Sympathetic-mediated blunting of forearm vasodilation is similar between young men and women

Background: The in-vivo regulation of vascular conductance (VC) is a continuous balance between endothelial vasodilation and sympathetic vasoconstriction. Although women may report blunted sympathetic vasoconstriction along with higher endothelial vasodilation than men, it is currently unknown whether the interaction between vasoconstriction and vasodilation leads to different regulation of VC between sexes. This study assessed sex differences in sympathetic-mediated blunting of endothelial vasodilation after a brief period of ischemia and whether any restriction of vasodilation blunts tissue blood flow (BF) and re-oxygenation. Methods: 13 young women and 12 young men underwent two 5-min forearm circulatory occlusions followed by reperfusion, one in basal conditions and the other during cold pressor test-induced sympathetic activation (SYMP). Brachial artery diameter and BF, mean arterial pressure, total peripheral resistance (TPR), and thenar eminence oxygenation were collected. Percent changes normalized to baseline values of forearm VC, brachial artery BF and flow-mediated dilation (FMD), TPR, and hand oxygenation after circulatory reperfusion were calculated. Results: TPR increased during SYMP in men (p = 0.019) but not in women (p = 0.967). Women showed a greater brachial artery FMD than men (p = 0.004) at rest, but sex differences disappeared after normalization to shear rate and baseline diameter (p > 0.11). The percent increases from baseline of peak and average forearm VC after circulatory reperfusion did not differ between sexes in basal conditions (p > 0.98) or during SYMP (p > 0.97), and were restrained by SYMP similarly in both sexes (p < 0.003) without impairing the hand re-oxygenation (p > 0.08) or average hyperemic response (p > 0.09). Conclusions: Although women may report blunted sympathetic vasoconstriction than men when assessed separately, the similar sympathetic-mediated restriction of vasodilation suggests a similar dynamic regulation of VC between sexes. SYMP-mediated restrictions of the normal forearm vasodilation do not impair the average hyperemic response and hand re-oxygenation in both sexes

Neural and contractile determinants of burst-like explosive isometric contractions of the knee extensors

Walking and running are based on rapid burst-like muscle contractions. Burst-like contractions generate a Gaussian-shaped force profile, in which neuromuscular determinants have never been assessed. We investigated the neural and contractile determinants of the rate of force development (RFD) in burst-like isometric knee extensions. Together with maximal voluntary force (MVF), voluntary and electrically evoked (8 stimuli at 300 Hz, octets) forces were measured in the first 50, 100 and 150 ms of burst-like quadriceps contractions in 24 adults. High-density surface electromyography (HDsEMG) was adopted to measure the root mean square (RMS) and muscle fiber conduction velocity (MFCV) from the vastus lateralis and medialis. The determinants of voluntary force at 50, 100 and 150 ms were assessd by stepwise multiple regression analysis. Force at 50 ms was explained by RMS (R2 = 0.361); force at 100 ms was explained by octet (R2 = 0.646); force at 150 ms was explained by MVF (R2 = 0.711) and octet (R2 = 0.061). Peak RFD (which occurred at 60 ± 10 ms from contraction onset) was explained by MVF (R2 = 0.518) and by RMS50 (R2 = 0.074). MFCV did not emerge as a determinant of RFD. Muscle excitation was the sole determinant of early RFD (50 ms), while contractile characteristics were more relevant for late RFD (≥100 ms). As peak RFD is mostly determined by MVF, it may not be more informative than MVF itself. Therefore, a time-locked analysis of RFD provides more insights into the neuromuscular characteristics of explosive contractions

Flat versus simulated mountain trail running: a multidisciplinary comparison in well-trained runners

