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  • 1. 143 Physiological responses and energy cost during a simulation of a Muay Thai boxing match Antonio Crisafulli, Stefano Vitelli, Ivo Cappai, Raffaele Milia, Filippo Tocco, Franco Melis, and Alberto Concu Abstract: Muay Thai is a martial art that requires complex skills and tactical excellence for success. However, the energy demand during a Muay Thai competition has never been studied. This study was devised to obtain an understanding of the physiological capacities underlying Muay Thai performance. To that end, the aerobic energy expenditure and the recruit- ment of anaerobic metabolism were assessed in 10 male athletes during a simulation match of Muay Thai. Subjects were studied while wearing a portable gas analyzer, which was able to provide data on oxygen uptake, carbon dioxide produc- tion, and heart rate (HR). The excess of CO2 production (CO2 excess) was also measured to obtain an index of anaerobic glycolysis. During the match, group energy expenditure was, on average (mean ± standard error of the mean), 10.75 ± 1.58 kcalÁmin–1, corresponding to 9.39 ± 1.38 metabolic equivalents. Oxygen uptake and HRs were always above the level of the anaerobic threshold assessed in a preliminary incremental test. CO2 excess showed an abrupt increase in the first round, and reached a value of 636 ± 66.5 mLÁmin–1. This parameter then gradually decreased throughout the simulation match. These data suggest that Muay Thai is a physically demanding activity with great involvement of both the aerobic metabolism and anaerobic glycolysis. In particular, it appears that, after an initial burst of anaerobic glycolysis, there was a progressive increase in the aerobic energy supply. Thus, training protocols should include exercises that train both aero- bic and anaerobic energetic pathways. Key words: martial arts, exercise, energy expenditure, oxygen uptake, anaerobic glycolysis, carbon dioxide excess. ´ ´ ¨ ¨ ´ Resume : Le muay thaı ou boxe thaılandaise est un art martial exigeant des habiletes complexes et une tactique de haut ´ ´ ´ ´ niveau pour reussir. Il n’y a pas encore d’etude sur les sources d’energie de cet art martial lors d’une competition. Le but ´ ´ ´ ´ ` ´ ´ de cette etude est d’evaluer les capacites physiologiques des individus en competition. A cette fin, on evalue la depense ´ ´ ´ ´ ´ d’energie aerobie (EE) et l’implication du metabolisme anaerobie chez dix sujets masculins au cours d’une competition si- ´ ¨ ´ ´ mulee de muay thaı. L’evaluation des sujets en competition se fait au moyen d’un analyseur de gaz portable fournissant ´ ` ´ les donnees de consommation d’oxygene, de production de gaz carbonique et de frequence cardiaque (HR). On evalue ´ ´ aussi le surplus de production de gaz carbonique afin d’obtenir un indice de la sollicitation de la glycolyse anaerobie. Au cours du match, la EE est en moyenne (± erreur type sur la moyenne) de 10,75 ± 1,58 kcalÁmin–1, ce qui equivaut a ´ ` ´ 9,39 ± 1,38 METs. Les valeurs de consommation d’oxygene et de HR sont toujours au-dessus du seuil anaerobie preala- ´ ´ ´ blement determine au cours d’un test d’effort progressif. Au cours du premier round, le surplus de dioxyde de carbone pro- duit presente une augmentation marquee et affiche la valeur de 636 ± 66,5 mLÁmin–1. Cette valeur s’abaisse graduellement ´ ´ ` ¨ au cours du match. D’apres ces observations, le muay thaı est une discipline sportive exigeante sur les plans de la sollicita- ´ ´ ´ ` ´ ´ ´ tion des deux metabolismes, aerobie et anaerobie. Apres une sollicitation marquee du metabolisme anaerobie au debut du ´ ´ ´ ` match, on observe un engagement graduel du metabolisme aerobie. Il faudrait donc veiller a solliciter les deux modalites ´ ´ ´ ˆ de fourniture d’energie dans l’elaboration d’un programme d’entraınement. ´ ´ ´ ` ´ Mots-cles : arts martiaux, exercice physique, depense d’energie, consommation d’oxygene, glycolyse anaerobie, surplus de production de gaz carbonique. ´ [Traduit par la Redaction]Introduction worldwide, with 5 continental federations, under a sole