Factors affecting the ability to undertake repeated sprint performance

The aims of this thesis were to: 1) to review research in the area of repeated sprint (RS) performance and diurnal/circadian rhythmicity; 2) to develop a new RS protocol that conforms to field based team sport time-motion analysis and determine its reliability and compare this with a RS protocol previously utilised in the literature; 3) to assess the sensitivity of the RS protocol following acute altitude exposure and simulated soccer specific exercise 4) to investigate diurnal variation of RS performance and assess whether modulating rectal and/or muscle temperatures lead to changes in RS performance. A review of the published research literature investigating the relationship between RS performance and time-of-day variation was conducted. Six studies made it through the whole analysis process for systematic review. It was established that there was evidence to support a late/early afternoon peak in peak power in RS performance around the peak of the rhythm of core temperature. However, there is a clear demand for more rigorous investigations which control factors specifically related to chronobiological investigations. A reliability study was then performed using running as the mode of exercise for the RS test using two different RS protocols to determine the number of trials required to establish high levels of reliability. The first RS test (consisting of a total of 10 sprints, 6-s in duration with 30-s of passive recovery) was a commonly used protocol in the literature and the second was a newly created RSA protocol which is better representative of field based team sports activity (consisting of a total of 10 sprints, 3-s in duration with 30-s of passive recovery). It was established that a number of performance measures of RSA non-motorised treadmill running in both protocols were reliable. However, measures of fatigue were not. Further, it was found that both protocols took 3 sessions to fully familiarise individuals. The main aim of the next study was to investigate the sensitivity of the RSA protocol by examining the effect of altitude and fatigue on RS performance. The first finding was that acute altitude exposure reduces RS performance by 3.1 to 6.5% at 1500-m and 6.2 to 12.8% at 3000-m. The second finding was that RS performance was reduced by 4.6 to 5.8% in a fatigued state. The newly created RS performance protocol is sensitive enough to detect a negative change following altitude acute exposure and a 90-min football-specific intermittent treadmill fatiguing protocol. A diurnal protocol was then employed in order to address the clear demand for more rigorous investigations in chronobiological studies of RS performance. A total of 20 participants took part in this study and it was found that RS performance was significantly higher in the evening compared to the morning ranging from 3.3 to 8.3% in all measures except fatigue index. Diurnal variation now established in RS performance, two studies assessed whether modulating rectal and/or muscle temperature leads to a change in RS performance and further determine how much can be attributed to the influence of an endogenous, temperature-dependent component. The first study (n = 12) established that raising morning rectal temperature to evening values by active warm-up did not increase RS performance to evening values. However, lowering evening rectal or muscle temperatures to morning values by pre-cooling decreased RS performance to values normally observed in the morning. The second study (n = 12) found passively raising morning rectal temperature to evening values, or passively raising morning and evening rectal temperatures to 38.5oC did not increase RS performance nor offset diurnal variation. Both studies concluded that although central temperature may provide some endogenous rhythm to RSA, the exact mechanism(s) for a causal link between central temperature and human performance are still unclear, and may involve multiple of components and mechanisms.