Aerobic Capacities of Freediving Mammals
Posted By Erik Seedhouse on 31 March 2003
Estimating Residual Lung Volume from Age, Stature, and Body Mass
In freediving, RLV affects the depth a diver may achieve without experiencing problems associated with a 'thoracic squeeze'. Normally, the free diver's TLC: RLV ratio at the surface will determine the maximum diving depth before experiencing a thoracic squeeze. One method a freediver is able to calculate RLV value is by performing the following calculations.
RLV Prediction Equations
Variables: age (y); St, stature (cm); BM, body
mass (kg).
Normal-weight males
RLV (L) = (0.022 x Age)
+ (0.0198 x St) - (0.015 x BM) - 1.54
Normal-weight
females (only age and stature used)
RLV (L) = (0.007) x Age) + (0.0268
x St) - 3.42
The mechanisms by which these 'divers' resolve the conflict between the energetic demands of diving and conserving limited oxygen stores are similar to the problems faced by terrestrial freedivers and are not fully understood. However, our marine counterparts do have some physiological advantages at their disposal.
For example, the maximum dive time is not determined solely by the seal's oxygen storage capacity because seals can function anaerobically. However, aerobic metabolism is favored over anaerobic because it is much more efficient. Lowering their metabolic rate allows seals to increase the amount of time they maintain aerobic respiration while diving because it allows the oxygen store to last longer. Also, by selectively perfusing tissues the seal is able to increase the duration of oxygen stores. The point at which a freediving seal -- or 'regular' freediver - must either take in oxygen or switch to anaerobic respiration is the ADL. Levels of lactate in the blood will increase above resting levels once the ADL has been reached and will result in a burning sensation in the muscles.
So how do seals function anaerobically? Unlike human tissues, seal tissues
have a high tolerance for the 'asphyxial triad': low oxygen, high carbon
dioxide, and low pH. The low oxygen concentration is caused by oxygen
consumption through aerobic respiration, the carbon dioxide is waste created
by working muscles and the low pH results from lactic acid produced by
anaerobic respiration. A high tolerance for this triad allows a seal to
function anaerobically after oxygen supplies have been depleted.
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