and unified regulatory body. Muay Thai, often translated into English as Thai boxing, Muay Thai requires complex skills and tactical excellenceis the national sport of Thailand and is a martial art with ori- for success. Matches are characterized by dynamic phases ofgins in the ancient battlefield tactics of the Siamese army. short duration, during which athletes try to strike their oppo-During the latter half of the 20th century, Muay Thai was nent or defend themselves from the attacks of their oppo-exported to many countries, and now the International Fed- nent. Fighters wear boxing gloves and use several parts oferation of Muaythai Amateur claims 110 member countries the body for offensive and defensive purposes, including Received 27 May 2008. Accepted 09 January 2009. Published on the NRC Research Press Web site at apnm.nrc.ca on 28 March 2009. A. Crisafulli,1 S. Vitelli, I. Cappai, R. Milia, F. Tocco, F. Melis, and A. Concu. Department of Science Applied to Biological Systems, Section of Human Physiology, University of Cagliari, Cagliari, Italy. 1Corresponding author (e-mail: crisafulli@tiscali.it).Appl. Physiol. Nutr. Metab. 34: 143–150 (2009) doi:10.1139/H09-002 Published by NRC Research Press
  • 2. 144 Appl. Physiol. Nutr. Metab. Vol. 34, 2009fists, elbows, knees, and feet, but headbutting an opponent is Experimental protocolnot allowed. Therefore, Muay Thai shares many similaritieswith several forms of martial arts and with boxing. A typical Preliminary testmatch usually consists of 3 to 5 rounds (depending on the Each subject underwent a preliminary incremental exer-category of fighters), 3 min per round, with a 1-min break cise test on a motorised treadmill (Runrace, Technogym,between each round. ` Forlı, Italy) to assess their anaerobic threshold (AT) and From a physiological point of view, Muay Thai appears _ maximal oxygen uptake (V O2 max). The test consisted of ato be an intermittent physically demanding sport, with linear increase of running velocity of 2 kmÁh–1 every 3 min,short phases of maximal or supramaximal intensity spaced starting at 6 kmÁh–1, up to exhaustion, which was consideredby brief recoveries. It is, thus, likely that both aerobic the exercise level at which the subject was unable to main-and anaerobic energy systems are recruited during a tain the running speed (i.e., muscular fatigue).match. Fighting simulation test To obtain an understanding of the physiological capacitiesunderlying Muay Thai performance, it would be useful to On a separate day from this preliminary test (the intervalknow the energy demands and whether the anaerobic metab- was at least 3 days), each subject underwent a simulation ofolism is recruited during a match. However, while there are a Muay Thai match. To construct a fighting simulation asstudies dealing with the energy demands of some martial real as possible, the assistance of a skilled trainer, who hadarts, such as Judo, Karate, and Taekwondo (Beneke et al. been involved in national and international competitions2004; Degoutte et al. 2003; Francescato et al. 1995; Ima- with excellent results, was enlisted. This simulation wasmura et al. 1999), to the best of our knowledge, the energy conducted in our laboratory, where a space with the samerequirement during a Muay Thai competition has never been dimensions as a Muay Thai ring was prepared. The subjectstudied. This information would provide benchmarks for im- under study performed a 15-min warm-up and then restedproving and monitoring athletes’ training. on a bench until his cardiorespiratory variables returned to the pre-exercise level. Recovery was considered complete This study was devised to study energy demand during a when HR was not more than 10 beatsÁmin–1 higher thancompetition of Muay Thai and to test the hypothesis that pre-exercise level, and when the respiratory ratio, calculatedMuay Thai is a physically demanding activity that recruits as the carbon dioxide : oxygen uptake ratio, was less thanboth aerobic and anaerobic energy systems. In particular, 0.9. The last 3 min of sitting were used to gather the