Reliability and validity of a low-cost, wireless sensor and smartphone app for measuring force during isometric and dynamic resistance exercises.

The aim of this study was to investigate the reliability and validity of an affordable wireless force sensor in measuring mean and peak forces during resistance training.A Suiff Pro wireless force sensor (Suiff, Spain) and a MuscleLab force platform (Ergotest, Norway) were used concurrently to assess tensile load and the ground reaction force resulting from an upright row exercise. Thirteen participants (28.2 ± 5.7 years, 76.2 ± 9.6 kg, 178.2 ± 9.2 cm) performed the exercise under three velocity conditions and isometrically. Each condition involved three sets of exercise. Mean (Fmean) and peak (Fpeak) force values from both sensors were collected and compared.Suiff Pro exhibited excellent reliability for Fmean and Fpeak (ICCs = 0.99). When compared to the criterion measures, Suiff Pro showed trivial standardized bias for Fmean (Mean = 0.00 [CI 95% = 0.00 to 0.01]) and Fpeak (-0.02 [-0.04 to 0.00]). The standardized typical error was also trivial for Fmean (0.03 [0.02 to 0.03]) and Fpeak (0.07 [0.05 to 0.09]). Correlations with the MuscleLab force platform were nearly perfect: Fmean (0.97 [0.94 to 0.98]; p<0.001); Fpeak (0.96 [0.92 to 0.97]; p<0.001).The findings demonstrate that the Suiff Pro sensor is reliable and valid device for measuring force during isometric and dynamic resistance training exercises. Therefore, practitioners can confidently use this device to monitor kinematic variables of resistance training exercises and to obtain real-time augmented feedback during a training session.

Ground Reaction Forces, Asymmetries and Performance of Change of Direction Tasks in Youth Elite Female Basketball Players.

The magnitude and direction of inter-limb asymmetries in a change of direction (COD) have increased interest in scientific research in recent years. This present study aimed to investigate the magnitude of asymmetries in an elite youth female basketball sample (n = 18, age = 17.79 ± 0.67 y) and determine its directionality using force platform technology. Participants performed 70° and 180° COD tests analyzing the following variables: time, ground contact time (GCT) and ground reaction forces (GRF) along the anterior-posterior, mediolateral, and vertical axes. Inter-limb asymmetries were evident in both COD tests, with substantial differences observed between limbs (p < 0.01). The asymmetry values ranged from 3.02% to 24.31% in COD 180° and from 1.99% to 21.70% in COD 70°, with anterior-posterior GRF consistently exhibiting the highest asymmetry magnitude. Additionally, the directionality exhibited variability between the tests, indicating poor agreement and suggesting the independent directionality of asymmetries across tasks. Moreover, players required more time to complete the COD 180°, the GCT was noticeably longer for the COD 180° than for the COD 70°, and GRF varied across the axis, suggesting that players adapt uniquely to the specific demands of each task. The utilization of force platforms presents a comprehensive approach to assess asymmetries and COD variables performance variables which are "angle-dependent", which could have important implications for COD screening and effective training interventions.

Effects of Exercise-Induced Neuromuscular Fatigue on Jump Performance and Lower-Limb Asymmetries in Youth Female Team Sport Athletes.

The objective of the present study was to examine the effect of acute neuromuscular fatigue on unilateral jump performance and inter-limb asymmetries. Thirty elite youth female team sport athletes (age: U-14 to U-18) performed the Unilateral Countermovement Jump (UCJ) and the Unilateral Drop Jump (UDJ) (18-cm box) tests before and approximately 10 minutes after the 30-15 intermittent fitness test (30-15 IFT). A paired samples t-test showed significant reductions in UCJ jump height in the right leg after the 30-15 IFT (p = 0.018; d = 0.33), but not in the left leg (p = 0.459; d = 0.48). For the UDJ, significant reductions in jump height were shown in both the right (p < 0.001; d = 0.33) and left (p < 0.001; d = 0.33) legs. In addition, for the reactive strength index (UDJ), significant reductions were seen in the left leg after the 30-15 IFT (p < 0.001; d = 0.31), but not in the right leg (p = 0.948; d < 0.001). Only UCJ inter-limb jump height asymmetries increased significantly post 30-15 IFT (p = 0.033; d = 0.46). In conclusion, the current study indicates that the 30-15 IFT provides a sufficient dose of activity for inducing acute fatigue in elite youth female team sport athletes. Therefore, monitoring jump height in unilateral jump testing is recommended given the tests' sensitivity to detect significant differences in physical performance and inter-limb asymmetries under acutely fatigued conditions in healthy youth female athletes.

