Table of Contents
In lessons 1 and 2 we discussed the physiology of exercise and our body’s adaptations to exercise training. These adaptations mainly occur within the nervous, musculoskeletal, cardiovascular, and respiratory systems. In addition to the performance benefits from these physiologic changes, there are many health benefits that accrue as well. We will discuss these health benefits and the recommended amounts of activity to obtain them in this lesson.
2018 Physical Activity Guidelines for Americans (PAGA)
The Physical Activity Guidelines for Americans (PAGA) was first published in 2008; a 2nd edition, governing ages 3 and older, was published in 2018. These were put together by a panel of experts and issued by the US Department of Health and Human Services. Click here for an overview of this process and the guidelines themselves. These guidelines complement the Dietary Guidelines for Americans (discussed extensively in my nutrition and weight management course).
Recommended Physical Activity LevelsI have reproduced the key recommendations of these guidelines in the note below.
Note: The 2018 Physical Activity Guidelines for Americans recommends:
- age 3-5 years: should be physically active throughout the day to enhance growth & development
- age 6-17 years: should perform 60 minutes or more of moderate-to-vigorous physical activity (MVPA) daily
- most of this should be aerobic activity
- they should perform vigorous-intensity physical activity (VPA) at least 3 days a week
- they should include both muscle-strengthening and bone-strengthening physical activity at least 3 days a week
- adults: should aim for 150-300 minutes of moderate-intensity physical activity (MPA) or 75-150 minutes of VPA spread throughout the week
- moving more & sitting less throughout the day is beneficial if VPA is <30-40 minutes daily and MPA is <60-75 minutes daily
- they should include muscle-strengthening activity of moderate or greater intensity involving all major muscle groups at least 2 days weekly
- if chronic conditions or disabilities are present then adults should consult their healthcare provider and perform as much activity to try to meet the guidelines as their limitations allow
- older adults: should follow the guidelines for adults
- they should also perform multi-component physical activity that includes balance training as well as aerobic & muscle-strengthening activities
- if there are chronic health conditions older adults should understand how this influences their ability to perform exercise
- if there are limitations such that older adults cannot meet the guidelines they should perform as much weekly MPA as possible
- pregnancy & postpartum: should perform at least 150 minutes of MPA weekly, preferably spread throughout the week
- for individuals who normally perform VPA they can continue VPA
- they should consult with their healthcare provider about how anything should be changed
- they should avoid exercises that involve lying on their back after the 1st trimester of pregnancy as this can restrict blood flow to the uterus & fetus
- additionally, they should also avoid contact/collision sports & activities with a high risk of falling or abdominal trauma such as soccer/basketball/horseback riding/downhill skiing
Muscle-strengthening activity is any activity against increased resistance (ie, lifting weights, push-ups, carrying something heavy, etc).
Bone-strengthening activity is any weight-bearing activity that involves impacts of some type, such as running, jumping jacks, and lifting weights.
The guidelines state that generally healthy individuals can begin to gradually increase physical activity without first consulting their healthcare provider. However, if physical symptoms develop or if individuals plan to start VPA consulting one’s healthcare provider is more advisable. Additionally, to help minimize health risks it is important to start at a small amount of activity. One should gradually increase the duration and frequency of sessions prior to increasing the intensity.
Of note, one big change from this version of the guideline compared to the prior one is the duration of activity needed to count towards the weekly total. In the 2008 version there was a minimum requirement of 10 minutes duration of MVPA to count. In this new guideline, any duration counts (even 1 minute).
Tip: The fact that even 1 minute of activity counts can be very helpful for a lot of people. You can simply incorporate sporadic “exercise snacks” throughout the day and this will assist in overall health.
Definitions of physical activity intensity
These guidelines are fairly straightforward; however, it is important to understand what qualifies as MVPA to be able to meet them. The guidelines provide definitions as indicated in the note below.
Note: According to the 2018 PAGA, the various activity levels are defined as follows:
- Inactive: people who perform no MVPA
- Insufficiently active: people who perform some MVPA but less than what is recommended in the guidelines
- Active: people with activity levels falling within the recommendations of the guidelines
- Highly active: people with activity levels beyond those recommended in the guidelines
People of any activity level will generally experience health benefits from increasing activity. However, the lower one’s activity at baseline the greater the benefits will be for any given increase.
