Biology 100 - Concepts of Biology
hat exactly do we mean when we say a person is physically fit?
You'll recall that many of the activities
required to sustain life (e.g. active transport, growth, movement) require energy.
This energy is produced by
the breakdown of food (carbohydrates, lipids, and proteins) through the process of respiration.
Also recall that the
most efficient release of energy occurs in the presence of oxygen (
However, unlike food,
oxygen cannot be stored in the body.
It must be constantly taken into the body and transported to all cells to sustain
Muscle cells used to produce movement in a physical activity demand large amounts of energy.
As the need for
energy increases with increased exertion, so does the need for oxygen in the muscle tissue.
Often during vigorous physical activity more oxygen is required by the muscles than the body can supply.
situations, the supply of oxygen is insufficient to produce all the energy needed by the muscles.
Instead of just giving
up, the muscles release energy from food molecules without oxygen, or
However, this conversion is
not very efficient, and soon the inadequate supply of energy along with the accumulation of anaerobic by-products
(the primary one being lactic acid) results in fatigue.
The more vigorous and prolonged the activity, the greater is the
” that develops, and the greater the stress on the heart, lungs, and muscles.
Once the activity is over, the
individual will continue to breathe rapidly for a time to provide the body with the oxygen that he or she was unable to
acquire while active.
The oxygen is used to convert the accumulated lactic acid into water and carbon dioxide.
way one makes up or "pays back" the oxygen debt incurred during exercise.
Regular participation in physical activities results in changes in the heart, blood vessels, blood, and lungs, that are
geared toward more efficiently supplying the body with oxygen (aerobic conditioning). Therefore, when we speak of
physical fitness, we are considering (1) how efficiently the lungs (respiratory system) can take oxygen into the body,
(2) how efficiently the heart, blood, and blood vessels (cardiovascular system) can transport it to the muscles during
times of physical stress, and (3) how rapidly the muscles can utilize the oxygen and food to release energy for
The following tests are designed to measure your physical fitness or aerobic conditioning.
Keep in mind the above
idea of physical fitness and try to relate the design of each test to that concept.