Artificial altitude can also be used for hypoxic exercise, where athletes train in an altitude simulator which mimics the conditions a high altitude environment. Athletes are able to perform high intensity training at lower velocities and thus produce less stress on the musculoskeletal system. This is beneficial to an athlete who had a musculoskeletal injury and is unable to apply large amounts of stress during exercise which would normally be needed to generate high intensity cardiovascular training. Hypoxia exposure for the time of exercise alone is not sufficient to induce changes in hematologic parameters. Hematocrit and hemoglobin concentrations remain in general unchanged. There are a number of companies who provide altitude training system, most notably Hypoxico, Inc. who pioneered the artificial altitude training systems in the mid-1990s.