Cellular Glucose Uptake During Breath-Hold Diving in Experienced Male Breath-Hold Divers
Authors: Nicola Sponsiello, Danilo Cialoni, Massimo Pieri and Alessandro Marroni
DOI / Source: https://doi.org/10.1186/s40798-018-0126-3
Date: 27 March 2018
Reading level: Intermediate
Why This Matters for Freedivers
This study suggests freediving can alter blood sugar and hormones in a way that doesn’t match “normal exercise,” even with moderate dives — which matters for how you feel during training sessions (energy, dizziness, fatigue) and for planning food/recovery. It also supports a bigger takeaway: breath-hold diving is a unique physiological stressor, so smart recovery and consistency matter as much as “fitness,” especially when you stack dives.
Synopsis
Freediving looks like “no movement, no effort” compared with running or swimming laps, but your body treats it as something very different. This study asked a practical question: does breath-hold diving change how the body handles sugar and hormones? In normal exercise, muscles pull in more glucose, but insulin usually doesn’t rise — the body uses other pathways. Breath-hold diving, however, includes pressure changes, cold water, and repeated short hypoxia/hyperoxia cycles, plus the diving reflex. The researchers wanted to see whether this unique mix triggers a different metabolic pattern. 
They studied 20 healthy, experienced male breath-hold divers (all instructors) doing a controlled series of five dives to 20 meters, with recovery time at the surface and a short stop at the bottom. Blood glucose was measured from a finger-stick immediately before and after the dive series, insulin was measured from blood samples, and catecholamines (stress hormones like adrenaline-related compounds) were estimated from urine collected during the session and compared with a similar sample on a non-diving day. 
The results were surprisingly clear. After the dive series, blood glucose fell significantly (about 94 → 84 mg/dl on average), while insulin rose significantly (median roughly 4.5 → 7.0). Catecholamines also increased. In plain language: after a fairly “easy” dive protocol for these instructors, their bodies showed a pattern that looks less like normal exercise and more like a response to intermittent hypoxia and the diving reflex, with hormones shifting in a way that could push glucose into cells. The authors discuss that the mechanism probably isn’t as simple as “insulin turns on the usual glucose transporters,” and they suggest the overall picture may involve uneven oxygen delivery to different tissues (blood shift, peripheral vasoconstriction) plus reflex/hormonal effects that we still don’t fully understand.
Abstract
Background: The physiological and pathophysiological mechanisms that govern diving, both self-contained underwater breathing apparatus (SCUBA) and breath-hold diving (BH-diving), are in large part well known, even if there are still many unknown aspects, in particular about cell metabolism during BH-diving. The scope of this study was to investigate changes in glycemia, insulinemia, and the catecholamine response to BH-diving, to better understand if the insulin-stimulated glucose uptake mechanism is involved in cellular metabolism in this sport.
Methods: Twenty male experienced healthy breath-hold divers were studied. Anthropometric information was obtained. Glycemia, insulinemia, and catecholamine response were investigated before and after the series of BH-diving. Results: We found a statistically significant decrease in the blood glucose levels between before and after dives (mean 94.3 ± 11.6 vs. 83.5 ± 12.5 mg/dl) P = 0.001 and a statistically significant increase in blood insulin value (median 4.5 range 3.4/6.4 vs. 7.0 range 4.2/10.2 mcgU/ml) P < 0.0001. Also, we found a statistically significant increase of catecholamine production (median 14.0 range 8/18 vs. 15.5 range 10.0/21.0 μg) P < 0.0001.
Conclusions: The increase in blood insulin during BH-diving associated with the decrease of blood glucose levels could indicate that the upregulating cellular uptake is not caused by activation of the specific glucose transporters. Particular diving-related conditions such as the diving reflex, the intermittent hypoxia/hyperoxia, and the particular environmental condition could play an important role in the mechanism involved in glycemia decrease in BH-diving. Our data confirm that the adaptations to BH-diving are caused by complex mechanisms and involve many peculiar responses still in large part unknown.