September 2013

Lower body mechanics bolster overhead throws

9SM-iStock20183106v1Lower extremity biomechanics  can significantly affect the risk of upper extremity injury in overhead throwing athletes, such as baseball and softball pitchers and catchers, and the functional stability of the lumbopelvic-hip  complex is essential to preventing those injuries.

By Gretchen D. Oliver, PhD, FACSM, ATC, LAT, Hillary Plummer, MAT, ATC, and Lisa Henning

It’s well known that overhead throwing athletes, such as pitchers in baseball and catchers in baseball and softball, are at risk for injuries to the shoulder, elbow, and other upper extremity structures. What’s less well known is that lower extremity biomechanics can significantly affect those injury risks, and that the stability of the lumbo­pelvic-hip complex [LPHC] is essential to injury prevention.

It’s known that the LPHC and lower extremity can contribute approximately 50% of kinetic energy and force to the overhead throwing motion.1 The lumbopelvic-hip complex is comprised of the abdomen, proximal lower extremity, hips, pelvis, torso, and spine, along with the musculature originating or inserting on these segments. The musculature of the LPHC becomes active during both lower extremity movements and upper extremity movements, such as overhead pitching, as well as during preparatory movements for spinal stability.2,3 The function of the LPHC is to maintain lumbo­pelvic stability as well as serve as a direct link in the transfer of forces from the lower extremity to the upper extremity.4

Lumbopelvic-hip stability in overhead movements is the ability to maintain postural control, particularly of the trunk/torso over the pelvis, and the pelvis over the stride leg. This stability then allows for efficient transfer of forces from the proximal links of the lower extremity to the distal links of the upper extremity. Thus, a lack of LPHC stability results in decreased force production and compensatory segmental movements that can eventually lead to injury in pitchers.5

So why do we focus on strengthening the shoulder in overhead throwers? Should our concentration be on the lower extremity and LPHC?

The kinetic chain

9SM-12901527v1In the overhead throwing motion, particularly in baseball pitching, postural control is required to stabilize the trunk/torso over a single leg support (throwing arm side), and allows for the sequential rotation of the upper body segments as they rotate toward the target of home plate. In bringing to light the significant role of the lower extremity in the throwing motion, it is important to understand the kinetic chain concept of the human body.

The body is a series of interdependent links that work together to perform dynamic activities.1,6,7 The dynamic activity of throwing and pitching requires the kinetic chain to work in a sequential fashion of generating, coordinating, sequencing, and summating forces from proximal (lower extremity) to distal (upper extremity).6,7 Coordinated movement occurs through sequential activation of muscle contractions.6

It has been reported that, when examining an activity such as the tennis serve, the musculature and segments of the LPHC have the largest contribution to the body’s total angular momentum,6,8-10 with more than half of the force utilized to propel the ball being supplied by the lower extremity and LPHC.1,10 Force development begins with the lower extremity exerting a force against the ground, and force is continually generated and transferred through the LPHC. Force is then funneled up the kinetic chain through a stable scapula and shoulder and out to the elbow, wrist, hand, and on to the ball. Thus, in order to utilize the greatest amount of force from the lower extremity, an athlete has to have a stable LPHC.

The LPHC allows for the connection of the lower extremity through the gluteal muscle group to the upper extremity through the latissimus dorsi muscles. The activity of these muscle groups allows for LPHC stability, which, as mentioned earlier, is the ability to maintain or resume torso position following static and dynamic activities.11 The inability of the LPHC musculature to properly position the torso during dynamic movement creates an unstable base of support for the athlete. When the LPHC is unstable, typically the result is postural collapse and movement inefficiencies that can be seen in both the lower and upper extremities.12,13 Additionally, it has been reported that normal shoulder movement is achieved through a stable LPHC,14 thus stressing the importance of the musculature of the LPHC to function as an initiator of overhead movement.15

9SM-iStock13290013v1The shoulder is composed of mostly dynamic stabilizers that require proper coordination to maintain normal shoulder function, with the key to shoulder movement efficiency being a stable scapula.16,17 Muscular imbalance, weakness, or fatigue in these stabilizers can alter shoulder mechanics, which, in overhead throwing in athletes, can result in injury.18 A weak proximal link in the kinetic chain is often the cause of injury. In order to achieve dynamic movement efficiency about the shoulder in the overhead throwing motion, the shoulder joint should function as a funnel for energy and force transfer as opposed to a force generator.

When examining normal movement patterns, it has been reported that the upper extremity requires lower extremity and LPHC muscle activation prior to movement.19,20 In addition, for upper extremity movement to occur there must be sequential muscle activation beginning with the legs and trunk.19-21 Thus, based on sequential muscle activation sequencing, performing a volitional dynamic activity such as overhead throwing should involve a kinetic chain approach,1 and the LPHC musculature should be the initiator of all shoulder movement. The key to this force summation and sequential energy transfer is, first, a stable base of control (the LPHC) and, second, a stable scapula. However, in order for the scapula to be stable, the more proximal links of the lower extremity and LPHC must also provide stability. Because movements and energy transfer are dependent on the adjacent segment histories, an integrated
kinetic chain system is crucial.

