Muscle Power

What is muscular fitness?

There are three core components relating to muscular fitness, which include; muscular strength, power and endurance. Muscular strength is the amount of force a muscle can produce with a single maximal effort. Muscle power combines speed and strength and refers to your body’s ability to produce maximum force in the shortest amount of time. Muscle endurance refers to a person's ability to exert force over a sustained period of time [1] Jump to reference section: [1] .

What role do genetics play in muscular fitness?

Muscle power and endurance vary considerably from person to person, and are influenced by both environmental factors such as training and lifestyle as well as a person's genetics. For most people, the affect of genetic variation on muscle attributes is small, but there are some major effects that have been discovered. For elite athletes, knowing your specific genetic variation may help to provide guidance when developing a personalised training regime, but this is still an area of active research.

PPARα (rs4253778) is one of the genes that influences the efficiency of switching from burning carbs to burning fats. Some versions of the gene can affect how flexible your body is at using fat as fuel. In sports that require sustained energy release (for example, long-distance running), different genetic variants may result in greater efficiency in burning fat. Individuals with the PPAR-α GG and GC genotypes burn fat at a greater rate in muscle cells compared to individuals with the CC genotype. PPAR-α C allele carriers are (on average) potentially better predisposed to intense anaerobic performance (e.g. sprinting or weightlifting).

Fast twitch vs slow twitch muscle fibers

Skeletal muscles are made up of bundles of individual muscle fibers (called myocytes) which contain many strands of proteins (actin and myosin). When these proteins attach to one another and pull, it causes your muscle to shorten which results in a muscle contraction [2] Jump to reference section: [2] .It is generally accepted that muscle fiber types can be broken down into two main types: slow twitch (type I) muscle fibers and fast twitch (type II) muscle fibers [3] Jump to reference section: [3] .

The gene ACTN3 (rs1815739) plays a role in muscle fiber composition specifically contraction of fast-twitch muscle fibers. Having a T allele at the position ACTN3 reduces the fast-twitch muscles fibers function. Therefore people with variant T in ACTN3 have a greater likelihood of activating slow-twitch muscles which are resistant to fatigue, and this could result in a potential advantages for endurance training. On the other hand, people with variant C in the ACTN3 gene do better with sprinting and or weightlifting which requires fast-twitch fibers.

The ACE gene codes for an enzyme that helps regulate blood pressure. ACE is able to convert Angiotensin I to Angiotensin II which causes the blood vessels to narrow. This increases blood pressure and can be beneficial for strength and power training.

Those with allele G for rs4343 have, on average, a higher level of the ACE enzyme, which may mean benefits for sprinting / power training. Those with allele A have less ACE enzyme on average, predisposing these people better for endurance training.

Angiotensinogen (abbreviated to AGT) is a regulator of blood pressure (body salt, and fluid balance) which works to convert angiotensin I to angiotensin II (similar to ACE). The G allele of rs699 is associated with an increased amount of AGT in the blood which leads to higher levels of angiotensin II. Higher levels of AGT would likely lead to greater muscle growth following power training.

How can knowing your genetic response to power and endurance training change the way you exercise?

Based on the analysis of your genetic predispositions in the genes affecting your muscle composition and activities, you may experience different benefits and challenges from engaging in power/endurance activities. It’s important to note that genetics plays only a partial role and for casual athletes, the effects are likely minimal compared to the effect of regular training. However, for elite athletes or for people falling on the extreme end of genetic predisposition the effects may be larger and more noticable.

Conclusion

We all have different genetic predispositions that affect our muscle fiber types, metabolic capacity, cardiac response and energy production. For most people, these pre-dispositions are small compared to differences due to training and lifestyle, but they may be large for people on extreme ends of the distribution or for elite athletes training to their limit. However, for the casual athlete it is usually beneficial to keep a balance between power and endurance training.