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The Potential for a Targeted Strength-Training Program to Decrease Asymmetry and Increase Performance: A Proof of Concept in Sprinting

March 2017
International Journal of Sports Physiology and Performance 12(10)

DOI:10.1123/ijspp.2016-0590

Authors:

Scott R. Brown

Aquinas College

Matt R Cross

Auckland University of Technology

Eric R Helms

Auckland University of Technology

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Purpose The global application of horizontal force (FH) via hip extension is related to improvements in sprint performance (e.g. maximal velocity [vmax] and power [Pmax]). Little is known regarding the contribution of individual-leg FH and how a difference between the legs (asymmetry) might subsequently affect sprint performance. Methods We assessed a single male athlete for pre-post outcomes of a targeted hip extension training programme on FH asymmetry and sprint performance metrics. An instrumented non-motorised treadmill was used to obtain individual-leg and global sprint kinetics and determine the athlete’s strong and weak leg, with regards to the ability to produce FH while sprinting. Following a 6-week control-block of testing, a 6-week targeted training programme was added to the athlete’s strength training regime which aimed to strengthen the weak leg and improve hip extension function while sprinting. Results Pre- to post-intervention, the athlete increased FH (standardised effect [ES] = 2.2; +26%) in his weak leg, decreased the FH asymmetry (ES = -0.64; -19%) and increased vmax (ES = 0.67; +2%) and Pmax (ES = 3.2; +15%). Conclusions This case-study highlighted a promising link between targeted training intervention to decrease asymmetry in FH and subsequent improvement of sprint performance metrics. These findings also strengthen the theoretical relationship between the contribution of individual-leg FH and global FH 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.

Relative horizontal force (Newtons per kilogram [N·kg −1 ]) produced during maximal sprinting on the instrumented nonmotorized treadmill for each individual leg across the 12 weeks. Solid gray and white circles represent the strong and weak legs, respectively. Solid black diamonds with vertical bars represent means and SD during the control block (weeks 1-6) and intervention block (weeks 10-12). Percentages are asymmetry scores for the difference between the means of the 2 legs at the end of the control block and intervention block. Shaded areas (solid light gray, dashed medium gray, and solid medium gray) correspond to case study block (control, transition, and intervention).

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Relative horizontal force (Newton per kilogramme [N∙kg-1]) produced during maximal sprinting on the instrumented non-motorised treadmill for each individual leg across the 12 weeks. Solid grey and white circles represent the strong and weak legs, respectively. Solid black diamonds with vertical bars represent means and standard deviations (SD) during the control- (weeks 1–6) and intervention-block (weeks 10–12). Percentages are asymmetry scores for the difference between the means of the two legs at the end of the control- and intervention-blocks. Shaded areas (solid light-grey, dashed medium-grey and solid medium-grey) correspond to case-study block (control, transition and intervention).

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Force-velocity-power sprint profiling on the instrumented non-motorised treadmill with four loads (0 [un-braked], 33, 66 and 99%). Solid white circles and solid light-grey lines represent control-block (weeks 1–6), dashed medium-grey lines represent transition-block (weeks 7–9) and solid grey circles and solid medium-grey lines represent intervention-block (weeks 10–12). Solid black diamonds with vertical bars represent mean maximal power (Pmax) and standard deviations (SD). All linear force-velocity and polynomial power-velocity fits showed R2 > 0.999.

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Evaluation of the Training Session in Elite Paralympic Powerlifting Athletes Based on Biomechanical and Thermal Indicators

Article

Full-text available

Aug 2023

Background: Paralympic powerlifting (PP) is performed on a bench press, aiming to lift as much weight as possible in a single repetition. Purpose: To evaluate thermal asymmetry and dynamic force parameters with 45 and 80% 1 Repetition Maximum (1 RM) in PP athletes. Methods: Twelve elite PP male athletes were evaluated before and after a training session regarding skin temperature (thermography) and dynamic force indicators (Average Propulsive Velocity-MPV, Maximum Velocity-VMax, and Power). The training consisted of five series of five repetitions (5 × 5) with 80% 1 RM. The force indicators and dynamics before and after (45% 1 RM) were evaluated in series "1" and "5" with 80% 1 RM. Results: The temperature did not present asymmetry, and there were differences between the moment before and after. In MPV, Vmax, and Power, with 45% 1 RM, there were differences both in asymmetry and in moments (p < 0.005). With 80% 1 RM, asymmetry was observed, but no differences between moments (p < 0.005). Conclusion: No thermal asymmetry was observed. There were reductions in MVP and VMax at 45 and 80% 1 RM but without significant differences between time points (before and after). However, there was asymmetry in the moments before and after within a safety standard, where Paralympic powerlifting was safe in terms of asymmetries.

