“Crank length is part of a system of hinges and levers that must operate in the larger context of an individual’s biomechanics.
Longer cranks increased flexion and the range of movement required at both the hip and knee.
Where there is indecision, cyclists should opt for a shorter crank to reduce the risk of injury.
There does not appear to be a strong argument for optimising crank length in terms of pure performance.
There was no significant change in power when cranks were as long as 200mm or as short as 150mm.
Longer cranks can make a difference, but only for short sprints from a standing start with a fixed gear ratio.”