Are the ground reaction forces altered by the curve and with the increasing sprinting velocity?

In 200- and 400-m races, 58% of the total distance to cover is in the curve. In the curve, the sprinting performance is decreased in comparison to the straight. However, the reasons for this decreased performance is not well understood. Thus, the aim of this study was to identify the kinetic parameters underpinning the sprinting performance in the curve in comparison to the straight. Nineteen experienced-to-elite curve specialists performed five sprints in the straight and in the curve (radius 41.58 m): 10, 15, 20, 30, and 40 m. The left and the right vertical, anterior-posterior, medial-lateral, and resultant ground reaction forces (respectively F V $$ {F}_{\mathrm{V}} $$ , F A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ , F M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ , and F TOT $$ {F}_{\mathrm{TOT}} $$ ), the associated impulses (respectively IMP V $$ {IMP}_{\mathrm{V}} $$ , IMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ , IMP M - L $$ {IMP}_{\mathrm{M}-\mathrm{L}} $$ , and IMP TOT $$ {IMP}_{\mathrm{TOT}} $$ ) and the stance times of each side were averaged over each distance. In the curve, the time to cover the 40-m sprint was longer than in the straight (5.52 ± 0.25 vs. 5.47 ± 0.23 s, respectively). Additionally, the left and the right F A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ and IMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ were lower than in the straight while the left and the right F M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ increased, meaning that the F M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ was more medial. The left F V $$ {F}_{\mathrm{V}} $$ was also lower than in the straight while the left stance times increased to keep the left IMP V $$ {IMP}_{\mathrm{V}} $$ similar to the straight to maintain the subsequent swing time. Overall, the sprinting performance was reduced in the curve due to a reduction in the left and the right F A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ and IMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ , that were likely attributed to the concomitant increased F M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ to adopt a curvilinear motion.

Effects of Acute Physical Fatigue on Gaze Behavior in Expert Badminton Players.

Perceptual cognitive skills in real game settings, under conditions of fatigue, such as the ability to gather relevant visual information, are key factors in achieving motor goals in sports. The objectives were to evaluate the effects of acute physical fatigue on gaze behavior during a badminton game (Study 1) and in an unfavorable force ratio situation (Study 2). Six international-level badminton players played two sets and unfavorable force ratio situations while wearing eye-tracking glasses before and after a fatiguing task. During the set, fatiguing physical exercise led to fewer fixations per exchange and more fixations on one area of interest. During unfavorable force ratio situations, fatiguing physical exercise led to shorter fixation durations per exchange, shorter fixation durations on two areas of interest, and longer fixation durations on one area of interest. The results showed that gaze behaviors were adapted in acute physical fatigue conditions to maintain performance.

Does Accelerometry at the Centre of Mass Accurately Predict the Gait Energy Expenditure in Patients with Hemiparesis?

BACKGROUND: The aim of this study was to compare energy expenditure (EE) predicted by accelerometery (EEAcc) with indirect calorimetry (EEMETA) in individuals with hemiparesis. METHODS: Twenty-four participants (12 with stroke and 12 healthy controls) performed a six-minute walk test (6MWT) during which EEMETA was measured using a portable indirect calorimetry system and EEACC was calculated using Bouten's equation (1993) with data from a three-axis accelerometer positioned between L3 and L4. RESULTS: The median EEMETA was 9.85 [8.18;11.89] W·kg-1 in the stroke group and 5.0 [4.56;5.46] W·kg-1 in the control group. The median EEACC was 8.57 [7.86;11.24] W·kg-1 in the control group and 8.2 [7.05;9.56] W·kg-1 in the stroke group. The EEACC and EEMETA were not significantly correlated in either the control (p = 0.8) or the stroke groups (p = 0.06). The Bland-Altman method showed a mean difference of 1.77 ± 3.65 W·kg-1 between the EEACC and EEMETA in the stroke group and -2.08 ± 1.59 W·kg-1 in the controls. CONCLUSIONS: The accuracy of the predicted EE, based on the accelerometer and the equations proposed by Bouten et al., was low in individuals with hemiparesis and impaired gait. This combination (sensor and Bouten's equation) is not yet suitable for use as a stand-alone measure in clinical practice for the evaluation of hemiparetic patients.

