Changes in Lower Limb Biomechanics Across Various Stages of Maturation and Implications for ACL Injury Risk in Female Athletes: a Systematic Review.

BACKGROUND: Female athletes are four to six times more likely to sustain an anterior cruciate ligament (ACL) injury than male athletes. Jump-landing biomechanics are influenced by maturation, with post-pubertal female athletes at a heightened risk of ACL injuries. OBJECTIVE: The aim of our systematic review was to identify and summarise the current evidence regarding the changes in kinematic and kinetic risk factors associated with ACL injuries during jump-landing tasks in female athletes at various stages of maturity. METHODS: A systematic search was conducted in PubMed, CINAHL, Web of Science, SPORTDiscus, EMBASE and Scopus. Articles were included if they: (1) conducted the research on uninjured female athletes with no restriction on playing level/experience; (2) provided information regarding the stage of the maturity and the scale used for estimating the maturity status of the participants; and (3) reported a biomechanical risk factor associated with ACL injuries during jump-landing tasks across at least two different maturity groups (e.g. pre-pubertal vs post-pubertal). RESULTS: Sixteen articles involving 2323 female athletes were included in our review. A total of 12 kinematic and 8 kinetic variables were identified across these studies. Of the 12 kinematic variables reported in our review, we found strong evidence for higher peak knee abduction angle in post-pubertal female individuals compared with pre-pubertal girls (p < 0.05). With regard to the 8 kinetic variables, we found strong evidence for lower relative peak vertical ground reaction force, higher external knee abduction moment and internal rotation moment in post-pubertal compared with pre-pubertal athletes. The strength of evidence for the remaining kinematic and kinetic variables ranged from conflicting to moderate and, in some instances, could not be determined. CONCLUSIONS: Our study provides an overview of the changes in biomechanical risk factors in female athletes during jump-landing tasks at various stages of maturity. We found moderate-to-limited evidence for most kinematic and kinetic variables, highlighting the need for further research.

Twelve Weeks of Progressive Resistance Training Positively Improves Physical Fitness and Golf Swing Performance in Talented Youth Golfers.

ABSTRACT: Shaw, J, Gould, ZI, Oliver, JL, and Lloyd, RS. Twelve weeks of progressive resistance training positively improves physical fitness and golf swing performance in talented youth golfers. J Strength Cond Res XX(X): 000-000, 2024-This aim of this study was to investigate the effects of a 12-week resistance training program in talented junior golfers. Eighteen talented youth golfers were pair matched by maturity status and handicap, and subsequently allocated to an experimental (EXP) or control group. During the 12-week intervention, both groups continued with their normal golf practice while the EXP group also completed a progressive twice-weekly resistance training program. At baseline, subjects performed multiple trials of an isometric midthigh pull (IMTP), countermovement jump (CMJ), standing long jump, golf movement screen (GMS), and isometric plank hold. Club head speed (CHS) and carry distance for a 6-iron and driver were also measured using a commercial launch monitor. When controlled for maturity offset, there were significant (p < 0.05) interaction effects in favor of the EXP group for absolute (g = 1.29) and relative (g = 2.06) peak force for the IMTP, CMJ absolute (g = 0.73) and relative (g = 0.66) peak power, jump height (g = 1.05), modified reactive strength index (g = 1.30), lateral (g = 0.48-0.88) and horizontal jump distance (g = 1.20), and GMS total score (g = 1.07). Significant interaction effects were also reported in 6-iron and driver CHS and carry distance in favor of the EXP group (p < 0.05; g = 0.41-1.64). These findings indicate that twice-weekly resistance training in combination with regular golf practice can stimulate increases in measures of strength, power, and movement competency in youth golfers, which should contribute to enhanced golf swing performance.

The Effects of Strength, Plyometric and Combined Training on Strength, Power and Speed Characteristics in High-Level, Highly Trained Male Youth Soccer Players: A Systematic Review and Meta-Analysis.

