There should be at least seven weeks and no more than 3 months of sea level training between the altitude bouts. Upon descent, time is needed before the adaptations acquired at altitude translate to improvements in performance. Generally, coaches agree that the optimal training duration at altitude should be three weeks in duration. However, two weeks has also been shown to be of benefit. Sea level heart rates are difficult to use as an indication of intensity at altitude.
Heart rate is only a loose relative guide to recovery at altitude.
Normal iron stores during this time are not sufficient to meet iron demand for hemoglobin synthesis2. When training at altitude, athletes fatigue quicker and require longer recovery periods. Thus, it is important for athletes to get adequate rest. Naps are worth including in the schedule. This can be a problem at altitude.