Comparison Between Unilateral and Bilateral Plyometric Training on Single- and Double-Leg Jumping Performance and Strength

Individual responses to encapsulated caffeine and caffeine chewing gum on strength and power in strength-trained males

BACKGROUND

Liquid-dissolved and encapsulated powder are two popular ways to consume caffeine for performance-enhancing effects. Caffeine in other delivery methods, such as chewing gums, orally dissolvable strips, gels, mouthwashes, energy drinks, and nasal sprays, is believed to be absorbed more quickly into the bloodstream. Inter-individual responses to caffeine's enhancing effects are recognized. The present study examined the inter-individual responses to the acute effects of encapsulated caffeine and caffeinated chewing gum on the lower-body isokinetic and isometric strength and power in strength-trained males.

METHOD

A randomized, cross-over, placebo-controlled study was conducted with 15 strength-trained males (age: 25  ±  4 years, height: 176  ±  7 cm, weight: 75  ±  11 kg, habitual caffeine intake: 66  ±  15 mg·day-1). Participants were randomly assigned to three conditions: i) caffeinated chewing gum (CG), ii) caffeine capsule (CC), and iii) starch capsule as a placebo (PLA). Participants consumed approximately 3 to 4.5 mg·kg-1 of caffeine 60 minutes before testing. The washout period between conditions was one week. Participants performed the Sargent jump test, followed by a 5-minute active recovery (walking). Subsequently, isokinetic strength and power (60°/s and 180°/s) and isometric strength (45° and 60°) parameters were measured for knee extensor and flexor muscles. Data were analyzed using one-way repeated measures ANOVA and Bonferroni post hoc tests, with significance set at p ≤ 0.05. Responders to the caffeine conditions were identified using the smallest worthwhile change (SWC) analysis.

RESULTS

In knee extensors, 1) average peak torque and power at 60°/s were higher in CC (p = 0.045; + 11.2% and p = 0.038; + 14.1%) and CG (p = 0.044; + 7.3% and p = 0.015; + 11.4%) compared to PLA with a co-response rate of 60% and 66%, 2) maximum voluntary isometric contraction at 45° (MVIC-45°) was higher in CC compared to PLA (p = 0.031; + 10.1%), and 3) MVIC-60° was higher in CG compared to PLA (p = 0.037; + 10.1%) with a co-response rate of 60%. In knee flexors, 1) time to peak torque at 60°/s was higher in CG compared to PLA (p = 0.011; + 18.2%) with a co-response rate of 46%, 2) average rate of force development at 60°/s was higher in CC (p = 0.007; + 24.1%) and CG (p = 0.050; + 20.6%) compared to PLA with a co-response rate of 53%, and 3) average power at 180°/s was higher in CC compared to PLA (p = 0.033; + 18%) with a co-response rate of 46%. However, there were no differences between other strength indicators in the knee extensors and flexors between the different conditions. Vertical jump height (VJH) was higher in CC (p = 0.001; + 5.5%) and CG (p = 0.001; + 6.) compared to PLA, with a co-response rate of 53%.

CONCLUSION

Caffeine supplementation in CC and CG forms significantly enhanced lower-body strength, power, and vertical jump height in strength-trained males, with over  ~50% of participants exceeding the SWC thresholds across key performance metrics. CC showed slightly higher responder rates for strength parameters, while CG excelled in time-dependent measures, supporting their use as effective and flexible ergogenic aids.

Effect of unilateral and bilateral plyometric training on jumping, sprinting, and change of direction abilities: a meta-analysis

BACKGROUND

Plyometric training is a commonly employed method to enhance explosive strength in athletes. However, to date, no study has provided a comprehensive and systematic evaluation of the effects of unilateral (UNI) versus bilateral (BI) plyometric training.

OBJECTIVES

This meta-analysis investigates the impact of UNI and BI plyometric training on jumping, sprinting, and Change of Direction (COD) abilities.

STUDY ELIGIBILITY CRITERIA

To be eligible for inclusion in the meta-analysis, the study had to be:(1)healthy individuals; (2)UNI and BI plyometric training ; (3)conducted on rigid surfaces; (4)the outcome indicators were jumping ability, sprinting, and change of direction ability; (5)randomized controlled trials (RCTs).

STUDY APPRAISAL AND SYNTHESIS METHODS

We used the random-effects model for meta-analyses. Effect sizes (standardized mean difference), calculated from measures of horizontally oriented performance, were represented by the standardized mean difference and presented alongside 95% confidence intervals (CI).

DATA SOURCES

PubMed, Web of Science, Scopus, ProQuest, CNKI and Google Scholar.

RESULTS

A total of 11 papers met the inclusion criteria. The meta-analysis revealed that UNI contrast training was more effective than BI contrast training in improving single-leg jump performance (ES = 0.53, 95% CI: 0.02-1.04; Z = 2.05, p = 0.04), double-legs jump performance (ES = -0.07, 95% CI: -0.23-0.09; Z = 0.88, p = 0.38),sprint performance (ES = -0.04, 95% CI: -0.07--0.01; Z = 2.32, p = 0.02), as well as COD (ES = - 0.08, 95% CI: - 0.12 to - 0.03; Z = 3.29, p = 0.001 < 0.01). Conversely, BI contrast training showed a greater effect on bilateral jump performance (ES = -0.07, 95% CI: -0.12--0.03; Z = 3.39, p = 0.0007). Training with low-ground-contact frequencies (LGCF, fewer than 900 contacts) was found to significantly enhance vertical jump performance (ES = 0.64, 95% CI: 0.01-1.27; Z = 2.00, p = 0.05).

CONCLUSIONS

UNI and BI plyometric training offer modality-specific benefits for enhancing single-leg jumping, sprinting, and COD performance, whereas BI is more effective for optimizing bilateral jump performance. The LGCF protocol significantly enhances vertical jump performance.

