The effect of blackcurrant juice consumption on motivation to exercise

INTERVENTION: This is a double‐blind, placebo controlled parallel design intervention study that will allow us to test the effect of the consumption of blackcurrant juice on the modulation of dopaminergic/noradrenergic nerve pathways and motivation to maintain a moderate intensity exercise. All prospective participants will be asked to attend a familiarisation session which will take approximately 1 hour. During the familiarisation session, participants will be introduced to the subjective scales and questionnaire that they will be asked to respond to during the main trial day. Participants will also be asked to perform a moderate intensity treadmill exercise that will allow us to estimate the intensity of the exercise they will be required to perform on the main trial day that is customised to their fitness level. On the main trial day, participants will be randomised into one of two treatment groups: (1) Blackcurrant group and (2) Placebo group. On the main trial day, participants will be asked to consume 200 mL of blackcurrant (adjusted to a dose of 500 mg polyphenol per 60 kg body weight) or placebo drink within 2 minutes. After consuming the their treatment drink, participants will be asked to sit in the waiting room provided in the facility and refrain from any exercise for 1 hr. Following this, participants will be asked to perform a moderate intensity exercise with their motivation and exertion subjectively measured at regular intervals. We estimate that participants will be required to be on‐site for approximately 4‐5 hours during the main trial day. CONDITION: Motivation to exercise PRIMARY OUTCOME: Biochemical motivation biomarkers including neurotransmitters (serotonin, 4‐dihydroxyphenylglycol (DHPG), 3‐methoxy‐4‐hydroxyphenylglycol (MHPG), homovanillic acid and normetadrenaline), plasma prolactin, B‐endorphins, cortisol and platelet MAO‐A and B activity will be measured using commercial assay kits or assays developed in‐house. Primary exercise/physicial activity parameters will include exercise duration (time and distance). The primary subjective motivation measure will be measured by scores on the Feeling Scale (FS) given by participants. SECONDARY OUTCOME: Ferric reducing capacity of plasma (FRAP) will be measured as a parameter of plasma antioxidant capacity. Heart rate during exercise will measured as a secondary measure of exercise/physical activity. Plasma ATP and blood glucose will be measured as composite secondary biological measures of energy. Plasma anthocyanin and polyphenol levels will be measured in blood samples collected from participants as composite measurements of bioavailabilty. Plasma oxidative capacity and lipid peroxidation will also be measured as composite measurements of oxidative stress. The Rate of Percieved Exertion (RPE) as a secondary subjective measure of motivation and effort by scores given by participants will be measured. INCLUSION CRITERIA: Healthy individuals who are not involved in any regular exercise routine and do not have a high habitual acitivy but can complete the physical requirements of this trial will be selected for this study. Participants will be required to complete a health questionnaire and provide written consent for this study.