Interval struggles

I’ve been using trainer road for two months and listening to the podcast since June and love the content. Since I’ve started, I seem to perform well with the low intensity level but struggle with the VO2 sessions, which I know are not easy. I know part of my issues may be timing of my activities and work schedule (60 hrs. a week for the last month). I’m always trying to top carbs off before bed and eat oats and have a small cup of coffee about an hour/hour and a half before I ride. I’m operating on a mag trainer and can never seem to match the power output according to my AI FTP when it’s beyond 180 and feel like I blow up after the first interval grouping. I am just using a speed sensor and HRM. Obviously a power meter in my format would be better, but no idea what the variance would be to know if it’s worth it.

  • Someone may correct me on this, but I think the 60-90 minute slot before a ride is not the best time to fuel. Seems to lead to a “slump” for many riders and is connected to what our body does related to blood sugar levels. Broadly speaking, I see the recommendation to eat 2-3 hours before OR immediately before a ride (around 15 minutes early max) before hitting a workout/ride.

  • With respect to VO2 Max, the power targets should be taken with some grain(s) of salt. VO2 is not directly linked to power for the first part. The second part is that people can have very different VO2 capabilities based upon age, training history and other factors. The common 110-120% FTP targets set by TR may work for some, but they are commonly too high for me on intervals exceeding 2 minutes. So, take some level of review of your workouts and consider if there is a more appropriate power target for you.

  • On top of that, many people advocate for ignoring power all together and just hitting the effort “as hard as you can” within the context of the workout. Interval duration, recovery duration, and interval count are all factors that may lead to someone needing to push harder or easier.

  • Per your comments, I’d think a slight reduction (5% lower at a test) would be worthwhile to see how you handle the workout. Review those results and fine tune. It’s an ongoing process for all of us and VO2 in particular is a tricky one that takes more than just following calculated targets.


Just to add to what Chad said so well already…if you go for the “as hard as you can” approach, some will say that means “and stay consistent across every interval”. So, don’t go “as hard as you can” the first interval, and then “as hard as you can” the second interval, etc., which will leave you cooked and barely able to hit it on the later intervals, but instead go “as hard as you can and maintain close to that for every interval” so that you can complete the full workout as intended. It’s tricky to do this though and definitely takes trial and error! There’s absolutely no shame in going a little easier than prescribed, and if it allows you to train consistently and not have to skip future workouts, all the better!


I think it would be worth it. Even an older wheel-off smart trainer would be worth it. I had a wheel-on tacx vortex with a not accurate power meter and then bought a used Kickr V2 off of a friend. Wheel off is a huge upgrade and, at least, the Kickr is way more consistent in power measurement.

You could also buy some power meter pedals or a simple $300 stages left arm power meter or some other budget option. I’d opt for the wheel off trainer first.

For me the first interval is the hardest. Once I plow thru that the following ones don’t feel as hard. Some psychological barrier I think. Maybe I just need to be more warmed up than the workout has planned.


Welcome to the TR community! :smiley:

VO2 workouts are toughies for sure.

With a speed sensor and HRM, it sounds like you’re probably using VirtualPower. With VirtualPower, it’s important to make sure a couple of things are consistent in your setup.

  • Make sure your tire pressure is set the same for every workout.

  • Tighten your trainer’s roller onto your wheel the same amount each session as well (for example, 3 full turns every time – I used to use VirtualPower back in the day and drawing a dot on the dial you use to tighten your trainer down could be helpful to know how many times you’ve turned the knob to tighten things down).

If your tire pressure and/or pressure of your trainer’s roller pressing up against your rear wheel are not consistent, your power readings may vary significantly from workout to workout – which could be part of why some workouts feel harder than others.

I’d also recommend exploring your cooling options if you haven’t already. Higher-intensity sessions can be very difficult inside as your core temperature rises while you exercise. A powerful fan is an excellent investment for indoor training.

Hope this is a good starting point – feel free to let us know if you have any additional questions!


Totally agree. And oddly, the 2nd to last interval is also hardest for me. I also feel it must be psychological since that one always seems like torture, but then the one after it (the last interval) is easier, presumably because my brain knows it doesn’t have to do another.


I run on the Apex AXS. Looking at the left arm PM after the first of the year. I always feel my efforts are harder than the output displayed.

All great points. This time of year the bike rarely leaves the trainer, but the turns and tire pressure are checked before every ride for sure. Thank you for the input.

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Years (decades) ago I used a magnetic resistance trainer and developed a good way for doing intervals with it.

First, do you know what your max heart rate is? Consider doing a ramp test or some other super intense ride that will give you a good idea of your max. If you are doing VO2 max intervals you want your HR to be more than 90% of max around 1/2 or 2/3 of the way through the interval.

Second, determine the resistance, gear, and cadence that will allow you to hit that HR during the interval. This will take some trial and error, but you are basically using this formula: Resistance (R) x Gear (G) x Cadence (C) = 90+% max HR during the interval. Any change to the inputs R, G, or C will change the power you are creating, so you want to keep it steady - do the intervals with that resistance setting, in that gear (you will always use the big ring so determine which cassette in the rear to shift into), at that specific cadence (within 1 or 2 on either side, so if you target 92 RPM you will keep it in the 90-94 range).

This will take two or three attempts but once you figure out the R, G, and C it’s easy to do. One thing to note is that, over time, you might find that with no change to R, G, and C, your heart rate actually increases during these intervals. For example, say you start with the goal of 90% being 180. After a couple weeks you might be hitting 185 or 186, even though RPE is the same or going down a little. This means your heart is adapting to the efforts and is not just increasing stroke volume, but also its rate, to provide blood to the working muscles.

Just remember that to keep steady power you need to keep R, G, and C constant.