Have you ever tried balancing a 50 kilo sack on top of your head? Now try riding a bike along a main road with a full sack. Sounds tricky? One needs strong neck muscles plus robocop features to be able to ride a bike as such.
I guess Manong is just training for a future bike competition… thus he is adding weight to his bike, so when there is no extra weight, he shall fly like a butterfly.