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Neuromuscular Responses to Short-Term Resistance Training With Traditional and Daily Undulating Periodization in Adolescent Elite Judoka

Ullrich, Boris1; Pelzer, Thiemo1,2; Oliveira, Sergio1; Pfeiffer, Mark2

The Journal of Strength & Conditioning Research: August 2016 - Volume 30 - Issue 8 - p 2083–2099
doi: 10.1519/JSC.0000000000001305
Original Research
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Ullrich, B, Pelzer, T, Oliveira, S, and Pfeiffer, M. Neuromuscular responses to short-term resistance training with traditional and daily undulating periodization in adolescent elite judoka. J Strength Cond Res 30(8): 2083–2099, 2016—The influence of different periodization models on neuromuscular outcomes after short-term strength training periods has not been examined in adolescent athletes. Eleven elite judoka (age: 14.8 ± 0.6 years, height: 163.2 ± 7.5 cm, body mass: 57.3 ± 11.1 kg, 5 boys/6 girls, and strength training experience: 2.7 ± 1.1 years) performed two 4-week strength training mesocycles (each with 12 sessions) with either traditional (TP) or daily undulating (DUP) periodization. Both mesocycles were separated by a 7-week washout period and added to the regular judo training. Strength training was performed as lifting and lowering of weights using squats, knee flexion curl, clean & jerk, snatch, bench press, barbell bench pull, and lat pull-down. The mesocycles were equated for the number of repetitions and different intensity zones (50–90% of 1 repetition maximum [1RM]), addressing the optimization of strength, power, or velocity. Laboratory and 1RM testing was carried out 2 times during the baseline (T1 and T2), after the TP mesocycle (T3), after the washout period (T4), and after the DUP mesocycle (T5). Isometric knee extensor and knee flexor maximum voluntary contractive capacity (MVC), electromyographic-estimated neural drive of the quadriceps femoris, vastus lateralis (VL) muscle architecture, and 1RMs of all training exercises were measured. ANOVA revealed moderate (5.5–13.5%) but significant (p ≤ 0.05) temporal gains in knee extensor MVC, 1RMs, and VL architecture during both the mesocycles. Wilcoxon tests detected no significant differences for the percentage changes of any outcome between the mesocycles. For adolescent judoka, TP and DUP were equally adept in improving neuromuscular outcomes during short-term training periods.

1Department of Biomechanics & Movement Science, Olympic Training and Testing Center of Rhineland-Palatinate/Saarland, Germany; and

2Department of Theory and Practical Performance of Physical Activities, JGU University of Mainz, Mainz, Germany

Address correspondence to Dr. Boris Ullrich, b.ullrich@olympiastuetzpunkt.org.

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Introduction

Competitive judo matches are composed of high-intensity intermittent actions that impose demanding technical, tactical, and fitness demands on the athletes (2,13,15). More specifically, the explosive technical movements performed to throw the opponent are related to lower-body muscular power (6), whereas some actions to immobilize the opponent require whole-body maximal strength (12,13). Thus, judo requires a wide range of total body strength qualities (12,15), and it was reported that approximately 70% of elite judo athletes conduct strength training sessions more than 3 days per week (14). Based on this information, it is reasonable to argue that enhancing the effectiveness of strength training interventions might optimize judo-specific performance (12).

Periodization is known to optimize neuromuscular outcomes in response to strength training regimens, but the most effective periodization model for many athletic populations is yet to be determined (11,18,41,44). Currently, the most frequently discussed strength training periodization models are traditional or linear periodization (TP) and undulating periodization (UP), also termed nonlinear periodization (11,18,36,44). Typically, TP uses high initial volume and low intensity training, shifting toward reduced volume and increased intensity over the training period (11,38). In contrast, Poliquin (1988) introduced the concept of UP, which applies more frequent alterations in intensity and volume. Depending on whether volume and intensity is changed on a weekly or daily basis, this approach can be programmed as weekly or daily UP (18,36,38).

Evidence suggests that both concepts of stimuli periodization, TP and UP yielded similar neuromuscular outcomes when key training variables such as exercise choice, number of repetitions per set, training intensities, and volume were equated for the compared models (18,26,41,44). In line with previous work (26), Ullrich et al. (2015) have recently reported that 14 weeks of isometric knee extensor training with TP and daily undulating periodization (DUP) yielded similar temporal alterations in muscle architecture, neural drive, and maximum strength in recreationally active women (44). Furthermore, a systematic review of the current literature indicated no differences in the effectiveness of TP vs. UP on upper- or lower-body strength (18). However, caution is needed when findings from laboratory studies (44) and training studies with nonathletic populations (18,35) are to be transferred into athletes' muscular power training regimens (17). To date, few studies have examined periodization effects in athletic populations (5,10,18,34), and no work in this field has been performed with adolescent athletes (18). In addition, most studies comparing periodization models addressed strength outcomes but did not examine the underlying structural or neural dimensions (10,11,40,44).

