Using Zwift races as VO2max workouts?

Question for any VO2max gurus out there …

I’m about to start a VO2max block and I’ve been reviewing my past workouts to see what keeps me in the zone for longest, based on heart rate.

I’ve looked at hard-start 8 min intervals, 40-20s, 5x5s etc but by far the most effective seems to be a 20-25 min Zwift race (Crit City course) where my heart rate stays unusually elevated from the start.

So should I just do these races as VO2max workouts? Talk me out of it. :slight_smile:

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Worth taking a look at your time in power zone rather than HR. There are all kinds of ways to peak and hold a high HR, but I’m not sure a high HR always translates to vo2 adaptations.

What training plan are you following? If you were in the specialty phase then I would replace any workout with a race.

VO2 max workouts are all about keeping you close to your maximum aerobic capacity so there can be a slight change in power.

No plan right now, I just want to do a dedicated VO2max block because I have the time and I’m curious to see what happens.

Regarding time at “VO2max power” , if I was aiming to maximise that that a regular TR workout with 4 or 5 min intervals would do it. But I am sure my heart and lungs would be working harder for longer in a shortish Zwift race.

Crit City Race is one hard race. Does not matter which Cat you are racing in, but you always go full gaz. Before considering it as VO2 Max training, I suggest to give it a try. Here I am attaching my last race.

It is like threshold with VO2Max sprints. Very similar to Jepson. It is fun but I would not take it as a WO


Yeah that’s exactly what it looks like for me too, every time. Also in the first minute my heart rate goes above 90% HR max and stays there until the end.

I guess I’m just wondering why this doesn’t count as a VO2max workout?

I guess because it is threshold mostly. Not sure

Firstly, I’m not a VO2 max guru!

But…I’ve spent a lot of time following the approach you’re considering, both in real life and in Zwift. In real life using either crit races or Wednesday night worlds type group rides. There’s a great weekly ride I used to do before lockdown which included a 20-25 minute section which was a gloves off hammerfest, my HR would be right up there for the duration. Since lockdown I’ve been getting that VO2 hit from Zwift races or group rides instead.

I’ve had pretty good results with it. I’ve always found the need to mix up my training with racing or group rides, I can’t do it all solo and structured or I lose enjoyment and motivation. And I find it hard to do the threshold and below stuff in a group. If it’s threshold or sweetspot it’s really hard to do sustained intervals at the right power while staying with other people. VO2 is easier to incorporate, and my (non-guru…) understanding is that what’s important is accumulating time with your oxygen update maxed out. So I think 20-25 minutes where your HR is high and you’re sucking in as much oxygen as you can, is a good VO2 workout, somewhat regardless of the power numbers. And it’s certainly a lot easier to motivate yourself to keep going than following a yellow line on a blue box. The danger of course is overdoing it. So many races in Zwift that it’s easy to start racing every day and lose the structure altogether. Cap yourself to 2-3 days/week max of racing.

same here, ML plan three days weekly, one or two crit racing zwift and one local gangs racing zwift every Wednesday night due lockdown in uk, Few society group on zwift between gaps. + one rest day

Probably not a terrible idea, but your recovery intervals are at the mercy of others…and therefore may be training sub optimally.

Guessing the races look quite “microbursty”?

Just do it. It’s more enjoyable and arguably more effective than a workout. I do them once or twice a week to supplement other riding and for that VO2 max / threshold hit.
It’s only half an hour but a good kick in the nuts. You can ride it how ever you want, if I want to really push I will try small attacks off the front every couple laps then try and recover in the pack at or near threshold.
It’s more fluid than a workout and more realistic to what riding in the wild is like. I think it works better than purely following all structured workouts.
Plus, they are way more fun, and that counts for a lot!


I’ve done quite a bit of Zwift racing and I’d agree that you probably won’t get optimal VO2 training from it.

Looking back at my most recent races, I usually spend about 25% of the race duration at VO2 or above. For a 20min race, that’s only 5mins (barely a VO2 workout). For a 1hr race, thats 15mins (not even equivalent to a 5x4min). Also, as you are racing, you generally won’t HOLD the VO2 power for any reasonable duration - you just spike up to it for 30sec to a couple of minutes at a time.

In general, my races are just as others have characterised - constant threshold/upper tempo effort with spikes into VO2. However, this will also depend on where you sit within your grade:

  • If you are at the bottom end of your grade, it will be VO2 until you get dropped, then probably only tempo.

  • If you are in the middle of the grade, it will likely be threshold for the full race with only a few VO2 (otherwise, you’ll get dropped).

  • If you are at the top of the grade, you’ll be riding upper tempo/threshold, throwing in attacks at VO2. This is probably your best chance of getting a proper VO2 workout, as you are in a bit more control of the duration of your VO2 efforts, however, you’re still in a race so can’t spend as long at VO2 as you could doing longer VO2 efforts in isolation.

Having said that, I do enjoy the races… If I were looking to substitute them for TR workouts though, I’d substitute them for straight up Threshold workouts or Over-Unders.

Finally, keep in mind the potential problem being that you can overdo it and not be able to recover properly for your next session… This is part of the reason the TR trainers seem to advocate Sweet Spot instead of Threshold work, as it provides most of the same benefits, but does not jeapordise being able to still do high level work the next session.


zwift racing is mostly threshold IME, not Vo2


Note that there isn’t an absolute correlation between high heart rate and high oxygen uptake (which is the adaptive purpose of vo2 workouts). In a sustained hard effort, your slow twitch muscles fatigue, and you start relying on less efficient muscle fibres to maintain the same power, which puts a greater demand on the heart. You’ll see this effect even in longer steady sweetspot intervals.

So even if you look at “time in heart rate zone” and the Zwift race has you in your top zone for longer, I wouldn’t necessarily take that to mean you were operating at a high % of your vo2 max for longer.

If you have WKO, Golden Cheetah, or (and some accurate data fed into them), I’d be tempted to use something like W’ / W’bal to see how far you were burning through your above-threshold capacity over the course of the workout.

My general hunch would be: Zwift races are great “give you some intensity to maintain your current fitness” sessions, but not so great “drive aerobic adaptations that will increase fitness” sessions.

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Nice idea and I discovered a chart in WKO5 that I hadn’t looked at before. :slight_smile:

So yeah not a huge amount of time at VO2Max according to the WKO5 model despite the heart rate:

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How does it compare to your vo2 workouts? e.g. the 5x5 or 40/20s?

The traditional VO2max intervals (like 4 or 5 mins) can get me more than 20 min over 85% Vo2Max according to that chart. 40-20s are around 12 mins.

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I think it’s all dependent on your experience of Zwift racing, course profile and how hard you are prepared to go/recover. If I want a VO2 max workout from a Zwift race I’ll look for a course with a climb such as Box Hill, Volcano climb, Reverse KOM and do the required effort up the hill. Most experienced racers know that these are the places the selection is made and will save their matches. There’s often a lull then until the next lap where it’ll all kick off again!

I use Zwift races as threshold and do specific VO2 max workouts as well. There’s no way in a 40 minute race I’m going to get 25 minutes+ at 120% FTP, so that adaptation just won’t be there.

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Depending on the course I would say Zwift races are more like extended over-unders or race winners where you’re at threshold and then sprinting once or more a lap. I’ve never managed to get enough rest between efforts to make them like TR VO2 workouts

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