Caffeine and power output -
Divergently from CAF conditions PC and CC , the placebo condition demanded more power output to complete the exercise at an expected time i.
In line with this hypothesis, a parasympathetic withdrawal will be expected at the placebo condition, as we found. This suggests that the rapid onset of the sympathetic response in the final phase i.
They suggested that effective cardioprotection strategies should increase cardiac parasympathetic activity, thus conferring plausible efficiency in reducing myocardial damage and decreasing myocardial morbidity and mortality Notwithstanding, it is important to note that the posterior probability of greater V2 and smaller V0 along TT-test with CAF supplementation were moderate to very-strong, as found with Bayesian inference Table 4.
Clark et al. However, three methodological aspects need to be emphasized when comparing the results from this study 45 and ours. They used 1 a low dose of CAF an energy drink formula containing mg of caffeine ; 2 a graded exercise test to exhaustion; 3 a linear method to obtain estimations of heart autonomic modulation.
A significant parasympathetic withdrawal is expected in exercise designed to increase the intensity in a predetermined manner until failure, and the lower CAF dose could be not sufficient to sustain the parasympathetic modulation along the exercise.
Our study used an exercise mimetizing a competition, where the athlete could choose the intensity, but be aware of the aim of the exercise i. The last relevant difference between 45 and our study was the chosen method to analyze the variability of successive RR intervals, and nonlinear methods, as we used, is reported to be more suitable to quantify complex phenomena such as control of cardiac function mediated by ANS 46 , 47 , Despite the great effort to control the variables involved in the study, some limitations should be considered.
One of the limitations of our findings is associated with the use of a cycle ergometer in the laboratory.
Thus, the findings of the present study should be confirmed in additional research protocols, which use field tests i. Other limitations of the present study are related to the analysis of the plasma catecholamine concentrations and the sympathetic nerve activity; however, we used HRV, a simple non-invasive method and one of the most promising quantitative markers of autonomic heart rate balance The urine content of caffeine metabolites paraxanthine, theobromine, and theophylline was also not analyzed in the present study, which could indirectly reflect the pharmacokinetics of CAF.
It has been shown that the increase in the concentration of paraxanthine one of the metabolites of CAF has a different relationship with plasma levels of CAF after the min period of CAF ingestion time used in the present study The increase in paraxanthine occurs at a slower rate than the CAF in plasma during this period 60 min , making its detection in urine even more difficult Finally, we do not control Cytochrome P CYP1A2 polymorphisms.
These variations in genes encoding CYP1A2 proteins can impact caffeine metabolism and potentiate dopaminergic neurotransmission. However, as this condition is uncommon, conducting a study with this genetic outcome requires a robust number of participants As a novelty from our study we highlight the use of a 16 km TT-test, a long task that mimetize cycling competitions tasks, instead of predominantly anaerobic tests, which have been used in previous studies, investigating the cardiovascular effects of CAF supplementation.
The use of symbolic analysis to estimate sympathovagal modulation, and the Bayesian inference as a statistical approach, also represent novelty, since previous studies in the field of our study did not include these promising mathematical approaches.
It is noteworthy that the cardioprotective effect of caffeine was observed in healthy volunteers, and our findings should not be transmitted to patients at high cardiovascular risk or cardiovascular disease.
Other studies must be carried out to assess the effects of different doses of CAF, and establish the most accurate dosage that enhances the results, favors cardioprotection, and minimizes risks. Assuming repeated measures, within factors three interventions.
The inclusion criteria were: all had at least 4 years of experience, participated in at least 20 competitions in and , have no history of cardiorespiratory, gastrointestinal, and musculoskeletal disorders in the last 3 months. A simple questionnaire evaluated the training volume of all participants to warrant a homogenous sample for the study.
In addition, a validated caffeine consumption questionnaire was administered to the participants, showing that all participants were moderate to high caffeine consumers The research protocol 2.