Comparación de las variables de rendimiento en las principales ligas europeas de hockey sobre patines / Comparação das variáveis de rendimento nas principais ligas europeias de hóquei em patins / Comparison of performance variables in the main European rink hockey leagues

El presente estudio tuvo como objetivo comparar las variables de rendimiento del hockey patines en los campeonatos nacionales de la máxima categoría masculina en España (OK Liga), Portugal (Primeira Divisao) e Italia (Serie A1). Se analizaron un total de 1.665 partidos disputados entre las temporadas 2018-2019 y 2020-2021, correspondientes a la OK Liga (654), Primeira Divisao (497) y la Serie A1 (514). Se realizaron comparaciones utilizando el análisis de varianza (ANOVA) con post hoc de Bonferroni y la prueba t-Student para comparar las variables según la localización del partido. Los resultados muestran que en España se marcan menos goles por partido, que en Italia se marcan más goles por partido y que en Portugal hay más ejecuciones y goles de penalti y de falta directa, mayor cantidad de faltas y de tarjetas y un mayor porcentaje de goles de pelota parada respecto a los goles totales. En los tres campeonatos las variables de rendimiento asociadas a la victoria fueron favorables a los equipos locales. La comparación de los campeonatos puede permitir a los entrenadores tener un mejor conocimiento de las variables de rendimiento de cada competición y ayudar a las federaciones a conocer que competiciones están mejor asociadas con las variables determinantes del espectáculo deportivo, especialmente los goles, para diseñar propuestas de mejoras en los campeonatos pertinentes. (AU)

The present study aimed to compare the rink hockey performance variables in the top national championships of Spain (OK Liga), Portugal (Primeira Divisao), and Italy (Serie A1). A sample of 1,665 matches corresponding to the OK Liga (654), Primeira Divisao (497), and Serie A1 (514) played between the 2018-2019 and 2020-2021 seasons was analyzed. Comparisons were made using an analysis of the variance (ANOVA) followed by Bonferroni's post hoc multiple comparison test. Additionally, the t-Student test was used to compare each variable according to match location. The results show that in Spain, teams score fewer goals per match and inItaly more goals per match. In Portugal, we observe more set-piece shots, more goals, a higher percentage of goals coming from set-pieces compared to total goals, more fouls, and cards shown. Moreover, the performance variables associated with victory were favourable to the local teams in all three championships. Championship comparison enables coaches to understand better specific and contextual performance variables. Our research could also help governing bodies and federations know what competitions arebetter associated with several key performance indicators and design proposals to improve each championship. (AU)

O presente estudo teve como objetivo comparar as variáveis de rendimento do hóquei em patins nos campeonatos nacionais do escalão masculino mais alto em Espanha (OK Liga), Portugal (Primeira Divisão) e Itália (Série A1). Foram analisados 1.665 jogos disputados entre as épocas 2018-2019 e 2020-2021, correspondendo à OK Liga (654), Primeira Divisão (497) e Série A1 (514). As comparações foram feitas usando a análise de variância post hoc de Bonferroni (ANOVA) e o teste t de Student para comparar as variáveis de acordo com a localização do jogo. Os resultados mostram que em Espanha marcam-se menos golos por jogo e em Italia mais golos per jogo. Em Portugal há mais execuções e golos de grandes penalidades e livres diretos, mais faltas e cartões e uma maior percentagem de golos de bola parada em relação ao total de golos. Nos três campeonatos as variáveis de rendimento associadas à vitória foram favoráveis às equipas locais. A comparação dos campeonatos pode permitir que os treinadores tenham um melhor conhecimento das variáveis de rendimento de cada competição e ajudar as federações a saber quais competições estão mais associadas às variáveis determinantes do espetáculo desportivo, em especial os golos, para traçar propostas de melhora nos aspectos relevantes dos campeonatos. (AU)

Acute effects of jaw clenching while wearing a customized bite-aligning mouthguard on muscle activity and force production during maximal upper body isometric strength.

