ABSTRACTMaloney, SJ. The relationship between asymmetry and athletic performanceA critical review. J Strength Cond Res 33(9)2579–2593, 2019—Symmetry may be defined as the quality to demonstrate an ...exact correspondence of size, shape, and form when split along a given axis. Although it has been widely asserted that the bilateral asymmetries are detrimental to athletic performance, research does not wholly support such an association. Moreover, the research rarely seeks to distinguish between different types of bilateral asymmetry. Fluctuating asymmetries describe bilateral differences in anthropometric attributes, such as nostril width and ear size, and are thought to represent the developmental stability of an organism. There is evidence to suggest that fluctuating asymmetries may be related to impaired athletic performance, although contradictory findings have been reported. Sporting asymmetries is a term that may better describe bilateral differences in parameters, such as force output or jump height. These asymmetries are likely to be a function of limb dominance and magnified by long-standing participation within sport. Sporting asymmetries do not seem to carry a clear influence on athletic performance measures. Given the vast discrepancy in the methodologies used by different investigations, further research is warranted. Recent investigations have demonstrated that training interventions can reduce sporting asymmetries and improve performance. However, studies have not sought to determine whether the influence of sporting asymmetry is independent of improvements in neuromuscular parameters. It may be hypothesized that the deficient (weaker) limb has a greater potential for adaptation in comparison to the strong limb and may demonstrate greater responsiveness to training.
Abstract
Galati, D, Turner, AN, Bishop, C, and Maloney, SJ. Contemporary practices of strength and conditioning coaches in high-level male ice hockey: a survey-based investigation.
J Strength Cond ...Res
37(11): 2241–2250, 2023—The aim of this study was to provide an updated view of the common practices, ideologies, education level, and professional environment of strength and conditioning (S&C) coaches in elite male ice hockey. Nineteen S&C coaches from professional, semiprofessional, and top-tier collegiate hockey teams in North America completed an anonymous online survey. This was composed of 10 sections: (a) background information; (b) technology use, (c) testing and periodization, (d) strength and power, (e) flexibility/mobility, (f) speed, (g) plyometrics, (h) aerobic and anaerobic conditioning, (i) rehabilitation, and (j) challenges and areas of improvement. Fixed-response questions were analyzed through frequency analyses. Thematic analyses were used to identify common themes from open-response questions. Strength and conditioning coaches had an average of 8 (±6.5) years of experience when they accepted their current role. The majority held a master's degree and S&C certification. Muscular power, linear speed, and body composition were the most frequently tested qualities. Neuromuscular fatigue was the most important consideration during the season and least important consideration during the off-season. Training frequencies for all physical capacities were lower during the season compared with the off-season. All S&Cs had access to technology, with wearables, with force plates identified as the most used devices. This information may be used by S&C coaches to compare working practices with those used by their peers and inform them of the likely requirements and skill sets needed for job applications. Educational institutions may use this information to align teaching to current practice and to inform future research.
Stiffness describes the resistance of a body to deformation. In regard to athletic performance, a stiffer leg-spring would be expected to augment performance by increasing utilisation of elastic ...energy. Two-dimensional spring-mass and torsional spring models can be applied to model whole-body (vertical and/or leg stiffness) and joint stiffness. Various tasks have been used to characterise stiffness, including hopping, gait, jumping, sledge ergometry and change of direction tasks. Appropriate levels of reliability have been reported in most tasks, although they vary between investigations. Vertical stiffness has demonstrated the strongest reliability across tasks and may be more sensitive to changes in high-velocity running performance than leg stiffness. Joint stiffness demonstrates the weakest reliability, with ankle stiffness more reliable than knee stiffness. Determination of stiffness has typically necessitated force plate analyses; however, validated field-based equations permit determination of whole-body stiffness without force plates. Vertical, leg and joint stiffness measures have all demonstrated relationships with performance measures. Greater stiffness is typically demonstrated with increasing intensity (i.e., running velocity or hopping frequency). Greater stiffness is observed in athletes regularly subjecting the limb to high ground reaction forces (i.e., sprinters). Careful consideration should be given to the most appropriate assessment of stiffness on a team/individual basis.
