Prolonged intermittent high intensity exercise impairs neuromuscular performance of the knee flexors

This study investigated the effect of prolonged intermittent high intensity exercise upon the isokinetic leg strength and electromechanical delay of the knee flexors. Seven male collegiate soccer players were exposed to: (i) a prolonged intermittent high intensity exercise task (PIHIET) which required subjects to complete a single-leg pedalling task, with the preferred limb, (75?rpm for all constant-load portions of the task) consisting of 48?×?1.8 minute cycles of exercise, and (ii) a control task consisting of no exercise. Pre-, mid- and post-PIHIET gravity corrected indices of knee flexion angle-specific torque (0.44 rad knee flexion (AST); 0 rad?=?full knee extension; [1.05?rad?·?s^?1]) were made for both intervention and control limbs. Electromechanical delay (EMD) of the m. biceps femoris during supine knee flexion movements was evaluated in the preferred leg on both intervention and control days. Repeated measures ANOVAs revealed significant condition (intervention; control) by time (pre; mid; post) interactions for both knee flexor AST (F_[2,12]?=?4.8; p<0.03) and EMD (F_[2,12]?=?4.1; p<0.05). AST was observed to decrease by 16% and EMD increase by 30% pre to post intervention. These observations suggest an impairment of neuromuscular control and the ability to maintain force generation in the knee flexors, near the extremes of the range of motion during prolonged intermittent high-intensity exercise activities. Changes of this magnitude may pose a threat to the integrity of the knee joint.     

The effect of sleep deprivation and exercise load on isokinetic leg strength and endurance

Isokinetic leg strength and fatigue were measured in 24 male U.S. Marine Corps volunteers in a simulated sleep loss and unusually heavy work scenario. Knee extension and flexion peak torque (PT) were measured at three isokinetic speeds (1.57, 2.62 and 3.66 rad·s⁻¹) followed by 45 consecutive maximal reciprocal contractions at 3.14 rad·s⁻¹ to measure fatigue index (FI). All subjects were retested 2 days later following 30-h sleep deprivation (SD). The exercise group (n = 12) spent 25 1-h sessions performing computer tasks, filling out questionnaires and walked 1.61 km with a 50% gross body mass pack load, during each of the 25 sessions. The control group (n = 12) did likewise but did not exercise. Repeated measures ANOVA indicated that flexion PT at 1.57 rad·s⁻¹ decreases (P < 0.013) after SD. Exercise did not affect Fl but did decrease PT. It was concluded that carrying a 50% load produces decrements in PT for both extension and flexion but more so for flexion. SD affected PT but had no effect on FI.     

Gender-specific knee extensor torque,flexor torque,and muscle fatigue responses during maximal effort contractions

The purpose of this study was to examine gender differences in knee extensor and flexor peak torque, work, power, and muscle fatigue during maximal effort isokinetic contractions. Subjects included 19 healthy male and 20 healthy female volunteers. Following a dynamic warm-up period, subjects performed 30 reciprocal, concentric maximal knee extension and flexion contractions at a pre-set angular velocity of 3.14 rad·s^–1 on the Biodex Isokinetic Dynamometer. Values for knee extensor peak torque, work, and power were calculated for each repetition over an angular displacement of 1.05 rad for each repetition. The single highest repetition value for knee extensor and flexor peak torque, work, and power was then calculated relative to body mass (N·m·kg^–1, J·kg^–1, W·kg^–1) and allometric-scaled (N·m·kg^{– n} , J·kg^{– n} , W·kg^{– n} ) units. The allometric-scaled units were derived from a log–log transformation and linear regression analysis to calculate the exponent to which body mass is raised. The rate of quadriceps femoris muscle fatigue was calculated as the decline in each isokinetic variable by the linear slope from the single highest repetition value through the 30th repetition, and by two different fatigue indexes. The results demonstrate higher knee extension and flexion peak torque, work, and power in absolute, relative, and allometric-scaled units for males compared to females. Males exhibited higher fatigue rates for both muscle groups of each isokinetic variable than females, as described by the slope and the fatigue index, except when adjusted for peak values via analysis of covariance. The findings suggest that during maximal-effort muscle contractions, males exhibit a higher susceptibility to muscle fatigue than females, a phenomenon that may be related to an inherent ability to generate higher knee extensor and flexor torque. Electronic Publication     

