Biological Engineering 1(4): 281-289 © 2008 ASABE ISSN 1934-2799 281 Quantifying Energy Expenditure During Water-Immersion in Non-Trained Cyclists W. H. Scott, Jr., F. C. Koh, K. Y.-S. Chiou, K. R. M. Mackey, A. T. Johnson* ABSTRACT. This research project was designed to compare energy expenditures dur- ing water-immersion and ambient-air states at three external work rates of 50, 100, and 150 W. Eleven participants were tested on two separate occasions on a bicycle ergometer in water-immersion and ambient-air environments for 3 to 4 min at 50 rpm. Oxygen consumptions and heart rates were monitored continuously throughout both sessions. Perceived exertion was assessed at each work rate during the final 30 s of the sampling period. Water-immersion produced higher oxygen consumption values (2.21 ±0.20 vs. 1.00 ±0.14 L min -1 at 50 W; 2.64 ±0.33 vs. 1.45 ±0.12 L min -1 at 100 W; and 2.86 ±0.41 vs. 2.00 ±0.16 L min -1 at 150 W). Heart rates were greater in water (142.70 vs. 97.90 at 50 W; 152.73 vs. 113.14 at 100 W; and 163.82 vs. 135.09 at 150 W). Perceived exertion scores were higher in water (11.7 vs. 8.5 at 50 W; 15.0 vs. 10.6 at 100 W and 17.2 vs. 12.7 at 150 W). Energy expenditure rates were greater in the water-immersion environment (769 vs. 348 W at 50 W; 919 vs. 505 W at 100 W; 995 vs. 696 W at 150 W). It was concluded that at a constant external load, water- immersion produces greater oxygen consumption and heart rate responses compared to values assessed in an ambient-air state. This difference reflects the external load required to move the viscous liquid instead of air. Keywords. Efficiency, Ergometer, Oxygen consumption, Pedaling. echanical engineering students at the University of Maryland were about to enter a human-powered submarine race. They had questions about power requirements to propel the submarine if the pedaling had to be done under- water. This study grew out of their queries. With estimates of submarine velocity and drag coefficient, they were capable of es- timating power requirements. However, they were not sure whether their calculations gave realistic power and velocity values attainable by working humans. A search of the literature revealed that some relevant measurements had been made, but nothing was found to answer their questions directly. Submitted for review in March 2007 as manuscript number BEJ 6956; approved for publication by the Biological Engineering Division of ASABE in February 2009. The authors are William H. Scott, Jr., Faculty Research Assistant, Frank C. Koh, Faculty Research Assistant, and Ken Y.-S. Chiou, Graduate Student, Fischell Department of Bioengineering, University of Maryland, College Park, Maryland; Kathryn R. M. Mackey, Graduate Student, Department of Civil and Environmental Engineering, Stanford University, Palo Alto, California; and Arthur T. Johnson, ASABE Fellow, Professor, Fischell Department of Bioengineering, University of Maryland, College Park, Mary- land. Corresponding author: Arthur T. Johnson, Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742; phone: 301-405-1184; fax: 301-314-9023; e-mail: artjohns@umd.edu. M