Altitude

Physical changes at high altitude after full acclimatization has been achieved include reduced production of lactate post-exercise, increased tissue carbon dioxide, increased red blood cell mass, increased hematocrit, decreased plasma volume, a higher concentration of capillaries in skeletal muscles, increased myoglobin, increased mitochondria, increased aerobic enzyme concentration, increase in 2,3-Bisphosphoglyceric acid, hypoxic pulmonary vasoconstriction, and right ventricular hypertrophy.

The decreased lactate production at altitude is called the "lactate paradox."