The effect of multi-directional sprint training on change-of-direction speed and reactive agility of collegiate tennis players.

Objective: The aim of this study was to evaluate the effect of random route multi-directional sprint training (MDST) compared to fixed route MDST on change-of-direction speed (CODS) and reactive agility (RA), and to investigate the correlation between CODS, RA and short-distance straight sprint speed (SDSS). Method: A total of 19 collegiate tennis players from Beijing Sport University were randomly assigned to either the random route MDST group (RR group, N = 9, age: 22.22 ± 2.22 years) or the fixed route MDST group (FR group, N = 10, age: 21.90 ± 1.66 years). Both groups completed a progressive load intervention training for 3 weeks, three times a week. The RR group's random route, mirroring the distance and number of change-of-direction (COD) in the FR group's fixed route, was specifically designed. The spider run, T-drill, RA test and 5-m straight line sprint test were performed before and after the intervention. Results: Both groups showed improved performance in the spider run (p < 0.05), T-drill (p < 0.01) and 5-m straight (p < 0.001) line sprint test after the intervention. Additionally, there was no significant difference in the improvement of CODS and SDSS between the two groups (p > 0.05). The RA of the RR and FR groups after the intervention was significantly higher than before intervention (p < 0.001), and RR group showed greater improvement in RA compared to the FR group. There was a moderate correlation between spider run and T-drill (r = 0.523), RA (r = 0.388), and no significant correlation between spider run and 5-m straight sprint (p > 0.05). T-drill was moderately correlated with RA (r = 0.347) and 5-m straight sprint (r = 0.321). RA was moderately correlated with 5-m straight sprint (r = 0.551). Conclusion: Three-week multi-directional sprint training can effectively improve the change-of-direction speed, reactive agility and short-distance straight sprint speed of collegiate tennis players. And random route multi-directional sprint training has better effect on improving reactive agility.

Agreement and Sensitivity of the Acceleration-Velocity Profile Derived via Local Positioning System.

Sprint performance is commonly assessed via discrete sprint tests and analyzed through kinematic estimates modeled using a mono-exponential equation, including estimated maximal sprinting speed (MSS), relative acceleration (TAU), maximum acceleration (MAC), and relative propulsive maximal power (PMAX). The acceleration-velocity profile (AVP) provides a simple summary of short sprint performance using two parameters: MSS and MAC, which are useful for simplifying descriptions of sprint performance, comparison between athletes and groups of athletes, and estimating changes in performance over time or due to training intervention. However, discrete testing poses logistical challenges and defines an athlete's AVP exclusively from the performance achieved in an isolated testing environment. Recently, an in situ AVP (velocity-acceleration method) was proposed to estimate kinematic parameters from velocity and acceleration data obtained via global or local positioning systems (GPS/LPS) over multiple training sessions, plausibly improving the time efficiency of sprint monitoring and increasing the sample size that defines the athlete's AVP. However, the validity and sensitivity of estimates derived from the velocity-acceleration method in relation to changes in criterion scores remain elusive. To assess the concurrent validity and sensitivity of kinematic measures from the velocity-acceleration method, 31 elite youth basketball athletes (23 males and 8 females) completed two maximal effort 30 m sprint trials. Performance was simultaneously measured by a laser gun and an LPS (Kinexon), with kinematic parameters estimated using the time-velocity and velocity-acceleration methods. Agreement (%Bias) between laser gun and LPS-derived estimates was within the practically significant magnitude (±5%), while confidence intervals for the percentage mean absolute difference (%MAD) overlapped practical significance for TAU, MAC, and PMAX using the velocity-acceleration method. Only the MSS parameter showed a sensitivity (%MDC95) within practical significance (<5%), with all other parameters showing unsatisfactory sensitivity (>10%) for both the time-velocity and velocity-acceleration methods. Thus, sports practitioners may be confident in the concurrent validity and sensitivity of MSS estimates derived in situ using the velocity-acceleration method, while caution should be applied when using this method to infer an athlete's maximal acceleration capabilities.

