Eccentric Phase Research Articles

Analysis of Concentric and Eccentric Power in Flywheel Exercises Depending on the Subjects' Strength Level and Body Mass.

Asencio, P, García-Valverde, A, Albaladejo-García, C, Beato, M, Moreno-Hernández, FJ, and Sabido, R. Analysis of concentric and eccentric power in flywheel exercises depending on the subjects' strength level and body mass. J Strength Cond Res 38(8): 1394-1400, 2024-The objective of this study is to describe how flywheel exercise mechanical outputs are affected by the athletes' body mass (BM) and strength level and by the exercise type. Forty-six recreational athletes came to a laboratory 3 times. On the first day, descriptive data, squat (1 repetition maximum: 1RM) and flywheel familiarization were performed. After a second day of familiarization, subjects performed a randomized flywheel exercise-testing protocol of squat and split squat exercises. The variables used for data analysis were peak concentric power and peak eccentric power, eccentric/concentric ratio, and their relationship with 1RM/BM. Subjects were assigned to a stronger or weaker group according to their 1RM/BM ratio. Group differences were found in absolute values of eccentric overload (EOL) ( p < 0.01; effect size [ES] = 0.51) and EOL/BM ( p < 0.01; ES = 0.46) only in the split squat. Absolute power values in the concentric phase showed differences between inertial load ( p < 0.01; ES = 0.41). The stronger group did not present significant differences between inertial loads during squat ( p < 0.01; ES = 0.46), but they showed different ratios with light inertias in comparison with the weaker group ( p < 0.01; ES = 0.46). There were significant differences between groups with light inertias in split squat (nondominant) and squat exercises ( p < 0.05; ES = 0.29) in the eccentric and concentric phases ( p < 0.116; ES = 0.20). Squat and split squat exercises present different profiles depending on the training level. In conclusion, it is recommended that practitioners perform a test to understand the inertial load-power profile (concentric, eccentric, and their ratio) for each exercise and also consider the user's strength level for selection of the inertial load and for the exercise to use in training.

Acute patellar dislocation during isokinetic knee strength testing: A case report

Key Clinical MessageIsokinetic testing is a maximal muscle strength test which requires adequate patient's preparation and observer's care. While the available data suggests that isokinetic devices are safe, their use may rarely cause severe injuries. The screening of predisposing anatomical factors could help preventing injuries before testing.AbstractA 29‐year‐old athletic man presented an acute patellar dislocation on a healthy right knee during isokinetic muscle strength testing, which was conducted in the setting of an intensive physical rehabilitation program, for persistent left knee pain after arthroscopic surgery for meniscal tear. This is the first case to occur in an adult male without clear risk factors such as patellar dysplasia. Predisposing factors may include slightly elevated patellar tilt and lateral shift compared to the contralateral knee (researched from subsequent review of pre‐injury X‐rays), and an elevated quadricipital strength in the context of recreational bodybuilding. The dislocation occurred during eccentric extension phase of testing. Medial patellofemoral ligament reconstruction was conducted 6 months later. Isokinetic muscle strength testing is generally considered as a safe method, despite limited data on the devices' safety. Since severe injuries might rarely occur, adequate patient preparation is needed, as well as the screening of predisposing factors.

Force-Time Characteristics of Repeated Bouts of Depth Jumps and the Effects of Compression Garments.

