Caffeine mouth rinse enhances performance, fatigue tolerance and reduces muscle activity during moderate-intensity cycling.

We investigated the effects of caffeine mouth rinse on endurance performance, muscle recruitment (i.e., electromyographic activity of the vastus lateralis and rectus femoris), rating of perceived effort and heart rate. Twelve physically-active healthy men cycled at 80% of their respiratory compensation point until task failure. The participants rinsed their mouths for 10 seconds with placebo (PLA, 25 mL of a solution composed of non-caloric mint essence) or caffeine (CAF, 25 mL of 1.2% of anhydrous caffeine concentration with non-caloric mint essence) every 15 minutes of exercise. Time until exhaustion increased 17% (effect size = 0.70) in CAF compared to PLA (p = 0.04). The wavebands of low-frequency electromyographic activity (EMG) of the vastus lateralis and rectus femoris was lower in CAF group than PLA at 50% of the time until exhaustion (p = 0.04). The global EMG signal was lower in CAF group than PLA at 100% of the time until exhaustion (p = 0.001). The rating of perceived effort pooled was higher in CAF mouth rinse (p = 0.001) than PLA group. No effect was found on the heart rate between the groups (p > 0.05). Caffeine mouth rinse increases endurance performance, rating of perceived effort and decreases muscle activity during a moderate-intensity exercise.

Dribbling speed predicts goal-scoring success in a soccer training game.

The aim of this study was to explore the underlying bases of goal-scoring ability of junior soccer players. Male players (mean age 17.2 years, SD = 1.3) were recruited from an elite Brazilian football academy. We assessed each individual's dribbling and sprinting speed along five 30 m paths varying in curvature from 0 to 1.37 radians/m. We also quantified each player's ability to dribble the ball through a series of 15 cones using six different techniques. Dribbling, sprinting, and technical dribbling were then compared with an individual's goal-scoring ability as assessed when competing against one defender and a goalkeeper protecting a full-sized goal (N = 20-48 attempts/ individual). Goal-scoring success was significantly positively associated with their sprint speed (r = .60; P = .014), dribbling speed (r = .81; P < .0001), and technical dribbling (r = .49; P = .022). An individual's percentage of shots saved was only significantly associated with their dribbling speed (r = -.81; P < .001), with faster dribblers less likely to have their shots saved. Based on the full multivariate model for goal-scoring success (adjusted r2  = .60; P < .001), dribbling speed was the only significant correlate (t = 3.51; P < .001). Our study demonstrates that our metric of dribbling speed, as measured along curved paths, was associated with goal-scoring success. Future studies should focus on specific training regimes aimed at improving dribbling ability, and measuring any impact on the creation of goal-scoring opportunities and number of goals scored.

Posturography Comparison and Discriminant Analysis Between Individuals With and Without Chronic Low Back Pain.

OBJECTIVE: The aims of this study were to evaluate the center of pressure (CoP) in individuals with chronic low back pain (LBP) compared with matched controls and perform discriminant analysis to detect which CoP variables differentiate the groups. METHODS: Thirty-two participants with LBP and 33 matched controls were evaluated on a force plate in a bipedal static position for 30 seconds in 2 conditions: eyes open (EO) and eyes closed (EC). Two discriminant analyzes were performed to detect which CoP variables could discriminate between groups. RESULTS: Those with LBP had higher values (ie, poorer balance) for most variables compared with the control group. With EO, total displacement of sway (TDS) was as follows: LBP group (median [25%-75%]) 31.77 (26.39-41.79) cm, control group 27.21 (22.29-31.78) cm, P = .008 and area: LBP group 3.31 (2.33-4.68) cm2, control group 1.77 (1.3-2.71) cm2. With EC, TDS was as follows: LBP group 49.6 (39.65-68.15) cm, control group 38.77 (30.36; 45.65) cm, P = .003 and area: LBP group 4.68 (2.6-7.28) cm2, control group 2.4 (2.1-3.34) cm2. The discriminating variables in the EO condition were the TDS for the LBP group and the anteroposterior mean velocity for the control group, while in the EC condition they were mediolateral dispersion and area for the LBP group. CONCLUSION: Individuals with chronic LBP had worse postural control performance than matched controls, and it is possible to characterize those with and without LBP with CoP variables.

The use of technology and sampling frequency to measure variables of tactical positioning in team sports: a systematic review.

