Development of a Realistic Inertial Load Cycle Ergometer

Abstract

Maximal mechanical power output is an important component of exercise and sport, but it is difficult to measure due to its instantaneous and dynamic nature. A common way to measure maximal mechanical power is cycle ergometry. Several methods of cycle ergometry are used to measure maximal power output including: force-velocity, Wingate, isokinetic and inertial-load methods. Each of these methods has inherent advantages and disadvantages owing to the intricacy of equipment, complexity of administration, accuracy of results, capability to measure instantaneous power and length of test. Of these methods, the inertial-load method is the only method that allows for instantaneous maximal mechanical power to be measured in a single bout. However, an inertial load ergometer that simulates over-ground cycling has yet to be developed. PURPOSE: Our purpose was to develop a realistic inertial load ergometer (RILE) that would accurately measure maximal mechanical power in a single exercise bout and be able to accurately simulate over-ground cycling. METHODS: Overall we modified an adjustable stationary bicycle to effectively have a large gear ratio driving a heavy flywheel. The large gear ratio is accomplished by having an intermediate gear drive installed between the crank and the flywheel. The bicycle drive uses a standard chain ring and cassette-hub so that subjects can use familiar gear ratios. On the left side of the cassette-hub we mounted a 54-tooth chain ring, which connects via a second chain to another cassette mounted on a flywheel. The secondary gear ratio can be changed by the investigator to produce an individualized realistic inertial load based on subject + bicycle mass. An optical encoder, that provides 100 pulses per revolution, measures angular position of the flywheel. Angular velocity and angular acceleration of the flywheel are then calculated in software. Maximal mechanical power is calculated as the product of the effective moment of inertia (Iflywheel•gear ratio2), angular velocity and angular acceleration of the flywheel. CONCLUSION: Construction of the RILE opens the door for testing of many research questions regarding maximal mechanical power. This ergometer can be used to evaluate: aspects of aging and development, muscle strength and speed, effects of athletic training programs, physiological differences in performance and cycling specific situations such as accelerating from a standing start and sprinting. A future goal is to make the RILE also able to simulate aerodynamic resistance. Incorporating both inertial and aerodynamic resistive forces into the ergometer will provide an accurate laboratory simulation of over-ground cycling.