BACKGROUND: Male youth soccer players competing at a high level will typically engage in large volumes of soccer training from a young age. However, it is not known whether the high levels of habitual training that these high-performing players are exposed to limit their ability to respond to strength, plyometric or combined training interventions. OBJECTIVE: The primary aim of our systematic review and meta-analysis was to compare the specific effects of strength, plyometric and combined training with active controls (standard soccer training) on the strength, power and speed characteristics of high-level, highly trained young male soccer players. METHODS: We performed a literature search across PubMed, Scopus, CINAHL, Web of Science and SPORTDiscus to identify controlled studies that implemented strength, plyometric or combined training in high-level male youth soccer players. Participants were defined as high level or highly trained based on established guidelines related to either competition level or age-related weekly hours spent in soccer training. Studies needed to report at least one outcome of lower body strength, squat jump, countermovement jump, horizontal power, acceleration (0-10 m), speed (15-40 m) or change of direction speed. A meta-analysis was then performed using a random-effects model to determine the magnitude (Hedge's g) of training responses and whether effects differed across modes of training. RESULTS: From an initial return of 5464 papers, n = 34 studies met the inclusion criteria and provided a total sample of n = 1396 high-level male youth soccer players. Strength, plyometric and combined training resulted in improvements in strength, squat and countermovement jump, horizontal power, acceleration, change of direction speed (all p < 0.05; g = 0.73-1.08, moderate) and speed (p < 0.05; g = 0.40-0.59, small). Lower body strength was the only outcome where training mode had a significant effect (p < 0.05), with plyometric training producing small effects (g = 0.27, p < 0.05) compared with moderate effects for strength (g = 1.07, p < 0.05) and combined (g = 0.75, p < 0.05) training. Prediction intervals for overall effects (all training modes combined) showed that the greatest confidence that future training will lead to positive effects was in the squat and countermovement jump, horizontal power and acceleration (prediction intervals = 0.03-1.81). CONCLUSIONS: High-level, highly trained male youth soccer players can experience positive gains in indices of strength, power and speed from strength, plyometric and combined training, and the magnitude of gains are mostly similar across modes of training. Based on prediction intervals, there is a good level of certainty that future strength, plyometric and combined training in this population would lead to positive improvements in vertical and horizontal power and sprint acceleration.

The influence of maturation and sex on intracranial blood velocities during exercise in children.

Cerebral blood velocity (CBv) increases in response to moderate exercise in humans, but the magnitude of change is smaller in children compared with postpubertal adolescents and adults. Whether sex differences exist in the anterior or posterior CBv response to exercise across pubertal development remains to be determined. We assessed middle cerebral artery (MCAv) and posterior cerebral artery (PCAv) blood velocity via transcranial Doppler in 38 prepubertal (18 males) and 48 postpubertal (23 males) with cerebrovascular and cardiorespiratory measures compared at baseline and ventilatory threshold. At baseline, MCAv was higher in both sexes pre- versus postpuberty. Females demonstrated a greater MCAv (P < 0.001) than their male counterparts (prepubertal females; 78 ± 11 cm·s-1 vs. prepubertal males; 72 ± 8 cm·s-1, and postpubertal females; 68 ± 10 cm·s-1 vs. postpubertal males; 62 ± 7 cm·s-1). During exercise, MCAv remained higher in postpubertal females versus males (81 ± 15 cm·s-1 vs. 73 ± 11 cm·s-1), but there were no differences in prepuberty. The relative increase in PCAv was greater in post- versus prepubertal females (51 ± 9 cm·s-1 vs. 45 ± 11 cm·s-1; P = 0.032) but was similar in males and females. Our findings suggest that biological sex alters anterior cerebral blood velocities at rest in both pre- and postpubertal youth, but the response to submaximal exercise is only influenced by sex postpuberty.NEW & NOTEWORTHY Cerebral blood velocity (CBv) in the anterior circulation was higher in females compared with males irrespective of maturational stage, but not in the posterior circulation. In response to exercise, females demonstrated a greater CBv compared with males, especially post-peak height velocity (post-PHV) where the CBv response to exercise was more pronounced. Our findings suggest that both CBv at rest and in response to acute submaximal exercise are altered by biological sex in a maturity-dependent manner.

The Influence of Maturity Status on Drop Jump Kinetics in Male Youth.

