Train for functional hypertrophy and strengthen your powerful fast-twitch fibers to perform better. Whether you are an elite strength athlete, a recreational trainee, or a your only goal is to lose weight, training the muscle fibers optimally will give you better results. Even endurance athletes will benefit from functional hypertrophy because it has been shown to increase time trial performance and speed.
A new review in the Journal of Strength and Conditioning Research shows how different training modes affect fiber type distribution. Remember, there are at least seven fiber types in the current literature, but for the purposes of this tip, we’ll look at the type I, type IIa and type IIx fibers.
The type I fibers are slow-twitch and they produce low amounts of strength and power, but are very fatigue resistant. The type II fibers are called fast-twitch and they produce high amounts of strength and power, making you fast and explosive. They fatigue quickly. Within the type II fibers, the IIa fibers are less powerful but have more endurance than the type IIx fibers, which are most powerful but fatigue most rapidly.
Strength and power athletes have been found to have significantly more fast twitch fibers (60 to 80 percent) than endurance athletes (40 to 10 percent), which is thought to be due both to the effect of training and natural fiber distribution. Research shows strong correlations exist between the percent of type IIa fibers and the 1RM in the snatch lift, and in vertical jump height and power, indicating the value for strength and power athletes. The benefits are just as great for the general population because stronger type II fibers will make you more coordinated and decrease your risk of falling and breaking a bone, especially as you age.
There is clear evidence that resistance training will shift type IIx fibers to type IIa, and there is emerging data that it’s possible to shift from type I to type II by doing a mix of high velocity training and heavy lifting. For example, one 6-week study showed a 50 percent decrease in type I fibers and the corresponding increase in type IIA fibers in participants who performed a heavy 3RM bench press for 5 sets on Mondays, 10 bench press throws on Wednesdays, and 5 sets of 10 stretch-shortening cycle push-ups on Fridays.
It’s this combination of high speed and heavy load training that appears key in producing a shift from slow- to fast-twitch fibers. In comparison, simply lifting with a heavy load doesn’t produce the shift.
Of interest, other studies show that immobilizing a limb will reduce the percentage of type 1 fibers by as much as 10 percent with an increase in type IIx fibers. Although this may appear to be a preferred fiber type profile for the power athlete, it is suggested that the type IIa fibers are most favorable because even though they produce slightly less power, they have the capacity to sustain that power production for real-world sports application.
To apply the evidence about fiber types to training, try a high speed, heavy load program to increase your strength, power, and type II fiber distribution.
Bodybuilders will benefit from targeting the fast-twitch fibers from training since cross sectional area of the muscle will be larger in type II than type I fibers, meaning growing these fibers will produce more mass and shape.
For the general population, doing a wave-like periodized program that includes accumulation and intensification should increase, type II fiber strength and build functional hypertrophy.
Endurance athletes can also benefit from training for greater type IIa fiber distribution. Research shows they won’t gain body mass because the aerobic training they do will inhibit muscle mass gains.
For example, a study of elite cyclists showed that concurrent strength and endurance training will increase the proportion of type IIa fibers and decrease type IIx, without inducing significant muscle mass gains. Rather body weight was maintained and the athletes experienced a small increase in muscle mass that was counteracted with a loss of body fat to produce a more favorable body composition for performance. Short- and long-distance time trial performance was increased in the cyclists by 5 percent and 8 percent, respectively.
To read more about muscle fiber types, and to have all your questions about Functional Hypertrophy Training answered, check out this article
Aagaard, P., Andersen J., et al. Effects of Resistance Training on Endurance Capacity and Muscle Fiber Composition in Young Top-Level Cyclists. Scandinavian Journal of Medicine and Science in Sports. 2011. Published Ahead of Print.
Wilson, J., Lenneke, J., et al. The effects of Endurance, Strength, and Power Training on Muscle Fiber Type Shifting. Journal of Strength and Conditioning Research. 2012. 26(6), 1724-1729.