The three 12-hour riding shifts in as many days have now raised over £340,000 for the NHS.
The 2018 Tour de France winner was riding on virtual riding platform Zwift and streamed live on Thomas' and Team INEOS' Facebook pages.
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"No exaggeration, the last two hours were the hardest I have ever had on the bike - I could barely sit down," said Thomas.
"I am going to have a week off to recover from this. It was 36 hours in the saddle over three days which would normally be a big training week for me.
"The longest ride I have done on the road is eight hours and 20 minutes in a group and that was with a coffee stop.
"On a turbo the longest was three hours and there is a lot of difference from that and riding outside where you have the scenery and downhill."

Thomas excited that Tour de France is going ahead this year

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