The vast majority of sport analysis centers around joint ROM, also called kinematics. Simple 2-D photography/video has been used to study sports for decades, where again the golf swing has been studied with the most frequency. Unfortunately, 2-D camera technology lacks both accuracy and precision. Although there is no ideal golf swing, Table 25.1 shows general trends of joint kinematics of major body segments about the spine based on more precise 3-D technology. These data are synthesized from skilled golfers among several peer-reviewed publications^{21,22,23,24,25} as well as the 3-D golf database at The University of Virginia.

These values suggest the difference between thorax and pelvis must be accounted for by the lumbar and thoracic spines, costovertebral joints, and sternocostal joints. For example, at ball contact, the lead side of the pelvis is elevated in the frontal plane approximately 11 degrees and the nipple line tilted ˜28 degrees. This leaves 17 degrees of side tilt for which the lumbar spine and some of the thorax are responsible. Likewise, the difference between head and thorax helps us understand the demands on the cervical spine. If the thorax is rotated 98 degrees but the head turned only 18 degrees at the top of the backswing, then the cervical spine is responsible for ˜80 degrees of rotation. If a golfer is unable to comfortably account for these demands, we can expect tissue insult and performance decrements.

Unfortunately, some golf instructors will ask athletes to reach the benchmarks in Table 25.1 despite them being incapable. A patient-centered approach implies the need to conduct a proper functional ROM assessment for the individual athlete. As emphasized by Soyeon (Sue) Lee, an elite golf coach, relying on averages or benchmarks to dictate technique is strongly discouraged. Medical and exercise professionals can inform sport coaches regarding the capabilities of a specific athlete. Strong communication between medical and sport personnel can improve physical function and sport performance simultaneously.

Current technology relegates our kinematic knowledge to general sections of the spine. There is a distinct lack of research tracking the distribution of motion among individual vertebral segments in athletes with and without LBP. It stands to reason that concentrating motion and forces to a particular segment (while others remain immobilized) could be problematic relative to a more even distribution.

Some sports place different demands on the vestibular system, eyes, and cervical spine. Rotational excursions may be larger in sports such as baseball and tennis because the feet often leave the ground. However, the principles remain the same: examine what the sport requires and assess if the athlete is capable of the task. While transverse plane motion is emphasized, rotational sports involve coordination in all three planes of motion as well as three translational movements. There is even some debate as to whether lumbar disc segments can be damaged from torsion alone.^26,27 In fact it may be the improper combination of sagittal, frontal, and transverse forces that most reliably damages disc integrity.^28,29

Rapid force development (power) is desired across sports and skill levels. The stretch-shortening cycle (SSC) is an important source of power. The SSC is why any athlete can jump higher with a countermove versus from a dead static start. In golf, the downswing lasts approximately 0.25 seconds and it’s not uncommon to see the club accelerate to 100 or more miles per hour in that short time. Such acceleration would not be possible without the SSC.

Essentially, the SSC increases potential energy by eccentrically loading relevant connective tissues (muscle, tendon, ligament, fascia). Much like a slingshot, the shortening cycle deploys accumulated potential energy to enhance force production that muscle alone can’t accomplish. One can think of SSCs globally (the entire chain of the athlete) but locally to each joint as well.

Coordinating local SSCs to a global pattern realizes the ultimate goal of precise and powerful skill execution. It is the essence of athleticism. Although the SSC is invaluable, it does increase stress on the tissues and their attachments. We must always mind the balance of performance and durability, and the SSC
is no exception. In general, there exist three keys to effective use of the SSC:

Most evaluation and training focuses on the first two bullet points. The most overlooked and perhaps most important factor is a proper anchor point to deploy the SSC in a precise and coordinated manner. Here the role of dynamic stability becomes paramount. For example, every golfer desires more power but this must be accompanied by a predictable club path. If the anchor of the slingshot is unstable, certain tissues can be excessively stressed and performance may suffer.

Examples from multiple sports support the concept of an idealized sequence of motions to maximize the SSC. This is commonly referred to as the kinematic sequence. A large majority of skilled athletes will first use proximal segments to start the transition from loading to acceleration.^23,30,31 When done properly, a transition adds to the SSCs already accumulated in the loading phase (e.g., a golfer’s backswing).

The sequence implies that some segments (distal) are still moving away from the target while others (proximal) have already changed direction. For example, the proximal pelvis may change direction and rotate toward the target while the trailing (right) shoulder continues to move the hands away from the ball via external rotation. Ideally, the trailing shoulder external rotation is held and even increased until more proximal segments have completed their change of direction. That chain of events helps to maximize SSCs. Keep in mind this guarantees the lumbar spine will be at the nexus of force transmission. Confronting those forces via dynamic stability of the lumbar spine remains a key challenge for virtually all athletes.

Figure 25.2 shows major body segment motions of two golfers, with vertical dashed lines for the club’s change of direction and ball impact. One can observe distinct sequences of loading, transition, and acceleration. In golfer A, the arms (dark blue) changed
direction before the proximal segments. (The dark blue line reached a minimum before the green or red proximal segments reached theirs.) Potential energy was either leaked or not maximized. In contrast, golfer B’s transition not only preserved potential energy but actually increased it. The proximal pelvis was first to bottom out and change direction, so forces were able to accumulate to more distal segments.

