1. The position of the muscle relative to the length-tension relationship
2. Number and size of motor units i.e. #number of cross-bridges in parallel (ideal for force)
3. Length of the muscle fibres i.e. # of cross-bridges in series (ideal for velocity)
Architecturally speaking, quadriceps and calf muscles are well designed to generate force due their low muscle fibre:muscle length ratios and large cross-sectional areas. However, hamstrings tibial muscles are well designed for velocity by nature of their high muscle fibre:muscle length ratios and long muscle fibres.