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Total or gross energy expenditure includes
the resting energy requirement; net energy expenditure represents the energy expenditure of the activity excluding the resting value.
Economy of movement refers to
the oxygen consumed during steady-rate exercise.
Mechanical efficiency evaluates the relationship between
work accomplished and energy expended doing the work.
Walking, running, and cycling produce mechanical efficiencies between
20 and 25%. Efficiencies decrease below 20% for activities with considerable resistance to movement (drag).
A linear relationship exists between walking speed and oxygen consumption at
normal walking speeds. Walking on sand requires about twice the energy as walking on firm surfaces. A proportionately larger energy expenditure exists for heavier persons during weight-bearing physical activities.
Running becomes more economical than walking at speeds that exceed
8 km∙hr-1.
Handheld and ankle weights can increase the energy expenditure of walking to values similar to
running.
The total caloric expenditure of running a given distance at steady-rate oxygen consumption remains
about the same independent of running speed.
Net energy expenditure during horizontal running approximates
1 kcal ∙ kg-1 ∙ km-1.
Shortening running stride and increasing stride frequency to maintain a constant running speed requires
less energy than lengthening stride and reducing frequency.
An individual subconsciously "selects" the combination of stride length and frequency to favor
optimal economy of movement, which represents a level of minimum effort
Energy expended to overcome air resistance accounts for
3 to 9% of the energy expenditure of running in calm air. This percentage increases considerably when a runner maintains pace while running into a brisk headwind.
Children generally require
more oxygen to transport their body mass while running than do adults. A relatively lower running economy accounts for the poorer endurance performance of children compared with adults of similar aerobic capacity.
Running a given distance or speed on a treadmill requires
similar energy output as running on a track under identical environmental conditions.
A person expends about four times more energy to swim a given distance than to
run the same distance because of greater energy to maintain buoyancy and overcome drag forces in swimming.
Elite swimmers expend
fewer calories to swim a given stroke at any velocity than less skilled counterparts.
Significant gender differences exist in body drag, mechanical efficiency, and net oxygen consumption during swimming. Women swim a given distance at approximately
30% lower energy expenditure than men.
The net energy expenditure of swimming the English Channel exceeds
5200 kcal or approximately twice the calories expended running a marathon.
Gross Energy Expenditure
total energy expenditure during a time period, including resting metabolism, exercise consumption and EPOC
Net Energy Expenditure
Gross Energy Expenditure - Resting Metabolism for the equivalent time.
Mechanical Efficiency Equation
(External Work Accomplished / Energy Expenditure) X 100
Movement Economy
energy required to maintain a constant movement velocity
Delta Efficiency Equation
(Δ Work Production / Δ Energy Expenditure) X 100
Negative Work
Body's center of mass moves in a downward vertical direction.
Mechanical Efficiency and Running Speed
Net energy expenditure is roughly the same regardless of pace, meaning you can run at 10 mph and burn roughly twice the amount of energy than 5 mph
Ways to Increase Running Speed
1) Number of steps per minute
2) Distance between steps
3) Increase both length and frequency of strides
Level of Minimum Effort
self selected stride length and frequency generally produce the most economical running performance. Meaning, their are trends, but variability makes modelling not useful.
Treadmill vs. Track Running
There are marginal, if any, energy requirement difference between running on a treadmill in a closed environment and a track. Possible difference with elite level athletes and air resistance.
Drafting
Running or cycling behind another person. Reduces the headwind and negative effect of air resistance, thus making the person more economical energy wise.
Drag Forces
The friction like forces exerted by a fluid and a solid on one another as the solid moves through the fluid.
-Swimming
Mechanical Efficiency and Swimming
Lower mechanical efficiency makes the energy expenditure during swimming on average more than 4 times that of competitive running
Wave Drag
waves that build up in front of a swimmer
Skin Friction Drag
produced as water slides over skin surface
Viscous Pressure Drag
pressure difference in front of and behind the swimmer