Sex differences in the intensity-duration relationships of the severe- and extreme-intensity exercise domains.

Extreme-intensity exercise is described by W'ext (analogous to J' for isometric exercise) that is smaller than W' of severe-intensity exercise (W'sev) in males. Sex differences in exercise tolerance appear to diminish at near-maximal exercise, however, there is evidence of greater contributions of peripheral fatigue (i.e.

Does creatine supplementation affect recovery speed of impulse above critical torque?

We previously reported that creatine supplementation improved intermittent isometric exercise performance by augmenting the total impulse performed above end-test torque (total IET'). However, our previous analyses did not enable mechanistic assessments. The objective of this study was to determine if creatine supplementation affected the IET' speed of recovery.

Heart rate and gas exchange dynamic responses to multiple brief exercise bouts (MBEB) in early- and late-pubertal boys and girls.

Natural patterns of physical activity in youth are characterized by brief periods of exercise of varying intensity interspersed with rest. To better understand systemic physiologic response mechanisms in children and adolescents, we examined five responses [heart rate (HR), respiratory rate (RR), oxygen uptake (V̇O ), carbon dioxide production (V̇CO ), and minute ventilation (V̇E), measured breath-by-breath] to multiple brief exercise bouts (MBEB). Two groups of healthy participants (early pubertal: 17 female, 20 male; late-pubertal: 23 female, 21 male) performed five consecutive 2-min bouts of constant work rate cycle-ergometer exercise interspersed with 1-min of rest during separate sessions of low- or high-intensity (~40% or 80% peak work, respectively).

The acute effects of passive heating on endothelial function, muscle microvascular oxygen delivery, and expression of serum HSP90α.

Passive heating has been a therapeutic tool used to elevate core temperature and induce increases in cardiac output, blood flow, and shear stress. We aimed to determine the effects of a single bout of passive heating on endothelial function and serum heat shock protein 90α (HSP90α) levels in young, healthy subjects. 8 healthy subjects were recruited to participate in one bout of whole-body passive heating via immersion in a 40 °C hot tub to maintain a 1 °C increase in rectal temperature for 60 min.

Neuromuscular recovery from severe- and extreme-intensity exercise in men and women.

Maximal voluntary contraction force (MVC), potentiated twitch force (Q), and voluntary activation (%VA) recover to baseline within 90 s following extreme-intensity exercise. However, methodological limitations mask important recovery kinetics. We hypothesized reductions in MVC, Q, and %VA at task failure following extreme-intensity exercise would be less than following severe-intensity exercise, and Q and MVC following extreme-intensity exercise would show significant recovery within 120 s but remain depressed following severe-intensity exercise.

Post-occlusive reactive hyperemia and skeletal muscle capillary hemodynamics.

Unlabelled: Post-occlusive reactive hyperemia (PORH) is an accepted diagnostic tool for assessing peripheral macrovascular function. While conduit artery hemodynamics have been well defined, the impact of PORH on capillary hemodynamics remains unknown, despite the microvasculature being the dominant site of vascular control. Therefore, the purpose of this investigation was to determine the effects of 5 min of feed artery occlusion on capillary hemodynamics in skeletal muscle.

Dissociation between exercise intensity thresholds: mechanistic insights from supine exercise.

This study tested the hypothesis that the respiratory compensation point (RCP) and breakpoint in deoxygenated [heme] [deoxy[heme], assessed via near-infrared spectroscopy (NIRS)] during ramp incremental exercise would occur at the same metabolic rate in the upright (U) and supine (S) body positions. Eleven healthy men completed ramp incremental exercise tests in U and S. Gas exchange was measured breath-by-breath and time-resolved-NIRS was used to measure deoxy[heme] in the vastus lateralis (VL) and rectus femoris (RF).

W' reconstitution rate at different intensities above critical torque: the role of muscle size and maximal strength.

