So I’m relatively new to Zwift racing… My first 2 were in CAT C where I almost died of a heart attack and could not hold a wheel anywhere close to the front or middle. My 3rd race I decided to drop to CAT D and managed a 2nd place podium(hurray). Of course I got disqualified with UPG. I accept this (sandbagging)but the people not disqualified all around me were riding at 2.2 W/KG with 135HR… I was at 2.6 with avg HR 157 and up to 187 at one point and not able to hold any wheel if I went slower. Again I’m not complaining(It’s clear to me now that I’m C) about the disqualification but how can the others be so fast with lower W/KG and walking HR? I was on Specialised Pro bike and not TT. Thanks for feedback.
Cat limit for Cat D is <2.6w/kg (see: ZwiftPower - Login )
So if they’re doing 2.2w/kg that is fine.
Categories are not based on heart rate in any way shape or form.
That said, 2.6w/kg at 157bpm is massive sandbagging in Cat D so on to Cat C you go 
Speed is also dictated by frame/wheel choice (specialized pro is NOT a good bike for flats & wheels have 3x the impact of frame, see here for some better options: Fastest Bike Frames and Wheels at Each Zwift Level | Zwift Insider ), height/weight, as well as power. And drafting. And powerups. So if you’re riding out front a lot, you’re gonna be putting out a lot higher average power than someone sitting in the draft saving 20-30% power for the whole race).
Thanks for the tips… Best regards, the Massive Sandbagger 
Why? I am doing 2.6-2.8 W/kg at about 155-160 bpm. I am at the real bottom of C (average of the three best in the last 90 days 2.61), it is not really funny to race (that’s why I am doing workout now, no races).
If you think someone riding at 157 bpm is sandbagging - that is nonsense, it depends - I am 62, did a FTP test with heart control last year and my max bpm should not extend 170 - means averaging 157 is 92%.
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Yup that’s very true. I’m 46 and 157 HR is not hugely taxing for someone of my age and level of fitness. I do however have a surgically fused ankle and lower limb dystonia. Anyway, my main question was about why I have to put in so much additional effort in comparison to others to get the same speed. Ben’s answer has pointed me in the right direction. Look out cat C, here I come
he said his max is 187
for comparison: my max is similar and i ride at 170-180 in races
157 is basically a recovery ride (with a max of 187)
if ur 62, then yea, totally different ball game…
To be fair my absolute max sprint HR is 187 and there is no possible way I could average anything over 167 for longer than 30 mins… so 157 over 35 mins feels more like a sweet spot ride for me… we are all different in the end.
Thanks for the feedback chaps
If your max is 187, then you upper lactate level will be around 167, hence why that’s uncomfortable over a long time. Nobody can maintain their max HR for more than about a minute, nobody can maintain their upper lactate level for hours and hours.
So yes, I’m with most everybody here. If you well above the Cat C power limit at 10 bpm under your approx upper lactate level, you’re a massive sandbagger, sorry
As for the 135 bpm-ers, maybe they’re sandbagging, maybe they’re old, maybe they struggle to get to high heart rates indoors. All are possible, neither you nor zwift can really know (unless they have other data in their history)
At no point did I challenge the sandbagging label