Abstract Background: The use of doxorubicin in chemotherapy has been associated with cardiotoxicity and heart failure. Physical exercise produces favorable morphofunctional adaptations in the cardiovascular system and may reverse cardiac dysfunction in patients undergoing chemotherapy. Objective: To assess the effects of physical training on myocardial structure, cardiac function, and exercise tolerance in Wistar rats initiated after the onset of cardiotoxicity-induced cardiotoxicity. Methods: This study investigated 30 adult male Wistar rats randomly divided into four groups: control (C), exercise (EX), doxorubicin (DX), and doxorubicin and exercise (DXEX). The DX and DXEX groups received six doses of doxorubincin from 1.25 mg/kg body weight up to a cumulative dose of 7.5 mg/kg. Injections were administered intraperitoneally three times a week for two weeks; after this stage, the EX and DXEX groups started physical training (swimming) sessions three times a week with a load of 5% of their body weight. Echocardiography and exercise tolerance tests were performed. Generalized linear models were used in statistical analysis, and a p<0.05 was set as statistically significant. Results: Left ventricular shortening fraction and ejection fraction were reduced in the DX group compared to C, EX, and DXEX. The DXEX group showed greater tolerance to effort when compared to the DX and C groups. Conclusion: Physical training, initiated after the onset of doxorubicin-induced cardiotoxicity, improved cardiac function and exercise tolerance in rats.

Objective Investigate the effect of GC-1 on tolerance to exercise in rats with experimental hypothyroidism. Materials and methods Hypothyroidism was induced with methimazole sodium and perchlorate treatment. Six groups with eight animals were studied: control group (C), hypothyroid group without treatment (HYPO); hypothyroidism treated with physiological doses of tetraiodothyronine (T4) or 10 times higher (10×T4); hypothyroidism treated with equal molar doses of GC-1 (GC-1) or 10 times higher (10×GC-1). After eight weeks, each animal underwent an exercise tolerance test by measuring the time (seconds), in which the rats were swimming with a load attached to their tails without being submerging for more than 10 sec. After the test, the animals were killed, and blood samples were collected for biochemical analysis, and the heart and soleus muscle were removed for weighing and morphometric analysis of the cardiomyocyte. Results Hypothyroidism significantly reduced tolerance to exercise and, treatment with GC-1 1× or T4 in physiological doses recover tolerance test to normal parameters. However, high doses of T4 also decreased tolerance to physical exercise. Conversely, ten times higher doses of GC-1 did not impair tolerance to exercise. Interestingly, hypothyroidism, treated or not with T4 in a physiological range, GC-1 or even high doses of GC-1 (10X) did not change cardiomyocyte diameters and relative weight of the soleus muscle. In contrast, higher doses of T4 significantly increased cardiomyocyte diameter and induced atrophy of the soleus muscle. Conclusion Unlike T4, GC-1 in high doses did not modify tolerance to physical exercise in the rats with hypothyroidism.

INTRODUÇÃO: O sistema cardiovascular sofre sobrecarga durante a prática de exercícios físicos. Entretanto, pouco se sabe sobre a resposta cardíaca em diferentes intervalos de recuperação (IR). OBJETIVO: O presente estudo teve como objetivo analisar a sobrecarga cardíaca, utilizando como parâmetro cardiovascular a frequência cardíaca (FC), pressão arterial sistólica (PAS) e duplo-produto (DP) em IR distintos (IR), sendo delimitados em 45'' (IR45''), 60'' (IR60'') e 90'' (IR90''). MÉTODOS: O estudo analisou 10 voluntários do gênero masculino, com idade 21,5 ± 6,04 anos, peso 77,5 ± 10,62 kg e altura 179 ± 7 cm, que foram submetidos a um protocolo de três séries de 12 repetições à 60% de uma repetição máxima (1RM) no aparelho leg press 45º. O teste de Wilcoxon foi utilizado para comparar as variáveis hemodinâmicas tendo nível de significância quando p ≤ 0,05. RESULTADOS: Houve diferença significativa de todas as variáveis quando compara-se o estado pré-esforço com as séries subsequentes. A PAS apresentou diferença entre a primeira e as demais séries. Foi observada diferença entre a segunda e terceira série com IR45'', além de na terceira série o IR45'' apresentar maiores valores quando comparados ao IR90''. De forma semelhante, a FC apresentou diferença entre a primeira e todas as séries, em todos os IR. Os IR45'' e IR60'' apresentaram diferença entre a segunda e terceira séries. Contudo, o DP demonstrou diferença entre a primeira e todas as séries em todos os IR, além de IR45'' e IR60'' apresentar diferença entre a segunda e terceira série. CONCLUSÃO: De acordo com os resultados encontrados, conclui-se que a PAS e FC é sensível ao número de séries intrasséries, porém, não houve diferença quando se compara os IR entre si. Contudo, há maior tendência do IR45'' causar aumento da sobrecarga cardíaca, principalmente pelo aumento da PAS.

INTRODUCTION: The cardiovascular system is the most submitted to overload during exercise practice. However, there is a lack of knowledge about heart response under different recovery intervals (RI). OBJECTIVE: The purpose of this study was to analyse the heart overload, using as cardiovascular parameter, the heart rate (HR), sistolic blood pressure (SBP) and double product (DP) under different recovery intervals (RI), delimited in 45'' (RI45''), 60'' (RI60'') and 90'' (RI90'') seconds. METHODS: The study analysed 10 volunteers, age 21.5 ± 6.04 years, weight 77.5 ± 10.62 kg and height 179 ± 7 cm, that was submitted a protocol of three sets of 12 repetition of 60% 1RM in Leg Press 45º apparatus. The Wilcoxon test was used to compare hemodynamic variables with significance level when p ≤ 0.05. RESULTS: There were significant differences of all variables when compared to pre-state effort with subsequent sets. The SBP was different between the first and the other sets. Also been observed difference between the second and third sets with RI45'', and in the third set, the RI45'' present greater values when compared to RI90''. Similarly, the HR present difference between the first and all other sets in all RI. The RI45'' and RI60'' showed differences between the second and third sets. However, the DP has demonstrated difference between the first and all others sets in all RI, and, the RI45'' and RI60'' showed difference between the second and third sets. CONCLUSION: According to the results, it is concluded that the SBP and HR is sensitive to the number of sets intra-sets, but there was no difference when comparing the RI with each other. However, there is a greater tendency of RI45'' cause increased cardiac overload, primarily by increased in SBP.