Knee Flexor Research Articles

Individual Control Strategies in Training: Myoelectric activity and recruitment strategies in the co-contraction training

BACKGROUND: The literature in motor control has abundant evidence on within-/between-person variability when it comes to control strategies in several behaviors - which largely influences intervention outcomes. Despite being an intervention itself, strength training paradigms are yet to be analyzed beyond the average behavior. Based on myoelectric activity (EMG) analyses, this study emerges as a descriptive analysis on how the co-contraction training paradigm provides stimuli for strength training of knee extensors and flexors. AIM: Considering the potential large interindividual variability in muscle activation patterns during resistance training, we explored the co-contraction paradigm considering the individual characteristics. METHOD: Ten active male adults participated in two days of co-contraction training paradigm with their EMG activity collected (sartorius, biceps femoris long and short heads, semitendinosus, semimembranosus, rectus femoris, vastus lateralis and medialis and tensor fascia-latae). RESULTS: On average, participants recruit 36% of their maximum EMG amplitude, decay 0.41% per repetition but increase 7.45% between sessions. The training stimulated similarly the knee flexors and extensors EMG ratio of all participants. However, participants demonstrated different average muscle recruitment patterns with few individuals modifying, largely, their recruitment over repetitions/days. Between and within-variability in recruitment pattern was maintained throughout repetitions and days. CONCLUSION: Thus, the co-contraction training demonstrated sufficient muscle activation to be employed and evoked similar muscular recruitment between agonists and antagonists. To the best of our knowledge, this is a pioneer study encompassing the complexity of movement control in evaluating a strength training protocol.

Recovery kinetics following sprint training: resisted versus unresisted sprints.

To determine the recovery kinetics of performance and exercise-induced muscle damage following different sprint-training protocols. In a crossover design, ten male and female athletes (20.6 ± 2.4years) performed 2× (3 × 20m: 2min rest) and 1× (3 × 30m: 3min rest) of: (a) unresisted sprints (UST), (b) resisted sprints with 10% of body mass (BM) load (RST10), (c) resisted sprints with 20% BM load (RST20), against a control trial (no-training). Blood lactate (mmol/L) increased post-training versus pre-training in all sprint-training trials (6.7 ± 2.4 vs 1.2 ± 0.2, 5.6 ± 2.4 vs 1.3 ± 0.3, 7.3 ± 2.7 vs 1.2 ± 0.3, in UST, RST10, RST20, respectively), as did creatine kinase (U/L) 24h, 48h and 72h post-training (UST: 251 ± 173, 238 ± 154, 209 ± 115 vs 155 ± 9, RST10: 252 ± 134, 240 ± 83, 218 ± 103 vs 164 ± 106; RST20: 237 ± 133, 323 ± 303, 262 ± 184 vs 179 ± 106, respectively). DOMS of knee-extensors (KE) and knee-flexors (KF) increased post-training up to 72h in all sprint-training trials versus pre-training (ranging from 1.6 ± 1.3 to 3.8 ± 2.8 vs 1.0 ± 0, respectively). Eccentric torque (Nm) of the KE of the non-dominant limb, decreased 24h post-training versus pre-training in all sprint-training trials (UST: 249 ± 49 vs 266 ± 54; RST10: 229 ± 52 vs 273 ± 72; RST20: 253 ± 6 vs 262 ± 56), as did that of the KF of the dominant limb (UST: 135 ± 29 vs 144 ± 26; RST10: 130 ± 29 vs 140 ± 25; RST20: 139 ± 33 vs 142 ± 26). 10-m sprint-time (s) increased 48h post-training versus pre-training (1.81 ± 0.15 vs 1.77 ± 0.11), and 30-m sprint-time increased 24h, 48h, 72h post-training versus pre-training (4.35 ± 0.36, 4.40 ± 0.44, 4.33 ± 0.41 vs 4.21 ± 0.34, respectively), only in RST20. Unresisted and resisted sprint-training induces prolonged reduction of muscle strength (24h), and sprinting performance (72h), associated with prolonged increase of DOMS and CK (72h).

Is the rate of force development scaling factor associated with the rate of agonist muscle activation scaling factor and the level of agonist-antagonist coactivation?

