How Fast — and How Far — Should I Run My Long Run?

Runners often ask me, “How fast should I run my long run?” They’re looking for a simple answer, some percentage of 5K or marathon race pace, or a range relative to their usual training paces. Unfortunately, my answer is never that clear.

The truth is, there isn’t a single “best” pace for your long run; the pace you choose will depend on your running goals, overall training program, current fitness — and what you mean by “long.”

It’s not complicated. You just want to know the magical pace that ensures you’ll get all the aerobic benefits of long runs without incurring any nasty side effects—like injuries, excessive fatigue, or cramps that interfere with your giant, post-long run breakfast.

But it is complicated. Because there isn’t a single pace that works equally well for runners of different fitness levels targeting different race goals.

Before discussing what pace is right for you, we should first agree on what constitutes “long.” An elite marathoner might consider 5 miles to be a morning shakeout run. But a 35-minute 5K runner will see it as a marathon. They’re both right. But the run is only “long” for the second runner, who will take over an hour to complete it. And that’s the key: It’s not length in miles that makes a run long, it’s length in minutes.

How many minutes makes a run long?

• New and less-fit runners go long simply by running longer than their normal runs.
• Experienced runners log up to 50% more than their usual daily running time on weekly long runs—with runners who train less than 5 times a week sometimes doing more than that.
• Competitive runners need to exceed 90 minutes, the point at which they begin to accrue many of the most sought-after benefits of long runs.
• Marathoners need at least one long run (pre-race) that matches the length, in time, of their projected marathon finish time (up to 3.5 hours max).

The training effect of each long run pace — or effort level

With that in mind, let’s discuss pace—or more accurately, effort. You produce aerobic energy by sending oxygen via capillaries (small blood vessels) to muscle fibers (muscle cells) where each fiber’s internal machinery (mitochondria) turns fats, carbs, and oxygen into aerobic energy. Your effort-level determines which muscle fibers and energy systems you’ll train during your run.

• Low effort (jogging or easy run, 3 or more minutes/mile slower than 5K race pace): This effort only activates about 35–65% of your slow-twitch (endurance) fibers, but it’s great for teaching your body to burn fat as fuel. At this effort level, you’ll use up to 75% fat to fuel your run, making it good for ultra runners.
• Medium-easy effort (2–3 minutes/mile slower than 5K race pace): You’ll activate 75–80% of slow-twitch fibers and more than 10% of intermediate (strength and speed) fibers, triggering an increase in those fibers’ carbohydrate fuel stores and aerobic-energy production. This is a good effort level for 10K, cross-country, half marathon, and marathon runners.
• Medium-fast effort (1.5–2 minutes slower than 5K pace): You’ll activate 90–100% of slow-twitch fibers and up to 25% of intermediate fibers. This is great for increasing aerobic-energy producing benefits in a larger percentage of intermediate fibers. This is a good effort level for middle-distance runners racing the mile to 5K.
• Fast Segments or Finish Finish: In this version of the long run, you interrupt medium-effort runs to insert periods of tempo or marathon-paced running. You train more than 50% of intermediate fibers, and your body learns to burn lactate (a carbohydrate energy source that’s produced within your muscle fibers at more intense efforts). Other versions of fast long runs include negative runs (first half medium, second half medium-fast—also called negative-split or progression runs) and fast-finish runs (you increase your pace over the final 30-90 minutes, finishing at near maximal effort). Runners getting ready for a marathon should include a few of these runs.

All these paces increase muscle/connective tissue strength and stride efficiency. The longer you run, the more muscle fibers you’ll train—as fibers run out of carbohydrate energy, other fibers are recruited to replace them.

But beware: The faster your long run pace, the longer it takes your body to recover, which may eclipse other essential training. So choose an effort-level (and length) that fits snugly into your overall training program and best serves your racing goals.