Figure 2. Normal and propulsion force orientations. Positive Propulsion Force is the force driving the pedals in a clockwise direction. Negative Propulsion Force is the force driving the pedals in a counterclockwise direction. Positive Normal Force is the force that is applied perpendicularly downward relative to the pedal-crack junction. Negative Normal Force is the force that is applied perpendicularly upward relative to the pedal-crack junction.