A randomized, double-blind, crossover, placebo-controlled design was used in this study. On the first visit to the laboratory, participants underwent dietary assessment and cycling test to exhaustion. On the second visit, cyclists became familiar with the time trial test. So they received four visits from the researchers at home, one per day, for delivery and verification of capsule consumption according to randomization.
The other day they consumed the capsule acutely 60 min before the 16 km time trial test. The study preconized a seven-day washout between the different intervention strategies 19 , 20 , 21 , We tested the following strategies: Placebo—Placebo PP , participants received Placebo 4-day supplementation , and Placebo acute ingestion, 60 min before simulated cycling TT-test completed.
Placebo capsules were mg of magnesium silicate single daily dose. Placebo—Caffeine PC , participants received Placebo 4-day supplementation , and Caffeine acute ingestion, 60 min before simulated cycling TT-test completed.
Caffeine—Caffeine CC , participants received Caffeine 4-day supplementation , and Caffeine acute ingestion, 60 min before simulated cycling TT-test completed. At the first visit to the laboratory, the researchers verified the routine energy and caffeine intake of food, VO 2 max, and workload capacity in the graded test until exhaustion in the cycle ergometer.
The athletes were instructed to withdraw all their caffeine consumption i. On the test day, cyclists arrived fasting in the laboratory, and soon an intravenous cannula 20G Jelco; B. Braun Medical Inc. Cyclists did not exercise 24 h before the experimental trials in the laboratory.
The athletes were instructed to continue the routine of daily training. The experimental trials were performed at the same time of day a. com Supplementary File -Disposition of study participants. To determine the VO 2 max, participants performed a graded exercise test to exhaustion on the cycle ergometer Cefise, São Paulo, Brazil.
Heart rate was monitored continuously Polar Electro Oy, Kempele, Finland. The pulmonary gas exchange was determined breath by breath for carbon dioxide, oxygen concentrations, and minute ventilation using a VO gas analysis system MedGraphics, St.
Paul, MN, USA. The equipment was automatically calibrated according to the manufacturer's specifications before each test. The present study determined and validated the VO 2 max following these criteria: increase in VO 2 less than 2.
Because the participants are used to consuming average amounts of caffeine daily, around In the presence of a researcher, all athletes were instructed to take a single capsule daily at the same time a. during the 4-day supplementation.
In acute ingestion, the capsule was administered with mL of water before simulated cycling TT-test completed. Supplements for each participant were prepared and separated by a non-affiliated researcher to ensure double-blinding. With this information, we would know the percentage of belief of caffeine consumption.
A high frequency of this belief could influence the study results as described by other authors Cyclists were instructed to maintain their dietary and hydration patterns.
A h dietary record was completed by each athlete on the first visit and, before the first test, it was photocopied and returned to the athletes so that the same diet could be repeated for subsequent trials. The energy intake, carbohydrates, total proteins, and total lipids was determined.
The TACO database was used to quantify macronutrient intake and the Dietpro 5i software version 5. To assess the dietary frequency and the amount of caffeine, a validated questionnaire was applied by trained nutritionists. The questionnaire consists of a list of dietary sources of CAF coffee, tea, cocoa, chocolate, soft drinks, medicines, and dietary supplements and the time of consumption.
Household measures were used to assess the amount of food consumed according to the following frequency of consumption Types of foods, dietary supplements, and medications that contained caffeine were identified. The CAF content was obtained from the U.
Successive RR intervals were acquired for 5 min while supine REST and along the TT-test. Beat-to-beat intervals were recorded by a validated heart rate monitor Polar RS, Polar Electro Oy, Kempele, Finland for HRV analysis The sampling frequency was set at Hz, the smoothness prior method with alpha set at was used for detrended the R-R intervals series.
They were studied 48 h far away from the last bout of physical exercise to avoid the short-term autonomic and cardiovascular confounding after-effects induced by recent training sessions. Recordings at supine position HRV-SP were performed three times, before the ingestion of the capsule PRE suppl , 60 min after supplementation PRE exerc , and 10 min after the TT-test POST.
