The effect of types of sensory feedback on the acquisition and retention of squat performance: A randomized, double-blind, controlled trial.

Various sensory feedback methods are considered important for motor learning, but the effect of each sensory feedback method on effective squat learning still needs to be clarified. This study aimed to investigate the effect of sensory feedback types on the acquisition and retention of a squat. A double-blinded, randomized controlled trial was carried out. Thirty-healthy people were recruited and randomly assigned to the visual feedback group (VFG = 10), tactile feedback group (TFG = 10), and control group (CG = 10). VFG received visual feedback through video data of the participant performing squats, and TFG received tactile feedback through manual contact with a physical therapist. Both groups received feedback on the movements that needed correction after each set was completed. CG maintained rest without receiving any feedback. The retro-reflexive marker, force plate, and electromyography were used to measure body angle, foot center of pressure (COP), and muscle activity. All assessments were measured to confirm a squat acquisition. VFG and TFG showed significant differences in neutral knee position (NKP), trunk forward lean (TFL), anterior knee displacement (AKD), and anteroposterior (AP) foot COP (p < 0.050). In addition, the acquisition was retained until 3 days later for NKP and a week later for TFL, AKD, and AP foot COP in VFG (p < 0.050), while the acquisition was not retained in TFG (p > 0.050). There was no statistically significant change in CG (p > 0.050). This study demonstrated that visual feedback positively affects the acquisition and retention of squats. Therefore, we recommend the use of visual feedback for squat acquisition and retention in exercise novices.

Feasibility of vertical force-velocity profiles to monitor changes in muscle function following different fatigue protocols.

PURPOSE: This study aimed to explore the feasibility of vertical force-velocity (F-V) profiles to monitor changes in muscle function following different fatigue protocols. The between-day reliability of vertical F-V profiles and the acute effects of two fatigue protocols on the changes of lower limb muscle function were examined. METHODS: Twelve resistance trained males completed a preliminary session to determine their back squat one-repetition maximum (1RM). Afterwards, they randomly performed two experimental sessions that only differed in the fatigue protocol applied: heavy-load traditional (HLT; five repetitions at 80% 1RM) and light-load ballistic (LLB; five repetitions at 30% 1RM) squat protocols. Participants' vertical F-V profiles (maximum theoretical force [F0], maximum theoretical velocity [v0], and maximum power output [Pmax]) were calculated before and immediately after each fatigue protocol. RESULTS: F0, v0, and Pmax showed acceptable to good between-day reliability (coefficient of variation ≤ 4.4%; intraclass correlation coefficient ≥ 0.84). Both fatigue protocols promoted a comparable reduction in Pmax (-10.1% for HLT and -12.2% for LLB). However, the LLB squat protocol reduced more v0 (-9.7%) than F0 (-0.4%), while the HLT squat protocol reduced F0 (-8.4%) more than v0 (-4.1%). CONCLUSIONS: The vertical F-V profile can be used to monitor changes in muscle function given its acceptable between-day reliability and its high sensitivity to detect the acute effect of force-oriented and velocity-oriented fatigue protocols on specific maximal neuromuscular capacities.

Investigating the impact of external load on muscle synergies during bipedal squats.

PURPOSE: A broad functional movement repertoire is crucial for engaging in physical activity and reducing the risk of injury, both of which are central aspects of lifelong health. As a fundamental exercise in both recreational and rehabilitative training regimes, the bipedal squat (SQBp) incorporates many everyday movement patterns. Crucially, SQBp can only be considered functional if the practitioner can meet the coordinative demands. Many factors affect coordinative aspects of an exercise, most notably external load. Since compound movements are assumed to be organized in a synergistic manner, we employed muscle synergy analysis to examine differences in muscle synergy properties between various external load levels during SQBp. METHODS: Ten healthy male recreational athletes were enrolled in the present study. Each participant performed three sets of ten SQBp on a smith machine at three submaximal load levels (50%, 62.5%, and 75% of 3 repetition maximum) across three non-consecutive days. Muscle activity was recorded from 12 prime movers of SQBp by way of electromyography (EMG). Muscle synergies were analyzed in terms of temporal activation patterns, i.e., waveform, as well as the relative input of each muscle into individual synergies, i.e., weight contribution. RESULTS: Waveforms of muscle synergies did not differ between loads. Weight contributions showed significant differences between load levels, albeit only for the gastrocnemius muscle in a single synergy. CONCLUSION: Taken together, our results imply mostly stable spatiotemporal composition of muscle activity during SQBp, underlining the importance of technical competence during compound movement performance in athletic and rehabilitative settings.

