Apple

I think the only useful information for VO2max is when you open the yearly graph and then you can see the trends. Otherwise, day-to-day, not accurate. Needs maybe a month of training to spit out a remotely useful number.

But speaking of this - VO2max of around 40 sounds about right, if you're not super active, running a few months. It's not really an indication of durability, how long you've run. The estimate is more about how much energy you can spend for a given heart rate.

In a year or so, if add some sprints, HIIT, hills, you'll be 50ish and rising :)

Maybe your average heart rate have increased a little

The Apple Watch likes you to kill yourself every run which isn’t the proper way to train. If you do a lot of zone2 running it will tank your VO2Max. I pay it no attention other than for giggles.

I've been increasing my running over the last 4 months. Most practice runs are slow, zone 2, heart rate 125. Sometimes I run the first 5k fast or mix it up by HIIT runs. The watch says my VO2Max has consistently increased and my last practice run, 5 days ago, hit a new personal high. 4 miles. So then two days ago, I'm at an actual 5k run, which is only 3 miles. I go all out, heart rate 157 average, time significantly faster than practices. My VO2Max goes down.

I know it's just an estimate, but this peeves me. I have two theories:

• distance matters. The real race was shorter so I get less credit.

• Race speed went up, but heart rate went way up. So maybe it's like in a car if you increased the RPM of the motor but the car speed didn't go up linearly. Like the transmission is slipping.

It depends on how hard you’re pushing. The higher your heart rate goes above a certain average across the total distance VO2Max may decrease because you’re pushing harder than you’re running farther.