New Findings: What is the central question of this study? Do muscle size, maximal force and exercise intensity influence the recovery time constant for the finite impulse above critical torque (τ )? What is the main finding and its importance? Muscle size and maximal strength have different influences on the parameters of the hyperbolic torque-time to task failure relationship. Greater muscle size and maximal strength, as well as exercise at an intensity of 60% MVC, prolong τ during intermittent isometric exercise.

Abstract: Muscle perfusion and O delivery limitations through muscle force generation appear to play a major role in defining the hyperbolic torque-time to task failure (T ) relationship.

Influence of muscular contraction on vascular conductance during exercise above versus below critical power.

We tested the hypothesis that limb vascular conductance (LVC) would increase during the immediate recovery phase of dynamic exercise above, but not below, critical power (CP) indicating a threshold for muscular contraction-induced impedance of limb blood flow (LBF). CP (115 ± 26 W) was determined in 7 men and 7 women who subsequently performed ∼5 min of near-supine cycling exercise both below and above CP. LVC demonstrated a greater increase during immediate recovery and remained significantly higher following exercise above, compared to below, CP (all p < 0.

Effects of Caffeine on Exercise Duration, Critical Velocity, and Ratings of Perceived Exertion During Repeated-Sprint Exercise in Physically Active Men.

Caffeine improves short-to-moderate distance running performance, but the effect of caffeine on repeated sprints are equivocal. This research determined if caffeine improved exercise tolerance during repeated-sprint exercise. iCV is a running velocity that distinguishes intermittent running velocities (velocities ≤ iCV) that are sustainable from those resulting in a predictable time to exhaustion (velocities > iCV).

Impact of supine versus upright exercise on muscle deoxygenation heterogeneity during ramp incremental cycling is site specific.

Purpose: We tested the hypothesis that incremental ramp cycling exercise performed in the supine position (S) would be associated with an increased reliance on muscle deoxygenation (deoxy[heme]) in the deep and superficial vastus lateralis (VLd and VLs, respectively) and the superficial rectus femoris (RFs) when compared to the upright position (U).

Methods: 11 healthy men completed ramp incremental exercise tests in S and U. Pulmonary [Formula: see text]O was measured breath-by-breath; deoxy[heme] was determined via time-resolved near-infrared spectroscopy in the VLd, VLs and RFs.

Effect of priming exercise and body position on pulmonary oxygen uptake and muscle deoxygenation kinetics during cycle exercise.

We hypothesized that the performance of prior heavy exercise would speed pulmonary oxygen uptake (V̇o) kinetics (i.e., as described by the time constant, [Formula: see text]) and reduce the amplitude of muscle deoxygenation (deoxy[heme]) kinetics in the supine (S) but not upright (U) body position.

Influence of blood flow occlusion on muscular recruitment and fatigue during maximal-effort small muscle-mass exercise.

Key Points: The heavy-to-severe intensity exercise threshold (i.e. critical force) distinguishes between steady-state and progressive metabolic and neuromuscular responses to exercise.

Impact of supine exercise on muscle deoxygenation kinetics heterogeneity: mechanistic insights into slow pulmonary oxygen uptake dynamics.

Oxygen uptake (V̇o) kinetics are slowed in the supine (S) position purportedly due to impaired muscle O delivery ([Formula: see text]); however, these conclusions are predicated on single-site measurements in superficial muscle using continuous-wave near-infrared spectroscopy (NIRS). This study aimed to determine the impact of body position [i.e.

Limb blood flow and muscle oxygenation responses during handgrip exercise above vs. below critical force.

This study compared the brachial artery blood flow (Q̇) and microvascular oxygen delivery responses during handgrip exercise above vs. below critical force (CF; the isometric analog of critical power). Q̇ and microvascular oxygen delivery are important determinants of oxygen utilization and metabolite accumulation during exercise, both of which increase progressively during exercise above CF.

Effect of differential muscle activation patterns on muscle deoxygenation and microvascular haemoglobin regulation.