It is worth noting that alterations in neural drive (32,39) and muscle architecture have been detected after short-term strength training periods of 3–6 weeks (7,39,41,42). Indirect evidence for rapid neuromuscular adaptations can also be derived from joint angle–specific strength changes that occurred after a few training weeks (7,45,46). Identifying the most effective periodization model for eliciting neuromuscular alterations during short-term training periods is important for many sports requiring a short off-season duration and preseason programs during their yearly training cycle (15,29). From our practical experience, short-term muscular power training regimens are routinely performed with nonprofessional adolescent elite athletes who are confronted with time limitations for the different training categories.

Therefore, the purpose of this study was to examine the effects of TP and DUP on the temporal changes of (a) vastus lateralis (VL) muscle architecture, (b) electromyographic (EMG)-estimated neural drive of the quadriceps femoris (QF), and (c) maximum voluntary dynamic upper-body, lower-body, and total body strength after two 4-week muscular power training mesocycles in adolescent athletes. As stated previously, we studied judo athletes because judo requires a wide range of total body strength qualities (12) and intensive strength exercises are regularly conducted by elite judoka (14). In addition, the present adolescent judoka were experienced with both machine and free-weight exercises. Based on the existing literature (18,44), it was hypothesized that there would be no differences between TP and DUP in enhancing the current outcomes.

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Methods

Experimental Approach to the Problem

This work compared the effects of TP and DUP on neuromuscular outcomes after 2 short-term strength training mesocycles with an emphasis on upper-body, lower-body, and total body muscular power enhancement in adolescent elite judo athletes. Therefore, a longitudinal crossover approach with a quasiexperimental design was adopted. The total duration of the study period amounted to 17 weeks (Figure 1). The first 2 weeks were used as a baseline period, where all athletes maintained their regular judo training but did not conduct systematic strength training. Thereafter, athletes performed a first 4-week strength training mesocycle using TP. After the TP mesocycle, athletes started their summer holidays during which they only performed recreational physical activities (7-week washout period: no regular judo training or competitions). After this washout, all athletes conducted a second 4-week strength training mesocycle using DUP. Supervised strength training was conducted 3 times per week during both short-term mesocycles, and the exercise choice, number of repetitions, and intensity zones were equated among the mesocycles. Standardized laboratory and 1 repetition maximum (1RM) testing was performed on 5 different occasions: twice during the baseline (T1 and T2), after the TP mesocycle (T3), after the washout (T4), and after the DUP mesocycle (T5) (Figure 1). Except for the washout period, similar regular judo training sessions were maintained during both short-term training periods.

Figure 1

Figure 1

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Subjects

The study was conducted on 11 adolescent judoka, aged from 14 to 16 years, from regional to elite levels (age: 14.8 ± 0.6 years, height: 163.2 ± 7.5 cm, body mass: 57.3 ± 11.1 kg, and 5 boys/6 girls) that were experienced in the present strength exercises for 2.7 ± 1.1 years. Anthropometric data during the course of the study are presented in Table 1. All athletes attended a specific high school offering combined schooling and athletic training. The third author of our work is the head judo coach at this high school, who supervised all regular judo and strength training sessions. The judo-specific training experience ranged between 5–8 years in this group. All athletes maintained their regular judo training during both short-term strength training mesocycles but conducted only recreational physical activities (average weekly amount: 4–6 hours) during the washout (Figure 1). These recreational activities included submaximal running and cycling and total body stretching exercises. During both compared mesocycles, the weekly amount for regular judo training and competitions and the emphasis of the different training areas were matched as far as possible. In detail, the weekly amount for regular judo training and competitions ranged from 11–13 hours including specific agility and coordination exercises (2–3 hours), technical training (6–7 hours), competition-related training (2–3 hours), and competitions (1–2 hours). To avoid bias from endurance exercises, none of the athletes spent more than 1 hour per week on running or cycling. The athletes maintained their normal diet and none of the athletes was involved in any process of weight loss during the course of this work. None of the athletes reported known medical conditions that may have confounded our results. All athletes and their parents were informed of the benefits and risks of the investigation before signing an institutionally approved informed consent document to participate in the study that was approved by the institutional ethics committee and was in accordance with the Declaration of Helsinki for the use of human subjects in research.

Table 1

Table 1

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Procedures

Anthropometric Measurements

At the beginning of each testing day and before any warm-up, body mass and thigh circumference were measured using electronic weighing scales and a manual tape. Height was measured using a wall-mounted stadiometer. Measurements of the thigh circumference of each subject's dominant leg were performed at midthigh (midway between the anterior superior iliac spine and the proximal border of the patella) as described elsewhere (26).

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Ultrasonographic Measurements of Vastus Lateralis Muscle Architecture

Ultrasonographic analysis was performed before any warm-up to avoid influences of blood flow as far as possible. A brightness-mode ultrasound apparatus (Vivid e; GE Medical System, Jiangsu, China) with a linear scanner (scanning frequency: 7.5 MHz) was used to determine the proximal, distal, and average muscle thickness, fascicle angle, and fascicle length values of M. vastus lateralis from each athlete's dominant leg using the procedures described by Ullrich et al. (2015). The subjects lay supine on a medical bench with the knee fully extended and remained relaxed during the ultrasound scanning. The measurement site was at the level of 50% of the thigh length, defined as the distance from the greater trochanter to the articular cleft between the femur and tibia condyles. At this site, the maximal cross-sectional area for the M. quadriceps femoris can be expected (24). The mediolateral width of the VL was determined over the skin surface and the position of one-half of the width was used to perform the ultrasound images. The transducer head was held perpendicular to the site without any visible depression occurring on the skin surface. An even and light pressure was maintained to prevent deformation of superficial structures as far as possible. These analyses were performed by the same investigator on all occasions. Once the image was optimized, 5 consecutive measurements were performed with the same image. All images were stored on an external device for later analysis. The individual anatomical measurement sides were marked during the first baseline testing with a water-resistant pencil to ensure identical positioning between the testing occasions as far as possible. All athletes received these pencils and re-marked the measurement sides throughout the course of the study.