Effect of 6-week single leg countermovement jump training on force time metrics in elite female youth footballers

Female football participation has grown exponentially. Unfortunately, females exhibit greater injury risk than male athletes, and experience increased mechanical stress during adolescence. Force plates provide accurate and reliable force-time characteristics enabling profiling of injury risk and benchmarking using a variety of jump and isometric tasks. The purpose of this study was to determine whether test-retest reliability and force-time characteristics of SLCMJ, bilateral countermovement jump (CMJ), countermovement rebound jump (CMJ-R) and isometric mid-thigh pull (IMTP) change with six weeks of SLCMJ training. Twenty-eight elite youth female footballers (13.7 ± 1.1 years, 53.27 ± 8.82 kg, 162.20 ± 5.37 cm) completed six weeks of SLCMJ as part of a routine strength and plyometric training program. SLCMJ training did not influence test-retest reliability and resulted in favourable adaptations indicated through small to large changes in force-time characteristics for SLCMJ. Significant (p < 0.05) yet trivial to small favourable changes were observed for the CMJ and CMJ-R, with small increases observed for IMTP. The results of this study demonstrate that six weeks of SLCMJ training does not influence phase-specific test-rest reliability (i.e. braking and propulsion) and causes weekly fluctuations in force-time characteristics leading to improvements in SLCMJ, CMJ, CMJ-R and IMTP. Practitioners can use such information to inform training design and monitor athlete performance.

Effects of Bilateral and Unilateral Plyometric Training on Physical Performance in Male Postpubertal Basketball Players

PURPOSE

The aim of this study was to analyze the effects of bilateral and unilateral plyometric-training (PT) programs on jumping, sprinting, and change-of-direction (COD) ability in male postpubertal basketball players.

METHODS

Forty-three young male basketball players (14.2 [1.2] y), from 4 squads belonging to an elite basketball club, were randomly assigned to 1 of 3 groups: (1) bilateral PT group (BG), (2) unilateral PT group (UG), and (3) control group (CG). The experimental groups followed a PT program twice weekly for 6 weeks, with BG and UG performing 2- and 1-legged jumps, respectively. Both groups completed the same number of vertical, horizontal, cyclic, and acyclic jumps. Pretraining and posttraining measurements included (1) countermovement jump (CMJ), (2) unilateral CMJ (CMJL and CMJR), (3) horizontal jump (HJ), (4) unilateral HJ (HJL and HJR), (5) straight-line sprint in 20 m (T20), and (6) V-Cut COD test (V-Cut).

RESULTS

CMJ, CMJL, and CMJR were significantly improved by BG and UG (P < .001), while CG did not change. Both the BG and the UG improved their performance significantly (P < .01) in HJL and HJR, but only BG significantly increased (P < .05) HJ and showed significantly greater improvements than CG. Furthermore, only BG improved V-Cut performance (P = .03). Neither group increased T20. CG did not improve in any tests.

CONCLUSIONS

BG enhances single-leg and double-leg jump performance in vertical and horizontal directions, as well as COD ability. In contrast, an equivalent volume of unilateral PT only improves vertical jumps and unilateral HJs.

The effects of plyometric training with speed and weight overloads on volleyball players' strength, power, and jumping performance

BACKGROUND

The principle of gradual overload is crucial in improving sports performance, yet the effects of combining speed and weight overloads in plyometric training remain understudied.

OBJECTIVE

This study investigated the effects of plyometric training with speed and weight overloads on isokinetic strength, explosive power, and agility in volleyball players.

METHOD

Forty male volleyball players were randomly assigned to four groups: plyometric training (PT), plyometric training with speed overload (PTS), plyometric training with weight overload (PTW), and plyometric training with both speed and weight overload (PTSW). Each group completed a four-week plyometric training regimen. Performance metrics, including Sarjent's jump height (SJH), Spike jump height (SPJH), Sheppard test (ShT), muscle voluntary isometric contraction (MVIC), rate of force development (RFD), absolute peak torque (PTQ), relative peak torque (RPT), and average power (AP) of knee extensors and flexors were measured before and after the intervention.

RESULTS

SJH improved significantly in PTS (P = 0.012), PTW (P = 0.041), and PTSW (P = 0.001) compared to PT. SPJH showed substantial gains in PTS (P = 0.002), PTW (P = 0.001), and PTSW (P = 0.001) compared to PT. Average jump height and highest jump in ShT were also significantly higher in PTS, PTW, and PTSW (P < 0.05). Additionally, RFDext240°/s was enhanced considerably in PTS (P = 0.001) and PTSW (P = 0.001).

CONCLUSION

Based on the results, plyometric training with speed and weight overloads (PTSW) demonstrated superior enhancements in isokinetic strength, explosive power, and jumping performance. This combined approach is highly effective and significantly benefits male volleyball players, aiming to enhance their physical abilities.

Effects of Unilateral, Bilateral and Combined Plyometric Jump Training on Asymmetry of Muscular Strength and Power, and Change-of-Direction in Youth Male Basketball Players

This study aimed to compare the effects of unilateral (UT), bilateral (BT), and combined (UBT) plyometric training on muscular strength, power, and change-of-direction performance in youth male basketball players. Sixty-six male youth basketball players (age: 16.1 ± 0.8 years) participated in this randomized experimental study, which lasted 8 weeks with a training frequency of 2 sessions per week. The UT group performed only single-leg plyometric exercises, while the BT group conducted similar plyometric drills using both feet. The UBT group combined both approaches, performing one session of UT and one session of BT each week. The players were evaluated at baseline and after the 8-week period using a force platform for the unilateral countermovement jump test (UCMJ), isometric squat test (IST), isometric knee flexor strength test (KFS), leg land and hold test (LHT), and 5-0-5 tests. The asymmetry between legs per outcome was measured using the symmetry angle. The UT, BT, and UBT all significantly improved outcomes in the IST, UCMJ, KFS, LHT, and 5-0-5 tests (p < 0.05) following the intervention, with no significant differences among the three methods. However, while UT and UBT significantly reduced asymmetries in the tests (p < 0.05), BT increased asymmetries. Only, the UT group showed significant improvements over the control group in asymmetry measures: IST asymmetry (mean difference: 1.2%, p = 0.049), KFS asymmetry (mean difference: 2.5%, p < 0.001), and LHT asymmetry (mean difference: 1.1%, p = 0.013). While there are no substantial differences among UT, BT, and UBT in terms of improvements in unilateral tests and symmetry levels, UT stands out for its effectiveness in enhancing neuromuscular performance and reducing asymmetries among basketball players compared to the control condition. UT was the only method that showed significant benefits in this context. Strength and conditioning coaches might consider incorporating UT, either alone or alongside BT, to optimize individual limb strength and coordination.