Background/objectives: The possible mechanisms supporting the relationship between the masticatory and the musculoskeletal systems have been recently investigated. It has been suggested that jaw clenching promotes ergogenic effects on prime movers through the phenomenon of concurrent activation potentiation (CAP). The purpose of this study was to analyse the effects of jaw clenching and jaw clenching while wearing mouthguard (MG) on muscle activity and force output during three upper body isometric strength tests. Methods: Twelve highly trained rink-hockey athletes were recruited for the study. A randomized, repeated measures within study design was carried out to compare the acute effects of three experimental conditions: jaw clenching while wearing MG (MG), jaw clenching without MG (JAW) and non-jaw clenching (NON-JAW). Results: Statistical analyses revealed significant higher force output (p < 0.05) in all tests for MG conditions with respect to NON-JAW. When comparing JAW and NON-JAW conditions an increased peak force was found in handgrip (p = 0.045, d = 0.26) and bench press (p = 0.018, d = 0.43) but not in biceps curl (p = 0.562, d = 0.13). When comparing MG and JAW conditions, no differences were observed in any force output. In terms of muscle activity, significant differences were found in the agonist muscles of the handgrip test for MG with respect to NON-JAW (p = 0.031-0.046, d = 0.25-1.1). Conclusion: This study demonstrated that jaw clenching, with and without MG, may be a good strategy to elicit the CAP phenomenon, which seems to promote ergogenic effects in upper body isometric force production. The non-significant differences observed between JAW and MG suggested that the use of MG doesn't make a difference in enhancing the isometric force production neither the muscle activity in upper body isometric strength.

Superimposed vibration on suspended push-ups.

Background: Superimposition of vibration has been proposed in sports training using several devices and methods to enhance muscle activation and strength adaptations. Due to the popularity of suspension training, vibration systems have recently been developed to increase the effects of this training method. The present cross-sectional study aims to examine the effects of superimposing vibration on one of the most popular exercises in strength and conditioning programs: push-ups. Methods: Twenty-eight physically active men and women executed push-ups in three suspended conditions (non-vibration, vibration at 25 Hz, and vibration at 40 Hz). OMNI-Res scale was registered, and surface electromyographic signals were measured for the activity of the right and left external oblique, anterior deltoid, triceps brachii, sternal, and clavicular heads of the pectoralis major. Results: A linear mixed model indicated a significant fixed effect for vibration at 25 Hz and 40 Hz on muscle activity. Suspended push-ups with superimposed vibration (25 Hz and 40 Hz) showed a significant higher activity on left (25 Hz: p = 0.036, d = 0.34; 40 Hz: p = 0.003, d = 0.48) and right external oblique (25 Hz: p = 0.004, d = 0.36; 40 Hz: p = 0.000, d = 0.59), anterior deltoid (25 Hz: p = 0.032, d = 0.44; 40 Hz: p = 0.003, d = 0.64), and global activity (25 Hz: p = 0.000, d = 0.55; 40 Hz: p = 0.000, d = 0.83) compared to non-vibration condition. Moreover, OMNI-Res significant differences were found at 25 Hz (6.04 ± 0.32, p = 0.000 d = 4.03 CI = 3.27, 4.79) and 40 Hz (6.21 ± 0.36 p = 0.00 d = 4.29 CI = 3.49, 5.08) compared to the non-vibration condition (4.75 ± 0.32). Conclusion: Superimposing vibration is a feasible strategy to enhance the muscle activity of suspended push-ups.

Relationship between Performance and Inter-Limb Asymmetries Using Flywheel Resistance Device in Elite Youth Female Basketball Players.

