Golf is played around the world in over 130 countries by approximately 55–80 million people (11). Major tournaments are held worldwide with globalization of the sport evident with its recent inclusion in the 2016 Olympics. Although most golfers worldwide are amateurs, regardless of the skill level, the objective is to hit the ball into the hole in as few strokes (shots) as possible, aiming to complete the round (18 holes) in as few strokes as possible. A lower score is superior and leads to a lower handicap, which is indicative of a player's golfing ability (67). Keogh et al. (27) highlighted that most golf practice concentrates on the technical and mental aspects of the game as well as continual skill refinement in an attempt to lower handicap. This is deemed necessary because the golf swing is considered one of the most difficult, complex motions in sport (7). The ability to harness functional variability when faced with new tasks/environments on the course is evident in highly skilled golfers (29).
Until recently, golf practice has primarily focused on the mental, technical, and skill aspects as the primary means to improve performance. Although these components have been well researched and deemed successful in improving a golfer's performance, practitioners are now focusing attention toward the physical components that influence success. This may be warranted as an improvement in club head speed, and carry distance can lead to fewer strokes per round. Accordingly, this review will investigate, in detail, various physical components that contribute to these measures of swing performance. Specifically, key muscles will be identified through the analysis of electromyography (EMG) research, and physical variables that affect performance will also be acknowledged. Anthropometric variables, balance and cardiovascular capacity along with strength, power, musculotendinous properties, and flexibility will all be explored in a golfing context along with their impact on club head speed and carry distance. This review will outline a range of contributions from these aspects with a view to identifying strategies that may aid in the improvement of golf performance.
To gather the literature for this review, electronic databases PubMed and Google Scholar were used. Search terms included “golf,” “physiology,” “strength,” “flexibility,” “power,” “body composition,” “stiffness,” “muscle-tendon properties,” “balance,” “warm-ups,” “resistance training” and “electromyography,” with combinations of search terms also applied. Additional sources were obtained through comprehensive use of article reference lists. After screening of titles and abstracts for relevance, 71 articles were used for further review.
Physical Components of the Golf Swing
Although technical, skill, and mental components are important contributors to golfing performance, balance, core strength, flexibility, and peripheral muscle strength and power similarly seem to be related to superior performance (67). A restricted approach adopted within golf often solely focuses on the technical, mental, and skill aspects rather than the physical components. The physical stress endured by a professional golfer is high with over 2,000 swings performed each week (45) and up to 300 powerful movements in a session (58), consequently relying on the physical functioning of the musculoskeletal system. Furthermore, it is suggested that the difference between highly proficient and poorer quality golfers is often influenced by mobility and strength at different movement points during the swing (54). It is evident within the literature that the physical characteristics of highly proficient players are different to those of lower-caliber players (54). Each of these elements will be examined below.
Through EMG analysis in both the upper and lower body, key muscle groups and relative activation of individual muscles utilized during the golf swing have been identified. Although activation patterns vary throughout the swing, the acceleration phase, starting from the horizontal club position to the impact of the ball (late part of down swing), is deemed the most active phase of the swing with key muscles in the upper body, trunk, and lower body all being implicated as contributors in the golf swing (36,38). More specifically, the pectoralis major, latissimus dorsi, external obliques, erector spinae, and flexor carpi ulnaris are all primary contributors from the upper body, sequentially rotating the torso and upper limbs to maximally transfer force to the golf ball. In the lower body, the biceps femoris, gluteus maximus, and vastus lateralis all provide a solid base for weight transfer and subsequent rotation of the upper body (12,17,36,38). This line of research may provide direction for strength coaches and practitioners offering an indication as to which key muscles may influence swing performance.
Anthropometric Aspects of Golf
An area that has received limited attention in golf involves physical body characteristics. Golf is a sport that focuses on continual refinement of ball striking and putting skills with kinanthropometric qualities often being neglected (27). This seems counterintuitive as the swing is largely dictated by the anatomical and physiological makeup of the body (54). However, this could be justified as anthropometric variables have shown to not be associated with club head speed (27). This study did report, however, that excessive muscular hypertrophy may limit range of motion and increase body segment moment inertia, leaving the assumption that too much muscle mass may be detrimental to performance. By contrast, Wells et al. (67) reported positive correlations in low-handicap golfers between putting distance after a sand shot and body mass index (r = 0.59; p = 0.04), driver ball speed and stature (r = 0.48; p = 0.05), driver ball speed and arm length (r = 0.61; p = 0.01), and a positive relationship with carry distance (r = 0.62; p = 0.01) and greens in regulation (r = 0.69; p = 0.01) with arm length. Lower handicap golfers also tended to have longer upper arms and a greater total arm length (27,72).
