Muscle fiber type composition and G-tolerance

The relationship between sustained G-tolerance and muscle fiber type composition was studied in 28 fighter pilots and 10 nonpilots. The G-tolerance, as assessed by the aerial combat maneuver (ACM) acceleration profile and modifications of it, was measured in a human centrifuge. Percutaneous muscle biopsies were obtained from m. vastus lateralis at rest. Histochemical analyses were carried out to identify and calculate the percentage of fast twitch (FT) and slow twitch (ST) fiber types. Additional analyses were performed for determination of muscle fiber size and capillary density. Mean (+/- S.D.) muscle fiber type composition in pilots and nonpilots, respectively, were 60 +/- 5 and 52 +/- 10% FT. There was no correlation of fiber type composition, fiber size, or capillary supply with G-tolerance. It is concluded that muscle fiber type composition and associated metabolic characteristics do not modify sustained G-tolerance to any significant extent.