No studies have reported ground reaction force (GRF) profiles of the repeated depth jump (DJ) protocols commonly used to study exercise-induced muscle damage. Furthermore, while compression garments (CG) may accelerate recovery from exercise-induced muscle damage, any effects on the repeated bout effect are unknown. Therefore, we investigated the GRF profiles of 2 repeated bouts of damage-inducing DJs and the effects of wearing CG for recovery. Nonresistance-trained males randomly received CG (n = 9) or placebo (n = 8) for 72hours recovery, following 20 × 20m sprints and 10 × 10 DJs from 0.6m. Exercise was repeated after 14days. Using a 3-way (set × bout × group) design, changes in GRF were assessed with analysis of variance and statistical parametric mapping. Jump height, reactive strength, peak, and mean propulsive forces declined between sets (P < .001). Vertical stiffness, contact time, force at zero velocity, and propulsive duration increased (P < .05). According to statistical parametric mapping, braking (17%-25% of the movement) and propulsive forces (58%-81%) declined (P < .05). During the repeated bout, peak propulsive force and duration increased (P < .05), while mean propulsive force (P < .05) and GRF from 59% to 73% declined (P < .001). A repeated bout of DJs differed in propulsive GRF, without changes to the eccentric phase, or effects from CG.

Changes in Countermovement Vertical Jump Force-Time Metrics Across Different Competitive Levels in Women’s Volleyball

As one of the most fundamental skills in volleyball, the countermovement vertical jump (CVJ) has been commonly implemented as a non-invasive and time-efficient method for the assessment of lower-body neuromuscular function. The purpose of the present study was to examine differences in CVJ performance between three different competitive levels in female volleyball players (i.e., national team [n=20], professional league [n=16], collegiate [n=16]). While standing on a uni-axial force plate system sampling at 1000 Hz, athletes performed three maximal-effort CVJs with no arm swing (i.e., hands on the hips during the entire movement). Each jump was separated by a 10-15 second rest interval to minimize the possible influence of fatigue. Significantly greater eccentric braking impulse, peak velocity, peak force, mean and peak power, vertical jump height, reactive strength index-modified, countermovement depth, and shorter braking phase, eccentric duration, and contraction times were observed for the national team and professional players when compared to collegiate athletes. Also, national team players demonstrated significantly greater eccentric braking impulse, peak velocity, mean and peak power, reactive strength index-modified, and countermovement depth than professional volleyball players. However, during the concentric phase of the CVJ, the only significant differences observed were between national team players and collegiate athletes, where national team players exhibited significantly greater peak velocity, impulse, and mean and peak power. Thus, it can be concluded that higher-level players may be more capable of effectively utilizing the eccentric phase of the CVJ and executing the stretch-shortening action more rapidly, which contributes to better CVJ height.

Comparison of vertical jump and sprint performances between 3 × 3 and 5 × 5 elite professional male basketball players.

Given its fast-growing popularity and unique on-court competitive demands, 3 × 3 basketball has captured a considerable amount of attention over recent years. However, unlike research focused on studying 5 × 5 basketball players, there is a lack of scientific literature focused on examining countermovement vertical jump (CMJ) and sprint performance characteristics of 3 × 3 athletes. Thus, the purpose of the present study was to compare force-time metrics during both eccentric and concentric phases of the CMJ and acceleration and deceleration capabilities between 3 × 3 and 5 × 5 top-tier professional male basketball athletes. Ten 3 × 3 and eleven 5 × 5 professional basketball players volunteered to participate in the present study. Upon completion of a standardized warm-up, each athlete performed three maximum-effort CMJs, followed by two 10 m sprints. A uni-axial force plate system sampling at 1,000 Hz was used to analyze CMJ force-time metrics and a radar gun sampling at 47 Hz was used to derive sprint acceleration-deceleration measures. Independent t-tests and Hedge's g were used to examine between-group statistically significant differences (p < 0.05) and effect size magnitudes. The findings of the present study reveal that 3 × 3 and 5 × 5 professional male basketball players tend to display similar neuromuscular performance characteristics as no significant differences were observed in any force-time metric during both eccentric and concentric phases of the CMJ (g = 0.061-0.468). Yet, prominent differences were found in multiple measures of sprint performance, with large effect size magnitudes (g = 1.221-1.881). Specifically, 5 × 5 basketball players displayed greater average and maximal deceleration and faster time-to-stop than their 3 × 3 counterparts. Overall, these findings provide reference values that sports practitioners can use when assessing athletes' CMJ and sprint performance capabilities as well as when developing sport-specific training regimens to mimic on-court competitive demands.

