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Caffeine ingestion enhances perceptual responses during intermittent exercise in female team-game players a
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Ajmol Ali , Jemma O’Donnell , Pamela Von Hurst , Andrew Foskett , Sherina Holland , c
Carlene Starck & Kay Rutherfurd-Markwick
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School of Sport and Exercise, Massey University, Auckland, New Zealand
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School of Food and Nutrition, Massey University, Auckland, New Zealand
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School of Sport and Exercise, Massey University, Palmerston North, New Zealand Published online: 05 Jun 2015.
Click for updates To cite this article: Ajmol Ali, Jemma O’Donnell, Pamela Von Hurst, Andrew Foskett, Sherina Holland, Carlene Starck & Kay Rutherfurd-Markwick (2015): Caffeine ingestion enhances perceptual responses during intermittent exercise in female teamgame players, Journal of Sports Sciences, DOI: 10.1080/02640414.2015.1052746 To link to this article: http://dx.doi.org/10.1080/02640414.2015.1052746
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Journal of Sports Sciences, 2015 http://dx.doi.org/10.1080/02640414.2015.1052746
Caffeine ingestion enhances perceptual responses during intermittent exercise in female team-game players
AJMOL ALI1, JEMMA O’DONNELL1, PAMELA VON HURST2, ANDREW FOSKETT1, SHERINA HOLLAND2, CARLENE STARCK3 & KAY RUTHERFURD-MARKWICK2 1
School of Sport and Exercise, Massey University, Auckland, New Zealand, 2School of Food and Nutrition, Massey University, Auckland, New Zealand and 3School of Sport and Exercise, Massey University, Palmerston North, New Zealand
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(Accepted 15 May 2015)
Abstract We examined the influence of caffeine supplementation on cognitive performance and perceptual responses in female teamgame players taking low-dose monophasic oral contraceptives of the same hormonal composition. Ten females (24 ± 4 years; 59.7 ± 3.5 kg body mass; 2–6 training sessions per week) took part in a randomised, double-blind, placebo-controlled crossover-design trial. A 90-min intermittent treadmill-running protocol was completed 60 min following ingestion of a capsule containing either 6 mg • kg−1 anhydrous caffeine or artificial sweetener (placebo). Perceptual responses (ratings of perceived exertion (RPE), feeling scale (FS), felt arousal scale (FAS)), mood (profile of mood states (POMS)) and cognitive performance (Stroop test, choice reaction time (CRT)) were completed before, during and after the exercise protocol, as well as after ~12 h post exercise. Caffeine ingestion significantly enhanced the ratings of pleasure (P = 0.008) and arousal (P = 0.002) during the exercise protocol, as well as increased vigour (POMS; P = 0.007), while there was a tendency for reduced fatigue (POMS; P = 0.068). Caffeine ingestion showed a tendency to decrease RPE (P = 0.068) and improve reaction times in the Stroop (P = 0.072) and CRT (P = 0.087) tests. Caffeine supplementation showed a positive effect on perceptual parameters by increasing vigour and a tendency to decrease fatigue during intermittent running activity in female games players taking low-dose monophasic oral contraceptive steroids (OCS). Keywords: affect, cognition, feel-good response, pharmacological ergogenic aid, soccer
Introduction Caffeine is the most commonly consumed drug in the world and used daily by approximately 90% of the adult population (Bishop, 2010). Caffeine use as an ergogenic aid is highly prevalent in the sports industry (Bishop, 2010), is known to enhance performance through both peripheral and central mechanisms (Davis & Green, 2009) and is used equally by males and females (Del Coso, Muñoz, & Muñoz-Guerra, 2011). However, data addressing the effects of caffeine in female athletes, particularly with respect to the central nervous system (CNS), is limited, and given the increasing participation of females in sport (Del Coso et al., 2011), as well as the sex-related differences (e.g. differing concentrations of sex hormones, lean body mass, effect of contraceptives) reported for caffeine metabolism (Abernethy & Todd, 1985; Lane, Steege, Rupp, & Kuhn, 1992), research in this area is necessary. While multiple mechanisms have been proposed to underlie the physical performance-enhancing
effects of caffeine, the main pathway appears to be stimulation of the CNS via inhibition of adenosine receptors (Fredholm, Bättig, Holmén, Nehlig, & Zvartau, 1999; Graham, 2001). As adenosine signalling has been shown to enhance pain perception, induce sleep, reduce arousal and depress spontaneous locomotor activity (Davis & Green, 2009), caffeine-mediated antagonism of adenosine receptor function also results in the modulation of perceptual responses (e.g. perceived exertion, affect and arousal (Davis & Green, 2009; Sökmen et al., 2008), the improvement of mood (Lieberman, 2001; Sökmen et al., 2008) and enhancement of cognitive performance (Lieberman, 2001; Sökmen et al., 2008). During aerobic, steady-state exercise caffeine ingestion has been shown to reduce ratings of perceived exertion (RPE), in both males and females during submaximal cycling (Duncan & Hankey, 2013) and constant-load exercise (Doherty & Smith, 2005). In contrast, the effect of caffeine on RPE during team-sports and exercise of an exhaustive or intermittent nature is unclear. Caffeine
Correspondence: Ajmol Ali, School of Sport and Exercise, Massey University, Albany, Auckland, New Zealand. E-mail: [email protected] © 2015 Taylor & Francis
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supplementation failed to influence RPE during a 10-km high-intensity cycling time trial in men (Astorino, Cottrell, Talhami Lozano, AburtoPratt, & Duhon, 2012), an 8.2-km time trial in women (Astorino, Roupoli, & Valdivieso, 2012), in female rugby (Del Coso et al., 2013) and soccer players (Lara et al., 2014), or in males performing a multiple-sprint protocol (Glaister et al., 2008). It is possible that the attenuating effects of caffeine on RPE are subject to the level of exercise intensity or that responses are sport and/or activity-dependent. It is also possible that participants may be doing more work at a similar level of exertion. These suggestions remain to be investigated. Although feelings of pleasure/displeasure and level of arousal are key factors in athletic performance (Astorino, Cottrell, et al., 2012), these measures are reported in only a limited number of exercise studies to date. Moderate doses of caffeine (3.7– 6 mg • kg−1) enhanced feelings of pleasure in trained males during endurance cycling (Backhouse, Biddle, Bishop, & Williams, 2011), high-intensity cycling (Astorino, Cottrell, et al., 2012) and simulated soccer activity (Gant, Ali, & Foskett, 2010), yet failed to affect changes in arousal. No comparable data has been published for female athletes. In addition to cognitive and perceptual parameters, caffeine has been found to have pronounced effects on mood, often assessed using the profile of mood states (POMS) (Berger & Motl, 2000). In an exercise setting, the majority of results show increased vigour and/or reduced fatigue following caffeine consumption (Smith, 2002). However, data on the effect of caffeine ingestion on “feel-good” aspects and/or mood in females is lacking, particularly in a teamsports setting. The effects of caffeine on cognitive function include increased alertness, vigilance, reaction time and skill performance (Fredholm et al., 1999). Caffeine supplementation improved vigilance, alertness and reaction time in sleep-deprived US Navy SEAL trainees (Lieberman, Tharion, Shukitt-Hale, Speckman, & Tulley, 2002) and improved the cognitive performance of trained cyclists following both a 1-hour time-trial (Hogervorst, Riedel, Kovacs, Brouns, & Jolles, 1999) and a time to exhaustion trial (Hogervorst et al., 2008). However, there is a dearth of information regarding caffeine ingestion on cognition in female team-sports athletes, despite findings that oral contraceptive steroids (OCS) and oestrogen have a significant impact on caffeine metabolism (Abernethy & Todd, 1985; Ali, O’Donnell, Starck & Rutherfurd-Markwick, 2015; Lane et al., 1992) and that cognitive performance declines in the highprogesterone, luteal phase of the menstrual cycle (Kumar, Mufti, & Kisan, 2013).