The aim of the study was to assess the use of different positioning systems and sampling frequencies to measure spatial-positioning variables in team sports. Articles were selected when the sampling frequency was detailed. 2,194 articles were identified and 59 works were selected for the systematic review. The sampling frequency used to measure tactical behaviour differed considerably among studies. For Global Navigation Satellite System, the sampling frequency ranged from 5- to 15 Hz for raw data, the most commonly used sampling frequency being 5 Hz. For Optic-based tracking systems, the sampling frequency ranged from 10- to 30 Hz. For Local Position System, the sampling frequency ranged from 45- to 100 Hz, the most commonly used sampling frequency being 42 Hz and 57.7 Hz. There is no common criterion in the sampling frequency used to measure each tactical variable. Further studies should investigate the impact of the sampling frequency on the measurement of the tactical variables.

Exploring the determinants of success in different clusters of ball possession sequences in soccer.

The purpose of this study was two-step: (1) classify ball possession (BP) according to the duration and number of passes and (2) identify which tactical variables most discriminate the different BP. We obtained 527 BPs from four official matches of the Brazilian Soccer Championship 2016. Forty-one "notational", "space occupation", and "displacement synchronization" predictor variables were used. The BPs were classified into three groups: short (11.07 ± 4.49 s, 1.93 ± 0.99 passes), medium (26.83 ± 7.33 s, 5.41 ± 1.84 passes), long (55.50 ± 14.97 s, 12.11 ± 4.61 passes). Discriminant analysis identified the five most relevant variables to describe each group: coefficient of variation (CV) of the defensive team's synchronization-Y, CV defensive team´s synchronization-X, successful pass last third, CV distance between offensive team's centroid and target, mean of the offensive team's width. The approach highlights important variables and could benefit the description of offensive and defensive game sequences to provide precise knowledge on the process.

Dribbling speed along curved paths predicts attacking performance in match-realistic one vs. one soccer games.

This study assessed whether a new, closed-skill dribbling or sprinting task could predict attacking performance in soccer. Twenty-five male players were recruited from the Londrina Junior Team Football Academy in Brazil and asked to either dribble the ball or sprint through five custom circuits that varied in average curvature (0-1.37 radians.m-1). These measures were then validated using a realistic one vs. one competition in which each player acted as attacker or defender in turn (N = 1330 bouts). Sprinting (ICC = 0.96) and dribbling (ICC = 0.97) performances were highly repeatable for individual players. Average dribbling speed decreased non-linearly with increasing circuit curvature (F = 239.5; P < 0.001) from 5.19 ± 0.11 ms-1 on the straightest path to 2.13 ± 0.03 ms-1 on the curviest. Overall, dribbling but not sprinting performance predicted attacking success in the one vs. one competition, explaining more than 50% of the variation in attacking success alone (rp = 0.70; P < 0.001). In conclusion, our new closed-skill dribbling assessment is a valid and reliable protocol to predict a soccer player's success in attacking performance in one vs. one situation, and can be used to identify talented players.

Analysis of the distances covered and technical actions performed by professional tennis players during official matches.

The purpose of this study was to analyse the physical and technical performances of professional tennis players during official matches. The trajectories of eight players were obtained during matches, using an automatic tracking method. The distances covered and technical performances were analysed for the first and second sets. The athletes covered (mean ± standard deviation) a total of 1702.4 ± 448.2 m in the first set, 1457.6 ± 678.1 m in the second set and 3160.0 ± 880.1 in the entire match. No differences were found between the sets for the physical variables (lateral and forward displacements, distance covered per rally, per game and per set, and the percentage of time spent in each range of velocity). However, the distances covered by the athletes during the rallies in which they were serving (median = 5.2; interquartile range (IQR) = 6.7 m) were statistically smaller than when they were returning (median = 6.2; IQR = 7.7 m). Forehand ground stroke proficiency decreased from the first (mean ± standard deviation: 75.2 ± 4.11%) to the second set (mean ± standard deviation = 65.5 ± 14.3%). In conclusion, tennis players did not present reduced physical performance from the first to the second set.

Coordination analysis of players' distribution in football using cross-correlation and vector coding techniques.