ABSTRACT: Kumar, NTA, Radnor, JM, Oliver, JL, Lloyd, RS, CSCSD, Pedley, JS, Wong, MA, and Dobbs, IJ. The influence of maturity status on drop jump kinetics in male youth. J Strength Cond Res 38(1): 38-46, 2024-The aim of this study was to examine the effects of maturity status on drop jump (DJ) kinetics in young male athletes (categorized as early-pre-peak height velocity [PHV] [<-2.51 years], late-pre-PHV [-1.99 to -1.00 years], circa-PHV [-0.50 to 0.50 years], and post-PHV [>1.00 years]). All athletes performed a DJ from a 30-cm box onto force plates with performance variables (jump height, ground contact time, and reactive strength index) and absolute and relative kinetic variables during the braking and propulsive phases assessed. Subjects were categorized into GOOD (no impact-peak and spring-like), MODERATE (impact-peak and spring-like), or POOR (impact-peak and not spring-like) stretch-shortening cycle (SSC) function. The post-PHV group exhibited significantly greater values for most absolute kinetic variables compared with early-pre-PHV, late-pre-PHV, and circa-PHV (p < 0.05). The differences observed between consecutive maturity groups were similar in magnitude for most absolute variables (Cohen's d = 0.53-1.70). Post-PHV male athletes outperform their less mature counterparts during a DJ, and this may be attributed to the growth and maturity-related structural and motor control strategy changes that occur in children. Stretch-shortening cycle function in boys seems to improve with maturity status reflected by a greater number of post-PHV participants displaying GOOD SSC function (65.8%) and a greater number of early-pre-PHV participants displaying POOR SSC function (54.4%). However, a number of mature boys displayed POOR SSC function (17.8%), suggesting that the development of SSC function is not exclusively related to maturation.

Youths Are Less Susceptible to Exercise-Induced Muscle Damage Than Adults: A Systematic Review With Meta-Analysis.

PURPOSE: This meta-analysis aimed to (1) provide a comparison of peak changes in indirect markers of exercise-induced muscle damage (EIMD) in youths versus adults and (2) determine if the involved limb moderated this effect. METHOD: Studies were eligible for inclusion if they (1) provided a human youth versus adult comparison; (2) provided data on muscle strength, soreness, or creatine kinase markers beyond ≥24 hours; and (3) did not provide a recovery treatment. Effect sizes (ES) were presented alongside 95% confidence intervals. RESULTS: EIMD exhibited larger effects on adults than in youths for muscle strength (ES = -2.01; P < .001), muscle soreness (ES = -1.52; P < .001), and creatine kinase (ES = -1.98; P < .001). The random effects meta-regression indicated that the effects of upper- and lower-limb exercise in youths and adults were significant for muscle soreness (coefficient estimate = 1.11; P < .001) but not for muscle strength or creatine kinase (P > .05). As such, the between-group effects for muscle soreness (ES = -2.10 vs -1.03; P < .05) were greater in the upper than lower limbs. CONCLUSION: The magnitude of EIMD in youths is substantially less than in their adult counterparts, and this effect is greater in upper than lower limbs for muscle soreness. These findings help guide practitioners who may be concerned about the potential impact of EIMD when training youth athletes.

Adaptation of Left Ventricular Twist Mechanics in Exercise-Trained Children Is Only Evident after the Adolescent Growth Spurt.

BACKGROUND: The extent of structural cardiac remodeling in response to endurance training is maturity dependent. In adults, this structural adaptation is often associated with the adaptation of left ventricular (LV) twist mechanics. For example, an increase in LV twist often follows an expansion in end-diastolic volume, whereas a reduction in twist may follow a thickening of the LV walls. While structural cardiac remodeling has been shown to be more prominent post-peak height velocity (PHV), it remains to be determined how this maturation-dependent structural remodeling influences LV twist. Therefore, we aimed to (1) compare LV twist mechanics between trained and untrained children pre- and post-PHV and (2) investigate how LV structural variables relate to LV twist mechanics pre- and post-PHV. METHODS: Left ventricular function and morphology were assessed (echocardiography) in endurance-trained and untrained boys (n = 38 and n = 28, respectively) and girls (n = 39 and n = 34, respectively). Participants were categorized as either pre- or post-PHV using maturity offset to estimate somatic maturation. RESULTS: Pre-PHV, there were no differences in LV twist or torsion between trained and untrained boys (twist: P = .630; torsion: P = .382) or girls (twist: P = .502; torsion: P = .316), and LV twist mechanics were not related with any LV structural variables (P > .05). Post-PHV, LV twist was lower in trained versus untrained boys (P = .004), with torsion lower in trained groups, irrespective of sex (boys: P < .001; girls: P = .017). Moreover, LV torsion was inversely related to LV mass (boys: r = -0.55, P = .001; girls: r = -0.46, P = .003) and end-diastolic volume (boys: r = -0.64, P < .001; girls: r = -0.36, P = .025) in both sexes. CONCLUSIONS: A difference in LV twist mechanics between endurance-trained and untrained cohorts is only apparent post-PHV, where structural and functional remodeling were related.

