Individuals with SCI experience physiological changes including decreased lean body mass, increased adipose tissue, and a higher risk of cardiovascular disease. These changes can contribute to oxidative stress, a condition where antioxidant defenses are overwhelmed by reactive oxygen species (ROS). High-intensity exercise, while beneficial, may exacerbate oxidative stress due to increased ROS production. This study aimed to investigate biomarkers of oxidative stress and antioxidants in SCI individuals during and after high-intensity arm cranking exercise, comparing their responses to healthy controls. The hypothesis was that SCI individuals would exhibit a lower reoxidation capacity after exercise.

Existing literature shows inconsistent findings regarding the health effects of high-intensity exercise in individuals with SCI. Some studies suggest that SCI patients have reduced plasma antioxidant levels and increased oxidative stress markers in the acute phase of injury, with some improvement over time. However, the optimal intensity, duration, and frequency of exercise for SCI individuals remain unclear. Concerns exist that high-intensity exercise might negatively impact health due to reduced antioxidant capacity.

Six participants with chronic SCI (AIS A, thoracic injury level T2-T8, >1 year post-injury) and six matched able-bodied controls participated. Participants underwent two maximal arm-cranking tests, with 1-3 days between tests. The second test involved three 4-minute bouts of high-intensity arm cranking (85-95% of peak heart rate). Blood and urine samples were collected at six time points: baseline, during high-intensity exercise, at maximal effort, and at 5, 30, 60 min, and 24 h post-exercise. Biomarkers assessed included oxidative stress markers (8-oxo-dG, 8-epi-PGF2α) and antioxidants (vitamin E, vitamin C, carotenoids, glutathione, cysteine, homocysteine). Statistical analyses used SPSS version 28.0, including independent samples t-tests and one-way ANOVA.

SCI participants showed significantly lower baseline levels of α-carotene, β-carotene, β-cryptoxanthin, albumin, and creatinine compared to controls. During high-intensity exercise, healthy controls had a significantly higher percentage increase in albumin compared to the SCI group. However, there were no significant between-group differences in the changes of other biomarkers from baseline to high-intensity exercise or maximal effort. The changes in urinary markers of oxidative stress (8-oxo-dG and 8-epi-PGF2α) from pre- to post-exercise were similar in both groups, although individual variation was higher in the SCI group. SCI participants exhibited lower levels of exogenous antioxidants at rest and throughout the study.

The study's findings suggest that the acute oxidative stress response to high-intensity arm exercise is similar in individuals with SCI and healthy controls. However, SCI participants consistently displayed lower levels of exogenous antioxidants, possibly due to factors such as diet, inflammation, or physiological responses to physical activity. The high individual variation in oxidative stress responses among SCI participants emphasizes the need for individually tailored exercise and nutritional strategies. The lower baseline levels of albumin in the SCI group might be related to inflammation, previously documented in SCI individuals.

This study demonstrated that while the acute oxidative stress response to high-intensity exercise is similar between SCI individuals and healthy controls, SCI participants have lower baseline levels of exogenous antioxidants. This highlights the need for individualized exercise programs and nutritional interventions to support antioxidant capacity and optimize training outcomes in individuals with SCI. Further research should investigate the combined effects of nutritional interventions and high-intensity exercise on oxidative stress and antioxidant status over time.

The small sample size limits the generalizability of the findings. Dietary intake and antioxidant consumption were not assessed, which could have influenced the results. The study focused solely on arm exercise; results may not be generalizable to other forms of exercise.