[quote]fama wrote:
[quote]BHOLL wrote:
except they arent on the fast twitch spectrum… … … they are mixed in most people, but of course this depends on your training as you can shift muscle fiber type per training[/quote]
Well, I don’t know. But on CP’s old site (now the Poliquin Group), this was posted a few years ago:
"Wednesday, September 01, 2010 7:15 AM
Tip 180: The external rotators of the humerus are mainly made of fast-twitch muscles and should be trained accordingly.
Structure dictates function, and the rotator cuff muscles are about 60 percent fast-twitch muscle fibers. The external rotators are power decelerators that need to produce high forces in minimal time. Because these muscles are usually undertrained, I usually recommend higher reps and slower velocities during the initial stages of training, gradually moving towards lower reps and higher training velocities."
If the above is correct, I guess even 60% FT could still be called “mixed” since that leaves a fair amount left over for Type I and Intermediate fibers.
Also, regarding “conversion” through training, I was under the impression, (and I’m sure that I’ve read this before), that fast-twitch fibers could be made to act like slow-twitch, but not vice-versa.
Lastly, regarding your answer to CT’s comment, that light ERH exercises can’t balance hundreds of pounds of pressing and rowing, I don’t think CT meant the % of ERH maximum (75% or whatever you said). I think he meant that there is a LOT of stress tugging on the joint in one direction (e.g. 300 lb Bench Press internal rotation) and very little the other direction (e.g. 15 lb Cuban Press external rotation), so even if those tiny muscles are working near their max in the latter exercise, it won’t do a whole lot for “balancing” in the long run. But maybe CT will clarify if I’m wrong.
[/quote]
First Part: only study looking at fiber concentration of cuff
TUDY DESIGN:
Descriptive cadaveric laboratory study.
OBJECTIVE:
To identify the fiber type composition of the rotator cuff and teres major muscles in human subjects.
BACKGROUND:
The rotator cuff is commonly injured in athletics and is a major focus of sports medicine. Although the anatomy and architecture of each muscle have been described in great detail, these muscles have never been fiber typed using immunohistochemistry or gel electrophoresis. Fiber typing is important in modeling function, exercise training, and rehabilitation.
METHODS AND MEASURES:
We harvested tissue samples for all 4 rotator cuff muscles, as well as the teres major muscle from cadavers. Tissues were frozen in liquid nitrogen and sectioned. Cryosections were labeled with commercially available antibodies against fast and slow isoforms of myosin heavy chain (MHC). We also harvested fresh (unembalmed) tissue from deceased subjects and labeled tissue sections with antibodies against fast or slow MHC and wheat germ agglutinin. Gel electrophoresis followed by silver staining was also used to identify and quantify MHC isoforms in fresh tissue samples.
RESULTS:
All of the muscles were of mixed fiber type composition. As a whole, 44% of rotator cuff fibers labeled positively for slow MHC, with slow MHC content of 54% in supraspinatus, 41% in infraspinatus, 49% in teres minor, 38% in subscapularis, and 40% in teres major. Mixed MHC isoform distribution was confirmed by SDS-PAGE, which also indicated that the IIa and IIx isoforms were roughly equally present across the muscles.
CONCLUSIONS:
Human rotator cuff muscles, at least in older subjects, have a mixed fiber type. Because we only examined older subjects, we must limit our interpretation to this population.
Obviously older population (who tend to lose FT) but gives a general sense of the cuff being mixed orientation
Part 2: Dr. Jacob Wilson wrote a review publish in NSCA a little while back on this topic. NO you can orient fiber type in either direction
I’m not sure what your meaning is for the last part. I was simply saying most people’s maximal isometric strength (which is greater than conc/ecc) is usually between 20-30 pounds into external rotation, therefore, training with 10-20 loads can induce a training effect.
However if your training simply to lift loads overhead then specificity of training the cuff overhead is important. I however do not see this “as a cure for shoulder pain, and something that will reduce many or most people’s shoulder problems.” For me I choose not to perform overhead lifts and I don’t like training the cuff at end range flexion/scaption where it is actively insufficient.