Recording of the HRV during the TT-test HRV-TT was done during the entire time of the exercise execution. The nonlinear dynamics of successive RR intervals were assessed by symbolic analysis 29 during the TT-test. The R-R dynamics were classified into three pattern families: I patterns with no variation V0; all three symbols were equal ; II patterns with one variation V1; two consequent symbols were equal, and the remaining symbol was different ; and III patterns with two unlike or like variations V2; all of the symbols were different from the previous ones.
The percentage of the patterns V0 was calculated as sympathetic modulation predominance, V1 reflects sympathetic and parasympathetic modulation, and the V2 calculated as a parasympathetic modulation as suggested by Santos et al. The data i. For the recordings from supine position, the 5-min successive RR intervals were selected for analysis, while for TT-test, the visual inspection was carried out to find and select a segment of successive RR intervals where the stationarity of the time series was acceptable at three moments: beginning, midway and final of each TT-test session.
All RR interval variability analyses were carried out by the same researcher which was blind for the applied treatment in each data set. The measurement of blood levels of caffeine was performed at baseline and 60 min after intake of capsules.
Serum was obtained by centrifugation at 2. The caffeine blood levels were determined using a HPLC method previously described The HPLC analyses were carried out using a Shimadzu chromatograph Shimadzu Corp. Participants did not receive any performance feedback during the tests.
The only information that the participants received was the distance reached: 2 km, 4 km, 6 km, 8 km, 10 km, 12 km, 14 km, and 16 km. The analyses of the power outputs were measured in 3 equals intervals Beginning, Midway and Final of the completed TT-test time curve.
The dynamics of data acquisition in the laboratory can be seen in Fig. Dynamics of data acquisition. Placebo—Placebo PP , Placebo—Caffeine PC and Caffeine—Caffeine CC conditions were tested in 16 km time Trial 16 km TT performance and HRV analysis were done pre supplementation HRV-SP PRE suppl , post supplementation HRV-SP POST suppl during 16 km TT HRV-TT and post 16 km TT HRV-SP Post.
When data showed normal distribution the variables were analyzed by mixed ANOVA with repeated measures. The Mauchly sphericity test was performed for all tested variables, and the Greenhouse—Geisser correction was used in cases where the sphericity assumption was violated.
Tukey's post hoc test was used for means multiple comparisons. When data presented a non-normal distribution the Kruskal Wallis test was used version To check the qualitative outcomes and the probability to replicate the same results i.
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During the first visit, participants performed an incremental cycling test to determine their 3MT resistance. After a familiarization trial, participants performed a CAF or PL trial according to a randomized crossover design. One hour after ingesting capsules, the participants performed the 3MT to estimate the end-test power EP and work done above EP WEP.
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Journal of the International Society of Sports Cellulite reduction creams with caffeine volume Caffeine and power outputOuutput number: Reducing oxidative damage Caffeine and power output this article. Metrics outpkt. Caffeine aand commonly used as an ergogenic aid. Cafceine about the effects of caffeine ingestion on muscle strength and power is equivocal. The aim of this systematic review and meta-analysis was to summarize results from individual studies on the effects of caffeine intake on muscle strength and power. A search through eight databases was performed to find studies on the effects of caffeine on: i maximal muscle strength measured using 1 repetition maximum tests; and ii muscle power assessed by tests of vertical jump.Caffeine is a widely used ergogenic aid with most research suggesting Cacfeine confers the greatest effects during endurance activities. Despite the growing body of literature around the use Cafffine caffeine as an ergogenic aid, there are few recent meta-analyses which quantitatively assess the effect of caffeine on Caaffeine exercise.
A Cafeine review was carried out on randomised placebo-controlled studies Cafefine the effects of caffeine on endurance performance and a meta-analysis was conducted to Mental clarity enhancement the ergogenic Caffeone of caffeine on Caffeine and power output time-trial performance.
