Standardized vs. Relative Intensity in CrossFit.

CrossFit is characterized by being a standardized training program that improves physical performance through the provision of several stimuli regardless of the participant's strength level. This study aimed to compare the acute response in total repetitions as a measurement of performance, jump ability, physiological demand (heart rate and blood lactate), and perceived effort considering the participants' strength level with individualized intensity in CrossFit. Thirty-five participants were assessed and asked to participate on two separate days in a standardized and relative 'As Many Repetitions As Possible' (AMRAP) CrossFit circuit. Both AMRAPs comprised strength, gymnastic and aerobic exercises, although only strength was individualized according to the participant's level. Before the statistical analysis, participants were allocated to higher- or lower-strength groups following the one-repetition maximum-bodyweight ratio in the push press exercise. Results support the existence of a strong relationship between strength level and total repetitions in both AMRAPs. In addition, differences in total repetitions and rate of perceived exertion between strength groups are discarded when AMRAP intensity is individualized while physiological demand and jump ability are maintained. Thus, the higher-strength participants may benefit from similar responses with a lower number of repetitions. Therefore, CrossFit trainers should be encouraged to prescribe strength tasks based on the percentage of 1RM for every training.

Assessing Motor Variability during Squat: The Reliability of Inertial Devices in Resistance Training.

Movement control can be an indicator of how challenging a task is for the athlete, and can provide useful information to improve training efficiency and prevent injuries. This study was carried out to determine whether inertial measurement units (IMU) can provide reliable information on motion variability during strength exercises, focusing on the squat. Sixty-six healthy, strength-trained young adults completed a two-day protocol, where the variability in the squat movement was analyzed at two different loads (30% and 70% of one repetition maximum) using inertial measurement units and a force platform. The time series from IMUs and force platforms were analyzed using linear (standard deviation) and non-linear (detrended fluctuation analysis, sample entropy and fuzzy entropy) measures. Reliability was analyzed for both IMU and force platform using the intraclass correlation coefficient and the standard error of measurement. Standard deviation, detrended fluctuation analysis, sample entropy, and fuzzy entropy from the IMUs time series showed moderate to good reliability values (ICC: 0.50-0.85) and an acceptable error. The study concludes that IMUs are reliable tools for analyzing movement variability in strength exercises, providing accessible options for performance monitoring and training optimization. These findings have implications for the design of more effective strength training programs, emphasizing the importance of movement control in enhancing athletic performance and reducing injury risks.

Analysis of Concentric and Eccentric Power in Flywheel Exercises Depending on the Subjects' Strength Level and Body Mass.

ABSTRACT: Asencio, P, García-Valverde, A, Albaladejo-García, C, Beato, M, Moreno-Hernández, FJ, and Sabido, R. Analysis of concentric and eccentric power in flywheel exercises depending on the subjects' strength level and body mass. J Strength Cond Res XX(X): 000-000, 2024-The objective of this study is to describe how flywheel exercise mechanical outputs are affected by the athletes' body mass (BM) and strength level and by the exercise type. Forty-six recreational athletes came to a laboratory 3 times. On the first day, descriptive data, squat (1 repetition maximum: 1RM) and flywheel familiarization were performed. After a second day of familiarization, subjects performed a randomized flywheel exercise-testing protocol of squat and split squat exercises. The variables used for data analysis were peak concentric power and peak eccentric power, eccentric/concentric ratio, and their relationship with 1RM/BM. Subjects were assigned to a stronger or weaker group according to their 1RM/BM ratio. Group differences were found in absolute values of eccentric overload (EOL) (p < 0.01; effect size [ES] = 0.51) and EOL/BM (p < 0.01; ES = 0.46) only in the split squat. Absolute power values in the concentric phase showed differences between inertial load (p < 0.01; ES = 0.41). The stronger group did not present significant differences between inertial loads during squat (p < 0.01; ES = 0.46), but they showed different ratios with light inertias in comparison with the weaker group (p < 0.01; ES = 0.46). There were significant differences between groups with light inertias in split squat (nondominant) and squat exercises (p < 0.05; ES = 0.29) in the eccentric and concentric phases (p < 0.116; ES = 0.20). Squat and split squat exercises present different profiles depending on the training level. In conclusion, it is recommended that practitioners perform a test to understand the inertial load-power profile (concentric, eccentric, and their ratio) for each exercise and also consider the user's strength level for selection of the inertial load and for the exercise to use in training.