Contribution of segmental kinetic energy to forward propulsion of the centre of mass: Analysis of sprint acceleration.

This study aimed to measure the contribution of each body segment to the production of total body kinetic energy (KE) during a 40-m sprint. Nine recreational sprinters performed two 40-m sprints wearing a MVN Biomech suit (Xsens). Data recorded were used to calculate total body KE, and the KE of each segment. The KE of each segment was then expressed as a percentage of the total body KE. We divided the sprint into three phases: 1 - start to maximal power (Pmax), 2 - Pmax to maximal velocity (Vmax), and 3 - Vmax to the end of the 40 m. Total body KE increased from the start to the end of the 40-m sprint (from 331.3 ± 68.4 J in phase 1 to 2378.8 ± 233.0 J in phase 3; p ≤ 0.001). The contribution of the head-trunk increased (from 39.5 ± 2.4% to 46.3 ± 1.1%; p ≤ 0.05). Contribution of the upper and lower limbs decreased over the three phases (respectively from 15.7 ± 2.5% to 10.6 ± 0.6% and from 44.8 ± 2.1% to 43.1 ± 1.5%; p ≤ 0.05). This study revealed the important contribution of the trunk to forward propulsion throughout the entire acceleration phase.

Sprint Acceleration Mechanical Outputs Derived from Position- or Velocity-Time Data: A Multi-System Comparison Study.

To directly compare five commonly used on-field systems (motorized linear encoder, laser, radar, global positioning system, and timing gates) during sprint acceleration to (i) measure velocity−time data, (ii) compute the main associated force−velocity variables, and (iii) assess their respective inter-trial reliability. Eighteen participants performed three 40 m sprints, during which five systems were used to simultaneously and separately record the body center of the mass horizontal position or velocity over time. Horizontal force−velocity mechanical outputs for the two best trials were computed following an inverse dynamic model and based on an exponential fitting of the position- or velocity-time data. Between the five systems, the maximal running velocity was close (7.99 to 8.04 m.s−1), while the time constant showed larger differences (1.18 to 1.29 s). Concurrent validity results overall showed a relative systematic error of 0.86 to 2.28% for maximum and theoretically maximal velocity variables and 4.78 to 12.9% for early acceleration variables. The inter-trial reliability showed low coefficients of variation (all <5.74%), and was very close between all of the systems. All of the systems tested here can be considered relevant to measure the maximal velocity and compute the force−velocity mechanical outputs. Practitioners are advised to interpret the data obtained with either of these systems in light of these results.

Running at altitude: the 100-m dash.

PURPOSE: Theoretical 100-m performance times (t100-m) of a top athlete at Mexico-City (2250 m a.s.l.), Alto-Irpavi (Bolivia) (3340 m a.s.l.) and in a science-fiction scenario "in vacuo" were estimated assuming that at the onset of the run: (i) the velocity (v) increases exponentially with time; hence (ii) the forward acceleration (af) decreases linearly with v, iii) its time constant (τ) being the ratio between vmax (for af = 0) and af max (for v = 0). METHODS: The overall forward force per unit of mass (Ftot), sum of af and of the air resistance (Fa = k v2, where k = 0.0037 J·s2·kg-1·m-3), was estimated from the relationship between af and v during Usain Bolt's extant world record. Assuming that Ftot is unchanged since the decrease of k at altitude is known, the relationships between af and v were obtained subtracting the appropriate Fa values from Ftot, thus allowing us to estimate in the three conditions considered vmax, τ, and t100-m. These were also obtained from the relationship between mechanical power and speed, assuming an unchanged mechanical power at the end of the run (when af ≈ 0), regardless of altitude. RESULTS: The resulting t100-m amounted to 9.515, 9.474, and 9.114 s, and to 9.474, 9.410, and 8.981 s, respectively, as compared to 9.612 s at sea level. CONCLUSIONS: Neglecting science-fiction scenarios, t100-m of a world-class athlete can be expected to undergo a reduction of 1.01 to 1.44% at Mexico-City and of 1.44 to 2.10%, at Alto-Irpavi.

