Seriously how's even possible? You looked malnourished to start with.
A row machine is one of the best exercise tools for this sport.
Easy slim!
Kyle, I recently started lifting hard again and training like no other since I entered B class. I gained 21 pounds in a couple months. What is going to help you most for long motos is cardio stuff. Running and mountain biking is best, and I highly recommend a rowing machine. I lift three days a week and run before each workout. I suggest timing your motos and run (not jog) the same time on a tread for the a few "motos". It adapts your heart and endurance to the regular time of a moto.
While cardio is very important, I found lifting is essential to maximum performance. I work my way from bottom to top, typically leg pressing, leg curl and do varied squats, some on balance boards, some planted, ect.. I work my way up to core doing suspended curl ups. Arm exercises are really important to eliminate arm pump. I typically do pull ups, back elevated pushups, benching, chest pressing and a few others. Lastly I finish up the day with some medicine ball exercises.
I just found this plan to work best for me. To find or modify your own, try Racer X.
http://www.racerxvt.com/category/daily-training-with-coach-seiji/16
http://www.racerxvt.com/
Lastly, some guys your protein supplement and some don't. That's up to you, but typically I mix a 32g muscle milk shake to drink during the workout or before. In my honest opinion muscle milk is the best route.
http://www.musclemilk.com/
Lastly, it's best to set aside a proper work out outfit. This prevents spread of gym sweat and shit as well as giving you a comfortable, non motion limiting outfit. Get a GOOD pair of clean tennis shoes. This is most important, because your street shoes will smell so bad your mom will throw them outside, and chicks defiantly don't like that. Athletic shorts or pants are very important, as well as a soft cotton t shirt.
good luck out there dude. Ride hard and stay gnarly, hope the links guide you.