Sequential Recruitment of Muscle Fibers For Maximal Muscle Gain

I was perusing the archives of Chris Highcock’s Conditioning Research blog, and I found this little nugget hidden amidst the rest of the June posts. The article is well-worth the read, but if you just want the abbreviated version, this is basically what it proposes: for strength and hypertrophy purposes, given that we want to maximize the amount of muscle fiber recruitment as much as possible, our exercise program should aim to target all fiber types (ie slow twitch and fast twitch muscle fibers).

Now, we’ve known about muscle fiber types for a long time, but the idea of programming our training to take all fiber types into account during one training session – even during one exercise – is new, at least to me.

Chris proposed that by performing a wall-sit exercise for a long enough duration, the body will automatically recruit all of the different fibers to maintain the pose. For instance, as the slow twitch fibers get fatigued, the fast twitch fibers will activate to compensate. It’s speculative, but that does make sense to me and seems plausible, but I’ve never been a huge fan of static contraction training as a standalone protocol. It’s a great exercise, yes, but how can we apply this idea to movements, which is what I’m really interested in?

So, here’s what I would propose is worth a test, and this is how I’d do it – if it were up to me. I’ve come up with two examples of applying the protocol to the squat exercise; one with a barbell, one without.

Barbell Squat: Example of Sequential Recruitment of Muscle Fibers

Going with Chris’ idea to target slow, intermediate, and fast twitch muscle fibers, here’s an example of manipulating the load to test the hypothesis. I would use the escalating intensity protocol (click here to learn about that) and do three blocks of each chosen exercise in a straight set format – resting 2-5 minutes between each set.

Slow Twitch Muscle Fiber Sets

1A: Barbell squat with working weight at approximately 30% of your 1RM – as many repetitions to achieve approximately 50% exertion
1B: Barbell squat with working weight at approximately 30% of your 1RM – as many repetitions to achieve approximately 70% exertion
1C: Barbell squat with working weight at approximately 30% of your 1RM – as many repetitions to achieve approximately 90% exertion

Intermediate Twitch Muscle Fiber Sets

2A: Barbell squat with working weight at approximately 60% of your 1RM – as many repetitions to achieve approximately 50% exertion
2B: Barbell squat with working weight at approximately 60% of your 1RM – as many repetitions to achieve approximately 70% exertion
2C: Barbell squat with working weight at approximately 60% of your 1RM – as many repetitions to achieve approximately 90% exertion

Fast Twitch Muscle Fiber Sets

3A: Barbell squat with working weight at approximately 90% of your 1RM – as many repetitions to achieve approximately 50% exertion (probably just 1 rep)
3B: Barbell squat with working weight at approximately 90% of your 1RM – as many repetitions to achieve approximately 70% exertion (about 1-2 reps)
3C: Barbell squat with working weight at approximately 90% of your 1RM – as many repetitions to achieve approximately 90% exertion (about 3 reps)

So, that’s 9 total sets of barbell squats using very different loads. There are 3 warmup sets, 3 working sets to build intensity, and 3 high intensity sets – and each bracket is using a very different load to target different muscle fiber types. Obviously, given that each bracket is done with a different weight, each set will produce very different repetition amounts as a result.

The question is, would it create the proper stimulus for hypertrophy, and if so, would it produce better results than a more traditional lifting protocol that does not take muscle fiber types into account (or my hypothesis of targeting the different fiber types with a specific load and speed protocol)?

Bodyweight Squat: Example of Sequential Recruitment of Muscle Fibers

Here’s another example using the bodyweight squat exercise that tests the hypothesis by manipulating the repetition speed.

Slow Twitch Muscle Fiber Sets

1A: Super-slow bodyweight squat or wall sit performed until 50% exertion
1B: Super-slow bodyweight squat or wall sit performed until 70% exertion
1C: Super-slow bodyweight squat or wall sit performed until 90% exertion

Intermediate Twitch Muscle Fiber Sets

2A: Normal pace bodyweight squats performed until 50% exertion
2B: Normal pace bodyweight squats performed until 70% exertion
2C: Normal pace bodyweight squats performed until 90% exertion

Fast Twitch Muscle Fiber Sets

3A: Jump squats (aka plyometric squats) performed until 50% exertion
3B: Jump squats (aka plyometric squats) performed until 70% exertion
3C: Jump squats (aka plyometric squats) performed until 90% exertion

Note: I tried the bodyweight squat version of this workout earlier this week, and I think it’s got some potential. My quads have grown 1.25 inches since Monday. Just kidding. I don’t take girth measurements. But I DID try the workout and it seems like it may be worth some more experimentation.

Of course, you could play around with the numbers a bit, but I think you get the general idea by now. Build intensity from set to set using an exercise protocol that will best target a specific muscle fiber type – and target each fiber type in the same workout. If you followed that protocol and chose 2 or 3 different exercises to work on each workout, you would likely be well served, but this is just theory, of course.

I’d also propose that if you know your dominant fiber type (ie if you know you’re more of a strength/power athlete as opposed to an endurance athlete, or vice versa (etc.)), that you should experiment with the order in which you do the exercises. You could try using your dominant fibers during your first work set or last set, for instance, and see which one allows you to do more work, and thus, obtain better results.

Then again, maybe we’re just making things way too complicated for ourselves. I’m a hopeless fitness geek. Thoughts?

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CST Coach, CST-KS
Health-First Fitness Coach

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P.P.S. As Chris pointed out in his post, you can do a little bit of further reading on this topic here and here.

P.P.P.S. Photo credit: http://www.flickr.com/photos/neeterz75/