The guidelines note that decreasing sedentary behavior in inactive individuals has several health benefits. These include decreasing the risk of all-cause mortality, cardiovascular disease, type 2 diabetes incidence, and cancer development/progression.
To define MVPA, they use metabolic equivalents of task (METs).
- MET: the ratio of the rate of energy expended during an activity to the rate of energy expended at rest
- If somebody normally burns 10 calories while at rest in 10 minutes, and while doing a specific activity for 10 minutes they burn 25 calories, that activity will have a MET value of 25/10 = 2.5.
- Sedentary behavior: waking activity at ≤ 1.5 METs while sitting, reclining, or lying
- Light physical activity (LPA): non-sedentary waking activity that is <3.0 METs
- absolute measurement: activity generating >3.0 but <6.0 METs
- relative measurement: activity considered to be 5-6/10 on a rating of perceived exertion (RPE) scale, in general one can talk but not sing
- absolute measurement: activity generating >6.0 METs
- relative measurement: activity considered to be 7-8/10 RPE, in general one cannot say more than a few words without becoming short of breath
Now let’s work through an example to tie all of this together.
Example: Let’s check some of these numbers and see how we can make them fit the guideline.
The guidelines state adults should perform 150-300 minutes of MPA or 75-150 minutes of VPA each week. They also suggest to spread this out throughout the week. Thus, you can perform 30 minutes of MPA Monday – Friday, 25 minutes of VPA on three separate days, or some other combination. This will meet the minimum requirements; any additional physical activity you do in your leisure time adds to this.
As MPA is at least 3.0 METs and VPA is at least 6.0 METs, then technically ~1 minute of VPA can count for ~2 minutes of MPA. At a minimum of 6.0 METs for VPA, this comes to at least 75 * 6.0 = 450 MET-minutes per week. Moreover, at the upper limit of the guideline this equals 900 MET-minutes/week or 15 MET-hours/week.
Looking at the above link for adults we find that:
- running at a 15 minute mile pace (4.0 miles per hour) equals ~6 METs
- running at a 10 minute mile pace (6.0 miles per hour) equals ~10 METs
- cleaning the home with moderate effort equals 3-4 METs
- resistance training equals 3-5 METs
- mowing the lawn without a power mower equals 5-6 METs
- raking leaves equals ~4 METs
- walking at a slow pace equals 2-3 METs
- walking briskly equals 3-4 METs or even greater if walking >4.0 miles per hour
Keeping the math simple, running a 6.0 mile per hour pace (~10 METs) for 60 minutes equals 600 MET-minutes. Thus, a 1 hour run at a 10 minute mile pace meets the weekly guidelines for MET-minutes of MVPA. To meet the time goal of 75 minutes this would equal 750 MET-minutes in one session. However, the guidelines do suggest spreading physical activity out to 3+ days weekly. Therefore, running a 10 minute mile pace for 25 minutes (2.5 miles total) 3 days weekly meets this guideline. Additionally, since running involves significant ground impact this counts for bone-strengthening activity. However, we need to perform additional muscle-strengthening activity.
If 25 minutes of running 3 days a week does not seem realistic, we can break this up further since the guidelines suggest no minimum needed duration of activity to yield health benefits. Thus, we can run 13 minutes 6 days a week at a 10 minute mile pace (13*6 = 78, which is >75). Running 7 minutes twice a day for 6 days a week is also adequate (12*7 = 84, which is >75). However, practically speaking most people will find it more convenient to perform one 13 minute session than two 7 minute sessions.
If we aim for 30 minutes of VPA daily to help offset the negative effects of an otherwise completely sedentary lifestyle (as indicated in the guideline box above), then we need 180 MET-minutes per day (30 minutes * 6.0 MET = 180 MET-minutes). Therefore, running at a 10 minute mile pace requires 18 minutes of running daily to meet this goal., though based on the time recommendation we would still need to run 30 minutes.
