## 4 Discussion
This resulted in statistically significant differences in \(\Delta\)(AG) between the groups. Previous studies with antioxidant treatments showed that the administration of 120 mg of beta-carotene significantly reduced pentane exhalation in normal subjects [50], while the administration of 592 mg of alpha-tocopherol equivalents, 1000 mg of ascorbic acid, and 30 mg of beta-carotene daily resulted in significantly lower resting and post-exercise levels of expired pentane and serum MDA [50]. Additionally, the daily consumption of a tomato-based juice supplemented with vitamin C (600 mg), vitamin E (400 IU, or 400 mg), and beta-carotene (30 mg) significantly decreased breath pentane excretion in smokers [51]. Spirulina contains a variety of antioxidant compounds [52; 53]; however, the only meta-analysis of RCTs on the subject showed a limited capacity of spirulina to affect lipid peroxidation and inflammation markers [54]. Thus, it seems that in our study, where spirulina was administered for a short period, alkanes resulting from the lipid peroxidation of unsaturated fatty acids are not increased. However, the observed increase in hexane, 2-methylhexane, 4-methyloctane, and undecane in the SPI group could be explained by the reduced clearance of these alkanes by hepatic cytochromes. Studies in rats have shown that the administration of spirulina may lead to downregulation in hepatic expression levels and inhibition of the enzymatic activities of CYP1A2 and CYP2E1 [55]. Nevertheless, this hypothesis needs to be confirmed with mechanistic experiments that would explain why only these specific alkanes are affected by the administration of spirulina. The study of the effects of exercise on the profile of volatile alkanes as markers of exercise-induced stress is limited. Early studies observed changes in ethane and pentane after aerobic exercise and showed that expired ethane and pentane flux levels increased above resting levels at the lactic acidosis threshold, continued to rise at 'VO2 max, and then declined during recovery [56]. Similar results were observed when comparing the changes in ethane and pentane after exercise in patients on chronic maintenance dialysis and control subjects. In addition, that study showed that patients on chronic maintenance dialysis have greater lipid peroxidation compared to control subjects at rest and post-exercise [57]. Similar studies have been conducted examining broader panels of VOCs [27; 58], yet without clear results regarding the selection of characteristic oxidative stress markers in exhaled air. In our study, for the first time, resistance exercise, capable of inducing EIMD, is combined with the measurement of volatile alkanes. Oxidative stress is a key pathogenic mechanism of the effects eccentric exercise has on the ergophysiological and clinical profile of athletes and affects their recovery rate. Our results show that in the PL group, there is a trend of increasing almost all alkanes immediately after exercise, with a gradual return to pre-exercise levels up to 72 h later. However, a statistically significant time effect is observed for 2-methylhexane, 3-methylhexane, heptane, octane, and undecane. The administration of spirulina appears to reduce the increases in alkanes after exercise, and a statistically significant attenuation is observed for 2-methylpentane and 2-methylhexane. To confirm that the reduced increases observed in the SPI group are due to changes in lipid peroxidation, we measured a crude marker of this, TBARSs. We found that spirulina may lead to statistically significant reductions in TBARSs after exercise, and there is a positive correlation between the iAUC of TBARSs and that of 2-methylhexane and 3-methylhexane. This indicates that the improvement in post-exercise lipid peroxidation caused by spirulina is also reflected in 2-methylhexane and 3-methylhexane. Therefore, these alkanes could serve as promising markers of exercise-induced stress following eccentric exercise.