Improving the ecological validity of isokinetic knee tests at different hip angles: reciprocal concentric-eccentric movements as a suitable alternative for discrete tests.

Isokinetic knee tests mostly evaluate reciprocal concentric-concentric flexor-extensor movements in a seated position. Discrete tests generate higher moments, but time requirements impede their widespread implementation. This study examined if hip angle (flexed vs. extended) and test modality (discrete vs. reciprocal) affect camera-based data (100 fps). Sixteen healthy males performed concentric (con) and eccentric (ecc) isokinetic knee flexor (H) and extensor (Q) movements (60°/s). Peak moments and contractional work of discrete and reciprocal tests (QconQecc, HconHecc) strongly correlated for extended (Q:91%≥R2≥71%; H:95%≥R2≥87%) and flexed hip (Q:88%≥R2≥70%; H:81%≥R2≥75%) without significant differences (p>0.05) between test modalities. Discrete and "traditional" seated QconHcon-tests revealed substantially lower correlations for extended (Q:44%≥R2≥43%; H:55%≥R2≥54%) and flexed hip (Q:81%≥R2≥77%; H:48%≥R2≥47%). Although most mean values did not significantly differ, moderate correlations were predominant and the respective limits of agreement demonstrated considerable effects of hip angle and test modality. These insights assist practitioners in interpreting isokinetic data of different test procedures. If time constraints prevent discrete knee tests (gold standard), concentric-eccentric movements provide highly correlated outcomes, independent of the hip angle.

What Are We Aiming for in Eccentric Hamstring Training: Angle-Specific Control or Supramaximal Stimulus?

CONTEXT: Different resistance exercise determinants modulate the musculotendinous adaptations following eccentric hamstring training. The Nordic Hamstring Exercise (NHE) can be performed 2-fold: the movement velocity irreversibly increases toward the end of the range of motion or it is kept constant. DESIGN: This cross-sectional study aimed to investigate if the downward acceleration angle (DWAangle) can be used as a classification parameter to distinguish between increasing and constant velocity NHE execution. Furthermore, the kinetic and kinematic differences of these 2 NHE execution conditions were examined by analyzing the DWAangle in relation to the angle of peak moment. METHODS: A total of 613 unassisted NHE repetitions of 12 trained male sprinters (22 y, 181 cm, 76 kg) were analyzed. RESULTS: The majority of analyzed parameters demonstrated large effects. NHEs with constant velocity  (n = 285) revealed significantly higher impulses (P < .001; d = 2.34; + 61%) and fractional time under tension (P < .001; d = 1.29; +143%). Although the generated peak moments were significantly higher for constant velocity (P = .003; d = 0.29; +4%), they emerged at similar knee flexion angles (P = .167; d = 0.28) and revealed on average just low relationships to the DWAangle (Rmean2=22.4%). DWAangle highly correlated with the impulse (Rmean2=60.8%) and δ (DWAangle-angle of peak moment; Rmean2=83.6%). CONCLUSIONS: Relating DWAangle to angle of peak moment assists to distinguish between significantly different NHE execution, which will potentially elicit different musculotendinous adaptations. These insights are essential for coaches and athletes to understand how to manipulate eccentric hamstring training to change its purpose.

Comparison of Dynamic Balance and Unilateral Hop Performance Between Women and Men Handball Players After Anterior Cruciate Ligament Reconstruction: A Pilot Study.

