QUESTION:

I have found that the heart and the musculoskeletal system seem to be the
areas most effected by zero gravity. Are there others and how do they help
or hinder an astrnauts performance?
 

ANSWER from Bonnie P. Dalton on April 2, 1998:

Your information is correct concerning the vascular and musculoskeletal
system.  You are probably aware that there is a program within NASA called
countermeasures which is the conduct of varioius studies to determine what
kind of activities should be conducted to counteract the effect of
microgravity on the body while in space.  Because of the effects of
microgravity on the human system, the crew has a regular regime of exercise
while up there and there has been a constant plea with the crew to continue
on a prescribed exercise regime when they return.  Unfortunately, it is up
to the crew persons to choose to follow these requests or to disregard
them.

Also the effects are more severe for the long term missions, e.g., MIR
space station where the crew has been up for 45-90 days.  It often takes 6
months to 3 years to recover and gain full muscular strength from such
missions.  How rapidly this occurs, is dependent on the return exercise and
the individual.

We know that bone cells are laid down differently in rats flown in space
(0g) then they are on earth (1g).  Of course the metabolism of a rat is
much more rapid than that of a human.  As an example, the maturation of a
neonate (baby rat) from conception to birth is 20 days versus 9 months for
a human.  But we can deduct similar bone happenings in human.  We don't
have enough statistical data on humans on long term missions, due to the
fact we've not had that many people up there and we've not seen long term
effects, e.g., does someone in space have greater muscular problems and
bone problems in older age.   In short, much still needs to be learned.

Some early information has been obtained on rats on the effects on the hair
cells in the air and thus the effects on balance.  Hopefully the Neurolab
mission will given increased information and also other info concerning the
brain specifically, e.g., memory retention, nerve firings, adaptation and
nerve firings involved in micro-g.

In terms of performance of the crew in space.  Remember, they are
performing in a weightless environment so they don't have to work against a
resistive force.  In terms of performance and space motion syndorome (space
sickness), processes have been developed and Russian and some US crews
trained to monitor their pulse, temperature, and heart rate and then
perform activities to counteract the increased elevation of these elements
and thus avoid motion sickness.