Not everyone has access to a gym or wants to go to a gym. If that is the case, you can complete an Isotonic training session using all, or some, of the following exercises.

Squats Without using a weight, perform the same motions as described elsewhere, but increasing the number of repetitions and working up to 100.
Sissy squats - Works lower quadriceps. Holding a wall or bench for support, rise up onto your toes and lean back very slightly. Then, still on your toes and your back straight, sink slowly into a shallow squat. Return to the start position and repeat. This is harder than you think, so start with ten and work up to 30.
Lunges - Works gluteals and quadriceps. Starting from an upright position, feet together, step forward with one leg, extending the other straight behind you. The heel of your front leg should be flat on the ground, and you should bend the knee so that you lunge into as deep a position as you can. Then return to the start position, by moving the bent leg, not the extended, rear leg.
Triceps press-ups You should be facing away from the bench, legs extended in front of you. Place the palms of your hands on the bench. Raise and lower your body by straightening and bending your arms at the elbow.
Press-ups - Chest, shoulders and biceps. With your arms slightly wider than your shoulders, place your hands on the bench and raise and lower your body by straightening and bending your arms
Partial sit-ups - Works abdominals. Lie on the floor with your knees raised. Place your hands behind your head, and keep your elbows pointing outward. Without pulling up on your head with your arms, raise up from the shoulders, then lower back to the ground.
Oblique sit-ups - Works abdominals and obligues. as above, but cross one leg over the other, resting the right foot on the left knee. As you raise yourself from the shoulders, twist from the waist and touch your right elbow to your left knee. Repeat for at least ten reps on one side, then change sides and complete an equal number of reps, to give you one set.