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Abstract: Sprinting is key in the development and final results of competitions in a range of sport disciplines, both individual (e.g., athletics) and team sports. Resisted sled training (RST) might provide an effective training method to improve sprinting, in both the acceleration and the maximum-velocity phases. However, substantial discrepancies exist in the literature regarding the influence of training status and sled load prescription in relation to the specific components of sprint performance to be developed and the phase of sprint.

Objectives
Our objectives were to review the state of the current literature on intervention studies that have analyzed the effects of RST on sprint performance in both the acceleration and the maximum-velocity phases in healthy athletes and to establish which RST load characteristics produce the largest improvements in sprint performance.

Methods
We performed a literature search in PubMed, SPORTDiscus, and Web of Science up to and including 9 January 2018. Peer-reviewed studies were included if they met all the following eligibility criteria: (1) published in a scientific journal; (2) original experimental and longitudinal study; (3) participants were at least recreationally active and towed or pulled the sled while running at maximum intensity; (4) RST was one of the main training methods used; (5) studies identified the load of the sled, distance covered, and sprint time and/or sprint velocity for both baseline and post-training results; (6) sprint performance was measured using timing gates, radar gun, or stopwatch; (7) published in the English language; and (8) had a quality assessment score > 6 points.

Results
A total of 2376 articles were found. After filtering procedures, only 13 studies were included in this meta-analysis. In the included studies, 32 RST groups and 15 control groups were analyzed for sprint time in the different phases and full sprint. Significant improvements were found between baseline and post-training in sprint performance in the acceleration phase (effect size [ES] 0.61; p = 0.0001; standardized mean difference [SMD] 0.57; 95% confidence interval [CI] − 0.85 to − 0.28) and full sprint (ES 0.36; p = 0.009; SMD 0.38; 95% CI − 0.67 to − 0.10). However, non-significant improvements were observed between pre- and post-test in sprint time in the maximum-velocity phase (ES 0.27; p = 0.25; SMD 0.18; 95% CI − 0.49 to 0.13). Furthermore, studies that included a control group found a non-significant improvement in participants in the RST group compared with the control group, independent of the analyzed phase.

Conclusions
RST is an effective method to improve sprint performance, specifically in the early acceleration phase. However, it cannot be said that this method is more effective than the same training without overload. The effect of RST is greatest in recreationally active or trained men who practice team sports such as football or rugby. Moreover, the intensity (load) is not a determinant of sprint performance improvement, but the recommended volume is > 160 m per session, and approximately 2680 m per total training program, with a training frequency of two to three times per week, for at least 6 weeks. Finally, rigid surfaces appear to enhance the effect of RST on sprint performance.

Reference
Pedro E. Alcaraz, Jorge Carlos Vivas, Bruno O. Oponjuru, and Alejandro Martinez-Rodriguez 2018. The Effectiveness of Resisted Sled Training (RST) for Sprint Performance: A Systematic Review and Meta-analysis. Sports Medicine Vol. 48, Issue 9, pp2143-2165.

Abstract – Background: It has previously been shown that conditioning activities consisting of repetitive hops have the potential to induce better drop jump (DJ) performance in recreationally active individuals. In the present pilot study, we investigated whether repetitive conditioning hops can also increase reactive jump and sprint performance in sprint-trained elite athletes competing at an international level.

Methods: Jump and sprint performances of 5 athletes wer randomly assessed under 2 conditions. The control condition (CON) comprised 8 DJs and 4 trials of 30-m sprints. The intervention condition (HOP) consisted of 10 maximal repetitive two-legged hops that were conducted 10 s prior to each single DJ and sprint trial. DJ performance was analyzed using a one-dimensional ground reaction force plate. Step length (SL), contact time (CT), and sprint time (ST) during the 30-m sprints were recorded using an opto-electronic measurement system.

Results: Following the conditioning activity, DJ height and external DJ peak power were both significantly increased by 11 % compared to the control condition. All other variables did not show any significant differences between HOP and CON.

Conclusions: In the present pilot study, we were able to demonstrate large improvements in DJ performance even in sprint-trained elite athletes following a conditioning activity consisting of maximal two-legged repetitive hops.This strengthens the hypothesis that plyometric conditioning exercises can induce performance enhancements in elite athletes that are even greater than those observed in recreationally active athletes.. In addition, it appears that the transfer of these effects to other stretch-shortening cycle activities is limited, as we did not observe any changes in sprint performance following the plyometric conditioning activity.

Reference

Jakob Kümmel, Julian Bergmann, Olaf Prieske, Andreas Kramer, Urs Granacher, Markus Gruber. 2018. Effects of conditioning hops on drop jump and sprint performance. Universitat Potsdam.


