This study investigated how varying body positions (seated, prone, supine) and knee joint angles (90 degrees, 120 degrees, 150 degrees) influence the bilateral deficit (BD) in isometric hamstring strength. Thirty physically active participants (15 males, 15 females) performed unilateral and bilateral maximal voluntary isometric contractions (MVICs) across the tested position & times; angle conditions. Peak force (Fmax) and rate of force development (RFD) measures (RFDmax, RFD50 ms, and RFD200 ms) were recorded. Results indicated that the seated position elicited a greater bilateral deficit (i.e., lower BD ratios) than the prone and supine positions, with differences that were more pronounced at more extended knee angles. These findings underscore the importance of considering position- and angle-specific influences when assessing BD in hamstring strength. Clinicians and researchers should standardize testing protocols to ensure accurate evaluation and data interpretation. From an applied standpoint, the results support the development of resistance-training strategies aimed at enhancing hamstring function at long muscle lengths-an approach relevant to both performance optimization and injury prevention.

The growing availability of high-frame-rate smartphone cameras and open-source video analysis software like Kinovea enable practitioners to assess athletic performance outside of advanced laboratory settings. The purpose of the present study was to evaluate the reliability and validity of Kinovea in comparison to force plates, the gold standard for the analysis of vertical jump performance. Sixteen professional female handball players performed three countermovement vertical jumps (CMJ), recorded simultaneously by a smartphone camera and force plates. Two raters, one experienced and one less experienced with using Kinovea, analyzed the videos to extract key CMJ variables, including eccentric and concentric phase durations, flight time, jump height, and reactive strength index modified. The level of agreement between measurements from two raters and force plates was assessed using intraclass correlation coefficients (ICC), coefficients of variation (CV%), standard error of measurement (SEM), and repeated measures ANOVA. Additionally, measurements were compared through Bland-Altman bias and limits of agreement. Results demonstrated excellent inter-rater reliability (ICC= 0.797-0.991; CV% < 10%) for most variables, with some minor discrepancies observed in phase durations for the less experienced rater. Validity was confirmed by strong correlations (r > 0.90) between Kinovea-derived and force plate measurements, with Bland-Altman further indicating minimal bias and narrow limits of agreement.These findings indicate that Kinovea is a reliable and valid tool for CMJ performance assessment, providing a practical and accessible alternative to force plates.

Vertical jump assessments are widely used to evaluate athletic performance. As demand grows for field-ready systems with laboratory-grade accuracy, portable devices like the CC Athletics PlateMate force plates offer affordable and accessible solutions. This study examined the concurrent validity of PlateMate compared to a gold-standard AMTI force plate during squat jump (SJ), countermovement jump (CMJ), and countermovement jump with arm swing (CMJH). Seventeen recreationally active participants performed five trials per jump while force data were recorded simultaneously from both systems. Agreement was evaluated using Bland-Altman plots, RMSE, Pearson's r, ICC, CV%, and SEM. Across conditions, raw force-time signals and most derived metrics showed excellent agreement (r >= 0.95; ICC > 0.93), with RMSE under 50 N and SEM for jump height between 0.2-0.9 cm. PlateMate demonstrated strong feasibility as a practical, low-cost alternative to laboratory force plates for field-based vertical jump testing.

This study aims to explore the reliability and validity of essential performance metrics derived from a modified 505 Change of Direction (CoD) test. Twenty-seven physically active male participants (age: 18.77 ± 1.73 years) who engaged in three to five training sessions per week were assessed using both standard and modified sprint and CoD protocols. The evaluation focused on sprint time, CoD time, total time, and the Limb Symmetry Index (LSI). The modified protocols demonstrated good reliability for sprint and CoD times (ICC > 0.8, CV < 3%) and high validity, with strong correlations between standard and modified tests for sprint (r = 0.59–0.80) and CoD times (r = 0.58–0.80). The total time metric showed excellent reliability (ICC > 0.9), supporting its utility as a comprehensive measure. Reaction-time inclusion increased variability (CV > 7%) but enhanced ecological validity by reflecting real-world conditions. However, the LSI exhibited lower reliability (ICC < 0.6), indicating the need for further refinement. Combining multiple performance measures, the modified protocols streamlined assessments, reducing fatigue and redundancy without compromising precision. These findings highlight the potential of integrating multidimensional agility metrics in athletic evaluations, bridging the gap between controlled testing and competitive demands. Future research should explore broader populations and sport-specific stimuli to enhance applicability.

