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This study aimed to examine the effects of incorporating 10-week elastic band strength training (EBST) program on change of direction, jumping ability, repeated sprint ability, and both muscular strength and power in adolescent female handball players. Participants aged 15.8 ± 0.2 years were divided by playing position, and players from each position were then randomly assigned between the elastic strength (n = 17) and control (n = 17) groups. The experimental group performed periodized upper and lower-body elastic band strength training twice weekly for ten weeks by substitution of some of their regular physical and game preparation. The control group only performed regular handball training. Two-way analyses of variance (group × time) assessed change of direction (COD) via the modified t-agility test, squat jump, countermovement jump, standing long jump, repeated sprint ability (RSA), 1-RM bench press and half squat, and cycle ergometer force-velocity tests for both upper and lower limbs. Relative to the control group, the experimental group enhanced COD performance [p < 0.001; Cohen's effect size (d) = 1.00]; squat and countermovement jump (p = 0.002, d ≥ 0.83), best, mean, and total RSA scores (all p < 0.001, d = 0.92-1.66), 1-RM bench press (p = 0.02, d = 0.59) and half squat (p = 0.009, d = 0.67), all indices of upper limb force-velocity performance (p ≤ 0.025, d = 0.56-1.66), and 3 of 4 indices of lower limb force-velocity performance (p ≤ 0.004, d = 0.75-0.92). We conclude that additional elastic band training performed twice a week for ten weeks improves measures relevant to handball game performance in adolescent female athletes.

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The purpose of this study was to investigate the effects of 6-week betaine supplementation during a preparatory period of collegiate athletes on muscular power and strength. Sixteen male collegiate athletes received 5 g/day of betaine (betaine group, n = 9) or carboxymethyl cellulose (placebo group, n = 7) for 6 weeks. All participants engaged in their regular training during the experimental period. The overhead medicine-ball throw (OMBT), countermovement jump, and maximal strength (one repetition maximum, 1-RM) on the bench press, overhead press, half squat, and sumo dead lift by the participants were assessed before and after betaine supplementation. Blood lipids were also analyzed before and after betaine supplementation. After supplementation, there were no significant differences between betaine and placebo groups on any variables. Compared to presupplementation, the performance of OMBT and 1-RM of overhead press and half squat in the betaine group had significantly improved (p < 0.05). By contrast, no significant differences were observed in the placebo group before and after supplementation. Blood analysis revealed no negative effect on blood lipid profiles. Betaine seems to be a useful nutritional strategy to improve and maintain performance during 6-week preparatory periods in collegiate athletes.

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RESUMEN El perfeccionamiento de la técnica deportiva tiene como premisa comparar los valores del movimiento motriz, esta debe ser caracterizada para corregir errores detectados como parte del proceso de dirección del entrenamiento deportivo. Se pone énfasis en los deportes eminentemente técnicos, como es el caso del entrenamiento del fisiculturismo. En tal sentido, la presente investigación tuvo como objetivo analizar la técnica de la media sentadilla en fisiculturistas profesionales y amateurs como método empírico (medición específica del deporte). La investigación es descriptiva-explicativa de orden correlacional. Se correlacionan seis variables de interés (X1: ángulo de la articulación del hombro; X2: ángulo de la articulación de la cadera; X3: Velocidad máxima alcanzada; X4: aceleración máxima alcanzada; X5: centro de gravedad en X; X6: centro de gravedad en Y). Las medias establecen diferencias entre grupos independientes, tanto en la variable X1 (Grupo 1: ≈66°; grupo 2: H"70°; p=0.247), la X2 (grupo 1: ≈73°; grupo 2: ≈86°; p=0.002), La X3 (grupo 1:≈1.03m/s; grupo 2: ≈1.36m/s; p=0.017), la X4 (grupo 1: ≈2.93m/s2; grupo 2: ≈4.78m/s2; p=0.011), la X5 (grupo 1: ≈0.43m; grupo 2: ≈0.65m; p=0.000), y la X6 (grupo 1: ≈0.61m; grupo 2: ≈0.83m; p=0.000). El grupo 1 posee una técnica más efectiva, mientras que los amateurs poseen menor eficiencia en el movimiento biomecánico dada su inexperiencia, se muestran valores altos en velocidad y aceleración, se incluyen ángulos de movimiento como el de cadera.