CONTEXT: After anterior cruciate ligament reconstruction (ACLR), long-term functional deficiencies can occur, with controversial results reported when comparing women and men. Dynamic balance and unilateral hop test performance are considered important indicators for the risk of reinjury of the lower extremity. Although both sexes seem to have a similar risk to experience a second anterior cruciate ligament injury, sex-specific differences of dynamic balance and unilateral hop performance in handball players following ACLR are unknown. OBJECTIVE: To compare dynamic balance and unilateral hop performance between women and men handball players at least 6 months after ACLR. DESIGN: Cross-sectional pilot study. PARTICIPANTS: Ten women (27.6 [4.5] y) and 10 men (26.5 [3.1] y) handball players 6 to 16 months after ACLR. OUTCOME MEASURES: Dynamic balance and unilateral hop performance were assessed using the Y-Balance Test and the Single-Leg Hop for Distance Test. RESULTS: Women players demonstrated significantly better results in the anterior direction of the Y-Balance Test for both legs compared with men players. Hop performance was not significantly different between sexes. CONCLUSION: Dynamic balance and single-leg hop performance seem not to differ between women and men handball players 6 to 16 months after ACLR. The difference between sexes in the anterior reach direction of the Y-Balance Test should be considered small, rather than representing a true difference.

Analyses of Isokinetic Thigh Muscle Strength: Camera-Based Assessment Alters the Magnitude, but Not the Message.

Background: Thigh muscle strength capacities are major modifiable risk factors for knee and thigh muscle injuries. Therefore, their valid assessment is essential. Most isokinetic knee tests are conducted in a seated position and rely on dynamometer-based data. However, their accuracy is doubtful because axis alignment is erroneous. Purpose: This study investigated if hip angle (flexed vs. extended) and assessment method (dynamometer-based vs. camera-based) affect isokinetic outcome parameters. Methods: Sixteen healthy male participants (27 years, 184 cm, 80 kg) performed discrete isokinetic tests of the knee flexors and extensors (60°/s) while their kinematics were captured (100 fps). Results: Both assessment methods revealed very strong linear relationships (94% ≤ R2 ≤ 98%) although peak moments (d ≤ 0.87), contractional work (d ≤ 1.26), and functional knee flexor:extensor ratios (d ≤ 0.81) significantly differed. Seated knee flexor tests demonstrated the largest knee trajectory center's misalignment (x = 4.0 cm, z = -2.5 cm; 1.37 ≤ d ≤ 4.74). Conclusion: Hip-angle induced kinematic changes did not affect the relation between the lever arms, thus causing highly proportional deviations of kinetic parameters. The assessment method altered the magnitude, but not the message of isokinetic knee tests, which should be preferentially performed with extended hip joint to improve axis alignment. Knowledge of these kinetic and kinematic interactions assists practitioners and scientists with isokinetic tests and/or rehabilitation training to ensure reasonable interpretations of gathered isokinetic outcomes.

Modulating the Nordic Hamstring Exercise From "Zero to Hero": A Stepwise Progression Explored in a High-Performance Athlete.

BACKGROUND: The Nordic hamstring exercise (NHE) is commonly implemented to selectively improve eccentric knee-flexor strength. However, the standard version of the exercise (leveled shanks, extended hip joint) is too strenuous for most individuals, whose muscle activity rapidly decreases at extended knee angles. Hitherto, a gradual approach to the exercise has been missing. In this exploratory case study, we investigated elite performance to introduce a stepwise progression to the NHE. OBJECTIVE: To determine the extent to which exercise modifications (shank inclination, additional load, hip flexion) altered NHE mechanics. DATA COLLECTION AND ANALYSIS: One male long jumper (age = 33 years, height = 171 cm, mass = 69 kg) with high-level expertise in the NHE performed 20 exercise variations. The corresponding kinematics, kinetics, and electromyographic activity of the biceps femoris long head (BFlh) and semitendinosus (ST) muscles were evaluated. RESULTS: Exercise variations demonstrated gradually increased peak moments from 69% (zigzag pose) to 154% (inclined bent single-legged version) versus a standard NHE. Shank inclination and additional load elicited small to moderate effects on peak moments, BFlh, and ST (0.24 ≤ d ≤ 0.72), whereas hip flexion largely affected all tested variables (2.80 ≤ d ≤ 6.66), especially muscle activity (BFlh = -63%; ST = -55% of maximal voluntary isometric contraction). COMMENTARY: These insights will help practitioners and scientists design multifaceted stepwise NHE progressions by creating differentiated stimuli that best match the strength capacities of individuals and address their specific needs.

