Introduction

Shoulder problems in the female athlete occur most commonly in sports that require repetitive or forceful use of the upper extremity. While there is extensive research in male overhead athletes, most notably baseball players and in particular pitchers, there is much less research involving female athletes. There is some research in sports where both male and female athletes compete in the same events or under the same set of rules, but research often includes only males. Injury to the rotator cuff or chronic overuse of rotator cuff musculature is often not clearly defined in observational injury prevalence studies, making it difficult to ascertain the true extent of rotator cuff problems. ^, Overuse problems may not be reported by the athlete who may fear loss of a position on the team or by the athletic training staff if the injury does not involve time lost from participation. Club sports often do not have access to athletic training staff to track or report injuries. For these reasons, it is difficult to know the actual incidence or prevalence of rotator cuff problems in the female athlete for most sports, outside of “captured” athlete populations, such as the National Collegiate Athletic Association (NCAA).

There are clear similarities between the movement patterns of various men’s and women’s overhead sports, but differences in muscle firing patterns may only be observed with electromyographic (EMG) studies correlated with kinetic and kinematic information for the specific sport. ^, This chapter will discuss rotator cuff injury patterns for various women’s sports and the activity of the rotator cuff musculature in female athletes participating in overhead sports and will incorporate information related to injury prevention programs.

Softball

The typical softball is 12 inches in circumference with a weight between 6¼ and 7 oz. A baseball has a circumference of 9¼ inch and a weight of 5¼ oz. Softball pitchers frequently throw far more innings and pitches over the course of a week in season than baseball pitchers. Werner et al. reviewed the number of pitches for a typical softball tournament weekend. The authors found that a pitcher may pitch as many as 10 games, with 7 innings per game, and a total of 1500–2000 pitches thrown over a 3-day period. There are no mandated pitch counts for fast pitch junior or senior division softball as there are for Little League Baseball. Little League Baseball mandates no more than 95 pitches per day for its oldest age group (13–16 years), with required rest periods depending on the number of pitches thrown. College and professional baseball and softball do not require pitch counts.

There is extensive literature detailing the overhead baseball pitch. EMG studies have described the muscle activation patterns ( Fig. 16.1 ). The rotator cuff acts to decelerate the arm and compress the glenohumeral joint in overhead throwing sports. The windmill pitch technique used in fast pitch softball is less studied, but the throwing cycle is well-described. The phases of the windmill pitch ( Fig. 16.2 ) include (1) windup, first ball movement to 6 o’clock; (2) 6 o’clock to 3 o’clock (ends with shoulder flexed 90 degrees); (3) 3 o’clock to 12 o’clock (shoulder flexed/abducted near 180 degrees); (4) 12 o’clock to 9 o’clock (shoulder abducted to 90 degrees); (5) 9 o’clock to ball release; and (6) ball release to completion of throw (follow-through). The total arc of movement during the windmill pitch is 450–500 degrees. ^,

Pitching phases and key events (adapted from Fleisig et al. with permission). ER , external rotation; IR , internal rotation; max , maximum.

From Escamilla RF, Andrews JR. Shoulder muscle recruitment patterns and related biomechanics during upper extremity sports. Sports Med . 2009;39(7):572. www.littleleague.org/playing-rules/pitch-count . Accessed May 2020.

Six phases of the windmill pitch.

From Maffet MW, Jobe FW, Pink MM, Brault J, Mathiyakom W. Shoulder muscle firing patterns during the windmill softball pitch. Am J Sports Med . 1997;25(3):370.

Werner et al. have described the kinematics and kinetics of the elite windmill (rising) softball pitch by evaluating 24 elite female Olympic pitchers by using high-speed cameras during the 1996 Olympic Games. The authors found that shoulder distraction forces averaged 80% body weight, and they postulated that these distraction forces, which are similar to those in overhead throwers, place windmill pitchers at risk for overuse injuries. Injury data was not reported in this study.

