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Effects on Strength, Power, and Flexibility in Adolescents of Nonperiodized Vs. Daily Nonlinear Periodized Weight Training

Moraes, Eveline1,2; Fleck, Steven J.3; Ricardo Dias, Marcelo2; Simão, Roberto1

Journal of Strength and Conditioning Research: December 2013 - Volume 27 - Issue 12 - p 3310–3321
doi: 10.1519/JSC.0b013e31828de8c3
Original Research
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Moraes, E, Fleck, SJ, Dias, MR, and Simão, R. Effects on strength, power, and flexibility in adolescents of nonperiodized vs. daily nonlinear periodized weight training. J Strength Cond Res 27(12): 3310–3321, 2013—The aim of this study was to compare 2 models of resistance training (RT) programs, nonperiodized (NP) training and daily nonlinear periodized (DNLP) training, on strength, power, and flexibility in untrained adolescents. Thirty-eight untrained male adolescents were randomly assigned to 1 of 3 groups: a control group, NP RT program, and DNLP program. The subjects were tested pretraining and after 4, 8, and 12 weeks for 1 repetition maximum (1RM) resistances in the bench press and 45° leg press, sit and reach test, countermovement vertical jump (CMVJ), and standing long jump (SLJ). Both training groups performed the same sequence of exercises 3 times a week for a total of 36 sessions. The NP RT consisted of 3 sets of 10–12RM throughout the training period. The DNLP training consisted of 3 sets using different training intensities for each of the 3 training sessions per week. The total volume of the training programs was not significantly different. Both the NP and DNLP groups exhibited a significant increase in the 1RM for the bench press and 45° leg press posttraining compared with that pretraining, but there were no significant differences between groups (p ≤ 0.05). The DNLP group’s 1RM changes showed greater percentage improvements and effect sizes. Training intensity for the bench press and 45° leg press did not significantly change during the training. In the CMVJ and SLJ tests, NP and DNLP training showed no significant change. The DNLP group showed a significant increase in the sit and reach test after 8 and 12 weeks of training compared with pretraining; this did not occur with NP training. In summary, in untrained adolescents during a 12-week training period, a DNLP program can be used to elicit similar and possible superior maximal strength and flexibility gains compared with an NP multiset training model.

1Physical Education Postgraduation Program, Rio de Janeiro Federal University, Rio de Janeiro, Brazil;

2Laboratory of Exercise Physiology and Morphofunctional Assessment, Granbery Methodist College, and Morphofunctional Assessmen Juiz de Fora, Brazil; and

3Health, Exercise Science, and Sport Management, University of Wisconsin-Parkside, Kenosha, Wisconsin

Address correspondence to Dr. Roberto Simão, robertosimao@ufrj.br.

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Introduction

Resistance training (RT) is a safe and effective method of conditioning for children and adolescents, when performed in a safe environment, with correct exercise technique and with proper supervision (8). Participation of children and adolescents in an RT program can improve strength and muscular endurance, body composition, blood lipid profile, bone mineral density (19), cardiovascular fitness, and mental health (1,30). Collectively, all these factors reduce the risk of injury in sports and recreational activities, and improve health (28).

The National Strength and Conditioning Association (NSCA) recognizes and supports the premise that many of the benefits associated with adult RT programs are attainable by children and adolescents who follow age-specific RT guidelines (8). Periodization or systematically varying the training program over time is well accepted (27). In a meta-analysis comparing the effectiveness of periodized vs. nonperiodized (NP) RT in the development of strength and power, Rhea and Alderman (23) determined that periodized RT was more effective than NP training was in both trained and untrained men and women of ages ranging from 18 to 65 years (effect size [ES] = 1.28, SD = 1.14 vs. ES = 1.03, SD = 0.98).