Physical determinants of golf swing performance in competitive youth golfers.

This study investigated measures of physical fitness and golf swing performance in competitive youth golfers. Sixty-four golfers, subdivided into three handicap groups (CAT0, <1 handicap, n = 21; CAT1, 1-5 handicap, n = 20; CAT2, >5 handicap, n = 23), were assessed for isometric strength, power, movement competency and core endurance. Clubhead speed (CHS) and carry distance for 6-iron and driver were also measured. When controlled for maturity offset, CAT0 golfers produced significantly greater peak power, isometric absolute and relative peak force, movement competency, and jump distance than higher handicap golfers (all p < 0.05). Maturity status was strongly associated with CHS and carry distance for both clubs (R2 = 0.552-0.784). Linear regressions showed maturity offset explained a larger amount of variance in CHS (driver = 78.4%, 6-iron = 71.3%) and carry distance (driver = 55.2%, 6-iron = 57.4%) than handicap. Multiple linear regression analyses showed that peak power explained 79.4% and 82.4% of variation in 6-iron and driver CHS, respectively, while isometric absolute peak force explained 69.6% and 74.3% of the variation in 6-iron and driver carry distance, respectively. Subsequently, interventions targeting the development of peak force and power could aid golf swing performance in young golfers.

Within- and Between-Session Reliability of Golf Swing Variables Using the TrackMan Launch Monitor in Talented Golfers.

ABSTRACT: Shaw, J, Gould, ZI, Oliver, JL, and Lloyd, RS. Within- and between-session reliability of golf swing variables using the TrackMan launch monitor in talented golfers. J Strength Cond Res 37(12): 2431-2437, 2023-The purpose of the current study was to establish the within- and between-session reliability of the TrackMan launch monitor to measure golf swing variables. Twenty-one golfers attended 2 test sessions, with data captured from 3 golf shots using a 6-iron and 3 using a driver. Club head speed (CHS), ball speed, smash factor, attack angle, club path, launch angle, spin rate, spin axis, carry distance, and total distance were determined from data collected using a TrackMan launch monitor. Within- and between-session reliability for each variable was calculated using repeated-measures analysis of variance, intraclass correlation coefficients (ICCs), and coefficients of variation (CVs) with 95% confidence intervals. Within-session measures of CHS, ball speed, carry distance, and total distance were found to be reliable for both 6-iron and driver (CV ≤ 5.8, ICC ≥ 0.87) and launch angle for the 6-iron (CV = 6.7-9.3%, ICC = 0.87-0.92). Between-session measures of CHS, ball speed, smash factor, launch angle, carry distance, and total distance for both 6-iron and driver (CV% = 0.7-9.1%, ICC = 0.5-0.99) and spin rate for 6-iron (CV% = 9.4%, ICC = 0.89) were also shown to be reliable. These findings indicate that the TrackMan launch monitor is a reliable method for measuring CHS, ball speed, carry distance, and total distance in talented golfers, both within and between sessions. Practitioners can confidently use these variables to assess golf swing performance in golfers and evaluate meaningful changes in response to training interventions.

Cerebral blood flow and cerebrovascular reactivity are modified by maturational stage and exercise training status during youth.