Effect of Step Load Based on Time under Tension in Hypoxia on the ACL Pre-Operative Rehabilitation and Hormone Levels: A Case Study.

The aim of the study was to determine the effect of step load in hypoxia on the effectiveness of preoperative rehabilitation (PR) and hormone levels based on a case study. Introduction: We assessed the impact of variables such as rate of movement and time under tension (TUT) in normobaric hypoxia on the levels of growth hormone (GH), insulin-like growth factor 1 (IGF-1), and erythropoietin (EPO). Additionally, the impact of step load on the hypertrophy and strength of knee extensors and flexors was assessed. Methods: The work uses a case study, the research subject of which was a 23-year-old female professional handball player. The tests included an isokinetic assessment of the peak torque of knee extensors and flexors as well as body composition analysis. Results: The results showed a more than (10.81-fold) increase in GH after the microcycle with time under tension (TUT). The deficit between the lower limbs was also reduced. Conclusions: Using a hypoxic environment based on an appropriate altitude, combined with changes such as a short rest break between sets and a controlled tempo of movement with an eccentric phase, TUT may offer an alternative to the PR process, especially among athletes who care about fast RTS.

Vertical jump neuromuscular performance of professional female handball players-starters vs. non-starters comparison.

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

LOWER LIMB PERFORMANCE AND KINETIC ASYMMETRIES IN PATIENTS FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

INTRODUCTION AND AIM Analyses of functional performance and movement strategies at key clinical milestones during rehabilitation are critical to guide rehabilitation and return-to-sport (RTS) decisions post-anterior cruciate ligament reconstruction (ACLR). The aim of this study was to evaluate lower limb performance and kinetics during jumping and hopping in patients post-ACLR. METHODS Seventy-one patients (39 males, 32 females; mean age 27.0 years; height 1.74m; weight 76.5kg) underwent lower limb evaluation at 6.1 and 10-months post-ACLR. Patient-reported outcomes (IKDC-2000, ACL-RSI) were collected at both time points. Ground reaction forces during bilateral and unilateral countermovement jumps (CMJ) on dual force plates were recorded, alongside unilateral horizontal hops for distance (HHD). Paired sample t-tests examined between-limb differences in eccentric and concentric phases of the bilateral CMJ and jump heights and distances of the unilateral CMJ and HHD, respectively, at both time points. Differences in limb asymmetries between the unilateral CMJ and HHD were also examined. Chi square tests were performed to examine differences in meeting known RTS thresholds (&amp;gt;90% limb symmetry index [LSI]). RESULTS Moderate to large asymmetries were observed for concentric (effect size [ES] = -1.06, P&amp;lt;0.001) eccentric phases (ES = 0.54, p&amp;lt;0.001) during the bilateral CMJ at both time points. Greater limb asymmetry was observed in the unilateral CMJ compared to the HHD at 6-months (ES = -0.52; p≤0.001) and 10-months (ES = -0.56; p≤0.001). Significantly more participants “passed” a horizontal hop test versus a vertical hop test at 6 months (χ2=7.07, p=0.008) and at 10 months (χ2=7.52, p=0.006). CONCLUSION Vertical performance metrics can better identify between-limb asymmetries than HHD and should be included in RTS testing batteries following ACLR. Between-limb deficits in key eccentric and concentric phases of the bilateral CMJ are also apparent at 6- and 10-months after ACLR, suggesting a persistent offloading strategy even at the time of RTS.

