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When poor reliability of "output" variables is reported, it can be difficult to discern whether blame lies with the measurement (ie, the inputs) or the overarching concept. This commentary addresses this issue, using the force-velocity-power (FvP) profile in jumping to illustrate the interplay between concept, method, and measurement reliability. While FvP testing has risen in popularity and accessibility, some studies have challenged the reliability and subsequent utility of the concept itself without clearly considering the potential for imprecise procedures to impact reliability measures. To this end, simulations based on virtual athletes confirmed that push-off distance and jump-height variability should be <4% to 5% to guarantee well-fitted force–velocity relationships and acceptable typical error (<10%) in FvP outputs, which was in line with previous experimental findings. Thus, while arguably acceptable in isolation, the 5% to 10% variability in push-off distance or jump height reported in the critiquing studies suggests that their methods were not reliable enough (lack of familiarization, inaccurate procedures, or submaximal efforts) to infer underpinning force-production capacities. Instead of challenging only the concept of FvP relationship testing, an alternative conclusion should have considered the context in which the results were observed: If procedures' and/or tasks' execution is too variable, FvP outputs will be unreliable. As for some other neuromuscular or physiological testing, the FvP relationship, which magnifies measurement errors, is unreliable when the input measurements or testing procedures are inaccurate independently from the method or concept used. Field "simple" methods require the same methodological rigor as "lab" methods to obtain reliable output data. [ABSTRACT FROM AUTHOR]

Ballistic actions are imperative in sports where performance depends on power production across a relevant range of contraction- and movement velocities. Force-velocity-power ( F v P ‾ ) profiling provides information regarding neuromuscular capabilities and vertical performances, but knowledge regarding its associative value towards horizontal movements is scarce. Therefore, we conducted F v P ‾ profiling and analysed associations with uni- and multidirectional ballistic performance tasks in 27 international- to national-level athletes (18.9 ± 2.6 years, 182.9 ± 7.1 cm and 79.2 ± 11.9 kg). Low to moderate correlations were observed between theoretical maximal power ( P ˉ max) and horizontal acceleration (R = −0.43), speed (R = −0.64), sprint (R = −0.60) and agility (R = −0.59) performances. Force-velocity imbalance (FvIMB) significantly (P ≤ 0.05) strengthened the correlations towards sprinting ability (from −0.60 to −0.74) and agility (from −0.59 to −0.68), however, both correlations remaining weaker than for jumping performances (R = 0.78–0.86). In conclusion, F v P ‾ profiling provides information of importance for horizontal and vertical performances with a significant positive effect of P ˉ max, but negative effect of FvIMB. Assessment of lower-extremity neuromuscular capabilities through F v P ‾ profiling and associated development of training programmes targeting compensation of either force- or velocity deficit may benefit the ability to utilise a given power potential. [ABSTRACT FROM AUTHOR]

Purpose: To compare the sprint mechanical force–velocity (F–V) profile between soccer and futsal players. A secondary aim was, within each sport, to study the differences in sprint mechanical F–V profile between sexes and players of different levels. Methods: A total of 102 soccer players (63 men) and 77 futsal players (49 men) who were competing from the elite to amateur levels in the Spanish league participated in this investigation. The testing procedure consisted of 3 unloaded maximal 40-m sprints. The velocity–time data recorded by a radar device were used to calculate the variables of the sprint acceleration F–V profile (maximal theoretical force [F0], maximal theoretical velocity [V0], maximal power [Pmax], decrease in the ratio of horizontal to resultant force [DRF], and maximal ratio of horizontal to resultant force [RFpeak]). Results: Futsal players showed a higher F0 than soccer players (effect size [ES] range: 0.11–0.74), while V0 (ES range: −0.48 to −1.15) and DRF (ES range: −0.75 to −1.45) was higher for soccer players. No significant differences were observed between soccer and futsal players for Pmax (ES range: −0.43 to 0.19) and RFpeak (ES range: −0.49 to 0.30). Men and high-level players presented an overall enhanced F–V profile compared with women and their lower-level counterparts, respectively. Conclusions: The higher F0 and lower V0 of futsal players could be caused by the game's specific demands (larger number of accelerations but over shorter distances than in soccer). These results show that the sprint mechanical F–V profile is able to distinguish between soccer and futsal players. [ABSTRACT FROM AUTHOR]

