Indices of leg resistance artery function are independently related to cycling V̇O2 max

Six weeks of localized passive heat therapy elicits some exercise-like improvements in resistance artery function

The purpose of this study was to examine the effects of 6 weeks of localized, muscle-focused (quadriceps femoris) passive heat therapy (PHT) on resistance artery function, exercise haemodynamics and exercise performance relative to knee extension (KE) exercise training (EX). We randomized 34 healthy adults (ages 18-36; n = 17 female, 17 male) to receive either PHT or sham heating sessions (120 min, 3 days/week), or EX (40 min, 3 days/week) over 6 weeks. Blood flow was assessed with Doppler ultrasound of the femoral artery during both passive leg movement (PLM) and a KE graded exercise test. Muscle biopsies were taken from the vastus lateralis at baseline and after 6 weeks. Peak blood flow during PLM increased to the same extent in both the EX (∼10.5% increase, P = 0.009) and PHT groups (∼8.5% increase, P = 0.044). Peak flow during knee extension exercise increased in EX (∼19%, P = 0.005), but did not change in PHT (P = 0.523) and decreased in SHAM (∼7%, P = 0.020). Peak vascular conductance during KE increased by ∼25% in EX (P = 0.030) and PHT (P = 0.012). KE peak power increased in EX by ∼27% (P = 0.001) but did not significantly change in PHT and SHAM groups. Expression of endothelial nitric oxide synthase increased significantly in both EX (P = 0.028) and PHT (P = 0.0095), but only EX resulted in increased angiogenesis. In conclusion, 6 weeks of localized PHT improved resistance artery function at rest and during exercise to the same extent as exercise training but did not yield significant improvements in performance. KEY POINTS: Many for whom exercise would be most beneficial are either unable to exercise or have a very low exercise tolerance. In these cases, an alternative treatment to combat declines in resistance artery function is needed. We tested the hypothesis that passive heat therapy (PHT) would increase resistance artery function, improve exercise haemodynamics and enhance exercise performance compared to a sham treatment, but less than aerobic exercise training. This report shows that 6 weeks of localized PHT improved resistance artery function at rest and during exercise to the same extent as exercise training but did not improve exercise performance. Additionally, muscle biopsy analyses revealed that endothelial nitric oxide synthase expression increased in both PHT and exercise training groups, but only exercise resulted in increased angiogenesis. Our data demonstrate the efficacy of applying passive heat as an alternative treatment to improve resistance artery function for those unable to receive the benefits of regular exercise.

NIRS-Derived Muscle-Deoxygenation and Microvascular Reactivity During Occlusion-Reperfusion at Rest Are Associated With Whole-Body Aerobic Fitness

Purpose: Near-infrared spectroscopy (NIRS) indices during arterial occlusion-reperfusion maneuver have been used to examine the muscle's oxidative metabolism and microvascular function-important determinants of whole-body aerobic-fitness. The association of NIRS-derived parameters with whole-body VO2max was previously examined using a method requiring exercise (or electrical stimulation) followed by multiple arterial occlusions. We examined whether NIRS-derived indices of muscle deoxygenation and microvascular reactivity assessed during a single occlusion-reperfusion at rest are (a) associated with maximal/submaximal indices of whole-body aerobic-fitness and (b) could discriminate individuals with different VO2max. We, also, investigated which NIRS-parameter during occlusion-reperfusion correlates best with whole-body aerobic-fitness. Methods: Twenty-five young individuals performed an arterial occlusion-reperfusion at rest. Changes in oxygenated- and deoxygenated-hemoglobin (O2Hb and HHb, respectively) in vastus-lateralis were monitored; adipose tissue thickness (ATT) at NIRS-application was assessed. Participants also underwent a maximal incremental exercise test for VO2max, maximal aerobic velocity (MAV), and ventilatory-thresholds (VTs) assessments. Results: The HHbslope and HHbmagnitude of increase (occlusion-phase) and O2Hbmagnitude of increase (reperfusion-phase) were strongly correlated with VO2max (r = .695-.763, p < .001) and moderately with MAV (r = .468-.530; p < .05). O2Hbmagnitude was moderately correlated with VTs (r = .399-.414; p < .05). After controlling for ATT, the correlations remained significant for VO2max (r = .672-.704; p < .001) and MAV (r = .407; p < .05). Individuals in the high percentiles after median and tritile splits for HHbslope and O2Hbmagnitude had significantly greater VO2max vs. those in low percentiles (p < .01-.05). The HHbslope during occlusion was the best predictor of VO2max. Conclusion: NIRS-derived muscle deoxygenation/reoxygenation indices during a single arterial occlusion-reperfusion maneuver are strongly associated with whole-body maximal indices of aerobic-fitness (VO2max, MAV) and may discriminate individuals with different VO2max.

