Chapter 13

Nutrition in Fitness and Sports

Physical FitnessPhysical Fitness

• The ability to perform moderate to vigorous activity without undue fatigue

• Increasing physical fitness means improved usage of fat for energy (switch metabolism from glucose to fat)

Benefits of Physical ActivityBenefits of Physical Activity

Healthy People 2020Healthy People 2020

• Reduce the number of adults engaging in no leisure physical activity by 10%

• Increase the number of adults who engage in aerobic physical activity of moderate and vigorous intensity

• Increase the number of adults who perform muscular-strengthening activities

Beginning an Exercise ProgramBeginning an Exercise Program

• Start out slowly

• Vary your workout—Make it fun

• Include others—Keep accountable

• Set attainable goals

• Set aside specific time

• Reward yourself (but not with food!)

• Focus on long-term and not on occasional setbacks

2008 Physical Activity Guidelines2008 Physical Activity Guidelinesfor Americansfor Americans

• 150 minutes/week of moderate–intensity aerobic exercise

• or 75 minutes/week of vigorous-intensity aerobic exercise

– Additional health benefits are gained by engaging in physical activity beyond this amount

• Plus muscle-strengthening activities that involve all major muscle groups

– 2 or more days a week

Types of Activities Types of Activities –– Aerobic ExerciseAerobic Exercise

• Moderate-intensity

– Aerobic activity that increase’s heart rate and breathing– Brisk walking, dancing, swimming, bicycling– 5 – 6 on Rating of Perceived Exertion scale

• Vigorous-intensity

– Aerobic activity that greatly increase’s heart rate and breathing

– Jogging, tennis, swimming (laps), bicycling uphill– 7 – 8 on RPE scale

Types of Activities Types of Activities –– Resistance ExerciseResistance Exercise

• Muscle-strengthening

– Activity that increases skeletal muscle strength, power, endurance, and mass

– Strength training, lift weights, resistance training, muscle strength and endurance exercises

Assessing Aerobic WorkoutAssessing Aerobic Workout• Ways to determine moderate level of intensity

– Percentage of age-predicted maximum heart rate sets Target Zone (note: normal heart rate 75 bps)

– 1) To estimate your maximum heart rate = 220 – your age

– 2) Then multiply by 0.60 and 0.90 to determine “Target Zone”

– For example: someone 20 years old

• 220 – 20 = 200 X .6 = 120 bps• 220 – 20 = 200 x .9 = 180 bps

Hea

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*MHR (maximum heart rate) = 220 - Age in years

7060Age

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90%–100% MHR*80%–90% MHR

70%–80% MHR

60%–70% MHR50%–60% MHR

Maximal effort zoneAnaerobic zoneAerobic zoneWeight-management zoneHeart health zone

© Tetra Images / SuperStock RF

Heart RateHeart Rate

Rating of Perceived Exertion ScaleRating of Perceived Exertion Scale

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

0 1 2 3 4 5 6 7 8 9 10* Rating of Perceived Exertion (RPE) beyond 10 is considered maximal.

Nothingat all

Veryweak Weak Moderate

RPE Scale*

Somewhatstrong Strong

Very, verystrong

Verystrong

What is the value of a “heart rate monitor”?

Fuel for Muscle WorkFuel for Muscle Work• ATP / molecular money

• Chemical energy

– Used by cells for muscle contractions

• Only small amount is stored in resting cells

– 2-4 seconds worth of work

• Other sources of energy are needed

• What must happen to your physiology when you start muscular activity?

PhosphocreatinePhosphocreatine ((PCrPCr))

• High-energy compound

– Formed and stored in muscle cells

PCr + ADP Cr + ATP

• Activated instantly /// Replenishes ATP

• Systems that lend P to ADP last 15 to 20 sec // will need to be “paid back” at a later time!

• When this system is exhausted then anaerobic fermentation (also called glycolysis) produces ATP from glucose

Anaerobic Anaerobic GlycolysisGlycolysis• Occurs with limited oxygen (anaerobic / but

intense physical activity like sprinting)

• Pyruvate is converted to lactate

• Produces 2 ATP per glucose / ~5% of energy potential

• Replenishes ATP quickly

• Cannot sustain ATP production / 30 seconds sprinting (up to 2 minutes if very low intensity)

• Lactate build-up / Changes acidity that inhibits glycolysis enzymes

Aerobic Aerobic GlycolysisGlycolysis• Plenty of oxygen available

• Low to moderate intensity (jogging)