Tip: There is one contradiction in the prior example; when we perform physical activity that is >6.0 METs we can meet the MET-minute goal without meeting the time requirement goal. Unfortunately, it’s not completely clear in the guideline if meeting the total time targets are necessary if we have already met the MET-minute targets. However most sources reference the time targets rather than the MET-minutes targets regarding recommendations. Additionally, as discussed below, more activity generally leads to better health outcomes. Thus, I advise you to meet the listed time targets even if you surpass the MET-minute targets.
Health benefits when following the guidelines
Within the 2018 PAGA many health benefits of exercise are discussed. Some of these include:
- lower risk of depression
- improved bone health, weight status, cardiorespiratory fitness, muscular fitness, cardiometabolic health, cognition
- Adults and older adults:
- lower risk of all-cause mortality, cardiovascular disease, hypertension, type 2 diabetes mellitus, abnormal blood lipids, several cancers, dementia, anxiety, depression, risk of falls & fall-related injuries
- improved cognition, quality of life, sleep, bone health, physical function
- can aid weight loss & help prevent weight regain
- Pregnant women:
- decreased risk of excessive weight gain, gestational diabetes, postpartum depression
- may help decrease the risk of complications such as preeclampsia and the risk of needing a c-section
2020 World Health Organization guidelines on physical activity and sedentary behavior
More recently the World Health Organization (WHO) came out with updated guidelines as well. This includes:
- a 2019 guideline discussing, physical activity, sedentary behavior, and sleep under age 5 that can be found here
- a 2020 update for their general guideline on physical activity and sedentary behavior for ages ≥5 that can be found here
The latter is largely based on the PAGA above; they additionally updated several of the systematic reviews that were used to derive the PAGA with literature searches near the end of 2019 and included a few topics that were not covered in the PAGA. An easy to read concise list compiling both of these guidelines can be found here. Given similarity to the 2018 PAGA above, I will simply highlight the differences for ages ≥5 in the note below. For the guidelines <5 years old please click on the prior linked compilation.
Note: The 2020 WHO guidelines on physical activity and sedentary behavior are largely in line with the 2018 PAGA. Differences include:
- these guidelines are for age ≥5, they have a separate guideline for age 1-4 (see the link provided above)
- children and adolescents: they highlight that MVPA should average at least 60 minutes daily while the PAGA states they should get at least 60 minutes every single day
- adults and older adults: they recommend aiming for the same exercise ranges as the PAGA but they emphasize greater health benefits are seen when going beyond this
- additionally for older adults: similar to the PAGA, they recommend including multi-component physical activity that incorporates balance & strength training but specify this should be at least 3 days weekly
- for all ages and conditions: they emphasize health benefits from converting sedentary time to physical activity of any intensity
The 2020 WHO guidelines also state health benefits from meeting the guidelines; much of this is consistent with the benefits seen in 2018 PAGA. They do list additional benefits of exercise for people with cancer, hypertension, type 2 diabetes, HIV, multiple sclerosis, spinal cord injury, impaired cognitive function, and disabilities as a whole. Most of these benefits align with those listed above.
Tip: The above guidelines are good minimum targets but increased health benefits are seen at progressively higher levels of exercise.(Blond, 2018; Franklin, 2020) To clarify, for insufficiently active individuals working towards meeting the guidelines is an excellent lifestyle change to work towards better health. However, if your goal is to optimize your overall health then consider gradual increases beyond the guidelines above.
Other health benefits of exercise indicated by the literature
The above guidelines were published in 2018 and 2020 with most of the included research being published by late 2019. Thus, while much of the included research is relatively recent, the summary statements in the guidelines are fairly general. Therefore, I will discuss more specific benefits here.
