Papers by Pierre Samozino
HAL (Le Centre pour la Communication Scientifique Directe), Jul 4, 2023
International Journal of Sports Physiology and Performance
When poor reliability of “output” variables is reported, it can be difficult to discern whether b... more 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 jum...
International Journal of Sports Physiology and Performance
Purpose: The aims of this study were to (1) assess the concurrent validity of global positioning ... more Purpose: The aims of this study were to (1) assess the concurrent validity of global positioning systems (GPSs) against a radar device to measure sprinting force–velocity (F–v) profiles and (2) evaluate the interunit reliability of 10-Hz GPS devices (Vector S7, Catapult Innovations). Methods: Sixteen male elite U18 rugby union players (178.3 [7.6] cm; 78.3 [13.2] kg) participated. Two 50-m sprints interspersed with at least 5 minutes of recovery were completed to obtain input (maximal sprint speed and acceleration time constant τ) and output (theoretical maximal horizontal force, sprinting speed, and horizontal power) F–v profile variables. Sprint running speed was concurrently measured with a radar and 2 GPS units placed on the upper back of each player. Concurrent validity and interunit reliability analyses were performed. Results: Moderate to nearly perfect correlations were observed between radar and GPS-derived F–v variables, with small to large typical errors. Trivial to small...
Background: The aim of this study was to test the effects of cycling shoe outsole stiffness on bo... more Background: The aim of this study was to test the effects of cycling shoe outsole stiffness on both performance and comfort parameters during sub- and supra-maximal cycling tests. Methods: Two groups of recreational women tested three cycling shoe conditions with differing outsole stiffness. One group of 8 women performed four cycling tests of 3 min composed of two intensities (100 and 140 W) and two pedaling rates (70 and 100 rpm) for each pair of shoes. Metabolic and subjective perception of comfort measurement was evaluated with each shoe. Another group of 12 women performed 6-s all-out sprints against two external resistances (0.4 and 0.7 N/kg) to determine force-velocity relationships with the three cycling shoe conditions. Results: The main findings are that the stiffness of the investigated outsole cycling shoes (i) does not influence cycling performance whatever the test (ii) while the perception of comfort is largely degraded compared to the most flexible shoe. Conclusion: ...
This study sought to determine the changes in maximal leg power output over the course of a decat... more This study sought to determine the changes in maximal leg power output over the course of a decathlon in order to better understand 1) the event’s functional demands, 2) the muscular mechanical capabilities determining performance in the event, and 3) their relationships with injury risk factors. It was conducted under field conditions during the 2010 French National Combined Events Championships with six national-level athletes and 11 control participants as subjects. No differences in the values for squat jump and cycling sprint were found between tests at the beginning and end of each day (P>0.05), while significantly lower squat jump values at the start of the second day were reported for the control participants (P<0.05). The results suggest that a decathlon does not induce measurable alterations in lower extremity force, velocity or power output affecting performance and that the accumulation of fatigue (and/or neuromuscular fatigue, if any) does not play a major role in...
International Journal of Environmental Research and Public Health, 2021
Clear decreases in horizontal force production capacity during sprint acceleration have been repo... more Clear decreases in horizontal force production capacity during sprint acceleration have been reported after hamstring injuries (HI) in football players. We hypothesized that lower FH0 is associated with a higher HI occurrence in football players. We aimed to analyze the association between sprint running horizontal force production capacities at low (FH0) and high (V0) velocities, and HI occurrence in football. This prospective cohort study included 284 football players over one season. All players performed 30 m field sprints at the beginning and different times during the season. Sprint velocity data were used to compute sprint mechanical properties. Players’ injury data were prospectively collected during the entire season. Cox regression analyses were performed using new HI as the outcome, and horizontal force production capacity (FH0 and V0) was used at the start of the season (model 1) and at each measurement time point within the season (model 2) as explanatory variables, adj...
Journal of Sports Sciences, 2021
ABSTRACT Comprehensive information regarding neuromuscular function, as assessed through force-ve... more ABSTRACT Comprehensive information regarding neuromuscular function, as assessed through force-velocity-power (FVP) profiling, is of importance for training optimization in athletes. However, neuromuscular function is highly task-specific, potentially governed by dissimilarity of the overall orientation of forceapplication. The hip thrust (HT) exercise is thought to be of relevance for sprinting considering its antero-posterior force orientation and considerable hip-extensor recruitment, however, the association between their respective FVP profiles remains unexplored. Therefore, to address the concept of force orientation specificity within FVP profiling, the maximal theoretical neuromuscular capabilities of 41 professional male footballers (22.1 ± 4.1 years, 181.8 ± 6.4 cm, 76.4 ± 5.5 kg) were assessed during sprint acceleration, squat jumping (SJ) and the HT exercise. No significant associations were observed for maximal theoretical force or velocity between the three FVP profiling modalities, however, maximal theoretical power (Pmax) was correlated between sprinting and SJ (r = 0.73, P < 0.001) and HT and SJ (r = 0.44, P = 0.01), but not between sprinting and HT (r = 0.18, P = 0.36). In conclusion, although Pmax may be considered a somewhat universal lower-extremity capability, neuromuscular function is associated with substantial task-specificity not solely governed by the overall direction of force orientation.