Smith machine squats pose high risk to ACL graft integrity after the ACL reconstruction and conventional squats are a safer alternative.

PURPOSE: The purpose of this study was to evaluate the impact of squats after the anterior cruciate ligament (ACL) reconstruction on the ACL graft, considering new data on biomechanics, posterior tibial slope (PTS) and anterolateral ligament (ALL). METHODS: Utilising finite element analysis on the new 14-component knee joint model, we have evaluated stresses on the knee elements separately for the knee with a native double-bundle ACL and with a single-bundle ACL graft for the 5° and 14° PTS variants during both conventional and Smith machine horizontal squats. RESULTS: Replacing a native ACL with a single-bundle graft causes an overstrain on the graft compared to the intact ACL under all conditions. Stresses on the ACL, ACL graft and ALL are much higher during the Smith machine squats compared to the conventional ones. The stress on the menisci is 3.6-4.9 times higher with conventional squats. PTS at the squats' lowest point minimally affects ACL stress but impacts menisci. CONCLUSIONS: The single-bundle ACL reconstruction (ACLR) does not reproduce the biomechanics of the native ACL and increases stresses in most knee joint elements, according to the current study. Conventional squats are relatively safe for the ACL graft at their lowest point. Passing the half-squat position is the most dangerous point. Smith machine horizontal squats produce stress on the ACL graft several times higher than its estimated breaking load and dangerous stress levels on the ALL. During the rehabilitation following ACLR, it is advisable to prioritise the conventional squats over Smith machine squats until ligamentisation is complete. LEVEL OF EVIDENCE: Level III.

Modern software and physical education: can online training enhance gym training?

BACKGROUND: This study discusses the effectiveness of a 12-week intervention aimed at improving squat jump and sprint performance among second-year sports students. METHODS: The students were randomly divided into experimental (n = 89) and control (n = 92) groups. In addition to gym training, students of the experimental group also underwent online PE training. The students' performance in Squat Jumps, 30 m sprint, and Progressive Aerobic Cardiovascular Endurance Run (PACER), as well as their situational motivation, were assessed before and after the intervention. Furthermore, the students assessed their physical activity weekly using self-reports. RESULTS: The implementation of online training has positively impacted intrinsic and identified motivation, as well as external regulation; however, it was less effective in reducing amotivation compared to traditional gym-based training. CONCLUSIONS: The findings of the study contribute to the data synthesis on the expediency of using modern software in physical education.

Does Overhead Squat Performance Affect the Swing Kinematics and Lumbar Spine Loads during the Golf Downswing?

The performance of the overhead squat may affect the golf swing mechanics associated with golf-related low back pain. This study investigates the difference in lumbar kinematics and joint loads during the golf downswing between golfers with different overhead squat abilities. Based on the performance of the overhead squat test, 21 golfers aged 18 to 30 years were divided into the highest-scoring group (HS, N = 10, 1.61 ± 0.05 cm, and 68.06 ± 13.67 kg) and lowest-scoring group (LS, N = 11, 1.68 ± 0.10 cm, and 75.00 ± 14.37 kg). For data collection, a motion analysis system, two force plates, and TrackMan were used. OpenSim 4.3 software was used to simulate the joint loads for each lumbar joint. An independent t-test was used for statistical analysis. Compared to golfers demonstrating limitations in the overhead squat test, golfers with better performance in the overhead squat test demonstrated significantly greater angular extension displacement on the sagittal plane, smaller lumbar extension angular velocity, and smaller L4-S1 joint shear force. Consequently, the overhead squat test is a useful index to reflect lumbar kinematics and joint loading patterns during the downswing and provides a good training guide reference for reducing the risk of a golf-related lower back injury.

