Updated, 3 May 2019 by Staff
If you want to grow muscle and/or burn more body fat – it is important to know muscle groups have three muscle fiber types that are stimulated to grow or endure physical activity. And during exercise or work activity, muscle also prefer certain fuel sources to achieve the fitness goal.
Research shows us, muscle is stimulated to grow when slow, intermittent and fast twitch muscle fibers within the chest, back, arms, abs and legs and buttocks contract at various rates of speed during low-to-high intensity exercise. Learn how to combine muscle fiber and fuel preference knowledge to select the proper training methods to naturally achieve yourÂ weight loss, strength and muscular endurance and competitive and recreational sports goals.
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Muscle Fiber and Fuel Knowledge is Invaluable to Achieve Set Fitness Goals
All muscles have various composition of primarily 3 types of muscle fiber. And when exercise is programmed to lose weight, or increase strength, or endure a physical task of duration and intensity a specific fuel source is preferred by the body.
Fast twitch muscle fibers are less vascular than slow and intermediate fiber types and appear white in color and are highly stimulated during anaerobic (speed, power and strength) training. These muscle fibers use carbohydrate fuel to produce the ATP (adenosine triphosphate) energy at 2 times the contraction rate of the red and vascular (oxygenated slow twitch endurance muscle fibers). Slow twitch muscle fibers contract at lower intensities and rate of speed and prefer fat fuel to produce the required ATP energy for long endurance activities. The 3rd muscle type intermediate makes use of both metabolic worlds to support the ramping up and down of exercise intensity and rate of physical movement (Katch and McArdle 1993).”
Human muscles contain a genetically determined mixture of both slow and fast fiber types. On average, we have about 50 percent slow twitch and 50 percent fast twitch fibers in most of the muscles used for movement. However, Olympic sprinters have been shown to possess about 80 percent fast twitch fibers, while those who excel in marathons tend to have 80 percent slow twitch fibers. These well-conditioned slow and fast twitch muscle fibers may be genetically provided within naturally lean-muscular body types (Quinn 2013).”
From a genetic perspective this is likely the reason most of us will never be Olympic contenders no matter how hard we train. One thing appears certain, if the average human muscle is comprised of 50% slow twitch muscle fiber; it stands to reason, the majority of us have a genetic and competitive advantage to burn body fat when participating in low intensity aerobic exercise.
There is also an order of muscular contraction where slow twitch fibers yield to fast twitch muscle fiber as physical effort increases. Also a muscle fiber fuel preference shifts from a low intensity fuel source [stored body fat] to [glucose and stored muscle glycogen] to produce the energy and muscle contraction rate necessary to achieve the speed, power and strength needed to accomplish the high intensity training task or goal.
For example, when you walk you’re mostly stimulating the leg muscles slow and intermediate muscle fibers to perform long endurance activity. When you sprint or squeeze out those last reps on a heavy bench or leg press station, the slow and intermediate twitch muscle fibers yield to the faster muscle twitch fibers to work at a higher rate of intense speed to achieve the high endurance and strength conditioning goal.
Sprinting with all-out effort is similar to squeezing out that last rep on the bench press. The fast twitch muscle fibers fire (contract)Â at a high rate of speed and intensity while the slow twitch muscle fibers yield or stand-by after high intensity effort produces lactic acid buildup – which allows a less intense effort to continue thereafter. Especially when short periods of rest between exercise is the case.
We all know a high level of muscular intensity has continued physical effort limitations.
That is fast twitch muscle fibers utilize a preferred- quick fuel source [glucose] first, which lasts only seconds.
The glucose fuels intense contractions for up to a maximum period of 10 seconds.
After this time and up to a period of 3 minutes – the next available fuel source is made available [stored muscle glycogen].
In contrast, slow twitch fibers use a combination of glucose and stored body fat fuel for low intensity and long duration exercise activities.
This is a much slower and less intense training process and can be maintained with constant intensity for a continued time period (Fitnessbeans 2012).
Now that we’ve reviewed some basics of muscle fiber characteristics and fuel preferences during specific types of exercise activity, lets answer the question…
What training method will grow muscle and burn more fat?â€
The answer is fairly straight forward, train task specific. If you want more bulk, strength and power, train anaerobically – lift heavier weights at increasing intensities of short duration [engage the lactic acid buildup]. If you want more endurance, train aerobically at high intensities that moderate and condition the muscles to limit-pacing or avoid chronic lactic acid buildup. E.g., sprinting, wrestling, karate, boxing, basketball, football, etc.
If you want to burn more body fat train aerobically by performing low intensity – long duration exercise activity, e.g., walking, jogging, biking, dance, etc.
If you want the best of both worlds, you must cross-train
For example take your exercise time and split into two training sessions daily (train aerobically and anaerobically). For instance, if you only have one hour to exercise, spend 5 minutes stretching, and then 25 minutes on aerobic exercise of choice [low-intensity walking, stationary bike, jogging, tread mill equipment, etc].
During the last 25 minutes increase resistance on free weights or stationary equipment and/or circuit weight training equipment – then 5 minutes stretching cool down. On alternating days if a secondary fitness goal is a competitive sport activity… spend a full exercise day participating in that activity: e.g., racquetball, basketball, baseball, soccer, dance, running, power lifting, boxing, karate, etc.
Somewhere mid-week be sure to take a day off to rest muscles so they can repair and metabolism recharges its battery. This is especially important if training at a high rate of intensity daily. If you over train muscles and don’t rest adequately they will be in a state of constant repair more so than making the muscle and endurance gains you desire.
If you can’t participate in your favorite intramural-team sport, or train in a gym for whatever reason, train the next best way possible. Head to the nearest public school, or community sports field, City park or trail system and perform repetitive sprint-jogging-walking exercise.
You can also make use of running up/down bleachers, perform sit ups, push-ups etc. Or exercise at home using a stationary bike, repetitive speed bag, jump rope – follow a daily aerobics DVD video dance or yoga program, etc.
If your goal is to lose body fat weight, chose activities of long-endurance and low-intensity physical effort (walking, jogging, biking).
If you want more muscle bulk, strength and speed, choose short-endurance and high intensity exercise exercises with increasing resistive weight loads.
If you want the best of both worlds: Cross-train to achieve your set fitness goals.
Citations and References
Fitnessbeans. “Muscle Fibers: Fast Twitch Versus Slow Twitch. FitnessBeans. BeansPublishing, 2012. Web. 19 Oct. 2013.
Katch, Frank I., William D. McArdle, and Frank I. Katch. “Chapter 11/Energy for Exercise.” Introduction to Nutrition, Exercise, and Health. Philadelphia: Lea & Febiger, 1993. 169-90. Print.
Loya, Dennis M. “Training Fast and Slow Twitch Muscles.” TotalFitnessExperience.com. TotalFitnessExperience.com, n.d. Web. 19 Oct. 2013.
Quinn, Elizabeth. “Fast and Slow Twitch Muscle Fibers.” About.com Sports Medicine. About.com, 18 Oct. 2013. Web. 19 Oct. 2013.
Author: Marc T. Woodard, MBA, BS Exercise Science, ARNG, CPT, RET. 2019 Copyright. All rights reserved, Mirror Athlete Inc., www.mirrorathlete.org, Sign up for your Free eNewsletter.