Editing Exercise intensity

{{Short description|Amount of energy expended when exercising}}
{{Sources exist|date=November 2021}}
{{use dmy dates|date=May 2023}}
[[Image:MatteoTosatto2.jpg|right|300px]]

'''Exercise intensity''' refers to how much energy is expended when [[exercise|exercising]]. Perceived intensity varies with each person. It has been found that intensity has an effect on what [[fuel]] the body uses and what kind of adaptations the body makes after exercise. Intensity is the amount of physical power (expressed as a percentage of the [[maximal oxygen consumption]]) that the body uses when performing an activity. For example, exercise intensity defines how hard the body has to work to walk a mile in 20 minutes.<ref>{{Cite web|title=Fitness Fundamentals: Guidelines for Personal Exercise Programs|website=www.fitness.gov|publisher=The President's Council of Physical Fitness and Sports|url=http://www.fitness.gov/fitness.htm|access-date=2011-04-05|archive-url=https://web.archive.org/web/20110403170118/http://www.fitness.gov/fitness.htm|archive-date=2011-04-03}}</ref>

==Measures of Intensity==
[[Heart Rate]] is typically used as a measure of exercise intensity.<ref>VO<sub>2</sub>max: 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.</ref> Heart rate can be an indicator of the challenge to the [[cardiovascular system]] that the exercise represents.

The most precise measure of intensity is oxygen consumption (VO<sub>2</sub>). VO<sub>2</sub> represents the overall metabolic challenge that an exercise imposes. There is a direct linear relationship between intensity of aerobic exercise and VO<sub>2</sub>. Our maximum intensity is a reflection of our maximal oxygen consumption ([[VO2 max|VO<sub>2</sub> max]]). Such a measurement represents a cardiovascular fitness level.<ref name="vehrs"/>

VO<sub>2</sub> is measured in [[Metabolic equivalent of task|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.<ref name="vehrs">Vehrs, P., Ph.D. (2011). Physical activity guidelines. In Physiology of exercise: An
incremental approach (pp. 351-393). Provo, UT: BYU Academic Publishing.</ref> 
 
Intensity of exercise can be expressed in absolute or relative terms. For example, two individuals with different measures of VO<sub>2</sub> max, running at 7&nbsp;mph are running at the same absolute intensity (miles/hour) but a different relative intensity (% of VO<sub>2</sub> max expended). The individual with the higher VO<sub>2</sub> max is running at a lower intensity at this pace than the individual with the lower VO<sub>2</sub> max is.<ref name="vehrs"/>

Some studies measure exercise intensity by having subjects perform exercise trials to determine [[peak power output]],<ref>{{cite journal|last1=Di Donato|first1=Danielle|last2=West|first2=Daniel|last3=Churchward-Venne|first3=Tyler|last4=Breen|first4=Leigh|last5=Baker|first5=Steven|last6=Phillips|first6=Stuart|display-authors=3|title=Influence of aerobic exercise intensity on myofibrillar and mitochondrial protein synthesis in young men during early and late postexercise recovery|journal=American Journal of Physiology. Endocrinology and Metabolism|date=2014|volume=306|issue=9|pages=E1025–E1032|doi=10.1152/ajpendo.00487.2013|url=http://ajpendo.physiology.org/content/306/9/E1025|access-date=14 June 2015|pmc=4010655|pmid=24595306}}</ref> which may be measured in [[watt]]s, 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.”<ref>{{Cite journal |last1=Persinger |first1=Rachel |last2=Foster |first2=Carl |last3=Gibson |first3=Mark |last4=Fater |first4=Dennis C. W. |last5=Porcari |first5=John P. |date=2004 |title=Consistency of the talk test for exercise prescription |url=https://pubmed.ncbi.nlm.nih.gov/15354048 |journal=Medicine and Science in Sports and Exercise |volume=36 |issue=9 |pages=1632–1636 |issn=0195-9131 |pmid=15354048}}</ref> The talk test results in similar exercise intensity as the [[ventilatory threshold]] and is suitable for exercise prescription.<ref>{{Cite journal |last1=Foster |first1=Carl |last2=Porcari |first2=John P. |last3=Anderson |first3=Jennifer |last4=Paulson |first4=Melissa |last5=Smaczny |first5=Denise |last6=Webber |first6=Holly |last7=Doberstein |first7=Scott T. |last8=Udermann |first8=Brian |date=2008 |title=The Talk Test as a Marker of Exercise Training Intensity |url=https://journals.lww.com/01273116-200801000-00005 |journal=Journal of Cardiopulmonary Rehabilitation and Prevention |language=en |volume=28 |issue=1 |pages=24–30 |doi=10.1097/01.HCR.0000311504.41775.78 |pmid=18277826 |issn=1932-7501|url-access=subscription }}</ref>