Analysis of Local Track Discontinuities and Defects in Railway Switches Based on Track-Side Accelerations.

Switches are an essential, safety-critical part of the railway infrastructure. Compared to open tracks, their complex geometry leads to increased dynamic loading on the track superstructure from passing trains, resulting in high maintenance costs. To increase efficiency, condition monitoring methods specific to railway switches are required. A common approach to track superstructure monitoring is to measure the acceleration caused by vehicle track interaction. Local interruptions in the wheel-rail contact, caused for example by local defects or track discontinuities, appear in the data as transient impact events. In this paper, such transient events are investigated in an experimental setup of a railway switch with track-side acceleration sensors, using frequency and waveform analysis. The aim is to understand if and how the origins of these impact events can be distinguished in the data of this experiment, and what the implications for condition monitoring of local track discontinuities and defects with wayside acceleration sensors are in practice. For the same experimental configuration, individual impact events are shown to be reproducible in waveform and frequency content. Nevertheless, with this track-side sensor setup, the different types of track discontinuities and defects (squats, joints, crossing) could not be clearly distinguished using characteristic frequencies or waveforms. Other factors, such as the location of impact event origin relative to the sensor, are shown to have a much stronger influence. The experimental data suggest that filtering the data to narrow frequency bands around certain natural track frequencies could be beneficial for impact event detection in practice, but differentiating between individual impact event origins requires broadband signals. A multi-sensor setup with time-synchronized acceleration sensors distributed over the switch is recommended.

Road to Paris 2024: force-velocity profile in different speed climbers' abilities.

Speed climbing will be a new discipline in Paris 2024. The physical requirements of speed climbing are different from the other climbing modalities due to the short event time requiring higher level of strength and power. These parameters have been measured through the Force-Velocity (F-V) profile in different climbing disciplines. However, there are no known results evaluating different speed climbing abilities to establish whether F-V relationship is a determining factor between performance levels. The purpose of this study was to evaluate the upper and lower limbs F-V profile in different speed climbing abilities considering sex. Twenty-six speed climbers were divided into two groups based on their level of performance: international level (men n = 7 and women n = 2) and national level (men n = 8 and women n = 7). Participants performed pull-ups and squat incremental tests and F-V profile variables [Maximum theorical values of force (F0), velocity (V0) and power (Pmax)], one-repetition maximum value (1RM) and %1RM where peak power was expressed were collected using a linear encoder. There were significant differences in F0, relative force, %1RM where peak power was expressed, and 1RM in pull-ups (p < 0.05) between groups. However, there were not significant differences between groups in squat variables. No significant sex differences were found in any variable. There were moderate-strong correlations between running time and 1RM (pull-ups and squat), F0 and FV-slope (pull-ups) (p < 0.05) analyzed in the whole group. In conclusion, F0 and 1RM in pull-ups were significantly higher in international climbers. Therefore, national climbers should focus their training on improving force by training with heavy loads. Additionally, squat F-V profile variables do not seem to be as important as in the pull-up for performance.

Effect of isolated and combined ingestion of caffeine and citrulline malate on resistance exercise and jumping performance: a randomized double-blind placebo-controlled crossover study.