The dynamic control ratio masks bilateral asymmetries - A gender-specific analysis of 264 healthy and ACL-injured athletes.

Isokinetic strength tests are frequently applied to assess anterior cruciate ligament (ACL) rehabilitation processes. However, diverging methodologies cause misleading conclusions. This cross-sectional study evaluated the effects of gender (male vs. female), group (healthy vs. ACL-injured) and limb (dominant/healthy vs. non-dominant/ACL-injured) on thigh muscle balance of 138 female and 126 male athletes (50% ACL-injured, averagely 12.8 months after surgery). Balance was analysed between legs (bilateral asymmetry) and between concentric knee extensor (Qcon) and eccentric knee flexor strength (Hecc) (DCR = dynamic control ratio, DCRe = DCR at the equilibrium point). Females were generally 17-27% weaker than males. Independent of gender and time after surgery, ACL-injured athletes demonstrated bilateral asymmetries (7-20%) in peak (PMQcon, PMHecc) and DCRe moments (p ≤0.030; 0.018≤ηp2≤0.215). ACL-injured athletes' affected (24-28%) and unaffected (12-24%) hamstrings and quadriceps peak moments were significantly weaker compared to healthy athletes (p<0.001; 0.061≤ηp2≤0.362). The bilateral asymmetries of PMQcon significantly decreased from early to late self-reported rehabilitation phases (p<0.001; ηp2=0.158). Peak and DCRe moments detected bilateral asymmetries, whereas DCR revealed ~50% false negative attributions. This knowledge provides guidance for future design and interpretation of isokinetic tests.

Test-Retest reliability of the internal shoulder rotator muscles' stretch reflex in healthy men.

Until now the reproducibility of the short latency stretch reflex of the internal rotator muscles of the glenohumeral joint has not been identified. Twenty-three healthy male participants performed three sets of external shoulder rotation stretches with various pre-activation levels on two different dates of measurement to assess test-retest reliability. All stretches were applied with a dynamometer acceleration of 104°/s2 and a velocity of 150°/s. Electromyographical response was measured via surface EMG. Reflex latencies showed a pre-activation effect (ƞ2 = 0,355). ICC ranged from 0,735 to 0,909 indicating an overall "good" relative reliability. SRD 95% lay between ±7,0 to ±12,3 ms. The reflex gain showed overall poor test-retest reproducibility. The chosen methodological approach presented a suitable test protocol for shoulder muscles stretch reflex latency evaluation. A proof-of-concept study to validate the presented methodical approach in shoulder involvement including subjects with clinically relevant conditions is recommended.

Leg length discrepancy: A systematic review on the validity and reliability of clinical assessments and imaging diagnostics used in clinical practice.

BACKGROUND: A variety of assessments to determine leg length discrepancy (LLD) is used in clinical practice and evidence about validity and reliability may differ. OBJECTIVE: The objective of this systematic review was to identify and describe the validity and reliability of different assessments and imaging diagnostics for the determination of LLD. MATERIALS AND METHODS: The review was conducted following the recommendations of Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA). The databases Medline (PubMed) and Index to Chiropractic Literature were systematically searched. Studies regarding clinical assessments and imaging diagnostics for the diagnosis of LLD, which reported the clinimetric properties for assessment of LLD, were included and screened for methodological quality using the Quality Assessment of Studies of Diagnostic Accuracy (QUADAS-2) tool for validity studies and the Quality Appraisal of Diagnostic Reliability (QAREL) tool for reliability studies. RESULTS: Thirty-seven articles on clinical assessments and 15 studies on imaging diagnostics met the eligibility criteria. Thirteen studies on the validity of clinical assessments and six studies on the validity of imaging diagnostics had a low risk of bias and low concerns regarding applicability for all domains. One study on the reliability of clinical assessments and one study on the reliability of imaging diagnostics had a low risk of bias. Main limitations were, that an analysis of sensitivity and specificity was only performed in a few studies and that a valid reference standard was lacking in numerous studies on clinical assessments. CONCLUSIONS: For the clinical assessment of LLD, the block test appears to be the most useful method. Full-length standing anteroposterior radiography seems to be the most valid and reliable method and may be used as global reference standard to measure the anatomic LLD when comparing clinical methods and imaging diagnostics.