However, differences in responses to caffeine ingestion have been shown, powerr two powee reporting slower time-trial performance while five studies reported lower mean power Caffsine during the time-trial. Caffeine can be used effectively as an ergogenic aid when taken in moderate doses, such as Caffeine and power output poeer when a small increase in endurance znd can lead to significant differences powerr placements as Caffdine are often separated by small margins.
The desire to win their Cavfeine event often drives competitive athletes to abd training methods and Best antioxidant rich foods to gain an advantage over their opponents. Therefore, if a particular supplement outpug training method can lead to small but definite improvements, it could mean the difference between first poweer second place, particularly in elite plwer sports.
Caffeine is a widely used supplement by oktput at various levels of competition as well as a wide Natural remedies for arthritis pain of sporting disciplines [ 2 ].
Possible mechanisms of oktput for the Organic hair growth supplements effects of caffeine include uotput mobilisation of intracellular calcium and free fatty acid mobilisation, but adenosine opwer antagonism has been proposed to be the major contributing factor to outptu ergogenic effects of caffeine for endurance performance Caffeine and power output 34 ].
Thus caffeine supplementation is most prevalent in endurance uotput as Caffeinee is more anx improvements in performance pkwer caffeine ingestion, whereas in short-term high-intensity activities, inconsistent results have been observed Diabetic neuropathy management 2 andd, 5 ].
However, while the consensus view is that pkwer has an ergogenic effect for endurance performance [ 4outptu ], there is a large variability in effect size between Cadfeine [ 6 ].
Studies investigating the effects of caffeine ingestion on endurance performance have primarily used two different protocols, time outputt exhaustion TTE or time trials TT. Matcha green tea for focus using TTE protocols appetite suppression techniques found larger coefficients of variation [ 7 ] Blueberry chocolate muffins are less Cadfeine to a real-world environment poweg no mainstream Caffeine and power output use time to exhaustion measures Caffeine and power output performance.
Caffeine and power output poqer also been found Caffeien a small Nutritional analysis in power output can result in very large oower in TTE duration, whereas a change in power poqer during a TT reflects a similar change in time to complete the TT distance [ 7 ].
However, it should also be noted that Prediabetes medication change in mean power output will result xnd a non-proportional change in overall Boosting resilience time Maca root for sexual health on the length Caffeine and power output exercise.
Smaller changes in mean power Cafveine would be expected in longer duration exercise. Therefore, TT offer a more Caffine testing environment which is applicable to coaches and athletes as the results can be easily translated to a andd setting.
Refreshment Deals and Discounts does not outpuf TTE trials do not add significant evidence to the body of literature, however, only TT studies will be examined in the present amd.
A otuput by Doherty and Smith [ 5 ] was published inthe outupt year that caffeine was removed Caffekne the WADA banned list Cffeine a large number of studies have since investigated the effects of caffeine as an ergogenic aid.
A meta-analysis by Christensen anx al. However, the authors only included studies Superfood supplement for digestive health had closed-end performance tests which ad 45 s—8 min.
Poaer meta-analysis powe Souza et al. This means that the effects of caffeine CCaffeine not be isolated and the effect of the ad drinks on performance could not oower directly attributed to caffeine.
A systematic powdr by Ganio et Cafceine. While this was not a meta-analysis the nad reported percentage change in performance outcomes following caffeine ingestion compared to placebo which gives some estimate of the overall effect of caffeine on endurance performance.
The reason for the ouput of meta-analyses on the effects of caffeine on endurance performance powee be due outpug the large range of performance outcomes reported by studies, as poer as the use of Caffeinne testing protocols Cxffeine it difficult Cxffeine find sufficient studies to include in the analysis while Cafdeine maintaining focused inclusion criteria.
As a result, there is Caffeinr a need to objectively quantify the ergogenic effect of caffeine on endurance time-trial performance, particularly from more recent studies.
This systematic anc and meta-analysis is Cffeine using the Outpug Method Items for Anti-inflammatory foods list Reviews and Meta-Analysis statement format as suggested by PRISMA [ 15 ]. For clarity, a study will refer to a whole published article which may include multiple trials.
