Structure and Function of the Muscular, Neuromuscular, Cardiovascular, and Respiratory Systems

PHEC 192 CDR D. D. Peterson, MS, CSCS Director, Aviation Survival Training Center

Lactate Threshold

Lactate

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• Metabolite produced in the muscle during the breakdown of glucose

• Previously thought a waste product, but can be retained by the muscle and used for energy

Lactate, Cont.

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• Once formed in the muscle, pyruvate has two possible fates: • Lactate • Combine with coenzyme A

to form acetyl coA and is used by the electron transport chain (ETC) to regenerate ATP

Lactate, Cont.

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• Lactate can also be absorbed by the liver and be converted back into glucose and released into the bloodstream to the working muscle

• Process is called gluconeogenesis

Lactate, Cont.

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• Production of large amounts of lactate indicates the body is using its last line of defense to maintain glycolytic ATP production

• Further increase in work rate will overwhelm the capacity for lactate production and result in acidosis, a drop in NAD levels, and fatigue

• VO2max: maximum amount of oxygen that can be utilized in one minute of maximal/exhaustive exercise

•Lactate Threshold (LT): point in exercise at which blood lactate starts to accumulate in the blood

• blood lactate ~ 4 mmol / liter

• Aerobic Threshold (AT): point in exercise just below LT and is used to conserve energy

• blood lactate ~ 2 mmol / liter

• Ventilatory Threshold (VT): point in exercise where the respiration rate (ventilation) starts to increase in a non-linear fashion

LT vs. VO2Max

LT vs. AT

LT vs. VT

LT w/ Training

LT Testing

LT Testing, Cont.

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• The objective is to identify the exercise intensity at which the body begins to relies heavily on glycolysis

• Generally reached after ~ 12-20 minutes

• Information can be used to: • Predict racing / training paces • Assess fitness • Assess efficacy of training program

Sample Sites for LT Testing

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• Finger Tips

• Earlobes

• Antecubital Vein

Means of Determining LT

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• 0.5 and 1.0 mml·L-1 Criteria

• Regression Analysis

• D-Max Method

• Maximal Lactate Steady State

0.5 and 1.0 mml·L-1 Criteria

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• Plots blood lactate concentrations against respective work rates

• LT is identified as the highest work rate that does not result in a 0.5 or 1.0 mmol·L-1

increase in blood lactate concentration in response to at least two consecutive increases in work rate

Regression Analysis

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• Divides lactate curve into two parts • Baseline (includes all lactate values up to the point at

which blood lactates levels begin to rise) • Exponential Portion (includes all values from inflection

point until test termination)

• Separate regression analyses are performed on each portion to generate two lines of best fit

• LT is determined by drawing a vertical line to x-axis from where the two lines of best fit intersect

D-Max Method

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• Requires subject to exercise until volitional exhaustion

• Plot all blood lactate levels then draw a straight line connecting the first and last lactate values

• Second line is drawn perpendicularly from the first line to point on plotted lactate value that is farthest from the first line

D-Max Method, Cont.

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• Third line is drawn downward from intersection of the second line and plotted lactate value until it intersects x-axis

• LT is said to be the point at which the third line intersects the x-axis

• Considered to be the most accurate method for estimating LT

Maximal Lactate Steady State

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• Monitors blood lactate during extended periods of consistent exercise intensity in order to identify the highest workload at which blood lactate levels remain stable

LT Test Results

Questions?