While the majority of research supports the significance of caffeine’s influence on cognitive and perceptual parameters for team-sports performance, these effects are complex compared with those observed for endurance exercise and require further examination. Often, simultaneous improvements in parameters of cognitive (Hogervorst et al., 2008) and physical (Astorino, Cottrell, et al., 2012; Astorino, Roupoli, et al., 2012) performances are observed, despite contradictory effects on perception; thus, additional research is needed to fully understand the contribution of caffeine to perceptual and mood responses during intermittent exercise. In particular, information relevant to the specific effects of caffeine in females performing team-sports exercise is scarce. As the use of OCS is widespread in female athletes (Rechichi & Dawson, 2009), and both OCS and menstrual-cycle stage play a significant role in determining the influence of caffeine ingestion on cognitive and perceptual parameters in females (Constantini, Dubnov, & Lebrun, 2005; Kumar et al., 2013), studies on caffeine response in males cannot be used to inform caffeine recommendations in females. Furthermore, research on central responses following caffeine ingestion in female exercisers has been primarily conducted without regard for menstrual-cycle stage or OCS use; indeed, the conflicting information between studies may be due to such methodological limitations. Therefore, research that addresses the effect of caffeine ingestion on perceptual responses and cognitive function in female athletes using OCS during an intermittent exercise protocol is warranted. For the first time, we aim to provide novel data addressing the effect of a moderate dose of caffeine in female games players using OCS on cognitive performance, perceptual responses and mood state during and following an intermittent exercise protocol. We hypothesise that caffeine will positively impact perceptual, mood and cognitive responses during and following exercise.
Methods Participants This study was part of a larger investigation examining the effects of caffeine ingestion in female teamsport players and the perceptual, mood and cognitive data will be presented here. Sample size was estimated using data from Kalmar and Cafarelli (1999) and an appropriate statistical package (GPower 3.1). A sample size of 10 was sufficient to detect 3.5% change in muscle strength performance between caffeine and placebo trials, with a power of 0.84 and P < 0.05. Ten healthy female team-games players (mean ± SD; 24 ± 4 years; 59.7 ± 3.5 kg body mass; 1.62 ± 0.06 m height; 2–6 training sessions per week
Caffeine and perceptual responses in females for soccer, hockey and/or netball at various levels of competition, from recreational to international) volunteered to participate in this study, which was approved by the local ethics committee. Participants were informed of all study requirements, benefits and associated risks prior to providing written consent. None of the participants were taking any other supplements.
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Experimental control The participants’ self-reported caffeine intake varied (estimated range 0–300 mg • day−1) based on daily consumption of common caffeine sources (not all participants consumed caffeine-containing products every day; some indicated they consumed products containing caffeine on a weekly basis). High caffeine consumers (more than four cups a day) and naïve users (those that actively refrained from consuming caffeine-containing products) were excluded from the study. All participants were asked to keep a food diary for two days before their first trial and to replicate this diet before their second trial to reduce the potential for diet-induced variability between trials. During this 48-h period, participants were asked to avoid alcohol and foods containing caffeine (coffee, tea, soft drinks, energy drinks and chocolate). In addition, they were asked to refrain from exercise for the final 24 h of this period and fast for 3 h (only water intake allowed) prior to the main trials. The food record diaries were analysed using dietary analysis software (Foodworks version 6.0.2562, 2009, Xyris Software). All participants were taking a monophasic oral contraceptive for at least 3 months prior to commencing the study. All oral contraceptives were of the same hormonal composition (Monofeme, Levlen ED, Microgynon or Nordette: 30 µg Ethinyloestradiol and 150 µg Levonorgestrel; (Roberts, 2008)). In order to control for possible differences during the oral contraceptive cycle all testing was performed during days 5–8 and 18–22 of one pillcycle. No changes in high-intensity intermittent exercise performance or energy metabolism have been reported between these periods of the menstrual cycle for participants taking a low-dose monophasic oral contraceptive (Lynch & Nimmo, 1998; Lynch, Vito, & Nimmo, 2001). Participants were asked to keep daily records of their oral contraceptive use by recording the day and time taken. To ensure similarity between trials, participants were asked to keep the timing as consistent as possible during the days of the main trial as well as the morning session that followed.
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Practice session Participants were asked to perform one preliminary session before commencing the main trials. Participants initially performed an incremental max_ 2) max test. This test was imal oxygen uptake (VO carried out on a treadmill (Woodway, ELG70; Munich, Germany) with a 1% incline, at an initial speed of 8 km • h−1, which increased by 1 km • h−1 every 2 min, until the participant signalled they could only continue for a further minute. Expired air was collected using the Douglas bag method; analysis of the expired air for CO2 and O2 concentrations was performed using a gas analyser (Servomex, Model ML206, AD Instruments, Australia) and gas volumes were measured using a Harvard dry gas meter (Serial number K015078, Harvard Apparatus, MA, USA). The gas analyser was calibrated prior to each test using commercially available mixtures of known gases (span gas: 5% CO2, 20% O2; zero gas: 100% N2; BOC, Auckland). Maximal oxygen uptake was determined using standard criteria (ACSM, 2000). Participants then completed two 15-min blocks of the intermittent treadmill running protocol (Atkinson et al., 2005) to familiarise themselves with the running patterns involved and the overall experimental procedures. Participants were also familiarised with the perceptual scales, the POMS questionnaire and the cognitive tests before, during and immediately following the two 15-min blocks of running.