A comparison of different two-dimensional approaches for the determination of the patellar tendon moment arm length

The purpose of this study was to estimate and compare the moment arm length of the patellar tendon (d) during passive knee extension using three different reference landmarks; instant centre of rotation (ICR), tibiofemoral contact point (TFCP) and geometrical centre of the posterior femoral condyles (GCFC). Measurements were taken on the right leg on seven healthy males during passive knee rotation performed by the motor of a Cybex Norm isokinetic dynamometer. Moment arms lengths were obtained by analysing lateral X-ray images recorded using a GE FlexiView 8800 C-arm videofluoroscopy system. The d–knee joint angle relations with respect to GCFC and ICR were similar, with decreasing values from full knee extension (~5.8 cm for d _GCFC and ~5.9 cm for d _ICR) to 90° of knee flexion (~4.8 cm for both d _GCFC and d _ICR). However, the d _TFCP–knee joint angle relation had an ascending–descending shape, with the highest d _TFCP value (~5 cm) at 60° of knee flexion. There was no significant difference between the GCFC and ICR methods at any knee joint angle. In contrast, there were significant differences (P < 0.01) between d _ICR and d _TFCP at 0°, 15°, 30° and 45° of knee flexion and between d _GCFC and d _TFCP at 0°, 15° and 30° of knee flexion (P < 0.01). This study shows that when using different knee joint rotation centre definitions, there are significant differences in the estimates of the patellar tendon moment arm length, especially in more extended knee joint positions. These differences can have serious implications for joint modelling and loading applications.     

Maximal lactate steady state,respiratory compensation threshold and critical power

Critical power (CP) and the second ventilatory threshold (VT₂) are presumed to indicate the power corresponding to maximal lactate steady state (MLSS). The aim of this study was to investigate the use of CP and VT₂ as indicators of MLSS. Eleven male trained subjects [mean (SD) age 23 (2.9) years] performed an incremental test (25 W·min⁻¹) to determine maximal oxygen uptake (V˙O_2max), maximal aerobic power (MAP) and the first and second ventilatory thresholds (VT₁ and VT₂) associated with break points in minute ventilation (V˙_E), carbon dioxide production (V˙CO₂), V˙_E/V˙CO₂ and V˙_E/V˙O₂ relationships. Exhaustion tests at 90%, 95%, 100% and 110% of V˙O_2max and several 30-min constant work rates were performed in order to determine CP and MLSS, respectively. MAP and V˙O_2max values were 344 (29) W and 53.4 (3.7) ml·min⁻¹·kg⁻¹, respectively. CP [278 (22) W; 85.4 (4.8)% V˙O_2max] and VT₂ power output [286 (28) W; 85.3 (5.6)% V˙O_2max] were not significantly different (p=0.96) but were higher (p<0.05) than the MLSS work rate [239 (21) W; 74.3 (4.0)% V˙O_2max] and VT₁ power output [159 (23) W; 52.9 (6.9)% V˙O_2max]. MLSS work rate was significantly correlated (p<0.05) with those noted at VT₁ and VT₂ (r=0.74 and r=0.93, respectively). VT₂ overestimated MLSS by 10.9 (6.3)% V˙O_2max which was significantly higher than VT₁ [+21.4 (5.6)% V˙O_2max; p<0.01]. CP calculated from a given range of exhaustion times does not correspond to MLSS. Electronic Publication     

Effect of immobilization and retraining on torque-velocity relationship of human knee flexor and extensor muscles

