Maturation-Related Effect of Low-Dose Plyometric Training on Performance in Youth Hockey Players

How effective are external cues and analogies in enhancing sprint and jump performance in academy soccer players?

This study investigated the effect of external (EC) and internal coaching cues (IC), analogies with a directional component (ADC) on sprint (20 m) and vertical jump performance in academy soccer players (n = 20). A repeated-measures analysis, with post-hoc comparisons, was used to identify any differences between these cues and a neutral (control) cue. Significant differences were found for both sprint (p < 0.001) and jump (p = 0.022) comparisons among cue types. In post-hoc analyses for the 20 m sprint, significant differences were observed between the EC and the IC, favouring the EC (p < 0.01, ES = 1.27 [CI: 0.24, 2.30]), and "away" ADC and the IC, favouring the "away" ADC (p < 0.01, ES = 1.21 [CI: 0.19, 2.22]). No other cues showed significant differences. For vertical jump, there was just one significant difference between comparisons, that being for the "away" ADC vs. the neutral cue, favouring the latter (p = 0.023, ES = 0.4 [CI: -0.04 to 0.84]). It appears that ECs and ADCs are most effective when coaching sprinting performance in academy soccer players. However, simply encouraging maximal effort from a youth athlete also appears to be a reasonable cueing strategy to drive performance in youth athletes.

Plyometric-Jump Training Effects on Physical Fitness and Sport-Specific Performance According to Maturity: A Systematic Review with Meta-analysis

BACKGROUND

Among youth, plyometric-jump training (PJT) may provide a safe, accessible, and time-efficient training method. Less is known on PJT effectiveness according to the maturity status.

OBJECTIVE

This systematic review with meta-analysis set out to analyse the body of peer-reviewed articles assessing the effects of PJT on measures of physical fitness [i.e., maximal dynamic strength; change of direction (COD) speed; linear sprint speed; horizontal and vertical jump performance; reactive strength index] and sport-specific performance (i.e., soccer ball kicking and dribbling velocity) according to the participants' maturity status.

METHODS

Systematic searches were conducted in three electronic databases using the following inclusion criteria: (i) Population: healthy participants aged < 18 years; (ii) Intervention: PJT program including unilateral and/or bilateral jumps; (iii) Comparator: groups of different maturity status with control groups; (iv) Outcomes: at least one measure of physical fitness and/or sport-specific performance before and after PJT; (v) experimental design with an active or passive control group, and two or more maturity groups exposed to the same PJT. The DerSimonian and Laird random-effects models were used to compute the meta-analysis. The methodological quality of the studies was assessed using the PEDro checklist. GRADE was applied to assess certainty of evidence.

RESULTS

From 11,028 initially identified studies across three electronic databases, 11 studies were finally eligible to be meta-analysed (n total = 744; seven studies recruited males; four studies recruited females). Three studies were rated as high quality (6 points), and eight studies were of moderate quality (5 points). Seven studies reported the maturity status using age at peak height velocity (PHV; pre-PHV values up to - 2.3; post-PHV up to 2.5). Another four studies used Tanner staging (from Tanner I to V). The training programmes ranged from 4 to 36 weeks, using 1-3 weekly training sessions. When compared to controls, pre-PHV and post-PHV participants obtained small-to-moderate improvements (ES = 0.35 - 0.80, all p < 0.05) in most outcomes (i.e., sport-specific performance; maximal dynamic strength; linear sprint; horizontal jump; reactive strength index) after PJT. The contrast of pre-PHV with post-PHV youth revealed that PJT was similarly effective in both maturity groups, in most outcome measures except for COD speed (in favour of pre-PHV). PJT induces similar physical fitness and sport-specific performance benefits in males and females, with a minimal exercise dosage of 4 weeks (8 intervention sessions), and 92 weekly jumps. Results of this meta-analysis are based on low study heterogeneity, and low to very low certainty of evidence (GRADE analysis) for all outcomes.

CONCLUSION

Compared to control participants, PJT resulted in improved maximal dynamic strength, linear sprint speed, horizontal jump performance, reactive strength index, and sport-specific performance (i.e., soccer ball kicking and dribbling velocity). These effects seem to occur independently of the maturity status, as both pre-PHV and post-PHV participants achieved similar improvements after PJT interventions for most outcomes. However, several methodological issues (e.g., low sample sizes and the pooling of maturity categories) preclude the attainment of more robust recommendations at the current time. To address this issue, consistency in maturity status reporting strategies must be improved in future studies with the general youth population and youth athletes.

Do verbal coaching cues and analogies affect motor skill performance in youth populations?

PURPOSE

The way coaching cues are worded can impact on the quality with which a subsequent motor skill is executed. However, there have been few investigations on the effect of coaching cues on basic motor skill performance in youths.

METHOD

Across several international locations, a series of experiments were undertaken to determine the effect of external coaching cues (EC), internal coaching cues (IC), analogies with a directional component (ADC) and neutral control cues on sprint time (20 m) and vertical jump height in youth performers. These data were combined using internal meta-analytical techniques to pool results across each test location. This approach was amalgamated with a repeated-measures analysis to determine if there were any differences between the ECs, ICs and ADCs within the different experiments.