Based on the aforementioned meta-analysis for adults, it is reasonable to suggest that children and adolescents who participate in well-designed, periodized RT programs will show greater fitness gains than with NP programs. Additionally, children and adolescents may be more likely to adhere to an RT program if it is periodized (8). However, research investigating the effects of periodized RT compared with NP training and comparisons of different types of periodized RT in younger populations is generally lacking. Studies concerning the effects of periodization in children and adolescents demonstrate that they are effective in causing strength and other fitness gains (9,29), but both of these studies used linear periodization programs. Daily nonlinear periodization (DNLP), during which training zones (i.e. 4–6, 8–10, 12–15 repetitions per set) are changed on a training session by training session basis, has been used to train overweight and obese children and adolescents. One study showed that DNLP increases strength in overweight and obese children during 8 weeks of training (18). However, this study did not compare DNLP with any other training model. Only 1 study (13) has compared DNLP with another type of training program. This study trained obese children and showed no significant difference in strength gains between DNLP and a linear periodization program; however, the percentage gain in strength with DNLP was greater. Thus, there is an apparent lack of information comparing DNLP with other training models in apparently healthy children and adolescents.

Considering the greater effectiveness of periodized RT compared with NP training in adults and the lack of studies investigating the effect of periodization in children and adolescents, more information about the effects of various types of periodization in untrained healthy adolescents seems warranted. Thus, the objective of this study was to compare NP training and DNLP training on strength, power, and flexibility in untrained apparently healthy adolescents. Periodized RT appears to be more effective than NP training in adults (23); thus, we hypothesized that DNLP would be more effective in increasing strength than NP training in apparently healthy adolescents.

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Methods

Experimental Approach to the Problem

The term adolescence refers to a period between childhood and adulthood (Tanner stages 3 and 4 of sexual maturation) that includes boys aged 14–18 years (8). Thirty-eight untrained male adolescents were randomly assigned to 1 of 3 groups: a control group (CG) that performed no RT and 2 training groups. One training group trained with an NP RT program and the other with a DNLP program. Dietary intake was not monitored, but the subjects and their parents were instructed to maintain their typical dietary practices.

Before group assignment, all the subjects performed all pretests. The timeline of the pretests was the following: day 1, 1 repetition maximum (1RM) tests for the machine bench press and 45° leg press; day 2, sit and reach test, a 2-hour rest period, a no-step countermovement vertical jump (CMVJ) test and standing long jump (SLJ) test; day 3, no testing; day 4, the same tests as on day 1; and day 5, the same tests as on day 2. Testing on days 1 and 2, and on days 4 and 5 was performed in a counterbalanced order. The machine bench press and 45° leg press were chosen for 1RM testing because they were performed in the training program and they are multijoint exercises that are commonly used for testing purposes in training studies and in testing of athletes and fitness enthusiasts. The CMVJ and SLJ were chosen because they are also commonly used measures of power, and the sit and reach test is a commonly used test to reflect flexibility. Additionally, all of these tests were shown to have good test-retest reliability in the pretesting for this project. This testing order allowed the determination of the reliability of all tests by comparing the results on days 1 and 2 vs. those on days 4 and 5. After pretesting, both training groups trained for 4 weeks followed by 5 days of testing using the same test order as during pretesting, including test-retest reliability determination. This same pattern of training 4 weeks and testing was followed for 2 more training cycles resulting in a total of 12 weeks of training. This pattern of training and testing allowed the testing to serve as a recovery period after each 4 weeks of training, and allowed the determination of test results and test-retest reliability after each 4 weeks of training. The total training duration of 12 weeks was chosen because previous studies have shown strength increases in children and adolescents after 8 weeks of training (11,15,18,24,29), and so a total of 12 weeks of training would be sufficient to cause significant strength gains.

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Subjects

Thirty-eight untrained male adolescents volunteered for this study, and they were randomly assigned to 3 groups: CG (n = 10), NP (n = 14), and DNLP (n = 14). There were no statistically significant differences (p > 0.05) between the characteristics of groups in pretraining and posttraining (Table 1). Study inclusion criteria were that the subjects (a) be physically active, but had not performed RT before the start of the study; (b) not perform any other type of regular physical activity for the duration of the study, other than the prescribed RT; (c) had no functional limitation for the performance of the prescribed RT program or any testing; (d) had no injuries or conditions that would affect the performance of the training program or any testing; and (e) had never taken any nutritional supplements (multivitamins, whey protein shakes, creatine) before or during the study. To determine the stage of sexual maturation, the subjects completed a questionnaire concerning maturation and were then evaluated by a researcher experienced with Tanner stage evaluation (7). This method of maturation evaluation has been shown to be reliable and reproducible (7). Five subjects in the NP group self-assessed in Tanner stage 4 and 9 subjects in Tanner stage 3 of sexual maturation. In the DNLP group, 4 subjects self-assessed in stage 4 and 10 subjects in stage 3. In the CG, 6 subjects self-assessed in stage 3 and 4 subjects in stage 4. All the subjects in the training groups had an adherence rate to training of at least 95%.

