Participants
An a priori power calculation was not completed prior to commencing this study as to the best of our knowledge, there are no prior studies which report the effects of Ibuprofen ingestion on our primary outcome (power output) during a short (~ 60 min) exercise protocol in humans. Thus, we aimed to collect a total of 15 participants; however, due to timing and funding constraints, we completed the study with a sample size of 8.
Eight healthy, recreationally active (Pauw et al.
2013) males (24 ± 6 years, 183 ± 9 cm, 81.2 ± 12.5 kg, 44.0 ± 5.1 mL/kg·min
−1) participated in this study and were screened for current and previous exercise and disease history using the adult pre-screening exercise tool (APSS) (Exercise and Sports Science Australia; ESSA). Exclusion criteria included any previous or current conditions, injury or medications likely to alter the neurophysiological state of the brain. Further exclusion criteria were any reoccurring or a recent (< 3 weeks) bout of influenza illness, taking anti-inflammatory or any other medications known to interfere with a normal inflammatory response or individuals with rheumatoid arthritis, recent and/or current periodontal disease, and any other conditions associated with an altered inflammatory state.
Study design
Participants reported to the laboratory on three occasions, consisting of one familiarisation and two experimental trials performed in a crossover design separated by at least 7–10 days. A maximal aerobic test (VO2peak) was performed during the familiarisation visit, followed by familiarisation of the exercise protocol and equipment used in the subsequent trials. During the experimental trials, subjects were required to cycle at a clamped RPE of 16 (i.e. ‘very hard’), according to the 6–20 Borg RPE scale (6 = no exertion, 20 = maximal exertion) (4) in a climate chamber set at 35 °C, 60% relative humidity.
The clamped RPE methodology was used because it has been shown that at a fixed RPE, self-selected power output is reduced according to the prevailing environmental conditions (Tucker
2009), and that α wave activity is associated with reductions in power output (Vargas and Marino
2018). In addition, thermoregulatory responses and self-selected exercise intensity are modulated by RPE (Schlader et al.
2011a). Therefore, clamping the RPE provided a predictable outcome for these variables (Schlader et al.
2011a,
2011b). A modified version of the clamped RPE protocol, extended to 60 min of exercise, was employed in the present study to elicit predictable reductions in power output as in our prior work (Vargas and Marino
2018). In this protocol, participants were required to perform a maximal 30 s sprint at the end of each 10 min period to increase exercise intensity for the purpose of obtaining an adequate intensity for cytokine release. Pilot testing of this protocol revealed an intra-individual and inter-individual CV of 10% and 3%, respectively, for power output, and 2% and 3%, respectively, for heart rate. Although the CV for power output was slightly higher than deemed acceptable, that for the physiological outcomes was in an acceptable range. Mean power output of the steady-state bouts of exercise and of each 30 s sprint were used as indicators of exertional fatigue.
Familiarisation trial
Subjects reported to the laboratory for baseline measures of body mass and stature and a VO2peak test to determine fitness level and peak power output (PPO) on a cycle ergometer (Veletron DynaFit Pro, RacerMate Inc., WA, USA). All ergometer measurements were recorded for future use to decrease within-subject variability on the equipment. During the VO2peak test, subjects completed a 5 min warm up at light–moderate intensity followed by 2 min of rest. The test commenced at 100 W and increased by 20 W every minute until volitional exhaustion, defined by the inability to maintain a cadence above 60, or the subject voluntarily terminating the test.
Following a sufficient rest period and explanation of the remaining testing procedures (~ 30 min), subjects cycled on an identical ergometer in a heat chamber for an initial 10 min at variable RPE ratings to ensure understanding of both how to change the resistance on the ergometer and how to interpret the RPE scale. After familiarisation of different RPE ratings, subjects were asked to cycle at an RPE of 16 (hard-very hard) (Borg
1982) for the remaining 20 min. Subjects also performed a maximal (RPE = 20) sprint every 10 min. Following 30 min of familiarisation with the protocol, subjects cycled at a comfortable pace to cool down for 5 min and were instructed that a reduction in power during the test was okay, provided that they were maintaining the required RPE throughout the whole protocol.
Data collection
Baseline measures for each experimental session consisted of resting heart rate (HR), Tc and skin temperature (Tsk), a 15 mL blood sample for IL-6, sIL-6R and sgp-130, neuronal indices (EEG and cerebral oxygenation via near-infrared spectroscopy (NIRS) at the frontal cortex) and RPE. A 15 mL blood sample was collected halfway through the protocol at 30 min, immediately following the cessation of exercise at 60 min and after 1 h passive recovery. A 90 s EEG recording and RPE were collected every 5 min during exercise. Power output (PO), HR, Tsk and cerebral oxygenation were recorded continuously. A post-exercise EEG measure was taken immediately after the exercise protocol ended.
Power output (PO; RacerMate, Seattle, WA) and HR (Polar, Kempele, Finland) were measured continuously at a sampling rate of 2000 Hz. HR data were also manually recorded every 5 min using an accompanying sports watch (RS300X, Polar, Kempele, Finland) for accuracy. Mean PO during steady-state periods was calculated as the average total PO for the steady-state time (e.g. min 0–9:30 every 10 min) during the 60 min cycling protocol. Mean PO during the sprint was calculated during the 30 s sprint at the end of every 10 min period (e.g. min 9:30–10:00).
