## 4 Discussion
This could result from the combination of strength training--which affects fatigue through inflammatory and metabolic pathways and helps preserve muscle mass, function, and body composition [15; 60; 71; 72], and aerobic training, which improves cardiorespiratory fitness and cardiovascular efficiency, thereby reducing fatigue perception [60]. HIIT programs, like resistance training (though with a slightly smaller effect size), also demonstrated consistent and significant effects with no heterogeneity, indicating a more uniform response to these interventions. HIIT has been shown to reduce inflammatory markers such as interleukins, improve body composition, and enhance cardiorespiratory fitness, notably increasing IL-15 levels, which may contribute to reduced fatigue and improved overall health in cancer survivors [73]. It is also highly effective in improving VO2 max, a key indicator of cardiorespiratory fitness [74], and provides significant benefits in a shorter time frame, allowing for higher training loads and improved adherence [75]. Moreover, HIIT positively impacts mitochondrial function, muscle capillarization, and fat oxidation capacity, all of which may lower fatigue during daily activities [76; 77]. Conventional aerobic training showed a smaller but still significant effect, with low heterogeneity. These results suggest that while all exercise modalities are beneficial, combined interventions may offer the greatest clinical impact, although they require more standardized implementation. On the other hand, the consistent effects of HIIT and resistance training may facilitate their use in resource-limited clinical settings due to their structured format and more predictable outcomes. Subgroup analysis based on program duration showed that all durations evaluated (\(\leq\)12 weeks, >12-24 weeks, and >24 weeks) were associated with significant reductions in fatigue, with moderate effect sizes. The greatest effect was seen in programs longer than 24 weeks, followed by those \(\leq\)12 weeks, while programs lasting 12-24 weeks had the smallest effect. Notably, substantial heterogeneity was observed among studies with \(\leq\)12-week programs, possibly reflecting variability in intensity, exercise type, or participant characteristics. In contrast, the absence of heterogeneity in longer-duration groups indicates more consistent outcomes, strengthening the evidence in favor of extended programs. The superior effectiveness of >24-week programs may be due to better physiological and psychological adaptation occurring over time, resulting in more sustained benefits and fatigue reduction. These programs may also enhance adherence, which is crucial for long-term effects [78]. While brief interventions also show benefits, the high heterogeneity suggests the need for further research to optimize their effectiveness. Subgroup analyses revealed differences in the magnitude of therapeutic exercise's effects on fatigue based on sex and cancer type. Among men, predominantly with prostate cancer, the effect size was notably higher, with moderate heterogeneity. Among women, primarily with breast cancer, the effect was more modest but more consistent across studies. These findings may reflect physiological or psychological differences or differences in exercise protocol implementation between men and women. Men in prostate cancer trials often received strength- or HIIT-focused interventions, while women with breast cancer typically participated in mixed programs with more varied frequencies or intensities. Clinically, these results suggest that therapeutic exercise is beneficial for both groups but may require tailoring to individual patient profiles to maximize effectiveness. Additionally, the greater heterogeneity in male-focused studies highlights the need to better standardize prostate cancer interventions, while the consistency in female-focused studies strengthens current recommendations in this population.