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Research Note: Effect of Load Reductions Over Consecutive Sets on Repetition Performance

Willardson, Jeffrey M1; Kattenbraker, Mark S1; Khairallah, Maureen1; Fontana, Fabio E2

Journal of Strength and Conditioning Research: March 2010 - Volume 24 - Issue 3 - p 879-884
doi: 10.1519/JSC.0b013e3181aeb0ea
Research Note

Willardson, JM, Kattenbraker, MS, Khairallah, M, and Fontana, FE. Research note: effect of load reductions over consecutive sets on repetition performance. J Strength Cond Res 24(3): 879-884, 2010-When performing consecutive sets of a resistance exercise, maintaining performance within a specified repetition range has been shown to be essential for achieving muscular adaptations conducive to different training goals. However, maintaining repetition performance can be difficult when using shorter rest intervals between sets (i.e., ≤1 min), which may require load reductions. Therefore, the purpose of the current study was to compare repetition performance when keeping the load constant or reducing the load by different percentages during a lower-body workout. Ten repetition maximum (10RM) loads were established for the back squat, leg curl, and leg extension exercises. Subjects performed 4 workouts under the following load conditions: (a) constant load for all sets, (b) 5% load reduction after each set, (c) 10% load reduction after each set, and (d) 15% load reduction after each set. Pairwise comparisons indicated that, when averaged across sets, significantly fewer repetitions were accomplished for the back squat and leg curl within the constant condition vs. the 15% condition (p < 0.05). Conversely, for the leg extension, there were no significant differences in the repetitions accomplished between conditions (p > 0.05). Pairwise comparisons also indicated that, when averaged across exercises, significantly fewer repetitions were accomplished for set 3 within the constant, 5%, and 10% conditions vs. the 15% condition (p < 0.05). In summary, the back squat and leg curl required 15% load reductions per set to maintain repetition performance. Conversely, load reductions were not necessary for the leg extension.

1Kinesiology and Sports Studies Department, Eastern Illinois University, Charleston, Illinois; and 2Health, Physical Education, and Leisure Services, University of Northern Iowa, Cedar Falls, Iowa

Research conducted at Eastern Illinois University Human Performance Laboratory.

Address correspondence to Jeffrey M. Willardson, jmwillardson@eiu.edu.

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Introduction

Resistance training programs are commonly designed to promote increases in power, absolute strength, hypertrophy, or localized muscular endurance. The degree to which these characteristics are increased is dependent on the manipulation of training variables such as exercise mode, intensity, repetitions per set, frequency, velocity, and rest between sets. Different combinations of such variables represent a specific stimulus, manifested by adaptations in several biological systems (1,3).

Previous research has established a repetition maximum continuum such that the number of repetitions performed with a given load results in specific neuromuscular adaptations (2,4,11). For example, absolute strength development generally involves performance of low repetition sets concurrent with high-intensity loads and long rest intervals betweens sets. Conversely, localized muscular endurance development generally involves performance of high repetition sets concurrent with low-intensity loads and short rest intervals between sets (1,3).

When performing consecutive sets of a resistance exercise, maintaining performance within a specified repetition range has been shown to be essential for achieving muscular adaptations conducive to different training goals (2,4,11). However, maintaining repetition performance can be difficult when using shorter rest intervals between sets (i.e., ≤1 min), which may require load reductions (7,8,15,16). Previous research has demonstrated significant reductions in repetition performance when resting 1 minute between back squat sets (15,16). Willardson and Burkett (16) examined repetition performance for the back squat over 4 sets with a constant 8 repetition maximum (8RM) load and 1 minute rest intervals between sets. Subjects performed 7.87 ± 0.52 repetitions on the first set, followed by 5.93 ± 1.90, 4.47 ± 1.85, and 4.20 ± 1.94 repetitions on the second, third, and fourth sets, respectively.

In a follow-up study, Willardson and Burkett (15) demonstrated similar results for the back squat over 5 sets with a constant 15RM load and 1 minute rest intervals between sets. Subjects performed 15.53 ± 0.99 repetitions on the first set, followed by 10.67 ± 2.87, 8.40 ± 3.27, 6.27 ± 2.46, and 6.33 ± 2.69 repetitions on the second, third, fourth, and fifth sets, respectively. These researchers suggested that maintaining repetition performance may require load reductions.

The amount of load reduction that might be necessary to maintain repetition performance has received limited attention in prior studies (7,8,15,16). Addressing this concept under controlled conditions would contribute valuable information for resistance exercise prescriptions, especially for those that involve moderate-intensity loads combined with shorter rest intervals between sets. Therefore, the practical purpose of the current study was to compare repetition performance when keeping the load constant or reducing the load by different percentages during a lower-body workout.