Effects of unilateral and bilateral contrast training on the lower limb sports ability of college basketball players

Objective: The purpose of this study was to compare the impact of unilateral (U) and bilateral (B) contrast training on lower limb explosiveness, agility, and balance in college basketball athletes. Methods: Twenty male college basketball players were randomly assigned to either a unilateral group (U, n = 10) or a bilateral group (B, n = 10). Both groups underwent an 8week strength training program, with sessions held twice a week. The unilateral group performed six Bulgarian split squats and ten reverse lunge jump squats, while the bilateral group performed six barbell rear squats and ten double-leg vertical jumps. To comprehensively assess the training effects, the study utilized one-repetition maximum (1RM), countermovement jump (CMJ), 20m sprint, and single-leg hop tests to evaluate explosive power; the 505 and t-test to assess change-of-direction ability; and the Y-balance test (YBT) to evaluate dynamic balance. Paired sample t-tests were used to evaluate within-group changes, and a 2 (pre- and post-) × 2 (experimental and control groups) repeated measures analysis of variance (ANOVA) was used to assess between-group differences. Results: Within-group comparisons indicated that both unilateral and bilateral contrast training significantly improved all performance metrics. Between-group comparisons revealed that bilateral training was superior to unilateral training in improvements in 1RM and CMJ (p > 0.05) (growth rate of 1RM: B: 8.4%, U: 5.15%; growth rate of CMJ: B: 15.63%, U: 6.74%). Unilateral training showed greater improvements in the 20m sprint, dominant leg single-leg hop, YBT left, and YBT right (p > 0.05) (growth rate of 20m sprint: B: 5.43%, U: 10.41%; growth rate of advantage foot touch high: B: 4.56%, U: 9.35%; growth rate of YBT left: B: 3.77%, U: 8.53%; growth rate of YBT right: B: 4.72%, U: 13.8%). Unilateral training also significantly outperformed bilateral training in non-dominant leg single-leg hop, t-test, 505 left, and 505 right improvements (p < 0.05). Conclusion: Unilateral contrast training may offer advantages for enhancing change-of-direction ability and explosive power in the non-dominant leg, and it may also provide benefits for improving short-distance sprinting ability, explosive power in the dominant leg, and dynamic balance. In contrast, bilateral contrast training appears to be more effective for enhancing bilateral explosive power and may be more advantageous for increasing maximal strength.

Plyometric training with additional load improves jumping performance and isokinetic strength parameters of knee extensors and flexors in young male soccer players

This study investigated the effect of plyometric training with and without additional load on young male soccer players' jumping ability and isokinetic strength. Methods: In this randomized controlled trial, 39 U-17 male trained soccer players were randomly divided into plyometric training with additional load (PT+AL), plyometric training with just bodyweight (PTBW) and control (CON) groups. PT+AL and PTBW were performed for six weeks (2 days/week). Absolute peak torque (APT), relative peak torque (RPT), average peak torque (AvPT), time-to-peak torque (TPT), average rate of force development (AvRFD), vertical jump height (VJH), standing long jump (SLJ) and 15-second repeated jump tests (RJ15s) were assessed before and after the interventions. The findings showed that the performance of knee extensors in TPT-60°/s and AvRFD-60°/s, and knee flexors in APT-60°/s, RPT-60°/s, AvPT-60°/s, AvPT-120°/s, AvRFD-60°/s and AvRFD-120°/s significantly increased after PT+AL, compared to the CON (p < 0.05). Also, a significant improvement in jumping ability was observed in PT+AL compared to CON (p < 0.05). Additionally, PTBW also improved the performance of knee flexors in TPT-120°/s and AvRFD-120°/s, as well as RJ15s performance compared to the CON (p < 0.05). Furthermore, knee flexors AvRFD-60°/s increased significantly after PT+AL, compared to PTBW (p < 0.05). SO, plyometric training, with or without additional load, improved young male soccer players' strength and jumping ability. However, strength parameters - especially the rate of force development - showed a greater increase following PT + AL compared to PTBW.

Equal Effects of Low- and Moderate-Volume Supplementary Plyometric Training on Sprint, Change of Direction Ability, and Lower-Limb Power in Preadolescent Female Handball Players

Background: This study compared the effects of low- and moderate-volume supplementary plyometric training in preadolescent female handball players. Methods: Thirty-nine preadolescent handball players (age: 12.9 ± 0.5 years, maturity offset: -1.50 ± 0.56 years) were randomly assigned into three groups: low-volume plyometric training group (LPT, n = 12); moderate-volume plyometric training group (MPT, n = 15); and control group (CG, n = 12). The supplementary plyometric training program was performed twice per week for 10 weeks, along with normal training (3 times/week). Each supplementary session included two upper- and three lower-body exercises performed for two sets (LPT, 36-54 foot contacts, duration 12 min) or four sets (MPT, 72-108 foot contacts, duration 24 min). The CG performed technical handball drills for 20 min. Results: Compared with the control group, both LPT and MPT resulted in similar improvements in modified T-test performance (15.1% and 18.6%, p < 0.01, respectively); linear sprint performance over 5, 10, and 20 m (between 5.1% and 8.8%, p = 0.02 to 0.001); countermovement jump (28.0% and 22.1%, p < 0.05, respectively); and standing long jump (12.6% and 12.5%, p = 0.024, respectively). Handgrip strength and overarm shot ball velocity improved similarly in all groups (CG, MPT, and LPT), by 8-11% (p < 0.01). Conclusions: Very-low-volume supplementary plyometric training performed for 12 min per session for two sessions per week results in considerable improvements in running speed, change of direction ability, and leg power and is as effective as a moderate-volume program. These findings are important for pre-adolescent female team sports players, who may benefit from a minimal but effective supplementary training, resulting in large benefits in leg speed and power.

