Maternal cardioautonomic responses during and following exercise throughout pregnancy

Blood pressure regulation during pregnancy is poorly understood. Cardiovagal baroreflex gain (BRG) is an important contributor to blood pressure regulation through its influence on heart rate. Heart rate fluctuations occur in response to various physiological stimuli and can be measured using heart rate variability (HRV). It is unclear how these mechanisms operate during pregnancy, particularly with regard to exercise. We examined BRG and HRV prior to, during, and following prenatal exercise. Forty-three pregnant (n = 10 first trimester (TM1), n = 17 second trimester (TM2), n = 16 third trimester (TM3)) and 20 nonpregnant (NP) women underwent an incremental peak exercise test. Beat-by-beat blood pressure (photoplethysmography) and heart rate (lead II electrocardiogram) were measured throughout. BRG (the slope of the relationship between fluctuations in systolic blood pressure and the R-R interval) and HRV (root mean square of the successive differences; RMSSD) were assessed at rest, during steady-state exercise (EX), and during active recovery. BRG decreased with gestation and was lower in the TM3 group than in the NP group (17.9 ± 6.9 ms/mm Hg vs 24.8 ± 7.4 ms/mm Hg, p = 0.017). BRG was reduced during EX in all groups. Resting HRV (RMSSD) also decreased with gestation and was lower in the TM3 group than in the NP group (29 ± 17 ms vs 48 ± 20 ms, p < 0.001). RMSSD was blunted during EX in all groups compared with rest. During active recovery, RMSSD was further blunted compared with EX in the NP group but not during pregnancy (TM1, TM2, and TM3). Compared with the nonpregnant controls, the pregnant women had lower BRG and HRV at rest, but comparable cardioautonomic control during both exercise and active recovery following peak exercise.

Physiological responses to partial-body cryotherapy performed during a concurrent strength and endurance session

This investigation examined the effect of partial-body cryostimulation (PBC) performed in the recovery time between a strength training and an interval running (IR) session. Nine rugby players (age, 23.7 ± 3.6 years; body mass index, 28.0 ± 2.6 kg·m^-2) were randomly exposed to 2 different conditions: (i) PBC: 3 min at -160 °C, and (ii) passive recovery at 21 °C. We performed the bioelectrical impedance analysis (BIA) and recorded temperature and cardiac autonomic variables at 3 time points: at baseline, after strength training, and after 90 min of recovery. In addition, blood lactate concentration was measured 1 min before and 2.5 min after the IR. Heart rate (HR), energy cost, minute ventilation, oxygen uptake, and metabolic power were assessed during the IR. Homeostatic hydration status was affected by the execution of an intense strength training subsession. Then, after PBC, the BIA vector was restored close to normohydration status. Autonomic variables changed over time in both conditions, although the mean differences and effect sizes were greater in the PBC condition. During IR, HR was 3.5% lower after PBC, and the same result was observed for oxygen uptake (∼4.9% lower) and ventilation (∼6.5% lower). The energy cost measured after cryotherapy was ∼9.0% lower than after passive recovery. Cryotherapy enhances recovery after a single strength training session, and during subsequent IR, it shows a reduction in cardiorespiratory and metabolic parameters. PBC may be useful for those athletes who compete or train more than once in the same day, to improve recovery between successive training sessions or competitions.

Higher exercise intensity delays postexercise recovery of impedance-derived cardiac sympathetic activity

Systolic time intervals (STIs) provide noninvasive insights into cardiac sympathetic neural activity (cSNA). As the effect of exercise intensity on postexercise STI recovery is unclear, this study investigated the STI recovery profile after different exercise intensities. Eleven healthy males cycled for 8 min at 3 separate intensities: LOW (40%-45%), MOD (75%-80%), and HIGH (90%-95%) of heart-rate (HR) reserve. Bio-impedance cardiography was used to assess STIs - primarily pre-ejection period (PEP; inversely correlated with cSNA), as well as left ventricular ejection time (LVET) and PEP:LVET - during 10 min seated recovery immediately postexercise. Heart-rate variability (HRV), i.e., natural-logarithm of root mean square of successive differences (Ln-RMSSD), was calculated as an index of cardiac parasympathetic neural activity (cPNA). Higher preceding exercise intensity elicited a slower recovery of HR and Ln-RMSSD (p < 0.001), and these measures did not return to baseline by 10 min following any intensity (p ≤ 0.009). Recovery of STIs was also slower following higher intensity exercise (p ≤ 0.002). By 30 s postexercise, higher preceding intensity resulted in a lower PEP (98 ± 14 ms, 75 ± 6 ms, 66 ± 5 ms for LOW, MOD, and HIGH, respectively, p < 0.001). PEP recovered to baseline (143 ± 11 ms) by 5 min following LOW (139 ± 13 ms, p = 0.590) and by 10 min following MOD (145 ± 17 ms, p = 0.602), but was still suppressed at 10 min following HIGH (123 ± 21 ms, p = 0.012). Higher preceding exercise intensity attenuated the recovery of indices for cSNA (from STIs) and cPNA (from HRV) in a graded dose-response fashion. While exercise intensity must be considered, acute recovery may be a valuable period during which to concurrently monitor these noninvasive indices, to identify potentially abnormal cardiac autonomic responses.

Associations between heart rate variability, metabolic syndrome risk factors, and insulin resistance

The purpose of this study was to examine differences in heart rate variability (HRV) in metabolic syndrome (MetS) and to determine associations between HRV parameters, MetS risk factors, and insulin resistance (homeostasis model assessment for insulin resistance (HOMA-IR)). Participants (n = 220; aged 23-70 years) were assessed for MetS risk factors (waist circumference, blood pressure, fasting plasma glucose, triglycerides, and high-density lipoprotein cholesterol) and 5-min supine HRV (time and frequency domain and nonlinear). HRV was compared between those with 3 or more (MetS+) and those with 2 or fewer MetS risk factors (MetS-). Multiple linear regression models were built for each HRV parameter to investigate associations with MetS risk factors and HOMA-IR. Data with normal distribution are presented as means ± SD and those without as median [interquartile range]. In women, standard deviation of R-R intervals 38.0 [27.0] ms, 44.5 [29.3] ms; p = 0.020), low-frequency power (5.73 ± 1.06 ln ms(2), 6.13 ± 1.05 ln ms(2); p = 0.022), and the standard deviation of the length of the Poincaré plot (46.8 [31.6] ms, 58.4 [29.9] ms; p = 0.014) were lower and heart rate was higher (68 [13] beats/min, 64 [12] beats/min; p = 0. 018) in MetS+ compared with MetS-, with no differences in men. Waist circumference was most commonly associated with HRV, especially frequency domain parameters. HOMA-IR was associated with heart rate. In conclusion, MetS+ women had a less favourable HRV profile than MetS- women, but there were no differences in men. HOMA-IR was associated with heart rate, not HRV.