This section aims to contextualise the role that sleep loss would play in elite cricket performance. As discussed at the beginning of the chapter, cricket players must possess a blend of tremendous physical skill and mental ability to enable them to fulfil specific roles in the team.45,82,86,87 No study has specifically investigated sleep behaviours in elite cricket during competition; therefore, the effect of sleep loss on cricket performance can only be hypothesised
34
using evidence from laboratory and field-based studies in other sports. However, caution must be taken as experimental results found in laboratory-based studies do not account for the external factors which exist in the 'real world'.11 Further, field-based results are only applicable to the specific group of athletes which were investigated. This issue highlights the importance of assessing the effect of sleep on match performance in elite cricket players, employing a 'field-based design', while using performance measures which are applicable to cricket.
2.5.1 Measuring cricket performance
The game result (win or loss) has been used to determine the success of competition in team- sports.63,120 However, measuring individual player performance within a team sport is more complex, especially in cricket, where tactical approaches and responsibilities differ between match formats and player positions, respectively.37,43,88 Moreover, external factors (e.g. weather, pitch type and opposition strength) can considerably change the nature of a match.273 Despite these complexities, specific performance measures have been developed in cricket dependent on player role. For example, batting ability is typically measured using a batting average (the sum of all scores divided by the number of innings the batter was out), batting consistency (standard deviation from average) and strike rate (average number of runs scored per hundred balls faced).274,275 Similarly, a bowler's average (runs conceded per wicket), economy rate (total number of runs conceded by the bowler divided by the number of overs bowled) and strike rate (total number of balls bowled divided by the number of wickets taken) are the criteria used to determine bowling performance.80,276 In the context for each match format, batting strike rate and bowling economy are identified as primary measures of performance during limited-overs formats, while batting and bowling averages are considered important in the longer format of the cricket (i.e. Test matches).277 For wicketkeeping, a measure combining the dismissal rate (catches and stumpings divided by matches played) and batting performance has been proposed.278 There is no standard measure for quantifying fielding performance, however, the number of catches and run-outs are accessible fielding measures on match scorecards.279
2.5.2 Relationship between sleep and performance
Although sleep deprivation studies reveal important performance implications, the findings are not always relevant to an elite athletic population, given it would be unlikely for an athlete to lose sleep in this manner.6,218,280 Consequently, to minimise potential confusion, this section
35
primarily considers former sleep restriction research (involving later sleep onset or earlier wake times which disrupt the normal sleep-wake cycle).6 A summary of several studies which investigated the effects of sleep restriction on various performance outcomes is found in Appendix B; however, a detailed review of the studies effects is beyond the scope of this thesis.
2.5.2.1 Sports performance and sleep loss: Field-based studies
There are conflicting findings between the few existing published data which explored potential relationships between sleep and match play. For example, results from elite Australian Rules football63 and elite female basketball66 players found no significant association between sleep patterns and average match performance. Although these studies presented small correlations at a team level, substantial variability in the strength of correlations between specific players demonstrated that the relationship between sleep and performance is highly individualised.63,66 Similarly, sleep duration and quality during competition did not influence overall performance ranking in cyclists.223 However, several investigations have demonstrated that competitive success is related to optimal sleep behaviours.31,78,79 In a study of netball athletes, the higher ranked teams in the tournament had significantly greater sleep quantity and subjective ratings of sleep quality compared with the lesser ranked teams.31 Further, a strong inverse correlation was identified between sleep duration during the competition and final tournament position.31 Similarly, poor sleep quality was an independent predictor of lost competition in elite male and female Brazilian athletes immediately before a national or international competition.78
2.5.2.2 Exercise performance and sleep loss: Laboratory-based studies
The effects of sleep loss are greater for short-duration anaerobic exercises and single exercise bouts (e.g. sprints, peak power output)281-284 than for sustained efforts (endurance > 30 minutes) and repeated exercise bouts.6,285-287 Further, there are reductions in pacing strategies and intermittent-sprint performance after sleep loss,136 with improvements in these factors exhibited after sleep extension interventions.65 These adverse effects are relatable to cricket performance which involves short bursts of high-intensity effort that requires a contribution from the anaerobic energy system, whether it be during batting,41 bowling39 or fielding.45 Furthermore, effective pacing strategies are particularity necessary for batters to conserve energy while sprinting between wickets.288 Upper body strength and peak power are essential during the overthrow bowling289 and bat-ball contact during batting.290 Reactive leg power is
36
required from wicket-keepers who hold a crouch position over prolonged periods and aid in dismissals by catches quickly coming off the bat.95
2.5.2.3 Physiological responses to sleep loss
Unfortunately, the effects of sleep restriction on physiological responses are unclear. Some studies have found a decrease in heart rate, minute ventilation and oxygen uptake (VO2) peak during submaximal and maximal exercise after restricted sleep.287,291 However, others did not find any significant effect in those same responses,292-294 as well lung function and power.285,286 The differences found across studies could be attributed to the exercise mode and protocol each study administered.280 The cited research is out-dated and newer research is required to assess the impact of sleep loss on physiological responses to exercise in elite athletes.
2.5.2.4 Cognitive and perceptual responses to sleep loss
The detrimental effect of sleep loss on most aspects of cognitive function is undisputable,295- 297 with a dose-response relationship previously identified whereby a shorter sleep durations were associated with impaired cognition.133,296,297 The fundamental mental requirements in cricket, irrespective of the position played, are quick reaction times, accuracy, executive function,87 positive mood states298,299 and extraordinary ability to focus for sustained periods.45,86 The effects of sleep restriction found on cognitive and perceptual performance include an increase in perceived exertion,286,292,300,301 slower reaction time,302-305 a decline in working memory,306 earlier fatigue onset,286,306 reduced attention,306-309 poorer accuracy,296,308,310,311 and lapses in speed during a psychomotor vigilance task.296,312,313 Additionally, a reduction in mood and vigour occurs after restricted sleep.300,302,306,312 These adverse effects after sleep loss augment the need for cricketers, who have a high reliance on these cognitive components, as well as critical decision making,93 to obtain optimal sleep.