Experimental trials All trials took place in the same laboratory. Environmental temperatures (20.3 ± 0.7°C and 20.4 ± 0.8°C, P = 0.07) and relative humidity (46.4 ± 1.2 and 48.6 ± 1.4%, P = 0.10) were not different between trials. Following the preliminary session, participants returned during days 5–8 and 18–22 of their OCS cycle to complete the main trials at approximately 6 pm. Treatments were randomly assigned using a placebo-controlled, double-blind crossover design. Figure 1 shows a schematic representation of the experimental protocol. After cannula insertion and blood sampling, participants ingested a gelatin capsule (Vegie Capsules, BioBalance, New Zealand) containing either 6 mg • kg−1 anhydrous caffeine (Fluka Sigma-Aldrich, St. Louis, MO, USA) or placebo (artificial sweetener, Equal) with a 500-mL bolus of water (capsules were swallowed intact to eliminate any organoleptic differences between treatments). The intermittent exercise protocol took place 60 min after ingestion and consisted of six 15-min blocks of treadmill running. Each block was made up of six 2-min periods at 40%, 60%, 80%, _ 2max followed by 1 min at 40%, 60% and 80% VO
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Figure 1. Schematic representation of protocol. Exercise was carried out intermittently in six 15-min blocks 60 min following ingestion of caffeine (CAFF) or placebo (PLA). Tests of cognitive performance (CRT and Stroop test, black arrow), perception (RPE, FS and FAS, hashed arrow), mood (POMS, white arrow) and blood glucose (grey arrow) were carried out at the time points indicated. Final measurements were taken the following day, approximately 12 h after the exercise protocol.
_ 2max and a 2-min walk at 4 km • h−1, to 60% VO simulate the activity patterns of a soccer match (Atkinson et al., 2005). Following the exercise, participants went home, consumed their evening meal (same for both trials) and then went to sleep. They returned to the laboratory the following morning for their 12 ± 2 h post-exercise measurements (in fasted state). Tests for cognitive function, perceptual parameters and mood were undertaken before, throughout and following the exercise protocol (Figure 1). Following completion of the study, participants were asked which trial they thought was the caffeine trial; 9 out of 10 participants correctly identified the caffeine trial.
measures changes in perceived arousal throughout exercise. This scale is based upon Apter’s Reversal Theory and is valid in an exercise setting as it requires a subjective assessment of the participant’s perceived arousal (Apter, 1989). High arousal is characterised as anger or excitement, while low arousal is representative of calmness or boredom. Although participants were familiarised with these scales during the practice session, one of the investigators read out a short standardised prompt for each scale prior to assessment. The order of the scales presented to the participants was RPE, followed by FS and then FAS for each sampling point. Assessment of mood
Perceptual measurements Perceptual responses were assessed pre-exercise, after every 15-min block of exercise, immediately post exercise and 12 ± 2 h post exercise (Figure 1), using the RPE scale (Borg, 1982), the feeling scale (FS; Hardy & Rejeski, 1989) and the felt arousal scale (FAS; Svebak & Murgatroyd, 1985). The RPE scale measured the subjective intensity of each 15-min block of exercise. It is a 15-point scale ranging from 6 to 20 with corresponding anchors that range from “No Exertion at all” to “Maximal Exertion”. Measures were taken throughout the exercise; however, this scale only indicates the level of exertion the participant is experiencing and does not give any indication of the participant’s other emotions during exercise and does not estimate the participant’s perceived activation. The FS assessed pleasure or displeasure felt during exercise. It is an 11-point scale ranging from −5 “Very Bad” to +5 “Very Good”. The FAS is a 6-point (0–5) scale that
Participants completed the POMS (Grove & Prapavessis, 1992) questionnaire pre-exercise, after 45 and 90 min of exercise and 12 ± 2 h post exercise (Figure 1). The POMS was used to assess changes in mood as a result of exercise and/or caffeine supplementation. The participant was presented with 40 adjectives that were grouped into seven subgroups (fatigue, anger, vigour, tension, esteem, confusion and depression). Participants selected how well each adjective described the way they felt at that point in time using a 5-point Likert scale that ranged from “Not at all” to “Extremely”. Cognitive function Cognitive function was assessed pre-exercise, after 45 and 90 min of exercise and 12 ± 2 h post exercise (Figure 1), using a computer software program (Computerised Mental Performance Assessment System [COMPASS], Northumbria University, Newcastle, United Kingdom). Participants were
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Caffeine and perceptual responses in females required to perform two tasks: the choice reaction time (CRT) test and the Stroop test. While performing the cognitive testing the participants wore earmuffs, and the computer was positioned facing a blank wall, to minimise distractions to the participant that might have impeded performance. The CRT test was used as a measure of decision-making time (Teichner & Krebs, 1974). Participants were presented with more than one possible response for each test, which involved an arrow displayed on the screen facing either the left or the right. The participant had to select the correct corresponding left or right button as quickly as possible. The test involved the presentation of 35 stimuli. The Stroop test was used as a measure of attention bias and reaction time (Bench et al., 1993). Participants were shown words for certain colours, although the actual colour of the word often differed from the colour the word represented, e.g. the word “blue” may be displayed in a red font. The participants were required to respond with the colour of the font and disregard the name of the colour. The duration of the task was 1.5 min. Blood sampling An 18-gauge, 1.3-mm intravenous cannula (Insyte, Becton Dickson, NJ, USA) was inserted into a medial antecubital vein. Blood samples were taken at rest, after blocks 1, 3 and 6 of exercise, and 12 ± 2 h post exercise. Regular flushing with saline (0.9% sodium chloride, Demo S.A. Pharmaceutical Industry, Athens, Greece) was used to keep the cannula patent. Four millilitre blood samples were collected in EDTA tubes, centrifuged for 10 min at 1250 × g (MF 50, Hanil Science Industrial Co. Ltd, Korea) and the plasma was stored at −80°C for later analysis of plasma glucose. Glucose analysis
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is presented as means ± SD and statistical significance was set at P < 0.05. Practical significance was reported using effect sizes (Cohen’s d); a large effect size was determined as 0.8, medium as 0.5 and small as 0.2 (Cohen, 1988).
Results Perceptual responses There was a tendency for lower RPE during exercise when caffeine was ingested compared with placebo (P = 0.068; Cohen’s d = 1.23; Figure 2). RPE increased over the duration of exercise for both trials (P < 0.001). Although there were no main effects of treatment (P = 0.095) or time (P = 0.109), there was an interaction of treatment × time for ratings of pleasure (P = 0.008). Furthermore, in terms of practical significance, ratings of pleasure were 82% higher when caffeine was ingested compared to placebo (Cohen’s d = 2.18). Post-hoc analysis showed higher FS ratings in the caffeine trial at the 15–30, 30–45, 45–60 and 75–90-min time points (P < 0.05; Figure 3A). There was no effect of treatment on perceived arousal (P = 0.151; Cohen’s d = 1.39; Figure 3B). However, ratings of arousal increased over time for both groups (P = 0.013), and there was an interaction of treatment × time (P = 0.002) with higher ratings in the caffeine trial at 45–60 and 60–75-min time points (P < 0.05). The FS and FAS values were additionally plotted in a circumplex model providing a visual description of changes in pleasure and arousal throughout the trial (Figure 4). In the caffeine trial, participants’ data indicated they were in the “high arousal, pleasure” quadrant (Figure 4A), whereas in the placebo trial they were in the “low arousal, pleasure” quadrant (Figure 4B).
