Enhancing the Tolerance to +Gz Acceleration by Optimizing the Use of Isometric Contractions in Combination with Straining Maneuvers
Abstract
Experiments were performed on 9 male subjects who exerted L-1 straining maneuvers in a pilot chair apparatus with a seatback at 30 and a spine-to-thigh angle of 110. The L-1 maneuvers were performed with or without simultaneous application of isometric contractions. Contractions were exerted at high levels of force in either a sustained fashion or in an intermittent fashion, in 15 sec periods, until fatigue occurred. Isometric contractions were exerted by either the forearm flexors (handgrip), quadriceps, or jaw muscles at tensions of 70% MVC (handgrip, quadriceps) or 100% MVC (jaw). During the experiments, changes in arterial pressure, heart rate and electromyographic activity, from the intercostals and the contracting muscle group, were recorded. During the L-1 maneuver along, mean blood pressure (MBP) increased to 205 mmHg initially at the onset of the maneuver, but then fell by 50 mmHg, to 155 mmHg during the first 5 seconds of the procedure. The MBP recovered to 170 mmHg and remained at this level during the last 5 sec of the procedure. When isometric contractions were simultaneously applied, initial MBP were essentially the same as with the L-1 maneuver alone, but there was significantly higher MBP maintained throughout the remainder of the L-1 procedure with the isometric contractions, such that MBP averaged almost 30 mmHg higher during the last 5 sec of the procedure.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1990
- Accession Number
- ADA230454
Entities
People
- A. R. Lind
- Carole A. Williams
- J. E. Douglas
- J. Moffatt
- Jonathan Martin
Organizations
- East Tennessee State University