The aim of this study was to compare the training effect of small-sided games played using large and small area per player on speed and endurance in college soccer players. Twenty male NCAA division ...1 soccer players were randomly assigned to one of two experimental groups: small-sided games using a large area per player (n = 10), or small-sided games using a small area per player (n = 10). During the 4-week intervention, both groups performed three sets of 4–8 min of 5 versus 5 small-sided games using either a large (300 m2) or small (75 m2) area per player. Pre- and post-training, players completed linear sprint (20- and 40-m), repeated sprint, and aerobic endurance tests. Following the intervention, both groups exhibited improvements in 20-m, 40-m, and maximum sprinting speed (all p < 0.05, g = 0.04–0.29). No differences or interaction effects in repeat-sprint ability were found for either group (p > 0.05). A decline in maximal aerobic speed occurred in the small area per player group (p = 0.010, g = 0.60) whilst no change was reported for the large area per player group. Following the intervention, anaerobic speed reserve was lower for the large area per player group versus the small area per player group (p = 0.013; g = −0.23). No further between-group differences were reported at either time-point. These results suggest that small-sided games played with a small area per player may not be adequate to maintain aerobic fitness.
Whilst the measurement and quantification of vertical leg stiffness (K
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) asymmetry is of important practical relevance to athletic performance, literature investigating bilateral asymmetry in K
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is limited. Moreover, how the type of task used to assess K
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may affect the expression of asymmetry has not been properly determined. Twelve healthy males performed three types of performance tasks on a dual force plate system to determine K
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asymmetries; the tasks were (a) bilateral hopping, (b) bilateral drop jumping and (c) unilateral drop jumping. Across all the three methods, K
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was significantly different between compliant and stiff limbs (P < 0.001) with a significant interaction effect between limb and method (P = 0.005). Differences in K
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between compliant and stiff limbs were −5.3% (P < 0.001), −21.8% (P = 0.007) and −15.1% (P < 0.001) for the bilateral hopping, bilateral drop jumping and unilateral drop jumping methods, respectively. All the three methods were able to detect significant differences between compliant and stiff limbs, and could be used as a diagnostic tool to assess K
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asymmetry. Drop jumping tasks detected larger K
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asymmetries than hopping, suggesting that asymmetries may be expressed to a greater extent in acyclic, maximal performance tasks.
Change of direction speed (CODS) underpins performance in a wide range of sports but little is known about how stiffness and asymmetries affect CODS. Eighteen healthy males performed unilateral drop ...jumps to determine vertical, ankle, knee and hip stiffness, and a CODS test to evaluate left and right leg cutting performance during which ground reaction force data were sampled. A step-wise regression analysis was performed to ascertain the determinants of CODS time. A two-variable regression model explained 63% (R
2
= 0.63; P = 0.001) of CODS performance. The model included the mean vertical stiffness and jump height asymmetry determined during the drop jump. Faster athletes (n = 9) exhibited greater vertical stiffness (F = 12.40; P = 0.001) and less asymmetry in drop jump height (F = 6.02; P = 0.026) than slower athletes (n = 9); effect sizes were both "large" in magnitude. Results suggest that overall vertical stiffness and drop jump height asymmetry are the strongest predictors of CODS in a healthy, non-athletic population.
Foam rolling and eccentric exercise interventions have been demonstrated to improve range of motion (ROM). However, these two modalities have not been directly compared. Twenty-three academy soccer ...players (age: 18 ± 1; height: 1.74 ± 0.08 m; body mass: 69.3 ± 7.5 kg) were randomly allocated to either a foam rolling (FR) or eccentric exercise intervention designed to improve dorsiflexion ROM. Participants performed the intervention daily for a duration of four weeks. Measurements of dorsiflexion ROM, isometric plantar flexion torque and drop jump reactive strength index were taken at baseline (pre-intervention) and at three subsequent time-points (30-min post, 24-hours post and 4-weeks post). A significant time x group interaction effect was observed for dorsiflexion (P = 0.036), but not for torque or reactive strength index. For dorsiflexion, there was a significant increase in both acute (30-min; P < 0.001) and chronic (4-week; P < 0.001) ROM for the eccentric group, whilst FR exhibited only an acute improvement (P < 0.001). Eccentric training would appear a more efficacious modality than foam rolling for improving dorsiflexion ROM in elite academy soccer players.
