Heart Rate Based Training for Runners
By GRP Skier Adam Martin
I use heart rate as an important metric to prescribe, log, and monitor my training. I think everyone can learn something from heart rate based training methodology whether it’s a better understanding of their current training style or a new training method to try.
When we exercise there are myriad physiological factors that contribute to fatigue, but heart rate responds to all of them. In efforts longer than 2 minutes, heart rate provides a reliable metric for how hard the body is working. Thinking about heart rate while training emphasizes effort rather than speed or pace. This allows for better comparisons between different terrains, surface types, wind conditions, and even different sports. Further, it brings our attention to the physiological systems that we aim to improve in each session.
In this blog, I provide necessary exercise physiology background, discuss heart rate levels, and conclude by talking about complete heart rate based training plans. To try these ideas yourself, you will need a heart rate strap that connects to your running watch. Most major watch brands sell straps that interface with their hardware for $50 to $100. A strap is important, because wrist based heart rate is not accurate enough at exercise level intensities.
Me enjoying a long level 1 run on one of my favorite trails in Marquette, MI.
Background Exercise Physiology
How the Body Meets Energy Demands
Within muscle cells, myofibril filaments contract, shorten the muscle, and move the body. These contractions require energy which is supplied from several categories of energy production. Two important ones for distance running are the anaerobic glycolytic system and aerobic oxidative system.
Glycolytic System
Glycogen → Energy + Pyruvate + H⁺
The glycolytic system involves a series of chemical reactions within the cytoplasm of our muscle cells. Glycogen (or stored sugar) is broken down releasing energy, pyruvate, and hydrogen ions. As the process continues, hydrogen ions buildup, which causes the acidity within the muscle cell to increase, which causes the enzymes controlling glycolysis to stop working. Consequently, without a system to process the hydrogen ions, the glycolytic system can only produce a limited quantity of energy.
Oxidative System
O₂ + Pyruvate + H⁺ → Energy + CO₂ + H₂O
The oxidative system comprises a series of chemical reactions within the mitochondria of our cells. The system is very complex, but two processes, known as the Krebs cycle and electron transport chain, ultimately convert oxygen, pyruvate, and hydrogen ions into energy, carbon dioxide, and water. The oxidative system can also burn protein and free fatty acids (fat), but these fuels require more oxygen per unit of energy produced. Lastly, the oxidative system’s capacity is limited by the size and number of mitochondria in our cells.
Lactate
Despite its bad name, lactate is crucial to athletic performance. Lactate is formed when a pyruvate molecule attaches to two hydrogen ions. Lactate molecules can then be removed from the muscle cell and transported elsewhere. In other muscles and the liver, the lactate molecules are converted back into pyruvate and hydrogen ions and processed by the oxidative system in these locations. This lactate shuttling lengthens the amount of time the glycolytic system can function above the oxidative system’s capacity. However, eventually lactate accumulates faster than it can be removed, and the glycolytic system will stop working due to the building acidity.
Circulatory System and the Lungs
The circulatory system supplies muscles with fuel, removes carbon dioxide, and shuttles lactate to other muscles. Consequently, heart rate provides an easy way to measure the whole energy pipeline. Finally, the lungs add oxygen and remove carbon dioxide from the blood.
Lactic Acid Threshold
At low level sustained exertion, the body's oxidative system is fully capable of meeting the required energy demand, so lactate doesn't build up. However as exercise intensity increases, eventually the oxidative system cannot process the pyruvate and hydrogen ions from the glycolytic system as quickly as they are produced. At some point, lactate (pyruvate + 2H⁺) builds up exponentially. Just before this point, when lactate shuttling and the body's oxidative system are just capable of keeping the buildup of lactate in check, is referred to as the lactic acid threshold. It's an important concept for running performance and a metric we aim to improve.
Notice that the oxidative system assists in two ways: it produces energy and also clears hydrogen ions allowing the glycolytic system to continue functioning. In the book The Uphill Athlete, the authors refer to the oxidative system’s capacity to process hydrogen ions as the aerobic vacuum, and they explain that a high aerobic capacity allows for higher sustained glycolytic energy production.
The red line references a third rapid energy system that we didn't discuss. Notice that the yellow line (glycolytic) peaks around 30 seconds but still contributes to energy production for longer durations. The green line (oxidative) increases as the duration increases. *Chart from MetriFit.com
Energy Availability
The body stores enough glycogen to run at marathon intensity for roughly 2 hours. This is sufficient for many running events, but for longer events, the body taps into fuel that is ingested during the effort and free fatty acids. Compared to the energy demands of a single running event, there is an unlimited amount of energy stored as fat in the body. However, the downside of this inexhaustible fuel source is that free fatty acids can only be burned by the oxidative system, and they require more oxygen to metabolize than glycogen. All this means that running feels harder when glycogen stores begin running low.
