I have these 1kg weights that I can strap to my ankle. If I wear them all day, how much extra energy will I expend?

Assume that on an average day I walk about 5km at roughly 1m per step, and go up and down a 3m staircase 15 times.

I think I’ve got the vertical component down (rounding g to 10 and assuming I raise each weight by 5cm per step, that’s 10 * (0.05 * 5,000 + 3 * 15) = 2,950 joules, or about 0.7 kilocalories, which ain’t much) - but have no idea how to work out the horizontal bit. It’s been quite some time since I did physics. Anyone care to help me out?