An assay based on the hexokinase method was used to establish plasma glucose concentrations using a commercially available kit (Wako Pure Chemical Industries, Ltd. Osaka, Japan). Statistical analysis Data were compared using a two-way ANOVA with repeated measures (SPSS version 19.0. Chicago, IL) to examine the main effects of (i) treatment and (ii) time as well as (iii) interaction of treatment × time. Mauchly’s test for sphericity was applied to the data. When sphericity was violated, the Huynh–Feldt estimate was used to correct the data. When significant differences between the interventions were identified by ANOVA, post-hoc Student’s t-test, using the Holm–Bonferroni adjustment, was performed. Data
Figure 2. Mean (± SD) ratings of perceived exertion (RPE) during caffeine (CAFF) and placebo (PLA) trials during the 90-min intermittent exercise protocol (n = 10).
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Figure 3. Mean (± SD) ratings of (A) pleasure–displeasure (feeling scale, FS) and (B) perceived activation (felt arousal scale, FAS) during caffeine (CAFF) and placebo (PLA) trials before, during and after the 90-min intermittent exercise protocol. *Significantly higher in CAFF trial (P < 0.05) (n = 10).
Mood responses The overall POMS score contains contributions from the seven different mood states of fatigue, anger, vigour, tension, esteem, confusion and depression and showed no difference with caffeine ingestion (P = 0.163; Cohen’s d = 0.916), but a decrease over time (P = 0.003; Figure 5A).
Figure 5. Profile of mood states (POMS) ratings in caffeine (CAFF) and placebo (PLA) trials before exercise, at the midpoint of exercise (45 min) and immediately post exercise (90 min). (A) Overall POMS ratings, (B) sub-scale ratings of fatigue and (C) sub-scale ratings of vigour (n = 10).
Figure 4. Circumplex model of affect in (A) caffeine (CAFF) and (B) placebo (PLA) trials based on feeling scale and felt arousal scale ratings before exercise (a), during, immediately post (b) and ~12 h post (c) the 90-min exercise protocol. Roman numerals indicate various activation and pleasure states: (i) high arousal and displeasure (e.g. anger); (ii) high arousal and pleasure (e.g. vigour); (iii) low arousal and displeasure (e.g. boredom or fatigue); (iv) low arousal and pleasure (e.g. calm) (n = 10).
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Caffeine and perceptual responses in females Post-hoc analysis revealed a higher POMS score prevs. post exercise (P < 0.05) for both caffeine and placebo trials. Analysis of individual mood states showed varying effects for the most relevant subsets to exercise, i.e. fatigue (Figure 5B) and vigour (Figure 5C). There was a tendency for lower fatigue scores in the caffeine trial compared with the placebo trial (P = 0.068; Cohen’s d = 1.66) and lower ratings over time (P = 0.084). Although there was no effect of caffeine ingestion (P = 0.493) or time (P = 0.221) on vigour, there was an interaction effect with vigour scores increasing in the caffeine trial but decreasing in the placebo trial over time (P = 0.007). Furthermore, there was a practically significant increase in vigour with caffeine ingestion of 13% (Cohen’s d = 0.608). Post-hoc analysis of vigour scores showed no differences at any specific time points between trials.
Cognitive function There was no effect of caffeine on the percentage of correct responses in the CRT (P = 0.136, Table IA) despite higher averages in the caffeine trial for all time points (Cohen’s d = 1.73). Caffeine ingestion had no effect on correct responses in the Stroop test (P = 0.890; Cohen’s d = 0.12; Table IB). However, there was a tendency for an interaction of treatment × time with a higher percentage of correct responses for the Stroop test in the caffeine trial (P = 0.072). There was a tendency for faster reaction times with caffeine ingestion for the CRT (P = 0.087; Cohen’s d = 1.46; Table I), but not for the Stroop test (P = 0.884; Cohen’s d = −0.038; Table II).
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There was, however, an effect of time in the Stroop test (P < 0.001) and a tendency for an interaction effect of treatment × time in the Stroop test, indicating non-significant faster reaction times in the caffeine trial over time (P = 0.07). Dietary analysis There were no differences in mean energy intake (placebo vs. caffeine trial; 7212 ± 2170 kJ vs. 6088 ± 1735 kJ, P = 0.105) or percentage intake of protein (17.0 ± 4.1% vs. 15.0 ± 2.9%, P = 0.192), fat (33.2 ± 8.6% vs. 33.4 ± 7.5%, P = 0.910) or carbohydrate (49.8 ± 12.2 vs. 51.2 ± 7.6%, P = 0.545) between trials. Plasma glucose There were no differences in blood glucose levels between treatments (P = 0.919), over time (P = 0.100) or for the interaction of treatment with time (P = 0.593; Table II). Discussion This study provides a more complete understanding of the perceptual responses experienced by female team-game players using caffeine as a supplement than other studies published to date. Moreover, it is the first time that FS and FAS data, and their relationship in the circumplex model, have been reported for females in response to caffeine ingestion. Caffeine intake significantly increased ratings of pleasure and arousal over the course of the exercise protocol and showed enhanced vigour and a tendency for reduction in fatigue. While there was no
Table I. Percentage of correct responses and mean (± SD) reaction time for (A) choice reaction time (CRT) test and (B) Stroop test in caffeine (CAFF) and placebo (PLA) trials (n = 10). Time Pre-exercise (A) Choice reaction time Correct answers (%) PLA 96.9 ± 2.5 CAFF 97.4 ± 3.7 Mean reaction time (ms) PLA 400.1 ± 23.6 CAFF 393.1 ± 43.8 (B) Stroop test Correct answers (%) PLA 97.0 ± 2.6 CAFF 97.8 ± 2.6 Mean reaction time (ms) PLA 629.2 ± 61.8 CAFF 659.2 ± 92.5
Mid-exercise
P values
Post exercise
~12 h Post exercise
Treatment
Time
Treatment × time
96.6 ± 3.8 97.4 ± 2.1
96.6 ± 2.3 96.9 ± 2.1
96.3 ± 3.6 96.9 ± 3.7
0.136
0.931
0.935
399.9 ± 52.0 374.0 ± 42.7
389.9 ± 25.3 377.2 ± 37.8
381.5 ± 29.8 374.1 ± 31.3
0.087
0.347
0.628
97.1 ± 2.9 97.0 ± 2.3
96.6 ± 3.7 98.3 ± 1.8
98.6 ± 2.2 96.6 ± 2.9
0.890
0.905
0.072
611.6 ± 80.2 600.0 ± 58.6
619.5 ± 76.5 589.6 ± 60.8
575.5 ± 25.5 591. 6 ± 61.2
0.884
9 mg • kg−1 ) have been reported to cause negative side effects, including dizziness, headache, jitteriness, nervousness, insomnia and gastrointestinal distress (Graham & Spriet, 1995; Sökmen et al., 2008). Plasma caffeine concentrations in our participants were 0.3 ± 0.3 mmol • L−1 (pre-supplementation), 9.6 ± 0.3 mmol • L−1 (mid-exercise), 9.2 ± 1.0 mmol • L−1 (postexercise) and 5.0 ± 1.8 mmol • L−1 (12-h postexercise) in the caffeine trial, whereas caffeine concentration was
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Caffeine ingestion enhances perceptual responses during intermittent exercise in female team-game players a
a
b
a
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Ajmol Ali , Jemma O’Donnell , Pamela Von Hurst , Andrew Foskett , Sherina Holland , c
Carlene Starck & Kay Rutherfurd-Markwick
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School of Sport and Exercise, Massey University, Auckland, New Zealand
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School of Food and Nutrition, Massey University, Auckland, New Zealand
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School of Sport and Exercise, Massey University, Palmerston North, New Zealand Published online: 05 Jun 2015.
