Isokinetic Hamstrings:Quadriceps Ratios in Intercollegiate Athletes

OBJECTIVE: To compare the differences in the concentric hamstrings:quadriceps (H:Q) ratio among athletes in different sports at 3 velocities. DESIGN AND SETTING: We measured the H:Q ratio of both knees using the Biodex Pro Isokinetic Device. SUBJECTS: Eighty-one male and female collegiate athletes. MEASUREMENTS: We performed analyses for sport, velocity, and side of body for each sex. To compare the means of the concentric H:Q ratios for mean peak torque and mean total work, a 2 x 3 x 4 mixed-factorial analysis of variance was computed for women and a 2 x 2 x 3 mixed-factorial analysis of variance was computed for men. RESULTS: We observed no significant interactions for men and women for the concentric H:Q ratio for mean peak torque. There was a significant mean difference among velocity conditions and a significant difference for men with respect to velocity. No significant differences were found for side of body or sport. CONCLUSIONS: The H:Q ratio increased as velocity increased. No differences existed for the H:Q ratio for sport or side of body.     

Isometric and isokinetic torque curves at the knee joint

Isometric and isokinetic torques of bilateral quadriceps and hamstrings were measured with Isokinetic Rehabilitation and Testing System (Model No. Cybex 340) on 40 normal untrained subjects, 20 males and 20 females, ranging between the ages of 23 and 35 years. The mean peak isometric and isokinetic torque values of both muscle groups showed no significant differences between dominant (right) and nondominant (left) limbs in both sexes; however there were significant differences between the male and the female. As the angular velocity increased, the peak torque significantly decreased, and the point of peak torque output occurred significantly later in the range of motion for quadriceps and hamstrings (p less than 0.01). There were no significant changes in the hamstrings to quadriceps (H/Q) ratios as the angular velocity increased. However, there were significant differences of mean H/Q ratio between male and female (p less than 0.01). Height had significant positive correlation with peak isometric and isokinetic torques for both quadriceps and hamstrings (p less than 0.01). Weight was found to correlate significantly with peak isometric and isokinetic torques (p less than 0.01). The mean isometric torques were significantly higher than the mean isokinetic torques for any joint angles in both sexes (p less than .01).     

Single-leg hop can result in higher limb symmetry index than isokinetic strength and single-leg vertical jump following anterior cruciate ligament reconstruction

BackgroundA single-leg vertical jump height (SLVJ) may reflect knee extension strength more than a single-leg hop for distance (SLH). This study aimed to examine the relationships between the isokinetic knee extension torque, SLH, and SLVJ after anterior cruciate ligament reconstruction (ACLR).MethodsForty-four patients post-ACLR (median 12.0 months) participated in the study. The isokinetic knee extension peak torque at 60°/s and 180°/s (Ext 60, 180), SLH, and SLVJ were measured. The limb symmetry index (LSI) was calculated as the ratio of the operated side to the unoperated side.ResultsThere were moderate-to-strong positive correlations between isokinetic knee extension torque and both SLH (r = 0.72–0.77, P < 0.001) and SLVJ (r = 0.73–0.79, P < 0.001). Significant side-to-side differences in isokinetic knee extension torque and SLVJ between the operated and unoperated sides were found (P < 0.05), but not for SLH (P = 0.065). The results of the analysis of variance (ANOVA) and post hoc analyses showed that the LSI of SLH (98.2%) was higher than that of the LSI of Ext 180 and SLVJ (P < 0.05). Fisher's exact test showed a significant relationship between the LSI of Ext 180 and that of SLVJ (cut-off 85%; P = 0.041). No patients had LSI < 85% in SLH.ConclusionsEven though SLH asymmetry improved approximately 12 months after ACLR, the asymmetry of isokinetic knee extension torque and SLVJ remained. The LSI of SLVJ could be an indicator of the recovery of isokinetic knee extension torque.     