Unilateral Plyometric Jump Training Shows Significantly More Effective than Bilateral Training in Improving Both Time to Stabilization and Peak Landing Force in Single-Leg Lend and Hold Test: A Randomized Multi-Arm Study Conducted Among Young Male Basketball Players

Enhancing peak landing forces and ensuring faster stabilization in the lower limbs during jumping activities can significantly improve performance and decrease the risk of injury among basketball players. This study aimed to compare the effects of unilateral (uPJT) and bilateral plyometric jump training (bPJT) programs on various performance measures, including countermovement jump (CMJ), squat jump (SJ), and single-leg land and hold (SLLH) test outcomes, assessed using force plates. A randomized multi-arm study design was employed, comprising two experimental groups (n = 25; uPJT and n = 25; bPJT) and one control group (n = 25), conducted with youth male regional-level basketball players (16.3 ± 0.6 years old). Participants underwent assessment twice, both before and after an 8-week intervention training period. The uPJT program exclusively involved plyometric drills (e.g., vertical jump exercises; horizontal jump exercises) focusing on single-leg exercises, whereas the bPJT program utilized drills involving both legs simultaneously. The outcomes analyzed included CMJ peak landing force, CMJ peak power, SJ peak force, SJ maximum negative displacement, SLLH time to stabilization, and SLLH peak landing force. The control group exhibited significantly greater SLLH time to stabilization compared to both the uPJT (p < 0.001) and bPJT (p < 0.030) groups. Additionally, time to stabilization was also significantly higher in bPJT than in uPJT (p = 0.042). Comparisons between groups in regards SLLH peak landing force after intervention revealed that the value was significantly smaller in uPJT than in bPJT (p = 0.043) and control (p < 0.001). In the remaining outcomes of CMJ and SJ, both uPJT and bPJT showed significant improvement compared to the control group (p > 0.05), although there was no significant difference between them. In conclusion, our study suggests that utilizing uPJT is equally effective as bPJT in enhancing performance in bilateral jump tests. However, it significantly outperforms bPJT in improving time to stabilization and peak landing forces during single-leg land and hold test. uPJT could be advantageous not for maximizing performance but also for potentially decreasing injury risk by enhancing control and balance during single-leg actions, which are common in basketball.

Countermovement Jump and Momentum Generation Associations to Fastball Velocity Performance Among Division I Collegiate Pitchers

ABSTRACT

Sakurai, M, Qiao, M, Szymanski, DJ, and Crotin, RL. Countermovement jump and momentum generation associations to fastball velocity performance among Division I collegiate pitchers. J Strength Cond Res 38(7): 1288-1294, 2024-The current study explored the relationships between countermovement jump (CMJ) profiles and baseball pitching performance. Nineteen Division I collegiate pitchers performed in-laboratory pitching and bilateral CMJs. Whole-body kinematics and ground reaction force were collected during both pitching and CMJ evaluations. Statistically significant correlations of concentric impulse and peak power in the CMJ test with fastball velocity were observed (r = 0.71 and 0.68). Concentric impulse in CMJ also showed a statistically significant correlation with linear momentum in the anterior-posterior direction during pitching (r = 0.68). Lean body mass and body mass showed statistically significant correlations with both of the 2 linear momentums during pitching (r = 0.71∼0.83), and concentric impulse in CMJ (r = 0.71 and 0.81). Pelvis and trunk pitching mechanics did not correlate with any of the CMJ variables at the statistically significant level, whereas the direction of the correlations varied (|r| < 0.45). Assessment of a baseball pitcher's CMJ should focus on concentric impulse and peak power because only these showed meaningful relationships with fastball velocity or momentum generation during pitching. An increase in lean body mass is also suggested to be able to generate more impulse and momentum. Baseball coaches, strength coaches, and clinicians are encouraged to include lower-body explosive training to enhance the force and power output capacity of baseball pitchers.

Effect of vertical, horizontal, and combined plyometric training on jump, sprint and change of direction performance in male soccer players

PURPOSE

The purpose of this study was to compare the effects of vertical (VPT), horizontal (HPT) and combined vertical and horizontal (V+HPT) plyometric training on sprint, jump and change of direction (COD) performance in adult male soccer players.

METHOD

Participants were randomly allocated into VPT (n = 8), HPT (n = 8) and V+HPT (n = 8) groups which undertook eight weeks of PT, executing 100 foot contacts per session, twice weekly.

RESULTS

Though demonstrably effective, no specific one of the three applied programmes enhanced performance to a greater extent than another with only the 40 m sprint for the HPT group (mean difference = 0.07 s [HPT] vs. 0.04 s [VPT] and 0.04 s [V+HPT]) and the vertical jump for the V+HPT group (mean difference = 4.5 cm [V+HPT] vs. 4.0 cm [VPT] and 3.25 cm [HPT]) appearing to deviate from a uniform pattern of group level adaptation across the performance tests.

CONCLUSION

A total volume of 100 foot contacts per session, twice per week for eight weeks was sufficient to achieve the observed changes. Though jump and changing direction performance were enhanced, linear sprint performance was largely unchanged and so a more complete and intense programme may have been warranted. No method was superior to another in eliciting changes across these tests and a directionally-specific pattern of adaptation was not apparent.

Short-Term Effects of Lower-Extremity Heavy Resistance versus High-Impact Plyometric Training on Neuromuscular Functional Performance of Professional Soccer Players

BACKGROUND

To compare the effects of short-term 8 week heavy-resistance or plyometric training protocols (HRT or PLY) incorporated into regular soccer practice on measures of neuromuscular functional performance in professional soccer players, a single-blind randomized controlled trial was conducted.