Table 1

Table 1

Before starting the study, all the parents and the subjects read and signed an informed consent form, which thoroughly explained the testing and training procedures that would be performed during the study. The experimental procedures were approved by a university Institutional Review Board before initiation of the project.

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One-Repetition Maximum Testing

Before pretesting and the RT phase, all participants underwent a 1-week (3 sessions per week) familiarization period, during which the subjects performed the same exercises as used in the 1RM tests, with the aim of standardizing the technique of each exercise. The sessions were performed for 3 sets of 15 repetitions, using a light weight. After the familiarization period, all the participants completed 3 familiarization sessions of the 1RM test protocol. The 1RM tests were then performed on the same day for a machine bench press and 45° leg press (Rotech, Goiás, Brazil), with a 10-minute rest interval between exercises, using a counterbalanced order. The test and retest of 1RM to determine test-retest reliability were separated by 72 hours as described above in the timeline of testing. The heaviest resistance achieved on either of the test days was considered the 1RM resistance of a given exercise. No exercise besides the other tests performed as described in the timeline was allowed in the period between 1RM test sessions, so as not to interfere with the test-retest reliability results.

To minimize error during the 1RM tests, the following strategies were adopted (27): (a) standardized instructions concerning the testing procedure were given to the participants before the test; (b) the participants received standardized instructions on specific exercise technique; and (c) verbal encouragement was provided during the testing procedure. The 1RM was determined in <5 attempts, with a rest interval of 5 minutes between 1RM attempts, and a 10-minute recovery period was allowed before the start of the 1RM testing of the next exercise.

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Sit and Reach Test

Sit and reach flexibility was tested on 2 days separated by 72 hours as described in the timeline above. Maximum sit and reach flexibility was measured using a standard sit and reach testing box and protocol (2). The best of 3 attempts with an interval of 10 seconds between attempts was used as sit and reach ability. Before the flexibility test, 4 static stretching exercises were performed for the major muscle groups stretched in the test. Each exercise was performed for 2 sets of two 10-second repetitions held at the point of slight discomfort. A 10-second interval was allowed between the last stretching exercise and the sit and reach test.

Given below is a detailed description of the 4 stretching exercises performed before the sit and reach test: (a) Sitting hamstring stretch—in a seated position with both knees straight, the subjects bent at the trunk attempting to grasp and hold both feet. (b) Hip flexor stretch—in a lunge position with the back knee touching the ground, the subjects were instructed to lean backward from the hips while maintaining a straight or arched spine. (c) Knee extensor stretch—in a standing position, the subjects were instructed to grasp 1 foot, flexing at the knee, and to pull the foot upward toward the buttocks. (d) Gastrocnemius stretch—in a lunge position, the subjects were instructed to lean forward and place the hands on the floor while straightening the rear leg and attempting to place the heel of the rear foot on the floor.

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Vertical Countermovement and Standing Long Jump Testing

A no-step CMVJ and SLJ were tested on 2 days separated by 72 hours as described in the timeline above. This testing protocol was used to determine jumping ability and test-retest reliability. All measurements were conducted according to standardized protocols (5). The jump tests were always performed in the following order: a no-step CMVJ and an SLJ. The participants performed 3 attempts of each jump type and were allowed 3 minutes of rest between CMVJ and SLJ attempts and 10 minutes between the CMVJ and SLJ tests.

During the CMVJ, the subjects began in an erect standing position, moved into a semisquat position, and then immediately jumped to allow the use of a stretch shortening cycle during the jump. An arm swing was allowed to maximize vertical jump height. Before jumping, the subjects chalked their right fingertips and then jumped as high as possible touching a chalk board at the highest point of the jump. The vertical jump height was determined by subtracting the standing reach height from the maximal jump height. The highest CMVJ height achieved was recorded.

