Klaus Wirth

Effects of different periodization models on rate of force development and power ability of the upper extremity.

Hartmann, H, Bob, A, Wirth, K, and Schmidtbleicher, D. Effects of different periodization models on rate of force development and power ability of the upper extremity. J Strength Cond Res 23(7): 1921-1932, 2009-The purpose of our study was to compare the effects of 2 different periodization models on strength and power variables under dynamic and static conditions in the bench press. Participants of the experimental groups were male sport students experienced in weight training (age: 23.98 ± 3.14 yr). Subjects were tested for the 1 repetition maximum (1RM) in the bench press, maximal movement velocity (Vmax) in the bench press throw (16.9 kg), maximal voluntary contraction (MVC), and maximal rate of force development (MRFD) in 90° elbow and shoulder angle in the isometric bench press. According to their 1RM, subjects were parallelized and assigned to 1 of either 2 training groups: strength-power periodization (SPP, n = 13) or daily undulating periodization (DUP, n = 14). Subjects trained for 14 weeks, 3 days per week. In the strength-power sessions, both groups were instructed to lift the weight as explosively as possible. In addition, a control group (n = 13) was used for comparison. One repetition maximum and Vmax improved significantly through training (p ≤ 0.05), with no significant changes in MVC and MRFD. Experimental groups showed no significant group differences in any variable. The results indicate that, in short-term training using previously trained subjects, no differences in 1RM and power are seen between DUP and SPP. As used in our undulating regime, additional training in strength endurance could lead to exhaustion effects and furthermore does not provide an adequate training stimulus for power because of its low training intensity. In spite of this, according to the present findings, it has no negative effect on the application of a neural stimulus that is needed for a strength-power session if adequate regeneration time between workouts is guaranteed.

Influence of squatting depth on jumping performance.

Abstract Hartmann, H, Wirth, K, Klusemann, M, Dalic, J, Matuschek, C, and Schmidtbleicher, D. Influence of squatting depth on jumping performance. J Strength Cond Res 26(12): 3243–3261, 2012—It is unclear if increases in 1 repetition maximum (1RM) in quarter squats result in higher gains compared with full depth squats in isometric force production and vertical jump performance. The aim of the research projects was to compare the effects of different squat variants on the development of 1RM and their transfer effects to Countermovement jump (CMJ) and squat jump (SJ) height, maximal voluntary contraction (MVC), and maximal rate of force development (MRFD). Twenty-three women and 36 men (mean age: 24.11 ± 2.88 years) were parallelized into 3 groups based on their CMJ height: deep front squats (FSQ, n = 20), deep back squats (BSQ, n = 20), and quarter back squats (BSQ¼, n = 19). In addition, a control group (C, n = 16) existed (mean age: 24.38 ± 0.50 years). Experimental groups trained 2 d·wk−1 for 10 weeks with a strength-power block periodization, which produced significant (p ⩽ 0.05) gains of the specific squat 1RM. The FSQ and BSQ attained significant (p ⩽ 0.05) elevations in SJ and CMJ without any interaction effects between both groups (p ≥ 0.05). The BSQ¼ and C did not reveal any significant changes of SJ and CMJ. The FSQ and BSQ had significantly higher SJ scores over C (p ⩽ 0.05). The BSQ did not feature any significant group difference to BSQ¼ (p = 0.116) in SJ, whereas FSQ showed a trend toward higher SJ heights over BSQ¼ (p = 0.052). The FSQ and BSQ presented significantly (p ⩽ 0.05) higher CMJ heights over BSQ¼ and C. Posttest in MVC and MRFD demonstrated no significant changes for BSQ. Significant declines in MRFD for FSQ in the right leg (p ⩽ 0.05) without any interaction effects for MVC and MRFD between both FSQ and BSQ were found. Training of BSQ¼ resulted in significantly (p ⩽ 0.05) lower MRFD and MVC values in contrast to FSQ and BSQ. Quarter squat training elicited significant (p ⩽ 0.05) transfer losses into the isometric maximal and explosive strength behavior. These findings therefore contest the concept of superior angle-specific transfer effects. Deep front and back squats guarantee performance-enhancing transfer effects of dynamic maximal strength to dynamic speed-strength capacity of hip and knee extensors compared with quarter squats.

Long-term strength training effects on change-of-direction sprint performance.