METHODS

Forty-seven participants aged 22.3 ± 3.52 years were assigned to three groups: HRT (n = 15), PLY (n = 15), and control (CON; n = 17). The HRT group performed 3 sets and 10 repetitions twice a week using 80% of their baseline 1-RM (weeks 1-3), followed by 8 repetitions at 85% 1-RM (weeks 4-6), and 6 repetitions at 90% 1-RM (weeks 7-8) of 6 lower-body strength exercises with a 1 min rest period between sets. The PLY protocol involved a preparatory phase (weeks 1-2), followed by two 3-week progressive periods (weeks 3-5 and weeks 6-8). The plyometric sessions consisted of four jump exercises/drills with progressively increasing number of sets and total number of foot contacts. The rest intervals between repetitions and sets were 15 and 90 s, respectively. Outcome measures included tests assessing 10 and 30 m speed (t10m and t30m), one-repetition maximum half-back squat (1-RM squat), isokinetic peak torques for the quadriceps and hamstring muscles (Qcon and Hcon), countermovement jump (CMJ), and squat jump (SJ).

RESULTS

Two-way ANOVA detected main effects of time and group×time interactions for all examined variables, except t30m, 1-RM, and relative 1-RM. Post hoc analyses revealed significant increases in the HRT group (t10m: 6.3%, t30m: 7.1%; absolute 1-RM: 29.6%; relative 1-RM: 30.3%, Qcon: 24.5%; Hcon: 14.4%; CMJ: 5.9%; SJ: 7.2%, all p < 0.001) and the PLY group (t10m: 3.1%; t30m: 4.1%; absolute 1-RM:19.1%; relative 1-RM: 20.3%; Qcon: 12.6%; Hcon: 8.7%; CMJ: 3.3%; SJ: 3.5%, all p < 0.001). HRT was superior compared to PLY in relative 1-RM, Qcon and Hcon (all p < 0.001). In addition, we found knee muscular strength imbalance in 70.5% of participants from the total sample (H/Q ratio < 60%). The HRT and PLY protocols resulted in improved neuromuscular functional performance compared to the regular soccer regime.

CONCLUSIONS

This study showed that during the pre-competitive season, additional HRT and PLY drills/exercises as a substitute for standard soccer training as part of a regular 90 min practice twice a week for 8 weeks, can produce acute physical performance-enhancing effects in professional soccer players.

Exploratory Investigation Into the Impact of Bilateral and Unilateral Jump Characteristics on Ground Reaction Force Applications in Baseball Pitching

ABSTRACT

Lis, R, Szymanski, DJ, Qiao, M, and Crotin, RL. An exploratory investigation into the impact of bilateral and unilateral jump characteristics on ground reaction force applications in baseball pitching. J Strength Cond Res 37(9): 1852-1859, 2023-Jump tests are effective, valid, and reliable in examining lower-body power that can influence ground reaction forces (GRFs) in baseball pitching. Relationships between drive and stride leg GRFs and fastball velocities while pitching from the wind-up and stretch were evaluated for performance influences across the following conditions: (a) lower-body GRFs from unilateral countermovement jumps (UCMJ) and bilateral countermovement jumps (BCMJ) and (b) BCMJ and drive and stride leg UCMJ height. Nineteen Division I collegiate baseball pitchers (age; 19.9 ± 1.5 years, height; 1.86 ± 0.06 m, body mass; 90.7 ± 13.8 kg) completed BCMJ and UCMJ tests and threw four-seam fastballs from a pitching mound with 2 embedded force plates. Three moderate associations ( r ≥ 0.47) were statistically significant ( p < 0.05) for BCMJ and UCMJ heights to pitching GRFs. Stride leg UCMJ height was significantly greater than drive leg UCMJ height, p < 0.01, η 2 = 0.34. Wind-up and stretch GRFs were statistically similar. Fastball velocities showed a statistically significant association that was moderately high with wind-up and stretch stride leg anterior-posterior GRFs ( r ≥ 0.65, p < 0.01). Collegiate pitchers jumped significantly higher with their stride leg, and the sum of vertical unilateral jump height of both legs was significantly greater (27%) than BCMJ height to indicate greater single-leg dominance in jumping. Although stride leg height was higher, improving stride leg jumping performance may be functionally more important in producing greater momentum into foot strike that has the potential to increase fastball velocity.

Plyometric Jump Training Exercise Optimization for Maximizing Human Performance: A Systematic Scoping Review and Identification of Gaps in the Existing Literature

BACKGROUND

Plyometric jump training (PJT) encompasses a range of different exercises that may offer advantages over other training methods to improve human physical capabilities (HPC). However, no systematic scoping review has analyzed either the role of the type of PJT exercise as an independent prescription variable or the gaps in the literature regarding PJT exercises to maximize HPC.

OBJECTIVE

This systematic scoping review aims to summarize the published scientific literature and its gaps related to HPC adaptations (e.g., jumping) to PJT, focusing on the role of the type of PJT exercise as an independent prescription variable.

METHODS

Computerized literature searches were conducted in the PubMed, Web of Science, and SCOPUS electronic databases. Design (PICOS) framework: (P) Healthy participants of any age, sex, fitness level, or sports background; (I) Chronic interventions exclusively using any form of PJT exercise type (e.g., vertical, unilateral). Multimodal interventions (e.g., PJT + heavy load resistance training) will be considered only if studies included two experimental groups under the same multimodal intervention, with the only difference between groups being the type of PJT exercise. (C) Comparators include PJT exercises with different modes (e.g., vertical vs. horizontal; vertical vs. horizontal combined with vertical); (O) Considered outcomes (but not limited to): physiological, biomechanical, biochemical, psychological, performance-related outcomes/adaptations, or data on injury risk (from prevention-focused studies); (S) Single- or multi-arm, randomized (parallel, crossover, cluster, other) or non-randomized.

RESULTS

Through database searching, 10,546 records were initially identified, and 69 studies (154 study groups) were included in the qualitative synthesis. The DJ (counter, bounce, weighted, and modified) was the most studied type of jump, included in 43 study groups, followed by the CMJ (standard CMJ or modified) in 19 study groups, and the SJ (standard SJ or modified) in 17 study groups. Strength and vertical jump were the most analyzed HPC outcomes in 38 and 54 studies, respectively. The effects of vertical PJT versus horizontal PJT on different HPC were compared in 21 studies. The effects of bounce DJ versus counter DJ (or DJ from different box heights) on different HPC were compared in 26 studies.

