Journal of Functional Morphology and Kinesiology

Background/Objectives: Positive self-perception, physical activity and fundamental movement skill (FMS) proficiency are important aspects of a child’s healthy development. The objective of this research was twofold: first, to explore associations between FMS, muscular fitness, self-perception and physical activity in school children; and second, to identify key predictors of FMS proficiency, athletic self-perception, physical activity levels in these participants and the differences between biological sexes. Methods: Primary school-aged children (n = 104; 53.85% female) from 8 to 10 years old (M = 9.04, SD = 0.69) engaged in two days of testing. All students were measured on FMS, standing long jump (SLJ), countermovement jump (CMJ), seated medicine ball chest throw and self-perception, followed by correlation and stepwise multiple linear regression analyses. Results: The findings revealed significant positive correlations between FMS proficiency, lower body muscular fitness (CMJ, SLJ), and athletic self-perception for the entire cohort, with varying results between male and female subgroups. Additionally, athletic self-perception showed strong relationships with other self-perception domains. Notably, forward stepwise regression analysis identified FMS proficiency as a significant predictor of physical activity levels, explaining 12.8% of the variance. SLJ, scholastic perception, and physical activity explained 45.5% of FMS variance for females. In males, FMS proficiency significantly predicted physical activity, accounting for 13.3% of the variance. SLJ and athletic competence self-perception explained 42.1% of FMS variance in males. Conclusions: The study indicates that FMS, self-perception, muscular fitness, and physical activity levels may mutually enhance each other, and that there is a need for biological sex-specific strategies to be considered in physical education programs. Full article

Background/Objectives: This study examined the activity profile of elite hurling referees during games in the National Hurling League (NHL) and All-Ireland Championship (AIC) and across all divisions of the NHL and phases of the AIC. Temporal changes between the first and second half and across the four quarters were also examined. Methods: Data were collected from 36 referees using 10-Hz global positioning system technology during 106 NHL and 85 AIC games and analyzed for duration, total distance, very low-speed movement (<0.69 m·s⁻¹), walking (≥0.69–1.59 m·s⁻¹), low-speed running (≥1.60–3.08 m·s⁻¹), moderate-speed running (≥3.09–4.62 m·s⁻¹), high-speed running (HSR) (≥4.63–6.34 m·s⁻¹), and very high-speed running (VHSR) (≥6.35 m·s⁻¹) distance and peak running speed. Results: Total distance was not significantly different between games in the NHL (120.7 ± 9.4 m·min⁻¹) and AIC (122.8 ± 9.9 m·min⁻¹, ES = 0.04). There was also no significant difference in HSR distance between the NHL (17.1 ± 6.5 m·min⁻¹) and AIC (18.0 ± 7.2 m·min⁻¹, ES = 0.10). The only significant difference between the NHL and AIC was in LSR distance, which was higher in the AIC (ES = 0.24). VHSR distance was significantly higher during games in Division 3A+3B (0.7 ± 0.8 m·min⁻¹) compared to Division 1A+1B (0.2 ± 0.3 m·min⁻¹) and Division 2A+2B (0.1 ± 0.3 m·min⁻¹). HSR distance was significantly lower during games in the All-Ireland Series (15.7 ± 6.7 m·min⁻¹) compared to games in the Leinster (21.1 ± 8.5 m·min⁻¹) and Munster (17.9 ± 5.4 m·min⁻¹) Championships. Conclusions: The findings of this study can be used to support the development of physical conditioning programs that are specific to the demands experienced during competitive match play. Full article

