Problems with humans spending expended time in space.
One of the problems is bone loss occurs at a rate of 1 to 1.5 percent a month also being in a weightless environment can also increase risk of kidney stones and bone fractures. microgravity alters the ability of bones to heal after fractures. There is loss of muscle mass, strength and endurance.
Solutions to the problems with spending time in space.
Astronauts and crews are carefully selected, trained, and monitored to minimize risks and to promote health and safety. Improvements are constantly being made to spacecrafts, in-flight medical care capabilities and countermeasure protocols, as well as post-flight rehabilitation.