@Knuxchan wrote: I plan on getting a Fitibit Charge HR to monitor my heart rate so I can accurately keep track of how much I'm burning when I workout. Although I have no experience with the Charge HR for the time being, I'm sure it's an excellent device. However, it's not going to be optimal for your stated purpose, for the reason explained here. Even if you do get the Fitbit Charge HR, you would therefore still want to log your workouts (strength training) separately, rather than use the calorie burn reported by your Fitbit for these activities. As to the "calorie suggestion", the general consensus is it's easier to build muscle when on a caloric surplus than on a deficit, so you would want to eat slightly more than what you burn. You would also want to make sure you get enough protein, since it's the main building material for muscle. However, your problem may not be that you need to build abs (with 12-15 hours of martial arts and parkour per week, one would think you already have decent abs), but rather to make them visible. If so (could well be the case, since you're posting on the Weight Loss forum), this would mean getting rid of some of the fat layer on top of your abs. Lowering your body fat while building muscle at the same time is usually a tall order. You may want to check books by Lyle McDonald, for instance The Stubborn Fat Solution.
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