IMMEDIATE EFFECTS OF A DYNAMIC ROTATION‐SPECIFIC WARM‐UP ON X‐FACTOR AND X‐FACTOR STRETCH IN THE AMATEUR GOLFER

Abstract

Background

Recent evidence suggests performing a warm‐up prior to golf can improve performance and reduce injuries. While some characteristics of effective golf warm‐ups have been determined, no studies have explored the immediate effects of a rotational‐specific warm‐up with elements of motor control on the biomechanical aspects of the full X‐Factor and X‐Factor Stretch during the golf swing.

Methods

Thirty‐six amateur golfers (mean ± SD age: 64 ± 8 years old; 75% male) were randomized into a Dynamic Rotation‐Specific Warm‐up group (n=20), or a Sham Warm‐up group (n=16). X‐Factor and X‐Factor Stretch were measured at baseline and immediately following the warm‐up. Mixed model ANCOVAs were used to determine if a Group*Time interaction existed for each variable with group as the between‐subjects variable and time as the within‐subjects variable.

Results

The mixed model ANCOVAs did not reveal a statistically significant group*time interaction for X‐Factor or X‐Factor Stretch. There was not a significant main effect for time for X‐Factor but there was for X‐Factor Stretch. These results indicate that neither group had a significant effect on improving X‐Factor, however performing either warm‐up increased X‐Factor Stretch without significant difference between the two.

Conclusions

The results of this study suggest that performing the Dynamic Rotation‐Specific Warm‐up did not increase X‐Factor or X‐Factor Stretch when controlled for age compared to the Sham Warm‐up. Further study is needed to determine the long‐term effects of the Dynamic Rotation‐Specific Warm‐up on performance factors of the golf swing while examining across all ages.

Level of Evidence

2b

INTRODUCTION

There are 55 million golfers world‐wide with 26 million in the United States alone.¹ Approximately 25% of these are seniors playing at a time in their life span when they are more prone to physical injury than golfers under the age of 65.² Golf‐related injury rates among amateurs have ranged from 16‐36.5%.^3,4 Unlike professional touring golfers, amateur golfers typically do not perform a warm‐up prior to play.^5-9 In fact, most amateur golfers lack knowledge regarding what constitutes an effective warm‐up. Additionally, they may have negative attitudes regarding performing a warm‐up or what it can accomplish.^6,7 If performed at all, most amateur warm‐up activity tends to occur at the driving range with a series of air swings or progressive distance hitting, and is not long enough to be effective.^5,6,9

Adequate warm‐up is essential for the amateur golfer, as researchers have indicated that it reduces the risk of injury and improves performance.^7,10,11 Several characteristics of effective golf warm‐ups have been identified including that a pre‐golf warm‐up need only be a minimum of 7–10 minutes long.^8,12 In addition, dynamic warm‐ups improve performance whereas passive stretching as a warm‐up decreases performance.^5,12 Sport‐specific flexibility training is considered an important part of the warm‐up process for sports that utilize extremes of movement.^9,13 This is the case with the full golf swing, which is primarily a rotational motion. Resistance warm‐ups in functional patterns focusing on rotational and stabilizing muscle groups along with motor patterning have been found to improve maximum driving distance, consistency of ball strike, and smash factor.¹⁴ Tilley and Mcfarlane¹⁴ define smash factor as “the ratio between the ball speed and the club speed, it tells us about the centeredness of impact and the solidity of the shot, an important factor relating to performance.” Due to the equipment needed, it would be difficult to perform a resisted warm‐up range‐side prior to play, an important factor for compliance in the amateur. Other warm‐ups that have been studied include general dynamic movements at the spine, hips and shoulders, but none have focused predominantly on the components of spinal rotation and motor control that could prove helpful in improving golf‐specific performance outcomes.^9,10,12,15