RESUMO A melhoria da técnica desportiva baseia-se na premissa de comparar os valores do movimento motor, que deve ser caracterizada a fim de corrigir erros detectados como parte do processo de gestão do treino desportivo. A tónica é colocada no desporto eminentemente técnico, como é o caso do treino de musculação. Neste sentido, o objectivo desta investigação era analisar a técnica de meio agachamento em musculturistas profissionais e iniciantes como um método empírico (medição específica do desporto). A investigação é descritiva-explicativa da ordem correlativa. Seis variáveis de interesse estão correlacionadas (X1: ângulo da articulação do ombro; X2: ângulo da articulação da anca; X3: velocidade máxima alcançada; X4: aceleração máxima alcançada; X5: centro de gravidade em X; X6: centro de gravidade em Y). Os meios estabelecem diferenças entre grupos independentes, tanto na variável X1 (Grupo 1: ≈66°; grupo 2: ≈70°; p=0,247), a X2 (grupo 1: ≈73°; grupo 2: ≈86°; p=0,002), a X3 (grupo 1: ≈1. 03m/s; grupo 2: ≈1.36m/s; p=0.017), o X4 (grupo 1: ≈2.93m/s2; grupo 2: ≈4.78m/s2; p=0.011), o X5 (grupo 1: ≈0.43m; grupo 2: ≈0.65m; p=0.000), e o X6 (grupo 1: ≈0.61m; grupo 2: ≈0.83m; p=0.000). O grupo 1 tem uma técnica mais eficaz, enquanto os iniciantes têm uma eficiência de movimento biomecânico mais baixa devido à sua inexperiência, eles mostram menos eficiência no movimento biomecânico. Dada a sua inexperiência, são mostrados valores elevados em velocidade e aceleração, e são incluídos ângulos de movimento como o ângulo da anca.

ABSTRACT The improvement of the sports technique is premised on comparing the values of the motor movement, this must be characterized to correct errors detected as part of the sports training management process. Emphasis is placed on highly technical sports, such as bodybuilding training. In this sense, the present research aimed to analyze the half-squat technique in professional and amateur bodybuilders as an empirical method (sport-specific measurement). The research is descriptive-explanatory of correlational order. Six variables of interest are correlated (X1: shoulder joint angle; X2: hip joint angle; X3: maximum speed reached; X4: maximum acceleration reached; X5: center of gravity in X; X6: center of gravity in Y). The means establish differences between independent groups, both in variable X1 (group 1: ≈66°; group 2: ≈70°; p=0.247 ), X2 (group 1: ≈73°; group 2: ≈86°; p=0.002 ), X3 (group 1: ≈1.03m/s; group 2:≈1.36m/s; p=0.017 ), X4 (group 1: ≈2.93m/s2; group 2: ≈4.78m/s2; p=0.011 ), X5 (group 1: ≈0.43m; group 2:≈0.65m; p=0.000 ), and X6 (group 1: ≈0.61m; group 2: ≈0.83m; p =0.000 ). Group 1 has a more effective technique, while the amateurs have less efficiency in biomechanical movement due to their inexperience, high values are shown in speed and acceleration, movement angles such as hip angles are included.

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Half-squat parachuting landing is a kind of activity with high impact force. Injuries on lower-extremity joints are common in half-squat parachuting landing and would be increased with a backpack. An ankle brace was used to prevent ankle injuries in landing. However, few quantitative studies reported about the protection of an ankle brace for lower-extremity joints in half-squat parachuting landing with a backpack. This study focused on evaluating the protective effects of an ankle brace in half-squat parachuting landing with a backpack. Seven male participants landed from 120 cm with a backpack and an ankle brace. Each participant performed three landing trials on every experimental condition. Kinetics and kinematics of the hip, knee, and ankle were analyzed. It was found that the ankle brace did not significantly affect the ground reaction force with backpack but increased the ground reaction force from 14.7 ± 2.0 bodyweight to 16.2 ± 1.9 bodyweight (p = 0.017) without the backpack. The ankle brace significantly (p < 0.05) decreased the angular displacement, angular velocity, and angular acceleration of the ankle both without and with the backpack. In conclusion, the ankle brace could restrict ankle motion and significantly increase ground reaction force without the backpack. However, the ankle brace did not significantly influence ground reaction force and still restricted ankle motion with the backpack. Therefore, the ankle brace was more effective in half-squat parachuting landing with the backpack than no-backpack landing.