Other Important Physiology Concepts
Neuromuscular Efficiency
Every running stride begins with a series of precise neural impulses in the brain. Through repeated firing, the pathways themselves become more efficient through enhanced myelination, and the movement patterns improve at both the macro and micro level.
Muscular Endurance
Every time we land in the running stride, our leg muscles perform eccentric muscle contractions to slow our fall. This contraction while the muscle is lengthening creates micro tears in the muscle similarly to lifting weights. These tears contribute to fatigue at the end of long runs and make us sore even when we’re well trained for the effort.
Elasticity of Tendons and Muscles
Although eccentric contractions while running are structurally taxing on our muscles, the tendons and leg muscles recapture some of the downward energy and return it in the following stride. As a simple demonstration, try jumping as high as you can with a standing broad jump. Now, if you first jump from a 1 foot high box and explode off the ground, you will probably be able to jump higher.
Muscular Strength
Finally, a runner’s strength to weight ratio can be a limiting factor when trying to sprint, run up steep hills, or support high forces of fast downhill running.
Training
The basic principle of training is that when a workout breaks down the body, the body will repair and grow so that it’s more capable of handling a similar stress in the future. The graph below illustrates how performance first decreases and then increases after recovery.
*Graph from Medium.com
A simplistic application of this principle is to repeatedly run a 5k all out every 3 - 6 days in order to prepare for a final 5k race. Especially, if the runner is not experienced, this will probably yield improvement, but training physiological components individually yields better results.
Division of Physiological Systems for Training Purposes
My college coach, Sten Fjeldheim, broke the physiological systems into two categories for training purposes. In the book, The Uphill Athlete, the authors describe a similar division with different names.
Peripheral Systems
Glycolytic energy production
Oxidative energy production
Lactate shuttling
Neuromuscular system
Blood capillarization around muscle cells
Muscular endurance, elasticity, and strength
The peripheral systems adapt slowly to training stimuli. However the body will continue to adapt for a long time and will lose these adaptations slowly in the absence of any stimulus.
Central Systems
The heart
The lungs
The central systems adapt relatively quickly to training stimuli. However the body has a limited window of optimal responsiveness and in the absence of training stimuli will lose these adaptations more rapidly.
Heart Rate Levels
Since heart rate corresponds to how hard the body’s energy pipeline is working, heart rate ranges enable us to dial in on specific physiological systems.
| Level | Primary Physiological Systems |
|---|---|
| 1 |
|
| 2 |
|
| 3 |
|
| 4 & 5 |
|
| All Out Intervals ≥ 1 min |
|
| Sprints ≤ 30 sec Speeds |
|
| Strength Plyometrics |
|
*For very short duration efforts, the bottom 3 rows, heart rate lags behind effort, so heart rate level is not a good indication of current intensity.
Notice that as the intensity level progresses from easy to hard to isolated strength, the primary physiological systems shift from peripheral to central and back to peripheral.
Importantly, the amount of training stress for any system corresponds to the amount of time that system is stressed. For example, even though levels 4 and 5 place maximal stress on oxidative energy production, the levels cannot be sustained as long as level 3, so levels 1 through 3 are better tools to stress the body's oxidative energy production.
Defining Heart Rate Levels
The upper and lower limits of each heart rate level are defined as a percentage of the person's maximum heart rate. If you use a heart rate monitor regularly for training and racing, you can find your maximum heart rate by looking back at the highest value you've recorded in the last year. If not, Alex Hutchinson designed a running test on the track to find your max heart rate.
Warm up running easy (at least 15 minutes).
On the Track:
Run 1 mile at tempo pace. (Depending on your half marathon time, this will be close to or a little faster than that race pace, but it's important you don't run too hard and flood your legs during the tempo piece.)
Then run directly into 400m gradually picking up your pace.
Finally, run directly into 400m all out.
(Cool down)
When you are done look at the highest heart rate you recorded. I suggest adding 2 bpm to this, because I think you could run a bit harder if you were being chased by a pack of wolves. In fact, I recommend this adjustment even if you regularly use a heart rate monitor and base your max heart rate on observed values within the last year.