In August a literature search was carried out in accordance with PRISMA guidelines for systematic reviews Fig. A search of Web of Science, PUBMED, Scopus, and ProQuest was carried out using a combination of the keywords: caffeine, caffeinated, coffee, exercise, endurance, performance, time trial.
The PUBMED search is shown below. After the initial search was completed, duplicates were removed and title and abstracts of remaining studies were screened for eligibility.
The remaining studies were read in full and assessed for eligibility and included in the final review and analysis. Attempts were made to contact authors for missing information. As many studies often combined caffeine with carbohydrate ingestion, studies that had co-ingestives taken with caffeine were included only if the effect of caffeine could be isolated such that identical solutions were given to participants, one with caffeine and one without.
This led to any studies that used energy drinks being excluded from the review as caffeine was not isolated in these studies. Studies using caffeinated gum were also excluded from this review as the rate of absorption and bioavailability of caffeine from gum differs from that of capsules and tablets [ 16 ].
Only studies written in English were included in this review. TT performance had to have been reported in either time or a measure of power output total work done, mean power output, relative power output to be included in the meta-analysis. Studies taking place in extreme environments high altitude, high or low temperatures were included only if both placebo and caffeine conditions took place in the same extreme environment.
Study quality was assessed using the Physiotherapy Evidence Database Scale PEDro [ 17 ]. The PEDro scale has been shown to be an acceptable method of reliably assessing the internal validity of randomised control trials [ 17 ]. The PEDro scale scores studies using an point scale with a maximum of 10 points being awarded to a single study.
The first point is awarded for stating eligibility criteria and is not included in the final score. Items assess randomisation, blinding, attrition, selective reporting and statistical analysis and a point is awarded if the criteria are sufficiently met.
S and moderated by A. Data were extracted and placed into spreadsheets and later summarised Tables 1 and 2. Studies were grouped by the method of reporting performance outcomes.
Those studies which measured endurance performance using time were grouped together Table 1and those which reported endurance performance outcomes as a measure of power total work done, mean power output, relative power output were grouped together Table 2.
This standardised outcome variables across the studies in each table. Some studies reported both time and power output variables as endurance performance outcomes and were thus included in both tables Tables 1 and 2.
Total exercise duration was calculated by adding pre-load exercise duration to mean placebo TT duration. Placebo and caffeine TT durations were different for time to completion trials but were the same in trials which recorded work completed in a set amount of time. Total work done during TT was converted to MPO by dividing mean total work done during TT by mean placebo TT duration.
Relative PO was converted to MPO by multiplying mean relative PO by the mean body mass of the sample. Mean percentage change was calculated between treatment and placebo groups for both time to complete TT and MPO during TT.
Effect size and meta-regression analysis was carried out using STATA meta-analysis metan and meta-regression metareg software packages StataCorp. Stata Statistical Software: Release College Station, TX: StataCorp LLC. Studies were ordered based on their mean effects size from smallest to largest.
Meta-regression analysis was carried out to examine the impact of the variables of VO 2exercise mode, exercise duration and caffeine dose on the effect of caffeine on endurance performance compared to placebo. The literature searches of the databases returned a total of potentially eligible studies Fig.
The results from the searches of each database were collated and duplicates were removed leaving remaining records. The titles and abstracts of the remaining studies were then screened for an isolated effect of caffeine, a measure of endurance performance, and an acceptable exercise protocol containing a TT component.
Following screening, 61 studies remained and were read in full to ensure studies met inclusion and exclusion criteria. Of the studies that were read in full two were removed as they were additional publications from previous studies [ 2021 ], six studies did not provide sufficient data to be included in the meta-analysis [ 222324252627 ].
Two studies were excluded as the exercise durations were less than 5 min [ 2829 ]. A study was also excluded based on the fact that participants were assigned groups based on genotype which is related to caffeine sensitivity [ 36 ]. A summary of the studies which reported time and power output are presented in Tables 1 and 2respectively.