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BACKGROUND: Females with different practice experience may show different body postures and movement patterns while squatting in different depths, which may lead to changes of biomechanical loadings and increase the risks of injuries. METHODS: Sixteen novice female participants without squat training experience participated in this study. A 3D motion capture system was used to collect the marker trajectory and ground reaction force data during bodyweight squatting in different depths. The participants' kinematic data and joint moment were calculated using OpenSim's inverse kinematics and inverse dynamics algorithm. In this study, authors adapted a model especially developed for squatting and customized the knee joint with extra Degree-of-Freedom (DoF) in the coronal and horizontal plane with adduction/abduction and internal/external rotation. A paired-sample t-test was used to analyze the difference of joint range of motions (ROM) and peak moments between full-squat (F-SQ) and half-squat (H-SQ). One-Dimensional Statistical Parametric Mapping (SPM1D) is used to analyze the difference of joint angle and moment between the process of squatting F-SQ and H-SQ. RESULTS: (1) Compared with H-SQ, F-SQ showed larger ROM in sagittal, coronal, and transverse planes (p < 0.05). (2) SPM1D found that the difference in joint angles and joint moments between F-SQ and H-SQ was mainly concentrated in the mid-stance during squatting, which suggested the difference is greatly pronounced during deeper squat. (3) Peak hip extension moment, knee extension moment, hip adduction moment, and plantar flexion moment of F-SQ were significantly higher than H-SQ (p < 0.05). (4) Difference of hip and knee extension moments and rotation moments between the F-SQ and H-SQ were exhibited during descending and ascending. CONCLUSIONS: The study found that novice women had larger range of joint motion during the F-SQ than H-SQ group, and knee valgus was observed during squatting to the deepest point. Greater joint moment was found during F-SQ and reached a peak during ascending after squatting to the deepest point. Novice women may have better movement control during H-SQ. The findings may provide implications for the selection of lower limb strength training programs, assist the scientific development of training movements, and provide reference for squat movement correction, thus reducing the risk of injury for novice women in squatting practice.

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Resistance training (RT) variables can affect sleep quality, strength recovery and performance. The aim of this study was to examine the acute effect of RT leading to failure vs. non-failure on sleep quality (SQ), heart rate variability (HRV) overnight and one-repetition maximum (1-RM) performance 24 hours after training. Fifteen resistance-trained male athletes (age: 23.4 ± 2.4 years; height 178.0 ± 7.6 cm; weight: 78.2 ± 10.6 kg) performed two training sessions in a randomized order, leading to failure (4x10) or non-failure (5x8(10) repetitions), with 90 seconds for resting between sets at 75% 1-RM in bench press (BP) and half squat (HS). The day after, the participants completed the predicted 1-RM test for both exercises. In addition, the subjective and actigraphic SQ and HRV during sleep were measured after each training session. The day after the training protocol leading to failure, the 1-RM of BP (MD = 7.24 kg; -7.2%; p < 0.001) and HS (MD = 20.20 kg; -11.1%; p < 0.001) decreased. However, this parameter did not decrease after a non-failure RT session. No differences were observed between failure and non-failure training sessions on SQ and HRV; therefore, both types of training sessions similarly affected the SQ and the autonomic modulation during the night after the training session. This study provides an insight into the influence of different training strategies on SQ, strength performance and recovery after moderate- to high-demand training. This information could be useful especially for professional coaches, weightlifters and bodybuilders, due to the potential influence on the programming processes.

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Due to COVID-19, wearing a face mask to reduce virus transmission is currently mandatory in some countries when participants practice exercise in sports centers. Therefore, the aim of the present study was to analyze the effect of wearing a surgical or FFP2 mask during a resistance training session. Fourteen people with sarcopenia (age: 59.40 ± 5.46 years; weight: 68.78 ± 8.31 kg; height: 163.84 ± 9.08 cm) that participated in the study performed three training sessions in a randomized order: 4 sets of 10 repetitions of a half-squat at 60% of the one-repetition maximum and 90 s of rest between set and were either (a) without a mask (NM), (b) wearing a surgical face mask (SM), and (c) wearing a FFP2 face mask (FFP2). We found that wearing face masks had no effect on strength performance (session mean propulsive velocity (m/s): WM: 0.396 ± 0.042; SM: 0.387 ± 0.037; and FFP2: 0.391 ± 0.042 (p = 0.918)). Additionally, no impact of wearing a mask was found on heart rate, heart rate variability, blood lactate concentration (WM: 4.17 ± 1.89; SM: 4.49 ± 2.07; and FFP2: 5.28 ± 2.45 mmol/L (p = 0.447)), or rating of perceived exertion. Wearing a surgical or FFP2 face mask during a resistance training session resulted in similar strength performance and physiological responses than the same exercise without a mask in persons with sarcopenia.