Comparison of Plantar Sensitivity, Dynamic Balance, and Lower Extremity Joint Range of Motion Between Experienced Female Ballet Dancers and Female Non-Dancing Athletes: A Cross-Sectional Study.

OBJECTIVES: Ballet dancers may increasingly use plantar sensory feedback to control foot position and movement during dance activities. Balance and joint range of motion (ROM) are important factors in ballet and may be related to plantar sensation in ballet dancers. Data on related functions of female ballet dancers compared to female non-dancing athletes are sparse. The aims of the study were twofold: 1. the relationships between plantar sensitivity and dynamic balance as well as between joint ROM and dynamic balance were determined in experienced female ballet dancers and female non-dancing athletes; and 2. the differences of plantar sensation, joint ROM of the lower limb, and dynamic balance between experienced female ballet dancers and female non-dancing athletes were investigated. STUDY DESIGN: In this cross-sectional study, 21 subjects (11 experienced female ballet dancers and 10 female non-dancing athletes; median age: 23, range: 11 years; median body height: 1.7 m, range: 0.2 m; median body mass: 59 kg, range: 36 kg) were included. Plantar sensitivity was determined by Semmes-Weinstein monofilaments, active ranges of motion of the hip, knee, and ankle joints were measured using a goniometer and dynamic balance was assessed by the Y-Balance test. Correlations between outcome measures were determined in both groups. Outcome measures were compared between ballet dancers and non-dancing athletes using parametric or non-parametric statistical tests (α = 0.05). RESULTS: For the fifth metatarsal head and the heel, higher correlations between plantar sensitivity and Y-Balance test scores in non-dancing athletes compared to ballet dancers were found. Higher correlations between joint ROM and Y-Balance test scores were determined for certain movements in non-dancing athletes compared to ballet dancers. A significantly lower cutaneous threshold was only found for the fifth metatarsal head in ballet dancers compared to non-ballet dancers (p < 0.05). Range of motion was significantly higher in ballet dancers for almost all movements (p < 0.05). Ballet dancers showed significantly higher normalized scores of the Y-Balance test (p ≤ .001). CONCLUSIONS: Results of correlation analyses may indicate that non-dancing athletes increasingly must rely on plantar sensation of the fifth metatarsal head and the heel while maintaining dynamic balance compared to ballet dancers, especially in posterolateral direction of the Y-Balance test. Active joint range of motion of the lower extremity and dynamic balance differ between female ballet dancers and non-dancing athletes. Plantar sensitivity is not different for most of the assessed localizations.

Comparison of EMG Activity between Single-Leg Deadlift and Conventional Bilateral Deadlift in Trained Amateur Athletes - An Empirical Analysis.

The purpose of the study was to compare the normalized-electromyographic (NEMG) activity of the gluteus maximus (GMAX), gluteus medius (GMED), biceps femoris (BF) and erector spinae (ES) muscles during the single-leg deadlift (SLDL) and the conventional-deadlift (DL). Additionally, a potential influence of body height on the NEMG activity was examined. Fifteen training-experienced male subjects completed the study. SLDL showed significantly higher average concentric NEMG values of the GMED (77.6% vs. 59.3% [p = 0.002, ES = 1.0]) and BF (82.1% vs. 74.2% [p = 0.041, ES = 0.6]). Significantly lower NEMG levels were found only in the left strand of the ES muscle (67.2% vs. 82.7% [p = 0.004, ES = 0.9]). A significant influence of body height on EMG activity was also observed for all muscles, with the exception of the GMED, during the SLDL. Body height correlated negatively with the concentric EMG activity of the ES (r = -0.54 to -0.58), the BF (r = -0.63) and the GMAX (r = -0.85). In the DL there was a negative correlation only in the BF (r = -0.59) and the GMAX (r = -0.7). This means that subjects with a lower body height showed a higher NEMG activity in corresponding muscles. The results of this study indicate that the SLDL is preferable to the DL in training the BF, and GMED. In addition, coaches should be aware that athletes body height can influence the extent to which the respective muscles are activated.

