Applied Exercise Science

Heart Rate Reserve, Fractional Utilization & Velocity-Duration

To kick off 2024, I sorted my most popular videos into playlists.

1. Applied Exercise Science

2. The Multisport Marathoner

3. Building Your Annual Training Plan

4. Dead Simple Loading

5. Lactate Testing

6. Building Your Annual Plan

7. Endurance Essentials Audio Book

Over time, all of the above will make their way into the eBook.

Today we’re going to link science to speed. We start with:

1. Heart Rate Reserve

2. Fractional Utilization

At the end, we are going to combine the two and add velocity.

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Heart Rate Reserve

Heart rate reserve lets us compare, roughly, between athletes, and between sports (for the same athlete).

The concept is simple:

• At rest, we have 100% of our heart rate reserve available to us.

• At our maximum heart rate, we have no reserve available.

For example, when running at a heart rate of 140 bpm…

• If our resting heart rate (RHR) is 50 bpm, and

• Our maximum heart rate (HRmax) is 170 bpm, then…

• Our effort is equivalent to 75% of heart rate reserve (HRR or HRreserve).

Walking you through the calculation:

• The reserve is 120 bpm (170 bpm HRmax - 50 bpm RHR).

• The 140 bpm effort uses 90 bpm of the reserve (140 bpm - 50 bpm RHR)

• Therefore it represents 75% of heart rate reserve (90 / 120 = 75%)

Figure 1 - A calculation of heart rate reserve (HRR or HRreserve)

Tips for calculating heart rate reserve:

• Use a seated resting heart rate. Take it in the morning, with both feet on the floor. We each have a normal range. Use the midpoint of the range.

• Maximum heart rate is sport specific. For example, most of us will have a higher maximum heart rate running than swimming/biking.

Even though we are working with numbers, our day-to-day physiology is not precise. There will be variation in the velocity we can produce for a given percentage of heart rate reserve.

You will find additional tips in the video (below).

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Fractional Utilization

In an athletic setting, the most common usage of “fractional utilization” is with respect to VO2max.

• In Chapter Two, we shared a protocol for determining running velocity at VO2max (vVO2 or vVO2max). The protocol is a six-minute best-effort test.

• If you haven’t performed the six-minute test, then you can estimate vVO2 by using the speed of the final step of The Full Profile test shared in Chapter Two.

• Similarly, for cycling, you can perform a six-minute test or use the average power from the final step of a recent Full Profile.

• Same thing applies for swimming and any other mode of exercise.

The calculation of fractional utilization is simple. An example:

• An athlete has pace at LT1 (the border between Easy / Zone 1 and Steady / Zone 2) of 12 kph.

• The same athlete has a Zone 4 pace of 15 kph, determined from a recent test or race.

• Finally, recent testing showed a vVO2max of 18 kph.

We can calculate the breakpoint percentages as follow:

• LT1 pace is 67% of vVO2max (12 / 18 = 0.67).

• LT2 pace is 83% of vVO2max (15 / 18 = 0.83).

The video below offers tips about interpreting breakpoints relative to personal fitness profiles. The framework applies more broadly than running.

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Combining The Two

Heart rate reserve and fractional utilization can be used to discuss optimal race strategy.

Consider:

• Where do I get the most relative speed for a given effort? Each of us has a velocity-duration profile by sport. We build this profile via key workouts, progressive sets and race data.

• What strategy makes an excellent result more likely? There are underperformance risks with every strategy. Aiming for a negative split (by effort) has a higher probably of success than a take-it-out-and-hold-on approach.

Our profiles change in important ways:

• Due To Time & Fatigue.

• Across A Multisport Event.

  • Triathlon: Swim, then Bike, then Run

  • Duathlon: Run, then Bike, then Run

  • SwimRun: Run, Swim, Run, Swim…

• For A Given Set of Environmental Conditions.

In building a race strategy, it is NOT a case of taking a series a lifetime bests, resting a bit then hoping to combine them on game day.

We are going to be racing “below the curve.” The curve being a plot of our best velocity-duration performances.

Start by looking at past race data.

• Where did I place my greatest relative effort?

• Did I achieve the expected velocity for my efforts, especially in the second half of the event?

• How might I generate additional overall speed, by changing where I place my efforts?

Most underperformance is hidden.

• When we “blow-up” at an event, it’s clear we underperformed.

• What’s more common is the herd racing off and damaging their collective late-race performance.

It takes uncommon patience to deliver our fitness on race day. Use these tools to be strong at the end. There is a massive psychological benefit from finishing strong.