Lecture 2 Principles

What differs anaerobic and aerobic energy sources?

Anaerobic

• Replenish ATP at a fast rate without requiring oxygen

• Phosphocreatine (1 enzyme reaction) and anaerobic glycolysis (multi enzyme pathway)

Aerobic

• Long term sources of ATP

• ATP supplied by the aerobic metabolism of CHO and fat in the mitochondria of the muscle, which requires sufficient oxygen

How is oxygen consumption measured?

• Measured by subtracting the volume of oxygen inhaled from the volume of oxygen inhaled

  • VO2 = VO2 inhaled - VO2 exhaled

• Room air (20.93% O2 and 0.03 CO2)

What is the respiratory exchange ratio?

• Ratio of CO2 production (VCO2) to O2 (VO2) consumption

• Identifies the type of fuel used during steady state exercise

(Image has R value and fuel use)

How does exercise intensity affect fuel utilization?

• Fat may provide more energy per gram, but it requires more oxygen to do so

• Muscle obtains about 6% more energy from each liter of oxygen when carbohydrate is used (5 kcal per L) compared to when fat is used (4.7 kcal per L)

• As exercise intensity increases, R increases, indicating that Carbohydrate plays a bigger role in generating ATP.

What happens oxygen use during and after exercise?

• At the onset of submaximal exercise, VO2 doesn’t increase immediately (O2 deficit)

  • ATP is supplied anaerobically by phosphocreatine (PPC) and glycolysis

• After exercise, VO2 remains elevated due to the following

  • Replenishing ATP and PC stores; replenishing O2 borrowed from hemoglobin and myoglobin; supporting the energy cost of elevated HR and breathing, increased body temperature and elevated NE and Epi; and synthesizing glucose from lactate (excess postexercise oxygen consumption) [EPOC]

What happens with training and oxygen deficit?

• Training reduces O2 deficit because VO2 increases more rapidly at the onset of work, allowing the steady state oxygen requirement to be reached more quickly

What is the criteria for VO2 max when a plateau doesn’t occur?

• An increase in VO2 in the last stage that was < 2.1 ml x kg x min higher than the previous stage of the GXT

• R > 1.10

• Blood lactate > 8 mmol per L

• HR near that of age predicted HRmax

What are the determinants of Maximal Aerobic Power?

• Type of test

• Endurance training and heredity

• Sex

• Age

• Altitude

• Cardiovascular and Pulmonary disease

What happens with Lactate and Ventilatory threshold?

Lactate: The exercise at which blood lactate concentration increases suddenly

Ventilatory: exercise intensity at which pulmonary ventilation increases suddenly

• Both typically occur 50 to 80% of VO2 max

• Both are good predictors of performance in endurance events

Both decrease in training*

What happens with training in HR and SV?

• HR decreases, SV increases!

• Maximal CO increases and O2 extraction also increases

• Systolic increases , diastolic decreases

What are the cardiovascular responses to isometric exercise and weightlifting?

• Isometric exercise results in increases in both SBP and DBP

• Peak BP can be high during dynamic, heavy resistance exercise

  • Compression of arteries by muscles

  • Reflex response due to static component of near max dynamic lifts

  • Valsalva maneuver

What does skeletal muscle do?

• Converts chemical energy of ATP into mechanical work

• Sarcomeres: fundamental units of muscle contraction

  • Contain thick filament myosin and thin filament actin

  • Bound by CT called the Z line

  • Look at Table 4.3 (slide 32)

What are the muscle fiber types dependent on in terms of genetics, sex and training?

• Distribution is highly variable and strongly by genetics

• Training doesn’t convert fast twitch fibers to slow twitch or vice versa

• Training increases mitochondrial number and capillary density (oxidative capacity)

What happens in recruitment of muscle fibre types?

• Order of recruitment is from most to least oxidative

• Exercise beyond 70% VO2 max involves all fiber types

• Higher the intensity you go from Type I to Type IIa to Type IIx

What are exercise induced muscle changes?

