Larger splenic emptying correlate with slower EPOC kinetics in healthy active participants

There is an ongoing debate in the literature as to whether an exercise-induced reduction in spleen volume, and a subsequent increase in erythrocyte concentration contribute to superior V̇O 2 uptake during exercise and recovery, and thus improve endurance performance. In the present study, we investigated whether larger splenic emptying contributes to faster excess post-exercise O 2 consumption (EPOC) after supine cycling. We hypothesized that a larger reduction in splenic volume would be associated with faster EPOC (including absolute values and recovery time constant, τ), since a larger splenic emptying has been reported in the literature as an advantage of aerobically trained individuals over healthy controls (Holmström et al., 2021). Here, fifteen healthy participants (age 24±4, 47% women) completed three laboratory visits at least 48 hours apart. After obtaining medical clearance and familiarizing themselves with the test, they performed a ramp V̇O 2 peak test in the supine position until task failure. Next, they completed three step-transition test from 20 W to a moderate-intensity power output (PO), equivalent to V̇O 2 uptake at 90% GET, where data on metabolic, cardiovascular, and splenic responses were recorded simultaneously. After step-transition test cessation, O 2 debt (EPOC fast ) was recorded, and the first 10 minutes of the recovery period were used for analysis. Blood samples were collected before and immediately after the end of exercise. In response to moderate-intensity supine cycling (V̇O 2 uptake ~2 L·min -1 ), we observed a ~35% (p=0.001) reduction in splenic volume resulting in a transient ~3-4% (p=0.001) increase in erythrocyte concentration in mixed venous blood. During recovery, mean τV̇O 2 was 45±18 sec., the amplitude was 2.4±0.5 L·min -1 , and EPOC fast was 1.69 L·min -1 . Significant correlations were observed between the percent change in spleen volume and i) EPOC fast (r=-0.657, p=0.008) and ii) τV̇O 2 (r=-0.619, p=0.008), but not for iii) V̇O 2 peak (p=.435, p=0.105) or iv) the amplitude of V̇O 2 recovery kinetics (r=0.447, p=0.941). Our work suggests that individuals with larger splenic emptying tend to have slower O 2 recovery kinetics and a greater O 2 debt. Apparently, the transient, exercise-induced increase in circulating erythrocytes observed here is rather insufficient to increase O 2 storage capacity in blood, and thereby improve endurance performance. References: Zubac D, Obad A, Šupe-Domić D, et al. (2022). No differences in splenic emptying during on-transient supine cycling between aerobically trained and untrained participants. Eur J Appl Physiol, 11;1-15. doi: 10.1007/s00421-021-04843-w ; Holmström PK, Karlsson Ö, Lindblom H, et al. (2021). Enhanced splenic volume and contraction in elite endurance athletes. J Appl Physiol, 131(2), 474-486, doi: 10.1152/japplphysiol.01066.2020 . All authors declare no conflict of interest. There was no external funding for this work. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.