CONCLUSIONS

Although 69 studies analyzed the effects of PJT exercise type on different HPC, several gaps were identified in the literature. Indeed, the potential effect of the PJT exercise type on a considerable number of HPC outcomes (e.g., aerobic capacity, flexibility, asymmetries) are virtually unexplored. Future studies are needed, including greater number of participants, particularly in groups of females, senior athletes, and youths according to maturity. Moreover, long-term (e.g., >12 weeks) PJT interventions are needed.

Methodological considerations for determining the volume and intensity of drop jump training. A systematic, critical and prepositive review

This systematic review provides critical and propositional information on criteria for determining the volume and intensity of drop jumps during plyometric training programs. Eligibility criteria were defined according to PICOS: Participants: male or female athletes, trained or recreationally active (16-40 years). Intervention duration: more than 4 weeks.

COMPARATORS

passive or active control group during a plyometric training program.

OUTCOMES

information on improvement with Drop Jump or Depth Jump, with other jumps, acceleration, sprint, strength, and power output.

DESIGN

randomized controlled trials. We searched articles published in PubMed, SPORTDiscus, Web of Science, and Scopus. The search was conducted until 10 September 2022 for English-language articles only. The risk of bias was assessed using Grading of Recommendations, Assessment, Development and Evaluation (GRADE) for randomized controlled studies. We identified 31495 studies, of which only 22 were included. We found that six groups presented results with women, 15 presented results with men, and the remaining four presented mixed studies. Of the 686 people recruited, 329 participants aged 25.79 ± 4.76 years were involved in training. Methodological problems in training intensity, volume distribution, and individualization were noted, but methodological recommendations for their solution are also provided. It is concluded that the drop height should not be understood as the intensity determinant of plyometric training. Intensity is determined by ground reaction forces, power output, and jump height, among other factors. Furthermore, the athletes' experience level selection should be based on the formulas recommended within this research. These results could be helpful for those who intend to conduct new plyometric training programs and research.

Non-Parametric Functional Muscle Network as a Robust Biomarker of Fatigue

Characterization of fatigue using surface electromyography (sEMG) data has been motivated for rehabilitation and injury-preventative technologies. Current sEMG-based models of fatigue are limited due to (a) linear and parametric assumptions, (b) lack of a holistic neurophysiological view, and (c) complex and heterogeneous responses. This paper proposes and validates a data-driven non-parametric functional muscle network analysis to reliably characterize fatigue-related changes in synergistic muscle coordination and distribution of neural drive at the peripheral level. The proposed approach was tested on data collected in this study from the lower extremities of 26 asymptomatic volunteers (13 subjects were assigned to the fatigue intervention group, and 13 age/gender-matched subjects were assigned to the control group). Volitional fatigue was induced in the intervention group by moderate-intensity unilateral leg press exercises. The proposed non-parametric functional muscle network demonstrated a consistent decrease in connectivity after the fatigue intervention, as indicated by network degree, weighted clustering coefficient (WCC), and global efficiency. The graph metrics displayed consistent and significant decreases at the group level, individual subject level, and individual muscle level. For the first time, this paper proposed a non-parametric functional muscle network and highlighted the corresponding potential as a sensitive biomarker of fatigue with superior performance to conventional spectrotemporal measures.

Paretic-Limb-Only Plyometric Training Outperforms Volume-Matched Double-Limb Training for Ameliorating Balance Capability and Gait Symmetry in Adolescents with Unilateral Cerebral Palsy: A Comparative Study

Adolescents with unilateral cerebral palsy (U-CP) experience an asymmetrical posture because the less-affected lower limb is preferred for bodyweight support as a strategy of compensating for the paretic side’s muscular weakness. This study was designed to compare the effect of 12 weeks of paretic-limb-only plyometric training (PLPT) and volume-matched double-limb training (DLPT) on balance capability and gait symmetry in adolescents with U-CP. Sixty-nine adolescents with U-CP were randomly assigned to PLPT, DLPT, or a control group (n = 23 each). Treatment was delivered twice/week (with at least 48 h recovery intervals) for 12 weeks in succession. The directional (LoSdirectional) and overall (LoSoverall) limits of stability in addition to the temporal (T-GSI) and spatial (S-GSI) gait symmetry indicis were assessed pre- and post-treatment. The LoSdirectional improved significantly in the PLPT group compared to either the DLPT or control group (for the forward (p = 0.027 and <0.001, respectively), backward (p = 0.037 and <0.001, respectively), affected-side (p = 0.038 and 0.004, respectively), and less-affected-side (p = 0.018 and 0.016, respectively)), and this was also the case for the LoSoverall (p < 0.001). Additionally, The T-GSI and S-GSI scores decreased significantly in the PLPT group compared to the DLPT (p = 0.003 and 0.047, respectively) or control (p = 0.003 and 0.036, respectively) group, indicating the development more symmetrical gait patterns. In conclusion, PLPT is likely more effective for enhancing balance capabilities and promoting symmetrical gait patterns than DLPT. Thereupon, it is worthwhile for physical rehabilitation practitioners to include the PLPT paradigm into the intervention plans for adolescents with U-CP.

Association and Agreement between Reactive Strength Index and Reactive Strength Index-Modified Scores

Since the reactive strength index (RSI) and reactive strength index-modified (RSI-mod) share similar nomenclature, they are commonly referred as interchangeable measures of agility in the sports research literature. The RSI and RSI-mod are most commonly derived from the performance of depth jumping (DJ) and countermovement jumping (CMJ), respectively. Given that DJ and CMJ are plyometric movements that differ materially from biomechanical and neuromotor perspectives, it is likely that the RSI and RSI-mod measure distinct aspects of neuromuscular function. The purpose of this investigation was to evaluate the association and agreement between RSI and RSI-mod scores. A mixed-sex sample of NCAA division I basketball athletes (n = 21) and active young adults (n = 26) performed three trials of DJ from drop heights of 0.51, 0.66, and 0.81 m and three trials of countermovement jumping. Using 2-dimensional videography and force platform dynamometry, RSI and RSI-mod scores were estimated from DJ and CMJ trials, respectively. Linear regression revealed moderate associations between RSI and RSI-mod scores (F = 11.0–38.1; R² = 0.20–0.47; p < 0.001–0.001). Bland–Altman plots revealed significant measurement bias (0.50–0.57) between RSI and RSI-mod scores. Bland–Altman limit of agreement intervals (1.27–1.51) were greater than the mean values for RSI (0.97–1.05) and RSI-mod (0.42) scores, suggesting poor agreement. Moreover, there were significant performance-dependent effects on measurement bias, wherein the difference between and the mean of RSI and RSI-mod scores were positively associated (F = 77.2–108.4; R² = 0.63–0.71; p < 0.001). The results are evidence that the RSI and RSI-mod cannot be regarded as interchangeable measures of reactive strength.

