There's nothing particularly special about economy class legroom in the A380.
Like Hotel Tango I have no experience of the Malaysian A380, but a look at Seatguru shows that it does have some exit row seats with extra legroom in the Economy cabin. However, I have no idea what the airlines policy is on these, i.e. whether you have to pay a fee to reserve them or if there are any restrictions in terms of physical ability.
If you have to get up regularly to exercise, I think it's inevitable that you'll disturb your neighbours if you have to squeeze round them, so unless you can get an exit row I would go for the aisle seats.