Robert Boushel

University of British Columbia | UBC · School of Kinesiology

The purpose of this study was to compare sex-based differences in the mean arterial blood pressure (MAP) response to limb and inspiratory metaboreflex activation, during relative and absolute workloads. Healthy males (M; n=9) and females (F; n=8) completed pulmonary function testing, forearm volume and circumference measurements, and bouts of limb...

Cardiac output (Q̇C) and leg blood flow (Q̇LEG) can be measured simultaneously with high accuracy using transpulmonary and femoral vein thermodilution with a single‐bolus injection. The invasive measure has offered important insight into leg hemodynamics and blood flow distribution during exercise. Despite being the natural modality of exercise in...

When high-intensity exercise is performed until exhaustion a "functional reserve" (FR) or capacity to produce power at the same level or higher than reached at exhaustion exists at task failure, which could be related to reactive oxygen and nitrogen species (RONS)-sensing and counteracting mechanisms. Nonetheless, the magnitude of this FR remains u...

The study aimed to determine the levels of skeletal muscle Angiotensin‐Converting Enzyme 2 (ACE2, the SARS‐CoV‐2 receptor) protein expression in men and women and assess whether ACE2 expression in skeletal muscle is associated with cardiorespiratory fitness and adiposity. The level of ACE2 in vastus lateralis muscle biopsies collected in previous s...

Key points Females have lower fatigability than males during single limb isometric and dynamic contractions, but whether sex‐differences exist during high‐intensity whole‐body exercise remains unknown. This study shows that males and females respond similarly to repeated supramaximal whole‐body exercise, and that at task failure a large functional...

Introduction Ageing is associated with vascular dysfunction and a reduced capacity of the central circulation to deliver O 2 to the contracting muscles. The purpose of present study was to investigate the role of lifelong physical activity level on vascular function and hemodynamics during whole‐body exercise. Methods Vascular function was determi...

Knowledge of the physiology of elite canoeing performance has gradually increased over the last decade, while new avenues of research on the physiology of athletic performance and the physiological responses to training are applied across a wide range of sports. This chapter builds upon previous comprehensive reviews on canoeing and provides a basi...

Sexual dimorphism is apparent in humans, however, to date no studies have investigated mitochondrial function focusing on intrinsic mitochondrial respiration (i.e., mitochondrial respiration for a given amount of mitochondrial protein) and mitochondrial oxygen affinity (p50mito) in relation to biological sex in human. A skeletal muscle biopsy was d...

As one of the most physically demanding sports in the Olympic Games, cross-country skiing poses considerable challenges with respect to both force generation and endurance during the combined upper- and lower-body effort of varying intensity and duration. The isoforms of myosin in skeletal muscle have long been considered not only to define the con...

Aim We examined the Fick components together with mitochondrial O2 affinity (p50mito) in defining O2 extraction and O2 uptake during exercise with large and small muscle mass during normoxia (NORM) and hyperoxia (HYPER). Methods Seven individuals performed two incremental exercise tests to exhaustion on a bicycle ergometer (BIKE) and two on a one‐...

Background/object: Inter-individual variability in weight loss during obesity treatment is complex and poorly understood. Here we use whole body and tissue approaches to investigate fuel oxidation characteristics in skeletal muscle fibers, cells, and distinct circulating protein biomarkers before and after a high fat meal (HFM) challenge in those...

The mechanisms that regulate bone blood flow (BBF) in humans are largely unknown. Animal studies suggest that nitric oxide (NO) could be involved and in the present study we investigated the effects of inhibition of nitric oxide synthase (NOS) alone and in combination with inhibition of cyclooxygenase (COX) enzyme, thus prostaglandin (PG) synthesis...

Introduction: High-dose recombinant human erythropoietin (rhEpo) has been shown to improve cognitive performance in both healthy volunteers and in patients suffering from diseases affecting the brain. The aim of this study was to examine whether administration of low-dose and even micro-dose rhEpo improves cognitive performance in healthy voluntee...

New Findings What is the central question of this study? Does manipulation of the work of breathing during high‐intensity exercise alter respiratory and locomotor muscle blood flow? What is the main finding and its importance? We found that when the work of breathing was reduced during exercise, respiratory muscle blood flow decreased, while locomo...

Inter-individual variation in running and cycling exercise economy (EE) remains unexplained although studied for more than a century. This study is the first to comprehensively evaluate the importance of biochemical, structural, physiological, anthropometric, and biomechanical influences on running and cycling EE within a single study. In 22 health...

