Anaerobic Threshold (OBLA)
• accumulation of lactate due to excessive amount produced,
compared to amount removed
• 4 mmol/l in the horse
– rest - 1 mmol/l
• low-moderate exercise, no build-up
• VLA4 = velocity of travel when lactate at 4 mmol/l
• % of VO2 max
– ex: OBLA @ 80%VO2 max to 60% VO2 max
• lactic acid in blood
– diffusion
– active transport from active skeletal muscle
• lactate production
– TB race
– trot/3 day event
– endurance race
25-30 mmol/l
8 mmol/l
2 mmol/l
Integration of Aerobic and Anaerobic
Pathways
• regulated by:
– relative concentrations of substrates and end products
– availability of enzymes
– effect of feedback mechanisms
• activate or inhibit enzyme activity
• most important regulators
– availability of O2
– ratio of ATP/ADP
Energy System
• ATP-Pcr
• glycogen
– muscle glycogen used more rapidly first minute
– liver glycogen
• fats
Onset of Exercise
• reserves of O2 (myoglobin and hemoglobin)
• ATP and CPr reserves
• along with glycogen
• O2 available
– O2 re-oxidizes NADH2 produced in cytoplasm
• energy production continues via aerobic pathway
• increased energy demand
– ATP/ADP ratio declines
• stimulates glycolytic pathway, increase in NADH2
and pyruvate
– stimulate activity of PFK
• low-mod exercise
– most pyruvate enters TCA cycle
– b-oxidation stimulated
• critical intensity of exercise
– NADH2 re-oxidized via pyruvate
– anaerobic pathway
– producing lactate
• above maximal O2 uptake
– all anaerobic metabolism
Interplay of Systems
• maximal intensity
– 0-20 sec - ATP-PCr primary system
• some glycolytic
– > 20 sec - glycolytic primary system
– longer efforts - aerobic primary system
• increasing intensity
– aerobic primary with addition of anaerobic as needed
– aerobic continues to rise to VO2 max (HR 200)
– above VO2 max - anaerobic primary system
• intermittent intensity
– aerobic primary
– bursts either ATP-PCr and/or glycolytic pathway
Fatigue
• depletion of energy system
– depletion of PCr and ATP
– glycogen
• accumulation of metabolic by-products
• failure of fibers to contract mechanically
• nervous system
Toxic By-Products
• lactic acid
– H+ accumulation causes muscle acidification (acidosis)
• buffers (HCO3) bicarbonate
– pH of muscle 7.1 to 6.6 (6.4 exhaustion)
• below 6.9 - decrease in glycolysis and ATP production
• 6.4 - glycogen and ATP breakdown stop
• unfit horse - 400 m/min or 150 HR
• fit horse - 500 m/min or 170 HR
Conditioning
• no conditioning effect on ATP-PCr system
• more skilled, energy demand to activity decreases
– more efficient in movement
• “mass action effect”
– large amounts of one fuel causes cells to rely more on
that source
– increase concentration of enzymes used for fat
metabolism
– increase muscle ability to use fats