Progressive elevations in muscle blood flow during prolonged exercise in swine

Area of Science:

• Physiology
• Exercise Science
• Cardiovascular Research

Background:

• Human studies suggest muscle blood flow may be compromised during prolonged exercise due to rising skin flow and stable cardiac output.
• Previous rodent studies indicated progressive increases in muscle blood flow during sustained submaximal exercise.

Purpose of the Study:

• To investigate muscle blood flow distribution in miniature swine during prolonged treadmill exercise.
• To resolve the apparent discrepancy between human and rodent findings on muscle blood flow during endurance activity.

Main Methods:

• Radiolabeled microspheres were used to measure cardiac output (QT) and its distribution in pigs during treadmill locomotion.
• Exercise intensity was maintained at 71% of maximal oxygen consumption (VO2 max) on a level treadmill.
• Measurements were taken at the 5th and 30th minutes of exercise.

Main Results:

• Cardiac output (QT) increased by 23%, while total skeletal muscle blood flow rose by 49% from the 5th to 30th minute.
• Increased muscle blood flow was attributed to decreased vascular resistance, as mean arterial pressure declined by 7%.
• Muscle blood flow increases were consistent across synergistic muscle groups, irrespective of fiber type composition.

Conclusions:

• Muscle blood flow increases significantly over time during prolonged treadmill exercise in quadrupedal animals like swine.
• The data align with previous findings in rats, indicating a pattern of increasing muscle perfusion during endurance locomotion.
• Elevated body temperature, reaching approximately 42 degrees C, appeared to be the limiting factor for exercise duration.