PURPOSE: The aim of this study was to explore the isolated and combined effects of caffeine and citrulline malate (CitMal) on jumping performance, muscular strength, muscular endurance, and pain perception in resistance-trained participants. METHODS: Using a randomized and double-blind study design, 35 resistance-trained males (n = 18) and females (n = 17) completed four testing sessions following the ingestion of isolated caffeine (5 mg/kg), isolated CitMal (12 g), combined doses of caffeine and CitMal, and placebo. Supplements were ingested 60 min before performing a countermovement jump (CMJ) test (outcomes included jump height, rate of force development, peak force, and peak power), one-repetition maximum (1RM) squat and bench press, and repetitions to muscular failure in the squat and bench press with 60% of 1RM. Pain perception was evaluated following the repetitions to failure tests. The study was registered at ISRCTN (registration number: ISRCTN11694009). RESULTS: Compared to the placebo condition, isolated caffeine ingestion and co-ingestion of caffeine and CitMal significantly enhanced strength in 1RM bench press (Cohen's d: 0.05-0.06; 2.5-2.7%), muscular endurance in the squat (d: 0.46-0.58; 18.6-18.7%) and bench press (d: 0.48-0.64; 9.3-9.5%). However, there was no significant difference between isolated caffeine ingestion and caffeine co-ingested with CitMal, and isolated CitMal supplementation did not have an ergogenic effect in any outcome. No main effect of condition was found in the analysis for CMJ-derived variables, 1RM squat and pain perception. CONCLUSION: Caffeine ingestion appears to be ergogenic for muscular strength and muscular endurance, while adding CitMal does not seem to further enhance these effects.

Effects of resistance exercise alone or with caffeine on hemodynamics, autonomic modulation and arterial stiffness in resistance-trained women.

AIM: Both an acute bout of resistance exercise (RE) and caffeine consumption can significantly alter hemodynamics, autonomic modulation, and arterial stiffness, which may correlate with adverse cardiovascular events. However, effects of an acute bout of RE and caffeine are unclear in resistance-trained women. PURPOSE: The purpose of this study was to compare the effects of an acute bout of RE with repetitions to failure on squat and bench press, with or without caffeine, on performance, resting and recovery measures of hemodynamics, autonomic modulation, as well as arterial stiffness in resistance-trained women. METHODS: Eleven women participated in a double-blind, placebo controlled cross-over design in which they consumed caffeine (4 mg/kg) or placebo at least 72 h apart. Sixty minutes following ingestion, participants performed two sets of 10 repetitions followed by a third set to failure on squat and bench press. Hemodynamics, autonomic modulation, and arterial stiffness were measured at rest, 60 min post-ingestion, and three minutes and 10 min following RE. RESULTS: Data demonstrated caffeine has no additive effects on performance, hemodynamics, autonomic modulation, or arterial stiffness (p > 0.05) before or following an acute bout of RE in resistance-trained women compared to a placebo. CONCLUSIONS: Resistance-trained women may not observe any alteration to RE performance on the squat and bench press in terms of repetitions to failure following caffeine ingestion. In addition, the data from the present study suggests that there may also not be any further negative effects on the cardiovasculature if caffeine is consumed prior to the RE bout.

Forward step down test - clinical rating is correlated with joint angles of the pelvis and hip: an observational study.

BACKGROUND: Clinical methods for assessing quality of movement and functional tests are important to clinicians. Typical deviations from normal kinematics during the clinical test of Forward Step Down Test (FSDT) are pelvic tilt and hip adduction which are associated with the risk of knee pain. OBJECTIVES: (1) to examine the correlation between clinical assessment of the FSDT and joint angle measurements of pelvis, hip, knee and ankle joints in males and females; (2) to examine the differences in joint angles between individuals rated as good, fair or poor in a FSDT performance test. METHODS: Ninety-two healthy individuals performing FSDT were video-taped with two-dimensional digital video cameras. The clinical assessment of the FSDT was rated by two experienced physical therapists as good, fair, or poor based on a Crossley et al. (2011) validated scale. Measurements of pelvic drop, hip adduction and knee valgus were taken using Image J software. RESULTS: Out of 177 lower limbs, 74 (37 in each limb) were clinically rated as "good/fair" (41.80%) while 103 (52 in the dominant leg and 51 in the non-dominant leg) were rated as "poor" (58.19%). No significant differences were observed between dominant and non-dominant legs or between males and females in clinical rating of the FSDT. Pelvic drop angle was significantly higher and hip adduction angle was significantly lower for "poor" clinical rating compared to "good/fair" in both dominant and non-dominant legs (p < 0.001) in males and females. Females demonstrated higher pelvic drop, lower hip adduction and higher knee valgus angles compared with males (p < 0.05). CONCLUSIONS: This study showed that the clinical rating of FSDT is correlated with joint angle measurements suggesting that this assessment can be utilized in clinical practice. Individuals with poor quality performance of FSDT showed higher pelvic drop and hip adduction movement. Further studies examining different populations with diverse disorders or pathologies are essential.

