INTRODUCTION
It is a common practice to consume alcoholic beverages after exercise training and athletic competitions. Indeed, daily alcohol consumption and regular physical activity are positively correlated according to a largescale survey of health behavior in the U.S. population [1]. College students who engage in vigorous exercise drink alcoholic beverages more often and in greater amounts than sedentary students [2]. Additionally, College athletes are more prone to participating in binge drinking than non-athletes, as they view alcohol use as more normative [3]. Considering the close link between alcohol consumption, exercise, and sports, it is important to investigate and clarify the effects of alcohol consumption on physical performance and recovery after exercise.
Acute [4-6] and chronic [7] alcohol consumption has harmful effects on physiological functions and sports performance. However, the effects of low-to-moderate amounts of alcohol, typically consumed by athletes and exercisers, remain highly controversial, and the number of available studies is limited. Barnes et al. reported that alcohol consumption aggravates the loss of muscular strength after strenuous and localized eccentric exercises using an isokinetic dynamometer [8-10]. By contrast, a different study conducted by another group [11] found that the same volume of alcohol intake had no effect on muscular strength after heavy eccentric resistance exercises involving squats. Additionally, delayed-onset muscle soreness (DOMS) occurs after intense eccentric exercise; however, no studies have shown a negative impact of alcohol consumption on the degree of DOMS after localized eccentric exercise [12,13] or resistance exercise [11]. The cause of this discrepancy is unclear, but it may be linked to variations in the types of eccentric exercises performed. Localized eccentric contractions may be an effective strategy to induce intensive DOMS in the laboratory setting but may differ from actual sports competition and training, limiting its translation to widely practiced forms of exercise and sports.
Downhill running on a treadmill is an eccentric-based exercise that has been established as a reliable, practical, and generalizable form of exercise that induces muscular damage [14,15]. To date, no studies have inves-tigated the relationship between alcohol consumption and recovery from muscular damage induced by downhill running. Additionally, most previous studies on the relationship between alcohol consumption and post-exercise recovery have been conducted in Western countries and Oceania [8,11-13]. Racial differences in alcohol metabolism are well known. In particular, 36-45% of East Asians exhibit facial flushing after alcohol intake, which has been attributed to the low activity of the enzyme that metabolizes acetaldehyde, an intermediate metabolite of alcohol [16]. Interestingly, acetaldehyde is also involved in the pain threshold and inflammation via histamine metabolism [17,18]. As such, racial differences in alcohol metabolism may affect the recovery of muscular performance and DOMS; however, no such studies have examined this in East Asians.
Given this background information, in the present study, we aimed to investigate whether moderate alcohol consumption after strenuous downhill running affects the recovery of muscular performance and DOMS in young East Asian men. We hypothesized that alcohol consumption would slow the recovery of muscular performance and increase pain perception.
METHODS
Participants
A total of 19 healthy Japanese men (25±7 years, mean ±SD) were assigned to either the alcohol intake group or control group. Five participants who could remain in the program for a prolonged period (>3 months) to avoid the long residual effects of eccentric exercise [19] completed the protocol twice, as participants in both groups in a randomized order. Each participant was treated as a distinct and independent individual in each trial. The participants were sedentary or recreationally active. Recreationally active adults participated in a variety of activities, but none had been performing downhill running. Exercise duration did not differ between the two groups (115±73 min/week in the alcohol group and 120±42 min/week in the control group). The participants were free of chronic diseases, as assessed by their medical history, and had no physical limitations. Participants were asked about their average daily alcohol consumption (type and amount) per week over the past month. All the participants habitually consumed alcoholic beverages, but nobody exceeded the recommended amount of alcohol consumption (40 g/day in Japan). The average daily alcohol intakes were 19±3 g/day in the alcohol group and 13±3 g/day in the control group. Six of the participants (50%) in the alcohol group had experienced an alcohol-flushing response (also known as “Asian flush” or “Asian glow”).
This study was carried out following the guidelines of the Declaration of Helsinki and approved by the Ethics Committee of Kokugakuin University (R03-013, September 28, 2021). All participants provided written informed consent before the study.
Procedures
The participants visited the research laboratory on four separate occasions. Participants were instructed to fast for at least 3 h before each measurement and to avoid strenuous exercise and caffeine-containing diets and drinks. Alcohol consumption (other than that administered) was restrained for 3 days before the baseline measurements and during the experimental period. During the first visit, the participants completed a standard health research questionnaire. They then familiarized themselves with the experimental protocol to introduce participants to downhill running on a treadmill and all the testing procedures involved. Maximal oxygen consumption (VO2 max) was measured to determine exercise intensity during subsequent downhill running.
