Weight gain with new exercise programs
To understand why we gain or lose weight when we begin a new exercise program, we first must understand the basics about human skeletal muscles and how they function. With that in mind, here is a very basic primer on muscles.
To begin, let’s define what we are talking about. Skeletal muscles are what provide motion of all kinds in the body, unlike involuntary muscles such as smooth muscle (e.g. intestinal walls) or organ muscles (e.g. the heart) which are both involuntary systems that we don’t consciously control, skeletal muscles, in most cases, respond to our requests in the force that we request (or require) to perform work. Within this sphere of skeletal muscle, there are two distinct types of muscle, with the second having two sub-classes. Type I muscle fibers perform work mostly within the aerobic capacity, using oxygen to a high degree to create energy to do the work required of them, these muscles generally can work for long periods of time at moderate exertion levels, for instance, a long distance runner would train type I muscle fibers to allow for higher maintained endurance and speed. Type II muscle fibers have a sub-categorization of Type IIa and Type IIb, Type IIb muscle fibers work mainly in the anaerobic capacity (no oxygen) and are mainly used for short, high power bursts. Type IIa fibers can be developed to have characteristics of either Type IIb. or Type I fibers, the predominance of which is determined by the type of activity that is trained.
Now that you know the basic muscle types, I’ll explain what the heck I mean by “muscle fibers” muscles are made up of long, thin cells called fibers, these cells connect to connective tissue or directly to bone, and they also connect with the central nervous system (CNS). The brain tells the CNS how much power to exert to a muscle to do the work it needs.
Muscle fibers have only 2 states fully contracted and fully extended, there is no in between. So the brain will tell each fiber in a muscle or a subset of the whole muscle (called a bundle of fibers or just a bundle) to contract. To put this into real world scenario, to curl a 2 lb. weight, your biceps needs (random guess) 2% of its total potential power, so your brain would tell the equivalent amount of fibers to contract fully, the rest remaining dormant. To make that exact same motion, but with a 30 lb. weight, you need maybe 75% of your total power, so the brain would delegate that many fibers. This becomes very important for the next section where we talk about weight gain from exercises.
OK, so now you basically understand how skeletal muscle is constructed and the types we have. Now let’s talk about how they are fueled. Muscle has 2 main types of fuel, aerobic fuel, and anaerobic fuel. Glucose and glycogen are one type, they use oxygen as a catalyst to create Adenosine Tri-Phosphate, which is the actual energy a cell uses (called ATP for short). The body keeps most glycogen stored in the liver, but some, for the really fast needed energy at the muscle site, this glycogen is stored with water around the muscle site extra cellular (outside the cells in fluid form). When we use muscles over an above normal daily need, that glycogen (which is just long chains of glucose) is tapped and then replaced by the liver. I won’t go into muscle metabolism any deeper, but just know that this barley scratches the surface.
The other thing to keep in mind is muscle states. When we are sedentary for a long period of time or don’t use a muscle to its maximum for a long time, some of the fibers are never used. The brain essentially turns them off so that they aren’t taking up resources (calories). This is called atrophy. This can happen because of an injury (look at someone who’s been in a cast for 2 or 3 months, the casted limb is usually far smaller and weaker). In most cases of sedentary activity, the atrophied muscle fibers haven’t been cannibalized to a large extent, just switched off. The brain will NOT store glycogen for muscle fibers that are “switched off”
Now let’s put it it all together. When we begin a new exercise program, lots of things change. WELL before you start “growing new muscle”, your body starts recognizing the need for increased strength, and begins activating those unused, partially atrophied muscle fibers. Only when your muscle fiber incorporation reaches around 95% do you begin putting on actual muscle mass. This is why you can see dramatic strength gains (and endurance gains) in the first 4 to 6 weeks; you are “switching on” those dormant muscle fibers. Along with those fibers come glycogen stores and the water which suspends in. Also those muscles require other liquid mediums. Add to this the increased need for extra cellular fluids and you have pounds of weight added to your frame without adding size (significant size) or fat (or muscle mass either). Increased active muscle amount also increases the needs of those muscles from the body, and that means increase plasma volumes in the body. For weeks, sometimes months, you can go through weight gain without any accompanying size increases (or not much at least) but with significant performance gains.
What does this mean? It means YOU DON’T PUT ON MUSCLE AT THE START OF AN EXERCISE ROUTINE! There are exceptions to this of course, well-conditioned athletes that are just changing up their routine could possibly achieve muscle mass gains much faster, but that’s usually because their muscles have not atrophied nearly as much, but in general, things to look for follow:
• Weight gain while still increasing strength.
• Weight gain while in a caloric deficit (moderate deficit).
• Weight gain with reduced measurement size.
To be clear, even though this is essentially fluid weight, it’s not temporary unless you stop working out, you will always keep most of this fluid as your muscle needs it to function. But it will level out eventually and usually weight loss will begin again. Please note, except in special conditions, you usually will never gain significant muscle mass while in a caloric deficit. But you absolutely can re-activate your existing muscle fibers while in caloric deficit. Which, many times, is why people who begin a new routine, can have a fast plateau?
Also note, everything I talk about here is with regards to adults with no medical conditions. Children and those over the age of 65 or have medical conditions may have different things happening and need different explanations. I am not a medical professional, please treat anything I write as such, I am simply an experienced armature that has read and researched on the topic of nutrition and human metabolism.