June  17, 2019 by NASE

Abstract 
Sprinting represents a result-relevant task in many sports. The correlation of sprinting performance and one-repetition maximum (1RM) in a squat has been assumed as assured. Results of the correlation with 1RM of the plantar flexors are still pending. Assuming an increasing relevance of the reactive working capacity with increasing distance, a decrease of the influence of maximum strength of the calves is conceivable.We investigated the correlation of 1RM in a calf raise and sprint performance in consecutive sections up to 30 meters. The results showed medium to strong, very significant correlations (p < 0.01) for absolute (r = −0.483 to r = −0.720) and relative (r = −0.460 to −0.577) strength, whereas an increase of the correlation throughout the course is observed.
The dynamic maximum strength of the calves is a basic prerequisite for short sprints and should be regarded as a performance reserve. 
Reference 
Sabastian Mock, Rene Hartman, Klaus Wirth, Gregor Rosenkranz, and Christoph Mickel. 2019. Correlation of dynamic strength in the standing calf raise with sprinting performance in consecutive sections up to 30 meters.  Research in Sports Medicine An International Journal Volume 26, 2018 – Issue 4

Research Study Objectives: To quantify changes in running kinetics and kinematics during a repeated-sprint test in football players, and explore the sensitivity and specificity with which these variables can identify previous hamstring injury.

Design: Western Australia State League footballers with previous unilateral hamstring injury and 20 players without completed a 10 × 6-s repeated-sprint test on a non motorized treadmill dynamometer.

Methods:Changes in horizontal force, vertical force, contact time and flight time were compared between previously injured and uninjured legs of participants.

Results:Mean horizontal force production of the previously injured leg in the injured group was 13% lower (p = 0.001), and this magnitude of change was used to identify the injured legs within the cohort with 77% specificity and 85% sensitivity. Furthermore, the area under the Receiver Operating Characteristics curve (0.846) demonstrated that the between-leg difference in mean horizontal force was a good instrument for identifying previous hamstring injury.

Conclusions:There is a greater fatigued-induced change in mean horizontal force during a repeated-sprint test in legs with previous hamstring injury than the non-injured legs of the injured players or the legs of uninjured players. Such asymmetry may contribute to impair performance in football players returning from a hamstring injury and also to the high rate of hamstring re-injury. Rehabilitation and return-to-play strategies should emphasize a reduction in asymmetry, particularly during repeated high-intensity efforts. Furthermore, binary regression and Receiver Operating Characteristic analyses suggest that changes in mean horizontal force could be used to assess risk of hamstring injury, re-injury and/or return to play.

Reference: Cameron Lord, Anthony J.Blazevich, Eric J. Drinkwater, Fadi Ma’ayah, and Plum X Metrics. 2018. Greater loss of horizontal force after a repeated-sprint test in footballers with a previous hamstring injury. Journal of Science and Medicine in Sport DOI: https://doi.org/10.1016/j.jsams.2018.06.008

This study reveals both hereditary sprint performance advantages and disadvantages of musculoskeletal structure in humans.       Abstract:
The musculoskeletal structure of the foot and ankle has the potential to influence human sprinting performance in complex ways. A large Achilles’ tendon moment arm improves the mechanical advantage of the triceps surae but also produces larger shortening velocity during rapid plantar flexion, which detracts from the force-generating capacity of the plantar flexors. The lever arm of the ground reaction force that resists the muscular plantar flexor moment during propulsive push-off is constrained in part by the skeletal structure of the foot. In this study, we measured the plantar flexion moment arms of the Achilles’ tendon, lateral gastrocnemius fascicle lengths and pennation angles, and anthropometric characteristics of the foot and lower leg in collegiate sprinters and height-matched non-sprinters. The Achilles’ tendon moment arms of the sprinters were 25% smaller on average in sprinters than in non-sprinters (P<0.001) whereas the sprinters’ fascicles were 11% longer on average (P=0.024). The ratio of fascicle length to moment arm was 50% larger in sprinters (P<0.001). Sprinters were found to have longer toes (P=0.032) and shorter lower legs (P=0.026) than nonsprinters. A simple computer simulation of the sprint push-off demonstrated that shorter plantar flexor moment arms and longer toes, like those measured in sprinters, permit greater generation of forward impulse. Simulated propulsion was enhanced in both cases by increasing the `gear ratio’ of the foot, thus maintaining plantar flexor fibre length and reducing peak fibre shortening velocity. Longer toes especially prolonged the time of contact, giving greater time for forward acceleration by propulsive ground reaction force.
Refrence
Sabrina S. M. Lee, Stephen J. Piazza. 2009. Built for speed: musculoskeletal structure and sprinting ability. Journal of Experimental Biology 212: 3700-3707; doi: 10.1242/jeb.031096

