Cardiorespiratory health
In this study, measurements of cardiorespiratory function and airway inflammation indicators were taken before and after each of the three exercise interventions. Table 3 presents the average differences in cardiorespiratory health measurements before and after exercise at three different levels of AP.
Table 3
Mean differences in baseline and post-exercise cardiorespiratory health measurements
Variable | Low | p Value* | Medium | p Value* | High | p Value* |
SBP (mm Hg) | -2.2 ± 8.0 | < 0.047 | -4.2 ± 13.4 | 0.126 | -4.3 ± 11.8 | 0.071 |
DBP (mm Hg) | -1.2 ± 3.7 | 0.063 | -0.8 ± 10.1 | 0.701 | 3.5 ± 7.8 | 0.03 |
HR (bpm) | 10.8 ± 7.4 | < 0.001 | 12.6 ± 6.5 | < 0.001 | 10.2 ± 5.2 | < 0.001 |
FVC (L) | 0.2 ± 0.6 | 0.041 | 0.3 ± 0.5 | 0.05 | -0.1 ± 0.4 | 0.498 |
FEV1 (L) | 0.2 ± 0.5 | 0.049 | 0.1 ± 0.5 | 0.591 | -0.2 ± 0.4 | 0.031 |
PEF (L/min) | 0.5 ± 1.6 | 0.087 | -0.0 ± 1.1 | 0.91 | -0.1 ± 0.8 | 0.381 |
FEF25 − 75% (L/s) | 0.2 ± 1.7 | 0.285 | 0.2 ± 0.8 | 0.0342 | -0.1 ± 0.6 | 0.461 |
FeNO (ppb) | -3.0 ± 4.0 | < 0.001 | -1.7 ± 3.9 | 0.038 | 1.0 ± 4.2 | 0.236 |
All data are presented as mean difference ± standard deviation. *: significant differences between baseline and post-exercise (paired t-test results). Abbreviations: SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate; FVC, forced vital capacity; FEV1, forced expiratory volume in 1 s; PEF, Peak expiratory flow; FEF25–75%, mean forced expiratory flow between 25% and 75% of FVC; FeNO, fractionated exhaled nitric oxide.
The results indicate that SBP significantly decreased after exercise in the low pollution level environment (-2.2 mm/Hg, p < 0.047), while the mean decreased in the medium and high pollution level environments after exercise, although without significant differences. Similarly, DBP decreased after exercise in the low and medium pollution level environment, with no significant differences observed, but increased significantly after exercise in the high pollution level environment (3.5 mm/Hg, p = 0.03).
For lung function, post-exercise mean values of FVC and FEV1 significantly increased in the low pollution level environment (0.2L, P = 0.041) (0.2L, P = 0.049), while mean values of PEF and FEF25 − 75% also increased, albeit without significant differences. Additionally, post-exercise FVC still showed a weak significant increase in the medium pollution level environment (0.3 ± 0.5, P = 0.05). However, post-exercise mean values of FEV1 significantly decreased in the high-level AP environment (-0.2 ± 0.4, P = 0.031), with other lung function indicators also showing decreases in the high pollution level environment, but without significant differences.
For airway inflammation indicators, we found that FeNO significantly decreased after exercise in both the low pollution level (-3 ppb, p < 0.001) and medium pollution level (-1.7 ppb, p = 0.038) environments, while it increased in the high pollution level environment, although without significant differences.
Based on the observed changes in cardiorespiratory function indicators pre- and post-exercise, it is evident that exercising in medium-level AP environments may not lead to as beneficial significant changes in cardiorespiratory function indicators as seen with exercise in low pollution environments. Conversely, exercising in high pollution environments yields adverse effects. This suggests that AP may diminish the benefits of PE on cardiorespiratory function.