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Methods

Experimental Approach to the Problem

A within-subjects design was used to assess repetition performance over consecutive sets during a lower-body workout. The first 3 weeks were the preparatory period, during which reliability was established for (10RM) loads for the back squat, leg curl, and leg extension exercises (6). All leg curl and leg extension sets were performed using machines (S3LPC and S3LE, Nautilus, Vancouver, WA, USA). The 10RM for each exercise was assessed 3 times (i.e., once during each testing session) during the preparatory period. The next 4 weeks were the data collection period, during which subjects completed 1 lower-body testing session per week under the following load conditions: (a) constant load for all sets, (b) 5% load reduction after each set, (b) 10% load reduction after each set, and (d) 15% load reduction after each set.

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Subjects

Eleven men volunteered to participate in this 7-week study (see Table 1 for demographic characteristics). The sample was classified as recreationally trained. To qualify for inclusion, subjects were initially screened using the Physical Activity Readiness Questionnaire. None of the subjects had lower back, knee, or ankle injuries during the previous year, and all subjects had performed the back squat, leg curl, and leg extension exercises on a weekly basis as part of their resistance training programs.

Table 1

Table 1

The current study was approved through the institutional review board, and subjects were required to sign a consent form in accordance with human subject regulations. Subjects were restricted from performing other lower-body resistance exercises during the study and were blinded as to the order of conditions to which they would be assigned during testing sessions.

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Procedures

Each subject completed 1 exercise session per week for 7 weeks. Each exercise session was conducted on a consistent day and time each week. A certified strength and conditioning specialist supervised each exercise session to ensure proper technique and provide spotting and verbal encouragement. Weeks 1, 2, and 3 were the preparatory period, during which 10RM loads were established for the back squat, leg curl, and leg extension exercises (in that order each testing session) according to previously published procedures (6). The 10RM for each exercise was assessed 3 times (i.e., once during each testing session) during the preparatory period.

Before the 10RM tests, each subject completed 5 minutes of low-intensity aerobic activity (i.e., jogging/walking). Two warm-up sets preceded testing of each exercise at 50% and 75% of the perceived 10RM load for 10 repetitions each. After the warm-ups sets were completed, the load was increased to the perceived 10RM, and 1 set was performed to voluntary exhaustion (i.e., muscle failure). The same spotters closely supervised each 10RM attempt, and subjects were instructed to give a verbal signal when voluntary exhaustion was reached. If less than or more than 10 repetitions were accomplished during a given 10RM attempt, the load was adjusted during the next testing session (6).

The 10RM loads established during the preparatory period were used to design the subsequent testing sessions. Weeks 4, 5, 6, and 7 were the data collection period, during which subjects completed 1 lower-body testing session per week under 1 of the following load conditions: (a) constant load for all sets, (b) 5% load reduction after each set, (c) 10% load reduction after each set, and (d) 15% load reduction after each set. The conditions were randomized and counterbalanced to control for order effects.

Each testing session during the data collection period began with 5 minutes of low-intensity aerobic activity (i.e., jogging/walking). However, warm-up sets were performed for the back squat only, at 50% and 75% of the predetermined 10RM for 10 repetitions each.

After the back squat warm-up sets, 3 consecutive sets of each exercise (i.e., back squat, leg curl, and leg extension) were performed to the point of voluntary exhaustion (i.e., full repetition maximums). Subjects were allowed exactly 1 minute of rest between sets and 2 minutes of rest between exercises. The rest intervals were precisely controlled through the use of a handheld stopwatch.

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Statistical Analyses

The independent variables for this experiment were 4 conditions (constant load, 5%, 10%, and 15% load reductions), 3 exercises (back squat, leg curl, and leg extension), and 3 sets (first, second, and third). The dependent variable was the number of repetitions performed. To assess the reliability of the 10RM loads, intraclass correlations (ICCs) were calculated for each exercise (i.e., back squat, leg curl, leg extension) based on the repetition maximum reached during the preparatory period (i.e., wk 1-3). A 4 (conditions) × 3 (exercises) × 3 (sets) repeated-measures analysis of variance (ANOVA) was used to compare repetition performance; the Greenhouse-Geisser correction was applied when the Mauchly's test of sphericity was violated. Significance of interactions and main effects was based on an alpha level of p < 0.05. All statistical comparisons were made using SPSS version 16.0 (SPSS, Inc., Chicago, IL, USA).

