The human body is a very complex machine, one that can specifically adapt to different types of training. For example, fast-twitch muscle fibers, those that bodybuilders are most concerned with, can be divided into two types with specific training protocols:
1) FOG (fast, oxidative, glycolytic) - This type has the ability to utilize oxygen at a more efficient rate, thereby enabling it to contract quickly and be somewhat fatigue resistant. It also has the greatest capacity for size increases.
2) FG (fast, glycolytic) - This type is better suited for pure power events such as the shot put and limit at tempts in powerlifting.
It has been conclusively demonstrated that fast-twitch muscle does have the ability to transform from FOG to FG with power training and vice versa with bodybuilding training.
The training methods for strength and muscle mass are similar in that they must both include resistance work at an elevated intensity level; however, FG, or strength, fibers require a significantly higher intensity. You get the best twitch response from strength oriented fibers when you emphasize acceleration in the concentric, or positive, portion of your repetitions. It also appears that you get a higher twitch response when you use compound movements, or exercises that involve two or more muscles in conjunction, such as squats. The repetition range for FG-fiber training is one to six, and the fewer the repetitions, the more FG isolation you get.
If you're a bodybuilder, you want to stress primarily the FOG fibers. To do this, you must also train hard, but it's more of a paced high intensity. FOG fibers, due to their somewhat fatigue-resistant qualities, need more repetitions. Eight to 15 appears to be the optimal number for building muscle mass.
Even so, it's actually the time the muscle spends in maximal exercise that's the true determinant of the primary fiber type. For optimal strength development it appears that the exercise should be around 90 percent anaerobic, or no more than a total of 15 seconds of actual performance time during any work set. For muscle mass the optimal energy production is 66 to 85 percent, or between 25 and 75 seconds of performance time.
For example, if you perform a set of only six repetitions but include an isometric contraction at the top of each rep as well as emphasizing the negative, or eccentric, phases, that could triple the tension time on the muscle, thereby making it an FOG-dominant, or bodybuilding, exercise.
If, on the other hand, you perform those six repetitions with very short pauses between them to allow the muscle to recover somewhat, rather than keeping constant tension on it, and you focus on acceleration, you stress the FG fibers, making it more of a strength-building set. If you're interested in muscle mass, your primary concern should be total tension time at a maximal paced intensity, rather than counting repetitions. Remember, each set should last 25 to 75 seconds.
Strength trainers should concentrate on quick, explosive sets with a short rest/pause between repetitions. It also appears that work sets performed for submaximum repetitions with short rest periods between sets (one of the basic concepts of the Bulgarian training style) specifically target the FG, or strength, fibers.
In simplest terms, to target FG, or strength, fibers, you perform your repetitions in a certain way, focusing on acceleration with the set lasting about 15 seconds. To target EGG, or muscle mass, fibers, you focus on keeping tension on the working muscles for 25 to 75 seconds and working till fatigue sets in.
Keep in mind that there's significant overlap between the two fiber types. For example, some FG-specific training aids in mass development due to the increase in strength and increase in recruitment of muscle fibers. Also, some FOG-specific training aids in strength development based on the increase in muscle size and endurance.
- Emphasize acceleration
- Perform each repetition like individual singles, with a rest/pause between repetitions
- Train with maximum intensity
- Do six or fewer reps per set
- Maintain a core time per set: 15 seconds (this is work time, not rest time)
- Use a heavier average resistance
FOG (Muscle Mass)
- Emphasize sets to failure
- Use more continuous-tension time for each individual repetition and between repetitions.
- Train with paced intensity
- Do eight to 15 reps per set
- Maintain a core time per set: 25 to 75 seconds (this is work time, not rest time)
- Use a lighter average resistance