Steady-state Exercise Research Articles

Exaggerated pressor responses, but unaltered blood flow regulation and functional sympatholysis during lower limb exercise in young, non-Hispanic black males.

Young non-Hispanic black (BL) males have displayed lower blood flow (BF) and vascular conductance (VC), but intact functional sympatholysis, during upper limb exercise when compared to non-Hispanic white (WH) males. This study sought to explore if similar differences were also present in the lower limbs. Thirteen young BL males and thirteen WH males completed one visit comprised of rhythmic lower limb (plantar flexion) exercise as well as upper limb (handgrip) exercise for a limb-specific comparison. Limb BF, mean arterial pressure (MAP), and VC were evaluated at three submaximal workloads (8, 16, and 24kg). To determine potential limb differences in functional sympatholysis, the impact of sympathetic nervous system activation (via cold-pressor test (CPT)) was evaluated at rest and during steady state exercise (30% of maximal voluntary contraction) on a subsequent visit. MAP responses to lower and upper limb exercise were elevated in young BL males (vs WH males), resulting in significantly lower VC responses in the upper limb, but not the lower limb. Further, BL males, when compared to WH males, revealed no differences in functional sympatholysis, evident by similar responses in both the exercising leg and arm VC during CPT. The findings of the current study indicate that although elevated MAP responses were observed during both lower and upper limb exercise in young BL males, vascular conductance was only hindered in the upper limbs. This may potentially highlight enhanced compensatory mechanisms in the lower limb (vs upper limb) to maintain perfusion in young BL males.

Alterations of pulmonary vascular afterload in exercise‐induced pre‐ and post‐capillary pulmonary hypertension

Exercise imposes increased pulmonary vascular afterload based on rises in pulmonary artery (PA) wedge pressure, declines in PA compliance, and resistance-compliance time. In health, afterload stress stabilizes during steady-state exercise. Our objective was to examine alterations of these exercise-associated stresses in states of pre- and post-capillary pulmonary hypertension (PH). PA hemodynamics were evaluated at rest, 2 and 7min of steady-state exercise at moderate intensity in patients who exhibited Pre-capillary (n=22) and post-capillary PH (n=22). Patients with normal exercise hemodynamics (NOR-HD) (n=32) were also studied. During exercise in all groups, PA wedge pressure increased at 2min, with no further change at 7min. In post-capillary PH and NOR-HD, increases in PA diastolic pressure and diastolic pressure gradient remained stable at 2 and 7min of exercise, while in pre-capillary PH, both continued to increase at 7 min. The behavior of the diastolic pressure gradient was linearly related to the duration of resistance-compliance time at rest (r2 =0.843) and exercise (r2 =0.760). Exercise resistance-compliance time was longer in pre-capillary PH associated with larger increases in diastolic pressure gradient. Conversely, resistance-compliance time was shortest in post-capillary PH compared to pre-capillary PH and NOR-HD and associated with limited increases in exercise diastolic pressure gradient. During steady-state, modest-intensity exercise-specific patterns of pulmonary vascular afterload responses were observed in pre- and post-capillary PH relative to NOR-HD. Longer resistance-compliance time related to greater increases in PA diastolic pressure and diastolic pressure gradients in pre-capillary PH, while shorter resistance-compliance time appeared to limit these increases in post-capillary PH.

Performing Dynamic Weight-Shifting Balance Exercises With a Smartphone-Based Wearable Telerehabilitation System for Home Use by Individuals With Parkinson's Disease: A Proof-of-Concept Study.

Telerehabilitation technology often helps individuals with Parkinson's disease (PD) to control their balance and improve postural stability. This proof-of-concept study describes the redesign of a smartphone-based wearable balance rehabilitation system, or Smarter Balance System (SBS) intended for in-home use, and determines the number of exercise sessions required to achieve steady-state balance exercise performance by people with PD who performed 6 weeks of in-home dynamic weight-shifting balance exercises. The redesigned SBS supplied real-time multimodal (visual and vibrotactile) biofeedback during dynamic weight-shifting balance exercises (WSBEs). A Technology Acceptance Model (TAM) questionnaire completed by participants validated its acceptability and use. The results of regression analyses of participants' balance exercise performance, based on the average cross-correlations and absolute position errors between the target motion and the exerciser's motion, showed exponential trends, a performance plateau after 3 weeks, and a quasi-steady state performance by the end of 6 consecutive weeks.