Acute Effect of Static and Dynamic Stretching on Activating Scapular Stabilizer Muscles During Pull-Up Movement in Gymnasts

Background and Aims Today, there is an argument about the effect of various stretching movements on the performance of athletes. Therefore, this study investigated the acute effect of static and dynamic stretching on muscle activity and co-contraction of scapular stabilizer muscles during pull-ups in gymnasts. Methods According to the inclusion and exclusion criteria, 15 professional gymnasts with a mean age of 23.25±2.57 years, height of 170.93±5.88 cm, and weight of 64.54±5.06 kg were selected as research samples and divided into three subgroups (each with 5 athletes). In the pre-test, subjects performed pull-up activity, and muscle activities of the serratus anterior, upper trapezius, middle trapezius, and lower trapezius muscles were measured using a biometric electromyography device. Then, each subgroup performed a different stretching protocol in each session, and a post-test was conducted like the pre-test. Repeated measures analysis of variance, the Bonferroni post hoc test, and the paired t test were used to test the study hypotheses. Results The results showed that static and dynamic stretching caused a significant decrease and increase in muscle activity in both concentric and eccentric phases, respectively. Also, the results showed that dynamic stretch caused a reduction in co-contraction of the serratus anterior and middle trapezius muscles in both concentric and eccentric phases. In addition, there is a significant difference between the effect of static and dynamic stretch and between dynamic stretch and control on the co-contraction of the serratus anterior and middle trapezius muscles in the concentric and eccentric phases. Conclusion The results showed that the co-contraction of the serratus anterior and middle trapezius muscles decreased after using dynamic stretching. Therefore, considering the importance of muscle co-contraction in the occurrence of shoulder joint injuries and preventing injuries in the shoulder joint of gymnasts, it is suggested that coaches and gymnasts use dynamic stretching exercises more carefully.

Residual Effects of Same Day Lower Extremity Strength Training on Countermovement Jump Performance in Collegiate Women Athletes.

Balancing of strength programming intensity with sport demands is necessary to avoid excessive workloads that could inhibit performance. To expand previous jump height focused literature, this study evaluated whether countermovement jump (CMJ) movement strategies, including eccentric characteristics, might reveal CMJ execution strategy shifts to achieve similar afternoon CMJ height following a morning resistance training session (RTS). Fifteen collegiate women's soccer and volleyball athletes (18-24 years, 73.6 ± 8.4 kg, 1.74 ± 0.19 m) participating in an offseason RTS completed five CMJs during two afternoon sessions (48 h apart), one 4-6 h post morning RTS, and one on a rest day. The RTS consisted of 2 sets of 10 repetitions at 70-80% 1RM for the back squat, the front squat, and the forward lunge. Vertical ground reaction forces were recorded from which 13 outcome measures describing elements of the eccentric and concentric CMJ phases were computed. No significant differences in jump height (p = 0.427, d = 0.17) or outcome measures (p = 0.091-0.777, d = -0.07-0.21) between sessions with exception of a significant concentric phase time decrease (p = 0.026, d = 0.23) following the RTS were identified. Given the magnitude of the mean concentric phase time change (0.01 s), the result likely has limited practical meaning. As these results confirm previous CMJ height literature, practitioners have further evidence that a morning RTS does not interfere or enhance afternoon CMJ performance in athletic women.

Effects of Eccentric Speed during Front Squat Conditioning Activity on Post-activation Performance Enhancement of Hip and Thigh Muscles.

The phenomenon of post-activation performance enhancement plays an unidentified role in movement eccentric speed and individual muscle group responses. Therefore, this study aimed to determine whether the loaded front squat (FSq) speed of the eccentric phase would influence the post-activation performance enhancement effect and whether the FSq would elicit similar performance enhancement of knee flexion, knee extension, hip flexion, and hip extension muscles. Twenty resistance-trained handball players performed the FSq under maximum eccentric-concentric speed and 2-s eccentric speed (only the eccentric phase performed), while pre- and post-front squat countermovement jump, knee, and hip isokinetic flexion/extension performance were tested. The FSq conditioning activity was performed in a single set of three repetitions with either 90% (maximum eccentric-concentric speed) or 120% (2-s eccentric speed) of one repetition maximum, and post-performance was measured 4-12 min after the FSq. Athletes randomly changed the FSq eccentric speed and tested the hip or knee isokinetic flexion/extension strength at 180°/s. ANOVA showed that the rate of force development during the jump increased (Cohen d = 0.59-0.77) with no differences between 2-s eccentric and maximum speed eccentric protocols. Isokinetic strength increased after the 2-s eccentric FSq in hip extension (d = 0.76-0.86), knee flexion (d = 0.74-0.88), and hip flexion (d = 0.82), with no differences in knee extension strength. After maximum eccentric-concentric speed, isokinetic strength increased in hip extension (d = 1.25). In conclusion, the FSq conditioning activity enhances hip extensors' performance more than knee extensors' performance. Different eccentric types of muscle action during a conditioning activity alter the level of local muscle enhancement.