Monitoring heart rate (HR) is vital for health management and athletic performance, and wearable technology enables scientists to obtain real-time cardiovascular insights. This study compares Machine Learning (ML) techniques, including Long Short-Term Memory (LSTM) networks, Physics-Informed Neural Networks (PINNs), and 1D Convolutional Neural Networks (1D CNNs). Then, we develop a hybrid Singular Spectrum Analysis (SSA)-Augmented ML technique to predict HR using wearable sensor data. Additionally, we investigate the impact of incorporating auxiliary physiological inputs, such as breathing rate (BR) and RR intervals, on predictive accuracy. The study utilizes the cardiorespiratory data acquired through wearable sensors while practising sports, including 126 recordings from 81 participants (53 males, 28 females) engaged in 10 different sports. Physiological signals were collected at 1 Hz using the BioHarness 3.0 (Zephyr Technology, Mangaluru, India). The dataset includes individuals with varied levels of sports experience (beginner, intermediate, and advanced), allowing for a more comprehensive evaluation of HR variability across different expertise levels. Our results demonstrate that the hybrid SSA-LSTM model reaches the lowest prediction error by effectively capturing HR dynamics. Furthermore, integrating HR, BR, and RR data significantly enhances accuracy over single or dual parameter inputs. These findings support adopting multivariate machine learning models for health monitoring, improving HR prediction accuracy for fitness and preventive healthcare.

The present study aimed to investigate changes in muscle mechanical properties (velocity, force, and power) during the seated medicine ball throw (MBT) test under conditions of voluntary reduced effort across various loadings. Twelve males (21.0 ± 1.2 years) performed the MBT against four loadings (0.43 kg, 2 kg, 4 kg, 6 kg) and three effort levels (50%, 75%, and 100%). Results revealed a consistent decrease in absolute velocity was observed across all loading levels (p < 0.01), with the most pronounced alterations at the lowest load (0.43 kg; p < 0.001). In contrast, reductions in absolute force and power under reduced effort were more significant with higher loadings (2-6 kg; p < 0.01). The relative decreases in velocity and force were notably smaller than those in power (p < 0.001), with the relative decrease in power closely following effort instructions across all loadings. These findings highlighting muscle power as a key indicator of effort during loaded submaximal MBT. The study supports the use of loaded submaximal MBT in rehabilitation and exercise programs as an effective method to assess neuromuscular performance and manage exercise intensity for individuals unable to perform at maximum effort.

Introduction:Human balance control is regulated by complex temporal processes that may be disrupted by injury or increased task difficulty. Methods:We examined long-range temporal characteristics of force platform recordings during quiet standing in 76 physically active participants with or without lower-limb injury, and in 13 non-injured participants standing with eyes closed or on one leg. Detrended fluctuation analysis (DFA) and wavelet transform spectral analysis (WTS) were used to quantify the temporal dynamics of postural control. Results:All recordings showed long-range autocorrelated behavior, with a visible crossover point separating random fluctuations at small time scales from structured dynamics at higher time scales (100 ms to 1 s). Changes in scaling behavior occurred only above the crossover point in response to altered stance or injury. Specifically, standing on one leg increased DFA and WTS slopes, likely due to enhanced amplitudes of characteristic peaks at approximately 250 ms and 650 ms. Two distinct postural responses to injury emerged: (1) compensation - characterized by increased amplitudes of all high-scale WTS modes and a crossover shift to smaller scales; and (2) underachievement - marked by decreased amplitudes and a shift of the crossover to larger time scales. Discussion:These findings support the potential of DFA, WTS, and similar time series techniques as sensitive tools for assessing subtle impairments in postural control.

