Physiological correlates of multiple-sprint ability and performance in international-standard squash players

Association between Lower Body Qualities and Change-of-Direction Performance: A Meta-Analysis

The aim of the present study is to determine the associations between lower body muscle strength qualities and change of direction (CoD) performance. Three databases were used to perform a systematic literature search up to September 30, 2022. Based on the studies that met the inclusion criteria, we calculated Pearson's r correlation coefficient to examine the relationships between muscle strength qualities and CoD performance. The quality of the studies included was evaluated by the modified version of the Downs and Black Quality Index Tool. Heterogeneity was determined via the Q statistic and I 2, and Egger's test was used to assess small study bias. The results revealed that lower body maximal strength (pooled: r=- 0.54, dynamic: r=- 0.60, static: r=- 0.41), joint strength (pooled: r=- 0.59, EXT-ecc: r=- 0.63, FLEX-ecc: r=- 0.59), reactive strength (r=- 0.42) and power (pooled: r=- 0.45, jump height: r=- 0.41, jump distance: r=- 0.60, peak power: r=- 0.41) were negatively and moderately related to CoD performance. To conclude, the results highlight that a number of muscle strength qualities are associated with CoD performance and are pertinent to specific phases of a directional change. It should be noted that the conclusions of this study do not establish causality, and further research is needed to better understand their training effects and underlying mechanisms.

Physiological and Performance Correlates of Squash Physical Performance

The physiological and performance attributes of elite squash players were investigated. Thirty-one players (21 males, world ranking [WR] 42-594; 10 females, WR 7-182) completed a battery of fitness tests which included an aerobic squash-specific physical performance test (SPPT), repeated-sprint ability (RSA), change-of-direction speed (COD), acceleration (5-m sprint), body composition and force development (countermovement jump) assessments. The SPPT provided a finishing lap score, V̇O_2max, average movement economy and the lap corresponding to a blood lactate concentration of 4 mM.L^-1. Players were ranked and assigned to HIGH or LOW performance tiers. Two-way ANOVA (performance level*sex) revealed higher ranked players performed better (p < 0.05) for SPPT final lap (d = 0.35), 4 mM.L^-1 lap (d = 0.52) and COD (d = 0.60). SPPT displayed a 'very-large' correlation with 4 mM.L^-1 lap (r = 0.86), 'large' correlations with COD (r = 0.79), RSA (r = 0.79), sum-of-7 skinfolds (r = 0.71) and V̇O_2max (r = 0.69), and a 'trivial' correlation with average movement economy (r = 0.02). Assessments of cardiovascular fitness (i.e. 4 mM.L^-1 lap), RSA, COD and body composition appear highly pertinent for performance profiling of squash players. Regular, submaximal assessment of the 4 mM.L^-1 lap during the SPPT may offer a practical athlete monitoring approach for elite squash players.

Reactive Strength Index and its Associations with Measures of Physical and Sports Performance: A Systematic Review with Meta-Analysis

BACKGROUND

Reactive strength index (RSI) is used frequently in the testing and monitoring of athletes. Associations with sports performance measures may vary dependent on the task but a literature synthesis has not been performed.

OBJECTIVES

The aim of this meta-analysis was to examine associations between RSI measured during rebound jumping tasks and measures of strength, linear and change of direction speed, and endurance performance.

METHODS

A systematic literature search with meta-analysis was conducted using databases PubMed, SPORTDiscus, Web of Science, and Ovid. Inclusion criteria required studies to (1) examine the relationship between RSI and an independent measure of physical or sporting performance for at least one variable; and (2) provide rebound test instructions to minimise ground contact time and maximise displacement of the jump. Methodological quality was assessed using a modified version of the Downs and Black Quality Index tool. Heterogeneity was examined via the Q statistic and I². Pooled effect sizes were calculated using a random-effects model, with Egger's regression test used to assess small study bias (inclusive of publication bias).

RESULTS

Of the 1320 citations reviewed, a total of 32 studies were included in this meta-analysis. RSI was significantly and moderately associated with strength (isometric: r = 0.356 [95% CI 0.209-0.504]; isotonic: r = 0.365 [0.075-0.654]; pooled strength measures: r = 0.339 [0.209-0.469]) and endurance performance (r = 0.401 [0.173-0.629]). Significant moderate and negative associations were indicated for acceleration (r = - 0.426 [- 0.562 to - 0.290]), top speed (r = - 0.326 [- 0.502 to - 0.151]), and significant large negative associations were noted for change of direction speed (r = - 0.565 [- 0.726 to - 0.404]). Heterogeneity was trivial to moderate across all measures (I² = 0-66%), and significant for isotonic strength and change of direction speed (p < 0.1). Evidence of small study bias was apparent for both acceleration and change of direction speed (p < 0.05).

CONCLUSIONS

We identified primarily moderate associations between RSI and independent measures of physical and sporting performance, and the strength of these relationships varied based on the task and physical quality assessed. The findings from this meta-analysis can help practitioners to develop more targeted testing and monitoring processes. Future research may wish to examine if associations are stronger in tasks that display greater specificity.

Case Study: The Effect of Nutritional Intervention on Body Composition and Physical Performance of a Female Squash Player

The body composition of a squash player may affect athletic performance as carrying excessive body fat may increase injury risk and impair agility and speed. This case study outlines the effect of a nutritional intervention on body composition, vitamin D status, and physical performance of a female squash player. A structured, 6-week, moderate energy-restricted diet (70-78% of estimated energy requirement of 2,300 kcal) was implemented with weekly support. A daily supplement of vitamin D, omega-3 fatty acids, and a multivitamin and whey protein was used. Full blood count, vitamin D status, body composition, and physical performance assessments were carried out at baseline and Week 6 of intervention. Body composition changes were measured using the BOD POD™ and skinfold calipers. Body fat was 23% at baseline and 22% at Week 6. Mean sum of eight skinfolds was 127.4 ± 2.2 mm at baseline and 107.3 ± 0.4 mm at Week 6. Lean body mass-to-fat mass ratio improved from 3.4 at baseline to 3.7 at Week 6. The greatest increments compared with baseline in serum markers were 25-hydroxyvitamin D3 (68%), ferritin (31%), eosinophils (20%), and triglycerides (16%). All physical performance measures improved, with reactive strength index (4.8%), and on-court repeated speed (6.0%) showing the greatest improvements from baseline. This intervention demonstrates that structured energy restriction alongside appropriately structured strength and conditioning training is an effective way to gradually reduce the body fat and improve the body composition of a female athlete.