**3. Results**

#### *3.1. Comparison of Changes in Arousal by TDMS before and after Training in PNI and Control Conditions*

As a result of comparing the amount of change in arousal by TDMS before and after training in the PNI and the control conditions, the amount of change in the arousal level under PNI condition (M = +7.30, SD = 1.90) was found to be significantly higher than that in the control condition (M = +3.3, SD = 1.24) (t = 3.52, p < 0.01) (Figure 4).

**Figure 4.** Comparing the amount of change in arousal by a Two-Dimensional Mood Scale (TDMS) in Positive-Negative Ions (PNI) and control conditions.

#### *3.2. Comparison of Changes in Arousal by EEG before and after Training in the PNI and the Control Conditions*

As a result of comparing the amount of change in arousal by EEG before and after training in the PNI and the control conditions, the amount of change in the arousal level under PNI condition (M = +8.16, SD = 2.14) was also found to be significantly higher than that in the control condition (M = +2.75, SD = 2.24) (t = 2.84, p < 0.05) (Figure 5).

**Figure 5.** Comparing the amount of change in arousal by electroencephalogram (EEG) in PNI and control conditions.

#### *3.3. Comparison of the Average Load (W) for Eight Sets of Interval Training in PNI and Control Conditions*

As a result of comparing the average load (W) of interval training in the PNI and the control conditions, the average load (W) under PNI condition (M = 146.22, SD = 13.54) was shown to be significantly higher than that recorded in the control condition (M = 141.14, SD = 12.32) (t = 1.46, p < 0.10) (Figure 6).

#### *3.4. Comparison of the Average of Training Load (W) during the Maximum Power Set in PNI and Control Conditions*

As a result of comparing the average of training load (W) during the maximum power set in the PNI the and control conditions, the average load (W) under PNI condition (M = 192.78, SD = 19.36) was also found to be significantly higher than that in the control condition (M = 181.67, SD = 16.03) (t = 1.99, p < 0.05) (Figure 7).

**Figure 7.** Comparing the average of training load (W) during the maximum power set in PNI and control conditions.

## **4. Discussion**

This study aimed to investigate the psychological e ffects of both the subjective and objective arousal levels of elite Japanese swimmers during physical training under a positive and negative ion environment.

First, the results of the comparison of the subjective arousal level indicated that the PNI condition significantly improved the arousal level compared to the control condition. Previous studies [12–15] have clarified the relationship between negative ions and positive emotions by using subjective evaluation. In addition, subjective research has also shown the relationship between positive ions and emotions in previous studies [18,19]. In this study, as a result of verifying the subjective arousal level in an environment in which PNI are simultaneously generated, it is suggested that athletes may have a higher arousal level under the PNI condition. These results are considered to be new findings in the literature on PNI and emotions.

Second, the results of the comparison of the objective arousal levels obtained from EEG indicated that the PNI condition significantly improved the arousal level compared to the control condition. A few studies in the past [28,29] tried to clarify the relationship between negative ions and emotions using brain waves. Watanabe et al. [29] examined the effect of negative air ions on EEG, and the results indicated that the alpha wave tended to be higher in the negative ion condition than in the control condition. On the other hand, the results of this study indicated that the PNI condition demonstrated a significantly higher arousal level (beta band power level) than the control condition. Therefore, the results of this study di ffer from the previous studies that were mentioned earlier. A subjective evaluation study by Charry and Hawkinshire [19] showed that positive ions contribute to the improvement of tension. In this study, since the experiments were conducted in the environment in which positive ions were also generated, it is speculated that positive ions may a ffect the arousal level extracted from the EEG. As mentioned, it might demonstrate the existence of relationships between PNI conditions, and states of subjective and objective arousal. However, as mentioned previously, there is some skepticism in the study of ions; thus, it would be necessary to further study the relationships between air ions and athletes' emotions in the field of sports science.

Finally, the results of comparing the average load (W) of interval training under the PNI and the control conditions show the average load (W) under the PNI condition tended to be significantly higher than that recorded in the control condition. Moreover, the result of comparing the average of training load (W) during the maximum power set under the PNI condition was that it was recorded as significantly higher than under the control condition.

Several researches have examined the association between physical exercise and negative ions [30,31]. Ryushi et al. [30] demonstrated that, under the negative ion condition, the levels of serotonin and dopamine were decreased in the recovery period after moderate endurance exercise than those recorded under the control condition. Thus, it suggested that the negative ion condition might a ffect the feeling of relaxation after endurance training. This study also found that the load on the maximum power set after a 10-min rest was significantly higher, and that negative ion e ffects reduced dopamine and serotonin during the rest which led to a more relaxed state. There is a possibility that the PNI condition might have a ffected the maximum power set results for the participants.
