Maximal aerobic speed (MAS) in running: understand it and use it

You've probably come across a plan that says "10 × 400 m at MAS" or "30-30 at 100%." The number is everywhere, but the explanation rarely is. The result: you run your intervals too fast or too slow, without knowing what this benchmark is for.

MAS isn't mysterious. It's a personal number in km/h that tells you how fast to aim when you want to work hard. Let's look at how to get it and turn it into workouts you can run on a track or follow on your watch.

MAS in plain terms

Your VO2max is the maximum amount of oxygen your body can use during effort. Your MAS is the speed at which you reach that ceiling. The first number is measured in a lab. The second is lived on the road, which is why runners use it.

MAS is expressed in km/h, but you set your effort by pace. At 15 km/h, you cover 1 km in 4 minutes: 60 divided by 15. A MAS of 12 km/h gives 5 minutes per kilometer. Everyone has their own benchmarks, and that's the point: you set your effort to your level.

MAS doesn't measure your endurance in a marathon or your resistance to fatigue. It's an intensity benchmark, not a verdict on your level.

How to measure your MAS

Léger and Boucher, from the Université de Montréal, published a stage-based field test in 1980 in the Canadian Journal of Applied Sport Sciences: the "Université de Montréal Track Test." It's continuous (no breaks) and stage-based (the speed increases steadily). It's called indirect because it estimates your aerobic capacity without measuring the oxygen you use. The authors consider it valid and reliable for estimating the targeted aerobic parameter.

Whichever version you choose, the key is to repeat the same test every time, under comparable conditions, so the results can be compared.

For a usable result, choose a track or a flat road, with little wind, a 15-minute warm-up, and a day when you're not already tired. A test run on a hill or after a bad night will give you a number that's too low.

Setting a workout from your MAS

High-intensity intervals (alternating fast efforts and recoveries) are among the most effective ways to improve cardiorespiratory and metabolic fitness, according to Buchheit and Laursen (2013, Sports Medicine). Their review describes a workout through nine variables. Four are easy to set:

• The duration or distance of each effort.
• The intensity, often expressed as a percentage of MAS.
• The recovery: its length and what you do during it (walking, jogging).
• The number of repetitions.

Here's what some efforts at your full MAS look like for a runner at 15 km/h:

To find your own times, divide the distance in meters by your speed in m/s: 15 km/h is about 4.17 m/s. A 10 × 400 m at this speed represents 16 minutes of effort, not counting recovery.

Studies describe the variables to set, but the exact MAS percentages and recovery durations you see in training plans come from coaching practice, not from a proven rule. Treat them as starting points and adjust them to how you feel.

Buchheit and Laursen also point out that time spent fast isn't enough. Other variables, such as the load on your heart, matter for understanding what a workout cost you. Two workouts with the same split time may not be equal.

Where MAS fits in your week

A MAS workout is demanding. Place it between easy days, never the day before a long run or right after another hard workout.

On official benchmarks, the American College of Sports Medicine (ACSM), a US professional society, gives a guideline for overall physical activity in healthy adults:

This benchmark covers all your activity. It says nothing about the number of MAS workouts. One 8 × 400 m at your MAS represents about 13 minutes of fast effort: one workout alone doesn't fill that volume, and your easy runs count toward the total too.

To build a full week, read how to improve your running with 3 workouts a week. If your goal is a specific distance, the 8-week plan for a 10K shows where the intervals fit.

Mistakes that skew your MAS

Starting too fast. On a 10 × 400 m, the first repetition feels easy. The last one is what counts. If you lose several seconds at the end, your starting speed was too high.

Using an outdated MAS. Your fitness changes. Coaches recommend retesting under the same conditions after a training block of several weeks, or when your workouts start to feel too easy or too hard.

Only watching pace. Also check your heart rate and how you feel, not just the time.

Shortening recovery to "do more." Without recovery, you can't keep running at your target speed. You slow down, and the workout becomes something else.

Doing MAS work all year. It's one workout among others. Easy runs, your long run, and rest also drive progress.

What you can do before your next workout

1. Measure your MAS with a field test, or use a recent value if you have one.
2. Convert it to pace with the pace calculator or the pace and speed converter.
3. Pick a simple format: 6 to 8 repetitions of 400 m, with a jog recovery.
4. Warm up for 15 minutes and finish with 10 easy minutes.
5. Compare your first and last repetition.

• ✓I have a recent MAS, measured under the same conditions as the previous one.
• ✓My workout paces are written down before I head out.
• ✓The day before and the day after are easy or rest days.

KILYO reads your workouts from your watch, analyzes your pace and heart rate, and adjusts your training plan to match.

Written with the help of AI.