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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 R² = 0.97). The maximal shortening velocity (VFmax) obtained during the no-load condition (NLc) ranged between 18.8 and 43.3 cm/s. VFmax values were very close to those of the maximal shortening velocity (Vmax), which was extrapolated from the F-V curve (the Hill model). Angular velocity reached during the NLc was significantly correlated with this VFmax (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 maximalvelocity muscle contraction. [ABSTRACT FROM AUTHOR]

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 VO2max (5.1±0.3ms-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 6.60m 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

People that the author would like to thank for their assistance in the creation of the book are mentioned.

Referees that the editors would like to thank for their contribution to the "European Journal of Applied Physiology" made between October 2014 and September 2015 are mentioned including Per Aagaard, Carl Ade and Kevin Ballard. [ABSTRACT FROM AUTHOR]

Abstract: 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 48h 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 48h 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 48h 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 48h 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. [Copyright &y& Elsevier]