The 3 Bears: A Story of Muscle Fiber Activation

By Lindsay Kent
BeautyFit Blog

Having a plan in place is one of the most important weapons you can have in your training arsenal. Without one you end up with a cluttered mess of loads and principles, lacking a planned progression of exercises and repetition ranges built to suit your individual needs and goals. There is so much information out there, and the scientific evidence for what are the “best practices” is constantly evolving, but there are some key principles that do not hinge on one training concept or trend. By incorporating them, you’ll be able to keep your individualized approach at the forefront, tweaking your program as needed to keep progressing.

The Goldilocks Load

The Goldilocks Load functions much like the tale that it is named after, offering an approach that is not too hot, not too cold, but just right regarding your body’s muscle fiber spectrum.

It will deliver optimal growth to help you create a lean, sleek, muscular physique. The Goldilocks Load focuses on the relationship between the load you are lifting and the time under tension by homing in on the body’s “three bears,” the three main muscle-fiber types—slow twitch, intermediate twitch, and fast twitch.

The slow-twitch fibers recover quickly and are used during longer, endurance-type training. The intermediates are more powerful but do not last as long as the slow-twitch fibers, while fast-twitch fibers, the slowest to recover, are the most powerful and engage in all-out-exertion efforts. Not to belabor the analogy, but the fast-twitch are the Papa Bears, the intermediates are the Mama Bears, and the slow-twitch are the Baby Bears.

These muscle fibers do not function individually but in groups called motor units. By recruiting and stimulating as many muscle fibers during a training session, you get the maximum benefit. With the Goldilocks Load, you want to produce an effort quickly, but in a way that recruits all three types of fibers in turn, extending the effort as you move from the slow-to-recover fast-twitch fibers, bringing in the intermediate and then slow-twitch fibers.

Structuring the Workout

The goal is to engage the full spectrum of muscle fibers by specifically structuring the types of exercises and the volume of work you do. The three types of lifts you use are heavy compound moves, intermediate compound lifts, and high-repetition isolation exercises. The heavy compound exercises tackle the high-threshold fast fibers, which function best when done for one to six repetitions per set. The intermediate compound lifts focus more on form and muscle activation, not power, and are done for eight to 10 reps. The final, high-repetition isolation exercises use a 12-to-20-repetition range to fully fatigue the muscle on the final set and create more time under tension.

Here is a sample back and biceps workout, including designated rests between sets:

Deadlifts, 4 sets x 4-5 reps, rest 3 minutes

Pull-ups, 4 sets x 9 reps, rest 90 seconds

Alternate sets

               One-arm lat pulldowns, 5 sets x 12-15 reps, rest 60 seconds

               One-arm rows, 5 sets x 15-20 reps, rest 60 seconds

Incline dumbbell curls, 4 sets x 15-20 reps, rest 30 seconds

There are other ways to arrange the engagement of muscle fibers—advanced techniques and practices such as “pre-exhaustion,” for example—but the takeaway is the same: for the best results, make sure you make friends with the Three Bears.

Lindsay Kent, Master Personal Trainer

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About the Author

As the captain of a Junior Olympic volleyball team, Lindsay Kent loved testing her limits and digging deep to push herself to the next level. Fitness and nutrition were such an ingrained part of her lifestyle that fitness was the obvious career choice. She’s a professor at the International Sports Sciences Association (ISSA) College of Exercise Science and also owns her own training business, Lindsay Kent Fitness. She holds the designation of Master Personal Trainer, with specialty areas in Fitness Nutrition, Strength and Conditioning, Exercise Therapy, Youth and Senior Fitness, and Athlete/Functional training. She is a spokesmodel for ISSA, writes for various fitness publications, and is a BeautyFit sponsored athlete.