JUSTIFICACIÓN

The main research question of the present study was whether an acute dose of blackcurrant supplement could reduce the effects physical fatigue on cognitive performance. Previous research produced a mixed, but somewhat significant body of research regarding the effects of a dietary intervention on cognitive performance. Overall the general consensus from dietary studies reveals that phytochemicals play a role in both cognitive and physical performance (Chung et al., 2012). For instance, prior literature revealed that phytochemicals have an ability to directly exert, positive influences through neuromodulation and neuroprotection in the brain (Kirkorian, Shilder et al., 2010; Miller & Shukitt-Hale, 2012; Papandreou et al., 2009; Shukitt- Hale et al., 2005; Sokolov et al., 2013). Primarily, dietary intervention studies

investigated the effects phytochemicals have on physical performance (McLeay et al., 2012; Malaguti et al., 2013) or separately on cognitive performance (Hoyland et al., 2008; Kirkorian et al., 2010; Kirkorian, Shidler et al., 2010). Thus, the present study may be one of the first studies to investigate a phytochemical extract’s ability to provide ameliorating effects from an acute generation of physical fatigue, whilst simultaneously investigating the extracts ability to influence cognitive performance. Therefore, based on consensus drawn from previous literary evidence, it was

anticipated that the present study would reveal ameliorated performance to cognition following acute generation of physical fatigue, in comparison to those that received the placebo before being physically fatigued.

It was anticipated that an acute dose of blackcurrant would act in one of two ways: firstly, through prevention of physical fatigue in those assigned to the exercising condition, and secondly, the blackcurrant would act as a barrier to any exercise induced effects on cognitive performance. However, while the exercising task

revealed a successful generation of acute physiological fatigue, cognitive performance did not result in any observable declined performance, as a result of a physically fatigued state. Therefore, the modality of anticipated fatigue effects was not

supported. The performance means differed only slightly between the experimental conditions and the intervention groups. These miniscule differences were not large enough to cause any significant effects for Cognitive performance x Condition x Intervention. Suggestive, that the blackcurrant extract did not reduce fatigue effects for participants’ to any greater degree than participants’ who received the placebo. Furthermore, the blackcurrant extract did not influence cognitive performance within either intervention groups, both revealing similar time related changes in cognitive performance from baseline to post-task measurement. Given these lack of effects relating to physical fatigue debilitating cognitive performance at Time 2, it is difficult to draw generalised conclusions regarding the effects of an acute dose of blackcurrant extract. It may be that had participants’ cognitive performance been impaired,

following the prescribed HIIT the effects from the blackcurrant extract would have been greater than what was observed.

In spite of the failure to support the second hypothesis, there are a number of possible explanations as to why the blackcurrant extract had no significant effects in the present study. For instance, just as sensitivity issues were important in regards the lack of support for the first hypothesis, sensitivity issues are also relevant to mention here. Particularly, these sensitivity issues once again refer to the cognitive tasks administered within previous studies, in relation to the present study. Not surprisingly there has been little correspondence between prior studies. Cognition functioning is vast, and thus, cognitive tasks mirror the vastness of cognitive domains. Therefore, in order for characterisation of dietary supplementation effects on human cognition,

researchers have needed to utilise a wide range of tasks in order to establish a comprehensive picture of cognitive ability, following ingestion of a dietary supplementation (Hoyland et al., 2008).

Previous research has revealed that phytochemicals are capable to crossing the BBB and accumulating directly within a range of regions in the brain (Nehlig, 2003). The direct association between phytochemicals and the brain is considered to be the manner through which phytochemicals will influence physical and cognitive

performance (Papandreou et al., 2009; Spencer et al., 2009). However, at present the direct mechanisms of causal actions of phytochemicals influence upon cognitive and physical performance remains unclear.

In light of this, it is possible that the blackcurrant extract used in the present study did not exploit these particular cognitive tasks domain function. Therefore, the lack of observable effects at present may be as a result of a lack of sensitivity for these cognitive tasks applied, and not due to a true absence of effect. Consequently, the present findings emphasise an important need for future studies to isolate the cognitive tasks that are sensitive to phytochemical manipulations. Furthermore, an assumption of a one to one correspondence between the different cognitive measures and the cognitive domain being assessed will continue to generate contradictory reports of conflicting evidence. Thus, a manner in which to equate different tests of a particular cognitive domain needs to be established (Hoyland et al., 2008; MacReady et al., 2010; Waters & Caplan, 2003).

The dose of the blackcurrant supplement used here may also play a contributing role to the currant null findings. It’s well known that foods demonstrate differing time course effects on cognitive performance, emphasising the need for dose response curves to be considered (Hoyland et al., 2008). Previous research has demonstrated significant effects from phytochemical consumption and performance, in both physical and cognitive domains. However, predominantly these studies are constructed as longitudinal and chronic supplementation of phytochemical compounds. The majority of which will supply subjects with phytochemical supplements from 7 days to 4 months (Papandreou et al., 2009; Katz et al., 2011; Miller & Shukitt-Hale, 2012; Shukitt-Hale et al., 2005). However, with limited

studies investigating the immediate actions of phytochemicals on cognitive and physical performance, gaps still remain within the literature (Sokolov et al., 2013). Shukitt-Hale et al. (2006) emphasised the importance of the dose-response curve with differing food sources of phytochemicals. For instance, consumption of a 10%

concentrated grape juice successfully reduced cognitive performance decrements, however, in order to observe an effect for physical performance, participants’ needed to consume a 50% grape juice supplemented diet. Additionally, Ratlidge (2014) revealed that a dose of 3.2mg/kg of body weight was not sufficient to produce and effect of motor performance changes resulting from cognitive fatigue. Thus, while published data reveal that phytochemical compounds, applied in either whole extract, or pure form clearly result in antioxidant activity in vitro (Ghosh & Konishi, 2007). The dose-response curve status quo currently indicates a gap in the literature. Representative of an area in need of clarification, in order to determine a consensus regarding the role phytochemical compounds play in overall cognitive performance evolution.

Furthermore, it is noteworthy to mention that sex differences in the actions of long term and acute ingestion of phytochemical remain largely unknown (Sokolov et al., 2013). These undetermined sex difference effects may have been a contributing factor in the present lack of significant findings. Previously, it has been reported that sex related variability e.g. female physiology and distinct menstrual cycle phases, could be a leading cause for observed lack of significant effects (Sokolov et al., 2013). While sex differences within the population tested in the present study was not overly disproportionate, there was overall more females. Thus, sex differences within the population tested may, in part, account for the lack of support achieved for the second hypothesis. In future it is important that research investigates any potential sex related differences, as menstrual cycles and menopausal phases may add to the already contradictory field of data.

In summary, the present study failed to support the hypothesis that blackcurrant supplement would ameliorate physical fatigue effects on subsequent measures of cognitive performance. Therefore, overall it was concluded that the blackcurrant extract provided did not generate any effects on cognitive performance within either of the two conditions (exercise vs. no exercise). Interpretation of the observed results

presented difficulties as the present study demonstrated no observable effects of physical fatigue on cognitive performance. Nonetheless, potential explanations for the lack of significant findings were warranted. These can be summed, as thus, firstly, the cognitive tasks employed may not have been sensitive to identify effects of the

blackcurrant extract; specifically the cognitive domain influenced by the blackcurrant extract was not the particular domain that was involved for the processing of the applied cognitive task. Secondly, the dose of the extract was not sensitive enough to produce observable effects, and thirdly, sex related differences not yet determined, may have accounted for the lack of significant effects.