alright, settle down, i'm not an expert and don't claim to be one (joking tone)and writing this doesn't mean your gonna take the fun out of riding. On the contrary, adding a little purposeful training to any type of riding you do whether it be rail trail, family style or hardcore singletrack can add tons of excitement and add a little pep to the daily grind. Knowing how your body acts and how to train it can make your riding even more fun and enjoyable so take this thread with that approach. I read journals not only for work but for biking related stuff. if you have info you want to share, please do, that's why i posted this.
Strength training: Many people think of wght training as working against cycling but research has shown that even for endurance athletes it's critical. The specialists at the Olympic training center have discussed this topic and says it's essential for endurance athletes along with short distance athletes as well. Max strength is directly related to endurance athletes esp in high intensity events(i.e. xc races) See endurance events can be 90min xc races as compared to short track or track racing. The more strength you can have will help with your overall fitness. The key is being specific.(Strength Conditioning Journal: 28/2006) This can be whittled down to road vs. mountain b/c of the upper body strength needed for mtn bike events. Bench press, squats, lunges etc are whole body(bench somewhat) movements which can help your overall performance. Pre-season is different that during the season. Try it out: do 1-2 workouts per/week during the season to see how it helps you last longer in races, recover quicker etc. Also, don't forget plyometrics to help with explosive movements. XC and esp DH require quick burst of energy to handle quick movements.
http://www.sport-fitness-advisor.com/plyometrics.html
the info is not set in stone. people respond to things differnetly so experiment SAFELY and always write it down so you can review what works and what doesn't