BACKGROUND: Rate of force development scaling factor (RFD-SF) is used to assess neuromuscular quickness across submaximal levels. It has been suggested that such metric would be associated with the magnitude of the agonist muscle activation and with the level of simultaneous antagonist muscle group activation, i.e., agonist-antagonist coactivation. AIM: To examine the associations between 1) the RFD-SF and the rate of agonist muscle activation scaling factor (RAgMA-SF) and 2) the RFD-SF and the agonist-antagonist coactivation. METHOD: Eleven healthy and physically active subjects (7 men and 4 women, aged between 18 and 22 years) performed maximal strength tests of the knee extensors and flexors and a test that involved the production of brief submaximal force pulses of the knee extensors. The force exerted was recorded by a load cell and the electromyographic activities of the vastus lateralis and biceps femoris muscles were obtained during the tests. In the brief force pulses test, individuals were asked to produce around 120 submaximal force pulses that ranged between 20 to 80% of their maximum force value, while trying to produce each force pulse as fast as possible. The values of RFD-SF, RAgMA-SF of the vastus lateralis muscle, and a coactivation index (ICOA) were computed. RESULTS: The RFD-SF is strongly associated with the RAgMA-SF (r=0.74; p=0.009) but not with the ICOA (r=0.29; p=0.38). CONCLUSION: The RFD-SF is directly associated with the rate of agonist muscle activation and is not affected by the degree of coactivation between agonist and antagonist muscles.

Bilateral Asymmetry and the Relationship Between Unilateral Isokinetic Strength and Balance Performance in Male Adolescent Football Players

Muscle strength and balance ability have been related to injury prevention and game actions performance in football. The aims of this study are twofold: (1) to examine bilateral asymmetries in isokinetic strength and balance assessments, and (2) to evaluate the relationship between muscle strength and balance measures. Eighty-eight male adolescent football players were assessed for body composition (InBody 770), isokinetic strength (Biodex System 4 Pro Dynamometer), and balance performance (Biodex Balance System). Paired samples t-tests were conducted to determine bilateral differences in strength and balance. Pearson correlations and multiple linear regression analyses evaluated the relationship between strength and balance. No significant bilateral strength differences were observed in knee flexors (KF) and knee extensors (KE) peak torque (PT) scores. No bilateral differences were found for balance measures, except in the lateromedial stability index, which was better while performing with the preferred leg (p ≤ 0.01; d = 0.29). Significant correlations were found between KE PT and balance tasks (p ≤ 0.01). KF and KE PT shared between 18 and 22% of the common variance in the overall stability index in the non-preferred and preferred leg, respectively. Monitoring strategies of bilateral asymmetries may be crucial to enhance performance in tasks underpinned by unilateral movements, such as changes of direction and sprints, and to identify players at risk of injury. Adopting these strategies during the early stages of football training might be crucial for players’ long-term development.

Exploring the issue of ‘functionality’ in isokinetic dynamometry

ABSTRACT Strength is a primary and modifiable contributor to performance, injury risk, and rehabilitative success. The gold standard measure of strength is the isokinetic dynamometer, providing the clinician with the opportunity to manipulate contraction modality, range, and speed about a joint. However, criticism has highlighted a lack of functional relevance, with arbitrary selection of speed across the full range. To better understand function, biomechanical analysis of movement can inform a bespoke isokinetic data collection protocol. In this case, we use walking gait, a function goal for daily living and clinically assessed following knee replacement surgery for example. Concentric knee flexor and extensor demand was evident at an average angular velocity of 70°·s−1, whilst eccentric knee flexor and extensor demands were evident at speeds of 192°·s−1 and 165°·s−1, respectively. The efficacy of isokinetic dynamometry can be enhanced with bespoke data collection protocols, which better reflect the functional demands of the clinical movement objective.

Adolescent and young adult hip and knee strength profiles relate to running gait biomechanics

ObjectivesCompare and assess relationships between strength and running biomechanics among healthy adolescents and young adult males and females. DesignRetrospective cohort. SettingClinic. Participants802 healthy participants (570 F, 232 M; 16.6 ± 2.3 years). Main outcome measuresMass-normalized knee flexor and extensor strength, hip adductor and abductor strength, hamstrings-to-quadriceps (H:Q), and abductor-to-adductor (Abd:Add) ratios were obtained using hand-held dynamometry. Mass-normalized peak vertical ground reaction force (vGRF), %stance, cadence, and stride length were obtained using an instrumented treadmill. Multivariate analyses of variance were used to compare strength and biomechanics across ages and sexes. Linear regressions were used to assess the relationships between strength and biomechanics, accounting for speed, age, and sex. Independent t-tests were used to compare strength between strength ratio profiles. ResultsStrength and running biomechanics significantly differed between sexes (p-range: <0.001–0.05) and age groups (p-range: <0.001–0.02). Strength and strength ratios were significantly associated with increased cadence (p-range:0.001–0.04) and stride lengths (p-range:0.004–0.03), and decreased vGRF (p < 0.001). Lower H:Q ratios had significantly lower strength measures (p < 0.001). Higher Abd:Add ratios had significantly increased abductor strength (p < 0.001). ConclusionsStrength and running biomechanics differed by sexes and ages. Hip and knee strength and strength ratios were related to select spatiotemporal and kinetic biomechanical features.