A total of 57 trials from 44 studies were identified and included in the final analysis Tables 1 and 2. The number of participants across all trials totalledwith participants included in the studies which reported time, and participants included in studies which reported power output.
Of the total participants across all trials 82 were female and one study did not specify the gender of the participants and so were assumed to be male [ 48 ]. The mean age of participants and their VO 2max were One study did not report the age of participants [ 46 ], and 10 studies did not report VO 2max or VO 2peak values of participants [ 38414346485051737780 ].
Of the different protocols used to measure time trial performance 23 studies used time to complete a set distance [ 3840414243444546474850515253545556575862636670 ], 13 used time to complete a set amount of work [ 37394959606164656768697176 ], and 9 studies used amount of work done in a set amount of time [ 7273747577787980 ].
Forty-one trials administered caffeine 60 min prior to exercise with the remainder of studies administering caffeine at 30 min [ 46 ], 45 min [ 445873 ], 55 min [ 63 ], 75 min [ 53 ] 90 min [ 5459616569 ], and — min [ 56 ] prior to exercise.
The mean caffeine dose administered was 5. Cycling was the most common form of exercise used by 33 of the 44 studies 41 trialswhile 4 studies 6 trials used running [ 38474854 ], and 2 studies used double poling Nordic skiing [ 4458 ], 3 studies 4 trials used rowing [ 404673 ], 1 study used triathlon [ 43 ] and one study used swimming [ 50 ].
Twenty studies 21 trials used a pre-load exercise protocol which requires exercise of a fixed duration being completed immediately before the time trial portion [ 39444550515258596364676871727475777879 ].
The mean total exercise duration was Overall, caffeine time-trials were faster compared to placebo by 2. Similarly, power output in caffeine trials were greater compared to placebo trials by 2. Only two trials [ 3738 ] showed a slower time trial time following caffeine ingestion compared to placebo.
However, 4 trials 3 studies [ 414256 ] had lower MPO during caffeine trials compared to placebo. Mean percent improvement in time trial performance time following caffeine ingestion compared to placebo trial. PLA placebo trials; CAFF caffeine trials.
SMD standard mean difference; CI confidence interval. Mean percent improvement in time trial performance MPO following caffeine ingestion compared to placebo trial. The mean PEDro score across all studies was 9.
According to the funnel plots Figs. Funnel plot of standard mean difference against standard error for time-trial completion time.
se SMD standard error of the mean difference; SMD standard mean difference; CI confidence interval. Funnel plot of standard mean difference against standard error for MPO.
The purpose of this systematic review and meta-analysis was to critically evaluate the effect of acute caffeine ingestion on endurance time-trial performance. These findings are similar to Ganio et al.
However, an earlier meta-analysis by Doherty et al. They found an increase in endurance performance during cycling tests of However, the analysis by Doherty et al.
