There is a growing body of literature that supports the importance of exercise in the prevention of cancer and cancer recurrence. Exercise helps increase lean body mass, reduces fat and decreases the likelihood of weight gain. To lose weight, activity and exercise must be increased. Bodies with more muscle mass require more energy expenditure than bodies with more fat, thus the more muscle you develop, the greater the amount of calories you burn. Any increase in activity and exercise is likely to have benefits and each person must increase their activity at a level that is appropriate for them. If you have been inactive, it may be important to check with your doctor about limitations, and then begin an exercise routine that starts slowly and increases in intensity and duration over a period of time. If you start too hard or too fast, you may injure yourself and stop exercising. Exercise really needs to be viewed as a lifetime process that has physiological and psychological benefits.
Activity is measured based on METs or metabolic equivalent. One MET is defined as the energy it takes to sit quietly for an hour. When at rest, each person uses the same amount of oxygen which is 3.5ml per kilogram per minute. For the average adult, this means that they will burn approximately one calorie for every 1 kilogram (2.2 pounds) of body weight per hour. A person who weighs 68kg, will burn about 68 calories while at rest. Moderate intensity activities are those that make you move fast or are strenuous enough to burn four to six times as much energy per minute as you do when you are sitting quietly. These types of exercises would include brisk walking (about 3-4 miles in an hour). Walking is an excellent exercise; however, it is important to do enough of it to increase the number of METs. While the American College of Sports Medicine (ACSM) has determined that people need 4-6 METs five days per week, some exercise research suggests that you need more and it is recommended that people strive for 15-20 METs per week. To figure out how many METs you are using and how to increase it, consider the following;
• Walking 1.6km (1 mile) in 20 minutes = 4 METs/hr, thus you would need to walk 4 hours per week to achieve 16 METS.
• Walking 1.6km (1 mile) in 15 minutes = 5 METs/hr, thus you would need to walk 4 hours per week to achieve 20 METS.
In a 2004 study, women diagnosed with invasive breast cancer who exercised greater than 17.2 METs per week had a greater survival rate compared to women who exercised less than that amount, suggesting that exercise is beneficial both in terms of prevention and survival.