Intermittent fasting compromises the performance of eutrophic rats submitted to resistance training.

OBJECTIVES: The aim of this study was to analyze the effects of intermittent fasting (IF) on the performance of rats subjected to resistance training ladder climbs (RTLCs). METHODS: Thirty-two Wistar rats (80-d-old) were placed into one of the following four groups (n = 8/group): control (C), which were fed a standard diet with no exercise; intermittent fasting (IF) rats underwent IF for 16 h/d, fed a standard diet for a period of 8 h/d with no exercise; trained control (TC) were fed a standard diet and submitted to RTLC; and trained intermittent fasting (TIF) underwent IF for 16 h/d, fed a standard diet for a period of 8 h/d, and submitted to RTLC. Training groups completed 6-wk of RTLC (3 × /wk). The maximal load test (MLT) was applied on two occasions: before the first RTLC session and at the end of week 6 of physical training. Its purpose was to compare changes in performance over time. Both blood collection and total extraction of the organs were performed at the end of the experimental period. RESULTS: Food intake was higher in the TC group than in either the IF or TIF groups. TC supported a higher load (g) during the final MLT compared with the C, IF, and TIF groups, respectively. TC (initial MLT: 371.4 ± 31.1; final MLT: 593.9 ± 33.5) and TIF (initial MLT: 402.3 ± 31.8; final MLT: 495.4 ± 83.3) presented higher values when the pre- and post-RTLC moments were compared. The relative weight of the stomach was higher in TIF than in C and TC rats. There was no difference in aspartate transaminase and alanine transaminase enzyme activities or in creatinine and total cholesterol levels. CONCLUSIONS: IF negatively affected RTLC performance. IF plus RTLC increased the relative weight of the stomach as well as reduced food intake, without an increase in body weight, suggesting this combination may have promoted dilation of this organ, due, hypothetically, to the scarcity of food for several hours and the energy expenditure generated by physical training.

High-Protein Diet Associated with Resistance Training Improves Performance and Decreases Adipose Index in Rats.

The study tested the hypothesis that a high protein diet based on isolated whey protein (IWP) associated with strength training improves performance and reduces body fat without promoting health damage. Male Wistar rats, 45 days old, were divided into four groups (n = 8/group): normoprotein sedentary (IWP 14%; NS); hyperprotein sedentary (IWP 35%; HS); normoprotein trained (IWP 14%; NT) and hyperprotein trained (IWP 35%; HT). All groups performed the maximum load test at the beginning and after the vertical ladder training protocol for 6 weeks (3x/week). The performance improved in HT when compared to other groups. There was no difference in the plasma levels of testosterone, IGF-1 and the hematological parameters remained normal. The relative weights of the kidneys were higher in the groups fed with high protein; the liver was higher in HT compared to NS and NT, and the heart was higher in HS compared to NS and NT. Concerning relative muscle weight, quadriceps, and gastrocnemius, HT showed higher value compared to NT. Diet containing 35% isolate whey protein associated with resistance training improved performance as well as increased muscles and organs weight of the animals, without damaging the tissues related to protein metabolism (confirmed by unchanged hematological parameters), which may minimize the risk of developing cardiometabolic disorders.

Reproducibility of Heart Rate Variability Threshold in Untrained Individuals.

The aim of this study was to evaluate the reproducibility of the heart rate variability threshold (HRVT) by different HRV indexes and determination criteria. 68 untrained participants, 17 women (24.09±4.91 years old; 21.54±1.97 kg∙m-2) and 51 men (24.52±3.52 years old; 26.51±6.31 kg∙m-2), were evaluated on 2 different days (test and retest). The HRVT was determined during an incremental exercise test using 2 indexes (SD1 and RMSSD) and criteria (HRTV1, first intensity of physical effort with index<3 ms, and HRVT2, first intensity of physical effort, in which the index presents a difference<1 ms between 2 consecutive intensities). There was no significant difference (p<0.05) between the test and retest for any of the variables evaluated. All variables, except for the rate of perceived exertion at HRVT2, presented moderate to high intraclass correlation coefficient (HRVT1: 0.55-0.85 and HRVT2:0.58-0.69). All variables at HRVT1 and the heart rate at HRVT2 showed coefficient of variation ~ 10%. The HRVT, regardless of criteria and HRV index used, showed satisfactory reproducibility. Thus, these criteria can be used to assess clinically autonomic cardiac modulation and aerobic capacity, and to analyze the effect of different interventions.