Fast Twitch/Slow Twitch-Which one are you?

A lot of you have heard the terms fast twitch and slow twitch muscles.   People are either fast twitch fiber dominant, slow twitch fiber dominant, or a little mix of both.  There is advantages to having slow twitch muscle and having  fast twitch muscle and if you understand how they work you can improve your training routine.  In this post I will cover what fast twitch and slow twith muscle fibers are, how you can roughly estimate if you lean towards fast twitch or slow twitch, and how you can train those muscles.

MUSCLE FIBER  AND THEIR ISOFORMS

A muscle contracts when the actin and myosin filaments form cross bridges and slide across each other inside a myofibril.  The myosin filaments are the thicker filaments and the actin is the thinner filaments.  All muscle fiber types are characterized by one specific component myosin heavy chain(MHC).  The MHC has three main isoforms- type I, type IIa, type IIx.

TYPE I(SLOW OXIDATIVE)

Type I muscle fibers are slow twitch muscle fibers.  They are called slow twitch because they have a slow shortening speed.  The ST fibers are thinner and reddish in color.  The ST fibers produce ATP in the presence of oxygen and are more mitochondria dense.  Since aerobic metabolism is much more effiecient way of ATP production than this makes the ST fibers a lot more fatigue resistant than other muscle fiber types. ST fibers size and contraction speed make them much less efficeint for power and strength.  ST fibers are the fibers predominantly used in acitivites with long duration and low intensity such as long distance running or holding different types of posture.

TYPE IIA(FAST TWICTH OXIDATIVE GLYCOLYTIC)

Type IIa muscle fibers can produce energy through glycolytic and aerobic processes.  The ability to draw from both glycolytic and aerobic mechanisms gives this fiber type the ability to produce fast low intensity movements.  They also have a decent amount of mitochondria giving it a fast recovery and a fatigue resistant aspect to it.  Bodybuilders actually have been found to have a large amount of  type IIA fibers leading to the assumption that these fibers adapt to hypertrophy.

TYPE IIX(FAST GLYCOLYTIC)

Type IIX are the fastest contraction of any muscle fiber type.  They actually contract approximately 10 times faster than their slow twitch counterparts.  Type IIX fibers are also the quickest to fatigue because of low oxidative capacity and low mitochondria.  Type IIX fibers are white in color and have a large diameter.  Type IIX fibers are recruited during high intensity and high power output movements.  Examples of this would be olympic lifts, sprints, and other short burst high powered explosive movements.

There is even more classifications of muscle fibers but these are the ones that are the most widely accepted.

RECRUITMENT OF MUSLCE FIBERS(SIZE PRINCIPLE)

All muscle fibers are recruited by motor units.  Slow twitch fibers will be recruited by smaller lower firing rate motor units.  The fast twitch fibers will be recruited by the larger higher firing rate motor units.    Now the size principle states that small motor units will be recruited first and the larger ones last.  Even if the force and velocity are high then the smallest motor units will usually be recruited first.  The low level athlete will recruit a much smaller amount of fast twitch fibers than a highly trained athlete.

SO WHICH ONE ARE YOU?

Individuals can be as much as 80% slow twitch or fast twitch muscle fiber type.  So now your probably wondering if your more fast twitch muscle or more slow twitch muscle.  The only real way to figure this out is by doing a muscle biopsy but who the hell is really going to do that!  So there is some ways that you can get a general estimate of what your dominant muscle fiber type might lean towards.  The 80% 1rep max test is probably the most widely used.

HOW TO PERFORM THE 80% 1REP MAX TEST

Ok so I am going to tell you how to perform the test with the bench press to determine your upper body fiber typer but after you know how to do with bench press you will know how to perform the test with a variety of different exercises.

To perform the test you need to figure out what your 1 rep max is for bench press.  Dont perform the test on the same day that your figuring out your bench press max because you will be fatigued for the test.

You will perform warm up sets until you get up to 80% of your 1 rep max.  So if you can bench 300lbs you will work your way up to 240lbs.  You will perform as many clean reps of your 80% 1rep max, so basically do it till  you feel like the next rep is either going to be super slow or the next rep you’re about to perform is questionable for completion.  The lower amount of reps you can do will generally mean that you are fast twitch dominant because fast twitch dominant muscle fatigues much faster and the more reps you can do will be an indicator that you are slow twitch dominant.  Here is a complete lists of how many reps you can complete and what it means, taken out of Christian Thibaudeaus Big Black Book of Training Secrets.

1-3 reps completed-fast twitch extremely dominant

4-6 reps-fast twitch very dominant

7-10 reps-fast twitch dominant

11-13 reps-equal ratio

14-17 reps-slow twitch dominant

18-21 reps-slow twitch very dominant

21+ reps- your a god damn tortoise!  No I’m just kidding you’re slow twitch extremely dominant and could out last me in workouts till  no end.

