On the other hand, several studies (2,3,5,6,8) have demonstrated no differences in strength development when training with low or high repetitions, provided that each exercise set fatigues the target muscles within the anaerobic energy system (approximately 20 to 90 seconds). Consider two of these studies completed in the past two years.

Study One
Chestnut and Docherty (3) divided 19 previously untrained men (mean age 24 years) into two exercise groups. One group performed 6 sets of 4 repetitions each and the other group completed 3 sets of 10 repetitions each, 3 days a week for a period of 10 weeks. The training exercises were the triceps bench press, triceps pressdown, barbell curl and dumbbell curl. All of these subjects were assessed for changes in their muscle strength (1RM) and muscle size (cross-sectional area). The researchers reported that both the 4-repetition training and the 10-repetition training elicited statistically significant and equal increases in muscle strength and muscle size. These findings suggest that shorter and longer bouts of high-effort resistance exercise produce similar results when muscle fatigue occurs within the anaerobic energy system.

Study Two
The second study (8) was conducted at the South Shore YMCA, and placed 44 previously untrained men and women (mean age 53 years) into two exercise groups. One group performed each resistance exercise for 1 set of 6 to 8 repetitions and the other group performed each resistance exercise for 1 set of 13 to 15 repetitions. The training exercises were the leg extension, leg curl, chest cross, chest press, pullover, lateral raise, biceps curl, triceps extension, low back extension, abdominal curl, neck flexion and neck extension. After 10 weeks of training, the 22 subjects who did about 7 repetitions per set averaged a 14.4–pound strength gain, and the 22 subjects who did about 14 repetitions per set averaged a 15.0-pound strength gain. Both training groups experienced statistically significant and essentially equal increases in muscle strength. Like Chestnut and Docherty’s research, our study showed no difference in the physiological adaptations associated with lower and higher repetition protocols when training to momentary muscle fatigue within the anaerobic energy system parameters.

Based on the results of these (3,8) and other studies (2,5,6) it would appear that you may receive similar strength building stimulus from various resistance training protocols that produce muscle fatigue within the anaerobic energy system. While some individuals (e.g., those with mostly fast-twitch or slow-twitch muscle fibers) may respond better to lower or higher repetition training, most of us should attain about the same strength gains training with a range of repetitions (e.g., 5 to 15 reps per set).

Repetition Ranges For Children
Because children are not simply small adults, we also studied their physiological response to lower and higher repetition resistance training (4). This study involved 43 boys and girls (mean age 8 years) who trained with one set of 6 to 8 repetitions or one set of 13 to 15 repetitions, or served as controls (non-training subjects). The strength training groups performed one set of each resistance exercise, twice a week for a period of 8 weeks, using the following youth-sized weightstack machines: leg extension, leg curl, leg press, hip abduction, pullover, chest press, seated row, abdominal curl and pulldown. Unlike our adult studies, the youth who trained with moderate weightloads and more repetitions (13 to 15 reps) gained 28 percent more strength whereas those who trained with heavier weightloads and fewer repetitions (6 to 8 reps) gained 18 percent more strength.