• The military has physical fitness standards.Jupiterimages/Comstock/Getty Images
  
  The Department of Defense sets the physical fitness standards for entry into every branch of the armed forces under Directive 6130.3. These standards, however, are extremely vague. Most people qualify to join the army based upon these standards. Once you're in, however, you'll be required to meet very strict physical standards and pass regular fitness tests.
  
  

Diseases

• You must be free of contagious or infectious diseases in order to join the military. Contagious or infectious diseases could include AIDS or HIV, measles, rabies, tetanus, Lyme disease and a host of other ailments. This requirement is in place to prevent you from making other soldiers sick or being unable to work yourself. Fortunately, some contagious and infectious diseases are treatable.
  
  

Medical Conditions

• You must be free of medical conditions or physical defects that would require excessive time lost from duty or would likely result in separation from the Service for medical unfitness. You can't join the armed services if you have some medical or physical condition that would prevent you from actually doing your job as a service person. This means that you cannot join the military while you are pregnant. You also cannot join if you have cancer and are expecting to go through chemotherapy.
  
  

Capable of Completing Training

• You must be medically capable of satisfactorily completing required training to join the military. This requirement is where enlistment gets tricky for some people. While there are no set-in-stone standards for fitness to join, once you are enlisted you will have to endure basic training and pass a series of physical fitness tests. These tests are different for every branch of the military and the military is allowed to judge whether you are capable of completing them without giving you a chance to try. This requirement may prevent obese people from enlisting.
  
  

Adaptability

• You must be medically adaptable to the military environment to join. This requirement is also purposefully vague in order to give the military leeway when it comes to judging potential recruits. Medical adaptability may prevent older recruits from joining up. Technically, you can join some branches until you are 42, but if you are not in good shape you may be denied on the basis of adaptability. This requirement also prevents you from joining if you have some allergies or sensitivities, such as to light.
  
  

Aggravated Conditions

• You must be medically capable of performing duties without aggravation of existing physical defects or medical conditions. This means that in order to join up, you must not be suffering from severe asthma or diabetes or some other health problem that could be aggravated by physical stress.