The Use of Incremental, Decremental or a Random Order of Loads does not Affect Peak velocity Values during Bench Press Throw Load-velocity Relationships.

The aim of this study was to assess the influence of the load order used (i. e. incremental, decremental or random loads order) during the bench press throw load-velocity profile on peak velocity achieved against four different loads (20-40-60-80% of one repetition maximum [1RM]). Both intraclass correlation coefficient (ICC) and coefficient of variation (CV) were calculated to assess the reliability of the measures. A repeated measures ANOVA was used to assess differences between protocols. A linear regression analysis was performed to assess the load-velocity relationships among the different protocols. Peak velocity showed good to high ICC values independently of the load used (ICC=0.83-0.92). CV scores showed good reliability (ranging between 2.2 and 6.2%). No significant differences in peak velocity attained at each load were found between the three testing protocols (p>0.05). In addition, peak velocity at each load was very large to almost perfect, correlated between protocols (r=0.790-0.920). The linear regression model showed a significant relationship between testing protocols (p<0.001; R2=0.94). In conclusion, due to some ICC scores below 0.9 and R2 below 0.95, the indistinct use of different load-order protocols to assess load-velocity relationships in the bench press throw exercise is not recommended.

High-speed stretch-shortening cycle exercises as a strategy to provide eccentric overload during resistance training.

Resistance exercises eliciting eccentric overload (EO) are considered to strongly promote muscular hypertrophy and broad neuromuscular adaptations but typically require specialized equipment. The aims of these experiments were to assess whether EO is achieved during common high-speed stretch-shortening cycle (SSC) exercises (rebound bench press throw [RBPT] and squat jump [SJ]), and to test the effect of the external load on the EO achieved. Twenty-nine under 18 handball players and fifteen physically active males (24.9 ± 3.2 years) took part in the experiments. Testing consisted of a single set of 6 repetitions with light (25%-30% 1-RM), moderate (50% 1-RM), and heavy (70%-75% 1-RM) loads. Eccentric and concentric force near the zero-velocity point (50-200 ms) as well as eccentric-concentric force ratio (EO; %) were calculated. In RBPT, higher EO values were found at 50% 1-RM than 70% 1-RM in the time interval 50 ms before and after the zero-velocity point. Higher EO values were also found at 50% 1-RM than both 30% 1-RM and 70% 1-RM 100 ms before and after the zero-velocity point. For the SJ, higher EO values were found at 50% 1-RM and 75% 1-RM than 25% 1-RM 100 ms before and after the zero-velocity point. Higher EO values were found at 50% 1-RM than 25% 1-RM 200 ms before and after the zero-velocity point. However, the higher EO values in the SJ were found far from the zero-velocity point. High-speed SSC resistance training provides similar EO to other methods and thus should promote muscle hypertrophy and other neuromuscular adaptations.

Right ventricular dysfunction and right ventricular-arterial uncoupling at admission increase the in-hospital mortality in patients with COVID-19 disease.