In examining the components of the golf swing, the term X‐Factor (XF) is used to describe the amount of transverse plane rotation differential between the shoulders and the pelvis at the top of the backswing and is a measurement of angular motion.¹⁶ Another term, X‐Factor Stretch (XFS), is used to describe the additional rotation that occurs following the backswing in the early downswing.¹⁷ Before the transition from the backswing to the downswing, it has been observed that the pelvis has already reversed its direction to rotate towards the target at a time when the upper torso is still moving away from the target. This increases the amount of rotation and separation between the upper and lower segments.¹⁷

Both the XF and XFS are positively correlated with increased distance in long drives.^17-21 There are differing opinions as to which is more important, XF or XFS.^17,21 When comparing professional golfers to amateur golfers, the amateurs typically over rotate from the pelvis and below while under rotating through the spine, thus not utilizing optimum XF.¹⁷ Given that golf is a popular sport for retirees, age related spinal stiffness makes it understandable that most aging amateur golfers obtain greater rotation through the legs and pelvis rather than through sufficient use of the XF and XFS. Additionally, amateur golfers may lack sufficient muscular stabilization through the legs and pelvis to control large amounts of spinal rotation needed for the full golf swing. In an effort to combine the two problems of inadequate warm‐up and an inefficient use of the XF and XFS in amateur golfers, research efforts related to motor control strategies and golf performance may prove to be helpful.²² Using motor control strategies to improve vertical forces in the lead foot has been shown to allow more effective rotational sequencing through the kinetic chain.^23,24 Professional golfers have been found to place greater vertical force into the lead foot (ground reaction forces [GRF]) during the downswing compared to amateur golfers.^23-25 Better use of these forces allows more time for effective rotational sequencing between the pelvis and spine, thus improving the power imparted into the ball. Use of motor control strategies addressing this issue have not typically been incorporated into golf warm‐ups. It is theorized that dynamic motor control drills designed to optimize the acceptance of vertical forces into the lead foot would assist amateur golfers in attaining the spinal rotation necessary for adequate XF and XFS.

The purpose of this study was to examine the effect of a Dynamic Rotation‐Specific Warm‐Up (DRSWU) on XF and XFS in the amateur golfer. To date no studies have been conducted on the effects of a rotational specific warm‐up on specific biomechanical parameters of the full golf swing. The results of this study could be helpful in guiding and encouraging amateur golfers to perform a DRSWU. It was hypothesized that performing a DRSWU would increase XF and XFS compared to performing a sham warm‐up (SWU).

METHODS

Subjects

Forty adult (18 years old and over), amateur golfers volunteered from area golf clubs. To qualify, golfers needed to report golfing at a minimum frequency of once weekly for most of the golf season. There were no restrictions on gender or handicap for inclusion. Subjects were excluded if they were, or ever had been a golf teaching or touring professional. They were also excluded if they reported pain while swinging their club or following play.

Instrumentation

The K‐Vest system (K‐Vest, K Motion Interactive, Inc., Milford, NH), utilizing TPI software (Titleist Performance Institute, Oceanside, CA), was used to measure angular velocity by time. This system captures 3‐dimensional biomechanical data during the golf swing using inertial sensors. These sensors (InterSense Inc., Billerica, MA) measure motion in three degrees of freedom, in 360 degrees at all axes, at a range of 0‐1200 degrees per second with an accuracy of one degree in yaw, and 0.5 degrees in pitch and roll at 25 degrees Celsius.²⁶ The sensors are attached at the upper back between the shoulder blades using a specially designed vest, at the sacrum using a belt, and at the gloved hand (Figure 1).

Figure 1.

K‐Vest System on model subject

The K‐Vest TPI software captures the kinematic sequence and produces a graph (Figure 2). An additional graph tracks the degrees of thoracic spine ­rotation relative to the pelvis (Figure 3). These graphs of time (seconds) by angular velocity (degrees per second) yields the angle in degrees of rotation between the pelvis and thorax (XF). Using these graphs, calculation of the XFS is accomplished using Cheetum's²⁷ protocol: degrees of rotation of the pelvis at transition (XF) are subtracted from degrees of rotation at the equal velocity line to determine the XFS, a value representing degrees of angular motion . Values for XFS are considerably smaller than those for XF as they represent the additional rotational stretch achieved following transition.

