If you wander by the magazine stands at Barnes and Noble, the fitness section is hard to miss. With images of bulging muscles, glistening biceps and fitness models with the perfect tropical tan, it’s easy to understand why many people believe that weight training will increase muscle size and make you look “bulky”.
Weight training can result in physical and/or functional changes to the working muscle including:
- Increases in muscle size
- Increases in muscle density
- Increases in muscular strength
These are the result of changes that occur within the structure of the muscle as well as the communication and connections between the muscle and the central nervous system.
To better understand the changes that occur due to weight training it is important to understand where it begins. All adaptations that occur from weight training start with the myofibril, the basic unit of a muscle (see diagram).
- Motor neuron: The neuron that directly or indirectly controls a muscle.
- Motor end plate: The end of a motor neuron that transmits neural impulses to a muscle.
- Muscle fiber: The long muscle cells that make up skeletal muscle.
- Myofibril: The smallest functioning until of a muscle.
The following sections will provide a better understanding of the adaptations to weight training and the important role of myofibrils.
Increases in Muscle Size
When a muscle increases in size it is known as “muscle hypertrophy”. The physical increase in size that we see in the mirror occur due to the following physiological changes:
- An increase in fluid found inside the myofibril.
- An increase in the contractile proteins (actin and myosin) found within the myofibril.
Muscle hypertrophy can be either classified as “short term” or “long term”.
Short term Muscle Hypertrophy – is the “muscle pump” that occurs from a single weight training workout. The immediate increase in size occurs in the myofibril. In this case, myofibrils are infused with nutrient-carrying fluid to feed the muscles that are being worked.
Long Term Muscle Hypertrophy – is associated with long term weight training. The myofibrils experience an increase in both the volume of contractile proteins and nutrient-carrying fluids. There is also an increase in the connective tissues surrounding each muscle fiber (a group of myofibrils bundled together).
Increases in Muscle Density
Density is defined as “the degree of compactness of a substance” (www.dictionary.com). The term “muscle density” is often misused and misunderstood. Muscle density refers to the proportion of contractile proteins to cellular fluid found within the myofibrils. A myofibril that contains more contractile proteins and less cellular fluid is more dense than one that has fewer contractile proteins and more cellular fluid.
Increases in Muscular Strength
Muscular strength refers to the muscle’s ability to generate force against an object. As it relates to weight training, most people measure strength by how much weight one can lift for a specific exercise.
During the first 2 to 8 weeks of a new weight training program you will experience increases in strength without physical increases in size. This phenomenon occurs because of specific changes in the central nervous system including:
- Increased activation of motor units (consists of a bundle of muscle fibers and a single motor neuron)
- Improved pathways of communication to these motor units
- Improved coordination of multiple motor units working together at one time
Next Steps …
Muscle size and muscle strength are two different things, as are the workout programs designed to achieve those results. In this series on muscle development you will learn how muscles work and adapt to weight training and how to structure your workout program to get the functional and/or physical changes you are looking to achieve.