Assessing the reliability of measurement instruments and equipment is essential to ensure the accurate tracking of athletes over extended periods, minimizing the measurement errors caused by chance or other factors. However, a less common but equally important analysis is the verification of inter-measurement agreement, which complements the reliability results. Purpose: To evaluate the intra- and inter-test reliability of an isometric hip adduction strength and asymmetries test in professional soccer players. Methods: Twenty-three professional male soccer players were evaluated on two occasions, 1 week apart. The force signal was collected using force plates (Pasco PS-2141), and the data processing was performed using Matlab software (R2023a, MathWorks, Natick, MA, USA). The peak force, interval RFD, peak RFD, peak force asymmetry and RFD were analyzed. Intraclass correlation coefficients (ICCs) and coefficients of variation (CV) were calculated to corroborate the intra- and inter-test reliability. In addition, the degree of agreement of the asymmetries was corroborated through the kappa index. Results: The peak force demonstrated an acceptable absolute reliability (CV < 10%) for the intra-test and test–retest condition, an excellent relative intra-test reliability and a good to moderate reliability for the test–retest reliability. However, the peak force asymmetry showed a moderate test–retest reliability and agreement. For the intra-test condition, the RFD variables demonstrate a moderate to excellent relative reliability; however, all demonstrate unacceptable absolute reliability (CV > 10%) in at least one of the evaluation sessions. A moderate to poor test–retest reliability and unacceptable absolute reliability were observed for all the RFD variables. Conclusions: The peak force is the variable with the highest intra- and inter-test reliability, so its use is recommended to longitudinally assess the maximum strength of the adductors in professional soccer players, but not the asymmetry orientation of the peak force. The RFD variables should be interpreted with caution due to their inconsistent reliability, and it is necessary to improve the methods used to achieve adequate reliability. Full article

Background/Objectives: The purpose of this research was to create a peak detection algorithm and machine learning model for use in triathlon. The algorithm and model aimed to automatically measure movement cadence in all three disciplines of a triathlon using data from a single inertial measurement unit and to recognise the occurrence and duration of cycling task changes. Methods: Six triathletes were recruited to participate in a triathlon while wearing a single trunk-mounted measurement unit and were filmed throughout. Following an initial analysis, a further six triathletes were recruited to collect additional cycling data to train the machine learning model to more effectively recognise cycling task changes. Results: The peak-counting algorithm successfully detected 98.7% of swimming strokes, with a root mean square error of 2.7 swimming strokes. It detected 97.8% of cycling pedal strokes with a root mean square error of 9.1 pedal strokes, and 99.4% of running strides with a root mean square error of 1.2 running strides. Additionally, the machine learning model was 94% (±5%) accurate at distinguishing between ‘in-saddle’ and ‘out-of-saddle’ riding, but it was unable to distinguish between ‘in-saddle’ riding and ‘coasting’ based on tri-axial acceleration and angular velocity. However, it displayed poor sensitivity to detect ‘out-of-saddle’ efforts in uncontrolled conditions which improved when conditions were further controlled. Conclusions: A custom peak detection algorithm and machine learning model are effective tools to automatically analyse triathlon performance. Full article

Background/Objectives: Team handball involves a high number of rapid and forceful muscle actions. Progressive heavy-load resistance training is known to enhance mechanical muscle function; however, its transfer into functional performance in team handball athletes remains largely unknown. The current study aimed to analyze the effects of eight weeks undulating heavy-load resistance training on lower limb mechanical muscle function and sports-specific performance in elite female team handball players. Methods: Players from the Danish Women’s Handball League were block randomized to perform an off-season resistance training program (RT, n = 12, 23.0 ± 2.7 yr) or follow a training-as-usual control program (CON, n = 15, 24.1 ± 3.8 yr). All study participants were tested before and after an eight-week period during the off-season phase, including assessments of maximal isometric knee extensor and flexor peak torque, rate of torque development, countermovement jump (CMJ) power/work, and sports-specific performance (maximal vertical countermovement jump height, sprint capacity, team handball-specific on-court agility). Results: Agility performance improved for RT (−3.5%, p = 0.008), different from CON (p < 0.001) following eight weeks of designated resistance training. Additionally, CON demonstrated impaired agility (+4.0–7.3%, p < 0.05) and 20-m sprint (+1.9%, p = 0.002) performance. Maximal knee extensor peak torque increased in RT (4.5%, p = 0.044). Vertical CMJ flight height (JH) increased in both groups (RT +4.8%, p = 0.012, CON +8.4% p = 0.044); however, jump height relative to ground level (JHGL) increased in RT only (+8.0%, p = 0.013). Conclusions: In conclusion, designated resistance training during the off-season period is effective in maintaining and improving essential components of sports-specific performance and maximal knee extensor strength in elite female team handball players. Comparable protocols of twice-a-week heavy-load resistance training may also be beneficial in other types of intermittent elite team sports (i.e., football, basketball) that include maximal jumping actions, short-distance sprints, and rapid change of direction movements. Full article

