Energy Expenditure

basal metabolic rate

energy to maintain vital functions in a wake state; 12 hour fast, no exercise in 24 hours, supine, thermoneutral (essentially perfect conditions)

• expressed as kcal or KJ per square meter of surface area

resting metabolic rate

energy to maintain vital functions plug digestion

• measured 3 to 4 hours after a meal

effect of resistance training on BMR

increases basal metabolic rate by increasing fat free mass

effect of endurance training on BMR

increases basal metabolic rate without increasing fat free mass

resting daily energy expenditure

BMRxM2

• contribution of diverse tissues

• muscle is more active than fat mass

• the brain has a high metabolic rate

• metabolism may increase nearly 100 times during exercise

factors that affect energy expenditure

• physical activity

• diet induced thermogenesis

  • calorigenic effect of food on exercise metabolism

  • energy required to digest, absorb, and assimilate nutrients

• climate

• pregnancy

MET

metabolic equivalent

2.5 ml O2 per kg of body weight per minute

factors that affect heart rate

• temperature

• humidity

• food intake

• static vs. dynamic work

• muscle groups worked (trying to do the same thing with less muscle will decrease expenditure)

• body position

• emotions (stress hormones)

gross energy expenditure

total energy required for an activitymet

net energy expenditure

gross energy expenditure - resting energy expenditure (what you need to stay alive)

mechanical efficiency

oxygen consumption it takes to do the measured work

• ratio of energy output/energy input

• reflects the amount of energy transferred into doing work

• external work measured as forcexdistance

economy of movement

the energy required to maintain a constant velocity of movement

• ex: more skilled athletes perform the same activity with a reduced energy requirement

• the more you train, the more efficient you tend to be; you spend less energy doing the same amount of work (some of this related to skill, some of this is mechanical makeup)

• increase comes from specificity

walking

• energy expenditure influenced by slope or grade

• energy expenditure is greater on soft surfaces

• very steep downhills require more energy to “brake”

• footwear can increase energy requirements, handheld and ankle weights too

competition walking

energy expenditure increases at a faster rate or a greater slope for competitive walking compared to runing therefore economy is not good

running

dependent on stride length, stride rate, and speed

speed is dependent on stride rate and length

net energy cost values for running a set distance are similar for different speeds

**children have lower economy for this than adults because they need more O2

affected by air resistance

swimming

drag force: wave drag, skin friction drag, viscous pressure drag

• can be reduced by wet suits

• can be reduced by drafting

skill makes you more efficient

resistance increases at higher velocities

energy cost different per stroke

cold water increases energy cost

the leaner you are, the less buoyant you are (therefore women more economical due to body fat distribution and buoyancy)

generality

high aerobic power usually indicates above average power in related activities

power test

used to measure brief maximal capacity

• measures ATP/PC system but sometimes too short so you could just be measuring power not metabolism

• generally less than 6 seconds

physiologic/biochemical test (for immediate energy systems)

evaluates:

• size of intramuscular ATP-PCr pool

• depletion rate of ATP and PCr in all-out short duration exercise

• O2 deficit calculated from initial phase of exercise O2 consumption curve

  • alactic portion of recovery O2 consumption (fast component of EPOC)

evaluation of short-term energy system

glycolysis generates increasingly more energy for ATP resynthesis

• lactate accumulates as rate of glycolysis increases

• blood lactate levels provide the most common indicator of glycolytic activity

• need maximum exercise for up to 3 minutes to activate glycolysis substantially

**if activity is longer, can look at lactate levels to see the rate of lactate generation but have to catch it in the window before you can clear it

males vs. females in power tests

• higher neuromuscular recruitment in men

• higher type II muscle fiber area in men

• more glycolytic enzyme activity/substrate utilization rates in men

• differences in circulating hormones

• difference in catecholamine responses to exercise (norepinephrine and epinephrine)

max accumulated O2 deficit

a regression line predicts supramaximal O2 consumption from this idea and actual O2 consumption during 2-3 minute all out run fatigue

• provides another indirect measure of anaerobic capacity

• determined using linear exercise intensity and O2 consumption relationship

• collected from submaximal treadmill trials

high intensity glycogen depletion

depletes type II (fast twitch) muscle fiber glycogen

low intensity glycogen depletion

depletes type I (slow twitch) muscle fiber glycogen

anaerobically trained effects

greater lactate generating capabilities

greater depletion of muscle glycogen

VO2max

max oxygen consumption; directly related to blood flow (HRxSV) and aVO2 difference (how well the muscle can extract O2 which depends on mitochondria, capillary density, myoglobin, etc.)

criteria for max O2 consumption

a leveling off in oxygen consumption despite an increase in exercise intensity generally assures VO2max has been reached

secondary criteria for VO2max

RER or R> 1.15

• indicates aerobic at max and now using anaerobic metabolism

• blood lactate 70-80 mg/dl

• attain age predicted max HR

factors that affect VO2max

• mode of exercise

• heredity (genetics)

• state of training

• sex

• body size and composition

• age

sex differences in VO2max

males 15-30% above females

• affected by muscle mass

• affected by hemoglobin concentration (ratio of RBCs, ability to extract oxygen)

age affect on VO2max

declines after age 25 (but lactate threshold can still increase with training)

training can’t prevent the decline but it can CHANGE the decline (lessens the steepness of the decline)