Reduction in LBNP tolerance following prolonged endurance exercise training

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology
• Human Physiology

Background:

• Endurance exercise training is known to induce significant cardiovascular adaptations.
• Understanding how these adaptations affect hemodynamic regulation during stress is crucial.

Purpose of the Study:

• To investigate the impact of an 8-month endurance exercise program on maximal oxygen uptake (VO2max), blood volume, and tolerance to lower body negative pressure (LBNP).
• To identify the physiological factors contributing to changes in LBNP tolerance post-training.

Main Methods:

• Eight young men completed an 8-month endurance training program.
• Measurements included VO2max, total blood volume (TBV), plasma volume (PV), and LBNP tolerance (cumulative stress index - CSI).
• Hemodynamic responses (cardiac output, heart rate, arterial blood pressure, forearm blood flow, leg volume) to LBNP were assessed pre- and post-training.

Main Results:

• VO2max increased by 27.4%, TBV by 15.8%, and PV by 16.5% post-training.
• LBNP tolerance (CSI) decreased by 24% post-training.
• Reduced peripheral vascular resistance response and greater systolic blood pressure reduction during LBNP were key predictors of decreased LBNP tolerance.

Conclusions:

• Prolonged endurance training enhances VO2max and blood volume but impairs LBNP tolerance.
• Adaptations in vasomotion and cardiac output regulation contribute to reduced LBNP tolerance after endurance training.