The purpose of this study was to investigate the coordination between teams spread during football matches using cross-correlation and vector coding techniques. Using a video-based tracking system, we obtained the trajectories of 257 players during 10 matches. Team spread was calculated as functions of time. For a general coordination description, we calculated the cross-correlation between the signals. Vector coding was used to identify the coordination patterns between teams during offensive sequences that ended in shots on goal or defensive tackles. Cross-correlation showed that opponent teams have a tendency to present in-phase coordination, with a short time lag. During offensive sequences, vector coding results showed that, although in-phase coordination dominated, other patterns were observed. We verified that during the early stages, offensive sequences ending in shots on goal present greater anti-phase and attacking team phase periods, compared to sequences ending in tackles. Results suggest that the attacking team may seek to present a contrary behaviour of its opponent (or may lead the adversary behaviour) in the beginning of the attacking play, regarding to the distribution strategy, to increase the chances of a shot on goal. The techniques allowed detecting the coordination patterns between teams, providing additional information about football dynamics and players' interaction.

Erratum for the article by Caetano et al. JAB 31(6).

In the article by Caetano FG, et al, "Characterization of the Sprint and Repeated-Sprint Sequences Performed by Professional Futsal Players, According to Playing Position, During Official Matches," in the J Appl Biomech, 31(6), pp. 423-429, http://dx.doi.org/10.1123/jab.2014-0159, the second author's name was incorrectly listed as Murilo José de Oliveira. The second author's name should have been listed as Murilo José de Oliveira Bueno.

Characterization of the Sprint and Repeated-Sprint Sequences Performed by Professional Futsal Players, According to Playing Position, During Official Matches.

The purposes of this study were to investigate sprints and to characterize repeated-sprint sequences (RS) performed by athletes during professional futsal matches. We analyzed 97 players during 5 official matches using the DVideo automatic tracking system. The sprints were analyzed during the first and second halves according to playing position, and RS were categorized according to the number of sprints and the time between them. The results showed an increase (F[1, 2520] = 3.96; P = .046) in the sprint duration from the first (mean = 3.1 ± 1.3) to the second half (mean = 3.2 ± 1.2). However, no differences were found for other variables (distance covered, peak velocity, initial velocity, recovery time between sprints, and sprints performed per minute) or among playing positions. In addition, when considering RS, the results showed that RS comprising two sprints interspersed with a maximum of 15 seconds of recovery were significantly more frequent than other RS. The findings of this study characterizing the sprinting features of futsal players can help coaches to plan physical training and assessments according to the requirements of the sport.

Analysis of football game-related statistics using multivariate techniques.

Abstract The purpose of this study was to explore football game-related statistics during a competition, using principal component and cluster analyses to determine if it is possible to distinguish the winning teams from the drawing and losing ones. We collected the game-related statistics of the group phase matches of the 2006 World Cup and organised them into a matrix. The principal components of the covariance matrix were calculated. The scores of the first and second components were used to represent the new data, and cluster analysis was applied to separate the elements in two groups (G1 and G2). To analyse the degree of separation between the groups, we calculated the Silhouette Coefficient for each group. Finally, we checked if the winning teams were classified into the same group. The Silhouette Coefficients found for G1 and G2 were 0.54 and 0.55, respectively. Results showed that 70.3% of the winning teams were classified into the same group (G1). Similarly, 67.8% of the drawing and losing teams were classified in G2. This study presented a different way to analyse game-related statistics that allowed the multivariate differences to be shown between successful and unsuccessful teams.

Analysis of the distance covered by Brazilian professional futsal players during official matches.

The purpose of this study was to measure and characterise the distances covered by Brazilian professional futsal players. The trajectories of 93 players during five matches were obtained using an automatic tracking method. The distances covered were analysed for different game conditions: over the entire game and during the times when the ball was out of play and in play separately. When the entire game was considered, the results showed that there was a reduction in the total distance covered per minute from the first [median ± IQR (interquartile range): 97.9 ± 16.2 m/min] to the second half (median = 90.3 m/min; IQR = 12.0), and when only the in-play time was considered (first half: 136.6 ± 17.2 m/min; second half: 129.2 ± 16.7 m/min). The percentage of distance covered in the standing and walking velocity range was higher in the second half than in the first when considering the entire game (30.8% and 28.0%, respectively) and during the in-play time (19.3% and 16.2%, respectively). In conclusion, this study verified that futsal players reduced the physical performance during the second half.

Kinematic gait analysis using inertial sensors with subjects after stroke in two different arteries.