Mechanics of standing and crouching sprint starts.

The aim of this study was to compare the kinetic and kinematic parameters of standing and crouch sprint starts. Parallel starts (PS), false starts (FS), jump starts (JS) and crouch starts (3PS) were compared. Eighteen participants performed each start on a force plate and six infrared cameras captured the three-dimensional coordinates of 36 retro-reflective markers. Performance during a five-metre sprint (T5m) was analysed. Duration of the start phase (Tstart), mean values of horizontal and total ground reaction forces (GRFs) (Fx_mean and Ftot_mean), ratio of force (RF), maximal power (Pmax) and kinetic energy (KE) of each limb were calculated. Significant differences were found for T5m, Tstart, KE, Pmax, Fx_mean, Ftot_mean and RF for the crouch start compared to the other starts (P ≤ 0.05). Significant correlations were found between T5m and Tstart (r = 0.59; P ≤ 0.001), and T5m and Pmax, Fx_mean and RF (-0.73 ≤ r ≤ -0.61; P ≤ 0.001). To conclude, the crouch start resulted in the best performance because Tstart was shorter, producing greater Pmax, Fx_mean with a more forward orientation of the resultant force. Greater KE of the trunk in each start condition demonstrated the role of the trunk in generating forward translation of the centre of mass (CM).

Effect of postural changes on 3D joint angular velocity during starting block phase.

Few studies have focused on the effect of posture during sprint start. The aim of this study was to measure the effect of the modification of horizontal distance between the blocks during sprint start on three dimensional (3D) joint angular velocity. Nine trained sprinters started using three different starting positions (bunched, medium and elongated). They were equipped with 63 passive reflective markers, and an opto-electronic Motion Analysis system was used to collect the 3D marker trajectories. During the pushing phase on the blocks, norm of the joint angular velocity (NJAV), 3D Euler angular velocity (EAV) and pushing time on the blocks were calculated. The results demonstrated that the decrease of the block spacing induces an opposite effect on the angular velocity of joints of the lower and the upper limbs. The NJAV of the upper limbs is greater in the bunched start, whereas the NJAV of the lower limbs is smaller. The modifications of NJAV were due to a combination of the movement of the joints in the different degrees of freedom. The medium start seems to be the best compromise because it leads, in a short pushing time, to a combination of optimal joint velocities for upper and lower segments.

Center of mass velocity comparison using a whole body magnetic inertial measurement unit system and force platforms in well trained sprinters in straight-line and curve sprinting.

BACKGROUND: Sprint performance can be characterized through the centre of mass (COM) velocity over time. In-field computation of the COM is key in sprint training. RESEARCH QUESTION: To compare the stance-averaged COM velocity computation from a Magneto-Inertial Measurement Units (MIMU) to a reference system: force platforms (FP), over the early acceleration phase in both straight and curve sprinting. METHODS: Nineteen experienced-to-elite track sprinters performed 1 maximal sprint on both the straight and the curve (radius = 41.58 m) in a randomized order. Utilizing a MIMU-based system (Xsens MVN Link) and compared to FP (Kistler), COM velocity was computed with both systems. Averaged stance-by-stance COM velocity over straight-line and curve sprinting following the vertical axis (respectively VzMIMU and VzFP) and the norm of the two axes lying on the horizontal plane: x and y, approximately anteroposterior and mediolateral (respectively VxyMIMU and VxyFP) over the starting-blocks (SB) and initial acceleration (IA - composed out of the first four stances following the SB) were compared using mean bias, 95 % limits of agreements and Pearson's correlation coefficients. RESULTS: 148 stances were analyzed. VxyMIMU mean bias was comprised between 0.26 % and 2.03 % (expressed in % with respect to the FP) for SB, 5.63 % and 7.29 % over IA respectively on the straight and the curve. Pearson's correlation coefficients ranged between 0.943 and 0.990 for Vxy, 0.423 and 0.938 for Vz. On the other hand, VzMIMU mean bias ranged between 2.33 % and 4.69 % for SB, between 1.44 % and 19.95 % over IA respectively on the straight and the curve SIGNIFICANCE: The present findings suggest that the MIMU-based system tested slightly underestimated VxyMIMU, though within narrow limits which supports its utilization. On the other hand, VzMIMU computation in sprint running is not fully mature yet. Therefore, this MIMU-based system represents an interesting device for in-fieldVxyMIMU computation either for straight-line and curve sprinting.