Acute oral antioxidant consumption does not alter brachial artery flow mediated dilation in young adults independent of exercise training status

Endothelium-dependent vasodilation can be tested using a variety of shear stress paradigms, some of which may involve the production of reactive oxygen species. The purpose of this study was to compare different methods for assessing endothelial function and their specific involvement of reactive oxygen species and influence of aerobic training status. Twenty-nine (10 F) young and healthy participants (VO2max: 34-74 mL·kg-1·min-1) consumed either an antioxidant cocktail (AOC; vitamin C, vitamin E, α-lipoic acid) or placebo (PLA) on each of two randomized visits. Endothelial function was measured via three different brachial artery flow-mediated dilation (FMD) tests: reactive hyperemia (RH-FMD: 5 min cuff occlusion and release), sustained shear (SS-FMD: 6 min rhythmic handgrip), and progressive sustained shear (P-SS-FMD: three intensities of 3 min of rhythmic handgrip). Baseline artery diameter decreased (all tests: 3.8 ± 0.5 to 3.7 ± 0.6 mm, p = 0.004), and shear rate stimulus increased (during RH-FMD test, p = 0.021; during SS-FMD test, p = 0.36; during P-SS-FMD test, p = 0.046) following antioxidant consumption. However, there was no difference in FMD following AOC consumption (RH-FMD, PLA: 8.1 ± 2.6%, AOC: 8.2 ± 3.5%, p = 0.92; SS-FMD, PLA: 6.9 ± 3.9%, AOC: 7.8 ± 5.2%, p = 0.15) or FMD per shear rate slope (P-SS-FMD: PLA: 0.0039 ± 0.0035 mm·s-1, AOC: 0.0032 ± 0.0017 mm·s-1, p = 0.28) and this was not influenced by training status/fitness (all p > 0.60). Allometric scaling did not alter these outcomes (all p > 0.40). Reactive oxygen species may not be integral to endothelium-dependent vasodilation tested using reactive, sustained, or progressive shear protocols in young males and females, regardless of fitness level.

Vascular dysfunction and the age-related decline in critical power

Ageing results in lower exercise tolerance, manifested as decreased critical power (CP). We examined whether the age-related decrease in CP occurs independently of changes in muscle mass and whether it is related to impaired vascular function. Ten older (63.1 ± 2.5 years) and 10 younger (24.4 ± 4.0 years) physically active volunteers participated. Physical activity was measured with accelerometry. Leg muscle mass was quantified with dual X-ray absorptiometry. The CP and maximum power during a graded exercise test (PGXT ) of single-leg knee-extension exercise were determined over the course of four visits. During a fifth visit, vascular function of the leg was assessed with passive leg movement (PLM) hyperaemia and leg blood flow and vascular conductance during knee-extension exercise at 10 W, 20 W, slightly below CP (90% CP) and PGXT . Despite not differing in leg lean mass (P = 0.901) and physical activity (e.g., steps per day, P = 0.735), older subjects had ∼30% lower mass-specific CP (old = 3.20 ± 0.94 W kg-1 vs. young = 4.60 ± 0.87 W kg-1 ; P < 0.001). The PLM-induced hyperaemia and leg blood flow and/or conductance were blunted in the old at 20 W, 90% CP and PGXT (P < 0.05). When normalized for leg muscle mass, CP was strongly correlated with PLM-induced hyperaemia (R2  = 0.52; P < 0.001) and vascular conductance during knee-extension exercise at 20 W (R2  = 0.34; P = 0.014) and 90% CP (R2  = 0.39; P = 0.004). In conclusion, the age-related decline in CP is not only an issue of muscle quantity, but also of impaired muscle quality that corresponds to impaired vascular function.

