Source: Lecture 17 | Biology, University of Michigan
Difficulty: Introductory to Intermediate. Familiarity with basic cell biology (mitochondria, ATP) is helpful.
Exercise provides benefits ranging from mental health improvements and cancer risk reduction to stronger bones and better cardiovascular function. The body produces ATP (its universal energy currency) through three systems: two anaerobic pathways in the cytosol (phosphagen and glycolysis, fast but short-lived) and one aerobic pathway in the mitochondria (slower but longer-lasting, fuelled by glucose and fat oxidation). Total daily energy expenditure breaks down into basal metabolism (60%), the thermic effect of food (10%), and activity energy expenditure (30%), of which most is non-exercise activity thermogenesis (NEAT).
ATP (adenosine triphosphate)
The energy source for all cells. Energy is released when the bond between the second and third phosphate group is broken, converting ATP to ADP. In simple terms, ATP is the battery that powers every cell in your body.
Anaerobic energy system
Energy production that takes place in the cytosol without oxygen. Fast but short-lived. Includes the phosphagen system and glycolysis.
Aerobic energy system
Energy production that takes place in the mitochondria using oxygen. Slower but longer-lasting. Fuelled by glucose oxidation and fat oxidation.
Phosphagen system (creatine phosphate)
The fastest anaerobic pathway. Creatine phosphate in skeletal muscle donates its phosphate group to ADP to rapidly regenerate ATP. In simple terms, it is the emergency reserve that kicks in during the first few seconds of intense effort.
Glycolysis
The anaerobic breakdown of glucose into pyruvate in the cytoplasm. Pyruvate is then converted to lactate when oxygen is insufficient. Produces ATP more slowly than the phosphagen system but faster than the aerobic system.
VO2 max (maximal oxygen consumption)
A measure of the maximum rate at which an individual can use oxygen during exercise. It is the gold standard for cardiorespiratory fitness.
MHR (maximum heart rate)
Estimated using the formula: MHR = 208 - (age x 0.7). Used to set training intensity zones.
BMR (basal metabolic rate)
The energy the body expends at rest to maintain basic life functions. Accounts for roughly 60% of total energy expenditure. Estimated as weight in kg x 23.3 (women) or weight in kg x 24 (men).
NEAT (non-exercise activity thermogenesis)
Energy expended on activities of daily living that are not planned exercise: fidgeting, walking, washing dishes, standing. NEAT accounts for about 70% of activity energy expenditure.
Thermic effect of food (TEF)
The energy required to digest, absorb, and process nutrients. Accounts for roughly 10% of total energy expenditure.
Cardiorespiratory exercise
Endurance or aerobic training. Recommendation: at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity exercise per week.
Resistance exercise
Strength training. Recommendation: train each major muscle group 2 to 3 days per week.
Neuromotor exercise
Exercise that develops balance, agility, and coordination. Note: endurance is not a neuromotor component.
Female athlete triad
A syndrome of three interrelated conditions: disordered eating, amenorrhoea (loss of menstrual periods), and osteoporosis. Seen in female athletes who restrict caloric intake.
Carbohydrate loading
A strategy to increase glycogen stores before endurance events by consuming 10 to 12 g of carbohydrate per kg of body weight per day.
Provides mental health benefits (this is specifically identified as a health benefit of exercise)
Improves immune function
Reduces risk of colon, breast, lung, and endometrial cancer
Helps maintain healthy body weight
Supports cardiovascular health
Strengthens muscles and skeleton
Reduces risk of type 2 diabetes
Cardiorespiratory (aerobic): At least 30 min of moderate-intensity exercise 5+ days/week (150 min/week total), or at least 25 min of vigorous-intensity exercise 3+ days/week (75 min/week total)
Resistance (strength): Train each major muscle group (legs, hips, back, abdomen, chest, shoulders, arms) 2 to 3 days per week
Neuromotor: Balance, agility, and coordination exercises, 2 to 3 days per week, 20 to 30 minutes per day. Endurance is not a neuromotor component.
Flexibility (stretching): 2 to 3 days per week. Stretch to the point of slight discomfort and hold for 10 to 30 seconds.
Anaerobic systems (cytosol, fast, short-lived):
Phosphagen (creatine phosphate): Fastest rate of ATP production. Creatine phosphate donates a phosphate group to ADP to regenerate ATP.
Glycolysis (glucose breakdown): Glucose is broken down to pyruvate, which converts to lactate. Slower than phosphagen but still fast.
Both phosphagen and glycolysis produce ATP.