Journal of Biomechanics, 2021
The orientation of the ground reaction force (GRF) vector is a key determinant of human sprint ac... more The orientation of the ground reaction force (GRF) vector is a key determinant of human sprint acceleration performance and has been described using ratio of forces (RF) which quantifies the ratio of the antero-posterior component to the resultant GRF. Different methods have previously been used to calculate step-averaged RF, and this study therefore aimed to compare the effects of three calculation methods on two key "technical" ability measures: decline in ratio of forces (DRF) and theoretical maximal RF at null velocity (RF0). Twenty-four male sprinters completed maximal effort 60 m sprints from block and standing starts on a fully instrumented track (force platforms in series). RF-horizontal velocity profiles were determined from the measured GRFs over the entire acceleration phase using three different calculation methods for obtaining an RF value for each step: A) the mean of instantaneous RF during stance, B) the step-averaged antero-posterior component divided by the step-averaged resultant GRF, C) the step-averaged antero-posterior component divided by the resultant of the step-averaged antero-posterior and vertical components. Method A led to significantly greater RF0 and shallower DRF slopes than Methods B and C. These differences were very large (Effect size Cohen's d = 2.06 - 4.04) and varied between individuals due to differences in the GRF profiles, particularly during late stance as the acceleration phase progressed. Method B provides RF values which most closely approximate the mechanical reality of step averaged accelerations progressively approaching zero and it is recommended for future analyses although it should be considered a ratio of impulses.
Frontiers in Sports and Active Living, 2021
To train hamstring muscle specifically to sprint, strengthening programs should target exercises ... more To train hamstring muscle specifically to sprint, strengthening programs should target exercises associated with horizontal force production and high levels of hamstring activity. Therefore, the objectives of this study were to analyze the correlation between force production capacities during sprinting and hamstring strengthening exercises, and to compare hamstring muscle activity during sprinting and these exercises. Fourteen track and field regional level athletes performed two maximal 50-m sprints and six strengthening exercises: Nordic hamstring exercises without and with hip flexion, Upright-hip-extension in isometric and concentric modalities, Standing kick, and Slide-leg-bridge. The sprinting horizontal force production capacity at low (F0) and high (V0) speeds was computed from running velocity data. Hamstring muscle performances were assessed directly or indirectly during isolated exercises. Hamstring muscle electromyographic activity was recorded during all tasks. Our res...
Scandinavian Journal of Medicine & Science in Sports, 2020
Specific force capacities might be a limiting factor for alpine skiing performance, yet there is ... more Specific force capacities might be a limiting factor for alpine skiing performance, yet there is little consensus on the capabilities in question, and whether they differ between disciplines. We aimed to test discipline (speed and technical) and performance (event‐specific world standing) effects on lower limb force‐production qualities. National‐level skiers (N = 31) performed loaded squat jumps and isometric mid‐thigh pulls to detect dynamic force output at extremely low and high velocities and maximum isometric force and rate of force development, respectively. Discipline differences were assessed via a general linear model including performance and allowing for interaction effects, with performance associations further characterized via distinct Pearson's correlations. Jump height did not differentiate disciplines, with absolute power slightly higher in speed athletes (F(1,27) = 4.42, P = .045, ω2 = 0.10), and neither variables were related to performance. Speed athletes possessed greater dynamic force at low velocities (F0; F(1,27) = 13.8, P < .001, ω2 = 0.17), and greater relative and absolute maximum isometric force (F(1,25) = 11.19‐20.70, ω2 = 0.16‐0.22, P < .003). Overall, higher ranked athletes possessed more force‐dominant profiles (F(1,27) = 16.28, ω2 = 0.34; r = 0.60 to 0.67, P < .001) and increased rate of force development characteristics (average and maximum, r = −0.50 to −0.82, P < .048). Very robust associations existed between maximum isometric force and speed performance (r = −0.88, P < .001), but only a trend for higher absolute isometric force in technical athletes (r = −0.49, P = .052). Alpine skiers display a preponderance for dynamic force output at low velocities, and isometric force for speed athletes, which highlights the interest in specific assessment and conditioning practices for ski athletes.