Background/Objectives: Fine motor movements are essential for daily activities, such as handwriting, and rely heavily on visual information to enhance motor complexity and minimize errors. Tracing tasks provide an ecological method for studying these movements and investigating sensorimotor processes. To date, our understanding of the influence of different quantities of visual information on fine motor control remains incomplete. Our study examined how variations in the amount of visual feedback affect motor performance during handwriting tasks using a graphic pen tablet projecting on a monitor. Methods: Thirty-seven right-handed young adults (20 to 35 years) performed dot-to-dot triangle tracing tasks under nine experimental conditions with varying quantities of visual cues. The conditions and triangle shape rotations were randomized to avoid motor training or learning effects. Motor performance metrics, including absolute error, time of execution, speed, smoothness, and pressure, were analyzed. Results: As visual information increased, absolute error (from 6.64 mm to 2.82 mm), speed (from 99.28 mm/s to 57.19 mm/s), and smoothness (from 4.17 mm²/s⁶ to 0.80 mm²/s⁶) decreased, while time of execution increased (from 12.68 s to 20.85 s), reflecting a trade-off between accuracy and speed. Pressure remained constant across conditions (from 70.35 a.u. to 74.39). Spearman correlation analysis demonstrated a moderate to strong correlation between absolute error and time of execution across conditions. The Friedman test showed significant effects of experimental conditions on all motor performance metrics except for pressure, with Kendall’s W values indicating a moderate to strong effect size. Conclusion: These findings deepen our understanding of sensorimotor integration processes and could potentially have implications for optimizing motor skills acquisition and training and developing effective rehabilitation strategies. Full article

Background/Objectives: Riding a bicycle is a foundational movement skill that can be acquired at an early age. The most common training bicycle has lateral training wheels (BTW). However, the balance bike (BB) has consistently been regarded as more efficient, as children require less time on this bike to successfully transition to a traditional bike (TB). The reasons for this greater efficiency remain unclear, but it is hypothesized that it is due to the immediate balancing requirements for learners. This study aimed to investigate the reasons why the BB is more efficient than the BTW for learning to cycle on a TB. Methods: We compared the variability of the child–bicycle system throughout the learning process with these two types of training bicycles and after transitioning to the TB. Data were collected during the Learning to Cycle Program, with 23 children (6.00 ± 1.2 years old) included. Participants were divided into two experimental training groups, BB (N = 12) and BTW (N = 11). The angular velocity data of the child–bicycle system were collected by four inertial measurement sensors (IMUs), located on the child’s vertex and T2 and the bicycle frame and handlebar, in three time phases: (i) before practice sessions, (ii) immediately after practice sessions, and (iii), two months after practice sessions with the TB. The largest Lyapunov exponents were calculated to assess movement variability. Conclusions: Results supported the hypothesis that the BB affords greater functional variability during practice sessions compared to the BTW, affording more functionally adaptive responses in the learning transition to using a TB. Full article

Background: In karate, the ability to execute high-velocity movements, particularly kicks and punches, is heavily dependent on the strength and power of the lower limb muscles, especially the knee extensors. As such, this study aimed to evaluate the effects of an 8-week eccentric training program utilizing the reverse Nordic exercise (RNE) integrated into karate training compared with regular karate training only on measures of physical fitness in youth karate athletes. Methods: Twenty-seven youth karatekas were recruited and allocated to either RNE group (n = 13; age = 15.35 ± 1.66 years; 7 males and 6 females) or an active control group ([CG]; n = 14; 7 males and 7 females; age = 15.30 ± 1.06 years). To track the changes in measures of physical fitness before and after training, tests to assess linear sprint speed (i.e., 10 m), change of direction (CoD) speed (i.e., modified 505 CoD), vertical jumping (i.e., countermovement jump [CMJ] height) and horizontal jumping distance (i.e., standing long jump [SLJ]), and lower-limb asymmetry score (i.e., the difference between SLJ-dominant and non-dominant legs) were carried out. Results: The results indicated significant group-by-time interactions in all measures of physical fitness (effect size [ES] = 1.03 to 2.89). Post-hoc analyses revealed significant changes in the RNE group across all performance measures (effect size [ES] = 0.33 to 1.63). Additionally, the asymmetry score exhibited a moderate decrease from pre to posttest (∆46.96%, ES = 0.64). In contrast, no significant changes were observed in the CG across all fitness measures. Moreover, the individual response analysis indicated that more karatekas from the RNE group consistently achieved improvements beyond the smallest worthwhile change threshold across all fitness measures. Conclusions: In summary, RNE training is an effective approach to enhance various physical fitness measures besides lower-limb asymmetry scores in youth karatekas and is easy to incorporate into regular karate training. Practitioners are therefore encouraged to consistently integrate RNE training to enhance essential physical fitness components in young karatekas. Full article