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Purpose: To analyze the reliability and validity of a simple computation method to evaluate force (F), velocity (v), and power (P) output during a countermovement jump (CMJ) suitable for use in field conditions and to verify the validity of this computation method to compute the CMJ force-velocity (F-v) profile (including unloaded and loaded jumps) in trained athletes. Methods: Sixteen high-level male sprinters and jumpers performed maximal CMJs under 6 different load conditions (0-87 kg). A force plate sampling at 1000 Hz was used to record vertical ground-reaction force and derive vertical-displacement data during CMJ trials. For each condition, mean F, v, and P of the push-off phase were determined from both force-plate data (reference method) and simple computation measures based on body mass, jump height (from flight time), and push-off distance and used to establish the linear F-v relationship for each individual. Results: Mean absolute bias values were 0.9% (± 1.6%), 4.7% (± 6.2%), 3.7% (± 4.8%), and 5% (± 6.8%) for F, v, P, and slope of the F-v relationship (SFv), respectively. Both methods showed high correlations for F-v-profile-related variables (r = .985-.991). Finally, all variables computed from the simple method showed high reliability, with ICC >.980 and CV <1.0%. Conclusions: These results suggest that the simple method presented here is valid and reliable for computing CMJ force, velocity, power, and F-v profiles in athletes and could be used in practice under field conditions when body mass, push-off distance, and jump height are known. [ABSTRACT FROM AUTHOR]

Jiménez-Reyes, P, Garcia-Ramos, A, Párraga-Montilla, JA, Morcillo-Losa, JA, Cuadrado-Peñafiel, V, Castaño-Zambudio, A, Samozino, P, and Morin, J-B. Seasonal changes in the sprint acceleration force-velocity profile of elite male soccer players. J Strength Cond Res 36(1): 70–74, 2022—This study aimed to describe the seasonal changes in the sprint force-velocity (Fv) profile of professional soccer players. The sprint Fv profile of 21 male soccer players competing in the first division of the Spanish soccer league was evaluated 6 times: preseason 1 (September 2015), in-season 1 (November 2015), in-season 2 (January 2016), in-season 3 (March 2016), in-season 4 (May 2016), and preseason 2 (August 2016). No specific sprint capabilities stimuli other than those induced by soccer training were applied. The following variables were calculated from the velocity-time data recorded with a radar device during an unloaded sprint: maximal force (F 0), maximal velocity (v 0), Fv slope, maximal power (Pmax), decrease in the ratio of horizontal-to-resultant force (DRF), and maximal ratio of horizontal-to-resultant force (RFpeak). F 0 (effect size [ES] range = 0.83–0.93), Pmax (ES range = 0.97–1.05), and RFpeak (ES range = 0.56–1.13) were higher at the in-seasons 2 and 3 compared with both preseasons (p ≤ 0.006). No significant differences were observed for v 0, Fv slope, and DRF (p ≥ 0.287). These results suggest that relevant Fv profile variables may be compromised (F 0 more compromised than v 0) toward the end of the competitive season when specific sprint stimuli are not systematically applied. [ABSTRACT FROM AUTHOR]

The aim of study was to examine the effects of the world's most challenging mountain ultramarathon (Tor des Geants [TdG]) on running mechanics. Mechanical measurements were undertaken in male runners (n - 16) and a control group (n = 8) before (PRE), during (MID), and after (POST) the TdG. Contact (tc) and aerial (ta) times, step frequency if), and running velocity (v) were sampled. Spring-mass parameters of peak vertical ground-reaction force (Fmax), vertical downward displacement of the center of mass (Δz), leg-length change (ΔL), and vertical (kvert) and leg (kleg) stiffness were computed. Significant decreases were observed in runners between PRE and MID for ta (P < .001 ), Fmax (P < .001 ), Δz (P < .05), and kleg (P < .01 ). In contrast, /significantly increased (P < .05) between PRE and MID-TdG. No further changes were observed at POST for any of those variables, with the exception of kleg, which went back to PRE. During the TdG, experienced runners modified their running pattern and spring-mass behavior mainly during the first half. The current results suggest that these mechanical changes aim at minimizing the pain occurring in lower limbs mainly during the eccentric phases. One cannot rule out that this switch to a "safer" technique may also aim to anticipate further damages. [ABSTRACT FROM AUTHOR]