Sports, 2020
We tested the hypothesis that the degree of adaptation to highly focused sprint training at oppos... more We tested the hypothesis that the degree of adaptation to highly focused sprint training at opposite ends of the sprint Force-Velocity (FV) spectrum would be associated with initial sprint FV profile in rugby athletes. Training-induced changes in sprint FV profiles were computed before and after an eight-week in-season resisted or assisted sprint training protocol, including a three-week taper. Professional male rugby players (age: 18.9 ± 1.0 years; body height: 1.9 ± 0.0 m; body mass: 88.3 ± 10.0 kg) were divided into two groups based on their initial sprint FV profiles: 1) Heavy sled training (RESISTED, N = 9, velocity loss 70–80%), and 2) assisted acceleration training (ASSISTED, N = 12, velocity increase 5–10%). A total of 16 athletes were able to finish all required measurements and sessions. According to the hypothesis, a significant correlation was found between initial sprint FV profile and relative change in sprint FV profile (RESISTED: r = −0.95, p < 0.01, ASSISTED: r =...
European Journal of Applied Physiology, 2020
Purpose Lower limbs' neuromuscular force capabilities can only be determined during single sprint... more Purpose Lower limbs' neuromuscular force capabilities can only be determined during single sprints if the test provides a good fit of the data in the torque-velocity (T-V) and power-velocity (P-V) relationships. This study compared the goodness of fit of single sprints performed against traditional (7.5% of the body mass) vs. optimal load (calculated based on the force production capacity and ergometer specificities), and examined if reducing the load in fatigued state enhances TV and P-V relationship goodness of fit. Methods Thirteen individuals performed sprints before (PRE) and after (POST) a fatiguing task against different loads: (1) TRAD: traditional, (2) OPT: optimal, and (3) LOW-OPT: optimal load reduced according to fatigue levels. Results At PRE, OPT sprints presented a higher R 2 of the TV relationship (0.92 ± 0.06) and lower time to reach maximal power (P max) (48 ± 9%) when compared with TRAD sprints (0.89 ± 0.06 and 66 ± 22%, respectively, p < 0.01). At POST, the range of velocity spectrum was greater in the LOW-OPT (33 ± 4%) vs. TRAD (24 ± 3%) and OPT (26 ± 8%, p < 0.007). Similarly, the time to reach P max was lower in the LOW-OPT (46 ± 12%) vs. TRAD (76 ± 24%) and OPT (70 ± 24%, p < 0.006). Conclusion Sprints performed against an OPT load and reducing the OPT load after fatigue improve the fit of data in the TV and P-V curves. Sprints load assignment should consider force production capacities rather than body mass.
International Journal of Sports Medicine, 2018
This study aimed to compare the effect of a 40-min submaximal rowing exercise performed on ergome... more This study aimed to compare the effect of a 40-min submaximal rowing exercise performed on ergometers with fixed and free-floating designs. Heart rate, blood lactate concentration, force and rate of force development (RFD) at the handle, stroke rate, duty factor, movement kinematics of upper and lower limbs, and muscle activity of lumbar spine muscles iliocostalis and erector spinae (IC and ESL) were measured at the beginning and at the end of a 40-min rowing exercise at ~60% of peak power output, in eleven competitive rowers. Force of lumbar extension decreased, and blood lactate increased following submaximal exercise on both ergometers. No changes in RFD, duty factor, and muscle activity of IC occurred in response to submaximal exercise. Rowing on DYN elicited higher heart rate and modified rowing kinematics (stroke rate, acceleration of the lower limbs) without changes in temporal or force application patterns compared to rowing on STAT at the same power output. Rowing on DYN wa...
Journal of Strength and Conditioning Research, 2020
Seasonal changes in the sprint acceleration force-velocity profile of elite male soccer players. ... more Seasonal changes in the sprint acceleration force-velocity profile of elite male soccer players. J Strength Cond Res XX(X): 000-000, 2020-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 (P max), decrease in the ratio of horizontal-to-resultant force (D RF), and maximal ratio of horizontal-to-resultant force (RF peak). F 0 (effect size [ES] range 5 0.83-0.93), P max (ES range 5 0.97-1.05), and RF peak (ES range 5 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 D RF (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.