Figure 2.

The Kinematic Sequence of the full golf swing representing rotational velocities for the pelvis (red), thorax (green), and club shaft at grip (brown). The X‐axis measures time in seconds from address to follow‐through. The black vertical lines sequentially represent (from left to right): address, top, impact, and follow‐through. The Y‐axis represents rotational velocities in degrees per second. Positive Y‐axis values represent rotation toward the target, while negative values represent rotation away from the target.

Figure 3.

Spine rotation graph (pelvis – torso differential) The X‐axis measures time in seconds from address to follow‐through. The black vertical lines sequentially represent (from left to right): address, top, impact, and follow‐through. The Y‐axis represents degrees of thoracic spine rotation relative to the pelvis in degrees. The gray horizontal line is the zero baseline representing no rotation. The Y‐axis positive values represent rotation toward the target, negative values represent rotation away from the target.

Procedures

This study was a prospective, randomized within and between (mixed model) subjects design. Subjects were assigned to a group using an online randomization program for two groups of 20 subjects. Subjects were required to wear golf shoes, a golf glove and use their own, non‐hybrid 5 or 6 iron. As a condition of testing, subjects had to avoid all golf play or exercise of any type the day of the testing session. The subject donned the K‐Vest system and was allowed to perform five practice swings hitting a golf ball into a net prior to obtaining three baseline swing captures, also hitting a golf ball into a net. The 5 practice swings allowed subjects to get used to swinging the club while wearing the K‐Vest system as well as to mimic typical golf behavior of performing practice swings prior to hitting. A movement screen consisting of lumbar, cervical, and shoulder active range of motion was performed to further rule out pain or injury and was performed following the first round of swing captures so as not to function as a warm‐up, therefore meeting the criteria of no prior exercise. Subjects were eliminated if they reported pain during the screen. Four subjects from the SWU group were excluded: three due to pain during the screening and one for inability to follow the warm‐up instructions. Subjects who successfully passed this screen progressed to the warm‐up of their respective group: 20 subjects in the DRSWU group and 16 subjects in the SWU group.

The DRSWU is a previously unpublished golf warm‐up developed for the purpose of this study in order to investigate the ability to improve full‐golf swing performance (Table 1). It was developed in consultation with several golf fitness professionals and several golf instructors, all with background in golf biomechanics. It is a 10 minute warm‐up performed at the driving range, which requires no equipment other than the golf club. Compliance factors as well as elements of known, effective warm‐ups have been built into this warm‐up.^{5,7,8,9,10,11,12,13,} The DRSWU used in this study not only has components of dynamic rotational mobility, but also includes drills to address GRFs, and motor control training of XFS considered important in the ability to incorporate the gains in spinal mobility into the actual swing to increase XF and XFS.¹⁴ The intent of the parameters of the DRSWU is to facilitate incorporation of a warm‐up into the golfer's pre‐play routine while effectively improving performance. Although not currently examined in this study, the DRSWU may have the potential to have a positive effect in reducing injury however, the prospect of improving driving distance may provide greater motivation for the amateur golfer.⁶ The SWU was intended to mimic the duration of the DRSWU yet differed due to the emphasis on sagittal plane movements. (Table 2) Subjects were shown an instructional video of their respective group warm‐up in order to facilitate their understanding of the movements required during the warm‐up. Subjects were then led through their warm‐up and allowed five additional practice swings. The final three swing captures were then obtained. Since K‐Vest with TPI software allows for real‐time analysis, any swings with artifact were eliminated and golfers repeated swings until there were three adequate swing captures for each pre‐test, post‐test scenario.

Table 1.