The SLJ was tested and performed as previously described (5). Briefly, the subject stood with their toes just behind a starting line with feet approximately hip width apart. They then jumped forward as far as possible using an arm swing. The length of the jump (centimeters) was measured as the distance from the takeoff line to the point where the back of the heel nearest to the takeoff line landed. The best score was considered the SLJ distance. No exercise besides the other tests performed as described in the timeline was allowed in the period between jumping ability test sessions, so as not to interfere with the test-retest reliability results.

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Training Procedures

After pretesting, the subjects were randomly assigned to the NP group, DNLP group, and CG. The sets and maximum repetitions per set used by the NP and DNLP are shown in Table 2. Training included 3 weekly sessions, performed every other day, for 36 total sessions. Before each training session, the subjects performed a specific warm-up and 20 repetitions using 50% of the weight used in the first exercise of the training session. The exercise order for both groups was machine bench press, 45° leg press, front lat pull-down, leg extension, military press, seated leg curl, pulley triceps extension, abdominal crunches, and arm curl. All exercises were performed using RT machines (Rotech, Goiás, Brazil). This training program was chosen because previous studies demonstrate DNLP and 3 set programs result in significant strength gains in children and in adolescents (11,13,15,29). No other types of training, such as plyometric or flexibility, were performed during the study.

Table 2

Table 2

Three sets of all exercises in a session were performed to voluntary concentric failure with the number of repetitions varying according to the intensity prescribed for a training session. All the sessions were individually monitored by an RT professional. The RT professional provided verbal encouragement to achieve concentric failure for all sets performed and adjusted the resistance when 2 repetitions more than the programmed repetitions training range for the exercise were performed. The increased resistance maintained the repetitions performed in the prescribed training zone. Rest periods between sets and exercises were of 1–1.5 minutes except when 3–5RM was performed where 2- to 3-minute rest periods were used (6). The total training volume (sets × repetitions) between training programs was equated.

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Statistical Analyses

All data are presented as mean ± SD. The Shapiro-Wilk normality test and a homoscedasticity test (Levene criterion) were used to test the normal distribution of the data. All variables presented a normal distribution and homoscedasticity. Intraclass correlation coefficients (ICCs) and dependent t-tests were used to determine 1RM, CMVJ, SLJ, and sit and reach measures test-retest reliability. A 2 (baseline and post 4, 8, and 12 weeks of training) by 3 (CG and 2 periodization models—NP and DNLP) analysis of variance was used to analyze the difference between periodization models, followed by the Tukey post hoc test when necessary. The independent t-test was used to verify the difference between training total volume (sets × repetitions × load), between both groups of training. Effect size for all dependent variables (the difference between pretest and posttest scores divided by the SD of pretest), and the scale proposed by Rhea (22) was used to examine the magnitude of the treatment effect. Percentage increases compared with that of pretraining were calculated after 4, 8, and 12 weeks of training. The percentage of 1RMs was calculated using the training weight in the last training session before 1RM testing at all time points. Self-assessed maturational stage was analyzed using the sign test and Wilcox paired test. The significance level adopted was p ≤ 0.05 for all tests. The Statistical software version 6.0 (Statsoft, Inc., Tulsa, OK, USA) was used in all analyses.

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Results

There were no statistically significant differences between groups in the pretraining and posttraining variables: body mass, height, age, maturational stage, and 1RM per body mass (Table 1). Adherence to training for all the subjects was at least 95%, and no injuries related to training or testing occurred. The ICC presented high correlations pretraining for 1RM (bench press, r = 0.91; leg press, r = 0.96), CMVJ (r = 0.97), SLJ (r = 0.98), and sit and reach (r = 0.95). After 4, 8, and 12 weeks of training, all measurements also presented high ICC values (range 0.94–0.98). Dependent t-tests showed no significant difference between the 2 test values for any variable at pretraining or after 4, 8, and 12 weeks of training. There were no statistically significant differences between groups in the total volume expressed as sets × repetitions of the training programs (NP = 9,922.3 ± 55.9 repetitions; DNLP = 9,926.8 ± 54.1 repetitions; p = 0.836) or the total training volume expressed as sets × repetition × resistance (kilograms) (NP = 1,010,420 ± 106,975 kg; and DNLP = 1,019,543 ± 118,146 kg; p = 0.668; F = 0.209). The only difference between the training groups in terms of total training volume was the pattern of training intensity used.