The current study aimed to compare locomotive outputs across English U16, U18 and U23 academy soccer and investigate possible relationships with neuromuscular and aerobic capacities. Participants ...included 46 outfield players from an English Category Two soccer academy. Global positioning system (18 Hz) data were utilised to analyse locomotive outputs across twenty eleven-a-side matches in each age group. Maximal sprinting speed (MSS) and aerobic speed (MAS) were assessed at the beginning of the season. Absolute total distance (TD), high-speed running (HSR), acceleration and deceleration workloads were higher in U18’s and U23’s vs. U16’s (g = 1.09–2.58; p < 0.05), and absolute sprinting distances were higher in U23’s vs. U16’s (g = 0.96; p < 0.05). In addition, relative HSR outputs were higher in U23’s vs. U18’s (g = 1.84–2.07; p < 0.05). Across the whole cohort, players’ MSS was positively associated with absolute HSR and sprinting distances (ρ = 0.53–0.79; p < 0.05) but not with relative parameters. MAS was positively associated with total distance, decelerations, and both absolute and relative HSR outputs (ρ = 0.33–0.56; p < 0.05). Overall, absolute locomotive outputs were significantly higher in U23’s and U18’s vs. U16’s. Locomotive outputs were also associated with maximal sprinting and aerobic speeds. Thus, training programmes should be tailored to competition demands to optimally prepare each age group for competition and reflect the increasing demands of each level of competition. Further, improving physical fitness (speed and endurance) is likely to drive greater outputs in competition.
Currently, it is unclear which physical characteristics may underpin the change of direction deficit (COD-D). This investigation sought to determine if momentum, speed-, and jump-based measures may ...explain variance in COD-D.
Seventeen males from a professional soccer academy (age, 16.76 0.75 y; height, 1.80 0.06 m; body mass, 72.38 9.57 kg) performed 505 tests on both legs, a 40-m sprint, and single-leg countermovement and drop jumps.
The regression analyses did not reveal any significant predictors for COD-D on either leg. "Large" relationships were reported between the COD-D and 505 time on both limbs (r = .65 to .69; P < .01), but COD-D was not associated with linear momentum, speed-, or jump-based performances. When the cohort was median split by COD-D, the effect sizes suggested that the subgroup with the smaller COD-D was 5% faster in the 505 test (d = -1.24; P < .001) but 4% slower over 0-10 m (d = 0.79; P = .33) and carried 11% less momentum (d = -0.81; P = .17).
Individual variance in COD-D may not be explained by speed- and jump-based performance measures within academy soccer players. However, when grouping athletes by COD-D, faster athletes with greater momentum are likely to display a larger COD-D. It may, therefore, be prudent to recommend more eccentric-biased or technically focused COD training in such athletes and for coaches to view the COD action as a specific skill that may not be represented by performance time in a COD test.
ABSTRACTMaloney, SJ, Richards, J, Jelly, L, and Fletcher, IM. Unilateral stiffness interventions augment vertical stiffness and change of direction speed. J Strength Cond Res 33(2)372–379, 2019—It ...has previously been shown that preconditioning interventions can augment change of direction speed (CODS). However, the mechanistic nature of these augmentations has not been well considered. The current study sought to determine the effects of preconditioning interventions designed to augment vertical stiffness on CODS. Following familiarization, 10 healthy males (age22 ± 2 years; height1.78 ± 0.05 m; body mass75.1 ± 8.7 kg) performed 3 different stiffness interventions in a randomized and counterbalanced order. The interventions were(a) bilateral-focused, (b) unilateral-focused, and (c) a control of CODS test practice. Vertical stiffness and joint stiffness were determined preintervention and postintervention using a single-leg drop jump task. Change of direction speed test performance was assessed postintervention using a double 90° cutting task. Performances following the unilateral intervention were significantly faster than control (1.7%; p = 0.011; d = −1.08), but not significantly faster than the bilateral intervention (1.0% faster; p = 0.14; d = −0.59). Versus control, vertical stiffness was 14% greater (p = 0.049; d = 0.39) following the unilateral intervention and 11% greater (p = 0.019; d = 0.31) following the bilateral intervention; there was no difference between unilateral and bilateral interventions (p = 0.94; d = −0.08). The findings of the current study suggest that unilateral preconditioning interventions designed to augment vertical stiffness improve CODS within this experimental cohort.
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