Dynamic Rotation‐Specific Warm Up

Crossed‐arm torso twist without neck rotation	Stand in golf address position Cross hands to opposite shoulders Rotate torso to the right and then left Keep chin over breast bone 20 reps each direction
Thoracic combined motions	Stand in golf address position with club behind shoulders Side bend your torso to the Right, then twist to the Left, then repeat the other way 20 each direction
Neck only rotations/ lateral flexion with hands wrung	Stand in golf address position Place hands in “wrung” position: twist forearms into pronation bringing palms together, fingers interlocked Without moving your shoulders rotate your head side to side for 10 reps Without moving your shoulders laterally flex your head side to side for 10 reps
Ground Reaction Force (GRF) of the legs in opposition to rotation	Stand in golf address with club in hands As you move slowly into your backswing (BS), press the trail foot forward and the lead foot backwards From the BS proceed into your downswing with focus on shifting most of your weight on the lead leg. Perform 20 reps
Crossed‐arm torso twist with neck rotation	Stand in golf address position Cross hands to opposite shoulders Rotate torso to the right and then left Keep chin over breast bone 20 reps each direction
Backswing with focus on internal rotation of the loaded hip	Stand in address position with club in hands Place your lead leg behind you and rest your toe on the ground With near total weight on the trail leg perform a backswing Perform 10 reps
Pelvic lead into downswing	Start in golf address with club in hands Twist to backswing with the club held vertical Initiate downswing at the pelvis, moving and rotating it first and allowing the shoulders to follow Perform 20 reps
Swing for remaining time	Hitting a golf ball into a net for remaining time until 10 minutes total of warm‐up

Table 2.

Sham Warm‐Up

Heel walk	For 40 steps
Toe walk	For 40 steps
March in place	For 40 steps Lifting knees high
Lunge walk	Step forward with one leg and perform a lunge bending both knees Repeat with the other leg 20 steps
Walking with alternating Quad stretch	Take a step onto one leg and reach behind you with the opposite hand and grab the free ankle and stretch up and back toward the buttock Release without holding Take next step performing a quad stretch on the other leg 20 steps
Leg swings from hip in flexion/extension	Stand on one leg using your club for balance Swing your free leg forward and back Perform 20 on each leg
Shoulder flexion/extension	Leading with your thumb, raise the arm up overhead and as far back as you can Reverse and lower the arm bringing it behind you as far as you can Perform 20 reps on each arm
Neck flexion/extension	Lower your chin down towards the chest Gently lift the chin up towards the ceiling Perform 20 reps of the full motion
Swing for remaining time	Hitting a golf ball into a net for remaining time until 10 minutes total of warm‐up

Statistical Methods

Descriptive analyses of continuous variables included mean, standard deviation, and 95% confidence intervals. Correlations were examined for relationships between age or handicap and pre‐test XF or XFS. Independent t‐tests were used to determine differences between groups for variables of age and ­handicap. The average of the values obtained from each of the three swings for XFS and XF were used to examine differences following the two warm‐up protocols. SPSS software (version 22.0; IBM Corp., Armonk, NY) was used to administer a 2x2 mixed‐model ANCOVA with age as a covariate and with an alpha level of p ≤ 0.05. As spinal range of motion tends to reduce with age, it was used as a covariate to eliminate differences due to age in order to focus on the response to warm‐up. Warm‐up group (DRSWU versus SWU) served as the between‐subjects variable and time (pre‐test, post‐test) served as the within‐subjects variable.

