Human Energy

What is energy?

o  Energy is the capacity to do work

n   May be in the form of:

p  Mechanical

p  Light

p  Nuclear

p  Electrical

p  Heat

p  chemical

How do we measure energy?

o  Work = force x distance

o  Power = work/time

n   How fast work is done

o  Units

n   English

n   Metric

n   System of International units (SI)

p  Eventually hope to move all measures of energy to this system

Chemical Energy

o  How many calories are in food?  How did we find out?

n   Bomb calorimeter

p  Measures the amount of heat given off from food that is combusted in a chamber surrounded by water

p  This heat measurement gives us calories if we remember that:

n   A Calorie = amount of heat needed to raise the temperature of 1 kilogram of water, 1OC

Energy yields from calorimeter

o   1 gram CHO = 4.3 calories

o   1 gram Fat = 9.45 calories

o   1 gram Protein = 5.65 calories

o   1 gram Alcohol = 7.0 calories

                After digestion:

o   1 gram CHO = 4.0 calories

o   1 gram Fat = 9.0 calories

o   1 gram Protein = 4.0 calories

o   1 gram Alcohol = 7.0 calories

Chemical “Human” Energy

o    How do we measure calories that we expend from exercise?

n    Use of O2 measurement devices

p  Metabolic cart

n   Its oxygen analyzers measure amount of O2 that we consume during exercise; picked up through expired gases via tubing from mouth
n   1 liter of O2 consumed ~ 5 Calories burned

n    Use of doubly-labeled water

p  Labeled water with H2 and O2 is ingested

n   Urine and blood samples are measured for H2 and O2
o    Labeled O2 is eliminated as water and CO2
o   Labeled H2 is eliminated as only water
o   Subtract H2 losses from water which gives measure of CO2; the CO2 is converted to energy expenditure

Energy in the Body

o  ATP

n   Immediate form of energy

n   Stored in small amounts in a variety of tissues

o  Phosphocreatine (PCr)

n   Rapidly replenishes used ATP

n   Not an immediate source of energy

n   Stored in small amounts

 

How are ATP derived from CHO, Fat, and Protein

          Protein                 CHO                        Fat

The Energy Systems Necessary for Exercise

o   ATP-PC System

n    Phosphogen system

p  Direct source of ATP for quick energy

p  Supplies energy for “max” events of 0 -10 seconds

p  ATP used for energy; PC replaces lost ATP

o   Lactic Acid System

n    Anaerobic glycolysis (breakdown of glucose without use of O2)  [glucose                     lactic acid]

n    Rebuilds ATP quickly for events of “near-maximal” efforts (30-120 seconds)

n      Lactic acid, resulting from glucose breakdown, can be used by other tissues as an energy source

The Energy Systems Necessary for Exercise

o   Oxygen system

n    Aerobic system

p  Produces ATP in large quantities from several energy sources in the body

n   e.g. muscle & liver glycogen; blood glucose & FFA; triglycerides in muscle, blood & adipose tissue; and body protein

p  Rebuilds ATP for sporting events of long duration from 5 km (3.1 mi) to marathon and beyond

p  Sometimes subdivided as:

n   Aerobic glycolysis – glucose + O2 for energy
n   Aerobic lipolysis – fat + O2 for energy

 

Other nutrients responsible for energy metabolism

o   Water

n    Helps break up (hydrolysis) and transform necessary energy compounds

o   Vitamins

n    Needed for energy release from cells

n    e.g. - Niacin serves in glycolysis

           - Thiamin needed to convert products

              to acetyl-CoA

o   Minerals

n    Essential for cellular processes

n      e.g. - Iron needed for proper utilization of O2

           - Calcium needed to initiate muscle contraction

Metabolism

o   Sum total of all physical and chemical changes that take place within the body

o   Involves 2 processes:

n    Anabolism – building-up process

n    Catabolism – tearing-down process

o   Metabolic rate – how rapidly the body uses its energy stores

n    Accounted for by:

p  Resting energy expenditure

p  Energy expenditure due to eating a meal

p  Physical activity

Metabolism

o  Basal Metabolic Rate

n   The energy requirements of the cellular and tissues processes that are necessary to continue physiological activities in a resting, postabsorptive state throughout the day

n   It is the lowest rate of energy expenditure

n   Determined by measuring O2 while in a reclined position, after a 12-hour fast

Metabolism

o  Resting Metabolic Rate (RMR) or Resting Energy Expenditure (REE)

n   Represents the BMR + small amounts of energy expenditure associated with previous muscle activity

n   Slightly higher caloric expenditure than BMR (< 10% difference)

Effect of Eating on Metabolic Rate

o  Metabolic rate raises resulting in what is called dietary-induced thermogenesis (DIT) or thermic effect of food (TEF)

n   Increased caloric expenditure due to:

p  Absorption, transport, storage, and metabolizing the food consumed

p  Highest about 1 hour after a meal and lasts up to about 4 hours

n   The greater the caloric content of food, the greater the TEF effect

Effect of Eating on Metabolic Rate

o  The DIT or TEF:

n   Affected by type of food:

p  TEF for protein ~ 25%

p  TEF for CHO ~ 8%

p  TEF for fat ~ 4%

n   The TEF from a mixed meal of CHO, Fat, and Protein is ~ 5-10% above RMR

n   One study suggests that obesity is associated with a decreased TEF; obese appear to store fat more efficiently.