Training load and intensity distribution for sprinting among world-class track cyclists.

BACKGROUND: Only few studies analyzed real training programs of sprinters while that should be a valuable step in the understanding of sprint training. The present study aimed at characterizing track cycling sprinter training by training load and intensity distribution. METHODS: Twenty-nine weeks of prechampionship training data were retrospectively analyzed for 6 world-class athletes. Training load was measured by the ratio of volume completed to maximal volume and categorized by five intensity zones (endurance: zones1-2; sprinting: zones3-5) and exercise type (on-bike or resistance). Intra-week (training monotony) and inter-week (acute-chronic workload ratio) variation was also studied. RESULTS: On-bike training represented 77.4±15.3% of total training load; resistance training, 22.6±15.2% (note high standard deviation). Total weekly training load significantly varied (P=0.0002) with high acute-chronic workload ratio (12.0±3.2 weeks >1.5 or <0.8), but low intra-week variations (training monotony, 1.81±0.20). Zone4 and zone5 made up 74.4±16.9% of total training load; zone1, 15.8±11%. Training load was seldom in zone2 (6.4±5.3%) or zone3 (3.3±4.2%). From the first to the second half of the period, zone3-4 training load decreased (39.3±3.3 to 27.4±1.7%; P=0.01), while zone5 increased (34.9±2.4 to 50±3.7%; P=0.002). CONCLUSIONS: In this reduced group of elite athletes, training appeared to mainly consist of on-bike exercises within the highest intensity zones. As demonstrated by monotony and acute-chronic workload ratio overloading and unloading are based on high variations over weeks, not days. Essentially, this study describes a polarized intensity distribution on the highest intensities which increased with world championships approach.

Effects of Acute Physical Fatigue on Gaze Behavior and Performance During a Badminton Game.

In badminton, the ability to quickly gather relevant visual information is one of the most important determinants of performance. However, gaze behavior has never been investigated in a real-game setting (with fatigue), nor related to performance. The aim of this study was to evaluate the effect of fatigue on gaze behavior during a badminton game setting, and to determine the relationship between fatigue, performance and gaze behavior. Nineteen novice badminton players equipped with eye-tracking glasses played two badminton sets: one before and one after a fatiguing task. The duration and number of fixations for each exchange were evaluated for nine areas of interest. Performance in terms of points won or lost and successful strokes was not impacted by fatigue, however fatigue induced more fixations per exchange on two areas of interest (shuttlecock and empty area after the opponent's stroke). Furthermore, two distinct gaze behaviors were found for successful and unsuccessful performance: points won were associated with fixations on the boundary lines and few fixation durations on empty area before the participant's stroke; successful strokes were related to long fixation durations, few fixation durations on empty area and a large number of fixations on the shuttlecock, racket, opponent's upper body and anticipation area. This is the first study to use a mobile eye-tracking system to capture gaze behavior during a real badminton game setting: fatigue induced changes in gaze behavior, and successful and unsuccessful performance were associated with two distinct gaze behaviors.

Improving Health of People With Multiple Sclerosis From a Multicenter Randomized Controlled Study in Parallel Groups: Preliminary Results on the Efficacy of a Mindfulness Intervention and Intention Implementation Associated With a Physical Activity Program.