The Effect of Unilateral Versus Bilateral Strength Training on Isometric-Squat Peak Force and Interlimb Asymmetry in Young, Recreationally Strength-Trained Men

Article

Jan 2023
Int J Sports Physiol Perform

Purpose: To compare the effects of bilateral strength training (BLST) versus unilateral strength training (ULST) on changes in peak force (PF) and interlimb asymmetry (ILA) in the isometric squat at a 120° knee angle (ISq120). Method: A total of 31 young, recreationally strength-trained men performed either BLST (n = 18) or ULST (n = 13), twice per week for 6 weeks. The total number of repetitions, duty cycle, and effort were standardized between training groups (ie, differing only in the exercises performed). Changes in PF and ILA were assessed pretraining and posttraining. Results: Comparable increases in PF were observed in the BLST group (mean [SD] change; 17.4% [20.5%], P = .001, standardized mean difference [SMD] = 0.45) and the ULST group (11.4% [19.1%], P = .042, SMD = 0.25). No significant changes in symmetry index (SI) scores were observed following BLST (mean [SD] change; 0 [5.7], P = .526, SMD = -0.12) or ULST (+3 [6.0], P = .702, SMD = 0.4). Individual analyses of subjects with marked ILA (ie, baseline SI score > baseline coefficient of variation) revealed a trend toward BLST being more effective at attenuating SI scores in the ISq120. Conclusions: Overall, both BLST and ULST are effective for increasing ISq120 PF. However, it appears that BLST may be more effective at reducing SI scores in those with marked ILA.

Countermovement Jump in Female Sprinters: Kinetic Parameters and Asymmetry

Article

Full-text available

May 2022

Analyzing asymmetry from biomechanical parameters of the lower extremities has be�come a standard practice for accurate assessment of athletic performance, injury prevention, and rehabilitation. The aims of this study were (1) to determine differences between explosive strength and asymmetry of the lower extremities using kinetic parameters of the CMJ jump test in young female athletics, and (2) to investigate correlation between speed and asymmetry, as speed and kinetic parameters. The two groups of nine female sprinters (mean ± SD; G1-age 15.6 ± 1.34 years, height 170.1 ± 0.57 cm, body mass 62.54 ± 7.73 kg, and BMI 21.6 ± 2.05; G2-age 16.2 ± 1.3 years, height 168.4 ± 0.61 cm, body mass 57.69 ± 3.12 kg, and BMI 20.37 ± 1.38) performed the CMJ test without using an arm swing, as well as a 100 m test. Two tensiometric platforms were used for the kinetic parameters and asymmetry. Asymmetry was calculated by an AI equation, and the values of the takeoff velocities and jump height parameters were obtained by integral formula and the trape�zoidal rule of impulse-momentum methods. The results show differences in four kinetic parameters: height (G1- 26.82 ± 3.56 cm, vs. G2- 17.45 ± 2.01 cm), concentric impulse, (G1- 96.05 ± 16.95 N·s, vs. G2- 68.41 ± 4.77 N·s), takeoff velocity, (G1- 2.29 ± 0.14 m/s, vs. 1.83 ± 0.12 m/s), and concentric velocity, m/s (G1- 1.5 ± 0.175 m/s, vs. 1.17 ± 0.122 m/s), as well as a negative strong and very strong correlation between asymmetry and kinetic parameters for three parameters: Peak Force (G1- r = −0.878, and all subjects r = −0.633), Eccentric Impulse of left leg (G1- r = −0.865) and Concentric Impulse of right leg (G2- r = −0.878), (p <.05). The younger sprinters did not show the principle of muscle activation in the form of a longer preparatory phase of contact time, eccentric and concentric phase, as well as a force impulse that is optimal. There was no correlation between asymmetry and sprint performance

Evaluating Novel Methods of Classifying Interlimb Asymmetries Within Collegiate American Football Players