The Relationship between Symmetrical and Asymmetrical Jumps and Their Influence on Speed Abilities: Gender Consideration

Purpose: Plyometric exercises, in the form of jumping, are extreme physical activities. The aim of the study was to determine how symmetrical-single versus asymmetrical-continued plyometric exercises differ between men and women and affect speed abilities. Methods: Twenty-two healthy females and forty-four males from different sports practices participated in the investigation. The countermovement jump (CMJ) and drop jump (DJ) of 40/60 cm box were performed on two independent and synchronized force platforms (Bilateral Tensiometric Platform S2P, Ljubljana, Slovenia). The measurement of a standing long jump (SLJ) and all continuous jumps: standing five jumps (SFJ), standing bounce triple jump (SBTJ), five double-leg jumps (FD-LJ), and a 10 m horizontal single leg jump (HSLJ-10mL/R) were performed using OptoJump–Next Microgate (OptoJump, Bolzano, Italy). Results: Statistically significant differences were noted in all jump kinematic and somatic parameters, in favor of the men. The correlations between values of height of symmetrical jumps (bilateral) and distance (SLJ) were stronger in women despite the shorter jumps than the men. When an alpha-level of 0.01 was set, this study demonstrated a stronger correlation between symmetrical-single and asymmetrical-continuous plyometrics exercises and sprints, both men and women. This relationship is due to their similar kinematic and dynamic structures with sprinting steps. Conclusions: The results showed a large dispersion of the relationship (p < 0.05) between jumps and sprints divided into 10, 20 and 30 m, both in men and women. Both types of exercises implemented as a plyometric training regime are an extremely important tool for sprint speed development.

A Comparison of Bilateral vs. Unilateral-Biased Strength and Power Training Interventions on Measures of Physical Performance in Elite Youth Soccer Players

Stern, D, Gonzalo-Skok, O, Loturco, I, Turner, A, and Bishop, C. A comparison of bilateral vs. unilateral-biased strength and power training interventions on measures of physical performance in elite youth soccer players. J Strength Cond Res 34(8): 2105-2111, 2020-The aim of the present study was to compare the effects of bilateral and unilateral-biased strength and power training programs on measures of physical performance in male youth soccer players. Twenty-three elite youth players (age: 17.6 ± 1.2 years) were randomly assigned to either a unilateral (n = 11) or a bilateral (n = 12) group, who completed a strength and power intervention, twice per week for 6 weeks. The unilateral group completed rear foot elevated split squats (RFESS), single-leg countermovement jumps (SLCMJs), single-leg drop jumps (SLDJs), and single-leg broad jumps (SLBJs). The bilateral group intervention performed back squats, CMJs, drop jumps (DJ), and broad jumps (BJ). A 2 × 2 repeated measures analysis of variance showed no between-group differences. However, within-group differences were evident. The bilateral training group showed significant (p < 0.05) improvements in back squat strength (d = 1.27; %Δ = 26.01), RFESS strength (d = 1.64; %Δ = 23.34), BJ (d = 0.76; %Δ = 5.12), 10-m (d = -1.17; %Δ = 4.29), and 30-m (d = -0.88; %Δ = 2.10) performance. The unilateral group showed significant (p < 0.05) improvements in RFESS strength (d = 1.40; %Δ = 33.29), SLCMJ on the left leg (d = 0.76; %Δ = 9.84), SLBJ on the left leg (d = 0.97; %Δ = 6.50), 10 m (d = -1.50; %Δ = 5.20), and 505 on the right leg (d = -0.78; %Δ = 2.80). Standardized mean differences showed that bilateral training favored improvements in back squat strength and unilateral training favored improvements in RFESS strength, SLDJ on the right leg and 505 on the right leg. These results show that although both training interventions demonstrated trivial-to-large improvements in physical performance, the notion of training specificity was evident with unilateral training showing greater improvements in unilateral test measures.

Unilateral Plyometric Training is Superior to Volume-Matched Bilateral Training for Improving Strength, Speed and Power of Lower Limbs in Preadolescent Soccer Athletes

This study compared the effects of unilateral and bilateral plyometric training on strength, sprint performance and lower limb power. Sixty-eight preadolescent soccer athletes were randomly assigned to a unilateral plyometric training group (n=23), a bilateral plyometric training group (n=23) and a control group (n=22). Both plyometric training groups trained with equal volumes of unilateral or bilateral exercises for 15 minutes in each session, at which time the control group performed soccer-specific drills. Plyometric exercises were executed twice weekly for 10 weeks during the competitive season. The following tests were performed before and after the intervention: single-leg and double-leg countermovement jump, squat jump, horizontal jumps in different directions, maximal isometric strength of quadriceps and hamstrings, sprint performance, agility and balance. Unilateral plyometric training resulted in greater improvements compared to the control group in the following variables: hamstrings strength (ES: 0.91, p=0.037), 5m sprint time (ES: 0.93, p=0.004), single-leg countermovement jump (ES: 0.90, p=0.006), single- and double-leg squat jump (ES: 0.87, p=0.030 and ES: 0.73, p=0.067, respectively) and single-leg hop performance (ES: 1.01, p=0.004). The only tests where there was an improvement of BPT compared with the CG were the single-leg and double leg SJ (ES: 0.76, p=0.026; ES: 0.70, p=0.050). Quadriceps strength, side hop test, double-leg horizontal jump test, flamingo balance test and modified agility T-test were equally improved in all three groups (p<0.001). In conclusion, unilateral lower-limb plyometric training is more effective in increasing muscle strength and power in preadolescent soccer players when compared to bilateral training or soccer training alone.