You could also do this test off of a track, but any downhills or steep uphills will make it less likely to reach your max heart rate.
Heart Rate Levels Chart
With your maximum heart rate and the percentages below, you can calculate the upper and lower limits for each level.
Since heart rate is a whole unit measure, for each level, I multiply the lower percentage limit by my maximum heart rate and round the result to find that level’s lower heart rate limit. Then I use 1 heart beat less than the lower limit of the next level as the level’s upper heart rate limit.
| Level | Percent of Max Heart Rate | Max HR = 160 | Max HR = 175 | Max HR = 190 |
|---|---|---|---|---|
| 1 | 50 - 72% | 80 - 114 | 88 - 125 | 95 - 136 |
| 2 | 72 - 82% | 115 - 130 | 126 - 143 | 137 - 155 |
| 3 | 82 - 87% | 131 - 138 | 144 - 151 | 156 - 164 |
| 4 | 87 - 92% | 139 - 146 | 152 - 160 | 165 - 174 |
| 5 | 92% - Max HR | 147 - 160 | 161 - 175 | 175 - 190 |
Notice how low the heart rate is for level 1. My level 1 running pace is about 3 minutes per mile slower than my half marathon pace, so even when we’re running quite slowly, we’re applying a stress to our oxidative energy system. And if we’re also thinking about proper technique, we’re honing our neuromuscular control for higher speeds too.
Most watch brands allow you to program in custom heart rate zones. This makes it easy to see which level you’re exercising at and also provides helpful summaries at the end of each workout.
A Heart rate based training Plan
Workout Outlines
The chart below illustrates how to build a workout around a particular heart rate level.
| Level | Approximate Interval Duration | Total Time | Frequency | Sample Workout |
|---|---|---|---|---|
| 1 | 20 min - 5 hours | ≤ 10x / week | 2.5 hour long run or bike with 5 pickups | |
| 2 | 20 min - 1 hour | ≤ 5x / week | 30 min pre-work run | |
| 3 | ≥ 6 & < 12 min | ≤ 1 hour | ≤ 2x / week | 20 min L1, 5x8 min L3 with 2 min rest, 10 min L1 |
| 4 | ≥ 3 & < 5 min | ≤ 24 min | ≤ 2x / week | 20 min L1, 6 min L3 with 3 min rest, 4x4 min L4 with 3 min rest, 10 min L1 |
| 5 | ≥ 2 & < 3 min | ≤ 12 min | ≤ 1x / week | 20 min L1, 6 min L3 with 3 min rest, 4x3 min with 3 min rest (L4 for 1 min, L5 for 2 min), 10 min L1 |
Generally, aim for 1 to 2 (maybe 3) total workouts above level 2 each week.
At this point, we’ve covered enough background to understand why it is so important to run slowly in dedicated recovery workouts. Consider a training plan with an easy 1 hour level 1 run in the evening and hard level 4 intervals the following morning. The athlete may feel good and be tempted to run faster, more like level 2, for the evening run. If they do this, they may induce slightly more adaptions for the level 1 and 2 systems, but they will also accumulate significantly more fatigue. Now, due to the extra fatigue, when the athlete tries to do level 4 intervals the following morning, they aren’t able to run much harder than level 3. In this exaggerated scenario, the athlete isn’t able to stress their central systems and doesn’t run long enough to properly stress their level 3 systems. The result is that they fall short on adaptions from one of their two key weekly workouts and still accumulate the fatigue from slogging through the workout. Prioritize feeling good for high intensity workouts!
A General Heart Rate Based Training Plan
As a starting point, pick a target date to reach peak performance. The training plan will cover from now until that date and will be divided into two periods. Working backwards, the later period will be about 10 weeks long or ½ the training plan length, whichever is shorter, and the first period will span the time until the second period begins. Based on the physiology we’ve covered, we will prioritize stressing different physiological systems within each period.
Period 1
Period 1 lasts at least ½ of the training plan and is very important for long term development.
Workouts to Prioritize
Levels 1, 2, & 3
Pickups & sprints ≤ 30 sec
Strength & plyometrics
Notice the emphasis on intensity levels corresponding to the peripheral systems. These adaptations will last through the end of the training plan and provide a springboard for more effective central system training later on.
Period 2
Period 2 will take up roughly the last 10 weeks or second half of the training plan (whichever is shorter).
Workouts to Prioritize
Levels 4 & 5
Sprints ≥ 1 min
Race and sport specific workouts
These intensity levels correspond to the central systems. After the base building in period one, the central cardiovascular system will respond rapidly to level 4 and 5 workouts. Even though low level sessions are not a priority, they will still play a role in warm ups, cool downs, and recovery sessions.