A Respiratory Sensor-Based Study of the Relationship between Voluntary Breathing Patterns and Aerobic and Anerobic Exercise Capacity-An Exploratory Applied Study.

(1) Background: Exploring the relationship between spontaneous breathing patterns and aerobic and anerobic running exercise performance can greatly improve our understanding of optimizing physical fitness. Spontaneous breathing patterns refer to how the rhythm and depth of breathing affect performance and physical adaptation during exercise. (2) Methods: This study aimed to investigate this relationship by enrolling 240 college students (120 males and 120 females, aged 18-22). We evaluated their resting respiratory rate (RR), the combined total of abdominal and thoracic movements (AM+TM), the proportion of abdominal movement to the overall respiratory movement (AM/(AM+TM)), and the inhalation to exhalation ratio (I/E ratio). Additionally, their performance in a 50 m sprint (measuring anerobic capability), an 800- or 1000 m run (assessing mixed aerobic and anerobic capacity), and a 12 min distance run (evaluating aerobic capacity) was recorded. (3) Results: Our findings, through both correlational and comparative analyses, indicate that a larger AM+TM is predictive of a greater distance covered in the 12 min run, suggesting enhanced aerobic capacity. Interestingly, among female participants, a lower body mass index (BMI) coupled with a higher proportion of abdominal movement (AM/(AM+TM)) was linked to better performance in the 800 m run, indicative of superior mixed aerobic and anerobic capacities. These results imply that women with a larger tidal volume and those with a lower BMI but higher abdominal contribution to breathing at rest may exhibit better aerobic and mixed exercise capacities, respectively. (4) Conclusions: Based on these findings, we recommend that healthcare professionals and physical education instructors incorporate respiratory pattern assessments into their practices to potentially improve the physical health of their clients and students, with a particular emphasis on female populations. This study underscores the importance of understanding the intricate relationship between spontaneous respiratory patterns and exercise capabilities in enhancing overall physical fitness and health.

Acute ingestion of caffeinated chewing gum reduces fatigue index and improves 400-meter performance in trained sprinters: a double-blind crossover trial.

BACKGROUND: This study investigated the effects of caffeinated chewing gum on fatigue index and 400-meter performance in trained sprinters. METHODS: Nineteen participants (age: 20.9 ± 1.0 years; height: 175.6 ± 4.9 cm; mass: 66.5 ± 5.6 kg; training age: 7.9 ± 1.0 years) were randomly assigned to either a caffeine trial (CAF) or a placebo trial (PL) using a double-blind, randomized crossover design. The participants in the CAF trial chewed a gum containing 3 mg/kg of caffeine for a period of 10 minutes, while those in the PL trial chewed a gum containing a placebo with no caffeine. Following a 15-minute period of rest, the fatigue index was tested by six maximal 35-meter sprints with a 10-second rest between efforts. After this, at least 30 minutes of rest was permitted, during which time the participants engaged in brief warm-up activities prior to the commencement of the 400-meter sprint test. Saliva samples were collected before chewing gum, before the fatigue test and before 400-meters sprinting. RESULTS: The fatigue index was significantly lower in the CAF trial compared to the PL trial (CAF: 8.1 ± 2.5%; PL: 9.6 ± 4.8%; p = 0.046, Cohen's d = 039). The CAF trial demonstrated significantly lower sprint time for the 300-400 meter segment (CAF: 14.73 ± 1.35 seconds; PL: 15.23 ± 1.30 seconds; p = 0.019, Cohen's d = 0.37) and total sprint time compared to the PL trial (CAF: 53.87 ± 2.88 seconds; PL: 54.68 ± 3.37 seconds; p = 0.003, Cohen's d = 0.27). Saliva caffeine and α-amylase concentration were significantly higher in the CAF trial compared to the PL trial (p < 0.05). CONCLUSION: The present study demonstrated that caffeine gum supplementation prior to exercise significantly reduced the fatigue index and increased the capacity to maintain speed, particularly in the final 300 to 400 meters, as well as enhancing 400-meter sprint performance.

