The short answer? Neither. It depends on your goal and where you are in your training.
If you're chasing a PB, it can be tempting to think you need to run faster every session. Equally, if you're training for a marathon, you might assume that simply adding more miles is the answer.
In reality, speed and mileage do different jobs, and the best training plans use both in the right proportions.
So what are you training for?
If you're training for a 5K or 10K?
Speed becomes more important. Your training should include some faster running, such as intervals, tempo runs or race-pace efforts, alongside enough easy mileage to build your aerobic fitness.
If you're training for a half marathon?
You'll need a combination of both. Increasing your weekly mileage and long-run distance builds endurance, while tempo and race-pace sessions help you hold a faster pace for longer.
If you're training for a marathon?
Mileage and time on your feet become increasingly important. Your body needs to adapt to running for several hours, so gradually building your long runs and weekly mileage should be a priority. Speed work still has a place, but it doesn't need to dominate your training.
Or just running for fitness or enjoyment?
You don't necessarily need to chase either. A mixture of comfortable runs, the occasional faster session and gradually increasing your mileage can help you become fitter without turning every run into a workout.
So, how much speed do you actually need?
You don't need every run to be fast. A useful rule of thumb is to make most of your running easy, then add one or two purposeful quality sessions each week, depending on your experience and training goal.
These could include:
- Intervals: shorter, faster efforts with recovery between them
- Tempo runs: a sustained effort that feels comfortably hard
- Race-pace running: practising the pace you want to hold on race day
- Hill sessions: shorter uphill efforts that build strength and running power
And don't underestimate hills. They might not produce your fastest pace or biggest mileage, but they're a brilliant way to strengthen your glutes, quads, hamstrings and calves while improving running efficiency.
A stronger runner will often find running on the flat feels easier, helping you become faster and making higher mileage more manageable.
And how much mileage?
This is where time on your feet really matters — particularly for longer-distance runners.
A long run isn't simply about ticking off a certain number of miles. You're teaching your body to keep moving when you're tired, building endurance and preparing yourself mentally for the later stages of a race.
But that doesn't mean you should suddenly add miles because you have a marathon coming up.
Don't make this mistake.
The biggest mistake isn't choosing speed over mileage, or mileage over speed — it's increasing either one too quickly.
If you're adding mileage, do it gradually. If you're introducing speed work, start with a manageable amount and allow your body time to adapt.
For marathon runners, for example, I like athletes to be comfortable completing a 16-mile long run before starting a 12-week marathon plan. For newer runners whose goal is simply to complete the distance, being comfortable with around 12 miles can be a good starting point before beginning structured marathon training.
From there, the focus should be on gradually building towards your longest runs. Many marathon plans include a 20-mile run, while more experienced and faster runners may complete several 20-mile runs or occasionally go beyond that.
But your longest run shouldn't be decided by someone else's training plan. Your running history, experience, goal and how well you're recovering should all influence how much mileage is appropriate for you.
What about injury risk?
This is one of the most important things to remember:
More isn't always better. Better training is better.
Whether you're increasing your mileage or adding faster sessions, give your body time to adapt. Avoid making big jumps in distance, intensity or both at the same time.
And recovery is just as important as training. Strength work, mobility, conditioning, sleep and rest days all help your body cope with the demands you're putting on it.
I also find wearing my ENERTOR insoles while running and my ENERTOR recovery slides after runs helps me better prevent injuries and support my feet and tired legs.
Coach April's Takeaway
Don't choose between speed and mileage — use both strategically. Build your mileage according to your experience and goal, include purposeful speed work, use hills to develop strength, and prioritise recovery.
The best training plan isn't the one with the most miles or the fastest sessions. It's the one that helps you arrive at your goal healthy, confident and ready to perform.