The physiological basis of the aerobic dive limit (ADL), the dive duration associated with the onset of post-dive blood lactate elevation, is hypothesized to be depletion of the muscle oxygen (O2) store. A dual wavelength near-infrared spectrophotometer was developed and used to measure myoglobin (Mb) O2 saturation levels in the locomotory muscle during dives of emperor penguins (Aptenodytes forsteri). Two distinct patterns of muscle O2 depletion were observed. Type A dives had a monotonic decline, and, in dives near the ADL, the muscle O2 store was almost completely depleted. This pattern of Mb desaturation was consistent with lack of muscle blood flow and supports the hypothesis that the onset of post-dive blood lactate accumulation is secondary to muscle O2 depletion during dives. The mean type A Mb desaturation rate allowed for calculation of a mean muscle O2 consumption of 12.4 ml O2 kg–1 muscle min–1, based on a Mb concentration of 6.4 g 100 g–1 muscle. Type B desaturation patterns demonstrated a more gradual decline, often reaching a mid-dive plateau in Mb desaturation. This mid-dive plateau suggests maintenance of some muscle perfusion during these dives. At the end of type B dives, Mb desaturation rate increased and, in dives beyond the ADL, Mb saturation often reached near 0%. Thus, although different physiological strategies may be used during emperor penguin diving, both Mb desaturation patterns support the hypothesis that the onset of post-dive lactate accumulation is secondary to muscle O2 store depletion.
This work was supported by NSF grants OPP 0229638, 0538594 and 0944220. C.L.W. was supported by an NIH Marine Biotechnology Training Program Fellowship and a UC Regents Fellowship. J.U.M. was supported by a Los Angeles Achievement Rewards for College Scientists fellowship and a Philanthropic Educational Organization Scholar Award.
LIST OF SYMBOLS AND ABBREVIATIONS
- aerobic dive limit
- inspired O2 fraction
- light emitting diode
- muscle blood flow
- near-infrared spectrophotometer
- partial pressure of oxygen
- time–depth recorder
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