Whether it is from your coach of from your hours of online research regarding “how do I run faster????” you’ve probably heard that the answer to this question is to cool the jets. The following will hopefully provide some insight as to why running your long runs or slow runs slowly is helpful. Firstly, the simple truth is that running wears you out and if you do all of your runs at a moderate to high intensity, you won’t be able to hold a substantial volume of running training without breaking down. The physiology behind this works as follows: your sympathetic nervous system is strained when you spend an extensive amount of time near your threshold intensity. By lowering the intensity into the aerobic zone, you allow your mitochondria to build in size and number which results in sustained energy production during long runs. Working in your aerobic running zone also allow you to expand your capillaries. As a result, you become more efficient at delivering oxygen to your muscles. Thus the time spent in the lower zones is valuable to your physiology as well as beneficial to preserving your sympathetic nervous system.
Secondly, running slowly helps to build your aerobic capacity. You can think of your aerobic capacity as a boat. In that boat you can put things such as power, speed, speed endurance, and a long list of other helpful components that make you a better and stronger runner. However, if your aerobic capacity is small- ie you have a small boat- you can’t fit much in there. By working in your lower zones you are building the lower end of your heart rate fitness and designing a wider boat into which you can put all of your other running components. If you only focus on higher intensity training, you are only building half of the boat that your body is capable of building and therefore your capacity to build upon your fitness will be limited.
The pesky thing about running slowly is that it is not a fancy or glamorous workout. You don’t win Strava points from running slowly…nor do you experience any of the endorphin highs that come with a certain heart rate while running. However, the value of running slowly or at a low heart rate, is incredibly useful for endurance athletes by way of saving your legs and a key component to building a strong aerobic capacity.