Associations between environmental factors and running performance: An observational study of the Berlin Marathon.

Extensive research has delved into the impact of environmental circumstances on the pacing and performance of professional marathon runners. However, the effects of environmental conditions on the pacing strategies employed by marathon participants in general remain relatively unexplored. This study aimed to examine the potential associations between various environmental factors, encompassing temperature, barometric pressure, humidity, precipitation, sunshine, cloud cover, wind speed, and dew point, and the pacing behavior of men and women. The retrospective analysis involved a comprehensive dataset comprising records from a total of 668,509 runners (520,521 men and 147,988 women) who participated in the 'Berlin Marathon' events between the years 1999 and 2019. Through correlations, Ordinary Least Squares (OLS) regression, and machine learning (ML) methods, we investigated the relationships between adjusted average temperature values, barometric pressure, humidity, precipitation, sunshine, cloud cover, wind speed, and dew point, and their impact on race times and paces. This analysis was conducted across distinct performance groups, segmented by 30-minute intervals, for race durations between 2 hours and 30 minutes to 6 hours. The results revealed a noteworthy negative correlation between rising temperatures and declining humidity throughout the day and the running speed of marathon participants in the 'Berlin Marathon.' This effect was more pronounced among men than women. The average pace for the full race showed positive correlations with temperature and minutes of sunshine for both men and women. However, it is important to note that the predictive capacity of our model, utilizing weather variables as predictors, was limited, accounting for only 10% of the variance in race pace. The susceptibility to temperature and humidity fluctuations exhibited a discernible increase as the marathon progressed. While weather conditions exerted discernible influences on running speeds and outcomes, they did not emerge as significant predictors of pacing.

Theropod trackways as indirect evidence of pre-avian aerial behavior.

Body fossils set limits on feasible reconstructions of functional capacity and behavior in theropod dinosaurs, but do not document in-life behaviors. In contrast, trace fossils such as footprints preserve in-life behaviors that can potentially test and enhance existing reconstructions. Here, we demonstrate how theropod trackways can be used as indirect evidence of pre-avian aerial behavior, expanding the approaches available to study vertebrate flight origins. This involved exploring the behavioral implications of a two-toed Cretaceous-aged theropod trackway produced by a small, bird-like microraptorine moving at high speed. Applying first principle running biomechanics, we were able to conclude that the trackway is atypical, indirectly evidencing pre-avian aerial behavior. This trackway documents the evidence of wing-assisted aerodynamic force production during locomotion, supporting a broader distribution of this behavior than currently known. These findings support previously proposed aerial behavior in early bird-like theropods, showing how trackways will help to deepen our understanding of theropod flight origins.

Very high-speed running (VHSR) profile in elite female football: An update.

The aim of the present study it's a providing an update of the profile of very high-speed running (VHSR) of professional female football players. In this study 23 official matches of the Spanish First Division of Women´s Football were analysed. A total of 15 players participated, who were classified according to their location on the matches played: central-corridor (CCP, n = 7), and lateral-corridor (LCP, n = 8). The variables recorded were: 1) Very High-Speed Running (VHSR), considering the accumulated distance, duration, and frequency, and the individual characteristics of the efforts (distance and duration); 2) Recovery between efforts (VHSRe) and; 3) VMAX. The results show that LCP described higher values in accumulative VHSR and VHSR by distance bands, with greater distances, durations and VMAX of VHSRe, with less recovery between efforts. There seems to be an evolutionary trend in the distribution of the efforts, with a higher % of efforts in the 10-20 m band. The results provide useful information that coaching staff of professional women's football teams could use to design specific very high-speed running training to optimize performance in competition.

Sex difference in IRONMAN age group triathletes.