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Isometric Maximum Voluntary Contractive Capacity of the Knee Extensors and Flexors

Before starting the maximum voluntary contractive capacity (MVC) measurements, all athletes performed 10 minutes of submaximal treadmill running at individual speeds corresponding to each athlete's estimated running speed during an extensive (predominantly aerobic) 45-minute run. Afterward, all athletes conducted 4 minutes of submaximal isometric knee extension and knee flexion contractions on the Biodex dynamometer (Biodex Medical Systems, Inc., Shirley, NY, USA). Thereafter, athletes conducted unilateral isometric MVC knee extension and knee flexion contractions with their dominant lower extremity. Athletes started the MVC testing with either the knee extensions or knee flexion contractions according to random assignation. For both muscle groups, athletes executed 3 MVCs separated by a 3-minute rest period. Knee extensions were executed at a knee joint angle of 70° and a corresponding hip joint angle of 70°. Knee flexions were executed at a knee joint angle of 30° and a corresponding hip joint angle of 70°. Maximum MVC of these muscle groups can be expected in these positions (21,33). Knee and hip joint angles of 0° correspond to full knee and hip extension, respectively. Athletes were seated upright and their upper-body was fixed with rigid straps. The axis of the knee joint was aligned with the axis of the lever arm of the dynamometer. The upper extremities were crossed over the chest during all MVCs. During testing, athletes were asked to build up their MVC within at least 3 seconds and to hold the peak plateau for at least 2 seconds. Trials were repeated if a maximal effort was not sustained for this set period or when subjects judged the attempt to be less than maximal. Athletes were given verbal encouragement and visual online feedback of their moment-time curves by the Biodex software. Gravity correction was applied for all contractions using the Biodex software.

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Electromyographic Measurements for the Quadriceps Femoris

During the isometric knee extensions, muscular excitation from the M. rectus femoris (RF), M. vastus medialis (VM), and M. vastus lateralis was assessed at peak MVC using an EMG telemetry system with preamplification (TeleMyo G2; Noraxon, Inc., Scottsdale, AZ, USA) and the following specifications: CMRR >100 dB, band pass 10–500 Hz, and a 16-bit resolution. The recording frequency was set to 1,000 Hz. The EMG system was synchronized with the dynamometer using a telemetric synchronization apparatus (TeleMyo 2400T receiver; Noraxon, Inc.) to allow time-synchronized assessment of isometric MVC and EMG signals. Adhesive surface electrodes (Blue Sensor; Medicotest, Ballerup, Denmark) were positioned with an interelectrode distance of 20 mm above the midpoint of the muscle belly as assessed by palpation, parallel to the presumed direction of the muscle fibers. Before attaching the electrodes, the skin underneath the electrodes was shaved and cleaned with alcohol. Before starting the protocol, tests including near-maximal contractions were undertaken to determine whether adequate EMG signals could be obtained. Final data calculation was performed with the MyoResearch XP software (MyoResearch XP Master Edition; Noraxon, Inc.). As was described for muscle architectural analysis, the individual anatomical electrode positions that were used during the first baseline testing were marked with a water-resistant pencil. Thereafter, athletes received these pencils to re-mark the respective positions.

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One Repetition Maximum Testing for Maximal Upper-Body, Lower-Body and Total Body Strength

