Muscle activity during the golf swing (P3)
Muscle function at point of impact
Although the impact of the golf swing is a specific point in time, and instantaneous muscle activity is difficult to evaluate, it is important to know what is occurring in the body at this time. This is important because most golf injuries occur at impact. Just before impact there is an increase in right wrist flexor activation, the flexor burst, which corresponds to combined flexion and pronation of the right forearm that occurs through impact. If there is a sudden decrease in clubhead acceleration—for example hitting the ground or tree root etc—there is a sudden change from concentric to eccentric contraction in the wrist flexors. This stretch based injury is likely to be acute if forces are large enough, or overuse-type if it occurs regularly.
The early follow through of the golf swing occurs after ball impact and is the phase at which deceleration of the trunk rotation occurs. The pectoralis major muscles continue to be very active, continuing their action of the acceleration phase. The other muscles that are active in the follow through are the right trunk external rotators and the left side internal rotators. This rotational activity is associated with similar paired activity in the shoulder. In the shoulder, the active muscles are the right subscapularis and the left infraspinatus. These muscles are active during impact, where there is a ‘‘rolling’’ of the forearms, which results in left arm supination and right arm pronation. This movement continues through early follow through resulting in left arm external rotation and right arm internal rotation. The rotator cuff muscles contract to control this movement.
It is noteworthy that a lack of trunk rotation may require the much smaller shoulder rotators to become excessively active to maintain the swing momentum or decelerate it. Such a scenario may result in the shoulder dysfunction often noted in golfers, particularly instability in professionals. It is also noteworthy that those with back problems may potentially induce a shoulder problem in their attempt to reduce the loads on a painful lower back. Bulbulian et al noted similar observations in his research on a modified golf swing where the back swing is shortened. This research reported that the forces generated in the lower back were reduced by this swing, but the forces generated in the shoulder were greater.
The lower body muscle activity is similar to the acceleration phase, with the left side acting as a stable base and the right side rotating around the left.
In the late follow through, the muscle activity decreases as the golfer nears the end of the swing. The muscle activity in this phase is similar to the early follow through, but with a lesser degree of activity. The only exception occurs in the upper body where the right serratus anterior shows increased activity, as it aids the protraction of the scapular around the trunk.
During the follow through of the golf swing, a number of muscles are eccentrically loaded to aid the deceleration of the body and golf club. This is particularly true of the rotator cuff musculature. Eccentric muscle has the potential for injury because of the forces produced on muscle fibres.20–22 This review proposes that such a mechanism is inherent in the genesis of golf related shoulder injury.
There are a number of methodological concerns about many of the studies on the EMG activity of the golf swing. All of the golfers selected in the studies were right handed. This aids standardisation of the data, and the results can be extrapolated to most golfers as most are right handed. However, left and right handed golfers may be different, and it is an assumption that EMG activity in the left handed golfer is a mirror image of the right handed golfer.
Secondly, most studies were conducted on highly skilled golfers (professional or low handicap, amateurs). In the United States, the average handicap is 16.1 for male golfers and 29.2 for female golfers and in Australia, they are 18.1 and 27.5 respectively. 25 Although the data collected may represent what ideally should occur during the golf swing, it may not accurately reflect the actual swings of most golfers. The ‘‘average’’ golfer is a very different quality of player, who would be expected to have a less reproducible and efficient golf swing, with potentially different muscle activity during the swing from a highly skilled golfer. Extrapolation of the data from one cohort to the other may therefore be problematic.
Finally, the methods sections of the included studies do not have a description of the golf swing used by the subjects. As described previously, there are a number of different swing types in golf. Each swing has a distinct characteristic body motion, which may produce different muscle activation throughout the golf swing and alter the data collected. In addition, a third swing has begun to emerge. Components of both the classic and modern swing have been incorporated to produce what may be termed the ‘‘hybrid swing’’. The hybrid swing uses a similar back swing to the modern swing, with limited lumbopelvic rotation, whereas the follow through is similar to the classic swing, with a relatively neutral spine position (less hyperextension). The momentum of the follow through is directed into left rotation in the right handed golfer.
It is important that further studies of the EMG activity of the golf swing target the aforementioned methodological issues. Future studies could investigate both the upper and lower body activity in beginner/low level golfers (handicap), the average golfer, and the advanced golfer (professional and handicap). These groups will allow a comparison between skill levels in golfers in terms of muscle activity and may identify potential reasons for the differences in handicaps. Studies on muscle activity that occurs during both the classic and modern swing are needed to identify if there is a difference between these swings.
Ultimately, such data could be related to prospective injury data on these swings to better explain the causes of golf related injury. These data would also help clinicians to manage golf related injury, with the prescription of appropriate exercise protocols to rehabilitate and prevent injury.