BACKGROUND: The sex difference in athletic performance has been thoroughly investigated in single sport disciplines such as swimming, cycling, and running. In contrast, only small samples of long-distance triathlons, such as the IRONMAN® triathlon, have been investigated so far. AIM: The aim of the study was to examine potential sex differences in the three split disciplines by age groups in 5-year intervals in a very large data set of IRONMAN® age group triathletes. METHODS: Data from 687,696 (553,608 men and 134,088 women) IRONMAN® age group triathletes (in 5-year intervals from 18-24 to 75+ years) finishing successfully between 2002 and 2022 an official IRONMAN® race worldwide were analyzed. The differences in performance between women and men were determined for each split discipline and for the overall race distance. RESULTS: Most finishers were in the age group 40-44 years. The fastest women were in the age group 25-29 years, and the fastest men were in the age group 30-34 years. For all split disciplines and overall race time, men were always faster than women in all groups. The performance difference between the sexes was more pronounced in cycling compared to swimming and running. From the age group 35-39 years until 60-64 years, the sex differences were nearly identical in swimming and running. For both women and men, the smallest sex difference was least significant in age group 18-24 years for all split disciplines and increased in a U-shaped manner until age group 70-74 years. For age groups 75 years and older, the sex difference decreased in swimming and cycling but increased in running. Considering the different characteristics of the race courses, the smallest performance gaps between men and women were found in river swimming, flat surface cycling and rolling running courses. CONCLUSIONS: The sex difference in the IRONMAN® triathlon was least significant in age group 18-24 years for all split disciplines and increased in a U-shaped manner until age group 70-74 years. For 75 years and older, the sex difference decreased in swimming and cycling but increased in running.

The effect of post-activation enhancement on the performance of Chinese national skeleton athletes in the "ice push sled"-a first cross-sectional study.

Objective: To investigate the impact of post-activation potentiation (PAP) induced by resisted sled sprint at different loads on the subsequent 30 m ice push sled performance of Chinese skeleton athletes, and to identify the resisted sled sprint load that most effectively enhances PAP for Chinese skeleton athletes. Methods: Seven elite athletes from the Chinese skeleton team participated in four tests with more than 48 h intervals. During the tests, on the first test, athletes completed a 40 min standard warm-up, rested for 6 min, and then performed a 30 m test. On the second, third, and fourth test, athletes completed the standard warm-up, then performed 20 m sprints with resisted sled (RS) at 75%, 50%, and 25% of body mass (BM), respectively, rested for 6 min, and then performed the 30 m test. Results: No significant differences were found in morning pulse, blood urea, and creatine kinase levels among four tests. The percentage of maximum heart rate (%HRmax) within different intensity ranges showed no significant differences among four tests. However, significant differences were observed in ice push sled performance among four tests (No BMRS: 5.08 ± 0.27; 25% BMRS: 5.05 ± 0.29; 50% BMRS: 5.02 ± 0.27; 75% BMRS: 5.04 ± 0.28). Post hoc analyses revealed that the 50% BMRS test had faster speed compared to the no resistance (p < 0.05), the 25% BMRS (p < 0.05), and the 75% BMRS (p < 0.05) tests. Additionally, the 75% BMRS test had faster speed than the no resistance test (p < 0.05). Conclusion: A 20 m sprint with 50% BMRS effectively enhances the PAP effect in skeleton athletes, improving their ice push sled performance. Coaches can incorporate this resisted sled sprint in athletes' training routines for performance enhancement in both daily training and pre-competition preparations.

Custom Smartphone Application to Guide Locomotor-Respiratory Coupling in the Field Using Step-Adaptive Breathing Sounds.

While running is amongst the most popular activities for competition and leisure, an estimated 20-40% of runners may suffer from respiratory limitations. Some of these runners may benefit from breathing techniques to improve performance or alleviate respiratory discomfort. One such technique is locomotor-respiratory coupling (LRC), a frequency and phase synchronization of breath to step. Studies have demonstrated that LRC may benefit ventilatory efficiency via "step-driven flows," and some experts have argued it could be used for pacing exercise or increasing positive emotional states. Nevertheless, it may be difficult to perform without coaching or guidance. Here we propose RunRhythm, a custom smartphone application to deliver step-synchronized sound guidance for LRC. This concept builds on previous evidence that sound guidance can be effective and integrates features to maximize adherence and individualization. Preliminary results show that this application is a promising and efficacious method suitable for research on LRC in field exercise. Recommendations for use and further development are discussed to further develop this concept for the benefit of a wider population.

