International Journal of Sports Physiology and Performance, 2016, 11, 214 -220 http://dx.doi.org/10.1123/ijspp.2015-0073 © 2016 Human Kinetics, Inc.
ORIGINAL INVESTIGATION
Improvement of Sprint Performance in Wheelchair Sportsmen With Caffeine Supplementation Terri S. Graham-Paulson, Claudio Perret, Phil Watson, and Victoria L. Goosey-Tolfrey Purpose: Caffeine can be beneficial during endurance and repeated-sprint exercise in able-bodied individuals performing leg or wholebody exercise. However, little evidence exists regarding its effects during upper-body exercise. This study therefore aimed to investigate the effects of caffeine on sprint (SPR) and 4-min maximal-push (PUSH) performance in wheelchair sportsmen. Methods: Using a double-blind, placebo-controlled, crossover design, 12 male wheelchair rugby players (age 30.0 ± 7.7 y, body mass 69.6 ± 15.3 kg, training 11.1 ± 3.5 h/wk) completed 2 exercise trials, separated by 7–14 d, 70 min after ingestion of 4 mg/kg caffeine (CAF) or dextrose placebo (PLA). Each trial consisted of four 4-min PUSHes and 3 sets of 3 × 20-m SPRs, each separated by 4 min rest. Participants responded to the Felt Arousal (a measure of perceived arousal), Feeling (a measure of the affective dimension of pleasure/displeasure), and rating-of-perceived-exertion (RPE) scales. Salivary caffeine secretion rates were measured. Results: Average SPR times were faster during CAF than PLA during SPR 1 and SPR 2 (P = .037 and .016). There was no influence of supplementation on PUSHes 2–4 (P > .099); however, participants pushed significantly farther during PUSH 1 after CAF than after PLA (mean ± SD 677 ± 107 and 653 ± 118 m, P = .047). There was no influence of CAF on arousal or RPE scores (P > .132). Feeling scores improved over the course of the CAF trial only (P = .017) but did not significantly differ between trials (P > .167). Pre-warm-up (45 min postingestion) salivary CAF secretion rates were 1.05 ± 0.94 and 0.08 ± 0.05 μg/min for CAF and PLA, respectively. Conclusion: Acute CAF supplementation can improve both 20-m-sprint performance and a 1-off bout of short-term endurance performance in wheelchair sportsmen. Keywords: spinal-cord injury, endurance, upper-body exercise Since caffeine’s removal from the World Anti-Doping Agency (WADA) list of prohibited substances in 2004, there has been substantial research into its effects on exercise performance. Low to moderate doses of caffeine (3–6 mg/kg; 210–420 mg for a 70-kg individual) typically ingested 60 minutes before exercise have been shown to have a beneficial effect on both short-term1 and endurance2,3 performance. The available evidence on repeated-sprint (running) performance also appears to support the use of caffeine.4,5 Caffeine’s effects are wide ranging, but a possible mechanism for its ergogenic effect relates to its influence on the central nervous system (CNS). Caffeine is a lipid-soluble molecule that can pass through cell membranes and, notably, cross the blood–brain barrier. It is structurally similar to adenosine and can therefore act as an adenosine (most likely A1 and A2a) -receptor antagonist,6 thereby reducing the influence of adenosine and producing motor-activating and arousing effects. Adenosine-receptor antagonism may also act by increasing the turnover of some neurotransmitters (eg, dopamine and noradrenaline), resulting in the central stimulatory effects seen after the ingestion of caffeine.6 Furthermore, a dose of 10 mg/kg caffeine increased dopamine release in the brain of rats and significantly improved run time to fatigue by ~30% compared with saline.7 The exact mechanisms explaining caffeine’s beneficial effects in humans remain unknown; however, nonselective adenosine antagonism has received much support in recent years. It has been suggested that certain individual characteristics such as genetics,8 training status,9 impairment,10 and habitual intake11 Graham-Paulson, Watson, and Goosey-Tolfrey are with the School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UK. Perret is with the Swiss Paraplegic Center, Inst of Sports Medicine, Nottwil, Switzerland. Address author correspondence to Victoria GooseyTolfrey at [email protected]. 214
may affect how a person responds to caffeine. The response will also depend on the duration, intensity, and time of caffeine ingestion and the mode of exercise. The majority of the aforementioned studies have employed running or cycling exercise modalities in which the leg muscles provide the speed-generating force. The physiological responses to these modes of exercise differ from those of upper-body exercise,12 which is largely due to the smaller skeletal-muscle mass used. The response to upperbody exercise in individuals with an impairment such as a spinal-cord injury (SCI) also differs from that of able-bodied individuals due to the amount of active muscle mass available,13 the distribution of muscle fiber types,14 and the potential issue of prolonged gastrointestinal transit times.15 Consequently, it may not be possible to directly transfer the findings from able-bodied running/cycling exercise modalities to individuals with a physical impairment performing upper-body exercise. However, given that the potential mechanism of action for performance enhancement after caffeine ingestion is the same in individuals with an impairment, a similar ergogenic benefit could be expected during upper-body exercise. Use of nutritional supplements is common among athletes with an impairment,16 and yet data investigating their efficacy in this population are scarce.10,17 Aside from an uncertainty as to whether caffeine is beneficial in this population, a lack of evidence raises concern given the potential for, or more acute sensitivity to, side effects in some sportspeople with a physical impairment.18 The influence of caffeine on subjective feelings and mood has also been investigated in able-bodied participants whereby low to moderate doses of caffeine appear to improve mood and increase arousal.19 A meta-analysis also revealed that caffeine can reduce ratings of perceived exertion (RPE) during exercise.20 These factors, in part, contribute to the performance-enhancing effects seen during various exercise modalities but have not been investigated during upperbody exercise in a physically impaired population. For this reason, the
Caffeine and Wheelchair Sprint Performance 215
current study employed both the Feeling21 and Felt Arousal22 scales to assess the influence of caffeine on feelings of pleasure/displeasure and perceived arousal before, during, and after exercise. Given the dearth of evidence in the area of caffeine and upperbody exercise, this study aimed to determine the effects of caffeine supplementation on aspects of wheelchair sports performance. Wheelchair sports such as rugby, basketball, and tennis are intermittent in nature and require short bursts of high-intensity movements superimposed on a background of aerobic activity. The current study employed previously used wheelchair-sport field tests23,24 to assess both sprint and short-term endurance performance. For this reason, the performance tests consisted of the time to complete multiple 20-m sprints and the total distance covered in four 4-minute maximal-push tests.
wheelchair sportsmen’s training venues, which was standardized within participants.
