Mixed martial arts (MMA) is a physically demanding combat sport involving 3–5, 5-minute rounds with short periods (6–14 seconds) of high-intensity explosive activity interspersed with longer (15–36 seconds) periods of rest or low-intensity movement (30). Mixed martial arts athletes compete in weight classes and to gain an advantage over their opponents; they will often attempt to lose a large amount of weight in the days and weeks before “weighing in” for the event (colloquially termed “cutting weight”). Athletes then seek to regain the cut weight rapidly before the competition (16). In the week before competition, MMA athletes have been reported to lose an average of 9% of body mass with a further 5% lost in the 24 hours before the weigh-in (10).
Fluid loss and fluid restrictions are among the most common weight-loss methods in combat sports (5,21). The effect of dehydration without a rehydration period on aerobic and anaerobic performance has been well documented, with previous research indicating a negative effect on exercise performance (9,17,26,27,39). To date, much of the research examining the influence of acute dehydration on performance in combat sports has examined performance 2–5 hours after dehydration (3,18,29,32,36). These studies found dehydration to compromise upper-body, lower-body, anaerobic, and aerobic performance (18,32,36) or to have no effect on combat sports–specific performance or repeat effort capacities (3,29). A case study of 2 well-trained wrestlers observed rapid weight loss of 5.1–5.8% over 3 days to negatively influence exercise performance even after a 16.5-hour recovery period (34). However, much of the research investigating acute dehydration does either not investigate the effects after a sufficient recovery period to represent professional MMA competition (3,15,18) or does not investigate the magnitude of dehydration likely used in MMA competitions (10). Furthermore, much of the research investigates a mix of different weight-loss methods and does not provide a clear answer on the influence of acute dehydration on exercise performance (3,14,15,29,34). We are unaware of research that has extensively examined the effects of acute dehydration on physical performance 24 hours after. This is important because athletes are weighed 24 hours before professional combat sports events (boxing, kickboxing, Thai boxing, and MMA). It is plausible that performance is still compromised 24 hours after dehydration in combat athletes, with research indicating that dehydration can negatively affect total hemoglobin mass and blood volume for more than 24 hours (37,38). Further research examining the effects of dehydration on indices of performance in MMA athletes is therefore warranted.
There is evidence to suggest that after dehydration weight loss, MMA athletes are not adequately rehydrating before competing (21). Urinary measures of hydration and measures of body mass taken at the weigh-in 24 hours and 2 hours before competition indicate that athletes gained 4.4% of their body mass over the 22 hours period, yet 39% of athletes were still competing in a state of significant dehydration (urine specific gravity [USG] of >1.021) (21). To date, little research has examined the degree of rehydration during ad-libitum fluid replacement in recovery from rapid dehydration before competition in combat sports. Furthermore, we are unaware of research systematically examining the effects of such dehydration and rehydration on repeat effort performance of MMA athletes. The aim of this study was to examine the influence of 5% acute dehydration on performance and physiology of MMA athletes.
Experimental Approach to the Problem
This study involved 1 familiarization session and 2 experimental sessions in a randomized counterbalanced within-subject crossover design. All experimental sessions were performed at the same time of the day and separated by at least 14 days. Each athlete was asked to record their nutritional intake for the 24 hours before and after the first experimental session and then to replicate this diet during the second experimental session. Experimental sessions were performed in a randomized and counterbalanced order of either a dehydration (DHY) or a control protocol (CONT). During the familiarization session, athletes completed a series of performance tests in the same order that would be completed during experimental sessions, i.e., a vertical jump test, a medicine ball chest throw, a handgrip strength test, and a repeated sled push test. These performance tests were then performed 3 hours and 24 hours after the experimental interventions (described below), with these timeframes chosen to approximately replicate the time period between weigh-in and competition in both amateur and professional MMA competitions, respectively (18,29).
Fourteen male MMA athletes (± SD age 23 ± 4 years [age range: 18–34 years old], height 1.76 ± 0.4 m, and body mass 76.8 ± 9.3 kg) with at least 2 years of amateur competitive experience in MMA were recruited. All athletes were informed of the procedures and risks associated with taking part in the study before data collection, with written informed consent obtained in accordance with Edith Cowan University's Human Research Ethics Committee that approved the study.
To confirm euhydration immediately before both DHY and CONT, both serum and urine osmolality were measured. A 6-ml blood sample was drawn from the antecubital vein, and urine was collected in a 30-ml sterilized container. Both serum and urine osmolality were assessed with an Advanced 3250 single-sample osmometer (Advanced Instruments, Norwood, MA, USA). Using 250 μl of the urine sample, USG was measured using a calibrated urinary refractometer (Atago hand refractometer, model UNC-NE; Atago, Tokyo, Japan). In addition to these euhydration measures, nude body weight was measured using calibrated floor scales (Mettler 1D1 multirange, FSE, Melbourne, Australia). Based on previous literature (13,35), euhydration was defined as a serum osmolality <295 mOsm·kg−1, urine osmolality <700 mOsm·kg−1, USG of <1,020, and change of body mass less than 750 g compared with the previous trial.