Both NP and DNLP groups exhibited a significant increase in the 1RM for the bench press and 45° leg press posttraining. The increase in the bench press 1RM for the DNLP group increased pretraining to 4 weeks, from 4 to 8 weeks and from 8 to 12 weeks. The NP group did not show an increase in the bench press 1RM pretraining to 4 weeks, but did show a significant increase pretraining to 8 and 8–12 weeks. The increase at 12 weeks for both the NP and the DNLP groups was greater than that for the CG at 12 weeks. For the 45° leg press, both training groups showed significant increases from the previous time point for all time points tested and a significant difference from the CG at 4, 8, and 12 weeks. But, there were no significant differences between training groups for either the bench press or 45° leg press 1RM. The 1RM resistances and the respective percentage improvements and ES are shown in Tables 3 and 4. The DNLP group showed greater percentage improvements and ESs compared with pretraining than the NP group did for 1RM resistances in the bench press and 45° leg press after 4, 8, and 12 weeks of training. Both training groups showed consistent significant 1RM increases during the training program with the only difference between groups being that the DNLP program showed a significant increase from pretraining to 4 weeks of training in the 45° leg press, whereas the NP did not.

Table 3

Table 3

Table 4

Table 4

The average training intensity (percent of 1RM) for 10–12RM for the bench press and 45° leg press for the NP and DNLP groups did not change significantly at any time point in the training (Table 5). The average training intensity for the 10–12RM zone was not significantly different between the 2 training groups or between the bench press and 45° leg press at any time point. The average training intensity was significantly different between the 10RM and 12RM zone of both the NP and the DNLP groups and the other training zones used by the DNLP group at all time points, except for the 13–15RM intensity. The training intensity of the DNLP group for a specific zone at a time point was in almost all comparisons significantly different from all other training zones of the same exercise except for training zones immediately higher or lower (5–7RM different from all other zones except for 3–5RM and 8–1RM).

Table 5

Table 5

The CMVJ and SLJ ability of the NP and DNLP groups showed no significant change, with no difference between the groups at any time point in training. Neither training group showed a significant difference in either the CMVJ or SLJ compared with the CG at any time point (Tables 6 and 7). The DNLP group showed a significant increase in the sit and reach test after 8 and 12 weeks of training compared with that for pretraining, whereas the NP group showed no significant change at any time point compared with that for pretraining. There was no significant difference between the 2 training groups or between training groups and CG at any time point for the sit and reach test, but the DNLP showed higher percent changes (Table 8).

Table 6

Table 6

Table 7

Table 7

Table 8

Table 8

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Discussion

The main purpose of this study was to compare upper and lower body strength gains in untrained adolescents performing an NP and a DNLP RT program. Both training groups showed significant 1RM strength gains (bench press and 45° leg press) compared with that for pretraining, but there was no significant difference between the 2 training programs. However, the ESs and percentage improvements indicated greater gains with the DNLP program. Therefore, the initial hypothesis that DNLP would result in greater strength increases was in part confirmed, because the values of ES and % change after 12 weeks of intervention, were greater in the DNLP program compared with that in the NP program for both the bench press (ES = 3.4 vs. 1.2; % change = 35.5 vs. 18.9), and 45° leg press (ES = 6.3 vs. 5.1; % change = 106.9 vs. 88.2). The secondary purpose was to compare CMVJ, SLJ, and sit and reach changes because of the 2 programs. The CMVJ and SLJ performances were not significantly affected by either program. Although the sit and reach performance was not significantly different between training programs, the DNLP program showed a significant improvement at 8 and 12 weeks compared with that for pretraining and compared with that for the CG at these same time points.

