Although observational studies cannot prove a causal relationship, when studies in different populations have similar results and when a possible mechanism for a causal relationship exists, this provides evidence of a causal connection.
What is known about the relationship between physical activity and cancer risk?Įvidence linking higher physical activity to lower cancer risk comes mainly from observational studies, in which individuals report on their physical activity and are followed for years for diagnoses of cancer. Examples of sedentary behaviors include most office work, driving a vehicle, and sitting while watching television.Ī person can be physically active and yet spend a substantial amount of time being sedentary. Sedentary behavior is any waking behavior characterized by an energy expenditure of 1.5 or fewer METs while sitting, reclining, or lying down ( 1). Light-intensity activities expend less than 3 METs, moderate-intensity activities expend 3 to 6 METs, and vigorous activities expend 6 or more METs ( 1). One MET is the rate of energy expended by a person sitting at rest. Physical activity can include walking, running, dancing, biking, swimming, performing household chores, exercising, and engaging in sports activities.Ī measure called the metabolic equivalent of task, or MET, is used to characterize the intensity of physical activity. Physical activity is defined as any movement that uses skeletal muscles and requires more energy than resting.
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