Peak Locomotor Intensity in Elite Handball Players: A First Insight Into Player Position Differences and Training Practices.

ABSTRACT: Fleureau, A, Rabita, G, Leduc, C, Buchheit, M, and Lacome, M. Peak locomotor intensity in elite handball players: a first insight into player position differences and training practices. J Strength Cond Res 37(2): 432-438, 2023-The aims of the study were to (a) describe the peak locomotor intensity sustained during handball matches and (b) compare them with small-sided games (SSGs) programmed during training in elite handball players. Small-sided game ( n = 342) and match ( n = 121) data were collected among 11 players (25 ± 7 years, 191 ± 8 cm, 89 ± 12 kg) belonging to an elite French Handball team. Players' locomotor activity was recorded using 20-Hz Local Positioning System. Peak total (TD[m]) and high-speed running distance (HS[m]) and mechanical load (Accel'Rate [a.u.]) were calculated during different time periods (1-15 minutes different rolling averages). A plot of log (locomotor variables) against log (time) allowed to obtain a straight line with a slope and an intercept for each variable. Between-position differences during matches and difference between matches and SSGs were assessed with linear mixed model and magnitude-based decisions. Almost certainly higher peak locomotor intensity (intercept) was found in Wingers (TD: 156 ± 13; HS: 96 ± 12; Accel'Rate: 13 ± 3) compared with other playing positions for TD (Back players: 127 ± 10; Pivots: 136 ± 13), HS (Back players: 56 ± 9; Pivots: 57 ± 11), and Accel'Rate (Back players: 11 ± 2; Pivots: 11 ± 2). However, no clear between-position difference was found regarding the slope. Additionally, none of the SSGs format produced an overload in peak locomotor intensity in comparison with matches (TD: 138 ± 16; HS: 66 ± 20; Accel'Rate: 12 ± 2). Because reaching the peak locomotor intensity sustained during match is not possible using SSGs, practitioners should consider using isolated conditioning drills (e.g., short or long intervals, repeated sprints). Moreover, specific attention should be paid for Winger's work supplementation because they present the highest peak locomotor intensity in the team.

A Novel Accelerometry-Based Metric to Improve Estimation of Whole-Body Mechanical Load.

While the Player Load is a widely-used parameter for physical demand quantification using wearable accelerometers, its calculation is subjected to potential errors related to rotational changes of the reference frame. The aims of this study were (i) to assess the concurrent validity of accelerometry-based Player Load against force plates; (ii) to validate a novel metric, the Accel'Rate overcoming this theoretical issue. Twenty-one recreational athlete males instrumented with two triaxial accelerometers positioned at the upper and lower back performed running-based locomotor movements at low and high intensity over six in-series force plates. We examined the validity of the Player Load and the Accel'Rate by using force plates. Standard error of the estimate was small to moderate for all tested conditions (Player Load: 0.45 to 0.87; Accel'Rate: 0.25 to 0.95). Accel'Rate displayed trivial to small mean biases (-1.0 to 6.1 a.u.) while the Player Load displayed systematic very large to extremely large mean biases (17.1 to 226.0 a.u.). These findings demonstrate a better concurrent validity of the Accel'Rate compared to the Player Load. This metric could be used to improve the estimation of whole-body mechanical load, easily accessible in sport training and competition settings.

Validity of an ultra-wideband local positioning system to assess specific movements in handball.

The aim of this study was to examine the concurrent validity of the Kinexon local positioning system (LPS) in comparison with the Vicon motion capture system used as the reference. Five recreationally active men performed ten repetitions of linear sprints, medio-lateral side-to-side and handball-specific movements both in the centre and on the side of an indoor field. Validity was assessed for peak speed, peak acceleration and peak deceleration using standardised biases, Pearson coefficient of correlation (r), and standardised typical error of the estimate. With the exception of peak decelerations during specific movements in the centre and peak acceleration and deceleration during linear sprints on the side of the field, the standardised typical error of the estimate (TEE) values were all small to moderate (0.06-0.48), standardised bias ranged between 0.01 and 2.85 and Pearson coefficient values were all > 0.90 for all variables in all conditions. Peak acceleration and deceleration during linear sprints on the side of the field showed the largest TEEs and the greatest differences between the two systems. The ultra-wideband based (UWB) local positioning system had acceptable validity compared with Vicon to assess players' movements in handball with the exception of high accelerations and decelerations during linear sprints on the side of the field.