In a similar line of enquiry, a cross-sectional assessment of body size and somatotype characteristics in male golfers reported physical differences between professional golfers, amateur golfers, college golfers, recreational golfers, and nongolfing subjects (25). Specifically, professionals had larger limb girths and highlighted that somatotype tended to increase in mesomorphy with an increase in skill (lower handicap). Professionals also recorded a heavier body mass and greater fat-free mass measurements than the amateur and control group, suggesting that lean muscle mass is an important aspect of golfing ability. In contrast to the control group, all golfers showed higher values of mesomorphy, which suggests that golf is a sport that requires muscular strength. Similarly, in a high- vs. low-handicap cross-sectional study, Keogh et al. (27) also reported that the lower handicap group tended to record greater fat-free mass along with larger chest and arm girth measurements. Furthermore, a recent study revealed that left and right arm muscle mass, along with trunk mass, was greater in both amateur and professional golfers compared with nongolfers (55). These results suggest that development of muscle regions that contribute to golf performance may be important. As the literature examining body type and composition is limited, further research examining different body types/compositions directly with golf performance measures such as club head speed seems warranted. More specifically, investigation into the effect of altering a player's body mass or somatotype through training intervention may also offer insight into the effect of body type on golf performance.
Cardiovascular Aspects of Golf
Golf is rarely associated with cardiovascular stress due to its low-moderate intensity nature. However, Murray et al. (40) highlighted that golfers can walk between 6 and 12 km over 18 holes and accumulate between 11,245 and 16,667 steps. In a recent review, it was demonstrated that intensity of golf match-play was 52.1–78.7% of maximal heart rate, with middle-aged men functioning at a mean exercise intensity of 35–41% of V̇o2 max (54). The lower intensities observed above coincide with findings from Unverdorben et al. (65) who reported lactate recordings of approximately 0.8–1.1 mmol/L through a round of golf. Although the golf swing itself is deemed to be a power-orientated action requiring rapid force generation (8,38,67), these findings suggest that the sport is primarily aerobic in nature, with a decrease in blood glucose levels and a concomitant increase in the use of free fatty acids for metabolism as the round progresses (39). This is can likely be attributed the large amount of time spent walking from one shot to the next (40).
Despite the inherent aerobic nature of the sport, metabolic stress has been observed with an increase in levels of epinephrine and norepinephrine (39) and an increase in cortisol levels in competition as opposed to practice due to stress (9). Furthermore, energy expenditure can range from 531 to 2,467 kcal per 18 holes, and walking 18 holes requires between 46 and 85% of functional capacity depending on terrain and modality (walking vs. riding in a cart) (9,40). Although cardiovascular and metabolic fitness may not be the primary concern for golfers or strength and conditioning coaches, Lennon (5) incorporated cardiovascular training into a year-long periodized training program, with subjects recording their best performance on tour. However, as this program incorporated multiple training modalities across the year, professional lessons, and no control group, it is difficult to determine the specific effect of the individual training components. Similar issues were present in recent studies where increases in club head speed of 4.9% occurred following a training program that incorporated endurance training concurrently with other modalities of training (60). Despite an array of research regarding the cardiovascular and metabolic demands, there is little direct evidence on the effect of cardiovascular training protocols and its relationship with golfing performance.
Balance Aspects of Golf
From a clinical perspective, balance is the ability to maintain the body in equilibrium by keeping the center of mass within the individual's base of support (52). It seems that balance is an important component of golf performance as players with a relatively low handicap (HCP < 0) have demonstrated superior balance on their dominant leg when compared with relatively high handicappers (HCP 10–20) (50). This relationship may be due to those with superior single-leg balance aptly handling the weight shifts that occur during the swing as well as the ability to cope with difficult stance positions (19,50). In a correlation study with low-handicap golfers, Wells et al. (67) also highlighted the potential importance of single-leg balance as they recorded a relationship between dominant leg balance and greens in regulation and nondominant leg balance and effectiveness of chip shots. Similar to the findings of Sell et al. (50), the authors concluded that the ability to shift weight from side to side and cope with difficult and varying ball lies is important (50,67).
