Run Recovery Series: the Cool Down Run

Good run recovery has benefits across the board, from reducing the amount of time needed between runs to less overall fatigue, fewer injuries, and improved performance. In fact, what you do after your run is arguably as important as the run itself.

In the Run Recovery series, we will be looking at optimizing your post-run recovery. Today we dig into why it’s a good idea to run again after you’ve finished running. Let’s get into it!

Myth Busting

You might be aware of the term ‘recovery run’. This is a short run performed at a slow pace, after a hard effort. As the name suggests, it is supposed to help your legs recover by ‘flushing out’ the built-up lactic acid and replenishing the blood supply to the muscles. This, in turn, reduces muscle soreness and shortens the gap required between hard efforts.

This has been standard practice for years. There’s just one problem: it’s based on poor science!

Lactic Acid: Fuel or Foe?

Historically we have believed lactic acid to be a waste product, a by-product of the energy production process. Glucose and glycogen are metabolized in muscle cells using oxygen. During a hard effort when oxygen is in short supply, cells produce lactic acid as a kind of metabolic waste. Lactic acid, we have been told, causes muscle fatigue, pain, and reduced performance.

Contrary to popular understanding, however, lactic acid is not a waste product that needs to be flushed out of the muscles. In fact, lactic acid will naturally empty from the muscles within an hour of a hard effort, regardless of whether you perform a ‘recovery’ run or not.

Lactic acid or lactate is actually one of the body’s major sources of fuel and is produced by cells all the time, not just when there is a lack of oxygen. During intense activity, when the body is under stress, the heart and brain even prefer to use lactate over glycogen or fat as fuel.

Lactic acid is not your enemy. It does not need ‘flushing out’ and it is not the cause of muscle fatigue. Muscle soreness is most likely caused by muscle fiber micro-tearing and resulting inflammation.

Pre-Fatigued Running

Now that we have dispelled the lactic acid myth, you may be wondering why you should still perform a ‘recovery run’. If recovery runs don’t actually help with recovery, what do they do?

The significant benefit of running after a hard effort is to increase fitness. Running slowly in a “pre-fatigued” (already tired) state helps the body adapt to running on tired legs. You will often see elite runners performing a hard effort or key workout in the morning and running slowly again in the afternoon.

This also helps the body adapt to metabolizing fat more efficiently as fuel over glycogen, enabling you to run further for longer on fewer sugary gels or sports drinks.

You will also notice some runners, having just completed a fast 5k or 10k race, jogging immediately afterward. Running on tired legs is proven to improve fitness over simply resting.

Heart Health

Performing a cool down run immediately after a hard effort is also sensible in terms of maintaining healthy heart function and returning your body to its resting state. This is also why you should warm up before a key workout. We want to avoid putting the heart under too much stress at the beginning or end of our workout.

Gradually increasing our HR is preferable to shocking it into a sudden all-out effort. In the same way, gradually reducing HR at the end of a workout or race is preferred to a sudden stop. This will also help prevent dizziness or fainting.

Zwift Workouts

You will notice that all workouts in Zwift, whether they are individual or group workouts, have a cool down period built into the end of the session. But races do not! So it is important to remember to jog lightly for a few hundred meters at the end of your race on Zwift, as you would outdoors.

Your cool down run should be carried out in heart rate zones 2 (green) or 3 (yellow) as seen at the top left of the Zwift screen.

Wrapping It Up

While cool down runs have nothing to do with ‘flushing out’ lactic acid, performing a cool down at the end of a key session will help your heart and breathing return gradually to resting levels. Additionally, running slowly on tired legs either immediately after or within 24 hours of a hard session will improve fitness and enable you to run further for longer on less processed sugar.