Inorganic nitrate supplementation may improve diastolic function and the O2 cost of exercise in cancer survivors: a pilot study

In non-cancer populations, inorganic dietary nitrate (NO3-) supplementation is associated with enhanced cardiorespiratory function but remains untested in patients with a history of cancer. Therefore, this pilot study sought to determine if oral NO3- supplementation, as a supportive care strategy, increases left ventricular (LV) function and exercise performance in survivors of cancer treated with anticancer therapy while simultaneously evaluating the feasibility of the methods and procedures required for future large-scale randomized trials. Two cohorts of patients with a history of cancer treated with anticancer chemotherapy were recruited. Patients in cohort 1 (n = 7) completed a randomized, double-blind, crossover study with 7days of NO3- or placebo (PL) supplementation, with echocardiography. Similarly, patients in cohort 2 (n = 6) received a single, acute dose of NO3- supplementation or PL. Pulmonary oxygen uptake (VO2), arterial blood pressure, and stroke volume were assessed during exercise. In cohort 1, NO3- improved LV strain rate in early filling (mean difference (MD) [95% CI]: - 0.3 1/s [- 0.6 to 0.06]; P = 0.04) and early mitral septal wall annular velocity (MD [95% CI]: 0.1m/s [- 0.01 to - 0.001]; P = 0.02) compared to placebo. In cohort 2, NO3- decreased the O2 cost of low-intensity steady-state exercise (MD [95% CI]: - 0.5ml/kg/min [- 0.9 to - 0.09]; P = 0.01). Resting and steady-state arterial blood pressure and stroke volume were not different between conditions. No differences between conditions for peak VO2 (MD [95% CI]: - 0.7ml/kg/min [- 3.0 to 1.6]; P = 0.23) were observed. The findings from this pilot study warrant further investigation in larger clinical trials targeting the use of long-term inorganic dietary NO3- supplementation as a possible integrative supportive care strategy in patients following anticancer therapy.

Measurement of thermal sweating at rest and steady-state exercise in healthy adults: Inter-day reliability and relationships with components of partitional calorimetry.

Inter-day reliability of sweat measurements, including the absorbent patch and modified iodine-paper techniques, at rest and exercise were evaluated. We further evaluated the effect of iodine paper size and the method of establishing sweat gland activation (sweat gland counting or surface area covered) on reliability. Furthermore, the relationships between all measurement techniques and metabolic heat production [Ḣprod] and evaporative requirement for heat balance [Ėreq] were determined. Twelve participants were assessed for whole-body sweat loss (WBSL), local sweat rate (LSR; absorbent patch) and sweat gland activation (SGA; iodine-paper) during rest and sub-maximal cycling at ~200, ~250 and ~300 W/m2 Ḣprod in the heat. Variations in iodine paper (1 x 1 cm-9 x 9 cm) were used to quantify SGA by counting sweat glands or surface area covered. The 'optimal' area of SGA was also determined based on the highest density of recruited glands. All measures of the sweating response were positively related with Ḣprod and Ėreq (r = 0.53-0.84), with the 9 x 9 cm and 6 x 6 cm iodine paper sizes being the strongest (r = 0.66-0.84) for SGA. Superior inter-day reliability was found for all measures during exercise (CV% = 6-33.2) compared to rest (CV% = 33.5-77.9). The iodine-paper technique was most reliable at 9 x 9 cm (CV% = 15.9) or when the 1 x 1 cm (CV% = 17.6) and 3 x 3 cm (CV% = 15.5) optimal SGA was determined, particularly when measuring the sweat gland number. WBSL, LSR and SGA measurement techniques are sufficiently reliable to detect changes in thermal sweating typically reported. We recommend 9 x 9 cm paper sizes or 1 x 1 cm-3 x 3 cm optimal areas, using either gland counting or surface area to determine SGA.

Abstract 12714: Impact of Reduced Left Ventricular Filling Pressure on Diastolic Function During Exercise in Patients With HFpEF

