This article originally appeared on Triathlete
Yes, because the two are inextricably tied together: Distance x Pace = Time. More generally speaking, you likely approach any given run both by the rough distance of the route you've chosen and by the approximate time that it will take you to complete it. You've made sure that you won't be 2 miles from home when you reach the end of your planned run time or that you'll have sufficient consume-calories-every-30-minutes fueling for your 10-mile run.
But also no, because of the different intents of workouts defined by time versus those defined by distance. A workout defined by time has an intended training volume: run for this amount of time, regardless of distance. A workout defined by distance has an intended training, well, distance: run this many miles, no matter how long it takes you.
So the real question is: Should you pay more attention to training volume or training mileage? And the answer is: That depends on the overall context of your run training.
Running by time vs. Running by distsance
If your runs exists within swim-bike-run(or bike-run) training for a multisport event, then volume dictates your training. A typical multisport training plan builds overall weekly training volume in accordance with the expected duration of your event. It then balances that volume across swim, bike, and run (or bike and run) in general proportion to the typical relative duration of each leg. Multisport plans have the freedom to do this because the fitness built within each discipline bleeds over and benefits the others. Cycling fitness in particular does a great job of supporting run fitness. For multisport training, this means that you don't have to build all of your run fitness by running.
A typical multisport training plan also considers recovery in the overall swim-bike-run balance. Because your run fitness is developed concurrently with bike and swim fitness, there just aren't enough days in the week to place easier days before and after every hard run session. Multisport training plans must therefore carefully consider the fatigue that's created during each workout, and run workouts create the greatest amount of fatigue. Running by time, then, creates a ceiling for your run volume – particularly your long run volume – which serves to manage the fatigue created by those runs within your multisport plan.
If, however, your runs exist within single-sport training for a run-only event (or within the training for a swim-run event), then distance dictates your training. Your run fitness will only be developed through running and it must be sufficient for the distance of your event. Additionally, there are enough days in the week in this context to have easier (or swim) days before and after key run sessions. Running by distance, then, creates a floor for your run distance – both weekly and for your long runs – which serves to ensure your preparedness for your run-only (or swim-run) event.
Whether you're running by time or distance, your run workouts will look very similar in structure. The following interval run and long tempo run examples show how the same workout can be structured both by time and by distance.
Running Time vs. Distance: Interval Run
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