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BACKGROUND: It is important for clinicians and researchers to perform dynamic postural control evaluation for predicting musculoskeletal conditions, injury prevention, and rehabilitation. OBJECTIVE: The purpose of this study was to investigate the relationship (1) between the eccentric strength of the knee extensors and star excursion balance test (SEBT), and (2) between the knee proprioception and SEBT. METHODS: Forty healthy young adults participated in this study. The eccentric peak torque (EPT) of the knee extensors, joint position sense, and force sense were measured. The participants also performed SEBT. Pearson’s product-moment correlation and multiple linear regression analysis were used to determine the relationship between the variables and SEBT. RESULTS: The posteromedial direction of the SEBT was positively and strongly correlated with EPT (r= 0.74, P< 0.01). The anterior and posterolateral directions were positively and moderately correlated with EPT (r= 0.46, P< 0.01, and r= 0.69, P< 0.01, respectively.). However, knee proprioception was not correlated with all the directions of SEBT (P> 0.05). According to the results of multiple linear regression analysis, EPT of the knee extensors significantly predicted SEBT reach distances. CONCLUSION: The eccentric strength of the knee extensors seems to be an essential factor in dynamic postural control. However, the knee proprioception did not show a significant correlation with SEBT.

We examined whether the magnitude of muscle damage indicated by changes in maximal voluntary isometric contraction (MVIC) strength 1 to 3 d after unaccustomed eccentric exercise (ECC) was correlated with changes in central and peripheral neuromuscular parameters immediately post-ECC.Twenty participants (19-36 yr) performed six sets of eight eccentric contractions of the knee extensors. Rate of force development (RFD) during knee extensor MVIC, twitch force, rate of force development (RFDRT) and rate of relaxation (RRRT) of the resting twitch, maximal M-wave (MMAX), voluntary activation, silent period duration, motor-evoked potentials (MEP) and short-interval intracortical inhibition were assessed before, immediately after, and 1 to 3 d post-ECC. Relationships between changes in these variables immediately post-ECC and changes in MVIC strength at 1 to 3 d post-ECC were examined by Pearson product-moment (r) or Spearman correlations.Maximal voluntary isometric contraction strength decreased (-22.2% ± 18.4%) immediately postexercise, and remained below baseline at 1 (-16.3% ± 15.2%), 2 (-14.7% ± 13.2%) and 3 d post-ECC (-8.6% ± 15.7%). Immediately post-ECC, RFD (0-30-ms: -38.3% ± 31.4%), twitch force (-45.9% ± 22.4%), RFDRT (-32.5% ± 40.7%), RRRT (-38.0% ± 39.7%), voluntary activation (-21.4% ± 16.5%) and MEP/MMAX at rest (-42.5% ± 23.3%) also decreased, whereas the silent period duration at 10%-MVIC increased by 26.0% ± 12.2% (P0.05). Decreases in RFD at 0 to 30 ms, 0 to 50 ms, and 0 to 100 ms immediately post-ECC were correlated (P0.05) with changes in MVIC strength at 1 d (r = 0.56-0.60) and 2 d post-ECC (r = 0.53-0.63). Changes in MEP/MMAX at 10%-MVIC immediately post-ECC were correlated with changes in MVIC strength at 1 d (r = -0.53) and 2 d (r = -0.54) post-ECC (P0.05).The magnitude of decrease in MVIC strength at 1 to 3 d after ECC was associated with the magnitude of changes in RFD and MEP/MMAX immediately post-ECC. However, based on individual data, these markers were not sensitive for the practical detection of muscle damage.

Purpose: The purpose of this study was to assess neuromuscular performance capabilities over an in-season mesocycle in early-career professional soccer players and examine the relationship with training workload. Methods: Neuromuscular performance capabilities (isometric knee extensor: peak force, rate of force development, and peak twitch force) of 12 professional soccer players were assessed weekly over a 6-week period. Training and match workload were also recorded over the same period for each player (high-intensity running distance). Changes in neuromuscular performance and workload variables were analyzed. Results: There was evidence of fluctuations in neuromuscular performance capability over the mesocycle that reached statistical (P P Conclusion: Neuromuscular performance capabilities fluctuate over an in-season mesocycle and are influenced by high-intensity running workload, emphasizing the need for acute monitoring in elite soccer players.

PURPOSE We previously reported that the cross-sectional area of the quadriceps femoris is correlated with the sprint performance of preadolescent sprinters. This finding suggests a close relationship between knee extensor torque-enhancing morphology and sprint performance in this young population. To further clarify this issue, in this study, we examined the relationships of the quadriceps femoris muscle volume (MV) and knee extensor moment arm (MA) with sprint performance in preadolescent sprinters. METHODS The quadriceps femoris MV and knee extensor MA in 15 sprint-trained preadolescent boys were measured using magnetic resonance imaging. Sprint performance was evaluated using a personal best 100-m sprint time and the higher 50-m sprint velocity of two 50-m sprint tests. RESULTS The quadriceps femoris MV and knee extensor MA were significantly correlated with personal best 100-m sprint time (r = -0.810 and -0.752, P ≤ 0.001 for both) and 50-m sprint velocity (r = 0.814 and 0.702, P

The generalized joint hypermobility (GJH) syndrome is a condition characterized by a connective tissue disorder that may negatively affect the muscle function and muscle balance in the lower limbs. The aim of study was to compare isometric and dynamic maximal strength, total work, active optimum angle, electromyographic activity strategy, and the muscle imbalance of the knee extensors and flexors using the hamstrings/quadriceps ratio (H:Q) in individuals with GJH and without GJH (NGJH). Forty healthy untrained men and women (20 with GJH and 20 without GHJ) participated in the study. Dynamic, isometric (30° and 60°) peak torque, total work, active optimum angle, and agonist and antagonist muscle activation of knee extensors and flexors were obtained. The conventional and functional H:Q ratio were calculated using peak torque, rate of torque development, muscle activation, and total work. The dynamic and isometric peak torque, total work, active optimum angle, and agonist and antagonist muscle activation were not different between GJH and NGJH (p > 0.05). Conventional and functional H:Q ratios calculated using the different neuromuscular parameters were considered below the normative values for both groups, with no difference between groups (p > 0.05). The lack of difference between groups suggests that hypermobility does not have a greater influence on maximal strength and in underlying mechanisms related to knee extensors and flexors muscle activation and muscle balance in the knee joint.