Methods
Participants’ body mass was measured to the nearest 0.1 kg, using wheelchair beam scales (Marsden MPWS-300, Henley-on-Thames, UK). Participants were familiarized with the experimental testing procedures by completing three 20-m-sprint tests (SPRs), at least two 4-minute maximal pushes (PUSHes), and a 3-minute salivasample collection. They were also familiarized with the Feeling,21 Felt Arousal,22 and Borg 6-to-20 category RPE scales.25
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Participants Twelve male wheelchair rugby players, mean ± SD age 30.0 ± 7.7 years, body mass 69.6 ± 15.3 kg, wheelchair rugby experience 6.7 ± 6.0 y, and training 11.1 ± 3.5 h/wk, volunteered to participate in this study. Participants’ impairments were cervical-level SCI (n = 7), cerebral palsy (n = 2), osteogenesis imperfecta (n = 1), distal limb weakness (n = 1), and vanishing-white-matter disease (n = 1). The participants’ wheelchair-rugby classifications ranged from 0.5 to 3. A health-screen questionnaire was completed by all participants to ensure they were free from any injury or illness that might have prevented them from safely completing the protocol. Average daily caffeine intake was assessed using a standardized caffeine-consumption questionnaire. All procedures were approved by the local ethical advisory committee and performed following the Declaration of Helsinki. Informed consent was obtained from all participants included in the study.
Experimental Design A double-blind, placebo-controlled, randomized cross-over design was employed. Participants performed 2 experimental trials separated by 7 to 14 days. All data collection occurred at the
Pretrial Procedures Participants were asked to refrain from caffeine consumption in the 48 hours preceding each trial and from exercise and alcohol consumption in the 24 hours preceding the trial. They were asked to complete a 24-hour food diary before the first experimental trial and to replicate this diet before the second. Participants were asked to consume only water in the hour preceding each trial to help reduce the influence of eating on the saliva-sampling procedure.
Familiarization
Experimental-Trial Procedures On arrival at the testing venue, participants responded to the Feeling and Felt Arousal scales. They provided a precapsule 3-minute saliva sample via the passive dribble method26 before ingesting either placebo (PLA) (4 mg/kg dextrose) or anhydrous caffeine (CAF) (4 mg/ kg). Both CAF and PLA were consumed in powder form in cellulose capsules (G & G Food Supplies Ltd, West Sussex, UK). Participants then rested and prepared for exercise (wheelchair setup, gloves, standardization of wheel-tire pressure, clothing, bladder voiding, etc) for 45 minutes before repeating the 2 perceptual scales and 3-minute saliva collection pre-warm-up. A standardized 20-minute warm-up was started at 50 minutes before the performance tests: 3 SPR sets and 4 PUSHes (alternating counterclockwise and clockwise) with 4-minute rests between (Figure 1). The 2 perceptual
Figure 1 — Schematic of the experimental-trial protocol. Abbreviation: SPR, sprint. IJSPP Vol. 11, No. 2, 2016
216 Graham-Paulson et al
scales and saliva collection were repeated postexercise. Participants were also asked whether they had experienced any side effects during the protocol and to indicate which trial they believed they were on. Participants were permitted to consume only water ad libitum throughout each trial. Environmental conditions across the 2 training venues were temperature 20.9°C ± 2.4°C (range 17.1–25°C), humidity 45% ± 8% (range 34–54%), and pressure 999 ± 110 hourPa (range 978–1012 hourPa).
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Performance Tests Adapted from West et al,23 for the SPR, from a stationary position participants were asked to sprint through 20 m. Times to complete the SPR were recorded using wireless timing gates (Brower, UT, USA) at 0 and 20 m. Participants were given ~30 seconds to recover between SPRs. One SPR set was composed of 3 single SPRs. For the PUSH, markers were placed every 2 m (1.5 m at the corners) to produce a rectangle with rounded corners and to enable the total distance covered to be recorded (1 lap = 72 m). Participants self-selected their speed with the goal of covering the greatest distance possible in 4 minutes. Communication between participants was encouraged to ensure that overtaking was completed efficiently. Verbal encouragement was provided throughout all experimental trials by the same investigators, all of whom were blind to which trial the participants were completing. Participants were blinded to their results.
RPE scales are reported as median (quartiles) and were analyzed using Friedman and Wilcoxon tests. Statistical significance was accepted at P < .05.
Results Performance Tests Average 20-m-SPR times were significantly faster during CAF than with PLA during SPR 1 and SPR 2 (P = .037 and .016, respectively) (Figure 2). Total SPR time was significantly faster during CAF than with PLA (61.2 [58.5, 68.6] and 62.5 [58.5, 69.7] s, respectively) (P = .006). Ten (of 12) participants produced faster total SPR times. Times did not significantly change between sprint points during CAF or PLA (P = .254 and .212). There was no significant difference in PUSH distance between CAF and PLA (P = .111), nor did it differ over the course of the protocol in either trial (PUSHes 1–4) (P = .864). However, participants did cover more distance during PUSH 1 during CAF (677 ± 107 m) than with PLA (653 ± 118 m) (P = .047) (Figure 3). Total
Subjective Feelings The Feeling scale21 assessed the participants’ mood on a scale of +5 (very good) to –5 (very bad). The Felt Arousal scale22 was used to assess how aroused a participant was on a scale of 1 (low arousal) to 6 (high arousal). The Borg 6-to-2025 category scale was used to obtain participants’ RPE scores after each PUSH and SPR set.
