Please make time for the Challenger Sierra suggested training program. The hike may have as much as 13 miles in a day. Training for a half marathon will be appropriate and helpful. Hal Higdon's training will help with all conditioning levels: https://www.halhigdon.com/training/half-marathon-training/

Core training is very helpful to get your body ready for the demands of the trail. HIIT workouts can be found on YouTube. 20-30 minutes 3 times a week is recommended for 8 weeks prior to Challenger.  

It is important to hike at least 50 miles in the boots you plan to wear on the trail. There are lots of loose rocks and elevation changes on the trail, so good boots are important. They do not need to be high-top boots, yet good fitting and sturdy. Running shoes will not be sufficient with the terrain and the weight of the pack. Learning to use trekking poles will be very helpful as they engage your upper body and reduce fatigue in your legs. They also assist with balance and the steep elevation changes experienced daily on the hike.  

Properly adjusting your pack, with weight is important. Please consult your local hiking supply store, or REI for assistance. Hiking several times with 25 pounds or more will be helpful. Each hiker will need to carry 15-25% of their body weight on the trail.