According to literature guidelines (26), 1RM testing was performed for all training exercises on each occasion. 1RM testing was always conducted 2 days after the laboratory testing. Maximum voluntary dynamic strength was determined as the maximum load that could be moved once throughout the defined range of motion (ROM) using a proper technique (12). On all occasions, 1RM testing that predominantly affected the total body and the lower extremities (squat, clean & jerk, snatch, and knee flexion curl) was performed in the morning (between 9 and 12 AM), whereas upper-body 1RM testing (bench press, barbell bench pull, and lat pull-down) was conducted in the afternoon (between 3 and 6 PM). Within these sessions, the order of exercises was chosen according to random assignation. Before testing, athletes conducted a 20-minute warm-up including 10 minutes of running at individual speeds corresponding to each athlete's estimated running speed during an extensive (predominantly aerobic) 45-minute run and dynamic total body stretching exercises. For all 1RM exercises, athletes performed a warm-up set of 10 repetitions with a load approximating 30% of their estimated 1RM. This was followed by warm-up sets of 10 repetitions of 50% of their estimated 1RM and 5 repetitions of 75% of their estimated 1RM. A load approximating 3RM was then applied for each exercise, and the athletes were asked to lift it not more than 3 times. Taking into consideration the number of lifts and the movement technique during this performance, the 1RM load was estimated. Thereafter, trials for 1RM assessment were conducted. Successful trials were followed by a 4-minute rest period, with heavier loads being attempted until the 1RM was determined. This process generally took no more than 5 trials and verbal encouragement was provided for all attempts. Except for the knee flexion curl and lat pull-down (bilateral machine exercises), 1RM testing was conducted using free weights. The movement techniques for all free-weight exercises were adopted from Kraemer and Fleck (1993). For free-weight exercises and the lat pull-down, each athlete's hand positioning on the bar was measured with a manual tape during the first baseline and recorded for successive occasions. The distances between the feet were measured with a manual tape to standardize foot positioning. The ROMs and movement techniques were judged visually by our first 3 authors. Carrying the load a few centimeters below the shoulder, the ROM for the squat was set from the upright standing position to a knee flexion angle of 90°. Successful clean & jerk movements required both phases, translation of the bar from the ground to the chest and promotion of the bar into a balanced position above the head. Laying prone, the knee flexion curl was conducted as a bilateral machine exercise using a commercially available device (Schnell GmbH, Peutenhausen, Germany) with the knees fully extended (starting position) toward a knee flexion angle of 90°. Bench press and barbell bench pull were assessed with the athletes lying on a horizontal bench. For the barbell bench pull, the athletes were lying on an elevated bench (i.e., no contact of the loads with the floor), with the chest, abdomen, and thighs keeping steady contact with the bench. For the bench press, the loaded bar had to be moved from the chest (approximately 90° of elbow flexion) toward full elbow extension. For barbell bench pull, the athletes had to move the bar from nearly full elbow extension toward approximately 90° of elbow flexion (i.e., the bar touched the lower boundary of the bench). The lat pull-down was performed in an upright sitting position (i.e., the back remained straight and rigid) at a commercially available device (Schnell GmbH, Peutenhausen, Germany) using a ROM from nearly full elbow extension until the bar was moved behind the head and touched both shoulders.

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Experimental Strength Training

Each training session took approximately 90 minutes, including warm-up and cool-down periods. Warm-up consisted of 10-minute submaximal running followed by a 10-minute dynamic full-body stretching routine. Cool-down included 5-minute submaximal cycling on ergometers followed by a 10-minute full-body isometric hold-and-relax stretching routine. The strength exercises that were used during both mesocycles have been recommended for adolescent wrestlers by Kraemer and Fleck (1993) and were adopted several years ago by our judo coach. The training regimen consists of both machine exercises and free weights and shows an emphasis on upper-body, lower-body, and total body muscular power enhancement (25) (Tables 2 and 3). The exercises were as follows: squats, clean & jerk, snatch, knee flexion curl, bench press, barbell bench pull, and lat pull-down. The present athletes were experienced with these exercises to a degree of 2.7 ± 1.1 years. The ROMs and movement techniques have been explained in the paragraph on 1RM testing. Training was executed on Monday, Wednesday, and Friday and all athletes gave their written assurance of foregoing additional strength training during the course of the study. Referring to guidelines for muscular power enhancement (17), sessions were separated into “strength sessions” (80, 85, and 90% of 1RM), “power sessions” (65, 70, and 75% of 1RM), and “velocity sessions” (50, 55, and 60% of 1RM). The compared mesocycles were equated for these intensity zones and the number of repetitions within each zone (Tables 2 and 3). In detail, both mesocycles were programmed to have the same number of overall training sessions (n = 12), same number of sessions within each intensity zone (n = 4), total number of sets (n = 342), and total number of repetitions (n = 1513) (Tables 2 and 3). Using TP, sessions 1–4 were performed in the “strength zone,” sessions 5–8 accounted for “power,” and sessions 9–12 were performed in the “velocity zone” (Table 2). In contrast, these intensity zones were applied in a daily undulating scheme during the DUP period (Table 3). During each session, it was randomly determined whether athletes started with either the lower-body and total body exercises (clean & jerk, snatch, squats, and knee flexion curl) or with the upper-body exercises. The order within these “exercise groups” was assigned by randomization during each session. All training sessions were supervised by our second and third authors. Within each contraction cycle, athletes were asked to “accelerate the load as forcefully as possible” (explosive positive lifting phase) and to “lower the load in a controlled fashion” (slow negative lowering phase). Whenever these guidelines were violated, athletes received direct verbal feedback. Rest periods of approximately 3 minutes were given between the sets. None of the athletes missed any session resulting in 100% training compliance during both mesocycles.