The purposes of this study were to quantify inter-limb asymmetries from unilateral jumps, change of direction (COD) speed, and flywheel resistance skill tests and to examine their relationship with physical performance in a sample of elite youth female basketball players. Eleven female basketball players (age = 17.56 ± 0.60 year; body mass = 75.13 ± 12.37 kg; height = 1.83 ± 0.08 m; BMI = 22.42 ± 2.28; sports experience = 6.31 ± 1.73 year; years post-peak height velocity = 4.79 ± 0.68 year) performed a battery of fitness tests in the post-season consisting of the Single Leg Countermovement Jump in vertical (SLCJ-V), horizontal (SLCJ-H), and lateral (SLCJ-L) directions, 135° and 90° COD tests, and four skills (acceleration step, deceleration step, sidestep, and crossover step) with an flywheel resistance device. The results showed significant differences between the higher performing and lower performing limbs across all tasks (p < 0.05). The mean asymmetry index values ranged from 1.26% (COD 135°) to 11.75% (SLC-V). Inter-limb asymmetries were greatest during the flywheel resistance skills. Spearman's correlations (ρ) for all tests were only significant for inter-limb asymmetries during the sidestep test and reduced performance in SLCJ-L (ρ = −0.61; p = 0.046) and all COD deficits (ρ range = −0.72 to −0.81). The findings of the present study showed that inter-limb asymmetries are task-specific in female youth basketball players and suggest that the use of flywheel devices can be included in the battery of tests to detect inter-limb asymmetry.

The Influence of Individual Set-Pieces in Elite Rink Hockey Match Outcomes.

The main objective of this study was to analyze the influence of individual set-pieces (Free Direct Hits and Penalties) in elite rink hockey match outcomes in different game situations. A sample of 161 matches played between high-standard teams during ten consecutive seasons (2009-2010 to 2018-2019) were analyzed using a binary logistic regression. The full evaluated model was composed of an explanatory variable (set-pieces scored) and five potential confounding and interaction variables (match location, match level, match importance, extra time, and balanced score). However, the final model only included one significant interaction variable (balanced score). The results showed that scoring more individual set-pieces than the opponent was associated with victory (OR = 6.1; 95% CI: 3.7, 10.0) and was more relevant in unbalanced matches (OR = 19.5; 95% CI: 8.6, 44.3) than in balanced matches (OR = 2.3; 95% CI: 1.2, 4.5). These findings indicate that individual set-pieces are strongly associated with match outcomes in matches played between high-standard teams. Therefore, it is important for teams to excel in this aspect, and it is suggested that these data can encourage coaches to reinforce the systematic practice of individual set-pieces in their training programs. Additionally, it is suggested that teams have specialist players in this kind of action to mainly participate in these specific match moments.

Effects of wearing a customized bite-aligning mouthguard on powerful actions in highly trained swimmers.

BACKGROUND/OBJECTIVES: The potential advantages of wearing customized bite-aligning mouthguards on several performance parameters such as muscular strength, power and reaction time have been reported. Literature shows that the concurrent activation potentiation phenomenon, elicited by a powered and balanced jaw clenching, can provide athletes with several neuromuscular advantages. The aim of the present study was to investigate the acute effects of jaw clenching while wearing a customized bite-aligning mouthguard on swimming start, countermovement jump and swim bench test, in contrast to two other conditions: non-jaw clenching and jaw clenching without mouthguard. METHODS: A randomized, repeated measure within study design was used to compare the condition effect on eight highly trained elite male and female swimmers. RESULTS: Statistical analysis revealed a significant increase in the countermovement jump height (p = 0.041) when comparing the use of mouthguards with the non-jaw condition. In the swim bench, a significant greater time to peak force (p = 0.049) was found when comparing the use of mouthguards with the jaw condition. Although, non-significant effects, small differences were found in the start reaction time and 15-m freestyle swimming when comparing the use of mouthguards with the non-jaw condition. CONCLUSION: This study demonstrated that wearing customized, bite-aligning mouthguards had an ergogenic effect on specific measures of vertical jump and swim bench test, whereas non-meaningful but small differences were found in swimming start.

sEMG Activity in Superimposed Vibration on Suspended Supine Bridge and Hamstring Curl.