This study aimed to compare neuromuscular alterations and perceptions of effort and muscle pain induced by concentric and eccentric cycling performed at the same power output or effort perception. Fifteen participants completed three 30-min sessions: one in concentric at 60% peak power output (CON) and two in eccentric, at the same power output (ECCPOWER ) or same perceived effort (ECCEFFORT ). Muscle pain, perception of effort, oxygen uptake as well as rectus femoris and vastus lateralis electromyographic activities were collected when pedaling. The knee extensors maximal voluntary contraction (MVC) torque, the torque evoked by double stimulations at 100 Hz and 10 Hz (Dt100; Dt10), and the voluntary activation level (VAL) were evaluated before and after exercise. Power output was higher in ECCEFFORT than CON (89.1 ± 23.3% peak power). Muscle pain and effort perception were greater in CON than ECCPOWER (p 0.43). MVC torque, Dt100, and VAL dropped in all conditions (p

Identifying the factors that contribute to individual differences in mid-level intensity neuromuscular fatigue is essential to improve performance and effective exercise in training and rehabilitation. This study investigated factors affecting individual differences in knee extensor fatigue induced by sustained isometric mid-level contractions. Twenty-six healthy young men performed a sustained fatiguing contraction to task failure at 40% maximal voluntary contraction (MVC) torque of the knee extensors. The MVC torque (TQMVC), evoked triplet torque (TQTRI), and voluntary activation (VA%) of the knee extensors were determined before and after the fatiguing task. Differences in TQMVC, TQTRI, and VA% before and after the fatiguing task were examined, and the relationship between TQMVC and TQTRI or VA% after the fatiguing task normalized to baseline was examined using Pearson product-moment correlation analysis. TQMVC and TQTRI decreased significantly after the fatiguing task (31.1% decrease for TQMVC, 38.8% decrease for TQTRI, p < 0.001), whereas VA% did not change significantly (4.2% increase for VA%, p = 0.057). After the fatiguing task, the normalized TQMVC was significantly correlated with the normalized TQTRI (r = 0.617, p < 0.001), but not with the normalized VA% (r = 0.348, p = 0.082). Individual differences in knee extensor fatigue induced by sustained mid-level contraction were more affected by peripheral fatigue than by central fatigue. Therefore, focusing on fatigue resistance in peripheral areas is important to improve endurance in moderate-intensity exercises.

Background and objective: There are many studies that have examined the differences in isokinetic strength performance differences in athletes; however, observing these angular velocity-dependent differences on surface maps is a very practical and useful application. The aim of this study was to determine the angular velocity-dependent isokinetic knee extensor/flexor muscle strength and jump performance and to compare the test results and 3D torque-angle-velocity surface maps of amateur and professional volleyball players. Materials and methods: We included 25 well-trained male volleyball players (14 professionals and 11 amateurs) with a mean age of 21.8 ± 2.6 years (range 18–27 years) in this cross-sectional study. The dominant knee concentric muscle contractions were analyzed at 300, 120, and 60∘/s angular velocities to determine peak torque (PT), total work (TW), mean power (MP), angle of peak torque (APT), and hamstring-to-quadriceps torque ratio (H:Q). Vertical jump performance was assessed using countermovement jump (CMJ) test. These data were processed using a MATLAB algorithm for constructing the 3D torque-angle-velocity surface maps. Results and conclusions: Significant differences were identified for extensor–flexor PT between PRO and AT at 300 and 120∘/s (p < 0.05). Moreover, there were significant differences between groups for MP and APT at 300 and 120∘/s for TW at all velocities. CMJ test results were significantly different between the groups (p < 0.05). Amateur and professional male volleyball players showed different concentric knee strengths across isokinetic velocities and different eccentric strengths on CMJ test. 3D surface maps can play an important role in the comparative analysis of athletes with different sports backgrounds or in performance analyses when tracking individual development and provide a detailed and understandable perspective in revealing differences. It can also be of help in detection of possible deficits in muscle strength and load range before and after potential injuries.

Brandenberger, KJ, Warren, GL, Ingalls, CP, Otis, JS, and Doyle, JA. Downhill running impairs activation and strength of the elbow flexors. J Strength Cond Res 35(8): 2145-2150, 2021-The purpose of this study was to determine if knee extensor injury induced by 1 hour of downhill running attenuated force production in the elbow flexors. Subjects completed either downhill running for 1 hour (injured group; n = 6) or sedentary behavior (control group; n = 6). Strength and voluntary activation (%VA) were measured by isometric twitch interpolation of the elbow flexor and knee extensor muscles at the following time points in relation to the injury: before injury (Pre), after injury (Post), 24 hours after injury (24Post), and 48 hours after injury (48Post). Mean (±SE) knee extensor strength was significantly reduced (53.5 ± 9.9%) Post and remained reduced at 24Post and 48Post in the injury group. Knee extensor muscle twitch strength was reduced Post and 24Post after the downhill run (p0.022). Elbow flexor muscle strength was significantly reduced Post (13.2 ± 3.9%) and 24Post (17.3 ± 4.0%). Elbow flexor muscle twitch strength was not significantly different at any time point. Elbow flexor muscle %VA was not significantly reduced compared with Pre, at Post (16.2 ± 5.1%), 24Post (20.9 ± 6.7%), or 48Post (12.9 ± 4.5%). A 1-hour downhill run significantly injured the knee extensors. The elbow flexor muscles remained uninjured, but strength of these muscles was impaired by reduced %VA. These data suggest muscle injury can lead to prolonged strength deficits in muscles distant from the injury and should be accounted for when scheduling training that may lead to delayed-onset muscle soreness.

