How Do I Know if I Gained Body Fat or Lean Muscle Mass?

I’m 5’5″ and I have recently gained 10 pounds. When I came to school in September, I was 135 pounds and now I’m 145 pounds! I know it is not the whole “Freshman 15” thing because I workout regularly and I eat pretty healthy. I don’t understand where the weight came from. Did I gain muscle weight? That doesn’t seem right though because I looked at the pictures of your fitness models and they’re all the same height as me, have an incredible amount of muscle, and most weigh between 120-135 pounds. I guess I just don’t understand where it came from and was hoping you could help.

When in doubt, look in the mirror and visually review your physique. Better yet, take photos every week (on Sunday) and track your physique changes. You will easily be able to tell visually if you’re gaining muscle or gaining fat. The scale can be misleading since your weight gain could be from water retention (high sodium intake). Pound for pound, muscle takes up less space than fat, so if you gained 5 pounds of pure lean muscle and lost 5 pounds of body fat, you will actually look smaller. Also, make sure to track your calories to pinpoint if you are actually eating the amount of calories you believe you’re consuming.

To assume you gained 10 pounds of lean muscle tissue is very doubtful, especially if you’re a female. Women simply do not have the adequate amounts of the hormone testosterone in order to gain a large amount of muscle mass. Even for men, gaining 10 pounds of muscle is very difficult, unless you are in your late teens and early twenties when your hormone levels are at their peak. If you can gain this amount of lean mass in a year, that is actually a huge success. So, when you ask yourself what exactly the extra 10 pounds you packed on might be, you should always focus more on water weight and body fat.

If you absolutely want to know for sure what constitutes your weight gain, I recommend contacting a local gym or University and inquire about taking a body fat test using either the hydrostatic method (going under water) or by using something called the “Bod Pod” which is a machine you sit inside to measure your levels of adipose tissue (body fat).

Bod Pod Body Fat Testing Method
The Bod Pod uses a very similar principle to the Hydrostatic method, except it determines how much air you displace, rather than water. It uses air displacement plethysmography which uses whole body densitometry to determine body composition (fat and fat-free mass) for highly accurate, fast and safe results.

The best advantage of using the Bod Pod is the very fast test time and the comfort of the machine. It consists of about 2 minutes inside the Bod Pod and around 5 minutes total test time. You sit in a comfortable, non-invasive machine that looks like a little pod (hence the name) and in a matter of minutes, you are all finished.

Hydrostatic Body Fat Testing Method
The Hydrostatic method is considered the “Gold Standard” for being the most accurate testing method for finding out your body fat percentage. It’s also referred to as “underwater weighing” and it is a technique for measuring the mass per unit volume of your body. You basically measure the density of the body, and from that figure calculate your percentage body fat.

There are a few disadvantages of hydrostatic body fat testing which should be covered. Finding a testing location (gym, university) might be very difficult since many do not have the expensive equipment needed to perform this method of testing (water tank, etc.). However, you might be able to find a few companies that offer portable testing in your area. They have all the equipment in a huge RV style truck that they drive around to different gyms and offer easy access to get your body fat measured. The actual process of doing this test is also a little uncomfortable. First, you have to get into your bathing suit and then blow all the air out of your lungs before dunking yourself into the water for a set period of time in order to get the correct measurements. The other disadvantage is the cost involved. It can be a little on the expensive side ranging anywhere from $60-$200.

It’s always best to get your body fat percentage tested before you start your fitness program in order to get a baseline number for both your lean muscle mass and the amount of body fat you currently have. Then, after about 3 months (90 days) it’s always good to go back in and see how much fat you have lost with your exercise and diet plan. From there you can start tweaking your program to dial in the correct nutritional plan and exercise routine to really start making serious physique changes. The key is to always measure and monitor your fitness plan and physique through weekly diet and exercise journals, weekly photos and body fat testing every 3-4 months. Remember that what gets measured gets managed, so make that extra step and start really documenting your fitness plan so you can be successful and achieve the body of your dreams!

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