At the second visit, the participants underwent baseline measurements, including body composition, subjective pain, peak isometric and concentric contraction torques, and squat jump performance. There were 3-7 days between the first and second visits. Following the measurements, participants performed downhill running. Within 90 min of the downhill running, participants in the alcohol group then consumed alcoholic beverages containing 1 g of alcohol per kilogram of body weight as distilled liquor (25% alcohol/volume, Kanoka, Asahi Breweries, Tokyo, Japan) with double the amount of water. The mean volumes of distilled liquor and mixed alcoholic beverage consumed per participant were 335±15 and 1006±43 ml, respectively. Participants in the control group consumed an equivalent volume of water (999±45 ml). An equal amount of the beverage was consumed every 15 min over 90 min. The alcohol consumption (1 g/kg body weight) and drinking duration (90 min) were chosen in accordance with a previous study [10]. Participants were not fed during the alcohol consumption period. Pain scores, muscular strength, and squat jump height were assessed when participants returned to the laboratory at 24 h (the third visit) and 48 h (the fourth visit) post-consumption. Participants consumed the same alcoholic beverage or an equivalent quantity of water after testing at 24 h post-test to make the influence of alcohol consumption, if any, more pronounced.
Downhill running
The participants warmed up on the treadmill at a level grade at the same speed as downhill running for 5 min. Following a warm-up period, the participants began running downhill. The downhill running protocol consisted of three 15 min sessions with 5 min rest intervals in a seated position. Participants performed downhill running at a -10% grade (slope) at a speed that corresponded with 70% of their VO2 max [20]. Heart rate (using a polar heart rate monitor) and rating of perceived exertion (RPE; Borg’s original scale for cardiorespiratory and lower limbs, respectively) were recorded every 5 min.
Anthropometric assessment
Height was measured to ±0.1 cm using a physician’s balance scale. Body weight (±0.1 kg) and body fat percentage were assessed using a bioelectrical impedance analysis system (Inbody-720, Biospace, Seoul, South Korea). This equipment has previously been shown to have high reliability and accuracy [21,22].
Maximal oxygen consumption
VO2 max was measured using an incremental treadmill protocol as previously described [23]. After a 5 min warm-up period, the participant ran at a speed that corresponded to 70-80% of the age-predicted maximal heart rate [24]. Treadmill speed remained constant throughout the test, and the grade was increased by 2% every 2 min until volitional exhaustion. The VO2 was measured using a respiratory gas analysis system (AE280S; Minato Medical Science, Osaka, Japan). A heart rate monitor (Polar Electro, Lake Success, NY) was worn to obtain the heart rate continuously. The RPE scale was obtained every minute. Each participant met at least two of the following three objective criteria: 1) a plateau in oxygen uptake as exercise intensity increased, 2) a respiratory exchange ratio of ≥1.1, and 3) reaching the age-predicted maximal heart rate [24].
Visual analog pain scale
We used a validated visual analog pain scale (VAS) to determine the level of subjective muscular pain as previously described [25]. The participants were asked to provide a subjective rating of muscular pain in their quadriceps, hamstrings, calves, and gluteus maximus during full squat motions. Participants were asked to mark the pain level on the 10 cm line with 0 describing “no pain” and 10 describing “worst pain.” The minimum unit was set as 1 mm.
Isometric and concentric contraction torque
Peak voluntary isometric and isokinetic concentric contraction torques of the dominant knee extensors were measured using an isokinetic dynamometry system (Cybex NORM, Lumex, Ronkonkoma, NY, USA), as previously described [20]. The participants were seated on a dynamometer and fixed with belts for the waist, shoulders, and thighs. Peak voluntary isometric contraction torque of the knee extensors was measured at a knee angle of 45°. The participants then performed three maximum knee extension contractions each with 60 s rests between trials. The protocol consisted of one set of three repetitions of concentric knee extension to the ending position (knee angle=0°) at 60°/s with passive knee flexion to the starting position (knee angle=95°). The averaged peak torque of three trials was used in the analyses. The test-retest reliability of the muscle strength measurements was determined by the coefficient of variation (CV) of the data for all participants (n=24) on the first day (pre-alcohol or control beverage consumption). The CV of isometric and concentric torques during the knee extension exercises were 4.2±1.8 and 3.4±2.5%, respectively.
