Energy expenditure and Physical Activity

Why do we measure physical activity?

Measuring physical activity is important for energy balance → intake and expenditure. Physical Activity is also very important to know when looking at associations of diseases and food, for example.

What is “Activity Continuum”?

The Activity Continuum refers to the spectrum of physical activity levels, ranging from sedentary to highly active. Helps understanding how different levels of activity can affect health outcomes/energy expenditure

→ only focussing at sports doesn’t give whole picture: we spend more hours with sedentary activity than we do sports in a day (= ‘an active couch potato’: doing sports, but otherwise being low in physical activity).

Define “physical activity”

Any bodily movement produced by the contraction of skeletal muscles resulting in caloric expenditure above a basal level (= you have a basal level and every time you contract the muscle, it’s physical activity)

The definition of physical activity is broad, and includes all movement from walking or cycling for transportation to household and occupational work to exercise and sports

Define “excercise”

subset of physical activity that is planned, structured and repetitive, and has as a final or intermediate objective the improvement or maintenance of physical fitness.

Exercise is a subcategory of physical activity; it’s planned, structured, repetitive and often performed with the goal of improving or maintaining fitness.

Define “sedentarity”

It’s characterized by very low energy expenditure (e.g. just sitting down)

Define “physical fitness”

Set of health and skill related attributes that relates to the ability to perform physical activity and include cardiorespiratory fitness, muscular strength and endurance, body composition and flexibility, balance, agility, reaction time and power.

Physical fitness = really your capacity/your skills. For example, when you are very strong, or you have a good aerobic performance.

What is the association between physical activity and health?

The more active you are, results in a decrease in the relative risk of disease (e.g. CVD or mortality).

We don’t know the optimal amount and there is no clear threshold, very extreme P.A. will probably slightly go up again in relative risk.

What are the ‘beweegrichtlijnen’ from the Health Council in NL to the general population?

Jeugd (4-18 jaar):
- 1 uur per dag matig intensief bewegen (ademhaling sneller)
- 3x per week spier- en botversterkende activiteiten (volleybal, dansen, buitenspelen, fietsen)

Volwassenen/ouderen:
- 2,5 uur (150 min) per week matig intensief bewegen
- 2x per week spier- en botversterkende activiteiten (ouderen: combineren met balansoefeningen)

More is better! Limit sedentarity

What are the five aspects of physical activity?

1. Energy Expenditure → for energy balance (decrease of obesity, decrease of disease (e.g. CMD)

2. Aerobic intensity

3. Weight bearing → not only important what someone does, but also how they exercise; running, resisting exercise, swimming, etc. Runners have a higher bone density than cyclists, for example.

4. Flexibility

5. Strength

→ these aspects matter, e.g. for bone health it's relevant wether it's weight bearing or not, as the pressure of your body weight stimulates bone formation.

What are the four domains of physical activity?

Domains → ‘when do you do physical activity?’:

1. Occupational (jobs: nowadays mostly office jobs)

2. Domestic (household)

3. Transport

4. Leisure (sport)

What are the four dimensions of Physical Activity? (relevant for more subjective measures of P.A.)

1. Mode → the type of activity: resistance, endurance, or balance exercising.

2. Frequency → how often you exercise

3. Duration → time spend on P.A.

4. Intensity → intensity of the exercise

What is the definition of the Total Energy Expenditure (TEE) and on which three components is TEE based?

Total Energy Expenditure (TEE) = total amount of energy expenditure over a 24 hour period. TEE consist of:

1. Resting Metabolic Rate (RMR)/resting energy expenditure

2. Thermic effect of food (TEF), also referred to as diet-induced thermogenesis (DIT)

3. Physical activity energy expenditure (PAEE)

What is the largest component of total energy expenditure?

The Resting Metabolic rate → energy required to maintain vital body functions while you are awake, at rest, in a post-absorptive state and in thermoneutral environment. 60-75%.

In addition:
→ 10%: thermogenesis (energy) from food (DIT)
→ 15-30% is due to physical activity, this is the most variable part.

What is the difference between Basal Metabolic Rate and Resting Metabolic Rate?

BMR is very similar to RMR, but BMR is measured under even stricter conditions. It represents the minimum energy required to sustain life at complete physical, mental and digestive rest (in practice we measure RMR more and BMR can be ±10% lower!)

How can you measure the Physical Activity Level (PAL)?

Total energy expenditure (TEE) / BMR

What is Metabolic Equivalent of Task (MET) and the ‘MET-score’?

MET describes the energy cost of a specific activity relative to resting energy expenditure (measures expressing the energy cost of physical activities).

Like PAL, it’s a ratio, but instead of representing a full day, it applies to individual activities.
Often used in sports.

MET is expressed as oxygen consumption per minute → 3.5 mLO2/kg.min → ±1 kcal/kg.h
Met score = VO2 activity / 3.5

Sedentarity = Physical Activity with MET < 1.5

The ratio of the physical activity level (PAL) classifies daily activity levels. What are the PAL values/categorisations?

< 1.2 → bed rested: most likely in care of others

1.2 - 1.55 → low activity level: sedentary lifestyle

1.55 - 1.71 → medium activity level: occasionally active (typical office workers)

1.71 - 1.95 —> considered the healthy value. High activity level: some manual work and/or exercise

1.95 → vary high activity level: a fair amount of manual work or exercise training.

What are the categorisations of the MET intensity?

< 3 → sedentary lifestyle / light physical activity

3 - 5.9 → moderate physical activity

6 - 8.7 → vigorous physical activity

For example:
Brisk walking requires about ±4 MET: it requires about 4 times the energy used at rest.

Slower walking/strolling has a lower energy cost, with a score of around 2.

Running has a higher MET score, typically 6 to 7. But depending on speed it carries 15 to even 20

What is the minimum MET score that needs to be achieved for moderate intensity?

For health benefits, daily physical activities should be at least of moderate intensity = corresponding to a MET value of 3 or higher.
→ Means that strolling does not qualify as health-enhancing physical activity, whereas brisk walking does (but any physical activity is always better than none)

Why is it difficult to measure physical activity?

it's difficult to capture because it's multi-dimensional, it varies from day to day. and it's prone to recall bias and behavioral changes when measured.

No single method accurately captures all aspects of movement.

Which two categories do we know that measure physical activity?

1. Subjective methods → questionnaires, logs/diaries

2. Objective methods → heart rate monitoring, pedometers, accelerometers, doubly labelled water

The choice depends on study design, budget, the research question.

What are ‘self-reported methods’?

Questionnaires, recall, diary → ask people about their physical activity to get an impression (not objective, but subjective!)

→ if you know frequency, duration, intensity and body weight for 24 hours → calculate energy expenditure.

→ but, it’s hard for people to know all these 4!!

What are the strengths of a questionnaire?

Participants report how much time they spend in activities of different intensities over a specified period (last 24h, to longer periods). ‘Recall’ is also an example.

Strenghts:

• low-cost/low burden.

• applicable to large numbers of individuals/populations (large population)

• It’s convenient/easy to use

• you can do a single time point assessment

• rank*

• you can assess different dimensions and domeins (leisure, sport, occupational).

• You can select appropriate method (face to face, online, paper)

ranking* → google:While self-reports are notoriously poor at pinpointing exact individual minutes of daily movement, they are highly valid at ranking individuals into broad groups (e.g., highly active vs. sedentary). In large epidemiological studies, these broad categorization profiles correlate remarkably well with overall population-level EE trends

What are the limitations of a questionnaire?

Limitations:

• self-reported; misreporting, subject compliance, miscoding of activities, inaccurate estimation of activity intensity/duration

• socially desirability

• recall bias

• care with interpretation of what people wrote down

• low for lifestyle PA, not for EE* → questionnaire is not valid in terms of assessing EE

• It needs to be population and culture specific: can’t just take a questionnaire from internet and use it for your population

• It contains low validity for assessing incidental or lifestyle physical activity.

• Poor correlation with Energy Expenditure (EE) (DLW), can rank individuals!

• differences in body mass

• Environment
  
  

*google:Lifestyle physical activity consists of spontaneous, low-intensity, and unstructured movements integrated into daily life (e.g., taking the stairs, folding laundry, pacing while on the phone, walking to the mailbox). Self-report questionnaires have very low validity here due to e.g. recall bias.

Energy Expenditure (EE), specifically Physical Activity Energy Expenditure (PAEE), is an absolute metric of caloric burn. Questionnaires perform better at predicting or ranking EE for different reasons:

• Driven by Big, Structure Blocks: The vast majority of a person's variable energy expenditure comes from deliberate, moderate-to-vigorous physical activity (MVPA)—like sports, heavy manual labor, or fitness training. Questionnaires excel at capturing these distinct events.

• The Power of Ranking: While self-reports are notoriously poor at pinpointing exact individual minutes of daily movement, they are highly valid atranking individuals into broad groups (e.g., highly active vs. sedentary). In large epidemiological studies, these broad categorization profiles correlate remarkably well with overall population-level EE trends

• MET Alignment: Researchers apply standardized Metabolic Equivalent (MET) multipliers to the structured sports or exercises that participants do remember. Because strenuous, memorable activities burn calories at a much higher rate, capturing these big blocks allows mathematical equations to generate a reasonable estimate of total active energy expenditure

Selecting a questionnaire - what to think about?

• advantage = you can include questions that are relevant for your populations: you can make a questionnaire population specific → ask different things in an older population, then to a younger one. Or in NL you have to ask about cycling, in another country: maybe less relevant (culture differences)

• PA aspect/dimension → PA level (intensity, duration, frequency), weightbearing, strength/endurance, etc.

• Objective questionnaire? → good at ranking individuals (who is moderate active, or low- or high active?) or estimating EE → you can find associations with all kind of outcome measures (not needed to exactly quantify the exact measure EE).

• Domain (leisure, sport, occupational, all?)

• Population

• Time-frame → you ask about PA in the last week? or last month? Or last year?

What are strenghts/limitations of a ‘activity recall’?

Recall = example of another self-reported method: ‘what did you do yesterday? the day before yesterday, five days ago, etc.?’ → written down.

• can be 24-h recall, up to 7 days

• can use MET scores → to give estimation of energy expenditure

• Telephone interview (trained investigator)

• whish-full answers (social desirability bias)

• Labor-intensive (for the researchers/ staff, do the interviews and check all the data sets)

• Correlation with DLW low*

• Recall bias

*activity recall measures subjective behavioral recall,while DLW measures objective metabolic energy expenditure.
While DLW is the biochemical "gold standard" for capturing total energy expenditure (TEE) in free-living individuals, subjective recall tools routinely result in weak correlations (typically averaging around r = 0.37) due to several distinct physiological and cognitive factors (mentioned above-limitations)

e.g:
five different people accurately write down"I walked for 60 minutes today."

graph → their self-reported activity score is identical. But when you look at their actualDLW data,their true energy expenditure is wildly different because:

• Person 1 weighs 100 kg and naturally burns twice as many calories walking as Person 2, who weighs 50 kg.

• Person 3 has high muscle mass and a fast metabolism.

• Person 4 walks efficiently with a smooth stride, burning fewer calories than Person 5, who has an inefficient stride.

Mathematically, you get avertical line of scattered data points (same reported activity, vastly different biological calories). This completely breaks the linear relationship needed for a high correlation.

People systematically over-report how much they exercise. If someone goes to the gym for 30 minutes, they might subconsciously log it as 60 minutes because they include the time spent changing clothes, driving, or resting between sets.

If Person A, B, and C all burned exactly 300 calories according to the DLW, they might write down 45 mins, 60 mins, and 90 mins on their recall forms. This creates a horizontal scatter of data points that should be in the exact same spot, weakening the mathematical correlation.

The ‘physical activity diary’

• 15 minutes intervals

• groups of activities

• Conversion to ADMR

• Combined with dietary record

But:

• Compliance/cooperation → people often complete such a diary at the end of the day (becomes recall!)

• Interferes with activities (reactivity bias) → when you write it down, you become very conscious of what you’re doing: e.g. ‘I should be more active’ or you don’t write down the chocolate that you eat

• Data processing can be quite labor-intensive

What are the strengths and limitations of a logs/diaries?

strengths: low costs, no memory, detailed info

limitations: self-reported, high burden, time consuming analysis

What is the ‘heart rate monitoring’ and when would you use this method?

When you are more active, heart rate goes up = good rate of energy expenditure. There is a close linear relationship: the higher energy expenditure, the higher the heart rate.

→ but differs from person to person (make this visual for each person, also age and body composition is important for example)

→ it gives good information on the intensity of the excersise, and it's a cheap method.

What are the strengths and limitations of Heart Rate monitoring?

Strenghts:

• relatively cheap method to use

• The relationship is strong with moderate to vigorous intensity: gives information about the intensity of the activity.

• It requires a low burden for short periods of time.

• gives individual calibration curve

Limitations:

• heart rate can be influenced by factors like stress, drugs, temperature, illness or caffeine intake → e.g. stressed: heart rate goes up, but your energy expenditure doesn't go up → for 24 hour base this is not a very good measure. It is a good measure for sports measurement. → relationship HR-metabolic rate lost.

• It’s poor in the range of low intensity physical activity (agreement with DLW poor)

• Toleration (band around waist can measure it better than wrist, but maybe not nice for people to wear?)

What are the strengths of Pedometer (stappenteller)?

Strenghts:

• low cost/burden

• applicable to large numbers of individuals (can be used for large interventions that are focused on walking behavior).

• The data is easy to process

• It can be used to motivate people

What are the limitations of Pedometer (stappenteller)?

Limitations:

• lack sensitivity: no quantification stride length/body displacement; they simply count the steps based on a set threshold.

• it does a pretty good indicator, but it’s not an accurate method for energy expenditure → very limited utility estimating Energy Expenditure. It cannot measure the mode/type of physical activity (only steps)

• It can happen that false steps are recorded (depends on the device used)
  
  + do you want to monitor behaviour? → then people should not be able to see the result as this can influence behaviour.

What is the Accelerometer and what are the strengths of Accelerometer?

Accelerometer measures measures amount and intensity (counts) → uniaxial vs tri-axial* → muscle force → fast → a lot of muscle force and energy expenditure.

Strenghts:

• low burden/small

• Detailed info: provide minute to minute data on activity intensity, frequency and duration = very detailed.

• you can store data for weeks at a time.

Conversion to outcomes → METs

*From google: An accelerometer is a sensor that tracks movement intensity.

• Uniaxialsensors measure movement in onlone direction(usually up and down, like basic step counting).

• Tri-axialsensors measure movement acrossthree dimensions(up-down, side-to-side, and front-to-back).
  → By upgrading from uniaxial to tri-axial, the device captures a far more accurate and complete picture of multi-directional body movements
  
  Accelerometers cannot directly look at your muscles, but they measure acceleration (how quickly you speed up or change direction). → acceleration recorded by device: direct mathematical proxy to estimate the mechanical force your muscles are exerting to move your body weight.

What are the limitations of Accelerometer?

Limitations:

• May not accurately capture certain activities (e.g. swimming, cycling, training or resistance), cannot account for all the different activities.*

• When accelerometer is worn on lower-back/hip, the upper-body activities are neglected.

• It is rather time consuming to process the data

*cycle at constant speed? → no acceleration/deceleration. if you combine it with heart rate monitor and seeing not much acceleration; could be an indication of cycling.
without heart rate measure → could be just sitting in the car :)

What advantages do ‘combined sensing’ have by adding other physiological measures to accelerometery? (e.g. HR and accelerometery)

Validity! This is considered second best; no interference with behaviour (free living P.A. monitoring), gives also day-to-day variation.

• adding other measures to acc.
  → could lead to better estimates of EE

• motion sensor as back-up to verify HR

• EE activity pattern
  → promising

What are the strengths of Doubly labeled water?

the difference in elimination rates between the two isotopes reflects carbon dioxide production, which can be used to calculate energy expenditure

Strenghts:

• objective, the gold standard method for measuring total energy expenditure (TEE) in free living individuals under normal daily living activities (participants live their ’normal, daily life’ and are not being confined to e.g. the laboratory)

• highly accurate method → high validity (precision and accuracy)

• convenient for the participants/patients → only small amount heavy water needs to be ingested + a few urine samples required.

• Does not interfere with daily activities and only a small amount of heavy water has to be ingested.

• can be used in many populations.

• Used to validate other methods and validate energy intake methods.
  
  deze ga je niet gebruiken als je 1000 mensen wilt meten. Maar hij is wel de goude standaard/goed voor de energy expenditure meten.

What are the limitations of Doubly labeled water?

Limitations:

• Expensive

• small groups

• Only provides info on total energy expenditure (EE) over the measurement period (and not in activity patterns!)

• requires specialized expertise/trained personnel and technical equipment

• only provides information about the total energy expenditure, not on the pattern/type of physical activity.

• TEE over 4-21 days; no information about other dimensions

• The measures of the thermic effect of the food and the resting metabolic rate required to derive PAEE

What is Calorimetry?

‘calo’ = heat. energy is heat. Measuring energy. → The measurement of heat production is called calorimetry.

Energy expenditure → energy released during the oxidation of any yielding substates in the body: food + oxygen → carbon dioxide, water and energy.

→ This energy is used to perform work, all energy is released as heat.

→ One calorie is defined as the amount of heat required to raise the temperature of one gram of water by one degree celsius.

→ In nutrition, we usually refer to kilocalories: one ‘food-calorie’ equals one kilocalorie or 1,000 calories.

What do we mean with ‘directly’ vs ‘indirectly measuring energy/heat production?

• Direct calorimetry = Allowing heat loss to be measured directly. This method is theoretically very accurate, it’s technically complex: extremely expensive and highly impractical. can be done by placing a person in a thermally insulated chamber or by using a thermally insulated suit.

