Sparked by the comment “you use the fat as fuel to build muscle I thought”, I wanted to research the specifics of building muscle. This is not about building strength, but specifically adding muscle to the body. This muscle may or may not be of the strongest variety.
Building muscle boils down to three items needed by the body:
- Muscular trauma
- Adequate nutrition
- Adequate rest
I will tackle these all together as the biomechanical processes are linked.
Muscle trauma sounds painful or incorrect, but it’s the most obvious of the three needs for muscular growth. If you do not stress your muscles, the body has no reason to add muscle mass to compensate. Muscular trauma (also known as microtrauma) is a collection of small tears to muscle fibers. When you lift a specific amount of weight that is beyond what your muscles could handle without issue, small tears occur at various spots of the fibers. This trauma must be repaired and that processes adds additional muscle fibers. This trauma is also believed to be the reason for delayed-onset muscle soreness, the aching soreness normally felt 24-72 hours after a weight lifting session.
The mechanism by which the body adds this muscle is important, complex and will help figure out what a person should do to help add muscle. The muscle trauma directly causes a process called myogenesis, or literally muscle creation. The process is started when the damaged fibers call upon inflammatory cells such as neutrophils and macrophages to help remove the damaged portions of the muscle. After cleanup, the regeneration process is activated. Specific stem cells, called satellite cells, are activated all along the damaged muscle fiber and begin to multiply and relocate near the damage site. Some of the cells return to an inactive form, to be used for the next repair cycle. This activation is correlated with a strong upregulation of Myf5 and MyoD factors but the true mechanism is currently unknown. In activated form, the stem cells are called myogenic precursor cells (mpc) or myoblasts. The multiplication and growth of the myoblasts is amplified by insulin-like growth factor (IGF) and human growth factor (HGF).
At this point, the Myf5 factor promotes cellular renewal and MyoD promotes cell terminal differentiation. Basically, Myf5 keeps the process of creating more myoblasts going while MyoD tells the new cells to stop proliferating and to get ready for the next stage. Myogenin and various cadherins are then activated to fuse the myoblasts together or to existing areas of damaged muscle, completing myogenesis. (1,2,5)
The formation of myoblasts requires excess insulin and somatropin(3) and testosterone (4). Testosterone is specifically used to signal the satellite cells to act as muscle precursors. These cells are a limited type of stem cell and can actually be turned into bone or fat cells by wholly different processes. In a nutshell, your body must produce enough testosterone so that the muscle precursors are in the correct form, you need enough in the way of muscle building blocks (protein is used to create additional myoblasts) and enough energy to build the fibers (insulin).
Nutrition plays a dramatic role in not only muscle growth, but recovery and muscular energy levels. The muscle stores carbohydrates (glycogen) to use as fuel when contracting. Numerous articles are available that discuss the proper foods to eat, when to eat them and what to avoid. The goals of these guidelines are to avoid insulin spikes (which can cause additional fat cell generation which takes away insulin from being used to build muscle) and to make sure the proper nutrients are available at all times. In general, the post-workout time frame is the only one where a different nutrition plan should be followed. In this key time frame, you need to make sure that easily digested carbohydrates and proteins are available. If available, the muscle will be able to quickly replenished depleted glycogen stores and be prepared to begin the muscle repair process (which usually doesn’t start for 12 hours after damage).
Myogenesis may not be complete for upwards of five days (6) so a constant flow of building blocks (protein) and energy (carbohydrates) are needed. The carbohydrate need is dramatically lower in comparison to immediately following a workout but is still required. Protein intake should be roughly 1 gram per pound of bodyweight and to keep insulin in control, should be spread out between at least five meals.
Back to the core comment about “using fat to build muscle”, the primary purpose for fat is as long-term energy storage. Fats are used for other key processes or structures within the body such as within cardiac cells and used within cellular membranes. Using carbohydrates as an energy source is cheaper due to a simpler metabolic pathway but the body can only store so much in the way of carbs.
The triggers for either burning or creating fat cells boils down to energy usage and calorie supply. If the body is sedentary and has extra calories, the body will convert the extra energy into fat to be stored in fat cells. If available normal energy sources (AKA carbs) are low and the body requires energy, fat will then be burned. Burning fat is an aerobic process (requires oxygen) and at high energy consumption (vO2 max greater than 75%), the rate at which fat is burned will decrease. Note that it isn’t black and white, the body will use a mixture of carbs and fat during the average workout. Even when the vO2 max rate is hit, fat will still be used, just in much lower quantities.
In a nutshell, if the body is trying to build muscle, it needs protein and energy. Normally, the body will utilize carbs for this purpose but I’m sure if carb availability was low, energy from fats could be used. I wonder if the low-carb craze forced any research into the idea of building muscle while on a low-carb diet. All I know is that when I went super low carb for a month, I lost fat rapidly (no carbs? gotta use fat for energy) and had a very difficult time putting on any muscle. All I know is that it’s best to add muscle if you want to lose fat. One pound of muscle burns approximately 25 calories per day. In contrast, a pound of fat only burns about three calories per day. The more muscle you have, the more calories you burn just sitting around, let alone using those muscles in the manner they were intended. All of you that try to lose weight by eating reduced fat Oreos and then hitting the elliptical for an hour? Maybe you should try hitting the free weights next time.
1. De Bari, C., Dell’Accio, F., Vandenabeele, F., Vermeesch, J., Raymackers, J. , Luyten, F. (2003). Skeletal muscle repair by adult human mesenchymal stem cells from synovial membrane, JCB 160, 6: 909-918
2. Groundsa, M.,Whitea, J., Rosenthalc, N., Bogoyevitchb, M. (2002) The Role of Stem Cells in Skeletal and Cardiac Muscle Repair, J Hist. Cyt. 50: 589-610
3. De La Haba, G., Cooper, G., Elting, V. (1966) Hormonal Requirements for Myogenesis of Striated Muscle in Vitro: Insulin and Somatotropin PNAS. 56, 6: 1719-1723
4. Rajan Singh, Jorge N. Artaza, Wayne E. Taylor, Nestor F. Gonzalez-Cadavid and Shalender Bhasin : Androgens Stimulate Myogenic Differentiation and Inhibit Adipogenesis in C3H 10T1/2 Pluripotent Cells through an Androgen Receptor-Mediated Pathway: Endocrinology Vol. 144, No. 11 5081-5088
5. SOPHIE B. P. CHARGE´ AND MICHAEL A. RUDNICKI (2004): Cellular and Molecular Regulation of Muscle Regeneration: Physiol Rev: 84: 209–238
6. McGeachie JK, Grounds MD., (1987): Initiation and duration of muscle precursor replication after mild and severe injury to skeletal muscle of mice. An autoradiographic study: Cell Tissue Res. 248:125-30