Preoperative high-intensity strength training combined with balance training can improve early outcomes after total knee arthroplasty

BackgroundTo investigate the effect of preoperative high-intensity strength training combined with balance training on the knee function of end-stage knee osteoarthritis (KOA) patients after total knee arthroplasty (TKA).MethodsA prospective study was conducted on end-stage KOA patients awaiting TKA. The patients were divided into an experimental group and a control group according to whether they received a preoperative training intervention. The differences in knee flexor–extensor strength, knee range of motion (ROM), timed up and go (TUG) test result, stair ascend/descend test result, Knee Society score (KSS) and Berg balance scale (BBS) score were assessed in both groups at baseline (T1), before operation (T2), 3 months after operation (T3), and 1 year after operation (T4).ResultsAfter high-intensity strength training and balance training, the knee flexor–extensor strength, TUG test result, stair ascend/descend test result, and KSS were all significantly improved at T2 in the experimental group over the control group. At T3, the knee ROM, knee flexor–extensor strength, TUG test result, BBS score, and KSS clinical and functional scores were all significantly superior in the experimental group. The experimental group enjoyed a superiority in KSS clinical and functional scores until T4. Group × time and between-group interactions were found in all assessment indicators in both groups (p < 0.01).ConclusionPreoperative high-intensity strength training combined with balance training can enhance the knee flexor–extensor strength and balance of patients with end-stage KOA in the short term and help improve early outcomes after KOA.Trial registration ChiCTR2000032857, 2020-05-13.

Hamstring Strain Injury Risk Factors in Australian Football Change over the Course of the Season.

This study aimed to determine which factors were most predictive of hamstring strain injury (HSI) during different stages of the competition in professional Australian Football. Across two competitive seasons, eccentric knee flexor strength and biceps femoris long head architecture of 311 Australian Football players (455 player seasons) were assessed at the start and end of preseason and in the middle of the competitive season. Details of any prospective HSI were collated by medical staff of participating teams. Multiple logistic regression models were built to identify important risk factors for HSI at the different time points across the season. There were 16, 33, and 21 new HSIs reported in preseason, early in-season, and late in-season, respectively, across two competitive seasons. Multivariate logistic regression and recursive feature selection revealed that risk factors were different for preseason, early in-season, and late in-season HSIs. A combination of previous HSI, age, height, and muscle thickness were most associated with preseason injuries (median area under the curve [AUC], 0.83). Pennation angle and fascicle length had the strongest association with early in-season injuries (median AUC, 0.86). None of the input variables were associated with late in-season injuries (median AUC, 0.46). The identification of early in-season HSI and late in-season HSI was not improved by the magnitude of change of data across preseason (median AUC, 0.67). Risk factors associated with prospective HSI were different across the season in Australian Rules Football, with nonmodifiable factors (previous HSI, age, and height) mostly associated with preseason injuries. Early in-season HSI were associated with modifiable factors, notably biceps femoris long head architectural measures. The prediction of in-season HSI was not improved by assessing the magnitude of change in data across preseason.

Rugby Players Exhibit Stiffer Biceps Femoris, Lower Biceps Femoris Fascicle Length to Knee Extensors, and Knee Flexors to Extensors Muscle Volume Ratios Than Active Controls.