Traditionally in strength and conditioning environments, vibration has been transmitted using platforms, barbells, dumbbells, or cables but not suspension devices. This study aimed to examine the effects on the lower limb of applying superimposed vibration on a suspension device. Twenty-one physically active men and women performed supine bridge and hamstring curl exercises in three suspended conditions (non-vibration, vibration at 25 Hz, and vibration at 40 Hz). In each exercise condition, the perceived exertion scale for resistance exercise (OMNI-Res) was registered, and the electromyographic signal was assessed for gastrocnemius (medialis and lateralis), biceps femoris, semitendinosus, gluteus maximus, and rectus femoris. A linear mixed model indicated a significant fixed effect for vibration at 25 Hz and 40 Hz on muscle activity in suspended supine bridge (p < 0.05), but no effect for suspended hamstring curl (p > 0.05). Likewise, the Friedman test showed a significant main effect for vibration at 25 Hz and 40 Hz in suspended supine bridge (p < 0.05) but not for suspended hamstring curl (p > 0.05) on OMNI-Res. Post hoc analysis for suspended supine bridge with vibration at 25 Hz showed a significant activation increase in gastrocnemius lateralis (p = 0.008), gastrocnemius medialis (p = 0.000), semitendinosus (p = 0.003) activity, and for semitendinosus under 40 Hz condition (p = 0.001) compared to the non-vibration condition. Furthermore, OMNI-Res was significantly higher for the suspended supine bridge at 25 Hz (p = 0.003) and 40 Hz (p = 0.000) than for the non-vibration condition. Superimposed vibration at 25 Hz elicits a higher neuromuscular response during the suspended supine bridge, and the increase in vibration frequency also raises the OMNI-Res value.

Assessing the Magnitude and Direction of Asymmetry in Unilateral Jump and Change of Direction Speed Tasks in Youth Female Team-Sport Athletes.

The direction of inter-limb asymmetries and the change of direction (COD) deficit are two aspects that have increased in recent years. The main objective of the present study was to assess the magnitude of neuromuscular asymmetries in an elite youth female team-sports sample and determine its directionality. Secondary objectives were to evaluate the relationship between COD deficit, linear speed and COD time performance. Elite female youth basketball and handball players (n = 33, age = 16 ± 1.17 y) performed the Single Leg Countermovement Jump in vertical (SLCJ-V), horizontal (SLCJ-H), and lateral (SLCJ-L) directions, the COD and the 10-m sprint. Results showed statistical differences between limbs in all the neuromuscular tests (p < 0.001). The Kappa coefficient showed poor to fair levels of agreement between tasks (K range = -0.087 to 0.233), indicating that asymmetries rarely favoured the same limb between skills. Additionally, small and non-significant correlations were found between the linear sprint capacity and the COD ability. The findings of the present study highlight the independent directionality of asymmetries across tests. The COD deficit does not appear to be much more advantageous than COD total time to measure asymmetry. Practitioners are encouraged to use a fitness testing battery to detect existing side differences and each ability should be specifically trained with functional tasks.

Analysis of the Individual Set-Pieces Influence on the Teams' Ranking in Rink Hockey.

The main objective of this research was to analyze the individual set-pieces influence on the final season ranking in rink hockey. For this purpose, 6,920 individual set-pieces from 1,680 matches corresponding to free direct hits (n = 4,332) and penalty shots (n = 2,588) were analyzed during seven consecutive seasons (2012-13 to 2018-19) in the First Spanish League (Ok Liga). The variables recorded were the following for each team: total points, free direct hits attempted, free direct hits scored, penalties attempted, penalties scored, total goals scored during the season, free direct hits received, goals received from free direct hits, penalties received, goals received from penalties and total goals received in the season. Results showed that 21.08% of the goals were scored by free direct hits and penalty shots (11.58% and 9.49%, respectively). Likewise, teams ranked in a better position achieved higher effectiveness in individual set-pieces and their goalkeepers were more effective in defending the free direct hits and penalties. Furthermore, results showed significant correlations between team season points and better performance in individual set-pieces variables. Therefore, the results of this study demonstrated the importance of systematic practice of free direct hits and penalty shots for teams' success in rink hockey. Additionally, it is suggested that teams possess special players to execute these particular elements of match play.

