There is a saying in the NFL that champions are made in the off-season. This is where you can make the biggest gains in your overall strength and athleticism. Since you won't be tearing you body up with constant practice and tournaments, you can devote all of your time to getting stronger, quicker, and faster. You'll also have plenty of time to get adequate rest between workouts. The off-season is the time to return to the basics; you can spend all the time you want during the season on plyos and sport-specific drills. In the off-season, concentrate on the core lifts that will build strength in your major muscle groups.
Ultimate is a dynamic sport played in the vertical plane, with one or both feet pushing off the ground to complete most actions. Consequently, you should train in a manner that most closely resembles this type of motion. Do away with leg presses, hamstring curls and quad extensions. These exercises are great for body builders or fitness gurus, but not athletes. You want to start out with exercises that use multiple muscles and multiple joints. When you explode upward to sky for a hanging huck, you're extending your ankle, knee, hips and back to generate the upward force needed to carry you aloft. When you train, you should concentrate on exercises that use all of these joints in conjunction with each other.
You may be thinking to yourself, "Self, the leg press seems to use all of these joints, but didn't I just see the leg press is on the bad list?" Good job inner monologue, you were paying attention earlier. You can think of your limbs as a chain of muscles and bones connected to your trunk. If the end of the chain is pushing on the ground (or another fixed object, like the wall of a swimming pool), then this is called a closed kinetic chain movement. The end of the chain is not moving, so it is closed. Push-ups and squats are a examples of closed kinetic chain movements (CKCM). If the end of the chain is free to move, then this is an open kinetic chain movement (OKCM). Bench press and leg extension are open kinetic chain movements. If you look at the game of ultimate, the primary lower body functions of running, jumping and pivoting are closed kinetic chain movements. The primary upper body functions of faking, throwing and catching are open kinetic chain movements. Consequently, when you're training, you should emphasize CKCMs for the lower body and OKCMs for the upper body. The leg press, although it utilizes all the joints used for running and jumping, is an OKCM. The dead-lift and the squat are CKCMs that are better suited to training for ultimate. So, when you're designing a program, try and select movements that match the sport. Also, whenever possible eschew the machines in favor of free weights. There's no Nautilus on the ultimate field keeping your limbs moving in the perfect plane, so you need to train your ancilliary muscles to do this for you on the field.
The godfather of all sport training exercises is the clean and jerk. This is the ideal lift for ultimate as it emphasizes CKCM for the lower body and OKCM for the upper body. It also promotes explosive movement, especially in the hips. It is a lift that requires a bit of technique, so it's good to start learning at the beginning of the off-season so that you'll have mastered the motion by the time the pre-season rolls around. There are several good variations of the clean and jerk that are a little easier to learn, such as the power clean (catching the bar with legs above parallel) and the hang clean (starting with the bar at the knees instead of on the floor). Here's a couple of videos showing good power clean form:
The key to executing any clean and jerk for increased sport performance is the hip action. Really concentrate on re-bending the hips and pulling your body under the bar. Once you catch the bar, explode upwards with the hips. The great thing about cleans is they're a total body workout. You can do 6 sets of 3 clean and jerks with a decent weight and feel wiped out. Cleans and squats are the only exercise that I do from January to October. Everything else cycles in and out in various forms, but cleans and squats are the staple of training for explosiveness.
Dusty Smith has used his weight training regimens in helping himself and his teams (University of Georgia Jojah and Atlanta Chain Lightning) to be more explosive and durable.