The Effect of Skeletal Muscle Oxygenation on Hemodynamics, Cerebral Oxygenation and Activation, and Exercise Performance during Incremental Exercise to Exhaustion in Male Cyclists

Simple Summary This study aimed to elucidate whether exercise intolerance with muscle blood flow restriction is located within the central nervous system or the heart, namely whether cardiac response constitutes the crucial point precipitating exercise cessation. Muscle blood flow restriction (venous occlusion) during whole-body dynamic exercise compared to control condition, accelerates: (a) the rate of skeletal muscle deoxygenation, (b) the increase in systolic blood pressure (c) the rating of perceived exertion; and (d) cerebral activation, without these variables will be different at exhaustion point between the two experimental conditions, despite a marked decrease in maximal exercise time and maximal aerobic output. Maximal cardiac responses (i.e., heart rate, stroke volume, and cardiac output) were also significantly limited with muscle blood flow restriction. These findings suggest that skeletal muscle oxygenation levels in combination with augmented blood pressure response and cerebral activation may be important determinants in setting the limits of exercise performance. Specifically, when the aforementioned variables reach a predetermined maximal level, exercise ability might be limited despite the fact that cardiac performance never ends up at peak values. Muscle blood flow restriction might simulate pathological conditions such as heart failure, hypertension, and peripheral vascular diseases, which are all characterized by skeletal muscle perfusion impairments, and, thus provide insights into exercise intolerance in health and disease. Abstract 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 V˙O2max (−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 V˙O2max. 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.