Recent studies have brought new insights into the evaluation of power-force-velocity profiles in both ballistic push-offs (eg, jumps) and sprint movements. These are major physical components of performance in many sports, and the methods the authors developed and validated are based on data that are now rather simple to obtain in field conditions (eg, body mass, jump height, sprint times, or velocity). The promising aspect of these approaches is that they allow for more individualized and accurate evaluation, monitoring, and training practices, the success of which is highly dependent on the correct collection, generation, and interpretation of athletes' mechanical outputs. The authors therefore wanted to provide a practical vade mecum to sports practitioners interested in implementing these power-force-velocity-profiling approaches. After providing a summary of theoretical and practical definitions for the main variables, the authors first detail how vertical profiling can be used to manage ballistic push-off performance, with emphasis on the concept of optimal force-velocity profile and the associated force-velocity imbalance. Furthermore, they discuss these same concepts with regard to horizontal profiling in the management of sprinting performance. These sections are illustrated by typical examples from the authors' practice. Finally, they provide a practical and operational synthesis and outline future challenges that will help further develop these approaches. [ABSTRACT FROM AUTHOR]

Purpose: To compare mechanical properties of overground sprint running in elite rugby union and rugby league athletes. Methods: Thirty elite rugby code (15 rugby union and 15 rugby league) athletes participated in this cross-sectional analysis. Radar was used to measure maximal overground sprint performance over 20 or 30 m (forwards and backs, respectively). In addition to time at 2, 5, 10, 20, and 30 m, velocity-time signals were analyzed to derive external horizontal force--velocity relationships with a recently validated method. From this relationship, the maximal theoretical velocity, external relative and absolute horizontal force, horizontal power, and optimal horizontal force for peak power production were determined. Results: While differences in maximal velocity were unclear between codes, rugby union backs produced moderately faster split times, with the most substantial differences occurring at 2 and 5 m (ES 0.95 and 0.86, respectively). In addition, rugby union backs produced moderately larger relative horizontal force, optimal force, and peak power capabilities than rugby league backs (ES 0.73-0.77). Rugby union forwards had a higher absolute force (ES 0.77) despite having ~12% more body weight than rugby league forwards. Conclusions: In this elite sample, rugby union athletes typically displayed greater short-distance sprint performance, which may be linked to an ability to generate high levels of horizontal force and power. The acceleration characteristics presented in this study could be a result of the individual movement and positional demands of each code. [ABSTRACT FROM AUTHOR]

An association has been reported between dynamic anterior pelvic tilt (APT) and hamstring injuries; however, no research has examined if a training-based preventive intervention could alter APT. Therefore, the aim of the present study was to examine if a specific 6-week multimodal intervention, based on the theoretical influence of neighbouring joints and biomechanical interactions between muscles that are inserted to the pelvis, induced changes in APT, during walking gait, hamstring flexibility and trunk endurance. Thirty-five active healthy males volunteered for this single-blind controlled trial and were split into two groups based on baseline data: a control group (CG, n = 20, continued their normal physical activities), and an intervention group (IG, n = 15, performed the intervention programme for 18 sessions over 6 weeks). A significant (p = 0.001) decrease in the APT kinematics during gait, significant increase in the Active Knee Extension Test (p = 0.001), and a significant increase in trunk endurance performance for flexion (p = 0.001), extension (p = 0.001) and side bridge (p = 0.001) were observed, in IG after the 6-week programme, compared to CG. [ABSTRACT FROM AUTHOR]

Successful sprinting depends on covering a specific distance in the shortest time possible. Although external forces are key to sprinting, less consideration is given to the duration of force application, which influences the impulse generated. This study explored relationships between sprint performance measures and external kinetic and kinematic performance indicators. Data were collected from the initial acceleration, transition and maximal velocity phases of a sprint. Relationships were analysed between sprint performance measures and kinetic and kinematic variables. A commonality regression analysis was used to explore how independent variables contributed to multiple-regression models for the sprint phases. Propulsive forces play a key role in sprint performance during the initial acceleration (r = 0.95 ± 0.03) and transition phases (r = 0.74 ± 0.19), while braking duration plays an important role during the transition phase (r = −0.72 ± 0.20). Contact time, vertical force and peak propulsive forces represented key determinants (r = −0.64 ± 0.31, r = 0.57 ± 0.35 and r = 0.66 ± 0.30, respectively) of maximal velocity phase performance, with peak propulsive force providing the largest unique contribution to the regression model for step velocity. These results clarified the role of force and time variables on sprinting performance. [ABSTRACT FROM AUTHOR]

