VO2 max on dumb trainers

Hi all

Just started SPBLV so last night I got my first taste of a serious VO2 max session. There are some in SSBLV2 but nothing with such short and intense intervals like this.

I found it really difficult to hold the prescribed wattage for the VO2 intervals and it seems to be either my choice of gearing or the momentum of the flywheel that I can’t get to grips with. I can do that power just fine but I end up constantly overshooting and undershooting the target power.

For example, if I click up a gear when jumping from 250w to 350w then the power increases, overshoots and then drops below target and then I have to spin like crazy or shift again to raise it back up to target. I then have the same problem when dropping back down to 250w. In other words, I spend the whole interval compensating for either too much power or not enough. It’s pretty tiring, frustrating when you’re already working hard and I fear it’s not as productive as it could be.

Does anyone have any tips for making sure I hit the prescribed wattage for more of the time? I also wondered if erg mode on smart trainers takes care of this and whether it’s worth me investing in one?

You don’t need ERG mode. I use a 4iiii power meter and a Tacx magnetic dumb trainer, with 5 second smoothing in TR - no issues at all.

What trainer do you got and what power meter? How much smoothing do you use in TR?


I use a jetblack whisper drive with a stages left PM and 5 sec smoothing.

I think it’s a mechanical issue rather than power meter or smoothing because when I ramp up to 350w I need some force to accelerate but then once I get the flywheel up to speed then less force is required and therefore more cadence is required to meet the power demands. Hence I either spin a lot or I change up a couple of gears. It may just be that I need more practice at doing this but either way, if I have an interval thats only 15 seconds long then I’m probably not getting the most out of it because I’m either overshooting it and tiring myself out for the following efforts or I’m undershooting and not getting as much training benefit.

This is basically what the whole workout looks like, this is one set of intervals. The workout is Pierce.

1 Like

I upgraded to a used TACX Neo at about 50% of the RRP - have never regretted that decision and I love ERG mode, no cheating! Be wary if you have disc brakes though.

I used to have this problem using my precision 4iii left sided meter - best way was to try and feel how much power I was putting out.

e.g. if I wanted to go at 150% FTP I would just go at about 60% full gas (RPE - rate of perceived exertion) and then after 15 seconds that might feel more like 70% full gas, after 30 seconds it would be 80%.

This all gets more complicated due to the nature of intervals getting harder when you are towards the end of them, and even harder when you are towards the end of the last set of intervals.

Do it by feel and don’t worry too much about the exact power - with a bit of practice, you’ll be able to judge how much effort is required to smooth out your average power. Bear in mind that when you are pedalling at a constant speed on a smart trainer, you only need to overcome the resistance. As you accelerate, you have to transfer your energy into both the resistance and accelerating the flywheel up to speed, hence you will need to keep changing gears as you accelerate but eventually you won’t need to accelerate to hold 350W because the trainer’s resistance alone is at that level. Likewise, decelerate slowly to maintain 250W while decelerating.

From your screenshot, just don’t push as hard initially and don’t drop too many gears when you finish - you could probably do this workout with one gear and just vary your cadence? Since you are measuring power at the left crank it will be much easier to do by feel, nice smooth changes in pace.


Thanks, what you’re saying makes a lot of sense. In an ideal world I would keep the same gear and just ramp up to the prescribed power, only changing gear if I was spinning too much. However, when your 350w interval is only 15 or 20 seconds there isn’t much time to do this (unless I start winding it up at the end of the 250w interval, but then I’d have almost zero recovery time).

I experimented with a few different approaches and using one gear worked ok but again, once I ramped up the cadence and power, the flywheel gained momentum and suddenly I found my power dropping and I needed to increase cadence again or choose a faster gear.

Sorry if this isn’t explained very well. It’s because I don’t really understand it very well myself. I’m totally open to the possibility that I just need to practice and practice!

Yeah, keep practising and try not to overreact to your power reading - you have nerves in your legs that tell you how much force you are creating, you just need to get them in tune with the watts that your meter reads! There’s nothing wrong with changing gear mid interval, but just be aware your cadence will drop then rise as you accelerate the flywheel and you don’t need to keep it constant at all times. Power is more important than cadence!


