Effects of plyometric training and beta-alanine supplementation on maximal-intensity exercise and endurance in female soccer players

Plyometric training and beta-alanine supplementation are common among soccer players, although its combined use had never been tested. Therefore, a randomized, double-blind, placebo-controlled trial was conducted to compare the effects of a plyometric training program, with or without beta-alanine supplementation, on maximal-intensity and endurance performance in female soccer players during an in-season training period. Athletes (23.7 ± 2.4 years) were assigned to either a plyometric training group receiving a placebo (PLACEBO, n = 8), a plyometric training group receiving beta-alanine supplementation (BA, n = 8), or a control group receiving p lacebo without following a plyometric training program (CONTROL, n = 9). Athletes were evaluated for single and repeated jumps and sprints, endurance, and change-of-direction speed performance before and after the intervention. Both plyometric training groups improved in explosive jumping (ES = 0.27 to 1.0), sprinting (ES = 0.31 to 0.78), repeated sprinting (ES = 0.39 to 0.91), 60 s repeated jumping (ES = 0.32 to 0.45), endurance (ES = 0.35 to 0.37), and change-of-direction speed performance (ES = 0.36 to 0.58), whereas no significant changes were observed for the CONTROL group. Nevertheless, compared to the CONTROL group, only the BA group showed greater improvements in endurance, repeated sprinting and repeated jumping performances. It was concluded that beta-alanine supplementation during plyometric training may add further adaptive changes related to endurance, repeated sprinting and jumping ability

Effects of plyometric training and creatine supplementation on maximal-intensity exercise and endurance in female soccer players

Objectives: To investigate the effects of a six-week plyometric training and creatine supplementation intervention on maximal-intensity and endurance performance in female soccer players during in-season training. Design: Randomized, double-blind, placebo-controlled trial. Methods: Young (age 22.9 ± 2.5 y) female players with similar training load and competitive background were assigned to a plyometric training group receiving placebo (PLACEBO, n = 10), a plyometric training group receiving creatine supplementation (CREATINE, n = 10) or a control group receiving placebo without following a plyometric program (CONTROL, n = 10). Athletes were evaluated for jumping, maximal and repeated sprinting, endurance and change-of-direction speed performance before and after six weeks of training. Results: After intervention the CONTROL group did not change, whereas both plyometric training groups improved jumps (ES = 0.25-0.49), sprint (ES = 0.35-0.41), repeated sprinting (ES = 0.48-0.55), endurance (ES = 0.32-0.34) and change-of-direction speed performance (ES = 0.46-0.55). However, the CREATINE group improved more in the jumps and repeated sprinting performance tests than the CONTROL and the PLACEBO groups. Conclusions: Adaptations to plyometric training may be enhanced with creatine supplementation

Kinematic and kinetic characteristics of unilateral jump assessments: Reliability, asymmetry and relationship to jump performance