Ergogenic Effects of Very Low to Moderate Doses of Caffeine on Vertical Jump Performance.

Although the ergogenic effects of 3-6 mg/kg caffeine are widely accepted, the efficacy of low doses of caffeine has been discussed. However, it is unclear whether the ergogenic effects of caffeine on jump performance are dose responsive in a wide range of doses. This study aimed to examine the effect of very low (1 mg/kg) to moderate doses of caffeine, including commonly utilized ergogenic doses (i.e., 3 and 6 mg/kg), on vertical jump performance. A total of 32 well-trained collegiate sprinters and jumpers performed countermovement jumps and squat jumps three times each in a double-blind, counterbalanced, randomized, crossover design. Participants ingested a placebo or 1, 3, or 6 mg/kg caffeine 60 min before jumping. Compared with the placebo, 6 mg/kg caffeine significantly enhanced countermovement jump (p < .001) and squat jump (p = .012) heights; furthermore, 1 and 3 mg/kg of caffeine also significantly increased countermovement jump height (1 mg/kg: p = .002, 3 mg/kg: p < .001) but not squat jump height (1 mg/kg: p = .436, 3 mg/kg: p = .054). There were no significant differences among all caffeine doses in both jumps (all p > .05). In conclusion, even at a dose as low as 1 mg/kg, caffeine improved vertical jump performance in a dose-independent manner. This study provides new insight into the applicability and feasibility of 1 mg/kg caffeine as a safe and effective ergogenic strategy for jump performance.

Smartphone Technology to Remotely Measure Postural Sway during Double- and Single-Leg Squats in Adults with Femoroacetabular Impingement and Those with No Hip Pain.

BACKGROUND: The COVID-19 pandemic has accelerated the demand for utilising telehealth as a major mode of healthcare delivery, with increasing interest in the use of tele-platforms for remote patient assessment. In this context, the use of smartphone technology to measure squat performance in people with and without femoroacetabular impingement (FAI) syndrome has not been reported yet. We developed a novel smartphone application, the TelePhysio app, which allows the clinician to remotely connect to the patient's device and measure their squat performance in real time using the smartphone inertial sensors. The aim of this study was to investigate the association and test-retest reliability of the TelePhysio app in measuring postural sway performance during a double-leg (DLS) and single-leg (SLS) squat task. In addition, the study investigated the ability of TelePhysio to detect differences in DLS and SLS performance between people with FAI and without hip pain. METHODS: A total of 30 healthy (nfemales = 12) young adults and 10 adults (nfemales = 2) with diagnosed FAI syndrome participated in the study. Healthy participants performed DLS and SLS on force plates in our laboratory, and remotely in their homes using the TelePhysio smartphone application. Sway measurements were compared using the centre of pressure (CoP) and smartphone inertial sensor data. A total of 10 participants with FAI (nfemales = 2) performed the squat assessments remotely. Four sway measurements in each axis (x, y, and z) were computed from the TelePhysio inertial sensors: (1) average acceleration magnitude from the mean (aam), (2) root-mean-square acceleration (rms), (3) range acceleration (r), and (4) approximate entropy (apen), with lower values indicating that the movement is more regular, repetitive, and predictable. Differences in TelePhysio squat sway data were compared between DLS and SLS, and between healthy and FAI adults, using analysis of variance with significance set at 0.05. RESULTS: The TelePhysio aam measurements on the x- and y-axes had significant large correlations with the CoP measurements (r = 0.56 and r = 0.71, respectively). The TelePhysio aam measurements demonstrated moderate to substantial between-session reliability values of 0.73 (95% CI 0.62-0.81), 0.85 (95% CI 0.79-0.91), and 0.73 (95% CI 0.62-0.82) for aamx, aamy, and aamz, respectively. The DLS of the FAI participants showed significantly lower aam and apen values in the medio-lateral direction compared to the healthy DLS, healthy SLS, and FAI SLS groups (aam = 0.13, 0.19, 0.29, and 0.29, respectively; and apen = 0.33, 0.45, 0.52, and 0.48, respectively). In the anterior-posterior direction, healthy DLS showed significantly greater aam values compared to the healthy SLS, FAI DLS, and FAI SLS groups (1.26, 0.61, 0.68, and 0.35, respectively). CONCLUSIONS: The TelePhysio app is a valid and reliable method of measuring postural control during DLS and SLS tasks. The application is capable of distinguishing performance levels between DLS and SLS tasks, and between healthy and FAI young adults. The DLS task is sufficient to distinguish the level of performance between healthy and FAI adults. This study validates the use of smartphone technology as a tele-assessment clinical tool for remote squat assessment.