Abstract Keiner, M, Sander, A, Wirth, K, and Schmidtbleicher, D. Long-term strength training effects on change-of-direction sprint performance. J Strength Cond Res 28(1): 223–231, 2014—The requirement profiles for sports such as soccer, football, tennis, and rugby demonstrate the importance of strength and speed-strength abilities, in addition to other conditional characteristics. During a game, the athletes complete a large number of strength and speed-strength actions. In addition to the linear sprints, athletes perform sprints while changing the direction (change-of-direction sprint [COD]). Therefore, this study aims to clarify the extent to which there is a strength training intervention effect on COD. Further, this investigation analyzes the possible correlations between the 1-Repetition Maximum/body mass (SREL) in the front and back squats and COD. The subjects (n = 112) were at pretest between 13 and 18 years of age and were divided into 2 groups with 4 subgroups (A = under 19 years of age, B = under 17 years of age, and C = under 15 years of age). For approximately 2 years, 1 group (control group [CG]) only participated in routine soccer training, and the other group (strength training group [STG]) participated in an additional strength training program with the routine soccer training. Additionally, the performances in the COD of 34 professional soccer players of the first and second divisions in Germany were measured as a standard of high-level COD. For the analysis of the performance development within a group and pairwise comparisons between 2 groups, an analysis of variance with repeated measures was calculated with the factors group and time. Relationships between the COD and SREL were calculated for the normal distributed data using a plurality of bivariate correlations by Pearson. Our data show that additional strength training over a period of 2 years significantly affects the performance in the COD. The STG in all subcohorts reached significantly (p < 0.05) faster times in the COD than did the CG. The STG amounted up to 5% to nearly 10% better improvements in the 10-m sprint times compared with that of the CG. Furthermore, our data show significant (p < 0.05) moderate to high correlations (r = −0.388 to −0.697) between the SREL and COD. Our data show that a long-term strength training improves the performance of the COD. Therefore, a long-term resistance training is recommended as early as in childhood and adolescence.

Influence of a 2-year strength training programme on power performance in elite youth soccer players

Abstract In soccer, strength, power and speed are very important because of the large number of power actions performed during the game. Therefore, the aim of this study was to examine the influence of periodised strength training for power performance more than 2 years. In this study, 134 elite youth soccer players were recruited from two youth training centres. The cohorts were arranged as follows: A (under 19 years), B (under 17 years) and C (under 15 years). The participants in each cohort were divided into two groups. One group (Strength training group [STG]) was subjected to regular soccer training in addition to strength training twice a week for 2 years. The other group (Control group [CG]) completed only the regular soccer training. The strength training was periodised with hypertrophy and intramuscular coordination blocks. For strength training, both the front squat and the back squat were performed once a week. The subjects were tested on the one-repetition maximum (1RM) of the front and back squat and a linear sprint over 30 m. There was significantly better performance from the STG on 1RM (p <0.001). In the sprint, the STG displayed significantly better improvements (p <0.05 to p <0.001) of up to 6%. The effects of strength training are reflected in the sprint performance. Therefore, it seems beneficial for youth to perform strength training to exploit the reserve capacity in sprint performances.

Analysis of the Load on the Knee Joint and Vertebral Column with Changes in Squatting Depth and Weight Load

It has been suggested that deep squats could cause an increased injury risk of the lumbar spine and the knee joints. Avoiding deep flexion has been recommended to minimize the magnitude of knee-joint forces. Unfortunately this suggestion has not taken the influence of the wrapping effect, functional adaptations and soft tissue contact between the back of thigh and calf into account. The aim of this literature review is to assess whether squats with less knee flexion (half/quarter squats) are safer on the musculoskeletal system than deep squats. A search of relevant scientific publications was conducted between March 2011 and January 2013 using PubMed. Over 164 articles were included in the review. There are no realistic estimations of knee-joint forces for knee-flexion angles beyond 50° in the deep squat. Based on biomechanical calculations and measurements of cadaver knee joints, the highest retropatellar compressive forces and stresses can be seen at 90°. With increasing flexion, the wrapping effect contributes to an enhanced load distribution and enhanced force transfer with lower retropatellar compressive forces. Additionally, with further flexion of the knee joint a cranial displacement of facet contact areas with continuous enlargement of the retropatellar articulating surface occurs. Both lead to lower retropatellar compressive stresses. Menisci and cartilage, ligaments and bones are susceptible to anabolic metabolic processes and functional structural adaptations in response to increased activity and mechanical influences. Concerns about degenerative changes of the tendofemoral complex and the apparent higher risk for chondromalacia, osteoarthritis, and osteochondritis in deep squats are unfounded. With the same load configuration as in the deep squat, half and quarter squat training with comparatively supra-maximal loads will favour degenerative changes in the knee joints and spinal joints in the long term. Provided that technique is learned accurately under expert supervision and with progressive training loads, the deep squat presents an effective training exercise for protection against injuries and strengthening of the lower extremity. Contrary to commonly voiced concern, deep squats do not contribute increased risk of injury to passive tissues.