Peripheral arterial disease decreases muscle torque and functional walking capacity in elderly

ObjectivesThe aim of this study is to compare values of force–velocity and functional walking capacity in elderly patients with intermittent claudication with respect to the control group.Materials and methodsThe study involved 135 individuals: 85-peripheral arterial disease (PAD) group diagnosed with stage II chronic lower limb ischemia, according to Fontaine's classification, and 50-control group. The studies included an assessment of walking capacity using a six-minute walk test (6MWT) and measurement of force–velocity parameters (peak torque—PTQ, total work—TW, average power—AVGP) of the lower limbs obtained by means of a functional dynamometry under isokinetic conditions.ResultsThe peripheral arterial disease group is characterized by significantly lower values of force–velocity parameters compared to the control group (p < 0.005). Walking capacity in this group is significantly reduced due to significant differences in the distance covered (p < 0.0001), walking speed (p < 0.01), and its intensity (p < 0.01). Further, a positive correlation was found between the maximum distance specified in the six-minute walk test and lower limb muscle strength in the isokinetic test.ConclusionsMean values of all force–velocity parameters and walk distance were significantly higher in the control group than in the peripheral arterial disease group. In the PAD group, in both men and women, the value of the agonist/antagonist ratio of both lower limbs are lower in men and women comparing to the control group. A rehabilitation program for patients with intermittent claudication must consider exercises improving strength, exercise capacity, and endurance in patients with PAD.     

Fatigue-Induced Hip-Abductor Weakness and Changes in Biomechanical Risk Factors for Running-Related Injuries

ContextDespite overlap between hip-abductor (HABD) weakness and fatigue-induced changes in running, the interaction of these theorized contributors to running injuries has been underevaluated.ObjectiveTo assess the effects of a fatiguing run on HABD torque and evaluate the correlation between HABD torque and previously identified running-related injury pathomechanics while participants were rested or fatigued.DesignCrossover study.SettingLaboratory.Patients or Other ParticipantsA total of 38 healthy, physically active males (age = 21.61 ± 4.02 years, height = 1.78 ± 0.08 m, body mass = 76.00 ± 12.39 kg).Intervention(s)Data collection consisted of rested-state collection, a fatiguing treadmill-run protocol, and fatigued-state collection. For the HABD measures, side-lying handheld-dynamometer isometric tests were performed and converted to torque using femur length. For the gait analysis, kinematic (240 Hz) and kinetic (960 Hz) running (4.0 m/s) data were collected for 3 trials. The fatigue protocol involved a graded exercise test and 80% o₂max run to exhaustion. Immediately after the run, fatigued-state measures were obtained.Main Outcome Measure(s)Variables of interest were HABD torque and peak angles, velocities, and moments for hip and knee adduction and internal rotation. Differences between conditions were compared using paired t tests. Pearson correlation coefficients were calculated to evaluate relationships between HABD torque and biomechanical variables.ResultsFatigue decreased HABD torque and increased hip-adduction angle, knee-adduction velocity, and hip and knee internal-rotation velocities and moments (all P values < .05). In the rested state, HABD torque was correlated with hip-adduction velocity (r = –0.322, P = .049). In the fatigued state, HABD torque was correlated with hip-adduction velocity (r = –0.393, P = .015), hip internal-rotation velocity (r = –0.410, P = .01), and knee-adduction angle (r = 0.385, P = .017) and velocity (r = −0.378, P = .019).ConclusionsChanges in joint velocities due to fatigue and correlations between HABD torque and hip- and knee-joint velocities highlight the need to consider not only the quantity of HABD strength but also the rate of eccentric control of HABDs.     

Bilateral eccentric and concentric torque of quadriceps and hamstring muscles in females and males

Summary This study assessed maximum eccentric (ECC) and concentric (CON) torque of quadriceps (QUAD) and hamstring (HAM) muscle groups in healthy females (n=13) and males (n=27). Peak torques (PT) of bilateral muscle actions were recorded at constant angular velocities of 0.52, 1.57 and 2.61 rad·s⁻¹. The QUAD_con and HAM_con PT decreased (p<0.05) with increasing angular velocity. The QUAD_ecc and HAM_ecc PT increased (p<0.05) in females, whereas QUAD_ecc PT decreased (p<0.05) and HAM_ecc PT showed no change in males. In general, ECC PT was higher (p<0.05) than CON PT and QUAD PT was higher (p<0.05) than HAM PT, for any given angular velocity. Males displayed higher (p<0.05) PT than females but when PT were adjusted for body mass the sex differences in QUAD_con and HAM_con were reduced (p<0.05), whereas the differences in QUAD_ecc and HAM_ecc were abolished. The CON and ECC PT were, on average, 60% and 41% greater, respectively, in males than in females. The corresponding differences, when adjusted for body mass, were 23% and 8%. ECC:CON PT for QUAD were higher (p<0.05) in females than in males. CON and ECC HAM:QUAD PT ratio increased (p<0.05), as a function of velocity. This study suggests, that bilateral ECC PT is higher than CON PT and CON HAM:QUAD PT ratio is higher than ECC HAM:QUAD PT ratio. Moreover, females and males display different ECC torque-velocity patterns, whereas CON torquevelocity patterns are similar and females possess greater QUAD_ecc PT relative to QUAD_con PT than males.     

