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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 13  |  Issue : 1  |  Page : 23-29

Acute effects of softball pitching to fatigue on the glenohumeral internal rotation range of motion


Department of Physical Therapy, Simmons University, Boston, MA, USA

Date of Submission20-Aug-2018
Date of Acceptance14-Jan-2019
Date of Web Publication29-Jun-2019

Correspondence Address:
Dr. Amitabh Dashottar
Simmons College, Boston, MA 02215
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/PJIAP.PJIAP_30_18

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  Abstract 

BACKGROUND: The effects of baseball pitching on the glenohumeral joint (GHJ) range of motion (ROM) have been widely studied. Specifically, internal rotation (IR) ROM reduction of the pitching arm, an adaptation to repeated overhead throwing, is linked to increased risk of injuries in baseball pitchers. However, there is a lack of literature on the effects of softball pitching on the GHJ ROM.
HYPOTHESIS: Softball pitching to fatigue will result in significant reduction of GHJ supine IR ROM.
DESIGN: Test–retest, quasi-experimental study.
METHODS: Twelve softball pitchers (age: 19.5 ± 1.8 years) volunteered to participate in this study. GHJ ROM in supine IR, horizontal adduction, low flexion (shoulder joint flexed to 60°; added IR), extension with IR (shoulder joint abducted to 60° in the plane of scapula and then horizontally abducted 90° with the elbow maintained in 90° flexion; add GH IR), and supine external rotation were compared before and after a single bout of softball pitching to fatigue or a maximum of 100 pitches, whichever occurred first.
RESULTS: Maximum ROM change post softball pitching was observed in horizontal adduction but not in supine IR.
CONCLUSIONS: Maximum ROM change was observed in horizontal adduction. Supine IR ROM measurement may not be appropriate for assessing softball pitchers' shoulder ROM because this measurement was not affected by the softball pitching.

Keywords: Clinical measurements, range of motion, shoulder, softball, windmill pitching


How to cite this article:
Dashottar A. Acute effects of softball pitching to fatigue on the glenohumeral internal rotation range of motion. Physiother - J Indian Assoc Physiother 2019;13:23-9

How to cite this URL:
Dashottar A. Acute effects of softball pitching to fatigue on the glenohumeral internal rotation range of motion. Physiother - J Indian Assoc Physiother [serial online] 2019 [cited 2019 Nov 19];13:23-9. Available from: http://www.pjiap.org/text.asp?2019/13/1/23/261818


  Introduction Top


Fast-pitch softball is one of the most popular women's team sports, and shoulder overuse injury prevalence in softball pitchers is comparable to that of baseball pitchers.[1] Upper extremity in softball pitchers has been reported as the primary region of injury, with up to three times the risk of reinjury to shoulder and rotator cuff.[2] Even though the injury rates are comparable between baseball and softball, softball pitchers have not been studied as extensively as baseball pitchers.[3]

Softball and baseball are similar sports in that both involve pitching to a batsman; however, there are some important differences. For example, unlike baseball pitchers, softball pitchers throw from a flat-pitching circle, the distance of the base plate from the pitching circle is 12.2 m compared to the 18.4 m in baseball. The regulation weight of the softball is 7 oz compared to baseball that weighs 5 oz. Moreover, most softball games are doubleheaders, which means that softball pitchers may pitch in as many as ten games (seven innings each) over a weekend. It is also estimated that, over a 3-day period, a pitcher may throw as many as 1500–2000 pitches.[4] In addition, the number of pitchers in softball teams is usually much lower compared to that of baseball teams. (A quick review of the US softball national team reveals that there are three pitchers on roster (www.teamusa.org/USA-Softball/Team-USA/Women) compared to 14 pitchers on roster for US national baseball team.) This means that the volume of pitches thrown by a softball pitcher is much higher than that of the baseball pitchers.[4]

