How Do You Know If You Are Training The Right Way?

Muscle Types, Strength Gains, and Energy Systems
used in Various Sports:

MUSCLE FIBERS

It is generally accepted throughout the world that there are two different types of muscle fibers. Slow twitch (Type I) muscle and fast twitch (Type II) muscle fiber. From there, you can further categorize fast twitch muscle fiber into Type II-a and Type II-b.

Type I Muscle Fibers

Type I muscle fibers have the slowest-contractile speed, the smallest cross-sectional area, the highest oxidative (aerobic) capacity, and the lowest glycolytic (anaerobic) capacity. They contract slowly and are able to hold a steady paced twitch for long durations without fatigue. Type I muscle fibers are predominately used in endurance activities. Long distance runners, swimmers, and cyclists mostly use Type I fibers.

Type II Muscle Fibers

Type II-b muscle fibers have the fastest-contractile speed, the largest cross-sectional area, the lowest oxidative capacity, and the highest glycolytic capacity. They are ideally suited for short fast bursts of power. These muscle fibers are used in such activities as sprinting, power lifting, and bodybuilding. Type II-a muscle fibers are intermediate and their properties lay between types I and type II-b.

How Type I & Type II Muscle Fibers Are Different

Type I fibers are different than type II-b fibers for many reasons. You can think of them as opposites. Type I is for long endurance activity while type II-b is for short fast bursts. Type I fibers are highly oxidative (more oxygen supplied through blood) and are not likely to grow in size as much. Type II-b fibers are highly gycolytic (not as much oxygen supplied) and tend to grow in size more than type I fibers.

How Your Body Recruits Muscle Fibers

Even the small muscle groups in your body have over 100,000 muscle fibers. A motor neuron is what stimulates our muscles to contract. It carries impulses (messages) from our brain and spinal cord to our muscles. One motor neuron controls anywhere from 2 to 2,000 muscle fibers. A single motor neuron and the fibers it stimulates are called a motor unit. Each motor unit mainly contains muscles of its kind. Also, the motor unit fires with a frequency that is conducive to the fibers it stimulates. Simply put, a slow twitch motor neuron will cause the muscles in it to contract slowly while a fast twitch unit will fire quickly. The quicker it fires the more power it produces. If the activity is light, it will mainly stimulate type I muscle fibers. When it becomes too intense it will call upon type II-a muscle fibers. And finally, for the highest intensity movements, it will recruit the type II-b fibers. This is why type I fibers are called low threshold, and fast type II-b fibers are called high threshold. Low threshold because they are the first muscle fibers to be recruited and high threshold because they are only recruited under the most intense circumstances. Your body always activates its muscle fibers in this fashion.

Recruitment In Low Rep Sets

Low repetition work (in the 1-5 rep range) provides an extremely unique adaptation. To overcome the weight, your body must recruit as many motor units as humanly possible. This will cause your nervous system to become more efficient at this process. Over time, you will learn to lift the heavier weight with all (or close to as possible) of your motor units in one rep. Power lifters are brutally strong for this reason. They can basically make all the their motor units fire at once.

This is an excerpt taken from Developing Killer Speed. The book was written by Mark Strasser M.S. CSCS, a professional strength and conditioning coach.

To view more information or purchase the book, visit www.strength-conditioning.net