Women have lesser absolute aerobic power because of their decreased muscular mass (Perez-Gomez, Rodriguez et al. 2008). Because muscle consumes the most oxygen during exercise, males have more muscle mass than women, which contributes to their higher absolute VO2 max. However, due to their smaller body size, men cannot carry as much fat as women can, which also contributes to their higher absolute VO2 max. The average male athlete has a relative VO2 max of 60-80% of the average female athlete, with a range of 50-100%. This is because men have greater maximal oxygen consumption values than women. The maximum heart rate of an average man is 150-190 bpm, while that of an average woman is 120-150 bpm. At these levels, men are able to perform more intense exercises for longer periods of time before reaching maximal exertion. The maximum workload an individual can sustain for an hour is called his or her absolute VO2 max. This value can be estimated from a simple test that requires participants to breathe heavily into a tube attached to a machine called a metabolic cart. The technician measuring the test results adjusts the resistance on the treadmill or cycle ergometer so that each participant walks or cycles at a speed easy but still challenging. The amount of oxygen in the participants' lungs provides an indication of their fitness level. A high percentage of oxygen indicates better fitness.