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.     

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.     

Isokinematic muscle mechanics in four groups of women of increasing age

Summary The purpose of this study was to evaluate the effects of age on dynamic muscle attributes of the knee extensors and flexors in postmenopausal women. Young healthy women (3rd decade,n = 15; 4th decade,n = 5) and older healthy women (6th decade,n = 9; 7th decade,n = 6) were tested at six angular velocities from 60° · s^–1 to 400° · s^–1. The 3rd and 4th decade groups produced greater extensor and flexor values for strength related variables at all angular velocities (peak torque, angle specific torque, work, power) than both the 6th and 7th decade groups (P<0.05). However, relative changes in these variables, with increments in angular velocity, were equivalent among the groups. Analysis of the flexor: extensor ratios for these variables demonstrated a differential loss in flexor function with increased age, perhaps indicative of type II motor unit loss or muscle fibre atrophy. It is suggested that such changes may be present even within 4th decade subjects.     

Co-activation and tension-regulating phenomena during isokinetic knee extension in sedentary and highly skilled humans

The aim of this study was to examine isokinetic torque produced by highly skilled (HS) and sedentary (S) human subjects, during knee extension, during maximal voluntary and superimposed electrical activation. To verify the level of activation of agonist (vastus lateralis, VL, and vastus medialis, VM) and antagonist muscles (semi-tendineous, ST), during maximal voluntary activation, their myo-electrical activities were detected and quantified as root mean square (rms) amplitude. Ten HS and ten S subjects performed voluntary and superimposed isometric actions and isokinetic knee extensions at 14 angular velocities (from –120 to 300°·s^–1). The rms amplitude of each muscle was normalized with respect to its rms amplitude when acting as agonist at 15°·s^–1. Whatever the angular velocity considered, peals torque and constant angular torque at 65° HS were significantly higher (P < 0.05) than those of S. Eccentric superimposed torque of S, but not HS, was significantly higher (P < 0.05) than voluntary torque at –120, –90, –60 and –30°·s^–1 angular velocities. For a given velocity, the rms amplitude of VL and VM were significantly lower (P < 0.05), during eccentric than during concentric actions, in S, but not in HS. However, whatever the angular velocity, ST co-activation in HS was significantly lower (P < 0.05) than in S. We concluded that co-activation phenomenon could partly explain differences in isokinetic performances. Differences between voluntary and superimposed eccentric torques as well as lower agonist rms amplitude during eccentric action in S, support the possibility of the presence of a tension-regulating mechanism in sedentary subjects.     

Eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man

Summary The primary purpose of this investigation was to study the eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man using a recently developed combined isometric, concentric and eccentric controlled velocity dynamometer (the SPARK System). A secondary purpose was to compare the method error associated with maximal voluntary concentric and eccentric torque output over a range of testing velocities. 21 males (21–32 years) performed on two separate days maximal voluntary isometric, concentric and eccentric contractions of the quadriceps femoris at 4 isokinetic lever arm velocities of 0° · s^–1 (isometric), 30° · s^–1 120° · s^–1 and 270° · s^–1. Eccentric peak torque and angle-specific torques (measured every 10° from 30° to 70°) did not significantly change from 0° · s^–1 to 270° · s^–1 (p>0.05) (with the exception of angle-specific 40° torque, which significantly increased;p<0.05). The mean method error was significantly higher for the eccentric tests (10.6%±1.6%) than for the concentric tests (8.1%±1.7%) (p<0.05). The mean method error decreased slightly with increasing concentric velocity (p>0.05), and increased slightly with increasing eccentric velocity (p>0.05). A tension restricting neural mechanism, if active during maximal eccentric contractions, could possibly account for the large difference seen between the present eccentric torque-velocity results and the classic results obtained from isolated animal muscle.     

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.     

Effects of isokinetic training of the knee extensors on high-intensity exercise performance and skeletal muscle buffering

Twenty-three subjects isokinetically trained the right and left quadriceps femoris, three times per week for 16 weeks; one group (n=13) trained at an angular velocity of 4.19 rad · s^–1 and a second group (n=10), at 1.05 rad · s^–1. A control group (n=10) performed no training. Isometric endurance time at 60% quadriceps maximum voluntary contraction (MVC), mean power output and work done (W) during all-out cycling, and the muscle buffer value (B) and carnosine concentration of biopsy samples from the vastus lateralis, were all assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of these variables (P < 0.05). No significant difference in either 60% MVC endurance time or impulse [(endurance time × force) at 60% MVC] was observed for any group after the 16 week period (P > 0.05). However, the post-training increase (9%) in W during high-intensity cycling was greater in the training group than in the control group (P=0.04). NeitherB nor carnosine concentration showed any significant change following training (P=0.56 andP=0.37, respectively). It is concluded that 16 weeks of isokinetic training of the knee extensors enables subjects to do more work during high-intensity cycling. Although the precise adaptations responsible for the improved performance have yet to be identified, they are unlikely to include an increase inB.     