Hoof slip duration at impact in galloping Thoroughbred ex-racehorses trialling eight shoe-surface combinations.

Horseshoes used during racing are a major determinant of safety as they play a critical role in providing traction with the ground surface. Although excessive hoof slip is detrimental and can predispose to instabilities, falls and injuries, some slip is essential to dissipate energy and lower stresses on the limb tissues during initial loading. This study aimed to quantify hoof slip duration in retired Thoroughbred racehorses galloping over turf and artificial (Martin Collins Activ-Track) tracks at the British Racing School in the following four shoeing conditions: 1) aluminium; 2) steel; 3) GluShu (aluminium-rubber composite); and 4) barefoot. High-speed video cameras (Sony DSC-RX100M5) filmed 389 hoof-ground interactions from 13 galloping Thoroughbreds at 1000 frames per second. A marker wand secured to the lateral aspect of the hoof wall aided tracking of horizontal and vertical hoof position in Tracker software over time, so the interval of hoof displacement immediately following impact (hoof slip duration) could be identified. Data were collected from leading and non-leading forelimbs at speeds ranging from 24-56 km h-1. Linear mixed models assessed whether surface, shoeing condition or speed influenced hoof slip duration (significance at p≤0.05). Day and horse-jockey pair were included as random factors and speed was included as a covariate. Mean hoof slip duration was similar amongst forelimbs and the non-leading hindlimb (20.4-21.5 ms) but was shortest in the leading hindlimb (18.3±10.2 ms, mean ± 2.S.D.). Slip durations were 2.1-3.5 ms (p≤0.05) longer on the turf than on the artificial track for forelimbs and the non-leading hindlimb, but they were 2.5 ms shorter on the turf than on the artificial track in the leading hindlimb (p = 0.025). In the leading hindlimb, slip durations were also significantly longer for the aluminium shoeing condition compared to barefoot, by 3.7 ms. There was a significant negative correlation between speed and slip duration in the leading forelimb. This study emphasises the importance of evaluating individual limb biomechanics when applying external interventions that impact the asymmetric galloping gait of the horse. Hoof slip durations and the impact of shoe-surface effects on slip were limb specific. Further work is needed to relate specific limb injury occurrence to these hoof slip duration data.

Inter-Individual Variability in Muscle Fiber-Type Distribution Affects Running Economy but Not Running Gait at Submaximal Running Speeds.

Running economy is an important determinant of endurance running performance, yet insights into characteristics contributing to its inter-individual variability remain limited. Although slow-twitch muscle fibers are more energy-efficient than fast-twitch fibers during the (near-)isometric contractions common during submaximal running, current literature lacks a consensus on whether a relationship between muscle fiber-type distribution and running economy exists. This study aims to resolve the ongoing debate by addressing potential confounding factors often overlooked in prior research, such as the effect of different running speeds, the homogeneity of investigated groups, and the potential impact of the adopted running gait. We selected two groups with predetermined distinct muscle fiber-type distribution in their triceps surae muscle by measurement of carnosine via 1H-MRS, one predominantly slow (ST; n = 11; carnosine z-score = -1.31) and the other predominantly fast (FT; n = 10; z-score = 0.83). Across a range of running speeds (2-4 m/s), we measured running economy (W/kg) through indirect calorimetry, along with running kinematics, kinetics and muscle activity of the lower limb. The ST-group exhibited, on average, 7.8% better running economy than the FT-group (p = 0.01) and this difference was consistent across speeds. Both groups demonstrated almost identical kinematics, kinetics, and muscle activity patterns across submaximal running speeds. Overall, our findings indicate that distinct muscle fiber-type distribution explains some of the observed variability in running economy, for which a predominance of energy-efficient slow-twitch fibers appear beneficial. In contrast, muscle fiber-type distribution does not affect running gait substantially.

Methods for Evaluating Tibial Accelerations and Spatiotemporal Gait Parameters during Unsupervised Outdoor Movement.