Objectives: The objective of this study is to investigate the efficacy of psychological Interventions - Mindfulness or Implementation Intention - associated with a Physical Activity program, delivered via internet, in reducing Multiple Sclerosis symptoms. Method: Thirty-five adults were randomly assigned to one of the three groups: a Mindfulness-Based Intervention group (N = 12), Implementation Intention group (N = 11), and a Control Group (N = 12). All the groups received the same Physical Activity program. The Mindfulness condition group received daily training in the form of pre-recorded sessions while the Implementation group elaborated their specific plans once a week. Mobility, fatigue, and the impact of the disease on the patient's life were measured. Two measurement times are carried out in pre-post intervention, at baseline and after eight weeks. Results: Overall, after 8 weeks intervention, results show that there was a significant increase in Walking distance in the three groups. In addition, the within-group analysis showed a statistically significant improvement between pre and post intervention on the physical component of the Disease Impact scale in the Implementation Intention group (p = 0.023) with large effect size, in the Mindfulness-Based Intervention group (p = 0.008) with a medium effect size and in the control group (p = 0.028) with small effect size. In the Implementation Intention group, all physical, psychosocial and cognitive Fatigue Impact subscales scores decreased significantly (p = 0.022, p = 0.023, and p = 0.012, respectively) and the physical component was statistically and negatively correlated (r = -0.745; p = 0.008) when Implementation Intention group practice a mild to moderate physical activity. In the Mindfulness-Based Intervention group, the physical component (MFIS) showed a statistically significant improvement (p = 0.028) but no correlation with moderate-to-vigorous physical activity (MVPA); the control group outcomes did not reveal any significant change. Conclusion: The results of this study are very encouraging and show the feasibility of Mindfulness interventions associated with physical activity to improve the health of people with MS. Further study should assess Mindfulness interventions tailored to MS condition and using both hedonic and eudemonic measures of happiness.

Kinematic and kinetic comparisons of elite and well-trained sprinters during sprint start.

The purpose of this study was to compare the main kinematic, kinetic, and dynamic parameters of elite and well-trained sprinters during the starting block phase and the 2 subsequent steps. Six elite sprinters (10.06-10.43 s/100 m) and 6 well-trained sprinters (11.01-11.80 s/100 m) equipped with 63 passive reflective markers performed 4 maximal 10 m sprint starts on an indoor track. An opto-electronic motion analysis system consisting of 12 digital cameras (250 Hz) was used to record 3D marker trajectories. At the times "on your marks," "set," "clearing the block," and "landing and toe-off of the first and second step," the horizontal position of the center of mass (CM), its velocity (XCM and VCM), and the horizontal position of the rear and front hand (X(Hand_rear) and X(Hand_front)) were calculated. During the pushing phase on the starting block and the 2 first steps, the rate of force development and the impulse (F(impulse)) were also calculated. The main results showed that at each time XCM and VCM were significantly greater in elite sprinters. Moreover, during the pushing phase on the block, the rate of force development and F(impulse) were significantly greater in elite sprinters (respectively, 15,505 +/- 5,397 N.s and 8,459 +/- 3,811 N.s for the rate of force development; 276.2 +/- 36.0 N.s and 215.4 +/- 28.5 N.s for F(impulse), p < or = 0.05). Finally, at the block clearing, elite sprinters showed a greater XHand_rear and X(Hand_front) than well-trained sprinters (respectively, 0.07+/- 0.12 m and -0.27 +/- 0.36 m for X(Hand_rear); 1.00 +/- 0.14 m and 0.52 +/- 0.27 m for X(Hand_front); p < or = 0.05). The muscular strength and arm coordination appear to characterize the efficiency of the sprint start. To improve speed capacities of their athletes, coaches must include in their habitual training sessions of resistance training.

Mechanics of pole vaulting: a review.

A good understanding of the mechanics of pole vaulting is fundamental to performance because this event is quite complex, with several factors occurring in sequence and/or in parallel. These factors mainly concern the velocities of the vaulter-pole system, the kinetic and potential energy of the vaulter and the strain energy stored in the pole, the force and torque applied by the athlete, and the pole design. Although the pole vault literature is vast, encompassing several fields such as medicine, sports sciences, mechanics, mathematics, and physics, the studies agree that pole vault performance is basically influenced by the energy exchange between the vaulter and pole. Ideally, as the athlete clears the crossbar, the vaulter mechanical energy must be composed of high potential energy and low kinetic energy, guaranteeing the high vertical component of the vault. Moreover, the force and torque applied by the vaulter influences this energy exchange and these factors thus must be taken into consideration in the analysis of performance. This review presents the variables that influence pole vault performance during the run-up, take-off, pole support, and free flight phases.

Effect of a 16-Day Altitude Training Camp on 3,000-m Steeplechase Running Energetics and Biomechanics: A Case Study.