Barrentine et al. also examined the kinematics and kinetics of the windmill fastball pitch in eight healthy female collegiate or previous collegiate pitchers. The authors found that peak forces resisting shoulder distraction occurred during the acceleration phase, as opposed to overhead pitching where the peak resistance to distraction is during deceleration. The supraspinatus and infraspinatus muscles had their highest EMG activity during phase 2. The distractive force at the shoulder was approximately 20%–40% body weight during the upward swing of the arm, resisted by the supraspinatus and infraspinatus. During phase 3, teres minor and infraspinatus reached peak activity, facilitating external rotation and resisting the approximately 50% body weight distractive force. Rapid downward acceleration and internal rotation (2000–3000 degrees/second) occur in phase 4, with the subscapularis muscle showing increased activity and peaking during phase 5. Subscapularis activity resists the distractive force, which peaks to full body weight distractive force, meaning a distractive force equal to the athlete’s body weight that the subscapularis must resist. Shoulder internal rotation also peaks at 4600 degrees/second.

Maffet et al. studied collegiate softball pitchers whose release included contact of the arm with the lateral thigh at ball release, decreasing the need for shoulder muscles to decelerate the arm ( Table 16.1 ). The study included EMG and high-speed cinematography motion analysis. The authors found that the supraspinatus was most active between 6 o’clock and 3 o’clock during arm elevation. The posterior cuff and infraspinatus were most active from 3 o’clock to 12 o’clock, and the pectoralis accelerated the arm from 12 o’clock to ball release. Activity in all muscles decreased during follow-through, due to arm contact with the body, which slowed the forward momentum of the arm, decreasing the need for muscles to decelerate the arm. Escamilla and Andrews reviewed EMG studies of several overhead sports and made a distinction between the overhead throw, which involves high forces and torques during the follow-through after ball release when muscles are decelerating the arm, and the windmill pitch, which has the highest forces and torques during the acceleration phase. This is an important difference to note between the overhead pitch and the windmill pitch, in which the rotator cuff muscles are not firing to decelerate the arm during the windmill pitch compared to the overhead throw, where the rotator cuff is active in decelerating the arm.

Lear and Patel reviewed the literature on softball injury risk in youth and collegiate softball players, noting overuse injuries to be generally more common than acute injuries and shoulder injuries to be more common than injuries to other joints, especially in pitchers. Many of the studies they reviewed focused on injuries sustained by pitchers. There was no consensus as to whether there are more reinjuries versus acute injuries or whether serious injuries (i.e., those that involve time loss from participation) are more common than nonserious injuries.

In 1992, Loosli et al. surveyed athletic trainers regarding injuries to pitchers from 8 of the top 15 NCAA collegiate softball teams that season, noting a significant number of minor to severe rotator cuff injuries among pitchers. All were reported as a strain or tendinitis/overuse injuries. No full-thickness or partial thickness rotator cuff tears were reported, likely, at least in part, because this study predated the widespread use of magnetic resonance imaging (MRI).

An interesting study by Chu et al. made a comparison of female versus male overhead baseball pitchers. Although females predominantly play softball, there is growing interest in baseball for females. The authors studied 11 female overhead baseball pitchers, noting a few significant differences compared with male pitchers including a shorter more open stride, lower ball velocity, and lower maximal proximal forces at the shoulder and elbow. Females also took longer to progress through the pitching cycle.

Volleyball

While ankle injuries are the most common injury in volleyball, shoulder injuries account for approximately 8%–10% of all injuries in high-school and collegiate volleyball players. Studies often do not distinguish between rotator cuff and other shoulder injuries. In female collegiate volleyball players, the shoulder accounted for 10% of non-time-loss injuries versus only 4% of time loss injuries.

The volleyball serve and spike involve overhead use of the arm, but unlike the throwing motion, the ball is only in contact with the hand for a brief period at the point of ball impact. In the United States, competitive volleyball is a sport played most commonly by female athletes. Rokito et al. studied glenohumeral muscle firing patterns in the volleyball serve and spike. Each skill is divided into five phases: (1) windup, consisting of shoulder abduction and extension; (2) cocking, initiation to maximum external rotation; (3) acceleration, which begins at maximum external rotation and transitions into internal rotation to ball impact; (4) deceleration, ball impact to arm perpendicular to trunk; and (5) follow-through, arm perpendicular to the end of arm movement ( Figs. 16.3 and 16.4 ).