Background: During exercise, patients with heart failure with preserved ejection fraction (HFpEF) have an exaggerated increase in pulmonary capillary wedge pressure (PCWP) and left atrial-left ventricular pressure gradient (E wave velocity), as well as a blunted increase in early diastolic recoil (e’ velocity). It is unknown if non-invasive markers of diastolic function improve when exercise PCWP is acutely ameliorated. Methods: Patients with invasively proven HFpEF (n = 34, 71±6 years, 59% female, PCWP > 25 or Δ15 mm hg at peak exercise) underwent 2 seated cycle exercise tests with sublingual nitroglycerin (NTG) and placebo (PLB) in a cross-over design. PCWP (right heart catheter), tissue Doppler velocities of the mitral annulus (e’) and mitral inflow velocities (E) were measured at rest and during 20-watt submaximal steady state exercise. Differences between placebo and GTN conditions were assessed by repeated measures mixed model. Results: PCWP was 7.6±3.9 mmHg at rest and 21.1±7.8 mmHg with sub-maximal exercise and was decreased by 14% and 24% respectively by NTG (Drug effect p < 0.001, Figure ). Mean E’ was 6.2±1.5 cm/sec at rest and 8.8±1.7 cm/sec during exercise and was decreased by 6% and 8% respectively by NTG (p = 0.003), but augmentation during exercise was unchanged (NTG +36%, PLB +41%, p = 0.211). The E wave velocity was 69.6±21.2 cm/sec rest and 101.9±31.3 cm/sec during exercise and was decreased by 12% and 11% with NTG respectively (p <0.001), but augmentation during exercise was unchanged (NTG +48%, PLB +46%, p = 0.507). Conclusions: NTG significantly and acutely lowered exercise PCWP in patients with HFpEF but did not improve diastolic function as assessed by echocardiography. The symmetrical slowing of E wave velocity and e’ with reduced PCWP demonstrate that higher preload helps maintain diastolic recoil and early diastolic filling for patients with HFpEF. Therapies that reduce preload in HFpEF may result in apparently worsened markers of diastolic function.

Changes in submaximal and maximal measures of cardio-respiratory fitness resulting from 6-days of mountain walking

ABSTRACT Trekking is a popular activity associated with cardiovascular benefits. The aim of the present study was to investigate changes in the submaximal heart rate, oxygen uptake, oxygen pulse, and blood lactate concentration associated with a 6-day mountain walk. Over a 12-year period, 134 male (age 21.0 ± 1.4 years) and 124 female undergraduates (age 20.8 ± 1.6 years) participated. Three days before the trek submaximal and maximal laboratory measures were made on participants walking on a motorized treadmill using a breath-by-breath system to measure oxygen uptake (VO2) during exercise. Oxygen uptake and heart rate were recorded during steady-state exercise at treadmill gradients 0, 4, 8, 12, and 16%. Measurements were made, at the same time of day, two days after the trek. There were significant improvements in both the walking economy and the relative exercise intensity (%VO2max) at submaximal treadmill gradients 0-16%. Post-trek, heart rate was lower while oxygen pulse was higher, at each treadmill gradient. There was a significant increase in the maximal oxygen uptake for men (+2.7%) and women (+2.9%). The results of the present study suggest that improvements in cardiorespiratory fitness are associated with a 6-day mountain walk with no sex difference in the exercise response. .

Fuel Selection in Skeletal Muscle Exercising at Low Intensity; Reliance on Carbohydrate in Very Sedentary Individuals.

Background: Resting skeletal muscle in insulin resistance prefers to oxidize carbohydrate rather than lipid, exhibiting metabolic inflexibility. Although this is established in resting muscle, complexities involved in directly measuring fuel oxidation using indirect calorimetry across a muscle bed have limited studies of this phenomenon in working skeletal muscle. During mild exercise and at rest, whole-body indirect calorimetry imperfectly estimates muscle fuel oxidation. We provide evidence that a method termed "ΔRER" can reasonably estimate fuel oxidation in skeletal muscle activated by exercise. Methods: Completely sedentary volunteers (n = 20, age 31 ± 2 years, V̇O2peak 24.4 ± 1.5 mL O2 per min/kg) underwent glucose clamps to determine insulin sensitivity and graded exercise consisting of three periods of mild steady-state cycle ergometry (15, 30, 45 watts, or 10%, 20%, and 30% of maximum power) with measurements of whole-body gas exchange. ΔRER, the RER in working muscle, was calculated as (V̇CO2exercise -V̇CO2rest)/(V̇O2exercise - V̇O2rest), from which the fraction of fuel accounted for by lipid was estimated. Results: Lactate levels were low and stable during steady-state exercise. Muscle biopsies were used to estimate mitochondrial content. The rise of V̇O2 at onset of exercise followed a monoexponential function, with a time constant of 51 ± 7 sec, typical of skeletal muscle; the average O2 cost of work was about 12 mL O2/watt/min, representing a mechanical efficiency of about 24%. At work rates of 30 or 45 watts, active muscle relied predominantly on carbohydrate, independent of insulin sensitivity within this group of very sedentary volunteers. Conclusions: The fraction of muscle fuel oxidation from fat was predicted by power output (P < 0.001) and citrate synthase activity (P < 0.05), indicating that low mitochondrial content may be the main driver of fuel choice in sedentary people, independent of insulin sensitivity.

