By Garrett Giles
To understand muscle groups and how training certain muscle groups can be advantageous to your workout and increase efficiency, we must first understand muscle contraction and muscle recruitment. Skeletal muscle is made up of very small contractile units. There are two types of units: thick filament called myosin and thin filament called actin. These filament slide over each other thus causing a muscular contraction. Myosin has finger like structures that grab onto the actin, and then pulls the actin to cause a contraction. In order for the myosin to attach on the actin a few other processes must happen first. First, an action potential, also called a nerve impulse, is sent to the muscle via the T- tubules, which then releases calcium from the Sarcoplasmic Reticulum. The calcium then binds onto a structure which sits on the actin called troponin. Once calcium is attached to the troponin, tropomyosin, which acts like a cover keeping myosin from attaching, moves allowing myosin to complete the cross-bridge and grab ahold of the actin to then perform a muscle contraction.
Next, we will discuss muscle recruitment. To begin you need to understand what a motor unit is. A motor unit is the motor neuron and all the muscles it innervates. A motor neuron can innervate different muscles that are near each other, and muscles can have more than one motor neuron, which will produce a stronger muscular contraction. According to the all or none principle when a sufficient electrical signal is sent to a motor unit all the muscles it innervates will contract. Sending a stronger electrical signal does not produce a stronger muscular contraction, however recruiting more motor units that innervate the same muscle that is being used will. This process typically happens naturally. If you are bench pressing a submaximal load, you may not need to recruit as many motor units to lift that weight as opposed to a maximal or near maximal load.
Now that you have some basic knowledge on muscles and muscle recruitment we will discuss muscle groups and different styles of training. Compound exercises recruit more than one muscle group to perform that exercise, whereas isolation exercises only recruit one specific muscle group to perform that exercise. Some examples of compound lifts include bench, squat, deadlift, and bent over row and some examples of isolation exercises include bicep curls, triceps extension, chest fly. The more muscle groups you use during an exercise you will burn more calories, develop greater strength, and build more muscle than isolation work. Compound movements are going to give you the greatest benefit while saving time in the gym because you hit multiple muscle groups at once rather than spending time on only one muscle group at a time.
Typically, when training for performance you pick muscles groups that imitate the movements of sports and then pick exercises starting with power movements, moving to core compound movements, and finishing with accessory and isolation movements. This training style is a great way to increase performance because you are directly increasing force production and power output from the muscle groups directly involved in your sport. On the other hand, it would not be the best training method for aesthetics because the focus is on strength and power, as opposed to muscle size. Also, this training style does not typically put emphasis on isolation movements, which are beneficial for aesthetics to help maintain muscular balance and symmetry. Another benefit to this training style is it reduces the risk of injury by recruiting large muscle groups in the beginning of the workout that require high skill and focus, and as the body fatigues it focuses on lower skill, isolation exercises. Instead of training only one or two specific muscle groups, these programs typically focus on full body workouts that are well balanced to reduce muscular imbalances, ensure each muscle is adequately stimulated each week to promote strength and power, and start with high skill exercises and finish with low skill exercises to reduce risk of injury. This style is best utilized when time is not a limiting factor and you are looking for performance over aesthetics.
Training only one muscle group a day like a bodybuilding is an ineffective long term training routine ex. Monday- chest, Tuesday- back, Wednesday- legs, Thursday- shoulders, and Friday- arms. This routine will be effective for beginners but as they continue to train using this style it will eventually not be enough stimulus to elicit and muscular or strength gains. This style of training does not provide enough stimulus frequently enough for more advanced lifters to continue growth because too much rest time will pass between training muscle that particular muscle group again which leads to a detraining affect. The reason this happens with more advanced lifters is because they adapt to this training style, and there is an insufficient overload in the programming. Just like many other aspects of the human body it needs to constantly be pushed and challenge to improve, and like most skills they need to be practiced regularly to become better at said skill or progress will become stagnate.
Another training method for targeting the same muscle groups is called a giant or compound set. A giant set is starts with typically a compound movement for one group of muscles then pick 2-3 more exercises, typically isolation or other accessory exercises, that train the same muscles and complete one set then move to the next exercise. Using the chest as an example, you would start with a bench press, then move to a dumbbell incline chest press, then to chest fly, and then finishing with push-ups. This training method is a great method to use to really bring up one lagging muscle group by increasing the volume for that muscle. It is also a great method to use while traveling and equipment is limited, or does not get heavy enough.
Another common training method is to superset opposing muscle groups such as the bench press and a row in the horizontal plane. This is also known as a push-pull training session. Another example of a superset would be doing leg extension followed by leg curl. By using this method of training, you can keep your body balanced thus reducing overuse injuries, maximize strength by increasing stability and control during lifts by training opposing stabilizing muscles, increase training efficiency by building in rest for one muscle group while working the opposing muscle group, and increase intensity of workout. This is a great training method when time is limited.