Background: The majority of people who work as tea plantation pickers are powerful. They carry heavy loads of tea on their backs while the roads are quite dangerous and sometimes cause problems. A balance training program has proven to reduce postural sway, increasing leg muscle strength and improving balance strategies. Objective:The aim of this study was to determine the effect of Vladimir Janda balance training methods with an external load on postural sway and leg muscle strength of tea pickers. Methods: The study design used was quasi-experimental with a randomized control group pretest-posttest design. Subjects were tea pickers consisting of a productive age group of 15 people and 15 people as a control treatment group. The Vladimir Janda method balance exercises were conducted over five weeks consisting of 5 phases. Phase I-IV were carried out 5 times a week, while the V phase was done 3 times a week and each session lasted 15 minutes. Postural sway was measured with a posturometer. Leg muscle strength was measured by a back-leg dynamometer. The statistical tests used were Independent T-test and the Mann-Whitney test. Results:The statistical test for the control and treatment groups using the Mann-Whitney test showed p = 0.001, meaning no external load effects on postural sway. Independent t-test showed p = 0.000, meaning there are differences in the effect between the treatment and control groups after being given balance exercises to increase leg muscle strength. Logistic regression test results obtained the ROC value of 0.917, meaning the Vladimir Janda balance training can affect the postural sway and knee extensor muscle strength by 91.7%. Conclusion: The Vladimir Janda balance exercise method can reduce postural sway and increase the strength of knee extensor muscles and ankle flexor Dorsi muscles. External loads can affect the postural sway.

We compared the acute effects of parallel back squat performed from different resistance training configurations on neuromuscular performance. Twenty-eight young adults underwent 4 experimental conditions: inter-repetition rest, traditional, traditional to failure, and rest-pause in the parallel back squat in a randomized, counterbalanced, and cross-over design. The neuromuscular performance was assessed through peak torque of knee extensors and flexors at two angular velocities (90 and 120 º/s) in three moments (before, post, and post-30 min). The peak torque of the knee extensors and flexors at 90 and 120 º/s decreased immediately after training for traditional, traditional to failure, and rest-pause (–8.1% to –17.7%, P0.05). Our results suggest the inter-repetition rest configuration seems to be a more appropriate strategy for maintaining the lower limb neuromuscular performance after a resistance training session.

The main purpose of the present study was to investigate maturation-related changes in force-related factors in gymnasts and untrained girls. A total of 60 female participants were divided into two groups of gymnasts and untrained individuals. Each group had three subgroups of preadolescents, adolescents, and adults according to Tanner's scale. Informed consent forms were obtained from each participant. After familiarity and initial measurements, each subject performed three maximal voluntary isometric contractions (MVIC) of the knee extensors at five different angles to determine the optimal angle of force production. The rate of force development (RFD) was calculated using the torque data. The EMG signal of the rectus femoris muscle was recorded during the MVIC test to measure voluntary activation (RMS). Gymnasts had more absolute torque in all three age groups (P

The spectral properties of surface electromyographic (EMG) signal in the rectus femoris (RF) and the coactivation in the medial hamstrings (MH) were investigated in 45 stroke subjects (22 ± 12 days post-onset) and 30 age-matched healthy controls who performed unilateral knee extensions at maximum effort (100% MVC) and during 5-s force-matching tasks (10, 30, 50% MVC). The spectral properties were obtained through a power spectrum analysis based on Fast Fourier Transform. The coactivation was measured as the MH amplitude (%max) and MH/RF amplitude ratio. Force variability was expressed as the coefficient of variation. Both knee extensors and flexors were weaker in the paretic leg than the non-paretic and control legs (p

BACKGROUND Lower-limb amputees have increased metabolic costs during walking that may be mitigated by maintaining quadriceps strength and power following amputation. However, there are no current studies investigating the relationship between thigh strength and walking performance in individuals with transfemoral amputation. OBJECTIVE To quantify the relationship between intact limb quadriceps strength in transfemoral amputees and six-minute walk test (6MWT) performance. DESIGN Descriptive laboratory study. SETTING Laboratory. PARTICIPANTS Eleven participants with unilateral transfemoral amputations from trauma or osteosarcoma (4 women/7 men, 46.21 ± 12.68 years old, 28.24 ± 20.57 years following amputation). INTERVENTIONS Strength and power testing on the intact limb followed by 6MWT with a flowmeter to measure oxygen uptake (VO2 ). MAIN OUTCOME MEASURES Strength included mass-normalized peak torque, average torque, and average power. 6MWT measures included total distance traveled and VO2 normalized to distance and mass. Significant correlations (P ≤ .05) were retained for a regression analysis. RESULTS Peak isokinetic knee extensor torque was correlated with total VO2 (r = -.60, P = .05) and distance traveled (r = .84, P = .001). Average isokinetic knee extensor torque was correlated with total VO2 (r = -.61, P = .046) and distance traveled (r = .85, P = .001). Average knee extensor power was correlated with total VO2 (r = -.67, P = .026) and distance traveled (r = .88, P

Purpose This study examined the relationships of knee extensor strength and quadriceps femoris size with sprint performance in sprinters. Methods Fifty-eight male sprinters and 40 body size-matched male non-sprinters participated in this study. The knee extensor isometric and isokinetic strengths were measured using a dynamometer. The isokinetic strength measurements were performed with slow and fast velocities at 60°/s and 180°/s, respectively. The quadriceps femoris muscle volume (MV) was measured using magnetic resonance imaging. The relative knee extensor strengths and quadriceps femoris MV were calculated by normalizing to body mass. Results Absolute and relative knee extensor strengths during two velocity isokinetic contractions, but not during isometric contraction, were significantly higher in sprinters than in non-sprinters (P = 0.047 to P = 0.018). In sprinters, there were positive correlations between all three knee extensor strengths and quadriceps femoris MV (r = 0.421 to 0.531, P = 0.001 to r = −0.477 and −0.409, P = 0.001 and Conclusions These findings suggest that despite the presence of the relationship between muscle strength and size, the knee extensor strength may be related to superior sprint performance in sprinters independently of the quadriceps femoris muscularity.