To elucidate the mechanisms underlying the differences in adaptation of arm and leg muscles to sprint training, over a period of 11 days 16 untrained men performed six sessions of 4–6 × 30-s all-out sprints (SIT) with the legs and arms, separately, with a 1-h interval of recovery. Limb-specific VO2peak, sprint performance (two 30-s Wingate tests wi...

Adipose tissue metabolism and circulation play an important role in human health. It is well-known that adipose tissue mass is increased in response to excess caloric intake leading to obesity and further to local hypoxia and inflammatory signaling. Acute exercise increases blood supply to adipose tissue and mobilization of fat stores for energy. H...

With considerable interest, we are following developments concerning the increasingly popular practice of breathing oxygen (O2)-enriched air (normobaric hyperoxia) in an attempt to improve both athletic performance and recovery, especially by elite endurance athletes. Administration of supplemental O2 is not prohibited by the World Anti-Doping Age...

In the oxygen (O2) cascade downstream steps can never achieve higher flows of O2 than the preceding ones. At the lung the transfer of O2 is determined by the O2 gradient between the alveolar space and the lung capillaries and the O2 diffusing capacity (DLO2). While DLO2 may be increased several times during exercise by recruiting more lung capillar...

We recently reported the circulatory and muscle oxidative capacities of the arm after prolonged low-intensity skiing in the arctic (Boushel et al., 2014). In the present study, leg VO2 was measured by the Fick method during leg cycling while muscle mitochondrial capacity was examined on a biopsy of the vastus lateralis in healthy volunteers (7 male...

In humans, arm exercise is known to elicit larger increases in arterial blood pressure (BP) than leg exercise. However, the precise regulation of regional vascular conductances (VC) for the distribution of cardiac output with exercise intensity remains unknown. Hemodynamic responses were assessed during incremental upright arm cranking (AC) and leg...

During evolution, mitochondrial DNA haplogroups of arctic populations may have been selected for lower coupling of mitochondrial respiration to ATP production in favor of higher heat production. We show that mitochondrial coupling in skeletal muscle of traditional and westernized Inuit habituating northern Greenland is identical to Danes of western...

Background: Age-related decline in cardiac function can be prevented or postponed by lifelong endurance training. However, effects of normal ageing as well as of lifelong endurance exercise on longitudinal and radial contribution to stroke volume are unknown. The aim of this study was to determine resting longitudinal and radial pumping in elderly...

To determine the contribution of convective and diffusive limitations to (V) over dot(O2 peak) during exercise in humans, oxygen transport and haemodynamics were measured in 11 men (22 +/- 2years) during incremental (IE) and 30s all-out cycling sprints (Wingate test, WgT), in normoxia (Nx, P-IO2: 143mmHg) and hypoxia (Hyp, P-IO2: 73mmHg). Carboxyha...

Intense exercise training is a powerful stimulus that activates mitochondrial biogenesis pathways and thus increases mitochondrial density and oxidative capacity. Moderate levels of reactive oxygen species (ROS) during exercise are considered vital in the adaptive response, but high ROS production is a serious threat to cellular homeostasis. Althou...

Temperature-sensitive mechanisms may contribute to blood flow regulation, but the influence of temperature on perfusion to exercising and non-exercising human limbs is not established. Blood temperature (TB ), blood flow and oxygen uptake (VO2 ) in the legs and arms were measured in 16 healthy humans during 90 min of leg and arm exercise and during...

Type I diabetes mellitus (T1DM) is a chronic disorder, characterized by an almost or complete insulin deficiency. Widespread tissue dysfunction and deleterious diabetes-complications are associated with long-term elevations of blood glucose. The aim of this study was to investigate the effects of type I diabetes, as induced by streptozotocin, on th...

To determine the accuracy and precision of constant infusion transpulmonary thermodilution cardiac output (CITT-Q) assessment during exercise in humans, using indocyanine green (ICG) dilution and bolus transpulmonary thermodilution (BTD) as reference methods, cardiac output (Q) was determined at rest and during incremental one- and two-legged pedal...

It is investigated if recombinant human erythropoietin (rHuEPO) treatment for 15 weeks (n = 8) reduces extracellular accumulation of metabolic stress markers such as lactate, H+, and K+ during incremental exhaustive exercise. After rHuEPO treatment, normalization of blood volume and composition by hemodilution preceded an additional incremental tes...

The accuracy and reproducibility of transpulmonary thermodilution (TPTd) to assess cardiac output (Q) in exercising men was determined using indocyanine green (ICG) dilution as a reference method. TPTd has been utilized for the assessment of Q and preload indices of global end-diastolic volume (GEDV) and intrathoracic blood volume (ITBV), as well a...