The purpose of this study was to investigate the effect of a 16-day training camp at moderate altitude on running energetics and biomechanics in an elite female 3,000-m steeplechase athlete (personal best: 9 min 36.15 s). The 16-day intervention included living and training at 1,600 m altitude. A maximal incremental test was performed at sea level to determine the maximal oxygen uptake ( V ∙ O 2 max ). Before (pre-) and after (post-) intervention, the participant performed a specific training session consisting of 10 × 400 m with 5 hurdles with oxygen uptake ( V ∙ O 2 ), blood lactate, stride length and stride rate being measured. A video analysis determined take-off distance and landing around the hurdle (DTH and DLH), take-off velocity and landing around the hurdle (VTH and VLH), and the maximal height over the hurdle (MH). The results demonstrated that the mean V ∙ O 2 maintained during the ten 400 m trials represented 84-86% of V ∙ O 2 max and did not change from pre- to post-intervention (p = 0.22). Mean blood lactate measured on the 6 last 400-m efforts increased significantly (12.0 ± 2.2 vs. 17.0 ± 1.6 mmol.l-1; p < 0.05). On the other hand, post-intervention maximal lactate decreased from 20.1 to 16.0 mmol.l-1. Biomechanical analysis revealed that running velocity increased from 5.12 ± 0.16 to 5.49 ± 0.19 m.s-1 (p < 0.001), concomitantly with stride length (1.63 ± 0.05 vs. 1.73 ± 0.06 m; p < 0.001). However, stride rate did not change (3.15 ± 0.03 vs. 3.16 ± 0.02 Hz; p = 0.14). While DTH was not significantly different from pre- to post- (1.34 ± 0.08 vs. 1.40 ± 0.07 m; p = 0.09), DLH was significantly longer (1.17 ± 0.07 vs. 1.36 ± 0.05 m; p < 0.01). VTH and VLH significantly improved after intervention (5.00 ± 0.14 vs. 5.33 ± 0.16 m.s-1 and 5.18 ± 0.13 vs. 5.51 ± 0.22 m.s-1, respectively; both p < 0.01). Finally, MH increased from pre- to post- (52.5 ± 3.8 vs. 54.9 ± 2.1 cm; p < 0.05). A 16-day moderate altitude training camp allowed an elite female 3,000-m steeplechase athlete to improve running velocity through a greater glycolytic-but not aerobic-metabolism.

Elite long sprint running: a comparison between incline and level training sessions.

PURPOSE: We compared incline and level training sessions as usually used in elite 400-m runners through stride kinematics and muscular activity measurements. METHODS: Nine highly trained 400-m runners (international and French national level) performed two maximal velocity sprints: 1) 300-m on level ground (LEV) and 2) 250-m on an incline ground (INC) characterized by a mean +/- SD grade of 5.4 +/- 0.7%. Kinematics (250 Hz) and electromyography parameters (root mean square [RMS] and integrated electromyography [iEMG] measurements) were analyzed (from 40- to 50-m phases). RESULTS: INC induced a decrease in running velocity compared to LEV (6.28 +/- 0.38 vs 7.56 +/- 0.38 m.s) explained by a reduction in stride length (-14.2%) and stride rate (-7.4%) and by an increase in push-off time (+26.4%). Kinematics analysis indicated that the lower limbs were more flexed during INC running. Concerning the level of activity of the lower limb muscles, the major findings pointed out the decrease in RMS for semitendinosus and biceps femoris muscles during the contact phase and for vastus lateralis during its concentric phase. However, iEMG of both semitendinosus and biceps femoris muscles remained constant during both contact and push-off phases. CONCLUSION: Our results are clearly different from those of previous studies carried out at similar absolute velocities in both LEV and INC conditions, which were not the case in this study. The lower running velocity marking INC running was associated with a decrease in the activation of the hamstrings. Trainers should particularly consider this lower level of activation of the hamstrings muscles during INC maximal sprint.

Changes in spring-mass model parameters and energy cost during track running to exhaustion.