Preliminary investigation of rate of torque development deficits following total knee arthroplasty

BackgroundTo assess changes in maximal strength and rate of torque development (RTD) following TKA, and examine the relationships between these measures and physical function.MethodsThirty-five TKA patients and 23 controls completed isometric knee extensor torque testing preoperatively, 1, and 6 months after surgery. Maximal strength was calculated as the peak torque during a maximal voluntary isometric contraction (MVIC) of the knee extensor muscles, peak RTD (RTD_peak) was calculated as the maximum value from the 1st derivative of the isometric knee extension torque data, RTD_25% and RTD _50% were calculated as the change in force over the change in time from force onset to 25% and 50% MVIC. Physical function was measured using a timed-up-and-go (TUG) and stair climbing test (SCT).ResultsRTD was significantly lower in the TKA group, at all-time points, compared to the Controls. MVIC and RTD significantly decreased 1-month following surgery (p = 0.000 for all measures). RTD_peak measures added to linear regressions with strength improved the prediction of TUG scores (p = 0.006) and the SCT scores (p = 0.015) 1-month post-surgery. Adding RTD_50% to the regression model, following MVIC, improved predicting both TUG (p = 0.033) and SCT (p = 0.024). At 6-months, the addition of RTD_25% to the regression model, following MVIC, improved the prediction of TUG (p = 0.037) and SCT (p = 0.036).ConclusionFollowing TKA, physical function is influenced by both the maximal strength and the rate of torque development of the knee extensors, and the prediction of function is improved with the addition of RTD compared to that of maximal strength alone.     

Knee function in 10-year-old children and adults with Generalised Joint Hypermobility

PurposeKnee function is reduced in patients with Benign Joint Hypermobility Syndrome. The aim was to study knee function in children and adults with Generalised Joint Hypermobility (GJH) and Non-GJH (NGJH)).Materials and methodsIn a matched comparative study, 39 children and 36 adults (mean age children 10.2 years; adults 40.3 years) were included, comprising 19 children and 18 adults with GJH (Beighton ≥ 5/9; Beighton ≥ 4/9), minimum one hypermobile knee, no knee pain (children), and 20 children and 18 adults with NGJH (Beighton < 5; Beighton < 4). Totally, 85% of the adults were parents to these children.Knee function was determined by self-reported physical fitness (100 mm VAS), Knee injury and Osteoarthritis Outcome Score (KOOS) (only adults), measured maximum isokinetic knee strength (60°/s) and peak vertical jump displacement (PVJD), with calculated knee strength balance, Hamstring/Quadriceps (H/Q) ratio and peak rate of force development (PRFD).ResultsAdults with GJH had lower knee function (KOOS: pain, p = 0.001; symptoms, p = 0.001; Activities of Daily Living, p = 0.001; Sport/Recreation, p = 0.003; knee-related quality of life, p < 0.001), and H/Q ratio (0.46 vs. 0.54, p = 0.046) than adults with NGJH, regardless of age and knee pain. Both GJH groups had normal physical fitness, isokinetic knee strength, and (only children) H/Q ratio.ConclusionsChildren at 10 years with GJH have normal, but adults with GJH have impaired knee function. To track the risk of developing impaired knee function, children with GJH must be followed longitudinally. Meanwhile, attention to knee function may be given to children with GJH who have parents presenting GJH.     

