Understanding Lactate Threshold and Other Run-Limiting Factors

Understanding your lactate threshold can transform your running performance. It’s a key factor that separates casual joggers from competitive runners. This post explains what happens in your body at the lactate threshold, how you can measure it, the difference between LT1 and LT2, and how to train effectively to improve your thresholds, running pace and endurance.

Runner's legs in motion on a forest trail during sunrise

What Is Lactate Threshold in Running?

Lactate threshold (LT) refers to the exercise intensity at which lactate begins to accumulate in the blood faster than it can be removed. Lactate is a byproduct of anaerobic metabolism, which kicks in when your muscles need energy faster than oxygen can be supplied.

When running below this threshold, your body clears lactate efficiently, allowing you to sustain the pace for a long time. Once you cross it, lactate builds up, causing muscle fatigue and a burning sensation, which limits how long you can maintain that effort.

This threshold is a strong predictor of endurance performance because it marks the highest pace you can hold without fatiguing quickly.

The Physiology Behind Lactate Threshold

Your muscles produce energy through two main pathways:

• Aerobic metabolism: Uses oxygen to convert carbohydrates and fats into energy. It’s efficient but slower.

• Anaerobic metabolism: Produces higher energy levels but without oxygen, generating lactate as a byproduct.

  
  

At low to moderate intensities, aerobic metabolism dominates. As intensity rises, anaerobic metabolism contributes a greater percentage of energy requirements, increasing lactate production.

The lactate threshold is the tipping point where lactate production exceeds clearance. Your body can buffer and remove lactate up to a certain rate, but beyond that, lactate accumulates, leading to:

• Increased acidity (from hydrogen ions) in muscles

• Reduced muscle contraction efficiency

• Fatigue and decreased performance

  
  

Improving your lactate threshold means your body can sustain higher intensities before fatigue sets in.

Understanding LT1 and LT2: The Two Lactate Thresholds

There are two commonly recognised lactate thresholds:

LT1 (Aerobic Threshold)

• Occurs at a lower intensity, roughly 50-60% of VO2max (depending upon training status).

• Marks the point where blood lactate starts to rise above resting levels but remains low (around 2 mmol/L).

• You can maintain this pace for hours; it’s often called the "easy" or "conversational" pace - or labelled as the upper limit of Zone 2 training.

Adaptations from LT1 training include:

• Increased Mitochondrial Efficiency & Density: Training at this intensity boosts the number and efficiency of mitochondria, which are responsible for oxidising fat.

• Increased Fat Oxidation Enzymes: Consistent LT1 training increases the capacity of enzymes that break down fat.

• Improved Capillary Density: Enhanced capillary network surrounds muscle fibres, improving oxygen delivery to muscles and furthering the ability to burn fat for fuel.

• Greater Fat Oxidation Rates: Endurance training, specifically at lower intensities, allows athletes to burn more fat at higher absolute and relative intensities.

In short, the higher you can push this threshold, the longer you'll be able to run aerobically, without using up carbohydrate stores through anaerobic respiration and without producing limiting lactic acid.

LT2 (Anaerobic Threshold)

• Occurs at a higher intensity, about 80-90% of VO2max (depending upon training status)

• Blood lactate rises sharply (around 4 mmol/L), indicating a shift to anaerobic metabolism. This point is sometimes referred to as the Onset of Blood Lactate Accumulation (OBLA).

• This pace is sustainable for roughly 30-60 minutes in trained athletes.

• Training near LT2 improves your ability to clear lactate and delay fatigue.

Adaptations to LT2 training include:

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• Enhanced Lactate Clearance and Utilisation: While LT2 marks a high production rate, training at this level forces the body to improve its ability to shuttle and reuse lactate as fuel in type I (slow-twitch) muscle fibres.

• Improved Buffering Capacity: High-intensity training at LT2 increases the body’s ability to manage metabolic acidosis (the accumulation of hydrogen ions that cause muscle burn and fatigue).

• Increased Mitochondrial Function/Density: Though more associated with zone 2, high-intensity training at LT2 also increases mitochondrial density and efficiency, allowing for higher aerobic energy production.

• Increased Capillary Density: Training improvements in this zone increase the density of capillaries around muscle fibres, enhancing oxygen delivery and waste removal.

• Delayed Metabolic Fatigue: Through repeated exposure, athletes improve their capacity to sustain higher power outputs or speeds (e.g., 10k to half-marathon pace) for longer periods before hitting fatigue

In short, the higher you can push this threshold, the more you'll be able to work anaerobically without fatigue.

Graph showing LT1 and LT2 vs blood lactate levels

Both thresholds are important for runners. LT1 builds endurance and efficiency, while LT2 pushes your speed and stamina.

How to Measure Lactate Threshold

Measuring lactate threshold can be done in several ways, ranging from lab tests to field methods.

Laboratory Testing

• Blood Lactate Testing: The gold standard involves taking small blood samples during incremental exercise tests to measure lactate concentration.

• VO2max Testing: Measures maximum oxygen uptake and can help estimate LT percentages and corresponding heart rates.

  
  

Field Testing Methods

• Time Trials: Running a 30-minute all-out effort and calculating average pace or heart rate can estimate LT2.

• Talk Test: If you can speak comfortably, you’re likely below LT1; if speaking is difficult but possible, you’re near LT2.

• Heart Rate Zones: Using heart rate monitors, LT1 usually falls around 60-70% of max heart rate, LT2 around 80-90%.