RESULTS

173 participants took part. There were no differences between the neutral control and experimental cues in any of the internal meta-analyses except where the control was superior to the IC for vertical jump (d = -0.30, [-0.54, -0.05], p = 0.02). Just three of eleven repeated-measures analyses showed significant differences between the cues at each experimental location. Where significant differences were noted, the control cue was most effective with some limited evidence supporting the use of ADCs (d = 0.32 to 0.62).

CONCLUSION

These results suggest the type of cue or analogy provided to a youth performer has little subsequent effect on sprint or jump performance. Accordingly, coaches might take a more specific approach that is suited to the level or preferences of a particular individual.

Effects of Maturation Stage on Sprinting Speed Adaptations to Plyometric Jump Training in Youth Male Team Sports Players: A Systematic Review and Meta-Analysis

Purpose

To determine the effects of maturation stage (eg, classified in the same intervention protocol as early-, and late-mature) on linear sprinting speed adaptations to plyometric jump training (PJT) in youth (aged <18 years) male team sports players.

Patients and Methods

Eligibility criteria was determined based on PICOS: (P) healthy youth male team sport players classified in the same intervention protocol in ≥2 maturation-related categories, based on a recognized maturation stage-determination method, including (but not limited to) Tanner stage; peak height velocity (eg, Mirwald method); radiography-based method (eg, Fels method); (I) athletes exposed to PJT with a minimum of 4 weeks duration; (C) athletes non-exposed to PJT (non-dedicated intervention, ie, only field-based regular training) or performing a parallel intervention not-related with PJT organized by maturation levels; (O) sprinting speed (eg, time, maximal sprint speed) measured in any linear sprint test trajectories before and after the intervention; (S) only randomized controlled and/or parallel trials. Searches were conducted on December 2021 in EMBASE, PubMed, Scopus, SPORTDiscus and Web of Science, restricted to Portuguese, Spanish and English languages, with no restrictions regarding publication date, and no filters applied. The PEDro scale was used to assess the risk of bias in the included studies. Meta-analysis was computed using the inverse variance random-effects model. The significance level was set at p < 0.05.

Results

The search identified 1219 titles. From those, four studies were selected for qualitative and quantitative synthesis. Four studies provided data for sprinting performance, involving 10 experimental and 8 control groups showing a small effect of trained participants on sprinting performance (ES = 0.31; p = 0.064; I2 = 41.3%) when compared to controls. No significant moderator effect was noted for somatic maturity (p = 0.473 between groups).

Conclusion

PJT had no significant effect on sprinting performance, although the inclusion criteria partially may explain that.

The maturity status but not the relative age influences elite young football players' physical performance

Talent identification and selection process in young football is based on coaches' decisions regarding the players' performance at early ages. The aim of this study was to show how the maturity status and the relative age impact on young football players' physical performance and their coaches' efficacy expectations. The physical performance (1RM, Peak power output [PPO], 30-m sprint and T-test) of 118 young football players (U13 to U15; and their coaches' efficacy expectations were assessed. Relative age was calculated according to the players' date of birth within their selection year. The maturity status was estimated as the years from/to their peak height velocity (PHV). Linear regression analyses showed a significant relationship between players' physical performance and their maturity status but not with their relative age. In contrast, the maturity status of players only was associated to the coaches' efficacy expectations in the 1RM and PPO tests, whereas the relative age was a predictor of the coaches' expectations about players' performance in the T-test. These findings may be important for coaches and managers in young football academies since inter-individual differences in the maturity status but not in the relative age are related to physical performance despite the coaches' expectations.

Effect of Resisted Sprint and Plyometric Training on Lower Limb Functional Performance in Collegiate Male Football Players: A Randomised Control Trial

The main objectives of this study were to evaluate the short-term effects of resisted sprint and plyometric training on sprint performance together with lower limb physiological and functional performance in collegiate football players. Ninety collegiate football players participated in this three-arm, parallel group randomized controlled trial study. Participants were randomly divided into a control group and two experimental groups: resisted sprint training (RST) (n = 30), plyometric training (PT) (n = 30), and a control group (n = 30). Participants received their respective training program for six weeks on alternate days. The primary outcome measures were a knee extensor strength test (measured by an ISOMOVE dynamometer), a sprint test and a single leg triple hop test. Measurements were taken at baseline and after 6 weeks post-training. Participants, caregivers, and those assigning the outcomes were blinded to the group assignment. A mixed design analysis of variance was used to compare between groups, within-group and the interaction between time and group. A within-group analysis revealed a significant difference (p < 0.05) when compared to the baseline with the 6 weeks post-intervention scores for all the outcomes including STN (RST: d = 1.63; PT: d = 2.38; Control: d = 2.26), ST (RST: d = 1.21; PT: d = 1.36; Control: d = 0.38), and SLTHT (RST: d = 0.76; PT: d = 0.61; Control: d = 0.18). A sub-group analysis demonstrated an increase in strength in the plyometric training group (95% CI 14.73 to 15.09, p = 0.00), an increase in the single leg triple hop test in the resisted sprint training group (95% CI 516.41 to 538.4, p = 0.05), and the sprint test was also improved in both experimental groups (95% CI 8.54 to 8.82, p = 0.00). Our findings suggest that, during a short-term training period, RST or PT training are equally capable of enhancing the neuromechanical capacities of collegiate football players. No adverse events were reported by the participants.

