Karina Krepp
5 min readJun 15, 2021


I’ve been coaching runners toward their goals for years. A key to success for those tackling the couch to 5k and runners interested in going toe to toe against their personal best? The interval run! When we first lace up our shoes and decide whether to turn left or right out the door we begin a journey to an inner destination as well. Every breath married movement aligns us with our bodies and our thoughts. Interval runs give us the structure to integrate our upgraded thoughts during shorter challenges. They also provide unique physiological upgrades; helping us shift our metabolism, burn more fat and safely improve our run pace.

Before I knew anything about the sport, I thought I was a terrible runner. I would go and run as hard as possible until I had to quit. And since I couldn’t go very far at my full out pace, I thought I was no good! Little did I know I had tapped into the format for greatness without understanding the mechanism.

Interval run training refers to a fixed use of time to change the intensity of the run and build in an active recovery. There are great interval timing apps that are free to download. The apps allow you to set the timer to your length of choice. The bell dings to begin your set ‘on’ interval and then dings again to begin the recovery ‘off’ interval you preset.

Last week, I had my runners work with a 30 second ‘on’ interval at the rate of perceived exertion 7 or 8. Then they recovered for 1 minute at an RPE of 4 or 5. RPE of 7–8 is what I call: short answer running. Your fellow runner asks, ‘How was brunch with your Mom?’ You are only willing and able to give a short answer: ‘Good.’ RPE 4–5 is what I call: long answer running. Same question ‘How was brunch with your Mom?’ And you feel like you can give the long answer: ‘So good, thanks for asking. She’s settled into her new house and is making new friends.’ Interval training can work with any time and RPE ratios to meet your desired outcome.

When I look at my runners’ interval workouts, I want to see a heart rate spike for the ‘on’ timer and a big drop in their heart rate for the ‘off’ time. If that means you need to walk or pace for the recovery portion, do so! The benefits come from the peaks AND valleys. We need the recovery to stimulate the training benefits. This seems to be the hardest part for many runners, keying into the easy recovery will make you stronger tomorrow. So leave your ego for the ‘on’ segments and roll it way back for the ‘off’ interval.

Interval running moves us into and out of our habituated pace for several key benefits. Firstly, we can change the intensity demand on the body and stimulate more of a fitness response within the same time duration. So your 20 minute run has greater physiological benefits with interval running than with steady state running. Secondly, we become more aware of our physical experience when we are changing the demands. So we stay in our body and feel how pace intensity changes sensation on a physical level and also on a mental level.

We are able to practice and then eventually habituate a new pace using the interval format. This is a great way for beginners to combine the walk/run interval as they are normalizing the stress of a new sport on their joints, ligaments, muscles and tendons. It also is how the elite runners shave seconds off their winning times, by practicing the push pace until their body grows more efficient at that pace.

What do I think is the greatest value? Listening to our thoughts when things get harder. Whenever we move outside our comfort zone we have a whole slew of thoughts that may not be very helpful to our overall goals. During these short bites of hard work you can witness your self-talk during the hard parts. I use the recovery time to rewrite my mental script. I ask myself the three questions: Is it true? Is it kind? Is it productive? If I’m being really hard on myself I’ll also ask myself: Would you say that to someone else? Most of the sport is supported by making friends with your mind. Interval training offers great opportunities.

As you wander into the wonderful land of interval running, keep your ratios kind. Start with short pickup sections and triple long recoveries. So jog for 15 seconds and 1 minute fast walk. Or an easy run for 15 seconds and then slow jog for 1 minute. Keep your time out on the run the same, if you usually go for 20 minutes, do a five minute low pace warm up then 5 minutes at your usual pace. Work your intervals for 8 minutes and recover for 2 minutes at your low pace. Since we are adding intensity we don’t also add time. Play with it. If I don’t have a timer on me, I use light posts, trees or I count my steps. Sprint for two light posts, walk for one light post and jog for three light posts then repeat.

In some training plans you will see ‘fartlek’ in your plan. A fartlek is a Swedish word that means ‘speed play’. Fartleks are similar in that they change the pace of the run during the workout. However, there isn’t a built in recovery phase. A fartlek workout mimics the surges during a race to pass another runner. So we start at our race pace and surge up then return to our race pace. We wouldn’t see the tell tale heart rate peaks and valleys of a good interval run. The heart rate of a fartlek will look more like rolling hills.

Most training plans have one quality workout per week when we are focused on changing how we load the body by changing the stimulus. It is often a midweek day and you will see requests for hill work, tempo work and intervals, too. The workouts usually aren’t terribly long and can be good fun. I love doing them with a group! Make sure you can chat during your recovery intervals. If not, they need to be slower and longer to add the benefits we seek.

Intervals add quality. They give us time to feel discomfort and the safety of knowing it is only a short term. We can watch our thoughts during the difficult work and change our mind on the recovery. Give yourself the gift of knowing who you are when things get hard. Practice increasing your self kindness using the interval run as a format. You will get faster, leaner and more fit for service.



Karina Krepp

NYC personal trainer for over 26 years. Certified CHEK IMS2, Holistic Lifestyle Coach, Yoga Alliance 500, RRCA, ACE and TRX.