This is an excerpt from Sport Therapy for the Shoulder With Online Video by Todd S. Ellenbecker & Kevin E. Wilk.
Golf Swing Mechanics
Similar to the situation with the other sports reviewed in this chapter, to isolate and identify the functions of the major muscles controlling the various body segments during the golf swing, dynamic EMG and high-speed motion analysis has been used and helps to provide a greater understanding of the demands of golf on the shoulder complex. For discussion and analysis purposes, the golf swing has been broken down into the following five phases (Pink et al. 1993):
- Take-away: from address to the ball to the end of the backswing
- Forward swing: from the end of the backswing until the club is horizontal
- Acceleration: from horizontal position of the club to ball contact
- Early follow-through: from ball contact to horizontal club position
- Late follow-through: from horizontal club position to the end of the swing
Muscles used in three of the five phases of the golf swing: (a) take-away, (b) acceleration, and (c) follow-through.
This section describes and compares the muscle activity patterns of the primary shoulder and scapular muscles (but note that there are also significant contributions from other body segments during a golf swing).
Before initiation of the backswing, proper setup and ball address must be achieved. This initial posture greatly influences the balance of forces throughout the golf swing and is therefore critical to the achievement of the proper swing plane. The take-away phase has been described as a "coiling" or "loading" of the body in order to enhance the velocity and kinetic energy of the club head (Pink et al. 1990). Electromyographic analysis reveals relatively low activity of the trunk musculature during this segment of the golf swing, as the trunk is simply preparing for the swing (Pink et al. 1990). Electromyographic analysis of the scapular muscles of the trailing arm reveals relatively high activity of the upper, middle, and lower portions of the trapezius during take-away in order to help the scapula retract and upwardly rotate (Kao et al. 1995). Similarly, the levator scapulae and rhomboid muscle of the trailing arm are active during this period to help with such scapular movements (Kao et al. 1995). In the leading arm during take-away, the activity of the scapular stabilizing muscles is relatively low to allow for scapular protraction.
Electromyographic analysis of the rotator cuff muscles exhibits contributions from the supraspinatus and infraspinatus in the trailing arm as they act to approximate and stabilize the shoulder (Jobe et al. 1986, Pink et al. 1990). Of the rotator cuff muscles in the leading arm, only the subscapularis was shown to display marked activity during the take-away phase. It should be noted that the pectoralis major, latissimus dorsi, and the deltoid muscles of both arms are relatively inactive in the backswing of the golf club (Jobe et al. 1986, Pink et al. 1990).
During forward swing, trunk rotation movement is initiated. Analysis of the trailing arm scapular muscles shows that the three portions of the trapezius have lower activation to allow for scapular protraction (Kao et al. 1995). However, the levator scapulae and rhomboid muscles display marked activity to control scapular protraction and rotation of the trailing arm. Analysis of the serratus anterior muscle in the trailing arm shows increased activity during forward swing to aid in scapular protraction and stabilization (Kao et al. 1995). Electromyographic studies of the lead arm demonstrate high activity of the trapezius, levator scapulae, rhomboids, and serratus anterior as they all contribute to scapular motion and stabilization as the arms move toward the ball (Kao et al. 1995).
Of the trailing shoulder muscles during forward swing, the subscapularis, pectoralis major, and latissimus begin firing at marked levels as the trailing arm increasingly accelerates into the internal rotation and adduction. The lead arm subscapularis and latissimus dorsi are both moderately active during the forward swing phase.
During the acceleration phase, the body segments work together in a coordinated sequence in order to maximize club head speed at ball impact. The serratus anterior is the primary scapular stabilizer that is active in the trailing arm during acceleration (Kao et al. 1995). The serratus has high levels of involvement in order to allow for a strong scapular protraction and contribute to maximizing club head speed. Conversely, EMG analysis reveals strong contractions of the scapular muscles in the lead arm during acceleration (Kao et al. 1995). The trapezius, levator scapulae, and rhomboid muscles are firing to aid in scapular retraction, upward rotation, and elevation. The serratus anterior of the lead arm continues to display high levels of activation throughout. This important muscle is highly involved during the golf swing, similarly to what is seen during throwing and the tennis serve as discussed in earlier sections of this chapter.
Electromyographic investigations display high levels of subscapularis, pectoralis major, and latissimus dorsi activity to provide power to the trailing arm during acceleration (Jobe et al. 1986). These important muscles further increase in activity from forward swing to assist in rotation and forceful adduction of the arm during this phase. The latissimus dorsi contributes most of its power in the forward swing, while the pectoralis major supplies the most power during acceleration (Pink et al. 1990). Similarly, the subscapularis, pectoralis major, and latissimus dorsi of the lead arm fire at high rates during the acceleration phase (Jobe et al. 1986, Pink et al. 1990).
After ball contact has been made, the follow-through phase is initiated. During early follow-through, nearly all the body segments work to decelerate their rotational contributions, often through eccentric muscle contractions (Jobe et al. 1986, Pink et al. 1993). The scapular muscles of both the trailing and lead arms display decreased activity throughout the follow-through phases, allowing for coordinated scapular protraction (Kao et al. 1995). Despite this decrease in scapular activity, the serratus anterior muscles of both arms show fairly consistent muscle firing patterns providing vital scapular stabilization throughout the follow-through phases (Kao et al. 1995).
In the trailing shoulder, marked activity of the subscapularis, pectoralis major, and latissimus dorsi muscles continues into the early follow-through phase (Jobe et al. 1986). For the lead shoulder, the subscapularis continues its high level of activity, while the pectoralis major and latissimus dorsi decrease their contributions (Jobe et al. 1986, Pink et al. 1990).
Activity of the scapular muscles of both arms decreases to lower levels as the swing comes to an end (Kao et al. 1995). The subscapularis of the trailing shoulder is one of the only muscles that remains highly active during this phase (Jobe et al. 1986, Pink et al. 1990). Analysis of the lead arm reveals marked activity of the infraspinatus and the supraspinatus rotator cuff muscles used for glenohumeral stabilization (Pink et al. 1990).
One final discussion regarding the golf swing concerns a common mechanical fault that many golfers have, placing their glenohumeral joints at risk. During take-away, the lead arm is placed into increasing degrees of internal rotation and cross-body adduction. This position may predispose the golfer to impingement-type problems as the rotator cuff tendons and bursae are compressed within the shoulder (Mallon 1996). Additionally, at the end of the backswing, forces on the acromioclavicular joint of the lead arm are shown to be high, contributing to the incidence of pain often seen in the golfer's shoulder. The posterior rotator cuff and scapular muscles of the lead arm are also at risk for injury at the TOB as they are placed under a stretch load to achieve that position (Mallon 1996).
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