Abstract: A novel approach of analyzing complete ground reaction force waveforms rather than discrete kinetic variables can provide new insight to sprint biomechanics. This study aimed to understand how these waveforms are associated with better performance across entire sprint accelerations. Twenty‐eight male track and field athletes (100‐m personal best times: 10.88 to 11.96 seconds) volunteered to participate. Ground reaction forces produced across 24 steps were captured during repeated (two to five) maximal‐effort sprints utilizing a 54‐force‐plate system. Force data (antero‐posterior, vertical, resultant, and ratio of forces) across each contact were registered to 100% of stance and averaged for each athlete. Statistical parametric mapping (linear regression) revealed specific phases of stance where force was associated with average horizontal external power produced during that contact. Initially, antero‐posterior force production during mid‐late propulsion (eg, 58%‐92% of stance for the second ground contact) was positively associated with average horizontal external power. As athletes progressed through acceleration, this positive association with performance shifted toward the earlier phases of contact (eg, 55%‐80% of stance for the eighth and 19%‐64% for the 19th ground contact). Consequently, as athletes approached maximum velocity, better athletes were more capable of attenuating the braking forces, especially in the latter parts of the eccentric phase. These unique findings demonstrate a shift in the performance determinants of acceleration from higher concentric propulsion to lower eccentric braking forces as velocity increases. This highlights the broad kinetic requirements of sprinting and the conceivable need for athletes to target improvements in different phases separately with demand‐specific exercises.
Reference
S.L. Colver, R. Nagahara, and A.I. T. Salo. 2018. Kinetic demands of sprinting shift across the acceleration phase: Novel analysis of entire force waveforms. Scandinavian Journal of Medicine and Science in Sports. 06 April 2018 https://doi.org/10.1111/sms.13093

Abstract: Backward running (BR) is a form of locomotion that occurs in short bursts during many overground field and court sports. It has also traditionally been used in clinical settings as a method to rehabilitate lower body injuries. Comparisons between BR and forward running (FR) have led to the discovery that both may be generated by the same neural circuitry. Comparisons of the acute responses to FR reveal that BR is characterized by a smaller ratio of braking to propulsive forces, increased step frequency, decreased step length, increased muscle activity and reliance on isometric and concentric muscle actions. These biomechanical differences have been critical in informing recent scientific explorations which have discovered that BR can be used as a method for reducing injury and improving a variety of physical attributes deemed advantageous to sports performance. This includes improved lower body strength and power, decreased injury prevalence and improvements in change of direction performance following BR training. The current findings from research help improve our understanding of BR biomechanics and provide evidence which supports BR as a useful method to improve athlete performance. However, further acute and longitudinal research is needed to better understand the utility of BR in athletic performance programs.

Coaching Implications
Performance in numerous sports such as football, basketball, soccer, field hockey, rugby, lacrosse, tennis and others can be enhanced by incorporating backward sprinting into the regular training sessions both in-season and off-season. Although backward sprinting for short distances is commonly required in various sports, training to improve movement efficiency and the speed-strength of the specific muscles involved is quite uncommon. 
ReferenceAaron Uthoff, Jon Oliver, John Cronin, Craig Harrison and Paul Winwood. 2018. A New Direction to Athletic Performance: Understanding the Acute and Longitudinal Responses to Backward Running. Sports Medicine May 2018, Volume 48, Issue 5, pp 1083–1096.

This study provides new information concerning specific training exercises that elicit a higher vertically-directed ground reaction force (GRF); a key factor in determining maximum mph speed.

Abstract

External load training (ELT) is a supplemental training method used to potentially improve high intensity task performance. However, biomechanical parameters such as ground reaction forces (GRF), ground contact time, and time to peak GRF during a drop vertical jump (DVJ) following an ELT intervention have yet to be examined. Therefore, this study investigated the impact of ELT on certain biomechanical parameters of a DVJ task. Well-trained females stratified into two groups (ELT = 9, Control = 10) completed a DVJ from a 45.72 cm box onto a force platform at baseline, post-ELT, and post-detraining (DET). ELT consisted of wearing weight vests (WV) with 8% body mass for 32 h/week during daily living and 3 training sessions/week for 3 weeks. After ELT, a 3 week DET phase was completed. The control group replicated procedures without ELT intervention. The vertical, medial/lateral, and anterior/posterior components of the GRF were assessed during the initial contact, minimum force following initial contact, push-off, and second landing periods. Dependent variables were analyzed using a 2 (group) × 3 (time) mixed model ANOVA (p < .05). Significantly greater peak vertical GRF during the initial contact period was identified for the ELT group. Significant increases in the minimum vertical GRF following the initial contact period from baseline to post-ELT following the were observed for the ELT group, while significant increases in peak vertical GRF during the second landing period at post-ELT and post-DET in comparison to baseline was observed for both groups. The combination of greater vertical GRF during the initial contact period and the period following initial contact suggests that ELT may increase GRFs during a DVJ in comparison to routine training without a weighted vest.