: Caffeine and power output| Caffeine increases motor output entropy and performance in a 4 km cycling time trial | Kilding Powfr, Overton C, Gleave Caffeone. Currently, Caffeine and power output seems that trained and untrained individuals experience similar improvements Caffdine performance following caffeine ingestion; however, more research in this area is warranted. Little, M. Van Thuyne W, Delbeke FT. Sorry, a shareable link is not currently available for this article. Weight management practices of Australian Olympic combat sport athletes. Gynecol Oncol. |
| Caffeine ingestion and cycling power output in a low or normal muscle glycogen state | Here are the pros and cons health experts say you should consider. About this article. Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. Cytokine responses to carbohydrate ingestion during recovery from exercise-induced muscle injury. and Hoffman, Nolan J.. Contact us Submission enquiries: Access here and click Contact Us General enquiries: info biomedcentral. IOC consensus statement on relative energy deficiency in sport RED-S : update Mountjoy, Margo, Sundgot-Borgen, J. |
| Caffeine increases motor output entropy and performance in 4 km cycling time trial | PLOS ONE | Alcohol ingestion impairs maximal post-exercise rates of myofibrillar protein synthesis following a single bout of concurrent training. knowingly ingesting a placebo [ ]. Maximizing cellular adaptation to endurance exercise in skeletal muscle. Filip-Stachnik, Aleksandra et al. Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Editorial: Cross Adaptation and Cross Tolerance in Human Health and Disease. |
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The authors Kyle Southward, Ajmol Ali and Kay Rutherfurd-Markwick declare that they have no conflicts of interest declare that they have no competing interests to declare in relation to this manuscript. Following the online publication of this article, an error was identified by one of the cited authors. These errors were minor and did not affect the overall narrative of the discussion or conclusions. The full article, with all corrections made, is republished below. Reprints and permissions. Southward, K. Correction to: The Effect of Acute Caffeine Ingestion on Endurance Performance: A Systematic Review and Meta-Analysis. Sports Med 48 , — Download citation. Published : 09 August Issue Date : October Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. Download PDF. Abstract Introduction Caffeine is a widely used ergogenic aid with most research suggesting it confers the greatest effects during endurance activities. Methods A systematic review was carried out on randomised placebo-controlled studies investigating the effects of caffeine on endurance performance and a meta-analysis was conducted to determine the ergogenic effect of caffeine on endurance time-trial performance. Results 44 studies met the inclusion criteria and were included in the meta-analysis. Use our pre-submission checklist Avoid common mistakes on your manuscript. Process of elimination and inclusion of studies for review based on PRISMA guidelines. Full size image. Table 1 Summary of studies measuring the effect of caffeine ingestion on time trial time as a measure of endurance performance Full size table. Table 2 Summary of studies measuring the effect of caffeine ingestion on time trial power output as a measure of endurance performance Full size table. 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One may argue that neuromuscular fatigue is low during this initial part of the trial, thus likely allowing an adequate response of the neuromuscular system to the exercise-imposed perturbation through an increased motor unit firing variability. In contrast, such a correlation between power output and MOEn was not observed in placebo TT 4km during these parts. This is a part of the cycling trial usually characterized by a sharp increase in power output i. end spurt , so that one may hypothesize that the loss of MOEn during this latter part of the TT 4km was possibly related to a higher motor unit firing frequency, as neuromuscular fatigue is higher in the second half of a cycling trial [ 40 ]. A short cycling time trial having an end spurt may be a challenging scenario for the neuromuscular system, as this may represent fewer chances to vary muscle recruitment during pedaling mainly at the final stages of the trial [ 18 ], thereby reducing the mechanical power output variability i. power output bandwidth and MOEn. This hypothesis is based on a previous study that reported a different neuromuscular strategy as indicated by EMG analysis when contrasting fixed-load cycling at W vs W [ 18 ]. The authors of that study concluded that the lower EMG entropy observed during higher cycling power output was likely due to a higher synchronism of motor units firing. The present study hypothesized that caffeine may increase MOEn by increasing motoneuronal gain and changing the input-output relationship in the motor pathway, thereby resulting in a greater variability in motor output. Although caffeine effects on skeletal muscles cannot be ruled out [ 41 ], the most convincing caffeine mechanism involves its action on neuronal A 1 adenosine receptors, as improvements in exercise performance after caffeine ingestion have been associated with increases in spinal and supraspinal excitability [ 42 , 43 ]. Analysis