PED 291 - Chapter 7Notes

The Basal Metabolic Rate-its components

1. resting metabolic rate 60-75%

2. Thermal effect of feeding-you burn energy when you eat.

3. Thermal effect of physical activity.

The minimum energy requirement sustaining the body's functions in the waking state (i.e. breathing) - the basal metabolic rate.

It averages 5 to 10 % lower in females than males because of: more body fat and less muscle mass.

The BMR declines about 2% per decade because of changes in body composition (more fat): however endurance and weight training offsets this decrease.

Factors affecting energy expenditure

1.   physical activity: accounts for between 15-30 of a person's daily energy expenditure. Most people can sustain metabolic rates that average 10 times the resting value during big muscle exercises such as fast walking, running, cycling, and swimming.

2.   Dietary induced thermo genesis- where consuming food increases the metabolism from the energy requiring processes of digesting, and absorbing of food. The time this process takes depends on what you eat. It usually reaches its maximum one hour after eating.

The range of thermo genesis ranges from 10-35% of ingested food. Protein has a 25% thermic effect- which has led to some people promoting a protein filled diet, but there is so much potential strain on the kidneys and liver, and that a lot of protein allows fatty acids to put a lot of glucose into the system. Remember from chapter 2 only carbohydrates provide energy for exercise and conserve lean tissue often lost through dieting.

People with poor body weight control have poor thermic response to eating, and a lot of times it's genetic (the 80 percent obese rule when both parents are obese). The obesity gene.

Exercising (going for a walk) after a meal increases the thermic response to food intake.

3.   Climate- tropical climates have individuals with up to 20% higher resting metabolisms. People who exercise in hot weather can increase it about 5 percent, and people who engage in activity in very cold weather can double or triple their metabolism because shivering generates heat to maintain body temp.

4.   Pregnancy- moderate exercise presents no greater physiologic stress to the mother than imposed by the additional weight gain. The increased weight adds to the exercise effort during weight bearing activities.

How do we determine the number of calories burned during an activity? Consuming a liter of oxygen burns about 5 calories, so if you burned 10 liters during a test on a treadmill, you would have burned 50 calories. This is called the gross energy expenditure.

The net energy expenditure is the gross energy expenditure minus the requirement for rest (usually around 10 percent of calories burned) so you have actually burned off 45 calories (50-5).

Energy costs of recreational and sport activity: table 2 on page 162.

Body mass plays an important role: heavier people expend more energy to perform the same activity than people who weigh less. The WEIGHT BEARING of the activity increases directly with the body mass transported (a 300 pound person is carrying 300 pounds while they run). This measurement of energy expenditure is just as accurate as measuring oxygen uptake.

A non weight bearing or weight supported exercise (stationary bike), there is very little relationship between body mass and exercise energy cost.

Compare energy expenditure for heavier people doing the activities on table 7.2.

Energy expenditure comparison between men and women are on table 7.3. Men have around 700-800 more calories burned on a daily basis than women. (3000/2200)

Two factors affect the rating of the difficulty of a particular task: duration of activity and intensity of effort. The typical person spends 75% of the day in sedentary activities.

Examples:

1.   45 minute run at 60% max heart rate.

2.   30 minute run at 80% max heart rate

The harder someone works: the person's heart rate will kick up, thus requiring them to consume and utilize more oxygen (when the body can not take in what it needs to sustain exercise to the muscles, the heart rate is at a max (220-age), and the person probably will stop the activity)

See figure 7.4.

Energy expenditure example

a. A male who runs for 20 minutes in a light intensity level will burn 5 calories per minute so they may burn 100 calories in that time.

b. Another male who runs for 14 minutes at a moderate pace will burn 7.5 calories per minute, so they will burn 100 calories.

c. A third male will run for 10 minutes at a heavy pace and burn 10 calories per minute, which means they burned 100 calories.

All these occur because they take in more oxygen as they increase the intensity, which burns more energy.

Remember: the more someone does cardiovascular exercise and specific muscle and body systems are trained, they can take in more oxygen during their activity at a specific heart rate.

Example: someone runs for the first time, they may be taking in 1.5 liters of oxygen when their heart rate is at 160. A month later with training that person is taking in the same amount of oxygen at a heart rate of 140.

Economy of human movement- the quantity of energy to perform a particular task in a quality effort. (some people have to use up a lot of energy to swim to one end). With practice, economy of movement gets better because the movement is more efficient. The more efficient your movement is the less oxygen you use during the activity, which burns less energy.