The DHY session involved prolonged (3 hours) submaximal cycling on a Velotron cycle ergometer (Velotron ergometer; Racermate, Seattle, WA, USA) at 60 W in an environmental chamber (temperature 39.8 ± 2.41° C and humidity 22.8 ± 6.5%.). Participants wore a plastic sweat suit (plastic sweat suit; Wrap Yourself Slim, Melbourne, Australia) and were not permitted to consume fluids during the protocol with the aim of reducing body mass by 5% at 3 hours. The CONT condition involved the same exercise in thermoneutral conditions (i.e., 3 hours cycling at 60 W but at 25 ± 5° C and 31 ± 10% relative humidity), with participants free to consume fluids. The low power output of 60 W was chosen to increase core temperature and promote sweating but minimize muscle glycogen depletion (43). Throughout the experimental trials, core temperature was continuously recorded using gastrointentinal pill ingested 4.5 hours before exercise commencement (CorTemp Ingestible core body temperature sensor; HQ, Inc., Palmetto, FL, USA), and heart rate was recorded using a Polar heart rate monitor (Model S810i; Polar Electro Oy, Kempele, Finland).
Immediately before, immediately after, 20 minutes, 3 hours, and 24 hours after the experimental trials, nude body mass, blood pressure (Automatic blood pressure monitor; OMRON, Singapore), core temperature, tympanic temperature (ThermoScan, Braun, Germany), and heart rate were recorded. At each of these time points, a midstream urine sample followed by a 6-ml venous and a 32-μl capillary blood sample were also obtained. The venous blood sample was then spun at 12,000 rpm for 15 minutes at 4° C in a centrifuge (Multifuge 3 S-R; Kendro, Weaverville, NC, USA) after which 250 μl of serum was pipetted into an aliquot and analyzed for osmolality. Finger prick blood samples were collected using safety lancet (Unistik 2; Owen Mumford, Oxford, United Kingdom) into capillary tubes (Capilette MPW-212; MPW Med. Instruments, Thebarton, South Australia, Australia) and spun at 3,600 rpm to determine hematocrit. Both serum and urine osmolality were assessed with an Advanced 3250 single-sample osmometer (Advanced Instruments).
After both DHY and CONT, athletes were free to consume food and fluid ad libitum with athletes being encouraged to consume food and fluid as they would in preparation for a competition. At 3 hours and 24 hours after completion of the experimental conditions, athletes repeated all performance tests.
Measurements of Upper-Body Power, Lower-Body Power, and Grip Strength
Lower-body power was assessed using Yardstick vertical jump apparatus (Yardstick, SWIFT, Australia). Upper-body power was assessed using a medicine ball chest throw. Grip strength was assessed using a hand dynamometer (Hand dynamometer; Lafayette Instrument Company, Lafayette, IN, USA). For each assessment, 3 maximal efforts were performed with 1-minute rest between efforts and tests. The maximal result of each test was used for analysis.
Repeat Sled Push Test
To assess repeated effort capacity in a controlled manner, athletes were required to push a sled (The Predator Sled; Aussie Strength Equipment, Wetherill Park, NSW, Australia) weighing 75% of their body mass over a 10-m distance for a total of 30 efforts. Athletes were provided with verbal encouragement to give maximal effort during each sled push effort. At the completion of each 10-m effort, the athlete was given 20 seconds to complete a 20-m recovery before the next effort began. The time taken to complete each 10-m effort was recorded using infrared wireless timing gates (Speedlight TT wireless timing system; SWIFT). Heart rate and rating of perceived exertion (RPE) (Borg's 6–20 RPE scale) were recorded after each effort. Pilot testing indicated the total test time, peak, and mean 10-m effort time to be within acceptable reliability limits (ICC > 0.95; CV% < 4,0; TE < 0.45).
The test was designed to be reflective of MMA competitions, with a high-to-low intensity ratio of 1:3–1:5 and a total duration of more than 12 minutes (12,30,31). The test was terminated when athletes completed all 30 sled pushes, reached volitional exhaustion (i.e., was unable to continue), or the sled stopped moving mid distance for 2 consecutive efforts. Sled push effort times, heart rate, and RPE were averaged into 5 effort blocks (1–30) for data analysis. Peak time was calculated based on the fastest 10-m effort. Although the mean sled push time was calculated based on a mean of all 10-m efforts completed, a fatigue index was calculated based on the difference between the mean of the first 5 and the last five 10-m efforts.
