Carlos Janssen Gomes da Cruz

Objectives: To determine whether caffeine supplementation and its expectancy influence muscle strength (ST) and muscle endurance (ME) using a balanced-placebo design. Methods: Using a randomized, double-blind, balanced-placebo design, resistance-trained men (18–30 years; n = 16) participated in two assessment/familiarization visits (demographics; one repetition maximum (1RM) followed by four counterbalanced sessions: C/C (informed caffeine/used caffeine), P/C (informed placebo/used caffeine), C/P (informed caffeine/used placebo), P/P (informed placebo/used placebo). Caffeine dose was 5 mg/kg. Peak torque (PT) and maximum work (MW) were measured in the knee extensors at 0, 60, 180, and 300°/s, which was followed by ME testing (three sets of maximal repetitions using 60%1RM). Capillary blood lactate was measured after ME testing. Results: Caffeine increased PT only during static and 60°/s contractions (4%; p ≤ 0.003; d = 0.3 for both speeds), while MW increased across all speeds (4%; p < 0.001; d = 0.2). Caffeine did not increase ME (3%; p = 0.184; d = 0.1), but it did increase blood lactate levels (1.2 mmol/L; p < 0.001; d = 0.7). Caffeine expectation did not improve ST or ME, but increased blood lactate levels (0.7 mmol/L; p = 0.003; d = 0.4). Across ST and ME, responses to caffeine were markedly heterogeneous, with 50–88% of individuals considered responders (∆ > 0), and improvements in responders ranged from 1–16%. Conclusions: Caffeine significantly increased ST, despite ME increasing in 50% of participants, this was not significant. No placebo effect was observed in ST or ME, but it significantly increased lactate. Further research is necessary to elucidate the mechanisms behind this variability in the ME response, especially the role of fiber-type predominance.

Aim: This study evaluated the association between heart rate recovery (HRR) and cardiac parasympathetic reactivation following a submaximal exercise test with resting heart rate (RHR) in the supine and orthostatic positions. Methods: The heart rate (HR), HRR, relative HRR (Δ% HRR), and cardiac parasympathetic reactivation (r-MSSD) values during passive orthostatic recovery at the 1st, 3rd, and 5th min following the submaximal exercise test were correlated with RHR in both the supine (RHRsup) and orthostatic (RHRort) positions in 24 physically active men. The statistical analysis employed Pearson and Spearman correlation tests with a two-tailed p-value set at ≤ 0.05. Results: At the 1st min, HR was significantly correlated with RHRort (r = 0.40; p = 0.05). HR, HRR, and Δ% HRR at the 3rd and 5th min were significantly correlated with RHR (r = from -0.67 to 0.73; p ≤ 0.02; R2 = 32-53%), independent of the body position at rest. At the 3rd and 5th min, the r-MSSD was significantly correlated with RHRsup (r = -0.60, -0.46; p ≤ 0.02). At the 3rd min, the r-MSSD was significantly correlated with RHRort (r = -0.46; p = 0.02). Conclusion: Faster HRR and parasympathetic reactivation on the 3rd and 5th minute after the submaximal exercise test were associated with low RHR in the supine and orthostatic positions in active young men.

Sedentary lifestyle and inadequate diet are associated with 2.6 billion deaths each year. Health education could improve health habits in childhood. We investigated the effects of a health education program on physical activity (PA) level, eating habits, body composition, and cardiorespiratory fitness in schoolchildren. A total of 50 children from Brazilian public school were evaluated into a PA level and food consumption (questionnaire), cardiorespiratory fitness (PACER), and body composition (skinfolds), allocated to either an 8-week intervention at Fun Education Group (FEG, n=19, 8.2±0.5yr) or control group (CG, n=31, 8.1±0.5yr). FEG was exposed to an educative website (1h - TOODS KIDS), filled a sticker album according to habits (PA and eating) of each weekday, and families received instructions (leaflets and lecture) on how to improve their habits. The generalized linear models analysis revealed an improvement to FEG at cardiorespiratory fitness (6.4 laps, p=0.042; and 0.4 km/h, p=0.031), more fruits and vegetable consumption (1.4 unities, p=0.029) and body fat reduction (-1.5%, p=0.001), compared to CG. The participation at Program suggest that a short period of feasible intervention, with low-cost materials, aroused and motivated children to healthier habits with positive effects on cardiorespiratory fitness, body fat, and consumption of fruits and vegetable.

It is well established that endurance exercise has positive effects on cardiac autonomic function (CAF). However, there is still a dearth of information about the effects of regular high-intensity interval training combined with different types of exercises (HIITCE) on CAF. Objective: The aim of this study is to compare CAF at rest, its reactivity, and reactivation following maximal exercise testing in HIITCE and endurance athletes. Methods: An observational study was conducted with 34 male athletes of HIITCE (i.e., CrossFit^®) [HG: n = 18; 30.6 ± 4.8 years] and endurance athletes (i.e., triathlon) [TG.: n = 16; 32.8 ± 3.6 years]. We analyzed 5 min of frequency-domain indices (TP, LF, HF, LFn, HFn, and LF/HF ratio) of heart rate variability (HRV) in both supine and orthostatic positions and its reactivity after the active orthostatic test. Post-exercise heart rate recovery (HRR) was assessed at 60, 180, and 300 s. Statistical analysis employed a non-parametric test with a p-value set at 5%. Results: The HG showed reduced HFn and increased LFn modulations at rest (supine). Overall cardiac autonomic modulation (TP) at supine and all indices of HRV at the orthostatic position were similar between groups. Following the orthostatic test, the HG showed low reactivity for all HRV indices compared to TG. After the exercise, HRR does not show a difference between groups at 60 s. However, at 180 and 300 s, an impairment of HRR was observed in HG than in TG. Conclusion: At rest (supine), the HG showed reduced parasympathetic and increased sympathetic modulation, low reactivity after postural change, and impaired HRR compared to TG.

Objective: The present study sought to expand upon prior investigations of the relationship between the post-exercise heart rate recovery (HRR) and the cardiac autonomic responsiveness after orthostatic stress test. Method: HRR at the 1st, 3rd, and 5th min after maximal exercise test were correlated with relative change (Δ%) of time-domain (CV, pNN50, and rMSSD) and frequency-domain (TP, LF, HF, and LF/HF ratio) indices of heart rate variability (HRV) after active orthostatic test in 46 healthy men. Statistical analysis employed non-parametric tests with a p-value set at 5%. Results: HRR at 1st min correlated with Δ%pNN50 (r_s:0.36 – p = .02). In the 3rd and 5th min, these measures correlated with Δ%pNN50, Δ%rMSSD, Δ%CV, Δ%TP, and Δ%HF indices (r_s:0.33, 0.59 – p ≤ .05). Coefficient of HRR at the 1st min correlated with Δ%pNN50, Δ%rMSSD, and Δ%HF (r_s:0.28, 0.45 – p ≤ .05). The 3rd and 5th min showed correlation with Δ%pNN50, Δ%rMSSD, Δ%HF, Δ%CV, and Δ%TP (r_s:0.37, 0.64 – p ≤ .05). No correlation was found with indices combined sympathetic-parasympathetic modulation and HRR. After the sample was divided into high and low parasympathetic responsiveness subgroups after the orthostatic test, faster HRR was associated with the degree of parasympathetic responsiveness (reduction) following postural change (p ≤ .05). Conclusion: HRR throughout the 1st to 5th min is positively correlated with parasympathetic responsiveness and overall cardiac autonomic modulation of HRV after the orthostatic stress test, and faster HRR is positively correlated with the relative degree of parasympathetic responsiveness after the active postural change at rest in healthy men.