Effects of Progressed and Nonprogressed Volume-Based Overload Plyometric Training on Components of Physical Fitness and Body Composition Variables in Youth Male Basketball Players

ABSTRACT

Palma-Muñoz, I, Ramírez-Campillo, R, Azocar-Gallardo, J, Álvarez, C, Asadi, A, Moran, J, and Chaabene, H. Effects of progressed and nonprogressed volume-based overload plyometric training on components of physical fitness and body composition variables in youth male basketball players. J Strength Cond Res 35(6): 1642-1649, 2021-This study examined the effect of 6 weeks of progressed and nonprogressed volume-based overload plyometric training (PT) on components of physical fitness and body composition measures in young male basketball players, compared with an active control group. Subjects were randomly assigned to a progressed PT (PPT, n = 7; age = 14.6 ± 1.1 years), a non-PPT (NPPT, n = 8, age = 13.8 ± 2.0 years), or a control group (CG, n = 7, age = 14.0 ± 2.0 years). Before and after training, body composition measures (muscle mass and fat mass), countermovement jump with arms (CMJA) and countermovement jump without arms (CMJ), horizontal bilateral (HCMJ) and unilateral jump with right leg (RJ) and left leg (LJ), 20-cm drop jump (DJ20), sprint speed (10 m sprint), and change of direction speed (CODS [i.e., T-test]) were tested. Significant effects of time were observed for muscle and fat mass, all jump measures, and CODS (all p < 0.01; d = 0.37-0.83). Significant training group × time interactions were observed for all jump measures (all p < 0.05; d = 0.24-0.41). Post hoc analyses revealed significant pre-post performance improvements for the PPT (RJ and LJ: ∆18.6%, d = 0.8 and ∆22.7%, d = 0.9, respectively; HCMJ: ∆16.4%, d = 0.8; CMJ: ∆22.4%, d = 0.7; CMJA: ∆23.3%, d = 0.7; and DJ20: ∆39.7%, d = 1.1) and for the NPPT group (LJ: ∆14.1%, d = 0.4; DJ20: ∆32.9%, d = 0.8) with greater changes after PPT compared with NPPT for all jump measures (all p < 0.05; d = 0.21-0.81). The training efficiency was greater (p < 0.05; d = 0.22) after PPT (0.015% per jump) compared with NPPT (0.0053% per-jump). The PPT induced larger performance improvements on measures of physical fitness as compared to NPPT. Therefore, in-season progressive volume-based overload PT in young male basketball players is recommended.

Effects of Plyometric, Strength and Change of Direction Training on High-School Basketball Player's Physical Fitness

The study aim was to compare the effects of a 7-week plyometric, strength and change of direction (COD) training program on basketball-specific performance measures in high-school players. Forty male players were randomly assigned to one of the four groups: plyometric (PG, n = 10), strength (SG, n = 10), COD (CODG, n = 10), and control group training (CG, n = 10). Two training sessions were performed at weekly intervals before basketball training. Performance of the counter movement jump (CMJ), Abalakov jump (ABKJ), 10 m zig-zag sprint, 20 m in line sprint (measurements at 10 and 20 m), and sit and reach flexibility test (SRFT) was assessed before and after the intervention. A 4 (group) × 2 (time) repeated measures analysis of variances (ANOVA) was conducted for each variable. Bonferroni post-hoc tests were used when the interaction was significant. Significant (all p < 0.05) time x group interaction was noted for SRFT, CMJ, ABK, sprint, and zig-zag 10 m, in favor of the experimental groups compared to the control group. However, improvements in physical fitness were similar between the three experimental groups. In conclusion, 7 weeks of specific plyometric, strength and COD training produced similar medium to large improvements in physical fitness of high-school basketball players.

Effects of 4 Weeks of a Technique-Specific Protocol with High-Intensity Intervals on General and Specific Physical Fitness in Taekwondo Athletes: An Inter-Individual Analysis

The aim of this research was to compare the effects of a technique-specific high-intensity interval training (HIIT) protocol vs. traditional taekwondo training on physical fitness and body composition in taekwondo athletes, as well as to analyse the inter-individual response. Utilising a parallel controlled design, sixteen male and female athletes (five females and 11 males) were randomly divided into an experimental group (EG) that participated in the technique-specific HIIT and a control group (CG) that participated in traditional taekwondo training. Both groups trained three days/week for four weeks. Squat jump (SJ), countermovement jump (CMJ), 5-metre sprint (5M), 20-metre shuttle run (20MSR), taekwondo specific agility test (TSAT), multiple frequency speed of kick test (FSKT_MULT), total kicks, and kick decrement index (KDI), as well as body composition were evaluated. Results indicate that there are no significant differences (p > 0.05) in the factors group and time factor and group by time interaction (p > 0.05). Although percentage and effect size increases were documented for post-intervention fitness components in TSAT, total kicks, KDI, and 20MSR, responders and non-responders were also documented. In conclusion, a HIIT protocol based on taekwondo-specific technical movements does not report significant differences in fitness and body composition compared to traditional taekwondo training, nor inter-individual differences between athletes.