Skeletal muscle mechanics in osteoporotic and nonosteoporotic postmenopausal women

The purpose of this study was to evaluate single-joint, dynamic muscle function of osteoporotic (OST) and nonosteoporotic (N-OST) women. Knee flexor and extensor function in postmenopausal women (6th decade OST,n = 15; 7th decade OST,n = 10; 6th decade N-OST,n = 6; 7th decade N-OST,n = 5) were evaluated at five angular velocities from 60° · s^–1 to 300° · s^–1. All subject groups had similar anthropometric measurements, but the 6th decade N-OST group were more physically active than the age-matched OST group. The OST and N-OST women produced peak torque at similar knee angles. The 6th decade N-OST women produced significantly greater knee extensor mean peak torque and angle specific torque, and mean work than any of the other three groups (P<0.05). However, knee flexor function was equivalent throughout the groups for most comparisons, except those between the 6th decade N-OST and 7th decade OST. While previous research has shown an early loss of flexor muscle function in ageing women, our data indicated that women with osteoporosis also experience a deterioration in quadriceps muscle function not encountered within the N-OST subjects. It is possible that such a change is precipitated by reduced physical activity, and may mirror deterioration in bone mineral content.     

The effect of range of motion and isometric pre-activation on isokinetic torques

Summary The effect of an increased angle of excursion and isometric pre-activation on isokinetic torques of knee extensors was investigated in five male subjects, mean age 35.0 years, SD 9.6. Peak torque and isoangular torque at 0.52 rad from full knee extension (FKE) were measured when contractions were carried out at 3.14, 4.19 and 5.24 rad·s^–1 starting: 1) from a standard knee angle (SA) of 1.57 rad from FKE, 2) from the same starting angle as SA, plus an isometric preload (P) equivalent to 25% of isometric maximal voluntary contraction and 3) from an increased angle of knee flexion (1A), 2.09 rad from FKE plus P. Surface integrated electromyograms (iEMG) of the vastus lateralis muscle in SA and IA+P were also recorded. The IA+P had the effect of increasing peak torque, as compared to SA, on average by 12.0%, SD 7.5% (P<0.001) at 3.14 rad·s^–1, 19.5%, SD 5.5% (P<0.001) at 4.19 rad·s^–1, 21.6%, SD 10.7% (P<0.001) at 5.24 rad·s^–1 and of increasing mean iEMG by 15.7%, SD 7.0% (P<0.001) at 5.24 rad·s^–1. The IA+P also had the effect of increasing the angle from FKE at which peak torque occurred: from means of 0.80 rad, SD 0.11 to 1.00 rad, SD 0.07 at 3.14 rad·s^–1, from 0.65 rad, SD 0.11 to 0.92 rad, SD 0.09 at 4.19 rad·s^–1 and from 0.60 rad, SD 0.11 to 0.88 rad, SD 0.11 at 5.24 rad·s^–1 (P<0.0001). Mean isoangular torque rose by 12.6%, SD 5.1% at 5.24 rad·s^–1 (P<0.01); mean iEMG values by 8.5%, SD 5.2% (P<0.02) and 11.6%, SD 6.4%(P<0.02) at 4.19 and 5.24 rad·s^–1, respectively. The mean time for both peak and isoangular torque development was significantly increased (P<0.0001). The effect of SA+P on peak torque was smaller than that of IA+P, a mean increment of 3.4%, SD 6% (P<0.02) only being observed at 5.24 rad·s^–1. The increase in isoangular torque was of the same magnitude as that of IA+P. It was concluded that when isokinetic contractions were carried out from a standard position of the knee at a right angle, neuromuscular activation at high angular velocities (>4.19 rad·s^–1) was submaximal. The underestimation of torque seemed to be counteracted by starting the contraction from a flexed position and by utilizing a submaximal P.     