Table 2-a

Table 2-a

Table 2-b

Table 2-b

Table 3-a

Table 3-a

Table 3-b

Table 3-b

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Data Analysis

Volume load (kg) was calculated for each exercise and as the sum of all exercises (total training volume load) with the following equation: volume load (kg) = sets × repetitions × load (18,28). A synchronization apparatus (TeleMyo 2400T receiver; Noraxon, Inc.) allowed time-synchronized assessment of MVC knee extensions and flexion moments and raw EMG signals. MVCs and EMG data were organized in the MyoResearch XP software (MyoResearch XP Master Edition; Noraxon, Inc.). Isometric knee extension and knee flexion MVC was defined as the average maximum for a time window of 500 milliseconds at peak MVC. Maximal voluntary EMG activity of RF, VM, and VL was described by the integrated EMG over a time period of 500 milliseconds at peak isometric knee extension MVC. To facilitate data representation (44), QF EMG was estimated as the average sum EMG (RF + VM + VL)/3. VL architectural analysis was performed with the analyzing software of the ultrasound apparatus (Vivid e; GE Medical System). Muscle thickness was defined as the vertical distance between the deeper and superficial aponeurosis and was analyzed at the most proximal and most distal ends and at sides located equidistant from the midline between the most distal and proximal ends (4,44). Pennation angle was measured as the angle of insertion of the muscle fascicles into the deep aponeurosis. Proximal, distal, and average muscle thickness, and pennation angle were measured 5 times in the same image, and these measurements excluding the largest and smallest values were averaged. VL fascicle length was defined as the length of the hypotenuse of a triangle with an angle equal to pennation angle and the side opposite to this angle equal to the muscle thickness, and was estimated by the following equation (4): fascicle length = average muscle thickness/sin (pennation angle). Notably, this model does not account for fascicle curvature. The ratio between VL fascicle length and thigh length was defined as normalized fascicle length. Average VL muscle thickness was normalized to thigh length. In addition to the absolute values, the individual percentage changes of all major outcomes were calculated for both mesocycles. These percentage alterations were calculated between the testing occasions T2 and T3 for the TP mesocycle, and between T4 and T5 for the DUP mesocycle, respectively (Figure 1).

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Statistical Analyses

The statistical analyses were performed using an SPSS standard package for Windows (version 13.0; SPSS, Inc., Chicago, IL, USA), and the initial level of statistical significance was set as α = 0.05. Interday variability (T1 and T2) of thigh circumference, knee extensor and knee flexor MVC, average VL muscle thickness, VL fascicle length, and all 1RM data was estimated by the coefficient of variation (CV) and quantified with an intraclass correlation coefficient (ICC). Because this work used a longitudinal crossover design, Wilcoxon tests with the absolute outcomes were performed between the testing occasions T2 (second baseline testing) and T4 (postwashout testing) to account for possible “carry-over-effects” (Figure 1). A general linear model repeated measures (accounting for 5 testing occasions) analysis of variance (ANOVA) with Bonferroni adjustments was used to detect temporal alterations in our outcomes. In addition, the percentage changes of the major outcomes that occurred during both mesocycles were analyzed with paired Wilcoxon tests. Finally, we calculated effect sizes for the major outcomes during both mesocycles using the following formula: ([meanposttest − meanpretest]/SDpretest) according to the suggestions made by Rhea et al. (2003). Effect size values were then adjusted to sample size bias in smaller (n < 20) sample sizes (19,20). Results are presented as mean ± SD in the tables, and as mean ± SE in the figures, respectively. A post hoc power analysis (α = 0.05, 2-tailed) showed that statistical power for the maximal temporal changes occurring during the course of the study was approximately 28% for knee extension MVC, approximately 36% for average VL muscle thickness, approximately 29% for VL fascicle length, and varied between 38 (lat pull-down) and 66% (squat) for the statistical significant 1RM alterations. A priori sample size calculations that used estimations of 15% for maximal periodization effects on the temporal alterations of MVC, 1RM, and VL architecture yielded sample size values ranging from 20–28 athletes to prove these effects with a statistical power of 60%. Therefore, our work was performed with a smaller sample size (n = 11) than would have been needed to document moderate periodization effects.

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Results

Baseline Variability and Carry-Over Effects

No significant pretraining differences (T1 vs. T2) were detected for any outcome of the present work (Tables 1 and 4; Figures 2–4). Interday reliability measurements (T1 vs. T2) for thigh circumference, knee extensor and knee flexor MVC, average VL muscle thickness, VL fascicle length, and all 1RM data showed significant (p ≤ 0.05) ICCs ranging from 0.88 to 0.99. The corresponding CV values ranged from 0.8 (squat 1RM) to 7.1 (isometric knee flexor MVC). Notably, no significant carry-over-effects were detected for any outcome; i.e., Wilcoxon comparisons yielded no significant differences between T2 and T4.

Table 4

Table 4

Figure 2

Figure 2

Figure 3

Figure 3

Figure 4

Figure 4

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Training Volume Load and Intensity

Training volume load for each exercise and total training volume load (sum of all exercises) are presented in Figure 6. Except for lat pull-down, bench press, and knee flexion curl, significant (p ≤ 0.05) higher training volume loads occurred during the DUP mesocycle (Figure 6). Showing statistical significance (p ≤ 0.05), the total volume load was approximately 7% higher during the DUP mesocycle (Figure 6).

Figure 6

Figure 6

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Changes in Anthropometric Values

Anthropometric data of the athletes throughout the course of the study are given in Table 1. Height was significantly (p ≤ 0.05) increased after the DUP mesocycle relative to the testing occasions T1–T3. Body mass, thigh length, and thigh circumference remained unaltered during the course of the study. With one exception between T1 and T4, no significant BMI alterations occurred during the study period (Table 1).