Article

Full-text available

Mar 2022

International Journal of Exercise Science 15(6): 473-487, 2022. Over the last few years, researchers and sport scientists have expressed an increased interest in the effects of interlimb asymmetry on aspects of sport performance such as jumping, sprinting, and changing direction. This study aimed to evaluate the diagnostic utility of three different means of classifying asymmetry to highlight if a 6-week resistance training intervention can meaningfully reduce levels of asymmetry, and to determine the relation between asymmetry reduction and improvements in change of direction (CoD) performance, if any. Eighteen, division-two collegiate American football skill position players completed all pre-and post-intervention procedures. These procedures involved the completion of the Bulgarian Split Squat (BSS) exercise from which asymmetries in relative average power (Rel.AP), and relative peak power (Rel.PP) were derived. Additionally, participants completed three repetitions within the 505 and L-drill tests to quantify CoD performance. Results from our study show that participants classified as asymmetrical, exhibiting observed asymmetry in Rel.PP scores larger than the sample mean plus one standard deviation, had the greatest likelihood of reducing asymmetry (OR = 6.99, 95% CI: 1.4, 12.5) and improving L-drill performance (OR = 1.33, 95% CI:-2.1, 4.8). Further, our training intervention meaningfully reduced Rel.AP asymmetry (p = 0.027, Cohen's d = 0.73). At the group level, these reductions in asymmetry were accompanied by improvements in L-drill performance that were larger than the sample smallest worthwhile change (SWC). At the individual level, however, change scores in asymmetry and change scores in CoD performance only showed small, non-significant correlations.

The Effects of Training Interventions on Interlimb Asymmetries: A Systematic Review With Meta-analysis

Article

Full-text available

Dec 2021
Strength Condit

Inter-limb asymmetries have been recently investigated in athletic populations. However, the effects of training interventions on inter-limb asymmetries have been scarcely examined. Therefore, the aim of this study was to determine the effects of training interventions on changes in inter-limb asymmetries from pre-to post-training. Furthermore, to examine the effects of training programs on intervention groups compared to control groups. A database search was completed (MEDLINE, CINAHL, and SPORTDiscus). Eight studies were then included in the meta-analysis. Results showed small reductions in inter-limb asymmetries in single leg broad jump (SLBJ) and change of direction (COD) speed from pre-to post-training interventions, whereas moderate effects were found in single leg countermovement jump (SLCMJ) and single leg (SL) lateral jump. When comparing the training interventions to the control groups, results showed small effects in favour of the training groups for reducing inter-limb asymmetries in SLBJ and large effects in SLCMJ, and COD speed. Thus, training interventions can evoke small to moderate reductions in inter-limb asymmetries from pre-to post-training programs. Strength training performed unilaterally or bilaterally may elicit these reductions. Furthermore, training interventions showed larger effects compared to the control groups in reducing inter-limb asymmetries. However, further research is needed.

An exploration into the assessment of hip extension strength and its importance for performance in professional soccer.