The effect of 2 weeks immobilization of the uninjured right knee and 10 weeks of retraining on muscle torque-velocity characteristics was investigated in nine young subjects. Left and right knee extension and flexion maximal voluntary isometric torque (T_max) and dynamic torque at 60°·s^–1 (T₆₀) and 180°·s^–1 (T₁₈₀) were measured before (PRE) and after immobilization (POST) and after 3 (R3) and 10 (R10) weeks of dynamic retraining. The torque-velocity relationship was quantified by expressing T₆₀ and T₁₈₀ relative to T_max (NT₆₀ and NT₁₈₀, respectively). For the right extensor muscles, percutaneous biopsy samples were obtained from the vastus lateralis muscle and fibre type distribution was measured. POST extension and flexion torque (mean of T_max, T₆₀ and T₁₈₀) decreased by 27% and 11%, respectively. During the course of the experiment, the changes in NT₆₀ and NT₁₈₀ were similar. POST extensor muscle NTV (mean of NT₆₀ and NT₁₈₀) was decreased significantly (12%, P<0.05), but no significant change was found for flexor muscle NTV (+3%). At R3 T_max, dynamic torque and NTV were restored to normal. Unlike isometric torque, NTV did not change from R3 to R10. No changes in fibre type distribution were found. The adaptation of muscle length is suggested as the mechanism to explain the change in NTV. Electronic Publication     

Scaling skeletal muscle function to mass in patients with moderate-to-severe COPD

Skeletal muscle performance and muscle mass are commonly reduced in patients with advanced chronic obstructive pulmonary disease (COPD). It is currently unclear, however, whether negative changes in muscle structure and function are proportionately related to each other in these patients. In a cross-sectional study, 39 patients (post-bronchodilator FEV₁ = 49.7 ± 15.5% pred) and 17 controls were submitted to knee isokinetic dynamometry [peak torque (PT), isometric strength (IS), and total work (TW)] and dual energy X-ray absorptiometry for the evaluation of leg muscle mass (LMM). Muscle function (F) was normalised for LMM by using ratio standards (F·LMM⁻¹), power function ratios (F·LMM^−b , where b is usually ≠ 1), and analysis of covariance (ANCOVA). Patients with COPD presented with reduced PT, IS, TW, and LMM as compared to controls: there were significant linear correlations among these variables in both groups (P < 0.05). Ratio standards of PT·LMM⁻¹ and TW·LMM⁻¹ were, on average, 14% lower in patients than controls (P < 0.01). The coefficients for allometric correction of IS and TW were significantly higher in patients as compared to controls (0.975 vs. 0.603 and 1.471 vs. 0.824, respectively, P < 0.05), i.e. more LMM was needed to generate a given functional output in patients than normal subjects. In addition, adjusted means of muscle function variables by ANCOVA were 11–18% lower for patients than controls with LMM as the covariate (P < 0.05). We conclude that factors other than simple atrophy (i.e. mass-independent mechanisms) might play a role in explaining the COPD-related skeletal muscle dysfunction.JA Neder is an established investigator of the CNPq (level II).     

Postactivation potentiation of knee extensor muscles in power- and endurance-trained, and untrained women

This study compared postactivation potentiation (PAP) in knee extensor muscles after a 10 s conditioning isometric maximal voluntary contraction (MVC) in female power- (PT, n = 12) and endurance-trained (ET, n = 12) athletes, and untrained (UT, n = 12) women aged 20–24 years. Isometric twitch characteristics of the knee extensor muscles were assessed in pre-MVC condition and during 15 min post-MVC period using supramaximal electrical stimulation of the femoral nerve by rectangular pulses of 1 ms duration. A significant (P < 0.05) potentiation of twitch peak torque (Pt, 30–51% in different groups), maximal rates of torque development (50–125%) and relaxation (76–124%) occurred immediately (2 s) post-MVC. PAP declined sharply at 1–3 min of recovery, whereas a significant potentiation of twitch Pt was still present for ET athletes at 1 min, and for UT women and PT athletes at 5 min of recovery, respectively. There were no significant (P > 0.05) changes in twitch contraction and half-relaxation times after a 10 s conditioning MVC. We concluded that PAP in knee extensor muscles is enhanced in PT but not in ET female athletes. The magnitude of PAP was greater when measured immediately after the conditioning MVC and its decline was slower in PT compared with ET athletes. Immediately post-MVC, twitch speed-related characteristics were potentiated to a greater extent than twitch Pt. The time-course of isometric twitch was not significantly altered by conditioning MVC.     