restingwe were interested in measuring aerobic energy expenditure values of the variables and, after this period, the simulationduring a competition and in discovering whether and to match began.what extent anaerobic glycolysis was recruited. This The simulation consisted of 3 rounds, each followed byinformation would be useful for coaches to design specific 1 min of recovery, during which the subject sat on a bench.training programmes capable of inducing the specific adap- The rounds consisted of a series of 6 attacks and 6 defensivetations required by Muay Thai. To this end, some physio- _ actions, each lasting 15 s, for a total duration of 180 slogical variables, such as oxygen uptake (V O2), carbon (3 min). During the attack phases, the subject fought againstdioxide production (V _ _ CO2), pulmonary ventilation (V E), a sparring partner, who was the aforementioned skilledand heart rate (HR), were assessed during a simulation trainer equipped with padded arm-shields (Fig. 1). The se-match, during which athletes wore a portable gas analyzer quence of strikes was planned ahead, and included strikesable to measure these variables. with knees, elbows, fists, and kicks. The fighter was ver- bally encouraged to perform maximally throughout the test. After the recovery following the last round, 3 min of furtherMaterials and methods recovery was allowed (final recovery). Hence, the wholeSubjects simulation test lasted a total of 18 min: 3 min of resting be- Ten male Muay Thai athletes (mean ± standard error of fore the beginning of the match; 3 rounds, each lastingthe mean (SEM) of age, height, and body mass were 3 min, spaced with 3 min of recovery (for a total of23.7 ± 1.5 years, 174.3 ± 0.9 cm, and 65.1 ± 1.2 kg, re- 12 min); and 3 min of final recovery. At the end of the test,spectively), who regularly took part in competitions in the athletes were asked to compare the effort expended duringprevious 2 years, were enrolled in the study. None had any the simulation with that expended during a real Muay Thaihistory of cardiac or respiratory disease or was taking any match. They gave a score ranging from 1 to 5, with 1 indi-medication at the time of the study, and none showed any cating not similar and 5 indicating very similar.abnormalities on physical examination or on resting elec- All experiments were conducted between 0900 and 1400trocardiogram. Subjects were skilled athletes who trained hours in a temperature-controlled room (room temperaturefor 8 to 10 h a week and had been involved in regular set at 22 8C, relative humidity at 50%). Subjects had a lighttraining program for at least 3 years. In the previous year, meal at least 2 h before exercising. Subjects were also asked6 of them had participated in international competitions, to avoid caffeine and alcohol ingestion the day before testswhile the other 4 participated in matches at the national were scheduled.level. Thus, our group represented the Muay Thai fighterat the middle–upper level. The study was performed ac- Variablescording to the Declaration of Helsinki and was approvedby a local ethics committee. All subjects gave written in- Assessment of respiratory variables and heart rateformed consent. _ _ _ Values of V O2, V CO2, V E, and HR were obtained Published by NRC Research Press
  • 3. Crisafulli et al. 145Fig. 1. (A) One of the subjects in the study wearing the portable _ _ metabolic system, which provided average of V O2, V CO2,metabolic system (MedGraphics VO2000) while sitting on a bench _ E, and HR values throughout the test. Vbefore starting the simulation. The face mask, breathing valve, har-ness, and battery pack can be seen. The metabolic unit, which is Measurement of aerobic energy expenditure and anaerobicplaced on the back, can be seen in (B), which shows the subject glycolysisengaged in simulated fighting. During the simulation match, the aerobic energy expendi- ture (EE, expressed as kcalÁmin–1) was calculated with the Weir equation (Weir 1949; Mansell and Macdonald 1990): _ _ EE ¼ 3:941  V O2 þ 1:106  V CO2 This equation was used when the respiratory exchange