Again, start low, go slow. For the chest and triceps, begin with knee push-ups, build up to classic push-ups, and eventually make these more difficult by putting on your pack and adding weight. For biceps and back, progress from modified chin-ups (bar at chest height, with feet on ground and body in piked position, underhand grip) to regular chin-ups. Eventually switch to an overhand grip. Also enhance abdominal strength with sit-ups. Don't go all the way up--just curl to about a 45-degree angle. Make these progressively harder by holding a weight on your chest. For each, start with one set of 8 to 12 reps and move up to three sets.