Dynamic multivoxel‐localized 31P MRS during plantar flexion exercise with variable knee angle

Exercise studies investigating the metabolic response of calf muscles using ³¹P MRS are usually performed with a single knee angle. However, during natural movement, the distribution of workload between the main contributors to force, gastrocnemius and soleus is influenced by the knee angle. Hence, it is of interest to measure the respective metabolic response of these muscles to exercise as a function of knee angle using localized spectroscopy. Time‐resolved multivoxel ³¹P MRS at 7 T was performed simultaneously in gastrocnemius medialis and soleus during rest, plantar flexion exercise and recovery in 12 healthy volunteers. This experiment was conducted with four different knee angles. PCr depletions correlated negatively with knee angle in gastrocnemius medialis, decreasing from 79±14 % (extended leg) to 35±23 %(～40°), and positively in soleus, increasing from 20±21 % to 36±25 %; differences were significant. Linear correlations were found between knee angle and end‐exercise PCr depletions in gastrocnemius medialis (R²=0.8) and soleus (R²=0.53). PCr recovery times and end‐exercise pH changes that correlated with PCr depletion were consistent with the literature in gastrocnemius medialis and differences between knee angles were significant. These effects were less pronounced in soleus and not significant for comparable PCr depletions. Maximum oxidative capacity calculated for all knee angles was in excellent agreement with the literature and showed no significant changes between different knee angles. In conclusion, these findings confirm that plantar flexion exercise with a straight leg is a suitable paradigm, when data are acquired from gastrocnemius only (using either localized MRS or small surface coils), and that activation of soleus requires the knee to be flexed. The present study comprises a systematic investigation of the effects of the knee angle on metabolic parameters, measured with dynamic multivoxel ³¹P MRS during muscle exercise and recovery, and the findings should be used in future study design.     

The effect of prolonged submaximal exercise on gas exchange kinetics and ventilation during heavy exercise in humans

This study compared ventilation, gas exchange (oxygen uptake, V̇O₂) and the surface electromyogram (EMG) activity of four major lower limb muscles during heavy exercise before (Pre-Ex) and after (Post-Ex) a sustained 90-min cycling exercise at 60% V̇O_2peak. The 90-min exercise was incorporated under the hypothesis that sustained exercise would alter substrate availability in the second exercise bout causing differences in fibre recruitment patterns, gas exchange and ventilation. Nine trained male subjects [V̇O_2peak=60.2 (1.7) ml·kg⁻¹·min⁻¹] completed two identical 6-min bouts of cycling performed at high intensity [~90% V̇O_2peak; 307 (6) W, mean (SE)]. Ventilation and gas exchange were measured breath-by-breath and the EMG was recorded during the last 12 s of each minute of the two 6-min bouts. EMG signals were analysed to determine integrated EMG (iEMG) and mean power frequency (MPF). V̇O₂ at min 3 and min 6 in Post-Ex were significantly higher (i.e., +201 and 141 ml·min⁻¹, respectively, P<0.05) than in Pre-Ex but there was a ~25% decrease of the slow component, taken as the difference between min 6 and min 3 [187 (27) vs 249 (35) ml·min⁻¹, respectively, P<0.05]. The greater whole-body V̇O₂ after 3 min of exercise in Post-Ex was not accompanied by clear alterations in the iEMG and MPF of the examined leg muscles. Ventilation and heart rate were elevated (~12–16 l·min⁻¹ and ~10 beats·min⁻¹, respectively, P<0.05) as were the ratios V̇ _E/O₂ and V̇ _E/V̇CO₂ in the Post-Ex tests. It was concluded that the V̇O₂ and ventilation responses to high-intensity exercise can be altered following prolonged moderate intensity exercise in terms of increased amplitude without associated major changes in either iEMG or MPF values among conditions.     

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.     

Critical power of knee extension exercises does not depend upon maximal strength

A possible dependence of critical power (CP) and the Y-intercept of the work/exhaustion time relationship (Y _intercept) on maximal muscular strength of the same muscle group has been studied in nine endurance-trained subjects, seven gymnasts, and seven weight-lifters. CP was calculated as being equal to the slope of the linear relationship between exhaustion time and the work performed at exhaustion on a knee extension ergometer. Y _intercept was equal to the intercept between this relationship and the work axis. The muscular strength of the knee was evaluated by measuring the torques exerted on a Biodex knee isokinetic dynamometer at four angular velocities: 0° · s⁻¹ (T₀), 90° · s⁻¹ (T₉₀), 180° · s⁻¹ (T₁₈₀) and 240° · s⁻¹ (T₂₄₀). The results of the present study do not support the hypothesis that CP depends upon maximal strength. Indeed, CP was not correlated with T₀, T₉₀, T₁₈₀ or T₂₄₀ (|r| < 0.01). Y _intercept was significantly and positively correlated only with T₉₀. Accepted: 1 November 1999     

How do elite cross-country skiers adapt to different double poling frequencies at low to high speeds?