This study aimed to determine if hamstring-strain-injury risk factors related to muscle structure and morphology differed between rugby union players and controls. The biceps femoris long head (BFlh) fascicle length and passive muscle stiffness and relative and absolute muscle volume of knee flexors (KF) and extensors (KE) were measured in 21 male subelite rugby players and 21 male physically active nonathletes. BFlh fascicle length was significantly longer (mean difference [MD] = 1.6 [1.7]cm) and BFlh passive muscle stiffness was significantly higher in rugby players (MD = 7.8 [14.8]kPa). The absolute BFlh (MD = 71.9 [73.3]cm3), KF (MD = 332.3 [337.2]cm3), and KE (MD = 956.3 [557.4]cm3) muscle volumes were also significantly higher in rugby players. There were no significant differences in the relative BFlh and KF muscle volumes. The relative KE muscle volumes were significantly higher in rugby players (MD = 2.3 [3.7]cm3/kg). However, the percentage BFlh fascicle length:KE (MD = -0.1% [0.1%]), BFlh/KE (MD = -0.9% [1.9%]), and KF:KE (MD = -4.9% [5.9%]) muscle volume ratios were significantly lower in the rugby players. BFlh muscle volume significantly correlated with BFlh fascicle length (r = .59, r2 = .35) and passive muscle stiffness (r = .46, r2 = .21). Future prospective studies should examine whether there are threshold values in BFlh passive muscle stiffness and BFlh fascicle length:KE, BFlh:KE, and KF:KE muscle volume ratios for predicting hamstring strain injuries.

The relationship of knee flexor and extensor muscle strength and tightness with squat performance in children with cerebral palsy

The relationship of knee flexor and extensor muscle strength and tightness with squat performance in children with cerebral palsy

Reduced peripheral and respiratory muscle strength in pediatric patients after kidney transplantation.

Reduced muscle strength and low-exercise capacity are well documented in adults, but there are few studies examining those impairments in children and adolescents after kidney transplantation. The objective of this study was to evaluate peripheral and respiratory muscle strength and the association with submaximal exercise capacity in children and adolescents after kidney transplant. Forty-seven patients between six and 18 years of age clinically stable after transplantation were included. Peripheral muscle strength (isokinetic and hand-grip dynamometry), respiratory muscle strength (maximal inspiratory and expiratory pressure), and submaximal exercise capacity (six-minute walk test - 6MWT) were assessed. Patients had a mean age of 13.1 ± 2.7 years and an average of 34 months had elapsed since the transplantation. Flexors of the knee showed a significant reduction in muscle strength (77.3% of predicted) and knee extensors had normal values (105.4% of predicted). Hand-grip strength and maximal respiratory pressures (inspiratory and expiratory) also were significantly lower than expected (p < 0.001). Although distance walked in the 6MWT was significantly lower than predicted (p < 0.001), no significant correlation was found with peripheral and respiratory muscle strength. Children and adolescents after kidney transplantation have reduced peripheral muscle strength of knee flexors, hand-grip, and maximal respiratory pressures. No associations were found between peripheral and respiratory muscle strength and submaximal exercise capacity.

Effect of contraction type at varying angular velocities on isokinetic muscle strength training.

The aim of this study is to determine whether concentric and eccentric isokinetic training performed at certain angular velocities in sedentary individuals is effective only in the angular velocities and contraction type where the training is performed, or at other angular velocities and contraction types that are not being trained. Twenty-eight sedentary individuals (matched according to weight, age and gender) volunteered to participate in this case study. The study was conducted on a total of 56 extremities belonging to 28 individuals (14 women, 14 men) aged between 24 and 60 years. Concentric and eccentric strength tests were performed at 30-60-90-120-150-180°/sec. The participants were randomly divided into two groups as concentric training group and eccentric training group, through stratified randomization matching. The training was done 3 days a week for a total of 6 weeks. At the end of the study, no difference was found between the pre- and posttraining measurements in the concentric training group (P>0.05). In the eccentric training group, the eccentric muscle strength of the knee flexors and extensors at angular velocity of 90°/sec, the eccentric strength of the knee extensors at angular velocity of 120°/sec, and the eccentric muscle strength of the knee flexors at angular velocity of 180°/sec were found to be different and an increase was seen after the training (P=0.032, P=0.049, P=0.041, P=0.032). These results demonstrate that eccentric training may be preferred in cases where muscle strength increase is needed in short time.

