We report on the results and validation of the model NELME (Numerical Emulation of Long-Term Microgravity Effect) across a wide variety of altered gravity scenarios. Computer simulations have become increasingly available tools for making predictions on the outcomes of complex physiological systems in extreme environments. However, technical limitations and difficulties of finding out opportunities to produce large series of experimental data to validate the models have made it difficult for these models to become available. In the recent years, this situation has changed as supercomputer facilities have increased their power; and more experimental data from parabolic flights and other altered gravity platforms are available to researchers as well. Results are provided about different simulations that have been conducted for short, medium-term and long exposures to microgravity; along with different events embedded. These simulations may include simulation of physical aerobic exercise during a mission, EVAs, thermal stress or human exposure to altered gravity scenarios (centrifuges, Martian or Lunar gravity, rocket launch, etc.). Risks for human health that may put in jeopardy a manned space mission in a variety of scenarios are evaluated and discussed.