The Effect of Low-Volume Preseason Plyometric Training on Force-Velocity Profiles in Semiprofessional Rugby Union Players

ABSTRACT

Watkins, CM, Gill, ND, Maunder, E, Downes, P, Young, JD, McGuigan, MR, and Storey, AG. The effect of low-volume preseason plyometric training on force-velocity profiles in semiprofessional rugby union players. J Strength Cond Res 35(3): 604-615, 2021-Rugby union is a physically demanding and complex team sport requiring athletes across all positions to express speed and acceleration. Plyometrics can effectively improve speed profiles by enhancing both force- and velocity-(FV) characteristics; however, the optimal dose and exercise direction for trained athletes is still relatively unknown. Therefore, the aim of this investigation was to determine the efficacy of a low-dose, directionally specific plyometric training program for improving speed profiles in semiprofessional rugby players. Players were randomly allocated to one of 2 plyometric training groups that performed low-volume (40-60 ground contacts per session) plyometrics twice weekly, or a control group that did not participate in any plyometric training. The 2 training groups underwent reverse back-to-back three-week vertically and horizontally focused plyometric training programs, with a 12-day washout. Body composition, aerobic capacity, and sprint performance (10-, 20-, 30-m split time, horizontal FV profile) were measured. During the intervention, HV-1 (horizontal/vertical training group 1) improved sprint performance (n = 12; ∆30 m = -0.020 seconds; p = 0.038), VH-2 (vertical/horizontal training group 2) maintained sprint performance (n = 8; ∆30 m = +0.049 seconds; p = 0.377), and the control group progressively declined in sprint performance (n = 12; ∆30 m = +0.071; p = 0.019). In addition, vertical plyometrics may preferentially benefit secondary acceleration (∆10-20 m split time: -0.01 seconds; p = 0.03) and many force-oriented FV profile characteristics. Correlational analyses (r2 = -0.568 to 0.515) showed sprint improvements were hindered in athletes with lower initial aerobic fitness, suggesting accumulated fatigue may have limited the magnitude of adaptation. Therefore, including low-volume plyometric training may be beneficial for improving sprint profiles or attenuating decrements realized during periods of high-volume sport-specific training.

PLYOMETRIC TRAINING IMPROVES SWIMMING PERFORMANCE IN RECREATIONALLY-TRAINED SWIMMERS

ABSTRACT Introduction: Plyometric training significantly improves strength performance, including in aquatic sports. Objective: To compare changes in thigh girth, hamstring flexibility, squat jump height, and 200m swimming trial time induced by plyometric training in recreationally-trained swimmers. Methods: Eighteen recreationally-trained male swimmers (age=18-20 years) were randomly divided into a plyometric training group (PTG) and a control group (CG). All the swimmers completed a six-week speed swimming training plan. In the PTG only, the last ~15 min of each session was replaced with plyometric exercises. The physical characteristics and the thigh girth were measured before and after the six weeks of training. In addition, sit-and-reach flexibility and squat jump tests were conducted, as well as a 200m swimming trial. Results: Two-way ANOVA with post-hoc analysis revealed an increase in sit-and-reach flexibility (PRE: 4.5±5.3 cm; POST: 10.9±5.9 cm, p<0.01) and squat jump height (PRE: 24.9±3.7 cm; POST: 28.3±4.2 cm, p<0.01) and a decrease in 200m-swimming time (PRE: 220±26.5 sec; POST: 204±24.4 sec, p<0.01) for the PTG only. Comparing the absolute changes (post-pre) between the groups by the Student's t-test, the PTG showed a greater increase in distance reached in the sit-and-reach flexibility (PTG: 6.34±0.6 cm vs. CG: 2.4±1.2 cm, p<0.01) and squat jump height (PTG: 3.4±0.7 cm vs. CG: 0.7±0.3 cm, p<0.01) than the CG. In addition, the 200m swimming time decreased significantly more than in the CG (PTG: -15.1±2.4 sec vs. CG: -0.8±2.7 sec, p<0.01). Conclusion: Plyometric training improves jump height, flexibility, and 200m swimming performance in recreationally-trained adult swimmers. Level of Evidence II; Lesser quality RCT.

