Erg mode and sprints

I have a few questions about short power workouts, erg mode vs resistance, and maybe about my specific trainer.
I have been using TR since this summer. First General Base (LV with a Sunday ride added), and now Short Power (also LV with an added Sunday ride). I have been using Erg mode for all trainings, usually with Zwift running in the background. If it is relevant: I am 60 yrs old, 179 cm, 80 kg (which is 10 kg above race weight) and my FTP is just under 300 at the moment. I use a Tacx Genius (wheel on) as trainer.

It has been mentioned before, but the Tacx Genius needs some time to ramp up the Watts. It takes about 10-12 seconds to go from 114 W to 560 W (which are the numbers I need to hit in rest and for a sprint). That means short sprints (6 - 10 seconds) are not very effective, as I don’t reach the power needed. Sprints from 12-15 sec reach the power, but only just. Longer sprints are ok-ish - I do less work than intended, but am getting close.
First question: is reaching the power enough for training purposes? Or do I need to sit at the the prescribed power for most of the time?
Second: Only way of doing the amount of work prescribed in the sprints (in erg mode) seems to be the lenghten each sprint with about 5-6 seconds. But that is quite a bit of work… Any other suggestions?

For today I had to do Thor -1. ( 3 short hard sprints each interval, followed by 4 minutes at FTP). I tried to do this in resistance mode, to get the sprints right. First time in resistance mode for me… So, at start I simply could not get the pedals around. Only at the lightest gear (30/28; I got an old bike with a 3 x 9 as training bike) could I get going, and even then I got 200 W at 60 RPM. Resistance mode showed a % slider (on a PC here), at a default 67%. Dropping it to 33% got me going. Even then, I had 150W at 80 RPM in lightest gear, and had to go to one of my highest gears (50/13) to get to 560 W without spinning out. This much gear changes (with a double shift at the front, and the risk of dropping a chain) was pretty annoying.
Question: Do I anything wrong here? Can’t believe this is what other people use….

So after a few intervals I changed back to erg mode. The first interval I wasn’t quick enough ramping up the legspeed and got bogged down. It felt like the power ramped up quicker - did the % slider change cause this? Or was I just distracted and forgot to prepare? I did go back to resistance mode (during the recovery) set the slider to 50% and got back to erg mode. I think this made things better - in that erg mode now reached 560 W without me bogging down - but it could be me paying more attention.
Question: does the % slider change the speed with which the trainer ramps up the resistance? (and if it does: maybe keep the slider visible when in erg mode?).

That seems to be it - I am curious how others with a comparable trainer do trainings like this one…


My Tacx Neo ramps up in 3-4 seconds. Power smoothing is set at 3 seconds.


Spanish Needle:

On Spanish Needle with 15s sprints, my average power per interval were all within 5% of target, some over some under. Some were within 1 watt.

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Some trainers are better than others in ERG mode. Direct drive and higher end tend to do much better than wheel-on or mid-range trainers in short type intervals.
Personally I like to turn erg mode off when doing sprints even longer 1-3 min intervals. I think the whole idea behind these workouts is to chase after new limits not follow a prescribed wattage. Others might have a different opinion though!

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I just got a smart trainer (wahoo kickr core) and tried a workout with sprints 20 mins sweet spot with 15 second max sprints thrown in every 5 mins (This was a prescribed workout not from TrainerRoad sorry!)

My turbo ground to a complete halt and I hit a brick wall of power as the prescribed power from my training peaks file (approx. 850w) obviously wasn’t compatible with my trainer!

So id say don’t use erg mode for sprints i definitely won’t be again! How do I use my smart trainer non erg mode when I load a workout on my wahoo ELEMNT it automatically goes into erg mode?

I use a Wattbike Atom, and with the current s/w, it takes around 3-4 seconds to build to a higher power, seemingly no matter what the differential is. I tend to try to ramp the effort up at the end of the current interval, but sometimes that means that I can’t get a steady power for the next (higher power) interval.

I try not to do <10 second intervals, as it takes time to wind up, but drops the power instantly at the end of the interval. 20 second intervals are fine, 15 OK, but shorter I feel don’t give an accurate result.

I have used Wattbike model Bs before investing in the Atom, and the ability to feed power in almost instantly made short intervals easy. I did a lot of 8 sec tabata style sessions for instance.

The newer (?) TR sessions with the build up are easy to cope with though, but that kind of defeats the object of getting higher power short on / off sprints.

I have my smoothing at 6 seconds.