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BACKGROUND: The objective is to compare the effects of a self-designed and self-manufactured novel prophylactic ankle brace [Chinese parachute ankle brace (CPAB)] and two ordinary ankle braces on the ankle joint during a half-squat parachute landing (HSPL) via biomechanical assessment. METHODS: Twenty elite paratroopers were in four different conditions: no brace, elastic brace, semi-rigid brace, and CPAB. Each participant was instructed to jump off a platform with three different heights, 40, 80, and 120 cm, and land on the force plate in a half-squat posture. The vertical ground reaction forces (vGRFs), joint angles, moments, powers, and works were calculated. After the experiment, every participant completed the questionnaires designed for this study. RESULTS: Increasing the dropping height increased all of the parameters significantly (P<0.01), except for time to peak vGRF (T-PvGRF). Applying three braces can all slightly increase vGRF (P=0.237) and reduce T-PvGRF by 6-10 ms, as well as decrease the joint angles, velocities, and moments on the sagittal and coronal planes. Wearing CPAB and a semi-rigid brace more efficiently restricted dorsiflexion and inversion (P<0.05), and they both significantly reduced ankle work (t=5.107, P<0.01; t=3.331, P<0.01) and peak power (t=7.237, P<0.01; t=6.711, P<0.01) at 120 cm. The total scores from low-to-high were semi-rigid brace (19.20±2.99), elastic brace (21.91±3.25), and CPAB (23.37±3.08). CONCLUSIONS: The CPAB was more effective at restricting ankle joint motion on the coronal and sagittal planes than the other two prophylactic ankle braces. Therefore, the CPAB had the advantages of a novel appearance, high efficiency, and superior comfort, providing a reliable choice for parachute jumping and training in China.

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BACKGROUND: Balance and mobility impairments, declined musculoskeletal strength and performance, limited range of motion, and poor flexibility are fairly common among older adults. OBJECTIVES: To determine the lower extremity muscle force and to verify the correlation with the gait characteristics and balance in community dwelling older adults. METHODS: Seventy-five adults with a mean age of 75.07 ± 6.28 years were included in the study. All participants were evaluated with the following tests: half squat (HS), decline squat (DS), foot print analysis (step length, step wide, stride length, walking velocity and cadence) and Tinetti Performance Oriented Mobility Assessment (POMA). RESULTS: HS and DS test scores were significantly correlated with Tinetti Balance and Gait Assessment scores and gait characteristics, except step wide (p< 0.01). The results of this study showed that the participants who have higher scores in the squat tests, showed higher scores in terms of POMA (p< 0.01). CONCLUSION: Appropriate and direct assessment of lower limb power and performance in balance and gait tests should be done to identify functioning of the older adults. Half and eccentric decline squat tests used in this study were useful, cheap and easy. The squat tests can be used to determine the relationship between balance and gait characteristics, in addition to predicting the musculoskeletal performance in older adults.

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Post-activation potentiation (PAP) has been defined as a major enhancement of muscular performance following a preload stimulus. The eccentric actions seem to cause a potentiating effect on subsequent explosive exercises. The aim of this study was to determine whether a protocol of squat exercise using an inertial flywheel could have a potentiating effect on jump performance. Sixteen physically active volunteers participated in the study (age: 21.8 ± 2.7 years; body mass index: 23.6 ± 3). All participants completed two different protocols on separate days: a Traditional Protocol (using a half squat with a guided barbell) and an Inertial Flywheel Protocol (using a half squat with an inertial flywheel). Both protocols were similar and consisted of 3 x 6 reps at the load that maximized power, with a 3-minute rest interval between sets. The squat jump (SJ) was measured by a contact platform at baseline, and four, eight and twelve minutes after the PAP stimulus. A two-way ANOVA with repeated measures was performed to analyze significant differences over time. There were significant increases of SJ height (p = 0.004, d = 0.665), velocity (p = 0.003, d = 0.688) and power (p = 0.004, d = 0.682) from baseline after the inertial flywheel protocol. A significant interaction effect (time x protocol) was observed, showing that the inertial flywheel protocol had a potentiating effect on the jump performance compared to the traditional protocol, more specifically at 4 and 8 minutes after the PAP stimulus. In conclusion, the inertial flywheel protocol showed a potentiating effect on the squat jump performance, thus this pre- conditioning activity could be useful during the warm-up before the competition.