Athletes who were unable to complete the sled push test were excluded from data analysis for speed and time, total test time, heart rate, and RPE. The data were assessed for normality, homogeneity, and sphericity before testing for main effects. A repeated-measures ANOVA was conducted using the first 5 sprint efforts to ensure that there were no statistical differences between subjects who completed and failed the test before the subjects being removed. For all data, 2-way repeated measures ANOVA testing was used to identify main effects. Where differences were observed, post hoc tests with the Holm–Bonferroni sequential correction adjustment were used to determine the location of the differences (19). Statistical analyses were performed using SPSS version 19.0 (SPAA, Inc., Chicago, IL, USA). Performance data were reported as mean (±SD), 90% confidence intervals (CI), and Hedges' g effect sizes. An effect size of 0.2 was considered a small effect, 0.5 a moderate effect, and >0.8 a large effect. All other data were reported as mean (±SD), and statistical significance was accepted as p ≤ 0.05.
There was no significant difference in body mass between conditions before any intervention (76.6 ± 9.7 and 76.8 ± 9.3 kg, respectively; p = 0.525). Body mass was significantly reduced immediately after the DHY (73.1 ± 9 and 76.1 ± 9.3 kg, respectively; p < 0.001) and did not return to baseline at any other time point (Table 1). Serum osmolality and hematocrit increased significantly 20 minutes after DHY compared with CONT and returned to baseline 3 hours after exercise (Table 1). No significant differences in urine osmolality were observed in either session, whereas USG was significantly elevated from baseline after DHY and was significantly greater than CONT at 20 minutes and 24 hours after DHY (Table 1).
Acute dehydration resulted in impaired repeat sled push performance at 3 hours and 24 hours after the DHY compared with the CONT (Figure 1A; Table 2). The mean sled push time after the DHY was slower than the CONT 3 hours (6.68 ± 1.48 and 5.23 ± 0.66 seconds, respectively, p = 0.001, CI [0.88–2.02], g = 1.229) and 24 hours after DHY (5.94 ± 1.42 and 5.15 ± 0.77 seconds, respectively, p = 0.012, CI [0.42–1.18], g = 0.671). The peak sled push time was also slower than the CONT 24 hours after DHY (4.18 ± 0.73 and 3.9 ± 0.5 seconds, respectively, p = 0.042, CI [0.13–0.44], g = 0.434). Furthermore, fewer participants completed the repeat sled push test 3 hours after the DHY than the CONT (10 vs. 13 completions); (Table 2). No significant differences in heart rate during the repeat sled push test were observed between the DHY and the CONT 3 hours or 24 hours after DHY (Figure 1B). Increased RPE during the repeat sled push was observed at both 3 hours and 24 hours after DHY when compared with the CONT (Figure 1C).
Acute dehydration reduced handgrip strength 3 hours after DHY (51 ± 8 and 53 ± 8 kg, respectively, p = 0.044, CI [−4.04 to −0.66], g = 0.243) but not 24 hours after DHY; medicine ball chest throw ability declined 24 hours after DHY (449 ± 44 and 474 ± 52 cm, respectively, p = 0.016, CI [−0.36 to −0.13], g = 0.253) but not 3 hours after DHY, and no significant differences were found in vertical jump height (Table 2). Heart rate was higher 0 minutes, 20 minutes, and 3 hours after DHY (155 ± 20, 97 ± 19, 85 ± 22 b·min–1) than the CONT (105 ± 20, 72 ± 13, 74 ± 15 b·min–1). Core temperature was higher than the CONT immediately after and 20 minutes after DHY but was not significantly different between conditions at any other time point. Tympanic temperature was greater than the CONT immediately after and 20 minutes after DHY, with no other statistically significant differences being observed between conditions. No statistically significant differences were observed in blood pressure (Table 3).
This investigation examined the influence of acute dehydration of 5%, achieved by 3 hours of cycling in the heat, on subsequent physical performance, body temperature, and hydration status. Although previous studies have examined the acute effects of dehydration on physical performance, a novel aspect of this study was the evaluation of the influence of acute dehydration on repeat effort capacities over the subsequent 24 hours. The main observations from this study were that (a) ad libitum fluid/food consumption after acute dehydration of 4.85% returned most physiological markers of hydration back to baseline but did not recover body mass 3 hours and 24 hours after the DHY and (b) aerobic and anaerobic performance (i.e., repeat sled push performance, grip strength, and medicine ball throw) was compromised 3 hours and 24 hours after the DHY.