You can use this method with squat, hamstring curls, shoulder press, etc.

You can also use common sense too, imagine that.  If you have been able to jump higher than your friends and you were more times the winner than loser in a short distance race with your friends, its probably safe to assume that you are a fast twitch dominant.  If you lift weights and you easily put on quality muscle size than you are probably fast twitch dominant.  If you can run long distances longer than most and never have been good with jumping or explosive movemens than you are probably slow twitch dominant.

HOW TO TRAIN FOR YOUR MUSCLE

One of the most frequent questions is can you  change slow twitch muscle fibers into fast twitch muslce fibers or vice versa.  Some of the research suggests that that this can happen under certain conditions.  Fast twitch type IIX can definetly turn into type IIA but slow twitch turning into fast twitch muslces is much more rare.  Interesting note about muscle plasticity is their was an experiment done on rats where scientist switched fast twitch nerves onto slow twitch muslces and the slow twitch muscles behaved like fast twitch muscles.  So the nervous system determines the way a muscle behaves even more so than the struture of the fiber.

Their might be a chance that you can change your muscle fiber type to a slight degree but lets go with a more realistic approach.  Instead of trying to change your muscle fiber type it is definetly possible to increase the size of the fibers in a muscle to take up more volume in the muscle.  Lets say your tricep is 50% slow twitch and 50% fast twitch and your trying to gain more muscle.  Your goal is to recruit those fast twitch muscle fibers and grow that 50% type II so it actually makes up the majority of the size in the triceps but the muscle fiber proportion never changes. It is still 50% fast twitch muscle fibers and 50% slow twitch muscle fibers. Since most people are not gifted with fast twitch muscle, the methods of training will address how to tap into the fast twitch muscle fibers.

PLYOMETRICS AND BALLISTIC EXERCISES

We talked about the size principle and about how the slow twitch muscles are recruited first.  The use of ballistic and plyometric exercises can actually invert the recruitment pattern of muscles and start recruiting FT fibers first.  I would suggest doing some form of PAP training which will combine lots of ballistic and plyometric based exercises with heavy resistance exercises.  Here is a link to a post I did about PAP training https://kofitness2010.wordpress.com/2012/04/23/need-a-new-workout-try-pap-post-activation-potentiation-training/

Another method of using plyometrics and ballistic exercises to change the recruitment pattern is to do some plyo push ups, push press, olympic lifts, ball throws, and jumps before you workout at a light or moderate weight.  Doing this will stimulate the CNS and help recruit the FT muscle fibers that are harder to stimulate.  Personally I prefer this method because it lets me concentrate on my lifts and does not break up the flow of my workout with the ballistic and plyometric exercises.  Both ways have their benefits.

BANDS AND CHAINS

The use of bands and chains will also greatly increase your chances of recruiting FT fibers because when you use bands and chains you have to accelerate the bar much faster.  Acceleration generates force and a lot of time generates more force than heavy weights leading to greater recruitment of FT fibers.  You can use bands and chains with heavyweight but use it with 40% or the highest 70% of your one rep max and move the bar with as much speed as possible.   Rep ranges should be anywhere from 2-5 reps.  Westside method does no more than 3 usually but for changing body composition higher rep ranges are fine.

ACCELERATE WEIGHTS WITH SPEED

I know a lot of people have said lift slow and feel the muscle.  Gym science is bitch becasue for the most part they are wrong.  Slow eccentrics is good to some point but strive to accelerate the bar on the concentric action. Slow eccentrics should only be trained for short periods but for the most part lower the weight with control and then move it with the intent to move it as quickly as possible.  Even if it is a super heavy lift, move the weight with the intent to accelerate the bar as fast as possible.  Why?  You will recruit more high threshold motor units which is key to recruiting those fast twitch muscle fibers.  Lifting the weights with the intent of speed increases the intramuscular tension and that will also lead to greater muscle gain.  Last but not least lifting with the intent to accelerate the weights will increase calorie expenditure and boost insulin sensitivty.  Both of those aspects make it beneficial for weight loss.

LIFT HEAVY

Yes! Females included! Dont be scared and lift some god damn heavy weights because it will recruit high threshold motor units.

WRAP UP

Add some plyo’s, ballistic exercises,  bands, chains, intent to accelerate and you should see changes in strength, muscle tone,and size.  Sprinters tap into a large amount of muscle fibers and usually have lean, hard, muscular physiques because of the fast movements they have to perform.  Physique training is starting to change and lean towards more performance oriented training .  It is time to evovle your training and use new improved methods.  In with the new and out with the old.  Until next time.