Seasonal variation of inter-limb jumping asymmetries in youth team-sport athletes.

The main objective of the present study was to provide seasonal variation data for inter-limb asymmetry in youth elite team-sport athletes. Fifty-nine players performed the single-leg countermovement jump (SLCMJ) and the one leg hop for distance (OLHT) tests during pre-season, mid-season and end-season. A repeated-measures analysis of variance was conducted to determine magnitude differences in asymmetry scores between time points. Kappa coefficients (κ) were calculated to determine the levels of agreement for the direction of asymmetry. When comparing inter-limb asymmetry magnitudes across the season, the SLCMJ test showed significantly higher asymmetries at mid-season in comparison with pre-season and end-season (p< 0.01, d= -1.03 for pre to mid; p< 0.01, d= 1.12 for pre to end). However, OLHT inter-limb asymmetry magnitude remained consistent throughout the season (ES range = -0.02 to -0.06). For the direction of asymmetry, levels of agreement ranged from poor to slight in the SLCMJ (k= -0.10 to 0.18) and in the OLHT (k= -0.21 to 0.18). No significant differences were found between mean asymmetry values at any time point or for either test when comparing males and females. In conclusion, jump height asymmetry during the SLCMJ was the only metric to show significant magnitude changes across the season.

Acute Effects of Wearing Bite-Aligning Mouthguards on Muscular Strength, Power, Agility and Quickness in a Trained Population: A Systematic Review.

The purpose of the present systematic review was to determine the acute effects of wearing bite-aligning mouthguards on muscle strength, power, agility and quickness in athletes. A search of the current literature was performed using the electronic databases (until 1 May 2021) Web of Science, Scopus and Medline. The inclusion criteria were: (1) descriptive design studies; (2) with randomized clinical trials; (3) examining the within-subject acute effects of wearing mouthguards on functional and neuromuscular performance parameters; (4) in physical active, recreational or high-standard athletes. Twenty-seven studies met the inclusion criteria. Sixteen reported positive effects in some of the variables assessed, two reported negative effects and the rest found no significant differences. Overall, the main findings described in the literature are inconclusive concerning the neuromuscular advantages of using mouthguards in muscle strength, power, agility and quickness. These discrepancies might be related to several factors such as differences in testing protocols, poor control of the jaw magnitude and improper mouthguard designs. Despite these differences, after conducting the present systematic review, the authors speculate that jaw clenching while wearing custom-made, bite-aligning oral devices might promote beneficial effects in lower limb power actions, especially in jump ability and knee extension movements. Thus, athletes might consider the use of mouthguards, not only for their protective role but also for the potential ergogenic effects in specific actions, mainly those for which lower limb muscular power are required.

Predicting the Unknown and the Unknowable. Are Anthropometric Measures and Fitness Profile Associated with the Outcome of a Simulated CrossFit® Competition?

The main objective of this research was to find associations between the outcome of a simulated CrossFit® competition, anthropometric measures, and standardized fitness tests. Ten experienced male CrossFit® athletes (age 28.8 ± 3.5 years; height 175 ± 10.0 cm; weight 80.3 ± 12.5 kg) participated in a simulated CrossFit® competition with three benchmark workouts ("Fran", "Isabel", and "Kelly") and underwent fitness tests. Participants were tested for anthropometric measures, sit and reach, squat jump (SJ), countermovement jump (CMJ), and Reactive Strength Index (RSI), and the load (LOAD) corresponding to the highest mean power value (POWER) in the snatch, bench press, and back squat exercises was determined using incremental tests. A bivariate correlation test and k-means cluster analysis to group individuals as either high-performance (HI) or low performance (LO) via Principal Component Analysis (PCA) were carried out. Pearson's correlation coefficient two-tailed test showed that the only variable correlated with the final score was the snatch LOAD (p < 0.05). Six performance variables (SJ, CMJ, RSI, snatch LOAD, bench press LOAD, and back squat LOAD) explained 74.72% of the variance in a k = 2 means cluster model. When CrossFit® performance groups HI and LO were compared to each other, t-test revealed no difference at a p ≤ 0.05 level. Snatch maximum power LOAD and the combination of six physical fitness tests partially explained the outcome of a simulated CrossFit competition. Coaches and practitioners can use these findings to achieve a better fit of the practices and workouts designed for their athletes.

