Muscle Fibres (Fibers)

Some are born to sprint (Usain Bolt) while others are born for endurance (Paula Radcliffe). This is because Bolt has a higher percentage of fast twitch fibers as compared to Radcliffe. Normal people are just average and not gifted with the extreme ends of things that are necessary for those particular kind of sports such as Sprinting or Marathon running. For instance I prefer weightlifting over aerobic activities and I'd rather sprint than run a marathon so I suspect I have more fast twitch fibers than slow twitch. The only way to find out in quantitatively is to do a biopsy on each muscle group. This is a bit extreme for most people so a more down to Earth method is just to see which sports and activities you prefer or do various exercises and see which ones suits you best.

In order to develop "big" muscles one needs to exercise both the fast and slow twitch fibers so the muscle can look full and ripped. Weightlifting with heavy low reps triggers the fast twitch while high rep for endurance triggers the slow twitch. This is comparable to sprinting where it is high intensity for short burst vs. Marathon running where it is relatively lower (anaerobic vs aerobic) intensity for longer durations. When muscle size and/or strength stalls one not only needs to consider switching up the routine but also switching up the approach to weight training.

Right now the traditional 5x5,9 8x8, or 5x10 is stalled out for me and I am switching to a HIT program starting next week working out 3 days a week, 1 day rest in-between and 2 days off after the last day (MWF on, Sat, Sun off, etc). In the HIT program I will also cycle between low weight high rep first to not only learn HIT but to trigger the slow twitch muscles. Then I will increase the weight and drop the reps, so on and so forth. This will help me to slowly transition into a heavy HIT program before I swing back into the high rep low weight program for the final week (4 weeks total). Ideally doing this should trigger the slow twitch and then develop the fast twitch muscles and also shock the body as I will be doing HIT.

There is NO way to change the percentage or ratio of muscle fibers for any muscle group in your body. So if you don't have the genetics to be a marathon winner no matter how hard you train you won't win marathons against those who train equally hard but have the genetics. You CAN, however, change the relative volume of fast vs. slow twitch fibers through exercise. This means that if you lift weights all the time the volume (size) of your fast twitch fibers will be larger compared to the relative size of the slow twitch fibers. Good news indeed!

I concluded my second to last workout routine this week before HIT by doing the following:

5x10@65lbs - Stiff legged Good Mornings
5x20@Bodyweight - Situps (1,1,2) (+,hold,-)
5x10@35lbs+bar - T-bar (narrow)

Not too intense, not too easy. :) Just right.