ratio (RER) was <1, while an oxygen caloric equivalent of 5.04 was used when EE became >1. In this case, it was assumed that all aerobic energy was derived from carbohydrate oxi- dation. To obtain an index of anaerobic glycolysis, excess CO2 production (CO2 excess) was assessed, as follows (An- derson and Rhodes 1989): _ _ CO2 excess ¼ V CO2 À ðRERrest  V O2 Þ where RERrest is the respiratory exchange ratio at rest, and CO2 excess represents an index of lactic acid and H+ accumu- lation, since, at tissue pH, lactic acid dissociates and pro- duces H+, which is buffered by –HCO3 and other cell buffers. The amount being buffered by –HCO3 leads to H2CO3 production, then to H2O and CO2 (Beaver et al. 1986b; Hirakoba et al. 1993). In this way, CO2 excess is pro- duced and is superimposed on the CO2 normally derived from aerobic metabolism. Actually, CO2 excess was found to correlate well with the rate of lactate accumulation in the blood during exercise and with the anaerobic capacity (Hir- akoba et al. 1993, 1996; Yano et al. 2002). The start of the lactate increase and CO2 excess were found to have good in- tercorrelation, even though the interindividual prediction of lactate concentrations from CO2 excess is not straightforward (Roeker et al. 2000). This parameter has been recently uti- lized to assess the rate of anaerobic glycolysis during var- ious kinds of exercise, including field testing and training sessions involving dynamic phases and recoveries (Crisafulli et al. 2002, 2006a, 2006b). Statistical analysisthroughout the preliminary and the simulation tests, by Data were averaged for 3 min during the rest period be-means of a portable metabolic system (MedGraphics fore the simulation match, during rounds, and during recov-VO2000, St. Paul, Minn.), which provides a 3-breath aver- ery after the simulation, while a 1-min average wasage of variables through telemetric transmission. This sys- employed for the recovery periods between rounds. In thistem has been shown to be reliable and to have good way, information about the time course of studied variablesagreement with a standard metabolic cart for laboratory use was gathered, and differences among the various periods of(Byard and Dengel 2002; Olson et al. 2003). The device the protocol were detected. Responses are reported asweighs about 1.2 kg and includes the metabolic unit, battery means ± SEM. Comparisons between periods were per-pack, harness, chest belt for HR monitoring, face mask, and formed using the repeated measures analysis of variancebreathing valve. It is worn on the subject’s chest with a har- (ANOVA), followed by Neuman–Keuls post hoc, when ap-ness, and does not limit the athlete’s movements. Prior to propriate. Significance was set at a p value of < 0.05. De-testing, the VO2000 was calibrated according to manufac- scriptive statistics were performed on each variable beforeturer’s instructions. During the incremental test, AT was de- the ANOVA to confirm the assumptions of normality bytermined using the V-slope method, which detects AT using means of the Kolmogorov–Smirnov test. The a level was _computerized regression analysis of the slopes the of V CO2 set at p < 0.05. Statistics were calculated with a commer- _vs. V O2 plot during exercise (Beaver et al. 1986a), while cially available software (Graph-Pad Prism). _ _V O2 max was calculated as the average V O2 during the last30 s of the exercise test. Results During the simulation test, subjects wore the portable All subjects completed the study protocol. Table 1 shows Published by NRC Research Press