Thesis

Dec 2020

***For a copy of this full text please send a private message on research gate to Tom King.*** _____________________________________________________________________________________ Hip extension is a joint action that contributes to athletic movement during performance in various sports. Within the sport of professional soccer, high intensity efforts encompass an important proportion of athletic movement and optimal hip extensor functioning can be seen as a crucial action for the successful performance of such actions. Perhaps related to the importance placed upon high intensity efforts in soccer, the number of hamstring strain injuries that occur are of major concern to practitioners within the field. As such, great efforts are made to establish methods of managing and mitigating these injuries, one of which being improving hip extension function. Methods of establishing an individual’s maximal hip extension strength capacity are available yet are not void of several clinical and practical limitations. As such, understanding the relationship between the specific ability of hip extension with performance and injury related measures are difficult to investigate. Therefore, it may be of use to investigate the development of new strength assessment methods. _____________________________________________________________________________________ In study 1 (chapter 3) a framework of considerations was outlined that surround various methodological and theoretical concepts believed to influence the subsequent validity, reliability and operational success of hip extension assessment tools in the applied field. These considerations arose from information in previous scientific research and from the research team’s (PhD candidate and supervisors) wealth of experience working in applied professional sport. Throughout the framework of considerations, the assessment tools currently available for hip extension strength were critiqued and a rationale for the development of a new tool was outlined. Further into the chapter the adherence of these considerations was presented throughout the development of a new assessment tool (Hip Extension Bench). Finally, the ultimate section of this chapter then introduced information surrounding practical application of the Hip Extension Bench. _____________________________________________________________________________________ In study 2 (chapter 4) the sensitivity of the Hip Extension Bench was investigated where the research team assessed muscle activity and force changes in response to various hip flexion positions. The investigations were undertaken with a mixed population of elite soccer players (n = 10), competitive sprinters (n = 10) and recreationally active males (n = 5) and consisted of assessment across 6 different hip positions (70, 60, 45, 30, 15 and 0 hip flexion). Results displayed precise and specific changes in individual hip extensor muscle activity and force production under maximal isometric contractions at different hip joint angles. Gluteus maximus muscle peak activity was pronounced at positions of inner range hip flexion (0 and 15 deg) whereas maximum force and biceps femoris long head and semitendinosus peak activity was pronounced at positions of greater hip flexion (60 and 70 deg). These data suggest that the Hip Extension Bench can be manipulated to selectively target specific hip extensor muscles and careful precisions must be adhered to upon assessment setup to confirm standardised conditions. _____________________________________________________________________________________ In study 3 (chapter 5) the test-retest reliability of the Hip Extension Bench under non- fatigued conditions was investigated. A group of 40 elite youth soccer players and 15 competitive sprinters undertook maximal isometric hip extension contractions at two angles (15 and 60 deg) on two occasions with a minimum and maximum of 7 and 14 days between test days. Generally, both cohorts demonstrated good reliability of bilateral and unilateral isometric hip extension strength assessments. The findings also demonstrated the difficulties surrounding data collection in the applied field where several complications may arise that influence the subsequent findings and informed decisions that are made on reflection of the data. _____________________________________________________________________________________ In study 4 (chapter 6) the first implementation of the Hip Extension Bench within research surrounding isometric hip extension strength and sprint-acceleration and jump performance associations was presented. A sample of 10 competitive sprinters completed a minimum of three 40 m sprints on test day 1 and a comprehensive battery of strength and power assessments on test day 2 with a minimum and maximum of 7 and 14 days between each test day. The main findings confirmed that isometric hip extension strength was highly correlated with several force-based variables of sprint-acceleration performance (theoretical maximum force; F0, total force; FT Peak, total force across distances of 2, 20 and 40 m; FT 2, 20 & 40 m, mean horizontal force; FH Mean, horizontal force across distances of 2 and 20 m; FH 2 & 20 m and peak power; Pmax) and jump performance in the horizontal direction (the sum of left and right leg horizontal countermovement jumps; UL HCMJ Sum). These findings provide evidence for the role and importance of hip extension strength, specifically under isometric conditions, in high intensity effort performance. _____________________________________________________________________________________ Overall, these findings suggest that a new assessment tool for isometric hip extension strength has been developed that is suitable for application in the environment of applied professional sport. The findings also confirmed the important of hip extension for high intensity effort performance and in conclusion provide a strong rationale for the implementation of the Hip Extension Bench for future research and application in performance and injury management.

A Narrative Review of Limb Dominance: Task- Specificity and the Importance of Fitness Testing

Article

Aug 2020

Preferential limb function must be sustained through repetitious asymmetrical activities for continuous athletic development and ultimately, optimal athletic performance. As such, the prevalence of limb dominance and between-limb differences are common in athletes. Severe between-limb differences have been associated with reductions in athletic performance and increased injury risk in athletes. However, in the current literature, the terms limb preference and limb dominance have been used interchangeably. Together, these terms include a limb which is subjectively preferred and one that is objectively dominant in one or more performance measures from a variety of athletic tasks. In this review, we 1) discuss reported correspondence between task-specific limb preference and limb dominance outcomes in athletes, 2) provide greater context and distinction between the terms limb preference and limb dominance, and 3) to offer pragmatic strategies for practitioners to assess context-specific limb dominance. A limb which is subjectively preferred is not necessarily objectively dominant in one or more athletic qualities or sport-specific tasks. Further to this, a limb which is objectively superior in one task may not exhibit such superiority in a separate task. Thus, limb preference and limb dominance are both task-specific. As such, we propose that practitioners intentionally select tasks for limb dominance assessment which resemble the most relevant demands of sport. Because limb dominance profiles are inconsistent, we suggest that practitioners increase assessment frequency by integrating limb dominance testing into standard training activities. This will allow practitioners to better understand when changes reflect sport-specific adaptation versus potential performance or injury ramifications.

