What Are The Adaptations to Running Training?

Endurance training provides a stimulus that your body must adapt to, to better meet the demands of your training and improve your performance. Most endurance training adaptations are similar, however this blog will focus on the specific adaptations to running training.

Understanding these adaptations will help you understand the importance of the different types of training run,  the different adaptations they elicit and therefore guide you in deciding which type of training is optimal for you to reach your training and fitness goals.

Please note this won’t be an exhaustive list but will provide context to further your understanding of running training, if there’s something you feel we should add then please contact us at: training@caffeinebullet.com

What Are The Aerobic And Anaerobic Energy Pathways?

There are two types of energy pathways – The aerobic and anaerobic energy pathways. 

They are responsible for supplying your muscles with the fuel they need to work. 

The primary energy pathway used will vary depending on the intensity of exercise, with more strenuous exercise (e.g. faster running) increasing the muscle’s demand for oxygen and energy.

This means you’ll need a faster-acting energy pathway with a reduced reliance on a steady oxygen supply to meet these increased demands.

All energy pathways have the same end goal, to supply the body with energy in the form of a molecule called adenosine triphosphate (ATP). 

ATP is known as the energy currency of the body and is broken down into adenosine diphosphate (ADP), the energy released from breaking ATP down into ADP can be used as fuel for the muscles to contract.

It is important to understand that these energy systems work together simultaneously and do not “turn off” when another energy system is in motion. Instead, they vary in the amount they contribute depending on the demands on the body.

What Are The Aerobic Energy Pathways?

Aerobic means “with oxygen”, so aerobic fitness requires oxygen to function. Aerobic pathways are more energy efficient and don’t cause as much fatigue, however they are slower to work than anaerobic energy systems as they require a higher number of chemical reactions to occur before energy can be supplied. Therefore, they are only the primary energy pathway when oxygen and energy demands are lower, such as during longer distance and slower runs (e.g. 5k, 10k, half marathon, marathon and easy paced runs). There are two main energy pathways the body uses during aerobic exercise: 

1. The Fat Oxidation Pathway (oxidative phosphorylation) – The most energy-efficient pathway as you can generate lots of ATP with fewer resources. However, it is also the slowest and takes a little while (a few minutes) to fully activate. It uses fatty acids as fuel when oxygen is readily available, so it is only the primary energy system at lower exercise intensities such as brisk walking, easy runs, marathon paced runs, half marathon paced runs and 5-10k paced runs.
2. Aerobic glycolysis – A slightly faster but less efficient aerobic pathway that is the primary energy pathway during middle-distance races but is also relevant to longer distances (e.g. as you begin to pick up the pace in the last few miles of a marathon). When exercise intensity is high (e.g. during 800m-1500m races) aerobic glycolysis breaks muscle glycogen down into glucose, which over time leads to physical exhaustion due to depleted glycogen stores – this is what leads to runners “hitting the wall”. 

Running too fast during a longer race such as a marathon will make you more reliant on aerobic glycolysis for energy, instead of the fat oxidation pathway. Causing you to burn through your glycogen too quickly, meaning you run out of fuel and are forced to slow down or even walk.

Oh and don’t get aerobic exercise confused with aerobics!

What Are The Anaerobic Energy Pathways?

Anaerobic means “without oxygen”, so anaerobic exercise doesn’t require a steady supply of oxygen. Anaerobic energy systems are the primary energy pathway used when oxygen availability is low and you need energy fast. For example, during sprints or fast interval sessions where exercise is so intense and the demand for energy is so high that your muscles can’t extract oxygen fast enough to use aerobic energy pathways. There are two main energy systems that the body uses during anaerobic exercise:

1. The anaerobic glycolysis energy system – When exercise is too intense for the aerobic energy system to handle (e.g. 200 and 400m races/ intervals), glucose is converted to lactate which can be used to generate ATP even faster and without the need for oxygen. However, using lactate as fuel releases hydrogen ions as a byproduct, which dissolve in the blood causing it to become more acidic. Increased blood acidity contributes to the burning feeling you get when you’re running hard, making it harder to continue running as your blood becomes more and more acidic and eventually forcing you to stop exercising due to physical exhaustion and pain.
2. The ATP and Creatine Kinase system – This is the fastest energy system in the body. This system breaks ATP down into ADP, whilst Creatine Kinase works as a shuttle, turning ADP into ATP again. This pathway generates energy very quickly and can be used to supply very high-intensity, short bursts of exercise. However, this system can only be used for approximately 10 seconds before it is depleted as ATP and Creatine stores are relatively small,  so it is mostly only helpful in fuelling high-intensity efforts such as short sprints and heavy lifting.