Approximately 6 h prior to reporting to the laboratory, subjects ingested a wireless telemetry pill (Jonah™ Core body temperature capsule, VitalSense Company, Inc., Bend, OR) for the measure of
Tc. After ingesting the pill, subjects were only permitted their small breakfast meal, and water prior to the trial. Upon arrival to the laboratory, a small amount of water was consumed with the Ibuprofen or placebo tablet. Participants were able to ingest water ad libitum throughout the trial. Measures of
Tsk were collected using Four Thermodata TDHC thermologgers (Brisbane, QLD) fixed to the skin (Opsite Flexifix, Smith & Nephew, AU) on the left side at the bicep, chest, mid-thigh and mid-calf area with data were sampled every minute. Mean
Tsk was calculated as 0.2 × (Thigh + Calf) + 0.3 × (Bicep + Chest) (Ranamathan
1976).
To determine plasma concentration of IL-6, sIL-6R and sgp-130, 15 mL blood was collected at each time point using a standard 22 g cannula (Becton Dickinson, NJ, USA) that remained in the arm for the duration of the protocol. Approximately 2 mL of the sample was discarded and 13 mL was transferred immediately to an ethylenediaminetetraacetic acid (EDTA) tube and centrifuged at 4 °C, 3500 rpm−1. After centrifuging for 15 min, 1 mL of plasma was immediately aliquoted into two microfuge tubes and stored at − 80 °C. Blood samples were analysed in duplicate using Merck Millipore Multiplex Assay human cytokine/chemokine magnetic bead panel kit for IL-6 (intra-assay coefficient of variation (CV): 12%; inter-assay CV: 11%, HCYTOMAG-60 K, Magpix, Luminex, Austin TX) sgp130 (intra-assay CV: 16%; inter-assay CV: 7%) and sIL-6R (intra-assay CV: 7%; inter-assay CV: 7%, HSCRMAG-32 K, Magpix, Luminex, Austin TX).
Subjects were fitted with a 20-channel wireless EEG system (BAlertX24, ABM, CA) based on the circumference of their head at a level just superior to the glabella, the measure of the distance from the glabella to the occipital protuberance and between external acoustic meatus. EEG electrodes were filled with Synapse Conductive Electrode Cream (ABM, CA). All electrodes and the paired mastoid reference sites were cleaned and abraded prior to checking scalp-electrode impedance (Ω). The impedance of each EEG site of interest was maintained below 20 kΩ as directed by the manufacturer. Signals were collected at a sample rate of 256 Hz and acquired wirelessly across an RF link via RS232 interface. Data were sampled with a bandpass filter from 0.5 to 65 Hz and raw signals monitored during rest and exercise. EEG signals were collected from all 20-electrode sites but only those from the frontal cortex (FC; F3, F4, Fz), motor cortex (MC; C3, C4, CZ) and parietal cortex (PC; P3, P4, Pz) were used for analysis. Data were processed and analysed using B-Alert Lab (Version 2.0, ABM, CA). Eye blink and muscle artefact was removed by B-Alert decontamination algorithms and each 90 s recording was manually inspected for artefact (Polyman, version 1.153.1065). Decontaminated data were then fast Fourier transformed with a Kaiser window applied to give mean power spectral density (PSD) for α (8–12 Hz) and β (13–30 Hz) frequencies. The percent change from baseline PSD in each measured site for both α and β frequencies was averaged for each 90 s snapshot.
Measures of oxy- (O2Hb) and deoxy- (Hhb) haemoglobin from the left prefrontal cortex (PFC) were collected from two optodes placed 40 mm apart using double side adhesive tape for the measure of cerebral blood flow using near-infrared spectroscopy (NIRS) (Niro-200 × Hamamatsu Photonics, Hamamatsu, Japan). Data were obtained at a frequency of 60 Hz using wavelengths of 735, 810 and 850 nm to calculate the change (Δ) in O2Hb and ΔHhb. Total haemoglobin concentration (Hbtotal) was calculated as the sum of O2Hb and Hhb. The haemoglobin difference (Hbdifference) was calculated by subtracting Hhb from O2Hb. These indices are reliable indicators of cerebral blood flow and tissue deoxygenation, respectively (3, 33).
Data and statistical analysis
Continually recorded data (i.e. PO, Tc, HR, Tsk) were binned as 60 s averages every 5 min to represent steady-state exercise at 5, 15, 25, 35, 45 and 55 min. Mean PO during the sprint was calculated over the full 30 s duration for each sprint. EEG and NIRS data were analysed only during the steady-state exercise bouts and averaged over the full 90 s snapshot. All data are reported as absolute data except EEG (reported as a percent change from baseline to account for daily variation within an individual) and NIRS (reported as absolute change from baseline). These data were analysed using a two-way (condition x time) repeated measures or mixed model (where data were missing) ANOVA. All data were checked for normality using a Shapiro–Wilk test. Most data sets (59 out of 64) met normality. Due to the small sample size, whether the data meet a normal Gaussian distribution is unlikely, therefore we continued with parametric testing. Violations of sphericity were accounted for using the Geisser–Greenhouse correction. When an ANOVA revealed a significant F test for main effect or interaction, Sidak post hoc analyses were performed. One-tailed paired t tests were used to determine differences in total work, average RPE, mean sprint PO, and end-trial change in Tc, Tsk, IL-6, sgp130 and sIL-6R. A one-tailed paired t test was also used to determine differences in average trial EEG and NIRS activity between conditions. All analyses were performed using GraphPad Prism Software (V6, La Jolla, CA). Statistical significance was set at P ≤ 0.05. Cohen’s d effect sizes were calculated and reported for the primary outcomes with small effect = 0.2; medim effect = 0.5; large effect ≥ 0.8.