The purpose of this investigation was to assess the muscular strength of the knee extensors and flexors muscles, agility and functionality between dominant leg (DL) vs. non-dominant leg (NDL) of professional soccer players during pre-season. Twenty-two healthy male professional soccer players (25.1 ± 3.8 years; 182.1 ± 5.9 cm; 79.3 ± 5.4 kg; body fat 14.6 ± 3.8%) from a club of the Brazilian second-division soccer league participated in this study. All soccer players underwent three tests to assess strength, power, and physical performance with an interval of 48 h inter-sessions. During the first assessment session, isokinetic tests were performed in which athletes performed maximal isokinetic concentric and eccentric contractions, as well as maximal isometric contractions. In the second and third assessment sessions, single leg step down and agility tests were performed, respectively. Maximum voluntary isometric contraction (MVIC) results showed a significant difference (p

Em geral, diferentes tempos de prática de treinamento podem se associar com alterada resposta neuromuscular em esportistas, durante períodos de fadiga aguda e recuperação pós-esforço. O presente trabalho foi proposto para analisar o desempenho eletromiográfico de músculos extensores do joelho após fadiga e protocolo de resfriamento muscular em universitários com diferentes históricos de prática esportiva. Os participantes (n=24) foram distribuídos em dois grupos, segundo experiência prática: G1 (6,60±0,70 anos) e G2 (11,57±0,44 anos); os procedimentos de eletromiografia foram realizados em músculos extensores do joelho durante um exercício isométrico em cadeira extensora. Não foram verificadas diferenças nas comparações entre grupos (p>0,05). Considerando-se o momento de análise, as medidas de root mean square (RMS) dos músculos vasto lateral e vasto medial foram maiores no momento pós-resfriamento, comparado aos momentos inicial e pós-exaustão (p

Neuromuscular deficits in post-anterior cruciate ligament reconstruction (ACLR) individuals result in the adoption of compensatory movement strategies that alter how the knee and ACL are loaded. While it is understood that post-ACLR individuals load the knee and ACL differently than healthy controls, the challenge is quantifying the loading in the ACL as it can provide insight regarding secondary ACL tears. Computational modeling is advantageous because it provides a way to compute the forces in the ACL in individuals during dynamic tasks. Thus, this study sought to employ computational modeling to investigate differences in how the ACL is loaded during running in healthy controls and post-ACLR individuals. Sixteen post-ACLR individuals and twelve healthy controls performed a running protocol where they were instructed to run at a self-selected speed. Subject-specific computational models were generated for each participant, and joint kinematics, joint kinetics, and muscle and ACL forces were extracted from the simulations. Despite the post-ACLR individuals exhibiting significantly lower peak knee flexion angles and peak knee extensor moments than the controls, the peak ACL forces were marginally higher in post-ACLR individuals than in healthy controls (p = 0.33). These findings suggest that secondary ACL tears may be more of a reflection of the challenges faced in mimicking the structural and functional roles of the ACL with transplanted tissues rather than the effects of elevated ligament loading. The knowledge gained from this study will have significant implications for regenerative engineering and the design of more robust tissues. Individuals after an anterior cruciate ligament reconstruction (ACLR) suffer from diminished muscle function that causes them to adopt new movement patterns. A consequence of these new movement patterns is a change in the forces that are placed on the newly transplanted ACL. This study used computational modeling to compare the forces experienced by the ACL in healthy controls and post-ACLR individuals during running. No differences in ACL forces were measured between the two groups, suggesting that secondary ACL tears may be due to the altered structural integrity of the newly transplanted grafts.

Ikeda, N and Ryushi, T. Effects of 6-week static stretching of knee extensors on flexibility, muscle strength, jump performance, and muscle endurance. J Strength Cond Res 35(3): 715-723, 2021-The purpose of this study was to evaluate the changes in flexibility and muscular performance after stretching training for 6 weeks. Twelve healthy young men were assigned to a stretching group and 13 to a control group. The subjects of the stretching group performed static stretching of knee extensors for 6 weeks. Knee flexion range of motion (KFROM), leg extension strength, rate of force development (RFD) in leg extension, jump performance (squat and countermovement jump height, and index of rebound jump), and strength decrement index of 50 repetitions of isokinetic knee extension (muscle endurance) were measured before and after the interventions. In the stretching group, KFROM significantly increased from 145.2 ± 17.3 to 158.7 ± 6.3° (p < 0.05), whereas RFD significantly improved from 10,173 ± 2,401 to 11,883 ± 2,494 N·s-1 (p < 0.05). By contrast, leg extension strength and jump performance of each jump type did not improve significantly. Furthermore, muscle endurance decreased significantly. All variables remained unchanged in the control group. In conclusion, 6 weeks of stretching training of knee extensors improved KFROM and RFD in leg extension, but not leg extension strength and jump performance; moreover, muscle endurance decreased. These findings indicate that this stretching training protocol can be used by athletes in sports who require high flexibility and those who require high-power exertion.

Purpose: The purpose of this study was to verify the effectiveness of repetitive sit to stand training to improve knee extensor strength and walking ability of total knee replacement patients. Methods: In this study, 12 patients with total knee replacement patients were recruited from a rehabilitation hospital. They were divided into two groups: a repetitive sit to stand group (n=6) and a control group (n=6). They all received 30 minutes of continuous passive motion (CPM). After that, the repetitive sit to stand group performed repetitive sit to stand training, and the control group performed re sistance exercise for 15 minutes five times a week for 2 weeks. After 2 weeks of training, knee extensor strength and spatiotemporal gait parameters were measured. Knee extensor strength was measured by Biodex system 3, walking ability was measured by Biodex gait trainer 2. Paired t test was performed to verify the difference between before and after intervention within the group, and analysis of co variance was used to verify the differences between the two groups. Results: After the training periods, the repetitive sit to stand group showed a significant improvement in knee extensor muscle strength, walking speed, step length of the operated side, and step length of the non-operated side (p

Traditional warm-up in sport contents the stretching. The stretching effects are a frequent subject of research in physical education, but the results are conflicting. The aim of current study is to check how acute stretching (static and dynamic) influences to the strength of hamstring and quadriceps, as well as their mutual ratio. These variables were monitored at different velocities of contraction (60 and 240&#186/s). On the sample of 10 students in good health, modern isokinetic diagnostics (4000 Hz the sampling rate) was applied. Higher strength values in both muscle groups were measured during slow contraction, while HRQ values were higher during fast contractions. The results show that the muscle strength of hamstring and quadriceps can be increased by applying acute stretching (p p > 0.05). The same conclusions were drawn for both low and high contraction velocities.

