If I stand on the Zwift trainer it rocks and feels like it’s going to tip over. Does not give me confidence to stand and try to hit those high watt outputs on the workouts. Any tips to help with this?
Have faith, it won’t tip over. It’ll actually only be rocking by a few degrees.
It takes some monumental effort to tip over a turbo trainer.
Make sure you’re trying to stay in control when you stand. For massive efforts, you might see people in IRL races throwing their bikes side to side. But even then, their bodies are very stable. For a bike on a trainer, you need to try to limit the amount that your body is shifting/flying/rocking side to side. In the same way, it’s good training to try to be able to stand without leaning too much on the bars. If you can stand and put power through the pedals with a very light touch on the bars, you know you’re in control of yourself. And being in control means you can put your power where it needs to go. Much of the time, throwing your weight side to side is limiting the amount of power you can put through the pedals anyway. 
For a reference, check out Elena’s sprinting form at 16:42 of this vid. Elena is a beast, a far better rider than me But I guarantee, and you can see it in other vids in the series, that she does not sprint on a real bike on tbe road like she does in this vid. She’s all over the place. Compare that to the other women, much more controlled. And Elena isn’t a sprinter, and again she doesn’t do that IRL in the other episodes. So I’m not trying to dog her Just saying that this is the form I was always told to avoid when standing, sprinting, etc. You can bet your trainer will be flying around at that point.
Thanks Stuart - is this advice including the Zwift Hub? I’m wondering if it’s less stable than some of the others?
Thanks Tom. This is very useful and does make sense that it would be a technique issue - especially as I know I tend to throw the bike around IRL if I’m standing up. I’m a 256 FTP and 85 kg so I was finding it hard to see how I could hit and maintain a 680 10-second burst (asked for in the workout) even using my full weight on the pedals.
Bob,
You are pretty much the same weight and FTP as me. You should be able to hit 680w seated. In fact I’d say sprinting on Zwift should mostly be seated so definitely a technique to work on.
I’ve not ridden the Zwift Hub personally but i can’t imagine that any modern trainer hasn’t been thoroughly tested for such issues.
Some reviews of the Zwift Hub have noted that it is less stable than other trainers due to the design of its feet.
Strapping it to a rocker board would probably help a lot, if you can afford that solution. That would let you get as crazy as you want in the sprints.