  
  

Wearables and Apps

Some devices estimate lactate threshold using measured factors such as: heart rate variability and running pace data for set distances. As these are indirect measures, they are not as accurate as lab-based measurements. However, they do offer a significant benefit when setting your training pace zones.

VO2 Max and it's Relationship with Lactate Threshold

VO2 Max relates to the 'size' of your engine. Lactate Thresholds relates to the percentage of that engine you can use. Put another way, your VO2 Max can be considered your 'ceiling' (your maximum oxygen utilisation), whereas LT is the level of intensity of effort that you can sustain.

So, from a fitness acquisition perspective, that gives you two options:

1. Raise your ceiling by increasing your VO2 Max - even without raising your actual Lactate threshold, you'll still be operating at faster paces without fatigue.

2. Raise your Lactate Threshold and ability to work anaerobically. Without raising your VO2 Max, you'll hit faster paces without fatigue.

These two methods are not completely separate from each other, as training for one will likely benefit the other. However, you can focus on each during different blocks of training if you wish.

Training to Improve Lactate Threshold

Improving your lactate threshold means you can run faster without fatigue. Training focuses on pushing the boundary where lactate accumulates.

Training Zones for Lactate Threshold

• Below LT1: Easy runs to build aerobic base and recovery - this will extend the period and intensity of training that you can achieve before the onset of lactate accumulation..

• At or just below LT1: Long steady runs to improve fat metabolism.

• Near LT2: Tempo runs and threshold intervals to increase lactate clearance.

• Above LT2: High-intensity intervals to boost VO2max, raising the ceiling and thus giving you a bigger anaerobic capacity.

  
  

Effective Workouts

• Tempo Runs

Run at a 'comfortably hard' pace, just below or at LT2, for 20-40 minutes. This improves your ability to sustain faster paces.

• Threshold Intervals

Repeat 3-5 minute intervals at or slightly above LT2 pace with equal rest. This trains your body to tolerate and clear lactate.

• Long Slow Distance (LSD) or Low Intensity Steady State (LISS) - Zone 1&2

Runs at or below LT1 to build endurance and improve fat utilisation.

• Hill Repeats

Running uphill at high intensity can improve 'strength' and anaerobic capacity.

Lots has been written about how to combine all of the above training workouts into a 'periodised' plan. The reality is, there is no 'one size fits all'. We all respond differently to different training stimuli and we all have different tolerances, for high intensity v volume training.

Consistency and Progression

If you're serious about raising your thresholds, consistency is key to progression:

• Start with 1-2 threshold type workouts per week.

• Gradually increase duration or intensity.

• Combine with easy runs and recovery days to avoid burnout.

Practical Example of a Weekly Lactate Threshold Training Plan - Beginner

| Day Workout Type Description

Monday Easy Run 45 minutes at or below LT1 pace

Tuesday Threshold Intervals 5 x 4 minutes at LT2 pace, 4 min jog recovery

Wednesday Rest or Cross-Train Light activity or rest

Thursday Tempo Run 30 minutes at LT2 pace

Friday Easy Run 40 minutes at LT1 pace

Saturday Long Run 90 minutes at or below LT1 pace

Sunday Rest Full rest or gentle stretching

Monitoring Progress and Adjusting Training

Track your pace, heart rate, and perceived effort during threshold workouts. If the workouts feel easier over time, your lactate threshold is improving.

Re-test your threshold every 6-8 weeks using time trials or lab tests if possible. Adjust training paces accordingly to keep challenging your body.

Other Factors Affecting Running Performance

Of course, VO2 Max and Lactate Threshold are just two of the factors that limit performance in running. Other factors include:

Running economy: The amount of oxygen required to run at a given pace or the 'amount of energy required to move'.

Running economy is influenced by a number of factors including: 

1. The composition of muscle fibres.

   •  It has been suggested that a higher percentage of slow-twitch type 1 muscle fibres  is  associated  with a better  economy (similar to cycling efficiency).

2. Myocardial VO2 also constitutes a significant fraction of whole body  ̇VO2 during exercise.

   • Reductions in myocardial  ̇VO2 would result in improved  Running Economy  from a more efficient combination of HR and stroke volume.

3. Elastic energy storage and return in the Achilles tendon and tendons in the arch of the foot causing more 'spring' within each stride.

4. Postural tension - meaning less wastage of energy from unwanted torso movement.

5. Biomechanics.

   • Vertical Oscillation.

     • Excessive vertical oscillation increases oxygen cost.

   • Stride length.

     • In the majority of cases, athletes subconsciously self-select the most economical stride length.

6. Morphological

   1. Lower weight in the lower limbs results in better economy.

      • Small feet/light shoes.

      • Lower calf mass.

7. Genetics

   • A large portion of the factors above is set by your genetics. Some people bounce better than others, and some people have a naturally higher percentage of type 1 fibres.

Summary

Lactate threshold is a powerful concept for runners aiming to improve endurance and speed. It marks the intensity where your body shifts from aerobic to anaerobic metabolism, causing lactate buildup and fatigue.

• LT1 and LT2 represent two key thresholds with different physiological and training implications.

• Measuring lactate threshold can be done through lab tests or practical field methods.

• Training near your lactate threshold improves your ability to sustain faster paces longer.

• A balanced training plan includes easy runs, tempo runs, intervals, and recovery.

  
  

By understanding and training your lactate threshold, you can run smarter and faster. Start incorporating threshold workouts into your routine and watch your performance grow.

I hope this helps. If you need more detail, then please comment or drop me a message!

Paul