Effects of Maturation on Physical Fitness Adaptations to Plyometric Drop Jump Training in Male Youth Soccer Players

Vera-Assaoka, T, Ramirez-Campillo, R, Alvarez, C, Garcia-Pinillos, F, Moran, J, Gentil, P, and Behm, D. Effects of maturation on physical fitness adaptations to plyometric drop jump training in male youth soccer players. J Strength Cond Res 34(10): 2760-2768, 2020-The objective of this study was to compare the effects of maturation on physical fitness adaptations to a twice weekly, 7-week plyometric drop jump training program. Seventy-six young male soccer players (aged 10-16 years) participated in this randomized controlled trial. Before and after the intervention, a physical fitness test battery was applied (countermovement jump; drop jump from 20 to 40 cm; 5 multiple bounds test; 20-m sprint time; change of direction speed; 2.4-km running time-trial; 5 repetition maximum [RM] squat; and maximal kicking distance). Participants were randomly divided into an active soccer-control group (CG) with Tanner stage maturation of 1-3 (CG-early; n = 16) or Tanner stage 4-5 (CG-late; n = 22), and to plyometric drop jump training groups with Tanner stage 1-3 (plyometric jump training [PJT]-early; n = 16) or 4-5 (PJT-late; n = 22). The analysis of variance and effect size (ES) measures revealed that when compared with their age-matched controls, the PJT-early (ES = 0.39-1.58) and PJT-late (ES = 0.21-0.65) groups showed greater improvements (p < 0.05) in sprint time, 2.4-km running time-trial, change of direction speed, 5RM squat, jumping, and kicking distance. The PJT-early exceeded the PJT-late group with greater (p < 0.05) improvements in drop jump from 20 cm (ES = 1.58 vs. 0.51) and 40 cm (ES = 0.71 vs. 0.4) and kicking distance (ES = 0.95 vs. 0.65). Therefore, a 7-week plyometric drop jump training program was effective in improving physical fitness traits in both younger and older male youth soccer players, with greater jumping and kicking adaptations in the less-mature athletes.

Influence of Maturation Status on Eccentric Hamstring Strength Improvements in Youth Male Soccer Players After the Nordic Hamstring Exercise

PURPOSE

This study examined the effects of a 6-week Nordic hamstring exercise (NHE) program in youth male soccer players of less mature (pre-peak height velocity [PHV]) or more mature (mid/post-PHV) status.

METHODS

Forty-eight participants were separated into pre-PHV (11.0 [0.9] y) or mid/post-PHV (13.9 [1.1]) groups and further divided into experimental (EXP) and control groups with eccentric hamstring strength assessed (NordBord) both before and after the training program. Participants in the EXP groups completed a periodized NHE program performed once or twice weekly over a 6-week period.

RESULTS

The NHE program resulted in moderate and small increases in relative eccentric hamstring strength (in newtons per kilogram) in the pre-PHV EXP (d = 0.83 [0.03-1.68]) and mid-PHV EXP (d = 0.53 [-0.06 to 1.12]) groups, respectively. Moderate increases in the same measure were also seen in the between-groups analyses in the pre-PHV (d = 1.03 [0.23-1.84]) and mid-PHV (d = 0.87 [0.22-1.51]) groups, with a greater effect observed in the former.

CONCLUSION

The results from this study demonstrate that a 6-week NHE program can improve eccentric hamstring strength in male youth soccer players, with less-mature players achieving mostly greater benefits. The findings from this study can aid in the training prescription of NHE in youth male soccer players.

Effects of Maturation on Physical Fitness Adaptations to Plyometric Jump Training in Youth Females

Romero, C, Ramirez-Campillo, R, Alvarez, C, Moran, J, Slimani, M, Gonzalez, J, and Banzer, WE. Effects of maturation on physical fitness adaptations to plyometric jump training in youth females. J Strength Cond Res XX(X): 000-000, 2019-The aim of this study was to compare the effects of maturation on physical fitness adaptations to plyometric jump training (PJT) in youth females. Jumping, sprinting, change of direction speed, endurance, and maximal strength were measured pre-post 6 weeks of PJT in 7th- and 10th-grade subjects. In the seventh grade, subjects formed a PJT group (Plyo-7, n = 10; age, 12.7 ± 0.6 years; breast maturation stages IV [n = 2], III [n = 7], and II [n = 1]) and an active control group (Con-7, n = 9; age, 12.8 ± 0.6 years; breast maturation stages IV [n = 2], III [n = 6], and II [n = 1]). In the 10th grade, subjects conformed a PJT group (Plyo-10, n = 9; age, 16.3 ± 0.5 years; breast maturation stages V [n = 5] and IV [n = 4]) and an active control group (Con-10, n = 9; age, 16.2 ± 0.5 years; breast maturation stages V [n = 5] and IV [n = 4]). Magnitude-based inferences were used for data analysis, with effect sizes (ESs) interpreted as <0.2 = trivial; 0.2-0.6 = small; 0.6-1.2 = moderate; 1.2-2.0 = large; and 2.0-4.0 = very large. The Plyo-7 and Plyo-10 showed meaningful improvements in all physical fitness measures (ES = 0.21-2.22), while Con-7 and Con-10 showed only trivial changes. The Plyo-7 and Plyo-10 showed meaningful (ES = 0.16-2.22) greater improvements in all physical fitness measures when compared with their control counterparts. The Plyo-10 showed meaningful greater improvements in 20-m sprint, 2-km running time trial, maximal strength, squat jump, and drop jump from 20 cm (ES = 0.21-0.42) when compared with Plyo-7. In conclusion, PJT is effective in improving physical fitness in younger and older female youths. However, greater adaptations were observed in more mature subjects.