High sodium intake differentially impacts brachial artery dilation when evaluated with reactive versus active hyperemia in salt resistant individuals

This study sought to determine if high sodium (HS) intake in salt resistant (SR) individuals attenuates upper limb arterial dilation in response to reactive (occlusion) and active (exercise) hyperemia, two stimuli with varying vasodilatory mechanisms, and the role of oxidative stress in this response. Ten young, SR participants (9 males, 1 female) consumed a 7-day HS (6,900 mg/day) and a 7-day recommended sodium intake (RI: 2,300 mg/day) diet in a randomized order. On the last day of each diet, brachial artery (BA) function was evaluated via reactive (RH-FMD: 5 min of cuff occlusion) and active [handgrip (HG) exercise] hyperemia after consumption of both placebo (PL) and antioxidants (AO). The HS diet significantly elevated sodium excretion (P < 0.05), but mean arterial blood pressure was unchanged. During the PL condition, the HS diet significantly reduced RH-FMD when compared with RI diet (P = 0.01), but this reduction was significantly restored (P = 0.01) when supplemented with AO (HS + PL: 5.9 ± 3.4; HS + AO: 8.2 ± 2.7; RI + PL: 8.9 ± 4.7; RI + AO: 7.0 ± 2.1%). BA shear-to-dilation slopes, evaluated across all HG exercise workloads, were not significantly different across sodium intervention or AO supplementation. In SR individuals, HS intake impaired BA function when assessed via RH-FMD, but was restored with acute AO consumption suggesting oxidative stress as a contributor to this dysfunction. However, exercise-induced BA dilation was unaltered, potentially implicating an inability of HS intake to influence the mechanisms responsible for effectively maintaining skeletal muscle perfusion during exercise.NEW & NOTEWORTHY This study examined if high sodium (HS) intake in salt resistant (SR) individuals attenuates brachial artery (BA) flow-mediated dilation in response to reactive (occlusion) and active (exercise) hyperemia. In SR individuals, HS intake impaired reactive hyperemia-induced BA dilation, but not exercise-induced BA dilation. This finding suggests that although brachial artery nitric oxide bioavailability may be reduced following HS intake, the redundant mechanisms associated with adequate upper limb blood flow regulation during exercise are maintained.

Impact of Interrepetition Rest on Muscle Blood Flow and Exercise Tolerance during Resistance Exercise

Background and Objectives: Muscle blood flow is impeded during resistance exercise contractions, but immediately increases during recovery. The purpose of this study was to determine the impact of brief bouts of rest (2 s) between repetitions of resistance exercise on muscle blood flow and exercise tolerance. Materials and Methods: Ten healthy young adults performed single-leg knee extension resistance exercises with no rest between repetitions (i.e., continuous) and with 2 s of rest between each repetition (i.e., intermittent). Exercise tolerance was measured as the maximal power that could be sustained for 3 min (PSUS) and as the maximum number of repetitions (Reps80%) that could be performed at 80% one-repetition maximum (1RM). The leg blood flow, muscle oxygenation of the vastus lateralis and mean arterial pressure (MAP) were measured during various exercise trials. Alpha was set to p ≤ 0.05. Results: Leg blood flow was significantly greater, while vascular resistance and MAP were significantly less during intermittent compared with continuous resistance exercise at the same power outputs (p < 0.01). PSUS was significantly greater during intermittent than continuous resistance exercise (29.5 ± 2.1 vs. 21.7 ± 1.2 W, p = 0.01). Reps80% was also significantly greater during intermittent compared with continuous resistance exercise (26.5 ± 5.3 vs. 16.8 ± 2.1 repetitions, respectively; p = 0.02), potentially due to increased leg blood flow and muscle oxygen saturation during intermittent resistance exercise (p < 0.05). Conclusions: In conclusion, a brief rest between repetitions of resistance exercise effectively decreased vascular resistance, increased blood flow to the exercising muscle, and increased exercise tolerance to resistance exercise.