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Changes in Vastus Lateralis Muscle Architecture

ANOVA detected significant (p ≤ 0.05) temporal changes in VL muscle architecture (Table 4) during the study period. Proximal VL muscle thickness was significantly (p ≤ 0.05) higher after the TP mesocycle (T3) compared with T1. Distal, mean, averaged, and normalized VL muscle thickness was significantly (p ≤ 0.05) higher at T3 relative to both baseline testing occasions (Table 4). After the DUP mesocycle (T5), mean VL muscle thickness was significantly (p ≤ 0.05) increased compared with the washout testing occasion (T4). Significant (p ≤ 0.05) increases in VL fascicle length occurred at T3 relative to the second baseline testing occasion (T2). Similar pennation angles were detected on all occasions (Table 4). Importantly, the percentage changes of the studied muscle architectural dimensions displayed no significant differences between the mesocycles (Table 4, Figure 5A). Effect size calculations (Hedges' g) yielded values of 0.49 and 0.34 for average VL muscle thickness and 0.50 and 0.07 for VL fascicle length during the TP mesocycle and DUP mesocycle, respectively (Table 5).

Figure 5

Figure 5

Table 5

Table 5

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Absolute Isometric Strength Changes in the Knee Extensors and Flexors

ANOVA detected significant (p ≤ 0.05) temporal changes in isometric knee extensor MVC during the course of the study (Figure 2). In contrast, knee flexor MVC remained statistically unaltered during the study period (Figure 2). Knee extensor MVC showed no statistical alterations during the TP mesocycle, but significantly (p ≤ 0.05) increased after the DUP mesocycle (T5) compared with baseline testing (T1 and T2) and the washout testing occasion (T4) (Figure 2). The percentage changes in absolute knee extensor MVC were 6.5 ± 10% during the TP mesocycle and 8.5 ± 5.3% during the DUP mesocycle, respectively. Body-mass-normalized knee extensor MVC was significantly (p ≤ 0.05) higher at T5 relative to T4 (Figure 2). It is worth noting that the percentage changes of knee extensor MVC showed no statistical differences between the mesocycles (Figure 5A). In addition, effect size values of 0.29 and 0.33 for isometric knee extensor MVC and 0.26 and 0.01 for isometric knee flexor MVC were calculated during the TP mesocycle and DUP mesocycle, respectively (Table 5).

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Changes in Maximal Voluntary Electromyographic Activity of the Quadriceps Femoris

ANOVA detected no significant temporal alterations in maximal voluntary EMG activity of the QF during the study period (Figure 3). Despite this lack of statistical significance, there was a moderate EMG increase during both mesocycles (Figure 3). These average EMG increases were approximately 13% during the TP mesocycle and approximately 11% during the DUP mesocycle (Figure 5A). Similar effect size values of 0.28 and 0.25 were computed for maximal voluntary EMG activity of the QF during the TP mesocycle and DUP mesocycle, respectively (Table 5).

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Changes in Maximum Dynamic Upper-Body, Lower-Body, and Total Body Strength

The temporal changes of all absolute 1RM data are given in Figure 4, whereas the percentage 1RM changes during both mesocycles are shown in Figure 5B. ANOVA detected significant (p ≤ 0.05) temporal gains in 1RM values of the squat, bench press, barbell bench pull, and lat pull-down (Figure 4). In contrast, no significant temporal alterations were found for 1RM of the knee flexion curl, clean & jerk, and snatch (Figure 4). Squat 1RM was significantly (p ≤ 0.05) increased after the TP mesocycle (T3) and the DUP mesocycle (T5) compared with both baseline measurements (T1 and T2). Bench press 1RM displayed significant (p ≤ 0.05) gains after T3 relative to T1 and T2, and furthermore was significantly (p ≤ 0.05) enhanced at T5 compared with T1, T2, and T4 (Figure 4). Significant (p ≤ 0.05) 1RM increases for the barbell bench pull only occurred after the DUP mesocycle (T5) relative to both baseline testing occasions. Significant (p ≤ 0.05) gains for lat pull-down 1RM occurred after the TP mesocycle relative to T1 and T2 (Figure 4). Importantly, the average percentage 1RM changes occurring during both mesocycles varied between approximately 3.5–13.5% but displayed no significant differences between TP and DUP (Figure 5B). For most 1RMs, similar effect size values ranging from 0.04 (clean & jerk) to 0.62 (squat) were calculated for the compared mesocycles (Table 5).

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Discussion

This study is the first, to our knowledge, to compare the effects of TP and DUP on neuromuscular outcomes after short-term strength training in adolescent athletes. Separated by a washout period, adolescent judo athletes performed two 4-week training regimens with an emphasis on muscular power enhancement using either TP or DUP. Both training periods were equated for the exercise intensity zones and the number of repetitions. The main findings were that significant gains in muscle architecture and maximal lower-body, upper-body, and total body strength occurred after both short-term training periods, without systematic periodization influences. In line with other studies (4,8), our results may indicate that force-velocity characteristics of the exercises act as a key trigger for rapid neuromuscular adaptations during short-term training periods, rather than periodization.

