Enhanced splenic volume and contraction in elite endurance athletes

Abstract

Splenic contraction, which leads to ejection of stored erythrocytes, is greater in athletes involved in regular freediving or high-altitude activities. As this response facilitates oxygen carrying capacity, similar characteristics may be expected of elite endurance athletes. Therefore, our aims were to compare resting and apnea-induced splenic volume in endurance athletes and untrained individuals, and to assess the athletes' exercise-induced splenic volume. Twelve elite biathletes (7 women) and 12 controls (6 women) performed a maximal effort apnea in a seated position. In addition, the biathletes completed a maximal roller-skiing time trial. Splenic dimensions were measured by ultrasonic imaging for subsequent volume calculations, while Hb was analyzed from capillary blood samples and cardiorespiratory variables were monitored continuously. Baseline splenic volume was larger in the biathletes (214±56 mL) compared to controls (157±39 mL, p=0.008) and apnea-induced splenic contraction was also greater in the biathletes (46±20 mL versus 30±16 mL, p=0.035). Hb increased immediately after apnea in the biathletes (4.5±4.8%, p=0.029) but not the controls (-0.7±3.1%, p=0.999). Increases in exercise-induced splenic contraction (p=0.008) and Hb (p=0.001) were greater compared to the apnea-induced responses among the athletes. Baseline splenic volume tended to be correlated with V̇O2max (r=0.584, p=0.059). We conclude that elite biathletes have greater splenic volume with a greater ability to contract and elevate Hb compared to untrained individuals. These characteristics may transiently enhance O2-carrying capacity and possibly increase O2 uptake, thereby helping biathletes to cope with high intermittent O2 demands and severe O2 deficits that occur during biathlon training and competition.

No differences in splenic emptying during on-transient supine cycling between aerobically trained and untrained participants

“…However, the role of the spleen in O 2 transport during aerobic exercise has not been carefully studied. Moreover, direct evidence that splenic contraction also augments aerobic performance during exercise in humans is lacking, as there is still an on-going debate in the literature regarding the role of the spleen in O 2 transport under different scenarios (Gatterer and Burtscher 2021 ; Schagatay and Holmström 2021 ; Holmström et al 2021b ). Therefore, the correlation between the spleen volume changes, circulating RBC release and uptake parameters was explored here.…”

“…Here, we reasoned that the reduction in splenic volume during supine cycling would be clearly observed, while the on-going debate in the literature regarding the role of the spleen in oxygen transport during aerobic exercise warrants further investigation. Recent work by Holmström and co-authors ( 2021b ) suggested that apnea-induced splenic contraction (reduction in splenic volume by ~ 46) leads to a transient increase in Hb concentration (by 4.5%), and thereby arguments O 2 uptake in endurance trained athletes, but not in sedentary controls. This, however, contradicts recently published short report, in which we found no correlation between max.…”

The cardiosplenic axis: the prognostic role of the spleen in heart failure

“…The spleen varies in size between individuals, but it is typically ~ 10 × 6 × 3 cm 3 , weighs ~ 120 g, and is highly vascularized, storing 20–30% of total blood volume [ 21 ]. Larger-than normal spleen sizes have been reported in “Sea Nomads” (or Bajau people) who engage in breath-hold diving and in elite endurance athletes [ 25 , 26 ]. Although splenic contraction is a part of the human diving response, it is thought that those who engage in breath-hold diving have physiologically and genetically adapted to the hypoxic environment, which has led to the development of a larger-than normal sized spleen.…”

Test–retest reliability of splenic volume assessment by ultrasonography

“…On the other hand, ultrasonography is a useful non-invasive, portable method, which is applicable in both laboratory settings and during fieldwork contexts. Ultrasonic imaging is particularly suited to experiments involving various stressors, such as maximal exercise 3 , 16 , voluntary apnea 8 , 17 , normobaric hypoxia 18 or hypobaric hypoxia 19 , which often includes a time-constrained protocol where windows for collection of splenic measurements are short. The length of the spleen display a strong correlation with splenic volumes from measures of cadavers 20 and with CT scan measurements 14 , 21 .…”

“…Nonetheless, other formulas exist, one, in particular, was designed to account for individual differences in splenic diameters, which could plausibly result in varying splenic volumes. This particular formula has been broadly used in physiological laboratory research, involving apneic diving 8 , 25 , 26 , normobaric hypoxia exposure 18 , 27 – 29 and during maximal exercise 16 . Additionally, it has been used during field-based contexts involving hypobaric hypoxia and exercise 17 , 19 , 30 , 31 .…”