Modification of the Monark bicycle ergometer for underwater exercise

A standard Monark bicycle ergometer was modified for underwater exercise by removal of the friction belt and attachment of one to six metal fins to the flywheel. Three fins could be fastened to either side of the flywheel. The fins used on the left side of the wheel were made of standard perforated angle iron with the perpendicular side measuring 38 mm; those on the right side were made from the same length of nonperforated angle iron but with a perpendicular side of only 26 mm. Net surface area of the two types of fins (excluding area of perforation) was the same. Oxygen uptake (VO₂) was found to be: VO₂ = a(rpm)^b + 0.25, 1.min^-1, with a = 0.00164 - 0.00104n + 0.000266n² - 0.00002n³; b = 1.64 + 0.506n - 0.104n² + 0.00667n³, when n is the number of fins. The correlation coefficient (r) between measured and predicted VO² was r = 0.98. The preferable range of pedaling speeds was 29-40 rpm to maintain a constant speed for up to 1 h. Major advantages of this modified ergometer for underwater exercise are 1) the modification is simple and the same ergometer can be used for land exercise, 2) the ergometer can be biologically calibrated and used for a wide range of exercise oxygen uptakes, and 3) subjects can perform for a proportionally longer time period than other modifications of the same ergometer.