In part one of Muscular adaptations we learned how "gains" are made in muscles, the increased diameter of smaller proteins actin and myosin coupled with the additional myofibrils create bigger muscles. In addition, to increased muscle size resistance training has an effect on the type of muscles.
For the most part skeletal muscle fibers can be divided into two groups: Type 1 and Type 2 or also called slow twitch and fast switch. In a nutshell Type 1 are more geared towards aerobic activities such as long-distance running, cycling or walking. They are smaller, fatigue resistant fibers that work much like a car engine. The engine runs off timing and fires cylinders at different times. This is done to balance the engine block, and to ensure that power is constantly produced. This is an over simplified as we can deep dive it later on a different post. Since this is a post centered around adaptations to resistance training. We will deep dive Type 2. Type 2 are your larger muscle fibers that are used in fast motions (hence the name quick twitch). Sprinting, jumping and lifting weights all predominantly use type 2 muscle fibers. When you resistance train your type 2 muscle fibers respond more than your type 1 due to the makeup. I can completely nerd out between the two at a later date. As long as you have a decent background you can follow along with this post. Genetics dictates the breakdown of muscle fibers. As you would imagine an Olympic marathoner will have predominantly type 1 muscle fibers while an Olympic Shot Putter will have predominantly type 2 muscle fibers. One theory is that individuals with a larger ratio of type 2 muscle fibers will experience more growth in the weight room then individuals with more of a ratio of type 1. This is due to the more responsiveness of type 2 muscle fibers for resistance training. This theory of course is dictated on no illegal drugs.
Type 2 muscle fibers can be broken down in classifications. Type 2 includes 11x, 11ax, 11a, 11c. In order these are the least oxidative to the most oxidative, in other words the force production from left to right is listed from most force production to the least. More training that stresses the anaerobic system (sprinting/jumping/resistance training) causes a change in 11x to 11ax to 11a to 11a to 11c. On the flip side detraining (period of time where adaptations revert to pre training state) will cause the shift in the other direction.
Another adaptation for muscle fibers is the increase in pennation angle of the fibers themselves. Pennation angle creates an opportunity where the fibers line up to fire at once instead of alternating like you would see in type 1 muscle fibers. When you jump you want all the fibers in the legs to fire at once to maximize the height of the jump. Additionally, increasing the pennation angle increases the range of motion of said muscle fibers. Resistance training really boils down to weighted stretching. Increasing that range of motion increases the opportunity for those muscle fibers to extend the eccentric movement. As you continue to lift weights your muscles become better at muscle buffering. After a set of squats your legs might feel "burnt out "This is due to the increased H+ deep down in the fiber causing the PH balance to decrease making more acidic. Muscle buffering delays that reaction increasing the amount of volume that can be used during a training day.
Continued resistance training also causes more of a "Supercompensation effect." As you exhaust the muscle fiber of creatine and ATP. Creatine and ATP storage increases by 28% (creatine) and 18% (ATP). Keep in mind this study was conducted with a good amount of volume (5 sets of 8-10 reps with 2 min rest).
Resistance training not only increases the size of the muscle but increases other variables that will eventually lead to better performance.
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