Effects of Surface Properties on Gastrocnemius Medialis and Vastus Lateralis Fascicle Mechanics During Maximal Countermovement Jumping.

Interactions between human movement and surfaces have previously been studied to understand the influence of surface properties on the mechanics and energetics of jumping. However, little is known about the muscle-tendon unit (MTU) mechanics associated with muscle activity and leg adjustments induced by different surfaces during this movement. This study aimed to examine the effects of three surfaces with different properties (artificial turf, hybrid turf, and athletic track) on the muscle mechanics and muscle excitation of the gastrocnemius medialis (GM) and vastus lateralis (VL) during maximal countermovement jumping (CMJ). Twelve participants performed maximal CMJs on the three sport surfaces. GM and VL muscle fascicles were simultaneously imaged using two ultrafast ultrasound systems (500 Hz). MTUs lengths were determined based on anthropometric models and two-dimensional joint kinematics. Surface electromyography (EMG) was used to record GM and VL muscle activity. Surface mechanical testing revealed systematic differences in surface mechanical properties (P = 0.006, η2: 0.26-0.32, large). Specifically, the highest force reduction and vertical deformation values have been observed on artificial turf (65 ± 2% and 9.0 ± 0.3 mm, respectively), while athletic track exhibited the lowest force reduction and vertical deformation values (28 ± 1% and 2.1 ± 0.1 mm, respectively) and the highest energy restitution (65 ± 1%). We observed no significant difference in CMJ performance between the three surfaces (∼35-36 cm, P = 0.66). GM and VL fascicle shortening (P = 0.90 and P = 0.94, respectively) and shortening velocity (P = 0.13 and P = 0.65, respectively) were also unaffected by the type of surface. However, when jumping from greater deformable surface, both GM muscle activity (P = 0.022, η2 = 0.18, large) and peak shortening velocity of GM MTU (P = 0.042, η2 = 0.10, medium) increased during the push-off phase. This resulted in a greater peak plantar flexion velocity late in the jump (P = 0.027, η2 = 0.13, medium). Our findings suggest that maximal vertical jumping tasks in humans is not affected by common sport surfaces with different mechanical properties. However, internal regulatory mechanisms exist to compensate for differences in surface properties.

Surface properties affect the interplay between fascicles and tendinous tissues during landing.

PURPOSE: Muscle-tendon units are forcefully stretched during rapid deceleration events such as landing. Consequently, tendons act as shock absorbers by buffering the negative work produced by muscle fascicles likely to prevent muscle damage. Landing surface properties can also modulate the amount of energy dissipated by the body, potentially effecting injury risk. This study aimed to evaluate the influence of three different surfaces on the muscle-tendon interactions of gastrocnemius medialis (GM), and vastus lateralis (VL) during single- and double-leg landings from 50 cm. METHODS: Ultrasound images, muscle activity and joint kinematics were collected for 12 participants. Surface testing was also performed, revealing large differences in mechanical behavior. RESULTS: During single-leg landing, stiffer surfaces increased VL fascicle lengthening and velocity, and muscle activity independent of joint kinematics while GM length changes showed no difference between surfaces. Double-leg landing resulted in similar fascicle and tendon behavior despite greater knee flexion angles on stiffer surfaces. CONCLUSION: This demonstrates that VL fascicle lengthening is greater when the surface stiffness increases, when performing single-leg landing. This is due to the combination of limited knee joint flexion and lower surface absorption ability which resulted in greater mechanical demand mainly withstood by fascicles. GM muscle-tendon interactions remain similar between landing surfaces and types. Together, this suggests that surface damping properties primarily affect the VL muscle-tendon unit with a potentially higher risk of injury as a result of increased surface stiffness when performing single-leg landing tasks.

Interactions between fascicles and tendinous tissues in gastrocnemius medialis and vastus lateralis during drop landing.