Muscle activation during maximal voluntary eccentric and concentric knee extension

Summary The aim of this investigation was to study the relationships among movement velocity, torque output and electromyographic (EMG) activity of the knee extensor muscles under eccentric and concentric loading. Fourteen male subjects performed maximal voluntary eccentric and concentric constant-velocity knee extensions at 45, 90, 180 and 360° · s^–1. Myoelectric signals were recorded, using surface electrodes, from the vastus medialis, vastus lateralis and rectus femoris muscles. For comparison, torque and full-wave rectified EMG signals were amplitude-averaged through the central half (30°–70°) of the range of motion. For each test velocity, eccentric torque was greater than concentric torque (range of mean differences: 20%–146%,P < 0.05). In contrast, EMG activity for all muscles was lower under eccentric loading than velocity-matched concentric loading (7%–31%,P < 0.05). Neither torque output nor EMG activity for the three muscles changed across eccentric test velocities (P > 0.05). While concentric torque increased with decreasing velocity, EMG activity for all muscles decreased with decreasing velocity (P < 0.05). These data suggest that under certain high-tension loading conditions (especially during eccentric muscle actions), the neural drive to the agonist muscles was reduced, despite maximal voluntary effort. This may protect the musculoskeletal system from an injury that could result if the muscle was to become fully activated under these conditions.     

A new dynamometer measuring concentric and eccentric muscle strength in accelerated,decelerated, or isokinetic movements

Summary A new computerized dynamometer (the SPARK System) is described. The system can measure concentric and eccentric muscle strength (torque) during linear or nonlinear acceleration or deceleration, isokinetic movements up to 400° · s^–1, and isometric torque. Studies were performed to assess: I. validity and reproducibility of torque measurements; II. control of lever arm position; III. control of different velocity patterns; IV. control of velocity during subject testing; and, V. intra-individual reproducibility. No significant difference was found between torque values computed by the system and known torque values (p>0.05). No difference was present between programmed and external measurement of the lever arm position. Accelerating, decelerating and isokinetic velocity patterns were highly reproducible, with differences in elapsed time among 10 trials being never greater than 0.001 s. Velocity during concentric and eccentric isokinetic quadriceps contractions at 30° · s^–1, 120° · s^–1 and 270° · s^–1 never varied by more than 3° · s^–1 among subjects (N=21). Over three days of testing, the overall error for concentric and eccentric quadriceps contraction peak torque values for 5 angular velocities between 30° · s^–1 and 270° · s^–1 ranged from 5.8% to 9.0% and 5.8% to 9.6% respectively (N=25). The results indicate that the SPARK System provides valid and reproducible torque measurements and strict control of velocity. In addition, the intra-individual error is in accordance with those reported for other similar devices.     

A comparison of voluntary and electrically evoked isokinetic plantar flexor torque in males

Summary The angle-specific isokinetic torque- and power-velocity relationships of the triceps surae were examined in ten male sprint athletes aged [mean (SD)] 22.4 (3.2) years, ten non-trained adult men aged 27.4 (4.8) years and six elderly male subjects aged 68.5 (2.4) years. Normal voluntary contractions were compared with those obtained using maximal tetanic stimulation and a release technique which standardised the level of muscle activation during isokinetic contractions. When the isokinetic data was normalized to the maximum isometric torque the stimulated release contractions at 5.18–5.29 rad · s^–1 produced significantly (P < 0.05) greater torque than the voluntary no-release contractions at the same angular velocity in each group of subjects. The three subject groups generated their peak power at 3.07 rad · s^–1 during the voluntary no-release contractions. However, with the stimulated release contractions, power had still not reached a peak at 5.29 rad · s^–1, the highest angular velocity that could be tested. It appears that at higher angular velocities the triceps surae is capable of greater torque and power generation when contractions are evoked using a stimulated release technique. It is suggested that the stimulated release technique gives a more complete picture of the torque-velocity characteristics of the contractile component of the triceps surae.     

Effects of isokinetic training of the knee extensors on isometric strength and peak power output during cycling

Summary Isokinetic training of right and left quadriceps femoris was undertaken three times per week for 16 weeks. One group of subjects (n=13) trained at an angular velocity of 4.19 rad·s^–1 and a second group (n=10) at 1.05 rad·s^–1. A control group (n=10) performed no training. Maximal voluntary contraction (MVC) of the quadriceps, and peak pedal velocity (_p,peak) and peak power output (W _peak) during all-out cycling (against loads equivalent to 9, 10, 11, 12, 13 and 14% MVC) were assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of the performance variables (P>0.05). No significant difference in MVC was observed for any group after the 16-week period (P=0.167). The post-training increases in averageW _peak (7%) and _p,peak (6%) during the cycle tests were each significantly different from the control group response (P=0.018 andP=0.008, respectively). It is concluded that 16 weeks of isokinetic strength training of the knee extensors is able to significantly improve _p,peak andW _peak during sprint cycling, an activity which demands considerable involvement of the trained muscle group but with its own distinct pattern of coordination.     