Background: Since studies on the subject of weight reduction in wrestlers vary in opinions regarding health, performance, and legal regulations, a review of the most cited literature in other combat sports was carried out. Methods: By searching the WOS and Scopus scientific databases, the top 60 cited papers were identified, and ultimately, 13 articles that met the inclusion criteria for this review were selected. Findings and conclusions: Apart from the advantages gained in strength and mass through weight reduction, a mental advantage is also obtained. The period between weigh-ins and the actual bouts is considered crucial for the preservation of performance. When the rules allow for a longer recovery period, this enables aggressive, harmful, or prohibited weight reduction methods to be employed by some wrestlers. A chronic reduction in body weight is regarded as a long-term health issue but may be ignored by wrestlers. There has been no progress in the attempt to regulate the problem of rapid weight loss (RWL) within wrestling in the past thirty-five years. If any change is to be brought about, the engagement of all federations, clubs, WADA, and all individuals involved in this issue (athletes, coaches, parents, doctors, etc.) is deemed necessary. Full article

Background: Evaluations of the usability of hydraulic resistance for resisted sprint-training purposes remains rare. Thus, this study compared step-by-step changes in spatiotemporal characteristics during the first 10 m of sprints with varying hydraulic resistance loads. Methods: Fourteen male athletes performed 20 m sprints under minimal (10 N, considered as normal sprint), moderate (100 N), and heavy (150 N) hydraulic resistance loads. Split times at 10 m, contact time (CT), step length (SL), flight time, and step speed (SS) from the first to the sixth step were measured. A two-way repeated measures ANOVA (load × step) and a one-way ANOVA (load) with post hoc comparisons were used to assess the effects on spatiotemporal characteristics and split times, respectively. Results: Under higher loads, the 10 m times were significantly longer (η² = 0.79). The CT, SL, and SS varied significantly from step to step within all loads (η² = 0.45, 0.41, and 0.54, respectively). The CT, SL, and SS of the first, fourth, fifth, and sixth steps of normal sprint differed significantly from most steps under moderate and heavy load (Cohen’s d = −3.09 to 5.39). In contrast, the smallest differences were observed between the second and third step of normal sprint and second to sixth steps under heavy load (Cohen’s d = −0.67 to 1.32, and −0.71 to 1.38, respectively). Conclusions: At the same load settings, a hydraulic resistance device induces changes in step characteristics comparable with those of other motorized devices and is therefore a viable option for resisted sprint training. If the goal of the training is to replicate the steps of the initial sprint acceleration phase, ~150 N of hydraulic resistance would be optimal. Full article

Background/Objectives: A manual approach combined with therapeutic exercise versus therapeutic exercise alone is a debated issue in the literature. The American College of Rheumatology guidelines “conditionally recommended against” manual therapy for the management of hip osteoarthritis. Manual therapy followed by exercise, instead, appears to lead to a faster return to sport than exercise alone for adductor groin pain. There is a need to understand which is the most effective treatment in the management of hip nonspecific musculoskeletal diseases. The aim of this systematic review is to determine which is the most effective treatment between manual therapy combined with therapeutic exercise and therapeutic exercise alone in subjects with hip nonspecific musculoskeletal diseases. Methods: This systematic review complies with the guidelines of the 2020 Prisma Statement. The databases consulted were Pubmed, Cinahl, and Web Of Science. The search was conducted from October 2004 to November 2023. The search string was developed following the PICO model. Free terms or synonyms (e.g., manual therapy, exercise therapy, hip disease, effectiveness) and Medical Subject Headings terms were combined with Boolean operators (AND, OR, NOT). The risk-of-bias assessment was conducted using Version 2 of the Cochrane risk-of-bias tool for randomized controlled trials and the Newcastle Ottawa Scale for observational studies. A qualitative analysis of the results was conducted through narrative synthesis of key concepts. When possible, quantitative analysis was conducted through statistical parameters. Results: Ten articles were analyzed. Results show no differences between the interventions analyzed. Preliminary evidence seems to favor the combined intervention for the outcomes of pain, ROM, and patient satisfaction, with other studies claiming an absence of differences. Only one study claims that therapeutic exercise alone is more effective for quality of life. Preliminary evidence seems to show that manual therapy does not seem to bring any benefit in addition to therapeutic exercise in mid- and long-term functionality, especially for hip osteoarthritis. Conclusions: There seems to be no difference in effectiveness between manual therapy combined with therapeutic exercise and therapeutic exercise alone in individuals with hip nonspecific musculoskeletal diseases. Full article

