Muscle fibers are the cells of the muscles. Their type determines the action of the muscle. In this article, we will be discussing skeletal muscle fibers, which allow the bones of the body to move.
There are 3 types of skeletal muscle:
Type 1: Slow-Twitch (Red)
Type 1 fibers use aerobic metabolism (oxygen fueled) for less-explosive, sustained movements. They do not contact forcefully, so they use less energy.
*These fibers are more well-suited for distance running because they do not fatigue as quickly as other fiber types.
Type 2a: Fast-Twitch Oxidative (Red and white)
Type 2a fibers have higher myosin ATPase activity than type 1 fibers, giving them a faster contraction time. Type 2a fibers use both aerobic and anerobic metabolic pathways.
*Suited for activities involving speed, strength, and power like weight training and a 400m sprint.
Type 2b: Fast-Twitch Glycolytic (White)
Type 2b fibers have a very fast contraction time, using anaerobic metabolism (without oxygen). They have very high force production but fatigue very easily.
*Can be used during power lifting and a 100m sprint.
Which muscle fiber type do I have?
The predominant muscle fiber type in each person is mainly determined by genetics. Most people have roughly even distribution of fast and slow muscle fiber types. While our genetics player a large role in our muscle fiber types, we are able to train our muscles to use more aerobic metabolism (for endurance) or more anaerobic metabolism (for speed). This training can allow athletes to take their speed and explosive power to the next level.
How Can I Develop Fast-Twitch Muscle Fibers?
Three ways that fast-twitch muscle fibers can be affected through training:
Hypertrophy of the fibers, increasing their power output.
Muscles learn to recruit fast-twitch fibers more quickly.
Conversion of Type I fibers to Type II fibers.
Ways to improve through strength training:
Power Lifting: Performing power lifts (Bench, Squat, Deadlift) with a high weight at low reps can create hypertrophy of fast-twitch muscle fibers.
Plyometric Training & Olympic Lifting: These movements use the Stretch Shortening Cycle (SSC), which involves stretching the muscle, immediately followed by a rapid contraction of the same muscle. This results in the production of maximum force.
Plyometric Exercise Examples: Broad Jumps, Depth Jumps, & Tuck Jumps
Olympic Exercise Examples: Power Cleans & Power Snatches
Ways to improve through speed training:
Sprints: 100m sprint at full speed with at least a 4:1 rest-work ratio.
Agility Drills: Ladder, box, and footwork drills performed at full-intensity.
Long distance running (>2 miles) will recruit and develop slow-twitch muscle fibers over time.
But My Sport Requires Me To Have Muscular Endurance Too
For athletes like cross-country runners, soccer players, and long-distance swimmers, training will be slightly different. The mistake that many coaches and athletes make is training for endurance by only going on long runs or swims. This is a recipe for injury. All athletes should include strength training, agility, and plyometric exercises into their training program to greatly reduce their risk for injury and improve muscular endurance.
The best way to train for endurance without losing speed is through middle-distance sprints with gradually reduced recovery time. For example: 400m and 800m sprint repeats with a 1-3 minute recovery time.
*Safe practices in speed and strength training must be utilized in order to avoid injury. Having a proper coach present is the best way to ensure exercises are performed correctly and in proper volume.