BACKGROUND: Coronavirus disease 2019 (COVID-19) frequently involves cardiovascular manifestations such as right ventricular (RV) dysfunction and alterations in pulmonary hemodynamics. We evaluated the application of the critical care ultrasonography ORACLE protocol to identify the most frequent alterations and their influence on adverse outcomes, especially those involving the RV (dilatation and dysfunction). METHODS: This cross-sectional study included 204 adult patients with confirmed COVID-19 admitted at three centers. Echocardiography and lung ultrasound images were acquired on admission using the ORACLE ultrasonography algorithm. RESULTS: Two-hundred and four consecutive patients were evaluated: 22 (11.9%) demonstrated a fractional shortening of < 35%; 33 (17.1%) a tricuspid annular plane systolic excursion (TAPSE) of < 17 mm; 26 (13.5%) a tricuspid peak systolic S wave tissue Doppler velocity of < 9.5 cm/sec; 69 (37.5%) a RV basal diameter of > 41 mm; 119 (58.3%) a pulmonary artery systolic pressure (PASP) of > 35 mm Hg; and 14 (11%) a TAPSE/PASP ratio of < .31. The in-hospital mortality rate was 37.6% (n = 71). Multiple logistic regression modeling showed that PASP > 35 mm Hg, RV FS of < 35%, TAPSE < 17 mm, RV S wave < 9.5, and TAPSE/PASP ratio < .31 mm/mm Hg were associated with this outcome. PASP and the TAPSE/PASP ratio had the lowest feasibility of being obtained among the investigators (62.2%). CONCLUSION: The presence of RV dysfunction, pulmonary hypertension, and alteration of the RV-arterial coupling conveys an increased risk of in-hospital mortality in patients presenting with COVID-19 upon admission; therefore, searching for these alterations should be routine. These parameters can be obtained quickly and safely with the ORACLE protocol.

Use of pulmonary ultrasound to predict in-hospital mortality in patients with COVID-19 infection.

INTRODUCTION: Lung ultrasound (LUS) implementation in patients with COVID-19 can help to establish the degree of pulmonary involvement, evaluate treatment response and estimate in-hospital outcome. OBJECTIVE: To evaluate the application of a LUS protocol in patients with COVID-19 infection to predict in-hospital mortality. METHODS: The study was carried out from April 1 to August 1, 2020 in patients with COVID-19 infection admitted to the Intensive Care Unit. Lung evaluation was carried out by physicians trained in critical care ultrasonography. RESULTS: Most patients were males, median age was 56 years, and 59 % required mechanical ventilation. In-hospital mortality was 39.4 %, and in those with a LUS score ≥ 19, mortality was higher (50 %). The multiple logistic regression model showed that a LUS score ≥ 19 was significantly associated with mortality (hazard ratio = 2.55, p = 0.01). CONCLUSIONS: LUS is a safe and fast clinical tool that can be applied at bedside in patients with COVID-19 infection to establish the degree of parenchymal involvement and predict mortality.

INTRODUCCIÓN: La implementación del ultrasonido pulmonar (LUS) en los pacientes con COVID-19 puede ayudar a establecer el grado de afectación pulmonar, evaluar la respuesta al tratamiento y estimar el desenlace intrahospitalario. OBJETIVO: Evaluar la aplicación de un protocolo LUS en pacientes con infección por COVID-19 para predecir mortalidad intrahospitalaria. MÉTODOS: El estudio se realizó del 1 de abril al 1 de agosto de 2020 en pacientes con infección por COVID-19, ingresados en la Unidad de Terapia Intensiva. Se realizó evaluación pulmonar por médicos entrenados en ultrasonografía crítica. RESULTADOS: La mayoría de los pacientes fue del sexo masculino, la edad mediana fue de 56 años y 59 % requirió ventilación mecánica. La mortalidad intrahospitalaria fue de 39.4 % y en aquellos con puntuación de LUS ≥ 19, de 50 %. El modelo de regresión logística múltiple mostró que la puntuación de LUS ≥ 19 se asoció significativamente a mortalidad (cociente de riesgo = 2.55, p = 0.01). CONCLUSIONES: El LUS es una herramienta clínica segura y rápida que puede realizarse al lado de la cama de los pacientes con infección por COVID-19, para establecer el grado de afectación parenquimatosa y predecir la mortalidad.

