Effects of WeightLifting on Muscle Fiber Composition

July 7th, 2008 by Paul Johnson

You may have heard some bodybuilders talk about how weight training has a permanent effect on your muscle fibers. Two different ways that the muscles can change through vigrous weight training routines over a course of a few weeks, is through muscle fiber composition changes and hyperplasia.

Before we look at studies and theories, let's understand how the muscle is made up. There is two major types of muscle fibers, type I and Type II. Type I are functionally best for endurance. Type II are good for strength and power, but not good for endurance. Type II can actually be dividedfurther into fiber subtypes. Type IIB and Type IIA. Type IIB are white colored, unlike the other fibers IIA and I. They are also the most responsive to hypertrophy (Muscle growth). There are many other fiber sub-types in the body, but the most common are Type I, IIA, and IIB.

There is evidence from studies I have found, that muscle fibers type changes from weight training. In other words, One Type can become more like another fiber type, depending on your type of training. This tells us that our muscles adapts to weight training, so it can try to gain muscle easier in the future. When there is more Type II and less Type I acting fibers, it means it's easier to stimulate future muscle gains. If their is more type I and less Type II, than it becomes harder to gain muscle. It also tell us, that we have to make sure we do the right kind of training to stimulate the right changes in fibers for maximum muscle growth.

Muscle Fiber change research studies

A study published in Eur J Appl Physiol. 2002 Nov;88(1-2):50-60. Epub 2002 Aug 15. 32 men who were untrained were put into low rep, intermediate rep, high rep, and control groups. High rep group did between 20 to 28 reps with 1 minute rest. The intermediate group did between 9 to 11 reps with 2 minutes of rest for 3 sets. The low rep group did 3 to 5 reps with 3 minutes of rest for 4 sets. The excercises chosen for all groups were squat, leg press, and knee extension done 2 times a week for first 4 weeks, then 3 times a week for the final 4 weeks. The low and intermediate rep group had muscle growth (hypertrophy), but the control and high rep group did not have nearly any. Most interesting however, is that all resistance trained groups had a decrease in IIB fibers and increase in IIAB fibers. Type IIAB sub-type fibers are slightly less effective at building muscle and strength than pure IIB fibers. This study tells us that although high reps around 20 or so do not do much for hypertrophy, they induced the same muscle fiber type changes as even the very low rep ranges(3 to 5 reps).

Another study J Gerontol A Biol Sci Med Sci. 2000 Jul;55(7):B336-46 was done on 18 older men. Half did resistance training, the other half served as control. The routine was leg press, half squat, and leg extension for 16 weeks with 6 to 8 reps to muscular failure and 1 to 2 minutes of rest. Results showed that everyone's muscles hypertrophied, but IIB fibers decreased and IIA fibers increased. Once again, the fibers are changing away from the IIB fibers.

One other study I found published in Eur J Appl Physiol Occup Physiol. 1990;61(1-2):37-41 They had 12 college age men do strength resistance training for 7.5 weeks, than 5 week break to then go onto 5.5 weeks of endurance training (high reps light weight). The other group started with endurance then went to strength. Results showed that both groups in phase 1 had hypertrophy and increase in sizes of all the major fiber types. The endurance group that did strength in the 2nd phase, also had more hypertrophy gains in all fibers during the 2nd phase. However, the group that went from strength to endurance in 2nd phase, reversed all hypertrophy gains in all fibers. This tells us that endurance training after strength training reverses all hypertrophy in all the muscle fiber types. The reason the endurance group probably had some hypertrophy even in phase one, is probably cause they were untrained (not previous lifters).

