Can an astronaut get a backache while in space, since there is no gravity?

Yes, astronauts can experience backache while in space. Despite the lack of gravity, they still experience physical strain due to their bodies adapting to microgravity conditions.

In a recent study conducted by NASA’s Human Research Program and Life Sciences Division, it was found that nearly two-thirds of astronaut participants reported low back pain during long duration spaceflight missions. The research also indicated that even with countermeasures like exercise, approximately 75% of spacewalking crew members experienced discomfort or radiating symptoms in the lumbar spine after returning from an extravehicular activity (EVA) mission.

Other studies have suggested that because there is no gravitational force pressing down on the vertebrae and disks in the spine – allowing them to move independently and freely – astronauts could be more prone to herniated discs as well as bone demineralization over time due to increasing intervertebral height differences between each vertebrae when suspended in microgravity environments. It's theorized this increases stress on structures such as ligaments and muscles which can lead to increased levels of fatigue.

Finally, scientists believe that some astronauts may be predisposed genetically or through activity habits prior to flight which could lead them more susceptible injuries associated with weightlessness; however further research is needed before definitive conclusions are made regarding this theory.