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Results

The ICCs for each exercise all exceeded 0.90, which indicated that the 10RM loads were reliable (15,16). The 4 (conditions) × 3 (exercises) × 3 (sets) repeated-measures ANOVA indicated that the 3-way interaction for conditions*exercises*sets was not significant (F = 1.53; p = .24). However, the 2-way interactions for conditions*exercises (F = 3.22; p = 0.04) and conditions*sets (F = 39.35; p = 0.0001) were significant. The 2-way interaction for exercises*sets was not significant (F = 2.05; p = .14). Post hoc pairwise comparisons were then conducted on the significant 2-way interactions (5). The significance of post hoc pairwise comparisons was determined using the Bonferroni correction.

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Conditions*Exercises

Post hoc pairwise comparisons indicated that, when averaged across sets, significantly greater repetitions were accomplished within the constant condition for the leg extension vs. the back squat (p = 0.002) and the leg curl (p = 0.022). However, the repetitions accomplished within the constant condition were not significantly different for the back squat vs. the leg curl (p = 1.000). Within the 5%, 10%, and 15% conditions, the repetitions accomplished were not significantly different between exercises (p > 0.05) (Figure 1).

Figure 1

Figure 1

Post hoc pairwise comparisons also indicated that, when averaged across sets, significantly fewer repetitions were accomplished for the back squat within the constant condition vs. the 10% condition (p = 0.002) and within the constant condition vs. the 15% condition (p = 0.0001); there were no other significant differences between conditions (p > 0.05). For the leg curl, significantly fewer repetitions were accomplished within the constant condition vs. the 15% condition (p = 0.002); there were no other significant differences between conditions (p > 0.05). For the leg extension, there were no significant differences in the repetitions accomplished between conditions (p > 0.05) (Figure 2).

Figure 2

Figure 2

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Conditions*Sets

Post hoc pairwise comparisons indicated that, when averaged across exercises, significantly greater repetitions were accomplished within the constant, 5%, and 10% conditions for set 1 vs. set 2 (p < 0.01) and for set 1 vs. set 3 (p < 0.01). Within the constant, 5%, and 10% conditions, the repetitions accomplished were not significantly different for set 2 vs. set 3 (p = 1.000). Within the 15% condition, the repetitions accomplished were not significantly different between sets (p > 0.05) (Figure 3).

Figure 3

Figure 3

Post hoc pairwise comparisons also indicated that, when averaged across exercises, the repetitions accomplished for set 1 were not significantly different between conditions (p > 0.05). For set 2, significantly fewer repetitions were accomplished within the constant condition vs. the 10% condition (p = 0.001), within the constant condition vs. the 15% condition (p = 0.0001), and within the 5% condition vs. the 15% condition (p = 0.005); there were no other significant differences between conditions (p > 0.05). For set 3, significantly fewer repetitions were accomplished within the constant condition vs. the 5% condition (p = 0.011), within the constant condition vs. the 10% condition (p = 0.0001), within the constant condition vs. the 15% condition (p = 0.0001), within the 5% condition vs. the 15% condition (p = 0.0001), and within the 10% condition vs. the 15% condition (p = 0.019); there were no other significant differences between conditions (p > 0.05) (Figure 4).

Figure 4

Figure 4

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Discussion

When performing consecutive sets of a resistance exercise, maintaining performance within a specified repetition range has been shown to be essential for achieving muscular adaptations conducive to different training goals (2,4,11). However, maintaining repetition performance can be difficult when using shorter rest intervals between sets (i.e., <1 min), which may require load reductions (7,8,15,16). For the constant load condition, there were large discrepancies in repetition performance between the first vs. the third sets for all exercises (e.g., back squat 10.55 ± 1.75 vs. 3.00 + 2.00). These results were consistent with prior studies that examined the bench press and back squat with a constant load (15,16).

Willardson and Burkett (16) examined repetition performance for the bench press and back squat over 4 sets with a constant 8RM load and 1 minute rest intervals between sets. For the bench press, subjects performed 7.47 ± 1.06 repetitions on the first set, followed by 4.40 ± 1.64, 2.87 ± 1.30, and 2.40 ± 1.18 repetitions on the second, third, and fourth sets, respectively. For the backs squat, subjects performed 7.87 ± .52 repetitions on the first set, followed by 5.93 ± 1.90, 4.47 ± 1.85, and 4.20 ± 1.94 repetitions on the second, third, and fourth sets, respectively.