Effects of Different Recovery Periods Following a Very Intense Interval Training Session on Strength and Explosive Performance in Elite Female Ice Hockey Players.

Petré, H, Tinmark, F, Rosdahl, H, and Psilander, N. Effects of different recovery periods following a very intense interval training session on strength and explosive performance in elite female ice hockey players. J Strength Cond Res 38(7): e383-e390, 2024-This study investigates how different recovery periods after high-intensity interval training (HIIT) affects strength and explosive performance during a power training (PT) session. Fifteen female elite ice hockey players (22.5 ± 5.2 years) performed PT, including 6 sets of 2 repetitions (reps) of isometric leg press (ILP) and 6 sets of 3 reps of countermovement jump (CMJ), following a rested state and 10 minutes, 6 hours, or 24 hours after HIIT (3 sets of 8 × 20 seconds at 115% of power output at maximal oxygen consumption on a cycle ergometer). Peak force (PF) and peak rate of force development (pRFD) were measured during the ILP. Peak jump height (PJH), concentric phase duration (ConDur), eccentric phase duration, total duration, peak power (PP), velocity at peak power (V@PP), and force at peak power were measured during CMJ. The following variables were significantly reduced when only a 10-minute recovery period was allowed between HIIT and PT: PF was reduced by 7% ( p < 0.001), pRFD by 17% ( p < 0.001), PJH by 4% ( p < 0.001), ConDur by 4% ( p = 0.018), PP by 2% ( p = 0.016), and V@PP by 2% ( p = 0.007). None of the measured variables were reduced when PT was performed 6 and 24 hours after HIIT. We conclude that strength and explosive performance of elite female ice hockey players is reduced 10 minutes after HIIT but not negatively affected if a rest period of at least 6 hours is provided between HIIT and PT.

Why Should Athletes Brake Fast? Influence of Eccentric Velocity on Concentric Performance During Countermovement Jumps at Different Loads.

The aim of the present study was to analyze the effect of different eccentric tempos on eccentric kinetics and kinematics and the subsequent concentric performance when performing countermovement jumps against different loads. After 1-repetition-maximum assessment and 2 familiarization sessions, 13 well-trained participants performed, in randomized order, 12 sets (4 tempos × 3 loads) of 4 repetitions of the loaded countermovement-jump exercise. The eccentric tempos analyzed were 5 and 2seconds, as fast as possible, and accelerated (ie,without pause between repetitions), while the loads used were 30%, 50%, and 70% of 1-repetition maximum. Several kinetic and kinematic variables during both phases were recorded by linking a linear position transducer to the barbell. The eccentric work was greater in the accelerated condition despite no changes in the eccentric depth. The peak and mean propulsive velocities were greater in the as-fast-as-possible and accelerated conditions. Correlation analysis showed that, compared with the 5-second condition, the increased concentric performance in the accelerated condition was related to the difference in eccentric work performed in the last 100milliseconds of the eccentric phase (r > .770). Contrary to current practices, the current study highlights the need for performing the eccentric phase of loaded countermovement jumps, a common exercise performed by athletes for both training and evaluation purposes, as fast as possible. This allows not only a greater eccentric work but also improved concentric performance.

Joint-specificity dictates contribution of eccentric phase biomechanics and amortization time toward countermovement jump performance in children

Joint-specificity dictates contribution of eccentric phase biomechanics and amortization time toward countermovement jump performance in children

Starters vs. non-starters differences in vertical jump force-time metrics in female professional volleyball players.