The purpose of this paper is to introduce a method of measuring spatiotemporal gait patterns, tibial accelerations, and heart rate that are matched with high resolution geographical terrain features using publicly available data. These methods were demonstrated using data from 218 Marines, who completed loaded outdoor ruck hikes between 5-20 km over varying terrain. Each participant was instrumented with two inertial measurement units (IMUs) and a GPS watch. Custom code synchronized accelerometer and positional data without a priori sensor synchronization, calibrated orientation of the IMUs in the tibial reference frame, detected and separated only periods of walking or running, and computed acceleration and spatiotemporal outcomes. GPS positional data were georeferenced with geographic information system (GIS) maps to extract terrain features such as slope, altitude, and surface conditions. This paper reveals the ease at which similar data can be gathered among relatively large groups of people with minimal setup and automated data processing. The methods described here can be adapted to other populations and similar ground-based activities such as skiing or trail running.

Predicting Athlete Workload in Women's Rugby Sevens Using GNSS Sensor Data, Contact Count and Mass.

The use of session rating of perceived exertion (sRPE) as a measure of workload is a popular athlete load monitoring tool. However, the nature of sRPE means the contribution of salient, sport-specific factors to athlete load in field sports is challenging to isolate and quantify. In rugby sevens, drivers of load include high-speed running and physical contact. In soccer and men's rugby, union acceleration/deceleration also influences load. These metrics are evaluated using data from global navigation satellite system (GNSS) sensors worn by athletes. Research suggests that sensor data methods for identifying load in men's rugby do not accurately quantify female athlete loads. This investigation examined how mass, contact, and accelerations and decelerations at different speeds contribute to load in women's rugby sevens. The study evaluated 99 international matches, using data from 19 full-time athletes. GNSS measures, RPE, athlete mass, and contact count were evaluated using a linear mixed-model regression. The model demonstrated significant effects for low decelerations at low and high speeds, mass, distance, and contact count explaining 48.7% of the global variance of sRPE. The use of acceleration/deceleration and speed from GNSS sensors alongside mass, as well as contact count, presents a novel approach to quantifying load.

Evaluation of the ActiMotus Software to Accurately Classify Postures and Movements in Children Aged 3-14.

BACKGROUND: ActiMotus, a thigh-accelerometer-based software used for the classification of postures and movements (PaMs), has shown high accuracy among adults and school-aged children; however, its accuracy among younger children and potential differences between sexes are unknown. This study aimed to evaluate the accuracy of ActiMotus to measure PaMs among children between 3 and 14 years and to assess if this was influenced by the sex or age of children. METHOD: Forty-eight children attended a structured ~1-hour data collection session at a laboratory. Thigh acceleration was measured using a SENS accelerometer, which was classified into nine PaMs using the ActiMotus software. Human-coded video recordings of the session provided the ground truth. RESULTS: Based on both F1 scores and balanced accuracy, the highest levels of accuracy were found for lying, sitting, and standing (63.2-88.2%). For walking and running, accuracy measures ranged from 48.0 to 85.8%. The lowest accuracy was observed for classifying stair climbing. We found a higher accuracy for stair climbing among girls compared to boys and for older compared to younger age groups for walking, running, and stair climbing. CONCLUSIONS: ActiMotus could accurately detect lying, sitting, and standing among children. The software could be improved for classifying walking, running, and stair climbing, particularly among younger children.

Analysis of the Validity and Reliability of the Photo Finish® Smartphone App to Measure Sprint Time.