The five phases of the volleyball serve.

From Rokito AS, Jobe FW, Pink MM, Perry J, Brault J. Electromyographic analysis of shoulder function during the volleyball serve and spike. J Shoulder Elbow Surg. 1998;7(3):257.

The five phases of the volleyball spike.

From Rokito AS, Jobe FW, Pink MM, Perry J, Brault J. Electromyographic analysis of shoulder function during the volleyball serve and spike. J Shoulder Elbow Surg. 1998;7(3):257.

Rokito et al. described peak supraspinatus EMG activity at deceleration (45% manual muscle test [MMT]) during the serve ( Table 16.2 ). Activity was much higher for the supraspinatus during the windup for the spike (71% MMT). EMG activity for the infraspinatus muscle was lower during windup for the serve but higher during windup for the spike. Teres minor had the lowest activity during windup for the serve (7% MMT) and increased to 54% MMT at acceleration during the serve. Teres minor had higher activity during windup for the spike at 39% MMT, with peak activity during cocking and acceleration at 51% MMT. Windup for the serve was associated with minimal activity in the subscapularis (8% MMT). Peak activity for subscapularis (56% MMT) for the serve occurred during acceleration. EMG activity in the subscapularis muscle during windup for the spike was relatively higher (46% MMT), dropping during cocking then rising to maximal activity (65% MMT) during acceleration.

Muscle activity during windup and follow-through was low for the volleyball serve. In contrast, supraspinatus and infraspinatus had peak activity during windup of the spike. Infraspinatus and teres minor had high activity during cocking to produce external rotation. The rotator cuff is also necessary for joint compression to resist the shoulder distraction force generated by these motions. An important difference in muscle firing occurs during the acceleratory phase between spike and serve. The acceleratory muscles (subscapularis, teres major, latissimus dorsi, and pectoralis major) are much more active in the spike than the serve, as velocity is the primary goal for a spike, whereas a more parabolic trajectory is used for the serve. During deceleration, infraspinatus and supraspinatus activity was greatest during the serve rather than the spike. During the spike, the ball is struck and the ball in turn imparts an opposing force on the arm. This may help decelerate the arm, thereby requiring less activation from the rotator cuff muscles to control arm deceleration, which differentiates this action from throwing, where muscles must decelerate the arm.

Lajtai et al. studied 84 professional beach volleyball players (54 males and 30 females) using a questionnaire, physical examination, and ultrasound, as well as MRI, in 29 male athletes to assess typical clinical and imaging findings in the hitting shoulder of this population. The mean age of athletes was 28 years (range, 20–39 years). About 63% (50 of 80) of players reported shoulder pain in the hitting shoulder. Infraspinatus muscle atrophy was noted in 25 of 84 (30%) athletes without evidence of suprascapular nerve compression. Male and female athletes were not significantly different in this measure (31% vs. 27%, respectively). External rotation strength was significantly decreased in the hitting shoulder for both male and female athletes. Five of the male (9%) and four of the female (13%) players had undergone previous shoulder surgery. Among the 84 players, 12 (14%) had a partial rotator cuff tear as documented by ultrasound. One explanation for external rotation weakness and infraspinatus atrophy in the absence of a compressive structure, such as thickened spinoglenoid or transverse scapular ligament or ganglion cyst, is a stretch neuropathy of the suprascapular nerve.

Notarnicola et al. evaluated perfusion of the supraspinatus tendon at its insertion to the tuberosity of male and female elite volleyball players using oximetry to study microcirculation, based on the theory that relative hypoxia caused by functional overload of the tendon can lead to a neovascularization response within the tissue. Only athletes with no complaints or physical findings of shoulder pain or problems were included in the study. The authors found no difference between male and female athletes, but they did note a difference between athletes playing different positions. Rotator cuff oximetric percentages increased by position, with the middle hitter having the lowest percentage and the outside hitter having the highest in the dominant arm.