1This paper compares cardiopulmonary and neuromuscular parameters across three running aerobic speeds in two conditions that differed from a treadmill's movement: flat condition (FC) and unpredictable roll variations similar to mountain trail running (URV). Twenty well-trained male runners (age 33 ± 8 years, body mass 70.3 ± 6.4 kg, height 1.77 ± 0.06 m, V˙O2max 63.8 ± 7.2 mL·kg-1·min-1) voluntarily participated in the study. Laboratory sessions consisted of a cardiopulmonary incremental ramp test (IRT) and two experimental protocols. Cardiopulmonary parameters, plasma lactate (BLa-), cadence, ground contact time (GT) and RPE values were assessed. We also recorded surface electromyographic (sEMG) signals from eight lower limb muscles, and we calculated, from the sEMG envelope, the amplitude and width of peak muscle activation for each step. Cardiopulmonary parameters were not significantly different between conditions (V˙O2: p = 0.104; BLa-: p = 0.214; HR: p = 0.788). The amplitude (p = 0.271) and width (p = 0.057) of sEMG activation peaks did not change between conditions. The variability of sEMG was significantly affected by conditions; indeed, the coefficient of variation in peak amplitude (p = 0.003) and peak width (p < 0.001) was higher in URV than in FC. Since the specific physical demands of running can differ between surfaces, coaches should resort to the use of non-traditional surfaces, emphasizing specific surface-related motor tasks that are normally observed in natural running environments. Seeing that the variability of muscle activations was affected, further studies are required to better understand the physiological effects induced by systematic surface-specific training and to define how variable-surface activities help injury prevention

Rate of force development as an indicator of neuromuscular fatigue: a scoping review

Because rate of force development (RFD) is an emerging outcome measure for the assessment of neuromuscular function in unfatigued conditions, and it represents a valid alternative/complement to the classical evaluation of pure maximal strength, this scoping review aimed to map the available evidence regarding RFD as an indicator of neuromuscular fatigue. Thus, following a general overview of the main studies published on this topic, we arbitrarily compared the amount of neuromuscular fatigue between the "gold standard" measure (maximal voluntary force, MVF) and peak, early (≤100 ms) and late (>100 ms) RFD. Seventy full-text articles were included in the review. The most-common fatiguing exercises were resistance exercises (37% of the studies), endurance exercises/locomotor activities (23%), isokinetic contractions (17%), and simulated/real sport situations (13%). The most widely tested tasks were knee extension (60%) and plantar flexion (10%). The reason (i.e., rationale) for evaluating RFD was lacking in 36% of the studies. On average, the amount of fatigue for MVF (-19%) was comparable to late RFD (-19%) but lower compared to both peak RFD (-25%) and early RFD (-23%). Even if the rationale for evaluating RFD in the fatigued state was often lacking and the specificity between test task and fatiguing exercise characteristics was not always respected in the included studies, RFD seems to be a valid indicator of neuromuscular fatigue. Based on our arbitrary analyses, peak RFD and early phase RFD appear even to be more sensitive to quantify neuromuscular fatigue than MVF and late phase RFD

Circadian and sex differences in carotid-femoral pulse wave velocity in young individuals and elderly with and without type 2 diabetes

The incidence of cardiovascular events is higher in the morning than in the evening and differs between sexes. We tested the hypothesis that aortic stiffness, a compelling cardiovascular risk factor, increases in the morning than in the evening in young, healthy individuals between 18 and 30 years (H18-30) or in older individuals between 50 and 80 years, either healthy (H50-80) or with type 2 diabetes (T2DM50-80). Sex differences were also investigated. Carotid-femoral pulse wave velocity (cf-PWV) recorded via Doppler Ultrasound, blood pressure and heart rate were checked at 6 a.m. and 9 p.m., at rest and during acute sympathetic activation triggered by handgrip exercise. Cf-PWV values were lower in the morning compared to the evening in all groups (p < 0.01) at rest and lower (p = 0.008) in H18-30 but similar (p > 0.267) in the older groups during sympathetic activation. At rest, cf-PWV values were lower in young women compared to young men (p = 0.001); however, this trend was reversed in the older groups (p < 0.04). During sympathetic activation, the cf-PWV was lower in women in H18-30 (p = 0.001), similar between sexes in H50-80 (p = 0.122), and higher in women in T2DM50-80 (p = 0.004). These data do not support the hypothesis that aortic stiffness increases in the morning compared to the evening within any of the considered groups in both rest and sympathetic activation conditions. There are differences between the sexes, which vary according to age and diabetes status. In particular, aortic stiffness is higher in older women than in men with diabetes during acute stress