The current average gains in isometric knee extensor and knee flexor MVC and upper-body, lower-body, and total body maximum dynamic strength varied from 3.5–13.5%. These changes are in line with those reported in the literature after short-term strength training periods with athletes (15,29,45). More specifically, Fukuda et al. (2013) presented average increases ranging from 7.7 to 26.7% for power, force, and velocity during countermovement jumps after a 4-week preparatory period with adolescent judo athletes. Mann et al. (2010) detected improvements of approximately 10% in bench press and squat 1RMs over a 6-week training period with collegiate football players. Similar gains in knee extensor MVC were found after 5 weeks of muscular power training in athletes from different team sports (45). The percentage strength changes were lower than those reported for nonathletic adults in response to short-term interventions (39,41), supporting an advanced training status of the studied judoka. Notably, the short-term intervention periods and advanced training status may also explain the small to moderate effect sizes that were found for most outcomes (37). Independent of the periodization model, the short-term regimen failed to induce significant 1RM gains for all exercises. In detail, the squat, clean & jerk, and snatch exercises seem to have provided a sufficient adaptation stimulus for the knee and leg extensors, whereas insufficient overall stimuli seem to have occurred for the knee flexors. Furthermore, clean & jerk and snatch 1RMs remained almost stable during the study. Most likely, the complex technical demands of these exercises (27) may have counteracted improvements during short-term training with adolescent athletes. In contrast, bench press and barbell bench pull 1RMs displayed moderate effect sizes during both mesocycles. Therefore, evidence occurred that short-term muscular power training periods can induce moderate gains in maximal lower-body, upper-body, and total body strength in previously trained adolescent judoka. Because the throwing and immobilization technical actions of competitive judoka require whole-body maximal strength and power (12,13), these findings can be used to optimize short-term preparatory judo training (16).

In agreement with this work, evidence suggests that TP and UP provokes similar development of upper- and lower-body strength (12,18,40). However, much work was performed with nonathletic subjects (18,26,41,44) that might show similar adaptations in response to any overload stimulus during the first several weeks of training (10). Thus, more studies need to be conducted using athletes with different training backgrounds (10,18). In line with our findings, Franchini et al. (2015) have recently reported that 8 weeks of linear and daily undulating strength training were equally effective to increase judo-specific performance and different strength categories in men judo athletes. Summarizing their findings and our work, no evidence occurred to prove the hypothesis that UP would result in better transfer for judo-specific fitness and larger strength gains for men and adolescent judoka (12). In contrast, Rhea et al. (2002) reported superior maximal strength gains for a DUP program compared with a TP regimen in previously trained subjects. In addition, Prestes et al. (2009) found that DUP produced greater percentage maximal strength increases in response to a 12-week training regimen compared with TP. In line with our work, Baker et al. (1994) showed that TP and UP evoked similar 1RM gains in previously weight-training men.

Some controversial debate exists on whether or not total volume load (also termed total work) needs to be equated for periodization comparisons (26,30,34,38,44). As previously proposed (26,30,38,43), a recent laboratory study suggested that from a muscle mechanical standpoint, all mechanobiological exercise characteristics need to be equated for periodization analysis (44). In contrast, arguing from a practical standpoint equated total volume load may obviate any strengths of the programming model and produce regimens that are not optimum (34). In the present work, average 1RMs for most exercises were slightly higher at the beginning of the DUP mesocycle compared with the baseline. In consequence, total training volume load was approximately 7% higher during the DUP period, but this did not evoke superior outcomes. This finding supports previous suggestions that small variations in training-volume load may not affect maximal strength outcomes (34), at least when the intensity zones are equated during short-term training periods.

Much work comparing periodization models has gone into assessing strength and power outcomes, but only a few studies have examined the underlying structural or neural dimensions (26,40,41,44). As previously reported after short-term strength training (7,39,41,42), the present gains in isometric knee extensor MVC and squat 1RM were accompanied by early VL muscle hypertrophy that was assessed via ultrasonographic analysis. Others have detected structural adaptations only after 8–12 weeks of resistance training (3,22,28,32,44). In line with our results, Blazevich et al. (2003) showed that muscle architectural adaptations occurred rapidly during explosive strength training. However, these initial small architectural changes may not always be detectable (39) and might be dependent on the force-velocity characteristics of the exercises (4,8,39). Considering the principles for muscular power training (17,25), the importance of explosive muscle actions for rapid architectural alterations (4,8), and the neuromuscular demands to conduct throwing movements in competitive judo matches (6,12), our athletes were encouraged to perform maximal explosive positive movement phases for all exercises. The finding of enhanced VL muscle thickness and fascicle length after only 4 weeks of muscular power training is different from the time course of architectural adaptations that occurred when slow cyclic isometric contractions were applied (44). Therefore, the current alterations suggest a rapid stimulation of both adaptational mechanisms and an addition of sarcomeres in parallel and in series (8,39,44). Increases in fascicle length affect a muscle's capacity in the force-length relation and force-velocity relation (4,7,44,45) and furthermore can reduce the risk of injury during explosive contractions (9). It is worth noting here that more statistical significant changes and higher effect sizes concerning VL-muscle thickness and fascicle length occurred after the TP-mesocycle. However, the percentage changes indicate that both periodization models were almost equally adept in improving muscle architectural dimensions. Thus, we suggest that the force-velocity characteristics of the exercises may act as a key trigger for muscle architectural adaptations during short-term training periods, rather than periodization (8,44).