  • 4. 146 Appl. Physiol. Nutr. Metab. Vol. 34, 2009 Table 1. Mean group values ± standard error of _ Fig. 4. Group values of HR (A) and V O2 (B) during the various the mean (SEM) of maximum oxygen uptake (ex- periods of the simulation. A horizontal dotted line identifies the le- pressed as absolute and indexed by body mass va- vel of anaerobic threshold. Values are means ± SEM (n = 10). lues), maximum heart rate, oxygen uptake at *, p < 0.05 vs. rest; {, p < 0.05 vs. final recovery. anaerobic threshold, and HR at anaerobic threshold reached by subjects during the preliminary incre- mental test. Parameter Mean SEM _ V O2 max (mLÁminÁkg–1) 48.52 1.7 _ V O2 max (mLÁmin) 3158.6 102.4 HRmax (beatsÁmin–1) 182.9 1.6 _ V O2 AT (mLÁminÁkg–1) 30.8 1.6 _ V O2 AT (mLÁmin) 2024.6 101.6 HRAT (beatsÁmin–1) 137.5 4.5 _ Note: V O2 max, oxygen uptake; HRmax, maximum heart _ rate; V O2 AT, oxygen uptake at anaerobic threshold; HRAT, heart rate at anaerobic threshold.Fig. 2. Example of time course of heart rate (HR) and pulmonary _ventilation (V E) of 1 subject during the simulated match. col, while Table 2 shows mean values of variables during the active phases of the match (excluding recoveries). HR (Fig. 4A) increased during the simulated fighting, in comparison with rest. This HR elevation was present during the whole test, including the recovery phases between _Fig. 3. Example of time course of oxygen uptake (V O2) and carbon rounds and the 3 min of final recovery after the test. Thisdioxide production (V_ CO2) of 1 subject during the simulated occurrence means that the resting periods between roundsmatch. did not allow complete recovery. Moreover, it is noteworthy that HR was above the value of AT assessed during the pre- liminary incremental test for the entire period of the simula- tion. _ Similarly, V O2 (Fig. 4B) rose during the match, compared with rest, reaching values well above the AT, with no signif- icant difference between rounds and recoveries. However, contrary to what was described for HR, during the period of _ final recovery, V O2 returned to values no different from _ rest. A very similar behaviour was shown by V CO2 and V E _ (Fig. 5A and 5B, respectively), which increased throughout the test but returned to baseline during the period of final recovery. Figure 6A shows the EE time course, which was obvi- _ ously very similar to that of V O2. It should be noted that the EE during the 9 min of the simulation match (i.e., ex-the results of the incremental preliminary test. Figures 2 and cluding recoveries) was, on average, 13.94 ± 0.7 kcalÁmin–1 _ _ _3 exhibit an example of HR, V E, V O2, and V CO2 time (or 0.21 ± 0.01 kcalÁmin–1Ákg–1), which corresponds tocourse in 1 subject during the simulation match. Figures 4–6 12.15 ± 0.64 metabolic equivalents (METs; Fig. 6B), whiledepict results of the ANOVA test applied to the mean during the whole test (i.e., including recoveries), this param-value of variables during the various periods of the proto- eter was, on average, 10.75 ± 1.58 kcalÁmin–1 (or 9.39 ± Published by NRC Research Press
  • 5. Crisafulli et al. 147 _ _Fig. 5. Group values of V CO2 (A) and V E (B) during the various Fig. 6. Group values of aerobic energy expenditure (EE), expressedperiods of the simulation. Values are means ± SEM (n = 10). *, p < as kcalÁmin–1 (A) and as metabolic equivalents (METs) (B), during0.05 vs. rest; {, p < 0.05 vs. final recovery. the various periods of the simulation. (C) Time course of excess of carbon dioxide production (CO2 excess). Values are means ± SEM (n = 10). *, p < 0.05 vs. rest; {, p < 0.05 vs. final recovery; {, p < 0.05 vs. recovery 1.1.38 METs). Figure 6C depicts the behaviour of CO2 excess.This variable showed an abrupt increase in the first round,and reached its maximum during the first recovery min be-tween rounds, when it reached a value of 636 ±66.5 mLÁmin–1. CO2 excess then gradually decreased, eventhough it never returned to baseline. Finally, as far as the similarity of the simulation to a realmatch was concerned, the mean score given by athletes was4.1 ± 0.3 (with 5 being very similar).Discussion This study aimed at characterizing the energetic require-ments during a typical Muay Thai match. According to theinitial hypothesis, from our data, it appears that Muay Thaiis a physically demanding activity that recruits both aerobic 1 min was probably not sufficient to recover from the effortand anaerobic energy systems. This finding is in accordance made during the previous round.with what has been found in studies dealing with the energy The suggestion that Muay Thai is physically