While the physical demands of softball are different than that of baseball, distraction forces across shoulder, produced during a softball pitch, are comparable to baseball pitching.[4],[5] These forces are, however, generated during different stages of pitching; for example, in baseball pitching, greatest forces across the shoulder joint are generated during the arm deceleration phase, whereas in underhand pitching, the greatest forces are observed during the arm acceleration phase.[6],[7] Furthermore, the muscle activity patterns during softball and baseball pitching are different.[7] The shoulder joint of baseball pitchers adapts in response to high-intensity chronic repeated overloading.[8],[9],[10],[11] For example, baseball pitchers are known to have altered humeral torsion magnitude,[10] thickening and contracture of the posterior GHJ capsule,[12],[13] and reduced extensibility of rotator cuff muscles.[14],[15],[16],[17],[18] While the osseous and capsular changes develop over an extended period of exposure to pitching, changes in the muscle extensibility may be observed immediately.[1],[10],[15],[19],[20]

Irrespective of the mechanism of immediate range of motion (ROM) loss, it is mostly accepted that continuing to pitch with decreased IR ROM puts the pitcher at a higher risk of injury.[21],[22] Based on the difference in the physical demands, biomechanical differences in the pitching action, different peak force generation points, and muscle activity, it is reasonable to assume that both, the delayed and immediate responses to repeated overloading in softball pitchers may be different from a baseball pitcher. There has been limited research on the immediate effects of softball pitching on the GHJ ROM in softball athletes. Understanding the acute effects of softball pitching on the ROM may assist in the evaluation and management of injured softball athletes. Therefore, the purpose of this study was to test the acute effects of softball pitching on the GHJ ROM in softball pitchers. Our hypothesis was that the supine internal rotation (IR), the most commonly used measurement of shoulder joint IR, will show maximum ROM change after a bout of softball pitching.


  Methods Top


Subjects

Twelve softball pitchers (mean age: 19.5 ± 1.8 years) without any current shoulder pain were recruited for the study. All but one were right-hand dominant [Table 1]. The Simmons College Institutional Review Board approved this study. All participants were informed about the study procedure and provided informed consent prior to participation.
Table 1: Demographics of the sample

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Study design

The study is of test–retest repeated measures design.

Procedure

The experiment began with baseline recordings of ROM across five measurements using a goniometer [Table 2]. Two examiners performed the measurements; examiner 1 oriented the shoulder joint to the test position and was blinded to the GHJ ROM values. Examiner 2 measured the ROM and was blinded to the hypothesis of the study. Both examiners were licensed physical therapists with 16- and 5-year experience in musculoskeletal physical therapy. All measurements were repeated five times, and the means were used for statistical analysis.
Table 2: Description of the clinical measurements of range of motion

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Range of motion measurements

Repeated measures of GHJ ROM across five measurements were recorded before and after softball pitching. Detailed procedure of ROM measurements is presented in [Table 2]. The order of measurements was randomized using a computer-generated sequence. All the measurements were taken at the end range with no overpressure. The effect of gravity on the arm was allowed to move the GHJ to the end of passive range for low flexion (LF),[13],[19],[23] IR with shoulder in extension (EIR),[14],[24] IR, and external rotation (ER) while the examiner moved the joint to the end of the passive ROM for horizontal adduction (HAD). For IR, ER, LF, and EIR, the moving arm of the goniometer was aligned with the radial styloid. For HAD, the moving arm was aligned with the lateral condyle of humerus. All measurements were done using a goniometer (baseline evaluation instruments, Fabrication Enterprise Inc., White Plains, NY, USA).

