Energetics of Underwater Swimming in Apnea

Abstract

Purpose: Dynamic apnea with fins (DYN) involves swimming the longest distance relying solely on the body's oxygen and anaerobic energy stores. The energy cost per unit distance ( C ) is therefore an important determinant of DYN performance, yet it has never been measured. This study aimed to assess the C of DYN and its aerobic (EO 2 ), anaerobic lactic (ELa), and alactic (EPCr) energy contributions.

Methods: In a 50-m swimming pool, 22 freedivers (3 females; 10 using bi-fins, 6 using monofin, 6 using both) performed a 50-m DYN, and 7 performed a 100-m DYN. Net C (above resting) was calculated from the O 2 debt measured at emersion plus ELa (calculated from the blood lactate increase). In nine subjects (six of whom performed also the 100-m DYN), determination of hemoglobin mass and total lung capacity allowed the estimation of EO 2 and, by subtraction, EPCr.

Results: C was unchanged between the 100-m and the 50-m DYN ( P = 0.81) and resulted higher with bi-fins than with the monofin (7.4 ± 2.2 vs 5.5 ± 1.6 J·kg -1 ·m -1 , P = 0.02) due to a higher O 2 debt and ELa. DYN personal best correlated better with the distance swum per unit of EO 2 at 50 m ( R2 = 0.70) than with C ( R2 = 0.25). From 50 to 100 m, fractional EO 2 decreased (58% ± 19% to 47% ± 13%, P = 0.02), ELa increased (10% ± 5% to 21% ± 5%, P < 0.001), and EPCr was unchanged (31% ± 20% to 32% ± 15%, P = 0.83).

Conclusions: The C of DYN seems compatible with published values for surface swimming with fins at the same speed. At 100 m, ELa and EPCr were disproportionately high for the exercise intensity, possibly due to a diving response. Sparing EO 2 is at least as important as C in determining DYN performance.

Keywords: AEROBIC METABOLISM; ALVEOLAR GAS; ANAEROBIC METABOLISM; BREATH-HOLD DIVING; FREEDIVING; SWIMMING ECONOMY.

FIGURE 1

Post-emersion time course of whole-body O₂ consumption (white dots) and the estimated O₂ cost of breathing during head-out water immersion (gray dots) in a representative subject. For clarity, their respective asymptotic baselines have been subtracted so that the volume of oxygen used to restore the O₂ debt contracted during the trials can be visualized as the gray area.

FIGURE 2

Personal best distances in dynamic apnea with fins (light gray: bi-fins; dark gray: monofin) correlated better with the meters swum per kJ expended above resting (1/C) (left panel) than with the meters swum per liter of O₂ store depletion (d/EO₂) estimated with the computational approach C1 (right panel), both assessed during the 50-m trial. Note the different number of data points: n = 28 for the left panel (10 subjects using bi-fins, 6 the monofin, and 6 both) and n = 9 for the right panel (6 subjects using bi-fins and 3 the monofin). Restricting the left panel to the same n = 9 participants would have abolished the correlation between personal best and 1/C (R² = 0.11, P = 0.38).

FIGURE 3

The fractional metabolic energy or power (O₂, aerobic; La, anaerobic lactic; PCr, anaerobic alactic) utilized between 0–50 m (first histogram) and 50–100 m (second histogram) of dynamic apnea with fins (DYN). The O₂ and PCr contributions were estimated using the computational approach C1. The second histogram was derived from the difference between the data measured at 100 and at 50 m shown in Table 2. Three subjects used bi-fins, three used monofin, and one used both (n = 8 observations).