Adjusting for muscle strength and body size attenuates sex differences in the exercise pressor reflex in young adults

Larger reductions in blood pressure during post-exercise standing, but not middle cerebral artery blood velocity, in resistance-trained versus untrained individuals

Dynamic resistance exercise (RE) produces sinusoidal fluctuations in blood pressure, with hypotension and cerebral hypoperfusion commonly observed immediately following RE. Whether the cerebral vasculature adapts to these regular blood pressure challenges is unclear. This study examined the cerebrovascular response to post-dynamic RE orthostasis. RE-trained (n = 15, female = 4) and healthy untrained individuals (n = 15, female = 12) completed five stands: one after seated rest, with each of the subsequent four stands occurring immediately following a set of 10 repetitions of unilateral leg extension exercise at 60% of their one repetition maximum. Beat-to-beat blood pressure, mean middle cerebral artery blood velocity (MCAvmean) and end-tidal carbon dioxide were measured throughout. During standing the mean arterial blood pressure (MAP) and MCAvmean nadirs were identified. There was no difference between groups for age (mean ± SD, 26 ± 7 RE-trained vs. 25 ± 6 years untrained, P = 0.683) or weight (78 ± 15 vs. 71 ± 15 kg, P = 0.683). At MAP nadir during the post-exercise stand, a greater reduction in MAP was observed in the RE-trained group (e.g., set 4, -45 ± 11 vs. -36 ± 6 mmHg, training effect P = 0.026). However, post-exercise stand MCAvmean at MCAvmean nadir was not different (e.g., set 4, -20 ± 7 vs. -17 ± 6 cm/s, interaction effect P = 0.478). Rate of regulation was higher in the RE-trained group (set 1, 0.301 ± 0.170 vs. 0.167 ± 0.009, training effect P = 0.023). Despite RE-trained individuals demonstrating greater absolute reductions in MAP during orthostasis following RE, there were no differences in MCAvmean, suggesting that habitual RE may mitigate post-exercise cerebral hypoperfusion.

Consideration of absolute intensity when examining sex differences in blood pressure responses during static exercise

Low- to moderate-intensity submaximal static contractions are commonly used to study the effects of biological sex on the cardiovascular response to exercise. Under this paradigm, premenopausal females frequently demonstrate smaller blood pressure responses than age-matched males. These differences are preserved during postexercise circulatory occlusion, implicating the muscle metaboreflex as an important driver of sex differences in the blood pressure response to static exercise. The mechanisms responsible for these differences are incompletely understood but often attributed to innate sex differences in skeletal muscle fiber type distribution, muscle metabolism, and/or sympathetic control of the circulation. However, one potential confounding factor is that the majority of studies use relative intensity exercise (e.g., 30% of maximal voluntary contraction), such that on average, females are completing static contractions at a lower absolute intensity. In this review, we summarize human evidence showing that sex differences in blood pressure responses to static exercise are attenuated or abolished when controlling for absolute intensity and muscle strength, either by statistical methods or strength-matched cohorts. We highlight evidence that the effect of higher absolute contraction intensity on exercise blood pressure likely occurs through increased mechanical occlusion of skeletal muscle microvasculature, leading to greater activation of the muscle metaboreflex. These findings highlight an important need to account for absolute intensity when studying and interpreting sex differences in cardiovascular responses to exercise.

Cardiovascular and hematological responses to a dry dynamic apnea in breath hold divers