An evaluation of different protocols for measuring the force-velocity relationship of the human quadriceps muscles

A modified Cybex II isokinetic dynamometer was used to evaluate the problems associated with measuring the concentric force-velocity characteristics of human knee extensor muscles. Three contraction protocols were investigated, simple voluntary contractions (VC); releases from maximal voluntary isometric contractions (VR) and releases from. isometric femoral nerve stimulated contractions (FNR). Percutaneous stimulation of the quadriceps was unsuitable for dynamic contractions as the proportion of the muscle activated varied with the angle of knee flexion. Isometric length-tension relationships and isokinetic contractions at seven angular velocities between 0.5 and 5.2 rad · s^–1 were recorded in five subjects. During isometric and slow dynamic contractions the voluntary forces were often greater than those obtained by femoral nerve stimulation, probably due to subjects stretching the rectus femoris during voluntary manoeuvres. It was found that the VC protocol produced acceptable isokinetic force recordings only at velocities below 3.1 rad · s^–1 in most subjects whilst VR contractions resulted in unexpectedly low forces at velocities below 1.57 rad · s^–1. Of the three techniques employed, FNR, although uncomfortable for subjects, provided the most accurate and reliable method of measuring force-velocity characteristics of knee extensor muscles. FNR contractions produced a force-velocity curve which showed a smooth decline in force with increasing velocity up to 5.2 rad · s^–1. VC contractions appear to be an acceptable alternative for testing the muscles provided the angular velocity is less than 3.1 rad · s^–1 and the subjects can be prevented from stretching the rectus femoris during the movement.     

Human skeletal muscle fibre types and force: velocity properties

It has been reported that there is a relationship between power output and fibre type distribution in mixed muscle. The strength of this relationship is greater in the range of 3–8 rad · s^–1 during knee extension compared to slower or faster angular knee extensor speeds. A mathematical model of the force: velocity properties of muscle with various combinations of fast- and slow-twitch fibres may provide insight into why specific velocities may give better predictions of fibre type distribution. In this paper, a mathematical model of the force: velocity relationship for mixed muscle is presented. This model demonstrates that peak power and optimal velocity should be predictive of fibre distribution and that the greatest fibre type discrimination in human knee extensor muscles should occur with measurement of power output at an angular velocity just greater than 7 rad · s^–1. Measurements of torque: angular velocity relationships for knee extension on an isokinetic dynamometer and fibre type distribution in biopsies of vastus lateralis muscles were made on 31 subjects. Peak power and optimal velocity were determined in three ways: (1) direct measurement, (2) linear regression, and (3) fitting to the Hill equation. Estimation of peak power and optimal velocity using the Hill equation gave the best correlation with fibre type distribution (r > 0.5 for peak power or optimal velocity and percentage of fast-twitch fibres). The results of this study confirm that prediction of fibre type distribution is facilitated by measurement of peak power at optimal velocity and that fitting of the data to the Hill equation is a suitable method for evaluation of these parameters.     

Reproducibility of isokinetic leg strength and endurance characteristics of adult men and women

Summary Day-to-day variability and single-measurement reliability of selected isokinetic knee extension-flexion strength and endurance indices were assessed in 10 adult men and 8 adult women. On three occasions separated by at least 5 days, the subjects completed 4 reciprocal maximal voluntary contractions (MVC) at different angular velocities (1.05 rad · s^–1 and 3.14 rad · s^–1). The men also completed a muscular endurance test consisting of 30 reciprocal, MVC at 3.14 rad ·^–1. Coefficient of variation, intra-class correlation coefficient and standard error of single-measurement scores support the continued use of gravity corrected peak torque (PT) and average peak torque (APT) as indices of isokinetic leg strength. Similarly, gravity corrected APT and total work should be the recommended indices of isokinetic leg muscular endurance in men. The results suggest that these isokinetic indices must be assessed using multiple day-to-day trial protocols adequately to describe performance capacity. Composite indices such as the ratio of Knee flexion to extension PT and fatigue measurements offer considerably reduced reliability and a greater potential for misinterpretation. The reliability of knee extension indices generally exceeds that of flexion indices. Similar variability and reproducibility of responses were observed between men and women and between reciprocal contractions performed at angular velocities of 1.05 rad · s^–1 and 3.14 rad · s^–1.     