Affordable high-frame-rate cameras and open-source software, such as Kinovea (ver. 2025.1.0), have expanded the potential for conducting kinematic assessments outside laboratory settings. This study examined the reliability and validity of Kinovea’s semi-automated linear kinematics tracking tool by comparing its outputs with those from a 3D marker-based motion capture system (Qualisys). Ten recreationally active male basketball players (x̄ ± SD: age 23.7 ± 1.7 years; height 183 ± 5 cm; body mass 76.8 ± 9.8 kg) performed three CMJ trials, simultaneously recorded using both systems. Reflective markers placed on the shoulder, hip, and knee were tracked in Kinovea by two raters with different levels of experience to extract core CMJ variables (total take-off time and maximum vertical displacement) and complementary variables (eccentric and propulsion duration, and minimum vertical displacement). Inter-rater reliability and concurrent validity were evaluated using intraclass correlation coefficients (ICCs), coefficients of variation (CV%), standard error of measurement (SEM), and Bland–Altman analysis. Results showed excellent inter-rater reliability (ICC = 0.73–0.99) across all markers, with the hip and knee demonstrating the highest consistency. Strong validity relative to Qualisys was observed for both raters (ICC = 0.68–0.99; r > 0.80), with small systematic biases primarily in temporal variables. Collectively, these findings demonstrate that Kinovea’s semi-automated 2D analysis yields reliable and valid CMJ measurements comparable to 3D motion capture, even for less experienced users. As a free and easily deployable tool, it offers a widely accessible alternative for field-based performance monitoring and applied biomechanics research where laboratory-grade equipment is not available.

Given the complex nature of the handball as a game, players are required to possess a distinct set of physical and physiological attributes to attain peak performance. With the countermovement vertical jump (CVJ) being widely implemented as a non-invasive and time-efficient testing modality in sports settings, the purpose of the present study was twofold: (a) to establish a CVJ profile of professional female handball players and (b) to examine differences in force-time metrics between starters and non-starters. Forty-two professional female handball players (e.g., SuperLeague) volunteered to participate in this study. Each athlete performed three maximum-effort CVJs with no arm swing while standing on a uni-axial force plate system sampling at 1,000 Hz. Independent t-tests were used to examine differences in each variable between starters and non-starters. The results revealed that starters attained superior performance within the eccentric phase of the CVJ when compared to non-starters, particularly in terms of eccentric peak velocity (−0.957 ± 0.242 vs. −0.794 ± 0.177 m·s−1), eccentric mean power (320.0 ± 77.7 vs. 267.1 ± 75.2 W), and eccentric peak power (929.0 ± 388.1 vs. 684.4 ± 214.2 W). While not reaching the level of statistical significance, moderate-to-large effect sizes were observed for concentric impulse, peak velocity, and mean and peak force and power, all in favor of players included in the starting lineup (g = 0.439–0.655). Overall, these findings suggest that at the top-tier level of handball competition, the ability to secure a spot in a starting lineup may be possibly influenced by the athlete's eccentric performance capabilities. Thus, the development of lower-body eccentric strength and power may positively impact on-court athlete performance and ultimately help the team secure the desired game outcome.

The present study aimed to explore the possibility of comprehensively assessing whole-body muscle strength by testing as few muscle groups as possible, using a single testing method (isometric or isokinetic dynamometry) and a single variable (maximal force or rate of force development). Knee, hip, shoulder and elbow extensors and flexors were evaluated in males with high (n = 26) and low strength levels (n = 32). The principal component analysis revealed three factors that explained 62.5% of the total variance, while the main factors were loaded by the different testing methods and strength variables for the muscles acting on the knee (first component), hip (second component) and arm joints (third component). These results were confirmed by a three-way ANOVA which revealed a significant factor of group (P < 0.001) and the interaction test type x group (P = 0.002), but not of test type (P = 0.644), muscle group (P = 0.999), or their interactions (P > 0.205). The correlations of strength outcomes across the muscles ranged from trivial to very large (r range = -0.17, 0.84), being generally higher for the antagonistic muscles. Overall, a comprehensive assessment of whole-body muscle strength can be obtained using isometric dynamometry and maximal force, but it should consider at least one muscle group from the antagonistic pair.

Standing long jump is a complex motor test that is typically used for the functional assessment of lower extremities. This study introduces a new approach in the analysis of rotational movement of body parts during performance of standing long jump. An experiment was conducted for collecting the jump database from 10 healthy trained students using inertial sensors. Segment and joint angle signals were calculated, and their shape was analysed and described with 10 features that were used for the distinction of jump correctness. A rule-based algorithm was developed for the recognition of SLJ regularity and achieved 91.67% accuracy. Compared to a decision tree trained using cross-validation, the developed algorithm showed better performance; however, additional testing on larger datasets is needed.

