Yes, leg fatigue can affect the outcome. However, there are data elements that can sort that out to some extent. If your tester knows what to look for they may be able to determine if you hit a true VO2 max.

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Simplify, Train, Live

Not an "expert" - didn't even stay at a holiday inn express...

But have been tested twice both in the stone age ('89). My thoughts are depending on how much you care about your #...

You want to be rested for this. I'm sure some people taper as though it's their "A" race. I didn't, but, you can't expect to reach you max if your legs are so fried that you can't "go."

Also, at least for me, the first one was partly a learning experience. I didn't plan it that way. I had no idea I'd get a second chance half a year later, but, the second one was better because I knew what to expect. For me running on a treadmill with wires and headgear isn't "natural" let alone having a crowd gather around in the last minutes yelling at me. Doing 2 tests helped me and my #'s (69, and 72 respectively).

If the test was on a Friday, I'd suggest an easy/medium Wednesday and off or light on Thursday. Also, figure out a way to get at least 15 minutes of comfortable warm-up before you get "strapped in" (if you can)

Post your results and comments.

Enjoy the journey

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I saw this on a white board in a window box at my daughters middle school...
List of what life owes you:
1. __________
2. __________
3. __________

The test looks for a plateau in oxygen consumption varying on fitness level. Leg fatigue may cause you to reach that plateau sooner; however, the ml/kg/min of oxygen should be about the same

I disagree. Your oxygen consumption continues to rise while your legs are churning along well past the point of discomfort. If your legs are tired, your limiter will be how long you can keep moving your legs, not your ability to continue to consume more and more oxygen.
I did a series of 4 vo2 max tests for a research study. They required at least 2 days between tests and one of the stated reasons was to allow full recovery.

To the OP, if you are doing it for the entertainment value, try to give yourself an easy day before and you'll be close enough. If you are looking for an exact figure, then maybe wait till you can be completely fresh.

I did 2 VO2max tests earlier this year. I got some data, but ultimately, I wouldn't do it again. I lost a day of training before the test, and I was fried for the day after the test. I think there are more effective ways to spend your training time.

No, that is not really what would happen. Leg fatigue would result in you not being able to reach your max VO2. You would be limited by leg fatigue, so you would stop prior to hitting max oxygen consumption. This assumes that your legs are too tired to complete a max test.

You don't always get a plateau. When you do, you can feel better about it being a true max. If not, you are never completely sure but some of the other data points can give you more confidence.

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Simplify, Train, Live

Thanks for all the feedback. I think I'm probably going to do it just to get a ballpark number. I'll just take an easy day tomorrow (active recovery) and then see what happens Saturday. I'm not in peak shape right now anyway.