Increased Resisted Sprinting Load Decreases Bilateral Asymmetry in Sprinting Kinetics Among Rugby Players

Article

Feb 2020

Mangine, GT, McNabb, JA, Feito, Y, VanDusseldorp, TA, and Hester, GM. Increased resisted sprinting load decreases bilateral asymmetry in sprinting kinetics among rugby players. J Strength Cond Res 35(11): 3076-3083, 2021-To examine the effect of resistance on sprinting kinetics and their bilateral symmetry, 15 male collegiate rugby players completed 3 maximal, 40-m sprints (S1-S3) while tethered to a robotic resistance device. Minimal resistance (9.81 N) was used on S1 (familiarization) and S2, while S3 was loaded at 147.1 N. Peak and average (AVG) power (P), velocity (V), force (F), and rate of force development (RFD) were averaged within the first stride, the acceleration and peak velocity phases, as well as across the 40-m sprint. Bilateral percent differences were calculated from step values within each stride for each variable. Friedman's rank tests revealed differences (p ≤ 0.02) between sprint trials and phases for each variable. During both trials, most kinetic measures increased from the first stride through the peak velocity phase (p ≤ 0.036), although reductions in RFDPEAK (p ≤ 0.015) and RFDAVG (S3 only; p < 0.001) were observed within the peak velocity phase. Comparatively, sprinting velocity and average stride (length and duration) were less during S3, while all other measures were greater within each phase. Across the entire 40-m sprint, S3 reduced (p < 0.05) asymmetry for average stride length (-2.1 to -17.0%), VPEAK (-0.8 to -4.9%), VAVG (-2.3 to -6.0%), FPEAK (-5.6 to -8.7%), FAVG (-3.4 to -7.1%), RFDPEAK (-4.3 to -36.7%), PPEAK (-5.9 to -12.4%), and PAVG (-5.4 to -9.8%). Applying sprinting resistance may be a tool for reducing acute bilateral asymmetries in sprinting kinetic measures.

The Effect of Application of Asymmetry Evaluation in Competitive Sports: A Systematic Review

Article

Full-text available

Nov 2022

Zixiang Gao

It has been widely asserted that the two side human body asymmetries are detrimental to the health and performance alike of athletes in training and competition. The current systematic review aims to promote a more refined understanding of bilateral asymmetry in competitive sports and explore the application of asymmetric assessment to performance, injury and rehabilitation. A systematic review of the articles was undertaken using the Web OF Science, ScienceDirect and PubMed databases in May 2022, retrieving a total of 386 studies published in all years. The study quality scoring system developed was used by two evaluators to assess the grading article quality. Twenty-two articles fulfilled our eligibility criteria. The average quality assessment rate for selected articles in this systematic review is 94.4 ± 6.3% (from 0.78 to 1.00). Articles investigated the effect of the application of asymmetry evaluation in one of the following sports types: gait related sports, upper limb sports, ball sports and multifarious sports. Asymmetry has a positive effect on physical performance in athletes engaged in upper limb movements, but it may lead to potential risk of injures in gait-related sports. When examining bilateral asymmetries among athletes in multifarious sports, the studies were primarily used to investigate the relationship between injury rehabilitation and return-to sport, with mixed findings. Further research needs to determine the possible injury-inducing threshold of asymmetry in multifarious sports and the detailed relationship between bilateral asymmetry and sports performance.

The Role of Resistance Training in Strategies to Reduce Injury Risk

Chapter

Jan 2022

Oliver Gonzalo-Skok

The main aim of this chapter is to review the role of strength training in reducing the risk of sports injuries, which are a major concern in any sport. As strength training has been recognized as one of the best strategies to minimize the risk of injury, we will focus on the current evidence-based information and how we can directly apply this to our practices. This chapter will also explain an alternative neuromuscular training approach based on dynamic correspondence, using the most common actions players employ throughout a soccer game (our examples are taken from soccer but can be extrapolated to other sports). Traditionally, soccer players train by lifting weights bilaterally in the vertical axis, focused on the concentric phase of the movement and with no making-decision actions. However, it is helpful to train several force-vectors (three-dimensional movements) applying force unilaterally (instead of bilaterally) with emphasis on the eccentric phase, and including stochastic or unexpected situations to mimic real game situations. After reviewing the theoretical concepts, a practical viewpoint is presented, allowing coaches and trainers to adapt their practices to the specific requirements of their sport.