NEW FINDINGS: What is the central question of this study? Gonadal hormones modulate cerebrovascular function while insulin-like growth factor 1 (IGF-1) facilitates exercise-mediated cerebral angiogenesis; puberty is a critical period of neurodevelopment alongside elevated gonadal hormone and IGF-1 activity: but whether exercise training across puberty enhances cerebrovascular function is unkown. What is the main finding and its importance? Cerebral blood flow is elevated in endurance trained adolescent males when compared to untrained counterparts. However, cerebrovascular reactivity to hypercapnia is faster in trained vs. untrained children, but not adolescents. Exercise-induced improvements in cerebrovascular function are attainable as early as the first decade of life. ABSTRACT: Global cerebral blood flow (gCBF) and cerebrovascular reactivity to hypercapnia ( CV R C O 2 ${\mathrm{CV}}{{\mathrm{R}}_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ) are modulated by gonadal hormone activity, while insulin-like growth factor 1 facilitates exercise-mediated cerebral angiogenesis in adults. Whether critical periods of heightened hormonal and neural development during puberty represent an opportunity to further enhance gCBF and CV R C O 2 ${\mathrm{CV}}{{\mathrm{R}}_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ is currently unknown. Therefore, we used duplex ultrasound to assess gCBF and CV R C O 2 ${\mathrm{CV}}{{\mathrm{R}}_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ in n = 128 adolescents characterised as endurance-exercise trained (males: n = 30, females: n = 36) or untrained (males: n = 29, females: n = 33). Participants were further categorised as pre- (males: n = 35, females: n = 33) or post- (males: n = 24, females: n = 36) peak height velocity (PHV) to determine pubertal or 'maturity' status. Three-factor ANOVA was used to identify main and interaction effects of maturity status, biological sex and training status on gCBF and CV R C O 2 ${\mathrm{CV}}{{\mathrm{R}}_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ . Data are reported as group means (SD). Pre-PHV youth demonstrated elevated gCBF and slower CV R C O 2 ${\mathrm{CV}}{{\mathrm{R}}_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ mean response times than post-PHV counterparts (both: P ≤ 0.001). gCBF was only elevated in post-PHV trained males when compared to untrained counterparts (634 (43) vs. 578 (46) ml min-1 ; P = 0.007). However, CV R C O 2 ${\mathrm{CV}}{{\mathrm{R}}_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ mean response time was faster in pre- (72 (20) vs. 95 (29) s; P ≤ 0.001), but not post-PHV (P = 0.721) trained youth when compared to untrained counterparts. Cardiorespiratory fitness was associated with gCBF in post-PHV youth (r2  = 0.19; P ≤ 0.001) and CV R C O 2 ${\mathrm{CV}}{{\mathrm{R}}_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ mean response time in pre-PHV youth (r2  = 0.13; P = 0.014). Higher cardiorespiratory fitness during adolescence can elevate gCBF while exercise training during childhood primes the development of cerebrovascular function, highlighting the importance of exercise training during the early stages of life in shaping the cerebrovascular phenotype.

Linear and Change of Direction Repeated Sprint Ability Tests: A Systematic Review.

ABSTRACT: Kyles, A, Oliver, JL, Cahill, MJ, Lloyd, RS, and Pedley, J. Linear and change of direction repeated sprint ability tests: a systematic review. J Strength Cond Res 37(8): 1703-1717, 2023-The ability to repeatedly sprint is important in many sports, but there is no established protocol for measuring repeated sprint ability (RSA). The purpose of this review was to identify overground RSA protocols previously reported in the literature and to recommend standardized protocols. A systematic review of the literature was used to identify studies that have used an RSA test, with data describing protocol design extracted. One hundred eight studies were included in the review, across which 47 unique protocols were identified. Eighteen protocols included at least one change of direction (COD), and this increased mean sprint time compared with linear RSA tests (7.26 ± 1.84 vs. 4.48 ± 1.02 seconds). There was considerable variability across protocols regarding sprint distance (20-40 m), sprint repetitions (3-15), recovery duration (10-60 seconds), recovery type (active vs. passive), and work-to-rest ratio (≤1:1.4-19.2). Separate protocols are needed for linear and COD tests, and these should reflect the brief nature of intense periods of competition and stress the ability to recover. Based on data across studies for protocol design and to ensure a demanding work-to-rest ratio, it is suggested that a linear RSA should comprise 6 × 30 m sprints separated by 15 seconds of active recovery. To provide some parity to linear tests, to keep work duration brief and to maintain a demanding work-to-rest ratio, a COD RSA should comprise 6 × 30 m shuttle sprints (15 + 15 m), providing one change of direction (180° COD), and maintaining a 15-second active recovery.

Neurovascular coupling and cerebrovascular hemodynamics are modified by exercise training status at different stages of maturation during youth.