Click for updates To cite this article: Ajmol Ali, Jemma O’Donnell, Pamela Von Hurst, Andrew Foskett, Sherina Holland, Carlene Starck & Kay Rutherfurd-Markwick (2015): Caffeine ingestion enhances perceptual responses during intermittent exercise in female teamgame players, Journal of Sports Sciences, DOI: 10.1080/02640414.2015.1052746 To link to this article: http://dx.doi.org/10.1080/02640414.2015.1052746
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Journal of Sports Sciences, 2015 http://dx.doi.org/10.1080/02640414.2015.1052746
Caffeine ingestion enhances perceptual responses during intermittent exercise in female team-game players
AJMOL ALI1, JEMMA O’DONNELL1, PAMELA VON HURST2, ANDREW FOSKETT1, SHERINA HOLLAND2, CARLENE STARCK3 & KAY RUTHERFURD-MARKWICK2 1
School of Sport and Exercise, Massey University, Auckland, New Zealand, 2School of Food and Nutrition, Massey University, Auckland, New Zealand and 3School of Sport and Exercise, Massey University, Palmerston North, New Zealand
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(Accepted 15 May 2015)
Abstract We examined the influence of caffeine supplementation on cognitive performance and perceptual responses in female teamgame players taking low-dose monophasic oral contraceptives of the same hormonal composition. Ten females (24 ± 4 years; 59.7 ± 3.5 kg body mass; 2–6 training sessions per week) took part in a randomised, double-blind, placebo-controlled crossover-design trial. A 90-min intermittent treadmill-running protocol was completed 60 min following ingestion of a capsule containing either 6 mg • kg−1 anhydrous caffeine or artificial sweetener (placebo). Perceptual responses (ratings of perceived exertion (RPE), feeling scale (FS), felt arousal scale (FAS)), mood (profile of mood states (POMS)) and cognitive performance (Stroop test, choice reaction time (CRT)) were completed before, during and after the exercise protocol, as well as after ~12 h post exercise. Caffeine ingestion significantly enhanced the ratings of pleasure (P = 0.008) and arousal (P = 0.002) during the exercise protocol, as well as increased vigour (POMS; P = 0.007), while there was a tendency for reduced fatigue (POMS; P = 0.068). Caffeine ingestion showed a tendency to decrease RPE (P = 0.068) and improve reaction times in the Stroop (P = 0.072) and CRT (P = 0.087) tests. Caffeine supplementation showed a positive effect on perceptual parameters by increasing vigour and a tendency to decrease fatigue during intermittent running activity in female games players taking low-dose monophasic oral contraceptive steroids (OCS). Keywords: affect, cognition, feel-good response, pharmacological ergogenic aid, soccer
Introduction Caffeine is the most commonly consumed drug in the world and used daily by approximately 90% of the adult population (Bishop, 2010). Caffeine use as an ergogenic aid is highly prevalent in the sports industry (Bishop, 2010), is known to enhance performance through both peripheral and central mechanisms (Davis & Green, 2009) and is used equally by males and females (Del Coso, Muñoz, & Muñoz-Guerra, 2011). However, data addressing the effects of caffeine in female athletes, particularly with respect to the central nervous system (CNS), is limited, and given the increasing participation of females in sport (Del Coso et al., 2011), as well as the sex-related differences (e.g. differing concentrations of sex hormones, lean body mass, effect of contraceptives) reported for caffeine metabolism (Abernethy & Todd, 1985; Lane, Steege, Rupp, & Kuhn, 1992), research in this area is necessary. While multiple mechanisms have been proposed to underlie the physical performance-enhancing
effects of caffeine, the main pathway appears to be stimulation of the CNS via inhibition of adenosine receptors (Fredholm, Bättig, Holmén, Nehlig, & Zvartau, 1999; Graham, 2001). As adenosine signalling has been shown to enhance pain perception, induce sleep, reduce arousal and depress spontaneous locomotor activity (Davis & Green, 2009), caffeine-mediated antagonism of adenosine receptor function also results in the modulation of perceptual responses (e.g. perceived exertion, affect and arousal (Davis & Green, 2009; Sökmen et al., 2008), the improvement of mood (Lieberman, 2001; Sökmen et al., 2008) and enhancement of cognitive performance (Lieberman, 2001; Sökmen et al., 2008). During aerobic, steady-state exercise caffeine ingestion has been shown to reduce ratings of perceived exertion (RPE), in both males and females during submaximal cycling (Duncan & Hankey, 2013) and constant-load exercise (Doherty & Smith, 2005). In contrast, the effect of caffeine on RPE during team-sports and exercise of an exhaustive or intermittent nature is unclear. Caffeine
Correspondence: Ajmol Ali, School of Sport and Exercise, Massey University, Albany, Auckland, New Zealand. E-mail: [email protected] © 2015 Taylor & Francis
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supplementation failed to influence RPE during a 10-km high-intensity cycling time trial in men (Astorino, Cottrell, Talhami Lozano, AburtoPratt, & Duhon, 2012), an 8.2-km time trial in women (Astorino, Roupoli, & Valdivieso, 2012), in female rugby (Del Coso et al., 2013) and soccer players (Lara et al., 2014), or in males performing a multiple-sprint protocol (Glaister et al., 2008). It is possible that the attenuating effects of caffeine on RPE are subject to the level of exercise intensity or that responses are sport and/or activity-dependent. It is also possible that participants may be doing more work at a similar level of exertion. These suggestions remain to be investigated. Although feelings of pleasure/displeasure and level of arousal are key factors in athletic performance (Astorino, Cottrell, et al., 2012), these measures are reported in only a limited number of exercise studies to date. Moderate doses of caffeine (3.7– 6 mg • kg−1) enhanced feelings of pleasure in trained males during endurance cycling (Backhouse, Biddle, Bishop, & Williams, 2011), high-intensity cycling (Astorino, Cottrell, et al., 2012) and simulated soccer activity (Gant, Ali, & Foskett, 2010), yet failed to affect changes in arousal. No comparable data has been published for female athletes. In addition to cognitive and perceptual parameters, caffeine has been found to have pronounced effects on mood, often assessed using the profile of mood states (POMS) (Berger & Motl, 2000). In an exercise setting, the majority of results show increased vigour and/or reduced fatigue following caffeine consumption (Smith, 2002). However, data on the effect of caffeine ingestion on “feel-good” aspects and/or mood in females is lacking, particularly in a teamsports setting. The effects of caffeine on cognitive function include increased alertness, vigilance, reaction time and skill performance (Fredholm et al., 1999). Caffeine supplementation improved vigilance, alertness and reaction time in sleep-deprived US Navy SEAL trainees (Lieberman, Tharion, Shukitt-Hale, Speckman, & Tulley, 2002) and improved the cognitive performance of trained cyclists following both a 1-hour time-trial (Hogervorst, Riedel, Kovacs, Brouns, & Jolles, 1999) and a time to exhaustion trial (Hogervorst et al., 2008). However, there is a dearth of information regarding caffeine ingestion on cognition in female team-sports athletes, despite findings that oral contraceptive steroids (OCS) and oestrogen have a significant impact on caffeine metabolism (Abernethy & Todd, 1985; Ali, O’Donnell, Starck & Rutherfurd-Markwick, 2015; Lane et al., 1992) and that cognitive performance declines in the highprogesterone, luteal phase of the menstrual cycle (Kumar, Mufti, & Kisan, 2013).