Sagittal knee joint kinematics and energetics in response to different landing heights and techniques

Single-leg and double-leg landing techniques are common athletic maneuvers typically performed from various landing heights during intensive sports activities. However, it is still unclear how the knee joint responds in terms of kinematics and energetics to the combined effects of different landing heights and techniques. We hypothesized that the knee displays greater flexion angles and angular velocities, joint power and work in response to the larger peak ground reaction force from 0.6-m height, compared to 0.3-m height. We further hypothesized that the knee exhibits elevated flexion angles and angular velocities, joint power and work during double-leg landing, relative to single-leg landing. Ground reaction force, knee joint kinematics and energetics data were obtained from 10 subjects performing single-leg and double-leg landing from 0.3-m to 0.6-m heights, using motion-capture system and force-plates. Higher peak ground reaction force (p < 0.05) was observed during single-leg landing and/or at greater landing height. We found greater knee flexion angles and angular velocities (p < 0.05) during double-leg landing and/or at greater landing height. Elevated knee joint power and work were noted (p < 0.05) during double-leg landing and/or at greater landing height. The knee joint is able to respond more effectively in terms of kinematics and energetics to a larger landing impact from an elevated height during double-leg landing, compared to single-leg landing. This allows better shock absorption and thus minimizes the risk of sustaining lower extremity injuries.     

Functional torque-velocity and power-velocity characteristics of elite athletes

Summary Technical limitations of some isokinetic dynamometers have called into question the validity of some data on human muscle mechanics. The Biodex dynamometer has been shown to minimize the impact artefact while permitting automatic gravity correction. This dynamometer was used to study quadriceps muscle torque and power generation in elite power (n = 6) and elite endurance (n = 7) athletes over 12 randomly assigned isokinetic velocities from 30° · s^–1 to 300° · s^–1. The angle at peak torque varied as a negative, linear function of angular velocity, with the average angle across test velocities being 59.5° (SD 10.2°). Power athletes developed greater peak torque at each angular velocity (P < 0.05) and experienced a 39.7% decrement in torque over the velocity range tested. En-, durance athletes encountered a 38.8% decline in peak torque. Torques measured at 60° of knee flexion followed a similar trend in both groups; however the greatest torques were recorded at 60° s^–1 rather than at 30° · s^–1 Leg extensor muscle power increased monotonically with angular velocity in both power (r ² = 0.728) and endurance athletes (r ² = 0.839); however these curves diverged significantly so that the power athletes produced progressively more power with each velocity increment. These inter group differences probably reflected a combination of natural selection and training adaptation.     

Responses to eccentric and concentric resistance training in females and males

The adaptive responses to 12 weeks of accommodated resistance training were compared in females (n= 11) and males (n= 11). They performed four to five sets of six maximum bilateral coupled concentric and eccentric quadriceps muscle actions at 1.05 rad s^-1 three times per week. Uni- and bilateral concentric and eccentric peak torque at different angular velocities (0.52, 1.57 and 2.62 rad s^-1), three repetition maximum half-squat and vertical jump height were measured before and after training. Both groups displayed marked increases (P < 0.05) in concentric and eccentric peak torque at all angular velocities. The relative increases (P < 0.05) in unilateral concentric (26 vs. 26%) and eccentric (28 vs. 36%) peak torque across speeds were similar in females and males. The corresponding increases (P < 0.05) in bilateral concentric and eccentric peak torque across speeds were 20 vs. 28% and 24 vs. 39% respectively. The three repetition maximum half-squat (20 vs. 25%) and vertical jump height (10 vs. 8%) increased (P < 0.05) equally in females and males. These results suggest that the overall increases in concentric and eccentric peak torque and functional strength, in response to short-term accommodated resistance training, occur at a rate that is independent of sex. The torque-velocity relationship, however, appears to change in males suggesting a relatively greater enhancement of maximum voluntary force in the slow-speed, high-force region.     