Literature in youth populations: Physical activity in youth under age 6 is beneficial for body composition, bone health, and possibly cognition, while the same benefits as well as other improvements in cardiovascular risk factors are seen from ages 6-17.(Pate, 2019) Additionally, resistance exercise in youth is associated with improved metabolic function; it is not clear if this is due to changes in body composition or if there are benefits independent of changes in body composition.(Bea, 2017) Moreover, muscular fitness itself in children and adolescents is associated with lower waist circumference and triglycerides.(Rodrigues de Lima, 2020)
In children with obesity concurrent aerobic plus resistance exercise compared to aerobic exercise alone yields beneficial changes in body weight, body fat, lean body mass, LDL cholesterol (the “bad” cholesterol), and adiponectin (a hormone that promotes positive health effects).(García-Hermoso, 2018) Lastly, resistance training in youth, even prior to puberty, can lead to skeletal muscle hypertrophy, increased strength, several other musculoskeletal benefits, and is safe.(Legerlotz, 2016; Peitz, 2018; Stricker, 2020; Faigenbaum, 2021)
Literature in elderly populations: Improvements in skeletal muscle hypertrophy with resistance training are possible into the eighth and possibly even into the ninth decades of life, so there really isn’t an age that is “too late” to start training to see benefits.(Straight, 2020) In fact, a recent analysis of many different types of exercise interventions in elderly populations found resistance training to be more beneficial than any other type.(Di Lorito, 2021)
Additionally, endurance training yields benefits for several body systems that help attenuate many of the effects of aging.(Valenzuela, 2020) Importantly, increased physical activity in general yields several additional benefits in the elderly. These include helping to prevent falls and associated injuries as well as helping to preserve physical function.(Dipietro, 2019) Both aerobic and resistance training seem to have positive effects on cognitive function and possibly slow cognitive decline in elderly populations, at least in those with more mild cognitive impairment as opposed to severe.(Liu-Ambrose, 2018)
Literature in pregnant populations: During pregnancy, and after delivery when breastfeeding, there are additional considerations regarding the safety, risks, and benefits of performing exercise. It is always best to check with your own healthcare provider regarding this topic, but recently a general overview with many considerations was published for those who would like further reading.(Meah, 2020) Additionally, there is a growing body of evidence (albeit with a significant portion of the research done in rodents) indicating that paternal and maternal exercise prior to conception, exercise during pregnancy, and exercising while breastfeeding may all impart significant health benefits to one’s children.(Beleza, 2021)
Literature on health impacts of sedentary behavior: Sedentary behavior is associated with several negative long-term health outcomes(Saunders, 2020) Recent literature indicates increasing overall activity levels can help counteract these negative effects.(Ekelund, 2019) However, it is unclear if simply incorporating more breaks is beneficial(Stamatakis, 2018), though a more recent systematic review does indicate benefit.(Loh, 2020) Additionally, individuals who are less fit likely benefit more readily from increased breaks.(Benatti, 2015) LPA (ie, walking, simple activities of daily living) leads to mild benefits(Chastin, 2019); more vigorous physical activity such as running even just once weekly may provide additional benefit.(Pedisic, 2020)
However, when comparing LPA to MVPA for an equal activity amount of 150 METs-minutes there may be more similar protection against cardiovascular mortality.(Qiu, 2020) MVPA likely has additional health benefits relative to LPA but engaging in LPA seems much better than being sedentary.
Literature on benefits of aerobic and resistance exercise: Aerobic and resistance training, even without significant weight loss, help decrease unhealthy body fat stores such as visceral adiposity in children(Kim, 2017) and myosteatosis (fatty tissue within muscle) in adults.(Ramírez-Vélez, 2020) Additionally, aerobic exercise helps prevent weight gain in adults, particularly at >150 minutes of weekly MVPA.(Jakicic, 2019) Regular aerobic exercise not only provides several heart benefits but can also reverse some of the pathology seen in diseased and aged hearts.(Moreira, 2020)
Resistance training alone aids cardiovascular risk markers, yielding benefits for cardiorespiratory fitness, blood pressure, fasting glucose, insulin resistance, cholesterol & triglycerides (moreso in individuals who are older and with greater health risks) and flow-mediated dilatation (a marker of endothelial function that indicates risk of future cardiovascular events).(Ashton, 2020) Additionally, resistance training decreases the risk of all-cause mortality and cardiovascular disease.(El-Kotob, 2020) Furthermore, resistance training benefits bone mineral density and connective tissue health.(Maestroni, 2020) Both resistance and endurance training yield several mental health benefits (including regarding depression, anxiety, mood, stress, and cognition).(Kramer, 2020)
Resistance training seems to help prevent many chronic diseases; however, when done with aerobic training this seems to have a larger impact on cardiometabolic biomarkers and mental health than either modality alone.(Bennie, 2020)
Potential health concerns of excessive exercise
Here I will briefly discuss what the literature suggests regarding safety of exercising well above recommendations in the guidelines. This will only impact a small percentage of people.