Critical care ultrasonography during COVID-19 pandemic: The ORACLE protocol.

BACKGROUND: Coronavirus disease 2019 (COVID-19) is characterized by severe lung involvement and hemodynamic alterations. Critical care ultrasonography is vital because it provides real time information for diagnosis and treatment. Suggested protocols for image acquisition and measurements have not yet been evaluated. METHODS: This cross-sectional study was conducted at two centers from 1 April 2020 to 30 May 2020 in adult patients with confirmed COVID-19 infection admitted to the critical care unit. Cardiac and pulmonary evaluations were performed using the ORACLE protocol, specifically designed for this study, to ensure a structured process of image acquisition and limit staff exposure to the infection. RESULTS: Eighty-two consecutively admitted patients were evaluated. Most of the patients were males, with a median age of 56 years, and the most frequent comorbidities were hypertension and type 2 diabetes, and 25% of the patients had severe acute respiratory distress syndrome. The most frequent ultrasonographic findings were elevated pulmonary artery systolic pressure (69.5%), E/e' ratio > 14 (29.3%), and right ventricular dilatation (28%) and dysfunction (26.8%). A high rate of fluid responsiveness (82.9%) was observed. The median score (19 points) on pulmonary ultrasound did not reveal any variation between the groups. Elevated pulmonary artery systolic pressure was associated with higher in-hospital mortality. CONCLUSION: The ORACLE protocol was a feasible, rapid, and safe bedside tool for hemodynamic and respiratory evaluation of patients with COVID-19. Further studies should be performed on the alteration in pulmonary hemodynamics and right ventricular function and its relationship with outcomes.

Effects of Maximal Strength Training on Perceived-Fatigue and Functional Mobility in Persons with Relapsing-Remitting Multiple Sclerosis.

Background and objectives: Fatigue is one of the most disabling symptoms that limit daily life activities in persons with multiple sclerosis (pwMS). This study aimed to evaluate the effects of maximal strength training (MST) on perceived-fatigue and functional mobility in pwMS. Materials and Methods: 26 participants with MS were balanced according to their pre-intervention fatigue scores and distributed into an MST group (n = 13) and a control group (CG; n = 13). The MST group completed eight weeks using high loads, evaluating detraining after ten weeks. Quadriceps and hamstring isokinetic (QPTIK; HPTIK) and isometric (QPTIM; HPTIM) peak torques were assessed using an isokinetic dynamometer. Effect size differences were estimated with the Hedges' g index (dg ). Fatigue was evaluated through the Fatigue Severity Scale (FSS), while functional mobility was assessed via the Timed Up and Go Test (TUG). Results: The MST significantly improved all the strength measurements after the intervention (Δ6.43-29.55%; p < 0.05) compared to the control group. FSS showed a significant reduction (59.97%, dg = 5.41, large). The MST group also reduced the TUG time (19.69%; dg = 0.93, large) compared to the control group. Improvements caused by the intervention did not remain after a 10-week follow-up, with decreases in strength performance from 4.40% to 13.86% (dg = 0.24-0.56, small to moderate), 112.08% in the FSS (dg = -3.88, large), and 16.93% in TUG (dg = -1.07, large). Conclusions: MST (up to 90% 1RM) seems to be a feasible and useful way to obtain clinically relevant improvements in the perceived-fatigue symptoms and functional mobility. Still, symptom improvements decrease after a 10-week detraining period.

Influence of Strength Level on the Rest Interval Required During an Upper-Body Power Training Session.