Strength gains during the first several weeks of training were mostly attributed to neural alterations (1,28,31,44). Rhea et al. (2002) suggested that DUP may exert a higher stress on the neuromuscular system compared with TP thereby inducing quicker neural adaptations. However, there is a lack of studies that have examined this hypothesis with neural outcomes, and TP and DUP provoked similar temporal gains in the neural drive of the QF during 14 weeks of isometric knee extensor training (44). Although showing no statistical significance, the maximal voluntary EMG activity of the QF displayed average improvements of approximately 13 and 11% during the TP and DUP mesocycles, respectively. As was expected for strength training–experienced athletes, these EMG alterations were lower than those reported for recreationally active subjects after short-term training (39,44). Strength training–induced gains in surface EMG were attributed to adaptations of the motoneuron recruitment, firing frequency, and synchronization of motor unit firing (1,16). Our results indicate that moderate neural and muscle architectural alterations may occur during short-term training periods with strength training–experienced adolescent athletes. Importantly, the current gains in isometric MVC, 1RM performance, muscle architecture, and EMG-estimated neural drive were not affected by either TP or DUP. These findings with elite adolescent judoka support previous results which state that periodization may not act as the key trigger for neuromuscular adaptations (26,44).

At the end of our discussion, we would like to acknowledge some limitations. This work used a longitudinal crossover approach, and therefore it remains possible that the adaptations during the first mesocycle would have influenced the subsequent mesocycle. However, Wilcoxon tests detected no carry-over-effects between the compared mesocycles that were separated by a 7-week washout period. In addition, crossover designs were recommended to overcome selection bias in rather small sample sizes (23) that are characteristic of training studies with elite athletes. It was assumed that the adaptations were caused by the supervised training sessions and not by confounding exercise stimuli. To overcome this drawback as far as possible, similar judo training sessions were conducted during both short-term mesocycles. It is also worth noting that control of the mechanobiological exercise characteristics may be limited during free-weight exercises (43,44), and total training volume load was approximately 7% higher during the DUP period. Technical variations in the execution of free-weight exercises may affect the underlying activation strategies, force-length relations, and the force-velocity relations (21,28). Our coaches gave direct feedback whenever the technical guidelines for any exercise were violated. Nevertheless, this aspect has to be considered as a limitation in athletic training studies using free weights (44). This work failed to equate for the total training volume load but used similar intensity zones and number of repetitions during the compared training periods. Because no superior outcomes were detected during the DUP period, this might be regarded as a minor limitation of the present study. Surface EMG measurements only provided an estimation of changes in neural drive (39,44), and the VL was used as a surrogate parameter of muscle architectural changes of the quadriceps muscles (4,39,44). Future studies may account for possible region-specific muscle architectural adaptations (8) and include the different quadriceps heads (8). Finally, a priori calculations for sample size adjustments showed that more athletes would have been needed to expose small to moderate periodization effects. However, because the temporal alterations for most outcomes were quite similar during both training periods, this might be regarded as a minor limitation.

In conclusion, for adolescent judo athletes, both TP and DUP were almost equally adept at provoking early alterations in VL muscle architecture and maximal voluntary lower-body, upper-body, and total body strength in response to a 4-week short-term muscular power training period that compared these periodization models. Thus, our results may indicate that the force-velocity characteristics of the exercises act as a key trigger for rapid neuromuscular adaptations during short-term training periods, rather than periodization. Further studies comparing periodization models with adolescent athletes during longer muscular power training regimens are needed to extend these findings.

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Practical Applications

Identifying the most effective periodization model for eliciting maximal neuromuscular alterations during short-term training periods is important for many sports requiring short duration off-season and preseason programs. This is the first study that compared TP and DUP on neuromuscular outcomes during short-term strength training with adolescent athletes. Independent of the periodization model, 4 weeks of muscular power training induced moderate gains in muscle architecture and maximal lower-body, upper-body, and total body strength in previously trained adolescent judoka. Because competitive judo requires whole-body maximal strength and power, judo coaches are encouraged to include muscular power training during short-term preparatory periods. In line with other studies (8), our data suggest that rapid muscle architectural alterations might occur when the exercises impose explosive force-velocity characteristics. Thus, coaches are encouraged to account for the key muscle mechanical adaptation triggers such as the force-velocity characteristics during short-term training periods. Thereafter, TP or DUP may be a matter of each athlete's preference resulting in similar outcomes.

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Acknowledgments

The authors confirm that no financial support or other kind of support was provided by any organization (despite the authors' institutional affiliations named above) to conduct the present research. Therefore, the authors did not receive funding from any of the following organizations: National Institutes of Health (NIH), Wellcome Trust; Howard Hughes Medical Institute (HHMI); and others.

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Keywords:

neuromuscular plasticity; muscle architecture; periodization models; total body strength; preseason programs

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