1. Little or no physical challenge is compulsory. Activities may include an optional short hike or bike ride. Pre-trip conditioning is generally not required.

2. Your heart rate will rise at times. Activities may include low altitude hikes of up to 4 hours, paddling in small rapids, or travel by horse. For an individual of reasonable fitness, pre-trip conditioning is not required, but doing so may improve your enjoyment level.

3. Expect to be challenged. Activities may include daily bicycle rides of up to 50 miles or daily hikes of up to 8 hours over varied terrain. If regular aerobic exercise isn't part of your life, you should start a pre-trip fitness routine.

4. Even if you're very fit, expect to be seriously challenged. Activities may include steep 12+ hour hikes at high altitude or consecutive daily 50+ mile bike rides in hot weather. Vigorous pre-trip aerobic workout is mandatory.

5. Not for novices. This category includes activities such as more than a month of hiking in deep snow at very high altitudes and possibly oxygen-enhanced final stages. You need to be in top cardiovascular condition and have excellent stamina.