The results are stunning for me from these studies. I thought it would show a change to more IIB at the lower rep ranges. Instead, all the common rep ranges of lifting for bodybuilders, whether they be in the 6 rep range or the 20 rep range, all had similiar changes in muscle fiber types. The studies also show us that the common rep range bodybuilders use between 6 to 12 reps, all stimulate the major 3 types I, IIA, and IIB for hypertrophy simultaneously. This is well known by bodybuilders and this is why it is the best rep range for muscle gains. The last study cited is useful in that it tells us that switching to endurance training after strength training, will lead to muscle shrinking. This is something bodybuilders have known all along from experience. You can't maintain muscles lifting weights at the 15 + rep range, as you had gained from lifting in the 6-12 rep range. This is one reason why I don't advocate high reps during dieting.

  1. Michael on June 19th, 2010

    These studies are far from being scientific. They all fail to hold up under peer revue. Also, they’re anywhere from 9-20 years old; more recent studies about hormonal and cellular responses to different rep ranges disprove them. For example, none of them take into account differences in myostatin and IGF-1 production between -20 rep and 20 rep ranges. The myostatin studies show that reps higher than 20 are ideal for building mass.

    The statement you make about not being able to maintain mass at 15 reps is ludicrous. Chris Cormier made the best gains in his career when he switched to doing high reps: no less than 30 per set. Shawn Ray built the majority of his mass doing 50 rep sets. Numerous other bodybuilders have made fantastic gains when switching from low reps to very high reps. I switched to 50-100 reps, and I put a half inch on my arms in a month, while on a diet. Figuring I lost a half an inch of fat off my arms, that’s a whole inch of pure muscle mass in one month.

    * Eugene Sandow: old-time strongman who built his physique doing reps in excess of 100.

    * Steve Reeves: got tired of not making any gains picking up heavy weights, so he came up with century sets: starting with a weight you can do 70 reps with, you go to failure, then rest-pause your way to 100 reps. He won bodybuilding contests and played Hercules from doing century sets, not from lifting heavy weights.

    * Lee Priest: does sets of 15-30 reps, taking about 4 seconds per rep, giving him higher times under tension equivalent to doing 60-120 normal speed reps.

    * Craig Titus: was known for doing lots of 100 rep sets. Big man before he went to prison. Still pretty big, despite no more steroids.

    * A huge Canadian bodybuilder from the 80’s (last name King) did sets of 30 reps on all bodyparts. He had massive arms at a time when even a 20″ arm was rare in pro bodybuilding.

    * Serge Nubret: never took steroids, but built 20″ arms with 20 rep sets.

    * Dave Draper: he varied his routines a lot, but his best gains always came when he did 20 sets of 20 reps.

    * Frank Zane: started with the 8-12 standard, but got his size up to win the Mr. Olympia doing 20 rep sets.

    * Chris Corney: not a huge man relative to other golden age bodybuilders, but very big relative to his short stature. He rarely did less than 20 reps per set.

    * Markus Ruhl: Has 24″ arms. The last 4″ he built doing higher rep sets, mostly 15-25 reps.

    Tom Platz: known for his outlandishly huge thighs, did lots of 50 rep squats to get them so huge. Not known for his upper body, but considering that he trained heavy on upper body, I can see why legs were his strong point.

    The Golden Age bodybuilders all did high reps pre-contest because it was the only way they could maintain size while dieting. Some of them trained with high rep sets even when bulking, because it gave them an edge over the steroid users. Serge Nubret is a prime example. He always trained high rep; he never got into lifting heavy, and he still has 19″ arms in his 70’s.

    Lab coats are not reliable sources of information on what actually works in real-world scenarios. Big guys only get big lifting heavy weights if they take drugs. A lot of natural trainers these days are switching to super high reps because it’s been proven to work by past bodybuilding greats, and even some modern greats. The latest scientific discoveries also prove it.

    More pump and more lactic acid from higher times under tension = fast gains. Reps lower than 20 stimulate myostatin production, which inhibits muscle growth. Reps over 20 (especially reps over 50) inhibit myostatin production and increase IGF-1 production, accelerating mass gains. Steroids will inhibit myostatin production, and so will creatine, but those things are only necessary if someone insists on limiting their growth by lifting heavy weights.

    Super high reps to failure works better than taking drugs or sups. Try it before you knock it.