The purpose of the study was to examine the biomechanical-physiological effects of different frequencies using the double poling technique in cross-country skiing. Nine elite skiers roller-skied using poling frequencies of 40, 60 and 80 cycles·min⁻¹ (Pf_40, Pf₆₀, Pf₈₀) at submaximal treadmill speeds (12, 18, 24 km·h⁻¹). Cycle characteristics, pole forces, joint angles and physiological responses were measured. Comparing Pf₄₀ versus Pf₆₀ versus Pf₈₀ (all variables different at P < 0.05), absolute poling time decreased by up to 46%, as did absolute and relative (% cycle time) recovery times, at almost all speeds. Peak force, impulse of force and time to peak force decreased, whereas impact force increased with frequency at almost all speeds. Elbow ranges of motion and angular velocities, hip and knee angle maxima and flexion/extension ranges of motion per cycle decreased, whereas hip and knee angle minima, ranges of motion per minute and angular extension velocities during recovery phase all increased with frequency at nearly all speeds. Oxygen uptake and heart rate increased up to 13% (Pf_40–60 versus Pf₈₀) at all speeds. Pulmonary ventilation increased most distinctly at the highest speed. Blood lactate was lowest at Pf₆₀ and highest at Pf₈₀ (J-shape curve) at 24 km·h⁻¹. Gross efficiency decreased with higher frequency at all speeds. These results demonstrate different biomechanical and physiological demands at different frequencies with the beneficial effects of lower poling frequencies at submaximal speeds. For training purposes, we suggest that cross-country skiers would benefit by training with different poling frequencies to vary their training load.     

Differences in physical fitness among indoor and outdoor elite male soccer players

This study compared anthropometric (body height, body mass, percent body fat, fat-free body mass) and physical fitness characteristics (vertical jump height, power-load curve of the leg, 5 and 15 m sprint running time and blood lactate concentrations ([La]_b) at submaximal running velocities) among 15 elite male indoor soccer (IS) and 25 elite male outdoor soccer (OS) players. IS players had similar values in body height, body mass, fat-free body mass and endurance running than OS players. However, the IS group showed higher (P < 0.05–0.01) values in percent body fat (28%) and sprint running time (2%) but lower values in vertical jump (15%) and half-squat power (20%) than the OS group. Significant negative correlations (P < 0.05–0.01) were observed between maximal sprint running time, power production during half-squat actions, as well as [La]_b at submaximal running velocities. Percent body fat correlated positively with maximal sprint time and [La]_b, but correlated negatively with vertical jump height. The present results show that compared to elite OS players, elite IS players present clearly lower physical fitness (lower maximal leg extension power production) characteristics associated with higher values of percent body fat. This should give IS players a disadvantage during soccer game actions.     

Comparison of drop jump landing biomechanics and asymmetry among adolescents with hamstring,patellar and quadriceps tendon autografts for anterior cruciate ligament reconstruction

Background

Adolescent anterior cruciate ligament reconstruction (ACLR) commonly utilizes hamstring (HT), patellar (PT) or quadriceps (QT) tendon autografts, but consensus is lacking regarding optimal graft choice. This study compared landing biomechanics and asymmetries among ACLR patients with HT, PT and QT grafts and uninjured controls.