I trained for years with a dumb trainer - the trick is to make the intervals « x seconds at xx rpm on gear X ». Use the warmup intervals to figure out what gear and cadence gets you in the right power range. Shift to that gear 5 seconds before the interval starts. Accelerate smoothly to the required cadence. Shift down for recovery if needed. Repeat. In many cases, I was using chainring shifts to go from recovery to interval - so for example 39x15 in recovery, 52x15 for the intervals.


Honestly this is just a trial and error thing. I’ve completed Taylor -2 with 30 second intervals just fine. You’ll need to commit to holding a cadence for the interval, let the power settle down and see if you need to spin up, slow down or change gears completely. It’s not uncommon for the power to shoot up way over target, just keep your cadence steady and it’ll fall into place


This is all great and part of what I do. The front chaining shift is particularly useful in most cases and reduces or eliminates the need to shift the rear. It makes the up/down transition in power quicker and less confusing (was it 2, 3, or 4 rear shifts…?)

Additionally, when using the warmup and first interval to find the gearing, make a mental note of the cadence that you find works with that gear.

When you hit subsequent intervals, make the shift and focus solely on hitting that right cadence. You can recheck power, but by just aiming for cadence, you tend to waffle less than chasing power up and down.



I was having the same issue but practice teaches you a lot of things. I realized by just changing my cadence I could hit the correct watts and get they the interval. If I shifted up it would jump watts too much. It becomes this balancing act but in real life cadence changes happen all the time and I see it as another way to train my legs for changes in surges.

Keep at it! :+1:


It’s totally possible to shift gears wildly and even stand up and pedal for 15-30 seconds without any of it showing on the power graph. Just keep practicing. I believe that you might have use of these skills out on the roads as well.

Regarding magnetic dumb trainers, as they heat up 30-120 seconds into an interval, they provide less resistance. I almost always have to shift up a notch after 30-60 seconds into an interval to maintain a comfortable cadence. Using virtual power this is of course not noticed - the interval is just harder in the beginning despite the power shown being the same.

1 Like

Thanks everyone for the tips. Aiming for cadence is something I’ve done in other, longer intervals so I’ll give that a go here. I did use the warmup to practice but was still struggling to find the “best” way of doing things 60 minutes later haha!

I’ve got Joe Devel +1 to do on Monday so will put all this to practice and report back

1 Like

I start intervals by ramping up power, gear and cadence in blocks of short time before the actual start of the interval. Typically -10 seconds, -5seconds and -3 seconds works for me. So for example if I’m recovering at say 150W and the interval prescribes 400W at -10 seconds I’ll bring it up to maybe 250W; -5 seconds 350W; -3 seconds just under 400W and manage it from there.

I think you are not yet used to the power being displayed being a 5-second average of your power (by default). That means you are pushing too hard because you haven’t gotten used to that yet (the displayed wattage is still much lower than your current output).

I have a dumb trainer, too, and it indeed takes time to get used to. I now start slowly ramping up about 5 seconds before my rest period is over and that works very well for me.

1 Like

I would also say to not be too worried about nailing the power target on VO2 intervals. The goal is to overload your oxygen uptake which can be done at any sufficient intensity. Go as hard as you can while still being able to produce z6 efforts at the end of the interval. It’s about wringing the watts out.


Thats what I normally do, except it gets a bit tricky when you only have 10 seconds of recovery in between intervals

1 Like

That’s actually a really good point and is something that’s easy to overlook. I’ll consider this next time

Check your gearing. On a dumb trainer, one tooth jumps on the cassette is best. It does not totally fix the issue but your power jumps should be smaller. This is another reason a dedicated trainer wheel is great. Rarely will the perfect outside cassette gearing be perfect for indoors on a dumb trainer. Get a cassette that has the cogs you need.

Don’t be a slave to hitting exact numbers. Power targets are ranges (read the workout instructions). You only get a fixed single number from the TR app because that’s how the app necessarily works so it can work in erg mode. If the target is 350 and 340 or 355 fits your gearing better, just go with it. Calculate the ranges Chad has in mind for the intervals and that my ease some of the tension you feel trying to hit an exact number.

One advantage to the dumb trainer is you actually have to think about and execute gear shifts This is just like riding hard efforts outside. So think of this as a feature not a defect!