The spring-mass model, representing a runner as a point mass supported by a single linear leg spring, has been a widely used concept in studies on running and bouncing mechanics. However, the measurement of leg and vertical stiffness has previously required force platforms and high-speed kinematic measurement systems that are costly and difficult to handle in field conditions. We propose a new "sine-wave" method for measuring stiffness during running. Based on the modeling of the force-time curve by a sine function, this method allows leg and vertical stiffness to be estimated from just a few simple mechanical parameters: body mass, forward velocity, leg length, flight time, and contact time. We compared this method to force-platform-derived stiffness measurements for treadmill dynamometer and overground running conditions, at velocities ranging from 3.33 m·s-1 to maximal running velocity in both recreational and highly trained runners. Stiffness values calculated with the proposed method ranged from 0.67% to 6.93% less than the force platform method, and thus were judged to be acceptable. Furthermore, significant linear regressions (p < 0.01) close to the identity line were obtained between force platform and sine-wave model values of stiffness. Given the limits inherent in the use of the spring-mass model, it was concluded that this sine-wave method allows leg and stiffness estimates in running on the basis of a few mechanical parameters, and could be useful in further field measurements. [ABSTRACT FROM AUTHOR]

This study aimed to analyse fatigue-induced changes in mechanical sprinting properties during a specific repeated-sprint test in elite rugby sevens athletes. Twenty elite rugby sevens players performed ten 40 m sprints on a 30 s cycle with participant's running back and forth in a marked lane. Radar was used to assess maximal overground sprint performance over each 40 m. Macroscopic mechanical properties (maximal horizontal force (F0), maximal horizontal power (Pmax), maximal ratio of horizontal force (RFpeak), decrease in the ratio of horizontal-to-total force (DRF), total force and maximal sprinting velocity (v0)) were drawn from horizontal force velocity relationships, using a validated method applied to the speed–time data. Fatigue-induced changes were analysed comparing the first sprint to an average of 2nd-4th, 5th-7th and 8th-10th. Repeated-sprint ability (RSA) testing induced substantial changes in the maximal velocity component, with a decrease (–15%) in v0 (effect size (ES) = –2.46 to –4.98), and to a lower extent (–5.9%) in the maximal force component F0 (ES = –0.59). DRF moderately decreased (14%; ES=–0.76–1.11), and RFpeak largely decreased in the later sprints (ES = –0.32 to –1.27). Fatigue observed in this RSA test appeared to have a greater effect on the technical ability to produce horizontal force at high velocities, likely due to an alteration in the ability to maintain horizontally oriented force application when velocity increases rather than during the initial acceleration phase, but also the overall force production capacity. The ability to maintain forward-oriented force at high velocities is of central importance for identifying fatigue and monitoring load. [ABSTRACT FROM AUTHOR]

Most running studies have considered level running (LR), yet the regulation of locomotor behaviour during uphill (UR) and downhill (DR) running is fundamental to increase our understanding of human locomotion. The purpose of this article was to review the existing literature regarding biomechanical, neuromuscular and physiological adaptations during graded running. Relative to LR, UR is characterized by a higher step frequency, increased internal mechanical work, shorter swing/aerial phase duration, and greater duty factor, while DR is characterized by increased aerial time, reduced step frequency and decreased duty factor. Grade also modifies foot strike patterns, with a progressive adoption of a mid- to fore-foot strike pattern during UR, and rear-foot strike patterns during DR. In UR, lower limb muscles perform a higher net mechanical work compared to LR and DR to increase the body's potential energy. In DR, energy dissipation is generally prevalent compared to energy generation. The increased demands for work as running incline increases are met by an increase in power output at all joints, particularly the hip. This implies that UR requires greater muscular activity compared to LR and DR. Energy cost of running ( C ) linearly increases with positive slope but C of DR decreases until a minimum slope is reached at −20 %, after which C increases again. The effects of slope on biomechanics, muscle contraction patterns and physiological responses have important implications for injury prevention and success of athletes engaged in graded running competitions. [ABSTRACT FROM AUTHOR]

Overground sprint studies have shown the importance of net horizontal ground reaction force impulse ( IMP H ) 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 ( IMP H +) and braking ( IMP H − ) components of the IMP H and seek whether, for an expected higher IMP H , faster elite sprinters produce greater IMP H +, smaller IMP H − , or both. Nine high-level sprinters (100-m best times range: 9.95–10.60 s) 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. IMP H and IMP H + were significantly correlated with 40-m mean speed ( r =0.868 and 0.802, respectively; P <0.01), whereas vertical impulse and IMP H − were not. Multiple regression analyses confirmed the significantly higher importance of IMP H + 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 IMP H +), but not necessarily those who also “braked less” (lower IMP H − ) in the horizontal direction. [ABSTRACT FROM AUTHOR]

