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Tracking of markers placed on anatomical landmarks is a common practice in sports science to perform the kinematic analysis that interests both athletes and coaches. Although different software programs have been developed to automatically track markers and/or features, none of them was specifically designed to analyze underwater motion. Hence, this study aimed to evaluate the effectiveness of a software developed for automatic tracking of underwater movements (DVP), based on the Kanade-Lucas-Tomasi feature tracker. Twenty-one video recordings of different aquatic exercises (n = 2940 markers' positions) were manually tracked to determine the markers' center coordinates. Then, the videos were automatically tracked using DVP and a commercially available software (COM). Since tracking techniques may produce false targets, an operator was instructed to stop the automatic procedure and to correct the position of the cursor when the distance between the calculated marker's coordinate and the reference one was higher than 4 pixels. The proportion of manual interventions required by the software was used as a measure of the degree of automation. Overall, manual interventions were 10.4% lower for DVP (7.4%) than for COM (17.8%). Moreover, when examining the different exercise modes separately, the percentage of manual interventions was 5.6% to 29.3% lower for DVP than for COM. Similar results were observed when analyzing the type of marker rather than the type of exercise, with 9.9% less manual interventions for DVP than for COM. In conclusion, based on these results, the developed automatic tracking software presented can be used as a valid and useful tool for underwater motion analysis. Key PointsThe availability of effective software for automatic tracking would represent a significant advance for the practical use of kinematic analysis in swimming and other aquatic sports.An important feature of automatic tracking software is to require limited human interventions and supervision, thus allowing short processing time.When tracking underwater movements, the degree of automation of the tracking procedure is influenced by the capability of the algorithm to overcome difficulties linked to the small target size, the low image quality and the presence of background clutters.The newly developed feature-tracking algorithm has shown a good automatic tracking effectiveness in underwater motion analysis with significantly smaller percentage of required manual interventions when compared to a commercial software.

Background Walking in water (WW) is frequently used as an aquatic exercise in rehabilitation programs for the elderly. Understanding gait characteristics of WW is of primary importance to effectively design specific water-based rehabilitation programs. Moreover, as walking speed in water is reduced with a possible effect on gait parameters, the age- and environment-related changes during WW have to be investigated considering the effects of instantaneous walking speed. Research question: how do gait kinematic characteristics differ in healthy elderly between WW and on land walking condition (LW)? Do elderly show different walking patterns compared to young adults? Can these kinematic changes be accounted only by the different environment/age or are they also related to walking speed? Methods Nine healthy elderly participants (73.5 ± 5.8 years) were acquired during walking in WW and LW at two different speeds. Kinematic parameters were assessed with waterproofed inertial magnetic sensors using a validated protocol. The influence of environment, age and walking speed on gait parameters was investigated with linear mixed models. Results Shorter stride distances and longer stride durations were observed in WW compared to LW. In the sagittal plane, hip and knee joint showed larger flexion in WW (>10deg over the whole stride and ∼28deg at foot strike, respectively). Furthermore, lower walking speeds and stride distances were observed in elderly compared to young adults. In the sagittal plane, a slightly more flexed hip joint and a less plantarflexed ankle joint (∼9 deg) were observed in the elderly. Significance: The results showed the importance of assessing the walking speed during WW, as gait parameters can vary not only for the effect environment but also due to different walking speeds.

The current study examined how sleep may be influenced by the scheduling of training and match load within 10 youth-soccer players. Sleep was measured over a 14-day in-season period using a commercially available wireless sleep monitor. Each collected sleep variable; lights out, sleep latency, total sleep time wake after sleep onset and final awakening, was compared for the specific day within the training schedule (e.g. match day [MD], day after match [MD + 1]) and to training/match load (high-speed distance (>5.5 m/s) [HSD] and rating of perceived exertion. The data were analysed using mixed models and effect sizes, to describe the magnitude of effects that training schedule and training load may have on sleep. A reduction of sleep duration was observed on the day after the match (MD + 1) in relation to the training days preceding the match (MD-2: −65 min, ES: 0.89 ± 0.79; MD-1 −61 min, ES: 0.82 ± 0.64) and reduction on match day (+45 min; ES: 1.91 ± 1.69). This may suggest youth-soccer players actively change their sleep scheduling behaviours in relation to the imposed soccer schedule. Increased high-speed running (for every 100 m) showed a small increase to total sleep time (+9 min; ES: 0.48 ± 0.31). This may suggest that increases in training load may be associated with small increases in sleep quantity. Such observations may highlight that the type of day and the associated load within the training microcycle may have important consequences for sleep within youth-soccer players.