Force measurements

Muscle force measurement was used as a marker of muscle fatigue. Several authors in the past have used fatigue as an objective marker of muscle fatigue.[3],[7],[14],[15] Muscle force was measured across four motions using a handheld dynamometer. The details of the force measurement procedure are provided in [Table 3]. Briefly, GHJ IR and ER strength were measured with the participant standing, arm by the side and elbow flexed 90°. For IR, the dynamometer was placed on the volar side of the wrist, between the radial and ulnar styloid processes. For ER, the dynamometer was placed on the dorsal side of the wrist, between the radial and ulnar styloid processes. Horizontal abduction force was measured with the participant prone and the arm in 90° shoulder horizontal abduction. The dynamometer was placed proximal to the lateral epicondyle. Scaption strength was tested in the seated position (back supported and feet flat on the floor), with the shoulder flexed to 120° in the scapular plane. The dynamometer was placed on the radial surface of the hand, just proximal to the radial styloid process.
Table 3: Description of the force measurement

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All measurements were collected before and immediately after pitching. A preset criterion was used to determine pitching endpoint. These criterions were (1) self-reported fatigue by the pitcher or (2) 100 pitches, whichever occurred first. The participants were instructed to self-select the pitching velocity.

Statistical analysis

The primary dependent variables in this study were the GHJ ROM across five measurements, before and after softball pitching. A two-factor ANOVA (condition – two levels and measurements – five levels) was used. For significant effects, post hoc paired t-tests were planned. The significance level for the paired t-test was set at P < 0.01 to minimize Type I error. To test the reliability of ROM measurements, intraclass coefficient (ICC) (3,3) was calculated for each measurement in each condition. Reduction in the muscle force production was calculated as the percent force reduction for each motion. All analyses were performed using NCSS 2013 (Kaysville, UT, USA).


  Results Top


Demographic data with the average number of pitches thrown and average time duration to fatigue and ICC (3,3) are presented in [Table 1] and [Table 4], respectively. Two-factor repeated measures ANOVA for ROM indicated a significant main effect of measurement, but no interaction effect among condition and measurement. Post hoc comparison using paired t-test revealed that there was statistically significant reduction in the ROM measured in HAD only. The detailed results are presented in [Table 5]. Pitching also leads to a reduction in muscle force production across all the motions, with maximum percent reduction observed in horizontal abduction and minimum in scaption [Table 6].
Table 4: Intraclass correlation coefficients (3,3) for the range of motion measurements

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Table 5: Range of motion before and after pitching

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Table 6: Muscle force production (kg), pre- and post-softball pitching

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  Discussion Top


Softball pitching has not received as much attention in the scientific literature as baseball pitching.[3] This might be because of the traditional thought that softball pitching is not as intense as baseball pitching, and underhand motion is a less injurious motion.[25],[26] However, softball pitchers have been reported to have significant muscle fatigue and experience significant time-loss injuries as a direct result of underhand pitching.[7],[17]

Shoulder injuries in baseball pitchers have been extensively studied, and the predictors of injury have been identified. For example, the ROM loss in the IR and GHJ horizontal adduction is considered a predictor of shoulder injury in baseball pitchers; however, this was not the case for softball pitchers.[21] In this study, we quantified the ROM changes across five commonly used clinical measurements of GHJ ROM, before and after softball pitching. To the best of our knowledge, this is the first study to compare ROM loss in softball pitchers as a direct result of softball pitching. We hypothesized that Supine internal rotation (SIR) will show the maximum ROM change after pitching. The hypothesis was developed because ROM loss in SIR measurement is a common finding in baseball pitchers and has been associated with an increased risk of injury.[11],[27] Contrary to our hypothesis, the greatest ROM change was observed in HAD but not in SIR. Due to lack of studies on the immediate effects of softball pitching on GHJ ROM, a direct comparison of our results with previous literature is not possible. However, Shanley et al.[21] reported no differences in the IR ROM between injured and uninjured softball pitchers, but found that HAD ROM was reduced in the softball pitchers with a history of injury. Interestingly, on retrospective analysis of the baseline HAD ROM, between pitchers with a history of shoulder injury (n = 5) and no history of injury (n = 4, missing data n = 3), we found that, on an average, HAD ROM in injured pitchers was 13.1° ±3.9° compared to 19.1° ±3.0° in uninjured players. A similar comparison for SIR revealed that SIR in players with a history of shoulder injury was 45.4° ±5.4° and in uninjured players, it was 43.6° ±9.2°. No further statistical analysis was done because of the small sample size in each group.