Hernández Davó, JL, Botella Ruiz, J, and Sabido, R. Influence of strength level on the rest interval required during an upper-body power training session. J Strength Cond Res 31(2): 339-347, 2017-The present study aimed to investigate the influence of subjects' strength level on both the ability to maintain power output performance and the physiological and perceived exertion responses during a power training session when different rest intervals (RI) are used. Thirty-eight (18 men and 20 women) subjects were divided into a stronger or weaker group based on their ability to produce peak power output. Testing was performed using the same protocol (5 sets of 8 repetitions with 40% of 1 repetition maximum) in the bench press throw exercise, but differing the RI between sets (1, 2, and 3 minutes). During the sessions, mechanical (peak power), physiological ([La]) and perceptual (RPE) variables were measured. In addition, delayed onset muscular soreness (DOMS) 24 and 48 hours after the training session was reported. Both stronger and weaker (men and women) groups showed significant impairments in mechanical, physiological, and perceptual data when resting 1 minute. Nevertheless, although stronger groups were able to sustain power output over the sets when using the 2-minute RI, weaker groups needed at least 3 minutes to maintain power output performance. Therefore, strength level heavily influences the rest interval required during a power training session and should be taken into account when prescribing such training sessions.

Why Should Athletes Brake Fast? Influence of Eccentric Velocity on Concentric Performance During Countermovement Jumps at Different Loads.

PURPOSE: The aim of the present study was to analyze the effect of different eccentric tempos on eccentric kinetics and kinematics and the subsequent concentric performance when performing countermovement jumps against different loads. METHODS: After 1-repetition-maximum assessment and 2 familiarization sessions, 13 well-trained participants performed, in randomized order, 12 sets (4 tempos × 3 loads) of 4 repetitions of the loaded countermovement-jump exercise. The eccentric tempos analyzed were 5 and 2 seconds, as fast as possible, and accelerated (ie, without pause between repetitions), while the loads used were 30%, 50%, and 70% of 1-repetition maximum. Several kinetic and kinematic variables during both phases were recorded by linking a linear position transducer to the barbell. RESULTS: The eccentric work was greater in the accelerated condition despite no changes in the eccentric depth. The peak and mean propulsive velocities were greater in the as-fast-as-possible and accelerated conditions. Correlation analysis showed that, compared with the 5-second condition, the increased concentric performance in the accelerated condition was related to the difference in eccentric work performed in the last 100 milliseconds of the eccentric phase (r > .770). CONCLUSIONS: Contrary to current practices, the current study highlights the need for performing the eccentric phase of loaded countermovement jumps, a common exercise performed by athletes for both training and evaluation purposes, as fast as possible. This allows not only a greater eccentric work but also improved concentric performance.

Effects of variable intensity and constant intensity flywheel resistance training programs on specific soccer players' performance.

Resistance training programs play a crucial role in optimizing soccer performance. The aim of this study is to compare performance outcomes in sport-specific tasks after implementing two different flywheel resistance training (FRT) programs: variable intensity (VI) and constant intensity (CI). Seventeen (n = 17) amateur footballers were divided into VI and CI groups with the same training volume. For the VI group, a decrease in inertial load was implemented every four sessions, whereas the CI group maintained a constant load during the entire program. After different familiarization sessions and testing (sprint, change of direction, jump, one-repetition maximum and flywheel strength variables), ten sessions of FRT were performed over 5 weeks. Both groups showed similar improvements in the one-repetition maximum (p < 0.01) but the CI group had significant improvements in the 10-m sprint (p = 0.04; ES = 0.72), emphasizing the potential benefits of medium inertial loads to maximize power and specificity in sport tasks. However, no significant differences were observed in the countermovement jump, change of direction and 30-m sprint, possibly attributed to neuromuscular fatigue from a high-volume training schedule and friendly matches. The study highlights the importance of considering training load distribution in FRT programs. The findings emphasize the need for complementary training to maximize the jump and change of direction abilities and caution against high-volume training and friendly match scenarios. In conclusion, FRT programs, whether varying in intensity or not, can yield medium-term performance improvements for soccer players.

Trunk muscle activation in prone plank exercises with different body tilts.