Gait Asymmetry During 400- to 1000-m High-Intensity Track Running in Relation to Injury History

Article

Full-text available

Dec 2016

Purpose: The aim of the present study was to quantify gait asymmetry in well-trained runners, with and without previous injuries during interval training sessions incorporating different distances. Methods: Twelve well-trained runners participated in eight high-intensity interval training sessions on a synthetic track over a 4-week period. The training consisted of 10 × 400 m, 8 × 600 m, 7 × 800 m, and 6 × 1000 m running. Using an inertial measurement unit, the ground contact time (GCT) of every step was recorded. To determine gait asymmetry, the GCTs between the left and right foot were compared. Results: Overall, gait asymmetry was 3.3 ±1.4%, and over the course of a training session, the gait asymmetry did not change (F1,33 = 1.673, P = .205). The gait asymmetry of the athletes with a previous history of injury was significantly greater than that of the athletes without a previous injury. However, this injury-related enlarged asymmetry was detectable only at short (400 m) but not at longer distances (600-1000 m). Conclusions: The gait asymmetry of well-trained athletes differed, depending on their history of injury and the running distance. To detect gait asymmetries, high-intensity runs over relatively short distances are recommended.

Optimal Loading for Maximizing Power During Sled-Resisted Sprinting

Article

Full-text available

Dec 2016
Int J Sports Physiol Perform

Purpose: To ascertain whether force-velocity-power relationships could be compiled from a battery of sled-resisted overground sprints and to clarify and compare the optimal loading conditions for maximizing power production for different athlete cohorts. Methods: Recreational mixed-sport athletes (n = 12) and sprinters (n = 15) performed multiple trials of maximal sprints unloaded and towing a selection of sled masses (20-120% body mass [BM]). Velocity data were collected by sports radar, and kinetics at peak velocity were quantified using friction coefficients and aerodynamic drag. Individual force-velocity and power-velocity relationships were generated using linear and quadratic relationships, respectively. Mechanical and optimal loading variables were subsequently calculated and test-retest reliability assessed. Results: Individual force-velocity and power-velocity relationships were accurately fitted with regression models (R2> .977, P < .001) and were reliable (ES = 0.05-0.50, ICC = .73-.97, CV = 1.0-5.4%). The normal loading that maximized peak power was 78% ± 6% and 82% ± 8% of BM, representing a resistance of 3.37 and 3.62 N/kg at 4.19 ± 0.19 and 4.90 ± 0.18 m/s (recreational athletes and sprinters, respectively). Optimal force and normal load did not clearly differentiate between cohorts, although sprinters developed greater maximal power (17.2-26.5%, ES = 0.97-2.13, P < .02) at much greater velocities (16.9%, ES = 3.73, P < .001). Conclusions: Mechanical relationships can be accurately profiled using common sled-training equipment. Notably, the optimal loading conditions determined in this study (69-96% of BM, dependent on friction conditions) represent much greater resistance than current guidelines (~7-20% of BM). This method has potential value in quantifying individualized training parameters for optimized development of horizontal power.

Methods of Power-Force-Velocity Profiling During Sprint Running: A Narrative Review

Article

Full-text available

Jul 2017
SPORTS MED

The ability of the human body to generate maximal power is linked to a host of performance outcomes and sporting success. Power-force-velocity relationships characterize limits of the neuromuscular system to produce power, and their measurement has been a common topic in research for the past century. Unfortunately, the narrative of the available literature is complex, with development occurring across a variety of methods and technology. This review focuses on the different equipment and methods used to determine mechanical characteristics of maximal exertion human sprinting. Stationary cycle ergometers have been the most common mode of assessment to date, followed by specialized treadmills used to profile the mechanical outputs of the limbs during sprint running. The most recent methods use complex multiple-force plate lengths in-ground to create a composite profile of over-ground sprint running kinetics across repeated sprints, and macroscopic inverse dynamic approaches to model mechanical variables

Strength and performance asymmetry during maximal velocity sprint running

Article

Full-text available

Sep 2016
SCAND J MED SCI SPOR

The aim of this study was to empirically examine the interaction of athlete-specific kinematic kinetic and strength asymmetry in sprint running. Bilateral ground reaction force and kinematic data were collected during maximal velocity (mean = 9.05 m/s) sprinting for eight athletes. Bilateral ground reaction force data were also collected while the same athletes performed maximal effort squat jumps. Using novel composite asymmetry scores, interactions between kinematic and kinetic asymmetry were compared for the group of sprinters. Asymmetry was greater for kinematic variables than step characteristics, with largest respective values of 6.68% and 1.68%. Kinetic variables contained the largest asymmetry values, peaking at >90%. Asymmetry was present in all kinematic and kinetic variables analyzed during sprint trials. However, individual athlete asymmetry profiles were reported for sprint and jump trials. Athletes' sprint performance was not related to their overall asymmetry. Positive relationships were found between asymmetry in ankle work during sprint running and peak vertical force (r = 0.895) and power (r = 0.761) during jump trials, suggesting that the ankle joint may be key in regulating asymmetry in sprinting and highlighting the individual nature of asymmetry. The individual athlete asymmetry profiles and lack of relationship between asymmetry of limb strength and sprint performance suggest that athletes are not "limb dominant" and that strength imbalances are joint and task specific. Compensatory kinetic mechanisms may serve to reduce the effects of strength or biological asymmetry on the performance outcome of step velocity.

