Louise Minchin, 51, is no stranger to physical challenges and putting her fitness levels to the test. But when it comes to her BBC Breakfast co-host Dan Walker, she voiced her concern about his preparation as he gears up to participate in her latest charity initiative.On Thursday, Comic Relief and Children In Need are joining together for one night to create The Big Night In, which will be broadcast on BBC One and iPlayer.As part of the fundraising effort, Louise will be host the Big Bike In alongside the main show, which will see her bike 100-miles on indoor cycling app Zwift, starting at 5pm with a planned break for the weekly Clap for Carers at 8pm.Dan is among others who have volunteered to join her in her mission to raise money to.