WISE-2005 Protective Effect of Exercise within LBNP Countermeasure Detected by Heart Rate Response to Low Levels of LBNP

Sixteen women were studied before, during and after a 60 day, continu ous 6" head-down bed-rest (HDBR). Subjects were randomly assigned to two groups: Control (no countermeasures) and Exercise+LBNP (supine ru nning within an LBNP chamber for 40-min followed by 10-min passive L BNP for 3-4 days/week, plus flywheel resistive training of the legs e very third day). Cardiovascular responses were observed before bed re st, on day 50 of HDBR and R+8 after bed rest. Subjects were supine in the LBNP device with suction applied at 0, -10, -20 and -30 mmHg LBN P for 2-min per stage. In the pre-bed rest testing, there was no diff erence in HR between the groups at rest or at -30 mmHg. On HDBR day 50, HR was elevated at supine rest for the Con not the Ex group, whil e at -30 mmHg HR was elevated above pre-HDBR for both groups, but the magnitude of increase from Pre- to HDBR day 50 was less for the Ex g roup than for the Con group. The change in HR on HDBR day 50 is an im portant indicator as it was less than 24-hours after the Exercise+LBN P countermeasure on day 49. After bed rest, no specific countermeasu res were provided in the first week, so HR responses on day R+8 refle cted the effects of bed rest with or without countermeasure plus any recovery from simply returning to the upright posture. Relative to th e Pre-bed rest responses, HR on day R+8 had recovered in the Ex group but was still elevated in the Con group. These results indicate that the cardiovascular response to LBNP is preserved to a greater degre e during bed rest by the countermeasures, and further that the cardio vascular response returned to pre-bed rest much more rapidly in the E xercise+LBNP group than hi the group that received no cardiovascular countermeasures.