Muscle Fiber Recruitment

One thing that tends to get lost when it comes to different training techniques is an understanding of muscle fiber recruitment.

I had a client of mine that is in my Fat Loss class come up to me this past week telling me how great she felt when she was out in Colorado and hiking around and how the class really prepared her for the endurance that she was going to need.

My class doesn't focus on slow steady cardio or aerobics. The focus is on fat loss and increasing strength and muscle.

So why did her endurance increase when she wasn't training for endurance?

It's because indirectly she was and it comes down to the types of muscle fibers that are used and recruited.

There are three different kind muscle fibers:

1. Type I muscle fibers (aka slow twitch muscle fibers) – These fibers develop force very slowly and at the same time, relax slowly and can withstand fatigue for long periods of time. These types of muscle fibers have a high capacity for activities such as a marathon, soccer and distance cycling. Basically, you are going at a sub maximal pace for a long period of time. These fibers are used in what is classically called “endurance” exercises and activities.

2. Type IIa muscle fibers (aka fast twitch muscle fibers) – These fibers can develop force faster than the type I fibers but, also get fatigued faster. These fibers involve activities that are a little more quicker and powerful with intensity than the type I fibers, such as an 800 meter run, some strength training workouts like in the Lean Body Fat Loss Training class, interval training, and what I like to call, metaval training.

3. Type IIb muscle fibers (aka fast twitch muscle fibers) – These are the most powerful muscle fibers that we have. These are the fibers that are able to develop force very rapidly, but, at the same time, they fatigue very rapidly. These include activities such as a 100-m sprint, a maximal lift of a weight, or a vertical jump.

No matter what type of activity you are doing (for the most part), your muscles are recruited in a particular order: First the Type I's are recruited, then if needed your Type IIa's are recruited, and finally if necessary your Type IIb's are recruited.

So if you're doing just a normal walk, you'll recruit your Type I muscle fibers but that will be about it. If you are doing some bodyweight squats or lunges, you'll first recruit your Type I muscle fibers, then you'll more than likely recruit your Type II muscle fibers. If you added a barbell full of weights onto your shoulders and completed more squats that was incredibly intense, you would first recruit the type I fibers, then the Type IIa muscle fibers, and finally you'd probably recruit Type IIb muscle fibers.

When you start to increase the maximal strength of your Type IIa and Type IIb muscle fibers, you are also at the same time increasing the strength of your Type I muscle fibers, because those have to be recruited as part of the mix when you are lifting things to strengthen the Type IIa and Type IIb muscle fibers.

So in essence, you are increasing your maximum abilities when training your Type IIa and Type IIb muscle fibers, and also increasing your SUB-MAXIMAL abilities of the Type I muscle fibers.

That's why my client had an easier time out hiking with the strength training she did in Lean Body Fat Loss class then if she simply did low, sub-maximal walking.

You can follow the same type training with the monthly fitness routines that I offer. It's a great way to train not only for gaining strength and building muscle but will also help you build up endurance for a 5K, 10K, a full marathon, as well as a hiking trip.

So don't be afraid to train at a higher intensity level than what you are going to use for. In the end, the order muscle fiber recruitment can be used to cover all increases in strength at all levels.

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