Saliva Collection and Analysis For saliva analysis, samples were weighed to the nearest 10 mg. Saliva volume was estimated assuming saliva density to be 1.00 g/mL, and saliva flow rate was calculated from saliva volume and collection time. Saliva samples were transferred into Eppendorfs and centrifuged at 12,000 rpm for 3 minutes in a high-speed microcentrifuge. Salivary CAF concentration was determined using a commercially available kit (Emit Caffeine Assay, Dade-Behring, Milton Keynes, UK) on an automatic photometric analyzer (COBAS Miras Plus, Roche Diagnostic Systems, Switzerland). The intraassay coefficient of variation for salivary CAF concentration was 3.5%. Salivary CAF secretion rates were subsequently calculated by multiplying CAF concentration by saliva flow rate due to the high variability in saliva flow in this population.26
Figure 2 — The effects of caffeine supplementation (CAF) on 20-m-sprint performance (3 sprints per set), median (quartiles). Abbreviation: SPR, sprint. *Significantly different from placebo (PLA) (P < .05).
Statistical Analysis The Statistical Package for the Social Sciences version 20 software (SPSS Inc, Chicago, IL) was used to analyze the data. Distance per PUSH and total PUSH distance (sum of all 4 PUSHes) were calculated. Total SPR time (all 9 sprints) and average SPR time for each set were calculated. Normal distribution of the outcome variables was confirmed by the Shapiro-Wilk test for PUSH, and therefore data are reported as mean ± SD. Subsequently, a repeated-measures 2 × 4 (trial × time) analysis of variance (ANOVA) was used to analyze all PUSH data. To assess the effect of CAF on each individual PUSH and total PUSH, paired-samples t tests were employed. Nonnormally distributed SPR data and ordinal Felt Arousal, Feeling, and
Figure 3 — The effects of caffeine supplementation (CAF) on 4-minute maximal push (PUSH) distance, mean ± SD. *Significantly different from placebo (PLA).
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PUSH distance was not significantly different between CAF (2686 ± 416 m) and PLA (2634 ± 392 m) (P = .111). Overall, 7 participants covered a greater total PUSH distance during CAF than with PLA.
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Subjective Feelings Felt Arousal (P = .001 and .006 for CAF and PLA, respectively), SPR RPE scores (P = .002 and .00007 for CAF and PLA, respectively), and PUSH RPE scores (P = .00001 and .015 for CAF and PLA, respectively) increased progressively over the course of each trial, but there was no significant effect of CAF supplementation (P > .132) (Table 1 and 2). Feeling scores improved significantly over the course of the CAF trial (P = .017), but not during PLA (P = .197), and this occurred precapsule (0 [0, 3]) to postexercise (3 [2, 3]) (P = .041) (Table 1). Side effects during CAF including increased spasticity, struggling with decision making, headaches (also experienced during PLA), and nausea were reported by 5 participants. Trial order was correctly identified by 7 participants. Mean ± SD daily CAF intake was 211 ± 201 mg/d. No participant reported having experienced a prior adverse reaction to CAF. Three participants reported the use of CAF supplementation (80–220 mg) in capsule format before training or competition (supplementation was not included in daily intake data).
Saliva Salivary CAF analysis revealed that participants followed the 48-hour CAF-withdrawal procedure before both PLA (0.06 ± 0.06 μg/min) and CAF (0.13 ± 0.17 μg/min) (Figure 4), and these did not differ (P = .201). The consumption of CAF caused an increase in salivary CAF secretion rates pre-warm-up (1.05 ± 0.94 μg/min) (P = .009) and postexercise (1.34 ± 1.09 μg/min) (P = .003).
Discussion The current study demonstrates that the consumption of 4 mg/kg CAF can improve wheelchair sprint performance. CAF also appears to improve a 1-off bout of short-term endurance exercise, seen as an improvement during PUSH 1 but not PUSHes 2 to 4. The following paragraphs will discuss the potential reasons behind these results.
Sprint Performance CAF improved repeated-sprint performance in athletes with a physical impairment, which was apparent in the first and second
Table 1 Felt Arousal and Feeling Scale Responses Precapsule, Pre-Warm-Up, and Postexercise (N = 12), Median (Quartiles) Placebo
Caffeine
2.5 (2, 3)
2 (1.25, 3)
pre-warm-up
3 (2.25, 3.75)*
3.5 (3, 4)*
postexercise
4 (3.25, 4)*
4 (3, 4.75)*
precapsule
2 (0, 3)
0 (0, 2.5)
pre-warm-up
2 (1, 3)
2.5 (1, 3)
postexercise
3 (1, 3.75)
3 (2.25, 3)*
Felt Arousal scale precapsule
Feeling scale
†Significantly different from precapsule (P ≤ .05).
Table 2 Rating of Perceived Exertion Immediately After Each Sprint Set and 4-min Maximal Push (N = 12), Median (Quartiles) Placebo
Caffeine
Sprint set 1
12 (9, 14)
12 (11, 13)
Sprint set 2
13 (10, 15)†
14 (12, 14)†
Sprint set 3
14 (11, 16)†‡
14 (10, 15)†
Maximal push 1
16 (13, 19)
15 (15, 17)
Maximal push 2
17 (15, 18)†
18 (15, 19)†
Maximal push 3
17 (16, 17)†
17 (16, 18)†
Maximal push 4
18 (16, 19)†*
18 (17, 19)†‡*
†Significantly different from set 1, ‡significantly different from set 2, and *significantly different from set 3 (P ≤ .05).
Figure 4 — Individual participants’ salivary caffeine secretion rates precapsule (0 min), pre-warm-up (45 min), and postexercise (2 h) (N = 12) in (A) the placebo trial and (B) the caffeine trial
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218 Graham-Paulson et al
SPR sets but not the third (Figure 2). This corroborates previous research in able-bodied individuals that has shown initial improvements in performance after CAF ingestion with a subsequent null or negative influence on latter bouts.5,27,28 Faster 30-m-sprint times in the first 3 (of 12) sprints after 5-mg/kg CAF supplementation have been reported.5 Those authors hypothesized that the mechanism responsible for this initial improvement was a CNS effect mediated by antagonism of adenosine receptors. A CNS effect may also be responsible for the current study results in which participants produced faster average 20-m and total SPR times. These improvements are small yet meaningful for individuals competing in intermittent sports, as they may allow a player to lead his or her opponent in a sprint situation and therefore meet the ball, player, or line faster. The effects of CAF (5 mg/kg) on performance in simulatedcontest tae kwon do have been investigated, whereby athletes performed 2 combats (3 × 2-min rounds with 1-min rest periods) separated by 20 minutes.27 The ingestion of CAF improved reaction times before the first combat, increased the intensity of round 1, and maintained the intensity observed in the first combat in the second.27 These findings provide support for the initial performance improvements seen during SPR 1 and SPR 2 in the current study. Participants were able to push faster in the first 2 SPRs, but this led to the development of fatigue, and therefore no further improvements were seen. The “signal” produced after the ingestion of CAF may result in a performance improvement initially yet lead to a decrement or lack of improvement in successive exercise bouts.28 This pattern was observed in the current study and lends support to the idea that CAF can exert its effects through fast-twitch fibers.