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This study aimed to investigate the fluctuations of muscle performance in the Smith machine half-squat exercise during three different phases of the menstrual cycle. Thirteen resistance-trained and eumenorrheic women volunteered to participate in the study (58.6 ± 7.8 kg, 31.1 ± 5.5 years). In a pre-experimental test, the half-squat one-repetition maximum (1RM) was measured. Body mass, tympanic temperature and urine concentration of the luteinizing hormone were estimated daily for ~30 days to determine the early follicular phase (EFP), the late follicular phase (LFP), and the mid-luteal phase (MLP) of the menstrual cycle. On the second day of each phase, performance of the Smith machine half-squats was assessed using 20, 40, 60 and 80% of one repetition maximum (1RM). In each load, force, velocity, and power output were measured during the concentric phase of the exercise by means of a rotatory encoder. The data were analyzed using one-way repeated measures ANOVA coupled with magnitude-based inferences. Overall, force, velocity and power output were very similar in all menstrual cycle phases with unclear differences in most of the pairwise comparisons and effect sizes >0.2. The results of this investigation suggest that eumenorrheic females have similar muscle strength and power performance in the Smith machine half-squat exercise during the EFP, LFP, and MLP phases of the menstrual cycle.

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Creatine supplementation has an ergogenic effect in an acute complex training bout, but the benefits of chronic creatine supplementation during long-term complex training remain unknown. The study aimed to evaluate the effects of 4-week complex training combined with creatine supplementation on sport performances and muscle damage biomarkers. Thirty explosive athletes were assigned to the creatine or placebo group, which consumed 20 g of creatine or carboxymethyl cellulose, respectively, per day for 6 days followed by 2 g of the supplements until the end of the study. After 6 days of supplementation, subjects performed tests of one repetition maximum (1-RM) strength of half squat and complex training bouts to determine the optimal individual post-activation potentiation time. Thereafter, all subjects performed a complex training programme consisting of six sets of 5-RM half squats and plyometric jumps 3 times per week for 4 weeks. Body composition, 30-m sprint and jump performances were assessed before and after the training period. Moreover, blood creatine kinase (CK) activity was analysed at the first and the last training bout. After the training, the 1-RM strength in the creatine group was significantly greater than in the placebo group (p < 0.05). CK activity after the complex training bout in the creatine group was significantly reduced compared with the placebo group (p < 0.05). No differences were noted for other variables. This study concluded that creatine supplementation combined with complex training improved maximal muscular strength and reduced muscle damage during training.

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Evaluation of muscular fatigue thresholds in athletes performing short-duration and explosive exercises is difficult because classic parameters do not suffer large variations. Therefore, the aim of this study was to develop a new method to estimate the fatigue threshold in single muscles. Our approach is based on electromyographic data recorded during a maximum incremental strength test until the one repetition maximum is reached. Ten men and 10 women performed a half-squat strength test consisting of five incremental intensities of one repetition maximum. Neither heart rate nor blood lactate concentrations showed significant differences at the various intensities tested. Surface electromyographic activities of vastus lateralis, vastus medialis, and rectus femoris were recorded, finding a break point corresponding to the fatigue threshold occurring in men at 70.74%, 71.48%, and 72.52% of one repetition maximum, respectively. In women, break-point values were 76.66% for vastus lateralis, 76.27% for vastus medialis, and 72.10% for rectus femoris. In conclusion, surface electromyography could be a useful, rapid, and noninvasive tool to determine the fatigue threshold of independent muscles during a maximal half-squat strength test.

