The Effects of HIIT vs. MICT and Sedentary Controls on Blood Lipid Concentrations in Nondiabetic Overweight and Obese Young Adults: A Meta-analysis.

With rates of obesity and dyslipidemia rising among young adults, this meta-analysis aimed to compare the effects of high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) and sedentary controls (CON) on low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglyceride (TG), and total cholesterol (TC) in nondiabetic overweight and obese young adults to determine if HIIT or MICT is more efficacious in improving dyslipidemia. Studies included in the analysis had to be randomized controlled trials or quasi-experimental studies, comparing the effects of HIIT versus MICT or CON on at least three variables of interest: LDL, HDL, TG, and TC, in nondiabetic adults, with body mass indexes (BMIs) above 25, and average ages between 18-30. The quality of the studies was evaluated using the Physiotherapy Evidence Database (PEDro) scale. Eight studies fulfilled the selection criteria, with a mean PEDro quality score of 5.8. Compared to CON, HIIT significantly decreased the concentrations of LDL (-12.14 mg/dL, p = < 0.00001) and TC (-9.27 mg/dL, p = 0.003), without significantly affecting HDL or TG. Compared to MICT, HIIT significantly decreased the concentrations of LDL (-6.23 mg/dL, p = 0.05) and TC (-7.85 mg/dL, p = 0.02), without significantly affecting HDL or TG concentrations. HIIT is superior to MICT and CON in improving the concentrations of LDL and TC in our target population. As early management of dyslipidemia improves long-term health, we recommend clinicians consider HIIT training protocols for their nondiabetic overweight and obese young adult patients.

Is V̇O2 suppressed during nonapnoeic facial submersion?

The mammalian dive response (DR) is described as oxygen-conserving based on measures of bradycardia, peripheral vasoconstriction, and decreased ventilation (V̇E). Using a model of simulated diving, this study examined the effect of nonapnoeic facial submersions (NAFS) on oxygen consumption (V̇O2). 19 participants performed four 2-min NAFS with 8 min of rest between each. Two submersions were performed in 5 °C water, 2 in 25 °C water. Heart rate (HR) was collected using chest strap monitors. A tube connected to the inspired port of a non-rebreathing valve allowed participants to breathe during facial submersion. Expired air was directed to a metabolic cart to determine V̇O2 and V̇E. Baseline (BL) HR, V̇O2, and V̇E values were determined by the average during the 2 min prior to facial submersion; cold shock response (CSR) values were the maximum during the first 30 s of facial submersion; and NAFS values were the minimum during the last 90 s of facial submersion. A 2-way repeated-measures ANOVA indicated that both HR and V̇E were greater during the CSR (92.5 ± 3.6 beats/min, 16.3 ± 0.8 L/min) compared with BL (78.9 ± 3.2 beats/min, 8.7 ± 0.4 L/min), while both were decreased from BL during the NAFS (60.0 ± 4.0 beats/min, 6.0 ± 0.4 L/min) (all, p < 0.05). HRCSR was higher and HRNAFS lower in 5 °C versus 25 °C water (p < 0.05), while V̇E was greater in 5 °C conditions (p < 0.05). V̇O2 exceeded BL during the CSR and decreased below BL during the NAFS (BL: 5.3 ± 0.1, CSR: 9.8 ± 0.4, NAFS: 3.1 ± 0.2 mL·kg-1·min-1, p < 0.05). The data illustrate that NAFS alone contributes to the oxygen conservation associated with the human DR.

Core temperature is a greater influence than endogenous 17ß-estradiol on the exercise-induced accumulation of myocardial heat shock protein mRNA.

Female rats typically do not show significant increases in myocardial Hsp70 after exercise unless trained (exercise over days or weeks). 17ß-Estradiol (E2) has been linked to this inhibition, but it varies considerably over the rodent estrus cycle. Consequently, we examined whether the inhibitory effects of endogenously produced E2 (measured immediately pre-exercise) were acute in exercised female Sprague-Dawley rats (60 min treadmill running at 30 m·min(-1)). Myocardial hsp70-1 and hsp70-2 mRNA were measured 30 min post-exercise, and their expression was inversely correlated with pre-exercise plasma Ε2 ( hsp70-1 mRNA, r(2) = 0.308, p = 0.011; hsp70-2 mRNA, r(2) = 0.238, p = 0.029). However, hsp70-1 and hsp70-2 mRNA exhibited much stronger correlations with core temperature achieved during exercise (r(2) = 0.812, p = 0.000; and r(2) = 0.738, p = 0.000, respectively). Consequently, although endogenous Ε2 in gonadally intact female rats may attenuate myocardial hsp70 mRNA accumulation, suggesting a reason why training maximizes this response in females, core temperature during exercise is still a greater stimulus to this response.

Myocardial Hsp70 phosphorylation and PKC-mediated cardioprotection following exercise.