The purpose of this thesis was to provide an in depth analysis of the kinematics and kinetics associated with unilateral vertical (VCMJ), horizontal (HCMJ) and lateral (LCMJ) countermovement jump performance. This thesis consists of i) two reviews of literature discussing the isoinertial assessment of eccentric force capability and acyclic jump assessment with the intention of providing recommendations for future research design and measurement of lower limb muscular capability; ii) a technical note determining the appropriate start threshold (2.5, 5 and 10% of bodyweight- BW) for the force-time curve analysis of the three different unilateral jumps; iii) a research note investigating the variability and influence of eccentric kinematics thought important determinants of VCMJ, HCMJ and LCMJ performance; and iv) an experimental study establishing the reliability of a variety of kinetic and temporal variables for the VCMJ, HCMJ and LCMJ, comparing the kinetic differences across the three jumps, examining the leg asymmetry between the dominant and non dominant legs in the variables of interest, and determining the best predictors of each jump performance. In terms of the experimental papers, the aim of the technical note was to determine the appropriate start threshold for analysis of a force-time curve. Ten state league soccer players (age 21.0 ± 3.1 years, height 178.6 ± 6.5 cm, mass 75.4 ± 5.0 kg) performed three trials of a bilateral countermovement jump. Significant differences (p \u3c 0.05) were found in all variables except eccentric and concentric peak force and force at zero velocity between 2.5% and 10% and 5% and 10% thresholds. Similar results were found for the 2.5% and 5% threshold variables except that no significant difference was found in the concentric ground contact time. The different thresholds did not appear to have any influence on the variability of the measurement and only concentric time to peak force was found to have high variability (coefficient of variation - CV= 51.7-55.5%). It was concluded that any of the start thresholds (2.5, 5.0 and 10% BW) could be used to determine the starting point of a CMJ considering their reliability; however, the 2.5% BW threshold was preferable as most of the force-time signal could be considered for analysis and differences in eccentric and concentric kinematic and kinetic variables where found when a higher threshold was used. For the research note, thirty team sport athletes (age 21.9 ± 3.8 years, height 1.77 ± 0.06 m, body mass 75.5 ± 9.0 kg) performed three trials of a unilateral VCMJ, HCMJ and LCMJ on both legs. It was observed that the variability (CV) of the eccentric variables (i.e. peak velocity, peak displacement, ground contact time) was the lowest for the VCMJ (CV = 8.5-10.6%), and the highest for the HCMJ (CV = 11.7-13.5%). The eccentric ground contact time was significantly (p \u3c 0.05) longer (-0.18 s) for the HCMJ and LCMJ compared to the VCMJ. The amplitude of the eccentric displacement was significantly (p \u3c 0.05) greater (3-5 cm) in the LCMJ compared to the other two jumps and eccentric displacement of the HCMJ was also significantly (p \u3c 0.05) greater (2 cm) compared to the VCMJ. The peak eccentric velocity was significantly faster (0.06 to 0.15 m.s-1 ) for the VCMJ compared to the other jumps and the LCMJ eccentric peak velocity was also significantly (p \u3c 0.05) faster (0.09 m.s-1 ) than that of the HCMJ. It seems that in the absence of instruction and standardization of the countermovement, eccentric phase kinematics remains relatively stable over trials and between legs. In terms of the between jump analysis, it seems that the eccentric phase kinematics are relatively unique to each jump type. The experimental study used the same thirty subjects as the research note. They performed, on two separate occasions, three trials of unilateral VCMJ, HCMJ and LCMJ on each leg. It was found that from the eighteen variables studied, eccentric and concentric peak force and concentric peak power were the only variables with acceptable reliability as determined by previously published criteria (CV= 3.3-15.1 %; ICC= 0.70-0.96). Comparisons of eccentric and concentric peak vertical ground reaction force (VGRF) and concentric peak power among the three jumps revealed that these three variables were significantly (p \u3c 0.01) greater in the VCMJ compared to the HCMJ and LCMJ (eccentric peak force: 14-16%; concentric peak power: 45-51 %), but no significant differences were found between the HCMJ and LCMJ. No significant leg asymmetries were found between the dominant and non dominant leg in any kinetic variables but significant differences (p \u3c 0.01) were found in the actual jump height or distance. The asymmetry index between limbs ranged from -2.1 % to 9.3% for all variables. Concentric peak vertical power output was found to be the best single predictor of VCMJ perfo1mance Gump height) accounting for 79% of the shared variance between the two variables. The addition of concentric peak VGRF and eccentric peak VGRF to the statistical model improved the common variance associated with vertical jump to 95.9%. The best predictor model for HCMJ performance (distance jumped) included only one variable, horizontal concentric peak power which accounted for a shared variance of 42.6% with horizontal jump distance. Eccentric peak VGRF was the only variable entered into the predictor model of LCMJ performance (i.e. distance jumped) and accounted for only 14.9% of that performance. It was concluded that eccentric and concentric peak force and concentric peak power can be used confidently as measures of functional strength and power. The differences found in VGRF and vertical power between the VCMJ and HCMJ or LCMJ, confirmed that the vertical force and power requirements between multidirectional unilateral jump movements are different. Differences between the dominant and non-dominant leg are likely to be found in a healthy athletic population the magnitude of this asymmetry differing depending on the direction of force application. However, it is advised that these differences should fall within a 10 to 15% range in order to reduce potential injury risk and optimize performance. Finally, developing and monitoring changes in horizontal and vertical concentric leg power seem appropriate for improving HCMJ and VCMJ performance respectively. As different strength and power characteristics were associated with different jump performances depending on the movement direction, leg power assessment needs to include assessment in all three directions and/or match sport or activity specific needs. It is fundamental to keep such information in mind when the goals of a training program are being set and monitoring of progress is undertaken

