This lesson discusses three types of physical activities: aerobic activities, muscle strengthening activities, and bone strengthening activities. Aerobic activities deliver oxygen to the muscles to sustain physical exertion for extended periods. Examples are jogging and swimming. Muscle strengthening activities cause muscle fibers to contract and repair, making muscles stronger over time through exercises like pushups. Bone strengthening activities apply physical stress to bones through muscle contraction, stimulating bone growth and increased density through activities such as running. The lesson emphasizes the importance of the FITT principle of frequency, intensity, time and type when designing a physical activity routine.