Efficacy of a home-based training program for older adults using elastic tubing

The purpose of this study was to investigate the efficacy of, and the adherence to, a 12-week home-based progressive resistance training program for older adults utilizing elastic tubing. Sixty-two adults (mean age, 71.2 years) qualified to participate in the study. Subjects were randomly assigned to either the exercise (E) (n=31) or non-exercise (NE) group (n=31). Pre-and post-testing included isokinetic (1.05 rad · s ^–1) concentric/eccentric knee extension/flexion strength testing and flexibility measures of the hip, knee, and ankle. The E group trained three times per week, performing one to three sets of 10–12 repetitions for each of 12 resistance exercises. The exercises involved muscles of both the lower and upper body. Within the E group, 25 of the 31 subjects (80.6%) completed the study. Of the E subjects completing the study adherence to the three training sessions per week was 90% (range 72%–100%). Training resistances used during workouts increased significantly with the average estimated increase being 82% (P<0.001). The E group also demonstrated significant (P<0.05) increases in isokinetic eccentric knee extension (12%) and flexion (10%) strength. No other significant changes were observed between E and NE groups. These results suggest that home-based resistance training programs utilizing elastic tubing can serve as a practical and effective means of eliciting strength gains in adults over the age of 65.     

Comparison of muscle cross-sectional area and strength between untrained women and men

The cross-sectional areas (CSA) of fat, muscle and bone tissues of the limb as well as maximal voluntary isokinetic strength were measured in untrained men (n=27) and women (n=26) aged 18–25 years. Anatomical CSA of the three tissues were determined by ultrasound on the upper arm and thigh. The isokinetic strength of the elbow and knee extensor and flexor muscles were measured by an isokinetic dynamometer (Cybex 11) at 1.05 rad · s^–1. The women had significantly (P<0.001) larger fat CSA and smaller bone and muscle CSA than the men in both the upper arm and thigh. Among tissue CSA, the largest difference between the women and men was found in fat CSA regardless of the measurement sites. The sex differences in bone and muscle CSA were found largely in the upper arm compared to the thigh, even when expressed per unit second power of the limb length. Regression analyses of the data for respective samples for the men and women showed significant correlations (r=0.411–0.707, P < 0.05–P < 0.001) between CSA and strength in all muscle groups except for the elbow extensors of the men (r=0.328, P>0.05) and the elbow flexors of the women (r=0.388, P>0.05). No significant difference between sexes was observed when strength was expressed per unit of muscle CSA (F · CSA^–1) for the elbow flexors and extensors. However, the men showed significantly higher F · CSA^–1 than the women for the knee flexors and extensors (P < 0.001). These results would indicate that, although the difference between sexes in muscle CSA is smaller in the thigh than in the upper arm, differences in the ability to develop dynamic strength proportional to the CSA appeared mainly in the thigh muscles compared to the upper muscles.     

The effect of short and long duration exercise on serum erythropoietin concentrations

Summary The effects of short and long duration exercise on serum erythropoietin concentrations [EPO]_s were studied in seven male cross-country skiers of national team standard and eight male marathon runners, respectively. The short duration exercise was performed as 60 min of cycling at an intensity of 80%–95% of maximal heart rate. Arterial blood oxygen saturations monitored by pulse-oximetry remained unchanged throughout exercise. The partial pressure of O₂ at which haemoglobin was half-saturated with O₂ calculated from forearm venous blood gas tension and blood O₂ saturation, and the erythrocyte 2,3-diphosphoglycerate did not change significantly during the exercise. Blood lactate concentrations were increased at the end of exercise [from 1.3 (SEM 0.1) to 3.6 (SEM 0.3) mmol · 1^–1]. The [EPO]_s determined (by enzyme-linked immunosorbent assay) pre-exercise, 5 min, 6 h, 19 h, and 30 h after the exercise were unchanged [from 16.1 (SEM 2.6) to 19.1 (SEM 3.2), 17.9 (SEM 3.0), 17.0 (SEM 2.5), and 18.6 (SEM 2.9) U·l^–1, respectively]. The [EPO]_s were not correlated to the earlier parameters. The long duration exercise consisted of habitual training, a 3 week break from training followed by 2 and 4 weeks of re-training. The [EPO]_s, body fat (BF), and serum free-testosterone concentrations determined at the end of each period remained unchanged. The maximal oxygen uptakes were decreased after the break from training and increased during retraining (P=0.04). Body mass (m _b) increased after the break in training (P=0.02). The [EPO]_s were correlated to BF,r=0.42,P=0.02;m _b,r=0.45,P=0.01; and free-testosterone concentrations,r=0.44,P=0.01. Thus, short and long-duration exercise had no direct influence on [EPO]_s; but relationships among [EPO]_s, free-testosterone concentrations and body composition were noted.     

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.