The countermovement vertical jump (CMJ) is widely used in sports science and rehabilitation to assess lower body power. In controlled laboratory environments, a complex analysis of CMJ performance is usually carried out using motion capture or force plate systems, providing detailed insights into athlete’s movement mechanics. While these systems are highly accurate, they are often costly or limited to laboratory settings, making them impractical for widespread or field use. This study aimed to evaluate the accuracy of MMPose, a markerless 2D pose estimation framework, for CMJ analysis by comparing it with force plates. Twelve healthy participants performed five CMJs, with each jump trial simultaneously recorded using force plates and a smartphone camera. Vertical velocity profiles and key temporal variables, including jump phase durations, maximum jump height, vertical velocity, and take-off velocity, were analyzed and compared between the two systems. The statistical methods included a Bland–Altman analysis, correlation coefficients (r), and effect sizes, with consistency and systematic differences assessed using intraclass correlation coefficients (ICC) and paired samples t-tests. The results showed strong agreement (r = 0.992) between the markerless system and force plates, validating MMPose for CMJ analysis. The temporal variables also demonstrated high reliability (ICC > 0.9), with minimal systematic differences and negligible effect sizes for most variables. These findings suggest that the MMPose-based markerless system is a cost-effective and practical alternative for analyzing CMJ performance, particularly in field settings where force plates may be less accessible. This system holds potential for broader applications in sports performance and rehabilitation, enabling more scalable, data-driven movement assessments.

This study aimed to validate the automated temporal analysis of countermovement vertical jump (CMJ) using MMPose, a markerless pose estimation framework, by comparing it with the gold-standard 3D marker-based motion capture system. Twelve participants performed five CMJ trials, which were simultaneously recorded using the marker-based system and two smartphone cameras capturing both sides of the body. Key kinematic points, including center of mass (CoM) and toe trajectories, were analyzed to determine jump phases and temporal variables. The agreement between methods was assessed using Bland–Altman analysis, root mean square error (RMSE), and Pearson’s correlation coefficient (r), while consistency was evaluated via intraclass correlation coefficient (ICC 3,1) and two-way repeated-measures ANOVA. Cohen’s effect size (d) quantified the practical significance of differences. Results showed strong agreement (r > 0.98) with minimal bias and narrow limits of agreement for most variables. The markerless system slightly overestimated jump height and CoM vertical velocity, but ICC values (ICC > 0.91) confirmed strong reliability. Cohen’s d values were near zero, indicating trivial differences, and no variability due to recording side was observed. Overall, MMPose proved to be a reliable alternative for in-field CMJ analysis, supporting its broader application in sports and rehabilitation settings.

This study explored the changes in the rate of torque development scaling factor (RTD-SF) and maximum voluntary isometric contraction (MVC) variables following six weeks of unilateral isometric electromyostimulation (EMS) and voluntary (VOL) exercises. Twenty-six physically active participants were randomly assigned to EMS (n = 13) or a VOL group. MVC and RTD-SF of the quadriceps femoris of both legs were assessed before and after training. EMS and VOL exercises had identical frequency (three sessions/week), intensity (60% MVC), volume (40 contractions), and work-to-rest ratio (18 min: 6.25 s of work/20 s of rest). There were no between-group differences for the trained leg with overall increases in maximal torque (Tmax) of ~29% (d = 2.11–2.12), ~13% for RTDmax (d = 0.92–1.10); ~23% for Intercept (d = 0.72–0.78), and reduction in RTD-SF by ~15% (d = 1.01–1.10). In the non-trained leg, significant moderate change was only observed after EMS for RTD-SF which decreased by 12.5% (d = 0.76). Both EMS and VOL training applied at equivalent workloads positively impact on Tmax, RTDmax, and Intercept, but they negatively affect the quickness with which muscle contracts across a wide range of submaximal forces. Using a moderate training intensity in regularly physically active participants could explain the absence of cross-education in the VOL group.