In athletic training and research, the evaluation of sprint speed is widely used, and its accurate measurement is especially demanding. High-cost photocells are the gold-standard system for sprint time assessment, although low-cost smartphone applications can be a suitable option. This study assesses the validity and reliability of an application to measure sprint time compared to photocells. Five physically active subjects completed six sprints of 10 m and 20 m at maximal speed and a 5 m go and return sprint to evaluate the validity of the Photo Finish® app (Version 2.30). To assess reliability, six trials of 5 m go and return sprints were measured by two smartphones. The validity results showed a mean bias of 0.012 s (95% CL: 0.000, 0.024) between the application and the photocells for the 10 m sprint, 0.007 s (95% CL: -0.007, 0.022) for the 20 m sprint and 0.005 s (95% CL: -0.005, 0.017) for the 5 m go and return test. The results also found R2 between both systems (R2= 0.9863, 0.990 and 0.958) for each distance (10 m, 20 m and 5 m go and return, respectively). As for reliability, the application showed outstanding consistency between two smartphones operating simultaneously (ICC 0.999; R2: 0.999). This study shows that the Photo Finish® app is an accurate and reliable tool to measure sprint time with an error of 0.09 s.

How Do Technical and Tactical Demands of Football Matches Affect the Physical Performance of Elite Football Referees? Exploring the Role of Experience.

ABSTRACT: Martinez-Torremocha, G, Alonso-Callejo, A, Garcia-Unanue, J, Gallardo, L, Sanchez-Sanchez, J, and Felipe, JL. How do technical and tactical demands of football matches impact the physical performance of elite football referees? Exploring the role of experience. J Strength Cond Res 38(11): e664-e669, 2024-This study aimed to analyze whether the physical demands on elite football referees during matches are influenced by both the physical intensity of the game and the technical-tactical context, to assess the impact of elite experience on the physical demands of referees, and to compare the physical performance of the referees with the performance of the players divided by positions in each match analyzed. Physical demands were recorded on 20 Spanish male football referees during the 2020/21, 2021/22, and 2022/23 seasons over a total of 73 official matches, using Global Positioning Systems for physical demands (total distance [TD], high-speed running [HSR], sprint, and high-intensity acceleration [HI ACC] and deceleration) and WyScout for technical-tactical actions (ball circulation, possession, shot, passes, total turnovers, quick turnovers, and long passes). Referees showed lower values for all variables except in TD (p < 0.05). No significant differences (p > 0.05) were found in referees' physical demands based on experience. Low-experience referees correlated HSR and sprint distances with high-intensity decelerations distances in matches. Medium-experience referees linked HSR, sprinting, and HI ACC distances with greater sprint distances in matches. High-experience referees correlated HSR distance with HSR, sprint, and HI ACC distances match demands. Low-experience referees positively correlated HSR and sprint distances with ball circulation, passes, quick turnovers, and forward passes. In conclusion, referees' experience influenced the adaptation of their physical demands to the technical-tactical and physical factors of competitive matches. This information will help professionals working with referees to develop training programs that better prepare referees for specific challenges.

Acute responses and recovery in the femoral cartilage morphology following running and cool-down protocols.

This study compared the immediate effects of two common post-exercise cool-down methods to a control condition on subsequent morphologic change in femoral cartilage and vascular response in the posterior tibial artery after running. Sixteen healthy young males (23.6 ± 2.2 years, 172.8 ± 4.9 cm, 72.2 ± 7.1 kg) visited the laboratory during three separate sessions and performed 30-min of treadmill running (7.5 km/h for the initial 5-min, followed 8.5 km/h for 25-min). After running, participants experienced one of three 30-min cool-down protocols: active cool-down, cold application, or control (seated rest with their knee fully extended), in a counterbalanced order. Ultrasonographic assessments of femoral cartilage thickness (intercondylar, lateral, and medial) and posterior tibial artery blood flow were compared. To test condition effects over time, two-way analysis of variances and Tukey tests were used (p < 0.05) with Cohen's d effect sizes (ES). There was no condition by time interaction in femoral cartilage thickness (intercondylar: F30,705 = 0.91, p = 0.61; lateral: F30,705 = 1.24, p = 0.18; medial: F30,705 = 0.49, p = 0.99). Regardless of time (condition effect: F2,705 > 3.24, p < 0.04 for all tests), femoral cartilage in the cold application condition was thicker than the control condition (intercondylar: p = 0.01, ES = 0.16; lateral: p < 0.0001, ES = 0.24; medial: p = 0.04. ES = 0.16). Regardless of condition (time effect: F15,705 > 10.31, p < 0.0001 for all tests), femoral cartilage thickness was decreased after running (intercondylar: p < 0.0001, ES = 1.37; lateral: p < 0.0001, ES = 1.58; medial: p < 0.0001, ES = 0.81) and returned to baseline levels within 40-min (intercondylar: p = 0.09; lateral: p = 0.64; medial: p = 0.26). Blood flow volume was different (condition × time: F30,705 = 2.36, p < 0.0001) that running-induced blood flow volume was maintained for 30-min for the active cool-down condition (p < 0.0001, ES = 1.64), whereas it returned to baseline levels within 10-min for other conditions (cold application: p = 0.67; control: p = 0.62). Neither blood flow nor temperature had a significant impact on the recovery in femoral cartilage after running.

