Out of all the training variables none is more important and less understood then the number of repletion one should complete. For many years it has been debated what is the right amount. There were a few studies done that might just help us understand that there is not one number that is the right amount of reps. The reason is related to our muscle fiber type.
Muscle Fiber Types
The two primary types of muscle fibers are called slow-twitch (Type 1) and fast-twitch (Type 2) and each has unique characteristics. Slow-twitch fibers (Type 1) are fatigue resistant fibers that are smaller in cross section than the fast-twitch fibers. They are well suited for low intensity activities such as distance running, cycling and walking.
Fast-twitch fibers (Type 2) are recruited for short bursts of high-intensity activities such as jumping, sprinting and weight lifting. These fibers fatigue more quickly but allow for powerful muscular contraction.
If you were a fast runner, or if you had a high vertical jump, your fast-twitch muscle fibers predominate. If you shunned all speed related activities and preferred long slow distance, you have a preponderance of slow-twitch fibers. If you were somewhere in between, excelling at speed or distance, you have a fairly even mixture of the two.
Consider the results of a research study in which 87 men and women performed as many repetitions as possible with 75 percent of their maximum resistance.
Specifically, all of the subjects were tested for the maximum weight load they could perform one time on the Nautilus 10-Degree Chest machine. After a five-minute rest, they completed as many repetitions as possible with 75 percent of their maximum weight load.
Most of the participants performed between 8 and 13 repetitions. This median group represented normal individuals with a relatively even mix of Type 1 and Type 2 muscle fibers. There were a few subjects who completed fewer than 8 repetitions. These are excellent power athletes (sprinters, jumpers) who typically have a higher percentage of Type 2 (low endurance) muscle fibers.
There were a few subjects who completed more than 13 repetitions. These are outstanding endurance athletes (marathoners, triathletes) who typically possess a higher percentage of Type 1 (high endurance) muscle fibers.
It would seem that individuals who have an even mix of Type 1 and Type 2 muscle fibers may obtain best results by training with about 10 repetitions per set. It would also appear that individuals who have predominantly Type 2 muscle fibers may obtain best results by training with fewer repetitions per set. Conversely, individuals with predominantly Type 1 muscle fibers should train with more repetitions per set to achieve maximum results.
This observation was supported by a follow-up study in which the middle-endurance athletes trained with 9 to 11 repetitions per set, the low-endurance athletes trained with 6 to 8 repetitions per set, and the high-endurance athletes trained with 12 to 14 repetitions per set. All of the athletes made similar improvements in muscle strength after 8 weeks of training with a personalized repetition protocol. These results indicate that predominantly Type 2 muscles respond well to low-repetition training, Type 1 muscles respond well to high-repetition training, and evenly mixed muscles respond best to mid-repetition training.
Of course, muscles are not aware of the number of repetitions they complete.
The key to muscle performance and fatigue is the relationship between force and time. Generally speaking, you can produce a high level of muscle force for a relatively short time and a low level of muscle force for a relatively long time. However, to stimulate strength development, you should train your muscles within the anaerobic energy system. This system provides large amounts of energy for up to 90 seconds of high effort exercise.
For best strength results, it is recommended that you use enough resistance to fatigue your muscles within 30 to 90 seconds. As general guidelines, persons with predominantly Type 2 muscles should train about 30 to 50 seconds per set. At 6 seconds per repetition (two seconds lifting and four seconds lowering), this represents about 5 to 8 repetitions.
Persons with predominantly Type 1 muscles should train about 70 to 90 seconds per set. At 6 seconds per repetition, this represents about 12 to 15 repetitions. Persons with an even mix of muscle fibers should train about 50 to 70 seconds per set. At 6 seconds per repetition, this represents about 8 to 12 repetitions.
Because most people possess a relatively even mix of muscle fibers, a 50 to 70 second bout of strength exercise is an excellent training recommendation.
If you choose to train in a slowed manner, completing 14-second repetitions (10 seconds lifting and four seconds lowering), you should use enough resistance to complete four to five repetitions. In this manner, the muscles again reach fatigue within the 50 to 70 second anaerobic range.
Depending on the type of activity you undertake, you may want to adjust your training accordingly. To determine the optimum number of repetitions for a particular muscle group, such as the quadriceps, follow this procedure:
1. Perform 10 leg extensions with a relatively light weight.
2. After a two-minute rest, perform one leg extension with a relatively heavy weight.
Continue in this manner until you determine the heaviest weight load you can perform once with proper technique. This is your maximum weight load.
After a five-minute rest, perform as many leg extensions as possible with 75 percent of your maximum weight load. This represents the approximate number of repetitions you should perform in this exercise.
If you complete 6 repetitions, for example, you most likely have a higher percentage of Type 2 muscle fibers and should probably train with about 5 to 8 repetitions per set. At the other extreme, if you complete 13 repetitions, you most likely have a higher percentage of Type 1 muscle fibers and should probably train with about 12 to 15 repetitions per set.
Overall, it would appear that best strength results are attained when you match your training repetitions to your muscle fiber type. Although muscle fiber type may vary somewhat among muscle groups, we have found this factor to be relatively consistent in most people.
Regardless of your muscle fiber type, the key to strength development is high-effort, anaerobic exercise. The resistance should be sufficient to fatigue the target muscle group within 30 to 90 seconds of exercise. By matching the optimum repetition range with your muscle type and by systematically increasing the repetitions and resistance, you will make safe, steady and solid progress toward your ultimate strength potential.
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