Longitudinal intervention studies incorporating single-leg balance have induced improvements in club head speed (2.98%) and carry distance (6.59%) (31). In addition, exercise programs have been incorporated to enhance stability of the lower body by increasing balance and hip strength while improving hip flexion and extension ability (33). With a significant improvement in strength, flexibility, and single-leg balance, Lephart et al. (33) revealed a moderate increase in carry distance (d = 0.65) and club head speed (d = 0.65). Despite these positive results, and no practice occurring between pre-testing and post-testing, no control group was used along with multiple training modalities across multiple joints, thus limiting the applications of the findings. Furthermore, subjects displayed a mean handicap of 12.1 (±6.4), meaning that such training adaptations may not apply to high- or low-end handicappers. As evident with cardiovascular fitness, although benefits may exist around this trainable phenomenon (60), and with professionals having exhibited improved dynamic balance (4), there are limited studies solely assessing the effect of balance training on golfing performance.
A greater carry distance often requires a higher club head speed, which relies on high levels of muscle activation and strength (54). Because club head speed correlates with carry distance and handicap, it is clear that strength directly influences golf performance (14). Although an increase in strength may be beneficial for performance, there is some concern as to whether hypertrophy from training will limit joint range of motion and hinder performance (27). Despite this concern, the literature has shown that this decrement in performance, if it does exist, may be outweighed by the benefits received from improvements in strength and this will be explored through evaluation of strength in the lower body, trunk, upper body, and arms.
Because forces are developed from the ground upward, the lower body offers stability so that the linkage between upper- and lower-body segments can efficiently transfer kinetic energy to the ball (54). An effective golf swing requires a stable base on which the upper body and trunk can effectively rotate (50,64). Higher levels of muscle activity noted in the lower body (36–38) may further warrant inclusion of lower-body exercises within a strength and conditioning program. Doan et al. (8) conducted a longitudinal training study with intercollegiate golfers and reported a moderate effect (d = 0.66) from preintervention to postintervention in 1-RM squat measures. Although other exercises were included in this program, club head speed increased to a small degree (d = 0.22) and putting distance control in men largely improved (d = 1.64), highlighting the importance of the lower-body musculature. Similarly, Fletcher and Hartwell (13), adopting a randomized control design, incorporated squats and lunges, along with other exercises, into their training study but neglected to collect preintervention and postintervention strength measures. It is therefore difficult to distinguish the contribution of different muscle groups regarding the small increases in club head speed (d = 0.37) and moderate increases in driver distance (d = 0.74) evident after the intervention.
The importance of the gluteal muscle group is evident in the literature because studies have reported a relationship between handicap and hip abduction (r = −0.32) along with superior values of adduction strength in low-handicapped golfers when compared with higher handicapped golfers (d = 0.59). This suggests that increased hip strength may assist in achieving a lower handicap, which is an indicator of golfing success (50,64). Furthermore, Lephart et al. (33) reported significant improvements in hip abduction strength along with a moderate increase in club head speed (d = 0.65) after an 8-week longitudinal training intervention. Multiple training protocols incorporating lower-body strength training interventions have also reported positive results with increases in club head speed and carry distance, confirming the importance of this physical attribute (10,26,27,33,35,43).
The contribution of trunk muscle strength and coordination toward effective rotation during the golf swing was established by Watkins et al. (66), with this property ultimately enabling high muscular forces to be transmitted to the ball. Myers et al. (41) also identified a relationship between maximum torso rotational velocity during the downswing and ball velocity, again potentially warranting the consideration of this physical variable within a training context. Furthermore, others reported high levels of muscle activation, particularly in the acceleration phase, within the obliques and erector spinae (36,38). Wells et al. (67) reported a series of significant correlations with abdominal endurance measures and driver carry distance (r = 0.38) as well as putt distance after a chip shot (nondominant side, r = −0.59; dominant side r = −0.43) in low-handicap golfers. These findings suggest that the core musculature is important in not only producing long-distance shots but also stability and control around the greens. Similarly, in recreational golfers of all ages, Loock et al. (35) reported strong associations with lower back strength and club head speed and carry distance when using both driver (r = 0.56 and r = 0.47, respectively) and 5-iron (r = 0.58 and r = 0.44, respectively). This study computed that lower back strength accounts for up to 36% of variance in club head speed and is accordingly a priority area for optimizing golf performance. Additional studies also recognized the importance of core endurance and strength associating increases in carry distance (2–10.8%) with core strength improvements after implementation of a training program (13,27,31,33,49,57,61,70).
