Our bodies contain three types of muscle: smooth muscle, cardiac muscle, and skeletal muscle. The smooth muscle is controlled subconsciously by our brain and carries out bodily functions like digesting food. The cardiac muscle is also controlled subconsciously and acts by contracting around the chambers of the heart in order to pump blood. We can train and develop this muscle when doing cardiovascular activities (hence the name “cardio”). By making the heart muscles stronger, it is able to pump more blood with a single contraction, thus being able to deliver more oxygen to the body. Lastly, our skeletal muscles are the ones attached to our skeleton. We control these muscles and have the ability to train them in order to increase strength.
Individual skeletal muscles are composed of smaller bundles of muscle fascicles, which in turn are composed of smaller bundles of muscle fibers, which in turn are composed of smaller myofibrils. Inside the myofibril is the structural unit where protein filaments connect and contract. The amount of these connections (or cross-bridges) is a determinant in the amount of force your muscle can produce.
At the level of the muscle fiber, we recognize three basic categories of fiber types: Type I, Type II A, and Type IIX. These fiber types get their energy from different means and have a trade off between amount of force generation and fatigue.
The Type I fibers are called “slow twitch,” this is because they have a slower contraction velocity. While they do not produce much force, they are extremely fatigue resistant. These fibers get their energy through oxidative means, so they have a large blood supply. When a muscle is composed of primarily Type I developed fibers, the muscle appears red due to this large blood supply. If you eat a duck breast compared to a turkey leg, you will notice that the duck breast is bright red but the turkey leg is white. This is because ducks need a lot of slow twitch, fatigue resistant fibers in their breast so they can fly thousands of miles for migration. However, a turkey uses their legs only for short, powerful bursts, so their legs are made up very developed fast twitch types.
Type IIA fast twitch fibers use both oxidative and glycolytic means of energy consumption. This allows them to produce high force while being moderately resistant to fatigue. Type IIX fast twitch fibers use primarily glycolytic means, so they are very strong and fast, but offer very poor fatigue resistance. Both of the fast twitch are used to create powerful bursts of energy.
When we contract our muscle, we do not use every single fiber every time. A motor unit is the term that describes a group of muscle fibers that are innervated together. When we contract our muscles for something that requires little force, we only recruit a few motor units, primarily composed of slow twitch fibers. When we need all of our force for something strong, we contract more/all of our motor units, including those primarily composed of slow twitch and fast twitch.
Gaining Strength
Exercise produces acute stress, which elicits a response from the body. Training produces a chronic stress over time, which leads to an adaptation from the body. Resistance training, over time, can cause increases in both muscle size and strength. By understanding how our bodies react to exercise and training, we can tailor our workouts towards your personal goals, in order to attain better results.
Strength gains come in two forms: Neural adaptation and Hypertrophy. Neural adaptation is the broader term for increases that unrelated to muscle size change. Performing repetitions increases our synchronization of motor unit recruitment, decreases autogenic inhibition (your muscle wanting to give up when fatigued), and decreases activation of antagonist muscle (if you want to contract your bicep to bring your arm up, you want your triceps to be as relaxed as possible so it does not inhibit the movement). Most neural adaptation takes place in the beginning of training and also during skilled movements, which requires greater coordination.
Hypertrophy refers to an increase in muscle size. Resistance training over time will lead to muscle hypertrophy, which takes place in two ways. One of called fiber hyperplasia, which means you actually increase the total number of muscle fibers inside your muscle. This does not occur in great numbers and is a rather minor factor in overall muscle hypertrophy. The other form is fiber hypertrophy, when the individual muscle fiber gets larger. Simply speaking, the larger the fiber, the more cross-bridges are formed between the protein filaments of myofribils.
These extra connections allow for greater force to be generated, thus an increase in strength. This increase takes place by training over time. A “muscle pump” refers to your muscles appearing larger during exercise. This is not muscle hypertrophy, but rather an increase in fluid build up in interstitial space.
The term “no pain, no gain” is actually correct. We increase our strength by increasing our cross-bridge connections, through microscopic, focal tearing. This focal tearing, which leads to delayed onset muscle soreness, is beneficial. However, this is not to be confused with tearing a muscle at the macroscopic level, which damages the muscle.
By manipulating how much resistance we are lifting, along with the time we lift for and rest time between sets, we can better target the types of muscular gains we want to see. In general, low repetition numbers at high resistance train our fast twitch fibers, leading to great gains in strength and power (ideal for a power lifter). High repetition numbers at low resistance train our slow twitch fibers, leading to gains in endurance muscles (ideal for endurance runners). Medium resistance for a moderate amount of repetitions is a balance between the two. This chart shows general recommendations for rest between sets and repetition recommendations.
| Workout Variables | Strength/Power | Hypertrophy (body shaping) | Endurance |
| Sets (min-max) | 1-4 | 2-5 | 1-3 |
| Reps (min-max) | 1-8 | 8-14 | 15-25 |
| Time Under Tension | 4-30 seconds | 30-70 seconds | 60-100 seconds |
| Rest between Sets | 2-4 minutes | 1-2 minutes | 30 secs -1 minute |
The term “super-setting” refers to using the rest time of an exercise for one muscle group to complete an exercise for a different muscle group, alternating sets. This provides an additional cardiovascular component, but typically only done for moderate or endurance resistance.
There are three types of muscular contractions, all of which can be used during workouts as means of resistance training. Isometric contractions are when the muscle is firing, but maintains the same length (such as doing a plank). Concentric contractions are when the muscle shortens (raising the arm in a bicep curl) eccentric contractions are when the muscle lengthens (lowering the arm in a bicep curl). Both the raising and lowering of the arm in a bicep curl is done by the action of the biceps.
“Negative resistance training” is the term for when the lifter does an eccentric contraction, to lower the weight, and then allows a spotter to lift the weight back up (either entirely or greatly assisting). For example, when performing a bench press, the lifter slowly lowers the bar from extension down to their chest and then the spotter raises the bar back up. This type of exercise takes advantage of the motor unit recruitment our bodies do during an eccentric contraction. Our bodies recruit less motor units when doing an eccentric contraction, which raises the amount of force per unit This greater force per unit allows for greater focal muscle tearing, thus leading to greater delayed muscle soreness, and greater strength increase.