While there have been no publicly available, peer-reviewed scientific studies published on the physical effects of the Ranger course on students, it is not uncommon for these individuals to lose 35 - 50 pounds during the course. Common military folk wisdom has it that suffering through Ranger School takes a toll on the body not unlike years of natural aging; high levels of fight-or-flight stress hormones (such as adrenalin, noradrenalin, and cortisol), along with standard sleep deprivation and consistent physical strain, prohibit the students full physical and mental recovery throughout the course. This has a "snowball effect" and takes quite a physical toll on the student, making even the simplest task difficult.
Common maladies during the course include extreme weight loss, dehydration, trench foot, heatstroke, frostbite, chilblain, bone fractures, tissue tears (ligaments, tendons, muscles), swollen hands/feet/knees, nerve damage/general loss of sensitivity in the limbs (which may or may not fully return), cellulitis, cuts requiring stitches, and insect, spider, and bites from venomous wildlife (including the brown recluse, fire ant, scorpion, and water moccasin).
In addition to the physical ailments and damage suffered by the body, students must also recover from a drastic change in their metabolic status, brought on by the large calorie deficiency experienced during the course.