Clinical effects of shadow throwing instruction on improving the “elbow dropped” position: an examination of reproducibility during net and partner throwing drills

Abstract

[Purpose] This study investigated whether shadow throwing-based form instruction improves the “elbow dropped” position during net and partner throwing drills among youth baseball players who have recovered from throwing related shoulder or elbow injuries. [Participants and Methods] Forty-six right-handed male players (ages: 11–15 years) who exhibited the “elbow dropped” position during shadow throwing were analyzed after returning to throwing without pain following recovery from throwing-related shoulder or elbow injuries. The “elbow dropped” position during shadow throwing, net throwing, and partner throwing was evaluated using the SPLYZA Motion application, and occurrence rates were compared. [Results] The occurrence rates of the “elbow dropped” position were 0.0% for shadow throwing, 13.0% for net throwing, and 58.7% for partner throwing. The rate during partner throwing was significantly higher than during the other throwing conditions. [Conclusion] Shadow throwing instruction is effective for early form correction; however, this effectiveness decreases under actual throwing conditions. Phased instruction that incorporates realistic environmental factors, such as net and partner throwing drills, is necessary to maintain proper throwing mechanics.

INTRODUCTION

Throwing is a full-body motion that relies on the kinetic chain, in which energy generated by the lower limbs is transmitted through the trunk to the throwing arm¹⁾. In addition to upper limb mechanics, lower limb flexibility, trunk stability, and appropriate throwing form are essential to this coordinated chain movement^{2, 3)}. Disruption of any of these components can break the kinetic chain, resulting in inefficient throwing and excessive stress on the throwing-side shoulder and elbow joints, leading to throwing-related injuries¹⁾.

The pathology of throwing-related shoulder and elbow injuries is complex and is difficult to clarify due it often manifesting solely during the throwing motion⁴⁾. The throwing motion is commonly divided into five phases: wind-up, early cocking, late cocking, acceleration, and follow-through^{5, 6)}. A decrease in shoulder abduction angle from the late cocking phase to the acceleration phase is known as the “elbow dropped” position⁷⁾, which is frequently reported as a contributing factor to throwing injuries^{8, 9)}. Previous biomechanical studies have reported that repetitive pitching generates substantial valgus stress at the elbow and high mechanical loads at the shoulder joint¹⁰⁾. Furthermore, the “elbow dropped” position has been associated with increased elbow varus torque and increased stress on the shoulder complex^{8, 9)}. Factors contributing to this form include decreased muscle strength and flexibility^{10, 11)}, reduced performance⁹⁾, and dysfunctions of the trunk and lower limbs¹⁾.

Throwing injuries arise from a combination of structural and functional problems, but poor throwing form is often a key contributor^{8, 9)}. Therefore, throwing form instruction by physical therapists constitutes an important treatment and injury prevention strategy. However, space and safety limitations in orthopedic clinic settings make it difficult to perform throwing exercises with actual balls, leading to shadow throwing being used as the primary means of instruction. Although this method allows for form correction and improvement, it differs from actual throwing because environmental factors such as ball release, throwing distance, and the presence of a target are absent. This limitation may mean that despite shadow throwing being useful for repetitive form instruction in clinical settings, its direct transfer to actual ball-throwing motion could be insufficient. Motor learning studies suggest that these contextual differences can affect the transferability of acquired movement patterns^12,13,14).

Working from the hypothesis that improvements to the “elbow dropped” position achieved during shadow throwing would progressively decrease under more realistic throwing conditions, particularly during partner throwing which approximates actual game conditions, this study examined how effectively throwing form instruction focused on correcting the “elbow dropped” position within an orthopedic clinic is reflected in actual throwing motions during subsequent net throwing and partner throwing.

PARTICIPANTS AND METHODS

This study was performed at three orthopedic clinics where the author works part-time. Initially, 51 right-handed male baseball players (school grades: 5–9) diagnosed with throwing-related shoulder or elbow injuries and exhibiting the “elbow dropped” form were considered for participation. No restrictions were placed on field position, but players who reported pain during activities of daily living or had a history of upper/lower extremity or trunk injuries were excluded; only players who experienced pain exclusively during throwing motions were included to ensure consistency in participant characteristics. Ultimately, 46 players who underwent exercise therapy and throwing form instruction by physical therapists, demonstrated improvement of the “elbow dropped” position during shadow throwing instruction, and were able to return to throwing without pain were included in the analysis. Assessments were performed at an average of 1.5 months after the initiation of physical therapy. The participants’ mean age, height, and body weight were 12.8 ± 1.4 years (range: 11–15 years), 157.0 ± 6.8 cm (145–171 cm), and 53.4 ± 8.9 kg (38–70 kg), respectively.

This study was conducted in accordance with the Declaration of Helsinki. The study purpose and use of anonymized data were explained, and written informed consent was obtained from all participants and their guardians.

The incidence of the “elbow dropped” position during net and partner throwing was analyzed in players whose “elbow dropped” position had improved following shadow throwing instruction. For net throwing, participants were instructed to throw a ball toward a net placed at a distance of 10 m as if they were throwing to a partner. The throwing distance during partner throwing was standardized to approximately 27 m, which corresponds to the distance between the bases on a regulation baseball field.