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High-intensity exercises are known to provoke delayed onset muscle soreness (DOMS). Delayed onset muscle soreness typically occurs within the first 24 h, peaks between 24 and 72 h, and can last as long as 5-7 days post-exercise. Delayed onset muscle soreness is a multifactorial process involving both mechanical and biochemical components, associated with clinical features that may limit range of motion, and athletes seek for effective recovery strategies to optimize future training sessions. TensLess® is a food supplement developed to help manage post-exercise recovery. The supplement has been investigated on 13 recreationally active athletes of both sex, during a randomized, double-blind, and crossover clinical investigation, including a 3-week washout period. The clinical investigation was based on the study of TensLess® effects for DOMS management and on the reduction of associated muscle damages following an eccentric exercise protocol. Supplementation with TensLess® induced significant decrease in DOMS perception (-33%; p = 0.008) as of the first 24 h; this was significantly correlated with a lowered release of muscle damage-associated biomarkers, namely myoglobin, creatinine, and creatine kinase, for the whole length of the recovery period. Taken together, these positive results clearly indicate that post-exercise supplementation with TensLess® may preserve myocytes and reduce soreness following eccentric exercise-induced damages, and, accordingly, significantly shorten muscle recovery. Copyright © 2017 John Wiley & Sons, Ltd.

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The purpose of this study was to examine the relationships between muscle cross-sectional area (CSA), maximal strength, power output, and maximum potentiation characteristics. The vastus lateralis and biceps femoris CSA, one repetition maximum (1RM) back squat, 1RM concentric-only half-squat (COHS) strength, static jump power output, and maximum potentiation characteristics of 17 resistance-trained men was assessed during several testing sessions. Pearson's correlation coefficients were used to examine the relationships between CSA, strength, power output, and maximum potentiation measures. Moderate-to-strong relationships existed between CSA and strength measures (r = 0.462⁻0.643) as well as power output (r = 0.396⁻0.683). In addition, moderate-to-strong relationships existed between strength and power output (r = 0.407⁻0.548), while trivial relationships existed between strength and maximum potentiation (r = -0.013⁻0.149). Finally, small negative relationships existed between CSA and maximum potentiation measures (r = -0.229⁻-0.239). The results of the current study provide evidence of the interplay between muscle CSA, strength, power, and potentiation. Vastus lateralis and biceps femoris CSA may positively influence an individual's back squat and COHS maximal strength and squat jump peak power; however, muscle CSA and absolute strength measures may not contribute to an individual's potentiation capacity. Practitioners may consider implementing resistance training strategies that improve vastus lateralis and biceps femoris size in order to benefit back squat and COHS strength. Furthermore, implementing squatting variations-both full and partial-may benefit jumping performance.

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OBJECTIVE: To assess reliability and validity of three single leg standing clinical tests in patients with plantar heel pain syndrome (PHPS). DESIGN: Cross-sectional reliability study. PARTICIPANTS: Forty patients diagnosed with PHPS. MAIN OUTCOME MEASURES: Patients stood on their affected foot in a static stance for up to 30seconds, a half squat for up to 10 repetitions, and a heel rise for up to 10 repetitions. The first sensation of pain (p1) determined the termination of each test, and established a positive test result. The level of p1 was measured using a visual analogue scale (VAS); time or repetitions for each test were recorded. Prior to performing the tests, all patients completed the Foot & Ankle Computerized Adaptive Test to measure functional status (FS). RESULTS: Detection of p1 in each test showed good reliability for inter- and intrarater assessment (Kappa=0.60 to 0.78 and 0.56 to 0.77, respectively). The intraclass correlation coefficient for the VAS measures was 0.85 to 0.95 for inter-rater assessment and 0.78 to 0.92 for intrarater assessment. However, the Bland and Altman limits of agreement were wide, indicating that these measures were less reliable than the correlation coefficients suggested. Thirty-five patients (88%) experienced a positive pain response to at least one test. Significant correlations were found between the VAS measures in each test and FS (r=0.63 to 0.72). CONCLUSIONS: The static stance, half squat and heel rise tests were easily implemented, and found to be reliable and valid according to one analysis, yet less reliable with another, for pain provocation and VAS levels in patients with PHPS. All three VAS levels correlated well with FS.