Improved neuromuscular function may also account for improvements evident in club head speed with golf-specific exercises. Utilizing strength measures from a golf-specific cable wood chop has effectively discriminated between relatively low and relatively high handicappers (d = 1.88) and correlated with club head speed (r = 0.71) (27). This highlights the importance of incorporating sport-specific exercises into training.
To develop maximum acceleration during the downswing, the weight of lower body must be shifted and musculature of the upper body must be properly activated (1). The upper-body limbs must carry on the sequential acceleration of body parts to assist with the maximization of final velocity (13). Similar to the lower body and trunk, upper-body training protocols are deemed necessary because of the activation demonstrated by muscles in the top half of the body (36,38). Compound movement exercises utilized within the upper body have demonstrated a positive relationship with club head speed (8,13,20,21,27,59). Wells et al. (67) reported a significant relationship between upper-body exercises such as pull-ups and push-ups with both driver ball speed (r = 0.55 and r = 0.48, respectively) and distance (r = 0.53 and r = 0.61, respectively), implicating the importance of superior strength within the pectoralis major, triceps brachii, latissimus dorsi, rhomboids, and biceps brachii. Positive associations have been reported between chest strength measures and carry distance as well as club head speed, suggesting that the pectoralis major and triceps brachii may account for up to 47% of variance in performance measures (18,20,35). Furthermore, studies have identified a positive relationship between trail shoulder internal rotation, as well as external rotation in both sides, and golfing performance measures (50,71). This may reflect the importance of the pectoralis major in internally rotating the shoulder. In addition, large increases in a shoulder press 1-RM test (d = 0.95) coincided with significant increases in club head speed in high-level golfers (8,13).
Moving distally in the upper body, after an 8-week training program, moderate improvements were recorded in arm curl strength (d = 0.67) along with a small increase in club head speed (d = 0.31) potentially implicating the biceps brachii as an important contributor to performance (60). Farber et al. (12) also reported heightened levels of muscle activation in the flexor carpi ulnaris during the acceleration phase, which may be important because it has been demonstrated that grip strength is related to driver and 5-iron ball speed (r = 0.65 and r = 0.60, respectively) along with driver and 5-iron carry distance (r = 0.64 and r = 0.60, respectively) (67). Furthermore, trivial improvements in grip strength (d = 0.15) have coincided with small increases in club head speed (d = 0.40) following a training intervention (17,21). In addition, the effects of fat grip training have also been examined in collegiate golfers with significant increases in left hand grip strength, ball speed, carry distance, and total distance (6). These changes were not demonstrated by the control group, potentially implicating the importance of grip strength in the lead arm for swing performance. Increased grip strength may positively influence the flexor activation that occurs just before impact which contributes to high endpoint velocity (17,21).
Within their review, Torres-Rhonda et al. (63) reported that as handicap improved, so too did swing performance, noting a correlation between skill (handicap) and strength. The authors reported increases in club head speed between 1.6 and 6.3%, whereas Smith et al. (53) reported improvements of 1.5–9.5% in a review on strength and conditioning training protocols for golfers. Several studies have failed to induce performance improvements utilizing training protocols (42,47) with reasoning originating in the training intervention design. Some studies failed to account for the dynamic nature of the sport, implementing isometric exercises (47), whereas others may not have exposed subjects to a sufficient stimulus, opting for 1 session per week (42) as opposed to the 2–3 sessions per week evident in other studies (8,13,33). Furthermore, notable limitations within intervention studies include the absence of a control group along with small sample sizes. Despite the majority of studies possessing adequate power to detect changes in outcomes, few reported effect sizes, making it difficult to compare results between studies. Few studies were adequately powered, incorporated a control group with subjects randomly allocated, and quantified improvements in performance using effect sizes, consequently providing scientific rigor. In addition, all studies have assessed or trained more than 1 joint or mode of intervention, making it difficult to distinguish the contribution of each component to improvements in golf performance.