What Are The Aerobic Adaptations To Running Training?

In general, aerobic adaptations will improve your ability to run at faster speeds fuelled by your fat or glucose (your aerobic energy system), without relying as much on lactate or ATP (your anaerobic energy as your aerobic energy systems is better able to keep up with higher energy demands.

Ideally in long distance running we want to use fat as fuel instead of carbohydrates, reducing the accumulation of fatigue by preserving muscle glycogen. 

Endurance training also improves how quickly you can break down glycogen (aerobic glycolysis), so you can use it more efficiently and reduce your reliance on anaerobic energy, therefore reducing your build-up of blood lactate. This allows you to run faster without exceeding your lactate threshold, meaning you can run faster whilst reducing the accumulation of fatigue.

Endurance training will also improve your VO2max. This is the maximal ability of the muscles and cells of the body to extract oxygen from the blood. The higher your VO2max value is, the more effective your body is at working aerobically. Put simply, a higher VO2max means you can run 100% aerobically at faster running speeds. However, there is a point of diminishing returns for runners  once your VO2max is high enough (usually around 60-70 ml/kg/min). Therefore, highly experienced runners will likely not benefit from training designed to improve VO2max.

What Are The Fat Burning Adaptations To Running Training?

There are three main adaptations to running training. These improve your ability to burn fat, so you can use it as your primary source of fuel at faster running speeds, sparing muscle glycogen that can be used to run further and faster. For example, you may be able to run using mostly fat as fuel at 10:00 min/mile pace instead of 10:30 min mile pace after a period of training, meaning you’re running faster without accumulating as much fatigue or depleting glycogen stores.

1. Increased size and number of mitochondria – Mitochondria are used to convert fatty acids into ATP so that they can be used as fuel for the muscles. Having a greater number of large mitochondria means your ability to burn fat is significantly improved.
2. Increased number and activity of fat metabolising enzymes – Improves the speed and efficiency of fat burning.
3. Increased triglyceride storage in the muscle – Triglycerides are made up of glycerol and three fatty acid molecules. They are how fat is stored in the muscle to be used as fuel. Increased muscle triglycerides means a greater availability of fat as fuel.

What Are The Central Adaptations To Running Training?

There are six main central adaptations due to running training. These are changes to the heart and blood vessels that improve oxygen uptake and contribute to improved endurance performance. Increasing blood and oxygen supply to the muscles can allow you to work aerobically at faster running speeds, reducing your reliance on fatigue-causing anaerobic energy pathways (which burn limited glycogen stores and create a build-up of blood lactate).

1. Increased blood plasma volume – This means that your blood will contain more water and have an overall higher volume. When entering the heart a higher volume of blood will stretch the muscles of the heart even further leading to a more forceful elastic rebound and contraction. This allows more blood to leave the heart per beat (the amount of blood leaving the heart per beat is called stroke volume). Making each contraction of the heart more efficient.
2. Reduced HR at rest and submaximal exercise – Due to an increased stroke volume, your heart does not need to contract as many times to pump the same amount of blood, meaning you can run at the same speed as before, but with a lower heart rate. This will improve your ability to run at slower speeds without fatiguing.
3. Increased maximal cardiac output – This means your heart can pump out more blood per minute when working at its maximum capacity, which allows more oxygen to reach the muscles. Therefore, the muscles have a greater supply of oxygen to work aerobically.
4. Increased oxygen carrying capacity of the blood – Increased levels of Erythropoietin (EPO) lead to an increased production of red blood cells and haemoglobin (which carries oxygen in the blood). Therefore, the same amount of blood can carry more oxygen, improving the amount of oxygen available to your muscles.
5. Increased muscle myoglobin – This means you can store and transport more oxygen within your muscles.
6. Improved blood flow to working muscle fibres – Capillary networks expand so that oxygen can transfer from your blood to your muscles (and vice versa) more efficiently.