Oxygen uptake, cardiac output and muscle deoxygenation at the onset of moderate and supramaximal exercise in humans

[(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , [(Q)\dot] \dot{Q} and muscular deoxyhaemoglobin (HHb) kinetics were determined in 14 healthy male subjects at the onset of constant-load cycling exercise performed at 80% of the ventilatory threshold (80%_VT) and at 120% of [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (120%_Wmax). An innovative approach was applied to calculate the time constant (τ₂) of the primary phase of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and [(Q)\dot] \dot{Q} kinetics at 120%_Wmax. Data were linearly interpolated after a semilogarithmic transformation of the difference between required/steady state and measured values. Furthermore, [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , \mathop Q ^· \mathop Q\limits^{ \cdot } and HHb data were fitted with traditional exponential models. τ₂ of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics was longer (62.5 ± 20.9 s) at 120%_Wmax than at 80%_VT (27.8 ± 10.4 s). The τ₂ of [(Q)\dot] \dot{Q} kinetics was unaffected by exercise intensity and, at 120% of [(V)\dot]\textO_2max , \dot{V}{\text{O}}_{2\max } , it was significantly faster (τ₂ = 35.7 ± 28.4 s) than that of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} response. The time delay of HHb kinetics was shorter (4.3 ± 1.7 s) at 120%_Wmax than at 80%_VT (8.5 ± 2.6 s) suggesting a larger mismatch between O₂ uptake and delivery at 120%_Wmax. These results suggest that [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} at the onset of exercise is not regulated/limited by muscle’s O₂ utilisation and that a slower adaptation of capillary perfusion may cause the deceleration of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics observed during supramaximal exercise.     

Optimising high-intensity treadmill training using the running speed at maximal O(2) uptake and the time for which this can be maintained

The aim of this study was to compare the effects of two high-intensity, treadmill interval-training programs on 3000-m and 5000-m running performance. Maximal oxygen uptake (V˙O_2max), the running speed associated with V˙O_2max (vV˙O_2max), the time for which vV˙O_2max can be maintained (T _max), running economy (RE), ventilatory threshold (VT) and 3000-m and 5000-m running times were determined in 27 well-trained runners. Subjects were then randomly assigned to three groups; (1) 60% T _max, (2) 70% T _max and (3) control. Subjects in the control group continued their normal training and subjects in the two T _max groups undertook a 4-week treadmill interval-training program with the intensity set at vV˙O_2max and the interval duration at the assigned T _max. These subjects completed two interval-training sessions per week (60% T _max=six intervals/session, 70% T _max group=five intervals/session). Subjects were re-tested on all parameters at the completion of the training program. There was a significant improvement between pre- and post-training values in 3000-m time trial (TT) performance in the 60% T _max group compared to the 70% T _max and control groups [mean (SE); 60% T _max=17.6 (3.5) s, 70% T _max =6.3 (4.2) s, control=0.5 (7.7) s]. There was no significant effect of the training program on 5000-m TT performance [60% T _max=25.8 (13.8) s, 70% T _max=3.7 (11.6) s, control=9.9 (13.1) s]. Although there were no significant improvements in V˙O_2max, vV˙O_2max and RE between groups, changes in V˙O_2max and RE were significantly correlated with the improvement in the 3000-m TT. Furthermore, VT and T _max were significantly higher in the 60% T _max group post- compared to pre-training. In conclusion, 3000-m running performance can be significantly improved in a group of well-trained runners, using a 4-week treadmill interval training program at vV˙O_2max with interval durations of 60% T _max. Electronic Publication     

Pacing strategy during the initial phase of the run in triathlon: influence on overall performance

The aim of the present study was to determine the best pacing strategy to adopt during the initial phase of a short distance triathlon run for highly trained triathletes. Ten highly trained male triathletes completed an incremental running test to determine maximal oxygen uptake, a 10-km control run at free pace and three individual time-trial triathlons (1.5-km swimming, 40-km cycling, 10-km running) in a randomised order. Swimming and cycling speeds were imposed as identical to the first triathlon performed and the first run kilometre was done alternatively 5% faster (Tri-Run_+5%), 5% slower (Tri-Run_−5%) and 10% slower (Tri-Run_−10%) than the control run (C-Run). The subjects were instructed to finish the 9 remaining kilometres as quickly as possible at a free self-pace. Tri-Run_−5% resulted in a significantly faster overall 10-km performance than Tri-Run_+5% and Tri-Run_−10% (p < 0.05) but no significant difference was observed with C-Run (p > 0.05) (2,028 ± 78 s vs. 2,000 ± 72 s, 2,178 ± 121 s and 2,087 ± 88 s, for Tri-Run_−5%, C-Run, Tri-Run_+5% and Tri-Run_−10%, respectively). Tri-Run_+5% strategy elicited higher values for oxygen uptake, ventilation, heart rate and blood lactate at the end of the first kilometre than the three other conditions. After 5 and 9.5 km, these values were higher for Tri-Run_−5% (p < 0.05). The present results showed that the running speed achieved during the cycle-to-run transition is crucial for the improvement of the running phase as a whole. Triathletes would benefit to automate a pace 5% slower than their 10-km control running speed as both 5% faster and 10% slower running speeds over the first kilometre involved weaker overall performances.     