Response of growth and myogenic factors in human skeletal muscle to strength training

Objective: To investigate the response to different strength training techniques of growth and myogenic factors in human skeletal muscle, with particular emphasis on satellite cell (SC) activation. Methods: 24 volunteers were divided into two groups and performed a 6-week strength training (group A trained with maximum contraction and group B had training combined with maximum contractions, ballistic movement and stretching–shortening cycles). Muscle biopsies were obtained from triceps brachii 3 days before and 7 days after training. For estimating gene expression of insulin-like growth factor (IGF-1), mechano growth factor (MGF), MyoD and myogenin, real-time RT-PCR was performed. Results: In group A, there was an increase in the 1 repeat maximum (1RM), but no change in Vmax (maximum movement velocity) and an increase in MHC (myosin heavy chain) IIa and a decrease in MHC IIx; in group B both 1RM and Vmax increased significantly along with an increase in MHC IIa and a decrease in MHC I. The MGF gene expression increased significantly in both groups (by 1160% and 59%, respectively), and IGF-1 increased only in group A (by 335%). MyoD and myogenin gene expression increased in group A (by 107% and 94%, respectively) but did not change in group B. Conclusions: Response of growth and myogenic factors occurs during muscular adaptation to a prolonged training, and strength training with different strategies caused different responses with respect to gene expression of these factors. These results suggest that SC activation is involved in the muscular adaptation process to training and might be attributed to MHC isoform transition.

Strength performance in youth: trainability of adolescents and children in the back and front squats.

Abstract Keiner, M, Sander, A, Wirth, K, Caruso, O, Immesberger, P, and Zawieja, M. Strength performance in youth: trainability of adolescents and children in the back and front squats. J Strength Cond Res 27(2): 357–362, 2013—A basic question for many athletic coaches pertains to the maximum attainable strength level for youth athletes. The aim of this investigation was to establish reference values for the strength performance in the front and back squats in youth athletes. The strength performance in front and back squats of 141 elite youth soccer players was tested by a 1 repetition maximum (1RM) and 1RM related to bodyweight (SREL). The subjects aged between 11 and 19 years and were divided into 2 groups and 4 subgroups (A = younger than 19 years, B = younger than 17 years, C = younger than 15 years, and D = younger than 13 years). For approximately 2 years, one group (control group [CG]) only participated in routine soccer training and the other group (strength training group [STG]) participated in an additional strength training program along with the routine soccer training. Additionally, the strength performance in a 5RM in both squat variants of 105 young elite weightlifters (National Weightlifting Organization Baden Württemberg, [BWG]) was examined to show the high level of trainability of children and adolescents and to determine the reference strength values for young athletes. The STG performed in the parallel front squat SREL in the subgroups A 1.7 +/− 0.2, B 1.6 +/− 0.2, C 1.4 +/−0.2 and D 0.9 +/− 0.3. The STG had significantly (p < 0.001) higher strength values in 1RM and SREL than CG. The BWG had higher strength values than STG, but the BWG was not part of the statistical analysis because of the different test protocols (1RM vs. 5RM). Our data show that the SREL in parallel squat for young elite athletes with long-term training experience should be a minimum of 2.0 for 16- to 19-year-olds, 1.5 for 13- to 15-year-olds, and 0.7 for 11- to 12-year-olds.

Effects of functional exercises in the warm-up on sprint performances.