Athletes lost on average 4.85% body mass during the DHY and 0.9% during the CONT; these reductions are similar to those previously found before competition in combat sports (5,10,25). In addition to this, physiological markers indicated severe dehydration up to 20 minutes after DHY (Table 1). Despite ad libitum fluid and food consumption, body mass did not return to baseline 3 hours or 24 hours after DHY, although body weight had returned much closer to baseline 24 hours after DHY. We provide evidence that despite athletes being able to consume fluid/food ad libitum after the DHY, athletes may have remained dehydrated 3 hours and 24 hours after DHY (Table 1). However, other markers of dehydration such as hematocrit, serum osmolality, and USG were not significantly different between conditions 3 hours after DHY (Table 1). Furthermore, at 24 hours after DHY, USG was greater than 1.020 and a smaller but statistically significant difference in body mass between conditions remained; yet, hematocrit and serum osmolality were not significantly different between conditions at this time. These results highlight that caution must be taken when using a single measure to assess hydration. Indeed, hydration status is complex and influenced by fluid shifts among several regions within the body making it difficult to measure (2). As such, using a single or even several measures of hydration, as we report, does not necessarily indicate that other physiological changes that occurred during high levels of dehydration have also returned to baseline. Given that severe dehydration can influence many physiological processes (9,28,40), future research investigating the physiological alterations and time course of recovery from severe dehydration is warranted, with a system biology approach.
Reductions in aerobic and anaerobic performance were observed up to 24 hours after the DHY protocol when compared with the CONT. Indeed, a large negative effect on mean sled push time was observed 3 hours after DHY (g = 1.229), whereas at 24 hours after, a moderate effect remained (g = 0.671). Other indicators of performance were similarly reduced (Table 2; Figure 1), providing evidence that short-term explosive performance and repeated effort capacities are adversely affected by acute dehydration even after prolonged (24 hours) recovery with ad libitum fluid and food consumption. Similar reductions in high-intensity exercise performance have been observed 1–5 hours after dehydration in studies using rowing, cycling, and boxing protocols (6,9,18,26,32). These results do deviate from some previous research investigating rapid weight loss in combat sports such as studies by Artioli et al. (3) and Mendes et al. (29), which gave athletes 5 days to lose 5% of their body weight. A key difference between this study and these previous studies is that the studies by Artioli et al. (3) and Mendes et al. (29) allowed multiple days to lose a similar amount of body weight to this study, which would not reflect that magnitude of weight lost in MMA (10). Because of the nature of combat sports, assessing performance in controlled laboratory conditions is difficult. Although this study does not measure MMA performance specifically, it does indicate that acute dehydration negatively effects both anaerobic and aerobic performance. Given that both the anaerobic and aerobic systems significantly contribute to both striking and grappling combat sports performance (1,4,7,11,20,24), the results indicate that a rapid reduction in body mass through dehydration may compromise an athletes' ability to compete, even 24 hours after the weight loss. Such findings are important because acute dehydration is highly prevalent in many combat sports (5,10) because of these sports being weight category based with athletes being weighed for competitions either the same day or the day before competition.
There are multiple physiological mechanisms that could have contributed to the observed decrements in performance such as an increase in cardiovascular strain due to decreases in blood volume (23,33), changes in blood flow to the cells impacting substrate exchange, impaired thermoregulation accelerating central fatigue (8,9,23,41), changes to the electrolyte balance in the body affecting muscle contractility (22,40,42), and decreased muscle glycogen (23,36). Investigation of these mechanisms in detail was outside of the scope of this study. However, we did observe a higher resting heart rate (15 ± 20%) 3 hours after DHY, indicating the potential for reduced blood volume, thus increasing cardiovascular strain (9,23). Resting tympanic and core temperature were within normal ranges at both 3 hours and 24 hours after DHY, but core temperature was not measured during exercise in this study, reducing our ability to determine whether thermoregulation was influenced during exercise. Although an increased perceived exertion was observed during the repeat sled push test at both 3 hours and 24 hours after DHY than the CONT. It is important to note that is was not possible to blind participants in this study to the intervention (i.e., DHY) and the effects of this, particularly on measures such as RPE and performance are unclear. Regardless, even if a nocebo effect is present during acute dehydration, it is still an effect of the process of losing such weight, which negatively affects exercise performance.
We report that acute dehydration of 4.8% body mass negatively influences exercise performance at both 3 hours and up to 24 hours after weight loss. Although providing for ad libitum fluid/food intake, athletes may not adequately rehydrate to recover from weight loss up to 24 hours after. Considering these findings, athletes and coaches need to reconsider their current weight-loss strategies before competitions and recovery strategies after weight loss. Indeed, athletes and coaches will need to consider whether the benefits of fighting in a lower weight class outweigh the decrements in performance that the weight reduction will result in. Although the battery of tests was developed to examine physical performance in MMA athletes, the findings of this study can be applied to a large number of weight-category–based or weight-restricted sports.
The authors thank all the participants for their efforts during the study.
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