While the majority of research supports the significance of caffeine’s influence on cognitive and perceptual parameters for team-sports performance, these effects are complex compared with those observed for endurance exercise and require further examination. Often, simultaneous improvements in parameters of cognitive (Hogervorst et al., 2008) and physical (Astorino, Cottrell, et al., 2012; Astorino, Roupoli, et al., 2012) performances are observed, despite contradictory effects on perception; thus, additional research is needed to fully understand the contribution of caffeine to perceptual and mood responses during intermittent exercise. In particular, information relevant to the specific effects of caffeine in females performing team-sports exercise is scarce. As the use of OCS is widespread in female athletes (Rechichi & Dawson, 2009), and both OCS and menstrual-cycle stage play a significant role in determining the influence of caffeine ingestion on cognitive and perceptual parameters in females (Constantini, Dubnov, & Lebrun, 2005; Kumar et al., 2013), studies on caffeine response in males cannot be used to inform caffeine recommendations in females. Furthermore, research on central responses following caffeine ingestion in female exercisers has been primarily conducted without regard for menstrual-cycle stage or OCS use; indeed, the conflicting information between studies may be due to such methodological limitations. Therefore, research that addresses the effect of caffeine ingestion on perceptual responses and cognitive function in female athletes using OCS during an intermittent exercise protocol is warranted. For the first time, we aim to provide novel data addressing the effect of a moderate dose of caffeine in female games players using OCS on cognitive performance, perceptual responses and mood state during and following an intermittent exercise protocol. We hypothesise that caffeine will positively impact perceptual, mood and cognitive responses during and following exercise.
Methods Participants This study was part of a larger investigation examining the effects of caffeine ingestion in female teamsport players and the perceptual, mood and cognitive data will be presented here. Sample size was estimated using data from Kalmar and Cafarelli (1999) and an appropriate statistical package (GPower 3.1). A sample size of 10 was sufficient to detect 3.5% change in muscle strength performance between caffeine and placebo trials, with a power of 0.84 and P < 0.05. Ten healthy female team-games players (mean ± SD; 24 ± 4 years; 59.7 ± 3.5 kg body mass; 1.62 ± 0.06 m height; 2–6 training sessions per week
Caffeine and perceptual responses in females for soccer, hockey and/or netball at various levels of competition, from recreational to international) volunteered to participate in this study, which was approved by the local ethics committee. Participants were informed of all study requirements, benefits and associated risks prior to providing written consent. None of the participants were taking any other supplements.
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Experimental control The participants’ self-reported caffeine intake varied (estimated range 0–300 mg • day−1) based on daily consumption of common caffeine sources (not all participants consumed caffeine-containing products every day; some indicated they consumed products containing caffeine on a weekly basis). High caffeine consumers (more than four cups a day) and naïve users (those that actively refrained from consuming caffeine-containing products) were excluded from the study. All participants were asked to keep a food diary for two days before their first trial and to replicate this diet before their second trial to reduce the potential for diet-induced variability between trials. During this 48-h period, participants were asked to avoid alcohol and foods containing caffeine (coffee, tea, soft drinks, energy drinks and chocolate). In addition, they were asked to refrain from exercise for the final 24 h of this period and fast for 3 h (only water intake allowed) prior to the main trials. The food record diaries were analysed using dietary analysis software (Foodworks version 6.0.2562, 2009, Xyris Software). All participants were taking a monophasic oral contraceptive for at least 3 months prior to commencing the study. All oral contraceptives were of the same hormonal composition (Monofeme, Levlen ED, Microgynon or Nordette: 30 µg Ethinyloestradiol and 150 µg Levonorgestrel; (Roberts, 2008)). In order to control for possible differences during the oral contraceptive cycle all testing was performed during days 5–8 and 18–22 of one pillcycle. No changes in high-intensity intermittent exercise performance or energy metabolism have been reported between these periods of the menstrual cycle for participants taking a low-dose monophasic oral contraceptive (Lynch & Nimmo, 1998; Lynch, Vito, & Nimmo, 2001). Participants were asked to keep daily records of their oral contraceptive use by recording the day and time taken. To ensure similarity between trials, participants were asked to keep the timing as consistent as possible during the days of the main trial as well as the morning session that followed.
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Practice session Participants were asked to perform one preliminary session before commencing the main trials. Participants initially performed an incremental max_ 2) max test. This test was imal oxygen uptake (VO carried out on a treadmill (Woodway, ELG70; Munich, Germany) with a 1% incline, at an initial speed of 8 km • h−1, which increased by 1 km • h−1 every 2 min, until the participant signalled they could only continue for a further minute. Expired air was collected using the Douglas bag method; analysis of the expired air for CO2 and O2 concentrations was performed using a gas analyser (Servomex, Model ML206, AD Instruments, Australia) and gas volumes were measured using a Harvard dry gas meter (Serial number K015078, Harvard Apparatus, MA, USA). The gas analyser was calibrated prior to each test using commercially available mixtures of known gases (span gas: 5% CO2, 20% O2; zero gas: 100% N2; BOC, Auckland). Maximal oxygen uptake was determined using standard criteria (ACSM, 2000). Participants then completed two 15-min blocks of the intermittent treadmill running protocol (Atkinson et al., 2005) to familiarise themselves with the running patterns involved and the overall experimental procedures. Participants were also familiarised with the perceptual scales, the POMS questionnaire and the cognitive tests before, during and immediately following the two 15-min blocks of running.