Efficacy of foam rolling with additional vibration stimulation on the mobility of the thoracolumbar fascia. An observational study.

INTRODUCTION: Observations show that foam rolling improves joint movements. Likewise, it can be stated that a vibration stimulation of the tissue leads to improved joint mobility. METHOD: This study investigates whether the combination of foam rolling and vibrations (31 Hz) can influence the sliding of the thoracolumbar fascia more effectively than normal foam rolling. 45 subjects participated in the study and were divided into a foam roll with additional vibration group (FRV), a foam roll group (FR) and a control group (CG). The intervention groups rolled out the gluteal muscles, the lateral trunk and the upper and lower back. Mobility measures were taken pre and post the respective intervention. Subsequent cross correlation software analysis quantified the sliding of the fascia and calculated its shear strain mobility (SSM). RESULTS: The sliding of the thoracolumbar fascia improved significantly within the FRV by 2.83 mm (SD ± 1.08/p < .001), in the FR by 0.96 mm (SD ± 0.43/p < .001) and in the CG decreased the sliding by 0.1401 mm (SD ± 0.28/p = .076). The fascia/fascia SSM increased in the FRV by 22.61% (SD ± 15.64/p < .001), in the FR by 11.41% (SD ± 20.38/p = .056) and in the CG decreased the SSM by 0.9473% (SD ± 11.35/p < .751). The lumbar movement increased in both intervention groups, but showed no significant result. CONCLUSION: The use of a foam roll with additional vibration and standard intervention have increased thoracolumbar fascia sliding and lumbar movements. The improved shear strain mobility can be attributed to the multi-activity of mechanoreceptors, such as Pacini- and Ruffini-Bodies.

Assisted or unassisted Nordic Hamstring Exercise? - Resistance exercise determinants at a glance.

The Nordic Hamstring Exercise (NHE) effectively strengthens the knee flexors. Typically conducted without assistance, extended knee angles are not reached with sustained muscle activation in the presence of insufficient eccentric strength and/or fatigue. This might impair the desired neuromuscular adaptations and assessment accuracy. This study investigated kinetic and kinematic differences between assisted and unassisted NHEs (3 × 3 repetitions) performed by sixteen male sprinters (22 years, 181 cm, 76 kg). Kinetic (peak moment, impulse) and kinematic parameters (e.g., time under tension, range of motion to excessive downward acceleration (ROMDWA) were investigated. All analysed parameters significantly differed between assisted and unassisted NHEs (p ≤ 0.003; 0.635≤ Î·p² ≤ 0.929) favouring assisted execution, except for peak moments and maximal hip flexion. Repetition 1 of assisted NHEs revealed 21% higher impulses rising to 82% during repetition 9. Equivalent interactions of mode and repetition became apparent for time under tension, ROMDWA, mean and fractional angular velocity. Unassisted NHEs elicited substantially greater inter-repetition fatigue (rep1 vs. rep9): +79% fractional angular velocity (d = 1.01), -41% impulse (d = 1.53), -31% ROMDWA (d = 0.99) and -29% time under tension (d = 1.45). Assisted NHEs ensured higher execution quality and lower between-participant variability by facilitating a controlled full-ROM movement. Three sets of 3 NHEs sufficed to induce substantial fatigue within and across sets.

Swing Phase Mechanics of Maximal Velocity Sprints-Does Isokinetic Lower-Limb Muscle Strength Matter?

