Of the training variables associated with strength development, none is more important or less understood than repetitions. Perhaps the most significant factor in a personalized program of strength exercise is the number of repetitions performed per set. The reason is related to our muscle fiber type.
Muscle Fiber Type
All of our muscles are composed of Type 1 and Type 2 muscle fibers. Type 1 muscle fibers are often referred to as slow twitch, while Type 2 muscle fibers are often termed fast twitch. Type 1 fibers are characterized by smaller size, less force capacity and more endurance capacity. They are the dominant muscle fibers in endurance activities such as long distance running, cycling and swimming. Type 2 fibers are characterized by larger size, more force capacity and less endurance capacity. They are the dominant muscle fibers in power activities such as sprinting, jumping and throwing.
Due to the physiological differences, Type 1 fibers fatigue more slowly and can complete more repetitions with a given resistance. Conversely, Type 2 fibers fatigue more quickly and can complete fewer repetitions.
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.
As illustrated in Figure 1, most of the participants performed between eight and 13 repetitions. This median group represented normal individuals with a relatively even mix of Type 1 and Type 2 muscle fibers. At the left side of the chart are a few subjects who completed fewer than eight repetitions. These are excellent power athletes (sprinters, jumpers) who typically have a higher percentage of Type 1 (low endurance) muscle fibers. At the right side of the chart are 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 predominately Type 2 muscle fibers may obtain best results by training with fewer repetitions per set. Conversely, individuals with predominately 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 nine to 11 repetitions per set, the low-endurance athletes trained with six to eight repetitions per set, and the high-endurance athletes trained with 12-14 repetitions per set. As presented in Table 1, all of the athletes made similar improvements in muscle strength after eight 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 30-90 seconds. As general guidelines, persons with predominantly Type 2 muscles should training about 30-50 seconds per set. At six seconds per repetition (two seconds lifting and four seconds lowering), this represents about five to eight repetitions.
Persons with predominantly Type 1 muscles should train about 70-90 seconds per set. At six seconds per repetition, this represents about 12-15 repetitions. Persons with an even mix of muscle fibers should train about 50-70 seconds per set. At six seconds per repetition, this represents about 8-12 repetitions. These time and repetitions relationships are summarized in Table 2.
Because more people possess a relatively even mix of muscle fibers, a 50 to 70- seconds 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 upon 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 relatively light weight.
2 – After a two-minute rest, perform five leg extensions with a moderate weight.
3 – 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 six repetitions, for example, you most likely have a higher percentage of Type 2 muscle fibers and should probably train with about five to eight 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 12-15 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 30-90 seconds of exercise. For most of us, this is best accomplished with a double progressive training system using a protocol of eight to 12 repetitions. First, select a resistance that fatigues the target muscle within 8-10 repetitions. Second, train with this resistance regularly until you can complete 12 repetitions. Next, add 2.5 to five pounds and progress in the same manner until you can perform 12 repetition with the new resistance. 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.
Wayne Westcott, Ph.D., is Fitness Research Director at the South Shore YMCA, national strength consultant, and author of several fitness books including Building Strength and Stamina and Strength Training Past 50.
Strength gains for athletes training with muscle specific repetition range
|Muscle Fibre Type||Repetition Range||Strength Improvement 10-Degree Chest Machine|
|Sprinters||Predominantly Type 2||6-8||22.5 lbs.|
|440-880 Runners||Even Mix||9-11||21.0 lbs.|
|Distance Runners||Predominantly Type 1||12-14||20.0 lbs.|
Time and Repetitions Relationships for Different Muscle Fiber Make-up
|Type 2 Muscles||30-50 seconds||5-8 reps|
|Even Mix Muscles||50-70 seconds||8-12 reps|
|Type 1 Muscles||70-90 Seconds||12-15 reps|