In fitness there are three ways to access your metabolism:
1. Anaerobic (very short bursts of breathless work, unsustainable),
2. Interval training (i.e. HIIT, Tabata, etc., containing 20-30 seconds of hard work followed by a resting period), and
3. Aerobic (elevated heart rate for 45-60 minutes). Aerobic is the oldest and most commonly used method of targeting the metabolism, however we take it farther by adding in muscle fatigue. When you fatigue your muscles you are building lactic acid.
The more you fatigue, the more your muscles shake, the more lactic acid you build. Then your body breaks it down into lactate and metabolizes it for energy. The more lactate your body has to metabolize, the more it burns through your fat and carbohydrate storage. So the more you shake = the more calories you burn.