Bilateral Deficit and Bilateral Performance: Relationship with Sprinting and Change of Direction in Elite Youth Soccer Players

The purpose of the study was to examine the differences in bilateral deficit (BLD) at different loadings during the half-squat jump (SJ) and horizontal countermovement jump (HCMJ) to determine if there is a relationship with linear sprint or change of direction (COD). The second goal was to check if fast players were more powerful in SJ and HCMJ than slow players in bilateral performance (BP). Twenty-seven male youth soccer players participated in the study. Players were divided in two groups, faster and slower, according to their sprint performance (10 and 40 m). BLD average power with body weight (BW) and 25%BW were significantly higher than 50%BW (p < 0.01). BLD during HCMJ was significantly higher than BLD during SJ with BW, 25%BW and 50%BW (p < 0.01). There were no statistical relationships between BLD and sprint or COD performance (p > 0.05). Fast players showed significantly higher SJ power with all the different loads and HCMJ than slow players (p < 0.01), and fast players lost more time executing COD-90° than slow players (p < 0.01). There were no statistical differences between fast and slow players in BLD. BLD seems to be dependent on motor task, contraction type and load and could not be a proper measure to estimate sprint and COD performance. Faster players are confirmed to be more powerful players than slow players, and decrements in COD could be a key benchmark to identify deficit between linear and COD performance.

Do asymmetry scores influence speed and power performance in elite female soccer players?

This study examined the relationships between vertical jump asymmetries and speed and power performance in elite female soccer athletes. Sixteen professional female soccer players (age: 23.0 ± 3.8 years; body mass: 60.2 ± 7.3 kg; height: 165.1 ± 5.5 cm) from the same professional club participated in this study. Athletes performed unilateral and bilateral squat jumps (SJ) and countermovement jumps (CMJ) on a portable force plate; 30-m sprinting test; Zigzag change-of-direction (COD) test; and muscle power testing using the jump squat (JS) exercise. Asymmetry scores were obtained from the results of the unilateral SJ and CMJ by the percentage difference between the dominant and non-dominant legs. The Pearson product-moment coefficient of correlation was used to analyse the correlations between the bilateral and unilateral vertical jump variables and the physical tests. The bilateral vertical jump performance (in both SJ and CMJ) was closely related to sprinting and JS power performances (r values ranging from 0.50 to 0.73; P< 0.05). In contrast, no significant associations were found between jump asymmetries and performance measures. Our data suggest that asymmetry scores derived from unilateral vertical jumps are not capable of influencing the speed-power performance of professional female soccer players.

Muscle activity of Bulgarian squat. Effects of additional vibration, suspension and unstable surface

Practitioners of strength and conditioning are increasingly using vibration and unstable environments to enhance training effects. However, little evidence has been found comparing the use of suspension devices and vibratory platforms used in the Bulgarian squat. The purpose of this cross-sectional study was to examine the effect of suspension devices (TRX®), unstable surfaces (BOSU®), and vibration plates on muscle activity and force during the Bulgarian squat. Twenty physically active male students (age = 24.40 ± 3.63 years) performed a set of five repetitions of Bulgarian squats, suspended lunges, suspended lunges-BOSU, suspended lunges-Vibro30, and suspended lunges-Vibro40 (vibration 30 Hz or 40 Hz and 4 mm of amplitude). A randomized within-subject design was used to compare leg muscle activity, vertical ground reaction forces, and force exerted on the strap across the five exercises. Results showed no significant differences in muscle activity between the Bulgarian squat and suspended lunge (p = 0.109, d = 2.84). However, the suspended lunge significantly decreased muscle activation compared to the suspended lunge-BOSU (p = 0.012, d = 0.47), suspended lunge-Vibro30 (p = 0.001, d = 1.26), and suspended lunge-Vibro40 (p = 0.000, d = 1.51). Likewise, the Bulgarian squat achieved lower activity than the suspended lunge-Vibro40 (p = 0.010, d = 0.96). The force on the strap significantly decreased in the suspended lunge-BOSU compared to the suspended lunge-Vibro30 (p = 0.009, d = 0.56). The suspended lunge achieved higher front leg force production than the Bulgarian squat (p = 0.006, d = 0.48). In conclusion, leaning the rear leg on a suspension device does not provoke an increase in the activation of the front leg during the Bulgarian squat but increases the vertical ground reaction forces. Thus, the use of unstable surfaces or vibration plates for the front leg increased muscular activity when performing a suspended lunge.

Methodological Characteristics and Future Directions for Plyometric Jump Training Research: A Scoping Review

Recently, there has been a proliferation of published articles on the effect of plyometric jump training, including several review articles and meta-analyses. However, these types of research articles are generally of narrow scope. Furthermore, methodological limitations among studies (e.g., a lack of active/passive control groups) prevent the generalization of results, and these factors need to be addressed by researchers. On that basis, the aims of this scoping review were to (1) characterize the main elements of plyometric jump training studies (e.g., training protocols) and (2) provide future directions for research. From 648 potentially relevant articles, 242 were eligible for inclusion in this review. The main issues identified related to an insufficient number of studies conducted in females, youths, and individual sports (~ 24.0, ~ 37.0, and ~ 12.0% of overall studies, respectively); insufficient reporting of effect size values and training prescription (~ 34.0 and ~ 55.0% of overall studies, respectively); and studies missing an active/passive control group and randomization (~ 40.0 and ~ 20.0% of overall studies, respectively). Furthermore, plyometric jump training was often combined with other training methods and added to participants' daily training routines (~ 47.0 and ~ 39.0% of overall studies, respectively), thus distorting conclusions on its independent effects. Additionally, most studies lasted no longer than 7 weeks. In future, researchers are advised to conduct plyometric training studies of high methodological quality (e.g., randomized controlled trials). More research is needed in females, youth, and individual sports. Finally, the identification of specific dose-response relationships following plyometric training is needed to specifically tailor intervention programs, particularly in the long term.

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.