The mammalian dive reflex, characterized by bradycardia and peripheral vasoconstriction, occurs in all mammals, including humans, in response to apnea. However, the dive reflex to a single, maximal, dry, dynamic apnea (DYN) and how it compares to a time-matched exercise control trial (EX) or dry static apnea (SA) has not been studied. We examined the hypotheses that, compared with EX and SA, the magnitude of the 1) cardiovascular response and 2) hematological response to DYN would be greater. Cardiovascular parameters [heart rate (HR), systolic (SBP), diastolic (DBP), and mean arterial (MAP) blood pressure] were continuously collected in 23 (F = 6 females) moderate and elite freedivers, first during a maximal DYN, then during a time-matched SA and EX on a swimming ergometer in randomized order. Venous blood draws were made before and following each trial. The change in calculated oxygen saturation (DYN: -17 ± 13%, EX: -2 ± 1%, ΔSA: -2 ± 1%; P < 0.05, all comparisons) was greater during DYN compared with EX and SA. During DYN, ΔSBP (DYN: 104 ± 31 mmHg; EX: 38 ± 23 mmHg; and SA: 20 ± 11 mmHg), ΔDBP (DYN: 45 ± 12 mmHg; EX: 14 ± 10 mmHg; and SA: 15 ± 8 mmHg), and ΔMAP (DYN: 65 ± 17 mmHg; EX: 22 ± 13 mmHg; and SA: 16 ± 9 mmHg) were increased compared with EX and SA, while ΔHR was greater during EX (DYN: -24 ± 23 beats/min; EX: 33 ± 13 beats/min; and SA: -1 ± 10 beats/min) than either DYN or SA (P < 0.0001, all comparisons). Females had a greater pressor response to EX (ΔSBP: 59 ± 30 mmHg; ΔDBP: 24 ± 14 mmHg; and ΔMAP: 35 ± 8 mmHg) than males (ΔSBP: 31 ± 15 mmHg; ΔDBP: 11 ± 6 mmHg; and ΔMAP: 18 ± 8 mmHg; P < 0.01, all comparisons). Together, these data indicate that DYN elicits a distinct, exaggerated cardiovascular response compared with EX or SA alone.NEW & NOTEWORTHY This study performed a dry dynamic apnea with sport-specific equipment to closely mimic the physiological demands of competition diving. We found the cardiovascular and hematological responses to dynamic apnea were more robust compared with time-matched exercise and dry static apnea control trials.

The effects of habitual resistance exercise training on cerebrovascular responses to lower body dynamic resistance exercise: A cross-sectional study

Dynamic resistance exercise (RE) produces sinusoidal fluctuations in blood pressure with simultaneous fluctuations in middle cerebral artery blood velocity (MCAv). Some evidence indicates that RE may alter cerebrovascular function. This study aimed to examine the effects of habitual RE training on the within-RE cerebrovascular responses. RE-trained (n = 15, Female = 4) and healthy untrained individuals (n = 15, Female = 12) completed four sets of 10 paced repetitions (15 repetitions per minute) of unilateral leg extension exercise at 60% of predicted 1 repetition maximum. Beat-to-beat blood pressure, MCAv and end-tidal carbon dioxide were measured throughout. Zenith, nadir and zenith-to-nadir difference in mean arterial blood pressure (MAP) and mean MCAv (MCAvmean) for each repetition were averaged across each set. Two-way ANOVA was used to analyse dependent variables (training × sets), Bonferroni corrected t-tests were used for post hoc pairwise comparisons. Group age (26 ± 7 trained vs. 25 ± 6 years untrained, P = 0.683) and weight (78 ± 15 vs. 71 ± 15 kg, P = 0.683) were not different. During exercise average MAP was greater for the RE-trained group in sets 2, 3 and 4 (e.g., set 4: 101 ± 11 vs. 92 ± 7 mmHg for RE trained and untrained, respectively, post hoc tests all P = < 0.012). Zenith MAP and zenith-to-nadir MAP difference demonstrated a training effect (P < 0.039). Average MCAvmean and MCAvmean zenith-to-nadir difference was not different between groups (interaction effect P = 0.166 and P = 0.459, respectively). Despite RE-trained individuals demonstrating greater fluctuations in MAP during RE compared to untrained, there were no differences in MCAvmean. Regular RE may lead to vascular adaptations that stabilise MCAv during RE.

Various modalities of resistance exercise promote similar acute cognitive improvements and hemodynamic increases in young, healthy adults