Resynthesis of muscle glycogen after soccer specific performance examined by 13C-magnetic resonance spectroscopy in elite players

The purpose of this study was to examine using ¹³C-magnetic resonance spectroscopy whether muscle glycogen (Gly) utilized during a simulation of a fatiguing soccer match followed by repeated sprints would be resynthesized during the next 24 h while players consumed their habitual diet. A group of 12 elite young players [mean age 17.5 (SD 0.8) years, mean body mass 68.9 (SD 6.6) kg, mean height 177.0 (SD 5.4) cm] participated in the study. Average muscle Gly content before the simulation was 134 (SD 16) mmol·(kg wet mass)^–1 and decreased during the test (P<0.001) to 80 (SD 29) mmol·(kg wet mass)^–1. The value had increased (P<0.01) to 122 (SD 33) mmol·(kg wet mass)^–1 24 h later but it was not significantly different from the value obtained before the soccer test. Dietary analysis of the food intake during the 24 h after the running test revealed that players consumed an average of 2,681 (SD 970) kcal·day^–1. Mean daily protein, fat, and carbohydrate (CHO) intakes were 85 (SD 29), 99 (SD 44), and 327 (SD 116) g, respectively. The mean amounts of CHO intake normalised to body mass were 4.8 (SD 1.8) g·(kg body mass)^–1. In conclusion, the results of this study showed that despite a CHO intake of less than 5 g·(kg body mass)^–1 the habitual diet of soccer players might be sufficient to replenish in 24 h the muscle Gly utilized during soccer specific performance. However, cumulative deficits of about 10% in Gly replenishment as found in the present study might provoke decrements in performance. Thus, players should pay attention to their habitual diets and add more carbohydrates to replenish their daily deficits and perhaps increase their basal levels of intake. Electronic Publication     

Metabolic and cardiorespiratory responses to maximal intermittent knee isokinetic exercise in young healthy humans

There have been many studies on the effects of isokinetic exercise on muscle performance in training and rehabilitative programmes. On the other hand, the cardiovascular and metabolic responses elicited by this type of exercise have been poorly investigated. This study was specifically designed to describe the relationships, if any, between metabolic and cardiorespiratory responses and power output during maximal intermittent knee isokinetic exercise when a steady state is reached. A group of 18 healthy subjects (10 men and 8 women, age range 25–30 years) were requested to perform at maximal concentric isokinetic knee extensions/flexions 60° · s⁻¹ and 180° · s⁻¹ for 5 min, with a 5-s pause interposed between consecutive repetitions. The power output (W˙) was calculated; before and during the tasks heart rate (f _c) and arterial blood pressure (AP_a) were continuously monitored. Pulmonary ventilation (V˙ _E) and oxygen uptake (V˙O₂) were measured at the 4th and at the 5th min of exercise and blood lactate concentration at rest and at the 3rd min of recovery. From the 4th to the 5th min only a slight decrease in W˙ was observed, both at 60° · s⁻¹ and 180° · s⁻¹. The V˙O₂, V˙ _E, f _c and AP_a showed similar values in the last 2 min of exercise, suggesting that a steady state had been reached. The V˙O₂ increased linearly as a function of W˙, showing a significantly steeper slope at 60° · s⁻¹ than at 180° · s⁻¹. The f _c, in spite of a large interindividual variation, was linearly related to metabolic demand, and was not affected by angular velocity. Systolic and diastolic AP_a were not related either to V˙O₂ or to angular velocity. In conclusion it would appear that the metabolic response to maximal intermittent knee isokinetic exercise resembles that of dynamic exercise. Conversely, the cardiocirculatory responses would seem to reflect a relevant role of the isometric postural component, the importance of which should be carefully evaluated in each subject. Accepted: 21 September 1999