Training Slow to Race Fast: A Look At My Recent Run Data

Last weekend I ran one of the fastest 5Ks of my ten year running career after two months of slow, low-intensity marathon training. I crunched some numbers to show just how slow my training has been and mention why I think this unique approach of slowing down to speed up is so effective.

A Unique Approach to Endurance Training

Four years ago, I adopted an entirely new approach to marathon/triathlon training that relies on heart rate monitoring to build endurance in an optimal way. The approach focuses on doing most cardio training at relatively low intensities based on heart rate.

I’ve improved my speed significantly and gained a lot of confidence with this type of training for longer races like half/full marathons over the last few years, but was still surprised when I nearly PR’d a 5K last weekend without any speed work leading up to the race. As I’ll show later – I spent only 1% of my training at paces faster than 6:30 min/mile over the last two months, but was still able to hold a 6:00 min/mile pace at the race.

How can that be? The short answer lies in the fact that it’s your aerobic system (not anaerobic) that dominates during even the shortest road races, and the best way to build aerobic fitness is through low intensity exercise …

Training Slow to Race Fast

The training slow to race fast philosophy is a result of the principle of specificity – basically, we need to focus our training around exactly what we are trying to excel at. For example, a powerlifter is not going rely on hundreds of pushups to improve their 1 rep max on bench press, they need to build strength by lifting heavy. Similarly, a marathon run improves their performance not from 100m sprints at the track, but from long, sustained, sub-maximal efforts. Sprints primarily target the anaerobic system while low-intensity, long-duration exercise benefits the aerobic system. 

While many people know that the aerobic system is mainly responsible for the energy consumed during long events like marathons, most don’t realize just how important aerobic fitness is to shorter races like 5Ks. Check out the table below:  

The aerobic system produces around 90% of the energy needed for a 5K, and over 99% of the energy needed for a half/full marathon.  So – it’s clear that we need to focus on building aerobic fitness to succeed in endurance races and spend relatively little time on anaerobic capacity. The other piece of the puzzle is that the aerobic system is primarily utilized/improved while operating at low heart rates and intensities. This is motivation behind slowing down to speed up

While I could go on and on about this training philosophy (and will do so in a separate blog post in the future), here I’ll just focus on a data analysis study I did on all of my training run data from the last two months. This approach is also called the MAF method, and I’ve borrow a lot of my training ideas from this book, if you’re interested.

Crunching the Numbers

I analyzed my running data from the last couple months (11/19/18 – 1/10/19) leading up to the 5K race I did on 1/12/19 to break down my training intensity over that period. In total, I did 22 run workouts covering 190 miles over 27.5 hours

My target aerobic heart rate based on my age and running history is 150BPM, so I do a vast majority of my training at/below this heart rate to build endurance. The main result of my run data analysis is the following chart, showing the break down of my heart rate over the span of the 22 training runs considered:

The breakdown of my heart rate over two months of training runs

You can see that I spent 82% of my training time at a heart rate below 150BPM! And only 6% of my time at a heart rate over 160BPM. This means I only spent about 1:20 over the last two months running at what I consider to be high intensity. My guess is that this is probably pretty surprising to people who aren’t familiar with this specific type of training. 

Next, I looked at the breakdown of my pace over the last two months of training, which can be seen below:

The breakdown of my pace over two months of training runs

What I think is especially cool here is that I spent very little time running at my high end speed (only 1% of time spent running faster than 6:30 min/mi), but was still able to run my 5K at 6:00 min/mile pace! That’s only about 15 minutes over the last two months spent running “fast”! I think that this is really a testament to the importance of the aerobic system even for shorter races, and the ability to build aerobic fitness through low intensity exercise. 

Obviously, “fast” and “slow” are relative here. My slow might be your fast, and I’ll get smoked at my next race by plenty of faster people. But low intensity according to heart rate is more transferable. Chances are if you went out to run at 150BPM (or lower if you are older than me), it’s going to feel relatively easy. The coolest part of this type of training is that I’ve continued to get faster and faster at low heart rates as I’ve consistently practiced over the last few years. 

I visualized my running data in a couple other ways as well to take a more detailed look at my training. Below are histograms of my training pace and heart rate over the past two months, showing a more complete distribution of training intensity:

The histograms show most of my training centered around a pace near/below 8:00 min/mi and a heart rate of 150BPM.

Finally, I plotted my heart rate over time for each one of my 22 training runs, the graph is shown below:

Again, my focus of keeping my heart rate at or below my target of 150BPM for a majority of my training is clear. There are just a few exceptions of higher intensity training.

The Moral of the Story

I’ve been a strong proponent of the train slow to race fast philosophy to endurance training since I adopted it four years ago, training both myself and others to tackle half/full marathons and triathlons using the approach. The aerobic system is responsible for nearly all of the energy consumed during these long races, and the best way to build aerobic fitness is through low-intensity training based on heart rate. I was surprised, however, at how well I performed at a shorter 5K race using this type of approach, where I spent almost no time on speed work in the preceding two months. I attribute this to the fact that the aerobic system is still the dominating force behind powering you through even these shorter types of races.

If I wasn’t sold before on slowing down to speed up for endurance training, I certainly am now. And I have some data to back it up 🤓.

Have questions about the train slow to race fast approach? Interested in trying it out for your next endurance race? Contact me at!

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Jim Warner Fitness & Endurance Training

*USA Triathlon Certified Coach *ACE Certified Personal Trainer *NPTI Kettlebell Certification *NPTI TRX Suspension Training Certification *Conditioning Coach at Jungle Gym Strength & Conditioning, Newport News, VA *Amateur Endurance Athlete -Boston Marathon Qualifier -Ironman Triathlete -Cross-country Cyclist

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