The aim was to examine the effects of modalities of acute resistance exercise (RE) on cognition and hemodynamics including internal carotid artery (ICA) blood flow (BF). Twenty adults completed familiarization and experimental visits. One-repetition maximum (1RM) for bilateral leg extension was quantified, and baseline executive functioning was determined from three run-in visits. Subsequent visits included three randomized, volume-equated, acute exercise bouts of 30 %1RM+blood flow restriction (BFR), 30 %1RM, and 70 %1RM. Both 30 %1RM trials completed four sets of exercise (1 × 30, 3 × 15), and the 70 %1RM condition completed four sets of 8 repetitions. BFR was induced with 40 % of the pressure to occlude the femoral arteries. 11 min following each exercise, participants completed the Stroop and Shifting Attention Tests. Baseline and post-exercise values were used to calculate change scores. The resulting mean change scores were evaluated with mixed factorial ANOVAs. A p≤0.05 was considered significant. All measured outcome variables increased in response to exercise. The ANOVAs for cognitive scores indicated no significant (p>0.05) interactions. For cognitive flexibility and executive function index, there were main effects of Sex. Change scores of the females were significantly greater than the males for cognitive flexibility (7.6 ± 5.9 vs. -2.6 ± 8.4 au; p=0.007) and executive function index (7.4 ± 4.6 vs. -2.5 ± 6.5 au; p=0.001). For ICA BF, there was no significant interaction or any main effect. The females exhibited a smaller exercise-induced increase in blood pressure compared to the males (17.7 ± 5.9 vs. 11.0 ± 4.1 mmHg; p=0.010). Each RE modality yielded acute improvements in cognition, but only for females. There were no cognitive improvements related to BFR such that each RE bout yielded similar results.

The influence of oral contraceptives on the exercise pressor reflex in the upper and lower body

Previous research has demonstrated that oral contraceptive (OC) users have enhanced cardiorespiratory responses to arm metaboreflex activation (i.e., postexercise circulatory occlusion, PECO) and attenuated pressor responses to leg passive movement (PM) compared to non-OC users (NOC). We investigated the cardiorespiratory responses to arm or leg metaboreflex and mechanoreflex activation in 32 women (OC, n = 16; NOC, n = 16) performing four trials: 40% handgrip or 80% plantarflexion followed by PECO and arm or leg PM. OC and NOC increased mean arterial pressure (MAP) similarly during handgrip, plantarflexion and arm/leg PECO compared to baseline. Despite increased ventilation (VE) during exercise, none of the women exhibited higher VE during arm or leg PECO. OC and NOC similarly increased MAP and VE during arm or leg PM compared to baseline. Therefore, OC and NOC were similar across pressor and ventilatory responses to arm or leg metaboreflex and mechanoreflex activation. However, some differences due to OC may have been masked by disparities in muscle strength. Since women increase VE during exercise, we suggest that while women do not display a ventilatory response to metaboreflex activation (perhaps due to not reaching a theoretical metabolite threshold to stimulate VE), the mechanoreflex may drive VE during exercise in women.

Inverse Association between Exercising Blood Pressure Response and Left Ventricular Chamber Size and Mass in Women Who Habitually Resistance Train

Exercise is a major modifiable lifestyle factor that leads to temporarily increased systolic blood pressure (SBP), which is thought to influence left ventricular mass normalized to body surface area (LVM/BSA). This relationship has never been studied in women who habitually perform resistance exercise.

PURPOSE

To determine if a direct correlation exists between the SBP response to resistance exercise (change from rest; eSBP) and LVM/BSA in young healthy women who habitually resistance train.

METHODS

Leg extension resistance exercise was performed while continuously monitoring blood pressure using finger plethysmography. LVM was estimated using echocardiography. Data are shown as mean ± SD.

RESULTS

Thirty-one women participated (age 23 ± 3 years, height 164 ± 7 cm, body mass 63.7 ± 10.3 kg). Resting SBP (110 ± 8 mmHg, r = 0.355, p = 0.049) was shown to be directly correlated to LVM/BSA (72.0 ± 28.4 g/m2). Conversely, eSBP (30.8 ± 14.6 ∆mmHg, r = -0.437, p = 0.014) was inversely related to LVM/BSA. eSBP was not correlated to interventricular septum width (0.88 ± 0.12 cm, r = -0.137, p = 0.463) or posterior wall thickness (0.91 ± 0.15 cm, r = -0.084, p = 0.654). eSBP was inversely related to left ventricle internal diameter during diastole (LVIDd) (4.25 ± 0.33 cm, r = -0.411, p = 0.021).

CONCLUSION

Counter to the hypothesis, these data suggest an inverse association between eSBP during resistance exercise and LVM/BSA in healthy young women who resistance train. This relationship is due to a smaller LVIDd with greater eSBP.