[Hayden Giuliani recently finished her Master’s degree at the University of North Carolina Chapel Hill, where she now works as a research coordinator. She is currently in the Coaching Mentorship Program at Athletic Lab.]
A rotational athlete is any athlete who uses twisting within the torso in order to perform their sport-specific movement. This is done in order to transfer forces generated from the lower body through the core to accelerate the upper body and dominant limb. Sports that incorporate this type of movement include, but are not limited to, baseball (swinging and throwing), tennis, and a few field events in track & field. The ball (or object) can be either stationary or be moving, but the intent is the same – accelerate it outwardly, as hard and/or fast as possible. These movements are very dependent on the adequate use of the body’s kinetic chain. In this case, we are speaking of a closed kinetic chain, due to the foot (feet) being planted on the ground. Ground reaction forces generated from foot contact and the strength of the lower body are transferred through the pelvis and torso to move the upper extremity, whether that is one or both arms. Because humans are naturally stronger in their lower body, it is very important to be able to properly utilize the body’s intrinsic kinetic chain. This is will increase the amount of strength and power that they can generate, but also minimize the stresses at the shoulder and upper extremity joints that contribute to injuries. First, let’s discuss the kinetic chain a little bit further…
Simply speaking, a kinetic chain refers to the body’s segments that are linked to allow for the sequential transfer of forces and motions. This can be directly seen with tasks such as throwing and hitting, in a few different sports. An efficient kinetic chain requires optimal flexibility, strength, motor-pattern learning, and mechanics throughout all of the segments involved. (Chu 2016) In these rotational sports we are discussing, the kinetic chain involves almost every aspect of the body from the foot to the hand. On one hand, that is advantageous to create more strength and power to the distal segment, while on the other hand, it can be a disadvantage if there is a breakdown in any one of those links. For instance, the baseball pitching motion is a very technical and complicated series of actions, and anywhere from the ankle to the wrist can affect a pitcher’s performance. One principle, known as the “summation of speed,” explains how each moving part starting from the bottom of the chain works to advance the force to accelerate the upper extremity at maximum capacity (velocity). A baseball pitching motion follows this pattern similarly, therefore I will be making reference to it throughout this article.
For the pitching motion, the first three phases are of particular importance for the utilization of the entire kinetic chain and summation of speed principle. (Figure 1) The lower body provides the base of support and helps generate the kinetic energy that will be translated (51-55%). (Chu 2016) The first phase (a) is the windup, which consists of a single leg stance of the dominant leg. This relies heavily on pelvic stabilization stemming from the strength of the dominant hip abductors (glutes). The glutes will continue to play a vital role in the second phase (b), in which the pitcher strides the non-dominant leg. In this phase, the hips will begin to rotate, and in the third phase (c), the torso will also rotate to create maximal shoulder external rotation. Now the stride leg must stabilize and utilize the flexibility and strength of the hip musculature. It has been shown that the gluteus medius muscle and scapular stabilizers are highly correlated during this phase. (Oliver 2015) In these phases, we can see that the lower body sets it all in motion, but obviously, it is the shoulder and arm that finishes the pitch. It is easy to see how a “catch-up” phenomenon may occur, which means that one broken link in the chain will disrupt another due to compensation.
If there is a 20% decrease in kinetic energy from the hip and trunk to the arm, there must be a 34% increase in rotational velocity of shoulder to impart the same amount of force to the hand. (Seroyer 2010) After the lower body generates a significant amount of force, it moves through the trunk, which is the next important link. For example, Oyama et al (2014) found that improper trunk sequence demonstrated a greater maximal shoulder external rotation angle and torque, likely a symptom of the “catch-up.” But this can be improved like anything else, as we see a difference in the timing of a pitcher’s torso rotation between experience levels. A later rotation leads to less joint load and a conservation of momentum. (Aguinaldo 2007) Last but not least, we have the shoulder. It seems the shoulder gets all the attention when it comes to overhead athletes, and I suppose rightly so. Seventy-five percent of time loss in college baseball is due to upper extremity injury, with overuse accounting for the majority for that. A couple possible reasons are that angular velocities can be up to 7,250°/sec, and the shear forces at the shoulder can be up to 50% body weight. If the shoulder is dysfunctional, these high forces and angles can cause major or recurrent issues. Many of these injuries seen in overhead athletes are associated with scapular dyskinesis. Scapular dyskinesis is an alteration or deviation in the normal resting or active position of the scapula during shoulder movement. It is often caused by either injury or the inhibition or disorganization of activation patterns in the scapular stabilizing muscles. (Kibler 1998) Many things can contribute to scapular dyskinesis, from bony deformities to joint misalignment or instability, and the rotator cuff is the center of attention. These muscles (infraspinatus, supraspinatus, subscapularis, and teres minor) provide the stability behind the great forces the shoulder can produce. No stability, no force.