Specificity of training velocity and training load on gains in isokinetic knee joint strength

The present study investigated the effects of three different strength training regimes on the isokinetic strength profile of the knee extensors (quadriceps, Q) and flexors (hamstrings, H) and if increases in isokinetic strength were accompanied by an enhanced performance during a more complex leg movement, the soccer kick. Twenty-two elite soccer players performed 12 weeks of strength training (three times per week) at either high resistance (HR group: 4 sets, 8 reps, 8RM loading), low resistance (LR group: 4 sets, 24 reps, 24RM loading), loaded kicking movements (LK group: 4 sets, 16 reps, 16RM loading) while one group served as controls (CO group). Isokinetic concentric and eccentric moment of force was obtained (KinCom) as peak moment (M_peak) and moment at 50° knee flexion (M₅₀) at angular velocities of 30, 120, 240° s^-1. Isokinetic knee joint strength was unchanged in groups LR, LK, CO. However, after the HR strength training, concentric M_peak (±SD) increased (P<0.01) at 30° s^-1 (Q, 258±37 to 297±57 Nm; H, 122±22 to 140±21 Nm). Furthermore, eccentric M_peak increased at 30, 120 and 240° s^-1 (Q, 274±60 to 345±57 Nm (P<0.01), 291±56 to 309±49 Nm and 275±43 to 293±36 Nm (P<0.05), respectively; H, 143±32 to 158±25 Nm, 152±39 to 169±31 Nm and 148±27 to 163±19 Nm (P<0.05)). Corresponding increases (P<0.05) were observed for M₅₀. The H/Q ratio calculated as eccentric hamstring strength divided by concentric quadriceps strength (H_ecc/Q_con, representative for knee extension) at 240° s^-1 increased (P<0.05) from 107 to 118% (based on M_peak) and from 90 to 105% (M₅₀). Kicking performance estimated by maximal ball flight velocity was unaffected by any of the strength training regimes investigated. In conclusion, only heavy-resistance strength training induced increases in isokinetic muscle strength in the absence of learning effects. Concentric strength gains were observed at the actual velocity of training, while eccentric strength gains were found over the entire range of velocities examined. The capacity of the hamstring muscles for providing stability to the knee joint during fast extension was augmented as a result of the heavy-resistance strength training. Strength training should be integrated with other types of training involving the actual movement pattern in order to increase the performance within more complex movement patterns.     

The condition of the contralateral knee may induce different degrees of knee extensor strength asymmetry and affect functionality in individuals with unilateral or bilateral osteoarthritis

BackgroundLoss 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.MethodsSixty-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)).ResultsParticipants 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 < 0.05).ConclusionsIndividuals 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.     

Isokinetic hamstring/quadriceps strength ratio: influence from joint angular velocity,gravity correction and contraction mode

This study investigated isokinetic peak- and angle-specific hamstring/quadriceps strength ratios (conventional H/Q ratio) obtained during concentric and eccentric muscle contraction and examined the influence of joint angular velocity and the effect of gravity correction on these ratios. Also, a ‘functional’ H/Q ratio was defined by calculating eccentric hamstring strength relative to concentric quadriceps strength (H_eee/Q_eon representative for knee extension) and calculating concentric hamstring strength relative to eccentric quadriceps strength (H_eon/Q_eee representative for knee flexion). The H/Q ratio was calculated based on isokinetic peak moment and 50^o-moment (0^o= full extension) obtained at joint angular velocities 30, 120 and 240^o s^-1. Gravity corrected conventional H/Q ratio remained constant across speeds and contraction mode, ranging from 0.47 to 0.54 and from 0.49 to 0.56 based on peak and 50^o moment, respectively. In contrast, non-corrected H/Q_ ratio increased during concentric contraction from 0.58 at 30^o s^-1 to 0.74 at 240^o s^-1 (P < 0.01). For knee extension at 240^o s^-1 an H_eee/Q_eon of 1.05 (peak) and 0.89 (50^o) was observed while for flexion at 240^o s^-1 an H_eon/Q_eee of 0.27 (peak) and 0.28 (50^o) was observed. In conclusion, gravity correction had high influence on the change in H/Q ratio with variation in extension velocity. A potential 1:1 hamstring/quadriceps strength relationship was demonstrated for fast knee extension, indicating a significant functional capacity of the hamstring muscles for providing muscular stability at the knee joint in such situations.     

