Physical activity is any movement produced by muscles that increases energy expenditure.
Leisure-time physical activity is any activity not related to a person’s occupation. Exercise is a
subcategory of leisure time physical activity and is purposeful, planned and structured. Physical
fitness is the ability to carry out daily tasks with vigour and alertness, without undue fatigue, and
with ample energy to enjoy leisure time pursuits and meet unforeseen emergencies. The
components of physical fitness include cardiorespiratory fitness, musculoskeletal fitness, and
Physical activity provides a multitude of health benefits, including reducing our risks for obesity
and many chronic disease and relieving anxiety and stress. Despite the many health benefits of
physical activity, approximately half of Canadians, including many children are inactive.
A sound fitness program has many components. First, it must meet your personal fitness goals,
such as reducing you risks for disease or preparing for competition in athletic events. Second, a
fitness program should be fun and include activities you enjoy. Third, it should include variety
and consistency to help you maintain interest and reap the benefits of regular physical activity.
Physical fitness is specific to each of the components of fitness: endurance, flexibility and
To improve fitness, you must place an extra physical demand, or an overload, on your body. To
achieve appropriate overload, the FIT principle should be followed; FIT stands for frequency,
intensity, and time of activity. Frequency refers to the number of activity sessions per week.
Intensity refers to how difficult the activity is to perform. Time refers to how long each activity
Warm-up, or preliminary exercise, is important to get prepared for exercise. Warm-up exercises
prepare the muscles for exertion by increasing blood flow and temperature. Cool-down activities
should be done at a low intensity, and cooling down after activity assists in the prevention of
injury and may help reduce muscle soreness.
ATP is the common energy source for all cells in the body. When one of the phosphate groups is
cleaved form the ATP molecule, energy is released. The amount of ATP stored in a muscle cell
is limited and can keep a muscle active for about one to three seconds. For maximal-physical
effort activities lasting about 3 to 15 seconds, creatine phosphate can be broken down in an
anaerobic reaction to provide energy and support the regeneration of ATP. To support activities
that last longer than two minutes, we must derive energy from the breakdown of carbohydrates,
fats and proteins.
To support activities that last from 30 seconds to three minutes, energy is produced from the
breakdown of glucose, in a process called glycolysis. Two ATP molecules are produced for
every glucose molecule broken down, and pyruvic acid is the primary end product of this
reaction. Lactic acid is formed when pyruvic acid is metabolized under anaerobic conditions. To
support activities that last from three minutes to four hours, energy is produced from the aerobic metabolism of pyruvic acid. During this process, pyruvic acid is broken down in the presence of
oxygen, and each molecule can yield 36 to 38 ATP molecules.
Fat can be broken down aerobically to support activities of low intensity and long duration. Each
fatty acid from a triglyceride molecule is broken down for energy, and the amount of energy
derived depends upon the length of the fatty acid chain. The two major advantages of using fat as
a fuel is that it is an abundant energy source and it provides more than twice the energy per gram
as compared with carbohydrate. The primary disadvantage of using fat as fuel is that the
breakdown process is relatively slow so it cannot support quick, high-intensity activities.
Amino acids may contribute from 3% to 6% of the energy needed during exercise, depending
upon the intensity and duration of the activity. Amino acids help build and repair tissues after
exercise. We generally consume more than enough protein in our diets to support regular
exercise, and there is typically no need for protein or amino acid supplementation, even for
The type, intensity and duration of activities you participate in will determine your nutrient
needs. Vigorous intensity exercise requires extra energy and male a