BACKGROUND: Body tilt changes could affect the intensity/difficulty of core stability exercises, but there is still a lack of knowledge about its impact. OBJECTIVE: To analyse the trunk muscles activation during prone plank exercises at different body tilts. METHODS: Twenty-four young adults who performed recreational gymnastic activities participated in this study. Electromyography activity of the rectus abdominis (RA), external oblique (EO), internal oblique (IO) and erector spinae (ES) was recorded during the performance of six variations of the prone plank exercise (planking with feet supported on the ground [conventional horizontal position] and planking with feet supported on wall bars at five different heights increasing the angle tilt) and an inverted position exercise. RESULTS: The RA, EO and IO activation in all prone plank variations were higher than those observed in the conventional prone plank. In addition, the coefficient of variation of the muscle activation increased with the declination angle, reaching the highest values in the inverted position for the RA and ES muscles. CONCLUSION: The results seem to indicate that the body tilt variation could be used as an easy and inexpensive strategy for modulating the neuromuscular demands and the motor control challenge during planking exercises.

Current Guidelines for the Implementation of Flywheel Resistance Training Technology in Sports: A Consensus Statement.

BACKGROUND: Flywheel resistance training has become more integrated within resistance training programs in a variety of sports due to the neuromuscular, strength, and task-specific enhancements reported with this training. OBJECTIVE: This paper aimed to present the consensus reached by internationally recognized experts during a meeting on current definitions and guidelines for the implementation of flywheel resistance training technology in sports. METHODS: Nineteen experts from different countries took part in the consensus process; 16 of them were present at the consensus meeting (18 May 2023) while three submitted their recommendations by e-mail. Prior to the meeting, evidence summaries were developed relating to areas of priority. This paper discusses the available evidence and consensus process from which recommendations were made regarding the appropriate use of flywheel resistance training technology in sports. The process to gain consensus had five steps: (1) performing a systematic review of systematic reviews, (2) updating the most recent umbrella review published on this topic, (3) first round discussion among a sample of the research group included in this consensus statement, (4) selection of research group members-process of the consensus meeting and formulation of the recommendations, and (5) the consensus process. The systematic analysis of the literature was performed to select the most up-to-date review papers available on the topic, which resulted in nine articles; their methodological quality was assessed according to AMSTAR 2 (Assessing the Methodological Quality of Systematic Review 2) and GRADE (Grading Recommendations Assessment Development and Evaluation). Statements and recommendations scoring 7-9 were considered appropriate. RESULTS: The recommendations were based on the evidence summary and researchers' expertise; the consensus statement included three statements and seven recommendations for the use of flywheel resistance training technology. These statements and recommendations were anonymously voted on and qualitatively analyzed. The three statements reported a score ranging from 8.1 to 8.8, and therefore, all statements included in this consensus were considered appropriate. The recommendations (1-7) had a score ranging from 7.7 to 8.6, and therefore, all recommendations were considered appropriate. CONCLUSIONS: Because of the consensus achieved among the experts in this project, it is suggested that practitioners and researchers should adopt the guidelines reported in this consensus statement regarding the use of flywheel resistance technology in sports.

The Effect of Three Different Resistance Training Programming Approaches on Strength Gains and Jumping Performance.

Background: A main goal of programming is to structure the optimal variations in training factors to optimize athletes' adaptations. Nevertheless, it remains unknown the optimal programming model leading to greater neuromuscular adaptations. Purpose: The aim of the present study was to assess the influence of three different magnitudes of variability within resistance training programs on performance adaptations. Methods: Forty participants were assigned to three different groups differing in the frequency of change in training contents: a weekly model (WM; n = 12), a daily model (DM; n= 14), and a session model (SM; n = 14). The training intervention lasted for six weeks, performing two sessions per week of back-squat exercise. Total training load (volume and intensity) of the six-week intervention was equated for all groups. Maximum dynamic strength (1RM) in the back-squat, countermovement (CMJ) and squat jump (SJ) were measured pre- and post-training intervention. Results: All groups showed significant increases (p< .05) in 1RM, with the SM showing greater increases than the WM (20.5 vs 13.6%; p= .022). Although not reaching statistical significance, the magnitude of the increases in CMJ tended to be greater for DM and SM group (9.5% and 8.1%, respectively,) than in the WM (4.4%). All groups showed similar increases in the SJ (7.7-9.9%). Conclusions: The results of the present study suggest that the use of more frequent stimuli variations within resistance training programming is a key factor to achieve concomitant increases in strength and jumping performance.

