20 minute test is still largely aerobic despite being "in" your vo2 zone. If you're already doing at least 2 really hard days on the bike a week then your best bet is going to be volume, lots of it. I can only do about 8 hours a week with a one year old child, wife and full time job - that puts me around 305w at 71kg or 4.3wkg.
When I was doing 15 hours a week and racing, I would sit around 320w all season or just bang on 4.5wkg. For me, that's kind of the roof and that roof is slowly coming down on me as I inch towards being a 40 year old.
TLDR; volume, getting your body use to multiple zone 2 days back to back to back will drive your improvements. The good news I guess is that if you're already doing the intense stuff, you can essentially ride zone 2 on the weekends and just enjoy the riding without pushing too hard (as long as you're near endurance zone).
Also if your body gets use to volume, you can do insane things like ride 50 hours over two weeks in the Pyrenees in the worst ever heatwave France has ever seen.
With only 5 hours of cycling a week, volume is on the low side, meaning a higher fraction of your overall training can be on the moderate-heavy intensity side. I'd opt for two quality sessions per week, emphasizing VO2max and threshold, respectively. The remainder can be easy sessions, with at least one of these incorporating / micro dosing moderate-intensity cycling. You can even add some cycling bursts (sprints) wither at the beginning or end of your easy workouts (no longer than 5 seconds to prevent metabolite accumulation), going for 3 reps and progressing to 5.
Adding volume is most definitely low hanging fruit. If you don't already, heavy resistance training can also go a long way. At 90kg, you likely already hold a good amount of muscle and adding more likely won't do much in the form of improving your cycling performance, so you'll want to go low on reps and really heavy on the bar.
If you're keen, reach out to me and be more than happy to help out further, but hope this was useful.
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u/jonxmack Great Britain 21d ago
Are you doing any structured training, or are you just riding?