Don’t attempt to squeeze in a full workout session in half the time. Crammed workouts increase your chance of injury, and stop you from lifting as heavy as you should (the shortened rest periods hinder full recovery). If you don’t have 45 minutes to devote to legs, cut back on isolation exercises and the total number of sets and reps performed. Make sure to give your scaled-back workout 100 percent effort. You can still get in an effective, time-pressed workout.