Variations induced by the use of unstable surface do not facilitate motor adaptation to a throwing skill.

Induced variability by the use of unstable surfaces has been proposed to enhance proprioceptive control to deal with perturbations in the support base better. However, there is a lack of evidence about its benefits facilitating motor adaptions in upper body skills. In this experiment, practice on an unstable surface was applied to analyze the adaptations in an upper limb precision throwing skill. After a pretest, twenty-one participants were randomly allocated into two groups: one group practiced the throwing task on a stable surface and the other group practiced the same task on an unstable support base. Differences in throwing performance between pre- and post-practice were analyzed in accuracy, hand movement kinematics and variability of the throw in both surface conditions. Fuzzy entropy of the horizontal force was calculated to assess the complexity dynamics of postural sway. Participants improved their performance on the stable and the unstable surface. Induced variability using an unstable surface reduced participants' variability and the complexity of postural sway, but it did not facilitate a superior adaptation of the throwing task. The results suggest that the variations induced by unstable surfaces would fall far from the family of specific motor solutions and would not facilitate additional motor performance of the throwing task.

Kinematics and performance of team-handball throwing: effects of age and skill level.

To assess the influence of age and skill level on handball throwing kinematics and performance, 126 participants were distributed into groups according to their skill level (elite or recreational) and age group (U12, U16 or +18). Each participant performed three sets of 10 throws, aiming to hit a target (40 × 40 cm) located in the right corner of the goal. During testing, kinematic data were recorded and throwing performance (accuracy and velocity) was measured. Results showed greater throwing velocity in the elite compared to recreational groups, whereas no differences were found for throwing accuracy. The elite U16 and +18 groups displayed higher segment velocities (hand, arm and pelvis) than the recreational groups. The participation of proximal segments was higher in older groups, showing the more skilled players (U16 and +18) greater pelvis velocities (1.62-1.75 vs 1.02-1.22 m/s). The increased velocity of the distal joints (hand peak velocity: 13.56 ± 1.65 vs 10.67 ± 1.98 m/s) are responsible for the difference in throwing velocity between the elite and recreational U12 groups. Several correlations were found between joint kinematics and throwing velocity. Coaches could use these results during training, to optimise specific throwing training.

Differences in kinetic characteristics during countermovement jump of football players with cerebral palsy according to impairment profiles.

Objectives: The purpose of this study was 1) to determine and compare kinetic parameters during the realization of a countermovement jump (CMJ) between footballers with cerebral palsy (CP) and non-impaired footballers, and 2) to analyze the differences in this action between different players' impairment profiles and a group of non-impaired footballers. Methods: This study involved 154 participants comprising 121 male footballers with CP from 11 national teams and 33 male non-impaired football players recruited as the control group (CG). The footballers with CP were described according to the different impairment profiles (bilateral spasticity = 10; athetosis or ataxia = 16; unilateral spasticity = 77; minimum impairment = 18). All participants performed three CMJs on a force platform to record kinetic parameters during the test. Results: The group of para-footballers presented significantly lower values than the CG in the jump height (p < 0.01, d = -1.28), peak power (p < 0.01, d = -0.84), and the net concentric impulse (p < 0.01, d = -0.86). Concerning the pairwise comparisons between CP profiles and the CG, significant differences were found for the bilateral spasticity, athetosis or ataxia, and unilateral spasticity subgroups compared to the non-impaired players for jump height (p < 0.01; d = -1.31 to -2.61), power output (p < 0.05; d = -0.77 to -1.66), and concentric impulse of the CMJ (p < 0.01; d = -0.86 to -1.97). When comparing the minimum impairment subgroup with the CG, only significant differences were found for jump height (p = 0.036; d = -0.82). Footballers with minimum impairment presented higher jumping height (p = 0.002; d = -1.32) and concentric impulse (p = 0.029; d = -1.08) compared to those with bilateral spasticity. Also, the unilateral spasticity subgroup reports a higher jump height performance than the bilateral group (p = 0.012; d = -1.12). Conclusion: These results suggest that the variables related to power production during the concentric phase of the jump are crucial for the performance differences between groups with and without impairment. This study provides a more comprehensive understanding of kinetic variables that would differentiate CP and non-impaired footballers. However, more studies are necessary to clarify which parameters better differentiate among different profiles of CP. The findings could help to prescribe effective physical training programs and support the classifier's decision-making for class allocation in this para-sport.