Ketone Ester Plus Carbohydrate Supplementation Impairs Physical Performance And Decreases Glucose Turnover Versus Carbohydrate Alone

BACKGROUND: Ketone esters combined with carbohydrate have been reported to enhance physical performance compared to carbohydrate alone. Improvements in physical performance are suggested to result from sparing of glucose for fuel use during exercise; however, no studies have examined the effect of ketone supplementation on glucose kinetics. PURPOSE: Determine the effect of ketone ester plus carbohydrate (KE + CHO) supplementation on physical performance and glucose kinetics during steady-state aerobic exercise. METHODS: Twelve men (mean ± SD; 29 ± 5 y, 26 ± 3 kg/m2) completed this randomized, double-blind, crossover study. After controlling exercise and diet for 48 h, participants consumed a KE + CHO (KE: 573 mg KE/kg body mass, CHO: 110 g glucose) or CHO (110 g glucose) drink before and during 90 min of steady-state treadmill exercise (54 ± 3 % VO2peak) with a weighted vest (30% body mass; 25 ± 3 kg). Glucose kinetics during exercise were determined using indirect calorimetry and tracer techniques ([6,6-2H2] glucose and 13C glucose). Participants performed an unweighted time to exhaustion test (TTE; 85 % VO2peak) following steady-state exercise. After 24 h of controlled feeding, participants consumed a bolus of KE + CHO or CHO and completed a weighted 4-mile time trial (TT; 25 ± 3 kg). RESULTS: β-hydroxybutyrate concentrations were higher (P < 0.05) after exercise (2.3 ± 0.8 vs. 0.1 ± 0.1 mM) and the TT (2.7 ± 0.8 vs. 0.1 ± 0.1 mM) in KE + CHO than CHO. TTE was lower (761 ± 429 vs. 865 ± 458 sec) and TT performance was slower (55.0 ± 7.4 vs. 52.9 ± 6.6 min) in KE + CHO than CHO (P < 0.05). Exogenous (0.5 ± 0.1 vs. 0.5 ± 0.1 g/min) and plasma (0.6 ± 0.1 vs. 0.6 ± 0.1 g/min) glucose oxidation rates in the last 40 min of steady-state exercise were the same between KE + CHO and CHO (P > 0.05). Glucose rate of appearance (6.5 ± 1.4 vs. 7.0 ± 1.6 mg/kg/min) and disappearance (6.7 ± 1.3 vs. 7.2 ± 1.6 mg/kg/min) during steady-state exercise was lower (P < 0.05) in KE + CHO than CHO, and metabolic clearance rate (MCR) did not differ between treatments (10.5 ± 3.0 vs. 10.1 ± 3.4 mL/kg/min; P > 0.05). CONCLUSION: KE + CHO impaired TT and TTE performance compared to CHO alone. Though glucose turnover was lower, similar rates of exogenous glucose oxidation and MCR during steady-state exercise in KE + CHO and CHO suggests performance decrements occur independent of glucose kinetics.

Influence Of Cardiac Output Response To The Onset Of Exercise On Cerebral Blood Flow

It is reported that the changes in cardiac output (Q) contribute to cerebral blood flow (CBF) regulation at rest and even during steady-state exercise. At the onset of cycling exercise, cardiac output (Q) increases acutely and largely via muscle pump, which may cause a larger elevation in CBF than an adequate value. However, the relationship between Q and CBF at the onset of exercise remains unknown. PURPOSE: The purpose of the present study was to examine whether onset exercise-induced large increase in Q contributes to CBF regulation at the onset of exercise. METHODS: In 11 young healthy participants, Q, mean arterial pressure (MAP), and mean blood velocities of middle and posterior cerebral arteries (MCA Vm and PCA Vm, respectively) were continuously measured during a 3-min light cycling exercise at 20 W on the ergometer. RESULTS: At the onset of exercise, Q increased acutely to the peak (P < 0.001), while MCA Vm and PCA Vm had two nadir and peak responses, but these CBF changes were not significant (MCA Vm and PCA Vm; P = 0.461 and P = 0.125, respectively). The change in Q was correlated with that of MCA Vm or PCA Vm from resting baseline to the steady-state exercise (r = 0.371, P = 0.008 and r = 0.418, P = 0.003, respectively). However, interestingly, the change in Q was not correlated with that of MCA Vm or PCA Vm at the onset of exercise (P = 0.223 and P = 0.151, respectively). CONCLUSION: These findings indicate that the change in Q does not contribute to CBF regulation at the onset of exercise for protecting cerebral vasculature against a large and acute elevation in Q at the onset of exercise.

