Slow Down to Run Faster

jogging track

The long run is the key base endurance session in any weekly endurance training program. It doesn’t matter if you’re training for Sprint Distance or Ironman, it is necessary to maintain your run endurance throughout the whole season with a weekly long run.

Being the key endurance session it is important to know how fast you should be running. If you run too slowly, you won’t produce significant stimulus and adaptation. Run too fast and you run the risk of not being recovered for your next session. Making things more difficult, long runs can serve multiple training purposes, each with its own set of intensity and pace parameters.

So, what is the optimal intensity for your easy long runs? The following outlines the different types of long runs and examines the scientific literature behind easier long runs to help you determine your ideal pace for those sessions. This is why it is important to always follow your Coaches designated intensities at any session.

What is the purpose of your long run?

The first step to determining the pace of your long run is assessing the purpose and intensity of the run itself.

Not all long runs are created equal. Some long runs are designed to simulate marathon conditions or teach you how to finish fast. These types of long runs are considered a hard workout and therefore, you need to have extra recovery scheduled after your session to recover fully from this style of session.

On the other hand, some long runs are done at an easier pace and lesser intensity to build aerobic endurance by improving oxygen transfer pathways and get used to being on your feet for longer periods fo time. These styles of long runs aren’t exactly recovery runs, but they aren’t designed to be hard either.

Understanding the purpose of your long run is important because long runs are just one piece to the training puzzle. For example, race-specific long runs are an integral part of a training plan and can help take your running to the next level. However, if your long run is designed to be a relatively easy day and you run too hard, you’ll start your next workout too fatigued and risk poor performance or injury.

The Physiological Benefits

If your long run is easy – i.e., not a specific workout — then what is the optimal pace? Let’s look at some of the physiological benefits of the long run and see how pace affects the intended benefit.

Capillary Development

Capillaries are the smallest of the body’s blood vessels and they help deliver oxygen and nutrients to the muscle tissues. The greater the number of capillaries you have surrounding each muscle fiber, the faster you can shuttle oxygen and carbohydrate into your muscles. Various studies have shown that capillary development appears to peak at between 65-82% of MHR intensity (~70-95% ThresholdHR).

This isn’t to say that running really slowly (or much faster) on occasion doesn’t have any benefit. However, running much faster or slower than this pace doesn’t significantly increase or decrease capillary development.

Increased Myoglobin Content

Myoglobin is a special protein in your muscles that binds the oxygen that enters the muscle fiber. When oxygen becomes limited during exercise, myoglobin releases the oxygen to the mitochondria for use in creating ATP, or energy. Simply speaking, the more myoglobin you have in your muscle fibers, the more oxygen your muscles will have available to use to produce energy.

While all muscle fibres contain myoglobin, the ones we’re most concerned with targeting during the long run are the Type-I (slow twitch) muscle fibres. Research has shown that maximum stimulation of Type I muscle fibre occurs at about 68-82% MHR intensity (~75-95% ThresholdHR).

Increasing Glycogen Storage

The body stores carbohydrates as glycogen in the muscles for usable energy. While this isn’t important for races that last under 90 minutes, when racing longer, the more glycogen you can store in your muscles, the longer you can prevent bonking.

New research suggests that the brain can anticipate glycogen depletion, and begins to slow the body down gradually. The more glycogen your muscles are capable of storing, then the longer it will take, and the further you will be able to run, before your brain starts to slow your body down.

The goal with easy long runs is to deplete the muscles of their stored glycogen. The body responds to this stimulus by learning to store more glycogen to prevent future depletion.

The faster you run, the greater the percentage of your energy will come from carbohydrates. While there isn’t any scientific research on the optimal pace that burns significant carbohydrate while still providing enough energy to get through a long run, run coach Jeff Gaudette’s experience and study of training of elite runners has shown that a pace of about 75-80% MHR intensity (~80-90% ThresholdHR).

Mitochondria Development

Mitochondria are the microscopic organelle found in your muscle cells that contribute to the production of ATP (energy). In the presence of oxygen, mitochondria break down carbohydrate, fat, and protein into usable energy. Therefore, the more mitochondria you have, the more energy you can generate during exercise, which will enable you to run faster and longer.

Two researchers, Holloszy (1967) and Dudley (1982) published some of the more defining research on optimal distance and pace for mitochondrial development. In short, Holloszy found that maximum mitochondrial development occurred at about 2 hours of running at 50-75 percent of V02max. Likewise, Dudley found that the best strategy for slow-twitch, mitochondria enhancement was running for 90 minutes at 70-75 percent V02 max (75-80% MHR intensity/~80-90%ThresholdHR)

Here is a neat chart to sum up the research:

Physiological system %LaTHR Intensity %max Heart rate Pace for a 20min 5km TT runner
Capillary development 70-95 % 65-82 % 6 – 5min/km
Myoglobin content 75-95 % 68-82 % 5:50 – 5min/km
Glycogen storage 80-90 % 75-80 % 5:25 – 5:10 min/km
Mitochondria development 80-90 % 75-80 % 5:25 – 5:10 min/km

The body of evidence is clear: your optimal “easy” long run pace is between 68-80% MHR (~75-90% ThresholdHR) intensity.

It’s also evident from this research that running faster than 80% MHR or 90% ThresholdHR intensity on your long run doesn’t provide a lot of additional physiological benefit. Therefore, pushing the pace beyond this only serves to make you more tired and hamper recovery.

The research indicates that it would be just as advantageous to run slower as it would be to run faster. Regardless of your ability level, 65% MHR or 70% ThresholdHR intensity is pretty easy, but the research clearly demonstrates that it still provides near optimal physiological benefits.

If you’re feeling tired and the long run isn’t scheduled to be a “hard” day, don’t be afraid to slow it down. Start on the slower side of the pace recommendations (65% MHR or 70% ThresholdHR intensity) and slowly pick it up throughout the run if you feel good. The long run is one of the staples of your training week – make it count!

*All references are from ‘How fast Should Your Long Run Be?’ by Jeff Gaudette – US Run Coach. Related Tag: Triathlon Training Club Melbourne

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