Both protein kinase C (PKC) activation and Hsp70 expression have been shown to be key components for exercise-mediated myocardial protection during ischemia-reperfusion injury. Given that Hsp70 has been shown to undergo inducible phosphorylation in striated muscle and liver, we hypothesized that PKC may regulate myocardial Hsp70 function and subsequent exercise-conferred cardioprotection through this phosphorylation. Hence, acute exercise of male Sprague-Dawley rats (30 m/min for 60 min at 2% grade) was employed to assess the role of PKC and its selected isoforms in phosphorylation of Hsp70 and protection of the myocardium during ischemia-reperfusion injury. It was observed that administration of the PKC inhibitor chelerythrine chloride (5 mg/kg) suppressed the activation of three exercise-induced PKC isoforms (PKCalpha, PKCdelta, and PKCepsilon) and attenuated the exercise-mediated reduction of myocardial infarct size during ischemia-reperfusion injury. While this study also demonstrated that exercise led to an alteration in the phosphorylation status of Hsp70, this posttranslational modification appeared to be dissociated from PKC activation, as exercise-induced phosphorylation of Hsp70 was unchanged following inhibition of PKC. Taken together, these results indicate that selected isoforms of PKC play an important role in exercise-mediated protection of the myocardium during ischemia-reperfusion injury. However, exercise-induced phosphorylation of Hsp70 does not appear to be a mechanism by which PKC induces this cardioprotective effect.

Exercise-mediated regulation of Hsp70 expression following aerobic exercise training.

An issue central to understanding the biological benefits associated with regular exercise training is to elucidate the intracellular mechanisms governing exercise-conferred cardioprotection. Heat shock proteins (HSPs), most notably the inducible 70-kDa HSP family member Hsp70, are believed to participate in the protection of the myocardium during cardiovascular stress. Following acute exercise, activation of PKA mediates the suppression of an intermediary protein kinase, ERK1/2, which phosphorylates and suppresses the activation of the heat shock transcription factor 1 (HSF1). However, following exercise training, ERK1/2 has been reported to regulate the transcriptional activation of several genes involved in cell growth and proliferation and has been shown to be associated with training-mediated myocardial hypertrophy. The present project examined the transcriptional activation of hsp70 gene expression in acutely exercised (60 min at 30 m/min) naïve sedentary and aerobically trained (8 wk, low intensity) male Sprague-Dawley rats. Following acute exercise stress, no significant differences were demonstrated in the expression of myocardial Hsp70 mRNA and activation of PKA between sedentary and trained animals. However, trained animals elicited expression of the hsp70 gene (P < 0.05) in the presence of elevated ERK1/2 activation. Given the association of ERK1/2 and the suppression of hsp70 gene expression following acute exercise in naïve sedentary rats, these results suggest that training results in adaptations that allow for the simultaneous initiation of both proliferative and protective responses. While it is unclear what factors are associated with this training-related shift, increases in HSF1 DNA binding affinity (P < 0.05) and posttranscriptional modifications of the Hsp70 transcript are suggested.

Exercise training improves myocardial tolerance to ischemia in male but not in female rats.

Acute exercise increases myocardial tolerance to ischemia-reperfusion (I-R) injury in male but not in female rat hearts, possibly due to a decreased heat shock protein 70 (Hsp70) response in the female hearts. This study examined whether repetitive exercise training would increase Hsp70 and myocardial tolerance to I-R injury in female rat hearts. Adaptations in myocardial manganese superoxide dismutase (MnSOD) and endothelial nitric oxide synthase (eNOS) were also assessed. Ten-week old male (M) and female (F) Sprague-Dawley rats (n = 40 total) exercise-trained for 14 wk; the last 8 wk consisted of running 1 h at 30 m/min (2% incline), 5 days/wk. Following training, left ventricle mechanical function (LVMF) was monitored for 30 min of reperfusion following 30 min of global ischemia (Langendorff procedure). Myocardial Hsp70 content was not different in M and F control groups, while increases were observed in both trained groups (M greater than F; P < 0.05). Although MnSOD content did not differ between groups, endothelial nitric oxide synthase (eNOS) levels were decreased in F, with no change in M, following training (P < 0.05). Hearts from control F demonstrated a greater recuperation of all indices of LVMF following I-R compared with control M hearts (P < 0.05). Hearts of trained M exhibited improved recovery of LVMF (left ventricular diastolic pressure, left ventricular end-diastolic pressure, +dP/dt, -dP/dt) during reperfusion compared with control M hearts (P < 0.05). In contrast, hearts of trained F did not show any change in recovery from I-R. Hence, exercise training is more beneficial to M than F in improving myocardial function following I-R injury.

Regulation of myocardial heat shock protein 70 gene expression following exercise.

Post-exercise induction of myocardial heat shock protein (Hsp70) gene expression involves the activation of the heat shock transcription factor (HSF1). While the exact mechanisms governing the regulation of HSF1 are unclear, activation is believed to occur subsequent to hyperphosphorylation of specific serine residues. As two important serine kinases, protein kinase A (PKA) and protein kinase C (PKC), have been implicated in many phosphorylative events in myocardial cells, we examined the role of these kinases in the activation of Hsp70 gene expression following exercise. In this report, we show that prior administration of a PKA inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide ?2HCl (H-89; 0.36 mg/kg), significantly suppressed the elevation in Hsp70 mRNA (P < 0.05) and protein synthesis (P < 0.05) in male Sprague-Dawley rats following a single bout of exercise. In contrast, this post-exercise elevation in Hsp70 mRNA and protein synthesis was not suppressed following the administration of a PKC inhibitor chelerythrine chloride (CHEL; 5 mg/kg) (P < 0.05). Of note, inhibition of PKA did not alter the nuclear localization and binding affinity of HSF1 to the promotor region of the Hsp70 gene. These data indicate that PKA, and not PKC, plays a necessary role in the early exercise-induced regulation of Hsp70 gene expression, downstream of DNA-binding acquisition. However, the current study does not support previous observations regarding major changes in HSF1 phosphorylation and suggests that other PKA-related mechanisms mediate the activation of Hsp70 gene expression following exercise.