New Findings: What is the central question of this study? Does the presence and extent of heterogeneity in the ratio of O delivery to uptake across human muscles relate specifically to different muscle activation patterns? What is the main finding and its importance? During ramp incremental knee-extension and cycling exercise, the profiles of muscle deoxygenation (deoxy[haemoglobin + myoglobin]) and diffusive O potential (total[haemoglobin + myoglobin]) in the vastus lateralis corresponded to different muscle activation strategies. However, this was not the case for the rectus femoris, where muscle activation and deoxygenation profiles were dissociated and might therefore be determined by other structural and/or functional attributes (e.g.

Microvascular blood flow during vascular occlusion tests assessed by diffuse correlation spectroscopy.

New Findings: What is the central question of this study? What are the characteristics of the time courses of blood flow in the brachial artery and microvascular beds of the skin and skeletal muscle following transient ischaemia? What is the main finding and its importance? Skeletal muscle blood flow was significantly slower than the transient increase in the cutaneous tissue, suggesting mechanistic differences between cutaneous and muscular blood flow distribution after transient ischaemia. These results challenge the use of the cutaneous circulation as globally representative of vascular function.

Abstract: Vascular function can be assessed by measuring post-occlusion hyperaemic responses along the arterial tree (vascular occlusion test; VOT).

Prediction of Emergency Capsule Egress Performance.

Critical mission tasks for Martian exploration have been identified and include specific duties that astronauts will have to perform despite any adverse effects of chronic microgravity. Specifically, astronauts may have to perform an emergency capsule egress upon return to Earth, which places specific demands on compromised cardiovascular and neuromuscular systems. Therefore, the purpose of this project was to determine the relationship between cardiorespiratory fitness and simulated capsule egress time.

Unaltered V̇o kinetics despite greater muscle oxygenation during heavy-intensity two-legged knee extension versus cycle exercise in humans.

Relative perfusion of active muscles is greater during knee extension ergometry (KE) than cycle ergometry (CE). This provides the opportunity to investigate the effects of increased O delivery (Q̇o) on deoxygenation heterogeneity among quadriceps muscles and pulmonary oxygen uptake (V̇o) kinetics. Using time-resolved near-infrared spectroscopy, we hypothesized that compared with CE the superficial vastus lateralis (VL), superficial rectus femoris, and deep VL in KE would have ) a smaller amplitude of the exercise-induced increase in deoxy[Hb + Mb] (related to the balance between V̇o and Q̇o); ) a greater amplitude of total[Hb + Mb] (related to the diffusive O conductance); ) a greater homogeneity of regional muscle deoxy[Hb + Mb]; and ) no difference in pulmonary V̇o kinetics.

Reduced insulin sensitivity in young, normoglycaemic subjects alters microvascular tissue oxygenation during postocclusive reactive hyperaemia.

New Findings: What is the central question of the study? Are measures of reduced insulin sensitivity in young, normoglycaemic subjects correlated with near-infrared spectroscopy-derived microvascular responsiveness [tissue oxygen saturation reperfusion rate (STO upslope)] during postocclusive reactive hyperaemia? What is the main finding and its importance? A sevenfold range of hepatic insulin sensitivity is significantly correlated (r = 0.44, P = 0.02) with STO upslope after transient tissue ischaemia.

Effect of assuming constant tissue scattering on measured tissue oxygenation values during tissue ischemia and vascular reperfusion.

The purpose of this study was to determine the effects of assuming constant tissue scattering properties on tissue oxygenation measurements during a vascular occlusion test (VOT). Twenty-one subjects (21.8 ± 1.

Prediction of Planetary Mission Task Performance for Long-Duration Spaceflight.

Introduction: This study aimed to determine values and ranges for key aerobic fitness variables that can individually map the level of success for planetary mission tasks performance for long-duration spaceflight, with the goal to develop a predictor-testing model that can be performed with in-flight equipment.

Methods: We studied a group of 45 men and women who completed a series of mission-critical tasks: a surface traverse task and a hill climb task. Participants performed each mission task at a low and moderate intensity designed to elicit specific metabolic responses similar to what is expected for ambulation in lunar and Martian gravities, respectively.