Animal tendons have been shown to act as shock absorbers to protect muscle fascicles from exercise-induced damage during landing tasks. Meanwhile, the contribution of tendinous tissues to damping activities such as landing has been less explored in humans. The aim of this study was to analyze in vivo fascicle-tendon interactions during drop landing to better understand their role in energy dissipation. Ultrafast ultrasound images of the gastrocnemius medialis (GM) and vastus lateralis (VL), lower limb electromyographic activity, 2-D kinematics, and ground reaction forces were collected from twelve participants during single- and double-leg drop landings from various heights. For both muscles, length changes were higher in tendinous tissues than in fascicles, demonstrating their key role in protecting fascicles from rapid active lengthening. Increasing landing height increased lengthening and peak lengthening velocity of VL fascicle and GM architectural gear ratio, whereas GM fascicle displayed similar length and velocity patterns. Single-leg landing lengthens the tendinous tissues of GM and, to a greater degree, VL muscles, without affecting the fascicles. These findings demonstrate the adjustment in fascicle-tendon interactions to withstand mechanical demand through the tendon buffer action and fascicle rotation. The higher VL fascicle contribution to negative work as the drop height increases would suggest muscle-specific damping responses during drop landing. This can originate from the distal-to-proximal sequence of joint kinetics, from differences in muscle and tendon functions (one- and two-joint muscles), architectural and morphological properties (eg, tendon stiffness), as well as from the muscle activity of the GM and VL muscles.

The slack test does not assess maximal shortening velocity of muscle fascicles in humans.

The application of a series of extremely high accelerative motor-driven quick releases while muscles contract isometrically (i.e. slack test) has been proposed to assess unloaded velocity in human muscle. This study aimed to measure gastrocnemius medialis fascicle shortening velocity (VF) and tendinous tissue shortening velocity during motor-driven quick releases performed at various activation levels to assess the applicability of the slack test in humans. Gastrocnemius medialis peak VF and joint velocity recorded from 25 participants using high frame rate ultrasound during quick releases (at activation levels from 0% to 60% of maximal voluntary isometric torque) and during fast contractions without external load (ballistic condition) were compared. Unloaded joint velocity calculated using the slack test method increased whereas VF decreased with muscle activation level (P≤0.03). Passive and low-level quick releases elicited higher VF values (≥41.8±10.7 cm s-1) compared with the ballistic condition (36.3±8.7 cm s-1), while quick releases applied at 60% of maximal voluntary isometric torque produced the lowest VF These findings suggest that initial fascicle length, complex fascicle-tendon interactions, unloading reflex and motor-driven movement pattern strongly influence and limit the shortening velocity achieved during the slack test. Furthermore, VF elicited by quick releases is likely to reflect substantial contributions of passive processes. Therefore, the slack test is not appropriate to assess maximal muscle shortening velocity in vivo.

Effect of Prior Fatiguing Sport-Specific Exercise on Field Hockey Passing Ability.

PURPOSE: To evaluate the effect of multiple sets of repeated-sprint-ability (RSA)-induced fatigue on subsequent passing-skill performance in field hockey players. METHODS: A total of 10 elite U-21 (under-21) male field hockey players performed 5 sets of a combination of RSA test (6 × 20 m, 20 s of passive recovery) followed by a 1-min passing-skill test (passing reception with subsequent passes at a predesigned target). Data on fastest sprint time and cumulated sprint time for RSA test; total number of balls played, targeted, and passing accuracy (number of balls targeted/total number of balls played) for passing-skill test; heart rate (HR), blood lactate concentration (BLa), and rating of perceived exertion (RPE)  were collected throughout the protocol. RESULTS: RSA performance was significantly impaired from set 1 to set 5 (fastest sprint time +4.1%, P < .001; cumulated sprint time +2.3%, P < .01). For a similar average number of balls played (12.8 [1.4]) during each set, number of balls targeted (-1.7%, P < .05) and passing accuracy (-3.1%, P < .05) decreased up to the third set before reimproving over the last 2 sets. Psychophysiological responses (HR, BLa, and RPE) progressively increased (P < .05) toward protocol cessation. The decrease in passing accuracy with increasing RSA cumulated sprint time was fitted to a 2nd-order polynomial function (r2 = .94, P < .05). CONCLUSION: Multiple-set RSA-induced fatigue was accompanied by passing-skill adjustment variation, suggesting a complex interaction between physiological and psychological/cognitive function to preserve passing skill under fatigued condition.