Context:Kinematic asymmetry is believed to be associated with elevated risk for muscle injury, but little is known about the links between hamstring injuries and asymmetry of sprinting mechanics.Objective:To evaluate the value of kinematic analysis of sprinting for the detection of injury-related asymmetry in athletes with a history of hamstring strain.Participants:Six sub-elite male sprinters, including two who sustained a hamstring strain injury.Outcome Measures:Absolute differences between left and right symmetry indices and symmetry angles were both calculated for ground contact time and selected angular displacements. Measurements were acquired at foot strike, during the stance phase, and at toe-off.Results:At toe-off, injured athletes exhibited greater knee flexion and less hip extension for the injured extremity compared to the uninjured extremity. Symmetry indices for these variables markedly exceeded an established 15% threshold for clinically relevant asymmetry. Each of the uninjured athletes exhibited a high degree of symmetry for all parameters, with mean values for symmetry indices significantly lower than the 15% threshold (P < 0.05).Conclusions:Kinematic analysis of sprinting asymmetry appears to be valuable for identification of elevated risk for hamstring injury.

This study aimed to compare the physiological responses to a running test often used to assess lactate thresholds in soccer players when performed with an identical protocol on treadmill (Tr), natural grass (Nat), and synthetic turf (Synt). Eighteen young soccer players (mean ± SD: age, 17.4 ± 0.8 years; body mass, 66.2 ± 6.7 kg; height, 175.8 ± 5.7 cm) performed on each surface a multistage running test, including 4-minutes stages separated by a 1-minute rest, with initial speed set at 8 km·h-1 and increased of 2 km·h-1 after each stage. Blood lactate concentration (La) and heart rate (HR) were assessed. The test ended when La exceeded 4 mmol·L-1. At each of the stages completed in the three conditions by all the subjects (8, 10, 12, and 14 km·h-1), La was higher in Synt vs. both Nat and Tr with differences of at least 0.6 mmol·L-1 (p < 0.05), whereas HR was higher (p < 0.05) in Synt vs. Nat with differences from 4.3 b·min-1 (at 10 km·h-1) to 6.4 b·min-1 (at 8 km·h-1). Running speed at the 4 mmol·L-1 La threshold was lower (p < 0.05) in Synt (13.1 ± 1.1 km·h-1) than in Nat (13.9 ± 1.2 km·h-1) and Tr (14.4 ± 1.3 km·h-1). The La/HR curve obtained in Synt was shifted upward compared with the Nat and Tr curves, indicating higher La values at given HRs. These results could be mostly explained by adaptations of running mechanical patterns to surface properties that affect the energy requirements of running. This study emphasized the importance of testing soccer players on the specific surface used for training activities when assessing lactate threshold indices to prescribe and monitor field training.

Listening to music during strength workouts has become a very common practice. The goal of this study was to assess the effect of listening to self-selected music on strength performances. Thirty-one resistance-trained men ( M age = 24.7yr., SD = 5.9; M height = 178.7cm, SD = 4.7; M body mass = 83.54kg, SD = 12.0) were randomly assigned to either a Music group ( n = 19) or to a Control group ( n = 12). Both groups took part in two separate sessions; each session consisted in a maximal strength test (1-RM) and a strength-endurance test (repetitions to failure at 60% 1-RM) using the bench press exercise. The music group listened to music in the second assessment session, while the control group performed both tests without music. Listening to music induced a significant increase of strength endurance performance and no effects on maximal strength. These findings have implications for the use of music during strength workouts.

This study aimed to analyse selected shot characteristics in top-level table tennis matches, with a special focus on comparing the playing style of Asian and European players. Ten men's matches played by 20 top-ranked players (14 Asians and 6 Europeans) were analysed. The indicators examined were the area of ball bouncing for serves (n =918), and the stroke type, footwork type and shot outcome for other shots (n=3692). The interrelationships between variables were analysed using chi-squared tests, log-linear modelling and multiple correspondence analysis. A strong association was found between strokes and footwork types, with most stroke types executed each after specific footwork types. Furthermore, a clear tendency to have a positive, negative or neutral outcome was observed for each stroke type. When compared to Europeans, Asians used more frequently the most aggressive strokes and footwork types, confirming anecdotal claims on their particularly offensive playing style. Asians showed also a better serving effectiveness, often sending the ball in those areas of the table from which a counterattack is difficult to make. In summary, this study gives a systematic description of highly relevant technical and tactical characteristics in top-level table tennis, thus providing valuable information for coaches and performance analysts.

The prevalence of weight disorders among school-aged children is an increasing phenomenon and it is of great importance to identify the characteristics of individuals at risk of gaining or retaining weight. This study aimed to examine the prevalence of weight disorders and their tracking over a 3-year period in a sample of Italian children. Body mass, body height and selected skinfold thicknesses were assessed in 355 children at the age of 7 and 10 years. Tracking of body mass index (BMI), inverted BMI (iBMI) and skinfold-based body fat were analyzed and the relationships between changes in BMI and body fat were examined. Children presenting with overweight or obesity at 7 years old showed a trend toward lower weight categories at 10 years old. Conversely, a trend to become overweight was observed among normal weight boys, and a trend to become underweight was observed among normal weight girls. BMI, iBMI and body fat showed good levels of tracking, with high correlations between measurements performed at 7 and 10 years of age. Furthermore, BMI and iBMI changes were correlated to body fatness changes. The present study shows the importance of carefully following children’s development over time because weight disorders may appear even in previously normal weight children.

