So, you are exercising. If you notice more pronounced muscles, then perhaps your actual body fat percentage is less than a calculated BMI estimate. If you belong to a health club or know someone in the Physical Education department at your local university, ask if there is an exercise physiologist or registered dietitian that can measure your body fat.
There are several electrical impedance body fat analyzers on the market. The problem with them is there are many variables that affect the reading.
The Journal of the Academy of Nutrition and Dietetics and probably the American College of Sports Medicine have advertising from companies that make these devices. They are not cheap. For reading, I would suggest an exercise physiology book by Frank & Vic Katch, 2 nationally known experts in this field for a description of methods to assess body fat.
Basically one places an electrode on the dominant hand and foot. A small electrical charge passes through the body. Muscle is 70% water and fat is 15%. Therefore, if you have more muscle, the charge moves faster. The problem is hydration, alcohol, menstruation all affect the results. The inherent errors are higher than a trained individual using calipers. Likewise, because a body fat measurement is a snapshot in time of your muscle mass, it will change daily, but not so much that the measurement discernible changes. It would only be wise to re-test every 3 – 6 months for change as a result of a regular exercise program.
Read my sports nutrition topic for other body fat assessments like hydrostatic weighing (underwater).
You are very lucky to be so tall. You burn more calories because you have a greater surface area than a shorter person. If you just follow the recommendations for a healthy lifestyle i.e. eat low fat (< 30% fat) foods based on My Plate Food Guide and exercise 30 minutes 5 times per week, you should be able to keep your weight and BMI in a healthy range.
That said, as an athlete, I would rely more on body fat than BMI. As you build muscle, your weight may go up and that would increase your BMI which would inaccurately reflect increased health risk. Whereas if you rely on body fat analysis, then as your body fat goes down, you are healthier and stronger to play. However, there is a point at which increased muscle mass (comparable to a bodybuilder) will negatively affect performance.
You are also fortunate in that males because of testosterone have a higher proportion of muscle to fat which is even more pronounced in African American males. This positive effect of testosterone on muscle mass should continue till you reach 70 when testosterone levels drop.
As I said, BMI is a health risk estimate based on a mathematical equation of a population. I am checking on the extremes of height’s effect on BMI but I don’t think height has anything to do with screwing up BMI assumptions. Your point about long legs, short legs is accurate in terms of muscle size. However, fat is distributed all over the body from the ankles to the neck, except in the brain (though some people are an exception to this rule). Hope you laughed.