Exercise intensity
notability.(November 2021) ) |
Exercise intensity refers to how much energy is expended when
Measures of Intensity
The most precise measure of intensity is oxygen consumption (VO2). VO2 represents the overall metabolic challenge that an exercise imposes. There is a direct linear relationship between intensity of aerobic exercise and VO2. Our maximum intensity is a reflection of our maximal oxygen consumption (VO2 max). Such a measurement represents a cardiovascular fitness level.[3]
VO2 is measured in METs (mL/kg/min). One MET, which is equal to 3.5 mL/kg per minute, is considered to be the average resting energy expenditure of a typical human being. Intensity of exercise can be expressed as multiples of resting energy expenditure. An intensity of exercise equivalent to 6 METs means that the energy expenditure of the exercise is six times the resting energy expenditure.[3]
Intensity of exercise can be expressed in absolute or relative terms. For example, two individuals with different measures of VO2 max, running at 7 mph are running at the same absolute intensity (miles/hour) but a different relative intensity (% of VO2 max expended). The individual with the higher VO2 max is running at a lower intensity at this pace than the individual with the lower VO2 max is.[3]
Some studies measure exercise intensity by having subjects perform exercise trials to determine peak power output,[4] which may be measured in watts, heart rate, or average cadence (cycling). This approach attempts to gauge overall workload.
An informal method to determine optimal exercise intensity is the talk test. It states that exercise intensity is “just about right”, when the subject can “just respond to conversation.”[5] The talk test results in similar exercise intensity as the ventilatory threshold and is suitable for exercise prescription.[6]
Intensity Levels
Physical Activity | MET |
---|---|
Light Intensity Activities | < 3 |
sleeping | 0.9 |
watching television | 1.0 |
writing, desk work, typing | 1.8 |
walking, 1.7 mph (2.7 km/h), level ground, strolling, very slow | 2.3 |
walking, 2.5 mph (4 km/h) | 2.9 |
Moderate Intensity Activities | 3 to 6 |
bicycling, stationary, 50 watts, very light effort | 3.0 |
walking 3.0 mph (4.8 km/h) | 3.3 |
calisthenics, home exercise, light or moderate effort, general | 3.5 |
walking 3.4 mph (5.5 km/h) | 3.6 |
bicycling, <10 mph (16 km/h), leisure, to work or for pleasure | 4.0 |
bicycling, stationary, 100 watts, light effort | 5.5 |
Vigorous Intensity Activities | > 6 |
jogging, general | 7.0 |
calisthenics (e.g. pushups, situps, pullups, jumping jacks), heavy, vigorous effort | 8.0 |
running jogging, in place | 8.0 |
rope jumping | 10.0 |
Fuel Used
The body uses different amounts of energy substrates (
VO2 max acts as a key determinant of fuel usage during exercise. Higher VO2 Max individuals can sustain higher intensities in the "fat-burning zone" before shifting to carbohydrates, enhancing their endurance and efficiency.
This table outlines the estimated distribution of energy consumption at different percentages of VO2 Max.[8]
Intensity (% of VO2 Max) | % Fat | % Carbohydrate | Fuel Usage |
---|---|---|---|
25 | 85 | 15 | Most energy from fatty acids. |
65 | 50 | 50 | Equal contribution from fatty acids, and carbohydrates. |
85 | 40 | 60 | Decreased fatty acid usage, high reliance on carbohydrates. |
These estimates are valid only when glycogen reserves are able to cover the energy needs. If a person depletes their glycogen reserves after a long workout (a phenomenon known as "
Exercise intensity (WMax) | |||||
---|---|---|---|---|---|
At rest | 40%Wmax
Very low-intensity |
55%Wmax
Low-intensity |
75%Wmax
Moderate-intensity | ||
Percent of substrate
contribution to total energy expenditure |
Plasma glucose | 44% | 10% | 13% | 18% |
Muscle glycogen | - | 35% | 38% | 58% | |
Plasma free fatty acids | 56% | 31% | 25% | 15% | |
Other fat sources
(intramuscular and lipoprotein-derived triglycerides) |
- | 24% | 24% | 9% | |
Total | 100% | 100% | 100% | 100% | |
Total energy expenditure (kJ min-1) | 10 | 50 | 65 | 85 |
See also
References
- ^ "Fitness Fundamentals: Guidelines for Personal Exercise Programs". www.fitness.gov. The President's Council of Physical Fitness and Sports. Archived from the original on 3 April 2011. Retrieved 5 April 2011.
- ^ VO2max: what do we know, and what do we still need to know. Levine, B.D. Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, TX 75231. The Journal of Physiology, 2008 Jan 1;586(1):25-34. Epub 2007 Nov 15.
- ^ a b c d Vehrs, P., Ph.D. (2011). Physical activity guidelines. In Physiology of exercise: An incremental approach (pp. 351-393). Provo, UT: BYU Academic Publishing.
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- ^ "Calories Burned Running Calculator". 29 October 2019. Retrieved 20 January 2024.
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