Bent-over Dumbbell Row

Major Muscles and Actions Involved in the Bent-Over Dumbbell Row

The bent-over dumbbell row with both the neutral and pronated grips is a good substitute for the seated row for developing almost all of the back musculature. In this exercise you do not have to contend with the upper body moving forward and back.  Variant 1: Neutral grip This variant involves shoulder joint extension, in which the lower pectoralis major, the lower latissimus dorsi, and the teres major participate. The action is assisted by the posterior deltoid. In this action your elbows move from a position in front of your body down and back until they are behind your trunk.  Downward rotation and adduction of the scapulae occur in the shoulder girdle when your arms go beyond the level of your back. In this action the lower edges of the scapulae turn inward toward the spine while the upper edges of the scapulae are turned outward on an axis through the center of each scapula when viewed from the rear. As your arms go back past your body, both scapulae move in closer to one another and to the spine.   Variant 2: Pronated grip variant In this variant the basic action is different from the neutral grip variant. It involves the posterior deltoid, the teres minor, and the infraspinatus in shoulder joint horizontal extension. In this action your arms travel in a horizontal plane (to the body) from a position in front of your body out to the sides and behind your trunk. In the shoulder girdle the middle trapezius and rhomboid muscles are involved in scapula (shoulder girdle) adduction. In this action the scapulae move from an out-to-the-sides position on the rib cage to close to the spine. In essence, they slide in toward one another and the spine. The arm actions are basically the same as in the neutral grip variant.     

Passive and Active Flexibility

Passive flexibility refers to the range of motion (ROM) available when an outside force (i.e., gravity, momentum, another body part or another person) is the causative force. Active (dynamic) flexibility is the ROM produced when muscle force (or gravity) creates the movement range. If the muscles are weak, the ROM will be less than it should be. A passive range of motion shows little correlation to an active ROM. Because you exhibit a great ROM in a static position, it does not mean that it relates to what you do when performing actively. The two are not related! If you desire an active range of motion, you must do active stretching. If you desire a static or passive range of motion, then you should do static stretching. In active stretching, the muscles that are actively involved do so primarily in the eccentric contraction. For example, when you raise your arms overhead as in the lateral arm raise, you are eccentrically stretching the latissimus dorsi and teres major. These muscles undergo an eccentric contraction as you raise the arms to not only control the movement but also to stop the arms from going beyond the capability of the joint. Another example is to lie on your back and then raise one leg as high as possible. Then lower and raise the other leg and repeat in an alternating manner. Every time you raise the leg, you are using the hip flexor muscles to eccentrically stretch the hamstrings and increase the range of motion in every repetition. You can also use gravity as the force to produce active stretching. For example, if you do a good morning exercise keeping the lower back in its normal slightly arched position as you bend over from the hips, you will elicit an eccentric contraction in the hamstrings. Gravity is responsible for pulling the trunk down and the hamstring muscles need the eccentric contraction to control the down movement. When you rise up and each time you go down, you should experience a slightly greater ROM. But you do not force an increase in the range of motion. It happens due to the muscle or gravity pulling. Note that these stretches are more natural since they duplicate what occurs in everyday and sports activities.

Why study the Kinesiology and Biomechanics of Exercise?

Biomechanics and kinesiology are important fields of study for students, educators, and trainers that are interested in exercise science. Here are some pragmatic reasons why.  By analyzing the movements that are performed in an exercise biomechanically and kinesiologically, you can you determine which joint actions and muscles play a major role and if the exercise is effective and safe. Characteristics of exercise such as grip, body, and limb position have an impact on muscle involvement, so it is important to understand how they affect the results you will obtain in a training program. Proper technique can help duplicate sports specific movements and improve athletic performance. 
Biceps Curl

Bicep Curls and the Angle of Muscle Pull

When your arm is straight, the angle of pull of the biceps is very weak. Almost all the force of the flexor muscles is directed to pulling the forearms into the upper arms, and only a small amount of residual force is used for rotating the forearm. However, as the forearm moves closer to the horizontal position, the angle of pull changes dramatically.  When the angle of pull is 90 degrees (when your forearm is close to the parallel position), the entire biceps muscle is being used to lift the forearm and the weights. At this time there is no or very little stabilization force (forces that pull into the elbow).  Because of this you are much stronger when your arms approach the 90-degree angle, and the weight that seemed heavy when your arms were straight now appears to be quite light. Thus, for maximum development of the muscle through the full range of motion, you should work it in the straight-arm and bent-arm variants. 
Levers in the Human Body

