Exercise intensity

Intensity is the amount of physical power (expressed as a percentage of the maximal oxygen consumption) that the body uses when performing an activity.

Recommendations to lead a healthy lifestyle vary for individuals based on age, weight, and existing activity levels.

“Published guidelines for healthy adults state that 20-60 minutes of medium intensity continuous or intermittent aerobic activity 3-5 times per week is needed for developing and maintaining cardiorespiratory fitness, body composition, and muscular strength.”[7] The body uses different amounts of energy substrates (carbohydrates or fats) depending on the intensity of the exercise and the VO2 Max of the exerciser.

Specifically, exercise physiology dictates that low intensity, long duration exercise provides a larger percentage of fat contribution in the calories burned because the body does not need to quickly and efficiently produce energy (i.e., adenosine triphosphate) to maintain the activity.

If a person depletes their glycogen reserves after a long workout (a phenomenon known as "hitting the wall"), the body will use mostly fat for energy (known as "second wind").

Ketones, produced by the liver, will slowly buildup in concentration in the blood, the longer that the person's glycogen reserves have been depleted, typically due to starvation or a low carb diet (βHB 3 - 5 mM).

Prolonged aerobic exercise, where individuals "hit the wall" can create post-exercise ketosis; however, the level of ketones produced are smaller (βHB 0.3 - 2 mM).

[9][10] Very low-intensity Low-intensity Moderate-intensity contribution to total energy expenditure (intramuscular and lipoprotein-derived triglycerides) The Centers for Disease Control and Prevention (CDC) recommends that pregnant women engage in at least 150 minutes of moderate-intensity exercise weekly to promote maternal and fetal health.

Studies support that an acute bout of high-intensity exercise in active pregnant women does not lead to fetal distress or adverse effects.

[13] Current evidence suggests that high-intensity exercises may be well-tolerated by healthy, active pregnant women in their late second and third trimesters.