Mitochondrial potassium channels have been implicated in myocardial protection mediated through pre-/postconditioning. Compounds that open the Ca2+- and voltage-activated potassium channel of big-conductance (BK) have a pre-conditioning-like effect on survival of cardiomyocytes after ischemia/reperfusion injury. Recently, mitochondrial BK channels...

Mitochondria form a reticulum in skeletal muscle. Exercise training stimulates mitochondrial biogenesis, yet an emerging hypothesis is that training also induces qualitative regulatory changes. Substrate oxidation, oxygen affinity, and biochemical coupling efficiency may be regulated differentially with training and exposure to extreme environments...

Aims: To determine the role played by adenosine, ATP and chemoreflex activation on the regulation of vascular conductance in chronic hypoxia. Methods: The vascular conductance response to low and high doses of adenosine and ATP was assessed in ten healthy men. Vasodilators were infused into the femoral artery at sea level and then after 8-12 day...

Background: The blood flow capacity in subcutaneous adipose tissue in humans remains largely unknown, and therefore the aim of this study was to determine the physiological range of blood flow in this tissue. Methods and results: The subcutaneous adipose tissue blood flow (ATBF) was measured in 9 healthy young men by positron emission tomography...

Aim: It is an ongoing discussion the extent to which oxygen delivery and oxygen extraction contribute to an increased muscle oxygen uptake during dynamic exercise. It has been proposed that local muscle factors including the capillary bed and mitochondrial oxidative capacity play a large role in prolonged low-intensity training of a small muscle g...

For over 50 years it has been known that elevated high-density lipoprotein (HDL) cholesterol is preventative against the development of atherosclerosis(1). Besides its role in cholesterol removal, HDL is also an antioxidant(2, 3), it inhibits inflammation(4) and thrombosis(5) and also stimulates endothelial nitric oxide (NO)(6) and prostacyclin(7)...

Human bone blood flow and metabolism during physical exercise remains poorly characterized. In the present study we measured femoral bone blood flow and glucose uptake in young healthy subjects by positron emission tomography in three separate protocols. In 6 women, blood flow was measured in femoral bone at rest and during one-leg intermittent iso...

Ageing is associated with vascular dysfunction and a reduced capacity of the central circulation to deliver O2 to the contracting muscles. The purpose of present study was to investigate whether a physical active lifestyle can maintain a sufficient exercise hyperemia and the influence of the active muscle mass. Central and limb hemodynamics were de...

Brown adipose tissue (BAT) is an energy-dispensing thermogenic tissue that plays an important role in balancing energy metabolism. Lineage-tracing experiments indicate that brown adipocytes are derived from myogenic progenitors during embryonic development. However, adult skeletal muscle stem cells (satellite cells) have long been considered unifor...

At the request of the authors, the above-mentioned article has been withdrawn from Diabetes . The letter below from Flemming Dela, MD, DMSci, and Celena Scheede-Bergdahl, BSc, MSc, PhD, explains the authors’ reasons for withdrawing the article: In November 2005, our group published the above-mentioned article. At the root of the paper was a series...

Muscle mitochondrial respiratory capacity measured ex vivo provides a physiological reference to assess cellular oxidative capacity as a component in the oxygen cascade in vivo. In this article, the magnitude of muscle blood flow and oxygen uptake during exercise involving a small-to-large fraction of the body mass will be discussed in relation to...

Prolonged exercise in the heat without fluid replacement represents a significant challenge to the regulation of mean arterial pressure (MAP). It is unknown, however, if MAP is equally challenged during the post-exercise period, and whether regular endurance exercise training can provide any benefit to its regulation. We examined MAP (Finometer) in...

New Findings What is the central question of this study? Are the enzymatic alterations in human skeletal muscle observed following 9–11 days of exposure to high altitude reflected in mitochondrial function? What is the main finding and its importance? The main findings of this study are that the capacity fat oxidation, individualized respiration ca...

Key points Several biochemical measures of mitochondrial components are used as biomarkers of mitochondrial content and muscle oxidative capacity. However, no studies have validated these surrogates against a morphological measure of mitochondrial content in human subjects. The most commonly used markers (citrate synthase activity, cardiolipin cont...

Nitric oxide (NO) and prostaglandins (PG) together play a role in regulating blood flow during exercise. NO also regulates mitochondrial oxygen consumption through competitive binding to cytochrome-c oxidase. Indomethacin uncouples and inhibits the electron transport chain in a concentration-dependent manner, and thus, inhibition of NO and PG synth...

Previous studies have investigated if cryopreservation is a viable approach for functional mitochondrial analysis. Different tissues have been studied, and conflicting results have been published. The aim of the present study was to investigate if mitochondria in human skeletal muscle maintain functionality after long term cryopreservation (1 year)...

