If you train clients who participate in activities that take place at higher altitudes (low altitude < 3,950 feet; moderate altitude = 3,950–7,900 feet; high altitude = 7,901-13,125 feet; very high altitude > 13,125 feet), there are many factors you need to take into consideration. As elevation increases, there is less oxygen available, which leaves less pressure to push oxygen into the blood as it passes through the lungs. This ultimately leads to reduced oxygen in the blood. Clients training at higher altitudes (> 3,950 feet) will not be able to deliver as much oxygen to the working muscles. Therefore, a decrease in intensity will be warranted. Additionally, the higher the elevation, the greater the potential for reduced physical performance. So What Do You Need to Know as a Fitness Professional? It is essential that you are aware of, and be alert to, the signs and symptoms of altitude sickness: Shortness of breath Headache Lightheadedness Nausea For additional tips on acclimatization, check out the following tips from the Centers for Disease Control and Prevention: Please visit the following link and refer to Box 2-02 for tips for acclimatization and Table 2-07 to help you identify which clients may be at risk for developing altitude sickness: http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travel-consultation/altitude-illness For more information on exercising at higher altitudes, please review Chapter 2 of ACE’s Essentials of Exercise Science for Fitness Professionals.