Given the multidirectional nature of the sport, handball athletes must frequently perform high-intensity decelerations to avoid defenders, generate space, or perform directional changes. The aim of the present study was twofold: (i) to investigate different kinematic measures of horizontal deceleration performance by comparing the acceleration-deceleration assessment (ADA) with the 5-0-5 test and (ii) to investigate relationships between force-time characteristics derived from the countermovement vertical jump (CVJ) and measures of horizontal deceleration performance. Eleven female handball players competing in the first-tier professional league in Europe performed three CVJs while standing on a uni-axial force plate system sampling at 1000 Hz, followed by two ADAs (i.e., maximal-effort acceleration over a 10 m distance, followed by rapid deceleration) and 5-0-5 test trials. Tripod-mounted radar sampling at 47 Hz, placed 5 m behind the start line, was used to record horizontal velocity data. Each test was separated by a 5–7 min rest interval to minimize the influence of fatigue. No statistically significant differences were found in horizontal deceleration performance parameters between ADA and the 5-0-5 test. However, athletes with a higher CVJ height and reactive strength index-modified showed better performance in terms of horizontal deceleration measures such as maximal approach velocity and average and maximal deceleration. Overall, these results may be of interest to practitioners working with multidirectional sport athletes such as handball players as they provide critical insight for the selection of assessments and training strategies targeted toward optimizing on-court athlete performance.

The purpose of the present study was (i) to explore the reliability of the most commonly used countermovement jump (CMJ) metrics, and (ii) to reduce a large pool of metrics with acceptable levels of reliability via principal component analysis to the significant factors capable of providing distinctive aspects of CMJ performance. Seventy-nine physically active participants (thirty-seven females and forty-two males) performed three maximal CMJs while standing on a force platform. Each participant visited the laboratory on two occasions, separated by 24–48 h. The most reliable variables were performance variables (CV = 4.2–11.1%), followed by kinetic variables (CV = 1.6–93.4%), and finally kinematic variables (CV = 1.9–37.4%). From the 45 CMJ computed metrics, only 24 demonstrated acceptable levels of reliability (CV ≤ 10%). These variables were included in the principal component analysis and loaded a total of four factors, explaining 91% of the CMJ variance: performance component (variables responsible for overall jump performance), eccentric component (variables related to the breaking phase), concentric component (variables related to the upward phase), and jump strategy component (variables influencing the jumping style). Overall, the findings revealed important implications for sports scientists and practitioners regarding the CMJ-derived metrics that should be considered to gain a comprehensive insight into the biomechanical parameters related to CMJ performance.

The rate of force development scaling factor (RFD-SF) has been used to assess neuromuscular quickness. However, the common protocols are lengthy. This study evaluated the validity and reliability of the reduced protocol to assess the RFD-SF and its validity in detecting inter-limb asymmetries. Eighteen participants (five females and thirteen males; mean age = 20.8 ± 0.6 years) performed the common and reduced RFD-SF protocols (five isometric pulse knee extensions at 30 and 70% of maximal voluntary contraction). A repeat measure design was employed including one test session of the common protocol and two test sessions of the reduced protocol. Correlation analysis was conducted to investigate the association between the two protocols, while a paired-sample t-test and a Bland–Altman plot assessed whether the reduced protocol provided valid results. The between-day reliability was assessed using an intra-class correlation coefficient, coefficient of variation, typical error of measurement, and paired-sample t-test. The validity to detect asymmetries was checked with the paired-sample t-test. The correlation between RFD-SF obtained using two protocols was significant (p < 0.001) and very large for the dominant (r = 0.71) and non-dominant (r = 0.80) legs. No significant difference occurred between protocols in the RFD-SF for the dominant (p = 0.480, d = 0.17) and non-dominant legs (p = 0.213, d = 0.31). The reliability was acceptable for both legs, with no between-day difference for the dominant (p = 0.393) and non-dominant legs (p = 0.436). No significant difference between the two protocols (p = 0.415, d = 0.19) was found in the detection of inter-limb asymmetries. The results of this study suggest that the reduced protocol could be used as a valid and reliable alternative to the common protocol, as well as to identify interlimb asymmetries.