RESULTS

Subjects

Table 3 contains demographics of the subject population including age, gender and golf handicap. Ages of subjects volunteering for this study were predominantly in the older adult (60‐80 years old) age group (78%, n = 28) with the remainder in the middle‐aged adult (40‐60 years old) group (22%, n=8). There were no subjects representing the young adult age group (20‐40 years old). Subjects reported the following pre‐golf warm‐up habits; 88.9% typically (n=32) performed some kind of warm‐up and 11.1% (n=4) reported no warm‐up. Of those performing a warm‐up, 96.9% hit range balls (n=31), 62.5% (n=20) performed static stretching, 12.5% (n=4) performed dynamic stretching, and 3.1% (n=1) walked for 20 minutes. Subjects were allowed to report more than one warm‐up strategy. A lower handicap was related to a higher pre‐test XF, but not XFS. Age was negatively correlated to XF, but there was not a relationship between age and pre‐test XFS. Independent t‐tests revealed no significant difference between groups for handicap, however there were significant age differences between groups (p = .02). For this reason age was used as a covariate in the mixed model analysis.

Table 3.

Participant characteristics^*

Group	Age (Years)	Handicap	Gender
DRSWU (n=20)	61.0 ± 9.1	13.9 ± 6.4	M = 15 (75%) F = 5 (25%)
SWU (n=16)	66.9 ± 3.8	16.9 ± 6.9	M = 12(75%) F = 4 (25%)
TOTAL (n=36)	63.6 ± 7.7	15.2 ± 6.7	M = 27 (75%) F = 9 (25%)

Abbreviations: DRSWU: Dynamic rotation‐specific warm‐up. SWU: Sham warm‐up. M: male. F: female.

^*All values except gender are mean ± standard deviation. Gender values are subject numbers.

Main results

Pre‐test and post‐test means for XF and XFS are listed in Table 4. The mixed model ANCOVAs did not reveal a statistically significant group*time interaction for XF (F = 2.479; p=.125) or XFS (F=0.631; p=.433). There was not a significant main effect for time for XF (F=0.398; p = .533), but there was for XFS (F = 13.293; p = .001). These results indicate that neither warm‐up had a significant effect on improving XF, however performing either warm‐up equally increased XFS with no significant difference between the two when adjusted for age.

TABLE 4.

Outcomes for X‐Factor (XF) and X‐Factor Stretch (XFS)

XF	Pre‐test	Post‐test*
DRSWU	31.0 ± 9.2	34.1 ± 9.0
SWU	30.3 ± 10.4	32.1 ± 9.3

XFS	Pre‐test	Post‐test*
DRSWU	1.4 ± 1.4	2.2 ± 2.5
SWU	2.8 ± 2.7	2.8 ± 2.4

Values represent pre‐test/post‐test means of X‐Factor and X‐Factor Stretch in degrees of rotation ± 1 standard deviation.

DRSWU = Dynamic Rotation‐Specific Warm‐up , SWU = Sham Warm Up.

^*Post‐test values were measured following a pain and injury screen and the warm‐up intervention approximately 30 minutes later.

Discussion

The purpose of this study was to examine the immediate effects of two warm‐ups on XF and XFS. The authors hypothesized that the DRSWU would significantly increase both biomechanical measures. Findings from this study did not support this hypothesis. As there has been no prior research into interventions to produce an immediate change in XF and XFS, it is difficult to draw comparisons to other studies. A study by Tilley and Macfarlane¹⁴ compared a resisted rotational golf warm‐up to a linear resisted warm‐up. They found the rotational warm‐up improved some measures (immediate maximal driving distance, smash factor and consistent ball strike), but not others (drive accuracy or maximum club head speed). The Tilley and Mcfarlane¹⁴ study did not measure XF or XFS and was performed on a much younger, elite, all‐male golfer population making it difficult to draw comparisons with the current study.

The long‐term effects of the DRSWU on golf performance are unknown and warrant further ­investigation based on prior findings that indicate that long‐term effects of consistent use of a warm up exceed those seen as initial or immediate effects.¹⁰ Myers et al.²² posed the question of how to increase torso‐pelvis separation in the golfer and stressed the importance of investigating strategies to do so. Based on the results of this study, the utility of long‐term exercise or motor control programs need to be examined. Further, there may be limited possibilities to improve spinal mobility and thus improve XF or XFS with the older golfer since 33 out of 36 golfers studied were over the age of 50.

