Diving response after a one-week diet and overnight fasting

Background We hypothesized that overnight fasting after a short dietary period, especially with carbohydrates, could allow performing breath-hold diving with no restraint for diaphragm excursion and blood shift and without any increase of metabolism, and in turn improve the diving response. Methods During two separate sessions, 8 divers carried out two trials: (A) a 30-m depth dive, three hours after a normal breakfast and (B) a dive to the same depth, but after following a diet and fasting overnight. Each test consisted of 3 apnea phases: descent, static and ascent whose durations were measured by a standard chronometer. An impedance cardiograph, housed in an underwater torch, provided data on trans-thoracic fluid index (TFI), stroke volume (SV), heart rate (HR) and cardiac output (CO). Mean blood pressure (MBP), arterial O 2 saturation (SaO 2 ), blood glucose (Glu) and blood lactate (BLa) were also collected. Results In condition B, duration of the static phase of the dive was longer than A (37.8 ± 7.4 vs. 27.3 ± 8.4 s respectively, P < 0.05). In static phases, mean ∆ SV value (difference between basal and nadir values) during fasting was lower than breakfast one (−2.6 ± 5.1 vs. 5.7 ± 7.6 ml, P < 0.05). As a consequence, since mean ∆ HR values were equally decreased in both metabolic conditions, mean ∆ CO value during static after fasting was lower than the same phase after breakfast (−0.4 ± 0.5 vs. 0.4 ± 0.5 L · min −1 respectively, P < 0.05). At emersion, despite the greater duration of dives during fasting, SaO 2 was higher than A (92.0 ± 2.7 vs. 89.4 ± 2.9 % respectively, P < 0.05) and BLa was lower in the same comparison (4.2 ± 0.7 vs. 5.3 ± 1.1 mmol∙L −1 , P < 0.05). Conclusions An adequate balance between metabolic and splancnic status may improve the diving response during a dive at a depth of 30 m, in safe conditions for the athlete’s health.