More often than not, when a runner’s performances start to stagnate it’s a sign that there’s not enough variety in the training program, they’re not recovering well from the work they’re doing day after day, or some combination of the two.
When looking at the entirety of the training week (or the entire cycle) it should resemble a EKG graph: a healthy amount of low- to mid-level rises (think steady state/progression runs all the way up to true tempo runs and medium-intensity intervals) and occasional spikes (think high-intensity speed workouts) surrounded by a bunch of dips and flatter lines (easy/recovery runs/rest). When there are too many spikes — or an overabundance of mid-level lines with no clear spikes or regular dips — it becomes increasingly more difficult for new adaptations to take place.
For example, if you’re a 3:30 marathoner (avg. pace of 8:00/mi), doing most of your “easy” runs at 8:15–8:30 pace — which, believe it or not, is not an uncommon practice — means you’re only running 10–25 seconds per mile slower than your most current marathon pace, which really isn’t all that much slower when you break it down. While that pace may feel easy (10–30 seconds per mile slower than marathon pace should feel fairly comfortable most of the time), it’s not easy enough for you to truly absorb the benefits of your quality workouts. Many competitive runners fall into this same trap where they’re essentially going medium-hard all the time, which compromises recovery and adaptation. Put another way: There are too many mid-level lines and/or high spikes on the EKG. In short, there needs to be more variety in the graph (i.e. the training program).
I generally recommend easy/recovery runs to be at least 60–90 seconds per mile slower than your marathon pace. For the 3:30 marathoner, that means somewhere between 9:00–9:30 per mile on your easy runs, if not slower. Yes, those paces will feel ridiculously slow, but it’s important to remind yourself that every workout — even a recovery run — has a specific purpose. In the case of easy runs, the idea is to absorb all the harder work you’re putting in the rest of the week. Remember, you’re not as good as the workouts you do — you are only as good as you recover from the workouts you do. When in doubt, slow down! (Or put another way, if it feels easy, back it off another notch.)
Here’s a real-life, learn-from-the-pros example: In 2004, I spent 10 days visiting and training with the now-defunct Team USA Monterey Bay Olympic development squad, coached by the legendary Bob Sevene. The group, which at the time consisted of a handful of very talented 5K/10K runners who would go on to become 2:13 and 2:14 marathoners (roughly an average pace of 5:06 per mile), ran some rather impressive workouts on Tuesdays, Thursdays and Saturdays. But it was their recovery runs on the days in between those key sessions that impressed me most: an average easy/recovery run topped out at low 7 minutes per mile, with a majority of those runs in the 7:30 per mile pace range — nearly two-and-a-half minutes per mile slower than the paces they could race a marathon! It was eye-opening for me, but it was a good reminder that the easiest days in your training schedule need to be taken as seriously as the most challenging workouts.