Acute high-intensity interval exercise is less pro-oxidative/thrombotic compared to isovolumic moderate-intensity steady-state exercise.

While high-intensity interval training (HIIT) has emerged as a more time-efficient alternative to moderate-intensity steady-state exercise (MISS), the impact on systemic free radical formation and link to activated coagulation remains unknown. We recruited sixteen healthy males aged 21 ± 3 y who performed incremental cycle ergometry to determine peak oxygen uptake ([Formula: see text] PEAK). Participants were randomly assigned single blind to two separate groups (MISS: n = 8; HIIT: n = 8) matched for [Formula: see text] PEAK. HIIT participants completed five exercise cycles, each consisting of 3min at 80%[Formula: see text] PEAK alternating with 3min at 40% [Formula: see text] PEAK, whereas MISS participants performed an isovolumic bout of 30min at 60% [Formula: see text] PEAK. Cephalic venous blood was assayed for ascorbate free radical (A•-, electron paramagnetic resonance spectroscopy) and clot fractal dimension (df, rheometry) at rest every hour over a 6-h period to determine critical difference (CD) and before/after submaximal/peak exercise. Submaximal MISS increased A• - and df to a greater extent compared to HIIT (P = 0.039 to 0.057) although elevations generally fell within CD boundaries (54.2% and 5.5% respectively). No further elevations were observed during peak exercise (P = 0.508 to 0.827) and no relationships were observed between A•- and df (r = 0.435 to - 0.121, P = 0.092 to 0.655). Collectively, these findings suggest that HIIT is less pro-oxidative/thrombotic compared to more traditional MISS, advocating its prescription in patients given the potential for superior vascular adaptive benefit.

Limits to submaximal and maximal exercise in patients with hypertrophic cardiomyopathy.

Patients with hypertrophic cardiomyopathy (HCM) often have reduced exercise capacity, and it is unclear whether cardiovascular regulation during exercise is intact in these patients. We aimed to determine the relationship between cardiac output (Q̇c) and oxygen uptake (V̇o2), and stroke volume (SV) reserve in HCM compared with healthy participants and participants with left ventricular hypertrophy (LVH) but not HCM. Sixteen patients with HCM (48 ± 7 yr, 44% female), 16 participants with LVH (49 ± 5 yr, 44% female), and 61 healthy controls (CON: 52 ± 5 yr, 52% female) completed submaximal steady-state treadmill exercise followed by a maximal exercise test. V̇o2, Q̇c, SV, and arteriovenous oxygen difference were measured during rest and exercise, and Q̇c/V̇o2 slopes were constructed, The Q̇c/V̇o2 slope was blunted in HCM compared with CON and LVH [HCM 4.9 ± 0.7 vs. CON 5.5 ± 1.0 (P = 0.027) vs. LVH 6.0 ± 1.0 AU (P = 0.002)] and participants with HCM had a lower SV reserve (HCM 53 ± 33%, controls 83 ± 33%, LVH 82 ± 22%; HCM vs. controls P = 0.002; HCM vs. LVH P = 0.015). Despite a blunted Q̇c/V̇o2 slope, 75% of patients with HCM achieved ≥80% predicted V̇o2max by augmenting a-vo2 difference at maximal exercise (16.0 ± 0.8 mL/100 mL vs. 13.8 ± 2.7 mL/100 mL, P = 0.021). Patients with HCM do not appropriately match Q̇c to metabolic demand, primarily due to inadequate stroke volume augmentation. Despite this central limitation, many patients achieve normal exercise capacities by significantly increasing peripheral oxygen extraction.NEW & NOTEWORTHY Through state-of-the-art hemodynamic and oxygen uptake methodologies, this study found the cardiac output response to increasing metabolic demand is blunted among patients with hypertrophic cardiomyopathy (HCM), primarily due to a reduced stroke volume reserve. Many patients with HCM augment their peripheral oxygen extraction during maximal exercise to achieve normal exercise capacity and overcome ineffective matching of cardiac output. Peripheral adaptations that compensate for cardiac limitations may contribute to the heterogeneity of functional limitations observed within this patient population.