Effects of a six-week hip thrust versus front squat resistance training program on performance in adolescent males: A randomized-controlled trial

Article

Full-text available

May 2016
J STRENGTH COND RES

The barbell hip thrust may be an effective exercise for increasing horizontal force production and may thereby enhance performance in athletic movements requiring a horizontal force vector, such as horizontal jumping and sprint running. The ergogenic ability of the squat is well known. The purpose of this study was to compare the effects of six-week front squat and hip thrust programs in adolescent male athletes. Vertical jump height, horizontal jump distance, 10 m and 20 m sprint times, and isometric mid-thigh pull peak force were among the measured performance variables, in addition to front squat and hip thrust three-repetition maximum (3 RM) strength. Magnitude-based effect-sizes revealed potentially beneficial effects for the front squat in both front squat 3 RM strength and vertical jump height when compared to the hip thrust. No clear benefit for one intervention was observed for horizontal jump performance. Potentially beneficial effects were observed for the hip thrust compared to the front squat in 10 m and 20 m sprint times. The hip thrust was likely superior for improving normalized isometric mid-thigh pull strength, and very likely superior for improving hip thrust 3 RM and isometric mid-thigh pull strength. These results support the force vector theory.

Sprint Acceleration Mechanics: The Major Role of Hamstrings in Horizontal Force Production

Article

Full-text available

Dec 2015

Recent literature supports the importance of horizontal ground reaction force (GRF) production for sprint acceleration performance. Modeling and clinical studies have shown that the hip extensors are very likely contributors to sprint acceleration performance. We experimentally tested the role of the hip extensors in horizontal GRF production during short, maximal, treadmill sprint accelerations. Torque capabilities of the knee and hip extensors and flexors were assessed using an isokinetic dynamometer in 14 males familiar with sprint running. Then, during 6-s sprints on an instrumented motorized treadmill, horizontal and vertical GRF were synchronized with electromyographic (EMG) activity of the vastus lateralis, rectus femoris, biceps femoris, and gluteus maximus averaged over the first half of support, entire support, entire swing and end-of-swing phases. No significant correlations were found between isokinetic or EMG variables and horizontal GRF. Multiple linear regression analysis showed a significant relationship (P = 0.024) between horizontal GRF and the combination of biceps femoris EMG activity during the end of the swing and the knee flexors eccentric peak torque. In conclusion, subjects who produced the greatest amount of horizontal force were both able to highly activate their hamstring muscles just before ground contact and present high eccentric hamstring peak torque capability.

Interpreting Power-Force-Velocity Profiles for Individualized and Specific Training

Article

Full-text available

Dec 2015
Int J Sports Physiol Perform

Recent studies have brought new insights into the evaluation of power-force-velocity profiles in both ballistic push-offs (e.g. jumps) and sprint movements. These are major physical components of performance in many sports, and the methods we developed and validated are based on data that are now rather simple to obtain in field conditions (e.g. body mass, jump height, sprint times or velocity). The promising aspect of these approaches is that they allow for a more individualized and accurate evaluation, monitoring, and training practices; the success of which are highly dependent on the correct collection, generation and interpretation of athletes' mechanical outputs. We 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, we have first detailed 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. Further, we have discussed these same concepts with regards to horizontal profiling in the management of sprinting performance. These sections have been illustrated by typical examples from our own practice. Finally, we have provided a practical and operational synthesis, and outlined future challenges that will help in further developing these approaches.