Muscular-Structural Arrangements in the Human Body

Wheel and Axle Wheel and axle-like arrangements in the body are needed for the transmission of force. A good illustration of this is shoulder joint medial and lateral rotation. For example, hold the upper arms in line with the shoulders, elbows bent 90 degrees, and the forearms vertical and holding a weight in the hands. Lower the forearm downward behind the head, maintaining the 90-degree angle (or greater) in the elbow to execute lateral rotation with the axis along the long shaft of the humerus. When you raise the hand in the opposite action you execute medial rotation in which the humerus rotates in the opposite direction (forward) on its long axis. In this case, there is a short radius of rotation of the humerus, but with the forearm bent at a 90-degree angle you generate considerable speed or force at the end of the forearm (the hand). Many strength exercises involve some rotation of the arms (or legs). To prevent injury to the muscles involved especially when executing medial and lateral rotation, you should not execute other actions in the same joint at the same time. This is often difficult to see but it typically happens quite naturally. Pulley Systems Another muscular-structural arrangement in the body is the pulley. Pulleys are very common in exercise machines such as in the lat pull-down to create a greater mechanical advantage and to move the limbs freely. In the body, we find a pulley type system in the knee joint, more specifically, with the patella. The quadriceps tendon (ligament) goes over the patella to insert on the tibia bone in the shin.Because of the patella protrusion, the quadriceps tendon inserts at a greater angle to create more of a straight-line force when the knee is in the bent position. As a result, you generate greater force which goes around the patella to change the direction of pull. There are few such pulley type muscle arrangements in the body. Most pulley (cable) systems (free weight machines) create the ability to guide and move the resistance handles in various directions, especially the free motion systems. Depending upon the configuration of the pulley or pulleys you can increase or decrease the amount of effective resistance. Some pulley machines even have an extremely strong negative component. After you execute the lift in an exercise, the weight stack is raised. At this time the amount of force involved in lowering the weights can be extremely high. Thus care must be taken on different exercise machines. To prevent an injury you should become familiar with the exercise machine before using appreciable weight.
Abdominal Machine Crunch

Major Muscles and Actions Involved in the Abdominal Machine Crunch Exercise

The upper rectus abdominis and internal and external obliques are most involved in the machine crunch. These muscles are responsible for flexion of the spine in which the upper trunk curls toward the hips. On some machines, after the crunch action the movement continues via hip joint flexion. In this action, the abdominal muscles undergo isometric contraction to hold the bent-over position, but only if you go through a maximum range of motion which also involves the hip flexors.
Bar Dips

The Bar Dip Exercise

The bar dip is one of the best exercises for the chest, back, shoulders, and triceps. Most dipping bars are similar to gymnastic parallel bars so that when you do the exercise you must use the neutral grip, with your palms facing your body. If you want even greater development, you should use bars on which you can also use a pronated, supinated or 45 degree grip as well as different widths for the grip as for example on adjustable dip bars. This allows for even greater strength of the muscles involved as well as bringing other muscles into play. 
Muscle Synergy

Muscle Synergy

Because the term synergy has been used in so many different ways in the popular press, its meaning has become somewhat diffused. In the field of exercise it should be used in two ways. One is helping synergy in which two muscles contract simultaneously to produce one movement for which they are suited, while their other actions cancel each other out. For example, in the sit-up, when the internal and external obliques contract, they have a tendency to not only perform spinal flexion but to rotate the shoulders. In order to prevent the shoulder movement, the internal and external obliques cancel out their rotational action and the resultant force is used for spinal flexion.  Second is true synergy in which a different muscle contracts to stop the secondary action of another muscle. For example, the biceps brachii is both a supinator of the forearm and a flexor of the elbow joint. Thus, in elbow flexion, the pronator quadratus comes into play to cancel the supinating tendency of the biceps so that only flexion occurs. The pronator teres also comes into play, but since it is a flexor of the elbow it acts as a helping synergist.  Synergy can also be used synonymously with the term neutralizer. In other words, a muscle acts as a neutralizer when it contracts to counteract or neutralize an undesirable action of another muscle during its contraction.
The Antagonist Muscle Role

The Antagonist Muscle Role

An antagonist muscle is one which has an action directly opposite that of the agonist. When an agonist undergoes a concentric contraction, the antagonist undergoes an eccentric contraction to guide the movement and to stabilize the joint. These are very important roles of antagonists. As the movement goes through the full range of motion, the antagonist muscle develops greater tension as the ROM increases and then stops the movement before it goes beyond the normal range of motion (ROM). It should be noted that the role of antagonist and agonist can change depending upon the action taking place. For example, in the biceps curl, the biceps is a prime mover while the triceps is the antagonist. When the triceps is involved in elbow extension it becomes a prime mover and the biceps becomes its antagonist. Thus, we see how one muscle can serve different functions. During a muscular contraction, especially when the weights are very heavy, both the agonist and antagonist, undergo contraction (known as cocontraction). This is needed to stabilize or hold the joint in place while the action occurs. When the resistance is very light, the agonist and especially the antagonist are not strongly contracted. The antagonist undergoes a strong eccentric contraction mainly to slow down and stop movement before there is injury to the joint. When the weights are very heavy, both agonist and antagonist are under contraction. In this case the antagonist contracts eccentrically and lengthens to make the movement possible.