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

Horizontal Force-Velocity-Power Profiling of Rugby Players: A Cross-Sectional Analysis of Competition-Level and Position-Specific Movement Demands

ABSTRACT

Watkins, CM, Storey, A, McGuigan, MR, Downes, P, and Gill, ND. Horizontal force-velocity-power profiling of rugby players: A cross-sectional analysis of competition-level and position-specific movement demands. J Strength Cond Res 35(6): 1576-1585, 2021-Speed and acceleration are crucial to competitive success in all levels of rugby union. However, positional demands affect an athlete's expression of force and velocity during the match. This study investigated maximal sprint performance and horizontal force-velocity (FV) profiles in 176 rugby union players participating in amateur club, professional, and international competitions. Rugby players were divided into 5 positional groups: tight-5 forwards (n = 63), loose forwards (n = 35), inside backs (n = 29), midbacks (n = 22), and outside (n = 27) backs. Sprint performance was averaged across 2 trials of a maximal 30-m sprint, separated by a 3-minute rest. The results demonstrated differences in sprint performance and FV profile characteristics across competitions and positional groups. Specifically, both international and professional players possessed significantly faster split times and superior FV profiles than club players (p < 0.01; effect size [ES]: 0.22-1.42). International players were significantly faster across 0-10 m than professional players (p = 0.03; ES: 0.44-0.47), whereas professional players had faster 10-20 m times (p = 0.03; ES: 0.37-0.41) and a more force-dominant profile (p < 0.01; ES: 0.71-1.00). Across positions, split times decreased and maximal velocity characteristics increased in proportion with increasing positional number, with outside backs being the fastest (ES: 0.38-2.22). On the other hand, both forwards groups had more force-dominant profiles and average sprint momentum across all distances than all backs positions. Interestingly, loose forwards had a more forceful profile and slower 10-, 20-, and 30-m split times but similar maximal velocity characteristics to inside backs, highlighting unique positional demands and physical attributes.

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

ABSTRACT

Virgile, A and Bishop, C. A narrative review of limb dominance: Task specificity and the importance of fitness testing. J Strength Cond Res 35(3): 846-858, 2021-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 is 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 that is subjectively preferred and one that is objectively dominant in 1 or more performance measures from a variety of athletic tasks. In this review, we (a) discuss reported correspondence between task-specific limb preference and limb dominance outcomes in athletes, (b) provide greater context and distinction between the terms limb preference and limb dominance, and (c) offer pragmatic strategies for practitioners to assess context-specific limb dominance. A limb that is subjectively preferred is not necessarily objectively dominant in 1 or more athletic qualities or sport-specific tasks. Further to this, a limb that is objectively superior in 1 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 vs. potential performance or injury ramifications.

Acute changes in acceleration phase sprint biomechanics with lower body wearable resistance

The aim of this acute cross-sectional study was to quantify the kinematic and kinetic changes that occur during sprint acceleration when lower body WR is worn. Fifteen male rugby athletes (19 years; 181 cm; 91 kg) were assessed during maximal effort over-ground and treadmill sprinting over 20 m under three different loading conditions: 0%, 3% and 5% body mass (BM) added weight attached to the lower body. Treadmill data provided a convenient estimate of kinetic changes in the absence of in-ground force plates. The loaded conditions resulted in significantly increased ground contact time (5 to 6%) and decreased step frequency (-2 to -3%) during sprint accelerations (effect size = 0.32-0.72). Moderate WR loading (3% BM) resulted in increased (9%; effect size = 0.66) theoretical maximum horizontal force (relative to BM) and unchanged 20 m sprint times (p > 0.05). Heavier WR loading (5% BM) resulted in a significant decrease (-4%) in vertical ground reaction forces (relative to total system mass) and slower (1 to 2%) 20 m sprint times (effect size = 0.38-0.70). Lower body WR loading up to 5% BM can provide specific sprint training overload, while affecting sprint acceleration biomechanics by ≤ 6%.

Greater loss of horizontal force after a repeated-sprint test in footballers with a previous hamstring injury

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

20 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-motorised 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 impaired performance in football players returning from hamstring injury and also to the high rate of hamstring re-injury. Rehabilitation and return-to-play strategies should emphasise 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.

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

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.