What's Up with Interval Runs Hurting So Much

As we get closer to spring track and community races, another companion will soon join us...interval runs!  There are many ways coaches organize these but there is one consensus point about them:

They HURT.

I’m here to tell you, they never stop hurting.  Even when you get in better fitness, you just do them faster or with less rest...sometimes both.  

Why do they hurt and how can you decrease the suck just a little bit?

Intervals runs are made to help you hold pace at higher speeds longer. 

To drop some science on you, in your muscles (and really all of your cells) you have an organelle called “mitochondria”.  This is the engine of your cell.  They take oxygen and the metabolized sugar (or fat) and turn it into a chemical called ATP, which is essentially energy itself.  

The more of these you have, the more energy you can use.

The more of these you have, the better you can buffer lactic acid, pushing back the “hitting the wall” feeling.

The more of these you have, the higher speeds you can run at because your body is more efficient at using energy. 

The adaptations of well done interval runs turn you from having the fuel efficiency of your grandad’s old pick up truck to the efficiency of a 2021 Tesla Model S. 

Intervals runs are in essence, repeated fast runs.  For sprinters, this is often in the form of 150m-400m repeat sprints, often 6-12 sprints depending on factors like time of year, athletic ability, fitness, etc.  For long distance runners these often range from 400m repeats to mile repeats.  

These are not the same as tempo runs.  Tempo runs are relatively slow compared to top speed with very short rest.  They are cardio, just not continuous.  Though they serve the same purpose, they are less intense.  Interval runs are fast & have a longer, but still incomplete rest that builds up throughout the workout.  Tempo runs take much longer to build up outstanding fatigue.

So why do they hurt?

Well, in order to get the mitochondria to increase in number, you have to prove to your body that you don’t have enough.  To do that, you have to run fast, get tired, rest ALMOST enough to replenish your energy, and then run again. 

And repeat that process over and over and over so that the fatigue chemicals (lactic acid and the gang of other by products of running fast) keep building up each rep until you can’t run at said pace any longer.

That hurts.  


Every time you improve after so many weeks, you must decrease the rest, add distance, increase speed, or increase reps to make sure your body gets more of a challenge. 

That’s why everyone from world class olympic athletes to 11 year old runners hate intervals. 

What can you do to make them hurt less?

  • Eat high quality carbs (particularly starchy plants) & veggies.  Making sure your body is full of glycogen (starch) and vitamins and minerals allows your body to push back the fatigue of the workout session by providing you with enough energy to make it through.  

  • Mentally prepare yourself for the suck.  

  • Improve your overall aerobic ability.  Your aerobic fitness influences how fast you recover.  Poor aerobic capacity makes you really bad at these and makes them hurt A LOT.  


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