Additionally, we calculated the percentage change of cardiorespiratory-related health indicators relative to the baseline to adjust for individual differences at the baseline level and analyzed the changes in cardiorespiratory health indicators among three different levels of AP. The specific changes are illustrated in Fig. 2. We observed that after exercise in environments with three different AP concentrations, blood pressure decreased in all three concentration environments, with SBP decreasing below 0, indicating a decrease after exercise. DBP decreased after exercise in environments with medium to low pollution concentrations, while it increased in environments with high pollution concentrations. Analysis of lung function indicators revealed that FVC, FEV1, and FEF25 − 75% increased after exercise in environments with medium pollution concentrations, while they decreased after exercise in environments with high pollution concentrations. Additionally, the percentage changes in lung function-related indicators after exercise in environments with low, medium, and high concentrations of pollution all showed a decreasing trend. Analysis of the airway inflammation indicator FeNO revealed a decrease after exercise in environments with low to medium pollution concentrations, while it increased after exercise in environments with high pollution concentrations. Moreover, after exposure to environments with three different concentrations of pollution, the percentage change in FeNO values showed an increasing trend.
Subsequently, we utilized LME to adjust for participants' gender, age, and BMI. Using the percentage change in cardiorespiratory health indicators after exercising in the low pollution level environment as the reference, we further confirmed the aforementioned results. The specific results were consistent with the description provided in Fig. 2 above, and the analytical outcomes are detailed in Table 4.
Table 4
Differences in cardiorespiratory health among three different AP levels
| SBP | DBP |
| Coefficient | 95% CI | p Value* | | Coefficient | 95% CI | p Value* |
M | -0.62 | -4.76 | 3.41 | 0.770 | | -3.44 | 5.21 | 7.66 | 0.685 |
H | -1.44 | -5.58 | 2.59 | 0.496 | | 6.45 | 2.11 | 10.75 | 0.005 |
| FVC | | FEV1 |
| Coefficient | 95% CI | p Value* | | Coefficient | 95% CI | p Value* |
M | -0.43 | -7.24 | 6.0 | 0.9 | | -6.57 | -13.44 | 0.01 | 0.062 |
H | -6.84 | -13.41 | -0.68 | 0.04 | | -8.97 | -15.62 | -2.63 | 0.009 |
| PEF | | FEF25 − 75% |
| Coefficient | 95% CI | p Value* | | Coefficient | 95% CI | p Value* |
M | -9.36 | -16.71 | -2.00 | 0.018 | | -0.87 | -13.29 | 2.93 | 0.828 |
H | -9.50 | -16.60 | -2.41 | 0.013 | | -4.35 | -15.88 | 0.63 | 0.248 |
| FeNO | | |
| Coefficient | 95% CI | p Value* | | | | |
M | 5.2 | -2.20 | 12.56 | 0.183 | | | | | |
H | 13.3 | 5.93 | 20.69 | 0.001 | | | | | |
Mixed effect models adjusted for gender, age, and BMI. Exposure scenario with reference to ‘Low level AP and PE exposure’. *: Statistical significance in the results of the linear mixed-effects model. M: Medium level AP and PE exposure; H: High level AP and PE exposure.
The LME analysis revealed that the changes in SBP at medium and high levels of AP environment both showed no significant difference compared to the low concentration. However, DBP showed a significant increase in the high concentration of AP compared to the low level (6.45, P = 0.05), with no significant difference observed in relative changes between medium and low levels.
Regarding lung function, compared to the changes after exercise in environments with low pollution concentrations, PEF significantly decreased after exercise in environments with medium (-9.36, P = 0.018) and high (-9.50, P = 0.013) pollution concentrations. FVC and FEV1 showed no significant differences after exercise in medium concentrations but significantly decreased after exercise in high concentrations (-6.84, P = 0.04) (-8.97, P = 0.009).
Regarding the airway inflammation indicator FeNO, compared to the changes after exercise in environments with low pollution concentrations, there was no significant difference after exercise in environments with medium concentrations, but FeNO significantly increased after exercise in environments with high concentrations (13.3, P = 0. 001).
The results further demonstrate that changes in cardiorespiratory health indicators post-exercise in high-level AP environments are significantly decreased compared to low-level AP environments. Conversely, in low- and medium-level AP environments, differences in cardiorespiratory health indicator changes are not statistically significant.
