We compared different approaches to analyze running mechanics alterations during repeated treadmill sprints. Thirteen active male athletes performed five 5-second sprints with 25 seconds of recovery on an instrumented treadmill. This approach allowed continuous measurement of running kinetics/kinematics and calculation of vertical and leg stiffness variables that were subsequently averaged over 3 distinct sections of the 5-second sprint (steps 2–5, 7–10, and 12–15) and for all steps (steps 2–15). Independently from the analyzed section, propulsive power and step frequency decreased with fatigue, while contact time and step length increased (P < .05). Except for step frequency, all mechanical variables varied (P < .05) across sprint sections. The only parameters that highly depend on running velocity (propulsive power and vertical stiffness) showed a significant interaction (P < .05) between the analyzed sections, with smaller magnitude of fatigue-induced change observed for steps 2–5. Considering all steps or only a few steps during early, middle, or late phases of 5-second sprints provides similar mechanical outcomes during repeated treadmill sprinting, although acceleration induces noticeable differences between the sections studied. Furthermore, quantifying mechanical alterations from the early acceleration phase may not be readily detectable, and is not recommended.
Comparison of Four Sections for Analyzing Running Mechanics Alterations During Repeated Treadmill Sprints
Olivier Girard, Franck Brocherie, Jean-Benoit Morin, Francis Degache, and Grégoire P. Millet
Opposition Skill Efficiency During Professional Rugby Union Official Games Is Related to Horizontal Force-Production Capacities in Sprinting
Paul Glaise, Isabelle Rogowski, Pierre Samozino, Jean-Benoit Morin, Baptiste Morel, and Cyril Martin
Purpose: This study aimed to determine relationships between parameters of force-production capacity in sprinting and opposition skill efficiency in rugby union games according to position. Methods: The sprint force–velocity profile of 33 professional rugby union players divided into 2 subgroups (forwards and backs) was measured on a 30-m sprint. Skill efficiencies (in percentage) of offensive duels, tackles, and rucks were assessed using objective criteria during 12 consecutive competitive games. Pearson correlation was used to determine the relationships between parameters of horizontal force-production capacity in sprinting (maximum propulsive power, theoretical maximum force [F 0], theoretical maximum velocity, maximum ratio of horizontal force [RFmax], and rate of decrease of this ratio of forces with increasing velocity) and skill efficiencies. Two multiple linear regression models were used to observe whether skill efficiencies could depend on determinants of horizontal force application in low- or high-velocity conditions. A first model including F 0 and theoretical maximum velocity was used as a macroscopic analysis, while a second model including RFmax and rate of decrease of this ratio of forces with increasing velocity was used as microscopic analysis to determine the most significant determinants of skill efficiency. Results: All skill efficiencies were strongly correlated with maximum propulsive power in forwards and backs. In forwards, F 0 and RFmax were the key predictors of dueling, rucking, and tackling efficiency. In backs, F 0 was the main predictor of dueling and rucking efficiency, whereas RFmax was the key predictor of dueling and tackling efficiency. F 0 and theoretical maximum velocity equivalently contributed to tackling performance. Conclusions: In rugby union forward and back players, skill efficiency is correlated with maximum propulsive power and may be more explained by horizontal force-production capacity and mechanical effectiveness at lower velocities than at higher velocities.
Concurrent Validity of GPS for Deriving Mechanical Properties of Sprint Acceleration
Ryu Nagahara, Alberto Botter, Enrico Rejc, Masaaki Koido, Takeshi Shimizu, Pierre Samozino, and Jean-Benoit Morin
To test the concurrent validity of data from 2 different global positioning system (GPS) units for obtaining mechanical properties during sprint acceleration using a field method recently validated by Samozino et al.
Thirty-two athletes performed maximal straight-line sprints, and their running speed was simultaneously measured by GPS units (sampling rate: 20 or 5 Hz) and either a radar or laser device (devices taken as references). Lower-limb mechanical properties of sprint acceleration (theoretical maximal force, theoretical maximal speed, maximal power) were derived from a modeling of the speed–time curves using an exponential function in both measurements. Comparisons of mechanical properties from 20- and 5-Hz GPS units with those from reference devices were performed for 80 and 62 trials, respectively.