The Behaviour of Home Advantage during the COVID-19 Pandemic in European Rink Hockey Leagues.

The primary purpose of the present study was to compare the home advantage (HA) and the home team performance in the most relevant European rink hockey leagues (Spanish, Portuguese and Italian), considering the presence or absence of spectators in the competition venues due to the effect of COVID-19 restrictions. The sample was composed of 1665 rink hockey matches (654 from the Spanish league, 497 from the Portuguese league, and 514 from the Italian league) played between the 2018-2019 and 2020-2021 seasons. The HA and match variables comparisons were established using several negative binomial regression models. Results showed that the effect of HA did not disappear despite playing without spectators but decreased from 63.99% to 57.41% (p = 0.002). Moreover, the comparison of the match variables showed that playing with spectators benefited local teams' performance, especially in the Portuguese and Italian leagues. Playing with spectators favoured local team performance in rink hockey matches, which is more evident in some analysed leagues. However, as HA does not disappear entirely without spectators, it is necessary to study other relevant performance factors that are not directly or indirectly attributable to crowd behaviour in rink hockey performance analyses.

Influence of the Amount of Instability on the Leg Muscle Activity During a Loaded Free Barbell Half-Squat.

This study aimed to understand the acute responses on the muscular activity of primary movers during the execution of a half-squat under different unstable devices. Fourteen male and female high-standard track and field athletes were voluntarily recruited. A repeated measures design was used to establish the differences between muscle activity of the primary movers, the body centre of mass acceleration and the OMNI-Perceived Exertion Scale for Resistance Exercise (OMNI-Res) in a half-squat under four different stability conditions (floor, foam, BOSU-up and BOSU-down). A significant correlation was found between the highest performance limb muscle activity and body centre of mass acceleration for half-squat floor (r = 0.446, p = 0.003), foam (r = 0.322, p = 0.038), BOSU-up (r = 0.500, p = 0.001), and BOSU-down (r = 0.495, p = 0.001) exercises. For the exercise condition, the half-squat BOSU-up and BOSU-down significantly increased the muscle activity compared to half-squat floor (vastus medialis: p = 0.020, d = 0.56; vastus lateralis: p = 0.006, d = 0.75; biceps femoris: p = 0.000-0.006, d = 1.23-1.00) and half-squat foam (vastus medialis: p = 0.005-0.006, d = 0.60-1.00; vastus lateralis: p = 0.014, d = 0.67; biceps femoris: p = 0.002, d = 1.00) activities. This study contributes to improving the understanding of instability training, providing data about the acute muscular responses that an athlete experiences under varied stability conditions. The perturbation offered by the two BOSU conditions was revealed as the most demanding for the sample of athletes, followed by foam and floor executions.

Temporal trend of cardiorespiratory endurance in urban Catalan high school students over a 20 year period.

