Abstract
The purpose of the present study was to assess the effects of aerobic interval training on muscle and brain oxygenation to incremental ramp exercise. Eleven physically active subjects performed a 6-week interval training period, proceeded and followed by an incremental ramp exercise to exhaustion (25 W min–1). Throughout the tests pulmonary gas exchange and muscle (Vastus Lateralis) and brain (prefrontal cortex) oxygenation [concentration of deoxygenated and oxygenated hemoglobin, HHb and O2Hb, and tissue oxygenation index (TOI)] were continuously recorded. Following the training intervention peak had increased with 7.8 ± 5.0% (P < 0.001). The slope of the decrease in muscle TOI had decreased (P = 0.017) 16.6 ± 6.4% and the amplitude of muscle HHb and totHb had increased (P < 0.001) 40.4 ± 15.8 and 125.3 ± 43.1%, respectively. The amplitude of brain O2Hb and totHb had increased (P < 0.05) 40.1 ± 18.7 and 26.8 ± 13.6%, respectively. The training intervention shifted breakpoints in muscle HHb, totHb and TOI, and brain O2Hb, HHb, totHb and TOI to a higher absolute work rate and (P < 0.05). The relative (in %) change in peak was significantly correlated to relative (in %) change slope of muscle TOI (r = 0.69, P = 0.011) and amplitude of muscle HHb (r = 0.72, P = 0.003) and totHb (r = 0.52, P = 0.021), but not to changes in brain oxygenation. These results indicate that interval training affects both muscle and brain oxygenation, coinciding with an increase in aerobic fitness (i.e., peak). The relation between the change in peak and muscle but not brain oxygenation suggests that brain oxygenation per se is not a primary factor limiting exercise tolerance during incremental exercise.
Highlights
Incremental ramp exercise tests are commonly used in healthy and pathologic populations to determine physical fitness, to identify intensity zones for training/rehabilitation, and to assess the efficacy of training and/or treatment interventions
The training intervention induced an increase in Ppeak of 7.9 ± 2.1% (P < 0.001), in V O2peak of 7.8 ± 5.0% (P < 0.001)
The present study showed that the changes in cerebral oxygenation parameters following the training intervention were not related to the changes in V O2peak
Summary
Incremental ramp exercise tests are commonly used in healthy and pathologic populations to determine physical fitness, to identify intensity zones for training/rehabilitation, and to assess the efficacy of training and/or treatment interventions. It is observed that muscle HHb, which is often considered as a reflection of fractional O2 extraction (Delorey et al, 2003; Grassi et al, 2003), increases following a sigmoid-like pattern, with a sluggish increase at the onset of the incremental exercise, followed by a linear increase to reach a plateau at high intensities (∼80–90%VO2max) (Ferreira et al, 2007; Spencer et al, 2012; Fontana et al, 2015) In this context, it has been shown from cross-sectional studies that trained subjects have a less steep increase but higher peak value in HHb, reflecting an improved matching between O2 supply and O2 demand and higher peak O2 extraction, respectively (Boone et al, 2009; Gifford et al, 2016; Okushima et al, 2016). The longitudinal effects of a training intervention on muscle oxygenation are scarcely documented. Prieur and Mucci (2013) found an increased amplitude of the HHb response (i.e., indicating an improved O2 extraction capacity) following 6 weeks of interval training at high intensities. Takagi et al (2016) found a similar impact on the amplitude of HHb following an aerobic training program in post-myocardial infarction patients
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