Blood Lactate Metabolism and Exercise

• This lab explores blood lactate response to exercise and blood sampling.
• By the end of this lab, you will be able to explain basic blood lactate metabolism, the relationship between blood lactate production and exercise performance, define lactate threshold and its relevance to exercise performance, and understand how endurance training influences blood lactate metabolism.
• The lab also covers sampling your own capillary blood, sampling someone else's capillary blood under resting and exercising conditions, analysing capillary blood samples, and safely disposing of infectious wastes.

Energy Production

• Muscle contraction during exercise requires energy.
• This energy is provided in the form of ATP (adenosine triphosphate).
• ATP is produced through the oxidation of fuels like carbohydrates, fats, and, to a lesser extent, protein.
• The chemical equation for this process is: C6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP (Energy) + Heat.

Blood Lactate Metabolism

• Lactate serves as a fuel source for the muscle, liver, and heart during both resting and exercise.
• Lactate can be reconverted into glucose and used to produce ATP (gluconeogenesis) via the Lactic Acid Cycle.
• A build-up of blood lactate creates an acidic environment due to the accumulation of H+ ions.
• Lactic acidosis (blood lactate > 5 mmol) limits the action of metabolic enzymes (pH-dependent activity).
• This can impair physiological processes such as skeletal muscle contraction.

Why Sample Blood?

• Sampling blood allows for determining the concentration of metabolites in the blood during exercise.
• It provides information about the internal state of the body.
• Commonly measured metabolites include blood lactate, pH, BGlucose, pO2, pCO2, and HCO3-.

Why Measure Blood Lactate?

• Blood lactate thresholds correlate well with endurance performance.
• Training can be prescribed based on the relationship between blood lactate threshold and heart rate.
• Blood lactate concentration can be measured by obtaining a capillary blood sample and analysing it with a blood lactate analyser.

Capillary Blood Sampling Procedure

• Prepare the necessary equipment: gloves, alcohol wipes, tissue, lancet/unistick, and capillary tubes.
• Ensure all equipment is ready before sampling.
• Locate a suitable area for puncture, with common sites being the earlobe or finger.
• Use the earlobe if hands are unavailable, preferably using the first three fingers and ideally the ring finger.
• Prick the finger/ear with a lancet, avoiding the fingertip and side/edge of the finger, aiming for the lower earlobe if using the ear.
• Squeeze blood out of the finger/ear and wipe away the first drop.
• For finger sampling, place the thumb on the underside of the finger, aim the finger downwards (towards gravity), and away from yourself.
• For ear sampling, grip the ear with the index finger and thumb, squeezing blood with the opposite index finger.
• Squeeze and then relax to allow blood to return to the finger (reperfuse) and wipe away any smeared blood.

Exercise Protocol

• The exercise protocol consists of 3-minute workloads at rest, 40W, 80W, 120W, 160W, and recovery (40W).
• In a continuous test, blood is sampled during the last minute of each workload.
• In a discontinuous test, blood is sampled during the recovery period.

Blood Lactate Response to Graded Exercise

• During low-intensity exercise, blood lactate production equals blood lactate clearance, with energy primarily derived from oxidative phosphorylation (oxygen facilitated).
• During high-intensity exercise, blood lactate production exceeds blood lactate clearance, with energy mainly derived from glycolysis (oxygen limited).

Lactate Thresholds

• Lactate Threshold 1 (LT1) is the lowest intensity at which there is a sustained increase in blood lactate concentration above resting levels.
• Lactate Threshold 2 (LT2) is the intensity that causes a rapid increase in blood lactate, indicating the upper limit between lactate production and clearance.
• LT1 and LT2 can be determined by analysing the blood lactate response to exercise.
• LT1 is defined as the increment in blood lactate that is > 0.4 mmol.L-1.
• The Modified Dmax Method for calculating LT2 involves drawing a straight line between LT1 and blood lactate peak, with LT2 being the greatest distance between this straight line and the blood lactate curve.

Blood Lactate Response & Training Zones

• The blood lactate curve can be used to determine heart rate training zones for endurance training.
• Lactate threshold training causes a rightward shift of the blood lactate curve.
• Athletes are able to exercise at a higher intensity before reaching LT2 with training.
• A high lactate threshold is beneficial to endurance performance.
• Exercising for longer at a higher intensity before fatigue prevails improves endurance capacity.
• Lactate threshold (LT2) can be improved by training at an intensity just above the lactate threshold for an extended period.
• The heart rate and blood lactate response to incremental exercise can be used to develop training zones designed to improve an athlete’s lactate threshold.
• Training zones are categorized by BLa relationship, BLa mmol.L-1, and other metrics.
• T1 (Light Aerobic) is BLa < LT1, <2.0 mmol.L-1, 60-75% HRmax, 60% VO2max, Very Light RPE, and > 3 hour duration.
• T2 (Moderate Aerobic) is BLa in lower half between LT1 & LT2, 1.0-3.0 mmol.L-1, 75-84% HRmax, 60-72% VO2max, Light RPE, and 1-3 hour duration.
• T3 (Heavy Aerobic) is BLa in upper half between LT1 & LT2, 2.0-4.0 mmol.L-1, 82-89% HRmax, 70-82% VO2max, Somewhat Hard RPE, and 30-90 min duration.
• T4 (Threshold) is BLa at LT2, 3.0-6.0 mmol.L-1, 88-94% HRmax, 80-85% VO2max, Hard RPE, and 20-60 min duration.
• T5 (Max Aerobic) is BLa >LT2, >5.0 mmol.L-1, 92-100% HRmax, 85-100% VO2max, Very Hard RPE, and 2-12 min duration.