Understanding training adaptations: how exercise transforms your body inside and out (part 2)

9 Aug

In part one of this series, we discussed the various body systems involved during exercise and how they respond to increased physical demands.

Now, we’ll delve deeper into the specific adaptations that occur within our muscles and cardiovascular system as a result of regular training.

These adaptations are crucial for improving overall fitness, enhancing performance and supporting long-term health.

VO2 max: the gold standard of cardiovascular fitness

VO2 max - or maximal oxygen uptake - is a measure of the maximum amount of oxygen your body can utilise during exercise.

It is widely considered one of the best indicators of cardiovascular fitness and aerobic endurance.

To look at this simplistically, the more oxygen you can breathe in during exercise, the more energy your muscles have to utilise, thereby performing more work.

Increasing your V02 max leads to several positive outcomes, such as enhanced endurance and performance, improved cardiovascular health and higher energy production.

Enhanced endurance: better stamina, meaning that the body can consume and utilise more oxygen during exercise allowing you to sustain higher levels of effort for longer periods.
Better performance: more aerobic capacity, allowing you to perform at a higher percentage of your maximum effort without becoming fatigued as quickly.
Improve cardiovascular health: a higher V02 max often correlates with a stronger, more efficient heart and reduces the risk of cardiovascular disease.
Higher energy production: the more oxygen your muscles can receive, the more nutrients they can utilise to create ATP - the energy source for our cells.

How training leads to increased cardiac output

Cardiac output is the amount of blood (stroke volume) your heart pumps (heart rate) each minute.

Cardiac output immediately increases in response to training and is directly related to the intensity of the exercise.

When you exercise, your body needs more oxygen to go to your muscles to work efficiently.

Oxygen is delivered to your muscles via your blood, which is why the efficiency of your cardiac output is important.

Regular aerobic exercise increases the stroke volume, which is the amount of blood ejected by the heart with each beat.

Cardiac output increases due to training by:

The greater flow of blood back to the heart which creates a larger stroke volume.
Vasodilation – the widening of blood vessels due to relaxation of the vessels’ muscular walls – which results in better blood flow
Less resistance to blood flow due to vasodilation.
An increased demand for oxygen and nutrients by the working muscles.
More carbon dioxide produced during exercise

It also results in a lower resting heart rate i.e. a more efficient heart pumps more blood with each beat.

Increased mitochondrial density

Mitochondria are the powerhouses of the cell, and their increased density allows for more efficient energy production.

Mitochondria are responsible for generating ATP (the energy currency of the cells) by converting oxygen and nutrients into ATP.

The number and location of mitochondria within a cell changes in response to metabolic conditions. This is called mitochondrial biogenesis - where existing mitochondria create new ones.

When biogenesis is stimulated, the density of mitochondria in muscle cells increases and the efficiency of how they convert nutrients and oxygen into ATP improves (i.e. aerobic respiration).

Given that endurance exercise is heavily reliant on our capacity to keep providing energy for muscle contraction, having muscle cells equipped with a greater density of efficiently working mitochondria is a great advantage.

Strength gains beyond muscle size

Strength refers to the amount of force your muscles can move.

Resistance training results in increased strength due to neuromuscular adaption, which means your nervous system learns to communicate more efficiently with your muscles.

Resistance training also results in many other positive body changes such as muscle hypertrophy, increased lean muscle mass, increased metabolism and increased bone density, to name a few.

Muscle hypertrophy: building muscle mass

Muscle hypertrophy in an increase in muscle mass and is a key goal for many individuals engaged in resistance training.

Muscle hypertrophy occurs due to the growth of individual muscle fibres i.e. the strain resistance training places on muscles causes damage to their fibres, which the body then repairs.

Regularly challenging your muscles causes them to adapt by growing in size and strength.

Regular strength/resistance training (2 – 3 times per week) is essential for muscle hypertrophy but rest is also key.

Rest allows the muscles time to recover, repair and grow.

A 2019 review of the literature suggests that individuals seeking to maximise their muscle growth should aim for resistance training that consists of multiple sets (3 – 6) of 6 to 12 repetitions, with short rest intervals (60 seconds) and moderate intensity effort (60 – 80%), with subsequent increases in training volume as time goes on.

Muscle fibre transitions: adapting to demands

Training also results in muscle fibre transitions, which play an important role in training outcomes and performance.  

Our muscles are a collection of individual muscle fibres that contract together (they look almost like a bunch of spaghetti).   

There are two key muscle fibre categories – fast and slow twitch.  

Slow twitch fibres contract relatively slowly but have the capacity to do so repeatedly over a long time. They are therefore suited for endurance activities.  

Fast twitch fibres (there are two types) are capable of powerful and rapid successive contractions, but tend fatigue quickly. They provide our capacity for power and strength.   

Each of our muscles will have a mixture of these three fibre types, depending on our genetic makeup, and on the specific function of that muscle (e.g. our postural muscles have a high percentage of the fibres that are good for endurance).  

There is evidence to suggest that we can alter the composition of fibres in our muscles, but genetics will determine how much of a shift can occur.

Below are the three fibre types and why they provide particular advantages:  

Type 1 (slow twitch): contract slowly and produce energy slowly but efficiently.
Type 2a (fast twitch oxidative): contract quickly and produce energy slowly but efficiently (similar to slow twitch).
Type 2b (fast twitch glycolytic): contract quickly and produce energy quickly to facilitate quick subsequent contractions but fatigue more quickly.

Understanding the composition and function of our muscle fibre types can help us tailor our training programs to maximise our strengths and address our weaknesses

Efficient fuel utilisation and metabolic flexibility

Metabolic flexibility refers to the body's ability to switch between different fuel sources (carbohydrates/glycogen and fats) based on availability and demand.

Poor metabolic flexibility (or metabolic inflexibility as it is known) is associated with metabolic disorders such as obesity, insulin resistance and type 2 diabetes.

When it comes to training, your ability to switch between fuel sources ensures you have sustained energy and can manage longer and harder sessions.

Skeletal muscle (the muscles that connect to your bones and allow you to perform a wide range of movements and functions) accounts for more than 95% of energy requirements during exercise.

Fuel sources combine and switch to provide the necessary energy for working muscles.

Therefore, exercise requires good metabolic flexibility to increase energy supply from all these different fuel sources to support the energy demands of our skeletal muscles.

Tendon adaptations: strengthening connections

Our tendons play an important role in movement performance as it is the tendons that transmit the forces produced by the muscles to the skeleton and, therefore, contribute to performance during various movements.

When it comes to training, tendons undergo significant adaptations in response to training such as increased collagen synthesis and increased resilience (tendon stiffness).

Tendons are mostly made of collagen. Collagen fibres are flexible, strong and resistant to damage.

A tendon’s structure is similar to a rope with small collagen fibres arranged together. The collagen fibres provide tendons with their mechanical durability and strength.

Resistance training stimulates collagen production, increasing the total number of collagen fibres, which strengthens tendons.

Training also enhances tendon stiffness. Stronger tendons can store and release more elastic energy, improving performance.

Conclusion

Training adaptations are the foundation of improved fitness, performance and health.

By understanding the physiological changes that occur with regular training, we can optimise our exercise programs to achieve specific goals, whether they are related to endurance, strength or overall health.

References:

Timothy Morris