Recently, ACSM recommended VO2 Reserve as a method to prescribe exercise intensity.
Lower intensities can illicit improvements in individuals with very low initial levels of fitness.
A walking program can progress in intensity by slowly increasing the speed every week or month. After several weeks have passed, the fast RPM is reduced with a corresponding increase in level or watts. The ACSM recommends 20 to 60 minutes of continuous aerobic activity. Time constrains of the individual must be considered. Initial programs may last 12 to 15 minutes and progress toward 20 minutes.