Climbing is a physically demanding activity, requiring proper conditioning and training. In addition to the strenuous activity of walking uphill with weight on your back, you will be breathing less oxygen because of the elevation. With less oxygen your muscles will be working at a diminished capacity.
Before climbing Mt. Hood, you should go on several training hikes. These hikes should consist of elevation gains of 3,000-5,000 feet and distances of 2-4 miles to simulate the slope of Mt. Hood. Locally these are climbs such as Table Mountain, Dog Mountain, Hamilton Mountain and Mount Defiance to name a few. During these hikes, if possible, carry the equipment you will climb with. If you do not own all the equipment you will need, put other items in to simulate weight. A pack of 20-30 pounds is average for a Mt. Hood climb.
A person who exercises regularly and is in good physical health should plan on doing 5-10 of these sorts of hikes before a climb. Those who do not get regular exercise or have other health problems should consult their doctor for an exercise routine appropriate for them, and slowly add in hikes with elevation and a weighted pack.
Every climber should also be trained and practiced in self arrest and crampon techniques. These are skills you will need for the climb. It is also important that each climber is familiar with other skills that conditions may require, for example: belays, rope-team travel, crevasse rescue, avalanche condition assessment, avalanche transceiver use, first aid, navigation and rappelling. Remember that the safety of every climber on the mountain is at risk whenever a single climber is unprepared.