Reports by subjects concerning their warm‐up habits were similar to prior studies indicating that amateur golfers often do not perform the kinds of warm‐ups that have been demonstrated effective in improving performance. A prior study by Fradkin et al.⁵ found less than 3% of amateur golfers performed an adequate warm‐up consisting of all three of the following components: some form of low–level aerobic activity, dynamic stretching, and sport‐specific movements. Based on these criteria, the percent of subjects in this study reporting an adequate warm‐up is 0%. Furthermore, the four subjects who reported a dynamic stretching warm‐up also reported performing static stretching, and the theoretical possibility exists that these two types of warm‐up could negate each other. While the current study results indicate that 11% of subjects performed no warm‐up, this is an encouraging finding compared to the 47% who did not warm‐up in the study by Fradkin et al.⁵.

This study had several limitations. While both groups made significant increases in XFS from pre‐test to post‐test, it is difficult to determine if that difference was a result of performing one of the warm‐ups or due to the passage of time because there was not a control group. However, it would not be expected that spinal range of motion would increase in a matter of 30 minutes between the two swing captures without any type of activity. The randomization of subjects prior to the pain screen resulted in an imbalance of group numbers with the DRSWU group having 20 subjects and the SWU group having 16. This would not have been an issue if the randomization occurred following the pain screen. By chance the four subjects who were eliminated by the screening procedures were all from the same group. High variance seen in the XFS results in the DRSWU was due to a grouping of four very high XFS outliers scoring 6‐8 degrees of rotation, while there were a significant number of subjects scoring less than 1 degree of XFS.

There were also age imbalances between the groups with the SWU group having a statistically older mean age than the DRSWU, thus using age as a covariate was necessary to control for differences. Some studies have reported golfers over the age of 65 represent 25% of all golfers, suggesting subject age ranges for this study did not accurately reflect those of the entire amateur golfer population.² This may have biased the main effect for time for both groups in a less responsive direction. Equal representation of subjects from young, middle, and older adult age groups would have allowed for examination of age‐related spinal stiffness as a potential factor ­diminishing the effect of the warm‐up. Future studies should examine the effects of warm‐ups on a more representative age distribution of amateur golfers.²

There was also an imbalance of gender with 75% of subjects being male across both groups. Horan et al.²⁸ recommend not generalizing any data concerning the torso and pelvis from males to females due to differences that exist in swing kinematics. Thus, there may be limited generalizability of the current results to female golfers.

Another limitation of the study could have been the selection of the exercises for the DRSWU and the SWU. It could be argued that the inclusion of some practice swings into the SWU could have been responsible for some improvement in spinal rotation, thus making less of a difference between groups. Regularly performing practice swings at each drive is typical practice by amateurs. Since prior research has illuminated that practice hitting alone is not an adequate warm‐up, the goal of the study was to examine what could be done as a warm‐up in addition to the typical practice swings.^5,6,8 Thus, adding a limited amount of practice swings more accurately mimics a baseline of what amateurs are already doing.

Lastly, this study was conducted in an indoor simulation environment with no direct measures of club head speed, driving distance, or driving accuracy, thus there may be limited generalizability to an outdoor golf environment or more direct performance measures. Future studies should continue to examine sport‐specific types of warm‐ups for improving golf performance by investigating outcomes over a longer time period, using varied direct and indirect measures of golf performance, and studying a varied age range.

CONCLUSIONS

In conclusion, performing a warm‐up prior to golf improves performance and reduces injury. Warm‐ups linked to improving performance will likely provide greater motivation for the amateur golfer. Higher XF and XFS are linked to improved golf performance.

The results of this study suggest that performing the DRSWU did not increase XF or XFS compared to the SWU. Neither warm‐up had a significant effect on improving XF, however performing either warm‐up equally increased XFS with no significant difference between the two. Further study is needed to determine the long‐term effects of the DRSWU on performance factors of the golf swing while examining across all ages.