Effects of progressive body-weight versus barbell back squat training on strength, hypertrophy and body fat among sedentary young women

The objective of this study was to compare the effects of progressive bodyweight training and barbell back squat on muscle strength, muscluar hypertrophy, and body fat percentage in sedentary young women. Thirteen sedentary young women (aged 19.77 ± 0.83 years, height 164.91 ± 6.01) were randomly assigned to either the progressive bodyweight group (n = 6, consisting of 10 levels of movements progressing from bilateral to unilateral) or the barbell squat group (n = 7, 60–80% 1RM). Both groups underwent two training sessions per week for 6 weeks. Measurements of muscle strength (isokinetic knee extensor and flexor muscle peak torque of each leg), muscle thickness (gluteus maximus, rectus femoris, and gastrocnemius muscles), and body fat percentage were taken at baseline and post-testing. Both groups showed a significant increase in isometric peak torque of the knee extensor and flexor (p < 0.05), but there were no significant between-group differences in isometric peak torque of the knee extensor and flexor (p > 0.05) or in the mean concentric peak torque of the knee H/Q ratio (p > 0.05). Both groups also showed significant increases in muscle thickness (p < 0.05), with no significant differences in Gastrocnemius, Rectus femoris and Gluteus maximus (p > 0.05). The percentage of body fat significantly decreased in the barbell group (pre: 28.66 ± 4.58% vs post: 24.96 ± 5.91%, p = 0.044), but not in the bodyweight group (pre: 24.18 ± 4.63% vs post: 24.02 ± 4.48%, p = 0.679). Our findings indicate that while both training methods increased maximum strength and muscle mass, barbell back squat training may be more effective in reducing body fat percentage.

Pistachios as a recovery food following downhill running exercise in recreational team-sport individuals

ABSTRACT We aimed to investigate the impact of pistachio nut consumption on muscle soreness and function following exercise-induced muscle damage. Using a randomised cross-over design, male team-sport players (n = 18) performed a 40-minute downhill treadmill run to induce muscle damage, which was conducted after 2-wks of consuming either control (CON, water), a standard dose of daily pistachios (STD, 42.5 g/d) or a higher dose of daily pistachios (HIGH, 85 g/d). Lower limb muscle soreness (visual analogue scale), muscle function (maximal voluntary isokinetic torque and vertical jump), and blood markers of muscle damage/inflammation (creatine kinase, C-reactive protein, myoglobin, superoxide dismutase) were measured pre (baseline) and post (24, 48, and 72 h) exercise. No trial order effects were observed for any outcome measurement across trials. Mean quadriceps soreness (non-dominant leg) during exercise recovery was reduced (p < 0.05) in HIGH vs. CON (mean difference (95%CI): 13(1–25) mm). Change in soreness in the dominant quadriceps was not different between HIGH vs. CON (p = 0.06; mean difference (95%CI): 13(−1 to 26 mm)). No main effects of time or trial were observed for mean soreness of hamstrings, or on isokinetic torque of knee extensors or knee flexors, during recovery. Serum creatine kinase concentration peaked at 24 h post-damage (mean(SEM): 763(158)µg/L) from baseline (300(87)µg/L), but had returned to baseline by 72 h post (398(80)µg/L) exercise in all trials, with no trial or trial × time interaction evident. These data suggest that high dose pistachio nut ingestion may provide some alleviation of muscle soreness, but no effect on muscle function, following modest muscle damage.

Analysis of technical characteristics of typical lower limb balance movements in Tai Chi: a cross-sectional study based on AnyBody bone muscle modeling.

Tai Chi is an excellent traditional Chinese physical fitness exercise, and its unique balancing movements are very important for improving human balance. In this study, the two most representative Tai Chi balance movements, "knee lift balance" and "leg stirrup balance", were selected to establish the lower limb bone muscle model of Tai Chi balance movements by using computer simulation modeling technology, aiming to analyze the characteristics of the lower limb movement mechanisms of typical balance movements, to provide a quantitative theoretical basis for improving the scientific level of Tai Chi. A total of 16 subjects were recruited for this study. the BTS three-dimensional motion capture system and three-dimensional force platform were used for motion data acquisition, the physiological electromyographic signals were collected using BTS surface electromyography, and the lower limb bone muscle model of Tai Chi balance movements was established by AnyBody human simulation. In the knee lift balancing movement, the balance leg hip abduction/adduction angle, hip flexion/extension moment, and the strength of the rectus femoris muscle, biceps femoris short capitis, and iliacus muscle of the amateur group was significantly smaller than that of the professional group (P<0.01). In the leg stirrup balance movement, the knee flexion/extension angle of the balancing leg in the amateur group was significantly greater than that in the professional group (P<0.01), and the hip flexion/extension angle, hip inversion/abduction angle, knee flexion/extension moment, hip flexion/extension moment, the strength iliacus, gluteus maximus, and obturator internus were significantly smaller than those in the professional group (P<0.01). The integral EMG of the biceps femoris of the support leg in the amateur group was significantly smaller than that of the professional group (P<0.01). The integral EMG of the lateral femoral muscle of the balance leg was significantly smaller than that of the professional group (P<0.01). In this study, we found that the balancing leg of the balancing movement has a larger hip joint angle, the stirrup balancing knee joint angle is smaller, and the hip and knee joint moments are larger. This is related to joint activity and muscle activation, and amateurs should pay attention to increasing the range of motion of the hip joint and decreasing the range of motion of the knee joint when practicing to better stimulate exercise of the lower limb joints. In addition, the practice of balancing movements should strengthen the iliacus muscle, which plays an important role in maintaining the stable balance of the lower limbs, and strengthen the knee flexor and extensor muscles and hip adductor/abductor muscles of the balancing leg, thus promoting the stability of the balancing leg movements.