PURPOSE: Concentric hip and eccentric knee joint mechanics affect sprint performance. Although the biarticular hamstrings combine these capacities, empirical links between swing phase mechanics and corresponding isokinetic outcome parameters are deficient. This explorative study aimed (1) to explain the variance of sprint velocity, (2) to compare maximal sprints with isokinetic tests, (3) to associate swing phase mechanics with isokinetic parameters, and (4) to quantify the relation between knee and hip joint swing phase mechanics. METHODS: A total of 22 sprinters (age = 22 y, height = 1.81 m, weight = 77 kg) performed sprints and eccentric knee flexor and concentric knee extensor tests. All exercises were captured by 10 (sprints) and 4 (isokinetics) cameras. Lower-limb muscle balance was assessed by the dynamic control ratio at the equilibrium point. RESULTS: The sprint velocity (9.79 [0.49] m/s) was best predicted by the maximal knee extension velocity, hip mean power (both swing phase parameters), and isokinetic peak moment of concentric quadriceps exercise (R2 = 60%). The moment of the dynamic control ratio at the equilibrium point (R2 = 39%) was the isokinetic parameter with the highest predictive power itself. Knee and hip joint mechanics affected each other during sprinting. They were significantly associated with isokinetic parameters of eccentric hamstring tests, as well as moments and angles of the dynamic control ratio at the equilibrium point, but restrictedly with concentric quadriceps exercise. The maximal sprints imposed considerably higher loads than isokinetic tests (eg, 13-fold eccentric knee joint peak power). CONCLUSIONS: Fast sprinters demonstrated distinctive knee and hip mechanics in the late swing phase, as well as strong eccentric hamstrings, with a clear association to the musculoarticular requirements of the swing phase in sprinting. The transferability of isokinetic knee strength data to sprinting is limited inter alia due to different hip joint configurations. However, isokinetic tests quantify specific sprint-related muscular prerequisites and constitute a useful diagnostic tool due to their predicting value to sprint performance.

Nordic Hamstring Exercise training induces improved lower-limb swing phase mechanics and sustained strength preservation in sprinters.

Nordic Hamstring Exercise (NHE) training improves eccentric hamstring strength and sprint performance. However, detraining causes rapid reductions of achieved adaptations. Furthermore, the transfer of improved hamstring capacity to swing phase mechanics of sprints is unknown. This longitudinal study aimed (a) to quantify NHE-induced adaptations by camera-based isokinetic assessments and sprint analyses, (b) to relate the magnitude of adaptations to the participants' initial performance level, (c) to investigate the transferability to sprints, and (4) to determine strength preservations after 3 months. Twelve sprinters (21 years, 1.81 m, 74 kg) were analyzed throughout 22 weeks. They performed maximal sprints and eccentric knee flexor and concentric knee extensor tests before and after a 4-week NHE training. Sprints and isokinetic tests were captured by ten and four high-speed cameras. The dynamic control ratio at the equilibrium point (DCRe) evaluated thigh muscle balance. High-intensity NHE training elicited significant improvements of hamstring function (P range: <.001-.011, d range: 0.44-1.14), thigh muscle balance (P < 0.001, d range: 0.80-1.08) and hamstring-related parameters of swing phase mechanics (P range: <0.001-0.022, d range: 0.12-0.57). Sprint velocity demonstrated small increases (+1.4%, P < 0.001, d = 0.26). Adaptations of hamstring function and thigh muscle balance revealed moderate to strong transfers to improved sprint mechanics (P range: <0.001-0.048, R2 range: 34%-83%). The weakest participants demonstrated the highest adaptations of isokinetic parameters (P range: 0.003-0.023, R2 range: 42%-62%), whereas sprint mechanics showed no effect of initial performance level. Three months after the intervention, hamstring function (+6% to +14%) and thigh muscle balance (+8% to +10%) remained significantly enhanced (P < 0.001, ƞp 2 range: 0.529-0.621). High-intensity NHE training induced sustained improved hamstring function of sprinters, which can be transferred to swing phase mechanics of maximal sprints. The initial performance level, NHE training procedures and periodization should be considered to optimize adaptations.

Biomechanical analysis of single-leg stance using a textured balance board compared to a smooth balance board and the floor: A cross-sectional study.