Intrarater and Interrater Reliability and Agreement of a Method to Quantify Lower-Extremity Kinematics Using Remote Data Collection.

CONTEXT: To assess the reliability of a remote 2D markerless motion tracking method (Kinovea) to quantify knee and hip angles during dynamic tasks. METHODS: Fourteen healthy adults performed body weight squats and lateral lunges while video recording themselves at home. Knee and hip angles were quantified in the sagittal plane for the squats and in the frontal plane for the lateral lunges. Two students each performed the video analysis procedure twice, 2 weeks apart. Intraclass correlation coefficients were used to calculate the intrarater and interrater reliability for angles at maximum depth. The intrarater and interrater agreement over the joint angle-time signals were quantified using a validation metric; an acceptable agreement threshold was set at a validation metric of 0.803 or higher. Standard error of measurement (SEM) was also calculated. RESULTS: Reliability was good to excellent (intraclass correlation coefficients = .80-.98) for all angle comparisons at maximum depth. The agreement over the entire joint angle-time signal was acceptable for all squat variables except for the interrater hip angle comparison (validation metric = 0.797). None of the lateral lunge variables met the threshold of acceptable agreement. The mean SEM across participants for all joint angle-time signal and for maximum depth was acceptable (<5°) for all measurements (SEM = 1.2°-4.9°). CONCLUSIONS: Overall, the reliability, agreement, and SEM quantified in this study support the integration of remote methods to quantify lower-extremity kinematics into research and clinical practice.

Quadriceps Function and Athletic Performance in Highly Trained Female Athletes.

CONTEXT: Quadriceps strength is considered a key contributor to performance in various athletic tasks. Yet, past research has reported conflicting results based on population, with little data available in highly trained female athletes. DESIGN: Cross-sectional. METHOD: To examine how athletic performance relates to quadriceps strength and neural function, we measured the quadriceps maximum voluntary isometric contraction force (MVIC) and rate of force development over 0 to 50 ms (rate of force development [RFD]0-50ms), and various performance measures in 34 highly trained female athletes. RESULTS: Stepwise multiple regression analysis revealed that the quadriceps variables explained 16 of 21 performance variables (R2 = .08-.36, P ≤ .10). Squat performance related to RFD0-50ms alone (R2 = .17-.20, P < .05; ßRFD = 0.41 to 0.45, P < .05) but only MVIC explained the variance in sprinting and vertical jump performance (R2 = .08-.34, P ≤ .10; ßMVIC = -0.51 to 0.58, P ≤ .10). The broad jump model included both parameters and their interaction (R2 = .20, P = .08; ßRFD = 0.06, P = .76; ßMVIC = -0.39, P = .03; ßRFD×MVIC = -0.24, P = .10). CONCLUSION: The contribution of the quadriceps MVIC or RFD0-50ms varies in size and nature depending on the task or leg dominance. While quadriceps are significant contributors to performance, because our models leave most of the variance in performance unexplained, rehabilitation and performance professionals should refrain from interpreting peak athletic performance as a reflection of knee-extensors function in highly trained female athletes.