==Intensity Levels==
[[Exercise]] is categorized into three different intensity levels. These levels include low, moderate, and vigorous and are measured by the [[metabolic equivalent]] of task (aka metabolic equivalent or METs).
The effects of exercise are different at each intensity level (i.e. [[training effect]]). 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.”<ref>{{cite journal | last1 = Elmahgoub | first1 = S. S. | last2 = Calders | first2 = P. | last3 = Lambers | first3 = S. | last4 = Stegen | first4 = S. M. | last5 = Van Laethem | first5 = C. | last6 = Cambier | first6 = D. C. | year = 2011 | title = The effect of combined exercise training in adolescents who are overweight or obese with intellectual disability: The role of training frequency | journal = Journal of Strength and Conditioning Research | volume = 25 | issue = 8| pages = 2274–2282 | doi = 10.1519/JSC.0b013e3181f11c41 | pmid = 21734606 | s2cid = 38959989 |display-authors=3| doi-access = free }}</ref>

{| class="wikitable" border="1"
|-
! Physical Activity
! MET
|-
! Light Intensity Activities
! < 3
|-
| sleeping 
| 0.9
|-
| watching television 
| 1.0
|-
| writing, desk work, typing 
| 1.8
|-
| walking, 1.7&nbsp;mph (2.7&nbsp;km/h), level ground, strolling, very slow 
| 2.3
|-
| walking, 2.5&nbsp;mph (4&nbsp;km/h)
| 2.9
|-
|-
! Moderate Intensity Activities
! 3 to 6
|-
| bicycling, stationary, 50 watts, very light effort 
| 3.0
|-
| walking 3.0&nbsp;mph (4.8&nbsp;km/h)
| 3.3
|-
| calisthenics, home exercise, light or moderate effort, general
| 3.5
|-
| walking 3.4&nbsp;mph (5.5&nbsp;km/h)
| 3.6
|-
| bicycling, <10&nbsp;mph (16&nbsp;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 ([[carbohydrates]] or [[fat]]s) depending on the intensity of the exercise and the [[VO2 max|VO2 Max]] of the exerciser. [[Protein]] is a third energy substrate, but it contributes minimally (around 3% of the total energy expenditure during exercise<ref>Clauss, M., & Jensen, J. (2025). Effect of exercise intensity, duration, and volume on protein oxidation during endurance exercise in humans: A systematic review with meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 35(4): e70038. https://doi.org/10.1111/sms.70038</ref>) and is therefore discounted in the percent contribution graphs reflecting different intensities of exercise. The fuel provided by the body dictates an individual's capacity to increase the intensity level of a given activity. In other words, the intensity level of an activity determines the order of fuel recruitment. 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. On the other hand, high intensity activity utilizes a larger percentage of carbohydrates in the calories expended because its quick production of energy makes it the preferred energy substrate for high intensity exercise. High intensity activity also yields a higher total caloric expenditure.<ref name="vehrs"/>

VO2 max acts as a key determinant of fuel usage during exercise. Higher [[VO2 max|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|VO2 Max]].<ref>{{Cite web |date=2019-10-29 |title=Calories Burned Running Calculator |url=https://caloriesburnedhq.com/calories-burned-running/ |access-date=2024-01-20 |language=en-US}}</ref>

{| class="wikitable" style="text-align: center"
! Intensity (% of VO<sub>2</sub> 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 "[[hitting the wall]]"), the body will use mostly fat for energy (known as "[[second wind]]"). [[Ketone bodies|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).<ref>{{Cite journal |last1=Koeslag |first1=J. H. |last2=Noakes |first2=T. D. |last3=Sloan |first3=A. W. |date=April 1980 |title=Post-exercise ketosis |journal=The Journal of Physiology |volume=301 |pages=79–90 |doi=10.1113/jphysiol.1980.sp013190 |issn=0022-3751 |pmc=1279383 |pmid=6997456}}</ref><ref>{{Cite journal |last1=Evans |first1=Mark |last2=Cogan |first2=Karl E. |last3=Egan |first3=Brendan |date=2017-05-01 |title=Metabolism of ketone bodies during exercise and training: physiological basis for exogenous supplementation |journal=The Journal of Physiology |volume=595 |issue=9 |pages=2857–2871 |doi=10.1113/JP273185 |issn=1469-7793 |pmc=5407977 |pmid=27861911}}</ref>
{| class="wikitable"
|+'''Exercise intensity (%W'''<sub>max</sub>''') and substrate use in skeletal muscle during aerobic activity (cycling)'''<ref>{{Cite journal |last1=van Loon |first1=L. J. |last2=Greenhaff |first2=P. L. |last3=Constantin-Teodosiu |first3=D. |last4=Saris |first4=W. H. |last5=Wagenmakers |first5=A. J. |date=2001-10-01 |title=The effects of increasing exercise intensity on muscle fuel utilisation in humans |journal=The Journal of Physiology |volume=536 |issue=Pt 1 |pages=295–304 |doi=10.1111/j.1469-7793.2001.00295.x |issn=0022-3751 |pmc=2278845 |pmid=11579177}}</ref>
| colspan="2" rowspan="2" |
! colspan="4" |'''Exercise intensity (W'''<sub>Max</sub>''')'''
|-
!'''At rest'''
!'''40%W'''<sub>max</sub>
Very low-intensity
!'''55%W'''<sub>max</sub>
Low-intensity
!'''75%W'''<sub>max</sub>
Moderate-intensity
|-
! rowspan="5" |'''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%
|-
! colspan="2" |'''Total energy expenditure (kJ min'''<sup>−1</sup>''')'''
|10
|50
|65
|85
|}