Foot strike identification has become an important topic since it may be related to injury risk and performance. Due to step variability and the influence of environmental features on running biomechanics, it is relevant to assess as many steps as possible in field conditions. Our purpose was to apply a novel simple method to assess foot strike and impact from continuous acceleration measurements over a 45 km trail running race. Three wireless tridimensional accelerometers were set on the left tibia and shoe (at the heel and metatarsals) of the current best ultratrail runner. Vertical, antero-posterior and resultant peak tibial accelerations and median frequencies were measured. Step frequency (SF) was calculated from tibial acceleration. Foot strike was quantified from the time between heel and metatarsal peak accelerations (THM). Foot strike classification was performed according to THM criteria and expressed in percentages of rearfoot, midfoot and forefoot steps. Multiple linear regressions were computed to assess relationships between the impact magnitude and slope, SF and THM. Over the first 20 km, 5530 steps were analysed. The pattern classification revealed on average 18.5% of rearfoot strike, 32.6% of midfoot strike and 48.9% of forefoot strike over the ∼82 min analysed in the runner studied. The impact magnitude for him may be related to slope, also taking into account speed, SF and landing technique. The main findings of this study were that (1) portable accelerometers make possible the assessment of foot strike and shock accelerationin situ, (2) the antero-posterior and resultant components of tibial acceleration should not be neglected in the measurement of stress severity, and (3) the trail running world champion presents an atypical foot strike profile. [ABSTRACT FROM PUBLISHER]

Impact reduction has become a factor of interest in the prevention of running-related injuries such as stress fractures. Currently, the midfoot strike pattern (MFS) is thought as a potential way to decrease impact. The purpose was to test the effects of two long-term interventions aiming to reduce impact during running via a transition to an MFS: a foot strike retraining versus a low-drop/low-heel height footwear. Thirty rearfoot strikers were randomly assigned to two experimental groups (SHOES and TRAIN). SHOES progressively wore low-drop/low-heel height shoes and TRAIN progressively adopted an MFS, over a 3-month period with three 30-min running sessions per week. Measurement sessions (pre-training, 1, 2 and 3 months) were performed during which subjects were equipped with three accelerometers on the shin, heel and metatarsals, and ran for 15 min on an instrumented treadmill. Synchronized acceleration and vertical ground reaction force signals were recorded. Peak heel acceleration was significantly lower as compared to pre-training for SHOES (−33.5 ± 12.8 % at 2 months and −25.3 ± 18.8 % at 3 months, p < 0.001), and so was shock propagation velocity (−12.1 ± 9.3 %, p < 0.001 at 2 months and −11.3 ± 4.6 %, p < 0.05 at 3 months). No change was observed for TRAIN. Important inter-individual variations were noted in both groups and reported pains were mainly located at the shin and calf. Although it induced reversible pains, low-drop/low-heel height footwear seemed to be more effective than foot strike retraining to attenuate heel impact in the long term. [ABSTRACT FROM AUTHOR]

Abstract: A theoretical integrative approach is proposed to understand the overall mechanical characteristics of lower extremities determining jumping ability. This approach considers that external force production during push-off is limited by mechanical constraints imposed by both movement dynamics and force generator properties, i.e. lower extremities characteristics. While the velocity of the body depends on the amount of external force produced over the push-off, the capabilities of force production decrease with increasing movement velocity, notably for force generators driven by muscular contraction, such as lower extremities of large animals during jumping from a resting position. Considering the circular interaction between these two mechanical constraints, and using simple mathematical and physical principles, the proposed approach leads to a mathematical expression of the maximal jump height an individual can reach as a function of only three integrative mechanical characteristics of his lower extremities: the maximal force they can produce (), the maximal velocity at which they can extend under muscles action () and the distance of force production determined by their usual extension range (). These three integrative variables positively influence maximal jump height. For instance in humans, a 10% variation in , or induces a change in jump height of about 10–15%, 6–11% and 4–8%, respectively. The proposed theoretical approach allowed to isolate the basic mechanical entities through which all physiological and morphological specificities influence jumping performance, and may be used to separate the very first macroscopic effects of these three mechanical characteristics on jumping performance variability. [Copyright &y& Elsevier]

