To improve our overall physique we must build lean muscle and burn fat. To accomplish both simultaneously let's forget about weight training combined with traditional cardio for a moment. The most effective method to burn fat and build muscle at the same time is using HIIT or high intensity interval training and more specifically the Tabata intervals protocol.
Tabata intervals are named after Dr. Izume Tabata who published a study in 1996 on an interval training protocol used by olympic speed skaters. The idea is to go all out for 20 seconds, slow down or rest 10 and repeat 7 more times for a total of 8 interval sets. Sounds easy but trust me Tabatas are extremely intense. In fact, when it was first used by the olympic speed skaters most couldn't get past 7 sets.
The great thing is during the study by Dr. Tabata found that aerobic and anaerobic capacity were improved significantly. After 6 weeks VO2 max, the ability to burn oxygen increased by 14%, one of the highest increases ever reported in exercise science, while anaerobic capacity increased by, get this, 28%. To put this in perspective a traditional cardio only group tested during the study increased VO2 max by 10% with no gain in anaerobic capacity.
If those numbers don't impress you they should. The traditional group's total workout time averaged 60 minutes while the group that performed the Tabata protocol took only about 15 minutes (10 minutes of warm up and 4 minutes of intervals). That's right, assuming you're warmed up a 4 minute workout is all it takes.
The word you're looking for is, wow! That's an incredible finding that could change the way we all approach exercise.
Tabata intervals can be performed in a variety of ways, with weights, cardio machines, body weight exercises, wind sprints, etc. The most effective exercises employ large muscle groups. Squats and thrusters using light weight are good candidates. I can't emphasize the light weight enough. When you try your first set you may want to do body weight squats, or air squats as some people call them, until you get a feel for your personal limits.
Avoid exercises that require a long setup. It makes it that much more difficult to maintain the 20 on 10 second off interval. For instance if it takes 3 seconds to get into position you're losing either rest or work time.