Neurovascular coupling (NVC) is mediated via nitric oxide signaling, which is independently influenced by sex hormones and exercise training. Whether exercise training differentially modifies NVC pre- versus postpuberty, where levels of circulating sex hormones will differ greatly within and between sexes, remains to be determined. Therefore, we investigated the influence of exercise training status on resting intracranial hemodynamics and NVC at different stages of maturation. Posterior and middle cerebral artery velocities (PCAv and MCAv) and pulsatility index (PCAPI and MCAPI) were assessed via transcranial Doppler ultrasound at rest and during visual NVC stimuli. N = 121 exercise-trained (males, n = 32; females, n = 32) and untrained (males, n = 28; females, n = 29) participants were characterized as pre (males, n = 33; females, n = 29)- or post (males, n = 27; females, n = 32)-peak height velocity (PHV). Exercise-trained youth demonstrated higher resting MCAv (P = 0.010). Maturity and training status did not affect the ΔPCAv and ΔMCAv during NVC. However, pre-PHV untrained males (19.4 ± 13.5 vs. 6.8 ± 6.0%; P ≤ 0.001) and females (19.3 ± 10.8 vs. 6.4 ± 7.1%; P ≤ 0.001) had a higher ΔPCAPI during NVC than post-PHV untrained counterparts, whereas the ΔPCAPI was similar in pre- and post-PHV trained youth. Pre-PHV untrained males (19.4 ± 13.5 vs. 7.9 ± 6.0%; P ≤ 0.001) and females (19.3 ± 10.8 vs. 11.1 ± 7.3%; P = 0.016) also had a larger ΔPCAPI than their pre-PHV trained counterparts during NVC, but the ΔPCAPI was similar in trained and untrained post-PHV youth. Collectively, our data indicate that exercise training elevates regional cerebral blood velocities during youth, but training-mediated adaptations in NVC are only attainable during early stages of adolescence. Therefore, childhood provides a unique opportunity for exercise-mediated adaptations in NVC.NEW & NOTEWORTHY We report that the change in cerebral blood velocity during a neurovascular coupling task (NVC) is similar in pre- and postpubertal youth, regardless of exercise-training status. However, prepubertal untrained youth demonstrated a greater increase in cerebral blood pulsatility during the NVC task when compared with their trained counterparts. Our findings highlight that childhood represents a unique opportunity for exercise-mediated adaptations in cerebrovascular hemodynamics during NVC, which may confer long-term benefits in cerebrovascular function.

Selection into youth cricket academies: The influence of relative age and maturity status.

The aim of the study was to examine the birth quartile and maturity status distributions of male academy cricketers. Participants included 213 junior cricket players, aged between 9 and 18 years. Players were separated into birth quartiles and also grouped as early, average or late maturers. For the whole cohort, there was a medium effect bias towards players born in BQ1, but the number of early, average and late maturers was as expected. However, there were significantly more early maturers in the U10 and U11 groups than expected, and maturity distributions of the BQ groups showed that there was a small effect size bias towards early maturers in BQ4. Selection biases towards cricketers who are born earlier in the competitive year are consistent from U9 to U16, but more prevalent in the U12 and U14 age groups. There is a bias towards early maturers at U10 and U11, but this reduces as age increases. Practitioners working in academy pathways should be encouraged to assess the maturity status of players to assist in the retention and progression of players. Relative age effects should also be considered, and strategies may be required to identify players born later in the year.

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.

Kinetic Responses to External Cues Are Specific to Both the Type of Cue and Type of Exercise in Adolescent Athletes.

