Name: LEISIANE GOMES DIAS

Publication date: 18/08/2022
Advisor:

Name	Role
ANDRÉ SOARES LEOPOLDO	Co-advisor *
DANILO SALES BOCALINI	Advisor *

Examining board:

Name	Role
ANA PAULA LIMA LEOPOLDO	Internal Examiner *
ANDRÉ SOARES LEOPOLDO	Co advisor *
DANILO SALES BOCALINI	Advisor *

Summary: Introduction: strength training promotes important adaptations in the neuromuscular system, however, little is known about the changes caused by this type of training in the contractility of the remaining myocardium of infarcted rats. Objective: evaluate the effect of strength training on left ventricular contractility in infarcted rats. Methods: after induction of sham surgeries in animals in group C and coronary occlusion in groups IM with confirmation of the IM by echocardiography, all animals remained at rest for six weeks for complete healing of the infarcted area. After the healing period, all animals with infarction greater than 35% of the left ventricle were selected and randomized in infarcted groups. Thus, 27 male Wistar rats were distributed in three groups, control (C, n:7), infarcted (IM, n:10) and trained infarcted (IMT, N: 10). The animals in C and IM groups remained at rest throughout the study period, however, the animals in the IMT group were submitted to a strength training program (climbing) consisting of a total period of 12 weeks, 5 days a week, 12 daily series with 90 seconds of interval and increasing intensities weekly in block. The training program was organized into three mesocycles of four weeks each, with an increase in training load organized in a linear fashion (60%, 65%, 70% and 75%) at each block, considering the weight established in the maximum load test. The following parameters were evaluated: maximum force (maximum load lifted), cardiac masses, water content in the lungs, parameters of myocardial contractility, nuclear volume and collagen concentration in the remaining myocardium. For comparative purposes, the ANOVA-one test was used with a significance level of p<0.05, with values presented as mean ± standard error of the mean. Results: No significant differences (p < 0.05) were found between groups in infarct size (MI: 45.20 ± 4.96%, IMT: 45.40 ± 5.81). Group C (215 ± 17g) presented greater strength at the beginning of the training protocol, and groups IM (198 ± 14g) and IMT (205 ± 14g) did not differ from each other. However, only IMT showed a gain (p<0.05) in strength at the end of the training program (1st: 365 ± 10, 2nd: 468 ± 19, 3rd: 526 ± 20; g). No differences were identified in the body mass of the animals before and after 18 weeks of the protocol, but both groups increased in weight throughout the protocol. The animals in group C (77.80 ± 0.46%) had lower pulmonary water content (p<0.05) than the IM (81.67 ± 0.50%) and IMT (79.89 ± 0.26 %) which also differed from each other. The absolute (A) and relative (R) mass of the atria in group C (A: 27.60 ± 1.21 mg; R: 0.10 ± 0.00 mg/g) was lower (p<0.05) than in the IM groups (A: 90.78 ± 13.65 g; R: 0.35 ± 0.05 mg/g) and IMT (A: 82.22 ± 15.66 mg; R: 0.32 ± 0.06 mg/g) that did not differ (p> 0.05) with each other. Considering the absolute and relative right ventricular mass, the values of the IM group (A: 296.10 ± 29.93mg; R: 1.16 ± 0.12 mg/g) were higher (p<0.05) than the C groups (A: 156.20 ± 8.22 mg; R: 0.61 ± 0.02 mg/g) and IMT (A: 222.20 ± 18.71 mg; R: 0.87 ± 0.06 mg/g) that did not differ (p>0.05) each other. The absolute and relative left ventricular masses of group C (A: 487.60 ± 9.41 mg; R: 1.92 ± 0.04 mg/g) were lower (p<0.05) than the IM groups (A: 793.10 ± 19.35 mg; R: 3.12 ± 0.08 mg/g) and IMT (A: 673.00 ± 6.15 mg; R: 2.67 ± 0.07mg/g) which also differed (p<0.05) between yes. Similar to the left ventricular mass, the cardiac mass of group C (A: 643.80 ± 9.86 mg; R: 2.53 ± 0.04 mg/g) showed lower values than the IM groups (A: 1089.00 ± 28 mg, 72; R: 4.29 ± 0.12 mg/g) and IMT (A: 895.20 ± 21.62 mg; R: 3.54 ± 0.08 mg/g) which also differed (p<0.05) from each other. The values of the parameters of developed tension (DT), +dT/dt and -dT/dt respectively of group C (6.24 ± 0.27 g/mm2, 61.56 ± 4.75 g/mm2/s; 45.47 ± 3.22 g/mm2/s) were higher (p<0.05) than the IM groups (2.36 ± 0.28 g/mm2; 18.83 ± 2.85 g/mm2 /s; 11.32 ± 1.66 g/mm2/s) and IMT (3.81 ± 0.24 g/mm2; 35.01 ± 1.64 g/mm2/s; 21.94 ± 1.33 g/mm2/s) which also differed (p<0.05) from each other. The values of TPT and TR50% respectively of the IM groups (259.90 ± 9.74 ms; 217.20 ± 14.36 ms) and IMT (233.30 ± 10.37 ms; 204.40 ± 12.84 ms) did not differ (p>0.05) from each other, however they were superior (p<0.05) to group C (174.00 ± 7.02 ms; 139.7.72 ± 7.72 ms). There were no differences (p>0.05) in the TR values between the groups. The relative post-pause contraction for a 60-second pause was significantly lower (p<0.05) in the IM group (0.96 ± 0.01) compared to the C (1.39 ± 0.03) and IMT (1. 21 ± 0.05) that also differed (p<0.05) from each other. After changing the Ca2+ solution from 1.5mmol to 2.5mmol, significant differences were found in TD, +dT/dt and -dT/dt only in C and IMT groups. No significant changes were found in the IM group. The nuclear volume of group C (140 ± 4.40 &#956;m3) was smaller (p<0.05) than IMT (212.6 ± 2.57 &#956;m3) which also differed (p<0.05) from the IM group (249 .60 ± 9.20 &#956;m3). Similarly, collagen content was significantly (p<0.05) higher in the IM group (3.24 ± 0.15 %) compared to the IMT (2.16 ± 0.22 %) and C (1. 44 ± 0.11 %) that also differed (p<0.05) from each other. Conclusion: infarcted animals submitted to a strength training program showed increased strength, attenuation of the increase in left ventricular and total cardiac mass. Regarding myocardial contractility, the animals in the IMT group exhibited attenuation of contractile performance, post-pause potentiation and calcium sensitivity with no change in the parameters of the strain-tension curve. Structurally, the animals in the IMT group also showed attenuation of the increase in nuclear volume and collagen deposition in the remaining myocardium.

Keywords: strength training, myocardial contractility, myocardial infarction, myocardial mechanics.

Access to document