Is it muscle, or is it fat?

Here's every athlete's dream: eat all the pizza, ice cream, and chips you want, and any weight you gain will be all muscle.  Sound too good to be true?  Well, of course.  I already said it's a dream.  In the real world, if you don't eat properly, you gain fat, not muscle.  And sometimes even if you do everything according to the book, you still gain weight -- maybe muscle, maybe fat.
   One of the great ironies of exercise is that it causes too many people to get fatter, not thinner.  This is especially true of those who are just beginning exercise programs at the local mega gym.  They feel so incredibly energized by their workouts that they assume that they can eat whatever they want.  So, naturally, many of them eat whatever they want, often consuming far more extra calories than they burned off during the workouts.  Let's face it: consuming 500 calories is a lot easier than burning 500 calories.
   Okay, so life isn't quite fair.  But suppose you're a senior martial artist who trains regularly.  And let's suppose further that you've incorporated strength training into your training regimen, because pumping a little iron is extremely important even to aging athletes.  Finally, let's suppose you begin gaining weight.  Is the new weight all muscle?  Is it fat?  Or is it a little of each?
   There are two simple ways to decide.  1.  Flip a coin, since any answer you give yourself is as accurate as another.  2.  Step on a bathroom scale that measures body-fat content in addition to weight.  I prefer method #2, because it gives me facts, not guesses.  And out of all the body-fat measuring schemes I've examined, this one is by far the most user-friendly.
   For well over 20 years now I've used a Tanita scale.  The folks at Tanita aren't paying me to say good things about their scales, and they haven't given me any freebees to tout the brand.  So what you're getting here is only what I believe: every athlete's bathroom or training room should include a Tanita scale.
   Tanita scales measure fat using a process called Bioelectrical Impedance Analysis, or BIA.   You step on the scale, and a small electrical impulse passes from one foot to the other.  No, you don't feel a thing.  But while the current passes through your body, it distinguishes between fat and muscle through a series of complex calculations that some scientist with a PhD might understand.  Fortunately, you and I don't need to know the math.  All we have to do is read the numbers.  First you get total body weight, and then you get  your percentage of body fat.  If you buy one of the slightly more expensive scales, you also get a third statistic: your body's water content [generally above 50%, since we're built mostly of water].
   How often you step on your Tanita scale is up to you.  I use it every day, because I like to track the effects of certain foods on my body weight and water content.  But over longer periods the scale helps me understand how my weight gain or loss is affecting my muscle mass.  The more muscle mass the better, of course, because among other things more muscle means a faster metabolism, and that translates into a more efficient fat-fighting machine.
   By the way, the Tanita scale comes with a useful booklet that helps you understand what your body-fat percentage should be.  For a 66-year-old male like me, the average healthy range is something like 13-25%.  For women of the same age the range is more like 24-35%.  Some Tanita scales also have an Athlete mode for those who are into serious training, and this mode does some extra calculations to reflect the fact that athletes of any age will likely have lower body-fat readings than non-athletes.
   Are the Tanita scales accurate?  Since I'm not a scientist, I can't answer this question authoritatively.  So I'll hedge a bit.  Once you've established a baseline figure -- let's say it's 14% body fat -- you can keep that number in mind and see how it changes from week to week or month to month.  All you're really after anyway is the direction of your body-fat content.  Are you gaining muscle, or are you gaining fat?  By the way, it's important to use the scale at roughly the same time each day, because the readings will change throughout the day as you exercise, eat, and drink. 
   Bottom line: training religiously is the key to peak performance in the martial arts, and part of your training program should be tracking whether your hard work is successfully keeping body fat under control.