PUSH Performance Notably, the same initial performance improvement was also observed in the PUSH results (Figure 3) despite no overall significant effect of supplementation. Participants benefited from CAF for a 1-off performance, covering a greater distance during PUSH 1, yet failed to show improvements in PUSHes 2, 3, or 4 compared with PLA. Previous research investigated the use of CAF before two 200-m freestyle time trials (TT) (~2 min duration) separated by a 30-minute rest.29 The authors revealed that CAF improved performance in TT 1 (P = .027), but participants swam 0.9% ± 1.1% slower in TT 2 after CAF than with placebo, and the conclusion was that the initial effort during TT 1 may have hindered performance in TT 2.29 This may also be true for the current PUSH results. However, another study reported opposing findings whereby CAF improved 100-m swim times in trained participants and prevented a drop in performance during a second 100-m swim (20 min passive recovery).9 The race distance (200 vs 100 m), CAF dose (~6.2 vs ~4.3 mg/kg), and recovery time (30 vs 20 min) may explain the differing results in these aforementioned studies.
Gastrointestinal Issues Gastrointestinal emptying and transit times can be delayed in individuals with an SCI,15 and this may be more prominent in those with a high lesion level,30 such as those in the current study (7 of 12 participants with tetraplegia). The pre-warm-up (45 min postingestion) saliva results suggest that 45 minutes may be inadequate time to develop sufficient CAF concentrations in some participants with a physical impairment (Figure 4). However, the participants then prepared for exercise and performed a 20-minute warm-up before the performance tests. The early performance improvements in SPRs 1 and 2 and PUSH 1 indicate that the supplement was absorbed
before the start of these tests (70 min postingestion). The only current study to investigate CAF use in wheelchair athletes showed no improvement in 1500-m performance (~3-min duration) after the ingestion of 6 mg/kg CAF 60 minutes before exercise.10 Those authors did not measure CAF concentration and therefore could not use this measure to help explain their results.10 The promising finding, however, was that 4 (of 9) participants produced their fastest times in the CAF trial compared with 3 other conditions (placebo, sodium citrate, and a combination of the 2).10 Furthermore, the current results suggest that the 60-minute absorption time employed by this study may have been sufficient for their athletes with paraplegia and spina bifida to produce these individual results. The time course for CAF absorption in individuals with an SCI, especially those with tetraplegia, should be further explored.
Subjective Feelings The side effects reported by 5 participants were similar to those reported in able-bodied participants, which include muscle trembling and shakiness/jitters, but were described as “increased spasticity” by those with an SCI or cerebral palsy. These side effects occurred despite a relatively moderate dose of 4 mg/kg CAF administered in this study compared with often larger doses of 5 to 10 mg/kg in the able-bodied literature. Notably, the reported side effects occurred in 2 of the 3 participants who reported the use of CAF supplementation before training/competition. The dose of 4 mg/kg was greater (1.5–2 times more) than their usual intake, which may explain the incidence of side effects in these individuals. This highlights the need to consider the dosing of CAF on an individual basis. It is likely that experiencing such issues during exercise could limit performance; however, there was no link between those who experienced side effects and those who did or did not improve. Despite the reported side effects during CAF, Feeling scale scores improved over the course of the trial after ingestion of the supplement. The psychostimulant effect of CAF is reported frequently19 and may have contributed to the improved SPR performance. Other common findings include increased arousal and an altered perceptual response after the ingestion of CAF,20 neither of which were apparent in the current study. However, an absence of changes in RPE was seen in conjunction with a greater distance covered during PUSH 1 and faster SPR times during CAF, which may suggest that the supplement influenced perceptual responses to some extent. The ability to successfully determine CAF or PLA is common in the CAF literature due to familiar side effects (eg, jitteriness and energetic sensations). In the current study only 7 participants correctly identified both trials, which increased our confidence that the CAF is responsible for the initial performance improvements.
Practical Applications The study protocol used trained (club-level) wheelchair rugby players performing in their own sport wheelchairs and reflected real-life pretraining/competition nutrition and hydration practices. Athletes taking part in, and coaches working with, similar intermittent wheelchair sports now have some evidence to show that CAF supplementation can be beneficial during wheelchair sprinting. The measurement of salivary CAF concentrations highlighted considerations for the timing of CAF supplementation in individuals with a physical impairment. CAF should therefore be trialed on an individual basis by wheelchair sportsmen (especially individuals with an SCI) and should initially use low doses of 1 to 3 mg/kg at least 60 to 70 minutes before exercise.
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Caffeine and Wheelchair Sprint Performance 219
A relatively small sample size was used in the current study, and participants had a variety of physical impairments, hence the findings can only be generalized to the sport, not to a specific impairment. As with all on-court testing, a combination of factors associated with the participant, the wheelchair, and the interfacing between the 2 may also have influenced performance, especially during cornering in the PUSH, during which a high element of skill was required. Given the nature of field-study protocols, the participants also performed in the presence of external interference (eg, participants, coaches, and researchers), which may have influenced performance. An attempt to minimize this influence was employed; participants performed the PUSH protocol with the same fellow participants where possible, they were motivated by the same investigators, and they were blind to their results.
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Conclusions This study supports the beneficial effects of CAF on sprint performance and on a 1-off bout of short-term endurance exercise in wheelchair sportsmen. The findings provide support for the psychostimulant effect of CAF, and yet the supplement did not improve participants’ RPE or Felt Arousal scores. The combination of side effects and potentially delayed CAF absorption highlights that its use in individuals with a physical impairment is highly individual. Acknowledgments The authors would like to thank all the participants for their effort and commitment to the project. Thanks also to Katie McGibbon and Lauren Delany for their help during data collection. No external funding was received to conduct this study.
