RESUMEN
INTRODUCTION: Engaging in exercise programs during cancer treatment is challenging due to the several chemotherapy-induced side effects. Using a pre-clinical model that mimics chemotherapy treatment, we investigated if a periodized-within-chemotherapy training strategy can maximize resistance training (RT) adaptations such as increasing muscle mass and strength. METHODS: Swiss mice were randomly allocated into one of the following five groups (n = 14): control (C), resistance training (RT), chemotherapy-treated non-exercised group (Ch), resistance training chemotherapy treated (RTCh), and resistance training periodized-within-chemotherapy (RTPCh). Doxorubicin (i.p.) was weekly injected for a total of 3 weeks (total dose of 12 mg/kg). Resistance training consisted of ladder climbing with progressive intensity, three times a week for 3 weeks, during chemotherapy treatment. RTPCh prescriptions considered "bad day" adjustments while RTCh did not. "Bad day" adjustments considered the presence or absence of clinical signs (e.g., severe weight loss, diarrhea, mice refusing to train) to replace RT sessions. At the end of the third week, animals were euthanized. RESULTS: Weekly doxorubicin injection promoted progressive body weight loss, muscle atrophy, strength loss, local oxidative stress, and elevated inflammatory mediators, such as TNF-α and IL-6. Non-periodized-within-chemotherapy RT promoted mild protection against doxorubicin-induced skeletal muscle disturbances; moreover, when periodized-within-chemotherapy was applied, RT prevented elevated skeletal muscle inflammatory mediators and oxidative damage markers and promoted muscle mass and strength gains. CONCLUSION: Considering chemotherapy-induced side effects is a crucial aspect when prescribing resistance exercise during cancer, it will maximize the effectiveness of exercise in enhancing muscle mass and strength.