The purpose of this study was to determine whether exhaustion modifies the stiffness characteristics, as defined in the spring-mass model, during track running. We also investigated whether stiffer runners are also the most economical. Nine well-trained runners performed an exhaustive exercise over 2000 meters on an indoor track. This exhaustive exercise was preceded by a warm-up and was followed by an active recovery. Throughout all the exercises, the energy cost of running (Cr) was measured. Vertical and leg stiffness was measured with a force plate (Kvert and Kleg, respectively) integrated into the track. The results show that Cr increases significantly after the 2000-meter run (0.192 +/- 0.006 to 0.217 +/- 0.013 mL x kg(-1) x m(-1)). However, Kvert and Kleg remained constant (32.52 +/- 6.42 to 32.59 +/- 5.48 and 11.12 +/- 2.76 to 11.14 +/- 2.48 kN.m, respectively). An inverse correlation was observed between Cr and Kleg, but only during the 2000-meter exercise (r = -0.67; P < or = 0.05). During the warm-up or the recovery, Cr and Kleg, were not correlated (r = 0.354; P = 0.82 and r = 0.21; P = 0.59, respectively). On track, exhaustion induced by a 2000-meter run has no effect on Kleg or Kvert. The inverse correlation was only observed between Cr and Kleg during the 2000-meter run and not before or after the exercise, suggesting that the stiffness of the runner may be not associated with the Cr.

The Effects of Repeated Sprints on the Kinematics of 3-Point Shooting in Basketball.

Fatigue modifies the kinematics of various sports-related movements. Basketball induces fatigue, however, the effects of fatigue on the kinematics of shooting have never been studied. This study analysed the effects of fatigue induced by repeated sprints on the kinematics of 3-point shooting (3PS) in young, elite basketball players (U18 level). 3D joint angles were calculated at the maximum and minimum heights of the centre of mass during 3PS, using inertial measurement units (Biomech system, Xsens Technologies BV, Enschede, The Netherlands). Height, velocity and the angle of the ball at the time of release were extrapolated from the wrist joint angles. All players performed four 3PS actions in dynamic conditions before and after a fatigue protocol at 70% of their maximal exercise capacity. The fatigue protocol consisted of a shuttle test with repeated 20-m sprints interspersed with sets of 5 jumps. There was no change in the kinematics of 3PS (p > 0.05), or the ball release variables (p > 0.05) following the fatigue protocol. This suggests that elite basketball players are able to cope with physical fatigue while performing coordinated movements such as 3PS.

Changes in internal mechanical cost during overground running to exhaustion.

PURPOSE: The purpose of this study was to determine, during an overground supra-threshold run, whether a change in the internal mechanical cost could occur during an exhaustive run and whether this change was related to the increase in the energy cost of running (C(r)). METHODS: The Cr of 14 endurance runners was measured from pulmonary gas exchange using a breath-by-breath portable gas analyzer (Cosmed K4b, Rome, Italy), at the third and the last minute of an exhaustive exercise performed at their velocity corresponding to 95% of the maximal oxygen uptake (4.88 +/- 0.38 m.s(-1)). At the same time, potential, kinetic, and internal mechanical costs (C(pe), C(ke), and C(int)) were measured with a 3D motion analysis system (ANIMAN3D). RESULTS: C(int) and C(r) increased significantly within the third minute and the end of the supra-threshold exercise (respectively, 0.55 +/- 0.07 vs 0.60 +/- 0.07 J.kg(-1).m(-1) and 4.10 +/- 0.39 vs 4.32 +/- 0.42 J.kg(-1).m(-1); P < or = 0.03). However, the percentage of variation of C(int) and C(r) were not correlated (r = 0.06; P = 0.84). Contrary to C(int), C(ke) and C(pe) remained constant during the exercise (respectively, 1.33 +/- 0.33 vs 1.38 +/- 0.29 J.kg(-1).m(-1) P = 0.79 and 0.47 +/- 0.11 vs 0.48 +/- 0.10 J.kg(-1).m(-1); P = 0.67), but both parameters were significantly correlated with C(r) (r = 0.43; P = 0.03 and r = 0.40; P = 0.03). CONCLUSION: During overground running to exhaustion, a significant increase in C(int) occurred, but this did not account for the increase in C(r). Moreover, the increase in C(int) has yet to be explained.