Motorless cadence control of standard and low duty cycle-patterned neural stimulation intensity extends muscle-driven cycling output after paralysis

BackgroundStimulation-driven exercise is often limited by rapid fatigue of the activated muscles. Selective neural stimulation patterns that decrease activated fiber overlap and/or duty cycle improve cycling exercise duration and intensity. However, unequal outputs from independently activated fiber populations may cause large discrepancies in power production and crank angle velocity among pedal revolutions. Enforcing a constant cadence through feedback control of stimulus levels may address this issue and further improve endurance by targeting a submaximal but higher than steady-state exercise intensity.MethodsSeven participants with paralysis cycled using standard cadence-controlled stimulation (S-Cont). Four of those participants also cycled with a low duty cycle (carousel) cadence-controlled stimulation scheme (C-Cont). S-Cont and C-Cont patterns were compared with conventional maximal stimulation (S-Max). Outcome measures include total work (W), end power (Pend), power fluctuation (PFI), charge accumulation (Q) and efficiency (η). Physiological measurements of muscle oxygenation (SmO2) and heart rate were also collected with select participants.ResultsAt least one cadence-controlled stimulation pattern (S-Cont or C-Cont) improved Pend over S-Max in all participants and increased W in three participants. Both controlled patterns increased Q and η and reduced PFI compared with S-Max and prior open-loop studies. S-Cont stimulation also delayed declines in SmO2 and increased heart rate in one participant compared with S-Max.ConclusionsCadence-controlled selective stimulation improves cycling endurance and increases efficiency over conventional stimulation by incorporating fiber groups only as needed to maintain a desired exercise intensity. Closed-loop carousel stimulation also successfully reduces power fluctuations relative to previous open-loop efforts, which will enable neuroprosthesis recipients to better take advantage of duty cycle reducing patterns.

Dihydrocapsiate does not increase energy expenditure nor fat oxidation during aerobic exercise in men with overweight/obesity: a randomized, triple-blinded, placebo-controlled, crossover trial.

ABSTRACTBackgroundPrior evidence suggests that capsinoids ingestion may increase resting energy expenditure (EE) and fat oxidation (FATox), yet whether they can modulate those parameters during exercise conditions remains poorly understood. We hypothesized that dihydrocapsiate (DHC) ingestion would increase EE and specifically FATox during an acute bout of aerobic exercise at FATmax intensity (the intensity that elicits maximal fat oxidation during exercise [MFO]) in men with overweight/obesity. Since FATmax and MFO during aerobic exercise appear to be indicators of metabolic flexibility, whether DHC has an impact on FATox in this type of population is of clinical interest.MethodsA total of 24 sedentary men (age = 40.2 ± 9.2 years-old; body mass index = 31.6 ± 4.5 kg/m2 [n = 11 overweight, n = 13 obese]) participated in this randomized, triple-blinded, placebo-controlled, crossover trial (registered under ClinicalTrials.gov Identifier no. NCT05156697). On the first day, participants underwent a submaximal exercise test on a cycle ergometer to determine their MFO and FATmax intensity during exercise. After 72 hours had elapsed, the participants returned on 2 further days (≥ 72 hours apart) and performed a 60 min steady-state exercise bout (i.e. cycling at their FATmax, constant intensity) after ingesting either 12 mg of DHC or placebo; these conditions were randomized. Respiratory gas exchange was monitored by indirect calorimetry. Serum marker concentrations (i.e. glucose, triglycerides, non-esterified fatty acids (NEFAs), skin temperature, thermal perception, heart rate, and perceived fatigue) were assessed.ResultsThere were no significant differences (P > 0.05) between DHC and placebo conditions in the EE and FATox during exercise. Similarly, no significant changes were observed in glucose, triglycerides, or NEFAs serum levels, neither in the skin temperature nor thermal perception across conditions. Heart rate and perceived fatigue did not differ between conditions.ConclusionsDHC supplementation does not affect energy metabolism during exercise in men with overweight/obesity.

Validation of Accelerometer-Based Estimations of Energy Expenditure During High-Intensity Interval Training

Accelerometers are used to assess free-living physical activity (PA) and energy expenditure (EE). Energy expenditure estimation algorithms have been calibrated using steady-state exercise. However, most free-living PA is not steady-state. Objective: The purpose of this study was to discern the differences between criterion-measured and accelerometer-estimated EE (kCals) during a non-steady-state High-Intensity Interval Training (HIIT) session. Methods: Recreationally active adults (N=29, 18-30 years) completed one of two HIIT protocols. Each participant wore ActiGraph GT3X+ accelerometers on the right hip and non-dominant wrist while EE was measured using portable indirect calorimetry. Data analysis was conducted using custom R scripts and bias [95% CIs] to determine significant differences between indirect calorimetry and EE estimates using previously developed algorithms. Results: All accelerometer algorithms underestimated EE during recovery intervals (range; -4.31 to -6.55 kCals) and overestimated EE during work intervals (0.57 to 5.70 kcals). Over the whole HIIT session, only the Hildebrand wrist method was not significantly different from the criterion measured EE. Conclusion: Current ActiGraph EE estimations based on steady-state activities underestimate EE during recovery periods of treadmill HIIT sessions. Future studies should investigate accelerometer signals immediately after high-intensity bouts to more accurately predict EE of the subsequent recovery period. KEYWORDS: ActiGraph; Accelerometer; HIIT; Indirect calorimetry; EPOC; Energy expenditure; Non-steady state; Calories