Young athletes after ACL reconstruction with asymmetric quadriceps strength at the time of return-to-sport clearance demonstrate drop-landing asymmetries two years later

BackgroundQuadriceps strength asymmetry at the time of return-to-sport (RTS) after anterior cruciate ligament reconstruction (ACLR) contributes to altered landing mechanics. However, the impact of RTS quadriceps strength on longitudinal alterations in landing mechanics, a risk factor for poor knee joint health over time, is not understood. The purpose of this study was to test the hypothesis that young athletes with quadriceps strength asymmetry at the time of RTS clearance after ACLR would demonstrate asymmetric landing mechanics 2 years later compared to those without quadriceps strength asymmetry.MethodsWe followed 57 young athletes (age at RTS = 17.6 ± 3.0 years; 77% females) with primary, unilateral ACLR for 2 years following RTS clearance. At RTS, we measured isometric quadriceps strength bilaterally and calculated limb-symmetry indices [LSI = (involved/uninvolved)×100%]. Using RTS quadriceps LSI, we divided participants into High-Quadriceps (HQ; LSI ≥ 90%) and Low-Quadriceps (LQ; LSI < 85%) groups. Two years later, we assessed landing mechanics during a drop-vertical jump (DVJ) task using three-dimensional motion analysis. We compared involved/uninvolved limb values and LSI between the HQ and LQ groups using Mann-Whitney U tests.ResultsThe LQ group (n = 26) demonstrated greater asymmetry (lower LSI) during landing at 2 years post-RTS for knee flexion excursion (p = 0.016) and peak vertical ground reaction force (p = 0.006) compared to the HQ group (n = 28). There were no group differences in uninvolved or involved limb values for all variables (all p > 0.093).ConclusionYoung athletes after ACLR with quadriceps strength asymmetry at the time of RTS favored the uninvolved limb during DVJ landing 2 years later. These landing asymmetries may relate to long-term knee joint health after ACLR.     

Deltoid muscle volume estimated from ultrasonography: in vitro validation and correlation with isokinetic abduction strength of the shoulder

Accurate prediction of muscle parameters can be used for customization of biomechanical models. A method is presented to estimate the volume of triangular-shaped muscles from ultrasonographic measurements. The deltoid muscle was used to validate the technique in a cadaver study of 12 shoulders. The relationship between isokinetic abduction strength and estimated deltoid muscle volume of the dominant shoulder of 30 healthy male subjects was analysed. Isokinetic joint moments were quantified using the Biodex System 3. A significant relationship (R = 0.87; p < 0.001) between the calculated deltoid volume and the isokinetic abduction peak torque was established.     

Neuromuscular control adaptations in elite athletes: the case of top level karateka

This paper aimed at investigating the neuromuscular response of knee flexor and extensor muscles in elite karateka and karate amateurs (Amateurs) during isokinetic knee flexion/extensions and during the execution of a front kick (FK). Surface electromyograms (sEMG) were recorded from the right vastus lateralis (VL) and biceps femoris (BF) muscles with a four-array electrode during maximal isometric knee flexion and extension (maximal voluntary contraction), during isokinetic contractions (30°, 90°, 180°, 270°, 340°, 400°/s), and during the FK. The level of VL and BF agonist (ago) and antagonist (ant) activation during the isokinetic and FK protocols was quantified through normalized sEMG root mean square value (%RMS_{ago/ant-ISOK/FK}). VL and BF average muscle fiber conduction velocity (CV) was computed for isokinetic and FK. Isokinetic flexion and extension torques and knee angular velocity during FK were also assessed. Analysis of variance was used to test the effect of group, angular velocity, and task on the assessed variables (P < 0.05). Elite karateka showed higher isokinetic knee flexion torque when compared with Amateurs. For all angular velocities, VL and BF %RMS_{ant-isokinetic} were lower in elite karateka, while their BF-CV_isokinetic BF-CV_{front kick} and BF %RMS_{ant-front kick} values were higher. For VL and BF, %RMS_{ago-front kick} was lower than %RMS_{ago-isokinetic} in both groups. Elite karateka demonstrated a typical neuromuscular activation strategy that seems task and skill level dependent. Knee flexion torque and CV results suggest the presence of an improved ability of elite karateka to recruit fast MUs as a part of training induced neuromuscular adaptation.     