Effect of biological maturation on strength-related adaptations in young soccer players

Strength training is crucial for soccer players’ long-term development at early ages and the biological maturation may influence specific strength-training adaptations. The aim of this study was to propose a strength-training programme for the strength development of pre-pubertal players and to analyse the adaptations to this training programme in players with different maturity status. One hundred and thirty young male soccer players participated in an 8-week strength-training programme consisting of two sessions per week (20-minutes of a combination of plyometric and resistance exercises) which was conducted prior to their normal soccer training. Three maturity groups were defined according to the years from/to their peak height velocity (PHV) as Pre-, Mid- and Post-PHV. Initial differences between the maturity groups were found in anthropometrical (weight and height) and physical performance variables (One Repetition Maximum (RM), Peak Power output (PP), 30-m sprint and T-test). The strength-training programme was beneficial for the three maturity groups (p< 0.05) with general greater improvements for the Pre- and Mid-PHV groups, with large effects in RM, PP and T-test, than for the Post-PHV group (moderate effects). The strength-training programme proposed in the present study seems to be positive for the strength-related development in young soccer players especially for Pre- and Mid-PHV players. The differences in the training adaptations for players with different maturity status suggest the individualization of the training stimulus for the correct long-term development of the players.

Effects of plyometric jump training on the physical fitness of young male soccer players: Modulation of response by inter-set recovery interval and maturation status

The effects of plyometric jump training on the physical fitness of male youth (age = 10-17 years) soccer players was examined in relation to inter-set recovery intervals and the maturity of the players in a single-blind, randomized-and controlled crossover trial. Jumping tests and kicking velocities were measured before (T₀), after a 6 week control period (T₁), after 6 weeks of plyometrics (T₂), after 6 weeks of wash-out (T₃), and after a further 6 weeks of plyometrics (T₄). Subjects were divided into pre- and post- peak-height-velocity (PHV) groups, and were randomly assigned to 30 s or 120 s inter-set intervals during periods T₂ and T₄. Any changes in jumping and maximum kicking velocities during T₁ and T_3, had trivial effect sizes (0.01-0.15), but small to moderate improvements (effect size = 0.20-0.99) were observed in both groups during T₂ and T₄. Gains in pre-PHV players were similar for the two inter-set intervals, but gains in post-PHV players were greater (p < 0.05) with an inter-set recovery of 120 s than with a 30 s recovery. We conclude that plyometric jump training improves the physical fitness of adolescents, irrespective of their maturity, but that in older individuals gains are greater with a longer inter-set recovery interval.

Effect of Plyometric Training on Jumping, Sprinting and Change of Direction Speed in Child Female Athletes

BACKGROUND

This study examined the effects of 8 weeks of plyometric training on jumping, sprinting, and change of direction (COD) performance.

METHODS

Fifty female 7-9-year-old gymnasts were randomly assigned to a plyometric training group (PG; n = 33), that performed supplementary plyometric training twice per week, and a control group (CG; n = 17) that continued regular training. The following tests were performed before and after the intervention: 10 and 20 m sprints, 5 + 5 m and 10 + 10 m COD tests, one-leg and two-leg countermovement jump (CMJ), drop jump (DJ), squat jump (SJ), and standing long jump (SLJ).

RESULTS

Only a main effect for time was found for all jumping performance parameters (p = 0.001). However, the improvement of one- and two-leg CMJ in PG had a greater effect size than CG (0.72 and 0.67 vs. 0.34 and 0.18, respectively). Group × time interactions were found for 10 and 20 m sprint tests (p = 0.018 and p = 0.011, respectively) and for 10 + 10 m COD (p = 0.008) with the post hoc test showing improvement only for the PG (p = 0.001, 0.001, and 0.003 and d = 1.1, 1.14, and 0.6, respectively).

CONCLUSIONS

Supplementary plyometric training increased sprint and COD performance more than regular gymnastics training, while jumping performance was equally improved in both groups.

A systematic review on the effects of resistance and plyometric training on physical fitness in youth- What do comparative studies tell us?

INTRODUCTION

To date, several meta-analyses clearly demonstrated that resistance and plyometric training are effective to improve physical fitness in children and adolescents. However, a methodological limitation of meta-analyses is that they synthesize results from different studies and hence ignore important differences across studies (i.e., mixing apples and oranges). Therefore, we aimed at examining comparative intervention studies that assessed the effects of age, sex, maturation, and resistance or plyometric training descriptors (e.g., training intensity, volume etc.) on measures of physical fitness while holding other variables constant.

METHODS

To identify relevant studies, we systematically searched multiple electronic databases (e.g., PubMed) from inception to March 2018. We included resistance and plyometric training studies in healthy young athletes and non-athletes aged 6 to 18 years that investigated the effects of moderator variables (e.g., age, maturity, sex, etc.) on components of physical fitness (i.e., muscle strength and power).