Muscle fascicle shortening behaviour of vastus lateralis during a maximal force-velocity test.

PURPOSE: Muscle fascicles-tendon interactions are the main determinant in production of high joint velocity. Currently, no study has investigated the muscle fascicles behaviour of knee extensor muscles until the highest reachable velocity (e.g., unloaded knee extension). We aimed to track the changes in vastus lateralis fascicles length during knee extensions to quantify muscle fascicles and tendinous tissues contributions to muscle-tendon unit shortening and to determine maximal muscle fascicles shortening velocity. METHODS: Fifteen participants performed isokinetic and isoinertial knee extensions, and ultrafast ultrasound imaging was used to observe the vastus lateralis fascicles from low to very high joint velocity. RESULTS: The muscle fascicles shortening velocity increased linearly with the increase in knee joint velocity up to the maximal joint velocity (mean R 2 = 0.93 ± 0.08). Muscle fascicles contribution to muscle-tendon unit shortening velocity was almost constant regardless of the condition (83 ± 23%). Using Hill's equation, the maximal velocity of knee joint and muscle fascicles was determined at 1000 ± 489°s-1 and 5.1 ± 2.0 L0 s-1 (47.4 ± 18.7 cm s-1), respectively. CONCLUSIONS: Contribution of muscle fascicles to the muscle-tendon unit shortening velocity was much higher for the vastus lateralis in this study compared to the gastrocnemius medialis in two previous studies. Moreover, this contribution of muscle fascicles shortening velocity was constant whatever the velocity condition, even at the highest reachable velocity. Thus, the vastus lateralis fascicles shortening velocity increases linearly with the knee joint velocity until high velocities and its behaviour strongly accorded with the classical Hill's force-velocity relationship.

Optimal Balance Between Force and Velocity Differs Among World-Class Athletes.

Performance during human movements is highly related to force and velocity muscle capacities. Those capacities are highly developed in elite athletes practicing power-oriented sports. However, it is still unclear whether the balance between their force and velocity-generating capacities constitutes an optimal profile. In this study, we aimed to determine the effect of elite sport background on the force-velocity relationship in the squat jump, and evaluate the level of optimization of these profiles. Ninety-five elite athletes in cycling, fencing, taekwondo, and athletic sprinting, and 15 control participants performed squat jumps in 7 loading conditions (range: 0%-60% of the maximal load they were able to lift). Theoretical maximal power (Pm), force (F0), and velocity (v0) were determined from the individual force-velocity relationships. Optimal profiles were assessed by calculating the optimal force (F0th) and velocity (v0th). Athletic sprinters and cyclists produced greater force than the other groups (P < .05). F0 was significantly lower than F0th, and v0 was significantly higher than v0th for female fencers and control participants, and for male athletics sprinters, fencers, and taekwondo practitioners (P < .05). Our study shows that the chronic practice of an activity leads to differently balanced force-velocity profiles. Moreover, the differences between measured and optimal force-velocity profiles raise potential sources of performance improvement in elite athletes.

In vivo maximal fascicle-shortening velocity during plantar flexion in humans.

Interindividual variability in performance of fast movements is commonly explained by a difference in maximal muscle-shortening velocity due to differences in the proportion of fast-twitch fibers. To provide a better understanding of the capacity to generate fast motion, this study aimed to 1) measure for the first time in vivo the maximal fascicle-shortening velocity of human muscle; 2) evaluate the relationship between angular velocity and fascicle-shortening velocity from low to maximal angular velocities; and 3) investigate the influence of musculo-articular features (moment arm, tendinous tissues stiffness, and muscle architecture) on maximal angular velocity. Ultrafast ultrasound images of the gastrocnemius medialis were obtained from 31 participants during maximal isokinetic and light-loaded plantar flexions. A strong linear relationship between fascicle-shortening velocity and angular velocity was reported for all subjects (mean R(2) = 0.97). The maximal shortening velocity (V(Fmax)) obtained during the no-load condition (NLc) ranged between 18.8 and 43.3 cm/s. V(Fmax) values were very close to those of the maximal shortening velocity (V(max)), which was extrapolated from the F-V curve (the Hill model). Angular velocity reached during the NLc was significantly correlated with this V(Fmax) (r = 0.57; P < 0.001). This finding was in agreement with assumptions about the role of muscle fiber type, whereas interindividual comparisons clearly support the fact that other parameters may also contribute to performance during fast movements. Nevertheless, none of the biomechanical features considered in the present study were found to be directly related to the highest angular velocity, highlighting the complexity of the upstream mechanics that lead to maximal-velocity muscle contraction.

