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Ch.9 Human Energy Expenditure During Rest and Physical Activity/Ch.10…

- - - - Movement economy in contrast, refers to the energy required (usually inferred from measurement of oxygen consumption) to maintain a constant movement velocity.
        
        Assessing movement economy involves measuring oxygen consumption during steady-rate exercise at a constant power output or velocity.
        
        At sub maximal running, cycling or swimming an individual with greater movement economy consumes less oxygen (lower steady-rate VO2).
        
        For example, African women who balance heavy loads on their heads have mastered a subtle adjustment in walking technique that allows them to carry 20% of their bodyweight with no increase in energy expenditure. They exhibit greater movement economy.
        
        Another example would be Lance Armstrong from an age of 21yrs to 28yrs he improved 8% in movement economy which translated to increased power production when cycling at a given oxygen uptake. How does his drug use impact this?
        
        Cyclists with greater economy possessed a larger percentage of slow-twitch (type I) muscle fibers in the vastus lateralis. Aerobic Type I fibers respond with greater mechanical efficiency.
        
        At identical submaximal speeds, an endurance athlete runs at a lower percentage of VO2max than an untrained person, although both maintain similar oxygen consumption rates.
        
        Walking economy decreases at faster speeds. This explains why per unit distance traveled, faster, less-efficient walking speeds require more total calories expended per unit distance traveled.
        
        Walking in sand requires almost twice the energy expenditure compared to walking on a hard surface because of sand's hindering effects on the forward movement of the foot and the added force required by calf muscles to compensate for foot slippage.
        
        Compared with level ground walking, walking on a declined grade decreases oxygen consumption; -9% at a speed of 5.4km x hr, -12% at 6.3km x hr. But expenditure increases at more severe grades. The additional energy expenditure to resist or brake the body from gravity's pull while trying to achieve a proper and safe walking rhythm increases the oxygen consumption.
        
        It requires considerably more energy to carry weight on the feet or ankles than to carry the same weight on the torso. A weight equal to 1.4% of body mass placed on the ankles increases energy expenditure of walking an average of 8%.
        
        A more softer-soled running shoe reduced oxygen consumption with increased economy of running at a moderate speed by -2.4% compared with a similar shoe with a firmer cushioning system, even though the softer-soled shoe weighed an additional 31g. This is explained by the greater elastic energy stored and released in the Lowe extremity during minimal shoe running.
        
        Running barefoot offers no metabolic advantage over running in light-weight, cushioned shoes.
        
        Considering the relatively small increase in energy expenditure with hand or ankle weights in running, it seems more practical to simply increase unweighted running speed or distance.
        
        Children are less economical runners than adults; they require 20-30% more oxygen per unit body mass to run at a given speed.This partly explains their poorer performance in distance running compared with adults. Children as improve their endurance performances through adolescence even though their aerobic capacity remains relatively unchanged.
        
        The linear relationship between oxygen consumption and running speed indicates an equivalency in total energy requirement for running a given distance (in steady state) that is about the same regardless of speed throughout a broad range of running speeds.
        
        Meaning running a mile at 10mph requires about twice the energy a minute as running a mile at 5mph. The net energy expenditure to traverse a mile remains about the same.
        
        Comparisons of net energy expenditure of locomotion per unit distance traveled for walking and running indicate greater energy expenditure when running a given distance.
        
        A person who weighs 62kg requires approximately 2600kcal (net) to run a 26.2mile marathon regardless of whether the run takes just over 2hr, 3hr or 4hr
        
        Competitive race walker does not increase speed the same way that a runner does. The race walker has to involve the trunk and arm musculature to move the leg forward and rapidly requires more energy expenditure; this explains the poorer economy for walking than running at speeds above 8 or 9 km x hr.
        
        Stride lengths that are too short or too long will increase oxygen consumption for a constant speed.
        
        In keeping with the concept that the body attempts to achieve a level of minimum effort, a self-selected stride length and frequency generally produce the most economical running performance.
        
        No "best" style characterizes elite runners.
        
        The effect of air resistance on energy expenditure of running varies with three factors: 1) air density 2) runner's projected surface area 3) square of wind velocity
        
        Depending on speed, overcoming air resistance requires 3-9% of the total energy expenditure of running in calm air.
        
        Wind tunnel tests show that clothing modification or even trimming one's hair improves aerodynamics and reduces air resistance effects up to 6%
        
        Women have a higher body fat percent and in water will float and gain hydrodynamic lift. This allows them to expend less energy to stay afloat than the average man. Women can swim a given distance at about 30% lower total energy expenditure than men. Meaning women can swim at higher velocities than men at the same energy expenditure.
      - Mechanical efficiency reflects the percentage of total chemical energy expended that contributes to external work, with the remainder lost as heat.
        
        Mechanical efficiency cannot be computed during horizontal walking because no external work is accomplished; reciprocal arm and leg movements negate each other without a net gain in vertical distance.
        
        Type I fibers probably act with greater mechanical efficiency than faster-acting type II fibers.
      - The much lower mechanical efficiency of swimming makes the energy expenditure during swimming a give distance average about four times more than the energy expenditure running the same distance.
  - - - Using heart rate to estimate energy expenditure seems practical but limited research has validated only a few general and large muscle activities.
        
        There is a linearity between heart rate and oxygen consumption but the same heart rate will not necessarily correspond to the same oxygen consumption.
        
        Factors other than oxygen consumption impact heart rate, including; temperature, emotions, previous food intake, body position, muscle groups exercised, continuous or discontinuous (stop-and-go) activity, and whether muscles act statically or dynamically.
        
        Higher heart rates occur in upper-body physical activity; they are also higher when muscles act statically in straining-type movements than in dynamic movements at any sub maximal oxygen consumption. This means using a HR-VO2 line developed during running or cycling will over predict the measured oxygen consumption.
      - With weight-supported physical activity (cycling, elliptical etc.) energy expenditure decreases significantly. Heavier people will only average about 5% more due to lifting heavier lower limbs.
      - The influence of body mass on energy metabolism during weight-bearing activities occurs whether the person has gained weight naturally (fat mass or fat-free mass) or wears a weighted vest.
        
        Simply allowing someone to support themselves with the treadmill handrails reduces the oxygen cost of physical activity by as much as 30%
      - For an activity like walking, persons with the same body mass there is practically very little variation in oxygen consumption. Thus body mass accurately predicts energy expenditure during walking.
- - - - Other studies corroborate this as well although it may be larger meals (1000kcal and up). A 350kcal meal did not apparently have the larger energy expenditure.