A crank assembly for a bicycle's bottom bracket assembly comprises a shaft extending along a longitudinal axis, at least one crank arm associated with at least one free end of said shaft, first front coupling means formed on said shaft and second front coupling means formed on said at least one crank arm, said first and second front coupling means being coupled together. In particular, the aforementioned first and second front coupling means comprise respective front toothings. The front coupling is located in an end zone, or on the outside, of a bottom bracket assembly's shaft's housing box formed in the bicycle's frame. The front coupling introduces a structural discontinuity between crank arm and shaft, for which reason the bending load exerted on the crank arm during pedaling is transmitted to the shaft to a small degree. Such a structural discontinuity is located at the shaft/crank arm interface.