Objectives: To compare the effects of explosive and strength resistance training on neuromuscular and functional parameters in older adults and to analyze the relationship between changes in walking speed and improvements in plantar flexor (PF) neuromuscular parameters following interventions. Methods: In total, 40 participants were randomly assigned to either an explosive resistance training group (EXG, n = 18; age = 80.41 ± 10.12 years; body mass index = 22.89 ± 2.77 kg/m²) or a strength resistance training group (STG, n = 22; age = 82.89 ± 5.32 years; body mass index = 23.81 ± 3.45 kg/m²). Both groups participated in the same PF resistance training regimen (three sessions per week for 12 weeks), engaging in identical exercises. However, EXG performed three to five sets of 12 to 14 repetitions at 40% to 45% of one-maximal repetition with a rapid concentric phase and a 3 s eccentric phase, while the STG performed three to four sets of 6 to 7 repetitions at 80% to 85% of one-maximal repetition, with both phases lasting approximately 3 s. Before and after the interventions, gait speed (m/s) was assessed using a 10 m walking test, and relative maximal force (Relative Fmax, N/kg) was evaluated during maximal voluntary isometric contraction of PF. From the force–time curve, early (0–50 ms) and late (100–200 ms) rates of force development (RFD) were extracted from the linear slopes (Δ force/Δ time). Results: Gait speed significantly improved in both groups (p < 0.05). However, the improvement was more pronounced in the EXG compared to the STG (p < 0.05). Relative Fmax showed a more significant increase in the STG than in the EXG (p < 0.05). Moreover, a significant 10% increase in early RFD in the STG and a 20.1% increase in the EXG were observed (p < 0.05). The improvement in early RFD was greater in the EXG (p < 0.05). Additionally, late RFD improved significantly only in the EXG (+20.4%, p < 0.05). Conclusion: Explosive resistance training appears particularly effective in improving the ability to rapidly generate force, which is essential for many daily activities requiring explosive movements and quick responses. Full article

Objectives: The objective of this paper is to introduce a method to measure the force or pressure over the carpal tunnel indirectly, using a new device to drive the pointer of a computer system. The measurements were compared with those obtained using an ergonomic mouse. Simultaneously, measurements of muscular stress on the digitorum extensor muscle were performed to correlate the applied force against muscle activity. Methods: An experimental setup was constructed using an infrared static receiver plus two wearable moving light emitters, which can be displaced inside a rectangular projected region. The pointer functions are performed through two finger gestures, while the hand is naturally extended. A microcontroller was used to communicate with the computer, which works as a human interface device and possesses firmware to associate the position of each light source with the pointer functions. Meanwhile, force and electromyography sensing circuits were developed to transmit and measure carpal tunnel strength and muscular stress. The system was tested on five healthy volunteers, who were encouraged to solve the same computational tasks using this new device and a trademark ergonomic mouse. Results: Our results show great differences (greater than one magnitude) between the efforts of the same volunteers performing the same predefined tasks using both pointer controllers. Only when the new device was used did the Pearson’s correlation coefficients show a higher correlation between the effort measured on the carpal tunnel and the muscular activity. Conclusions: The optic pointer driver diminishes the strength on the carpal tunnel, causing slightly increased stress on the digitorum extensor muscle. Full article

Background: Viscosupplementation consists of intraarticular hyaluronic acid injections applied to treat pain and improve joint mobility. The objective of the study was to analyze the improvement of the range of mobility of the first metatarsophalangeal joint with a single dose of cross-linked hyaluronic acid. Methods: Ten fresh frozen specimens of feet sectioned below the knee were selected. Before and after the infiltration procedure, the range of flexion was calculated for all specimen’s metatarsophalangeal joints. To detect complications due to the procedure, five feet were dissected and five were sectioned with a diamond saw. Results: The range of the first metatarsophalangeal joint flexion differences between the preoperative and the postoperative period was as follows: (1) 47° (range, 37–51.5) to 58° (range, 49–69.5) degrees of loaded dorsiflexion (p > 0.006); (2) 41° (range, 40–51.5) to 58° (range, 52.5–66.5) degrees of unloaded dorsiflexion (p > 0.009); and (3) 14° (range, 10.5–24.25) to 16° (range, 14.25–28.5) degrees of unloaded plantarflexion (p > 0.083). No injuries of anatomical structures were observed either by anatomical dissection or in the anatomical sections. Conclusions: The results obtained in this viscosupplementation study demonstrate the improvement of the range of mobility of the first metatarsophalangeal joint without evidence of extravasation and lesions of the periarticular anatomical structures. Full article