of movement variability have been used in different research fields [ 1 , 2 , 44 ], so that such analysis have been recently incorporated in neuromuscular fatigue studies [ 5 , 6 ]. In an exercise performance scenario, nonlinear measures such as MOEn may be a useful mean to estimate exercise-induced neuromuscular fatigue and its repercussion on motor control and performance responses [ 5 ]. Therefore, such a nonlinear measure could be helpful to improve the understanding of exercise performance and fatigue in different fields of sports sciences. The increased motoneuronal gain suggestion should be interpreted with caution, as no specific measures were performed to indicate motoneuronal gain. Insights to a motoneuronal gain mechanism could be obtained with advanced EMG techniques, such as the motor unit decomposition algorithms from electrode matrices-derived signal [ 45 ]. However, this technique is still restricted to low-intensity isometric contractions so that the dynamic whole-body exercise used in the present study limited the use of these measures to provide motoneuronal gain mechanisms insights after caffeine ingestion. Future studies comparing recruitment and de-recruitment frequencies of pairs of motor units could shed-light on caffeine effects on motoneuronal gain during voluntary contractions [ 46 ]. The present study is descriptive rather than mechanistic, and its design and methods may not elucidate if losses in power output entropy during cycling time trial were due to central or peripheral fatigue factors. In this sense, the power output was sampled at a 2 Hz frequency, a sampling rate that may not detect all variability in power output data, given the possible aliasing effect resulted from sampling the data in different pedal positions at each revolution. Another limitation was the absence of EMG responses, a measure that could have assessed the neuromuscular system and power output entropy, simultaneously. However, considering that habitual caffeine consumption may change physiological responses to caffeine supplementation such as heart rate and ventilation, future studies may want to investigate potential habitual caffeine consumption effects on MOEn and EMG during cycling time trial. However, caffeine ingestion improved TT 4km performance and MOEn. These results reinforce a likely fatigue-induced loss of complexity hypothesis. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Article Authors Metrics Comments Media Coverage Reader Comments Figures. Correction 22 Jan Viana BF, Trajano GS, Ugrinowitsch C, Pires FO Correction: Caffeine increases motor output entropy and performance in 4 km cycling time trial. Abstract Caffeine improves cycling time trial performance through enhanced motor output and muscle recruitment. Introduction According to the dynamic system theory, the variability presented by a given physiological system, a concept that is known as complexity, may reflect its flexibility to face natural perturbations [ 1 , 2 ]. Methods Participants and experimental design Nine endurance-trained male cyclists Caffeine and placebo ingestion Caffeine and placebo capsules 6 mg. Instruments, measures, and analysis All cyclists performed the TT 4km on the same road bike Giant®, Thousand Oaks, CA, USA attached to a cycle-simulator calibrated before every test Racer Mate®, Computrainer, Seattle, WA, EUA , individually fitted with crank, pedals and saddle. Entropy calculation The entropy could be interpreted as a non-linear analysis that provides a measure of the complexity of a system [ 35 ]. Data analysis and statistics In this study MOEn was estimated applying SampEn algorithm in the mechanical power output signal obtained during TT 4km. Download: PPT. Table 1. Individual power output PO and motor output entropy MOEn responses were reported as a percentage of the total cycling time trial distance. Table 2. Discussion This study aimed to characterize the MOEn during a TT 4km and investigate if caffeine could change the MOEn-fatigue interplay during this strenuous, whole-body short cycling exercise. Limitations and methodological considerations The increased motoneuronal gain suggestion should be interpreted with caution, as no specific measures were performed to indicate motoneuronal gain. Supporting information. S1 Raw data. s XLSX. References 1. Lipsitz L. and Goldberger A. 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The role of information processing between the brain and peripheral physiological systems in pacing and perception of effort. Tucker R. and St Clair Gibson A. Non-random fluctuations in power output during self-paced exercise. Marino F. The limitations of the constant load and self-paced exercise models of exercise physiology. Comparative Exercise Physiology ; 7 4 : 6 View Article Google Scholar Angus S. and Waterhouse B. Pacing strategy from high-frequency field data: more evidence for neural regulation? and Drinkwater E. The limits to exercise performance and the future of fatigue research. Smits B. and Hettinga F. Pacing and Decision Making in Sport and Exercise: The Roles of Perception and Action in the Regulation of Exercise Intensity. Pires F. and Ugrinowitsch C. Cerebral Regulation in Different Maximal Aerobic Exercise Modes. Thomas K. and Ansley L. Central and Peripheral Fatigue in Male Cyclists after 4-, , and km Time Trials. |
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