Acceleration capability in elite sprinters and ground impulse: Push more, brake less?

Overground sprint studies have shown the importance of net horizontal ground reaction force impulse (IMPH) for acceleration performance, but only investigated one or two steps over the acceleration phase, and not in elite sprinters. The main aim of this study was to distinguish between propulsive (IMPH+) and braking (IMPH-) components of the IMPH and seek whether, for an expected higher IMPH, faster elite sprinters produce greater IMPH+, smaller IMPH-, or both. Nine high-level sprinters (100-m best times range: 9.95-10.60s) performed 7 sprints (2×10 m, 2×15 m, 20 m, 30 m and 40 m) during which ground reaction force was measured by a 6.60 m force platform system. By placing the starting-blocks further from the force plates at each trial, and pooling the data, we could assess the mechanics of an entire "virtual" 40-m acceleration. IMPH and IMPH+ were significantly correlated with 40-m mean speed (r=0.868 and 0.802, respectively; P<0.01), whereas vertical impulse and IMPH- were not. Multiple regression analyses confirmed the significantly higher importance of IMPH+ for sprint acceleration performance. Similar results were obtained when considering these mechanical data averaged over the first half of the sprint, but not over the second half. In conclusion, faster sprinters were those who produced the highest amounts of horizontal net impulse per unit body mass, and those who "pushed more" (higher IMPH+), but not necessarily those who also "braked less" (lower IMPH-) in the horizontal direction.

Is muscle coordination affected by loading condition in ballistic movements?

This study aimed to investigate the effect of loading on lower limb muscle coordination involved during ballistic squat jumps. Twenty athletes performed ballistic squat jumps on a force platform. Vertical force, velocity, power and electromyographic (EMG) activity of lower limb muscles were recorded during the push-off phase and compared between seven loading conditions (0-60% of the concentric-only maximal repetition). The increase in external load increased vertical force (from 1962 N to 2559 N; P=0.0001), while movement velocity decreased (from 2.5 to 1.6 ms(-1); P=0.0001). EMG activity of tibialis anterior first peaked at 5% of the push-off phase, followed by gluteus maximus (35%), vastus lateralis and soleus (45%), rectus femoris (55%), gastrocnemius lateralis (65%) and semitendinosus (75%). This sequence of activation (P=0.67) and the amplitude of muscle activity (P=0.41) of each muscle were not affected by loading condition. However, a main effect of muscle was observed on these parameters (peak value: P<0.001; peak occurrence: P=0.02) illustrating the specific role of each muscle during the push-off phase. Our findings suggest that muscle coordination is not influenced by external load during a ballistic squat jump.

Mechanical and muscular coordination patterns during a high-level fencing assault.