Experimental Gerontology, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Isokinetics and Exercise Science, 2008
The aim of this study was to describe elliptical cycle locomotion by muscular, kinematics, physio... more The aim of this study was to describe elliptical cycle locomotion by muscular, kinematics, physiological and perceptual parameters during submaximal and maximal exercises. Seven men performed an incremental test until exhaustion. Pulse rate, ratings of perceived exertion (6-20 Borg's scale), muscular activity of 8 muscles (higher and lower limbs muscles) and elbow, shoulder, hip and knee joint amplitudes were continuously recorded. Pulse rate reached about 70% of the theoretical maximal pulse rate after 3 minutes of submaximal exercise and about 95% at the end of the maximal exercise; the sensation of this effort being respectively described as "weak" and "very hard". EMG analysis indicated that all investigated muscles were activated, especially knee and hip extensor muscles. Kinematic analysis showed that all joints were activated especially the elbow, shoulder and knee. The elliptical cycle locomotion led to global body activation (both higher and lower limbs activity) and therefore induced a relatively significant cardiac activation even at low intensity. We therefore suggest that elliptical cycle locomotion is a unique pattern.
Footwear Science, 2019
Objective: To investigate the relationship between the perception of cushioning and variable meas... more Objective: To investigate the relationship between the perception of cushioning and variable measured using tibia acceleration in heel-toe running. Method: Ten rearfoot strikers' runners ran at 3.9 m.s À1 on a stiff treadmill in seven footwear conditions presenting different mechanical properties through midsole geometries and/or materials. The perceived cushioning was quantified through a 100-mm visual analogic scale. Tibia accelerations were measured using a triaxial accelerometer from which six variables of interest were extracted based on time and frequency analyses. After pooling data of each subject in each condition (n ¼ 70), Pearson correlation coefficients were calculated to test the correlation between the perceived cushioning and each biomechanical variables. The Cohen's d effect size was calculated for significant correlation. Results: Significant correlations were found between the perceived cushioning and three axial acceleration-related variables which are the axial acceleration peak (r ¼ À0.246, p ¼ .04, small correlation), the kurtosis coefficient of the axial acceleration peak (r ¼ À0.281, p ¼ .056, small correlation), and the power spectral density of the axial acceleration within the 10-20 Hz bandwidth (r ¼ À0.300, p ¼ .018, small correlation). Conclusion: The present study highlights that the perception of running footwear cushioning was correlated to tibia impact peak and tibia vibration magnitude. Besides, no variable extracted from the transverse component of tibia acceleration was correlated to cushioning perception. These findings could have practical implications in running footwear design.
Isokinetics and Exercise Science, 2007
This study analysed muscular, mechanical and physiological parameters using a circular chainring ... more This study analysed muscular, mechanical and physiological parameters using a circular chainring (CC) and a non circular Osymetric chainring (OC). OC was characterized by the use of a lower radius during top and bottom dead center and a higher radius during downstroke and upstroke phases. Twelve triathletes performed (i) an 8 min submaximal test and (ii) two 8 s maximal sprint tests. Gross efficiency was calculated during the submaximal test. Instantaneous external force and pedalling rate were recorded and the instantaneous net crank torque was calculated during both tests. Lower limb muscles coordination pattern (timing and magnitude) were also recorded. During the submaximal test, the only significant differences were the lower net crank torque of OC vs. CC at 0 • and 180 • and the higher net crank torque of OC vs. CC at 90 • (P < 0.05). Concerning the sprint test, the only significant difference was the higher burst duration of the biceps femoris muscle with OC (P < 0.05). Present results indicate that OC facilitated mechanically the foot path at 0 • and 180 •. Nevertheless, this mechanical effect did not seem to be sufficient to improve performance since the muscles coordination pattern was not modified.
Measuring the ground reaction forces (GRF) underlying sprint acceleration is important to underst... more Measuring the ground reaction forces (GRF) underlying sprint acceleration is important to understanding the performance of such a common task, but until recently, direct measurements of GRF during sprinting were limited to only a few steps per trial. A simple method (SM) based on displacement- or velocity-time data fitted by an exponential model and basic computations applied to the runner’s center of mass was developed to estimate GRF across an entire sprint acceleration. The SM was validated against compiled force plate (FP) measurements, but because multiple-trials were required to generate a single acceleration profile fatigue and error may have introduced noise into the analyses. In this study, we replicated the original validation by comparing the main sprint kinetics and force-velocity-power variables (e.g. GRF and its horizontal and vertical components, mechanical power output, ratio of horizontal component to resultant GRF) between synchronized FP data and SM data derived f...
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Papers by Pierre Samozino