Power Development and Trainability in Youth

Power is regarded as a major attribute for most team sport players, therefore it’s advancement should be taken into consideration early in an athlete’s developmental pathway. However, the natural development of power and its trainability during growth and maturation remains relatively unaddressed by researchers. Subsequently, the purpose of this thesis was to investigate the variability of isoinertial force-velocity profiling and maximal strength assessment in youth and determine the role of maturation and training on the variables deemed reliable. A great deal of movement variability in the eccentric phase of counter movement jumps was found, especially prior to peak height velocity (PHV). Vertical concentric mean and peak power and eccentric mean power were deemed reliable to monitor stretch-shortening cycle performance, while the assessment of force-velocity-power and maximal strength can be measured reliably with a ballistic loading protocol after familiarization. Vertical and horizontal power can be normalised to body mass with a common sex allometric scaling factor in athletes between 9-12 years old and sex difference in relative acyclic power did not appear prior to male puberty in contrast to sprint and change of direction performance. Tracking somatotype, age, maturity and body mass during growth was found important to better understand the development of explosive actions. In male pre to post PHV, strength and power measures were found to have a greater dependency on body mass than velocity-related variables, and even after adjustment for body mass most differences remained substantial. Maturity dependant improvements, along with appropriate adjustment for body mass, need to be taken into account when comparing performance of maturing athletes. Percent differences in strength or power had percent effects on sprint performance that were similar at different stages of maturity. These relationships explained most of the maturity related improvements in sprint performance before PHV but only some improvements after, meaning that other neuromuscular factors are playing a role in sprint performance development. Specific strength training is recommended for athletes around PHV rather than prior to PHV to improve strength, power and speed, while maintenance programs in youth should be planned to reduce decay in these variables, especially in pre and post PHV boys. While the development of power is dependent on a multitude of factors, maturity had an influence on the timing and tempo of power development as well as the training dose-response relationship and rate of decay

The match-to-match variation of match-running in elite female soccer

Objectives The purpose of this study was to examine the match-to-match variation of match-running in elite female soccer players utilising GPS, using full-match and rolling period analyses. Design Longitudinal study. Methods Elite female soccer players (n = 45) from the same national team were observed during 55 international fixtures across 5 years (2012–2016). Data was analysed using a custom built MS Excel spreadsheet as full-matches and using a rolling 5-min analysis period, for all players who played 90-min matches (files = 172). Variation was examined using co-efficient of variation and 90% confidence limits, calculated following log transformation. Results Total distance per minute exhibited the smallest variation when both the full-match and peak 5-min running periods were examined (CV = 6.8–7.2%). Sprint-efforts were the most variable during a full-match (CV = 53%), whilst high-speed running per minute exhibited the greatest variation in the post-peak 5-min period (CV = 143%). Peak running periods were observed as slightly more variable than full-match analyses, with the post-peak period very-highly variable. Variability of accelerations (CV = 17%) and Player Load (CV = 14%) was lower than that of high-speed actions. Positional differences were also present, with centre backs exhibiting the greatest variation in high-speed movements (CV = 41–65%). Conclusions Practitioners and researchers should account for within player variability when examining match performances. Identification of peak running periods should be used to assist worst case scenarios. Whilst micro-sensor technology should be further examined as to its viable use within match-analyses

Validity and Reliability of Wearable Validity and Reliability of Wearable Satellite System Technology for Linear Sprint Profiling: Brief Review

This is a protocol registration for the systematic review entitled: "Validity and Reliability of Wearable Satellite System Technology for Linear Sprint Profiling". The purpose of this study is to systematically review the current literature available exploring satellite positioning system sensor usage for sprint modeling, consolidate the findings concerning sprint profiling, summarize the findings as well as identify gaps in the literature to guide future research

Validity and Reliability of Wearable Validity and Reliability of Wearable Satellite System Technology for Linear Sprint Profiling: Brief Review

This is a protocol registration for the systematic review entitled: "Validity and Reliability of Wearable Satellite System Technology for Linear Sprint Profiling". The purpose of this study is to systematically review the current literature available exploring satellite positioning system sensor usage for sprint modeling, consolidate the findings concerning sprint profiling, summarize the findings as well as identify gaps in the literature to guide future research