Coaching Application

The drop vertical jump exercise should be a regular part of a training program to increase vertically-directed ground reaction force and the maximum speed phase of a sprint.

Reference

Jeffrey D. Simpson, Brandon L. Miller, Erik K. O”Neal, Harish Chandlerr and Adam C. Knight. 2018. Ground reaction forces during a drop vertical jump: Impact of external load training.Human Movement Science Volume 59, June 2018, Pages 12-19

Abstract

This cross-sectional study aimed to investigate the association between hamstring muscle peak torque and rapid force capacity (rate of torque development: RTD) versus sprint performance in elite youth football players.

Methods:

Thirty elite academy youth football players (16.75 ± 1.1 years, 176.9 ± 6.7 cm, 67.1 ± 6.9 kg) were included. Isometric peak torque (Nm/kg) and early (0-100 ms) and late (0-200 ms) phase RTD (RTD100, RTD200) (Nm/s/kg) of the hamstring muscles were obtained as independent predictor variables. Sprint performance was assessed during a 30-m sprint trial. Mechanical sprint variables (maximal horizontal force production (FH0) (N/kg); maximal theoretical velocity (V0) (m/s); maximal horizontal power output (Pmax) (W/kg)) and sprint split times (0-5 m; 0-15 m; 0-30 m; 15-30 m) (s) were derived as dependent variables. Subsequently, linear regression analysis was conducted for each pair of dependent and independent variables.

Results:

Positive associations were observed between hamstring RTD100 and FH0 (r2=0.241, p=0.006) and Pmax (r2=0.227, p=0.008). Furthermore, negative associations were observed between hamstring RTD100 and 0-5 m (r2=0.206, p=0.012), 0-15 m (r2=0.217, p=0.009) and 0-30 m sprint time (r2=0.169, p=0.024). No other associations were observed.

Conclusion:

The present data indicate that early-phase (0-100 ms) rapid force capacity of the hamstring muscles plays an important role for the acceleration capacity in elite youth football players. In contrast, no associations were observed between hamstring muscle function and maximal sprint velocity.

Coaching Application:

Strength training focusing on improving early-phase hamstring rate of force development may contribute to enhance sprint acceleration performance in this athlete population.

Reference

Lassee Ishol, Per Aagaard, Mathias F. Nielsen, Kasper B. Thorton. 2018. The Influence of Hamstring Muscle Peak Torque and Rate Of Torque Development for Sprinting Performance in Football Players: A Cross-Sectional Study. Human Kinetics, Volume:0 Issue: 0 Pages:1-27 doi: 10.1123/ijspp.2018-0464

Abstract:

The purpose of this study was to determine the braking and propulsive phase kinetic variables underpinning reactive strength in highly trained sprint athletes in comparison with a nonsprint-trained control group. Twelve highly trained sprint athletes and 12 nonsprint–trained participants performed drop jumps (DJs) from 0.25, 0.50, and 0.75 m onto a force plate. One familiarization session was followed by an experimental testing session within the same week. Reactive strength index (RSI), contact time, flight time, and leg stiffness were determined. Kinetic variables including force, power, and impulse were assessed within the braking and propulsive phases. Sprint-trained athletes demonstrated higher RSI vs. nonsprint–trained participants across all drop heights {3.02 vs. 2.02; ES (±90% confidence limit [CL]): 3.11 ± 0.86}. This difference was primarily attained by briefer contact times (0.16 vs. 0.22 seconds; effect size [ES]: −1.49 ± 0.53) with smaller differences observed for flight time (0.50 vs. 0.46 seconds; ES: 0.53 ± 0.58). Leg stiffness, braking and propulsive phase force, and power were higher in sprint-trained athletes. Very large differences were observed in mean braking force (51 vs. 38 N·kg−1; ES: 2.57 ± 0.73) which was closely associated with contact time (r ±90% CL: −0.93 ± 0.05). Sprint-trained athletes exhibited superior reactive strength than nonsprint–trained participants. This was due to the ability to strike the ground with a stiffer leg spring, an enhanced expression of braking force, and possibly an increased utilization of elastic structures. The DJ kinetic analysis provides additional insight into the determinants of reactive strength which may inform subsequent testing and training.

Coaching Application

This study reinforces the importance of various training techniques to improve ground reaction force – the force applied the after the foot strikes the ground each stride during the start, acceleration, and maximum speed phase of a short sprint. In addition, leg stiffness at ground contact and braking and propulsive force are higher in trained sprinters indicating the value of proper sprint mechanics and speed strength training.

Reference

Douglas, J, Pearson, S, Ross, A, and McGuigan, M. Kinetic determinants of reactive strength in highly trained sprint athletes. J Strength Cond Res 32(6): 1562–1570, 2018