This study aimed to determine the within- and between-session reliability of different variables collected during the starting block phase with the KiSprint force starting block and to identify the number of trials that maximise the reliability of the measurement. Thirty high-level sprinters (23 men and 7 women) completed two sessions separated by 1 week. The first session consisted of two sets of five sprints and the second session of one set of five sprints. Outcomes of each set were calculated as Aver3 (average of the first three sprints), Aver5 (average of the five sprints) and CENTRAL (average of the three central sprints). The instrumented sprint starting blocks (KiSprint system) served to record a total of 20 push-off variables. Within-session reliability was acceptable (coefficient of variation (CV)<15%; intraclass correlation coefficient >0.70) for 103 out of 117 comparisons and between-session reliability was acceptable for 60 out of 117 comparisons. Aver5 provided a lower CV (within-session: 4.8% ± 2.9%; between-session: 13.0% ± 6.4%) than Aver3 (within-session: 8.2% ± 6.6% (CV ratio = 1.72); between-session: 14.5% ± 7.1% (CV ratio = 1.11)) and CENTRAL (within-session: 5.3% ± 3.6% (CV ratio = 1.10); between-session: 15.2% ± 9.7% (CV ratio = 1.17)). These results indicate that the KiSprint system can collect several variables with acceptable reliability in high-level sprinters, while the Aver5 procedure is recommended to maximise the reliability of the measurement.

During the past decade, self-massage of the muscular fascia using a foam roller (FR) has become an increasingly common way of supplementing traditional methods of soft tissue treatment, while both professional and recreational athletes use it as a tool for warm-up and/or post-training relaxation. Considering the relevance of this topic among researchers, coaches, and physiotherapists, the aim of this this paper is to present a narrative review with the systematization of the latest research on the effects of foam rolling on motor skills. Publication search was conducted using the following databases: Google Scholar, PubMed, and ScienceDirect. The following keywords were used in the search: foam rolling, self-myofascial release, fascia, and muscle soreness. The selection of papers was based on the following criteria: 1) publications written in English and published in the period 2019-2022, and 2) original scientific papers focused on examining the effects of soft tissue massage using FR on the range of motion (ROM), motor abilities (strength, power, speed, balance and others), acute muscle pain, and delayed muscle soreness. Recent research results confirm earlier findings that FR can have short-term, positive effects on flexibility and ROM, while findings regarding the effects on muscle strength, explosive power, and balance are equivocal. In addition, it has been noted that this type of treatment can delay the onset of fatigue, and alleviate the painful sensitivity of muscles after intensive work-out. Although foam rollers have been in use for a long time both in sports and in rehabilitation, due to the heterogeneity of methods applied in related studies, there is still no official recommendation on the optimal way of applying these tools (treatment duration, pressure and cadence, i.e. the frequency of vibration if such a roller is used)

The main objective of present study was to evaluate inter-rater reliability and concurrent validity of Side Hop Test stopwatch vs. force plates timing, and to determine the number of sessions and trials required to minimize the effects of learning on Side Hop Test total time and limb symmetry index. Fifteen healthy male physical education students (mean ± SD: age, 23 ± 3 years; height, 181 ± 9 cm; and weight 72 ± 6 kg) participated. Side Hop Test total time (stopwatch and force plates) of left and right leg, and limb symmetry index (force plates) were obtained over seven sessions conducted 5–7 days apart. Time recordings of two raters were similar (t = −0.56, p > 0.05) with high reliability (all ICC >0.99 and CV% <0.1) and no systematic bias when compared to force plate data (p > 0.05; for rater 1 and 2, respectively). Total time improved across the Sessions (F = 25.87, p < 0.01, ω 2 = 0.18) and Trials (F = 68.15, p < 0.01, ω 2 = 0.10), with no significant interaction between factors. No between-leg differences were detected (F = 0.52, p > 0.05, ω 2 = 0.001). Limb symmetry index ranged from 0.999 to 1.055 across all sessions and trials (all p > 0.05 and ω 2 < 0.00). Due to low coefficient of correlation, high interclass correlation coefficient, and the lack in heteroscedasticity, stopwatch measurements are valid to measure total time in the Side Hop Test. Moreover, stopwatch measurements could be reliably used to measure total time in the Side Hop Test, while the test could be administrated with only one experienced rater. Unlike total times, findings on limb symmetry index suggest it could be reliably assessed after seven familiarization sessions.