This study aimed to elucidate whether muscle blood flow restriction during maximal exercise is associated with alterations in hemodynamics, cerebral oxygenation, cerebral activation, and deterioration of exercise performance in male participants. Thirteen healthy males, cyclists (age 33 ± 2 yrs., body mass: 78.6 ± 2.5 kg, and body mass index: 25.57 ± 0.91 kg·m⁻¹), performed a maximal incremental exercise test on a bicycle ergometer in two experimental conditions: (a) with muscle blood flow restriction through the application of thigh cuffs inflated at 120 mmHg (with cuffs, WC) and (b) without restriction (no cuffs, NC). Exercise performance significantly deteriorated with muscle blood flow restriction, as evidenced by the reductions in $\dot{V}$O_2max (−17 ± 2%, p < 0.001), peak power output (−28 ± 2%, p < 0.001), and time to exhaustion (−28 ± 2%, p < 0.001). Muscle oxygenated hemoglobin (Δ[O₂Hb]) during exercise declined more in the NC condition (p < 0.01); however, at exhaustion, the magnitude of muscle oxygenation and muscle deoxygenation were similar between conditions (p > 0.05). At maximal effort, lower cerebral deoxygenated hemoglobin (Δ[HHb]) and cerebral total hemoglobin (Δ[THb]) were observed in WC (p < 0.001), accompanied by a lower cardiac output, heart rate, and stroke volume vs. the NC condition (p < 0.01), whereas systolic blood pressure, rating of perceived exertion, and cerebral activation (as assessed by electroencephalography (EEG) activity) were similar (p > 0.05) between conditions at task failure, despite marked differences in exercise duration, maximal aerobic power output, and $\dot{V}$O_2max. In conclusion, in trained cyclists, muscle blood flow restriction during an incremental cycling exercise test significantly limited exercise performance. Exercise intolerance with muscle blood flow restriction was mainly associated with attenuated cardiac responses, despite cerebral activation reaching similar maximal levels as without muscle blood flow restriction.

Breath-hold diving has been traditionally practiced for professional and recreational reasons and has recently emerged as a competitive sport. The physiological response during breath-holding, also known as diving response, consists mainly of bradycardia and peripheral vasoconstriction. Elite apneists can suppress the urge to breathe, sustain greater arterial desaturation and develop pronounced bradycardia, thus accomplishing impressively long breath-hold times. This study explored physiological responses during static apnea and their association with apnea duration in breath-hold divers with high physiological adaptations acquired from long-term apnea training. Nine well-trained competitive divers held their breath for as long as possible while floating motionlessly in a swimming pool (26–27 °C), simulating an actual “static apnea competition”. Long apnea durations (302 ± 60 s) as well as severe oxygen desaturation (minSaO₂ 46 ± 11%) and bradycardia (minHR 49 ± 8 bpm) were achieved. Apnea duration was positively correlated with forced vital capacity (r = 0.771) and apnea duration until initiation of desaturation (r = 0.736) and negatively correlated with minSaO₂ (r = −0.672) (p < 0.05). Moreover, minHR during apnea was correlated with pre-apneic hemoglobin concentration (r = 0.685) (p < 0.05). The prolonged apnea durations achieved by the well-trained divers in this study, while performing maximum immersed static apnea under competitive simulated conditions, were related to their high lung volumes and their delayed and profound O₂ desaturation, whereas their bradycardic response was not a decisive factor.

When combining two conditions of reduced oxygen availability, anemia and hypoxia, human physiological responses are highly challenged to maintain arterial oxygen delivery, especially during whole-body exercise. The aim of this study was to compare the cardiorespiratory responses of mildly anemic women with those of healthy controls, while cycling in normobaric hypoxia. Two groups of young females were matched for age, weight, height, and involvement in physical activity, one with normal hemoglobin, hematocrit, and ferritin levels and another suffering from mild iron deficiency anemia (10 < (Hb) < 12 g/dL, 34 < Hct < 37%, ferritin < 15 μg/L). They cycled to exhaustion under normoxia and hypoxia (FIO₂ 0.21 and 0.14), and their physiological responses were compared at 40, 80, and 100% VO_2max of the specific condition. The two groups differed (p < 0.05) mainly at the higher exercise intensities; the anemic participants exhibited similar heart rate but lower oxygen pulse than their control counterparts, as well as a larger drop in maximal oxygen uptake. However, they sustained maximal effort by employing the anaerobic metabolism to a larger extent, which stimulated a greater ventilatory response. It appears that iron deficiency anemia of mild severity, which is commonly observed in young athletic females, impacts physiological responses during whole-body exercise in the presence of moderate hypoxia.

This study tested the hypothesis that muscle blood flow restriction reduces muscle and cerebral oxygenation at rest. In 26 healthy males, aged 33 ± 2 yrs, physiological variables were continuously recorded during a 10-min period in 2 experimental conditions: a) with muscle blood flow restriction through thigh cuffs application inflated at 120 mm Hg (With Cuffs, WC) and b) without restriction (No Cuffs, NC). Muscle and cerebral oxygenation were reduced by muscle blood flow restriction as suggested by the increase in both muscle and cerebral deoxygenated hemoglobin (Δ[HHb]; p < 0.01) and the decrease of muscle and cerebral oxygenation index (Δ[HbDiff]; p < 0.01). Hemodynamic responses were not affected by such muscle blood flow restriction, whereas baroreflex sensitivity was reduced (p = 0.009). The perception of leg discomfort was higher (p < 0.001) in the WC than in the NC condition. This study suggests that thigh cuffs application inflated at 120 mm Hg is an effective method to reduce muscle oxygenation at rest. These changes at the muscular level seem to be sensed by the central nervous system, evoking alterations in cerebral oxygenation and baroreflex sensitivity. Novelty: Thigh cuffs application inflated at 120 mm Hg effectively reduces muscle oxygenation at rest. Limiting muscle oxygenation appears to reduce cerebral oxygenation, and baroreflex sensitivity, at rest. Even in healthy subjects, limiting muscle oxygenation, at rest, affects neural integration.