The golf swing is a complex, stretch-shorten cycle movement, involving maximal power generation which is then transferred to the golf ball to propel it great distances with accuracy (38). Owing to the short duration of the downswing (∼0.3 seconds), an increasing rate of force development (RFD) and power production may have greater benefits than increasing maximal force (8). Power training for golf performance may be justified as slower contraction velocities used in resistance training may not improve power production capabilities or reflect the dynamic nature of the sport. It is well known that leg power is of critical importance, and training the leg-hip complex is necessary for improving golf performance (20,43,51,63,67,68). Regarding the lower body, positive associations have been identified between squat jump performance (r = 0.817) (34), countermovement jump variables (10,43,68), and club head speed in professional golfers. Furthermore, Wells et al. (67) reported relationships between vertical jump and driver club head speed, carry distance, and greens in regulation (r = 0.50, 0.62, and 0.66, respectively). Interestingly, this study also discovered a moderate relationship between dominant leg vertical jump and driver ball speed and carry distance (r = 0.57 and 0.61, respectively). Alternatively, EMG research has reported that the trail leg (dominant leg in right-handed golfers) was more active during the backswing phase (36,38), a phase where power is not maximally exerted. Other studies have reported relationships between leg power and golf round score (28), club head speed (72), and ball speed (71). Despite the positive associations between power and swing mechanics, only 2 studies have incorporated power-based training modalities, both subsequently inducing increases in lower-body power variables (d = 0.37–1.24), ball speed (d = 0.66), and carry distance (d = 0.57) (10,43). However, upper-body strength and power-orientated exercises were also incorporated in these training designs but were not concurrently tested before or after intervention. Although lower-body mechanics seem to be important, this makes it difficult to elucidate the specific effect of this musculature on golf performance.
Common methods for assessing and training rotational trunk power involve the use of a medicine ball (8,13,18,21,34,51) or a Biodex isokinetic dynamometer (1,33,44,57). Studies incorporating medicine ball throws reported increases in rotational trunk power along with small improvements in club head speed (d = 0.22–0.37) (8,13). A further cross-sectional study conducted by Gordon et al. (18) revealed a relationship between rotational trunk velocity and club head speed (r = 0.54) accounting for 29% of variance in this measurement. This study incorporated a golf-specific medicine ball hip toss that was aimed at mimicking the backswing and downswing of a golf swing. Utilizing a rotational medicine ball throw on an incline bench has also demonstrated a relationship with professional golfers (r = 0.57) (34). Small-moderate differences were also evident using isokinetic dynamometry professional golfers. This cohort demonstrated superior peak torques on their lead side at all assessed speeds (d = 0.27–0.58) when compared with their trail side in isokinetic trunk rotation strength and a control group (1). No golf performance measures were examined in this research, which may have offered insight into the outcomes of the power imbalance. Training studies have reported changes in both the trail side and lead side isokinetic trunk rotation strength after a resisted swing training program which coincided with moderate increases in club head speed (d = 0.65), carry distance (d = 0.65), and ball velocity (d = 0.61) (33). Furthermore, 9 weeks of isokinetic training increased rotational force and power, which coincided with increases in ball speed (d = 0.31) and carry distance (d = 0.51) to a greater extent than isotonic training alone (d = 0.11 and d = 0.32, respectively), implicating the importance of RFD and power mechanics in the trunk (44).
Three studies have examined the influence of upper-body power in relation to golf performance. After splitting a cohort into high and low club head speed groups, the high club head speed group demonstrated small-large positive differences in concentric-only and countermovement push-up–derived power variables (51). Interestingly, countermovement push-up peak force (d = 0.75), concentric-only push-up peak force (d = 0.82), and concentric-only push-up relative power (d = 0.74) differences were more significant than isometric push-up strength indices (d = 0.52–0.56). This may indicate that the ability to generate force at a faster rate is important for superior club head speed and that improving these characteristics may improve golfing performance (51). Furthermore, concentric-only movements may be a superior determinant of performance with strong associations between seated medicine ball throws and club head speed in professional golfers (r = 0.71) (34). In addition, with amateur golfers, the seated medicine ball throw was most related to baseline club head speed (r2 = 0.38) and was most responsive to training (r2 = 0.25) (20). However, the previous 2 studies neglected a countermovement medicine ball throw variation in their assessment, which may have provided greater insight into the influence of the stretch-shorten cycle in the upper-body on golf swing performance. Training investigations that modify upper-body power indices and assess the subsequent change in swing mechanics may further elucidate the influence of upper-body power on club head speed.
Given the classification of the golf swings as a stretch-shorten cycle movement, it is often grouped as a plyometric exercise (13). Plyometric training after the initiation of a prestretch seeks to shorten the amortization phase between eccentric and concentric muscle contraction, consequently increasing the power output (46). Power training for golf performance may be justified as high muscular power will enable more mechanical work to be performed on the club during the swing per unit of time, thus increasing club head speed (18). Leary et al. (32) reported positive associations between RFD and club head speed (r = 0.36–0.39). Given the fast nature of the downswing, increasing RFD is pertinent and may have greater benefits than increasing maximal strength (8). Despite evidence of its value in the literature, similar to studies examining strength, various study designs have not incorporated a control cohort or used multiple exercises or modalities which could have contributed to the increase in club head speed. Although the literature exists which examines the lower body and trunk regarding power, there are few studies identifying the influence of the stretch-shorten cycle in the upper body involving muscles such as the pectoralis major and triceps brachii in a golfing context.