Measurement of regional blood flow to the respiratory muscles has traditionally been invasive. The blood flow index (BFI), a minimally invasive method using indocyanine green dye (ICG) and near infrared spectroscopy, allows assessment of within subject changes in regional blood flow. This study assessed regional BFI to the vastus lateralis muscle (...

Erythropoietin (Epo) treatment has been shown to induce mitochondrial biogenesis in cardiac muscle along with enhanced mitochondrial capacity in mice. We hypothesized that recombinant human Epo (rhEpo) treatment enhances skeletal muscle mitochondrial oxidative phosphorylation (OXPHOS) capacity in humans. In six healthy volunteers rhEpo was administ...

Regulation of subcutaneous adipose tissue blood flow (ATBF) remains poorly elucidated in humans, especially during exercise. In the present study we tested the role of adenosine in the regulation of ATBF adjacent to active and inactive thigh muscles during intermittent isometric knee-extension exercise (1 s contraction followed by 2 s rest with wor...

Plasma hyperosmolality and baroreceptor unloading have been shown to independently influence the heat loss responses of sweating and cutaneous vasodilation. However, their combined effects remain unresolved. On four separate occasions, eight males were passively heated with a liquid-conditioned suit to 1.0°C above baseline core temperature during a...

Glucose metabolism increases in hypoxia and can be influenced by endogenous adenosine, but the role of adenosine for regulating glucose metabolism at rest or during exercise in hypoxia has not been elucidated in humans. We studied the effects of exogenous adenosine on human skeletal muscle glucose uptake and other blood energy substrates [free fatt...

One-legged dynamic knee-extension exercise (DKE) is a widely used model to study the local cardiovascular and metabolic responses to exercise of the quadriceps muscles. In this study, we explored the extent to which different muscles of the quadriceps are activated during exercise using positron emission tomography (PET) determined uptake of [¹⁸F]-...

Polycystic ovarian syndrome (PCOS) is associated with skeletal muscle insulin resistance (IR), which has been linked to decreased mitochondrial function. We measured mitochondrial respiration in lean and obese women with and without PCOS using high-resolution respirometry. Hyperinsulinemic-euglycemic clamps (40  mU/min per m(2)) and muscle biopsies...

Evidence exists for locomotor muscle impairment in patients with chronic obstructive pulmonary disease (COPD), including fiber type alterations and reduced mitochondrial oxidative capacity. In this study high-resolution respirometry was used to quantify oxygen flux in permeabilized fibres from biopsies of the vastus lateralis muscle in patients wit...

Across a wide range of species and body mass a close matching exists between maximal conductive oxygen delivery and mitochondrial respiratory rate. In this study we investigated in humans how closely in-vivo maximal oxygen consumption (VO(2) max) is matched to state 3 muscle mitochondrial respiration. High resolution respirometry was used to quanti...

Aerobic fitness may be associated with reduced orthostatic tolerance. To investigate whether trained individuals have less effective regulation of cerebral vascular resistance, we studied the middle cerebral artery (MCA) mean blood velocity (V(mean)) response to a sudden drop in mean arterial pressure (MAP) after 2.5 min of leg ischemia in enduranc...

Twenty one healthy untrained male subjects were randomized to follow a high-fat diet (HFD; 55-60E% fat, 25-30E% carbohydrate, and 15E% protein) or a normal diet (ND; 25-35E% fat, 55-60E% carbohydrate, and 10-15E% protein) for 2(1/2) wk. Diets were isocaloric and tailored individually to match energy expenditure. At 2(1/2) wk of diet, one 60-min bou...

Exercising muscle releases interleukin-6 (IL-6), but the mechanisms controlling this process are poorly understood. This study was performed to test the hypothesis that the IL-6 release differs in arm and leg muscle during whole-body exercise, owing to differences in muscle metabolism. Sixteen subjects (10 men and six women, with body mass index 24...

Near-infrared spectroscopy (NIRS) in combination with indocyanine green (ICG) dye has recently been used to measure respiratory muscle blood flow (RMBF) in humans. This method is based on the Fick principle and is determined by measuring ICG in the respiratory muscles using transcutaneous NIRS in relation to the [ICG] in arterial blood as measured...

Skeletal muscle insulin resistance has been linked to mitochondrial dysfunction. We examined how improvements in muscular insulin sensitivity following rosiglitazone (ROSI) or pioglitazone (PIO) treatment would affect muscle mitochondrial function in patients with type 2 diabetes mellitus (T2DM). Muscle biopsies were obtained from 21 patients with...