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This study aimed to analyze the effects of power training using traditional vertical resistance exercises versus direction specific horizontal inertial flywheel training on performance in common sport-related tasks. Twenty-three healthy and physically active males (age: 22.29 ± 2.45 years) volunteered to participate in this study. Participants were allocated into either the traditional training (TT) group where the half squat exercise on a smith machine was applied or the horizontal flywheel training (HFT) group performing the front step exercise with an inertial flywheel. Training volume and intensity were matched between groups by repetitions (5-8 sets with 8 repetitions) and relative intensity (the load that maximized power (Pmax)) over the period of six weeks. Speed (10 m and 20 m), countermovement jump height (CMJH), 20 m change of direction ability (COD) and strength during a maximal voluntary isometric contraction (MVIC) were assessed before and after the training program. The differences between groups and by time were assessed using a two-way analysis of variance with repeated measures, followed by paired t-tests. A significant group by time interaction (p=0.004) was found in the TT group demonstrating a significantly higher CMJH. Within-group analysis revealed statistically significant improvements in a 10 m sprint (TT: -0.17 0.27 s vs. HFT: -0.11 0.10 s), CMJH (TT: 4.92 2.58 cm vs. HFT: 1.55 2.44 cm) and MVIC (TT: 62.87 79.71 N vs. HFT: 106.56 121.63 N) in both groups (p < 0.05). However, significant differences only occurred in the 20 m sprint time in the TT group (-0.04 0.12 s; p = 0.04). In conclusion, the results suggest that TT at the maximal peak power load is more effective than HFT for counter movement jump height while both TT and HFT elicited significant improvements in 10 m sprint performance while only TT significantly improved 20 m sprint performance.

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[Purpose] This study evaluated a specific rehabilitation protocol using a half squat after total knee reconstruction with distal femur megaprosthesis and tibial allograft-prosthesis composite. [Subject and Methods] Squat execution was recorded by a three-dimensional system before and after a specific rehabilitation program on a 28-year-old patient. Squat duration, body center of mass trajectory, and vertical range of motion were determined. Step width and joint angles and symmetry (hip flexion, extension, and rotation, knee flexion, and ankle dorsal and plantar flexion) were estimated. Knee and hip joint symmetry was computed using a bilateral cyclogram technique. [Results] After rehabilitation, the squat duration was longer (75%), step width was similar, and vertical displacement was higher. Hip flexion increased by over 20%, and ankle dorsiflexion diminished by 14%. The knee had the highest symmetry gain (4.1-3.4%). Angle-angle plot subtended areas decreased from 108° to 40°(2) (hip) and from 204° to 85°(2) (knee), showing improvement in movement symmetry. [Conclusion] We concluded that the squat is an effective multifactorial exercise to estimate rehabilitation outcomes after megaprosthesis, also considering that compressive and shear forces are minimal up to 60-70° of knee flexion.

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The objective of the study was to determine the effect of landing surface on plantar kinetics during a half-squat landing. Twenty male elite paratroopers with formal parachute landing training and over 2 years of parachute jumping experience were recruited. The subjects wore parachuting boots in which pressure sensing insoles were placed. Each subject was instructed to jump off a platform with a height of 60 cm, and land on either a hard or soft surface in a half-squat posture. Outcome measures were maximal plantar pressure, time to maximal plantar pressure (T-MPP), and pressure-time integral (PTI) upon landing on 10 plantar regions. Compared to a soft surface, hard surface produced higher maximal plantar pressure in the 1(st) to 4(th) metatarsal and mid-foot regions, but lower maximal plantar pressure in the 5(th) metatarsal region. Shorter T- MPP was found during hard surface landing in the 1(st) and 2(nd) metatarsal and medial rear foot. Landing on a hard surface landing resulted in a lower PTI than a soft surface in the 1(st)phalangeal region. For Chinese paratroopers, specific foot prosthesis should be designed to protect the1(st) to 4(th)metatarsal region for hard surface landing, and the 1(st)phalangeal and 5(th)metatarsal region for soft surface landing. Key PointsUnderstanding plantar kinetics during the half-squat landing used by Chinese paratroopers can assist in the design of protective footwear.Compared to landing on a soft surface, a hard surface produced higher maximal plantar pressure in the 1(st) to 4(th) metatarsal and mid-foot regions, but lower maximal plantar pressure in the 5(th) metatarsal region.A shorter time to maximal plantar pressure was found during a hard surface landing in the 1(st) and 2(nd) metatarsals and medial rear foot.Landing on a hard surface resulted in a lower pressure-time integral than landing on a soft surface in the 1(st) phalangeal region.For Chinese paratroopers, specific foot prosthesis should be designed to protect the 1(st) to 4(th) metatarsal region for a hard surface landing, and the 1(st) phalangeal and 5(th) metatarsal region for a soft surface landing.