RESULTS

Our systematic literature search revealed a total of 75 eligible resistance and plyometric training studies, including 5,138 participants. Mean duration of resistance and plyometric training programs amounted to 8.9 ± 3.6 weeks and 7.1±1.4 weeks, respectively. Our findings showed that maturation affects plyometric and resistance training outcomes differently, with the former eliciting greater adaptations pre-peak height velocity (PHV) and the latter around- and post-PHV. Sex has no major impact on resistance training related outcomes (e.g., maximal strength, 10 repetition maximum). In terms of plyometric training, around-PHV boys appear to respond with larger performance improvements (e.g., jump height, jump distance) compared with girls. Different types of resistance training (e.g., body weight, free weights) are effective in improving measures of muscle strength (e.g., maximum voluntary contraction) in untrained children and adolescents. Effects of plyometric training in untrained youth primarily follow the principle of training specificity. Despite the fact that only 6 out of 75 comparative studies investigated resistance or plyometric training in trained individuals, positive effects were reported in all 6 studies (e.g., maximum strength and vertical jump height, respectively).

CONCLUSIONS

The present review article identified research gaps (e.g., training descriptors, modern alternative training modalities) that should be addressed in future comparative studies.

Inter-individual Variability in Responses to 7 Weeks of Plyometric Jump Training in Male Youth Soccer Players

The purpose of this study was to compare the inter-individual variability in the effects of plyometric jump training (PJT) on measures of physical fitness (sprint time, change of direction speed, countermovement jump, 20- and 40-cm drop jump reactive strength index, multiple five bounds distance, maximal kicking distance, and 2.4-km time trial) in youth soccer players who completed a PJT program versus players who completed soccer training only. In a single-blinded study, participants aged between 10 and 16 years were randomly divided into a PJT group (n = 38) and a control group (n = 38). The experimental group participated in a PJT program twice weekly for 7 weeks, whereas the control group continued with their regular soccer training sessions. Between-group differences were examined using a Mann-Whitney U test. Nonresponders where defined as individuals who failed to demonstrate any beneficial change that was greater than two times the typical error of measurement from zero. The results indicated that the mean group improvement for all physical fitness measures was greater (p < 0.05) in the PJT group (Δ = 0.4 to 23.3%; ES = 0.04 to 0.58) than in the control group (Δ = 0.1 to 3.8%; ES = 0.02 to 0.35). In addition, a significantly greater (p < 0.05) number of responders across all dependent variables was observed in the PJT group (from 4 up to 33 responders) than in the control group (from 0 up to 9 responders). In conclusion, compared to soccer training only, PJT induced greater physical fitness improvements in youth soccer players, with a greater number of responders for all the physical fitness tests related to jumping, speed, change of direction speed, endurance, and kicking technical ability.

The Effects of 3-Month Skill-Based and Plyometric Conditioning on Fitness Parameters in Junior Female Volleyball Players

PURPOSE

This study compared the effects of skill-based and plyometric conditioning (both performed in addition to regular volleyball training twice a week for 12 wk) on fitness parameters in female junior volleyball players.

METHODS

The participants [n = 47; age: 16.6 (0.6) y; mass: 59.4 (8.1) kg; height: 175.1 (3.0) cm] were randomized into a plyometric (n = 13), a skill-based (n = 17), and a control (n = 17) groups. The variables included body height, body mass, calf girth, calf skinfold, corrected calf girth, countermovement jump, 20-m-sprint, medicine ball toss, and sit-and-reach test.

RESULTS

Two-way analysis of variance (time × group) effects for time were significant (P < .05) for all variables except body mass. Significant group × time interactions were observed for calf skinfold [η² = .14; medium effect size (ES)], 20-m sprint (η² = .09; small ES), countermovement jump (η² = .29; large ES), medicine ball (η² = .58; large ES), with greater gains (reduction of skinfold) for plyometric group, and sit-and-reach (η² = .35; large ES), with greater gains in plyometric and skill-based groups. The magnitude-based inference indicated positive changes in 1) medicine ball toss and countermovement jump for all groups; 2) sit-and-reach for the plyometric and skill-based groups; and 3) 20-m sprint, calf girth, calf skinfold, and corrected calf girth for plyometric group only.

CONCLUSION

Selected variables can be improved by adding 2 plyometric training sessions throughout the period of 12 weeks. Additional skill-based conditioning did not contribute to improvement in the studied variables compared with regular volleyball training.

Effects of Different Plyometric Training Frequencies on Components of Physical Fitness in Amateur Female Soccer Players