Keep in mind that the pelvis may not be the very first thing to change direction. However, it is the most proximal rigid body that is commonly measured. Measuring specific segments of the lumbar spine or deeply embedded structures is a far more challenging task that runs the risk of interfering with the athletic motion itself. There is always a balancing act between precise measurement and capturing the athlete in his or her native environment.

Newton’s first law of motion states that an object in motion stays in motion unless acted upon by an unbalanced force. Any change of direction requires a counterforce (e.g., friction) to buttress the segments. It is commonly thought, though not scientifically proven, that friction between foot and ground will serve this role. Like any athlete who would push left to turn right, the ground reaction force (GRF) initiates muscular cocontraction about the lower extremity. The resultant cocontraction provides a stable platform for proximal segments to change direction first. It is possible that the friction for transition comes from deeply proximal connective tissues (lumbar facets, deep fascia, ligaments, etc.). Such a hypothesis has not been tested to date and would require extremely invasive methods. Even if a transition was initiated by proximal connective tissues, a change in GRF would necessarily be observed as the resultant cocontractions rapidly filter down to the foot-ground interaction. This foot-ground interaction is far easier to measure and gives significant insight into how the athlete is managing SSCs. As a result, more
attention has been paid to the observation that ground forces change direction before a golf club does. The pattern is repeated across rotational sports: a change in friction between the foot and contact surface will precede a change of direction in the arms and hands.

Such observations have led sport coaches to advocate for a more forceful “push from the ground up.” The validity of this concept is questionable. Recent peer-reviewed research conducted with golf coach Sue Lee showed the timing and peak magnitudes of GRF parameters varied widely between 31 expert golfers.³² Over approximately 450 swing trials, between-golfer differences accounted for over 90% of the total variability, while the expert golfers themselves remained internally consistent (less than 10% of the total variability). Both our experience and these data indicate GRF-based coaching advice is likely to impair the performance of most athletes that rely on the precision of implements (e.g., bats, clubs, rackets) for skill acquisition. Following generalized blanket advice might add stress to the lumber spine, as well.

The awareness of SSCs has led researchers to study transverse plane dissociation between thorax and pelvis in sport performance (the x-factor). Greater dissociation theoretically increases the number and/or magnitude of SSCs. X-factor magnitude in transition and early downswing does correlate with increased swing speed in golf.^23,24,33 Unfortunately, some technical golf instructors turned these observations to a generalized advice. A number of instructors now advocate for restricting lower body and pelvic motion in the golf backswing. This concept has crept into other rotational sports, as well. Some highly skilled athletes are able to restrict lower body motion in the loading phase and still perform well. However, this requires substantial flexibility of the thoracic and cervical spines, which many athletes don’t possess. Importantly, SSCs can be built by a transition where the proximal segments lead the way.

The concept of lower body restriction does not exist as infants master the ipsilateral pattern via dynamic stabilization. In other words, stability is not the same as rigidity or deliberate restriction. Keep in mind movements and joint structures develop in concert with the CNS. It is reasonable to speculate that intending to restrict the lower body will disrupt the natural rhythm and timing of the pattern first mastered in ontogenesis. Conscious restriction is likely to interfere with innate athleticism. Furthermore, some instructors and medical professionals suggest the intent to restrict lower body motion in the backswing contributes to the incidence of LBP.

In fact, the magnitude of backswing pelvic rotation does not explain much variance between high- and low-speed golf swings.^23,24 In other words, power is not strongly related to how much one rotates the pelvis in the backswing. Rather than restricted lower body motion of the backswing, the rate of pelvis/thorax separation on the downswing may be a more robust performance metric.³³ Many legendary golfers had large backswing pelvic rotations, even allowing the lead heel to raise off the ground. Despite a small backswing x-factor, many legends of golf developed a tremendous separation of pelvis and torso in the transition and early downswing. It is possible modern equipment has affected this tendency. However, the aforementioned legends had long, durable careers.

The ultimate guide to mechanics of any sport is to evaluate the capacity of the individual athlete relative to his or her sport demands. The Titleist Performance Institute (TPI) has led the way in educating golf instructors on the importance of conducting a brief test of physical capacity, especially ROM about the hips and thorax. A cookie-cutter approach, as advocated in deliberately restricting body motion, is likely to place excessive stress on the lumbar spine in all but the most flexible of athletes. In fact, golfers with LBP exceeded their x-factor capacity during the golf swing, while asymptomatic controls did not.³⁴ The x-factor might be a desirable performance trait but as in much of life, timing is everything. An x-factor goal should not come at the expense of the athlete’s capacity. This type of advice has no scientific merit, nor does it show up in optimal human development.

A landmark 2014 study modeled ROM at each lumbar segment during a golf swing. IV disc torques were simulated under a variety of lumbar postures, from hyperlordotic to mildly kyphotic.³⁵ Estimates of mediolateral and anterior-posterior (AP) shear forces regularly exceeded 500 N (51 kg) per IV joint. As a matter of perspective, Axler and McGill reported AP shear forces of approximately 415 N at the L4 to L5 segment during a single sit-up.³⁶ Tensile-compressive forces in the golf swing regularly approached 1,600 N (163 kg) per IV joint. The most insulting swings (largest forces) occurred when the lumbar spine was hyperlordotic at the top of backswing, kyphotic in the transition to downswing and through impact, and then returning to hyperlordosis at the finish.