As one of the fundamental volleyball skills, countermovement vertical jump (CMJ) has been commonly implemented in the applied sports setting as a non-invasive and time-efficient assessment of athletes' lower-body neuromuscular function. The purpose of the present study was to examine the differences in CMJ characteristics between starters and non-starters within a cohort of professional female volleyball players. Nineteen athletes competing in one of the top European leagues (i.e., SuperLeague) volunteered to participate in the present investigation. Following the completion of a warm-up protocol, each athlete performed three maximal-effort CMJs with no arm swing while standing on a uni-axial force plate system sampling at 1,000 Hz. The following force-time metrics were used for performance analysis purposes: braking phase duration and impulse, eccentric and concentric duration, mean and peak force and power, contraction time, jump height, and reactive strength index-modified. Mann-Whitney U and independent t-tests revealed no statistically significant differences (p > 0.05) during both eccentric and concentric phases of CMJ between the players included in the starting lineup (n = 9) and their substitutions (n = 10), with the effect sizes being small to moderate in magnitude (g = 0.053-0.683). While further research is warranted on this topic, these results suggest that securing a position in a starting lineup at the professional level of volleyball play may be more contingent on the player's ability to proficiently execute sport-specific skills (e.g., blocking, attacking), rather than the performance on the CMJ assessment, considering that the observed values for both groups fall within the desired ranges for this specific population of athletes.

Investigating balance-related gait patterns and their relationship with maximum torques generated by the hamstrings and quadriceps in older adults - Results from the Baltimore longitudinal study of aging

BackgroundBalance-related gait patterns in older adults can be objectively discerned through the examination of gait parameters, maximum leg torques, and their interconnections. ObjectiveTo investigate the correlation between leg muscle strength and balance during gait concerning functional performance in healthy older adults. MethodsParticipants included 117 adults aged 60-95 years were recruited from the Baltimore Longitudinal Study of Aging (BLSA). They underwent evaluations of gait, balance, and maximum isometric leg torque (for both hamstrings and quadriceps). Analyses examined the association between leg torque and functional performance among those with higher and lower balances. ResultsIndividuals with lower balance (n = 43) were older, more prone to experiencing a fear of falling, and exhibited lower functional performance (gait speeds and Generalized Gait Stability Scores (GGSS), ps < 0.001) compared to their counterparts with higher balance (n = 74). At a usual walking pace, the GGSS showed a positive association with concentric Quadriceps Maximum Torque (QMT) in participants with lower balance (p = 0.013). Conversely, it displayed a positive association with eccentric QMT in those with higher balance (p = 0.014). At a fast walking pace, only individuals with higher balance demonstrated a positive muscle torque association with both gait speed and GGSS, encompassing concentric and eccentric actions in both the quadriceps and hamstrings (ps < 0.050). ConclusionEvaluating muscle strength capacity in both concentric and eccentric phases during dynamic high-effort events, along with investigating their associations with gait performance, can be beneficial for identifying subtle gait deficits. This comprehensive approach may assist in the early detection of gait deterioration among healthy older adults, given the intricate muscle activations involved in lower body functional performance.

Upper limb motor dysfunction is associated with fragmented kinetics after brain injury