Effects of repeated sprinting on hamstring shear modulus pattern and knee flexor neuromuscular parameters

The purpose of the present study was to examine the acute effects of a maximum repeated sprint protocol on (1) hamstring shear modulus and (2) knee flexor neuromuscular parameters such as peak torque (PT) and rate of torque development (RTD). Muscle shear modulus was assessed in 18 healthy males using shear wave elastography at rest and during 30° isometric knee flexion at 20% of maximal voluntary isometric contraction, before and after a 10 × 30 m repeated sprint protocol. There was a 9% decrease in average speed between the fastest and slowest sprint (p < 0.001; d = 2.27). A pre-post decrease was observed in PT (p = 0.004; η2p = 0.399) and in the 0–50 ms (p = 0.042; η2p = 0.222), and 50–100 ms (p = 0.028; η2p = 0.254) RTD periods. For the active shear modulus, the only significant change after the sprint task was in the biceps femoris long head (BFlh) with an increase of 10% (Pre: 26.29 ± 8.89 kPa; Post: 28.93 ± 8.31 kPa; p = 0.015; d = 0.31). The present study provides evidence that repeated sprinting leads to significant decreases in average speed, PT, early RTD (0–50 ms; 50–100 ms), and to an increase in BFlh active shear modulus without changing the shear modulus of the other hamstrings muscles.

Reproducibility of knee extensor and flexor contraction velocity in healthy men and women assessed using tensiomyography: A registered report.

Tensiomyography measures the radial displacement of a muscle during an electrically evoked twitch contraction. Different concepts to determine the rate of displacement (Vc) from the maximum twitch exist, but information on their reproducibility is scarce. Further, different inter-stimuli intervals during progressive stimulation are used, but the effect of different intervals on Vc is unclear. The first aim of this study was to investigate the within and between-day reliability of the five most frequently used Vc concepts. The second aim was to investigate the effect of different inter-stimuli intervals on Vc. On two consecutive days, we determined Vc of the biceps femoris long head and rectus femoris of twenty-four healthy subjects. The maximum displacement was determined twice within three minutes on day one and a third time 24 h later. Also, on day two, we applied three blocks of ten consecutive stimuli at a constant intensity of 50 mA, separated by 3 min each. Inter-stimuli intervals in randomly ordered blocks were 10 s, 20 s or 30 s, respectively. All Vc concepts displayed good to excellent relative (ICC 0.87-0.99) and generally good absolute within- and between-day reliability for both muscles. Across Vc-concepts, absolute reliability was higher for the rectus femoris (CV% 1.3-7.95%) compared to the biceps femoris (CV% 6.06-15.30%). In both muscles, Vc was generally not affected by different inter-stimuli intervals. For most Vc concepts, repeated stimulation induced an increase regardless of the inter-stimuli interval, but this effect was mainly trivial and small at most. The reproducibility of Vc concepts was generally good but varies between different muscles. A rest interval of 10 s seems preferable to longer intervals for less time required per measurement. Following this initial study, the effect of different inter-stimuli intervals on Vc should be further investigated.