demandingdemands of other martial arts (Beneke et al. 2004; Frances- also emerges from the analysis of the EE; during the wholecato et al. 1995). On average, during the whole simulation, simulation, which lasted 18 min, EE was, on average, _including both active phases and recoveries, V O2 and HR 10.75 ± 1.58 kcalÁmin–1, which corresponds to 9.39 ±were above the values of AT previously assessed, and ap- 1.38 METs, while during the 9 min of the 3 rounds, it was, _ _proached the level of V O2 max. Also, V E greatly increased, on average, 13.94 ± 0.7 kcalÁmin–1, (or 12.15 ± 0.64 METs).reaching, on average, the maximum value of 117.5 ± The sixth edition of the American College of Sports Medi-12.7 LÁmin–1 during the second round, with peaks in some cine (2000) guidelines for exercise testing and prescriptionsubjects that reached 200 LÁmin–1. It is noteworthy that reports that the aerobic requirements for ring boxing andeven during the recovery periods between rounds, the phys- Judo correspond to 13.3 and 13.5 METs, respectively. Theseiological variables did not decrease to resting values. Thus, values are very similar to what we found for Muay Thai, Published by NRC Research Press
  • 6. 148 Appl. Physiol. Nutr. Metab. Vol. 34, 2009 Table 2. Mean group values ± SEM of heart rate, oxygen uptake, carbon di- oxide production, pulmonary ventilation, energy expenditure (expressed as kcalÁmin–1 and as METs), and carbon dioxide excess during the 3 rounds (i.e., excluding recovery phases) of the simulation match. Round 1 Round 2 Round 3 HR (beatsÁmin–1) 159.7±13.7 165.2±16.4 174±10.9 _ V O2 (mLÁmin–1) 2526.5±112.5 2927.5±185.2 2912.7±125.4 _ V CO2 (mLÁmin–1) 2685±122.9 3166.4±178.6 2939.1±79.1 _ V E (LÁmin–1) 90.5±8.3 117.5±12.6 110±8.4 EE (kcalÁmin–1) 12.6±0.5 14.6±0.9 14.5±0.6 EE (METs) 10.9±0.4 12.7±0.8 12.7±0.6 CO2 excess (mLÁmin–1) 307.3±77.5 405.8±95.5 195.7±93.6 _ Note: For statistical results, see figures. HR, heart rate; V O2, oxygen uptake; _ _ V CO2, carbon dioxide production; V E, pulmonary ventilation; EE, energy expendi- ture; CO2 excess, carbon dioxide excess.suggesting that these fighting activities have similar meta- and the following recovery, whereas, during the remainingbolic requirements. time, there was a progressive reduction in its utilization. It is to be noted that this EE very likely underestimated This is in accordance with previous findings showing that,the real energy requirement, since it did not take into ac- during intermittent maximal bouts of exercise, the EE of thecount the energy derived from the anaerobic metabolism. first bout is derived mainly from phosphocreatine degrada-Actually, even the anaerobic lactacid metabolism seems to tion and anaerobic glycolysis, while, during the latter stageshave been widely recruited, as can be seen by the high level of exercise, there is a significant shift to aerobic metabolismof CO2 excess reached in athletes, especially during the first and a reduced anaerobic energy yield (Bogdanis et al. 1996;recovery between rounds (Fig. 6C). This respiratory index Gaitanos et al. 1993). Thus, it appears that in our simulationhas been found to correlate well with the rate of lactate ac- test, after an initial burst of anaerobic metabolism, there wascumulation in the blood and the anaerobic capacity during a progressive increase in the aerobic energy supply. Thisexercise (Hirakoba et al. 1993, 1996; Volkov et al. 1975; suggestion can also be seen in Table 2, which shows thatYano et al. 2002). Thus, its assessment allows continuous _ V O2 was higher during rounds 2 and 3 than during round 1,measuring of the recruitment of anaerobic lactacid metabo- even though statistics applied to the overall protocol phaseslism during exercise, without requiring the athlete to stop so (i.e., including rest and recoveries) did not find any differ-that blood can be drawn. This parameter has been recently ence among these conditions, probably because the numberused in various kinds of efforts to detect whether the lacta- of subjects enrolled was not sufficient to reach significance.cid metabolism is