The use of non-linear tools to analyze the variability of force production as an index of fatigue: A systematic review.

Background: Fatigue is a process that results in a decreased ability to produce force, and which could eventually affect performance and increase the risk of injury. Force variability analysis has been proposed to describe the level of fatigue with the purpose of detecting the development of fatigue. Variability is credited to play a functional and adaptive role through which the components of a system self-organize to solve a motor problem. Non-linear tools have been applied to analyze the variability of physiological signals, revealing that the structure of motor fluctuations provides relevant information about the functional role of variability. It has been suggested that the presence of lower complexity in the variability structure could reveal a less functional and adaptative state (e.g., ageing or illness). In the last years, an increased number of studies have applied these techniques to force variability analysis in relation to fatigue. Objective: To provide an overview of the current knowledge on the use of non-linear tools on force variability as a fatigue index. Methods: Following PRISMA guidelines, a systematic search of SPORTDiscus, Scopus, Web of Science and PubMed was carried out. Studies included were: a) original studies that analyzed the effect of fatigue on humans during an action focused on force production; b) published studies with their title and abstract in English; c) studies that applied non-linear tools on a signal directly related to force production. Results: Twenty-five studies were included in this review. The relationship between fatigue and the complexity of force variability, the type of action and relative intensity, the nature of the signal and the non-linear tools used, and the methods of data acquisition and processing were identified. Conclusion: The articles reviewed suggest that fatigue leads to a decrease in complexity mostly in isometric contractions, but this is not as clear in dynamic contractions. This fatigue-induced loss of complexity seems to be a result of changes in the nervous system at the central level, albeit triggered by peripheral mechanisms. It should be noted that non-linear tools are affected by the relative intensity of contraction, non-stationarity, and the acquisition and treatment of the signal.

Effects of Flywheel Resistance Training on Sport Actions. A Systematic Review and Meta-Analysis.

The purpose of the present meta-analysis was to examine the effect of flywheel resistance training (FRT) on main sport action (i.e., jumping performance, sprinting time and change of direction performance) improvements in athletes and healthy active people. A Boolean search strategy adapted for each of the databases employed was conducted to identify all studies measuring change in sport actions performance after FRT interventions up to July 2019. Outcomes were analysed using an average effect size (D+) and a 95% confidence interval (CI), which was calculated assuming a random-effects model. A total of 9 studies with 283 participants met the inclusion criteria and were selected for the analysis. The mean quality score (PEDro scale) of the articles included in the meta-analysis was 5.67. The meta-analysis showed significant positive effects on jumping performance (SMC 0.65; 95% CI, 0.11-1.19; p = 0.02), sprinting time (SMC 1.33; 95% CI, 0.39-2.28; p < 0.01) and change of direction performance (SMC 1.36; 95% CI, 0.58-2.14; p < 0.01) after FRT interventions compared to control/traditional resistance training groups. The results of the present meta-analysis provide evidence of the usefulness of FRT to improve variables related to sport performance in both athletes and healthy population.