Plyometric jump training (PJT) is a frequently used and effective means to improve amateur and elite soccer players' physical fitness. However, it is unresolved how different PJT frequencies per week with equal overall training volume may affect training-induced adaptations. Therefore, the aim of this study was to compare the effects of an in-season 8 week PJT with one session vs. two sessions per week and equal training volume on components of physical fitness in amateur female soccer players. A single-blind randomized controlled trial was conducted. Participants (N = 23; age, 21.4 ± 3.2 years) were randomly assigned to a one session PJT per-week (PJT-1, n = 8), two sessions PJT per-week (PJT-2, n = 8) or an active control group (CON, n = 7). Before and after training, participants performed countermovement jumps (CMJ), drop-jumps from a 20-cm drop-height (DJ20), a maximal kicking velocity test (MKV), the 15-m linear sprint-time test, the Meylan test for the assessment of change of direction ability (CoDA), and the Yo-Yo intermittent recovery endurance test (Yo-YoIR1). Results revealed significant main effects of time for the CMJ, DJ20, MKV, 15-m sprint, CoDA, and the Yo-YoIR1 (all p < 0.001; d = 0.57–0.83). Significant group × time interactions were observed for the CMJ, DJ20, MKV, 15-m sprint, CoDA, and the Yo-YoIR1 (all p < 0.05; d = 0.36–0.51). Post-hoc analyses showed similar improvements for PJT-1 and PJT-2 groups in CMJ (Δ10.6%, d = 0.37; and Δ10.1%, d = 0.51, respectively), DJ20 (Δ12.9%, d = 0.47; and Δ13.1%, d = 0.54, respectively), MKV (Δ8.6%, d = 0.52; and Δ9.1%, d = 0.47, respectively), 15-m sprint (Δ8.3%, d = 2.25; and Δ9.5%, d = 2.67, respectively), CoDA (Δ7.5%, d = 1.68; and Δ7.4%, d = 1.16, respectively), and YoYoIR1 (Δ10.3%, d = 0.22; and Δ9.9%, d = 0.26, respectively). No significant pre-post changes were found for CON (all p > 0.05; Δ0.5–4.2%, d = 0.03–0.2). In conclusion, higher PJT exposure in terms of session frequency has no extra effects on female soccer players' physical fitness development when jump volume is equated during a short-term (i.e., 8 weeks) training program. From this, it follows that one PJT session per week combined with regular soccer-specific training appears to be sufficient to induce physical fitness improvements in amateur female soccer players.

Specific Changes in Young Soccer Player's Fitness After Traditional Bilateral vs. Unilateral Combined Strength and Plyometric Training

The aim of this study was to compare changes in young soccer player's fitness after traditional bilateral vs. unilateral combined plyometric and strength training. Male athletes were randomly divided in two groups; both received the same training, including strength training for knee extensors and flexors, in addition to horizontal plyometric training drills. The only difference between groups was the mode of drills technique: unilateral (UG; n = 9; age, 17.3 ± 1.1 years) vs. bilateral (TG; n = 9; age, 17.6 ± 0.5 years). One repetition maximum bilateral strength of knee muscle extensors (1RM_KE) and flexors (1RM_KF), change of direction ability (COD), horizontal and vertical jump ability with one (unilateral) and two (bilateral) legs, and limb symmetry index were measured before and after an 8-week in-season intervention period. Some regular soccer drills were replaced by combination of plyometric and strength training drills. Magnitude-based inference statistics were used for between-group and within-group comparisons. Beneficial effects (p < 0.05) in 1RM_KE, COD, and several test of jumping performance were found in both groups in comparison to pre-test values. The limb symmetry index was not affected in either group. The beneficial changes in 1RM_KE (8.1%; p = 0.074) and 1RM_KF (6.7%; p = 0.004), COD (3.1%; p = 0.149), and bilateral jump performance (from 2.7% [p = 0.535] to 10.5% [p = 0.002]) were possible to most likely beneficial in the TG than in the UG. However, unilateral jump performance measures achieved likely to most likely beneficial changes in the UG compared to the TG (from 4.5% [p = 0.090] to 8.6% [p = 0.018]). The improvements in jumping ability were specific to the type of jump performed, with greater improvements in unilateral jump performance in the UG and bilateral jump performance in the TG. Therefore, bilateral strength and plyometric training should be complemented with unilateral drills, in order to maximize adaptations.

Effectiveness of Traditional Strength vs. Power Training on Muscle Strength, Power and Speed with Youth: A Systematic Review and Meta-Analysis

Numerous national associations and multiple reviews have documented the safety and efficacy of strength training for children and adolescents. The literature highlights the significant training-induced increases in strength associated with youth strength training. However, the effectiveness of youth strength training programs to improve power measures is not as clear. This discrepancy may be related to training and testing specificity. Most prior youth strength training programs emphasized lower intensity resistance with relatively slow movements. Since power activities typically involve higher intensity, explosive-like contractions with higher angular velocities (e.g., plyometrics), there is a conflict between the training medium and testing measures. This meta-analysis compared strength (e.g., training with resistance or body mass) and power training programs (e.g., plyometric training) on proxies of muscle strength, power, and speed. A systematic literature search using a Boolean Search Strategy was conducted in the electronic databases PubMed, SPORT Discus, Web of Science, and Google Scholar and revealed 652 hits. After perusal of title, abstract, and full text, 107 studies were eligible for inclusion in this systematic review and meta-analysis. The meta-analysis showed small to moderate magnitude changes for training specificity with jump measures. In other words, power training was more effective than strength training for improving youth jump height. For sprint measures, strength training was more effective than power training with youth. Furthermore, strength training exhibited consistently large magnitude changes to lower body strength measures, which contrasted with the generally trivial, small and moderate magnitude training improvements of power training upon lower body strength, sprint and jump measures, respectively. Maturity related inadequacies in eccentric strength and balance might influence the lack of training specificity with the unilateral landings and propulsions associated with sprinting. Based on this meta-analysis, strength training should be incorporated prior to power training in order to establish an adequate foundation of strength for power training activities.