The percentage bias showed a wide range of overestimation or underestimation for both systems (-7.9% to 9.7% and -5.1% to 2.9% for 20- and 5-Hz GPS), while the ranges of its 90% confidence limits for 20-Hz GPS were markedly smaller than those for 5-Hz GPS. These results were supported by the correlation analyses.
Overall, the concurrent validity for all variables derived from 20-Hz GPS measurements was better than that obtained from the 5-Hz GPS units. However, in the current state of GPS devices’ accuracy for speed–time measurements over a maximal sprint acceleration, it is recommended that radar, laser devices, and timing gates remain the reference methods for implementing the computations of Samozino et al.
A Simple Method for Measuring Stiffness during Running
Jean-Benoît Morin, Georges Dalleau, Heikki Kyröläinen, Thibault Jeannin, and Alain Belli
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.
Concurrent Validity and Reliability of Sprinting Force–Velocity Profile Assessed With GPS Devices in Elite Athletes
Pauline Clavel, Cedric Leduc, Jean-Benoît Morin, Cameron Owen, Pierre Samozino, Alexis Peeters, Martin Buchheit, and Mathieu Lacome
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 coefficients of variation were found regarding the GPS interunit reliability. Conclusion: The GPS devices tested in this study represent a valid and reliable alternative to a radar device when assessing sprint acceleration F–v profiles in team-sport players.
Differences in Sprint Mechanical Force–Velocity Profile Between Trained Soccer and Futsal Players
Pedro Jiménez-Reyes, Amador García-Ramos, Victor Cuadrado-Peñafiel, Juan A. Párraga-Montilla, José A. Morcillo-Losa, Pierre Samozino, and Jean-Benoît Morin
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 [F 0], maximal theoretical velocity [V 0], maximal power [P max], 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 F 0 than soccer players (effect size [ES] range: 0.11–0.74), while V 0 (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 P max (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 F 0 and lower V 0 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.
Very-Heavy Sled Training for Improving Horizontal-Force Output in Soccer Players
Jean-Benoît Morin, George Petrakos, Pedro Jiménez-Reyes, Scott R. Brown, Pierre Samozino, and Matt R. Cross
Sprint running acceleration is a key feature of physical performance in team sports, and recent literature shows that the ability to generate large magnitudes of horizontal ground-reaction force and mechanical effectiveness of force application are paramount. The authors tested the hypothesis that very-heavy loaded sled sprint training would induce an improvement in horizontal-force production, via an increased effectiveness of application.
Training-induced changes in sprint performance and mechanical outputs were computed using a field method based on velocity–time data, before and after an 8-wk protocol (16 sessions of 10- × 20-m sprints). Sixteen male amateur soccer players were assigned to either a very-heavy sled (80% body mass sled load) or a control group (unresisted sprints).
The main outcome of this pilot study is that very-heavy sled-resisted sprint training, using much greater loads than traditionally recommended, clearly increased maximal horizontal-force production compared with standard unloaded sprint training (effect size of 0.80 vs 0.20 for controls, unclear between-groups difference) and mechanical effectiveness (ie, more horizontally applied force; effect size of 0.95 vs –0.11, moderate between-groups difference). In addition, 5-m and 20-m sprint performance improvements were moderate and small for the very-heavy sled group and small and trivial for the control group, respectively.
This brief report highlights the usefulness of very-heavy sled (80% body mass) training, which may suggest value for practical improvement of mechanical effectiveness and maximal horizontal-force capabilities in soccer players and other team-sport athletes.
This study may encourage further research to confirm the usefulness of very-heavy sled in this context.
Supercompensation Kinetics of Physical Qualities During a Taper in Team-Sport Athletes
Bruno Marrier, Julien Robineau, Julien Piscione, Mathieu Lacome, Alexis Peeters, Christophe Hausswirth, Jean-Benoît Morin, and Yann Le Meur
Peaking for major competition is considered critical for maximizing team-sport performance. However, there is little scientific information available to guide coaches in prescribing efficient tapering strategies for team-sport players.
To monitor the changes in physical performance in elite team-sport players during a 3-wk taper after a preseason training camp.