Background This study was focused on the gait parameters of the knee extensor and hip abductor muscle groups, which are believed to contribute to knee joint function improvement in early postoperative TKA. The associations between patient-reported outcome measures (PROMs) 6 months after total knee arthroplasty (TKA) and the early postoperative internal knee extension moment, knee extension negative joint power, and internal hip abduction moment while walking were investigated. Methods Twenty-one patients who underwent primary TKA for knee osteoarthritis were included. Three weeks after TKA, gait at a comfortable speed was measured by three-dimensional motion analysis. The lower limb joint angle, internal joint moment, and joint power parameters on the operated side while standing were calculated. The PROMs 6 months after TKA were assessed using the Japanese Knee Osteoarthritis Measure (JKOM). The relationship between each gait biomechanical parameter and the JKOM was determined. Results The maximum internal knee extension moment and maximum knee extension negative joint power during the early stance showed moderate negative correlations with the JKOM scores. The maximum internal hip abduction moment was not correlated with the JKOM scores. The maximum internal hip extension moment during the early stance and internal hip flexion moment during the late stance showed moderate negative correlations with the total JKOM scores. Conclusion The early postoperative internal knee extension moment, maximum knee extension negative joint power, and internal hip extension and flexion moment are associated with patient PROMs 6 months after TKA.

Females have been reported to utilize a feedforward control strategy during landing in which they compensate for decreased rate of torque development (RTD) of the hip extensors through earlier pre-activation of the knee extensors. The purpose of this study was to determine the influence of a 4-week hip-focused training program on hip extensor RTD and feedforward control of the hip and knee extensors. Twenty-one females underwent hip extensor RTD evaluation and electromyographic assessment of the hip and knee extensors during a drop-jump task. Post-training, there was a significant improvement in hip extensor RTD (21.68 ± 5.44 to 23.33 ± 5.45 Nm/kg s

Objective Neuromuscular electrical stimulation (NMES) has been noted as an effective pre- contraction for an increase of neural and muscle factors during twitch contractions. However, it is unknown if this intervention is effective for the rate of force development (RFD), which is the ability to increase joint torque strength as quickly as possible, during tetanic contractions. NMES can be safely used by anyone, but, the strength setting of NMES requires attention so as not to cause pain. Therefore, the purpose of this study investigated whether NMES at less painful levels was effective for RFD during tetanic contractions. We also investigated effect activation by analyzing electromyogram (EMG) and RFD for each phase. Methods Eighteen healthy males were studied. Before and after NMES intervention at 10% or 20% maximal voluntary isometric contraction (MVIC) level (10%NMES, 20%NMES respectively), EMG activity and the initial phase (30-, 50-, 100-, and 200-msec) RFD were measured. Visual analog scale (VAS) was also measured as an indicator of pain during each NMES. Results 20%NMES increased EMG activity and 30-, 50-, and 100-msec of RFD during MVIC, but could not improve 200 msec of RFD. However, 10%NMES could be failed to increase all phases RFD, but VAS was lower than that of 20% NMES. Conclusion These results suggest that muscle pre-contraction using 20%NMES could induce moderate pain, but could be an effective intervention to improve RFD via neural factor activity.

Dancers spend large amounts of time practicing and performing, where fatigue may occur, resulting in adverse movement patterns. The purpose of this study was to compare sauté landings before and after acute physical fatigue in experienced female dancers. Twenty-one dancers completed 10 sauté jumps before and after a dance-specific fatigue protocol. A 12-camera motion capture system and a force plate were utilized to collect three-dimensional kinematic and kinetic data. After fatigue, dancers demonstrated an increase in mediolateral centre of mass displacement, pelvis excursion, peak knee abduction, peak ankle eversion and external rotation, as well as decreased peak metatarsophalangeal (MTP) joint extension, indicating less desirable movement patterns. Peak vertical ground reaction force was decreased after fatigue due to a softer landing strategy, demonstrated by increased peak hip flexion, knee flexion, and ankle dorsiflexion. There was some indication of shifting demands demonstrated by an increased peak knee extensor moment and decreased peak MTP flexor moment after fatigue. With jump landing kinematics and kinetics affected after only an average of 5 minutes of dancing, dancers may benefit from developing greater endurance and more eccentric strength to allow them to slow down properly while landing and to sustain the aesthetic demands throughout performance.

Background Loss of knee extensor strength in individuals with knee osteoarthritis (KOA) may induce inter-limb strength asymmetries and alter functionality. The aims were to analyse whether the condition of the uninvolved knee (advanced to severe KOA or no affection) may induce different degrees of knee extensor strength asymmetry in individuals with KOA and to study whether functionality may differ in cases of unilateral or bilateral KOA. Methods Sixty-eight subjects with advance-to-severe KOA were categorized into two groups (unilateral or bilateral KOA). The knee extensor strength ratio (KESR), and self-reported and performance-based functionality were analysed and compared. Sex and age were independent factors. One- and two-way analysis of variance assessed for significant between-group differences (95% confidence interval (CI)). Results Participants with unilateral KOA presented with 20% knee extensor strength asymmetry. The mean difference with the bilateral KOA group in terms of Knee Extensors Strength Ratio was 0.2 (95% CI 0–0.3; P = 0.021), of the Oxford Knee Scale score was 4.2 (95% CI 3.4–5.1; P = 0.037), and of the Timed Up and Go was 1.3 s (95% CI 0.5–2.2; P > 0.05). There were significant sex and age interactions (P Conclusions Individuals with unilateral or bilateral KOA present with different degrees of knee extensor strength asymmetry. The non-affected knee seems to help to better develop functional tasks in cases of unilateral condition. The findings may help the design of tailored strengthening interventions in which each knee condition in individuals with KOA should be considered.

Recently, we proposed the hypothesis that weekly running volume and preferred running pace may play a role in preserving ankle joint kinetics in middle-age runners as ankle joint kinetics were generally similar in young and middle-aged runners with similar running volume and preferred pace. To further address this hypothesis, we compared lower extremity joint kinetics between high and low training volume runners in both young and middle-aged groups. Joint kinetics calculated from 3D kinematic and ground reaction force data during over-ground running at 2.7 m·s-1 from young and middle-aged runners who ran low or high weekly volume were analyzed. A two-factor analysis of variance was used to compare joint kinetics between age and running volume groups. Positive hip work was greater in middle-aged compared to young runners (P = .005). Plantarflexor torque (P = .009) and positive ankle work (P = .042) were greater in young compared to middle-aged runners. Positive ankle work was also greater in the high compared to the low volume group (P = .021). Finally, age by volume interactions were found for knee extensor torque (P = .024), negative knee work (P = .018), and positive knee work (P = .019) but not for ankle and hip joint kinetics. These findings suggest less distal-to-proximal difference in positive joint work with high running volume in both young and middle-aged runners as a result of greater power generation at the ankle. Given the age main effects, our findings are also the first to suggest the age-related distal-to-proximal shift in joint kinetics appears in middle-aged runners.