Effects on circulating inflammation markers
Figure 3 illustrates the percentage change relative to baseline in inflammatory markers following exercise across three different levels of AP. Overall, the change in inflammatory markers after exercise in environments with high pollution concentrations was notably higher than those in medium and low concentrations, while the changes between medium and low concentrations were small. Moreover, the majority of inflammatory markers showed an increase after exercise regardless of the AP concentration, except monocytes and eosinophils, which exhibited a slight decrease in change after exercise in environments with medium and low concentrations.
Table 5
Differences in inflammatory marker changes among three different levels of AP
| WBC | | Neutrophils |
| Coefficient | 95% CI | p Value* | | Coefficient | 95% CI | p Value* |
M | 1.77 | -7.75 | 11.40 | 0.721 | | -3.51 | -18.44 | 11.74 | 0.653 |
H | 27.0 | 17.48 | 36.63 | 0.000 | | 26.76 | 12.06 | 41.90 | 0.000 |
| Lymphocytes | | Monocytes |
| Coefficient | 95% CI | p Value* | | Coefficient | 95% CI | p Value* |
M | 3.35 | -9.03 | 15.34 | 0.594 | | 2.11 | -6.90 | 10.97 | 0.647 |
H | 32.22 | 19.85 | 44.22 | 0.000 | | 28.23 | 19.28 | 36.95 | 0.000 |
| Eosinophils | | Basophils |
| Coefficient | 95% CI | p Value* | | Coefficient | 95% CI | p Value* |
M | 25.64 | 3.93 | 46.41 | 0.022 | | 14.33 | -4.89 | 32.78 | 0.142 |
H | 48.93 | 27.25 | 70.12 | 0.000 | | 11.5 | -8.00 | 29.79 | 0.236 |
| IL-1β | | | | | IL-10 | | | |
| Coefficient | 95% CI | p Value* | | Coefficient | 95% CI | p Value* |
M | 0.39 | -0.09 | 0.86 | 0.116 | | 0.05 | -0.09 | 0.19 | 0.503 |
H | 0.76 | 0.29 | 1.23 | 0.003 | | 0.17 | 0.03 | 0.32 | 0.020 |
| IL-6 | | | | | TNF-α | | | |
| Coefficient | 95% CI | p Value* | | Coefficient | 95% CI | p Value* |
M | 0.05 | -0.02 | 0.11 | 0.174 | | -0.00 | -0.08 | 0.07 | 0.920 |
H | 0.10 | 0.04 | 0.17 | 0.004 | | 0.97 | 0.02 | 0.17 | 0.011 |
| CRP | | | | | | | |
| Coefficient | 95% CI | p Value* | | | | |
M | 0.05 | -0.06 | 0.16 | 0.370 | | | | | |
H | 0.17 | 0.06 | 0.28 | 0.003 | | | | | |
Mixed effect models adjusted for gender, age, and BMI. Exposure scenario with reference to ‘Low level AP and PE exposure’. *: Statistical significance in the results of the linear mixed-effects model. M: Medium level AP and PE exposure; H: High level AP and PE exposure. Abbreviations: IL, interleukin; TNF-α, tumour necrosis factor α; CRP, C reactive protein.
Table 5 presents the results of LME analysis comparing the differences in percentage change of inflammatory markers between medium and high levels of AP with reference to the percentage change at the low pollution level. The results indicate that compared to the changes observed after exercise in the low pollution environment, there was a significant increase in the levels of white blood cells (27.0, p < 0.001), neutrophils (26.8, p < 0.001), lymphocytes (32.2, p < 0.001), monocytes (28.2, p < 0.001), eosinophils (48.9, p < 0.001), IL-1β (0.76, P = 0.003), IL-10 (0.17, P = 0.02), IL-6 (0.1, P = 0.17), TNF-α (0.97, P = 0.011), and CRP(0.17, P = 0.003) after exercise in the high pollution environment. Additionally, only eosinophils exhibited a significant increase (25.6, p = 0.022) in the medium-pollution environment, while the percentage change in other inflammatory cells after exercise in the medium-pollution environment did not significantly differ from that in the low pollution environment. The results above suggest that high levels of AP significantly increase inflammation in the body, while the difference in inflammation levels between medium and low pollution levels is smaller.