PURPOSE: This study aimed to investigate the coordination of lower limb muscles during a specific fencing gesture in relation to its mechanical effectiveness. METHODS: Maximal isokinetic concentric and isometric plantarflexor, dorsiflexor, knee and hip extensor and flexor torques of 10 female elite saber fencers were assessed and compared between both legs. Sabers completed three trials of a specific fencing gesture (i.e., marché-fente) on a 6.60-m-long force platform system. Surface EMG activities of 15 lower limb muscles were recorded in time with ground reaction forces and separated into four distinct assault phases. EMG signals were normalized to the muscle activity assessed during maximal isometric contraction. Mechanical and EMG data were compared between both legs over the entire assault and in each phase (ANOVA). Potential correlations between muscle strength and average EMG activities were tested (Bravais-Pearson coefficient). RESULTS: EMG activity patterns showed that rear hip and knee extensor and plantarflexor muscles were mainly activated during propulsive (concentric) phases, while front hip and knee extensor muscles were strongly solicited during the final braking (eccentric) phase to decelerate the body mass. Although fencers presented greater maximal hip (+10%) and knee (+26%) extensor strength in the front than in the rear leg (P < 0.05), rear hip and knee extensor strength was significantly correlated to the maximal anteroposterior velocity (r = 0.60-0.81). Moreover, muscle activity of the rear extensors was related to average velocity during the second propulsive phase (phase 3). CONCLUSIONS: This study gathers the first evidence of a crucial role of the rear extensor muscles in fencing speed performance. Such findings suggest interesting perspectives in the definition of specific training or rehabilitation programs for elite fencers.

Interaction between gastrocnemius medialis fascicle and Achilles tendon compliance: a new insight on the quick-release method.

The insufficient temporal resolution of imaging devices has made the analysis of very fast movements, such as those required to measure active muscle-tendon unit stiffness, difficult. Thus the relative contributions of tendon, aponeurosis, and fascicle to muscle-tendon unit compliance remain to be determined. The present study analyzed the dynamic interactions of fascicle, tendon, and aponeurosis in human gastrocnemius medialis during the first milliseconds of an ankle quick-release movement, using high-frame-rate ultrasonography (2,000 frames/s). Nine subjects performed the tests in random order at six levels of maximal voluntary contraction (MVC) (30% to 80% of MVC). These tests were carried out with the ultrasound probe placed on the muscle belly and on the myotendinous junction. Tendon, muscle fascicle, and aponeurosis length changes were quantified in relation to shortening of the muscle-tendon unit during the first few milliseconds following the release. The tendon was the main contributor (around 72%) to the shortening of the muscle-tendon unit, whereas the muscle fascicle and aponeurosis contributions were 18% and 10%, respectively. Because these structures can be considered in series, the quantified contributions can be regarded as relative contributions to muscle-tendon compliance. These contributions were not modified with the level of MVC or the time range used for the analysis between 10 and 25 ms. The constant contribution of tendon, muscle fascicle, and aponeurosis to muscle-tendon unit compliance may help to simplify the mechanism of compliance regulation and to maintain the important role of tendons in enhancing work output and movement efficiency.

The biomechanical effect of arm mass on long jump performance: A case study of a paralympic upper limb amputee.

BACKGROUND: The role of arm motion during the long jump has been well studied. The aim of this study was to quantify the effect of forearm mass on impulse and the kinematics of the flight phase in an upper limb amputee. CASE DESCRIPTION AND METHODS: A world-record paralympic long jumper carried out jumps in three conditions: wearing his usual forearm prosthesis and with 0.3 and 0.4 kg added mass. A motion capture system including force plates was used to record the jump. FINDINGS AND OUTCOME: At take-off, the addition of 0.4 kg to the prosthesis decreased the vertical velocity of the centre of mass but increased horizontal velocity. These modifications were associated with an increase in landing distance and an improvement of the synchronization between arms. CONCLUSION: Increasing forearm mass appears to improve long jump performance. Further studies need to evaluate the optimal prosthetic mass for both training and competition. CLINICAL RELEVANCE: This biomechanical analysis of the long jump highlighted the effects of changing prosthesis mass on performance. This methodological approach may be useful in the context of sport and performance research.

Changes in spring-mass behavior and muscle activity during an exhaustive run at V̇O2max.

