Nutrition and Physical Fitness
•Proper nutrition is vital to performance
Physical activity
•Can be activities like housework, lawn-mowing, walking
•30 minutes of activity at least 3 days a week can reduce chronic illness and early
mortality
•Is not the same as activities to attain and maintain physical fitness, or to keep weight
within optimal BMI range
•DRI Committee recommends at least 60 minutes of moderately intense activity every
day
Physical Fitness (according to the American College of Sports Medicine)
•“The ability to perform moderate to vigorous levels of physical activity without undue
fatigue and the capability of maintaining this level of activity throughout life”
What are the general benefits of physical fitness?
Components of Physical Fitness
•Flexibility-range of motion (yoga, ballet)
•Muscle strength-working against resistance (weight lifting)
•Cardiorespiratory endurance-ability to perform at med-high intensity for long periods
(distance running)
•See table 14-1 for guidelines
Benefits of aerobic exercise
•Increased cardiac output and O2 delivery
•Increased heart strength
•Slowed resting pulse
•Improved breathing efficiency
•Improved circulation
•Reduced blood pressure
Benefits of strength training
•Builds lean body mass
•Develops strength and endurance
•Improves posture, reduces risk of back injury
•Can maintain or improve bone mass
Benefits of flexibility training
•Improved range of motion
•May reduce risk of injury
•Yoga and tai chi are used as meditation--relaxation
How to get fit
•Training--practicing an activity regularly
•Progressive overload--pushing yourself further during training in frequency, intensity, or
duration
•Conditioning--physical effect of training
Muscles--use ‘em or lose ‘em
•Muscles respond to overload by increasing in size (hypertrophy)
–Myoglobin increases
–May store more glycogen
•When a muscle is unused (e.g., when you break your arm), the muscle shrinks (atrophy)
How to check your pulse
•Take fingers of one hand (not thumb) and press against wrist of the other hand,
underneath the fleshy pad of the thumb
•Count heart beats for 10 seconds
•Multiply by 6 to get beats per minute
How to determine (roughly) your maximum heart rate
•Subtract your age from 220
•To determine 70% of your max heart rate, multiply by 0.7
Three systems for fueling activity
•Creatine phosphate-anaerobic
•Lactic acid-anaerobic glycolysis
•Aerobic metabolism
•See table 14-3 for comparison of which pathway is used for which activity
Creatine phosphate (CP)
•Quickest system to derive ATP for muscles
•CP + ADP + H+
ATP + creatine
•Does not require oxygen
•Depleted very quickly in intensive activity (e.g., sprinting)
Glycolysis to lactate
•Also anaerobic
•Glucose comes from muscle glycogen
•Minimal ATP produced
•Slower than creatine phosphate pathway
•Lactate can be reconverted to glucose in liver via Cori cycle, OR can be used for energy
by other tissues
•500 meters or Kentucky Derby
Aerobic metabolism
•Glycolysis
•Pyruvate to acetyl coA
•Citric acid cycle
•Electron transport chain
•Also fatty acid beta-oxidation
•Marathon, hiking, distance swimming
VO2 max
•The maximum amount of oxygen that you can get into your body
•Proportional to maximum heart rate
Limiting nutrient for any activity is carbohydrate
•Remember that fat burns in a flame of carbohydrate
•Activities at ≤ 60% VO2 max use a higher proportion of fat than those at > 70% VO2
max
“Hitting the wall”
•The point in a marathon when muscle and liver glycogen are depleted
•Blood glucose level drops
•Fatigue rapidly develops
So what should one eat for maximum performance?
•Carb, carb, carb
The amount of available carbohydrate influences performance
•As glycogen, is absolutely required for high intensity events (sprints, gymnastics)
•As blood glucose, is limiting nutrient for ATP production
•High carb diet replenishes glycogen stores better than low carb diet
“Glycogen or carb loading”
•Utilized by endurance athletes to maximize glycogen stores
•See page 484 for details
•Not beneficial for casual athletes
Other macronutrients
•Fat--stick to TLC guidelines of 20-35% Calories from fat
•Protein--casual athletes can stick with RDA of 0.8 g/kg body weight/day
•Endurance athletes--1.2-1.6 g/kg
•Strength athletes--1.6-1.7 g/kg
Back to our 70 kg (154 lb.) man
•Assume he’s a triathlete
•1.2-1.6 g/kg BW protein = 84-112 g
–8 oz. Meat, fish or chicken = 56 g
–3 cups low fat milk and/or yogurt = 24 g
–7 servings whole grain bread, cereal, or pasta = 21 g
–3-5 servings of vegetables = 6-10 g
High protein intake has drawbacks
•Dehydration--body has to excrete more water in urine to get rid of extra urea
•High protein can contribute to bone problems
Micronutrients for athletes
•B vitamins--athletes should get plenty from intake of enriched and whole grain breads
and starches
•Calcium can be problematic for those who don’t get enough from foods
•Iron can be problematic for women of childbearing age
Fluids
•For short-duration activities, water is fine
•Longer duration--sports drinks with <10% carbohydrate
–May also need electrolytes (Na, K, Cl) in drinks to combat hyponatremia for events
lasting longer than 4 hours
Supplements and ergogenic aids for athletes
•Buyer and user beware
Anabolic steroids
•Mostly precursors to male hormone testosterone
•Examples--androstenedione, dehydroepiandrosterone (DHEA)
•In men, these reduce sperm count and shrink testicles
•In women, result in masculinization
•In youth, stunt growth
EPO, alias blood doping
•Recombinant form of kidney hormone that stimulates bone marrow to produce more
RBC’s
•Marketed to cancer and kidney failure patients as Procrit or Epogen
•Illegal in international competitions
Caffeine
•Can increase performance, BUT
–Optimal dose is 9 mg/kg BW (630 mg for our reference 70 kg man)
–The equivalent of over 4 cups of coffee
–Caffeine has diuretic effect
–Can also cause heart palpitations and gastric upset
Carnitine
•Shuttles fatty acids into mitochondria for beta-oxidation
•Found in adequate amounts in foods, so supplementation is not needed for healthy
people
•Supplements cause diarrhea in about half of users
The Female Athlete Triad
•Disordered Eating
•Amenorrhea
Osteoporosis
Female Athlete Triad
•Female athletes are more likely to be bulimic than nonathletes (incidence of anorexia
nervosa about the same)
•Low % body fat can lead to amenorrhea, as estrogen production falls
•Low estrogen production manifests itself as loss of bone density, leading to early
osteoporosis