Spanish Needle and other 'microburst' workouts

Hello fellow TR users, when completing Spanish Needle and other ‘microburst’ workouts is it recommended to change the Smart Trainer from ERG mode to resistance or another mode? Reason I ask is that I find the Trainer (Kickr19) when using Power Match struggles to catch up with the 15 second changes in Power.

I would really appreciate other users observations and recommendations on what setting to use.


1 Like

Flick it over to resistance mode and use your gears. That tends to be the recommendation if you’re having trouble with ‘microbursts’.

If not, you can drop your cadence just prior to the start of the interval and mash away as soon as it tries to spiral. Another trick is to use lower gears so the trainer can adjust quicker.



I do them in ERG mode w/out issue.

A couple of tips:

  • Small chainring, middle of your cassette, straight chain line. e.g., 36x21
  • Keep your cadence high and steady, even during the “rest” interval, as in at least 100rpm
  • Get your cadence up to 105-110 during the rest and as the work starts, during the first couple of seconds gradually back off closer to 100. This helps to ramp the resistance quicker.

You will see TR report that your avg is lower than the target after each interval. If this is really bothering you, then increase the loading 1-3%. Be careful! The avg is not telling the whole story. You might not be making the avg per interval, not even once. But, you will probably find your TSS is on target or maybe even a point or two higher. Why? Well, TR is measuring for the exact time interval specified in the workout (e.g., 10min-10min15s vs 15s). The former is what you see programmed into the workout. The latter is any 15s. The trainer takes 2-3sec to ramp up, but it also does not drop resistance immediately either. As a result, TR 15s avg is below target, but you may have actually met the target power over 15s (10min3s - 10min18s). Note the difference between green and yellow below:


Thanks for the feedback and tips guys. Good point around the TSS, historically the TSS is on the money yet the bar graph doesn’t always appear to have hit the target. I do run in the small ring / straight line so will try both options and see how it goes.

Usually 90-95 is a good cadence for me, depending on the workout. I assume once I start to fatigue keeping it up at 100 rpm is going to be a challenge, worth trying. Thanks again for the advice.


I’ll add my n=1 experience: I just did Junction yesterday, which has 3 of the Spanish Needle type sets at the end. Running a quarq and Kickr, for reference. I was fine leaving it in erg mode, however, I was finding that my quarq power readings I would see on my computer would get quite a bit higher than the TR target, 520W vs. target of 480ish and the interval is so short it doesn’t have time fully adjust down. So I dropped the intensity down to 97% and the numbers were much more in line with the target. I do agree with all the tips above (keep rest cadence high, small gear etc). I’ve yet to do one of these workouts in resistance mode, probably try that the next time it comes up.

Resurrecting this after a little search. Think I read this before my last workout as I was going into Wynne and wanted to know how I could make the high power intervals hit the target power quicker whilst keeping erg mode on.

It tend to always use the big ring and change gears when needed to hit the target power quicker but tried the little ring for the 3rd interval. First two were comfortably hard. Ie never thought I’d fail the third! However in the little ring it was just so much harder!!!

Why is that? Slower speed on flywheel so more torque needed?

On tacx flux 2 FYI.

Cheers :blush:

Opinions vary, but I feel that the slower flywheel demands more power through the pedal circle when compared to faster speeds.

Less debatable, and potentially able to explain the difference on it’s own, is the fact that most resistance units respond faster in ERG mode with a slower flywheel speed. You are essentially putting the trainer in it’s most advantageous setting that will work to hit the target power sooner and hold it more steady.

Thanks for input. Interesting you say that its less debatable with the little ring. I found that the ramp up to full power didn’t happen any quicker than when using the big ring. I dont think you can see particularly clearly in the screenshot, but just my thought whilst I was on the trainer (about to die…)

Doing 40/20s tonight so will experiment again!

I was asking myself the same. Knowing I’m on a vortex and wheter in ERG or resistance there is a 3 second lag between power output en the reading. It seems to be less of an issue on TR than Zwift though. On zwift it’s terrible. Imagine having a 3 second lag on a sprint. You start the sprint zwift takes 3 seconds for the reading… The sprint is over your avatar crosses the line as if the race was still on.

1 Like

The general feedback and pure physics show that the slower flywheel is easier for a resistance unit to “grab”. Just imagine trying to add resistance with your hand on a wheel spinning at 5 mph vs 20 mph. There is more energy in the faster one, and that will require more force to control.

Yep, exactly. I never really hit the ‘right’ average on these workouts, but by the end of the 15s intervals my instantaneous power is always higher than the target.

I have covered this issue a couple of times.

1 Like

I’ve got a Kickr18 and I plan on switching to resistance mode for VO2max intervals up to 2.5 minutes. What I’ve found is that my Kickr does not do well when I spin up to cadence for the interval.

When I’m in the valley I’m spinning about 85 rpm, I start spinning up to 100 rpm up to 15 seconds before the interval hits. When the interval hits my power is low and the kickr compensates by increasing the resistance which makes me feel like I’m hitting a wall, my cadence ends up dropping to 80 rpm and I have to grind it back up to 95. This then makes my power skyrocket and causes the kickr to drop the resistance, rinse and repeat until the end of the interval. You can see this effect in my workouts and it makes the interval much more difficult to get through.

I’ve found that longer intervals, probably 4 minutes or more, doesn’t have this rubber band effect because the power is significantly lower. Jumping from 100 watts to 220 watts is more manageable for the trainer than 100 watts to 320 watts.


Since TR sends the resistance change about 2 seconds before the actual countdown start, I plan the hit the gas on about 4-3 on the countdown. I plan a slight over-spin to help ramp into the effort, and the added resistance tends to pull me down to my actual cadence target.

1 Like

If you do decide to switch modes for those shorter, higher-intensity efforts, you can use keyboard shortcuts if you’re on desktop to do so. :grinning:

Hit the “M” key to switch trainer modes. Then you can quickly adjust the resistance % with the up/down keys.

We’ll also save your resistance % / slope setting, so you don’t have to fiddle with it too much when you change modes. Just figure out what works best before your workout, then we’ll automatically switch to that saved setting when you hit the “M” key.

1 Like

Yup, now we just need a way to do the same fast swap on mobile :stuck_out_tongue:


Right so 40/20s. Big ring in 4th gear for recovery intervals and clicking to 5th right at the start of each effort. Took 4 seconds to hit target power. Don’t think that’s too bad!

1 Like

This is almost exactly what I do. I’m using a TACX Flux and I’ve found this method really smooths things out.

1 Like