In a follow-up study, Willardson and Burkett (15) demonstrated similar results for the bench press and back squat over 5 sets with a constant 15RM load and 1 minute rest intervals between sets. For the bench press, subjects performed 14.67 ± 1.50 repetitions on the first set, followed by 5.93 ± 1.98, 3.60 ± 1.18, 3.33 ± 1.11, and 2.80 ± 1.32 repetitions on the second, third, fourth, and fifth sets, respectively. For the back squat, subjects performed 15.53 ± .99 repetitions on the first set, followed by 10.67 ± 2.87, 8.40 ± 3.27, 6.27 ± 2.46, and 6.33 ± 2.69 repetitions on the second, third, fourth, and fifth sets, respectively.

In both studies (15,16), greater fatigue resistance was demonstrated for the back squat vs. the bench press, as evidenced by less discrepancy in repetition performance between the first and the last sets. Therefore, the amount of load reduction to maintain repetition performance for upper-body exercises could be greater than exhibited in the current study for the lower body exercises. Further research is necessary that examines different muscle groups and movements.

A key finding from the current study was that subjects exhibited relatively greater fatigue resistance for the leg extension vs. the back squat and leg curl. For the constant load condition, the repetitions (averaged across sets) accomplished for the back squat and leg curl were 5.75 ± 2.02 and 6.27 ± 1.06 vs. 9.03 ± 1.52 for the leg extension, respectively. These were surprising findings given that the leg extension was performed last in the exercise sequence when greater fatigue could be expected. The back squat involves multiple muscle groups, and the lower back musculature may have fatigued before the point when the quadriceps were fully exhausted, thus limiting the repetitions accomplished for the back squat but subsequently allowing greater repetitions for the leg extension. Other possible explanations for such findings may include potentiation vs. fatiguing effects of the preceding exercise and reciprocal inhibition of antagonist muscle groups. However, these mechanisms should be examined in future research.

The percentage load reductions examined in the current study were subjectively chosen because this is a topic that has received limited attention in prior studies. Ratamess et al. (8) examined load reductions over 5 sets of the bench press exercise when performed at 2 different intensities (i.e., 10RM and 5RM) and with 5 different rest intervals between sets (i.e., 30 seconds, 1, 2, 3, 5 min). Load reductions of 2.3 to 6.9 kg were instituted when necessary to maintain repetition performance. The findings demonstrated that, irrespective of the intensity, the load significantly decreased with each set in succession when resting 30 seconds or 1 minute between sets. The load was maintained over 2 sets for 2 minutes, 3 sets for 3 minutes, and 4 sets for 5 minutes. Consequently, the authors recommended that at least 2 minutes of rest might be needed to minimize load reductions and maintain repetition performance.

The methods of Ratamess et al. (8) were different from the current study because of load reductions instituted in absolute terms rather than relative terms. Relative load reductions might be more appropriate to account for differences in strength levels between individuals. In the current study, 15% load reductions per set allowed for consistent repetition performance for the back squat and leg curl. Conversely, load reductions were not necessary for the leg extension.

Whether load reductions are necessary may depend heavily on training background. Kraemer et al. (7) demonstrated that consistent training with shorter rest intervals may lessen the need for load reductions. Nine competitive bodybuilders and 8 competitive power lifters were compared on a 10-station resistance exercise circuit. Three sets of each exercise were performed with a 10RM load and with 10 second rest intervals between sets. The key finding was that the bodybuilders required less load reductions vs. the power lifters to maintain repetition performance for the leg press and bench press.

Kraemer et al. (7) concluded that the bodybuilders demonstrated greater fatigue resistance because of adaptations associated with the bodybuilding style of training (e.g., moderate to high repetition sets with shorter rest intervals). These adaptations may have included development of the fast glycolytic energy system, with higher activities of anaerobic enzymes (e.g., phosphorylase, phosphofructokinase, and lactate dehydrogenase), thus delaying proton accumulation and metabolic acidosis (9,12-14). From a practical perspective, bodybuilders often perform workouts that involve load reductions over consecutive sets, as examined in the current study; this training technique is referred to as “descending sets” or “drop sets” (10).

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Practical Applications

Maintaining performance within a specified repetition range has been shown to be essential for achieving muscular adaptations conducive to different training goals. However, maintaining repetition performance can be difficult when using shorter rest intervals between sets (i.e., ≤1 min), which may require load reductions. For the back squat and leg curl, 15% load reductions per set allowed for consistent repetition performance. Conversely, load reductions were not necessary for the leg extension. The amount of load reduction may lessen over time as individuals train frequently with low- to moderate-intensity loading schemes and shorter rest intervals between sets, a topic that should be examined in future research.

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References

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Keywords:

rest interval; recovery; fatigue; strength

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