Read the following paragraphs, and complete the exercises below. When the human body adapts to weaker gravity during long spaceflights, it loses
muscle mass, bone minerals, and some coordination between the nervous system
and the muscles. After spaceflight, astronauts may find that they cannot exercise
in an upright position on Earth until their body readapts to Earth's gravity.
According to research, the way to counter the effects of reduced gravity is to
have astronauts exercise in space in ways that stress muscles while maintaining
normal blood-pressure distribution. Astronauts also need to experience the nerve
and muscle patterns that are normally experienced during walking or running.
A DEVICE TO HELP ASTRONAUTS EXERCISE
The lower-body negative pressure (LBNP) device was developed to help
astronauts exercise. The LBNP device is a treadmill with a partial-vacuum
chamber, which is sealed around the exerciser's lower body. The partial vacuum
pulls blood and other fluids away from the heart and creates a gravity-like force
on the feet. The device is designed for upright use during spaceflight. A version
used on Earth for testing and training has cables and pulleys that support subjects
in a horizontal position.

Why would more attention be paid to exercising lower-body muscles and
bones than upper-body muscles and bones during spaceflight?