Single-Leg Squat Test in the Clinical Setting Does Not Discriminate Patients With Femoroacetabular Impingement Syndrome From Asymptomatic Individuals.

CONTEXT: Laboratorial 3-dimensional kinematic analyses have shown changes in the single-leg squat's (SLS) pattern of patients with femoroacetabular impingement syndrome (FAIS). However, it is unknown whether clinicians are able to detect these changes using 2-dimensional kinematics. OBJECTIVE: To compare the frontal plane 2-dimensional kinematics of patients with FAIS and asymptomatic individuals in the SLS test performed in a clinical setting. DESIGN: Case-control study. SETTING: Physical therapy clinic. PARTICIPANTS: Twenty men with bilateral FAIS and 20 asymptomatic men. MAIN OUTCOME MEASURES: Two-dimensional kinematic analysis was collected in the frontal plane during the execution of the SLS test. The outcomes were squat depth, pelvic drop (pelvis angle relative to the horizontal plane), hip adduction (femur angle relative to the pelvis), and knee valgus (femur angle relative to the tibia). RESULTS: Most and least painful limbs of patients with FAIS had squat depth (9.8% [2.9%] and 9.5% [3.1%] of height), pelvic drop (4.2° [3.9°] and 3.7° [4.2°]), hip adduction (74.9° [5.8°] and 75.9° [5.7°]), and knee valgus (4.0° [11.0°] and 5.0° [9.9°]) similar to asymptomatic individuals (9.0% [2.3%], 4.8° [2.6°], 73.7° [4.9°], and -1.7° [8.5°]; P > .05 for all). CONCLUSION: The frontal plane 2-dimensional kinematic analysis of the SLS test in the clinical setting is not able to distinguish patients with FAIS from asymptomatic individuals.

Weight-Bearing Exercises on Slideboard Increase Quadriceps and Hamstring Activation Levels and Improve Hip- and Knee-Flexion Angles in Physically Active Individuals.

CONTEXT: Slideboards are commonly used in exercise programs, but there is limited information about how they affect muscle activities during exercise. We aim to compare the activation levels of quadriceps and hamstring muscles and hip- and knee-flexion angles during lunge and single-leg squat exercises between normal ground and slideboard in physically active individuals. DESIGN: Cross-sectional study. METHODS: Thirty healthy individuals (age: 23.83 [2.84] y, body mass index: 21.75 [1.72] kg/m2) were included in the study. Surface electromyography was used to measure vastus medialis, vastus lateralis, biceps femoris, and semitendinosus activation levels during reaching and returning phases of the forward, lateral, and back lunges and squats that were performed on the normal ground and slideboard. Exercises were performed at a slow pace (60 beats/min). Hip- and knee-flexion angles during the exercises were evaluated by using 2-dimensional motion analysis. Repeated measures of analysis of variance were used for statistical analysis. RESULTS: Vastus medialis and vastus lateralis activation levels were greater during reaching and returning phases of the exercises on slideboard compared with normal ground (P < .05). However, semitendinosus and biceps femoris activity were greater only during the returning phase of the forward lunge (P < .001) and the returning phase of the back squat (P = .002, P = .009, respectively). Hip-to-knee flexion ratios were closer to 1 when the forward lunge (P < .001), back lunge (P = .004), and forward squat (P = .001) exercises were performed on a slideboard. CONCLUSION: In exercise programs that target the quadriceps and hamstring muscles, slideboards can be effectively used in exercise progressions as they can increase muscle activity. Moreover, squat and lunge exercises on slideboard with a slow pace may also be helpful for improving the balance between hip- and knee-flexion angles.

Eccentric overload differences between loads and training variables on flywheel training.