BACKGROUND: Previous research showed that standing on textured surfaces can improve postural control by adapting somatosensory inputs from the plantar foot. The additional stimulation of plantar cutaneous mechanoreceptors by a textured surface during single-leg stance on a balance board may increase afferent information to the central nervous system to accelerate muscular responses and to enhance their accuracy. The additional impact of textured surface during single-leg stance on a balance board on postural control and muscle activity is unknown. RESEARCH QUESTION: To investigate the differences of a) postural control during single-leg stance on a textured balance board compared to a smooth balance board and b) activity of lower extremity muscles during single-leg stance on a textured balance board compared to a smooth balance board and the floor. METHODS: Twenty-six healthy adults (12 females, 14 males; mean age = 25.4 years) were asked to balance on their randomly assigned left or right leg on a force plate (floor; stable condition), a textured balance board and a smooth balance board (unstable conditions). Center of pressure (CoP) displacements (force plate, Bertec, 1000 Hz) and electromyographic activity (EMG) of eight leg muscles were measured and compared between conditions, respectively. RESULTS: Neither CoP-displacements, nor EMG activities differed significantly between the textured and the smooth balance board (p > 0.05). Significantly higher muscle activities (p < 0.05) were observed using the balance boards compared to the floor. SIGNIFICANCE: Single-leg stance using a textured balance board seems not to lead to reduced CoP-displacements compared to a smooth balance board. Muscle activation is significantly increased in both balance board conditions compared to the floor, however, it is not different when both balance board surfaces are compared. It could not be recommended to use a textured balance board for altering muscle activity and improving postural control during single-leg stance in favor of a smooth textured balance board.

Assessing thigh muscle balance of male athletes with special emphasis on eccentric hamstring strength.

Background: Hamstring strength is important to prevent thigh muscle and knee injuries. Different antagonist-agonist relationships of thigh muscle strength are applied to estimate the injury risk e.g. the intersection point of eccentric hamstring (Hecc) and concentric quadriceps (Qcon) moment-knee flexion angle curves (dynamic control ratio at the equilibrium point = DCRe) and the dynamic control ratio (DCR = Hecc:Qcon). Objective: The aim was to quantify the relationships between DCR, DCRe moments and angles as well as their correlations with peak moments and contractional work of eccentric hamstring and concentric quadriceps exercise. Methods: This cross-sectional study included data from 238 healthy male participants of different sports. They conducted unilateral isokinetic tests obtained at 30°/s and 150°/s for the hamstrings (prone) and the quadriceps (supine). Results: Correlations between DCR and DCRe moments were significant, but weak to moderate in strength (R230°/s = 20%, R2150°/s = 26%). In contrast to DCR (25% ≤ R2 ≤ 46%), DCRe moments (80% ≤ R2 ≤ 86%) showed very strong relations with peak moments and contractional work of eccentric hamstring exercise. Discussion: DCR and DCRe assess thigh balance by using the same isokinetic raw data. However, weak relations became apparent. DCRe moments were stronger related to eccentric hamstring strength and work than DCR. Therefore, the DCRe moment may serve as meaningful measure of thigh muscle balance because increased eccentric hamstring strength promotes dynamic joint stability and minimizes injury risk.

The dynamic control ratio at the equilibrium point (DCRe): introducing relative and absolute reliability scores.

Analytical methods to assess thigh muscle balance need to provide reliable data to allow meaningful interpretation. However, reproducibility of the dynamic control ratio at the equilibrium point has not been evaluated yet. Therefore, the aim of this study was to compare relative and absolute reliability indices of its angle and moment values with conventional and functional hamstring-quadriceps ratios. Furthermore, effects of familiarisation and angular velocity on reproducibility were analysed. A number of 33 male volunteers participated in 3 identical test sessions. Peak moments (PMs) were determined unilaterally during maximum concentric and eccentric knee flexion (prone) and extension (supine position) at 0.53, 1.57 and 2.62 rad · s-1. A repeated measure, ANOVA, confirmed systematic bias. Intra-class correlation coefficients and standard errors of measurement indicated relative and absolute reliability. Correlation coefficients were averaged over respective factors and tested for significant differences. All balance scores showed comparable low-to-moderate relative (<0.8-0.9) and good absolute reliability (<10%). Relative reproducibility of dynamic control equilibrium parameters augmented with increasing angular velocity, but not with familiarisation. At 2.62 rad · s-1, high (moment: 0.906) to moderate (angle: 0.833) relative reliability scores with accordingly high absolute indices (4.9% and 6.4%) became apparent. Thus, the dynamic control equilibrium is an equivalent method for the reliable assessment of thigh muscle balance.

