The objective of this paper is to present a technique to determine the effective work done by the rider in seated cycling condition by using the pure physical laws so that his pedalling efficiency can be easily evaluated. To this end, the rider-bike system is modelled by a two-dimensional mechanism consisting of crank, shank (lower leg), thigh (upper leg) and a stationary segment (framework) joining hip to the crank spindle. For convenience, the crank, lower leg (right or left) and upper leg (right or left) are called Rod1, Rod2 and Rod3, respectively, and the “critical angles” of Rod1, Rod2 and Rod3 in four “critical positions”, uppermost and lowermost positions of Rod3 along with horizontal and vertical positions of Rod1, are determined first. Next, the mathematical expressions for the instantaneous positions of Rod1 and Rod2 corresponding to any specified position of Rod3,  or those of Rod2 and Rod3 corresponding to any specified position of Rod1,  are derived. It has been found that the angle between Rod1 and Rod2 at any instant of time tis given by    with  and  denoting the angle between Rod1 and (vertical) y-axis and that between Rod2 and (horizontal) x-axis, respectively. In such a situation, the crank torque induced by the driving force  transmitted from the lower leg (Rod2) is given by  with  denoting the radius of crank (Rod1). Finally, the effective work done by each leg (right or left) in the downstroke of each pedalling cycle can easily be obtained from the integrations of  through the angles from  to  where  and  are the (critical) angles between Rod1 and y-axis when Rod3 is in its uppermost and lowermost positions, respectively. It is obvious that the larger the effective work, the higher the pedalling efficiency of the rider.

engineering mechanics, rider-bike system, pedalling efficiency, crank torque, effective work.