Also during this period, specific workouts mimicking the sport, terrain, and surface of the target event will help translate all of the general training adaptions built so far into race specific ability.
Personalizing the Training Plan Template
An ideal marathon training plan will look a lot different than an ideal 5k training plan, but I believe both can be drawn from the above general template. To design your own personalized plan, begin by anticipating the limiting factors for your target event and your own personal strengths and weaknesses. There are three main things to adjust: the length of each period, the degree to which you prioritize a training period’s primary workouts, and how you implement workouts for each level.
5k Running Race
VO₂ max is likely to be the primary limiting factor for a 5k race. VO₂ max represents an athlete’s cardiac capacity (a central system) and running muscle’s ability to draw oxygen from the blood (peripheral systems). Since cardiac capacity plays the bigger role, central systems will be the emphasis.
Considering this, I recommend beginning the second period a full 12 weeks before the target race (up to ⅔ the total plan duration). In the first period, I suggest keeping level 4 or 5 intervals (or workouts with sprints ≥ 1 min) every 1 -2 weeks, and in the second period, nearly every workout will be designed to stress the central system. Finally, in the first period, I advise limiting level 1 runs to 2 hours in duration. Muscular durability isn’t important for a 5k, and the extra effort is wasted fatigue.
Half Marathon
Lactic acid threshold will be an important factor for half marathon performance. While lactic acid threshold corresponds to peripheral systems, a small amount of central system training will ensure the central systems aren’t strained at race pace and will also better allow the athlete to dig at the end of the race.
For these goals, I advise preserving the period 1 and 2 time allotment and keeping a level 3 workout nearly every week in the second period. For level 4 workouts, try adding level 4 intervals directly after level 3 efforts (for example 4x[7 min L3 immediately followed by 3 min L4] w/ 3 min rest) and pushing a few period 2, level 3 style workouts to a low level 4 heart rate.
Marathon
The limiting factors for a marathon depend on finishing time, but muscular endurance, the body’s ability to consume energy while running hard, and lactic acid threshold will likely play big roles. Peripheral systems will be a priority in this training plan.
I recommend period 1 make up at least half of the training plan length, and within period 1, it won’t be necessary to run any level 4 or 5 workouts. Long level 1 runs and level 3 workouts with a high total on time (but at the low end of the heart rate range) will be the priority. During period 2, there will be a few workouts with level 4 heart rates, but they will be marathon focused implementations. Try an intensity day with a 50 min effort beginning at level 3 and slowing increasing to a really hard effort for the last 10 min. Another marathon specific period 2 workout is a long run with 30 to 40 minutes of level 3 or higher intensity at the end. Finally, since energy replenishment will be crucial on race day, it is important to practice fueling during the hard period 2 workouts.
My reflex is to immediately lap my watch at the finish line.
Words of Warning
Activities with a high muscular load will be more fatiguing than heart rate indicates, and fatigue and other factors can also reduce heart rate for a given effort level. If heart rate itself is the goal of the workout (like in levels 4 and 5), it’s best to replan for a more rested and effective workout. Further, if you suspect your heart rate is suppressed from fatigue, it’s probably an indication to back off and let your body super compensate. Otherwise, if it’s not a central system focused workout and you don’t feel tired, it will be fine to exercise at a lower heart rate; you’ll still effectively accrue peripheral adaptations.
Good Luck!
We’ve covered basic exercise physiology and how to optimally stimulate each system in specific workouts and a broad training plan. I hope this provides you with a better understanding of how each of your workouts will help you improve. And if I’ve also persuaded you to start monitoring heart rate while you run, I hope you enjoy this new power.
Resources
I’ve accumulated the information within this post from influential coaches, pivotal books, and a 10 year elite training history full of curiosity. It is worth mentioning the sources below.
Pepa Miloucheva GRP Skiing Head Coach: MS in Biomechanics
Sten Fjeldheim Northern Michigan University Division II Head Skiing and XC Running Coach (Retired): MS in Exercise Physiology
Influential Reading
Physiology of Sport and Excercise Textbook by W. Larry Kenney, Jack H. Wilmore, and David L. Costhill
The Uphill Athlete by Steve House, Scott Johnston, and Kilian Jornet
I also love Alex Hutchinson’s Outside Magazine Sweat Science column.
Additionally, I looked up these topics and charts specifically for this blog.