Transfer of energy

The efficient generation and transfer of energy from the proximal lower extremity to the distal upper extremity determine the effectiveness of the dynamic movement of pitching and overhead throwing. The legs supply the ultimate force generation through the windup and stride phase of the movement. Then the scapula assists in transferring that energy through the shoulder and elbow and out to the wrist, the hand, and the ball.

9SM-iStock14452761v1It has been reported that a 20% reduction in the kinetic energy supplied by the lower extremity and LPHC requires a 34% increase in rotational velocity of the shoulder in order to produce the same velocity on the ball.22 This increase in rotational velocity of the shoulder can contribute to upper extremity injuries. Therefore, in an attempt to gain the greatest ball velocity with minimal risk of upper extremity injury, the overhead pitching movement should incorporate a total body approach of summating the forces from proximal to distal throughout the kinetic chain.

Studies on overhead throwing in the medical literature, in particular those examining baseball pitchers and catchers, have been limited. However, recently, researchers have begun to explore the effects of the lower extremity in throwing. It has been reported that the gluteal muscle group plays a role in the function of the pelvis and trunk during baseball pitching.23,24

Data have revealed that, in high school baseball pitchers, gluteus maximus activity in the drive leg exceeded 100% maximum voluntary isometric contraction (MVIC).24 It has also been reported that the leg muscles become highly active during the leg drive phase of pitching in attempt to attain the greatest ball velocity.23,25 Additionally, variations in pitch velocity have been attributed to lower extremity kinematics.26-28 Furthermore, in an examination of both baseball and softball catchers throwing to second base, data revealed that the gluteal muscle group plays a direct role in stabilizing the LPHC.29 Specifically, the activity of the gluteus maximus was directly related to the rate of axial pelvic rotation and inversely related to the rate of axial torso rotation,29 thus facilitating proximal to distal sequencing. The gluteus maximus extends and externally rotates the hip, while the gluteus medius stabilizes the pelvis during open chain activities as well as internally rotates the hip. Pelvic stability is the key to efficient energy transfer during throwing. During throwing, the pelvis has to maintain stability in effort to produce the greatest ball velocity. The function of the gluteal muscle group is to stabilize the LPHC, and the inability to maintain a stable LPHC results in kinematic alterations throughout the rest of the distal kinetic chain.

The pitching cycle

When examining pitching as well as overhead throwing mechanics, there are typically four events in the pitching cycle that are highlighted: lead foot contact, maximum shoulder external rotation, ball release, and maximum shoulder internal rotation. The event of lead foot contact (nonthrowing side) encompasses the windup and stride, which allow the body to optimally generate force.

During the windup, the center of gravity should be over the back leg (throwing side) in attempt to generate momentum to stride forward. The event of striding forward has major implications for energy generation. It’s important for the athlete to go from single leg support (throwing side) to stride foot (nonthrowing side) contact while maintaining a stable LPHC and controlling the rate of pelvis and torso rotation. An unstable LPHC will lead to a lack of control of the pelvis and torso, and a break in their sequential rotations.

If pelvis and torso rotation are not controlled, then rotation will typically occur prior to lead foot (nonthrowing side) contact and much of the energy generated in the windup will be lost. This early rotation will be evident by the position of the foot (nonthrowing side) at lead foot contact. If the foot is open toward first base (in a right-handed pitcher), or pointing to the left of home plate, then pelvis and torso rotation have probably occurred simultaneously and prior to lead foot contact. Also, if at lead foot contact the foot is positioned closed in the direction of third base, or to the right of home plate of a right-handed thrower, the opposite holds true; meaning the pelvis and torso rotation are lagging and therefore the energy is not available to be transferred, and the pelvis and torso have not rotated efficiently.

In addition to pelvis and torso rotation, contralateral torso tilt has also been seen in overhead throwing and has been speculated to be associated with uncontrolled torso rotation and a lack of LPHC stability.30 In either scenario, the body has lost a large amount of the kinetic energy that it generated during the windup and now at the event of maximum external rotation, the shoulder must generate the energy as opposed to funneling it. The muscles about the shoulder are not as efficient at generating forces as they are at functioning as stabilizers. Thus, when performing volitional dynamic movements such as overhead throwing, particularly pitching, it is imperative that the upper extremity is performing at its most efficient capacity and that the lower extremity and LPHC are supplying the force production.

Training implications

9SM-iStock14153096v1Thus, in attempt to utilize the total kinetic chain and have efficient transfer of energy from the lower extremity to the upper extremity, conditioning focus should include a total body approach. Emphasis should be not only on the upper extremity but also on the lower extremity and, more importantly, the LPHC. The LPHC is the link between the upper and lower extremity. Thus, postural control and body weight exercises that target the LPHC are ideal in making the body an efficient kinetic chain with optimal energy transfer.

From the limited baseball and softball literature on overhead throwing, researchers have concluded the lower extremity plays a significant role in not only increasing ball speed but also as a mechanism of injury prevention. The lower extremity works most efficiently in the overhead throw when the whole body follows a proximal (lower extremity) to distal (upper extremity) kinematic sequence.

Gretchen D. Oliver, PhD, FACSM, ATC, LAT, is an assistant professor in the School of Kinesiology at Auburn University in Alabama and director of its Sports Medicine and Movement Laboratory. Hillary Plummer, MAT, ATC, and Lisa Henning are graduate students in the School of Kinesiology at Auburn University.

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