Here is how a coach I follow explains who I should approach easy runs including pace:
Easy Runs
I define an easy run as follows:
Easy runs are runs we do in order to promote recovery from our stress workouts while maintaining or advancing our cardiovascular fitness and our body’s adaptations to running. These runs should be kept short enough in duration and slow enough in pace that they do not significantly stress the body’s systems, while being quick enough to maintain bio-mechanical efficiency and provide cardiovascular benefit.
Duration
The duration of an easy run can be anywhere from 20 minutes to 90 minutes in duration depending on the fitness level of the runner and the weekly mileage level they are accustomed to. 20 minutes represents the low end as it takes 20 minutes of sustained exercise to provide the cardiovascular, enzyme and hormone benefits we are after. 90 minutes represent the upper most limit as it even for very fit runners runs over 90 minutes become significantly draining of the energy systems of the body and begin to resemble endurance stress workouts rather than easy recovery runs.
One helpful way to determine how much you should run on an easy run day is to use what I call the “5-15 rule” which says that your daily easy run mileage on a recovery day should be between 5% and 15% of your weekly mileage. Where in that range you would fall would depend on how many recovery days you have between stress workouts. If you only have 1 recovery day between stress workout then you would be lower in the range, probably somewhere between 5-10%. If you have 2 or 3 easy days between stress workouts then you can be a little higher in the range at between 10-15% each day.
For a 50 mile a week runner this means that if they only have 1 recovery day between stress workouts they would probably run between 3-5 miles that day. But if they had 2 or 3 recovery days between stress workouts they could probably handle 6-8 miles easy each day.
Speed
Going back to the definition of an easy run, we want to be sure to run it slow enough not to significantly stress any systems of the body so we can assure we are recovering, while being quick enough to remain bio-mechanically efficient and provide some cardiovascular benefits
Given these parameters, I have come up with 3 guidelines for us to follow to judge if we are running within the correct range on our easy days to satisfy our definition. We should use at least 2 of the 3 guidelines on any given run.
Feel: our easy run pace should feel comfortable and relaxed, never pushing the pace and we should be able to easily carry on a conversation with a running partner.
Heart Rate: our easy runs should average between 65% and 75% of maximum heart rate. For example of your maximum heart rate is 180 beats per minute than your average heart rate on your easy run should be between 117 (65% of 180) and 135 (75% of 180) beats per minute and you should stay somewhere in that range most of the run.
Pace: our easy run pace should roughly be between 20% and 30% slower than our lactate threshold pace. I have pace charts later on in this book to help you determine what this pace is for use based on recent race times. But basically we define lactate threshold as the pace you can hold for 60 minutes in an all out effort. So if you can run 60 minutes for a 10 mile race than your lactate threshold would be 6:00 per mile. This would put your desired easy run pace at between 7:12 (20% slower than 6:00) and 7:48 (30% slower than 6:00) per mile.
I recommend using the feel as your primary guide on these runs and then use either heart rate or pace as a secondary sanity check to make sure you in the right general ballpark.
Pitfalls
As a coach the 3 most common errors I see runners making on their easy runs are:
Running too fast. Competitive runners are driven individuals who want to improve, and sometimes that drive can cause them to run too fast on their easy runs. The pace does not seem physically hard to them so they can easily do it. But the end results is that it either does not allow them to adequately recover from their stress workout in the allotted time given or they need additional time to recover and so have to an extra recovery day. Often we see these runners sticking to their workout schedule and go into their next stress workout under recovered and thus not getting the full benefits of their last stress workout, and not being ready for the demands of the next one. As you get fitter your easy runs will get faster, but you don't get fitter by running your easy runs faster.
Running too slow. A far less number of runners error on the other side of the spectrum here and run too slow on their easy runs. They very slowly jog (what I like to call ‘slogging’) their runs at a pace that is too slow to provide any significant cardiovascular benefits and at a pace in which they are bio-mechanically inefficient. They fail to meet our definition for easy runs because they are not getting the cardiovascular benefits desired and they are teaching their body bad bio-mechanical habits which can hurt their efficiency when do try and run quickly in workouts and races.
Running too far. Even if a runner stays within the feel, heart rate and pace guidelines given they can sabotage their recovery by trying to run too far on their easy days, often in an attempt to up their mileage. If a runner pushes too far on an easy run, further than their fitness level is ready for, they will not recover sufficiently from their stress workout before their next stress workout and thus not get the full benefits from it. Increases in mileage levels on easy runs needs be kept small and gradual to allow the body to adapt and absorb the increases gradually.