Demonstration of CO2 rebreathing method to measure total hemoglobin mass in Olympic cross country ski athlete Liz Stephen. (Photo courtesy of Noah Hoffman.) Source: Altitude, Pollution, and Underwater Diving: Effects on Exercise Capacity, Exercise Physiology Citation: Porcari JP, Bryant CX, Comana F. Exercise Physiology; 2015 Available at: http://fadavispt.mhmedical.com/DownloadImage.aspx?image=/data/books/2182/exercphys_ch29_f004-1.png&sec=165660692&BookID=2182&ChapterSecID=165660607&imagename= Accessed: October 07, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved