Human Energy Expenditure During Rest and Physical Activity

HUMAN ENERGY EXPENDITURE

OVERVIEW

  • Presenters: Gianna Mastrofini, PhDc, MS, CSCS

  • Institution: University of South Carolina, Arnold School of Public Health

ENERGY EXPENDITURE AT REST

  • Components Include:

    • Resting Metabolic Rate (RMR): 60-75% of total energy expenditure

    • Thermic Effect of Physical Activity (TEPA) & Non-Exercise Activity Thermogenesis (NEAT): 15-30%

    • Thermic Effect of Food (TEF): 10%

  • Energy Intake: Consists of energy obtained from food and drink.

  • Total Daily Energy Expenditure (TDEE): Balance of energy in versus energy out.

METABOLIC RATE

  • Basal Metabolic Rate (BMR):

    • Energy required to maintain vital functions in a wake state, measured in a fasted state with no exercise.

  • Resting Metabolic Rate (RMR):

    • Energy necessary to maintain vital functions including digestion, measured 3-4 hours post-meal with no exercise and following an overnight fast.

METABOLIC SIZE CONCEPT

  • RMR and Surface Area: RMR correlates with body surface area.

  • Gender Differences:

    • Women have 5-10% lower RMR than men when considering absolute values.

  • Fat-Free Mass (FFM):

    • Each 1-lb gain in FFM increases RMR by 7 to 10 kcal·d$^{-1}$.

  • Decline in RMR with Age: 2-3% decline per decade due to loss of muscle mass and reduced activity levels.

METABOLIC SIZE CHART

  • Chart depicts metabolic rates across species (small birds, rodents, mammals, etc.) against stature and body mass (kg).

RMR AS A FUNCTION OF LBM

  • Graphs A & B:

    • Data illustrated shows RMR against Lean Body Mass (LBM) with gender differentiation and correlation coefficients:

    • Men: R$^{2}$ Linear = -0.361

    • Women: R$^{2}$ Linear = -0.407

    • Calculated values for both graphs highlight the differences in RMR for men and women against FFM and BMI.

PROTEIN INCREASE AND RMR

  • Resistance training with increased protein intake can raise RMR due to the higher energy required for protein digestion.

EXERCISE AND METABOLIC RATE

  • Effects of Regular Exercise:

    • Resistance Training: Increases BMR by enhancing FFM.

    • Endurance Training: Increases BMR even without FFM gains.

    • Regular exercise may counteract age-related declines in BMR and suppresses fat mass gain.

NORMALCY OF METABOLIC VALUES

  • Metabolic rates expressed in kcal or kJ per square meter of surface area (or per kg FFM) min/hour/day:

    • Body Surface Area (BSA): Calculated using the formula: extBSA=H0.725imesW0.425imes71.84ext{BSA} = H^{0.725} imes W^{0.425} imes 71.84 where H = height in cm and W = weight in kg.

    • Resting Daily Energy Expenditure (RDEE): RDEE in kcal can be estimated using:

    • extRDEE=extBMRimesextBSA(inm2)ext{RDEE} = ext{BMR} imes ext{BSA (in m}^{2}) or extRDEE=370+21.6imes(extFFMinkg)ext{RDEE} = 370 + 21.6 imes ( ext{FFM in kg})

    • Muscle is metabolically more active than fat; the brain has a high metabolic rate, and muscle metabolism may increase dramatically during exercise.

RMR ESTIMATION

  • Harris-Benedict Equations:

    • For men: extRMR=66.473+(13.751imesextmassinkg)+(5.0033imesextheightincm)−(6.755imesextageinyears)ext{RMR} = 66.473 + (13.751 imes ext{mass in kg}) + (5.0033 imes ext{height in cm}) - (6.755 imes ext{age in years})

    • For women: extRMR=655.0955+(9.463imesextmassinkg)+(1.8496imesextheightincm)−(4.6756imesextageinyears)ext{RMR} = 655.0955 + (9.463 imes ext{mass in kg}) + (1.8496 imes ext{height in cm}) - (4.6756 imes ext{age in years})

    • Example Calculation for Women:

    • extRMR=655.0955+(9.463imes59)+(1.8496imes170)−(4.6756imes28)=1396.9extkcalext{RMR} = 655.0955 + (9.463 imes 59) + (1.8496 imes 170) - (4.6756 imes 28) = 1396.9 ext{ kcal}

    • FFM Equation: extRMR=500+(22imesextFFMinkg)ext{RMR} = 500 + (22 imes ext{FFM in kg})

    • Example with FFM: 500+(22imes72.16)=2088extkcal500 + (22 imes 72.16) = 2088 ext{ kcal}

FACTORS AFFECTING TOTAL DAILY ENERGY EXPENDITURE (TDEE)

  1. Physical Activity:

    • Major variable contributing to TDEE (15-30%).

    • Elite athletes can nearly double TDEE with extensive training.

  2. Diet-Induced Thermogenesis (DIT):

    • Energy required for nutrient digestion, absorption, and assimilation.

    • Facultative Thermogenesis: Activation of the sympathetic nervous system, stimulating metabolism.

    • Obligatory Thermogenesis: Energy required in digestion processes.

    • Eating before exercise augments energy expenditure.

    • DIT of carbohydrates and protein exceeds that of fat.

  3. Climate:

    • Hot or cold environments affect energy expenditure.

    • Exercise in heat raises oxygen consumption by about 5%.

    • Heat increases core temperature and sweat activity; cold induces shivering thermogenesis.

  4. Pregnancy:

    • Increases BMR due to weight gain; women advised to stay active during pregnancy.

ENERGY EXPENDITURE IN PHYSICAL ACTIVITY

  • Classification of activities by energy expenditure.

  • Intensity and duration significant factors.

  • Physical Activity Ratio (PAR): Ratio of energy expenditure to BMR values.

    • Light work: 1-3 x BMR

    • Heavy work: 6-8 x BMR

    • Maximal work: > 9 x BMR

METABOLIC EQUIVALENT (MET)

  • Definition: 1 MET = 3.5 ml O$_{2}$ kg$^{-1}$ min$^{-1}$

  • Exercise requiring higher METs increases relative metabolism:

    • Exercising at 2 METs doubles resting metabolism; at 3 METs triples it.

  • MET used for exercise intensity prescriptions.

PHYSICAL ACTIVITY CLASSIFICATION TABLE

  • Five-Level Classification based on Energy Expenditure:

    • Males:

    • Light: 2.0-4.9 kcal.min$^{-1}$

    • Moderate: 5.0-7.4 kcal.min$^{-1}$

    • Heavy: 7.5-9.9 kcal.min$^{-1}$

    • Very Heavy: 10.0-12.4 kcal.min$^{-1}$

    • Unduly Heavy: ≥12.5 kcal.min$^{-1}$

    • Females:

    • Light: 1.5-3.4 kcal.min$^{-1}$

    • Moderate: 3.5-5.4 kcal.min$^{-1}$

    • Heavy: 5.5-7.4 kcal.min$^{-1}$

    • Very Heavy: 7.5-9.4 kcal.min$^{-1}$

    • Unduly Heavy: ≥9.5 kcal.min$^{-1}$

  • Note: L.min$^{-1}$ based on 5 kcal per liter of oxygen.

ENERGY EXPENDITURE IN VARIOUS ACTIVITIES

  • Energy costs of household, industrial, and recreational activities are adjusted for body mass.

  • Weight-bearing versus weight-supported exercises: measuring costs per kg body mass normalizes differences regardless of individual metrics (age, race, sex).

RELATIONSHIP BETWEEN BODY MASS AND OXYGEN UPTAKE

  • Graph visualizes the relationship illustrating varied oxygen uptake based on body mass (kg).

HEART RATE AS AN ESTIMATOR FOR ENERGY EXPENDITURE

  • A linear relationship exists between heart rate and oxygen consumption up to approximately 80% maximum heart rate.

  • Variability in heart rate responses due to:

    • Environmental factors (temperature, humidity)

    • Food intake

    • Work type (static or dynamic)

    • Muscle groups involved

    • Body position

    • Emotions

    • Drug effects