Squat jump
Squat jump height was used to estimate leg power [26,27]. A measuring scale (Jump Meter; Takei Kiki, Niigata, Japan) consisting of a round, flat jumping board was attached around the participant’s abdomen and a string was tied from the measuring tape to the center of the jumping board. The participants stood at the center of the test mat and performed squat jumps as high as possible while putting their arms across the chest without countermovement. The knee joint angle before the jump was set to 70° for standardization purposes; three measurements were performed, and the averaged values were used for the analyses. The CV of this measurement was <2% in our laboratory.
Statistical analyses
The sample size was determined from our previous study using the same exercise protocol as in the present study [20]. At least 12 participants per group were required to detect a significant difference at 80% power with an α-level of 5%. Changes in dependent variables were evaluated using a two-way (time × group) repeated measures ANOVA. Fisher’s least significant difference (LSD) was performed when statistical significance was achieved. Statistical significance was set at p<0.05. Numeric data were expressed as means±SEM in figures for better visual interpretation, but means±SD was used elsewhere (e.g., in tables). All statistical analyses were performed using the StatView 5.0 software (SAS Institute, Tokyo, Japan).
RESULTS
Selected participant characteristics
The anthropometric characteristics of the participants are presented in Table 1. The age, height, body weight, BMI, body fat percentage, and VO2 max did not differ significantly between the control and alcohol groups.
Downhill running
The exercise intensity, measured by the relative heat rate and RPEs during downhill running, is shown in Table 2. None of the indices differed significantly between the groups at any time point during downhill running, indicating that the exercise load was similar between the two groups.
Isometric and concentric contraction torque
The changes in isometric and concentric contraction peak torques are shown in Figure 1. Baseline isometric peak torque during isometric knee extension did not differ between the two groups (Alcohol; 187±16, Control; 190±18 Nm) nor did concentric peak torque during knee extension (Alcohol; 157±10 Nm, Control; 159±14 Nm). Two-way ANOVA revealed no significant differences in the pattern of changes in isometric and concentric peak torques between the experimental conditions (for isometric peak torque, group × time interaction effect: F=0.64, p=0.53; for concentric peak torque, group × time interaction effect: F=0.09, p=0.91). In both groups, isometric (Alcohol; -10±3%, Control; -15±2%) and concentric (Alcohol; -7±4%, Control; -6±2%) peak torques decreased similarly and significantly at 24 h and recovered to baseline by 48 h (for isometric peak torque, time effect; F=9.31, p<0.05, for concentric peak torque, time effect; F=5.27, p<0.05).
Squat jump
The squat jump height at baseline did not differ between the groups (Alcohol; 36.0±0.8, Control; 37.3±1.1 cm). Squat jump height decreased significantly at 24 h after downhill running in both groups (Alcohol; 34.4±1.0, Control; 35.2±1.3 cm) but returned to baseline values by 48 h after exercise (Alcohol; 36.3±1.1, Control; 36.3±1.4 cm). No significant group differences were observed in squat jump height (group effect; F=0.23, p=063, time effect; F=3.65, p<0.05, group x time interaction effect; F=0.35, p=0.71).
Pain scales
Visual analog pain scores for the quadriceps, hamstring, gastrocnemius, and gluteus maximus muscles increased significantly at 24 h and 48 h in both groups (Figure 2). Pain scores in the quadriceps decreased significantly from 24 h to 48 h in the control group (p<0.05) but tended to increase in the alcohol group (p=0.08). Two-way ANOVA revealed a significant group × time interaction effect (F=4.47, p<0.05) for pain scores. The pain scale increased significantly from 24 h to 48 h in the alcohol group (p<0.05) but not in the control group (time effect: F=20.04, p<0.05, group × time interaction effect; F=1.54, p=0.23). No significant interaction effects were observed for the pain scores of the gastrocnemius (F=0.11, p=0.89) or gluteus maximus (F=0.95, p=0.40).
DISCUSSION
In the present study, we determined whether and how alcohol consumption after unaccustomed downhill running induces exaggerated changes in muscle strength, perceived pain, and slower recovery in East Asian men. Neither isometric or isokinetic contraction torque nor squat jump heights after downhill running were influenced by moderate post-exercise alcohol consumption. However, alcohol consumption appeared to delay the recovery of eccentric exercise-induced pain ratings in key muscle groups among the East Asian men who participated in this study. These results indicate that moderate alcohol consumption after downhill running does not affect the recovery of muscular strength and power but may delay the recovery of pain perception in some muscle groups within this population.