Static and dynamic assessment of the Biodex dynamometer

Summary The validity and accuracy of the Biodex dynamometer was investigated under static and dynamic conditions. Static torque and angular position output correlated well with externally derived data (r=0.998 andr>0.999, respectively). Three subjects performed maximal voluntary knee extensions and flexions at angular velocities from 60 to 450° · s^–1. Using linear accelerometry, high speed filming and Biodex software, data were collected for lever arm angular velocity and linear accelerations, and subject generated torque. Analysis of synchronized angular position and velocity changes revealed the dynamometer controlled angular velocity of the lever arm to within 3.5% of the preset value. Small transient velocity overshoots were apparent on reaching the set velocity. High frequency torque artefacts were observed at all test velocities, but most noticeably at the faster speeds, and were associated with lever arm accelerations accompanying directional changes, application of resistive torques by the dynamometer, and limb instability. Isokinematic torques collected from ten subjects (240, 300 and 400° · s^–1) identified possible errors associated with reporting knee extension torques at 30° of flexion. As a result of tissue and padding compliance, leg extension angular velocity exceeded lever arm angular velocity over most of the range of motion, while during flexion this compliance meant that knee and lever arm angles were not always identical, particularly at the start of motion. Nevertheless, the Biodex dynamometer was found to be both a valid and an accurate research tool; however, caution must be expercised when interpreting and ascribing torques and angular velocities to the limb producing motion.     

Contraction history affects the in vivo quadriceps torque-velocity relationship in humans

We hypothesized that the history of contraction would affect the in vivo quadriceps torque-velocity relationship. We examined the quadriceps torque-velocity relationship of the human knee extensors at the descending and ascending limb of the torque-position relationship by initiating the knee extension at a knee angle position of 1.39 rad (80°) or 0.87 rad (50°) over a 0.52 rad (30°) range of motion under conditions of constant or linearly increasing velocity. Maximal voluntary isometric knee extension torque (M₀) was measured at 1.87 rad, 0.87 rad, and 0.35 rad, and concentric torque was measured. The subjects carried out ten maximal knee extensions at ten distinct velocities, each velocity ranging between 0.52 rad·s^–1 to 5.24 rad·s^–1 in steps of 0.52 rad·s^–1. Peak concentric torque was measured and mean torque calculated from the respective torque-time curves. Peak or mean torque, computed from the individual torque-time curves, and velocity data were fitted to the Hill equation under the four experimental conditions and the curve parameters computed. The M₀ was similar at 0.87 rad and 1.39 rad, but it was significantly lower at 0.35 rad. In the low-velocity domain of the torque-velocity curve where a plateau normally occurs, peak torque was always lower than M₀. Peak and mean torque were significantly greater under linearly increasing velocity conditions and the 1.39 rad starting knee position. Mean torque but not peak torque data could be well fitted to the Hill equation and the two computations resulted in significantly different Hill curve parameters including the concavity ratio, peak power, and maximal angular velocity. We concluded that the history of contraction significantly modifies the in vivo torque-velocity relationship of the human quadriceps muscle. Muscle mechanics and not neural factors may have accounted for the inconsistencies in the human torque-velocity relationships reported previously. Electronic Publication     

Moment and power generation during maximal knee extensions performed at low and high speeds

In the present study a method was developed to determine knee joint moment and power generated at low to very high velocities of knee extension. A group of 21 male subjects performed maximal knee extensions at four levels of external loading provided by a flywheel system. Knee extension was performed with no restrictions on joint angular velocity and acceleration. An interpolation procedure was employed to obtain moment and power at standard velocities. During each single knee extension peak velocity, peak moment, peak power and moment and power at 50° knee flexion were determined (0°=full extension). While maximal recorded angular velocity averaged 693°· s^–1 (range 479–1030), maximal recorded moment and power were 226 N · m (157–278) and 1140 W (573–1688), respectively, which were generated at velocities of 55° · s^–1 (12–148) and 523° · s^–1 (327–846). Isokinetic moment and power were obtained for comparison. The velocity range applied was larger using the flywheel method (21–1030° · s^–1 individual range) than that achieved isokinetically (30–240° · s^–1). Significant differences were observed between flywheel and isokinetic measurements. These discrepancies may be ascribed to differences in the time course of muscle length change and contractile force generation imposed by the two measuring methods. However, by the nonisokinetic measuring method presently employed, knee extension moment and power could be determined from low to very high angular extension velocity, at loading and contraction conditions comparable to those encountered during sport and exercise.