It has been suggested that a greater range of motion would allow a longer backswing which potentially allows more time to produce higher angular velocities and a resultant higher force (27). For examples, after match pairing subjects in a randomized control design, Fradkin et al. (15) induced a 24% increase in club head speed incorporating a warm-up protocol 5 times per week for 5 weeks. This protocol included both dynamic and static stretches. Accordingly, increasing range of motion in a joint through flexibility training is an important component of golfing performance because of its ability to potentially reduce the chance of injury as well as enhance performance (16,18,61). It has been identified that training protocols may have the ability to alter musculotendinous properties, which can affect golf performance measures (13,16,62).
Lower Body and Trunk
The sit and reach test provides a global measure of lower-back mobility along with hamstring flexibility. A number of studies have used the sit and reach protocol and reported a positive trend between this measure and swing variables (21,35,60). Thompson and Osness (61) reported that a large increase in trunk flexion (d = 0.99), following specific flexibility training, coincided with a significant increase in club head speed. Although this study also incorporated other strength exercises and joints within the protocol, it implies that mobility in the lower torso should not be discounted as a contributing factor to the golf swing because a lack of lower back and hamstring mobility may lead to affect a golfer's ability to maintain a proper pelvic position and limit the ability to rotate during the downswing (19). By contrast, Wells et al. (67) reported a negative correlation with this measure and driver and 5-iron carry distance (r = −0.36 and −0.41, respectively) along with a positive relationship with the golf round score (r = 0.43). This indicated that greater measures of sit and reach flexibility are associated with shorter carry distances and increases in the score, both counterproductive to achieving golfing success. This suggests that there are more complex flexibility aspects to consider for golf performance. Although potentially offering some insight, the sit and reach test is not specific to the action of the golf swing. Minimal flexion is required within the trunk throughout the action, and the hamstring group offers stability and power through a shorter range of motion in the backswing and downswing (36,38).
A more appropriate assessment of flexibility involves examining torso and trunk rotation in combination. The separation of the lower torso and upper torso, termed the “X-factor,” followed by the subsequent rotation of the pelvis toward the target, with a momentary stagnation of the shoulders and upper torso at the commencement of the downswing, produces the “X-factor stretch” and is considered an important generator of club head speed (24). This stretch is believed to facilitate a muscular elastic recoil effect from which faster club head speeds can be attained (3). A cross-sectional analysis revealed that professional golfers have significantly larger values of rotation toward the trail side (backswing) compared with less-proficient golfers (d = 1.07) (50). Although no performance measures were monitored, handicap was demonstrated to be related to skill and club head speed. From these results, the action of rotating toward the trail side could be interpreted as important (14). Other studies have demonstrated higher rotation in the torso to be beneficial in terms of golfing performance, (8,21,27,31,33,61) highlighting the potential to increase “X-factor.” This is supported by a recent study that induced significant increases in “X-factor” values (d = 0.22) with small increases in club head speed (d = 0.35) after hitting 100 shots (56). On the contrary, Gordon et al. (18) and Sheehan et al. (51) did not record a significant relationship between rotational flexibility and club head speed, which may indicate that the players with high swing speeds and low flexibility are still able to swing the club over a sufficient distance to generate maximum speed. However passive measures of rotation may be limited because 1 study revealed that axial rotation flexibility is not related to “X-factor” (23). This may provide insight as to why a relationship was not observed between previously measured axial rotation and club head speed. Alternatively, trunk extension and lateral bending were positively associated with “X-factor” along with a positive relationship with club head speed implicating these 2 assessments for future research (23). Alternatively, Kenny et al. (26) induced a moderate increase in club head speed (d = 0.59) through a lower-body–orientated strength and conditioning intervention and concurrently reduced “X-factor” angle (d = 0.97). This suggests that emphasis should be shifted toward increasing RFD within the swing period rather than range of motion in certain joints. Given the equivocal findings, it seems that additional research is required to further clarify the relationship between “X-factor” and changes in club head speed as well as the potential mechanisms behind these variances.