Experimental trials All trials took place in the same laboratory. Environmental temperatures (20.3 ± 0.7°C and 20.4 ± 0.8°C, P = 0.07) and relative humidity (46.4 ± 1.2 and 48.6 ± 1.4%, P = 0.10) were not different between trials. Following the preliminary session, participants returned during days 5–8 and 18–22 of their OCS cycle to complete the main trials at approximately 6 pm. Treatments were randomly assigned using a placebo-controlled, double-blind crossover design. Figure 1 shows a schematic representation of the experimental protocol. After cannula insertion and blood sampling, participants ingested a gelatin capsule (Vegie Capsules, BioBalance, New Zealand) containing either 6 mg • kg−1 anhydrous caffeine (Fluka Sigma-Aldrich, St. Louis, MO, USA) or placebo (artificial sweetener, Equal) with a 500-mL bolus of water (capsules were swallowed intact to eliminate any organoleptic differences between treatments). The intermittent exercise protocol took place 60 min after ingestion and consisted of six 15-min blocks of treadmill running. Each block was made up of six 2-min periods at 40%, 60%, 80%, _ 2max followed by 1 min at 40%, 60% and 80% VO
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Figure 1. Schematic representation of protocol. Exercise was carried out intermittently in six 15-min blocks 60 min following ingestion of caffeine (CAFF) or placebo (PLA). Tests of cognitive performance (CRT and Stroop test, black arrow), perception (RPE, FS and FAS, hashed arrow), mood (POMS, white arrow) and blood glucose (grey arrow) were carried out at the time points indicated. Final measurements were taken the following day, approximately 12 h after the exercise protocol.
_ 2max and a 2-min walk at 4 km • h−1, to 60% VO simulate the activity patterns of a soccer match (Atkinson et al., 2005). Following the exercise, participants went home, consumed their evening meal (same for both trials) and then went to sleep. They returned to the laboratory the following morning for their 12 ± 2 h post-exercise measurements (in fasted state). Tests for cognitive function, perceptual parameters and mood were undertaken before, throughout and following the exercise protocol (Figure 1). Following completion of the study, participants were asked which trial they thought was the caffeine trial; 9 out of 10 participants correctly identified the caffeine trial.
measures changes in perceived arousal throughout exercise. This scale is based upon Apter’s Reversal Theory and is valid in an exercise setting as it requires a subjective assessment of the participant’s perceived arousal (Apter, 1989). High arousal is characterised as anger or excitement, while low arousal is representative of calmness or boredom. Although participants were familiarised with these scales during the practice session, one of the investigators read out a short standardised prompt for each scale prior to assessment. The order of the scales presented to the participants was RPE, followed by FS and then FAS for each sampling point. Assessment of mood
Perceptual measurements Perceptual responses were assessed pre-exercise, after every 15-min block of exercise, immediately post exercise and 12 ± 2 h post exercise (Figure 1), using the RPE scale (Borg, 1982), the feeling scale (FS; Hardy & Rejeski, 1989) and the felt arousal scale (FAS; Svebak & Murgatroyd, 1985). The RPE scale measured the subjective intensity of each 15-min block of exercise. It is a 15-point scale ranging from 6 to 20 with corresponding anchors that range from “No Exertion at all” to “Maximal Exertion”. Measures were taken throughout the exercise; however, this scale only indicates the level of exertion the participant is experiencing and does not give any indication of the participant’s other emotions during exercise and does not estimate the participant’s perceived activation. The FS assessed pleasure or displeasure felt during exercise. It is an 11-point scale ranging from −5 “Very Bad” to +5 “Very Good”. The FAS is a 6-point (0–5) scale that
Participants completed the POMS (Grove & Prapavessis, 1992) questionnaire pre-exercise, after 45 and 90 min of exercise and 12 ± 2 h post exercise (Figure 1). The POMS was used to assess changes in mood as a result of exercise and/or caffeine supplementation. The participant was presented with 40 adjectives that were grouped into seven subgroups (fatigue, anger, vigour, tension, esteem, confusion and depression). Participants selected how well each adjective described the way they felt at that point in time using a 5-point Likert scale that ranged from “Not at all” to “Extremely”. Cognitive function Cognitive function was assessed pre-exercise, after 45 and 90 min of exercise and 12 ± 2 h post exercise (Figure 1), using a computer software program (Computerised Mental Performance Assessment System [COMPASS], Northumbria University, Newcastle, United Kingdom). Participants were
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Caffeine and perceptual responses in females required to perform two tasks: the choice reaction time (CRT) test and the Stroop test. While performing the cognitive testing the participants wore earmuffs, and the computer was positioned facing a blank wall, to minimise distractions to the participant that might have impeded performance. The CRT test was used as a measure of decision-making time (Teichner & Krebs, 1974). Participants were presented with more than one possible response for each test, which involved an arrow displayed on the screen facing either the left or the right. The participant had to select the correct corresponding left or right button as quickly as possible. The test involved the presentation of 35 stimuli. The Stroop test was used as a measure of attention bias and reaction time (Bench et al., 1993). Participants were shown words for certain colours, although the actual colour of the word often differed from the colour the word represented, e.g. the word “blue” may be displayed in a red font. The participants were required to respond with the colour of the font and disregard the name of the colour. The duration of the task was 1.5 min. Blood sampling An 18-gauge, 1.3-mm intravenous cannula (Insyte, Becton Dickson, NJ, USA) was inserted into a medial antecubital vein. Blood samples were taken at rest, after blocks 1, 3 and 6 of exercise, and 12 ± 2 h post exercise. Regular flushing with saline (0.9% sodium chloride, Demo S.A. Pharmaceutical Industry, Athens, Greece) was used to keep the cannula patent. Four millilitre blood samples were collected in EDTA tubes, centrifuged for 10 min at 1250 × g (MF 50, Hanil Science Industrial Co. Ltd, Korea) and the plasma was stored at −80°C for later analysis of plasma glucose. Glucose analysis
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is presented as means ± SD and statistical significance was set at P < 0.05. Practical significance was reported using effect sizes (Cohen’s d); a large effect size was determined as 0.8, medium as 0.5 and small as 0.2 (Cohen, 1988).
Results Perceptual responses There was a tendency for lower RPE during exercise when caffeine was ingested compared with placebo (P = 0.068; Cohen’s d = 1.23; Figure 2). RPE increased over the duration of exercise for both trials (P < 0.001). Although there were no main effects of treatment (P = 0.095) or time (P = 0.109), there was an interaction of treatment × time for ratings of pleasure (P = 0.008). Furthermore, in terms of practical significance, ratings of pleasure were 82% higher when caffeine was ingested compared to placebo (Cohen’s d = 2.18). Post-hoc analysis showed higher FS ratings in the caffeine trial at the 15–30, 30–45, 45–60 and 75–90-min time points (P < 0.05; Figure 3A). There was no effect of treatment on perceived arousal (P = 0.151; Cohen’s d = 1.39; Figure 3B). However, ratings of arousal increased over time for both groups (P = 0.013), and there was an interaction of treatment × time (P = 0.002) with higher ratings in the caffeine trial at 45–60 and 60–75-min time points (P < 0.05). The FS and FAS values were additionally plotted in a circumplex model providing a visual description of changes in pleasure and arousal throughout the trial (Figure 4). In the caffeine trial, participants’ data indicated they were in the “high arousal, pleasure” quadrant (Figure 4A), whereas in the placebo trial they were in the “low arousal, pleasure” quadrant (Figure 4B).