Various periodized programs have been shown to be effective in causing fitness increases in children and adolescents. Faigenbaum et al. (9) evaluated the efficacy of a 9-week multiset linear periodization program on physical fitness of boys with a mean age of 13.9 ± 4.0 years. The linear periodization program resulted in a significant improvement in the 10RM squat strength (19%), 10RM bench press strength (15%), sit and reach ability (10%), CMVJ test (5%), medicine ball throw (12%), and estimated cardiovascular endurance (Progressive Aerobic Cardiovascular Endurance Run test, 36%). In boys and girls aged 7–12 years, a linear periodization program also showed significant changes in fitness measures (24). Different groups trained for 8, 16, or 24 weeks. The group training 8 weeks did not show a significant increase in fat-free mass (dual-x ray absorptiometry). However, the groups training for 16 and 24 weeks showed increases in fat-free mass at 8 weeks (6.4 and 5.3%, respectively), 16 weeks (6.8 and 8.3%, respectively), and 24 weeks (11.5%). For squat jump ability, only the group that trained for 24 weeks showed a significant increase at 16 weeks that was maintained after 24 weeks of training. However, a DNLP program performed for 8 weeks by overweight and obese boys and girls with a mean age of 9.7 years also showed positive fitness changes (18). Because of training, the children showed significant increases in 1RM squat strength (74%), CMVJ height (8%), squat jump height (4%), and fat-free mass (dual-x ray absorptiometry, 5%). This study showed significant strength increases, which is in agreement with the findings of previous studies. However, this study did not show significant changes in jumping ability, which is in disagreement with the findings of previous studies. Only the DNLP program resulted in significant changes in sit and reach ability, which is in agreement with the findings of previous studies that RT can result in an increase in the sit and reach ability.

A comparison of linear periodization and DNLP programs performed by obese adolescents aged 16.5 ± 1.7 years because of 14 weeks of training showed that both programs resulted in fitness gains (13). The linear periodization and DNLP programs significantly increased bench press 15RM (175 and 219%, respectively), 45° leg press 15RM (395 and 455%, respectively), maximal oxygen consumption (9 and 10%, respectively), and fat-free mass (plethysmography, 2.8 and 3%, respectively). Although there was no significant difference between the periodized programs in changes of these measures, the DNLP program showed greater percent changes and ESs in the bench press 15RM, 45° leg press 15RM, and maximal oxygen consumption. The results of this previous study and a study described above training children with a DNLP program (18) indicate that periodized programs can increase fitness measures. This study agrees with the above conclusion. The novel finding of this study is DNLP and a nonvaried program result in similar strength, CMVJ and SLJ gains with the percent increases, and ES being greater for the bench press with DNLP.

A meta-analysis on the effect of periodized programs in adults indicates that periodized RT programs result in greater strength gains than nonperiodized programs, but the strength gain experienced by younger adults (age < 55 years, ES = 1.34, SD = 1.15) is greater than that of older adults (age > 55 years, ES = 0.85, SD = 1.05) (23). The results of this study on the effect of a DNLP program agree in part with the meta-analysis. The current results on adolescents show greater percentage increases in both the bench press and 45° leg press 1RM at 4, 8, and 12 weeks of training. Additionally, the ES of the bench press in particular after 12 weeks of training was greater with the DNLP program compared with the nonvaried training program. The calculation of ES is important when the sample size is small and the SD is increased after an intervention (22). An increase in the bench press and 45° leg press 1RM SD is the general trend of the data in this study. Thus, the ES for the bench press indicates an important practical outcome and suggests DNLP compared with nonvaried training increases the 1RM strength to a greater extent in the bench press because of a 12-week training period.

The for 10–12RM training zone intensities (percent of 1RM) for both training groups ranged 69.9 to 74.1% for the bench press and 45° leg press. These intensities are at the upper end of the NSCA recommendations (8) for novices (50–70% 1RM for 1–2 sets of 10–15 repetitions) and the middle of intensities for intermediate lifters (60–80% 1RM for 2–3 sets of 8–12 repetitions). Thus, the training intensities for the 10–12RM zone for these 2 exercises followed NSCA recommendations. Likewise, the training intensities for the 13–15RM and 18–20RM zones ranged between 64.7 and 69.7% and were also within the NSCA recommendations for training intensity. However, the training intensities for the 8–10RM, 5–7RM, and 3–5RM ranged between 84.1 and 94.8% and were above the NSCA recommended intensities. Generally, the training intensity used by the DNLP group at a specific time point for both the bench press and 45° leg press were significantly different from the intensity used for other training zones except for immediately higher or lower training zones (5–7RM different from all other zones except for 3–5RM and 8–10RM). The changes in training intensity because of the use of DNLP is one rational why DNLP results in superior strength gains compared with that in nonvaried training. Training intensity has been shown to generally not change in women with 14 weeks of nonvaried training (12). The training intensity of the bench press and 45° leg press did not change significantly in this study with training and were not significantly different among training programs. The women in this previous study were moderately trained before participating in the prescribed training program. Although the adolescents in this study were untrained before study participation. Thus, these 2 studies agree that training intensity does not change significantly in moderately trained or untrained individuals at least during the first 12–14 weeks of training.