Muscle synergies during the walk-run and run-walk transitions.

Background: Muscular synergies could represent the patterns of muscular activation used by the central nervous system (CNS) to simplify the production of movement. Studies in walking-running transitions described up to nine synergy modules, and an earlier activation of flexor and extension ankle muscular groups compared to running or walking. Our project aims to study the behaviour of muscle synergies in different stance and swing variations of walking-running (WRT) and running-walking (RWT) transitions. Methods: Twenty-four trained men participated in this study. A variable speed protocol on a treadmill was developed to record the activity of 14 muscle during walking, running and relative transitions. The protocol was based on five ramps of 50 seconds each around ± 10 and 20% of the WRT speed. WRT and RWT were identified according to an abrupt change of the duty factor. Analysing surface electromyography using non-negative matrix factorization (NMF) we obtained synergy modules and temporal activation profiles. Alpha threshold for statistical tests set at 0.05. Results: We described four different transition strides, two for increasing speed transitions, and two for decreasing speed transitions. Four to six synergy modules were found in each condition. According to the maximum cosine similarity results, the two identified WRT conditions shared five modules, while the two RWT conditions shared four modules. WRT and RWT overall shared 4.33 ± 0.58 modules. The activation profiles and centres of activation revealed differences among conditions. Discussion: Transition occurred at step level, and transition strides were composed by walk-like and run-like steps. Compared with previous studies in running and walking, both transitions needed earlier activation of a comparable number of synergy modules. Synergies were affected by acceleration: during RWT the need to dissipate energy, to decrease the speed, was achieved by increasing the number of co-activating muscles. This was reflected in fewer synergy modules and different activation profiles compared to WRT. We believe that our results could be enforced in different applied fields, like clinical gait analysis, physiotherapy and rehabilitation, where plans including co-activation of specific muscular groups could be useful. Gait transitions are common in different sports, and therefore also application in training and sport science would be possible.

Running in mice increases the expression of brain hemoglobin-related genes interacting with the GH/IGF-1 system.

The beneficial effects of exercise are partly mediated via local or systemic functions of the insulin-like growth factor-1 (IGF-1) system. As IGF-1 increases local brain hemoglobin beta (Hbb) transcripts, we hypothesized that exercise could have similar effects. Mice were single-housed with free access to running wheels for seven days. After sacrifice and saline perfusion, the expression of 13 genes was quantified using real-time quantitative polymerase chain reaction (RT-qPCR) in three brain regions: the prefrontal cortex, motor cortex, and hippocampus. In addition, plasma insulin, glucose, homeostatic model assessment of IR (HOMA-IR), C-peptide, and IGF-1 were investigated. We show that hemoglobin-related transcripts (Hbb and 5'-aminolevulinate synthase 2 [Alas2]) increased 46-63% in the running group, while IGF-1-related genes [Igf1 / growth hormone receptor (Ghr)] decreased slightly (7%). There were also moderate to large correlations between Hbb- and IGF-1-related genes in the running group but not in the sedentary group. HOMA-IR, plasma glucose, and insulin changed marginally and non-significantly, but there was a trend toward an increase in plasma-IGF-1 in the running group. In conclusion, seven days of running increased Hbb-related transcripts in three brain regions. Hbb-related transcripts correlated with components of the brain IGF-1 system only in the running group.