If you have red fibers you will never be able to have muscles. Or: if you have white fibers you will never have great resistance. How many times have we heard it repeated, in the gym as well as among endurance athletes? Well, according to a very recent study by the University of Ghent in Belgium, building muscle does not depend on slow or fast fibers. That is, increase muscle volume, or strength capabilities, it is not limited or predisposed by the prevailing muscle fiber type that each of us is genetically endowment. And furthermore, again according to this research, there would not even be an “interference” between the 2 types of muscle fibers. But let’s go in order.
Slow or fast fibers: what they are and how they are defined
Slow or fast fibers is a very popular way to distinguish between the type I muscle fibers (precisely so-called slow, red or ST, from the English slow titch) not type II muscle fibers (or fast twitch fibers, white or FT, from English almost impossible)which are in turn divided into type IIa and type IIb fibers. There is also a third type of fibre, called intermediate fibre, but for the moment let’s focus on the two main objects of study by the Belgian researchers.
The type I fibers, red or slow, are those that generate low levels of force contraction but they have high resistance to fatigue: they are typically used in endurance sports, from running to cycling to triathlon and so on, but also in work with overloads if the repetitions are numerous, for example for exercises with low load but more than 20 repetitions. By virtue of these characteristics they also have a low glycogen content.
The type II, or white, fibers can instead generate high contraction forcebut have low resistance to fatigue: they are therefore those recruited mainly for strength work in the gym, with other loads and few repetitions, and also have a high glycogen content, necessary and indispensable for that type of contraction.
White fibers and red fibers: does genetics really matter?
From what world began (in sport) it is said that genetics is in charge, and that if you are born white you will be able to excel in sports where you need a fast contraction with great expression of strength, and if you are born red you will be able to excel in endurance sports but you will hardly be able to become “muscular”. To the naked eye: a bodybuilder has muscles, and they’re made of white fibers, a marathon runner doesn’t have muscles, but red fibers.
Said by greatly simplifying the concept and talking about sporting excellence, because then of course nothing prevents those with red and slow fibers from lifting weights and those with white and fast fibers from running benefiting from it.
Building muscle does not depend on slow or fast fibers
Here it is: now the research conducted by Kim Van Vossel and Wim Derave of the University of Ghent in Belgium and published in the Journal of Physiology (Can muscle typology explain the inter-individual variability in resistance training adaptations) would prove that having endurance- or speed-oriented muscle fibers does not determine response to strength training. Which is interesting for athletes in the prime of their competitive activity, but also for those over 50 who have to start thinking that doing some strength training is the best insurance for aging well, as we reported in this article on strength training. strength after 50 years.
Thanks to a new non-invasive method for estimating the proportion of slow- and fast-twitch fibers in a given muscle, the Ghent University team had a group of 11 slow-fiber and 10 fast-fiber volunteers a ten-week strength training program. The workouts consisted of three to four sets of four different exercises, targeting specific muscles in the legs (quads and calves) and arms (biceps and triceps). Each series was performed until exhaustion, with a weight equal to 60% of the maximum.
And here’s the interesting part: they trained one arm and one leg on Monday, Wednesday and Friday, and the other arm and leg only on Monday and Friday. After measuring muscle size and force expression with an MRI it emerged that all subjects achieved bigger muscles, with overall increases ranging from 3 to 14%, and increased strength capabilities, with increases from 17 to 47%. But in all of this the type of fiber didn’t matter, i.e. the type of muscle fiber had no impact on the training outcome.
Even more interesting is that no interaction was found between fiber type and exercise frequency: The idea that fast-twitch subjects could have achieved better results with training twice a week has been debunked by the facts.
Instead, what was decisive was the amount of training. Both fiber types experienced larger increases in limbs trained three times a week compared to those trained twice a week. This may seem obvious (the more you train = the better results you get) but in reality it dispels the myth that the results in terms of strength and hypertrophy depend very much, if not exclusively, on the type of muscle fibers that genetics has given to each one our.
Right, slow-fiber subjects had to rack up more reps to get the same gains, which is why the test was performed with exhaustion runs of training sets with a load at 60% of the maximum. This is also quite obvious and normal, because fast-twitch muscles are more fatigued, so fast-twitch individuals tend to reach exhaustion sooner at a given relative intensity.
So much so that in the study the slow resistance subjects were able to complete a greater number of repetitions at 60% of the maximum, i.e. they lifted an average of 25% more weight over the course of the training period of ten weeks.
This suggests that if the training program had been assigned a certain number of repetitions at a certain relative intensity, the fast-twitch subjects would have gained more muscle. But if you train to a certain level of fatigue (failure, in this case), everyone gains the same amount of muscle.
READ ALSO: How to train with weights: reps, sets, load and recovery
Photo by Ryan Snaadt / John Arano / Anastase Maragos
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