• Produces 28-30 ATP per glucose / 95% of energy potential

• ATP replenished slowly

• Sustained ATP production / 2 minutes to 3 hours of work

Glucose UtilizationGlucose Utilization

GlycogenGlycogen• Temporary storage of glucose in liver and

muscle

• Muscle glycogen / Used only by that muscle

• Liver glycogen released into bloodstream

• During low to moderate intensity / Can sustain work for up to 2 hours

• “Bonking” – term used by competitive bikers– Low blood glucose level impairs thinking ability– Caused by depleted glycogen– Work at ~50% of maximal capacity

Modes of ATP Synthesis During Exercise

Aerobic respirationusing oxygen frommyoglobin

Glycogen–lactic acidsystem(anaerobicfermentation)

Phosphagensystem

Duration of exercise0 10 seconds 40 seconds

Aerobicrespirationsupported bycardiopulmonaryfunction

Repayment ofoxygen debt

Mode of ATP synthesis

•At rest we oxidize fatty acids to supply energy for our skeletal muscles

•Note: nervous system and RBC can only oxidize glucose, even in a resting state

As level of activity increases, skeletal muscles will shift from fat to glucose as an energy source.

After glucose reserves exhausted, shift back to fat metabolism

ATP FormationATP Formation

Maintaining Normal Blood Glucose LevelMaintaining Normal Blood Glucose Level

• Important // For activity lasting longer than 20-30 minutes

• After 90 min intense exercise glycogen in liver depleted

• Intake of 30-60 gm carbohydrates per hour (30 x 4 = 120 calories)

– During strenuous endurance activity

– Delays fatigue by 30-60 minutes

Fat Fuel (Fatty Acid)Fat Fuel (Fatty Acid)

• Majority of stored energy in the body

• Fatty acids // Converted to ATP by muscle cells

• 12 ATP produced per pyruvate

– Per each turn of the Citric Acid Cycle – 108 ATP for each 16 C fatty acid chain

• Trained muscles / conditioning results in

– More mitochondria– More blood capillaries– Shift in type of enzymes / have greater ability to

use fat as fuel

Fat FuelFat Fuel• When at rest your cells burn fat to produce ATP

• As intensity of exercise increases we shift from fat to glucose metabolism

• During prolonged exercise / Fat becomes main fuel source

• Intense activity– Fat is not a major source of fuel – Requires more oxygen for aerobic breakdown

(than glucose) – But when glycogen/glucose depleted / shift

back to fat

ProteinProtein——Minor Source of FuelMinor Source of Fuel

• During rest and low/moderate exercise // provides ~ 5% of energy needs

• During endurance exercise // Provides 10%-15% of energy needs

• Branched-chain amino acids provide most of the energy

• Resistance exercise uses protein less

• Average diet – Provides ample amount of these amino acids – Supplements not needed

Fuel Use During Physical ActivityFuel Use During Physical Activity

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FatCarbohydrateProtein

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Hard cyclingfor 1 hour

Championshipbasketball

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Energy Sources Used by CellsEnergy Sources Used by Cells

Calorie NeedsCalorie Needs

• Individual needs vary

• Monitoring weight and body fat

– If weight falls, increase intake

– If body fat increases, cut back in fat (& kcal) and maintain activity

• Desirable body fat for male athletes: 5%- 18%

• Desirable body fat for female athletes: 17%-28%

Carbohydrate NeedsCarbohydrate Needs

• Main fuel for many types of activity / 50% energy

• Consume ~60% of total kcal from carbohydrate

• Adhere to MyPlate – variety of foods

• > 5 gm of carbohydrate/kg body weight

• Aerobic and endurance athletes

– 7-10 gm carbohydrates/kg body weight

– ~ 500-600 gm of carbohydrates/day

Carbohydrate LoadingCarbohydrate Loading

• Events lasting longer than 60-90 minutes

• Maximize glycogen stores

• Tapering of exercise while increasing carbohydrate intake

• Additional water weight / carbs are hydrophilic

Carbohydrate (CHO) LoadingCarbohydrate (CHO) Loading

600600600450 450450CHO (grams)

rest20 20404060Exercise Time

123456Days Before Com-petition

Fat NeedsFat Needs

• ~35% of total kcal

• Rich in monounsaturated fats

• Limit saturated fats

• Limit trans fat

Protein NeedsProtein Needs

• Recommend 0.8 - 1.7 gm protein/kg body weight

• Up to 2.0 gm/km body weight for athletes beginning strength training

• Needs are easily met by a normal diet

– Protein supplements are not necessary

– Excessive protein has not been shown to be beneficial

– Excessive protein in diet dangerous!