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28. Greer F, McLean C, Graham TE. Caffeine, performance, and metabolism during repeated Wingate exercise tests. J Appl Physiol. 1998;85:1502–1508. PubMed 29. Pruscino CL, Ross MLR, Gregory JR, Savage B, Flanagan TR. Effects of sodium bicarbonate, caffeine, and their combination on
IJSPP Vol. 11, No. 2, 2016
ORIGINAL INVESTIGATION
Improvement of Sprint Performance in Wheelchair Sportsmen With Caffeine Supplementation Terri S. Graham-Paulson, Claudio Perret, Phil Watson, and Victoria L. Goosey-Tolfrey Purpose: Caffeine can be beneficial during endurance and repeated-sprint exercise in able-bodied individuals performing leg or wholebody exercise. However, little evidence exists regarding its effects during upper-body exercise. This study therefore aimed to investigate the effects of caffeine on sprint (SPR) and 4-min maximal-push (PUSH) performance in wheelchair sportsmen. Methods: Using a double-blind, placebo-controlled, crossover design, 12 male wheelchair rugby players (age 30.0 ± 7.7 y, body mass 69.6 ± 15.3 kg, training 11.1 ± 3.5 h/wk) completed 2 exercise trials, separated by 7–14 d, 70 min after ingestion of 4 mg/kg caffeine (CAF) or dextrose placebo (PLA). Each trial consisted of four 4-min PUSHes and 3 sets of 3 × 20-m SPRs, each separated by 4 min rest. Participants responded to the Felt Arousal (a measure of perceived arousal), Feeling (a measure of the affective dimension of pleasure/displeasure), and rating-of-perceived-exertion (RPE) scales. Salivary caffeine secretion rates were measured. Results: Average SPR times were faster during CAF than PLA during SPR 1 and SPR 2 (P = .037 and .016). There was no influence of supplementation on PUSHes 2–4 (P > .099); however, participants pushed significantly farther during PUSH 1 after CAF than after PLA (mean ± SD 677 ± 107 and 653 ± 118 m, P = .047). There was no influence of CAF on arousal or RPE scores (P > .132). Feeling scores improved over the course of the CAF trial only (P = .017) but did not significantly differ between trials (P > .167). Pre-warm-up (45 min postingestion) salivary CAF secretion rates were 1.05 ± 0.94 and 0.08 ± 0.05 μg/min for CAF and PLA, respectively. Conclusion: Acute CAF supplementation can improve both 20-m-sprint performance and a 1-off bout of short-term endurance performance in wheelchair sportsmen. Keywords: spinal-cord injury, endurance, upper-body exercise Since caffeine’s removal from the World Anti-Doping Agency (WADA) list of prohibited substances in 2004, there has been substantial research into its effects on exercise performance. Low to moderate doses of caffeine (3–6 mg/kg; 210–420 mg for a 70-kg individual) typically ingested 60 minutes before exercise have been shown to have a beneficial effect on both short-term1 and endurance2,3 performance. The available evidence on repeated-sprint (running) performance also appears to support the use of caffeine.4,5 Caffeine’s effects are wide ranging, but a possible mechanism for its ergogenic effect relates to its influence on the central nervous system (CNS). Caffeine is a lipid-soluble molecule that can pass through cell membranes and, notably, cross the blood–brain barrier. It is structurally similar to adenosine and can therefore act as an adenosine (most likely A1 and A2a) -receptor antagonist,6 thereby reducing the influence of adenosine and producing motor-activating and arousing effects. Adenosine-receptor antagonism may also act by increasing the turnover of some neurotransmitters (eg, dopamine and noradrenaline), resulting in the central stimulatory effects seen after the ingestion of caffeine.6 Furthermore, a dose of 10 mg/kg caffeine increased dopamine release in the brain of rats and significantly improved run time to fatigue by ~30% compared with saline.7 The exact mechanisms explaining caffeine’s beneficial effects in humans remain unknown; however, nonselective adenosine antagonism has received much support in recent years. It has been suggested that certain individual characteristics such as genetics,8 training status,9 impairment,10 and habitual intake11 Graham-Paulson, Watson, and Goosey-Tolfrey are with the School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UK. Perret is with the Swiss Paraplegic Center, Inst of Sports Medicine, Nottwil, Switzerland. Address author correspondence to Victoria GooseyTolfrey at [email protected]. 214
may affect how a person responds to caffeine. The response will also depend on the duration, intensity, and time of caffeine ingestion and the mode of exercise. The majority of the aforementioned studies have employed running or cycling exercise modalities in which the leg muscles provide the speed-generating force. The physiological responses to these modes of exercise differ from those of upper-body exercise,12 which is largely due to the smaller skeletal-muscle mass used. The response to upperbody exercise in individuals with an impairment such as a spinal-cord injury (SCI) also differs from that of able-bodied individuals due to the amount of active muscle mass available,13 the distribution of muscle fiber types,14 and the potential issue of prolonged gastrointestinal transit times.15 Consequently, it may not be possible to directly transfer the findings from able-bodied running/cycling exercise modalities to individuals with a physical impairment performing upper-body exercise. However, given that the potential mechanism of action for performance enhancement after caffeine ingestion is the same in individuals with an impairment, a similar ergogenic benefit could be expected during upper-body exercise. Use of nutritional supplements is common among athletes with an impairment,16 and yet data investigating their efficacy in this population are scarce.10,17 Aside from an uncertainty as to whether caffeine is beneficial in this population, a lack of evidence raises concern given the potential for, or more acute sensitivity to, side effects in some sportspeople with a physical impairment.18 The influence of caffeine on subjective feelings and mood has also been investigated in able-bodied participants whereby low to moderate doses of caffeine appear to improve mood and increase arousal.19 A meta-analysis also revealed that caffeine can reduce ratings of perceived exertion (RPE) during exercise.20 These factors, in part, contribute to the performance-enhancing effects seen during various exercise modalities but have not been investigated during upperbody exercise in a physically impaired population. For this reason, the
Caffeine and Wheelchair Sprint Performance 215
current study employed both the Feeling21 and Felt Arousal22 scales to assess the influence of caffeine on feelings of pleasure/displeasure and perceived arousal before, during, and after exercise. Given the dearth of evidence in the area of caffeine and upperbody exercise, this study aimed to determine the effects of caffeine supplementation on aspects of wheelchair sports performance. Wheelchair sports such as rugby, basketball, and tennis are intermittent in nature and require short bursts of high-intensity movements superimposed on a background of aerobic activity. The current study employed previously used wheelchair-sport field tests23,24 to assess both sprint and short-term endurance performance. For this reason, the performance tests consisted of the time to complete multiple 20-m sprints and the total distance covered in four 4-minute maximal-push tests.
wheelchair sportsmen’s training venues, which was standardized within participants.