Background and Objectives: This study investigates the effects of a five-week training program on the medial gastrocnemius muscle, comparing two approaches: blood flow restriction (BFR) training and normobaric hyperoxia (oxygen supplementation). It evaluates three strengthening modalities (dynamic, isometric, and the 3/7 method) analyzing their impact on maximal voluntary contraction (MVC), muscle architecture, and perceived exertion. Methods: A total of 36 young healthy participants (21 females, 15 males) were randomized into six subgroups (n = 6 each) based on the type of contraction and oxygen condition. Training sessions (three per week) were conducted for five weeks at 30% of MVC. Measurements of MVC, muscle circumference, pennation angle, fascicle length, and perceived exertion were taken at baseline (T0), mid-protocol (T1), and post-protocol (T2). Results: All groups demonstrated significant increases in MVC after five weeks, with no notable differences between BFR and oxygen conditions. Structural changes were observed in specific subgroups: the BFR-isometric group showed increased calf circumference (p < 0.05), and the 3/7 groups exhibited significant fascicle length gains (p < 0.05). Perceived exertion was consistently higher in BFR groups compared to oxygen supplementation, particularly in dynamic exercises. Conclusions: Both BFR and oxygen supplementation are effective in enhancing strength with light loads, though they elicit different structural and perceptual responses. Oxygen supplementation may be more comfortable and less strenuous, offering a viable alternative for populations unable to tolerate BFR. Future research should focus on optimizing training parameters and exploring applications tailored to specific athletic or clinical contexts. Full article

Background/Objectives: the purpose of this study was to determine the contributions of mechanical, neural, morphological, and muscle quality factors on individual differences in the maximal ankle dorsiflexion range of motion (ROM). Methods: A sample of 41 university students performed passive-dorsiflexion and morphological measurements. In the passive-dorsiflexion measurement, while the ankle was passively dorsiflexed, maximal dorsiflexion ROM was measured in addition to passive torque at a given angle and muscle–tendon junction (MTJ) displacement during the last 13° as mechanical factors, and stretch tolerance and muscle activation were measured as neural factors. In morphological measurements, the cross-sectional area, muscle thickness, muscle fascicle length, and pennation angle were measured. In addition, the echo intensity was evaluated as muscle quality. Subjects were divided into three groups (flexible, moderate, and tight) using the value of the maximal dorsiflexion ROM. Results: Maximal dorsiflexion ROM and stretch tolerance were greater in the flexible group than those in the moderate and tight groups. MTJ displacement was smaller in the flexible group than those in the moderate and tight groups. Stepwise multiple regression analysis revealed that stretch tolerance and passive torque at a given angle were selected as parameters to explain the maximal dorsiflexion ROM (adjusted R² = 0.83). Conclusions: these results indicate that individual differences in maximal ankle dorsiflexion ROM are primarily related to mechanical and neural factors. Full article

Background/Objectives: The aim of this study was to investigate the effects of a six-week integrated resisted sprint training (IRST) program on sprint performance and vertical jump height in a sample of U-14 male football players. This study also explored the potential benefits of incorporating variable resistive loads during pre-peak height velocity (pre-PHV) developmental stages, a period often overlooked in the training of young athletes. The IRST program alternated between heavy and light resistive sled loads to enhance sprint and jump capabilities, which are critical components of athletic performance in football. Methods: Nineteen healthy male football players (age: 13 ± 0.63 years) were divided into an experimental group (E, n = 10) and a control group (C, n = 9). The experimental group followed the IRST protocol, involving sled sprints with varying resistive loads (10–115% of the body mass) over specific distances, while the control group engaged in traditional unresisted sprint training. The sprint performance was assessed using 30 m sprint times, and the vertical jump height was measured using countermovement jump (CMJ) data collected via a force platform. Anthropometric measures and peak height velocity (aPHV) estimates were also recorded pre- and post-intervention. Results: The experimental group demonstrated significant improvements in 30 m sprint times (mean difference: −0.29 s; p < 0.01). Additionally, CMJ data revealed a positive trend in the take-off velocity and maximum concentric power, with an increase in jump height (mean difference: +0.44 cm). These results suggest enhanced sprint and explosive power capabilities following the IRST intervention. Conclusions: The findings suggest that the IRST program is an effective training method for enhancing sprint performance and maintaining jump capabilities in young football players. This approach highlights the importance of integrating variable resistance training in pre-PHV athletes to promote athletic development while ensuring safety and effectiveness. Full article

