I train between 90-95% of my 1 Rep Max and rest for only 2 minutes inbetween sets instead of the recommended 3-5 minutes during heavy lifting. Will my muscles start switching over to my slow twitch fibers because my fast twitch fibers hasn’t had enough time to rest or will my body use the other fast twitch fibers that hadn’t been used yet? The reason i ask is because i just want hypertrophy of the fast twitch fibers and i wanted more tension on my muscles with less rest inbetween sets, but was afraid it would switch over to slow twitch fibers with the limited resting time. I know my nervous system will get fatiqued quickly but i know i can with stand 5-10 sets of 90% 1RM cause I’ve done it. Thanks for any help
Your slow twitch fibers are actually recruited first. Otherwise, you’d be using fast twitch fibers for simple tasks like lifting a pencil. Basically, if you’re training at 90-95% of 1RM, you’re recruiting just about all your fibers.
E-C is dead-on. This is the Size Principle. For low force outputs, low threshold motor units are activated for the force production. Higher force outputs require higher threshold motor units and higher twitch forces, which are characteristic of Type II fibers. So at your intensity (i.e. high force output), you are recruiting the majority of your motor units.
Your first question about conversion of fast to slow twitch fibers can be answered simply: it’s not going to happen, with resistance training at least. With a lot, and I mean a lot, of oxidative stress (i.e. marathon running), you might get conversion of of IIc fibers to I fibers.
However, with resistance training, what will likely happen is a shift in fiber subtype. That is, it is likely that you will see a shift from IIb fibers to IIa fibers, the latter of which are more conducive to hypertrophy.
Interestingly, during a period of detraining, there will be subsequent conversion back to IIb fibers. This is one of the primary principles behind HST, I believe.
As long as you’re able to maintain the load with that rest, you should be fine. Obviously this is going to wreak havoc on your neural system, though, so be careful with that.
By the way, how many reps are you able to achieve at that intensity? And, are you able to sustain your reps with the given weight?
Actually, I imagine you’d pin yourself to the bench if the break wasn’t long enough. This is an extension of Timbo’s question about sustained reps.
DI
about 3-4 reps is what i can use with this weight, the reason im doing this is so i can weigh more but all i wanted was fast twitch growth. So do you think by going back to a strength program resting 3-5 minutes between sets after this hypertrophy program will switch the IIa fibers back to IIb fibers, also thanks for helping
also try doing some speed reps at a lower intensity if you want to induce high muscle tension. laters pk
Where did I say that longer rest intervals would shift IIa fibers back to IIb fibers? I said that detraining (i.e. a complete rest from training) would result in such.
And, actually, this is undesirable. You want the maximum amount of IIa fibers as they are the fibers prone to hypertrophy. IIb fibers are not going to hypertrophy. Rather, you want the conversion to the IIa subtype for the aforementioned reason.
I don’t understand why you’re so obsessed with fast-twitch growth. If you’re a bodybuilder, then you want maximal hypertrophy of any fiber type. If you’re a strength athlete, you want to maximize the neural connections and motor unit activation. No matter what, you want to increase the myosin and actin content of the fibers.
I’m sorry i didn’t pay attention when you said detraining, and i want fast twitch growth because i am into powerlifting and i want to get into a heavier class.
Well, DJ, then I see your point to some extent.
First off, I think you need to modify your training scheme somewhat. I think that you not only need to train at these high levels of force production but also at high levels of velocity production.
Therfore, you need to train with both extremely heavy weights (i.e. what you’re currently doing) and relatively lighter weights (i.e. 30-60% 1RM). The latter method should not be trained to failure and should be trained relatively few reps (i.e. less than six).
I’m sure some of the Westside brothers can be more helpful, though.
That said, the latter portion of training where you’re training for maximal velocity should be trained with nothing but extremely explosive movements. I believe that the WS group calls this their Dynamic day.
Your diet will dictate whether you’ll move up in weight class.
If you can do 5-10 sets of 3-4reps with 90% of your 1RM, with 2 minutes rest in between… you’re slow twitch, big time. 
That’s a good possibility, Ikester. In addition, it could be the fact that he has not yet established a neural efficiency and, therefore, cannot maximally activate all FT fibers.
I dont think I’m slow twitch at all. I weigh 135 and bench 250. I’m very close to a 2.0 ratio. I was able to do a front squat with 3-4 reps with that high of sets, with me GUESSING how close to my 1 rep max I was, but like Timbo said i dont think I have got my front squat very neural effecient. Last week was my first time to do front squat in like 5 months. Also i dont believe 3-4 reps is even close to being slow twitch fibers. When people train with 6 reps or less doing hypertrophy and only resting 2-3 minutes between sets, im fairly sure they will get a majority of hypertrophy from the fast twitch muscles. I just wanted fast twitch type IIb to hypertrophy but like I have learned I have to detrain.
Your max bench press versus your body weight is no corrolation of your dominant fiber type, I assure you.
Eric Cressey, I apologize and stand corrected.
sorry about the last post wrong thread.