From heart to muscle: pathophysiological mechanisms underlying long-term physical sequelae from SARS-CoV-2 infection

The long-term sequelae of the coronavirus disease 2019 (COVID-19) are multifaceted and, besides the lungs, impact other organs and tissues, even in cases of mild infection. Along with commonly reported symptoms such as fatigue and dyspnea, a significant proportion of those with prior COVID-19 infection also exhibit signs of cardiac damage, muscle weakness, and ultimately, poor exercise tolerance. This review provides an overview of evidence indicating cardiac impairments and persistent endothelial dysfunction in the peripheral vasculature of those previously infected with COVID-19, irrespective of the severity of the acute phase of illness. In addition, V̇o2peak appears to be lower in convalescent patients, which may stem, in part, from alterations in O2 transport such as impaired diffusional O2 conductance. Together, the persistent multi-organ dysfunction induced by COVID-19 may set previously healthy individuals on a trajectory towards frailty and disease. Given the large proportion of individuals recovering from COVID-19, it is critically important to better understand the physical sequelae of COVID-19, the underlying biological mechanisms contributing to these outcomes, and the long-term effects on future disease risk. This review highlights relevant literature on the pathophysiology post-COVID-19 infection, gaps in the literature, and emphasizes the need for the development of evidence-based rehabilitation guidelines.

Blood flow restriction in the presence or absence of muscle contractions does not preserve vasculature structure and function following 14-days of limb immobilization

PURPOSE

Limb immobilization causes local vasculature to experience detrimental adaptations. Simple strategies to increase blood flow (heating, fidgeting) successfully prevent acute (≤ 1 day) impairments; however, none have leveraged the hyperemic response over prolonged periods (weeks) mirroring injury rehabilitation. Throughout a 14-day unilateral limb immobilization, we sought to preserve vascular structure and responsiveness by repeatedly activating a reactive hyperemic response via blood flow restriction (BFR) and amplifying this stimulus by combining BFR with electric muscle stimulation (EMS).

METHODS

Young healthy adults (M:F = 14:17, age = 22.4 ± 3.7 years) were randomly assigned to control, BFR, or BFR + EMS groups. BFR and BFR + EMS groups were treated for 30 min twice daily (3 × 10 min ischemia-reperfusion cycles; 15% maximal voluntary contraction EMS), 5 days/week (20 total sessions). Before and after immobilization, artery diameter, flow-mediated dilation (FMD) and blood flow measures were collected in the superficial femoral artery (SFA).

RESULTS

Following immobilization, there was less retrograde blood velocity (+ 1.8 ± 3.6 cm s^-1, P = 0.01), but not retrograde shear (P = 0.097). All groups displayed reduced baseline and peak SFA diameter following immobilization (- 0.46 ± 0.41 mm and - 0.43 ± 0.39 mm, P < 0.01); however, there were no differences by group or across time for FMD (% diameter change, shear-corrected, or allometrically scaled) nor microvascular function assessed by peak flow capacity.

CONCLUSION

Following immobilization, our results reveal (1) neither BFR nor BFR + EMS mitigate artery structure impairments, (2) intervention-induced shear stress did not affect vascular function assessed by FMD, and (3) retrograde blood velocity is reduced at rest offering potential insight to mechanisms of flow regulation. In conclusion, BFR appears insufficient as a treatment strategy for preventing macrovascular dysfunction during limb immobilization.