[Purpose] The aim of the present study was described the kinematic characteristics of gait in stroke patients with two different arteries involved. [Subjects and Methods] Two patients who had suffered a basilar (A) or middle (B) cerebral artery ischemic stroke were compared with a control (C). Seventeen inertial sensors were used with acquisition rate of 120 Hz. The participants walked 3 times on a 10 meter walkway. From the raw data, the three gait cycles from the middle of each trial were chosen and analyzed. [Results] During the stance phase, patients A and B had a lower hip angle at initial contact and maximum flexion angle during load response than the control. Patient A and the control subject had similar knee angle values at initial contact, and patient B presented a flexed position in the initial phase of the gait cycle. The maximum flexion angles during loading response were also higher for patient B. The sagittal plane excursion for the ankle joint was lower for patient B in comparison with the other subjects. [Conclusion] Differences during walking between patients who had stroke in different arteries may be related to an alternative compensatory strategy. Patient A and the control subject had similar gait cycle curves at all joints, while patient B showed a rigid synergic pattern.

Who are the best passing players in professional soccer? A machine learning approach for classifying passes with different levels of difficulty and discriminating the best passing players.

The present study aimed to assess the use of technical-tactical variables and machine learning (ML) classifiers in the automatic classification of the passing difficulty (DP) level in soccer matches and to illustrate the use of the model with the best performance to distinguish the best passing players. We compared eight ML classifiers according to their accuracy performance in classifying passing events using 35 technical-tactical variables based on spatiotemporal data. The Support Vector Machine (SVM) algorithm achieved a balanced accuracy of 0.70 ± 0.04%, considering a multi-class classification. Next, we illustrate the use of the best-performing classifier in the assessment of players. In our study, 2,522 pass actions were classified by the SVM algorithm as low (53.9%), medium (23.6%), and high difficulty passes (22.5%). Furthermore, we used successful rates in low-DP, medium-DP, and high-DP as inputs for principal component analysis (PCA). The first principal component (PC1) showed a higher correlation with high-DP (0.80), followed by medium-DP (0.73), and low-DP accuracy (0.24). The PC1 scores were used to rank the best passing players. This information can be a very rich performance indication by ranking the best passing players and teams and can be applied in offensive sequences analysis and talent identification.

A biomechanical analysis of turning during gait in individuals with different subtypes of Parkinson's disease.

BACKGROUND: Turning while walking is a complex component of locomotor capacity, which can be challenging in the daily lives of people with Parkinson's disease. The aim of the study was to compare biomechanical strategies during turning of gait in individuals with Parkinson's disease and its different clinical subtypes. METHODS: A cross-sectional study, comprising of 43 individuals with idiopathic Parkinson's disease, divided in subgroups: akineto-rigid, dominant tremor and mixed. Motor impairment was assessed using the Unified Parkinson's Disease Rating Scale. The gait biomechanical parameters (number of steps, step length, cadence, amplitude, velocity and radius of the turn) were analyzed during turning in a kinematics laboratory. In the statistical analysis, a comparison was made between subgroups, and correlations between biomechanical parameters. FINDINGS: There was no statistically significant difference between the subgroups. In the correlation analysis, notable correlations were found between the anticipatory step length and the following variables: number of steps (r = -0.418), step length while turning (r = 0.805), step length after turning (r = 0.644), average velocity (r = 0.830), average velocity while turning (r = 0.755), and maximum velocity (rho = 0.835). INTERPRETATION: The difficulties primarily occur during the anticipatory phase of the turn, which affects the entire task. The greater the length of the anticipatory step, the greater the length of the step taken to turn as well as the step taken after turning. And the greater the velocity, the greater the step length, and to fewer steps taken to perform the task.

On the prediction of tibiofemoral contact forces for healthy individuals and osteoarthritis patients during gait: a comparative study of regression methods.

Knee osteoarthritis (OA) is a public health problem affecting millions of people worldwide. The intensity of the tibiofemoral contact forces is related to cartilage degeneration, and so is the importance of quantifying joint loads during daily activities. Although simulation with musculoskeletal models has been used to calculate joint loads, it demands high-cost equipment and a very time-consuming process. This study aimed to evaluate consolidated machine learning algorithms to predict tibiofemoral forces during gait analysis of healthy individuals and knee OA patients. Also, we evaluated three different datasets to train each model, considering different combinations of primary kinematic and kinetic data, and post-processing data. We evaluated 14 patients with severe unilateral knee OA and 14 healthy individuals during 3-5 gait trials. Data were split into 70% and 30% of the samples as training and test data. Test data was independently evaluated considering a mixture of pathological and healthy individuals, and only OA and Control patients. The main results showed that accurate predictions of the tibiofemoral contact forces were achieved using machine learning methods and that the predictions were sensitive to changes in the input data as training. The present study provided insights into the most promising regressions methods to predict knee contact forces representing an important starting point for the broader application of biomechanical analysis in clinical environments.