Ultrasonography-derived cross-sectional area (CSA) and echo intensity (EI) are increasingly utilized by investigators to study muscle size and quality, respectively. We sought to examine age, sex, and region (proximal, middle, distal) differences in vastus lateralis and rectus femoris CSA and EI, and determine whether correction for subcutaneous fat thickness influences the magnitude of EI differences. Fifteen younger men (mean age = 23 years), 15 younger women (aged 21 years), 11 older men (aged 74 years), and 15 older women (aged 70 years) participated. Clear differences were observed among age, sex, and region for vastus lateralis CSA (p ≤ 0.013, d = 0.38–0.73), whereas rectus femoris CSA was only different between younger and older participants at the proximal region (p = 0.017, d = 0.65). Uncorrected EI was greatest at the distal region of both muscles (p < 0.001, d = 0.59–1.38), with only the younger men having significantly lower EI values than the other groups (p ≤ 0.043, d = 0.37–0.63). Subcutaneous fat correction resulted in a marked increase in the magnitude of sex-specific EI differences (p ≤ 0.032, d ≥ 0.42). Additionally, subcutaneous fat correction increased the uniformity of EI throughout the thigh. These findings highlight considerable region-specific differences in muscle size and quality among younger and older men and women and highlight the need to correct for subcutaneous fat thickness when examining EI. Novelty Rectus femoris CSA is similar between younger and older adults except at the most proximal site evaluated. Age- and sex-specific differences in uncorrected EI are nonuniform across the thigh. Correction for subcutaneous fat thickness substantially increased EI in women, resulting in greater sex differences.

Purpose: The purpose of this study was to investigate comparisons of vastus medialis (VMO) and vastus lateralis (VL) muscle activities according to different heights during drop landing in flatfooted adults. Methods: Fifteen subjects with a flat foot arch and 15 subjects with a normal feet arch were participated. Subjects performed a double limb drop landing task from 20, 40, and 60 cm heights. Surface electromyography was used to measure the muscle activities of the VMO and VL during drop landing. Results: There were significant differences of muscle activities in the VMO, VL, and the VMO and VL ratio between groups. The electro myography values of VMO, VL, and the VMO and VL ratio in the normal group were significantly greater than in the flat foot group, and muscle activities and the VMO and VL ratio significantly increased with landing heights in the both groups. Conclusion: Our results indicated that muscle activity patterns of VOM and VL in the flat foot group were lower at heights than in the normal group, so calf tightness was negative effects on balance and gait ability, so assessment of muscle activation patterns in the knee extensors should be considered during exercise and treatment of flat feet.

Physics-based predictive simulations have been shown to capture many salient features of human walking. Yet they often fail to produce realistic stance knee and ankle mechanics. While the influence of the performance criterion on the predicted walking pattern has been previously studied, the influence of musculoskeletal mechanics has been less explored. Here, we investigated the influence of two mechanical assumptions on the predicted walking pattern: the complexity of the foot model and the stiffness of the Achilles tendon. We found, through three-dimensional muscle-driven predictive simulations of walking, that modeling the toes, and thus using two-segment instead of single-segment foot models, contributed to robustly eliciting physiological stance knee flexion angles, knee extension torques, and knee extensor activity. Modeling toes also slightly decreased the first vertical ground reaction force peak, increasing its agreement with experimental data, and improved stance ankle kinetics. It nevertheless slightly worsened predictions of ankle kinematics. Decreasing Achilles tendon stiffness improved the realism of ankle kinematics, but there remain large discrepancies with experimental data. Overall, this simulation study shows that not only the performance criterion but also mechanical assumptions affect predictive simulations of walking. Improving the realism of predictive simulations is required for their application in clinical contexts. Here, we suggest that using more complex foot models might contribute to such realism. ispartof: PLOS ONE vol:17 issue:1 ispartof: location:United States status: published

Transcutaneous electrical stimulation (TES) is used to activate muscles when volitional capacity is impaired but potential benefits are limited by rapid force loss (fatigue). Most TES fatigue protocols employ constant-frequency trains, with stimuli at a fixed interstimulus interval (ISI); however, a brief ISI between the first two pulses (variable-frequency train, VFT) to maximize the catchlike property of muscle can attenuate fatigue development. The purpose of this study was to investigate if a VFT that simulates intrinsic variability of voluntary motor unit discharge rates would also mitigate fatigue, owing to the sensitivity of muscle to acute activation history.On two visits, 24 healthy adults (25.3 ± 3.7 years; 12 females) received 3 min of intermittent TES to the quadriceps of the dominant leg. Trains of eight pulses at 10 Hz were delivered with a constant (100 ms) or variable ISI (80-120 ms). Contractile impulse, rate of force development (RFD), and rate of relaxation (RFR) were determined for each tetanus RESULTS: During fatigue and recovery, contractile impulse did not differ between protocols (p ≥ 0.796) and sexes (p ≥ 0.493), with values of 77 ± 17% control at task end and 125 ± 19% control 2 min later. RFD and RFR also showed no effect of the protocol (p ≥ 0.310) or participant sex (p ≥ 0.119). Both measures slowed (38 ± 23% and 33 ± 22%, respectively) but dissociated during recovery as RFD remained 16 ± 18% below control at 5 min, whereas RFR recovered to control by 30 s (101 ± 22%).Contrary to expectations, the VFT protocol did not attenuate fatigue development, which suggests no benefit to mimicking the inherent variability of motor unit discharge rates.

This study aimed to investigate the relationship between knee extensors maximum voluntary contraction (MVC) torque and rate of torque development (RTD) with jump performance and with echography intensity (EI) from the vastus lateralis muscle (VL). We assessed the MVC torque and RTD from knee extensors by a standard isokinetic device from 16 male professional soccer players (25.5 ± 3.9 years). Counter-movement jump (CMJ) and squat jump (SJ) height were calculated from their flight times. EI was determined from VL ultrasound images’ grayscale histogram acquired in the middle of the tight. Correlation between variables was investigated by the Pearson correlation coefficient. We observed a VL EI of 26.4 ± 7.8 a.u., and the SJ and CMJ heights were 36.0 ± 3.0 and 36.2 ± 4.1 cm, respectively. There was a significant correlation between the MVC torque and absolute late-phase RTD (r = 0.67 and 0.76—RTD200 and RTD250, respectively), between the CMJ height and absolute RTD50 (r = 0.50), and between the normalized early-phase RTD and SJ height (r = 0.53–0.60—RTD50 and RTD150). Additionally, normalized RTD200 (r = − 0.51) and RTD250 (r = − 0.56) were negatively correlated with EI. Such results suggest that athletes with the ability to produce torque explosively in the very beginning (between 50 and 150 ms) of knee extension can jump higher. Also, the muscle quality assessed by the VL IE seems to be more important to maximum strength and later periods of torque rise (> 200 ms).