The CMVJ and SLJ test results showed an insignificant increase after 12 weeks of training with both NP and the DNLP training with no significant difference between groups. For these measures, the percent change and ES were similar for both training models. Performance of these tasks depends on power, and the training in this study did not include training specific to power development, such as plyometrics, which may in part explain why performance was not significantly changed in these tasks. In our study, training zones in all sessions were performed until concentric failure and the velocity of repetitions was not controlled. Some studies have investigated the increase in muscle power with RT in children and demonstrated significant increases (9,10,21). As in adults, RT for children and adolescents with the goal of increasing power may require faster velocity movements than the repetition speed performed in the current study. Performance of sets to concentric failure during training in adults has been shown to limit power increases (16). Power increases in this study may have also been limited by not controlling the velocity of repetitions. A review indicates individuals who lift heavier resistances where velocity of movement may be reduced show smaller gains in vertical jump performance compared to lifting lighter resistances where velocity of movement can be faster (17). Thus, not having the subjects in this study perform the concentric portion of repetitions as fast as possible may have limited power increases. The above 2 factors may have limited power increases with both training models in this study.

The sit and reach test performance because of the DNLP program increased significantly after 8 and 12 weeks of training compared with pretraining (22.3%) and compared with the CG. Although the NP training did not show a significant improvement in the sit and reach ability, a 16.7% increase was shown after 12 weeks of training. These results were greater than and in agreement with the results of Faigenbaum et al. (9) who showed a 10% increase in the sit and reach ability in boys aged 13.9 years because of 9 weeks of RT. Our results are also in agreement with those of RT studies on adults showing significant increases in the sit and reach test (4,25,26). According to Simão et al. (26), the mechanisms that explain the flexibility increased derived from RT are not well explained, and a few hypotheses have been suggested. It seems that such increases might be because of neuromuscular responses and to variations in the mechanical properties of the muscular and connective tissues. The reflex activity of Golgi tendon organs is typically reduced with RT, which would result in an increase in strength (14,20). The RT may cause changes in the elastic and plastic structures of muscle tissue that might increase the maximum movement amplitude at a joint (3). It has also been suggested that RT increases tendon and ligament tensile strength and increases collagen synthesis, which may in some way result in a greater movement amplitude. Further research is needed to explain the mechanisms by which RT increases flexibility.

In summary, this was the first study the authors are aware of that compares DNLP and NP training in adolescents. Both training programs significantly increased maximal strength (1RM), but the percent increase and ESs indicate that DNLP may be superior to NP training in producing strength gains in some exercises. DNLP training may also offer an advantage compared with nonvaried training in increasing flexibility. In contrast, power improvements with DNLP and NP training were not significantly different between the 2 training models. Further investigations are needed to compare the effects of different periodization models and nonvaried RT in children and adolescents.

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Practical Applications

In view of the importance of manipulating training volume and intensity, more research on the comparison between periodization models and nonvaried training models in children and adolescents is necessary to establish the best model to increase strength and other training outcomes. Our study suggests that, at least in untrained adolescents during a 12-week training period, DNLP can be used to elicit similar and possible superior maximal strength and flexibility gains than an NP multiset model. Additionally, the DNLP model with variations in volume and intensity occurring from 1 training session to the next may reduce the “monotony” of performing repetitive training sessions and result in greater adherence. The results indicate that DNLP can be used in this age group successfully to increase maximal strength and power with these increases possible being greater than with nonvaried RT. More studies comparing different periodization models and nonvaried models are needed to further elucidate which training models are the most effective in causing increases in specific, strength, hypertrophy, or power, training outcomes.

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Acknowledgments

Dr. Roberto Simão would like to thank the Research and Development Foundation of Riode Janeiro State (FAPERJ).

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Keywords:

exercise programs; muscle strength; resistance training; youth

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