Influence of cardiac output response to the onset of exercise on cerebral blood flow.

Change in cardiac output (Q) contributes to cerebral blood flow (CBF) regulation at rest and even during steady-state exercise. At the onset of cycling exercise, Q increases acutely and largely via muscle pump. The purpose of the present study was to examine whether onset exercise-induced a large increase in Q contributes to CBF regulation at the onset of exercise. In 20 young healthy participants (10 males and 10 females), Q, mean arterial pressure (MAP), and mean blood velocities of middle and posterior cerebral arteries (MCA Vm and PCA Vm) were continuously measured during light cycling exercise for 3min. At the onset of exercise, Q increased acutely to the peak (P < 0.001), while the CBF peak responses were not significantly higher than the values during the steady-state exercise (MCA Vm and PCA Vm; P = 0.183 and P = 0.101, respectively). The change in Q was correlated with that of MCA Vm or PCA Vm from resting baseline to the steady-state exercise (r = 0.404, P < 0.001 and r = 0.393, P < 0.001, respectively). However, the change in Q was not correlated with that of MCA Vm or PCA Vm at the onset of exercise (P = 0.853 and P = 0.893, respectively). Any sex differences in the onset response of peripheral and cerebral hemodynamics to exercise were not observed. These findings suggest that the acute change in Q does not contribute to CBF regulation at the onset of exercise for protecting cerebral vasculature against a large and acute elevation in Q at the onset of exercise.

Effect of steady-state aerobic exercise intensity and duration on the relationship between reserves of heart rate and oxygen uptake.

BackgroundThe percentages of heart rate (%HRR) or oxygen uptake (%V̇O2R) reserve are used interchangeably for prescribing aerobic exercise intensity due to their assumed 1:1 relationship, although its validity is debated. This study aimed to assess if %HRR and %V̇O2R show a 1:1 relationship during steady-state exercise (SSE) and if exercise intensity and duration affect their relationship.MethodsEight physically active males (age 22.6 ± 1.2 years) were enrolled. Pre-exercise and maximal HR and V̇O2 were assessed on the first day. In the following 4 days, different SSEs were performed (running) combining the following randomly assigned durations and intensities: 15 min, 45 min, 60% HRR, 80% HRR. Post-exercise maximal HR and V̇O2 were assessed after each SSE. Using pre-exercise and post-exercise maximal values, the average HR and V̇O2 of the last 5 min of each SSE were converted into percentages of the reserves (%RES), which were computed in a 3-way RM-ANOVA (α = 0.05) to assess if they were affected by the prescription parameter (HRR or V̇O2R), exercise intensity (60% or 80% HRR), and duration (15 or 45 min).ResultsThe %RES values were not affected by the prescription parameter (p = 0.056) or its interactions with intensity (p = 0.319) or duration and intensity (p = 0.117), while parameter and duration interaction was significant (p = 0.009). %HRRs and %V̇O2Rs did not differ in the 15-min SSEs (mean difference [MD] = 0.7 percentage points, p = 0.717), whereas %HRR was higher than %V̇O2R in the 45-min SSEs (MD = 6.7 percentage points, p = 0.009).ConclusionSSE duration affects the %HRR-%V̇O2R relationship, with %HRRs higher than %V̇O2Rs in SSEs of longer duration.

