The present study aimed to determine whether there was a difference in the effects of taking 10 gram of creatine supplementation per session with Wingate-based HIIT on body composition, leg strength, and anaerobic power parameters when compared Wingate-based HIIT alone. For this purpose, fifteen physically active, healthy adult male participants divided into C-HIIT and HIIT groups and performed the same training for six weeks.
In the current research, it was found that six weeks of HIIT did not cause any changes in body composition independent of creatine intake. There was no significant change in any of the body weight, percent body weight, mass of body fat, lean body mass, total body water, BMI, BMR parameters in both groups. It is seen that different results have been obtained in other studies in the literature on this subject. For instance, Alonso-Fernández et al. (2019) investigated the effect of HIIT based functional body weight exercises that performed with a 20/10 work/rest ratio for 7 weeks in 26 children [37]. According to their results, while cardiorespiratory fitness increased, the percent body fat decreased. These findings differ from those obtained in the present research. The reason for this can be interpreted as the fact that the research group is not physically active adults as in the current research and the body composition values of children can change in a short time.
Forbes et al.'s study supports this interpretation. VO2max, ventilation threshold, lean body mass, mass of body fat, anaerobic power and insulin sensitivity were measured in the study examining the effects of HIIT training performed three days a week for a total of four weeks on some physical fitness parameters in 17 recreationally active adult women [38]. As a result, they reported an increase in anaerobic power value with no change in any of the body composition parameters. The increase in anaerobic power regardless of body composition is similar to current research. Unlike the current research, the increase in anaerobic power within four weeks without creatine supplementation may also be due to the research group. A study group with a lower level of physical fitness than in the current study may be the reason for the significant increase in a short time.
The more important point of this research is to examine the effects of creatine taken with Wingate-based HIIT on leg strength and anaerobic power values. According to the results, it was found that Wingate based HIIT with creatine intake increases the both absolute and relative anaerobic power values such as peak power, average power, minimum power and also total anergy expended significantly (p < 0.01). An improvement in the same direction was also seen in leg strength (p < 0.05). There are some studies in the literature that examine the effects of activity types similar to or different from the current study, together with creatine intake, on some performance parameters. In one of these studies Graef et al. [18] compared the effects of 10 g of creatine intake per session with HIIT that performed five days a week for four weeks with HIIT alone, and concluded that creatine supplementation had no additional positive effects on maximal oxygen consumption despite an increase in ventilatory threshold. However, it is observed in the literature that the positive effects of creatine on performance increase as the duration of the activity gets shorter. Examining the effect of 20 g creatine supplementation for 5 days on kayak ergometer performance over different durations, McNaughton et al. [39] divided the participants into creatine placebo, and groups and made them performed three maximum kayak ergometer tests of 90, 150 and 300 seconds. At the end of the research, they reported that creatine intake improves the amount of the work reached during the kayak ergometer performance at durations ranging from 90 to 300 seconds. In another study, Kendall et al. [19]’s investigated the effects of four-week HIIT program with 5 sets of 2-minute exercise bouts with 1 minute rest interval on the cycle ergometer and creatine supplementation on critical power and anaerobic working capacity in college-aged men. The subjects were assigned to creatine, placebo and control groups. According to their results, it was observed that the maximum power output increased in the creatine group, while the anaerobic working capacity did not change. Similarly, Romer et al. [40] found positive effects of 5-day creatine monohydrate loading of 0.075 g per kilogram of body weight four times a day and high intensity, intermittent exercises consisting of 10 sets of 2 repetitions of a simulated game in squash players. As a result of the study, a significant reduction in sprint time was observed. Balsom et al. [41] reported that six days of creatine loading (20 g per day) with HIIT sessions on a cycle ergometer did affect the power output in 10-second exercise period and increase the total muscle creatine and phosphocreatine concentration, but did not alter jump performance in physically active males. Unlike the current research, it has been observed that there are changes in body composition to the observed performance change. This may be due to the amount and frequency of creatine loading. However, some studies also show that creatine intake with HIIT does not have any positive effect on anaerobic performance. For instance, Biwer et al. did not observe any positive alterations on submaximal running interspersed with high-intensity intervals, after creatine monohydrate loading of 0.3 g per kilogram of body weight during six days [42]. The only significant change was the increase found in body mass of male participants.
There are also studies in the literature showing the positive effects of HIIT training without creatine intake on leg strength and anaerobic power. For example, in a study evaluating the effects of combined upper and lower body HIIT on muscular and cardiorespiratory fitness, leg extensor muscle strength, handgrip strength, and health-related quality of life in adults over 50 years of age, Hurst et al. [43] concluded that the exercise program performed using a hydraulic resistance ergometer, twice a week for 12 weeks caused significant difference in body weight, BMI, body fat thickness, maximum aerobic power and maximum anaerobic power. In Fatemeh et al.’s study [44] subjects performed HIIT on a treadmill for 3 weeks, three sessions for a week. According to the data obtained, there was a significant difference in body weight, BMI, body fat thickness, maximum aerobic power and maximum anaerobic power in the group performing HIIT (p = 0.001), while there was no change in waist-hip ratio (WHR). Different from the present research, the reason for reaching these results may be the differences in the training protocol and the initial performance levels of the participants.
Current research had some limitations. Firstly, due to sports injuries experienced, the number of participants was terminated with one less person than planned. Secondly, this study was conducted only on female subjects. Adding both genders in future studies may provide more detailed results. Another suggestion is to expand the research group with professional athletes from sports branches where different energy metabolisms are active. In this way, different results arising from the research group in the literature can be avoided. Finally, the addition of non-invasive measurement methods such as heart rate variability, which also provides information about the autonomic nervous system, will provide a broader understanding of the chronic effects of creatine and HIIT training.