Abstract Sander, A, Keiner, M, Schlumberger, A, Wirth, K, and Schmidtbleicher, D. Effects of functional exercises in the warm-up on sprint performances. J Strength Cond Res 27(4): 995–1001, 2013—The process of warming up prepares athletes for subsequent stress and increases their level of performance. Functional exercises are often included in warm-up programs for power sports, although a positive effect of functional exercises has not been confirmed. The aim of this study was to measure a possible effect of functional exercises on sprint performance included in a warm-up program. A total of 121 elite youth soccer players between 13 and 18 years of age participated in this study and performed 2 different warm-up programs. The first program (NWP) consisted of 5 minutes of nonspecific running, coordination exercises, stretching, and acceleration runs. The second program (WPS) was the same with additional functional exercises. The subjects were tested performing linear sprints of approximately 30 m and change-of-direction sprints of approximately 10 m. The t-test for dependent samples showed significant differences between the groups for each segment of the linear sprint (p < 0.01 for 5 m; p < 0.001 for 10, 15, 20, 25, and 30 m); however, the effect sizes are small. Also, in the change-of-direction sprint, the t-test showed significant differences between the groups (p < 0.01 for 10 m left, 10 m right; p < 0.001 for 5 m right). These effect sizes are also small. In the change-of-direction sprint time for 5 m left, the data showed no significant differences between the groups. The results show no effects of functional exercises on sprint performance that are implemented in addition to a general warm-up. It appears that a general warm-up program, such as the NWP, generates sufficient activation of the performance-limiting muscles for sprint performance. Functional exercises did not lead to a supplemental activation with a positive effect on sprint performance. Therefore, a warm-up for sprint performance should contain nonspecific running, coordination exercises, stretching exercises, and acceleration runs. These components lead to sufficient activation of the muscles involved in sprint performance. Coaches should use the limited time available for warm-up to work efficiently. The recommendation for warm-up is to pass on functional exercises that have no additional effect in enhancing performance.

Effects of Video-Based Visual Training on Decision-Making and Reactive Agility in Adolescent Football Players

This study investigated the trainability of decision-making and reactive agility via video-based visual training in young athletes. Thirty-four members of a national football academy (age: 14.4 ± 0.1 years) were randomly assigned to a training (VIS; n = 18) or a control group (CON; n = 16). In addition to the football training, the VIS completed a video-based visual training twice a week over a period of six weeks during the competition phase. Using the temporal occlusion technique, the players were instructed to react on one-on-one situations shown in 40 videos. The number of successful decisions and the response time were measured with a video-based test. In addition, the reactive-agility sprint test was used. VIS significantly improved the number of successful decisions (22.2 ± 3.6 s vs. 29.8 ± 4.5 s; p < 0.001), response time (0.41 ± 0.10 s vs. 0.31 ± 0.10 s; p = 0.006) and reactive agility (2.22 ± 0.33 s vs. 1.94 ± 0.11 s; p = 0.001) pre- vs. post-training. No significant differences were found for CON. The results have shown that video-based visual training improves the time to make decisions as well as reactive agility sprint-time, accompanied by an increase in successful decisions. It remains to be shown whether or not such training can improve simulated or actual game performance.

The Impact of Back Squat and Leg-Press Exercises on Maximal Strength and Speed-Strength Parameters

Abstract Wirth, K, Hartmann, H, Sander, A, Mickel, C, Szilvas, E, and Keiner, M. The impact of back squat and leg-press exercises on maximal strength and speed-strength parameters. J Strength Cond Res 30(5): 1205–1212, 2016—Strength training-induced increases in speed strength seem indisputable. For trainers and athletes, the most efficient exercise selection in the phase of preparation is of interest. Therefore, this study determined how the selection of training exercise influences the development of speed strength and maximal strength during an 8-week training intervention. Seventy-eight students participated in this study (39 in the training group and 39 as controls). Both groups were divided into 2 subgroups. The first training group (squat training group [SQ]) completed an 8-week strength training protocol using the parallel squat. The second training group (leg-press training group [LP]) used the same training protocol using the leg press (45° leg press). The control group was divided in 2 subgroups as controls for the SQ or the LP. Two-factorial analyses of variance were performed using a repeated measures model for all group comparisons and comparisons between pretest and posttest results. The SQ exhibited a statistically significant (p ⩽ 0.05) increase in jump performance in squat jump (SJ, 12.4%) and countermovement jump (CMJ, 12.0%). Whereas, the changes in the LP did not reach statistical significance and amounted to improvements in SJ of 3.5% and CMJ 0.5%. The differences between groups were statistically significant (p ⩽ 0.05). There are also indications that the squat exercise is more effective to increase drop jump performance. Therefore, the squat exercise increased the performance in SJ, CMJ, and reactive strength index more effectively compared with the leg-press in a short-term intervention. Consequently, if the strength training aims at improving jump performance, the squat should be preferred because of the better transfer effects.