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Are You Maximizing Your Heart Rate Monitor?

Updated: Jun 25, 2019

I’m an Instagram addict. My favourite content includes envious meals, other peoples’ vacations, and cats.


Though more often, users are snapping up-close photos of their Apple Watch faces post-workout and how many calories they burned. But are they doing anything else with these numbers?


Below, I’ll outline:

  • Why an athlete should consider collecting data related to calories burned.

  • What to look for when choosing a monitor.

  • How to use that data to support one’s performance goals.


Free downloadable handout that relates to this article: High-calorie fuel options and tips.



Why Collect Data?


Years ago when I began training for the Boston Marathon, I took notice of what my Endomondo app was predicting my calorie burn while exercising to be [a.k.a., exercise energy expenditure (EEE)]. When I converted the "calories burned" into how much fuel I would need to replace with, it took me by surprise. As a dietitian, I immediately realized I was unintentionally under-fueling my training runs.


For instance, imagine requiring 2,000 calories daily to promote optimal health and then burning 1,200 calories during a training session (image 1). If day after day you only replaced 500 calories from training then a deficit will occur, negatively impacting recovery, and poorly preparing you for tomorrow’s training session.


Image 1

Performance nutrition is meant to be individualized to the athlete. Collecting data, like EEE, helps the dietitian optimize the athlete’s performance, recovery, and overall health while reducing their risk of injury and illness. Consistently providing an athlete with adequate fuel can do wonders for the body (read my blog on the negative impacts of low-energy availability).


Having a sense of EEE means being responsible with that information and putting it into use. As a dietitian, I was taught to neither ask a question nor collect a data point that wouldn’t benefit the patient. Anything asked of them would be used in creating or modifying their nutrition care plan.


Keep in mind that training load and volume for an athlete will change. Collecting data once at the beginning of a 3-year relationship with an athlete isn’t helpful. Rather, collect data multiple times throughout the preseason, season, and offseason in addition to different types of training sessions or days (e.g., short run, long run, track workout, weight training). Read my blog on why athletes shouldn’t consume the same amount of fuel every day.



Choosing a Heart Rate Monitor


When I began using the Endomondo app, the only personal information it tracked was my age; sex; body weight; running pace, duration, and length; and GPS location. Meaning, EndoMondo makes assumptions for my heart rate and VO2 max.


Then I moved onto a Polar chest strap, watch, and app. Chest straps remain the most accurate, since they collect data directly from the electrical activity of the heart.


Watches and arm bands are becoming more popular. Their method of monitoring heart rate is called photoplethysmography (PPG; a.k.a., optical tracking). Sensors on the skin-facing side of the watch flash lights into your wrist to monitor how quickly blood is flowing past. The value is then extrapolated as heart rate.


For instance, watches have been shown to provide inaccurate readings by over-estimating heart rate during high-intensity bursts or intervals (e.g., indoor cycling), but provide accurate results for low-intensity, day-to-day activities (e.g., how many calories burned living your daily life). Although Polar sells chest straps, watches, and arm bands to measure heart rate, their blog states "optical heart rate tracking is more prone to errors than chest-strap based heart rate."


Ultimately, the old school chest strap remains the most accurate.


For wrist monitors, they work best when worn tight enough while exercising to allow the skin to breathe. After training, loosening the watch for daily comfort is fine.


Whatever method you choose to use, and to increase the accuracy of its results:

  • Keep your personal information updated (e.g., body weight, age).

  • Use the predicted EEE as a starting point rather than an absolute, 100% accurate data point.

  • Follow the manufacturer's directions regarding properly fitting the monitor.



Applying the Data


Scenario: An athlete goes on a 30-minute training run.


Potential realities:

  • Option 1: The athlete celebrates via Instagram how many calories they burned and changes nothing about how they fuel the remainder of the day = Inadequate fueling.*

  • Option 2: The athlete celebrates via Instagram and then consumes a 1,500-calorie brunch = Excessive fueling.


Ideal performance nutrition reality: Help the athlete use the numbers to their advantage.


*Granted, if the athlete is on a weight-loss plan then a caloric deficit is required. However, if an athlete is training for multiple hours per day and burning hundreds to thousands of calories, they will be inadequately fueling their body.



Below are two examples of how to apply the EEE data to real-life scenarios. As a reference, a rest day for this athlete would still result in them requiring 2,000 calories ("daily needs") to promote weight maintenance.