As expected, isometric and isokinetic muscle strength during knee extension exercises decreased substantially after downhill running. The magnitude of reductions in maximum isometric contraction torque (approximately -10% to 15%) was consistent with findings from our previous study, which employed a similar mode of exercise (downhill running) [20]. A moderate amount of alcoholic beverage consumption after exercise did not interfere with muscle strength recovery in the present study. Additionally, no adverse effects of alcohol consumption were evident on jump performance, which is used as a measure of explosive anaerobic power. The effect of post-exercise alcohol consumption on the recovery of muscle strength remains controversial, likely owing to a variety of experimental conditions, including diverse amounts of alcoholic beverages consumed, participant sex, and/or the type of eccentric exercise performed. In a series of studies conducted by the same group in young men, muscle strength following high-intensity eccentric exercise (300 repetitions of knee extensions on an isokinetic dynamometer) showed a greater decrease and delayed recovery when a relatively high dose of alcohol (1 g/kg body weight) was consumed (Barnes et al. 2010a, 2010b, 2012). Interestingly, these effects were absent when a lower dose of alcohol (0.5 g/kg body weight) was consumed (Barnes et al. 2011). In studies involving young women, an equivalent amount of alcohol consumption (1.09 g/kg body weight) after a similar eccentric exercise protocol produced no adverse effects on the recovery of muscle strength [12,13]. Regarding the exercise mode, ethanol consumption (~1.4 g ethanol per kg body weight) did not influence the recovery of muscular strength following traditional resistance exercises involving squats, lower limb presses, and bilateral knee extension [29]. Similarly, drinking alcohol after traditional resistance training did not affect jump performance measured at 24 h and 48 h after training [11,29]. In a study that simulated an actual sports setting, consumption of large amounts of alcohol after com-petitive rugby matches did not exert detrimental effects on muscular strength recovery [30,31]. Taken together with the results of the present study, the negative effects of alcohol consumption on muscle strength recovery appear to be absent when more familiar forms of exercise, such as running, are used. However, when the exercise mode is novel (i.e., eccentric exercise using an isokinetic dynamometer) and exercise-induced muscle damage is more severe, the adverse influence of alcohol consumption tends to appear more often.
Even though downhill running was performed at the same relative intensity and objective muscular performance was similar between the groups, subjective pain ratings of the quadriceps and hamstrings continued to increase in the alcohol group but not in the control group. Several research findings provide circumstantial support for our results regarding pain ratings. For instance, acute alcohol ingestion may increase the sensitivity of muscular pain to an external force because the muscular pressure pain threshold tends to be lower following recent drinking among binge drinkers [18]. Acetaldehyde, the primary product of ethanol metabolism, induces histamine release from mast cells [17], thereby elevating pain sensitivity. In the context of DOMS following muscle-damaging exercises, histamine receptor blockade reduces the perception of DOMS in leg muscles after downhill running [32]. Taken together, the delayed recovery of muscular pain observed in this study might be attributed to the effects of ethanol and/or acetaldehyde on histamine and its subsequent impact on pain sensitivity.
The present results are inconsistent with those of several previous studies reporting no effect of alcohol consumption on the recovery of pain ratings from eccentric or resistance exercise [8,11-13,33]. One notable difference was that all the participants in the present study were East Asians, more specifically Japanese. Upon consumption, alcohol is converted into acetaldehyde by the enzyme alcohol dehydrogenase (ADH) and it is further metabolized into acetic acid by the enzyme acetaldehyde dehydrogenase (ALDH). It is well established that East Asians (including Japanese) demonstrate a substantially higher expression rate of the low-activity ALDH gene (ALDH2*2 genotype) than Caucasians or Africans [16]. It is plausible that the effect of acetaldehyde on muscle pain sensitivity may have been exaggerated in East Asian participants as they were more likely to experience an alcohol-flushing response. Another issue that should be considered is that the participants in this study consumed alcoholic beverages after eccentric exercise as well as the day after exercise to make the influence of alcohol consumption more pronounced. The relatively high frequency of moderate alcohol consumption after downhill running might have affected these results.
This study has several limitations. First, the alcohol concentration consumed by the participants was standardized to a fixed level. Although this concentration was based on a previous study [10], it is possible that different levels of alcohol consumption, either lower or higher, would have yielded different results. Second, only young men were included in this study. Previous reports have suggested that alcohol consumption does not affect the eccentric exercise-induced decline in muscle performance in women [12,13]. Therefore, further studies involving female participants using the same protocol as in the present study are required.
In conclusion, we demonstrated that moderate alcoholic consumption did not affect the recovery of muscular performance after downhill running in young men. However, pain persisted for a longer period following alcohol consumption. These findings are inconsistent with those of previous studies conducted in non-Asian populations. Further research is needed to examine racial and ethnic differences in alcohol consumption in relation to exercise performance and pain ratings.
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