ABSTRACT: Barillas, SR, Oliver, JL, Lloyd, RS, and Pedley, J. Kinetic responses to external cues are specific to both the type of cue and type of exercise in adolescent athletes. J Strength Cond Res 37(3): 597-605, 2023-The purpose of this study was to examine how external cues influence kinetics during isometric and dynamic tasks in adolescent athletes. Fifteen adolescent male soccer players performed an isometric midthigh pull (IMTP), unloaded and loaded squat jumps (SJs) (15 and 30% of body mass), countermovement jump (CMJ), and drop jump (DJ) using a neutral or external force-specific or velocity-specific cues. Cue type had limited effects on outcomes in the IMTP or SJs, with mostly trivial ( g < 0.20), nonsignificant differences ( p > 0.05) across kinetic variables. In the CMJ and DJ, a force cue significantly ( p < 0.05) increased jump height ( g = 0.43 & 0.52) compared with a velocity cue, but in the DJ, a force cue significantly increased jump height ( g = 0.52) compared with both a neutral and velocity cue. However, a velocity cue significantly ( p < 0.05) reduced ground contact time ( g = 0.73-1.52) and time to peak force ( g = 0.50-1.29) in both the CMJ and DJ when compared with a force and neutral cue and increased force and power-related measures ( g = 0.33-1.12) in the CMJ and DJ when compared with a force cue. In adolescent athletes, the type of external cue had limited effects on kinetic measures in an IMTP and SJ but differential effects on both a CMJ and DJ, suggesting cues have more effect with increasing movement velocity. Consequently, practitioners working with adolescent athletes should consider both the type of exercise and the desired outcome when providing external cues.

The Acute Effects of Accentuated Eccentric Loading on Drop Jump Kinetics in Adolescent Athletes.

ABSTRACT: Lloyd, RS, Howard, SW, Pedley, JS, Read, PJ, Gould, ZI, and Oliver, JL. The acute effects of accentuated eccentric loading on drop jump kinetics in adolescent athletes. J Strength Cond Res 36(9): 2381-2386, 2022-The purpose of the study was to determine the acute effects of accentuated eccentric loading (AEL) on drop jump kinetics in adolescent athletes. Fifteen male rugby players (mean ± SD: age = 16.2 ± 1.01, body mass = 73.38 ± 9.94, and height = 178.91 ± 6.74) completed 3 trials of a drop jump with and without an accentuated eccentric load using a dumbbell release technique that equated to 15% body mass. The addition of the AEL stimulus resulted in significant, moderate increases in jump height (p < 0.05; Wilcoxon r = 0.47) and braking and propulsive impulse (p < 0.05, Hedges' g = 0.43; p < 0.05, g = 0.61, respectively) but did not significantly influence reactive strength index. Concurrently, there were significant, moderate increases in ground contact times (p < 0.05; r = 0.45) and reductions in spring-like correlations (p < 0.05; g = 0.94). Neither the magnitude nor timing of peak landing force were significantly altered in the AEL protocol (p < 0.05, g = 0.38; p < 0.05, r = 0.10, respectively). Cumulatively, these data indicate that implementation of AEL resulted in meaningful improvements in jump height, driven by significant increases in braking and propulsive impulse. Despite extensions in ground contact times and reductions in spring-like behavior, neither peak landing force nor time to peak force were negatively altered by the AEL. These results indicate that adolescent athletes can realize superior vertical jump heights during drop jumps using AEL, without displaying marked changes in the magnitude or timing of peak landing force.

The Influence of Competitive Level on Stretch-Shortening Cycle Function in Young Female Gymnasts.

This cross-sectional study investigated how stretch-shortening cycle (SSC) function and kinetic variables differed between young female gymnasts of varying competitive levels. Drop jump (DJ) force−time profiles were examined in 118 female gymnasts, sub-divided by competitive level (n = 21 recreational, n = 41 regional and n = 50 elite). DJ force−time data were analyzed to calculate performance and kinetic variables. Participants' SSC function was categorized as poor, moderate, or good, depending on the presence of an impact peak and spring-like behavior. A high proportion of gymnasts across each group were categorized as having "good" or "moderate" SSC function (i.e., >94.8%), with a trend of increasingly better SSC function observed with competitive level. Significant differences in reactive strength index, contact time, time of landing peak force, relative propulsive peak force, impulse, and ratio of braking: propulsive impulse were found between the elite and recreational group (p < 0.05). While SSC function was generally good to moderate, elite gymnasts had a more desirable kinetic jump-landing strategy than recreational level gymnasts. Drop jump kinetic variables appear to distinguish between elite and recreational gymnasts but not between regional standard gymnasts. Practitioners should consider the kinetic profile of gymnasts when benchmarking and setting training objectives.

Programming Plyometric-Jump Training in Soccer: A Review.

