I recently did a self supported full distance triathlon using Swift for the bike portion (180km). I did the ride at the same wattage and speed that I would outdoors. I have ridden and ran this distance multiple times before, however, this was my first time doing the bike portion on Swift. My legs were significantly more fatigued than after riding this distance outdoors and my marathon time was a full hour slower than what I would normally run. Has anyone else had the same experience? If so, why? Or am I just getting old and slow? Thanks!
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I expect the issue is simply down to the physics of working on the trainer.
Outside you gain inertia and the effort required to maintain that intertia, despite you putting out the same power, is different.
On the trainer you are constantly fighting a fly wheel that want to stop, so you really have to stay on top of that power.
Outside you will also get some micro rests (cornering, over crests of hills, short descents etc) and these added up over time will reduce the overall workload.
I’m sure someone will weigh in and discount my theory though…
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… not me - fully agree. If you compare a Zwift ride and a similar real world one, the real one will have a lot more variability in the power and cadence from moment to moment.
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Nope, I agree 
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Thanks! I feel better already. I will disregard any comments that contradict you. 
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Above is true, but some additional things:
- Cooling
- mental distractions
- descents - only 50% replicated gradient so far less opportunity to freewheel, if you do at all
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Riding the trainer - especially zwift - is significantly harder than racing Pro/1/2 criteriums around the US. This year I’ve struggled to finish bigger zwift events with the front group but I managed a few podiums and even more top 10’s in pro/1/2 races across the eastern us. Honestly I couldn’t imagine doing 180km on the trainer. Sounds like a miserable experience after the first couple hours.
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Leg fatigue after 180k ride on Zwift?
I rest my case
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I’m a B Rider in our Club (~2.8-3 w/kg). On Zwift, I have a Hard time staying with a C Ride @ 2.5 for 60”
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If your FTP is (~2.8-3 w/kg) then holding 2.5w/kg will not be easy.
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I had a similar chat today, as I’ve never had such sore glutes from biking outdoors as I’ve had with the rides inside. Not only is the above accurate, but also the fact that you aren’t really moving, shifting, and such. The bike is upright, and that’s that. The body dynamics are therefore also much less, well, dynamic, firing the same muscles, rather than changing it up while moving your bike around when biking outside.
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I completely agree. Overall, Zwift is much more intense than on the road. The load on your muscles almost never decreases. Bends and descents also do not give any recovery because you usually keep pedaling and never have to slow down. Climbing is a different story. Here Zwift comes pretty close to reality. I have climbed Mont Ventoux in France several times with mountain bike and racing bike and the feeling and muscle load differ little. The fan gives more wind cooling at the bottom of the ascent but the coolness at high altitudes actually compensates for this. Wind is a different story. In any case, I’m glad I can use the smarttrainer every now and then.
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It makes sense! I add that Training Stress Score is the best way to measure how much effort our body put on some workout, not Average Power.