For the time being I’m going to have to train on a stationary bike trainer (Lifefitness spin bike). No power device, just heart rate and “level of difficulty”. Has anybody had success training on one of these? Hopefully I can do the 5x5s, 2x10s, etc, but without power and accurate cadence from my bike, would it be hard to do? Thanks for your help.
I would even consider some good seated climb sessions as well.
You’ll be fine. Merckx and many others survived without power meter, HR monitor, cadence sensor etc. Put together the session you would ideally do and simply translate in RPE or/and HR.
I do 2-2.5hr sessions on the spin bike at 24hr fitness before work a couple times a week and ride outdoors on the weekend. I do eventually plan to get a trainer when I move to a bigger place. I even do these session with running shoes on! I use older non minimal run shoes (nike vomero), and switch to flats for a t-run if I am doing one (because I only run in flats now, I can’t run to and from the gym for a bike workout because it is uncomfortable to use flats on these bikes). I have been seeing great gains in races and on my normal loop area. I was worried at first, with all the lack of data, but I don’t even wear my HR any more. I do check my pulse on my neck for 6sec and multiply by 10 a few times to make sure my internal HR monitor is working correctly(I’m getting very good at predicting what my heart rate is within +/-5 beats). Sometimes it’s nice to not worry about every number, i.e, for the past few weeks the pace clock has been MIA from the pool. I’ve been winging it and getting great swims. Did I leave on 7:00 for my 400m reps? Doubt it, but I’m sure I was close enough…
Be sure to leave a pool of sweat behind ( and please consider cleaning it up ) and you should be fine 
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I trained for my first tri while I worked at a health club and did not own a bike. For 2 months I just did 45 minute Lifecycle ‘Hill’
programs until I could save my lifeguard pennies and buy a cheap road bike two weeks before race day. I did OK…
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I know this is hard to believe, but you can actually pedal a cycle without a power meter and cadence.
it’ll totally work.
try to set your position as similar as you can to your road bike. This is easier on a ‘spinning’ bike than a lifecycle.
There are a couple variables you can’t manage on a stationary bike such as crank length. The way around that is to try to be picky about saddle height. Most of the indoor/fitness club bikes now use an SPD style clipless pedal. If so, being careful about position on the bike is even more important since your foot can’t move much on the pedal to mitigate factors like the extra width of the bottom bracket on an exercise bike that could put increased lateral load on your connective tissues, especially at the knee, and the medial knee particularly.
I agree with everyone here though- you’ll get benefit from it and perhaps more than you may initially realize since the work is “concentrated”. You don’t have to stop at lights, etc.
Once or twice a week I do intervals on a hotel stationary bike. Rarely are they as nice as the Lifetime spinning bikes. I prop up my phone on it and do a sufferfest video. All of it with RPE. Even if the bike offers distance, speed, watts, etc… I ignore it all. It’s helped my riding more than had I just skipped those workouts for not having a bike.