What Are The Pulmonary Adaptations To Running Training?

There are three main pulmonary adaptations to running training. These are changes at the lungs that make your breathing more efficient by improving oxygen availability and reducing breathing discomfort. These adaptations will help you dispose of carbon dioxide and breath in oxygen more efficiently, improving your ability to work aerobically at faster running speeds. Therefore reducing your reliance on fatigue-causing anaerobic energy pathways (which burn limited glycogen stores and create a build-up of blood lactate).

1. Decreased respiratory work/ breathing effort at submaximal intensities – Breathing at slower running speeds becomes significantly easier, allowing you to run more comfortably at slower paces. This will reduce your perception of effort during a run, making it feel easier and decrease your mental fatigue whilst running.
2. Maximal exercise ventilation increased through lung and diaphragm adaptations – Your lungs and diaphragm adapt in a way that allows you to breathe in more air per minute, via more efficient breathing mechanics. You can then take oxygen and remove carbon dioxide faster, meaning you will be able to work aerobically at faster running speeds.
3. Reduced respiratory muscle fatigue – Meaning Your breathing muscles will generate less lactate, so they’ll contribute less to overall blood lactate accumulation and reduce their contribution to overall fatigue.

What Are The Anaerobic Adaptations To Running Training?

In general, these adaptations will improve your body’s ability to burn glycogen or lactate as fuel when your aerobic energy system can’t keep up with energy demands. Therefore, improving high-intensity exercise performance such as your ability to run fast (e.g. 800m pace) for longer periods of time.

What Are The Peripheral Adaptations To Running Training?

These are three main anaerobic adaptations to running training. These generally improve the muscle’s ability to work without a steady oxygen supply, using glucose, lactate or ATP as a primary fuel source. Meaning you can run at very fast speeds for longer before exhaustion.

1. Increased levels of the molecules ATP, PCR, creatine, and glycogen in the muscle – An increased number of these molecules means that you have a greater maximal capacity to generate energy anaerobically. This increases the maximum duration you can rely on anaerobic energy systems before exhaustion and improves the rate at which they can supply energy.
2. Increased ability to generate and tolerate blood lactate – Meaning you can increase the maximum amount of blood lactate you can accumulate until exhaustion, allowing you to run at faster speeds for longer.
3. Increased rate of lactate removal during exercise – This allows you to run at faster speeds for longer without accumulating high concentrations of blood lactate. Meaning you won’t fatigue as quickly.

What Are The Muscular And Connective Tissue Adaptations To Running Training?

There are four main muscular and connective tissue adaptations to running training. Generally, these will either improve your fatigue resistance or improve your running economy (how efficiently your muscles work when running). So you can run faster or further without tiring as quickly.

1. Muscle fibre conversion – Put simply, your muscle fibres can change and shift towards becoming more efficient, less fatigable types of muscle fibres. Meaning you can run faster, for longer without becoming as fatigued.
2. Improved running economy due to increased tendon stiffness – Stiffer tendons store more elastic energy, meaning less muscle force is required for each stride, reducing ground-contact time and making each of your strides more efficient. So you can run faster or further whilst accumulating less fatigue.
3. Increased resistance to muscle and connective tissue damage – Over time, running becomes less strenuous on your muscles and connective tissues as they become stronger and more able to handle the external forces exerted on them from running. This improves your ability to run longer distances and still have the ability to recover for your next run.
4. Increased size of slow twitch muscle fibres – Increased muscle fibre size increases your maximal capacity for glycogen storage. Increased glycogen storage means you have more glucose to use as fuel, allowing you to run for longer without “hitting the wall”.

Other Adaptation To Running Training

1. Regular endurance exercise will increase the number of calories you burn which can help with losing weight and body fat when combined with a calorie deficit.
2. Trained runners can exercise more comfortably in hot environments due to a larger blood plasma volume and improved thermoregulation mechanisms. Meaning you are able to dissipate heat faster and more efficiently.

How Fast Do You Adapt To Running Training?

All physiological adaptations have different time frames, some adaptations occur much sooner than others. The graph below summarises the timeline of most running adaptations, including how quickly they return to baseline after a period of detraining. 

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