BackgroundCharacterization of motor deficits after brain injury is important for rehabilitation personalization. While studies reported abnormalities in the kinematics of paretic and non-paretic elbow extension for patients with brain injuries, kinematic analysis is not sufficient to explore how patients deal with musculoskeletal redundancy and the energetic aspect of movement execution. Conversely, interarticular coordination and movement kinetics can reflect patients' motor strategies. This study investigates motor strategies of paretic and non-paretic upper limb after brain injury to highlight motor deficits or compensation strategies. Methods26 brain-injured hemiplegic patients and 24 healthy controls performed active elbow extensions in the horizontal plane, with both upper limbs for patients and, with the dominant upper limb for controls. Elbow and shoulder kinematics, interarticular coordination, net joint kinetics were quantified. FindingsResults show alterations in kinematics, and a strong correlation between elbow and shoulder angles, as well as time to reach elbow and shoulder peak angular velocity in both upper limbs of patients. Net joint kinetics were lower for paretic limb and highlighted a fragmented motor strategy with increased number of transitions between concentric and eccentric phases. InterpretationIn complement to kinematic results, our kinetic results confirmed patients' difficulties to manage both spatially and temporally the joint degrees of freedom redundancy but revealed a fragmented compensatory motor strategy allowing patients upper limb extension despite quality alteration and decrease in energy efficiency. Motor rehabilitation should improve the management of this fragmentation strategy to improve the performance and the efficiency of active movement after brain injury.

Evaluation of the Kinesio Taping and Real-Time External Feedback Effects on Lower Extremity Function During Single-Leg Squat in Individuals With Tibiofemoral Varus Alignment

Background and Aims People with postural malalignment such as tibiofemoral varus (TFRV) may experience movement patterns dysfunction during functional activities that are related to non-contact lower extremity injuries. Training protocols should be designed for these people to control and improve their functional dysfunctions. The present study aimed to investigate the effect of posterior X-taping (PXT) and real-time external feedback (RTF) on kinematic and electromyographic indices of the lower extremities during the single-leg squat task in individuals with TFRV. Methods Electromyographic and kinematic information of the lower extremities of 24 recreational athletes with TFRV (PXT=12, RTF=12) were recorded while participants in both groups performed single-leg squat 5 times consecutively and took a 2-minute rest between two different conditions (before and after the intervention). To analyze the data, 2-way analysis of variance and Bonferroni post hoc test were used at the significant level of P≤0.05. Results The present study results indicated an increase in gluteus medius muscle activity (P=0.013) in the eccentric phase and a decrease in hip adduction (P=0.001) in maximal knee flexion (P=0.034) after the intervention compared to before the intervention in the RTF group. Also, there was a reduction in external tibiofemoral rotation of the knee after the intervention compared to before intervention in maximal knee flexion (P=0.034), eccentric phase (P=0.001), and concentric phase (P=0.001) in the PXT group. In addition, there was a decreased ankle pronation after the intervention compared to before the intervention in the eccentric phase (P=0.001) and concentric (P=0.001) in the PXT group and in the eccentric phase (P=0.004) in the RTF group. Besides, there was an increased ankle abduction after the intervention compared to before the intervention in the concentric phase (P=0.001), eccentric phase (P=0.001), and maximum knee flexion (P=0.004) in the PXT group, and in the eccentric phase in the RTF group (P=0.006). Finally, there was a decrease in ankle flexion dorsiflexion at maximum knee flexion after the intervention compared to before the intervention (P=0.017) in the RTF group. Conclusion The results of the present study showed that PXT and RTF interventions can affect the kinematic parameters of individuals with TFRV malalignment in different ways and can be used to correct immediately postural defects during the single-leg squat task.

Acute Effects of Countermovement Jumps with Post-activation Potentiation Utilizing Additional Elastic Resistance during Eccentric Stretching Phase