The aim of this review was to describe and summarize the scientific literature on programming parameters related to jump or plyometric training in male and female soccer players of different ages and fitness levels. A literature search was conducted in the electronic databases PubMed, Web of Science and Scopus using keywords related to the main topic of this study (e.g., "ballistic" and "plyometric"). According to the PICOS framework, the population for the review was restricted to soccer players, involved in jump or plyometric training. Among 7556 identified studies, 90 were eligible for inclusion. Only 12 studies were found for females. Most studies (n = 52) were conducted with youth male players. Moreover, only 35 studies determined the effectiveness of a given jump training programming factor. Based on the limited available research, it seems that a dose of 7 weeks (1−2 sessions per week), with ~80 jumps (specific of combined types) per session, using near-maximal or maximal intensity, with adequate recovery between repetitions (<15 s), sets (≥30 s) and sessions (≥24−48 h), using progressive overload and taper strategies, using appropriate surfaces (e.g., grass), and applied in a well-rested state, when combined with other training methods, would increase the outcome of effective and safe plyometric-jump training interventions aimed at improving soccer players physical fitness. In conclusion, jump training is an effective and easy-to-administer training approach for youth, adult, male and female soccer players. However, optimal programming for plyometric-jump training in soccer is yet to be determined in future research.

Impaired Stretch-Shortening Cycle Function Persists Despite Improvements in Reactive Strength After Anterior Cruciate Ligament Reconstruction.

ABSTRACT: Read, PJ, Pedley, JS, Eirug, I, Sideris, V, and Oliver, JL. Impaired stretch-shortening cycle function persists despite improvements in reactive strength followingafter anterior cruciate ligament reconstruction. J Strength Cond Res 36(5): 1238-1244, 2022-Reactive strength index (RSI) during a single-leg drop jump (SLDJ) has been indicated to determine return-to-sport readiness after anterior cruciate ligament (ACL) reconstruction, but only cross-sectional studies are available. Ground reaction force data and characterization of stretch-shortening cycle (SSC) function also remain sparse. Single-leg drop jump performance, ground reaction force, and SSC function were examined in soccer players with ACL reconstruction (n = 26) and matched controls (n = 25). Injured players were tested at 2 time points (32 and 42 weeks postsurgery). Stretch-shortening cycle function was classified as good (no impact peak and spring like), moderate (impact peak but still spring like or no impact peak and not spring like), or poor (impact peak and not spring like). The involved limb displayed lower-jump height, poorer RSI, less spring-like behavior, earlier peak landing force, and a greater ratio of landing peak to take-off peak force compared with the uninvolved limb and controls at the initial assessment (p < 0.001). Proportionally, more involved limbs were categorized as poor or moderate at the initial assessment (69.2%) and follow-up (50%) in comparison with the control limbs (14%). The reactive strength index was the only variable to change significantly between the initial assessment and follow-up on the involved limb (p < 0.05). No changes in the proportion of ACL reconstructed individuals categorized as poor or moderate SSC function at the follow-up assessment were observed. Residual deficits are present in SLDJ performance, SSC function, and ground reaction force characteristics after ACL reconstruction. The reactive strength index should not be the sole metric, as observed increases did not correspond with changes in SSC function.

Relationships between Athletic Motor Skill Competencies and Maturity, Sex, Physical Performance, and Psychological Constructs in Boys and Girls.

The purpose of this study was to examine the relationships between athletic motor skill competencies (AMSC), maturation, sex, body mass index, physical performance, and psychological constructs (motivation to exercise, physical self-efficacy, and global self-esteem). Two-hundred and twenty-four children aged 11-13 years old were included in the study and sub-divided by sex. The athlete introductory movement screen (AIMS) and tuck jump assessment (TJA) were used to assess AMSC, while standing long jump distance assessed physical performance. Online surveys examined participants' motivation to exercise, physical self-efficacy, and self-esteem. Trivial to moderate strength relationships were evident between AMSC and BMI (boys: rs = -0.183; girls: rs = -0.176), physical performance (boys: rs = 0.425; girls: rs = 0.397), and psychological constructs (boys: rs = 0.130-0.336; girls rs = 0.030-0.260), with the strength of relationships different between the sexes. Higher levels of AMSC were related to significantly higher levels of physical performance (d = 0.25), motivation to exercise (d = 0.17), and physical self-efficacy (d = 0.15-0.19) in both boys and girls. Enhancing AMSC may have mediating effects on levels of physical performance and psychological constructs in school-aged children, which may hold important implications for physical activity levels and the development of physical literacy.