Energy
Transfer to Exercise
Short-term
Energy
§ The Lactic
Acid System
Glucose
Blood
Lactate Accumulation
Lactate
Threshold
§ Lactate
Threshold = point at which there is a non-linear increase in
blood lactate accumulation in the blood.
– Also known
as OBLA (onset of blood lactate accumulation)
– An important
predictor of aerobic fitness level
Blood
Lactate: Bad or Good?
§ Primarily known for:
–
Major contributor to fatigue and
muscle soreness
§ Important Energy Source:
–
Can be regenerated to glucose in
liver, kidney, or skeletal muscle
§ Sent back to muscle for use (Cori Cycle)
§ Stored as glycogen
–
Oxidized by heart
–
Oxidized by less active skeletal
muscle
–
Direct fuel source for active
skeletal muscle
Oxygen
Uptake During Exercise
§ VO2
= volume of oxygen consumed
per minute.
Steady
State
§ Definition = a balance between energy need and
supply
§ O2 is able to meet the energy demands of the exercise.
§ Lactic acid will not accumulate significantly
§ Can we stay in steady state forever?
–
No
–
Due to loss of fluids and energy
sources (glucose and glycogen- in liver and muscle)
Maximal
O2 Uptake
§ Definition = maximal
amount of oxygen that can be consumed per minute during exercise.
VO2
max
§ The higher the VO2 max, the greater the aerobic fitness level
of the individual. The greater the ability to resynthesize ATP.
Example:
Low High Elite
Women 20 ml/kg/min 50
ml/kg/min >70
ml/kg/min
Men 21 ml/kg/min 52
ml/kg/min >70
ml/kg/min
Highest recorded VO2 max = 94 ml/kg/min in a cross-country skier
What determines if we are Aerobic or Anaerobic Athletes?
§ Skeletal Muscle Fiber Types:
–
Slow-twitch (Type I)
§ Slow-contracting fibers
§ Numerous mitochondria
§ High number of aerobic enzymes
–
Fast-twitch (Type II)
§ Type IIa (anaerobic + aerobic) and Type IIb (anaerobic)
§ Fast-contracting fibers
§ Bigger fibers
§ Higher number of anaerobic enzymes
The
athlete advantage
§ Higher amount of slow-twitch fibers favor potentially greater
performances in aerobic sports: long-distance running, cross-country skiing,
etc.
§ Higher amount of fast-twich fibers favor potentially greater performances
in anaerobic sports: sprinting, weight-lifting, etc.
Aerobic vs Anaerobic
During Physical Activity
§ Based upon duration of activity
Aerobic vs Anaerobic
During Physical Activity
§ Based upon
intensity of activity
Nutrient-related
Fatigue
§ “Hitting the
Wall”
– the feeling of fatigue and an inability to
exercise efficiently
§ Due to:
– Decreased
amounts of glycogen in active muscles and the liver
– Inactive
muscles tend to retain stored glycogen
– Slower
release of fat from adipose tissue
– CNS’s need
for glucose
Oxygen
Deficit
§ The amount
of O2 that would have been used at the start of exercise if the body
could have consumed it.
What
happens after exercise?
§ Body will
have to make up the energy lost. To do this, we pay back the energy debt with
oxygen, i.e. the oxygen debt
Factors affecting amount of O2 Debt [or Excess
Postexercise O2 Consumption (EPOC)]
§ Resynthesis of ATP & PC
§ Converting of lactate to glucose
§ Oxidizing lactate for energy
§ Replenishing O2 lost from blood and body tissues
§ Elevated body temperature
§ Presence of stimulatory hormones, i.e. epinephrine (adrenaline)
§ Elevated HR and breathing
What’s the best way to Recover from Exercise?
§ If exercising at or below steady state, passive procedures tend to
produce more rapid recovery (e.g. sitting or lying down)
§ If exercising above steady state (vigorous exercise), active
procedures produce more rapid removal of lactate accumulation
–
Optimal recovery levels:
§ 30-45% VO2 max for untrained
(e.g.- walking)
§ 50-65% VO2 max for trained
(e.g.- jogging)