Submaximal fatiguing eccentric contractions of knee flexors alter leg extrapersonal representation

This study assessed the immediate and prolonged effects of eccentric-induced fatigue on position sense, utilizing position-pointing tasks, which had not been previously implemented for this purpose. Fifteen healthy adults underwent a fatiguing eccentric protocol that entailed sets of unilateral submaximal contractions of knee flexor muscles until reaching a 20% decrease in maximal isometric torque production. Evaluations of knee flexor neuromuscular function as well as position-pointing tasks at 40° and 70° of knee flexion were conducted prior to the fatiguing eccentric protocol, immediately after (POST), and 24 h after (POST24) exercise termination. To assess neuromuscular fatigue etiology, electrical myostimulations were administered during and after maximal voluntary isometric contractions. At POST, the voluntary activation level and evoked potentiated doublet amplitude at 100 Hz were significantly reduced. In addition, position-pointing errors exhibited a significant increase at POST regardless of the tested angle, with participants positioning the pointer in a more extended position compared to their hidden exercised limb. At POST24, neuromuscular function and position sense parameters had reverted to their baseline levels. The findings of this experiment demonstrate that position-pointing accuracy was impaired immediately after the fatiguing eccentric protocol, manifesting in the presence of both central and peripheral fatigue. As position-pointing accuracy relies heavily on extrapersonal representation of the body at the brain level, acute changes in exercised limb's extrapersonal representation might have resulted from central fatigue-related mechanisms altering the cognitive processes responsible for converting kinesthetic signals into extrapersonal coordinates.

Learning effect on an isokinetic knee strength test protocol among male adolescent athletes.

Learning effect occurs when the best performance is not achieved at the earliest trial of a repeated protocol of evaluation. The present study examined, within testing session, the intra-individual variation in an isokinetic strength protocol composed of five reciprocal concentric and eccentric contractions of knee extensors (KE) and knee flexors (KF) among male adolescent swimmers. Additionally, test-retest reliability was determined as intra-individual mean differences between two consecutive testing sessions. The sample included 38 swimmers aged 10.1-13.3 years. A subsample (n = 17) completed a second visit. Isokinetic dynamometry was used to assess concentric and eccentric contractions of KE and KF at an angular velocity of 60°.s-1. The protocol included three preliminary repetitions that were not retained for analysis, a 60-second interval, and five reciprocal maximal concentric contractions (cc). The preceding sequence was repeated for eccentric contractions (ecc) of KE and KF. Multilevel regression confirmed intra-individual and inter-individual levels as significant sources of variance in peak torque (PT) values. Intra-class correlation (ICC) fluctuated between 0.582 and 0.834 and, in general, a substantial percentage of participants need more than three repetitions to attain their best PT: KEcc (36.8%), KEecc (23.7%), KFcc (39.5%), KFecc (18.4%). For the subsample of 17 swimmers who completed a second testing session, intra-individual mean differences of the best PT were trivial or small. In summary, the validity of shorter protocols may be compromised if swimmers do not attain their best peak torque in the first few attempts, and the reliability of a 5-repetition protocol seemed acceptable.

Concentric Isokinetic Strengthening Program's Impact on Knee Biomechanical Parameters, Physical Performance and Quality of Life in Overweight/Obese Women with Chronic Meniscal Lesions.

Meniscal injuries are one of the most common intra-articular knee injuries. Different treatments are presented depending on the symptoms and duration of meniscus tears, such as arthroscopic partial meniscectomy, physiotherapy, or even pharmacological treatment. The purpose was to investigate the effect of a concentric isokinetic knee muscle strengthening program on strength, joint range of motion, physical performance, quality of life and pain tolerance in overweight/obese women with chronic meniscal lesions. Twenty-four overweight/obese women were randomized into two groups. A control group (CG) performed a usual rehabilitation program plus isokinetic muscle strengthening (IMS) in the continuous passive motion mode and measured with an isokinetic dynamometer. An experimental group (EG) performed the same program in combination with IMS in the isokinetic active mode. The peak torque of the knee extensors (PTE) and flexors (PTF), sit-to-stand test, stair climb test, joint amplitude, heel-to-buttock distance, Thessaly test, KOOS questionnaire of pain and quality of life were measured pre- and post-protocol. After the intervention, the sit-stand number for both groups was significantly higher (p < 0.001) and the time to climb stairs was significantly reduced for the EG (p < 0.001). A significant improvement in joint range of motion, life quality (p < 0.001), relief in knee pain (p < 0.001) and in the post-program evaluation at the EG (p < 0.05) was noted. There was no significant difference in PTE and PTF between groups at 60°/s and 180°/s. The IMS in the active mode could be an effective therapeutic modality in managing middle-aged patients suffering from a degenerative meniscal tear.