Estimating your RMR (or REE)

o   May determine rough estimate by:

n    1 Calorie per kg of body wt per hour

p  e.g.  For a 70 kg male

           1 x 70 kg x 24 hr = 1,680 Cal per day

                   for an average range + or – 10%

            e.g.   1,680 x .10 = 168

                             so

                     1,680 + 168 = 1,848

                               and

                     1,680 – 168 = 1,512

Range for caloric need at rest is 1,512 to 1,848 Cals

Genetic Factors Affecting REE

o    Age

n    REE much higher in children

o    Gender

n    REE ~ 10-15% lower in women than men

o    Natural hormonal activity

n    REE higher with greater thyroid activity

o    Body size and surface area

n    REE lower in leaner individuals; these individuals lose more body heat via radiation

o    Body composition

n    Amount of fat vs fat-free tissue

p  Muscle is more metabolically active so muscular person has higher REE

Body composition effect on REE

o  Larger individuals have higher REE

n   Loss of weight results in a reduction of REE

p  Reduction in REE with weight loss may be accompanied by lower level of thyroid hormones

p  It is possible to maintain weight through loss of weight but gain in muscle mass; this may keep REE from changing or elevate it.

Environmental Factors affecting REE

o  Caffeine

o  Smoking ↑

o  Exposure to cold environments ↑

o  Exposure to hot environments ↑

o  Higher altitude ↑

o  Exercise ↑

Energy Sources Used at Rest

o  Primarily CHO and Fat

n   From a mixed diet of CHO, Fat, & Protein         60% of REE is derived from fat

     40% of REE is derived from CHO

n   From diet rich in CHO

p  Greater % of REE derived from CHO

n   From diet rich in Fat

p  Greater % of REE derived from Fat

Effect of Exercise on
 Metabolic Rate

o  Exercise raises metabolic rate (energy expenditure)

n   Known as Exercise Metabolic Rate (EMR)

p  Also known as Thermic Effect of Exercise (TEE)

n   Dependent upon:

p  Fiber types

n   Type I or slow-twitch
n   Type II a or fast-twitch with both aerobic and anaerobic properties
n   Type II b or fast-twitch with anaerobic properties

Effect of Exercise on
 Metabolic Rate

o  Factors affecting metabolic rate

n   Intensity or speed of the exercise

p  Primary factor

p  High speeds increase caloric expenditure exponentially

n   Efficiency of movement

p  Less efficient, more calories burned

n   Body weight

p  Greater body weight, more calories burned

 

How is energy expenditure expressed?

o   Calories per minute

o   Kilojoules

n    1 Calorie = 4 kJ

o   Oxygen uptake

n    1 liter of O2 consumed = 5 Calories burned

o   METS

n    Unit of energy that represents multiples of RMR

p  1 MET = 3.5 ml of O2 consumed per kilogram of body weight per minute (ml/kg/min)

Calculation of Energy Expenditure

o   When measuring O2 from a treadmill run, a 154 lb individual achieves a value of 25 ml/kg/min at maximal effort.  What is the MET level and rate of calories being burned?

n    Steps to solve:

p  25 ml/kg/min divided by 3.5 = 7.14 METs

p  Convert 154 lb to kg; 154/2.2 = 70 kg

p    Determine total energy cost; 70 x 25 = 1,750 ml of O2

p  Convert ml to L; 1,750/1000 = 1.75 L of O2

p  Multiply 1.75 x 5 = 8.75 Calories/min

Best Activities for Caloric Expenditure

o    Intensity and duration are the key determinants of total energy expenditure

o    Walking and running are most popular

n    Slow, leisure walking expends ½  of the calories of running per 1 mile distance

n    Making  walking more vigorous

p  Walk faster, climb stairs, use 1-3 lb hand-held wts (can energy expenditure by 5-10%)

p  Walking with ankle wts not advised (possible injury)

o    Swimming has ~ 4 times the energy expenditure of running the same distance (i.e. ¼ mi swim = 1 mile run)

o    Bicycling has ¹/³ energy expenditure cost as running

o    Aerobic Dance can expend about 9-10 Calories per minute

Energy Expenditure after Exercise

o   Caloric expenditure remains elevated  after exercise

n    Often known as Excess post-exercise oxygen consumption (EPOC)

n    Dependent on intensity and duration of activity

n    May remain elevated from 15-20 minutes up to 4-5 hours; some suggest even longer

n    Weight training appears to exhibit greater EPOC response compared to other activities

p  Primarily due to level of resistance

 

 

Does Exercise have an Effect on the TEF?

o  No definitive findings yet to say that it increases or decreases the TEF

n   If any changes occurs, the  or only amounts to 5-9 Calories over several hours

What does the total daily energy expenditure look like?

Human Energy Spectrum (% contribution of energy systems to different time periods of Max Work)

Fatigue

o  A condition of physiological and/or psychological state of tiredness or showing a lack of energy to perform.

Potential Fatigue Sites

o       Central Locations

o       Brain

o       Spinal Cord

 

o       Peripheral Locations

o       Neuromuscular junction

o       Muscle cell  (primary suspect)

Possible Causes of Fatigue during Exercise

o  Increased formation of depressant neurotransmitters

o  Decreased levels of energy substrates

o  Disturbed intracellular environment

o  Disturbed acid-base balance

o  Decreased O2 transport

o  Increased core body temperature (dehydration)

o  Disturbed electrolyte balance

Can Fatigue be delayed?

o  Yes

o  Use of proper physiological, psychological, and biomechanical training are the best means to deter premature fatigue

Is Nutrition related to Fatigue Processes?

o   Yes

o   For low-level aerobic activity (longer than 2 hours)

n    Need fat and CHO stores

o   For moderate to heavy aerobic activity (1-2 hrs)

n    Need CHO stores

o   For high-intensity (1-2 min)

n    Need good buffering system (bicarbonate)

o   For extreme high-intensity (5-10 sec)

n    Need good phosphate operating system