Time vs Mileage: Which Should You Train By for Ultra-Marathons?

Ultra-runners love numbers. Weekly mileage, vertical gain, daily steps, sleep scores, we start collecting metrics like the Cookie Monster collects cookies. But the most important number in ultra training isn’t miles at all. It’s time.

Training by time rather than distance is one of the simplest ways to build sustainable fitness, reduce injury risk, and keep your training aligned with the effort the race actually demands. Mileage still has its place, especially for road-focused athletes, but for trail ultras and especially mountain trail ultras. Time is usually the smarter metric.

Centurion Coach Hayden Hawks says that he “changed from training by miles to time a few years ago. Training by time is more sustainable both physically and mentally”.

Here’s why.

1. Effort matters more than distance

Two runners both log “20 miles.”Runner A did it in 2 hours. Runner B did it in 4 hours over muddy bridleways and 2,500 feet of climbing.

Same mileage on paper, completely different training load.

Training by time automatically adjusts for:

• terrain
• hills
• how good your music is
• weather
• fatigue
• underfoot conditions
• how your legs actually feel

“Running 10 miles in the mountains is going to take you a lot more time than running 10 miles on the flat” says Hayden, “and that is a completely different training load and stress on the body.

It creates comparable training stress across different routes and days, instead of pretending that “20 miles” always means the same thing.

2. Time protects your long runs from becoming monsters

One of the biggest mistakes ultra-runners make is letting the long run become too long relative to their week.

A 5-hour long run within a 12-14 hour training week? Great. Manageable. Productive.

A 5-hour long run within a 5-hour training week? Disaster waiting to happen.

Training by time gives you clear guardrails:

• Long run is a set duration
• Weekly load is a set duration
• The long run stays in proportion

This prevents the dangerous pattern of trying to “hit the miles” at all costs, which usually leads to overuse injuries or total exhaustion.

3. Time encourages good pacing and reduces ego pressure

When you train by time, you stop caring about the pace your watch shows. Suddenly:

• you slow down naturally on hills
• you pay more attention to effort
• you stay patient on technical terrain
• you stop trying to “save the pace” of a run
• you recover better because the run ends when it should

Mileage invites comparison. With yourself, with others, with last week’s numbers. Time invites honesty. And honesty is gold dust in ultra training, especially when working with a coach.

4. Better for fuelling practice

Long runs are not just about running, they’re about fuelling, hydration, and pacing. A 3-hour session lets you practise:

• taking fuel every 30-45 minutes
• varying textures and timing
• adapting intake when pace changes
• managing gut fatigue

A “distance” long run doesn’t guarantee any of those exposures, especially if terrain changes your pace.

“Time is what we focus on in racing so why shouldn’t we focus on it in training?” questions Hayden.

Time-based long runs map far more closely to the actual demands of ultra-racing, especially if you aren’t on exactly the same terrain and profile for your training.

5. Time respects recovery (distance doesn’t)

If you run by mileage, a slow day becomes a long day, precisely when your body might need a shorter one. Time adapts seamlessly:

• tired legs? pace drops, but duration stays safe
• wild weather? pace drops, but strain stays controlled
• muddy winter trails? pace drops, but long run doesn’t double in length

Your musculoskeletal system experiences the right dose of training, not overloading for the sake of a number on Strava.

6. Mileage still has a place, but not the starring role

Mileage can be useful for:

• tracking progress over consistent routes
• preparing for runnable 50Ks or road-based ultras
• understanding your general tolerance over years
• keeping variety in easy midweek runs
• bringing confidence before racing new distances

But for the key elements, long runs, weekly load, endurance development, time gives you better control.

Mileage should be a supporting metric, not the master.

In summary

Mileage looks neat on paper, but time reflects reality. Ultra-running isn’t a sport of exact distances, it’s a sport of sustained effort, terrain, weather, fatigue management, and problem-solving. Training by time respects that complexity while keeping your weeks balanced and your long runs sensible.

Centurion Coaching Head of Endurance Robbie Britton adds that “we all might fall into the trap of chasing mileage from time to time, but it’s important to see that for what it is, one of many metrics we can use to monitor training load and there are several better options”

Your body will thank you when the race goes beyond anything your Strava graph could predict.