Now that I have discussed all the different parts and their roles, let’s see how it fits together. It rarely is just a shoulder issue. If we look a little closer at the phases of movement I described earlier in a pitcher, or that of a tennis serve or javelin throw, we see there is a staggered stance. Opposite sides of the body must work simultaneously and synergistically to create the best end result. These athletes also utilize the serape effect during this rotational movement, which basically is the stretching of muscles to the greatest length in order to create a “snap-back” effect. A few studies have looked at the connection between the upper and lower body, specifically the hip and shoulder. (Oliver, Scher, Laudner) This may help athletic trainers and strength and conditioning coaches address the kinetic chain, rather than attacking the rotator cuff and shoulder only. One author has shown that gluteus medius strength is highly correlated with scapular stabilization, meaning the hips must be stable to enhance the shoulder’s strength and has shown in a separate study that the pelvis and torso rotation rely greatly on gluteal activation. (Oliver 2015, 2010) More specifically, the flexibility of the stance leg’s hip extensors and stride leg’s internal and external rotators is associated with the amount of external rotation of the throwing shoulder. (Scher) If the lead leg cannot external rotate properly, the athlete will compensate by throwing across their body, decreasing the energy transfer, while increasing the torque and load at the shoulder. (Laudner) While most of these studies looked at baseball pitchers, a review of javelin throwers showed there is a negative association between the degree of front leg knee flexion and distance thrown. Basically, if the stride leg cannot withstand the load (which stems back to the hips) at foot plant, there is a less efficient energy transfer. Javelin throwers also depend on a large hip angular velocity and powerful rotation of the trunk for greater distance. (Bartlett and Best) Most of these principles can extend to all overhead athletes.
So, what do we do with this information? I would like to discuss some simple ways to assess the hip, which in turn supports and propels the rest of the chain. One simple screening method and measure of rehabilitation is a single-legged squat – it shows an individual’s pelvic and trunk stability, postural control, glute strength, and compensation methods. It can identify not only muscle weakness but where a lack of flexibility may be as well. From that information, and maybe the addition of a couple simple active and passive range-of-motion assessments, a coaching team can move detail-oriented (rotator cuff) training to a more global approach. From the single leg squat, there are many progressions to incorporate rotation and link the entire core, from the hip to shoulder. For example, lunges with a medicine ball thrown or a chopping motion can become more of a sport-specific exercise. Power distribution can now allow for better transfer up the chain. Of course, rotator cuff rehabilitation is important for all overhead athletes, but don’t get caught up in one link of the chain.
Chu SK, Jayabalan P, Kiber WB & Press J. (2016) The kinetic chain revisited: new concepts on throwing mechanics and injury. Physical Medicine and Rehab, 8:S69-S77.
Oliver GD, Weimar WH, & Plummer HA. (2015) Gluteus medius and scapula muscle activation in youth baseball pitchers. J Strength Cond Res, 29(6): 1494-1499.
Seroyer ST, Nho SJ, Bach BR, Bush-Joseph CA, Nicholson GP & Romeo AA. (2010) The kinetic chain in overhead pitching: its potential role for performance enhancement and injury prevention. Sports Health, 2(2): 135-146.
Oyama S, Yu B, Blackburn JT, Padua DA & Myers JB. (2014) Improper trunk rotation sequence is associated with increased maximal shoulder external rotation angle and shoulder joint force in high school baseball pitchers. Am J Sprts Med, 42(9): 2089-2094.
Aguinaldo AL, Buttermore J & Chambers H. (2007) Effects of upper trunk rotation on shoulder joint torque among baseball pitchers of various levels. Journal of Applied Biomechanics, 23:42-51.
Kibler WB, Sciascia A & Wilkes T. (1998) Scapular dyskinesis and its relation to shoulder injury. Journal of American Academy of Orthopaedic Surgeons, 20:364-372.
Scher S, Anderson K, Weber N, Bajorek J, Rand K & Bey MJ. (2010) Associations among hip and shoulder range of motion and shoulder injury in professional baseball players. Journal of Athletic Training, 45(2):191-197
Laudner K, Wong R, Onuki T, Lynall R & Meister K. (2015) The relationship between clinically measured hip rotational motion and shoulder biomechanics during the pitching motion. Journal of Science and Medicine in Sport, 18:581-584.
Bartlett RM & Best RJ. (1988) The biomechanics of javelin throwing: a review. J Sports Sci, 6(1):1-38.