Instead of spending 90-minutes at the gym, cut it down to 30 to 45 minutes of high-intensity interval training. By working out at a higher intensity and giving yourself less rest, you accomplish more work in less time.
By performing HIIT workouts, you create an oxygen debt within your body. So even though your workout is over and you're back to your daily activities, your body is still working to restore the oxygen debt you created in order to bring itself back to its normal levels. This process is called excess post-exercise oxygen consumption (EPOC), and it can add 10-15% to your overall calorie burn for that workout.
Let's face it: Steady state cardio is great for catching up on the last few episodes of Quantico or Supergirl. But without the entertainment, steady state cardio can be downright boring (and long!). So, to prevent boredom and maximize your calorie burn, fast-paced HIIT workouts are the way to go.
Seriously. You don't even need to go to the gym to get an awesome HIIT workout in. Have an hour lunch break? Close the office door, put on some music, and crank out a 20-minute HIIT session.
Because HIIT workouts are a combination of strength and cardio, you will continue to build lean muscle as you get stronger and challenge yourself more. The more lean muscle you have, the more calories you will burn at rest.