Corso, M, Liang, L, Tran, S, Howitt, S, Srbely, J, and Mior, SA. The immediate effect of spinal manipulation on ball velocity and neuromuscular function during an instep kick in former Varsity soccer players: a feasibility study. J Strength Cond Res 36(9): 2558-2565, 2022-Spinal manipulation (SM) has been shown to increase ball velocity (BV) in soccer players. Evidence suggests that SM modulates responses at spinal or cortical levels to enhance force production in asymptomatic populations. No studies have explored the underlying neuromuscular mechanisms contributing to changes in BV post-SM in soccer players. We assessed the feasibility of measuring change in BV and neuromuscular function after SM in former Varsity level soccer players with a pre-post study design. Three to 5 maximal instep kicks were performed before and after SM at the L3-5 level. Ball velocity was measured using high-speed camera. Activation of lower limb and trunk musculature was recorded with electromyography. Outcomes included ease of recruitment, scheduling and data capture, as well as expectation and perception of SM effect and adverse events (AE). Fifteen potential subjects were recruited over 1.5 months. Eleven were scheduled (24-31 years; 8 females, 3 males). Two subjects reported mild AE after maximal voluntary isometric contraction testing. A significant increase in BV (mean change: 1.75 m·s -1 [95% confidence interval: 0.5-3.0]) and a trend to increased peak-activation of knee extensors (90.7%) were observed post-SM. Findings suggest that our recruitment strategy and methodology are feasible in a larger trial with some modifications. Our preliminary findings support previous research by suggesting that increased BV may be mediated through increased activation of knee extensors during the kick. Our findings may offer additional insight into the underlying neuromuscular mechanisms contributing to immediate change in BV post-SM.

Abnormal tracking of the patella is a hallmark sign of patellar instability (PI). Gait deviations and strength deficits may exacerbate abnormal tracking. The identification of modifiable gait deviations and strength deficits can aid in developing more effective management strategies for individuals with PI. The purpose of this study was to identify modifiable gait and strength deficits in subjects with PI.32 subjects (16 PI, 16 controls, 3 males/13 females in each group, 21.1 years old, 23.5 BMI), performed an instrumented gait analysis while walking at 1.5 m per second. Subjects' peak hip adduction angles, external rotation angles, hip abduction moments, knee flexion angles, knee adduction angles, and knee extensor moments were measured during walking. Hip abduction, hip external rotation, and knee extension strength were assessed with a handheld dynamometer.Individuals with PI displayed significantly lower peak knee adduction angles (1.8 ± 2.8° PI, 5.5 ± 4.5° control, p .01) and peak hip abduction moments (0.2 ± 0.1 Nm/kg*m PI, 0.4 ± 0.1 Nm/kg*m control, p .01). Subjects with PI were weaker in knee extension strength (14.5 ± 4.1 kg/m PI, 23.8 ± 7.2 kg/m control, p .01), hip abduction strength (12.1 ± 2.0 kg/m PI, 17.8 ± 4.0 kg/m control, p .01), and hip external rotation strength (5.5 ± 1.9 kg/m PI, 7.1 ± 1.3 kg/m control, p = .01).Subjects with patellar instability have smaller joint moments and a more valgus knee position while walking. Coupled with deficits in muscle strength, this likely contributes to subjective reports of chronic patellar instability.III.

This study investigated the acute effects of seated and supine knee extension exercise on muscle swelling, torque, and work output. Twelve resistance-trained men performed two isokinetic concentric-only knee-extension training protocols at different hip positions in a counter-balanced order. They completed the knee extension exercise in the seated (hip angle at 85°) and supine (hip angle at 180°) positions. The torque and work output were assessed during each set. Moreover, muscle thickness of the middle and proximal vastus lateralis and rectus femoris were evaluated before and after each protocol and used as an indicator of muscle swelling. Middle rectus femoris and proximal vastus lateralis thickness increased significantly (p=0.01) with no difference between exercise variations. However, the middle vastus lateralis thickness increased (p=0.01) only after the seated knee extension exercise (~7%). Knee extensors’ peak torque and work output were approximately 8% higher (p=0.04) in the seated when compared to the supine hip position. There was a similar decrease in torque and work output throughout both protocols (p=0.98). In conclusion, seated knee extension exercises produced greater torque, work output, and muscle swelling in the vastus lateralis when compared to the supine knee extension exercise.

This study aimed to evaluate the influence of hamstrings and quadriceps strength on the hamstrings-to-quadriceps conventional (H:Qcon) and functional (H:Qfun) ratios in male soccer players. Quadric...

Electrotherapy modalities are one of the increasing ways of muscle strength and endurance. However, it is not clear which electrotherapy modalities are more effective. The purpose of this study is to compare the effect of Russian current (RC) and high voltage pulsed current (HVPC) on the strength and endurance of the quadriceps muscle. The study was performed on 10 volleyball athletes. The participants’ extremities were divided into two groups as RC and HVPC. Muscle strength and endurance levels were assessed by an isokinetic device. Isokinetic training and 20-min electrotherapy were given in each treatment session. This training program consisted of a total of 12 sessions, scheduled twice a week for 6 weeks. After training, knee extensor peak torque values and endurance ratios have increased in both groups, but it was determined that this increase was only significant in terms of the endurance ratio (P0.05). RC or HVPC have no advantages over each other, and therefore it has been determined that both currents can be used in order to strengthen muscles and increase muscular endurance. Additional studies whose longer-term effects will investigate are needed.