It is possible that, due to the different physical demands of the sports, the adaptive changes in and around the shoulder joint of a softball pitcher may be different from that of a baseball pitcher, and the clinical measures developed for baseball pitchers may not be useful for softball pitchers. The sequence of softball pitching can be divided into the following six distinct phases that are different from baseball pitching: (1) wind up; (2) 6 o'clock to 3 o'clock, where the arm moves from the side of the pitcher and attains about 90° of elevation; (3) 3 o'clock to 12 o'clock, where the arm elevation continues and reaches 180°; (4) 12 o'clock to 9 o'clock, where the arm is adducted and starts gaining momentum for ball release; (5) 9 o'clock to ball release, where the momentum is transferred to the arm which accelerates until the ball release; and (6) follow-through.[4],[5],[28] Another major difference reported by Barrentine et al.[28] between softball and baseball pitching is the timing of peak forces around the shoulder joint. In softball pitching, forces peak during delivery and acceleration phase, whereas in baseball pitching, the peak forces occur during the deceleration phase.[28] These phases correspond to the arm moving from 12 o' clock to 6 o' clock in softball pitching, compared to the maximum ER with elbow flexed to the ball release in overhead pitching. As the orientation of the GHJ in these phases of softball pitching is different from its orientation during the baseball pitching, it is plausible that the structures exposed to repeated overloading are different in softball pitchers.

Skeletal muscle activity also differs between a softball and a baseball pitch. For example, the posterior deltoid reaches its peak maximal voluntary Isometric contraction (MVIC) (68%) in the acceleration phase of baseball pitching, whereas it reaches its maximum MVIC (102%) in the third stage of softball pitching (3 o' clock to 12 o'clock)[6],[7] It is plausible that posterior deltoid is more active in softball pitchers. In this study, the fatigue due to softball pitching across four strength test was measured as precent reduction in the force production measured by a handheld dynamometer. Postpitching, there was an overall reduction in the force production capacity across all the motions; interestingly, we observed maximum reduction (42.3%) in the force production in horizontal abduction motion that primarily tests posterior deltoid.

LF [19] and EIR [14],[23],[24] have been reported as the measures of posterior GHJ capsule and posterior rotator cuff extensibility, respectively. The ROM in these measurements was unchanged between pre- and post-pitching conditions. LF has been shown to change in response to posterior capsule length and EIR in response to external rotator extensibility.[14],[23] Capsular adaptations happen over extended periods of repeated overloading, and only one bout of softball pitching probably did not induce any posterior capsule length changes. As for EIR, the ER force production in this study was reduced only by 19% compared to 42% for horizontal abduction. Furthermore, infraspinatus electromyographic activity during softball pitching has been reported to be 92% of MVIC compared to 102% for posterior deltoid.[6],[7]

Several limitations of the current study should be noted. First, the sample size was small with only 12 softball pitchers. Typically, a softball team has 1–2 pitchers, which makes the recruitment process difficult. However, this also means that, on an average, softball pitchers pitch more when compared to the baseball pitchers, increasing the likelihood of sustaining an overuse injury. Second, although HAD seems like a better measurement for softball pitchers, we do not know the magnitude of the ROM loss that might be used as a benchmark. Future studies should explore the relationship among the ROM loss in HAD in softball players with a history of shoulder injury. Third, we did not directly assess the results of posterior deltoid fatigue on the ROM measured in HAD. However, based on the findings reported by previous authors, it seems likely that HAD ROM is predominantly affected by posterior deltoid.


  Conclusions Top


After softball pitching to fatigue, we observed the maximum ROM loss in HAD measurement but not in SIR. It is plausible that, due to the differences in the nature of sports between softball and baseball, the ROM measurements used to predict injuries in baseball athletes might not be valid for softball athletes, and clinicians should modify their assessment procedure when examining a softball pitcher.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understand that name and initial will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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