• Indirect calorimetry = A more practical approach. Instead of measuring heat directly, this method measures gaseous exchange* (oxygen consumption and carbon dioxide production, resulting from the oxidation of carbohydrates, fat and protein).

*As energy production is closely linked to oxygen use and carbon dioxide release, energy expenditure can be calculated from these measurements using established equations.

With which methods can gaseous exchange be measured?

All same principle: air flow is measured and oxygen and carbon dioxide concentration of air entering and leaving the system are analysed: can be calculated:

1. with face mask → used to get MET-scores, usually used during various activities (measuring physical activity expenditure (PAEE)

2. a ventilated hood → measuring RMR/BMR

3. respiratory chamber → measuring total energy expenditure

Accurate methods if strict protocols are being followed, not suitable for measuring ‘free living energy expenditure’ over several days.

What method can we use to measure in ‘free living Energy Expenditure (under free living conditions)’?

The DLW-method! → measures a subject’s carbon dioxide production by measuring the elimination rate of two isotopes.

→ 2 stable isotopes; heavy hydrogen (deuterium) and oxygen are digested in the form of water.


→ isotopes mix with the body’s water pool.

→ as the body expands energy, water and carbon dioxide are produced and eliminated from the body (in breath, urine, sweat)

→ the deuterium leaves the body only as water, while oxygen-18 is lost as bulk water and carbon dioxide.
 18O is lost more rapidly than 2H as it is contained in CO2 & H2O; 2H only in H20. → washout oxygen is quicker than for hydrogen isotope.

→ the difference in elimination rates between the two isotopes reflects carbon dioxide production (rCO2)→ calculate energy expenditure. calculated from the subsequent difference in elimination between the two isotopes, is a measure of metabolism.

→ To determine these elimination rates, a body water sample is taken a few hours after ingestion of the doubly labeled water and another sample is collected 10 to 14 days later

What are the assumptions of the DLW-method?

• total body water remains constant during observation (lose weight → water becomes smaller and it would effect the isotopes)

• Losses only trough H2O and CO2 → no exchange of 2H and 18O with non-aqueous body tissue*

• determination of RQ (RER) is required; otherwise assumption of 0.85** → ΔRQ = 0.01 ~ ΔEE = 1%

• Can be improved by estimating VO2 (RQ) = oxygen consumption
  
  *In de geneeskunde en biologie verwijst dit naar weefsels in het menselijk lichaam die een zeer laag watergehalte hebben in vergelijking met andere (waterrijke of vloeibare) weefsels, e.g. vetweefsel of botweefsel.
  
  ** google: to accurately calculate a person's total energy expenditure, researchers need to know the mix of fuels (carbohydrates, fats, and proteins) the body is burning. The DLW method measures how much carbon dioxide your body produces. However, to turn that CO2 number into actual calories burned, you must know the Respiratory Quotient (RQ) or Respiratory Exchange Ratio (RER).
  → 0.85 represents a typical, balanced Western diet where the body is burning a mix of roughly half fat and half carbohydrates.

What are ‘motion sensors’? and in which two forms do they come?

These are computer devices that provide continuous monitoring (smartwatches, phones, etc.). Their validity varies and often requires comparison with more research grade instruments.

But they are:

• relatively small

• User friendliness (can use it in large populations, with less problems)

• Costs

What is a huge disadvantage of using smartwatches?

they measure your position and heart rate, etc. and it’s turned into energy expenditure. But we do not know how exactly it is done. They are good tools, but as scientist we want to know what is exactly happening.

→ this is a Global Positioning System (GPS) that captures pace and distance during outdoor activities → data are subsequently passed into a proprietary data-driven model that estimates EE.

→ different brands having different models and performance!

What do smartwatches measure?

Total (daily) energy expenditure = ± resting energy expenditure + activity energy expenditure.

• it’s an objective indirect measurement (you measure something) → recalculated to energy expenditure: an indirect estimate → much less precise than e.g. DLW (which is more direct in measuring EE)

• depends on body composition

• movement + heart rate + personal characteristics + activity type
  → estimated oxygen use → estimated calories.

Is there one perfect method to measure physical activity?

No! No single method is perfect for measuring PA.

Subjective tools like questionnaires and diaries are practical for large scale nutrition studies, but may lack precision.

Objective measures, like accelerometry and DLW, provide greater accuracy, but can be costly and burdensome.

Therefore many researchers combine methods. E.g. using accelerometers alongside questionnaires to improve validity.

Without accurately capturing physical activity, nutrition research cannot fully explain the complex relationship between diet, energy balance and health.