Power-Based Athletic Performance and IL6

Interleukin-6 (IL-6) is a cytokine — a signaling molecule released by cells to interact and communicate with other cells. It’s best known for its role in the immune response. Research shows that, depending on the situation, IL-6 can have either pro- or anti-inflammatory properties [R]. Its important role in the immune system may even contribute to some genetic differences in longevity.

But did you know that apart from the immune system, IL-6 also plays an important role in our muscles? So much so, in fact, that it has been dubbed an “exercise factor” by some scientists due to its effects [R].

Using your muscles causes them to make and release IL-6, which is why blood IL-6 levels increase during exercise. Exactly how much IL-6 gets produced depends heavily on the intensity and duration of the exercise. For example, IL-6 blood levels can increase by as much as 100-fold after a marathon race [R, R, R]!

Research suggests that muscle-derived IL-6 works mainly in an anti-inflammatory fashion, and that many of its effects are generally beneficial. Some studies have reported that it helps control blood sugar levels by signaling the liver, and that it may be responsible for fat-burning during exercise (by signaling the fat tissue). In addition, some studies found that muscle-derived IL-6 may also counteract the effect of other, pro-inflammatory cytokines, thereby potentially preventing insulin resistance, as well as cardiovascular issues such as hardening of the arteries (atherosclerosis) [R, R, R, R, R].

IL-6 is released by muscles during exercise. Some studies have shown that muscle-derived IL-6 works in an anti-inflammatory fashion, may help burn fat and maintain blood sugar levels, and may even prevent insulin resistance and promote overall cardiovascular health.

When it comes to exercise, there is one SNP in the IL6 gene in particular that stands out: rs1800795 (also known as the “-174G>C” polymorphism). Several studies have reported a link between the ‘G’ allele (especially the ‘GG’ genotype) of rs1800795 and the likelihood of a person engaging in power-oriented sports [R, R, R, R].

Based on these findings, some scientists suggest that carriers of the ‘G’ allele may have an advantage when it comes to performing in power-based sports, such as sprinting [R, R].

For example, power-oriented athletes (jumpers, throwers, sprinters) were more likely to have the ‘GG’ genotype compared to endurance athletes (cyclists, runners) and nonathletes [R, R].

Similarly, people with ‘CC’ or ‘CG’ genotypes were less likely to be power athletes [R].

However, it’s important to recognize some significant limitations of these studies. One is the limited number of participants — only a couple hundred per study — which is usually not considered a enough people to look at when trying to detect the subtle genetic influences of individual SNPs. Another is that these studies were more-or-less focused only on European populations. Therefore, while these findings are suggestive, they will still need to be fully verified by studies in larger and more diverse populations.

Studies suggest that the ‘G’ allele and the ‘GG’ genotype of rs1800795 may be more common in power athletes, and therefore may be beneficial for performance in power-based sports such as sprinting, jumping, and throwing.

Muscle tissue is dynamic — it adapts to both the nature and intensity of muscle use. That’s why your muscles get bigger when you exercise, and vice versa: if you don’t use your muscles, you gradually lose them [R].

When it comes to exercising, gradually increasing the intensity of exercise can help avoid muscle damage — which often happens in people who are less experienced and/or try to do too much too soon [R]. There is a specific type of exercise that may lead to greater gains in strength and muscle mass than other types of exercise — but it can also cause greater muscle damage. It’s called “eccentric” exercise [R]. Eccentric exercise refers to movements that lengthen a muscle under tension, such as lowering a weight/dumbbell, the downward motion of a squat or a push-up, or lowering the body during a crunch or a pull-up.

The inflammation that happens in response to eccentric muscle damage helps in muscle repair [R]. Research shows that IL-6 helps muscles recover after damage due to this type of exercise. For example, IL-6 generally stays in the blood longer after eccentric exercise compared to other types of exercise, such as running [R, R].

The ‘C’ allele of rs1800795 has been associated with lower blood IL-6 levels and greater increases in creatine kinase, a biological marker of muscle damage. As a result, scientists have suggested that ‘C’ allele carriers may have increased muscle damage following resistance training, and therefore may be under-represented among athletes that require such training [R].

Conversely, that’s why in power-oriented sports — which are associated with more muscle damage during training or competition — athletes with ‘GG’ genotypes may benefit from faster recovery times, giving them a slight genetic edge over their competition [R].

Studies suggest that IL-6 helps in muscle repair after damage due to eccentric exercise. The ‘C’ allele of rs1800795 has been associated with increased muscle damage after resistance training.

You can see your genetic data for this IL6 SNP in the table below. However, keep in mind that these results are based on association studies finding that certain genotypes are more common in particular kinds of athletes when looking at relatively large numbers of people. In other words, just because you have a certain variant for this SNP doesn’t mean that you can’t be a good power athlete!

IL6 rs1800795:

• ‘GG’ (homozygous major genotype): Relatively faster recovery after muscle damage from eccentric exercise; more likely to be a power athlete.
• ‘C’ allele: Relatively slower recovery after muscle damage from eccentric exercise; somewhat less likely to be a power athlete.

About 23% of people in the world carry the minor ‘C’ allele. This variant, however, is much more common in Europeans, where the majority of people (69%) have it.

However, remember that this doesn’t mean that all successful power athletes have the ‘GG’ genotype! It only means that, statistically, people with the ‘CC’ genotype tend to be less common in power sports compared to endurance sports, or compared to the general population.