You want to be lifting Upper, Core, and Lower Body throughout the week and also be doing cardio. Ill go to the gymn monday through friday, keep friday light if your planning to ride sat, and ill start up with a warm up on the stationary bike, or run....running ill do a faster pace maybe pick it up as i progress but ill do a mile n a half or 2 miles then go to lifting. If i do the Stationary bike ill do a good 10 minute interval program on it. On the ones at my univ you just hit hill plus and theres a list of diff programs for hills: cascades, speed interval, hills, interval, kilamajaro (sp?) etc Ill do interval to get my heart rate up well. It starts you out one just a flat surface then hit you with a small incline then flat then a bigger incline flat and the inclines will get to the max twice then they start goin down then you cool off. The heart moniters dont work on it for some reason during the interval probably becuase you heart fluctuates so much but it wont kick in until the cool down and when the cool down starts im at about 165-160 and it was for a 20 year old at 80% 160 is the ideal heart rate. So im sure when the interval is at its peak incline im pushin 180 i would guess. But anways....from here go lift
For lifting iv been doing the steve hatch workouts....hes got 5 different excercises for upper, core and lower. Heres the dvd
http://www.youtube.com/watch?v=gqKW455LuW8 Ill do those plus a couple other excercises. Either upper or lower, then the next day the opposite. After my upper or lower ill do 5 core excercizes. I have to different workout plans for them so one day ill do the one set of core excercises, the next day ill do the other.
Then back to cardio....at this point i strongly recomemend using the rowing machines.....my gymn at the univ luckily has 5 Concept 2 rowers, the ones endorsed by MTF and many MX trainers for the pros etc. I like to do circuits but when your starting out i would do a week of just steady rowing no pressure to get the form down and get a feel for it all After your ready i would start doing some interval circuits! They will kick ur @$$ but they are well worth it and they are really fun.....youll def feel good afterwards....well youll feel good about yourself moreso. Rowing is great for MX because you work your legs just like standing and sitting on the bike, your core which is also used on the bike, and your arms pulling the bars on the machine into your body just like pulling in the bars on the bike. Latly iv been doing a circuit where you do 200M sprint, then you have 45 secs to hop off and do 10 dips, 10 barbell pushups (set two barbells on the ground apart about the same distance your grips are on ur handle bars and grab those and do 10 pushups then do 10 weighted crunches with a 35 or 45 lbs plate held above your head then hop up n right back on the rower n 200 M sprint and so forth but heres a good list from Racerx of different motocross training circuits on the rower
http://www.racerxvt.com/category/concept2-rowing Videos 5,6,7, and 8 are great MX specific circuits
http://www.racerxvt.com/article/product-review-concept2-rower go half way down and there are some general workouts on the rowing machine
Hope this helps
