Chapter 10: Energy Expenditure During Walking, Jogging, Running, and Swimming

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