Objectives Running economy is a key determinant of endurance performance, and understanding the biomechanical factors that affect it is of great theoretical and applied interest. This study aimed to analyse how the ground-contact time and strike pattern used by competitive runners concurrently affect running economy. Design Cross-sectional. Methods Fourteen sub-elite male competitive distance runners completed a 6-min submaximal running trial at 14 km h −1 on an outdoor track using their habitual strike pattern ( n = 7 rearfoot strikers: average age, 25.3 years old (SD = 2.4); average weight, 64.7 kg (SD = 5.6); average height, 175.3 cm (SD = 5.2); n = 7 midfoot strikers: average age, 25.0 years old (SD = 2.8); average weight, 69.6 kg (SD = 4.0); average height, 180.1 cm (SD = 5.1). During the run, the oxygen uptake and ground-contact time were measured. Results Midfoot strikers showed a significantly shorter ( p = 0.015) mean contact time (0.228 s (SD = 0.009)) compared with rearfoot strikers (0.242 s (SD = 0.010)). Conversely, there was no significant difference ( p > 0.05) between the groups with respect to mean oxygen uptake (midfoot strikers: 48.4 ml min −1 kg −1 (SD = 5.3); rearfoot strikers: 49.8 ml min −1 kg −1 (SD = 6.4)). Linear modelling analysis showed that the effect of contact time on running economy was very similar in the two groups, with a 1 ms longer contact time involving an approximately 0.51 ml min −1 kg −1 lower oxygen uptake. In contrast, when controlling for contact time, midfoot striking involved an approximately 8.7 ml min −1 kg −1 lower oxygen uptake compared with rearfoot striking. Conclusions When adjusting the foot–ground contact biomechanics of a runner with the aim of maximising running economy, a trade-off between a midfoot strike and a long contact time must be pursued.

AIM: This study aimed to assess the mechanical and metabolic responses of competitive runners throughout a high-intensity circuit training (HICT) workout, designed to improve explosive strength under acute metabolic fatigue. METHODS: Eight high-level endurance runners (age: 21.8±3.7 y; body mass: 61.5±5.7 kg; height: 175.2±5.2 cm; 1500-m record: 3 min 54±7 s) completed an incremental exhaustive running test to determine the maximum oxygen uptake (VO2max) and maximum aerobic speed (MAS). The athletes then performed on a track a HICT workout, consisting of two identical circuits interspersed by 5-min of passive recovery. Each circuit was constituted by six 30-s dynamic or explosive strength exercises, alternated to 200-m runs (1000-m for the final run) at 90-95% of MAS. During a hopping exercise included in the circuit, and during the 1000-m run, lower limb stiffness measures were obtained from contact and flight times using a method based on the spring-mass model. RESULTS: Hopping stiffness was significantly lower (P0.05) in the first and the second circuit (8.08±1.49 vs. 7.87±1.31 kN·m⁻¹), as well as vertical stiffness (33.56±5.25 vs. 32.16±5.45 kN·m⁻¹). The mean VO2 in the 1000-m run of the two circuits was 93.17±3.56% and 93.47±3.91% of VO2max, respectively. CONCLUSION: Despite the occurrence of acute neuromuscular fatigue throughout the workout, the runners avoided an impairment of their stiffness during running. Furthermore, the relatively high percentage of VO2max achieved indicates the HICT involves also stimuli for aerobic conditioning.

This study aimed to analyze whether using full-body swimsuits affects the swimmer's body alignment and to what extent changes in the body position are responsible of the passive drag (Dp) reduction experienced by the swimmers when using these swimsuits. Fourteen swimmers performed 20-m towing trials using a full-body synthetic rubber swimsuit, a full-body textile swimsuit, a traditional brief swimsuit, and a traditional brief swimsuit with a pull buoy. In all trials, the speed-specific drag (k = Dp per v), the trunk incline (TI), and the lower limbs incline (LI) were determined. In comparison with both conditions in which a full-body swimsuit was not used, k was significantly lower when using the rubber swimsuit (-8.4 and -12.2% vs. the brief swimsuit with and without pull bouy, respectively), and the textile swimsuit (-6.9 and -10.8% vs. the brief swimsuit with and without pull bouy, respectively). No differences in TI were observed among conditions, whereas LI was significantly higher when using the rubber swimsuit or the brief swimsuit with pull buoy than when using the traditional brief swimsuit. A linear mixed model showed that k can be reduced by increasing LI (that is lifting the lower limbs), by decreasing TI (that is keeping the trunk more horizontal), and by using either the rubber or textile full-body swimsuit rather than the traditional brief swimsuit. In conclusion, full-body swimsuits involve a reduction of a swimmer's passive drag caused by intrinsic properties related to the "material composition" of the swimsuits and also influenced by changes in the swimmer's body position.