an exerciser’s resting HR and maximal HR (MHR). While resting HR can easily by measured by taking pulse rate when you first wake up in the morning, MHR can be more difficult to derive. The easiest way to estimate MHR is the recommended formula by the Journal of American College of Cardiology: 208 – (AGE x 0.7).

Functional Training Intensity, Work In Time, and Heart Rate Applied to Movement

HR and Intensity are closely related as HR increases depend on the muscle mass involved, the time and frequency of the movement, and cardiovascular response to neural input.

Functional fitness is defined by ACSM as “using strength training to improve balance, coordination, force, power, and endurance to enhance someone’s ability to perform activities of daily living.” Since functional training is performed with a focus on motion rather than muscles, it requires the entire neuromuscular system to be involved. Typically, functional movements involve large muscle mass and heightened neuromuscular control. Functional exercises have the potential to spike HR by challenging strength, power, and cardiovascular performance.

Here are some recommendations when selecting exercises for a functional small group class or a training circuit:

1. The larger the muscle mass involved in the exercise the greater the HR increase.
2. The higher the pace the higher the HR.
3. The limiting factor is muscle metabolism and strength affecting muscle endurance. When a muscle produces a high amount of force, it tires and depletes its energy sources before HR is allowed to rise.
4. F x D = W: The greater the force produced or distance covered (or both), the more Work is performed (leading to elevated HR).
5. HR needs continuous activity to reach its maximum level. This does not mean that a short interval is not conditioning. Instead, it means that HR cannot be the indicator of intensity, because intensity is not only time related but also workload related. 
6. 60% of maximum HR (MHR) is generally considered to be the ideal recovery HR.
7. The shorter the working interval the longer the rest (proportionally speaking). This is because shorter intervals are typically performed at high or highest possible intensity, therefore requiring longer recovery times to restore energy systems.

Functional Circuit Training: Work-to-Rest Ratio

When incorporating functional movements into circuit training, one of the golden rules is to pick exercises that allow exercisers to maintain intensity as well as HR. For instance, a push-up station should not be followed by a dip station, as this would result in muscles tiring and energy stores rapidly depleting. Instead, a preferred option would be to include a set of squats between the push-ups and dips so that the upper body has time to recover while the lower body is challenged.

The intensity of the training will determine different types of adaptations. Aerobic work performed below an individual’s lactate threshold will result in cardiovascular improvements, leading to improved stroke volume and cardiac output. Intensities above the lactate threshold will trigger peripheral adaptations to the muscles, like improved muscular capillarization, increased oxidative enzyme activity, increased mitochondrial density and volume, and increased fat utilization. The table below provides a reference for how to use this information when building functional circuits.

Example: Using the Table for Performance Gains

Performance training is aimed to increase work production at a given heart rate. Performance is usually trained and improved at 80-90% MHR or above. The duration of a bout at this intensity can be between 2 to 10 minutes depending on the fitness level of the participants. The rest will be in a 3-1 ratio. Four minutes of a circuit will require 1 minute and 20 seconds of rest. Ideally the rest period should allow the HR to reach its recovery zone at 60% MHR.

Short transition breaks between stations (such as 30 seconds on, 10 seconds off) are designed to maintain elevated intensity throughout the work period. The transition length will vary depending on an exerciser’s fitness level; the heart monitor in this case will be very useful to keep track of improvements or to scale down exercises.

Final Takeaways

1. To improve performance, select a program with intervals at 80-100% MHR. 85% is a good average.
2. Functional training means training movement. Dynamic, full body movements can be selected to elevate your heart rate.
3. Functional training is also strength. Muscles may fatigue locally before you achieve the HR target, so scale exercises appropriately for the client to maintain intensity.