VO2 max training, coached rep by rep

What is VO2 max, and how do you train it?

VO2 max is your maximal rate of oxygen uptake. Hard work close to your limit, repeated in intervals of a few minutes, is a classic way to train it. Apple Watch estimates it as Cardio Fitness from outdoor walks, runs and hikes (Apple).

In one eight-week study of 40 moderately trained men, four 4-minute high-intensity intervals, three times a week, raised VO2 max more than the same total work at moderate intensity or at lactate threshold (Helgerud et al., 2007). That's one study in one group. Responses vary from person to person, and the hard work sits on top of a mostly easy base rather than replacing it (Seiler, 2010).

Why are VO2 max intervals so hard to pace on your own?

Because the first rep feels easy, heart rate arrives late and recoveries drift.

• Going out too fast. The first rep feels easy. The last one falls apart.
• Heart rate arrives late. In a rep of a few minutes, it's still climbing just when you need to know your effort.
• Recoveries drift. Too short and the next rep suffers. Too hard and the session loses its shape.
• Hard days pile up. Two in a row, or one after a poor night, and the quality goes.

How does Gears coach VO2 max intervals?

Rep by rep: every Hard rep called live, sessions built for VO2 max, and hard days on the days your body is ready.

1. Every Hard rep, called live

Just before a Hard block the coach gets you ready, then counts you in. Your Hard gear is a pace range learned from your own running, so you steer by pace while heart rate catches up. Sit under it and you'll hear: “More. This is gear three, not a jog.” Countdowns tell you what's left. More on the voice coach.

2. Sessions built for VO2 max

Find a run has two training targets, VO2 max: long intervals and VO2 max: short intervals, plus presets including Norwegian 4×4 and 10-20-30. Or build your own in the run editor from Hard and Easy blocks, by time or distance. Each run's card shows its shape in gear colors, a one-line description, its difficulty and “Why it works”.

3. Hard days on the right days

With Gears Plus, your plan holds at most two hard runs a week, never back to back. Each morning, Today's gear reads your sleep, resting heart rate and heart rate variability (HRV, the beat-to-beat variation in your heartbeat) against your own usual. On a Gear 1 day the hard run swaps for an easy one, and “Keep the plan” undoes that for today. It's guidance for today's run, not a health verdict. More on the running readiness score.

What does a Norwegian 4×4 sound like?

How do I track my VO2 max over time?

In Apple Health, where your watch keeps its Cardio Fitness estimate. Watch the trend over weeks, not any single reading. Gears reads it as one of the sources that place your gears, and keeps VO2 max off its Today screen on purpose.

Inside Gears, watch pace at the same heart rate: “Getting fitter shows here first: the same heart rate buys a quicker pace. Measured from your own runs.” When your gears move, the coach says so. After each session, the grade judges how well you ran the run you set out to run; its pacing part compares your second half with your first. More on run analysis.

What Gears doesn't do

• It doesn't promise a VO2 max gain, or a number by a date.
• It doesn't measure VO2 max itself. Apple Watch estimates Cardio Fitness, and Gears reads it.
• It doesn't ignore warning signs. If your heart rate is very high, the coach tells you to ease off, at every toughness setting.
• It isn't medical clearance for hard intervals. If you have a heart condition or another health concern, talk to a doctor first, and read the health disclaimer.

Read next: How to raise VO2 max with running and The Norwegian 4×4 for runners.