Increased local blood supply is thought to be one of the mechanisms underlying oxidative adaptations to interval training regimes. The relationship of exercise intensity with local blood supply and oxygen availability has not been sufficiently evaluated yet. The aim of this study was to examine the effect of six different intensities (40-90% peak oxygen uptake, VO ) on relative changes in oxygenated, deoxygenated and total haemoglobin (ΔO Hb, ΔHHb, ΔTHb) concentration after exercise as well as end-exercise ΔHHb/ΔVO as a marker for microvascular O distribution. Seventeen male subjects performed an experimental protocol consisting of 3 min cycling bouts at each exercise intensity in randomized order, separated by 5 min rests. ΔO Hb and ΔHHb were monitored with near-infrared spectroscopy of the vastus lateralis muscle, and VO was assessed. ΔHHb/ΔVO increased significantly from 40% to 60% VO peak and decreased from 60% to 90% VO peak. Post-exercise ΔTHb and ΔO Hb showed an overshoot in relation to pre-exercise values, which was equal after 40-60% VO and rose significantly thereafter. A plateau was reached following exercise at ≥80% VO . The results suggest that there is an increasing mismatch of local O delivery and utilization during exercise up to 60% VO . This insufficient local O distribution is progressively improved above that intensity. Further, exercise intensities of ≥80% VO induce highest local post-exercise O availability. These effects are likely due to improved microvascular perfusion by enhanced vasodilation, which could be mediated by higher lactate production and the accompanying acidosis.

BackgroundAerobic adaptations following interval training are supposed to be mediated by increased local blood supply. However, knowledge is scarce on the detailed relationship between exercise duration and local post-exercise blood supply and oxygen availability. This study aimed to examine the effect of five different exercise durations, ranging from 30 to 240 s, on post-exercise muscle oxygenation and relative changes in hemoglobin concentration.MethodsHealthy male subjects (N = 18) performed an experimental protocol of five exercise bouts (30, 60, 90, 120, and 240 s) at 80 % of peak oxygen uptake in a randomized order, separated by 5-min recovery periods. To examine the influence of aerobic fitness, we compared subjects with gas exchange thresholds (GET) above 60 % (GET60+) with subjects reaching GET below 60 % (GET60−). and relative changes in concentrations of oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin were continuously measured with near-infrared spectroscopy of the vastus lateralis muscle.ResultsPost-exercise oxygen availability and local blood supply increased significantly until the 90-s exercise duration and reached a plateau thereafter. Considering aerobic fitness, the GET60+ group reached maximum post-exercise oxygen availability earlier (60 s) than the GET60− group (90 s).ConclusionsOur results suggest that (1) 90 s has evolved as the minimum interval duration to enhance local oxygen availability and blood supply following cycling exercise at 80 % ; whereas (2) 60 s is sufficient to trigger the same effects in subjects with GET60 + .

Blood flow (BF) in exercising muscles is an important factor for exercise capacity. Recently, a non-invasive method to estimate capillary BF (Q ) was introduced. Using this method, the Fick principle is re-arranged by using relative differences in deoxygenated haemoglobin (ΔHHb) as a surrogate for arteriovenous O difference and pulmonary oxygen uptake (VO ) instead of muscular oxygen uptake. The aim of this study was to examine (I) the relationship between Q and exercise intensity during and following exercise, and (II) to critically reflect the Q approach. Seventeen male subjects completed six bouts of cycling exercise with different exercise intensities (40-90% peak oxygen uptake, VO ) in randomized order. VO and ΔHHb were monitored continuously during the trail. Q was modelled bi-exponentially, and mean response time (MRT) was calculated during recovery as well as the dissociation of modelled VO and Q recovery kinetics (MRT/τVO ). End-exercise Q increased continuously with exercise intensity. This also applied to MRT. Postexercise MRT/τVO increased from 40 to 60% VO but remained stable thereafter. The results show that Q response to exercise is linearly related to exercise intensity. This is presumably due to vasoactive factors like shear-stress or endothelial-mediated vasodilation. MRT/τVO shows that postexercise Q is elevated for a longer period than VO , which is representative for metabolic demand following exercise ≥70% VO . This is a hint for prolonged local vasodilation. According to previous studies, Q could not be modelled properly in some cases, which is a limitation to the method and therefore has to be interpreted with caution.