Aerobic system (mitochondria, slower, longer-lasting):
Glucose oxidation and fat oxidation
Energy sources: pyruvate and fatty acids
Both glucose oxidation and fat oxidation lead to ATP
Key exam facts:
Phosphagen yields the fastest rate of ATP production
High-intensity exercise burns more carbohydrates than fat
As exercise duration increases, the aerobic pathway supplies the majority of ATP (True)
Total energy expenditure:
Basal metabolism: 60%
Thermic effect of food: 10%
Activity energy expenditure: 30% (of which 30% is exercise and 70% is NEAT)
Estimating BMR:
Women: weight in kg x 23.3
Men: weight in kg x 24
Factors that affect BMR: fat-free mass, age, sex, growth, hormones, starvation, illness, pregnancy and lactation, ethnicity, caffeine, smoking, sleep. All of these affect BMR (exam question: none are excluded).
NEAT: Activities of daily living. Examples include sitting, fidgeting, standing, walking, washing dishes, lawn mowing, stair climbing.
Each muscle cell has 750 to 1,000 mitochondria
US DHHS recommends at least 2 hours 30 minutes of moderate-intensity or 75 minutes of high-intensity exercise per week, plus muscle training
Exercise is better than none
VO2 max (maximal oxygen consumption)
MHR = 208 - (age x 0.7)
1 to 1.5 hours: low carbohydrate diet adequate
1.5 to 2.5 hours: moderate carbohydrate diet
2.5 to 5 hours: high carbohydrate diet
Purpose: increase glycogen stores
Consume 10 to 12 g of carbohydrate per kg of body weight per day
Resistance training increases muscle mass, strength, and fibre growth
Requires an adequate, balanced, varied diet meeting protein, vitamin, and mineral needs
Disordered eating
Amenorrhoea (cessation of menstrual periods)
Osteoporosis
Students often think endurance is a neuromotor skill. It is not. Neuromotor fitness includes balance, agility, and coordination only.
Students sometimes assume that high-intensity exercise burns mostly fat. The opposite is true: high-intensity exercise burns more carbohydrates than fat.
Students may believe that some factors (e.g. ethnicity, sleep) do not affect BMR. All listed factors, including ethnicity, sex, age, and sleep, do affect BMR.
⚠️ Endurance is NOT a neuromotor component (balance, agility, coordination are).
⚠️ Phosphagen system yields the fastest rate of ATP production.
⚠️ High-intensity exercise burns more carbohydrates than fat.
⚠️ As exercise duration increases, the aerobic pathway supplies the majority of ATP (True).
⚠️ All listed factors affect BMR (none of the above is the answer).
⚠️ Know the BMR estimation formulas: women = kg x 23.3, men = kg x 24.
⚠️ MHR formula: 208 - (age x 0.7).
⚠️ Female athlete triad: disordered eating, amenorrhoea, osteoporosis.
True or False: Endurance is a neuromotor component of physical fitness. (False)
Fill in the blank: The energy system that yields the fastest rate of ATP production is the ______ system. (phosphagen)
True or False: As exercise duration increases, the aerobic pathway supplies the majority of ATP. (True)
Fill in the blank: NEAT stands for ________ activity thermogenesis. (non-exercise)
True or False: High-intensity exercise burns more fat than carbohydrates. (False, it burns more carbohydrates)
Q: Which skill is NOT part of the neuromotor component of physical fitness: balance, agility, coordination, or endurance?
A: Endurance. Neuromotor fitness involves balance, agility, and coordination.
Q: Which energy system yields the fastest rate of ATP production?
A: The phosphagen (creatine phosphate) system.
Q: What are the three components of total energy expenditure and their approximate percentages?
A: Basal metabolism (60%), thermic effect of food (10%), and activity energy expenditure (30%).
Q: How do you estimate BMR for a woman weighing 60 kg?
A: 60 x 23.3 = 1,398 kcal/day.
Q: What three conditions make up the female athlete triad?
A: Disordered eating, amenorrhoea, and osteoporosis.
Q: What does a carbohydrate loading strategy involve, and when is it used?
A: Consuming 10 to 12 g of carbohydrate per kg of body weight per day to increase glycogen stores before prolonged endurance events.
The energy balance concepts here (total energy expenditure, BMR, NEAT) connect directly to Lecture 18 (Health Effects of Obesity) and Lecture 19 (Weight Loss Programs), where the same components are used to calculate estimated energy requirements. The female athlete triad ties back to Lecture 20 (Eating Disorders). ATP and mitochondrial function also underpin the discussion of alcohol metabolism in Lecture 21.
Exercise and health, ATP, adenosine triphosphate, anaerobic energy system, aerobic energy system, phosphagen, creatine phosphate, glycolysis, pyruvate, lactate, VO2 max, maximal oxygen consumption, MHR, maximum heart rate, BMR, basal metabolic rate, NEAT, non-exercise activity thermogenesis, thermic effect of food, cardiorespiratory exercise, resistance training, neuromotor exercise, flexibility, female athlete triad, amenorrhoea, osteoporosis, carbohydrate loading, glycogen, energy expenditure, exercise intensity, moderate intensity, vigorous intensity