A Short-Term Eccentric HIIT Induced Greater Reduction in Cardio-Metabolic Risk Markers in Comparison With Concentric HIIT in Sedentary Overweight Men

ABSTRACT Background: Steady-state eccentric exercise training improves cardiometabolic risk (CMR) despite lesser cardiovascular demands compared with load-matched concentric training. Whether a high-intensity interval eccentrictraining is also effective reducing CMR is unknown.Aim: To compare the effects of a short-term high-intensity interval eccentric training (ECC-HIIT) with high-intensity interval concentric training (CONC-HIIT) on CMR in sedentary overweight men.Methods: Twenty men (age: 27.9 ± 5.3y, body massindex: 29.1 ± 3.1 kg·m−2) were randomly assigned to ECC-HIIT (n = 10) or CONC-HIIT (n = 10) delivered as six sessions, including 4 x 5:2 min work-to-rest ratio, at 80% peak concentric power output. Heart rate (HR), rate of perceived exertion (RPE) and muscle soreness weremonitored during training sessions. Training effects on lipid profile, insulin sensitivity (HOMA-IR), body composition, thigh circumference, isometric knee extensors maximal strength, resting systolic and diastolic blood pressure (SBP and DBP) were determined.Results: Average training HR and RPE were −29%and −50%lower in ECC-HIIT in comparison with CONC-HIIT. Muscle soreness was initially greater after ECC-HIIT compared with CONC-HIIT. Significant changes in total and low-density lipoprotein cholesterol (−7.0 ± 8.7%; p = .02 and −6.3 ± 14.4%; p = .03), SBP (−9.8 ± 7.8%; p = .002), and maximal thigh circumference (+2.5 ± 3.1%; p = .02) were observed following ECC-HIIT. No changes in any CMR marker were observed after CONC-HIIT. Moderate-to-large training effect sizes were obtained in thigh circumference, SBP, total cholesterol and low-density lipoprotein cholesterol in response to ECC-HIIT.Conclusion: A two-week ECC-HIIT was well-tolerated and induced rapid onset improvements in cholesterol and blood pressure compared to conventional CONC-HIIT in sedentary overweight men.

Effects of nasal breathing on partial pressure of carbon dioxide in arterial blood during prolonged exercise in a hot environment

Prolonged exercise in a hot environment increases the minute ventilation (VE) and respiratory rate (RR) with an increase in core temperature. This hyperthermia-induced hyperventilation decreases the partial pressure of arterial blood carbon dioxide (PaCO2). Conversely, nasal breathing during exercise has been reported to produce low VE and RR values and high PaCO2 values; however, no studies have investigated this in hot environments. Therefore, the purpose of this study was to clarify the effect of nasal breathing on estimated partial pressure of carbon dioxide in arterial blood (PaCO2,estimate) during prolonged exercise in a hot environment. Twelve university endurance athletes participated in the study and performed a 40-minutes steady-state cycling exercise at an intensity of 55% of peak oxygen uptake in a hot environment (room temperature 35℃, relative humidity 40%). Using randomized crossover design, two experiments were performed—nasal breathing condition (NB) and mouth breathing condition (MB). Moreover, physiological indices were measured during the exercise. Rectal temperature increased in both conditions, but there was no significant difference between these conditions. PaCO2,estimate values were significantly higher in NB between 10 minutes and 40 minutes of exercise (p < 0.05) compared to MB, and decreased with time in MB. Compared to MB, the VE was significantly lower in NB between 30 minutes and 40 minutes (p < 0.05), while the RR was significantly lower in NB between 25 minutes and 40 minutes of exercise (p < 0.05). Therefore, nasal breathing during a prolonged moderate-intensity exercise in a hot environment prevented the decrease in PaCO2,estimate due to hyperthermia-induced hyperventilation.

Secondary Analysis of Walking Activities during the Acute Stroke Hospital Stay and Cerebrovascular Health.

Physical activity within the hospital post-stroke is recommended for cardiovascular and musculoskeletal health, but no studies have examined cerebrovascular health. We hypothesized individuals who walked farther distances (FARhigh) during the acute phase of stroke recovery in a hospital setting would have a higher resting middle cerebral artery blood velocity (MCAv) and a greater cerebrovascular response (CVR) to moderate-intensity exercise at 3-months post-stroke, compared to individuals who walked shorter distances (FARlow). At 3-month post-stroke, we recorded 90-seconds of resting baseline (BL) MCAv followed by 6-minutes of moderate-intensity exercise. We calculated CVR as the change in MCAv from BL to steady-state exercise. We retrospectively collected farthest distance walked within the hospital post-stroke from the electronic medical record. Participants were classified as FARhigh or FARlow based on average farthest walking distance. Twenty participants completed the study, age 63 (15) years. BL MCAv was not different between groups (p = 0.07). In comparison to FARlow, we report a higher CVR in FARhigh's ipsilesional ( = 7.38 (5.42) vs = 2.19 (3.53), p = 0.02) and contralesional hemisphere ( = 8.15 (6.37) vs = 2.06 (4.76), p = 0.04). Physical activity during the hospital stay post-stroke may support cerebrovascular health after discharge. Prospective studies are needed to support this finding.