How do you assess this? The amount of oxygen used. A person with greater movement economy uses less oxygen during the activity..

Training adjustments that improves economy of effort directly relates to improved performance.

Children show less economy in running compared to adults: they require up to 30% more oxygen per unit of body mass to run at a given speed.

Also: someone with more slow twitch fibers have greater economy of movement during an activity like running, biking, swimming. This is because they are less muscle mass and have a lower economy of movement.

From age 10 to age 18 running economy improves steadily (figure 7.6).

Walking-the most common form of exercise

The faster someone walks, they have a greater total caloric expenditure, but are less efficient and less economical.

There comes a point where fast walking is less economical than running (8 kilometers per hour). The economy of walking faster than that is about half of what running at the same speed would be.

This is called the crossover speed.

Oxygen uptake relates to running speed. If one runs a mile at 10mph, it requires twice as much energy as someone who runs 5 mph. One runner finishes it in 6 min while the other runs it in 12 min. The same net energy cost (calories), and oxygen uptake exists. Table 7.8

Race walkers take in almost the same amount of oxygen as people who run on treadmills

Effect of body mass- we will refer to the chart handed out.

Some people wear ankle weights to burn off more calories.

If you walk on a beach (because of the sand), you are burning up twice as many calories as on a hard surface. If you walk in snow, you can burn up to 3 times the calories. Or: if you wear boots instead of shoes (adding 100 grams of weight to footwear will cause a 1 percent increase in oxygen uptake during moderate running. (running shoes are for running, hiking shoes are for hiking: this aides the economy of movement).

Softer soled shoes also reduces the oxygen cost compared to firmer soles by up to 2.5 percent, even if the softer soled shoes weigh more. This is because the pounding is less with softer soles.

The ultimate energy cost: walking in soft sand at rapid speeds wearing heavy work boots and ankle weights.

Walking causes only one third of the strike force impact that running does when your foot strikes the ground.

Not recommended to walk with ankle weights or hand held dumbbells: someone with hypertension may elevate blood pressure.

Running

Jogging and running are different: the aerobic demands are different in terms of lowering the body's center of gravity and accelerating/decelerating phases of running. In terms however of how much oxygen someone uses during their activity: someone's jog can actually be someone's run.

If someone runs a mile at 10 mph, it requires twice as much energy as someone running a mile at 5 mph. However: the runner finishes the mile in 6 minutes running at 10mph, and the 5 mph runner runs it in 12 minutes. The energy costs for running that mile are the same, regardless of how fast or slow you run it. (table 7.8)

The energy cost per mile increases proportionately with the runner's body mass (a heavier person burns off more calories).Stating it another way:

Because of the force of the weight bearing exercise, the energy cost increases with the weight of the person.

Running speed can increase 3 ways:

a.    increase the number of steps

b.   increase the distance between steps

c.    increase both a and b

To run at a constant speed: stride length and frequency need to be comfortable: it produces an economical running performance: the body then can achieve a level of MINIMUM EFFORT. No one style is best for all people: body differences account for different running styles. Stride frequency becomes important only at faster speeds, and lengthening your stride to maintain speed when fatigued only further produces counterproductive results for oxygen cost (exercise economy).

Running into the wind: it accounts for 3-9 % of the total energy requirement of running in calm weather. Running into a head wind could account for up to 40 % additional energy expenditure to maintain your speed.

Wind tunnel tests show that running performance significantly increases with form fitting clothing (and even trimming your hair) up to 6%. Bikers have modified clothing and helmets, as well as the rider's body position, and bike frame to reduce the effects of air resistance on energy cost.

Drafting- running directly behind someone, blocking the wind. In a one mile race you can save a second per lap. In biking it can save up to 40% of the rider's energy expenditure.

Treadmill or Track running?

Tests show there are no measurable differences in aerobic requirements until you get to elite levels. There is obvious air resistance outside which will make a difference in energy expenditure.

Swimming: differences from walking or running:

1.    energy is used to maintain your float

2.    arms and legs are generating horizontal movement

3.    there are drag forces that slow the movement of an object through water

It requires about 4 times more energy to swim a given distance than to run the same distance.

Efficient or quality swimmers expend much less energy than someone who does not swim real well.

Women gain a hydrodynamic lift during a swim because of more total body fat (fat floats). Thus women have greater swim economy (30% lower energy cost) because they can maintain buoyancy better and be streamlined (men's legs swing down in the water, causing drag.

Economy of the swim also depends on what swim you perform (crawl or breast stroke).