Why aren’t marathon runners able to ace 200-meter dashes, and why do sprinters struggle to do long-distance running? Well, it is possible that their muscles favor either type of physical activity.
Certain genes influence the capabilities of our muscles and play a key role in shaping our athletic abilities.
Genes Influence Many Aspects Of Fitness, Including Your Weight Loss Ability With Exercise.
Types Of Muscle Fibers and Physical Performance
There are two main types of muscle fibers: slow-twitch (type I) and fast-twitch (type II).
Slow-twitch fibers, also known as "red" fibers, are rich in blood vessels and mitochondria and are used primarily for endurance activities such as marathon running.
Fast-twitch fibers, also known as "white" fibers, have fewer blood vessels and mitochondria and are used primarily for explosive activities such as weightlifting.
The proportion of slow-twitch to fast-twitch fibers in an individual's muscle tissue can influence their physical performance.
Individuals with a higher proportion of slow-twitch fibers tend to excel in endurance activities.
In comparison, individuals with a higher proportion of fast-twitch fibers tend to excel in explosive activities like sprinting and weightlifting.
Training can also influence the proportion of muscle fibers, as endurance training can increase the proportion of slow-twitch fibers and strength training can increase the proportion of fast-twitch fibers.
ACTN3 Gene and Muscle Fiber Distribution
The ACTN3 gene contains instructions to produce the alpha-actinin-3 protein, which is found primarily in fast-twitch muscle fibers.
Variations or changes in the ACTN3 gene have been linked to differences in muscle fiber type distribution and athletic performance.
For example, a change denoted by “R577X” (also called rs1815739) in this gene is associated with changes in muscle fiber distribution due to the levels of the alpha-actinin-3 protein.
People can have RR, RX, or XX type of ACTN3 gene.
| Genetic change | Implication |
| RR (or CC) | More fast-twitch fibers; likely better sprinting performance |
| RX (or CT) | A mix of fast and slow-twitch fibers; favors both sprinting and endurant activities |
| XX (or TT) | More slow-twitch fibers; likely better endurance performance |
However, this is not the only factor determining muscle fiber distribution and athletic performance; other genetic and environmental factors also play a role.
Did You Know?
The ACTN3 gene is not just an indicator of speed or endurance performance.
It also affects other aspects of physical performance like
- Exercise adaptation
- Exercise recovery
- Sporting injury risk
How To Build More Slow-twitch Muscle Fibers?
To build more slow-twitch muscle fibers, an individual can engage in endurance training, such as:
- Long-duration, low-intensity cardio: Activities such as steady-state running, cycling, or swimming at a moderate pace for prolonged periods can help increase the proportion of slow-twitch muscle fibers.
- High-rep resistance training: Performing resistance training exercises with a high number of reps (15-20) and a moderate weight can also help to increase the proportion of slow-twitch muscle fibers.
- Interval training: Alternating periods of high-intensity and low-intensity cardio, such as sprints and steady-state running, can also help increase the proportion of slow-twitch muscle fibers.
How To Build More Fast-twitch Muscle Fibers?
To build more fast-twitch muscle fibers, an individual can engage in power and strength training, such as:
- High-intensity, low-rep resistance training: Performing resistance training exercises with a low number of reps (1-5) and a heavy weight can help to increase the proportion of fast-twitch muscle fibers.
- Plyometric training: Jumping, bounding and other explosive movements can help to increase the proportion of fast-twitch muscle fibers.
- Heavy weight lifting: Doing exercises like powerlifting, deadlifting, squats, and Olympic weightlifting is known to be effective in building fast-twitch muscle fibers.
It's important to note that muscle fibers are not completely fixed, but they can adapt to different types of training.
The body can modify the proportion of fibers, but this process is slow and not completely predictable.
It's also important to remember that building muscle fibers is not the only factor in physical performance; proper nutrition, power and strength training techniques, and muscle recovery also play important roles.
Summary
Research has shown that variations or changes in the ACTN3 gene can impact muscle fiber type distribution and athletic performance.
The R577X variation in ACTN3 is related to an increase in slow-twitch muscle fibers and better endurance performance since it results in no/low ACTN3 protein activity.
On the other hand, high ACTN3 protein activity is connected to more fast-twitch fibers and improved power and sprint performance.
It's worth noting that the ACTN3 gene isn't the sole factor that affects muscle fiber distribution and athletic performance; other genetic and environmental factors are also involved.
Training methods such as endurance and strength training can also affect muscle fiber distribution, but it's a gradual process, and the outcome is not fully predictable.
