Chapter 10

Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Chapter 10

Energy Expenditure During Walking, Jogging, Running, and Swimming


Gross Versus Net Energy Expenditure

• Energy expenditure estimates– Gross energy expenditure

• Total energy required for an activity

– Net energy expenditure• Gross energy expenditure – Resting energy

expenditure


Economy of Human Movement

• Economy of movement refers to the energy required to maintain a constant velocity of movement.

• More skilled athletes perform the same activity with a reduced energy requirement.


Mechanical Efficiency

• Mechanical efficiency– Ratio of energy output / energy input– Reflects the amount of energy transferred into

doing work– External work is measured as F × D

• Ft-lb

• Kg-m

• kCal


Walking

• Influence of body mass– Equations may be used to calculate energy

expenditure.– Speed or pace is an important factor.– Mass is factored in as resistance.– Individuals with a larger mass expend more

energy at the same pace.



Walking

• Terrain and walking surface– Energy expenditure is greater on soft surfaces.

• Sand

• Snow

– Slope or grade influences energy expenditure.• Downhill walking requires less energy.

• Very steep downhills require energy to “brake.”

• Uphill grades require more energy.



Walking

• Footwear– Added weight to feet or legs increases energy

requirements.– Shoes need to balance cushioning effects with weight.

• Handheld and ankle weights– Increase energy expenditure– Used during walking, increase energy expenditure closer

to that of running– Have less of an impact on energy expenditure while

running


Competition Walking

• Economy is not good in this type of walking.– Energy expenditure increases at a faster rate or a

greater slope for competitive walking compared to running.



Running• Economy of running fast or slowly

– Net energy cost values for running a set distance are similar for different speeds.

• Stride length, stride frequency, and speed– Running

• Speed is dependent upon stride length & stride frequency.– Competition walking

• Speed is increased mainly by increasing stride frequency.– Optimum stride length

• Level of minimum effort• No “best” style


Running• Running economy: Children and adults

– Children have lower running economy than adults.– Children require 20 – 30% more oxygen per unit

of mass to run at the same pace as an adult.• Air resistance

– Factors that effect air resistance• Air density• Runner’s projected surface area• Square of runner’s velocity

– Drafting• Decreases resistance


Running• Treadmill versus track running

– Have similar energy requirements at the same speed

– Elite athletes at top speeds on the track may encounter increased air resistance.

• Marathon running– To be successful requires the ability to maintain

pace for an extended period of time


Swimming

• Methods of measurement– Portable metabolic systems may be worn.– Subjects may be tethered.– Subjects may swim in a flume.






Swimming

• Energy cost and drag– Total drag force

• Wave drag

• Skin friction drag

• Viscous pressure drag

– Ways to reduce effects of drag force• Wet suits

• Drafting


Swimming

• Energy cost, swimming velocity, and skill– Skilled swimmers are more efficient.

• More of their effort provides forward movement.

– The stroke used influences energy cost.• Freestyle or front crawl is more efficient than back

crawl or breaststroke.

• Breaststroke is less efficient than freestyle or back crawl.


Swimming• Effects of water temperature

– Cold water adds additional energy costs.– Optimal temperature is ~ 82 – 86°F.

• Effects of buoyancy: Men versus women– The leaner an individual, the less buoyant.– Women tend to be more economical due to

added buoyancy.– Endurance swimming is influenced by economy

and thermal insulation provided by body fat.

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Chapter 10