BACKGROUND: Physical fitness is considered an important indicator of health in adolescents. However, in recent years several studies in the scientific literature have shown a considerable lower trend and an alarming worsening of the current adolescents' physical condition when comparing with previous decades, especially in urban populations. The aim of the current study was to analyse the temporal trend in cardiorespiratory endurance (CRE) in urban Catalan adolescents over a 20-year period (1999-2019). METHODS: A cross-sectional analysis study considering the 20-m Shuttle Run test (SRT) results obtained in the last 20 years was carried out. 1,701 adolescents between 15 and 16 years old (914 boys and 787 girls) were divided into four groups, corresponding to consecutive periods of five years (Group 1: 1999-2004; Group 2: 2005-2009; Group 3: 2010-2014 and Group 4: 2015-2019). ANOVA was used to test the period effect on CRE and post hoc Bonferroni analysis was performed to test pairwise differences between groups (p < 0.05). RESULTS: Results showed a significantly lower performance in CRE in both sexes. The percentual negative difference was 0.67%, 9.6% and 7% for boys and 5.06%, 14.97% and 9.41% for girls, when comparing the performance in 20-m Shuttle Run test for the first period, respectively. CONCLUSIONS: Results suggest that the physical fitness of Catalan urban adolescents is lower in both sexes when comparing the different analysed periods of time. Therefore, CRE adolescents should be improved in order to help to protect against cardiovascular disease and other health risks in adulthood.

Effects of Wearing a Jaw-repositioning Intra-oral Device in Synchronized Swimming Athletes.

The effects of wearing an intra-oral device on several ventilatory and fatigue markers have been reported for a variety of sports. The quality of the figures performed in synchronized swimming is directly affected by fatigue, and can be monitored during training sessions (TS). The aim of the study was to investigate the acute effects of wearing customized intra-oral devices on heart rate variability, rating of perceived exertion, blood lactate accumulation, and salivary cortisol production during a competitive training session. Twelve highly trained elite female athletes (age: 21.0±3.6 years) participated in the study. Fatigue markers were assessed at the beginning and at the end of the 3rd and 5th afternoon TS for that week, once with and once without an intra-oral device, in random order. Salivary cortisol levels were higher in relation to the baseline in the intra-oral device condition (P<0.05) but not in athletes without an intra-oral device. No differences between conditions were found in rating of perceived exertion (P=0.465) and blood lactate (P=0.711). No time or condition interactions or main effects were shown for heart rate variability. Thus, there is no evidence that wearing a low-arch intra-oral device is a good recommendation for high-standard athletes performing long and stressful routines.

Inter-limb asymmetries are associated with decrements in physical performance in youth elite team sports athletes.

Actually, there is scarce literature looking for the relationship between inter-limb asymmetries and performance in youth elite team sports. The main purpose of this cross-sectional study was to examine the relationships between inter-limb asymmetries and physical performance in youth elite team-sports players. A secondary objective was to evaluate the presence of between-sexes differences in inter-limb asymmetries in elite youth team sports players. Eighty-one young elite team-sports athletes (age: u-14 to u-18) performed the star excursion balance test in the anterior direction (SEBT ANT), a single leg vertical countermovement jump test (SLCMJ), the one leg hop test for distance (OLHT), a 30 m sprint test, and the V-cut test. Inter-limb asymmetries were calculated for SEBT ANT, SLCMJ and OLHT. Pearson r was used to analyse the relationships between inter-limb asymmetries and physical performance. Results showed significant (p < 0.05) but small (r = 0.26) relationships between SLCMJ asymmetries and 30 m sprint time for the total group. Significant negative correlations with small to moderate magnitude of correlation were also found between SLCMJ asymmetries and SLCMJ performance on the lowest performing limb for the total group (p < 0.05; r = -0.26), males (p < 0.01; r = -0.48) and females (p < 0.05; r = -0.30). Moreover, significant negative correlations with moderate and large magnitude were also present between OLHT asymmetries and OLHT performance on the lowest performing limb for the total group (p < 0.01; r = -0.44), males (p < 0.01; r = -0.56) and females (p < 0.01; r = -0.64). No correlations were observed between asymmetries and either the V-cut test or SEBT ANT performance. No correlation were observed between SEBT ANT asymmetries and physical performance. In addition, when comparing asymmetry values between sexes there were no significant differences in vertical (p = 0.06) and horizontal (p = 0.61) jumping tests. However, there were significant differences in asymmetry between sexes in the ANT SEBT (p = 0.04). In conclusion, the current study indicated that jumping asymmetries were associated with decrements in sprint speed and jumping performance. Therefore, assessing inter-limb asymmetries would be recommended to improve training interventions for youth elite team-sports athletes.