Example #1: 45-minute Indoor Cycling Session


EEE: 540 calories

EEE + Daily Needs: 2,540 calories

Fuel Added to the Day:



Example #2: 2-hour Outdoor Hilly Cycling Session


EEE: 1,200 calories

EEE + Daily Needs: 3,200 calories

Fuel Post-ride:

  • Pressed by KIND bar (130)

  • 4 banana pancakes, each topped with peanut butter, plain Greek yogurt, and maple syrup (1,500)

  • 2 scrambled eggs (140)


Image 2

Example 1 defined the additional calories to compensate solely for the training session whereas example 2 listed a 1,770-calorie meal (more than the athlete burned while training). Consider what snacks and/or meals an athlete would skip had they not been training. In example 2, the athlete missed their morning snack, which wasn't fully replaced during training (i.e., with sport gels) and so were then added to their post-training meal. However, even though the morning snack and EEE were accounted for during the meal, the rest day's lunch calories are still unaccounted for.


Hence, long duration, high-EEE training sessions make it even harder for an athlete to meet their daily fueling needs—especially if they’re not consuming supplemental calories while training.


To account for this, get creative in how else you can add fuel to the athlete’s day:

  • Prescribe a higher-calorie breakfast than the athlete typically consumes.

  • Consume carbohydrates while training (e.g., energy chews and bars).

  • Consume a high-carbohydrate bar immediately after training.

  • Increase the calories within the post-training meal: For example 2, mashed and sliced bananas were added to the pancakes that were then layered with multiple high-calorie, high-protein options.

  • Continue to add calories throughout the day: For a taco dinner, add extra guacamole on tacos and with tortilla chips and use double-layered, larger-diameter corn tortillas (flour tortillas tend to add even more calories).

  • Replace water with high-calorie, nutrient-dense fluids (e.g., nut butter-based smoothies, flavored milk, and 100% juice).


The above high-calorie items can be added as snacks or ingredients throughout the day to help the athlete meet their high-EEE needs. Download my high-calorie handout here.


The harder, more intense the training session, the greater the likelihood of an upset stomach post-training. Athletes may not tolerate (or realistically be able to consume) 100% of their additional fuel needs at the post-training meal. It’s perfectly fine to spread this additional fuel throughout the day.



Take-home Message


If you decide to have an athlete collect EEE data, ensure you're explaining the purpose (tracking EEE) and what the end goal of doing so is (optimizing fueling and performance). Explain the benefits of fueling adequately plus the disadvantages of not doing so (read my blog on low energy availability).


Ultimately, be prepared to:

  • Look at the data!

  • Evaluate any EEE patterns: Have the athlete record multiple, different training sessions with a heart rate monitor. Does EEE for your athlete vary between training sessions or days (e.g., short run, long run, track workout, weight training)?

  • Create a fueling plan: Convert EEE into specific food and beverage suggestions for the athlete. Depending on their training schedule and EEE patterns, multiple fueling plans may be needed.

  • Be flexible and creative in how additional fuel is added throughout the day.



Further Reading


Organizes fluids and foods by group (e.g., cereals, bars) and provides tips per group on how to increase calories.


Whether it's intentional or unintentional, chronic low energy availability negatively impacts recovery, performance, and the body as a whole (e.g., fertility, mood).


If an athlete is drastically changing how they're training throughout the week, fueling needs also need to change. Otherwise, the ability to recover and improve performance will both suffer.


Apple walks you through best fit, choosing the right exercise, and updating your personal info.


A free online tool that helps you sync your Polar products and learn more about your training needs.


Plus, how each method works, plus the pros and cons.


Reviews the TomTom Cardio, Microsoft Band, and Fitbit Surge.

Thiebaud, R.S., Funk, M.D., Patton, J.C., Massey, B.L., Shay, T.E., . . . & Giovannitti, N. (2018). Digital Health,4:1-7.


Reviews the Polar H7 chest strap monitor; Scosche Rhythm+ forearm monitor; and the Apple Watch, Fitbit Blaze, Garmin Forerunner 235, and TomTom Spark Cardio watches.

Gilllinov, S. Etiwy, M., Wang, R., Blackburn, G., Phelan, D., . . . & Desai, M.Y. (2017). Med Sci Sports Exerc,49(8):1697-1703.

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