Sequential Recruitment of Muscle Fibers For Maximal Muscle Gain

muscular man

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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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/

4 Responses

  1. John

    Thanks for the link. I think perhaps you have overcomplicated things a bit. The idea in that piece was to get behind the size principle a little and understand that if a weight is too heavy or too light you do not do a good job at recruiting all of the fibres. There is nothing special about the wall sit. I sometimes recommend it because it is a simple exercise for people to learn (low skill), scaleable ( do not start at 90 degree knees if you are not strong enough) and it needs no equipment. Motionless isometrics like this are an option, but normal exercise can recruit fibres in the same way. There is some controversy over what is the optimum time that it takes to work through the fibre hierarchy, but the point is to keep going towards failure. (See the posts I linked to in the intro)

    The other misconception I think is that speed protocols hit different fibre types – I am not convinced. A slow set to failure will eventually hit all the fibres. It is an approach that Art DeVany used to recommend however.

    By the way I’ve not forgotten about my promise to write something for you – it is just that work has been busy and sleep is more of a priority just now!

    All the best

    Chris

    • Chris,

      I think we can both agree that training to muscle failure will recruit the highest number of muscle fibers regardless of exercise selection or training protocol, but I’m still not convinced this is the best way to train for health-first hypertrophy. Training to failure may be the best way to maximize hypertrophy, but in my experience, one can get nearly the same gains with sub-maximal training and at a much lower risk of injury and over-training.

      The more I think about this though, the more that I agree that I’m making this too complicated for our own good. I’d love to see some more research done in this area, but I wouldn’t expect the results to be earth-shattering.

      Thanks for your comments, and take your time with the article – no hurry at all, but I am looking forward to reading it!

  2. Regarding plyometics – explosive moves etc, I tend to be cautious anyway as there is some risk of injury. There is a good review paper at http://www.medicinasportiva.pl/new/pliki/ms_2011_03_08_Fisher.pdf which has as one of its conclusions:

    Persons should maintain steady force production throughout a range of motion, and reduce external forces such as momentum; movements should be of a pace that maintains muscular tension, not ballistic or explosive in nature.Faster movements cause greater peaks in both muscular and ground reaction forces which likely transfer through joints and connective tissue, potentially causing injury

    That is a big thing for me – safety – as far as possible I want to avoid injury. Training should keep me functional…..

    • I agree that caution is a must with plyometrics, and they should only be used when they can be done safely – with good form, and with a good intuition regarding when form is deteriorating. So, plyometrics are not for most beginners and some intermediate trainees. I also agree with this paper’s findings that plyometrics are not the best stimulus for hypertrophy, but I am still curious if they best target one muscle fiber type over another.

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