The Effects of Angular Velocity and Training Status on the Dynamic Control Equilibrium.

Thigh muscle imbalances may impair sports performance and cause injuries. Common diagnostic parameters of knee muscle balance lack practical applicability. This cross-sectional study aimed to evaluate the effects of angular velocity and training status on the dynamic control ratio at the equilibrium point representing the intersection of eccentric knee flexion and concentric knee extension moment-angle curves. 58 trained and 58 untrained male participants (22.1 years, 82.4 kg) performed concentric and eccentric knee flexions (prone position) and extensions (supine position) on an isokinetic dynamometer operating at 30 and 150°/s. Trained participants had significantly higher DCRe moments at all angular velocities compared with their untrained counterparts (trained 30,150 : 1.86, 1.90 Nm/kg; untrained 30,150 : 1.56, 1.60 Nm/kg; p<0.001, partial η²=0.345). Dynamic control equilibrium moments rose with increasing velocity (p=0.001, partial η²=0.095), whereas dynamic control equilibrium angles (trained 30,150 : 28.9, 30.8°; untrained 30,150 : 26.1, 27.0°) were influenced by training status (p=0.004, partial η²=0.072), but not by angular velocity (p=0.241, partial η²=0.012). Dynamic control equilibrium parameters detect thigh muscle balance and reflect the trained participants' capacity to resist high eccentric knee flexor moments, especially during fast movements. Direct links to muscular loading during sprinting are conceivable, but warrant further investigation. The assessment of dynamic control equilibrium moments and angles might help physiotherapists and coaches to improve functional muscle screening, injury prevention and purposeful return to sport.

High force development augments skeletal muscle signalling in resistance exercise modes equalized for time under tension.

How force development and time under tension (TUT) during resistance exercise (RE) influence anabolic signalling of skeletal muscle is incompletely understood. We hypothesized that high force development during RE is more important for post-exercise-induced signalling than submaximal and fatiguing RE with lower force development but similar TUT. Twenty-two male subjects (24 ± 6 years, 181 ± 9 cm, 79 ± 2 kg) performed three distinct RE modes in the fed state with equal TUT but distinct force output: (i) maximal eccentric RE (ECC, n = 7) three sets, eight reps, 100% eccentric dynamic force; (ii) standard RE (STD, n = 7), three sets, 10 reps, 75% dynamic force; and (iii) high fatiguing single-set RE (HIT, n = 8), 20 reps, 100% eccentric-concentric force; vastus lateralis biopsies were collected at baseline, 15, 30, 60, 240 min and 24 h after RE, and the signalling of mechanosensitive and mammalian target of rapamycin (mTOR)-related proteins was determined. The phosphorylation levels of pFAK(Tyr397), pJNK(Thr183/Tyr185), pAKT(Thr308/Ser473), pmTOR(Ser2448), p4E-BP1(Thr37/46), p70s6k(Thr389)/(Ser421/Thr424) and pS6(Ser235/236) were significantly higher in ECC than those in STD and HIT at several time points (P < 0.01). pJNK(Thr183/Tyr185) and pS6(Ser235/236) levels were significantly higher in type II myofibres in ECC compared with STD and HIT. HIT exerted throughout the weakest signalling response. We conclude that high force development during acute RE is superior for anabolic skeletal muscle signalling than fatiguing RE with lower force output but similar TUT. Our results suggest that this response is substantially driven by the higher activation of type II myofibres during RE.