Tennis

Tennis, similar to softball and baseball, involves considerable overhead use of the dominant arm for the serve and volley. There is limited research on EMG activity in the rotator cuff musculature of tennis players. Ryu and Kibler have conducted EMG studies in male tennis players. ^, The authors found that the subscapularis was most active in the overhead serve and the forehand stroke, while supraspinatus and infraspinatus were more active in the backhand stroke. Serratus anterior was active for all three strokes. Kibler et al. focused more on the timing of muscle firing patterns, noting that the scapular positioning muscles were active prior to the shoulder elevators and cuff musculature that serve as a force couple to center the humeral head. In addition, Kibler et al. found infraspinatus to be relatively inactive in the overhead serve. No EMG studies were found specific to the muscle firing patterns of the rotator cuff of female tennis players.

Lynall et al. reported on injury rates in men’s and women’s collegiate tennis players using the NCAA Injury Surveillance Program (ISP), which included data from 19 men’s varsity programs and 25 women’s varsity programs between the 2009/10 and 2014/15 seasons. Injury rates were similar between males and females, with the majority of injuries occurring to the lower extremities. About 14% injuries in males and 11.9% in females were to the shoulder/clavicle area, with an injury rate of 0.7 and 0.58 per 1000 athlete-exposures (AEs), respectively.

Dakic et al. evaluated injuries in 52 women’s professional tennis circuit players competing in the 2015 Australian Open. The authors found that 9.3% of injuries reported by players were to the shoulder/clavicle area for a rate of 8.2 injuries per 1000 match-hours. Lower extremity injuries were much more common, comprising 51% of injuries and an injury rate of 42.2 per 1000 match-hours by comparison. They did not report rotator cuff injuries separate from shoulder injuries, in general.

In 2012, Abrams et al. conducted a literature review of tennis injuries and found that shoulder injuries composed 4%–17% of all injuries. The study did not detail information on female players specifically. The authors noted that younger athletes tended to have more instability issues, while older athletes tended to have more rotator cuff issues. The authors cited scapular dyskinesis as well as glenohumeral internal rotation deficit as frequent contributing factors for shoulder injury in tennis players.

Swimming

Competitive swimming often begins at a young age with intense training hours. There are two main phases to the stroke cycle: (1) pull-through, where speed is generated, and (2) recovery, where the arm is out of the water and includes body roll for some strokes. The repetitive stroke cycle leads to overuse of the shoulder joint; in particular, the shoulder adductors and internal rotators become hypertrophied. About 40%–91% of competitive swimmers have reported shoulder pain, making it the most common musculoskeletal injury in this population. As with many sports where female athletes compete similar to male athletes, many studies are conducted using only male swimmers. This results in an unfortunate deficiency in our understanding of the female swimmer. It may not be safe to assume that the muscle firing patterns and response to various interventions will be the same for female swimmers as for male swimmers.

“Swimmer’s shoulder” is a common injury cited in the literature, with presenting symptoms of anterior shoulder pain due to repetitive impingement on the rotator cuff tendons. Both intrinsic and extrinsic factors contribute to the development of “swimmer’s shoulder.” Intrinsic factors include joint hypermobility, core instability, thoracic kyphosis, scapular dyskinesis, rotator cuff imbalance, and lack of flexibility ( Tables 16.3 and 16.4 ). ^, Extrinsic factors include increase in training hours, lack of dry-land shoulder strengthening, and use of resistance devices such as hand paddles. The supraspinatus tendon is most commonly involved because of subacromial impingement causing repetitive trauma to a relatively avascular region of the tendon. Supraspinatus tendinopathy was reported in up to 91% of elite swimmers and is associated with a positive impingement sign. Specifically, the supraspinatus tendon is put under stress during the recovery phase and the late pull-through phase of the swimmer’s stroke cycle.

Table 16.3

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