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.

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.

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.

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.

Progressive resistance versus relaxation training for breast cancer patients during adjuvant chemotherapy: design and rationale of a randomized controlled trial (BEATE study).

BACKGROUND AND RATIONALE: Cancer-related fatigue is a common severe symptom in breast cancer patients, especially during chemotherapy. Exercise appears to be promising in prevention or treatment of fatigue. Resistance training as an accompanying treatment to chemotherapy has been minimally investigated, yet might counteract muscle degradation and inflammation caused by many chemotherapeutics, and thus forestall or reduce fatigue. Previous exercise trials mostly compared the intervention with 'usual care'. Therefore, it is unclear to what extent the observed effects on fatigue are based on physical adaptations by exercise itself, or rather on psycho-social factors linked to the group support or attention by the trainer. METHODS AND DESIGN: The BEATE study is a randomized, controlled intervention trial comparing a 12-week supervised progressive resistance training program with a supervised group-based progressive muscle relaxation training in 100 patients with breast cancer under adjuvant chemotherapy. The primary endpoint is cancer-related fatigue; secondary endpoints include quality of life, depression, and cognitive capacity. In addition, isokinetic and isometric muscle strength, cardiorespiratory fitness, and body composition are measured, and biomarkers, such as inflammatory parameters, cortisol, and oxidative stress are analyzed in blood, saliva and urine. Safety of the resistance training during chemotherapy is monitored. DISCUSSION: Strengths of the BEATE study include the investigation of progressive resistance training parallel with chemotherapy, the choice of a control group that enables an evaluation of the physiological effects of exercise beyond potential psycho-social effects, and the comprehensive and high-quality assessment of physiological factors and biomarkers potentially related to fatigue.

Interactive processes link the multiple symptoms of fatigue in sport competition.

Muscle physiologists often describe fatigue simply as a decline of muscle force and infer this causes an athlete to slow down. In contrast, exercise scientists describe fatigue during sport competition more holistically as an exercise-induced impairment of performance. The aim of this review is to reconcile the different views by evaluating the many performance symptoms/measures and mechanisms of fatigue. We describe how fatigue is assessed with muscle, exercise or competition performance measures. Muscle performance (single muscle test measures) declines due to peripheral fatigue (reduced muscle cell force) and/or central fatigue (reduced motor drive from the CNS). Peak muscle force seldom falls by >30% during sport but is often exacerbated during electrical stimulation and laboratory exercise tasks. Exercise performance (whole-body exercise test measures) reveals impaired physical/technical abilities and subjective fatigue sensations. Exercise intensity is initially sustained by recruitment of new motor units and help from synergistic muscles before it declines. Technique/motor skill execution deviates as exercise proceeds to maintain outcomes before they deteriorate, e.g. reduced accuracy or velocity. The sensation of fatigue incorporates an elevated rating of perceived exertion (RPE) during submaximal tasks, due to a combination of peripheral and higher CNS inputs. Competition performance (sport symptoms) is affected more by decision-making and psychological aspects, since there are opponents and a greater importance on the result. Laboratory based decision making is generally faster or unimpaired. Motivation, self-efficacy and anxiety can change during exercise to modify RPE and, hence, alter physical performance. Symptoms of fatigue during racing, team-game or racquet sports are largely anecdotal, but sometimes assessed with time-motion analysis. Fatigue during brief all-out racing is described biomechanically as a decline of peak velocity, along with altered kinematic components. Longer sport events involve pacing strategies, central and peripheral fatigue contributions and elevated RPE. During match play, the work rate can decline late in a match (or tournament) and/or transiently after intense exercise bursts. Repeated sprint ability, agility and leg strength become slightly impaired. Technique outcomes, such as velocity and accuracy for throwing, passing, hitting and kicking, can deteriorate. Physical and subjective changes are both less severe in real rather than simulated sport activities. Little objective evidence exists to support exercise-induced mental lapses during sport. A model depicting mind-body interactions during sport competition shows that the RPE centre-motor cortex-working muscle sequence drives overall performance levels and, hence, fatigue symptoms. The sporting outputs from this sequence can be modulated by interactions with muscle afferent and circulatory feedback, psychological and decision-making inputs. Importantly, compensatory processes exist at many levels to protect against performance decrements. Small changes of putative fatigue factors can also be protective. We show that individual fatigue factors including diminished carbohydrate availability, elevated serotonin, hypoxia, acidosis, hyperkalaemia, hyperthermia, dehydration and reactive oxygen species, each contribute to several fatigue symptoms. Thus, multiple symptoms of fatigue can occur simultaneously and the underlying mechanisms overlap and interact. Based on this understanding, we reinforce the proposal that fatigue is best described globally as an exercise-induced decline of performance as this is inclusive of all viewpoints.

Evaluation of models used to study neuromuscular fatigue.

The mechanism(s) of neuromuscular fatigue depends on the approach or model used to study fatigue. We evaluate the physiological and functional relevance of the fatigue quantification system, the fatigue protocols, the preparations, and muscle environmental conditions used in various models involving either artificial stimulation or voluntary exercise to induce fatigue.