• Rhabodymyolysis: breakdown of muscle that can occur after prolonged intense exercise to which a person is unaccustomed

• DOMS (Delayed onset muscle soreness): microscopic damage to muscle fibers due to overload, typically occuring 24 to 48 hours after exercise

• Muscle cramps (invol. painful contractions)

What are the muscle sensory receptors?

• Muscle spindle

  • sudden change in muscle length will stimulate the muscle spindle, resulting in contraction

• Golgi Tendon Organ (GTO)

  • When stimulated by increased tension, the GTO inhibits muscle stimulation and causes relaxation

What are the muscular adaptations of endurance and resistance training?

• Endurance

  • Increased Oxidative capacity of the muscle due to increase in capillaries, myoglobin and mitochondria

• Resistance

  • Increased force production due to hypertrophy (major influence) or hyperplasia as well as muscle activation (synchronous firing, reduced inhibitory mechanisms)

What was the study by Hickson?

• Participants trained for 10 weeks, followed by a reduction in frequency, duration or intensity

• VO2 max clearly fell when the intensity of training was reduced by either one third or two thirds

Check table 4.4.

How does the body lose heat?

• Radiation, conduction, convection, evaporation of sweat (Primary mechanism for heat loss during exercise)

  • At higher work rates, more heat lost through evaporation, must increase as temperatures rise

How do we improve heat tolerance?

• At least 7 to 12 days, results in lower body temperature during submaximal exercise

• Adaptations include

  • Increased plasma volume

  • Earlier onset of sweating and higher sweat rate

  • Reduced salt loss through sweating

  • Reduced blood flow to the skin

How do we measure energy expenditure?

VO2 (oxygen consumption) is a measure of how much energy (measured in calories) is produced by the body

• Indirect calorimetry enables the estimation of energy production based on O2 consumption

• Where we measure VO2 uptake and then convert VO2 to kcal

CHO: 4, Fat: 9, Protein 4 kcals

What is the caloric equivalent of Oxygen?

• Calories of energy produced when 1 liter of O2 is consumed

• Average for 50:50 mix of CHO and fat, 4.85 kcal per liter of O2

• Little error in using 5..0 kcal per liter of O2

Why do we wear fitness trackers?

• help people establish and maintain a regular pattern of PA

• Pedometers measure steps taken and the total distance per day

• Accelerometer based devices measure steps taken and the intensity of activities being performed to generate an estimate of energy expenditure

  • Estimations of energy expenditure are typically reliable but have poor validity

How do we estimate the energy costs of activity?

• Typical standard deviation of ~10% with actual measured average value

• Assumes steady state conditions

  • Assumes instructions are followed

  • Assumes calibrated machinery

How does oxygen cost differ between walking and running?

• O2 cost of walking increases in a linear fashion b/w the speeds of 50 and 100m per min, it increases faster at higher walking speeds

• O2 cost of jogging or running increases in a linear fashion from slow jogging to fast running

• Net caloric cost of jogging or running a mile is twice that of walking a mile at a moderate pace

How does body weight affect energy expenditure?

• When walking at a given speed, a 220 lbs person expends 2 times more kcal per minute than a 110 lbs person walking at the same speed

• As a client loses weight, the energy cost of walking at a certain speed decreases because the energy cost of walking depends on body weight

How does arms differ between legs in ergometry?

• VO2 max for the arms is only 70% of that measured with the legs

• Smaller muscles of the arms fatigue more quickly

• HR and bp are higher for arm work compared with leg work for the same VO2

• Arm work is inefficient; I2 cost of 1 kilogram meter (kgm) is about 3 ml O2 x kgm

What is the compendium of physical activities?

• This source provides information on the energy costs of a wide range of physical activities

• The MET levels can be used to estimate the energy costs of physical activities

What is the impact of environmental conditions on exercise?

• Changes in temperature, relative humidity, pollution and altitude don’t change the energy requirements for submaximal exercise, BUT they do change the participant’s response to the exercise

  • HR response is the best indicator of relative stress

  • Cut back on intensity when environmental factors increase the HR response

(PRACTICE THE MATH)