PURPOSE: The aim of this study was to evaluate concomitantly the changes in leg-spring behavior and the associated modifications in the lower limb muscular activity during a constant pace run to exhaustion at severe intensity. METHODS: Twelve trained runners performed a running test at the velocity associated with VO(2max) (5.1 ± 0.3 ms(-1); mean time to exhaustion: 353 ± 69s). Running step spatiotemporal parameters and spring-mass stiffness were calculated from vertical and horizontal components of ground reaction force measured by a 6.60 m long force platform system. The myoelectrical activity was measured by wireless surface electrodes on eight lower limb muscles. RESULTS: The leg stiffness decreased significantly (-8.9%; P<0.05) while the vertical stiffness did not change along the exhaustive exercise. Peak vertical force (-3.5%; P<0.001) and aerial time (-9.7%; P<0.001) decreased and contact time significantly increased (+4.6%; P<0.05). The myoelectrical activity decreased significantly for triceps surae but neither vastus medialis nor vastus lateralis presented significant change. Both rectus and biceps femoris increased in the early phase of swing (+14.7%; P<0.05) and during the pre-activation phase (+16.2%; P<0.05). CONCLUSION: The decrease in leg spring-stiffness associated with the decrease in peak vertical ground reaction force was consistent with the decline in plantarflexor activity. The biarticular rectus femoris and biceps femoris seem to play a major role in the mechanical and spatiotemporal adjustments of stride pattern with the occurrence of fatigue during such exhaustive run.

Spring-mass behavior during exhaustive run at constant velocity in elite triathletes.

PURPOSE: The aims of this study were i) to evaluate changes in leg-spring behavior during an exhaustive run in elite triathletes and ii) to determine whether these modifications were related to an increase in the energy cost of running (Cr). METHODS: Nine elite triathletes ran to exhaustion on an indoor track at a constant velocity corresponding to 95% of the velocity associated with the maximal oxygen uptake (mean ± SD = 5.1 ± 0.3 m·s(-1), time to exhaustion = 10.7 ± 2.6 min). Vertical and horizontal ground reaction forces were measured every lap (200 m) by a 5-m-long force platform system. Cr was measured from pulmonary gas exchange using a breath-by-breath portable gas analyzer. RESULTS: Leg stiffness (-13.1%, P < 0.05) and peak vertical (-9.2%, P < 0.05) and propulsive (-7.5%, P < 0.001) forces decreased significantly with fatigue, whereas vertical stiffness did not change significantly. Leg and vertical stiffness changes were positively related with modifications of aerial time (R(2) = 0.66, P < 0.01 and R(2) = 0.72, P < 0.01, respectively) and negatively with contact time (R(2) = 0.71, P < 0.01 and R(2) = 0.74, P < 0.01, respectively). Alterations of vertical forces were related with the decrease of the angle of velocity vector at toe off (R(2) = 0.73, P < 0.01). When considering mean values of oxygen uptake, no change was observed from 33% to 100% of the time to exhaustion. However, between one-third and two-thirds of the fatiguing run, negative correlations were observed between oxygen consumption and leg stiffness (R(2) = 0.83, P < 0.001) or vertical stiffness (R(2) = 0.50, P < 0.03). CONCLUSIONS: During a constant run to exhaustion, the fatigue induces a stiffness adaptation that modifies the stride mechanical parameters and especially decreases the maximal vertical force. This response to fatigue involves greater energy consumption.

Neuromuscular fatigue following high versus low-intensity eccentric exercise of biceps brachii muscle.

PURPOSE: This study investigated neuromuscular fatigue following high versus low-intensity eccentric exercise corresponding to the same amount of work. METHODS: Ten volunteers performed two eccentric exercises of the elbow flexors: a high-intensity versus a low-intensity exercise. Maximal voluntary contraction torque and surface electromyography of the biceps brachii muscle were recorded before, immediately and 48 h after exercises. Maximal voluntary activation level, neural (M-wave) and contractile (muscular twitch) properties of the biceps brachii muscle were analysed using electrical stimulation techniques. RESULTS: Maximal voluntary contraction torque was significantly (P<0.01) reduced immediately and 48 h after exercise but the reduction was not different between the two conditions. Electromyography associated with maximal voluntary contraction significantly decreased (P<0.05) immediately and 48 h after exercise for both conditions while maximal voluntary activation level was only significantly reduced immediately after the high-intensity exercise. Peak twitch alterations were observed immediately and 48 h after exercise for both conditions while M-wave did not change. CONCLUSION: High and low-intensity eccentric exercises with the same amount of work induced the same reduction in maximal strength capacities of the biceps brachii muscles. The magnitude of peripheral and central fatigue was very similar in both conditions.