Muscle: the engine of our body
Skeletal muscle is made up of muscle fibers, which are the structures that allow it to contract and produce movement. There are different types of muscle fibers with specific characteristics: slow-twitch, fast-twitch, and intermediate fibers. Slow-twitch fibers, also known as type I or red fibers, obtain energy through the use of oxygen (aerobic metabolism) and are highly resistant to fatigue, but they produce less force and have a slower contraction speed. In contrast, fast-twitch fibers—also known as type IIx or white fibers—primarily rely on anaerobic metabolism (without using oxygen) and fatigue more easily, but they generate greater force and can contract much more rapidly. Intermediate fibers, or type IIa fibers, have characteristics that fall between slow- and fast-twitch fibers and have the ability to slightly “transform” their metabolism.
The proportion of different fiber types varies in each muscle and can differ from person to person. In other words, some individuals have a higher proportion of slow-twitch fibers, while others have more fast-twitch fibers.
How muscle composition influences different types of physical activity
Each type of sport places specific demands on muscle. For example, if we plan to run for an hour, we will mainly rely on fibers with strong aerobic metabolism that can tolerate fatigue as time passes—namely, slow-twitch fibers.
However, if the goal is to sprint 100 meters at maximum speed, we need to recruit fibers with a faster contraction capacity that can deliver maximum power. In this case, fast-twitch fibers will be used predominantly.
Think of muscle as the captain of a large army made up of soldiers with different characteristics. In a situation that requires fast, explosive force (such as throwing a heavy object as quickly as possible), the captain will rely on the strongest and fastest soldiers (fast-twitch fibers). On the other hand, if the task is to run all day to gather supplies, the captain will turn to the soldiers who are more resistant and tire less easily (slow-twitch fibers). Clearly, if most missions involve endurance-based tasks rather than power-based ones, having a higher proportion of resistant soldiers will always be more useful.
The same applies in sports. If the sport you practice has a strong endurance or power component, having a greater proportion of the fibers best suited to that demand will always be an advantage, as you will have more “resources” to draw on when needed. In fact, many studies have focused on analyzing which fiber types are predominant in athletes from different disciplines, revealing that there is indeed a relationship between fiber composition and suitability for certain sports.
Train however you want—but by your own rules
Although a certain muscle composition may improve aptitude for specific types of sport, this does not mean it limits us when practicing any activity, nor that improvement is not possible. In fact, training can slightly transform the metabolism of some fast-twitch fibers (IIx), making them behave more like intermediate fibers (IIa), which increases endurance capacity.
In addition, training can also increase the cross-sectional area occupied by a specific fiber type, enhancing endurance or strength depending on the stimulus applied and improving performance in a particular sport.
However, it is important to keep in mind that differences in muscle composition influence how we plan training programs. Returning to the muscle army analogy: if my team is made up mostly of strong but not very resistant soldiers, and I need them to gather supplies, where should I send them? They could go to a distant location along an easy route with few obstacles, or to a nearby place that requires much greater strength because they will need to lift very heavy loads along the way. Which option do you think would work better? As you may have guessed, the second strategy would likely be more successful. Forcing these soldiers into extreme endurance tasks would probably exhaust them and waste their true potential. The same applies to our muscles. While they can adapt to different loads, they will always perform better and make the most of their capabilities when training stimuli are aligned with their inherent characteristics.
In summary, depending on the predominant fiber type in each individual, it is advisable to adjust training intensity, volume, and rest periods to avoid overloading muscles and to optimize performance. That is why understanding your muscle composition is a great starting point when planning training routines or improving performance.
As you can see, biology also plays a major role in sports performance, and the same training plan does not have to work for everyone. Getting to know yourself better in this regard and applying personalized guidelines can help you reach your goals more efficiently while reducing the risk of injury and overtraining.
<p>Think of muscle as if it were the captain of a large army of soldiers with different characteristics. In a situation that requires quick, explosive force (such as throwing a heavy object as fast as possible), the captain will call on the fastest and strongest soldiers (fast fibres). If, on the other hand, they have to run for a whole day to fetch supplies, they will call on those soldiers who are more resistant and do not tire easily (slow fibres). Obviously, if most of this army’s missions consist of fetching supplies, an activity that requires more endurance than power, a higher proportion of resistant soldiers will always be more useful. </p><p>The same is true in the field of sport. <b>If the sport you practise has a very high endurance or power component, having more fibres suited to that effort will always be a plus</b>, as you will have greater ‘resources’ to draw on when the time comes. In fact, a large number of studies have focused on analysing which type of fibres are most prevalent in athletes from different disciplines, revealing that there is indeed a relationship between the proportion of these fibres and aptitude for certain sports. font-style: normal;”>Train however you want, but on your own terms<br /></h2><p style=”font-size: 18px; font-style: normal;”>Although a certain muscle composition can improve our aptitude for certain types of sport, this does not mean that it limits us when it comes to practising any of them or that a certain degree of improvement is not possible. In fact, <b>training can slightly transform the metabolism of some fast fibres</b> (IIx) to make them more like intermediate fibres (IIa), which would mean an increase in endurance capacity. </p><p>In addition, through training it is also possible to increase the muscle area occupied by a certain type of fibre, which can increase endurance or strength depending on the type of stimulus and improve our abilities for a specific sport.
However, it should be borne in mind that differences in muscle composition influence training planning. Returning to the example of the army of muscle fibres, if I want my team, which is mainly made up of soldiers who are not very resilient but very strong, to go and fetch supplies, where will I tell them to go to find them? They could go to a place that is very far away but with an undemanding route, without many obstacles, or to a place that is nearby but much more demanding in terms of the strength they will need to exert, as they will have to lift some very heavy weights along the way. Which do you think would be the best option? As you may have guessed, the second strategy would probably be more likely to succeed. Forcing these soldiers to follow extreme endurance guidelines would probably exhaust them and we would be wasting their true potential. The same is true of our muscles. Although we can subject them to certain types of loads and they will adapt, they will always perform better and make better use of their capabilities when we adjust the stimuli they receive to their own characteristics.
In summary, depending on the percentage of fibres that each person has, it is advisable to adjust the intensity, volume and rest periods to avoid overloading the muscle and optimise its performance. Therefore, knowing more about your muscle composition is a good start when it comes to planning your training routine or improving your performance.
As you can see, in the field of sports, our biology also has a lot to say and the same training routine does not necessarily work for everyone. Getting to know yourself better in this regard and applying personalised guidelines can help you achieve your goals more efficiently while reducing the risk of injury and overtraining.
