Every well-designed training plan for distance runners will contain elements of both hard runs and easy runs. The ratio of these elements will vary dependent upon the athlete, and the distance for which they are training. Many training plans, even of the most elite runners, favor an easy pace for 80-90% of training load with only 10-20% reserved for hard runs. Intuitively we all understand the importance of speed work and running hard for improved performance, but often overlooked is the importance of taking it easy.
Why Take It Easy?
There are many metabolic benefits to running easy that will contribute to your overall development as a runner. Some well-studied benefits include mitochondria development, capillary development, and increased myoglobin. As an added benefit, your body will prioritize body fat as a fuel source at lower intensities. Most importantly, you are able to achieve these benefits while keeping the stress on the body at a low level.
Stress + Recovery = Growth
It takes the body 30-60 hours to recover from a high-intensity workout. This includes long runs which, though done at easy pace, exhibit stress on the body simply due to the duration. Easy runs enable the body to reap the benefits of aerobic training and even recover better from high-intensity training without putting the body under high stress again.
Follow Your Heart
Training with a heart rate monitor is an excellent way for runners to make sure they are achieving the right intensities for the right workouts. Though ideal heart rates zone may vary a little from runner to runner, in general, you can use the following formula to find your easy and long run heart rate. First, find your maximum heart rate:
220 - age = Maximum Heart Rate
Use your maximum estimated heart rate to find your easy pace heart rate:
65-75% x Maximum Heart Rate = Easy Pace Heart Rate
Keep It Social
Don't have a heart rate monitor? no worries, folks have been running without heart rate monitors for longer than they have been running with them. Instead, run at a conversational pace. if you are able to carry on a conversation without gasping for breath between sentences, chances are you are in that easy pace sweet spot.
Walk If You Need Too
For some runners may find that their heart rate creeps up and out of easy even when running slowly. This can happen with beginner runners, or even with elite runners if the hills get steep enough. If this is the case...walk! Yup, I said it, sometimes walking is the best means to keep you in your target heart rate.
Are Long Runs Considered Easy Runs?
Sometimes, for race-specific training, long runs will be done at race pace or faster, but in general long runs should be done at an easy pace, but just because they are done at an easy pace runs longer than 1.5 hours should be considered a hard workout simply due to the stresses on the body due to the duration.
Easy Does It
There is a time and place for hard training runs, but that shouldn't be every day. Build the base of your training on easy runs and sprinkle in hard runs and race-specific training as your goal race nears, but even then, break up those hard days with easy recovery days, and on those easy days remember, easy does it.
More info:
2. Influence of exercise intensity and duration on biochemical adaptations in skeletal muscle
3. Lipid metabolism during endurance exercise