Increasing activity levels to 6-7 times higher than the guidelines is still associated with benefits without obvious harms.(Blond, 2018) Elite athletes have health benefits throughout their lifespan; there may be confounding regarding lifestyle choices but this implies very high levels of activity for many years does not induce harm.(Runacres, 2020) While large cohort studies have at times shown that the highest levels of physical activity associate with worsening mortality relative to more moderate physical activity, it appears this may be secondary to measurement error and reverse causation bias.(Lee, 2021)
Considering specifically the impact of high activity levels on cardiac adaptations, there seem to be several changes that occur, some potentially harmful. These cardiac adaptations have been discussed at length in several recent pieces of literature.(Franklin, 2020; O’Keefe, 2020; Parry-Williams, 2020; Stöhr, 2021) Collectively, they suggest there are some changes in myocardial fibrosis and coronary artery calcification, but there is no evidence to suggest these changes are inherently pathological. There may be an increase in risk of right ventricular dysfunction and there does seem to be an increased risk of atrial fibrillation. Importantly, none of these authors, nor a recent statement by the American Heart Association(Franklin, 2020), advocate limiting limiting activity levels due to these concerns.
Thus, for healthy individuals who enjoy engaging in physical activity levels well beyond the recommended guidelines, I do not see any reason to reduce activity levels as a prophylactic step to prevent heart disease or mortality. For individuals with baseline cardiac disease or specific genetic conditions who wish to engage in physical activity well beyond the guidelines there are additional considerations.(Franklin, 2020; consider discussing with your healthcare provider or cardiologist if this applies to you.
Use caution with certain health conditions and undesirable symptoms
While exercise is safe when done correctly, it is important to take some precautions to help ensure safety. The guidelines above suggest there is no need to consult a healthcare provider if one is in good health prior to exercise; however, for individuals with medical conditions there can be additional considerations(Hansen, 2018) and it is likely a good idea to check with your healthcare provider prior to working towards more vigorous activity. This is particularly true if you have any cardiovascular health conditions (ie, heart disease, uncontrolled hypertension, angina, peripheral artery disease, etc), diabetes mellitus, cirrhosis, or other conditions that can affect your heart, lung, or nerve supply throughout your body.
When people do have heart complications with new onset activity these typically occur when vigorous activity is performed without gradually acclimating to it (ie, when shoveling snow after being inactive for awhile).(Franklin, 2020) The risk is still small overall but it is imperative to slowly progress with exercise intensity to help minimize the risk of heart problems, injuries, and other health issues.
If at any point in time you start to develop chest pain, feel your heart beat in an unusual way, or believe you are unusually fatigued relative to the amount of exercise you are performing, you should stop exercising and discuss with your healthcare provider. It is possible any perception of abnormal fatigue is simply due to deconditioning (ie, being out of shape), but better safe than sorry.
Lastly, similar to how some individuals can take healthy eating “too far” and develop concerns with disordered eating or even eating disorders, the same can happen with exercise.(Marques, 2019) While exercise can effectively aid mental health in a variety of ways as indicated above, some people do develop body dysmorphia, exercise addiction, or other mental health issues related to increased activity. If at any point you feel this may be occurring with yourself I recommend stopping physical activity and consulting a mental health professional to determine how best to proceed.
There are official exercise guidelines for people of all ages to follow, and there is considerable evidence that following these guidelines leads to many health benefits. These benefits include, but are not limited to, positive changes in body composition, blood lipids, blood pressure, blood glucose metrics, blood flow throughout the body, cognition, mental health, overall fitness, pregnancy outcomes, cardiovascular disease incidence, and all-cause mortality. Even better outcomes are obtained by going beyond these guidelines. Caution should be taken to slowly increase activity levels to minimize the risk of injury or harm. Overall, regarding health outcomes, the substantial benefits far outweigh the risks when appropriate exercise strategies are utilized.
With the background obtained in the first three lessons providing a rationale regarding how the body performs movement and how exercise can benefit us, in the next lesson we will build on this by discussing terminology and concepts specific to resistance training.
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