Effect of simulated air combat maneuvering on muscle glycogen and lactate

Muscle glycogen and muscle and blood lactate were evaluated before and after a +4.0/7.0 Gz simulated air combat maneuvering (SACM) protocol in the human centrifuge. The subjects were eight healthy males, ages 25-43 years. Muscle glycogen and lactate were determined from biopsies of m. vastus lateralis in six subjects and whole blood lactate was analyzed in finger-tip blood samples from eight subjects. G-tolerance time was 256 +/- 33 s (Mean +/- S.E.M.). The decrease in glycogen concentration averaged 81 +/- 36 mmol.kg-1 dry wt (p = 0.07). The rate of glycogen utilization was low, averaging 0.4 +/- 0.1 mmol.kg-1.s-1. Muscle lactate increased significantly from 28 +/- 2 mmol.kg-1 dry wt pre-SACM to 51 +/- 4 mmol.kg-1 post-SACM. Post-SACM blood lactate was 4.2 +/- 0.3 mmol.L-1. Neither final blood nor muscle lactate values nor the difference between pre- and post-SACM muscle lactate concentrations were related to G-tolerance time. It was concluded that glycogen availability in m. vastus lateralis is not a limiting factor during exposure to headward acceleration of this type and duration. The lactate values, while high, cannot fully explain the muscular fatigue occurring during centrifuge exposures of the type used here. Therefore, the suggestion by others that anaerobic energy metabolism in skeletal muscles is the crucial factor limiting the ability to resist fatigue during exposure SACM is not supported and is likely an oversimplification of a much more complex problem.