Current Protein RecommendationsCurrent Protein Recommendations

Vitamins and MineralsVitamins and Minerals

• Vitamin E and C – Slightly higher needs– Antioxidant properties

• Thiamin, riboflavin, vitamin B-6, potassium, magnesium, iron, zinc, copper, and chromium needs

– May also be higher (role in metabolism or sweat / loss of water soluble vitamins)

• Increase intake of fruits and vegetables

Iron NeedsIron Needs

• Iron deficiency affects performance

• Sports anemia

– Increase in plasma volume but not RBCs

• Women at risk because of menstruation

• Focus on iron-rich foods

• Use of iron supplement may cause toxic effects

Calcium NeedsCalcium Needs• Restriction of dairy products by women when

they are trying to lose wt // cause Ca deficiency

• Irregular menstruation/Amenorrhea

– Severe bone loss and osteoporosis

– Extra calcium does not compensate for effects of menstrual irregularities

– Compromises bone health

• Calcium deficiency increases risk of stress fractures

Fluid NeedsFluid Needs• Needs of average adults

– 9 cups per day for women– 13 cups per day for men

• Athletes need more

• Maintenance of body’s cooling system

– Water helps dissipate heat from working muscles

• Avoid losing more than 2% of body weight during exercise

• For every 1lb. lost replace 2-3 cups of fluid

HydrationHydration• Thirst: Not reliable indicator of fluid needs // by time you feel

thirsty then it will take +/- 48 hrs to rehydrate

• General guidelines:

– Drink 2-3 C of fluids per each pound of weight loss during activity

– Check urine color

– Drink fluid freely 24 hours before event

– Drink 5-7 ml/kg body weight at least 4 hours before exercise

– Consume 1½ - 3½ Cups per hour for events lasting longer than 30 min.

– Within 4-6 hours after exercise, consume 2-3 C of fluid for every pound lost

Heat ExhaustionHeat Exhaustion• Heat stress causes depletion of blood volume

due to fluid loss

• Body heat is dissipated through evaporation of sweat (fluid)

• Fluid loss (sweat): ~3-8 C per hour

• Humidity interferes with sweat production

• Dehydration decreases endurance, strength, performance

• Signs: Profuse sweating, headache, dizziness, nausea, weakness, visual disturbances

Heat CrampsHeat Cramps

• Frequent complication of heat exhaustion

– Exercising in heat– Significant sweating– Consuming water without sodium

• Painful muscle contractions – 1-3 minutes at a time

• Ensure adequate salt and fluid intake

• Exercise moderately at first in the heat

Heat StrokeHeat Stroke• High blood flow to working muscles

– Overloads body’s cooling system– Sweating ceases– Internal body temperature reaches 104° F– Fatality rate high

• Symptoms:

– Nausea, confusion, irritability, poor coordination, seizures, coma

• Replace fluids

• Monitor weight change (fluid loss)

• Avoid exercising in hot humid conditions

Sports Drinks For Sports Drinks For Endurance ExerciseEndurance Exercise

• Recommended for activity > 60 minutes

– Help maintain blood glucose level and blood volume

– Delay “bonking” // metal confusion due to no glucose in blood

• Supply electrolytes

• If less than 60 minutes then nutrients are easily replaced by diet

Sports DrinksSports Drinks

CaffeineCaffeine--Containing Energy DrinksContaining Energy Drinks

PrePre--Endurance Event MealEndurance Event Meal• Light meal 2- 4 hours prior to event

• Consisting primarily of carbohydrate (top off glycogen stores)

• Low fat (<25% of energy intake)

• Little fiber (prevent bloating, gas)

• Moderate protein

• Avoid fatty, fried foods

• Blended or liquid meal recommended for meals eaten 1- 2 hours prior

Recovery MealRecovery Meal• Carbohydrate-rich meal within 30 min after

endurance event

– Glycogen synthesis is the greatest

– 1-1.5 gm CHO / kg body weight

• Repeat meal every 2 hours for the next 4-6 hours

• Choose high glycemic index foods

• Aim for 3:1 carbohydrate-to-protein

• Fluid and electrolyte replacement

Gels and BarsGels and Bars• Provide additional fuel

• Should be taken with fluids

• Expensive source of nutrients

• Ideal bars for endurance athletes

– Contain 40 gm carbohydrate, 10 gm of protein, 4 gm fat, 5 gm of fiber

– Fortified with vitamins and minerals

– Toxicities possible with overuse

Content of Energy Bars and GelsContent of Energy Bars and Gels

HyperHyper--hydrationhydration

• Excessive intake of water

• Intake without sodium and chloride

• During prolonged low-intensity activities

• Results in low blood sodium and low blood chloride

Replenishing Muscle GlycogenReplenishing Muscle Glycogen

• Availability of adequate carbohydrate

• Ingestion of carbohydrate soon after exercise

• Selection of high-glycemic-load carbohydrate

• Combination of carbohydrate and protein foods

ErgogenicErgogenic AidsAids

ErgogenicErgogenic AidsAids