Abstract: The aim of this study was to know whether subjects involved in a locomotion experiment modified their running pattern when made aware that data were being collected, and of the specific parameters studied. We used standardised actual and deceptive messages to induce increasing levels of awareness, and analysed subjects’ running pattern on a treadmill dynamometer, using lower limb stiffness as the key mechanical parameter. The five levels of awareness were: (1) subjects thought no sampling was performed, (2) they knew a sampling was about to take place, without knowing the parameter studied, (3) they knew this sampling was in progress, (4) they knew that sampling of lower limb stiffness was about to take place, and (5) they knew this sampling was in progress. Subjects’ running pattern significantly changed with the increasing level of information given, with a higher stiffness and step frequency, a reduced contact time and a lower change in leg length during contact. Post hoc tests showed that subjects changed their running pattern when knowing (i) that a sampling was performed and (ii) the mechanical parameter studied. These preliminary results suggest that experimental designs in locomotion protocols should take this potential “sampling” effect into account, whenever possible. [Copyright &y& Elsevier]

Net metabolic cost of walking normalized by body mass (CW∙BM-1; in J∙kg-1∙m-1 ) is greater in obese than in normal-weight individuals, and biomechanical differences could be responsible for this greater net metabolic cost. We hypothesized that, in obese individuals, greater mediolateral body center of mass (COM) displacement and lower recovery of mechanical energy could induce an increase in the external mechanical work required to lift and accelerate the COM and thus in net CW∙BM-1. Body composition and standing metabolic rate were measured in 23 obese and 10 normal-weight adolescents. Metabolic and mechanical energy costs were assessed while walking along an outdoor track at four speeds (0.75-1.50 m/s). Three-dimensional COM accelerations were measured by means of a tri-axial accelerometer and gyroscope and integrated twice to obtain COM velocities, displacements, and fluctuations in potential and kinetic energies. Last, external mechanical work (J∙kg-1∙m-1), mediolateral COM displacement, and the mechanical energy recovery of the inverted pendulum were calculated. Net CW∙BM-1 was 25% higher in obese than in normal-weight subjects on average across speeds, and net CW∙BM-67 (J∙kg-0.67∙m-1) was significantly related to percent body fat (r2 = 0.46). However, recovery of mechanical energy and the external work performed (J∙kg-1∙m-1) were similar in the two groups. The mediolateral displacement was greater in obese subjects and significantly related to percent body fat (r2 = 0.64). The mediolateral COM displacement, likely due to greater step width, was significantly related to net CW∙BM-67 (r2 = 0.49). In conclusion, we speculate that the greater net CW∙BM-67 in obese subjects may be partially explained by the greater step-to-step transition costs associated with wide gait during walking. [ABSTRACT FROM AUTHOR]

Identifying foot strike patterns in running is an important issue for sport clinicians, coaches and footwear industrials. Current methods allow the monitoring of either many steps in laboratory conditions or only a few steps in the field. Because measuring running biomechanics during actual practice is critical, our purpose is to validate a method aiming at identifying foot strike patterns during continuous field measurements. Based on heel and metatarsal accelerations, this method requires two uniaxial accelerometers. The time between heel and metatarsal acceleration peaks (THM) was compared to the foot strike angle in the sagittal plane (αfoot) obtained by 2D video analysis for various conditions of speed, slope, footwear, foot strike and state of fatigue. Acceleration and kinematic measurements were performed at 1000 Hz and 120 Hz, respectively, during 2-min treadmill running bouts. Significant correlations were observed between THM and αfoot for 14 out of 15 conditions. The overall correlation coefficient was r=0.916 (P< 0.0001, n = 288). The THM method is thus highly reliable for a wide range of speeds and slopes, and for all types of foot strike except for extreme forefoot strike during which the heel rarely or never strikes the ground, and for different footwears and states of fatigue. We proposed a classification based on THM: FFS < - 5.49 ms < MFS < 15.2 ms < RFS. With only a few precautions being necessary to ensure appropriate use of this method, it is reliable for distinguishing rearfoot and non-rearfoot strikers in situ. [ABSTRACT FROM AUTHOR]

The article reports on research which was conducted to determine the respective influences of the maximal power (P„„) and the force-velocity (F-v) mechanical profile of the lower limb neuromuscular system on performance in ballistic movements. Researchers evaluated 14 subjects who performed lower limb ballistic inclined push-offs. They found that high ballistic performances are determined by both maximization of the power output capabilities and optimization of the F-v mechanical profile of the lower limb neuromuscular system.