Knowledge Base

Power and speed predisposition

Predisposition to power/speed sports

Different sports have differing proportions of power/speed and endurance elements. In certain sports, more power potential is necessary, whereas in others it is about endurance. Power indicates how much work the muscle can perform in one go. Some people have high stamina and can easily handle a long run, but they are not as good at sprinting. While others are fast and can lift weights, but they fatigue quickly.

Sporting performance is partially determined genetically (by up to 70%), in having a predisposition to power/speed or endurance sports. This can be evident in the proportions of fast and slow twitch muscle fibres, the ability to utilise oxygen and the body’s energy reserves, the level of cardiac activity, the quantity of red blood cells, and the capacity of the lungs. Your gene variants affecting these properties can tell you which type of exercise is most effective for you.

ACTN3 gene variants

The ACTN3 gene is an example of a gene that has a significant impact on our predisposition to power-speed muscle properties. It is only used in fast twitch muscle fibres where it creates the protein alpha-actinin 3. Comparative studies have shown that people with mutations in both copies of the ACTN3 gene find it almost impossible to become Olympic athletes in power/speed sports. They have a genetically low proportion of fast-twitch muscle fibres . Estimates put the number of such people in the world at 24% of the global population.


Skeletal muscle makes up the majority of our muscles and accounts for approximately 40% of our body weight. The muscles are mostly attached to bones via tendons largely composed of collagen, and, as the name suggests, skeletal muscle is responsible for the movement of the skeleton. It consists of muscle fibres, which are amongst the largest cells in our bodies (their average length is around 3cm, but can reach up to around 30cm in the case of the sartorius muscle!), and they are formed by linking many individual germ cells.  

Muscle fibres are arranged parallel to the long axis of the muscle. Each fibre is sheathed in connective tissue that bundles the fibres in muscle groupings called fascicles (containing between 10 and 100 muscle fibres), that are combined to form the muscle. The entire muscle is sheathed in a layer of connective tissue that becomes tendons and ligaments at the end of the muscle attached to the relevant bone. Alongside collagen and elastic fibres, the connective tissue also houses nerves that control the muscles and blood vessels that nourish the muscles and supply them with oxygen. 

Types of muscle fibres
Muscle fibre can be divided into two basic types: fast and slow twitch fibres.

Type 1

Slow twitch fibres (also known as type I fibres) are mainly responsible for endurance, but they are not great for strength. They are relatively thin albeit with a rich blood supply and use the maximum supply of oxygen to work. They contain a large amount of myoglobin (a substance related to haemoglobin able to bind oxygen and help the working muscle with its oxygen supply) and mitochondria (cell energy “factories”, which help create energy for the working muscle). The high concentration of myoglobin gives muscles with a high proportion of slow twitch fibres their red colour.

Type 2

The second type of fibres are the fast twitch fibres (also known as type II fibres), which are responsible for muscle strength and speed, but they fatigue very quickly. They are bulkier than the slow twitch fibres and have either a moderate or low blood supply. The moderate blood supply muscle fibres (type IIA) have a little more endurance, yet are still able to develop intense strength. The low blood supply fibres (type II) contain very few mitochondria and are therefore unable to work for a long time, but they can develop the greatest strength and are able to work well under briefly reduced oxygen levels.