Methods

4.2.1. Participant

One female participant (age 32 years; height, 170 cm; mass, 85 kg; BMI, 29.4 kg/m2; VO2max 25.9 ml·kg−1 · min−1) volunteered to take part in the study. The participant

was previously sedentary (i.e., relatively inactive), defined here as a score of < 4 and with

≤ 2 on both items of the Occupational and Spare-Time Physical Activity Questionnaire

(OSTPAQ – Appendix B) (Saltin & Grimby, 1968). The participant’s habitual caffeine intake was ~170 mg per day, estimated using the Caffeine Consumption Questionnaire (CCQ – Appendix C) (Landrum, 1992), which is considered ‘low’. The study was approved by the School of Sport and Exercise Sciences Research Ethics Committee at the University of Kent. Prior to taking part, the participant completed an informed consent form along with a standard medical questionnaire (Appendix A) to confirm their present state of health. The participant was given an overview, detailing all procedures and requirements of the study and was informed that the study was testing the effect of two different substances (either tyrosine, or beta-alanine), in combination with caffeine, on physiological and psychological responses to HIIT – when in fact they received either caffeine alone, or placebo. Consequently, the participant was naive to the true aims and hypotheses of the study until the final session was complete, at which point they were debriefed about its genuine rationale (see General Human Methods section 3.1. “Caffeine

deception” for details).

4.2.2. Experimental design

The experiment was a double-blind blocked randomisation test design (Dugard, File, & Todman, 2012) in which the participant visited the laboratory on 18 occasions.

61 Visits 1, 11, and 18 involved a treadmill-based incremental test, visits 2-4 served as a familiarisation, with visits 5-10, and 12-17 comprising the 12 experimental visits. These 12 experimental visits encompassed a crossover design in which the participant was allocated to six visits for each of the two experimental treatment conditions (caffeine vs. placebo). The treatment received for the first visit of each block was randomised, though the treatment for the remaining five visits of each block alternated to maximise the number of choice pairs (see section on choice). Blocking the experimental period allowed for any necessary adjustments to training intensity, to maintain the training stimulus if there are changes in exercise capacity.

4.2.3. Caffeine dose and deception

For the experimental sessions, the participant received either caffeine (3 mg∙kg) or placebo (dextrose monohydrate). A deception was used to minimise the impact of the

participant’s familiarity with caffeine. For further details on drug administration and the

deception see General Human Methods section 3.2. “Caffeine and placebo capsules and

administration”, and section 3.1. “Caffeine deception” respectively.

4.2.4. Procedures

During visit 1, a treadmill-based incremental test was completed to establish

VO2max – from which subsequent training intensities were determined. See General

Human Methods section 3.3. “Determination of maximal oxygen uptake (VO2max)” for

details. This test was repeated during visits 11 and 18. Visits 2 – 10, and 12 – 17 comprised the training portion of the study, which were completed at a frequency of 2 – 3 times per week, supervised by an exercise physiologist. The participant was instructed

62 not to add any leisure exercise during the study period. All training consisted of uphill treadmill walking. See General Human Methods section 3.4. “HIIT protocol” for details.

4.2.5. Acute perceptual and HR responses to HIIT

During each of the HIIT sessions (visits 2 – 10, and 12 - 17) perception of effort, affect, exercise-induced muscle pain, and HR responses were recorded throughout. See General Human Methods section 3.5. “Measuring acute perceptual and HR responses to

HIIT” for details.

4.2.6. Psychological questionnaires before and/or after HIIT

The participant completed the fatigue and vigour subscales of the Brunel Mood Scale (BRUMS) immediately before and after HIIT. Scales for intrinsic motivation (IM), and potential motivation (PM) were complete before HIIT only. Whilst self-reported exercise enjoyment was measured immediately post HIIT only, using the PACES. See General Human Methods sections 3.6. “Mood-state around HIIT”; 3.7. “Task (HIIT)

motivation”; and 3.8. “Exercise enjoyment” for more details. Ten-minutes post-exercise,

whole session RPE was recorded using the Borg (1970) 6-20 scale, representing a single global rating of the intensity for the entire training session. See General Human Methods section 3.9. “Session RPE” for details.

4.2.7. Choice measurement

Our measurement of choice is simple. As described previously, the participant received either caffeine or placebo for their first experimental training session, the treatment alternated thereafter. After the second experimental training session, ten

63 minutes post-exercise, the participant was asked whether they preferred the session they had just completed or the session they completed during their previous visit. This process was completed after each subsequent session, so they had the opportunity to choose (forced choice) between caffeine and placebo on 11 occasions throughout the course of the study.

4.2.8. Statistical analyses

Randomisation tests (Dugard et al., 2012) were used to assess for mean differences between treatments (Caffeine/Placebo) in the following parameters: RPE, FS, PS, and HR during training; BRUMS (fatigue and vigour subscales) scores from pre- and post-exercise; intrinsic and potential motivation pre-exercise; exercise enjoyment post- exercise; exercise liking; and session RPE. For the variables measured during exercise (i.e., RPE, FS, PS, and HR) an aggregate of the scores reported at the end of each of the four high-intensity blocks was used as a single test value (for statistical analysis) from each session. For each of the randomisation tests, to test for statistical significance, mean values for each treatment condition were first calculated. The difference between these means was then obtained. These values provided the true experimental difference between treatments for the dependent variable. The randomised order of experimental treatments across the 12 visits represented one of many possible ways in which the treatment visits could have been arranged. Using a pre-designed macro (Dugard et al., 2012) the raw data from the 12 experimental treatment visits was randomly rearranged 2000 times to coincide with alternative visits in the original treatment allocation. For each of these 2000 rearrangements, only the raw data from treatment conditions was randomly rearranged with the allocated treatment order of the respective 12 experimental visits remaining the same. Specifically, this meant that the raw data for each visit was randomly

64 swapped between the allocated treatment visits 2000 times. Rearranging the raw data in proximity to the assigned visits in this manner permitted the calculation of a mean difference between treatment conditions for each of the 2000 treatment rearrangements. In order of magnitude from high to low, the true mean difference was then ranked amongst the 2000 mean differences that were obtained from the treatment rearrangements. Statistical significance was obtained if the mean difference for the experimental data was greater than 95% of the mean differences acquired from the 2000 treatment rearrangements. Statistical significance was set at p ≤ 0.05 (one-tailed) and the data analyses were conducted using a specified macro (Dugard et al., 2012) in Microsoft Excel 2010.

4.2.9. Choice analysis

As with the measurement, the analysis is simple, taken from consumer research where this choice paradigm is used often – termed ‘preference tests’ (Cochrane et al., 2005). A score of 1 was given for each choice made in preference for caffeine, and 0 for placebo. Using the number of "successes" (i.e., how many times caffeine was preferred), and the number of trials per experiment (i.e., the total number of choice opportunities), a sign-test was performed (http://graphpad.com/quickcalcs/binomial1/), assuming the probability of success in each trial was 0.5. Significance was set at p ≤ 0.05.

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