Diabetes peripheral neuropathy (DPN) leads to balance impairment among diabetes mellitus (DM). The aims of this study were to (1) distinguish between DM patients who have/do not have DPN and to (2) compare quadriceps’ strength and balance performance of DM, DPN, and healthy groups. Fifteen healthy females and 33 females with type 2 diabetic patients participated. The electrodiagnostic method was used to classify diabetic patients into DM and DPN. A dynamometer was used to measure quadriceps’ strength. Single-leg standing on a force plate was also used to quantify participants’ balance. Smaller conduction velocity and amplitude and greater distal latency of all nerves were observed in the DPN compared with the DM in particular for sensory nerve. In DPN, conduction velocity was asymmetrical. The quadriceps’ strength of both legs in DPN and the right leg in DM was smaller than in the control group. The root mean square of the center of pressure was similar between DM and DPN. But it was larger in DPN than in the control group. DPN is associated with asymmetrical conduction velocity, smaller quadriceps’ strength, and weaker balance performance that is suggestive of higher risk of falling. Balance training is recommended for the DPN group during their rehabilitation to reduce their falling risk.

The movement pattern during stair descent differs by gender, and this difference may be associated with gender differences in muscle strength or activation. The purpose of this study was to determine whether a gender difference in muscle activation exists by comparing the muscle activation amplitude and co-activation of lower extremity muscles during the stair-to-ground descent transition. Fifteen men and thirteen women descended stairs and the muscle activation was measured. Women showed a significantly lower peak normalized electromyography amplitude of the vastus lateralis (women: 171.7% peak EMG activation amplitude for level walking (PEALW), men: 297.0%PEALW, p

Recovery stepping in response to forward slips has the potential to not only rebuild the base of support to prevent backward falling, but also provide extra limb support to prevent downward falling. Hence, recovery stepping is often necessary for fall prevention following an unexpected slip. However, less is known about whether recovery foot placement could affect the likelihood of recovery following a slip. The purpose of this study was to determine whether there is an optimal recovery landing zone within which older adults have a higher likelihood of recovery. 195 participants experienced a novel, unannounced forward slip while walking on a 7-m walkway. The center of mass (COM) stability (computed from its position and velocity), vertical limb support (computed from change in hip kinematics), and recovery limb joint moments (computed from joint kinematics and ground reaction force) in the sagittal plane were analyzed. The results showed that a longer distance between recovery foot landing position and the projected COM position at recovery foot touchdown (relative recovery step placement) was conducive to stability improvement but adverse to limb support enhancement, and vice versa for a shorter distance. Relative recovery step placement could predict the recovery likelihood with an accuracy of 67.3%, and the recovery rate was greater than 50% when the distance between recovery foot and COM is less than 0.3 × foot length. This study also found more posterior stepping could be attributed to insufficient ankle plantar flexor and hip flexor moments in the pre-swing phase, while more anterior stepping was induced by insufficient hip and knee extensor moments in the following swing phase.

AIM To assess effects of growth on lower limb maximal isometric muscle strength (MIMS) development in children with developmental coordination disorder (DCD). METHOD This observational study used hand-held dynamometry to evaluate MIMS (hip abductors, flexors, extensors; knee flexors and extensors; ankle dorsiflexors) in children with DCD (n=33, 12 females, 21 males, 6-12y, mean [SD] age 9y [2y]). Regression analysis compared changes in MIMS for similar changes in growth (height or body mass) for children with DCD and typically developing children (pre-existing database, n=183), controlling for age and sex. RESULTS For the same height gain, the gain in muscle strength was 37.3% to 69.2% less in children with DCD compared with typically developing children, with significantly lower slopes (p-value between

[Purpose] One-repetition maximum is an essential statistic for physical therapists and coaches in rehabilitation and athletic settings. In a previous study, we showed that one-repetition maximum of the knee extensor could be predicted more accurately with the combination of maximal voluntary isometric contraction strength, as measured by a handheld dynamometer, muscle thickness, and thigh circumference, in young adults. However, there has been no study in older adults investigating the relationship between one-repetition maximum and maximal voluntary isometric contraction strength, or muscle thickness, and thigh circumference. Therefore, the aim of this study was to investigate the relationship between one-repetition maximum and maximal voluntary isometric contraction strength, or muscle thickness, and thigh circumference in older adults. [Participants and Methods] Twenty-eight older community-dwelling adults (18 males and 10 females) participated in this study. Muscle strength of the knee extensor was measured using one-repetition maximum and maximal voluntary isometric contraction strength. In addition, muscle thicknesses of the refutes femoris and the vastus intermedius, and thigh circumference were measured using ultrasonography and measuring tape, respectively. [Results] Stepwise regression analysis revealed that body mass, gender, thigh circumference at 15 cm above the patella, and maximal voluntary isometric contraction strength were significant and independent determinants (R2=0.868). [Conclusion] One-repetition maximum could be predicted more accurately using a combination of maximal voluntary isometric contraction strength, as measured with a handheld dynamometer, and thigh circumference in older adults.

Background: Aging results in adaptations which may affect the control of motor units. Objective: We sought to determine if younger and older men recruit motor units at similar force levels. Design: Cross-sectional, between-subjects design. Setting: Controlled laboratory setting. Participants: Twelve younger (age = 25 ± 3 years) and twelve older (age = 75 ± 8 years) men. Measurements: Participants performed isometric contractions of the dominant knee extensors at a force level corresponding to 50% maximal voluntary contraction (MVC). Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis. A surface EMG signal decomposition algorithm was used to quantify the recruitment threshold of each motor unit, which was defined as the force level corresponding to the first firing. Recruitment thresholds were expressed in both relative (% MVC) and absolute (N) terms. To further understand age-related differences in motor unit control, we examined the mean firing rate versus recruitment threshold relationship at steady force. Results: MVC force was greater in younger men (p = 0.010, d = 1.15). Older men had lower median recruitment thresholds in both absolute (p = 0.005, d = 1.29) and relative (p = 0.001, d = 1.53) terms. The absolute recruitment threshold range was larger for younger men (p = 0.020; d = 1.02), though a smaller difference was noted in relative terms (p = 0.235, d = 0.50). These findings were complimented by a generally flatter slope (p = 0.070; d = 0.78) and lower y-intercept (p = 0.009; d = 1.17) of the mean firing rate versus recruitment threshold relationship in older men. Conclusion: Older men tend to recruit more motor units at lower force levels. We speculate that recruitment threshold compression may be a neural adaptation serving to compensate for lower motor unit firing rates and/or denervation and subsequent re-innervation in aged muscle.