== High Intensity Exercise in Pregnancy ==
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.<ref>{{Cite web |last=CDC |date=2024-10-29 |title=Pregnant & Postpartum Activity: An Overview |url=https://www.cdc.gov/physical-activity-basics/guidelines/healthy-pregnant-or-postpartum-women.html |access-date=2024-11-14 |website=Physical Activity Basics |language=en-us}}</ref> Different parameters for high-intensity exercise have been researched to educate and determine their safety for the mother and fetus.

Studies support that an acute bout of high-intensity exercise in active pregnant women does not lead to fetal distress or adverse effects. Results were also similar in maternal and fetal responses to moderate-intensity and high-intensity training. Both intensity exercises were associated with normal maternal and fetal cerebral blood flow responses. It also showed healthy circulation in the fetus and mother, demonstrating vasodilation and improved placental perfusion.<ref>{{Cite journal |last1=Wowdzia |first1=Jenna B. |last2=Hazell |first2=Tom J. |last3=Berg |first3=Emily R. Vanden |last4=Labrecque |first4=Lawrence |last5=Brassard |first5=Patrice |last6=Davenport |first6=Margie H. |date=2023-09-01 |title=Maternal and Fetal Cardiovascular Responses to Acute High-Intensity Interval and Moderate-Intensity Continuous Training Exercise During Pregnancy: A Randomized Crossover Trial |url=https://link.springer.com/article/10.1007/s40279-023-01858-5 |journal=Sports Medicine |language=en |volume=53 |issue=9 |pages=1819–1833 |doi=10.1007/s40279-023-01858-5 |pmid=37213048 |issn=1179-2035|url-access=subscription }}</ref>

Current evidence suggests that high-intensity exercises may be well-tolerated by healthy, active pregnant women in their late second and third trimesters.<ref>{{Cite journal |last1=Beetham |first1=Kassia S. |last2=Giles |first2=Courtney |last3=Noetel |first3=Michael |last4=Clifton |first4=Vicki |last5=Jones |first5=Jacqueline C. |last6=Naughton |first6=Geraldine |date=2019-08-07 |title=The effects of vigorous intensity exercise in the third trimester of pregnancy: a systematic review and meta-analysis |journal=BMC Pregnancy and Childbirth |volume=19 |issue=1 |pages=281 |doi=10.1186/s12884-019-2441-1 |doi-access=free |issn=1471-2393 |pmc=6686535 |pmid=31391016}}</ref> The frequency, type, time, and volume of these exercises should be individually tailored to the patient, prescribed, and conducted by medical professionals and exercise specialists. Pregnant women are also advised not to participate in activities that will increase their heart rate to above 90% of their known maximum heart rate.<ref>{{Cite journal |last1=Anderson |first1=Julie |last2=Pudwell |first2=Jessica |last3=McAuslan |first3=Colin |last4=Barr |first4=Logan |last5=Kehoe |first5=Jessica |last6=Davies |first6=Gregory A. |date=December 2021 |title=Acute fetal response to high-intensity interval training in the second and third trimesters of pregnancy |url=https://cdnsciencepub.com/doi/10.1139/apnm-2020-1086 |journal=Applied Physiology, Nutrition, and Metabolism |language=en |volume=46 |issue=12 |pages=1552–1558 |doi=10.1139/apnm-2020-1086 |pmid=34433004 |issn=1715-5312|hdl=1807/108271 |hdl-access=free }}</ref>

==See also==
*[[Exercise physiology]]
*[[Human power]]
*[[Bioenergetic systems]]

== References ==
{{reflist|30em}}

[[Category:Physical exercise]]