There is considerable debate about the existence of a real eccentric overload in flywheel exercises. This study aimed to analyse the differences in concentric: eccentric mechanical output ratios between different loads and variables in the flywheel squat exercise. Twenty physically active men (22.9 ± 2.2 years, height: 1.8 ± 0.1 m, weight: 79.6 ± 8.2 kg) performed a loading test using five moments of inertia. Angular speed was measured using a rotary encoder, while the vertical force was measured using force plates. For each variable (angular speed, angular acceleration, power, vertical force, and torque), mean and peak values were calculated for concentric and eccentric phases to allow comparisons across the loads. We tested the possible differences in Load × Phase (concentric and eccentric) and Load × Variable. The level of significance was established as p < 0.05. A significant Load × Phase interaction was found in mean angular speed, peak vertical force, peak angular acceleration, peak power and peak torque. Higher eccentric overload values were observed with speed-derived variables (angular speed, angular acceleration and power). In conclusion, speed-derived peak variables and lower loads are more likely to show an eccentric overload and can be used to monitor responses to flywheel training.

Optimal velocity loss threshold for inducing post activation potentiation in track and field athletes.

The aim of this study was to determine the optimal velocity loss (VL) threshold that maximises the post activation potentiation (PAP) stimulus for achieving larger and more consistent performance gains in track and field athletes. Twenty-two athletes from athletics participated in four back squat PAP tests with four different VL threshold (5%, 10%, 15% and 20% VL) at an intensity of 85%1RM. Countermovement jump (CMJ) height, power, and momentum were assessed before, and 10 s, 4, 8, 12, 16 minutes after the PAP condition. Repetitions of the squat in all the PAP conditions were also recorded. Only the 5% VL condition produced significant improvements in height (ES = 0.73, P = 0.038), peak power output (ES = 0.73, P = 0.038) and momentum (ES = 0.72, P = 0.041) of CMJ, and these changes appeared 8 minutes after the condition. The total number of repetitions during the 5% VL condition was significantly lower than that observed in the 15% (P = 0.003) and 20% VL (P < 0.001) trials. The results from this study indicate that 5%VL during the 2 sets preconditioning squat at 85%1RM was optimal for eliciting PAP in a CMJ exercise, and resulted in significant increases at the 8-min recovery period. The same squat condition also had the least number of repetitions. However, considering the efficiency in practice, athletes can also choose the rest time of 4-min, which can also achieve similar results.

Relationship between vertical jump tests and ice skating performance in junior Polish ice hockey players.

The aim of this study was to determine the relationships between vertical jumps (VJ) and various on-ice skating performances of junior ice hockey players (n = 19). The three modes of VJ or off-ice measures were countermovement jump with arm swing (CMJ), squat jump (SJ) and depth drop jump (DDJ). The on-ice skating performance was measured by the skating multistage aerobic test (SMAT), forward and backward acceleration test, top speed test, and repeated sprint ability (RSA) test. The relationships between the variables were quantified using Pearson's product-moment correlation. DDJ showed a significant positive correlation with forward average skating speed (FASS) (r = 0.62) and strong correlations with backward average skating speed (BASS) (r = 0.81), and maximum skating speed (MSS) (r = 0.71). SJ was found to be strongly correlated with BASS (r = 0.82) and MSS (r = 0.76), whereas the only on-ice performance that significantly correlated with CMJ was BASS (r = 0.68). All three modes of VJ were inversely and non-significantly correlated with performance decrement index and fatigue index, as determined by the RSA test. SMAT was not significantly correlated with either VJ or RSA. Correlations between all three modes of VJ tests were significant. Therefore, this study concludes that: (1) DDJ can be used as a predictor of all the ice skating speed tests, whereas SJ can predict BASS and MSS. CMJ, on the other hand, can predict the performance of only BASS. (2) RSA performance cannot be predicted from CMJ, SJ, or DDJ tests, and (3) neither any of the VJ nor RSA can predict skating endurance of junior ice hockey players.