Lab 3b: Lactate Threshold (LT)

What is lactate threshold?

• Point at which blood lactate begins to increase substantially above resting

  • Sometimes termed “anaerobic threshold”

• Glycolysis produces pyruvate

  • Insufficient O₂ present to use pyruvic acid in oxidative phosphorylation

  • Pyruvate fermented into lactate

  • Lactic acid = lactate with a hydrogen ion (H+)

What are the negatives Lactic Acid Accumulation?

• Lactic acid dissociates into H+ and Lactate

  • We measure lactate as a proxy for lactic acid production

• Accumulation of H+ causes acidosis

  • Lowers pH of cells

• Acidic pH- limiting factors of exercise

  • Inhibits PFK (enzyme required for glycolysis)-

  • Can displace calcium in muscle fibers (needed for muscle contractions

How can we combat H+ Accumulation?

• Buffering controls levels of H+

  • Bicarbonate (HCO₃)

• Bicarbonate uses H+ to create 2 things

  • H₂O and CO₂

• Helps control pH and limit negative influence of H+-

  • Short term - breathed off in the lungs to lower pH -

  • Does NOT remove lactate

How do we remove lactic acid?

• Removal methods

• 70% of lactate is oxidized (turned into pyruvate to enter Krebs cycle)

  • Used as an energy substrate by heart and skeletal muscle (type 1 fibers)

• 20% converted to glucose (gluconeogenesis)

• 10% converted to amino acids

• Blood lactate concentration depends on:

  • Production, Diffusion, Oxidation, & Clearance

Typical Lactate Levels at rest and max?

• At rest

  • 1-2 mmol/kg of muscle

  • 0.5-2 mmol/L of blood*

• Maximum levels

  • 20-25 mmol/kg of muscle

  • 30 mmol/L of blood*

what is the Lactate Threshold differences between a Trained vs. Untrained person?

• Aerobically Trained

  • Higher lactate threshold (~70-80% VO2 max) (lactate produced “later”)

  • Clearance of lactate is faster

• Untrained

  • Lower lactate threshold (~50-60% VO2 max)-

  • Clearance is slower

Estimating LT Using Ventilatory Equivalents

• Ventilatory equivalent of oxygen: Ve /VO2

• Ventilatory equivalent of carbon dioxide: Ve /VCO2

• Why is there an increase in the Ve /VO2 , but not Ve /VCO2

  • Ventilation to remove CO2 (in order to buffer changes in blood pH due to H+ accumulation from anaerobic metabolism) becomes disproportionate to the body’s need to provide O2 to the active muscles

• Therefore:

  • Ventilatory equivalents can provide reasonably close estimates of lactate threshold

Does Lactic Acid cause DOMS?

No, lactate returns to resting about 2 hours after exercise cessation. DOMS (delayed onset muscle soreness) is caused by microscopic injury to muscle fibers leading to inflammation.

How do we measure blood lactate?

1. Finger Stick: Cleanse the skin with an alcohol pad. Let finger dry or the alcohol will influence results. Use the lancet to pierce the skin (towards side of fingertip)

2. Sample Collection: Insert test strip into analyzer. Wipe away first blood droplet with gauze (alcohol residue contaminated sample). Once new droplet has formed, hold test strip to droplet. Test strip should pull blood sample on its own

3. Results: Analyzer will reveal measure after brief countdown

4. Documentation: Record results in the shared class data sheet

What are the bicycle testing procedures?

Fitness testing on cycle ergometer

1. Record resting blood lactate

2. Complete the cycling protocol

   1. Begin at 1 kp and increase resistance by 0.5 kp each stage until exhaustion

   2. 2-minute stages-Pedal rate 50-60 RPM

3. Record HR, RPE, and lactate within the last 30 seconds of each stage, at the point of exhaustion, and 1 min post exercise