Methods
Participants’ body mass was measured to the nearest 0.1 kg, using wheelchair beam scales (Marsden MPWS-300, Henley-on-Thames, UK). Participants were familiarized with the experimental testing procedures by completing three 20-m-sprint tests (SPRs), at least two 4-minute maximal pushes (PUSHes), and a 3-minute salivasample collection. They were also familiarized with the Feeling,21 Felt Arousal,22 and Borg 6-to-20 category RPE scales.25
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Participants Twelve male wheelchair rugby players, mean ± SD age 30.0 ± 7.7 years, body mass 69.6 ± 15.3 kg, wheelchair rugby experience 6.7 ± 6.0 y, and training 11.1 ± 3.5 h/wk, volunteered to participate in this study. Participants’ impairments were cervical-level SCI (n = 7), cerebral palsy (n = 2), osteogenesis imperfecta (n = 1), distal limb weakness (n = 1), and vanishing-white-matter disease (n = 1). The participants’ wheelchair-rugby classifications ranged from 0.5 to 3. A health-screen questionnaire was completed by all participants to ensure they were free from any injury or illness that might have prevented them from safely completing the protocol. Average daily caffeine intake was assessed using a standardized caffeine-consumption questionnaire. All procedures were approved by the local ethical advisory committee and performed following the Declaration of Helsinki. Informed consent was obtained from all participants included in the study.
Experimental Design A double-blind, placebo-controlled, randomized cross-over design was employed. Participants performed 2 experimental trials separated by 7 to 14 days. All data collection occurred at the
Pretrial Procedures Participants were asked to refrain from caffeine consumption in the 48 hours preceding each trial and from exercise and alcohol consumption in the 24 hours preceding the trial. They were asked to complete a 24-hour food diary before the first experimental trial and to replicate this diet before the second. Participants were asked to consume only water in the hour preceding each trial to help reduce the influence of eating on the saliva-sampling procedure.
Familiarization
Experimental-Trial Procedures On arrival at the testing venue, participants responded to the Feeling and Felt Arousal scales. They provided a precapsule 3-minute saliva sample via the passive dribble method26 before ingesting either placebo (PLA) (4 mg/kg dextrose) or anhydrous caffeine (CAF) (4 mg/ kg). Both CAF and PLA were consumed in powder form in cellulose capsules (G & G Food Supplies Ltd, West Sussex, UK). Participants then rested and prepared for exercise (wheelchair setup, gloves, standardization of wheel-tire pressure, clothing, bladder voiding, etc) for 45 minutes before repeating the 2 perceptual scales and 3-minute saliva collection pre-warm-up. A standardized 20-minute warm-up was started at 50 minutes before the performance tests: 3 SPR sets and 4 PUSHes (alternating counterclockwise and clockwise) with 4-minute rests between (Figure 1). The 2 perceptual
Figure 1 — Schematic of the experimental-trial protocol. Abbreviation: SPR, sprint. IJSPP Vol. 11, No. 2, 2016
216 Graham-Paulson et al
scales and saliva collection were repeated postexercise. Participants were also asked whether they had experienced any side effects during the protocol and to indicate which trial they believed they were on. Participants were permitted to consume only water ad libitum throughout each trial. Environmental conditions across the 2 training venues were temperature 20.9°C ± 2.4°C (range 17.1–25°C), humidity 45% ± 8% (range 34–54%), and pressure 999 ± 110 hourPa (range 978–1012 hourPa).
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Performance Tests Adapted from West et al,23 for the SPR, from a stationary position participants were asked to sprint through 20 m. Times to complete the SPR were recorded using wireless timing gates (Brower, UT, USA) at 0 and 20 m. Participants were given ~30 seconds to recover between SPRs. One SPR set was composed of 3 single SPRs. For the PUSH, markers were placed every 2 m (1.5 m at the corners) to produce a rectangle with rounded corners and to enable the total distance covered to be recorded (1 lap = 72 m). Participants self-selected their speed with the goal of covering the greatest distance possible in 4 minutes. Communication between participants was encouraged to ensure that overtaking was completed efficiently. Verbal encouragement was provided throughout all experimental trials by the same investigators, all of whom were blind to which trial the participants were completing. Participants were blinded to their results.
RPE scales are reported as median (quartiles) and were analyzed using Friedman and Wilcoxon tests. Statistical significance was accepted at P < .05.
Results Performance Tests Average 20-m-SPR times were significantly faster during CAF than with PLA during SPR 1 and SPR 2 (P = .037 and .016, respectively) (Figure 2). Total SPR time was significantly faster during CAF than with PLA (61.2 [58.5, 68.6] and 62.5 [58.5, 69.7] s, respectively) (P = .006). Ten (of 12) participants produced faster total SPR times. Times did not significantly change between sprint points during CAF or PLA (P = .254 and .212). There was no significant difference in PUSH distance between CAF and PLA (P = .111), nor did it differ over the course of the protocol in either trial (PUSHes 1–4) (P = .864). However, participants did cover more distance during PUSH 1 during CAF (677 ± 107 m) than with PLA (653 ± 118 m) (P = .047) (Figure 3). Total
Subjective Feelings The Feeling scale21 assessed the participants’ mood on a scale of +5 (very good) to –5 (very bad). The Felt Arousal scale22 was used to assess how aroused a participant was on a scale of 1 (low arousal) to 6 (high arousal). The Borg 6-to-2025 category scale was used to obtain participants’ RPE scores after each PUSH and SPR set.