Videos were recorded using an iPad Air (Apple Inc., Cupertino, CA, USA). The distance between the camera and the participants was standardized at 10 m, and videos were recorded at 240 fps.

The “elbow dropped” position was defined based on stick-figure analysis using the markerless 3D motion analysis application SPLYZA Motion (SPLYZA Inc., Shizuoka, Japan)¹⁵⁾ as a throw in which the right elbow was positioned below the line connecting both shoulder joints during the late cocking phase⁷⁾ (Fig. 1). SPLYZA Motion enables simple, markerless visualization of the throwing motion and allows for rapid stick-figure analysis, making it a useful tool to provide immediate form instruction and feedback. This study did not seek to perform detailed quantitative kinematic analysis, but rather to clinically determine the presence or absence of the “elbow dropped” position. The high level of clinical applicability and practicality of the SPLYZA Motion application led to its selection as the clinical tool for this determination. The same analytical method utilizing SPLYZA Motion was applied in the author’s previous study¹⁵⁾. The SPLYZA Motion application was used for all throwing analysis (shadow throwing, net throwing, and partner throwing) following the methodology applied in the authors’ previous study¹⁵⁾.

Fig. 1.

The “elbow dropped” position: the elbow of the throwing arm (the right elbow in the above) is positioned below the line connecting both shoulder joints during the late cocking phase of the throwing motion.

Statistical analysis was performed using Fisher’s exact test to compare the occurrence rates of the “elbow dropped” position during shadow throwing, net throwing, and partner throwing. When significant main effects were found, the Bonferroni correction was applied. Significance level was set at p<0.01. Analyses were conducted using SPSS Statistics 22 (IBM Corp., Armonk, NY, USA).

RESULTS

The occurrence rates of the “elbow dropped” position were 0.0% during shadow throwing, 13.0% during net throwing, and 58.7% during partner throwing (Table 1). The rate during partner throwing was significantly higher than that during shadow throwing and net throwing (p<0.01).

Table 1. Occurrence rates of the “elbow dropped” position in different throwing conditions (n=46).

Throwing condition	Number of players with “elbow dropped”	Percentage
Shadow throwing	0/46	0.0%
Net throwing	6/46	13.0%
Partner throwing	27/46	58.7%

Fisher’s exact test & Bonferroni correction (post-hoc). Partner throwing >shadow throwing=net throwing (Bonferroni correction, p<0.01).

DISCUSSION

This study investigated differences in the occurrence rate of the “elbow dropped” position across throwing conditions among players whose form had improved during shadow throwing instruction and who had returned to throwing without pain. Findings revealed the occurrence rate of the “elbow dropped” position during partner throwing was significantly higher than the rate during shadow throwing and net throwing.

This suggests that form improvements achieved during shadow throwing instruction are maintained during the progression to net throwing but may not be sufficiently retained during partner throwing conditions, which are more closely related to actual game play. During partner throwing, external factors such as distance, speed, and the presence of a receiver increase cognitive load and alter the movement goals of the thrower¹²⁾. Consequently, the correct kinetic chain and throwing trajectory which have been re-acquired may not be consistently reproduced, leading to recurrence of the “elbow dropped” position. Furthermore, participants who exhibited the “elbow dropped” position during partner throwing may have not only a reduced reproducibility of corrected throwing mechanics, but also insufficient physical capacity or muscular function to correctly engage in longer-distance throwing. The potential recurrence of the “elbow dropped” position highlights the influence of environmental changes on the stability and reproducibility of motor patterns¹²⁾, emphasizing the clinical need for context-dependent, phased re-education of the entire throwing motion¹⁶⁾.

Furthermore, study results indicate that motor learning effects acquired in a controlled clinical environment may have limited transferability to actual sport environments. From the perspective of motor learning theory, stable reproduction of acquired motor patterns under various conditions requires a learning process that integrates variability in practice conditions and external feedback^{13, 14)}. Therefore, future instructional programs should incorporate a phased approach that moves from shadow throwing to net throwing and then to partner throwing, before moving onto unrestricted throwing activities. This approach should include throwing mechanics being evaluated and refined at each stage.

This study has several limitations. First, participants were limited to young male players in elementary and junior high school; thus, generalization to other ages, genders, or competitive levels requires caution. Second, the sample size was relatively small (n=46), potentially limiting statistical power and external validity. Third, differences in instruction period and frequency among players may have influenced outcomes, as the instructional content was not fully standardized. Finally, the cross-sectional methodology of this study does not allow for the evaluation of long-term retention of form correction and analysis of recurrence risk. In addition, participants’ physical capacity and muscle function related to throwing performance were not evaluated in this study, and the potential influence of these elements on the recurrence of the “elbow dropped” position cannot be excluded.

Future research should include larger, more diverse populations and longitudinally examine the learning and transfer effects of phased throwing programs (i.e. programs that progress through shadow throwing, net throwing, and partner throwing, before ultimately moving to actual throwing during games). Such investigations could clarify how effectively form correction achieved in clinical settings is maintained during actual gameplay and can contribute to injury prevention.

In conclusion, shadow throwing instruction is an effective method for initial re-education of throwing mechanics; however, to consolidate form improvement (such as correction of the “elbow dropped” position) in competitive environments, a more dynamic and contextually adapted phased instructional approach is necessary.

Conflict of interest

The author declares no conflict of interest.