# Question about bone density, muscle mass, and weight gain **URL:** \ **Category:** Factual Questions\ **Created:** [July 7, 2010, 2:27am UTC](https://boards.straightdope.com/t/question-about-bone-density-muscle-mass-and-weight-gain/545811 "2010-07-07T02:27:01Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![CorneaGenii](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@CorneaGenii](https://boards.straightdope.com/u/CorneaGenii)\ **Post date:** [July 7, 2010, 2:27am UTC](https://boards.straightdope.com/t/question-about-bone-density-muscle-mass-and-weight-gain/545811/1 "2010-07-07T02:27:01Z")
This whole mess came about as a result of watching “Losing It With Jillian Michaels”. I apologize, in advance, if the questions are indeed as mind-numbingly ignorant as they sound to my ears. I just need to hear the some facts from someone who actually knows. 1. Is a person genetically predisposed to being big-boned, or does bone density increase solely as the body’s response to additional weight gain whether from muscle or fat? 2. Also, if the weight gain is from fat caused by overeating, does muscle mass increase as a response to support the added weight? 3. Does genetics limit the amount of muscle mass a person can gain by body-building? For example, if Bruce Lee wanted to gain as much muscle as Arnold Schwarzenegger at the peak of his body-building career, could he? Feel free to point and laugh…:o ---
**Author:** ![Acid\_Lamp](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@Acid\_Lamp](https://boards.straightdope.com/u/Acid_Lamp)\ **Post date:** [July 7, 2010, 2:32am UTC](https://boards.straightdope.com/t/question-about-bone-density-muscle-mass-and-weight-gain/545811/2 "2010-07-07T02:32:54Z")
> [@CorneaGenii](#): > > 1. Does genetics limit the amount of muscle mass a person can gain by body-building? For example, if Bruce Lee wanted to gain as much muscle as Arnold Schwarzenegger at the peak of his body-building career, could he? Yes. Genetics plays the most important role in gaining muscle mass as there is a very real attainable limit without the use of steroids and the like. Take a look at bodybuilders of all different weight classes and you’ll see many different body types there. Primarily there are three: Ectomorph (defined with little muscle mass), mesomorph (well muscled all around medium definition) and endomorph (well muscled but trends to fat with little definition). Most people are a combination of two but many are purely one or the other. Genetics also plays a key role in such things as which muscle groups will be able to be best grown. Calves in particular seem to be genetic, with an immense amount of work required to gain mass if you don’t come “pre loaded” so to speak. ---
**Author:** ![Markxxx](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@Markxxx](https://boards.straightdope.com/u/Markxxx)\ **Post date:** [July 7, 2010, 12:20pm UTC](https://boards.straightdope.com/t/question-about-bone-density-muscle-mass-and-weight-gain/545811/3 "2010-07-07T12:20:07Z")
Yes the more fat you have the more muscle you will have to support that extra fat. Without steriods the average person can add only about 10 -15 pounds of pure muscle a year. Everything else will be fat. One of the things that confuses people is though you do absolutely control the amount you weigh, you do not control where it goes. For instance, I know many people of Puerto Rican heritage that happen to store their weight all over fairly evenly. (I do realize this is a generalization, it wouldn’t be hard to find exceptions). If you’re overweight but have fat in your stomach, your butt, your legs, your face, you’re still gonna look proportional. This opposed to the guy who is rail thin but has a gut that makes him look pregnant. That bubble butt is nothing more than fat being stored in a place people think is attractive rather than the stomach. Now there is a technique for adding additional muscle without steriods that seems to work for some people. As I said in general you can gain only 10 - 15 pounds of pure muscle per year, without steriods. But if you eat A LOT just shove it in, you will gain almost all fat but you will gain muscle to support that fat. Then you crash diet to lose it. What happens is you will find you can gain a bit more muscle per year that way. Maybe 3 pounds. Now that’s not a lot and frankly most people can’t lose the weight once they cram it on, and it’s definately not healthy. You have to remember that bodybuilders do it because the extra 2 or 3 pounds of muscle can make the difference between a first and second place finish. This translates to thousands of dollars for them. For the average Joe, that technique ain’t worth it. As for bone density, yes it does increase. This is VERY important to understanding why steriods are bad. Steriods allow more muscle to be gained, than you should. When you left weights you are telling your body to increase the muscle to accommodate this. But the body also increases the density of the bone as well as the flexibility of the tendons among other things. When you use steriods, you increase the muscle, but do nothing to increase the bone density or flexibility of the tendons. This is why steriod users easily break bones and tear tendons. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [July 7, 2010, 2:54pm UTC](https://boards.straightdope.com/t/question-about-bone-density-muscle-mass-and-weight-gain/545811/4 "2010-07-07T14:54:34Z")
> [@CorneaGenii](#): > > … > > 1. Is a person genetically predisposed to being big-boned, or does bone density increase solely as the body’s response to additional weight gain whether from muscle or fat? > > 2. Also, if the weight gain is from fat caused by overeating, does muscle mass increase as a response to support the added weight? > > 3. Does genetics limit the amount of muscle mass a person can gain by body-building? For example, if Bruce Lee wanted to gain as much muscle as Arnold Schwarzenegger at the peak of his body-building career, could he? > … 1. Gentics, BMI, and more. Yes, genetics has a lot to do with basic skeletal structure, and the amount of weight loading your bones have to deal with influences their density. Carrying around a load as BMI does increase bone density, as does a variety of weight bearing or impact loading physical activities. Vitamin D levels, calcium intake, and a variety of other factors also influence bone density. 2. Muscle does respond to carrying around more load, but that effect is often offset by the decrease in overall activity that a large BMI individual may be engaged in. A large sedentary person will likely have less muscle mass than an active lean individual. 3. Yes, we each have propensities to different builds. Obviously a woman couldn’t build herself to look like Arnold in his prime. But also individuals have different fractions of the different sorts of muscle fibers. Someone who is slow twitch predominant will be predisposed to do well in endurance events and will have a hard time bulking up no matter what they do. OTOH someone who is mostly the fast twitch populations will bulk up easily but could never train to the point of excelling in endurance athletics. I don’t know about Bruce Lee. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [July 8, 2010, 11:48am UTC](https://boards.straightdope.com/t/question-about-bone-density-muscle-mass-and-weight-gain/545811/5 "2010-07-08T11:48:41Z")
Funny enough, [this](http://www.medscape.com/viewarticle/723767_5) just happened to be on my Medscape homepage today. > [@](#): > > This study is one of the first to examine the independent impact of skeletal muscle mass alone on bone mineral content or to compare various estimates of skeletal muscle mass with respect to the relationship with bone mineral content in children. … When all three estimates of skeletal muscle mass and non-bone lean body mass (nbLBM) were included in one model, only MRI estimates of skeletal muscle mass independently predicted bone mineral content. In addition, when each variable was considered in a model alone, the use of skeletal muscle mass measured by MRI produced the best fitting model predicting bone mineral content and accounted for a larger proportion of the variance in bone mineral content compared with the other measures. Skeletal muscle mass was a predictor of bone mineral content after adjusting for other subject characteristics such that for two individuals of the same gender, age, height, race/ethnicity, and adipose tissue mass, the individual with greater skeletal muscle mass had a higher bone mineral content … In addition, Ackerman et al described the relationship between bone mineral content, fat mass, and nbLBM measured by DXA among 926 boys and girls ages 6 to 18 years.[4] They also reported that for individuals of the same weight, nbLBM was the strongest predictor of bone mineral content, and that fat mass was correlated with bone mineral content. This correlation between fat mass and bone mineral content only became negative after adjusting for total body weight. Given that fat free mass is a stronger predictor of bone, an increase in fat mass at a fixed body weight would predict a decrease in bone.