Saliva Collection and Analysis For saliva analysis, samples were weighed to the nearest 10 mg. Saliva volume was estimated assuming saliva density to be 1.00 g/mL, and saliva flow rate was calculated from saliva volume and collection time. Saliva samples were transferred into Eppendorfs and centrifuged at 12,000 rpm for 3 minutes in a high-speed microcentrifuge. Salivary CAF concentration was determined using a commercially available kit (Emit Caffeine Assay, Dade-Behring, Milton Keynes, UK) on an automatic photometric analyzer (COBAS Miras Plus, Roche Diagnostic Systems, Switzerland). The intraassay coefficient of variation for salivary CAF concentration was 3.5%. Salivary CAF secretion rates were subsequently calculated by multiplying CAF concentration by saliva flow rate due to the high variability in saliva flow in this population.26
Figure 2 — The effects of caffeine supplementation (CAF) on 20-m-sprint performance (3 sprints per set), median (quartiles). Abbreviation: SPR, sprint. *Significantly different from placebo (PLA) (P < .05).
Statistical Analysis The Statistical Package for the Social Sciences version 20 software (SPSS Inc, Chicago, IL) was used to analyze the data. Distance per PUSH and total PUSH distance (sum of all 4 PUSHes) were calculated. Total SPR time (all 9 sprints) and average SPR time for each set were calculated. Normal distribution of the outcome variables was confirmed by the Shapiro-Wilk test for PUSH, and therefore data are reported as mean ± SD. Subsequently, a repeated-measures 2 × 4 (trial × time) analysis of variance (ANOVA) was used to analyze all PUSH data. To assess the effect of CAF on each individual PUSH and total PUSH, paired-samples t tests were employed. Nonnormally distributed SPR data and ordinal Felt Arousal, Feeling, and
Figure 3 — The effects of caffeine supplementation (CAF) on 4-minute maximal push (PUSH) distance, mean ± SD. *Significantly different from placebo (PLA).
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PUSH distance was not significantly different between CAF (2686 ± 416 m) and PLA (2634 ± 392 m) (P = .111). Overall, 7 participants covered a greater total PUSH distance during CAF than with PLA.
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Subjective Feelings Felt Arousal (P = .001 and .006 for CAF and PLA, respectively), SPR RPE scores (P = .002 and .00007 for CAF and PLA, respectively), and PUSH RPE scores (P = .00001 and .015 for CAF and PLA, respectively) increased progressively over the course of each trial, but there was no significant effect of CAF supplementation (P > .132) (Table 1 and 2). Feeling scores improved significantly over the course of the CAF trial (P = .017), but not during PLA (P = .197), and this occurred precapsule (0 [0, 3]) to postexercise (3 [2, 3]) (P = .041) (Table 1). Side effects during CAF including increased spasticity, struggling with decision making, headaches (also experienced during PLA), and nausea were reported by 5 participants. Trial order was correctly identified by 7 participants. Mean ± SD daily CAF intake was 211 ± 201 mg/d. No participant reported having experienced a prior adverse reaction to CAF. Three participants reported the use of CAF supplementation (80–220 mg) in capsule format before training or competition (supplementation was not included in daily intake data).
Saliva Salivary CAF analysis revealed that participants followed the 48-hour CAF-withdrawal procedure before both PLA (0.06 ± 0.06 μg/min) and CAF (0.13 ± 0.17 μg/min) (Figure 4), and these did not differ (P = .201). The consumption of CAF caused an increase in salivary CAF secretion rates pre-warm-up (1.05 ± 0.94 μg/min) (P = .009) and postexercise (1.34 ± 1.09 μg/min) (P = .003).
Discussion The current study demonstrates that the consumption of 4 mg/kg CAF can improve wheelchair sprint performance. CAF also appears to improve a 1-off bout of short-term endurance exercise, seen as an improvement during PUSH 1 but not PUSHes 2 to 4. The following paragraphs will discuss the potential reasons behind these results.
Sprint Performance CAF improved repeated-sprint performance in athletes with a physical impairment, which was apparent in the first and second
Table 1 Felt Arousal and Feeling Scale Responses Precapsule, Pre-Warm-Up, and Postexercise (N = 12), Median (Quartiles) Placebo
Caffeine
2.5 (2, 3)
2 (1.25, 3)
pre-warm-up
3 (2.25, 3.75)*
3.5 (3, 4)*
postexercise
4 (3.25, 4)*
4 (3, 4.75)*
precapsule
2 (0, 3)
0 (0, 2.5)
pre-warm-up
2 (1, 3)
2.5 (1, 3)
postexercise
3 (1, 3.75)
3 (2.25, 3)*
Felt Arousal scale precapsule
Feeling scale
†Significantly different from precapsule (P ≤ .05).
Table 2 Rating of Perceived Exertion Immediately After Each Sprint Set and 4-min Maximal Push (N = 12), Median (Quartiles) Placebo
Caffeine
Sprint set 1
12 (9, 14)
12 (11, 13)
Sprint set 2
13 (10, 15)†
14 (12, 14)†
Sprint set 3
14 (11, 16)†‡
14 (10, 15)†
Maximal push 1
16 (13, 19)
15 (15, 17)
Maximal push 2
17 (15, 18)†
18 (15, 19)†
Maximal push 3
17 (16, 17)†
17 (16, 18)†
Maximal push 4
18 (16, 19)†*
18 (17, 19)†‡*
†Significantly different from set 1, ‡significantly different from set 2, and *significantly different from set 3 (P ≤ .05).
Figure 4 — Individual participants’ salivary caffeine secretion rates precapsule (0 min), pre-warm-up (45 min), and postexercise (2 h) (N = 12) in (A) the placebo trial and (B) the caffeine trial
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218 Graham-Paulson et al
SPR sets but not the third (Figure 2). This corroborates previous research in able-bodied individuals that has shown initial improvements in performance after CAF ingestion with a subsequent null or negative influence on latter bouts.5,27,28 Faster 30-m-sprint times in the first 3 (of 12) sprints after 5-mg/kg CAF supplementation have been reported.5 Those authors hypothesized that the mechanism responsible for this initial improvement was a CNS effect mediated by antagonism of adenosine receptors. A CNS effect may also be responsible for the current study results in which participants produced faster average 20-m and total SPR times. These improvements are small yet meaningful for individuals competing in intermittent sports, as they may allow a player to lead his or her opponent in a sprint situation and therefore meet the ball, player, or line faster. The effects of CAF (5 mg/kg) on performance in simulatedcontest tae kwon do have been investigated, whereby athletes performed 2 combats (3 × 2-min rounds with 1-min rest periods) separated by 20 minutes.27 The ingestion of CAF improved reaction times before the first combat, increased the intensity of round 1, and maintained the intensity observed in the first combat in the second.27 These findings provide support for the initial performance improvements seen during SPR 1 and SPR 2 in the current study. Participants were able to push faster in the first 2 SPRs, but this led to the development of fatigue, and therefore no further improvements were seen. The “signal” produced after the ingestion of CAF may result in a performance improvement initially yet lead to a decrement or lack of improvement in successive exercise bouts.28 This pattern was observed in the current study and lends support to the idea that CAF can exert its effects through fast-twitch fibers.