involved in the exercise being performed Another finding deserving attention is that, among meas-(Crisafulli et al. 2002, 2006a, 2006b). In our investigation, ured variables, HR was the only one that did not return tothe mean group value of CO2 excess during the active phases rest level during the 3 min of final recovery, with the note-of the test was about 341.9 ± 51.7 mLÁmin–1, with a peak of worthy exception of CO2 excess. This means that this variable636.2 ± 66.5 mLÁmin–1 during the first recovery between _ _ had a slower recovery time course than V O2, V CO2, androunds. This value is similar to what was reported in pre- _ V E. In particular, this occurrence suggests that there was avious investigations, where athletes performed maximal or _ sort of dissociation between HR and V O2, which caused aneven supramaximal exercise tests requiring massive recruit- increase in HR over the real metabolic engagement. A veryment of anaerobic glycolysis (Crisafulli et al. 2002, 2006a). similar HR behaviour was described in a recent paper (Cri-Moreover, it should be noted that during the dynamic phases safulli et al. 2006a), which reported that when a substantial _of the simulation fight, mean values of V O2 were above the amount of CO2 is produced, such as when the exercise is _level of AT, and close to 90% of V O2 max, especially during characterized by alternate phases of maximal exercise androunds 2 and 3 (Table 2). This high metabolic requirement recovery, HR provides overestimated values of oxygen up-likely led to lactate generation, as suggested by previous take. Magosso and Ursino 2001 explained this phenomenonfindings examining the production of lactate in humans over by considering that carbon dioxide has a significant impacta range of power outputs, from 25% to 250% of V O2 max _ on the systems controlling the cardiovascular apparatus, and(Spriet et al. 2000). Taken together, these findings (i.e., ele- that hypercapnia may induce tachycardia. In our study, a _vated CO2 excess and V O2 constantly above the level of AT substantial elevation of CO2 excess was present throughout _throughout the simulation and close to 90% V O2 max during the test, explaining the HR behaviour. Furthermore, maximalthe dynamic phases) strengthen the concept that during a and supramaximal bouts of exercise have a profound impactMuay Thai match there is the recruitment of lactacid ca- on cardiovascular homeostasis, since they modify cardiacpacity (i.e., the capacity of anaerobic glycolysis to resynthe- preload, afterload, and contractility, which stress the cardio-sise ATP). vascular regulatory systems and induce compensatory tachy- From the results of this work, it appears that anaerobic cardia (Crisafulli et al. 2004, 2006c). Hence, our studyglycolysis was recruited especially during the first round supports the concept that the use of HR monitoring to assess Published by NRC Research Press
  • 7. Crisafulli et al. 149the intensity of exercise may be unreliable in activities that in- method is based on 2 assumptions: that the proteins oxida-volve repeated bouts of maximal and supramaximal exercise tion during exercise is negligible; and that when RER be-and lead to a massive recruitment of anaerobic glycolysis. comes >1, only carbohydrates are being oxidized. Both Yet, other factors, such as heat stress and dehydration, assumptions are clearly wrong, since a slight quantity ofmay have caused disproportionate HR elevation in relation proteins is oxidized during exercise and a RER > 1 doesto metabolic stress (Gilman 1996). All these factors (i.e., not necessarily mean that fat oxidation is not occurring, asCO2 excess, cardiovascular stress caused by modifications in lactate accumulation and the consequent CO2 excess genera-preload and afterload, heat stress, and dehydration) may ex- tion lead to an overestimation of the actual RER. Thus, there _plain the noticed dissociation between HR and V O2 during is considerable uncertainty when assessing substrate oxida-the final recovery period, and suggest that caution should tion rates in vivo from gas exchange (Frayn 