Field monitoring of sprinting power-force-velocity profile before, during and after hamstring injury: two case reports

Article

Full-text available

Dec 2015
J SPORT SCI

Very little is currently known about the effects of acute hamstring injury on over-ground sprinting mechanics. The aim of this research was to describe changes in power-force-velocity properties of sprinting in two injury case studies related to hamstring strain management: Case 1: during a repeated sprint task (10 sprints of 40 m) when an injury occurred (5th sprint) in a professional rugby player; and Case 2: prior to (8 days) and after (33 days) an acute hamstring injury in a professional soccer player. A sports radar system was used to measure instantaneous velocity-time data, from which individual mechanical profiles were derived using a recently validated method based on a macroscopic biomechanical model. Variables of interest included: maximum theoretical velocity (V0) and horizontal force (FH0), slope of the force-velocity (F-v) relationship, maximal power, and split times over 5 and 20 m. For Case 1, during the injury sprint (sprint 5), there was a clear change in the F-v profile with a 14% greater value of FH0 (7.6-8.7 N/kg) and a 6% decrease in V0 (10.1 to 9.5 m/s). For Case 2, at return to sport, the F-v profile clearly changed with a 20.5% lower value of FH0 (8.3 vs. 6.6 N/kg) and no change in V0. The results suggest that the capability to produce horizontal force at low speed (FH0) (i.e. first metres of the acceleration phase) is altered both before and after return to sport from a hamstring injury in these two elite athletes with little or no change of maximal velocity capabilities (V0), as evidenced in on-field conditions. Practitioners should consider regularly monitoring horizontal force production during sprint running both from a performance and injury prevention perspective.

Novel Resistance Training-Specific RPE Scale Measuring Repetitions in Reserve

Article

Full-text available

Jun 2015
J STRENGTH COND RES

The primary aim of this study was to compare rating of perceived exertion (RPE) values measuring repetitions in reserve (RIR) at particular intensities of 1RM in experienced (ES) and novice squatters (NS). Further, this investigation compared average velocity between ES and NS at the same intensities. Twenty-nine individuals (24.0±3.4yrs.) performed a one-repetition maximum (1RM) squat followed by a single repetition with loads corresponding to 60, 75, and 90% of 1RM and an 8-repetition set at 70% 1RM. Average velocity was recorded at 60, 75, and 90% 1RM and on the first and last repetitions of the 8-repetition set. Subjects reported an RPE value that corresponded to an RIR value (RPE-10 = 0-RIR, RPE-9 = 1-RIR, and so forth). Subjects were assigned to one of two groups: 1) ES (n=15, training age: 5.2±3.5yrs.), 2) NS (n=14, training age: 0.4±0.6yrs.). The mean of the average velocities for ES were slower (P<0.05) than NS at 100% and 90% 1RM. However, there were no differences (P>0.05) between groups at 60%, 75%, or for the 1st and 8th repetitions at 70% 1RM. Additionally, ES recorded greater RPE at 1RM than NS (P=0.023). In ES there was a strong inverse relationship between average velocity and RPE at all percentages (r= -0.88, P<0.001), and a strong inverse correlation in NS between average velocity and RPE at all intensities (r=-0.77,P=0.001). Our findings demonstrate an inverse relationship between average velocity and RPE/RIR. ES exhibited slower average velocity and higher RPE at 1RM than NS, signaling greater efficiency at high intensities. The RIR-based RPE scale is a practical method to regulate daily training load and provide feedback during a 1RM test.

Profiling Sprint Mechanics by Leg Preference and Position in Rugby Union Athletes

Article

Jul 2016

Lower-extremity power characteristics are central to performance in rugby. However little is known regarding the effects of leg preference and playing position on sprint mechanics. The purpose of this study was to profile sprint kinetics and kinematics in rugby union athletes and compare between legs and between positions. Thirty male academy-level rugby union athletes, separated into forwards (n=15) and backs (n=15), participated in this cross-sectional analysis. Non-motorised treadmill ergometry was used to evaluate peak relative vertical (FV) and horizontal (FH) force and peak relative power (Pmax) of the preferred and non-preferred legs during maximal sprinting. The non-preferred leg of the forwards produced less FV, FH and Pmax than the preferred leg during acceleration (ES=-0.32, - 0.58 and - 0.67) and maximal velocity (ES=- 0.50, - 0.65 and - 0.60). Backs produced more FV, FH and Pmax than the forwards during initial acceleration (ES=0.51, 1.58 and 1.30) but less at maximal velocity (ES=- 0.74, -0.79 and - 0.81). Backs had faster split times at 2, 5, 10 and 15 m (ES=-1.03, -0.82, -0.63 and -0.50) but slower times at 35 and 40 m (ES=0.78 and 1.10) compared with forwards. Forwards produced larger sprint kinetics compared with backs, but also larger lower-extremity imbalances; potentially reducing sprint efficiency and/or increasing injury risk. © Georg Thieme Verlag KG Stuttgart · New York.

The Potential for a Targeted Strength-Training Program to Decrease Asymmetry and Increase Performance: A Proof of Concept in Sprinting

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