Effects of Different Training Intensity Distribution in Recreational Runners

Purpose: To compare the impact of two different training intensity distributions in terms of conditional and performance parameters and spent time to training in recreational athletes. Methods: Two different training intensity distribution model were performed for 8 weeks by 38 recreational runners. Runners recruited were randomly assigned to 2 different training models based on HR intensity detected with maximal test. The percentage distribution splitted in zone 1, 2 and 3 were by 77/3/20 and 40/50/10 in polarized endurance training group (PET) and focused endurance training (FOC) group respectively. Programs were balanced for total training impulse (TRIMP). To evaluate effects of training, before and after treatment were performed a maximal exercise test to determine Maximal Oxygen Uptake (V'O2max), Ventilatory Threshold (VT), respiratory-compensation point (RCT) Running Economy (RE) and 2 Km performance. To investigate the effects of training on muscular performance were performed one repetition maximum (1RM), squat jump (SJ) and counter movement jump (CMJ). Results: Both groups significantly improved their velocity at V'O2max (3.2% and 4.0%), at VT (4.0% and 3.2%), RCT (5.7% and 3.4%), the average velocity in 2 Km performance (3.5% and 3.0%) and RE (-5.3% and -8.7%) for PET and FOC respectively for each variable. No differences were found between the groups on any parameter investigated except about the total training time (PET = 29.8 3.1h and FOC = 24.8 2.0 h). Conclusion: Focused Endurance Training obtains similar improvements than Polarized Endurance Training saving 17% of training time in recreational runners

Comparison of plasma lipids changes after middle-distance running in euglycemic and diabetic subjects

Background: Although regular performance of aerobic physical exercise is pivotal for preserving or improving health and fitness, scarce information is available on plasma lipids changes after middle-distance running in euglycemic and diabetic subjects. Methods: Eleven male euglycemic amateur runners (mean age 41\ub16 years) and 9 male diabetic amateur runners (4 with type 1 and 5 with type 2 diabetes; mean age 55\ub114 years) participated to a 21.1-km running trial. All subjects belonged to an amateur running team, regularly engaged in amateur running. Blood was collected before the start of the trial and immediately after. The lipid profile, encompassing measurement of total cholesterol, triglycerides, low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C), was assayed with Roche Cobas 6000. Results: All athletes successfully completed the 21.1-km running trial, with running pace comprised between 9.6\u201312.8 km/h. In both categories of subjects the values of LDL-C significantly decreased by approximately 6% after the run, whilst HDL-C and triglycerides significantly increased by 6\u20139% and 30\u201336%, respectively. The post-run variations of all lipoprotein fractions after the running trial were virtually identical in diabetic and euglycemic subjects. Conclusions: The results of this study show for the first time that middle-distance running elicits acute favorable changes of lipid profile both in euglycemic and diabetic subjects. This form of endurance exercise shall hence be further fostered for purposes of public health promotion and improvement

Post-exercise hypotension and reduced cardiac baroreflex after half-marathon run: in men, but not in women

We examined whether trained women exhibit similar cardiovascular and cardiac baroreflex alterations after a half-marathon compared to men. Thirteen women (39.1 \ub1 9.3 years; 165 \ub1 6 cm; 58.2 \ub1 7.5 kg; maximal aerobic speed (MAS): 13.7 \ub1 2.2 km\ub7h-1) and 12 men (45.7 \ub1 10.5 years; 178 \ub1 7 cm; 75.0 \ub1 8.3 kg; MAS: 15.8 \ub1 2.2 km\ub7h-1) ran an official half-marathon. Before and 60-min after, cardiovascular variables, parasympathetic (heart rate variability analysis) modulation and cardiac baroreflex function (transfer function and sequence analyses) were assessed during supine rest and a squat-stand test. Running performance was slower in women than in men (120 \ub1 19 vs. 104 \ub1 14 min for women and men, respectively). However, when expressed as a percentage of MAS, it was similar (78.1 \ub1 4.6% and 78.2 \ub1 5.4% of MAS for women and men, respectively). Before the run, women exhibited lower mean blood pressure (BP), cardiac output (CO) and stroke volume (SV) compared to men, together with higher parasympathetic indexes. After the race, parasympathetic indexes decreased in both sexes, but remained higher in women. Reduced SV, systolic BP and cardiac baroreflex were observed in men but not in women. Contrary to men, a competitive half-marathon did not trigger post-exercise hypotension and a reduced cardiac baroreflex in women