Ten male international rugby sevens players were tested before (Pre) and after (Post) a 4-wk preseason training camp focusing on high-intensity training and strength training with moderate loads and once each week during a subsequent 3-wk taper. During each testing session, midthigh-pull maximal strength, sprint-acceleration mechanical outputs, and performance, as well as repeated-sprint ability (RSA), were assessed.
At Post, no single peak performance was observed for maximal lower-limb force output and sprint performance, while RSA peaked for only 1 athlete. During the taper, 30-m-sprint time decreased almost certainly (–3.1% ± 0.9%, large), while maximal lower-limb strength and RSA, respectively, improved very likely (+7.7% ± 5.3%, small) and almost certainly (+9.0% ± 2.6%, moderate). Of the peak performances, 70%, 80%, and 80% occurred within the first 2 wk of taper for RSA, maximal force output, and sprint performance, respectively.
These results show the sensitivity of physical qualities to tapering in rugby sevens players and suggest that an ~1- to 2-wk tapering time frame appears optimal to maximize the overall physical-performance response.
The Potential for a Targeted Strength-Training Program to Decrease Asymmetry and Increase Performance: A Proof of Concept in Sprinting
Scott R. Brown, Erin R. Feldman, Matt R. Cross, Eric R. Helms, Bruno Marrier, Pierre Samozino, and Jean-Benoît Morin
The global application of horizontal force (F H) via hip extension is related to improvements in sprint performance (eg, maximal velocity [v max] and power [P max]). Little is known regarding the contribution of individual leg F H and how a difference between the legs (asymmetry) might subsequently affect sprint performance. The authors assessed a single male athlete for pre-post outcomes of a targeted hip-extension training program on F H asymmetry and sprint-performance metrics. An instrumented nonmotorized treadmill was used to obtain individual leg and global sprint kinetics and determine the athlete’s strong and weak leg, with regard to the ability to produce F H while sprinting. Following a 6-wk control block of testing, a 6-wk targeted training program was added to the athlete’s strength-training regimen, which aimed to strengthen the weak leg and improve hip-extension function during sprinting. Preintervention to postintervention, the athlete increased F H (standardized effect [ES] = 2.2; +26%) in his weak leg, decreased the F H asymmetry (ES = −0.64; −19%), and increased v max (ES = 0.67; +2%) and P max (ES = 3.2; +15%). This case study highlighted a promising link between a targeted training intervention to decrease asymmetry in F H and subsequent improvement of sprint-performance metrics. These findings also strengthen the theoretical relationship between the contribution of individual leg F H and global F H while sprinting, indicating that reducing asymmetry may decrease injury risk and increase practical performance measures. This case study may stimulate further research investigating targeted training interventions in the field of strength and conditioning and injury prevention.
Quantifying Neuromuscular Fatigue Induced by an Intense Training Session in Rugby Sevens
Bruno Marrier, Yann Le Meur, Julien Robineau, Mathieu Lacome, Anthony Couderc, Christophe Hausswirth, Julien Piscione, and Jean-Benoît Morin
To compare the sensitivity of a sprint vs a countermovement-jump (CMJ) test after an intense training session in international rugby sevens players, as well as analyze the effects of fatigue on sprint acceleration.
Thirteen international rugby sevens players completed two 30-m sprints and a set of 4 repetitions of CMJ before and after a highly demanding rugby sevens training session.
Change in CMJ height was unclear (–3.6%; ±90% confidence limits 11.9%. Chances of a true positive/trivial/negative change: 24/10/66%), while a very likely small increase in 30-m sprint time was observed (1.0%; ±0.7%, 96/3/1%). A very likely small decrease in the maximum horizontal theoretical velocity (V0) (–2.4; ±1.8%, 1/4/95%) was observed. A very large correlation (r = –.79 ± .23) between the variations of V0 and 30-m-sprint performance was also observed. Changes in 30-m sprint time were negatively and very largely correlated with the distance covered above the maximal aerobic speed (r = –.71 ± .32).
The CMJ test appears to be less sensitive than the sprint test, which casts doubts on the usefulness of a vertical-jump test in sports such as rugby that mainly involve horizontal motions. The decline in sprint performance relates more to a decrease in velocity than in force capability and is correlated with the distance covered at high intensity.