Doxorubicin causes cachexia, sarcopenia, and frailty characteristics in mice.

While chemotherapy treatment can be lifesaving, it also has adverse effects that negatively impact the quality of life. To investigate the effects of doxorubicin chemotherapy on body weight loss, strength and muscle mass loss, and physical function impairments, all key markers of cachexia, sarcopenia, and frailty. Seventeen C57/BL/6 mice were allocated into groups. 1) Control (n = 7): mice were exposed to intraperitoneal (i.p.) injections of saline solution. 2) Dox (n = 10): mice were exposed to doxorubicin chemotherapy cycles (total dose of 18 mg/kg divided over 15 days). The body weight loss and decreased food intake were monitored to assess cachexia. To assess sarcopenia, we measured muscle strength loss using a traction method and evaluated muscle atrophy through histology of the gastrocnemius muscle. To evaluate physical function impairments and assess frailty, we employed the open field test to measure exploratory capacity. Doxorubicin administration led to the development of cachexia, as evidenced by a significant body weight loss (13%) and a substantial decrease in food intake (34%) over a 15-day period. Furthermore, 90% of the mice treated with doxorubicin exhibited sarcopenia, characterized by a 20% reduction in traction strength (p<0,05), a 10% decrease in muscle mass, and a 33% reduction in locomotor activity. Importantly, all mice subjected to doxorubicin treatment were considered frail based on the evaluation of their overall condition and functional impairments. The proposed model holds significant characteristics of human chemotherapy treatment and can be useful to understand the intricate relationship between chemotherapy, cachexia, sarcopenia, and frailty.

A spectral analysis of team dynamics and tactics in Brazilian football.

The purposes of this study were to characterise the total space covered and the distances between players within teams over ten Brazilian First Division Championship matches. Filmed recordings, combined with a tracking system, were used to obtain the trajectories of the players (n = 277), before and after half-time. The team surface area (the area of the convex hull formed by the positions of the players) and spread (the Frobenius norm of the distance-between-player matrix) were calculated as functions of time. A Fast Fourier Transform (FFT) was applied to each time series. The median frequency was then calculated. The results of the surface area time series median frequencies for the first half (0.63 ± 0.10 cycles · min⁻¹) were significantly greater (P < 0.01) than the second-half values (0.47 ± 0.14 cycles · min⁻¹). Similarly, the spread variable median frequencies for the first half (0.60 ± 0.14 cycles · min⁻¹) were significantly greater (P < 0.01) than the second-half values (0.46 ± 0.16 cycles · min⁻¹). The median frequencies allowed the characterisation of the time series oscillations that represent the speed at which players distribute and then compact their team formation during a match. This analysis can provide insights that allow coaches to better control the team organisation on the pitch.

Acute effects of transcranial direct current stimulation combined with physical therapy on the balance and gait in individuals with Parkinson's disease: A randomized controlled trial.

Application methods of transcranial direct current stimulation (tDCS) in Parkinson's disease (PD) are quite divergent making it difficult to define the clinical effectiveness of the tDCS on PD. Thus, the aim of this study was to verify the acute effects of tDCS when applied to different targets (Cz or C3-Cz-C4) combined to physical therapy to improve balance and gait in individuals with PD. A randomized controlled trial was conducted, with 50 individuals who were separated into four groups: 1) Real tDCS (Cz) + physical therapy, 2) Real tDCS (C3-Cz-C4) + physical therapy, 3) Sham tDCS + physical therapy and 4) Educational lecture + physical therapy. The current intensity was 2 mA, applied for 20 min. For the instrumental assessment of balance and gait, the 3D motion analysis system was used. For the biomechanical analysis of gait, three different conditions were performed: normal gait, dual task gait and obstacle gait. For balance analysis, the following positions were utilized: Romberg with eyes opened, Romberg with eyes closed, Tandem with eyes opened and Tandem with eyes closed. All evaluations were performed pre-intervention, post-intervention (immediately at the end of the intervention) and were followed-up on (24 h after the end of the intervention). No statistically significant differences were found for all gait and balance outcomes when considering the interaction between time (pre, post and follow-up assessments) versus group (Education, Sham, Cz and C3-Cz-C4). In conclusion, it was found that one session of tDCS, stimulating Cz or C3-Cz-C4 combined with physical therapy, was not effective in improving the balance and gait in people with PD as compared to sham tDCS or educational lecture plus physiotherapy.