Background: Balance tasks are critical for performance in acrobatic gymnastics, where athletes often train and compete in mixed-age groups with varying maturational stages. To improve individualized training, in this cross-sectional study, the relationship was examined between strength capacity and balance task performance in female gymnasts at two maturational stages based on peak height velocity (PHV). Methods: Circa-PHV (n = 17, 11.92 ± 1.7 years) and post-PHV (n = 17, 16.47 ± 1.8 years) participants performed static balance tasks (standing on blocks, tandem stance, headstand) while center of pressure (CoP) excursion was recorded, and a proactive balance task (time to stabilization after landing, TTS). Strength assessments included isometric mid-thigh pull, handgrip, countermovement jump (CMJ), and push-up tests. Results: Correlational, regression, and inter-group analyses highlighted differences in strength–balance relationships across groups. Maximal isometric strength and CMJ power were the strongest predictors of static standing balance, with greater predictive strength in the circa-PHV group, underscoring the role of maturation in strength–balance interactions. The results also revealed that strength parameters influenced balance differently depending on the task, suggesting that specific balance types (static–proactive) and tasks (standing–inverted) require distinct strength capacities. Conclusions: Strength’s influence on balance varies by maturational stage, emphasizing the need for tailored training programs to enhance balance and optimize performance in young gymnasts. Full article

Blood flow restriction (BFR) is a popular resistance exercise technique purported to increase metabolic stress and augment training adaptations over time. However, short-term use may lead to acute neuromuscular fatigue and higher exertion ratings. Objective: The purpose of the current study was to examine acute physiological responses to low-load resistance exercise utilizing BFR compared to higher-load, non-BFR resistance exercise. Methods: Recreationally trained males (n = 6) and females (n = 7) (mean ± standard deviation, age: 20 ± 1 yrs.; height: 172 ± 8 cm; weight: 73 ± 11 kg; BMI: 24.4 ± 2.2 kg·m⁻²; training experience: 4 ± 2 yrs.) had limb occlusion pressure determined (50%; right leg: 118 ± 11 mmHg; left leg: 121 ± 13 mmHg) using an automated, self-inflating cuff system during baseline testing. In subsequent sessions, using a randomized, cross-over design, participants completed one of two experimental conditions: (1) Low-load + BFR and (2) High load + non-BFR. In both conditions, participants completed one set of back squats at either 30% (BFR) or 60% (non-BFR) of an estimated 1RM for a max of 30 repetitions, followed by three additional sets with the same loads and a target of 15 repetitions per set. Blood lactate and countermovement jump (CMJ) height were measured pre- and post-back squat. Ratings of perceived exertion (RPE) were assessed following each set. Results: When collapsed across all sets, participants completed significantly more total repetitions in the BFR condition compared to non-BFR (75.0 ± 0.0 vs. 68.23 ± 9.27 reps; p = 0.015; ES: 1.03), but a lower training load volume (2380 ± 728 vs. 4756 ± 1538 kg; p < 0.001; ES: 1.97). There was a significant time-by-condition interaction (p < 0.001), with a greater increase in blood lactate occurring from baseline to post-back squat in the non-BFR condition (11.61 mmol/L, 95%CI: 9.93, 13.28 mmol/L) compared to BFR (5.98 mmol/L, 95%CI: 4.30, 7.65 mmol/L). There was another significant time-by-condition interaction (p = 0.043), with a greater reduction in CMJ occurring in the non-BFR condition (−6.01, 95%CI: −9.14, −2.88 cm; p < 0.001) compared to BFR (−1.50, 95%CI: −1.50, 4.51 cm; p = 0.312). Conclusions: Utilizing a low-load BFR protocol may allow for a higher training volume, yet lower metabolic stress and reduce neuromuscular fatigue compared to lifting at a higher load without the use of BFR. Full article