A potential contribution to creating a superior “X-factor” lies in the abduction and adduction of the hip joint. Keogh et al. (27) demonstrated that highly proficient golfers (HCP < 0) have moderately less lead external hip rotation (d = −0.77) and trail hip internal rotation (d = −1.12) than less proficient golfers, which may offer an important insight into the between-group difference seen in hip and shoulder rotation resulting in a greater “X-factor.” In support, Thompson and Osness (61) did not record increases in hip abduction or adduction mobility in their randomized control study but did largely increase trunk rotation (d = 1.48) along with small increases in club head speed (136.8 km/h to 140.2 km/h). Furthermore, Sheehan et al. (51) demonstrated a significant negative association with lead internal hip rotation and club head speed (r = 0.54). The lack of mobility in the hip may allow for a greater separation between the pelvic girdle and upper torso, resulting in a greater “X-factor.” In the sagittal plane, greater flexion (d = 0.54) and extension (d = 0.79) of the hip has proven beneficial, with lower handicap golfers recording superior measures (50) and moderate increases in club head speed (d = 0.65) and carry distance (d = 0.65) following a training protocol (33). Bechler et al. (2) highlighted the action of the hip extensors in aiding rotation during the downswing, which may help explain the difference seen in these measures between different playing abilities.
Assessment of shoulder range of motion has also offered insight into factors affecting golfing performance. Similar to the hip and trunk, Sell et al. (50) reported that highly proficient golfers had moderately larger values in shoulder extension (d = 0.70), external rotation (d = 0.76), and abduction (d = 0.50) in the trail side along with superior values of shoulder flexion (d = 0.43) and abduction (d = 0.59) in the lead side when compared with less-proficient golfers. Furthermore, improvements in range of motion in the shoulder joint have been demonstrated within training protocols which coincided with small-moderate increases in club head speed (d = 0.31–0.65) and carry distance (d = 0.65) (33,60,61). McHardy and Pollard (38) highlighted the importance of internal shoulder rotation in the downswing through activation of the pectoralis major. Increasing the range in which the glenohumeral joint can operate may help lengthen the backswing, allowing more time for force to be generated.
Although a range of studies have reported an improvement in performance variables along with improvements in range of motion (8,14,21,22,31,33,60,61,69), 1 study failed to align with the consensus despite increasing thoracic extension and trail-side trunk rotation (42). However, when assessing the effectiveness of this study, similar limitations to those evident in the strength investigations were present. No control group was included, and the performance testing protocol, which had subjects aiming at targets at a set distance, may have constrained the swing of subjects because of its accurate nature. The absence of a control group was also a limitation in other studies, and assessing and training of multiple joints make it difficult to establish the contribution of each component to improvements in club head speed. It is clear that future research should implement isolated flexibility training protocols along with golf performance measures to offer greater insight into the importance of range of motion within different joints. Furthermore, investigation of the neuromechanical changes that occur concurrently within the muscles and joints may offer further insight and help identify specific mechanisms responsible for performance improvement.
Muscle-Tendon Properties and Golf Performance
Although the potential benefits of increasing the range of motion of a joint as well as the force produced by that joint seem justified, benefit may also be seen through implementation of warm-up protocols immediately before play. In a comparison between a control condition, dynamic warm-up and a resistance band warm-up, both warm-up conditions resulted in similar increases in ball velocity implicating the benefits of warm-up protocols (30). In addition, implementation of a combined active dynamic (10 × practice swings with a 1.13-kg weighted club followed by 3 × practice swings with a sand wedge, 8-iron and 4-iron) and functional resistance warm-up (practice swings with golf specific Theraband exercises), largely improved driver distance over solely an active dynamic (d = 1.14) and a weights-only (barbell exercises) warm-up (d = 0.97) (62). However, in contrast to these findings, static stretching protocols alone seem to negatively affect club head speed and golf performance (16,48). Implementing static stretch protocols immediately before performance has led to small decreases in club head speed (d = −0.48) and large decreases in distance (d = −1.08) and accuracy (d = −1.17) (16). Collectively, these findings suggest that increasing range of motion through warming up may not be as beneficial as increasing RFD in terms of club head speed.