1983). How-be used in drawing conclusions about the intensity of an ef- ever, the potential error in assessing EE with this method isfort from HR. not wide, and was calculated within 2.5% (Mansell and MacDonald 1990). Furthermore, it should be consideredLimitations of the study that there is not a reliable alternative method for estimating One possible limitation of our study is that it did not ana- EE during exercise, especially during field tests. A finallyze a real Muay Thai match but a simulation. However, in- consideration is the fact that the exercise protocol did notasmuch as portable gas exchange analyzers are not allowed control for the effect of fatigue on power output being per-in official competitions, it is impossible to measure variables formed. For instance, whether or not fatigue was impairingduring a real fight. Therefore, a simulation test was set with performance during the final round, compared with the firstthe assistance of a skilled trainer. As testified by the mean round, was not controlled for. This is a clear limitation of allscore given by the fighters enrolled in the study, the effort field studies not conducted in the laboratory setting, where itmade during this simulation was similar to that experienced is possible to obtain physiological-biomechanical indexes ofduring a real match. Hence, it is conceivable that the simu- fatigue. Nevertheless, it is likely that athletes performedlation resembled a typical Muay Thai competition. The maximally during the third round, as can be argued bynumber of subjects enrolled was only 10 because of the dif- _ Fig. 4 and Table 2; neither HR nor V O2 decreased duringficulty of recruiting Muay Thai fighters who met the inclu- round 3, compared with the other 2 rounds. However, it cansion criteria. However, subjects appeared to be very not be excluded that power output was lower (i.e., that effi-homogenous in terms of age, height, body mass, and train- ciency decreased) in the last round.ing level. Therefore, it is conceivable that the number of In conclusion, these data suggest that Muay Thai is asubjects enrolled represent the typical Muay Thai fighter at physically demanding sport with great involvement of boththe middle–upper level. Moreover, other studies dealing aerobic metabolism and anaerobic glycolysis. This leads uswith martial arts employed the same or fewer subjects to speculate that training protocols should include exercise(Beneke et al. 2004; Francescato et al. 1995). Another po- that train this metabolic pathway. Moreover, interval periodstential limitation is the use of CO2 excess as a measure of between rounds do not allow a complete recovery. Coachesblood lactate accumulation. The relationship between this should consider these suggestions when preparing the train-parameter and blood lactate has been investigated several ing program of athletes.times, and some studies found a good correlation (Volkovet al. 1975; Hirakoba et al. 1993, 1996; Yano et al. 2002), Acknowledgementswhile others did not (Roeker et al. 2000). In particular, This study was supported by the University of Cagliari,Roeker et al. (2000) concluded that ‘‘the start of the lactate the Italian Ministry of Scientific Research, and PRISMAincrease and excess-CO2 showed good intercorrelation,’’ Onlus.even though ‘‘an inter-individual prediction of lactate con-centrations from the excess-CO2 would be difficult.’’ They Referencesalso thought that ‘‘this parameter could be more a measurefor the formation rate of new lactate than the blood lactate American College of Sports Medicine (ACSM). 2000. Generalconcentration alone.’’ Our study was not intended to indi- principles of exercise prescription. In ACSM’s guidelines for ex-rectly assess blood lactate level; rather, it was devised to ercise testing and prescription. 6th ed. Lippincott Williams &gather qualitative information (i.e., whether the anaerobic Wilkins, Philidelphia, Penn. pp. 152–153.lactacid metabolism was recruited or not). To the best of Anderson, G.S., and Rhodes, E.C. 1989. 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