An Active VS Sedentary Lifestyle

What happens to the body of a person who lives an inactive or even sedentary lifestyle and how does exercise affect the body?

I recently came across a relatively old report written by the CDC in 1999 that details what happens to the body during long periods of inactivity as well as long periods of exercise. Below is information from Chapter 3 of that report.

One of the important aspects of an inactive and even sedentary lifestyle is that not only does one miss out on the benefits of exercise, but one also experiences negative effects of the inactive/sedentary lifestyle—a double-whammy.

The other thing that struck me in the report was just how fast the body begins losing the benefits of exercise after one stops exercising altogether. For example;

With complete cessation of exercise training, a significant reduction in VO₂ max and a decrease in plasma volume occur within 2 weeks; all prior functional gains are dissipated within 2 to 8 months, even if routine low- to moderate-intensity physical activity has taken the place of training.

(Physical Activity and Health: A Report of the Surgeon General, 1999, p. 72)

Effects of sedentary lifestyle

The affects of a sedentary lifestyle are similar to the affects of reduced gravitational forces on astronauts* (Physical Activity and Health: A Report of the Surgeon General, 1999, p. 72):

• Decreased cardio-respiratory function
• Increased glucose intolerance and elevated blood levels of insulin in relation to glucose levels
• Loss of muscle protein
• Loss of muscle mass and strength
• Loss of bone mass and strength
• Loss of plasma volume (affecting aerobic power)
• Shrinking and weakening of ligaments and tendons

Effects of exercise

• Increased muscle mass (hypertrophy), as well as:
• Increased oxygen extraction rates by muscle tissue
• Improved choice of energy sources for muscle tissue
• Improved waste removal (lactic acid) by muscle tissue
• Increased VO₂ max
• Improved lactate threshold (activity endurance)
• Stronger ligaments and tendons
• Substantially increased size and number of mitochondria (cellular power plants)
• Increased capillaries and overall blood flow to muscles
• Increased use of fat stores as energy for muscles

Of course, all of the above is affected by age, sex, and even environmental conditions, but the overall impact is the same: bad shit happens to the body of a couch potato and good shit happens to the body of one who exercises.

References:

1. Physical Activity and Health: A Report of the Surgeon General. (1999). Centers for Disease Control and Prevention. https://www.cdc.gov/nccdphp/sgr/pdf/sgrfull.pdf