An assay based on the hexokinase method was used to establish plasma glucose concentrations using a commercially available kit (Wako Pure Chemical Industries, Ltd. Osaka, Japan). Statistical analysis Data were compared using a two-way ANOVA with repeated measures (SPSS version 19.0. Chicago, IL) to examine the main effects of (i) treatment and (ii) time as well as (iii) interaction of treatment × time. Mauchly’s test for sphericity was applied to the data. When sphericity was violated, the Huynh–Feldt estimate was used to correct the data. When significant differences between the interventions were identified by ANOVA, post-hoc Student’s t-test, using the Holm–Bonferroni adjustment, was performed. Data
Figure 2. Mean (± SD) ratings of perceived exertion (RPE) during caffeine (CAFF) and placebo (PLA) trials during the 90-min intermittent exercise protocol (n = 10).
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Figure 3. Mean (± SD) ratings of (A) pleasure–displeasure (feeling scale, FS) and (B) perceived activation (felt arousal scale, FAS) during caffeine (CAFF) and placebo (PLA) trials before, during and after the 90-min intermittent exercise protocol. *Significantly higher in CAFF trial (P < 0.05) (n = 10).
Mood responses The overall POMS score contains contributions from the seven different mood states of fatigue, anger, vigour, tension, esteem, confusion and depression and showed no difference with caffeine ingestion (P = 0.163; Cohen’s d = 0.916), but a decrease over time (P = 0.003; Figure 5A).
Figure 5. Profile of mood states (POMS) ratings in caffeine (CAFF) and placebo (PLA) trials before exercise, at the midpoint of exercise (45 min) and immediately post exercise (90 min). (A) Overall POMS ratings, (B) sub-scale ratings of fatigue and (C) sub-scale ratings of vigour (n = 10).
Figure 4. Circumplex model of affect in (A) caffeine (CAFF) and (B) placebo (PLA) trials based on feeling scale and felt arousal scale ratings before exercise (a), during, immediately post (b) and ~12 h post (c) the 90-min exercise protocol. Roman numerals indicate various activation and pleasure states: (i) high arousal and displeasure (e.g. anger); (ii) high arousal and pleasure (e.g. vigour); (iii) low arousal and displeasure (e.g. boredom or fatigue); (iv) low arousal and pleasure (e.g. calm) (n = 10).
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Caffeine and perceptual responses in females Post-hoc analysis revealed a higher POMS score prevs. post exercise (P < 0.05) for both caffeine and placebo trials. Analysis of individual mood states showed varying effects for the most relevant subsets to exercise, i.e. fatigue (Figure 5B) and vigour (Figure 5C). There was a tendency for lower fatigue scores in the caffeine trial compared with the placebo trial (P = 0.068; Cohen’s d = 1.66) and lower ratings over time (P = 0.084). Although there was no effect of caffeine ingestion (P = 0.493) or time (P = 0.221) on vigour, there was an interaction effect with vigour scores increasing in the caffeine trial but decreasing in the placebo trial over time (P = 0.007). Furthermore, there was a practically significant increase in vigour with caffeine ingestion of 13% (Cohen’s d = 0.608). Post-hoc analysis of vigour scores showed no differences at any specific time points between trials.
Cognitive function There was no effect of caffeine on the percentage of correct responses in the CRT (P = 0.136, Table IA) despite higher averages in the caffeine trial for all time points (Cohen’s d = 1.73). Caffeine ingestion had no effect on correct responses in the Stroop test (P = 0.890; Cohen’s d = 0.12; Table IB). However, there was a tendency for an interaction of treatment × time with a higher percentage of correct responses for the Stroop test in the caffeine trial (P = 0.072). There was a tendency for faster reaction times with caffeine ingestion for the CRT (P = 0.087; Cohen’s d = 1.46; Table I), but not for the Stroop test (P = 0.884; Cohen’s d = −0.038; Table II).
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There was, however, an effect of time in the Stroop test (P < 0.001) and a tendency for an interaction effect of treatment × time in the Stroop test, indicating non-significant faster reaction times in the caffeine trial over time (P = 0.07). Dietary analysis There were no differences in mean energy intake (placebo vs. caffeine trial; 7212 ± 2170 kJ vs. 6088 ± 1735 kJ, P = 0.105) or percentage intake of protein (17.0 ± 4.1% vs. 15.0 ± 2.9%, P = 0.192), fat (33.2 ± 8.6% vs. 33.4 ± 7.5%, P = 0.910) or carbohydrate (49.8 ± 12.2 vs. 51.2 ± 7.6%, P = 0.545) between trials. Plasma glucose There were no differences in blood glucose levels between treatments (P = 0.919), over time (P = 0.100) or for the interaction of treatment with time (P = 0.593; Table II). Discussion This study provides a more complete understanding of the perceptual responses experienced by female team-game players using caffeine as a supplement than other studies published to date. Moreover, it is the first time that FS and FAS data, and their relationship in the circumplex model, have been reported for females in response to caffeine ingestion. Caffeine intake significantly increased ratings of pleasure and arousal over the course of the exercise protocol and showed enhanced vigour and a tendency for reduction in fatigue. While there was no
Table I. Percentage of correct responses and mean (± SD) reaction time for (A) choice reaction time (CRT) test and (B) Stroop test in caffeine (CAFF) and placebo (PLA) trials (n = 10). Time Pre-exercise (A) Choice reaction time Correct answers (%) PLA 96.9 ± 2.5 CAFF 97.4 ± 3.7 Mean reaction time (ms) PLA 400.1 ± 23.6 CAFF 393.1 ± 43.8 (B) Stroop test Correct answers (%) PLA 97.0 ± 2.6 CAFF 97.8 ± 2.6 Mean reaction time (ms) PLA 629.2 ± 61.8 CAFF 659.2 ± 92.5
Mid-exercise
P values
Post exercise
~12 h Post exercise
Treatment
Time
Treatment × time
96.6 ± 3.8 97.4 ± 2.1
96.6 ± 2.3 96.9 ± 2.1
96.3 ± 3.6 96.9 ± 3.7
0.136
0.931
0.935
399.9 ± 52.0 374.0 ± 42.7
389.9 ± 25.3 377.2 ± 37.8
381.5 ± 29.8 374.1 ± 31.3
0.087
0.347
0.628
97.1 ± 2.9 97.0 ± 2.3
96.6 ± 3.7 98.3 ± 1.8
98.6 ± 2.2 96.6 ± 2.9
0.890
0.905
0.072
611.6 ± 80.2 600.0 ± 58.6
619.5 ± 76.5 589.6 ± 60.8
575.5 ± 25.5 591. 6 ± 61.2
0.884
9 mg • kg−1 ) have been reported to cause negative side effects, including dizziness, headache, jitteriness, nervousness, insomnia and gastrointestinal distress (Graham & Spriet, 1995; Sökmen et al., 2008). Plasma caffeine concentrations in our participants were 0.3 ± 0.3 mmol • L−1 (pre-supplementation), 9.6 ± 0.3 mmol • L−1 (mid-exercise), 9.2 ± 1.0 mmol • L−1 (postexercise) and 5.0 ± 1.8 mmol • L−1 (12-h postexercise) in the caffeine trial, whereas caffeine concentration was