PUSH Performance Notably, the same initial performance improvement was also observed in the PUSH results (Figure 3) despite no overall significant effect of supplementation. Participants benefited from CAF for a 1-off performance, covering a greater distance during PUSH 1, yet failed to show improvements in PUSHes 2, 3, or 4 compared with PLA. Previous research investigated the use of CAF before two 200-m freestyle time trials (TT) (~2 min duration) separated by a 30-minute rest.29 The authors revealed that CAF improved performance in TT 1 (P = .027), but participants swam 0.9% ± 1.1% slower in TT 2 after CAF than with placebo, and the conclusion was that the initial effort during TT 1 may have hindered performance in TT 2.29 This may also be true for the current PUSH results. However, another study reported opposing findings whereby CAF improved 100-m swim times in trained participants and prevented a drop in performance during a second 100-m swim (20 min passive recovery).9 The race distance (200 vs 100 m), CAF dose (~6.2 vs ~4.3 mg/kg), and recovery time (30 vs 20 min) may explain the differing results in these aforementioned studies.
Gastrointestinal Issues Gastrointestinal emptying and transit times can be delayed in individuals with an SCI,15 and this may be more prominent in those with a high lesion level,30 such as those in the current study (7 of 12 participants with tetraplegia). The pre-warm-up (45 min postingestion) saliva results suggest that 45 minutes may be inadequate time to develop sufficient CAF concentrations in some participants with a physical impairment (Figure 4). However, the participants then prepared for exercise and performed a 20-minute warm-up before the performance tests. The early performance improvements in SPRs 1 and 2 and PUSH 1 indicate that the supplement was absorbed
before the start of these tests (70 min postingestion). The only current study to investigate CAF use in wheelchair athletes showed no improvement in 1500-m performance (~3-min duration) after the ingestion of 6 mg/kg CAF 60 minutes before exercise.10 Those authors did not measure CAF concentration and therefore could not use this measure to help explain their results.10 The promising finding, however, was that 4 (of 9) participants produced their fastest times in the CAF trial compared with 3 other conditions (placebo, sodium citrate, and a combination of the 2).10 Furthermore, the current results suggest that the 60-minute absorption time employed by this study may have been sufficient for their athletes with paraplegia and spina bifida to produce these individual results. The time course for CAF absorption in individuals with an SCI, especially those with tetraplegia, should be further explored.
Subjective Feelings The side effects reported by 5 participants were similar to those reported in able-bodied participants, which include muscle trembling and shakiness/jitters, but were described as “increased spasticity” by those with an SCI or cerebral palsy. These side effects occurred despite a relatively moderate dose of 4 mg/kg CAF administered in this study compared with often larger doses of 5 to 10 mg/kg in the able-bodied literature. Notably, the reported side effects occurred in 2 of the 3 participants who reported the use of CAF supplementation before training/competition. The dose of 4 mg/kg was greater (1.5–2 times more) than their usual intake, which may explain the incidence of side effects in these individuals. This highlights the need to consider the dosing of CAF on an individual basis. It is likely that experiencing such issues during exercise could limit performance; however, there was no link between those who experienced side effects and those who did or did not improve. Despite the reported side effects during CAF, Feeling scale scores improved over the course of the trial after ingestion of the supplement. The psychostimulant effect of CAF is reported frequently19 and may have contributed to the improved SPR performance. Other common findings include increased arousal and an altered perceptual response after the ingestion of CAF,20 neither of which were apparent in the current study. However, an absence of changes in RPE was seen in conjunction with a greater distance covered during PUSH 1 and faster SPR times during CAF, which may suggest that the supplement influenced perceptual responses to some extent. The ability to successfully determine CAF or PLA is common in the CAF literature due to familiar side effects (eg, jitteriness and energetic sensations). In the current study only 7 participants correctly identified both trials, which increased our confidence that the CAF is responsible for the initial performance improvements.
Practical Applications The study protocol used trained (club-level) wheelchair rugby players performing in their own sport wheelchairs and reflected real-life pretraining/competition nutrition and hydration practices. Athletes taking part in, and coaches working with, similar intermittent wheelchair sports now have some evidence to show that CAF supplementation can be beneficial during wheelchair sprinting. The measurement of salivary CAF concentrations highlighted considerations for the timing of CAF supplementation in individuals with a physical impairment. CAF should therefore be trialed on an individual basis by wheelchair sportsmen (especially individuals with an SCI) and should initially use low doses of 1 to 3 mg/kg at least 60 to 70 minutes before exercise.
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Caffeine and Wheelchair Sprint Performance 219
A relatively small sample size was used in the current study, and participants had a variety of physical impairments, hence the findings can only be generalized to the sport, not to a specific impairment. As with all on-court testing, a combination of factors associated with the participant, the wheelchair, and the interfacing between the 2 may also have influenced performance, especially during cornering in the PUSH, during which a high element of skill was required. Given the nature of field-study protocols, the participants also performed in the presence of external interference (eg, participants, coaches, and researchers), which may have influenced performance. An attempt to minimize this influence was employed; participants performed the PUSH protocol with the same fellow participants where possible, they were motivated by the same investigators, and they were blind to their results.
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Conclusions This study supports the beneficial effects of CAF on sprint performance and on a 1-off bout of short-term endurance exercise in wheelchair sportsmen. The findings provide support for the psychostimulant effect of CAF, and yet the supplement did not improve participants’ RPE or Felt Arousal scores. The combination of side effects and potentially delayed CAF absorption highlights that its use in individuals with a physical impairment is highly individual. Acknowledgments The authors would like to thank all the participants for their effort and commitment to the project. Thanks also to Katie McGibbon and Lauren Delany for their help during data collection. No external funding was received to conduct this study.
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