Existing studies have attributed results of warm-up protocols to the properties of the musculotendinous unit (16,62). Gergley (16) suggested that the acute decrease in performance may be due to an increase in compliancy in the musculotendinous unit, decreased neuromuscular sensitivity, and neural inhibition. The author highlighted that stretching may have resulted in a decrease in force production due to the increase in slack within the tendon. This results in less force being applied to the skeletal system and a resultant reduction in performance. Tilly and MacFarlane (62) identified that the amount of elastic energy that can be stored in the musculotendinous unit is determined by the stiffness of the system. This stiffness, and subsequent increase in release of energy and force output, can be attributed to increased activation and strengthening of the musculotendinous unit. Using this concept, they opted for a specific thickness Theraband as it provided sufficient resistance to activate relevant muscle patterns and acutely increase the stiffness of the musculotendinous unit. Whether the reductions in performance were due to a change in the musculotendinous unit, or other neuromuscular effects, it is clear that further research is required to help clarify the mechanisms involved in this area (16).
Because alterations in stiffness may be influenced by warm-up protocols, and this potentially affects swing performance (16,62), the musculotendinous unit may play an important role in golf because of the potential role of musculotendinous unit stiffness to contribute to force generation as well as the incidence of injury. Owing to the short duration of the downswing (0.3 seconds), it is difficult for relevant muscles to generate maximal force values (8). Accordingly, manipulating stiffness levels across certain joints with resistance or flexibility interventions may increase the RFD during the acceleration phase or allow a greater backswing, potentially allowing time for more force to be produced. A recent cross-sectional analysis demonstrated a positive relationship between club head speed and lower-body stiffness (r = 0.50–0.78) and power (r = 0.42–0.55) along with no significant associations between strength or flexibility measures (51). The authors suggested that a stiffer system may reduce the time needed to remove the “slack” from the series elastic component of the involved muscles therefore reducing electromechanical delay and enhancing RFD. The large positive associations with stiffness and power production suggest that increasing these components may be superior focal components for training in golfers due to the short duration of the downswing (51).
Despite receiving limited attention in a golfing context, research regarding the physical characteristics of players has reported some common traits among highly proficient golfers. Excessive hypertrophy is suggested to be detrimental to performance as it may limit range of motion. Although this aspect is yet to be examined directly with golfing performance, professionals have demonstrated higher values of mesomorphy than amateur or control groups, highlighting the importance of lean muscle mass and strength in performance enhancement. Similarly receiving little attention, golf is rarely associated with cardiovascular stress due to the low-intensity nature of the sport. Despite this, research has identified the sport as primarily aerobic in nature with metabolic stresses evident during the round with increases in cortisol, epinephrine, and norepinephrine. Although minimal evidence exists on the effects of cardiovascular training and golf performance, it may be warranted as completion of a round requires up to 85% of functional capacity.
More recently, greater emphasis has been placed on balance, muscular strength, power, and muscle-tendon properties with positive associations demonstrated between these components and club head speed. Superior balance may allow for players to effectively deal with the need to shift weight during the swing as well as different stance positions, whereas improved lower-body muscular strength, power, and stiffness may allow for more mechanical work to be conducted on the club during the swing per unit of time, consequently increasing club head speed. Alternatively, although strength, power, and elevated levels of stiffness may enable a player to generate force at a faster rate, flexibility may also contribute to enhanced force production. A greater range of motion, particularly when generating the “X-factor,” may allow for a longer backswing, which would allow more time to produce higher angular velocities and a resultant higher force.
Training intervention studies focusing on the aforementioned components have demonstrated enhancements in golf performance. Targeting multiple muscle groups, including those implicated through EMG activation, as well as utilizing multiple modalities, has proven effective while concurrently reducing the resolution, making it difficult to identify the contributions of each aspect within the respective programs. Furthermore, although studies have identified alterations in musculotendinous stiffness as a potential contributor to enhancements, or decrements, in performance, this phenomenon is yet to be examined in a training context and is of particular interest for future research.
- Lower-body training programs that focus on the development of unilateral strength, balance, power, and stiffness, particularly in the trail limb, may promote increases in club head speed and carry distance.
- Upper-body strength, particularly in the pectoralis major and triceps brachii, and rotational trunk power have been associated with increased club head speed.
- Golf-specific strength and power exercises may, to a greater extent, induce larger increases in club head speed and carry distance than traditional exercises due to the swing-specific neuromuscular demands.
- Warm-ups incorporating active dynamic and functional resistance exercises seem to be more beneficial than static stretching alone due to negative influences on the musculotendinous unit.
- Lower-body flexibility does not seem to be important for generating club head speed. Alternatively, reduced hip flexibility, along with greater trunk rotational flexibility, may generate a greater “X-factor” which has been associated with increased club head speed.
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