What is a way to protect your skeletal and muscular systems from injury?

a.
lift heavy objects quickly.

b.
avoid exercise.

c.
carry at least 20 lbs. in your backpack at all times.

d.
lift heavy objects with your knees bent.

D.
Lift heavy objects with your knees bent.

People who utilizes the progression principle will ensure their exercise program increases in frequency, intensity, time, and type. the changes need to happen gradually in order to ensure they make gains in their fitness program. a person who doesn't utilize the progression principle can still gain health benefits from exercising, but will not continue to improve in cardiovascular fitness.

That’s what i was going to say.