&lt;p&gt;目的：本研究欲探究下蹲階段輔以彈性阻力之反向跳預先活動，對於6分鐘恢復時間後之跳躍表現的活化後增益效應。方法：本研究招募11名國立大學體育相關科系男性學生為受試對象，施以2循環、每循環5次的反向跳預先活動，且於下蹲制動階段介入外加彈性阻力，阻力強度分為0% BW、15% BW、30% BW三種情境，並於預先活動介入前與介入後第6分鐘後進行前測與後測。以兩塊測力板擷取前測與後測之反向跳過程中垂直地面反作用力值與時間，並計算發力率、跳躍高度、修正式反應力量指標以及下肢勁度。以相依樣本 t-test 進行統計檢驗，統計水準訂為 &amp;alpha; = .05，比較前測與後測的下肢動態力量特徵之參數是否有差異。結果：本研究結果顯示，三種介入模式皆顯著提升反向跳制動末點力值 (p &lt; .05)。15% BW與30% BW的介入模式顯著提升制動期與推蹬期發力率 (p &lt; .05)。30 % BW的介入模式顯著提升反向跳下肢勁度、修正式反應力量指標，並縮短制動期時間 (p &lt; .05)。結論：本研究之介入應有助於增進牽張反射機制之效益，尤其是在離心制動階段的肌力特徵表現上，因此，建議在進行具備牽張反射機制之動作執行前，可透過反向跳下蹲階段輔以30% BW彈性阻力進行下肢動態肌力活化之預先活動，以助於後續之運動表現。&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;&lt;p&gt;Purpose: The current study aimed at exploring the immediate effect of pre-activities of countermovement jumps, with elastic resistance and 6 minutes of recovery time, on post-activation potentiation during squatting phase. Method: Eleven male college students recruited from the Physical Education department at National Dong Hwa University were asked to perform pre-activities of countermovement jumps (2 cycles, 5 repetitions for each cycle), with elastic resistances (0% BW, 15% BW, and 30% BW) during the squatting phase, followed by pre-tests and post-tests before and after six minutes of recovery time. Two AMTI force plates were used to collect data on vertical ground reaction force and time during countermovement jumps for pre- and post-tests. Rate of force development, jump heights, reactive strength index modified, and lower extremity stiffness were calculated accordingly. Dependent sample t-test was conducted (&amp;alpha;=.05) to determine if there were significant differences in the parameters related to lower extremity dynamic strength between the pre- and post-tests. Results: Pre-activities with all three interventions significantly increased the ground reaction forces during the breaking phase (p &lt; .05). Pre-activities with elastic resistances of 15% and 30% BW significantly elevated the rates of force development during the breaking and propulsive phases (p &lt; .05). Pre-activities with 30% BW elastic resistance significantly led to increased lower extremity stiffness, reactive strength index modified, and decreased breaking time (p &lt; .05). Conclusion: The added elastic resistance enhanced the benefits of stretch reflex mechanism, especially the muscle strength characteristics during the eccentric breaking phase. Based on our finding, countermovement jumps with pre-activity with elastic resistance of 30% BW is recommended prior to performing movements concerning stretch reflex mechanism.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Concerns about the application of resistance exercise with blood-flow restriction and thrombosis risk in hemodialysis patients

BackgroundHemodialysis (HD) per se is a risk factor for thrombosis. Considering the growing body of evidence on blood-flow restriction (BFR) exercise in HD patients, identification of possible risk factors related to the prothrombotic agent D-dimer is required for the safety and feasibility of this training model. The aim of the present study was to identify risk factors associated with higher D-dimer levels and to determine the acute effect of resistance exercise (RE) with BFR on this molecule. MethodsTwo hundred and six HD patients volunteered for this study (all with a glomerular filtration rate of <15 mL/min/1.73 m2). The RE + BFR session consisted of 50% arterial occlusion pressure during 50 min sessions of HD (intradialytic exercise). RE repetitions included concentric and eccentric lifting phases (each lasting 2 s) and were supervised by a strength and conditioning specialist. ResultsSeveral variables were associated with elevated levels of D-dimer, including higher blood glucose, citrate use, recent cardiovascular events, recent intercurrents, higher inflammatory status, catheter as vascular access, older patients (>70 years old), and HD vintage. Furthermore, RE + BFR significantly increases D-dimer after 4 h. Patients with borderline baseline D-dimer levels (400–490 ng/mL) displayed increased risk of elevating D-dimer over the normal range (≥500 ng/mL). ConclusionThese results identified factors associated with a heightened prothrombotic state and may assist in the screening process for HD patients who wish to undergo RE + BFR. D-dimer and/or other fibrinolysis factors should be assessed at baseline and throughout the protocol as a precautionary measure to maximize safety during RE + BFR.