INTRODUCTION
Upper extremity injuries are a significant health concern among baseball pitchers across all levels, resulting in significant time-loss from sport.1–4 In the last 15 years, injury incidence rates have ranged from 0.98 to 5.8 injuries per 1000 athlete exposures among high school,2 collegiate,2,3 and professional players,4 with the greatest proportion of injuries occurring in the shoulder and elbow. In professional players 20% of elbow and 7% of shoulder injuries require a surgical procedure and extensive rehabilitation.5,6 Preventing upper extremity injuries is a high priority among players, coaches, and clinicians to improve short and long-term athlete health and maximize performance.
One approach to try preventing these injuries is through training load and fatigue monitoring. A proposed strategy to track training load and fatigue among baseball pitchers is to leverage technology that tracks measures of training load and fatigue during training regimens and game outings.7 A novel biomechanical pitch sleeve has been developed to track pitch counts and intensity, including arm velocity and elbow valgus torque measurements,8 variables that contribute to training load and are associated with upper extremity injury.9,10 To measure fatigue, a portable force plate can be used to perform counter movement jumps to measure ground reaction force and jump height, measurements that may serve as an objective proxy measure for full body fatigue to inform recovery prior to or after pitching.11 Preliminary research has demonstrated the potential for monitoring countermovement jumps as a proxy for monitoring pitcher fatigue (i.e., decreased peak force outputs) given its association with pitch velocity.12,13 By combining use of both the pitching sleeve and force plate analysis during training, these devices may emerge as tools to monitor training load and recovery, which my in turn improve overall performance and control the training process.
New technologies developed for training load or biomechanical data are often validated in throwing sport domains14,15; however, studies on new technology to investigate player use of these technologies is lacking in this throwing population. Outcomes such as uptake (i.e., the initial participation or proportion of use for a tool or intervention) and adherence (i.e., continued participation or proportion of use of a tool or intervention) are important outcomes to inform the feasibility of new technologies.16 Investigating the feasibility of biomechanical devices used by players prior to large scale studies may help discern proportion and pattern of use to maximize future effective adaptation (and limitations) of these tools in real world settings. Thus, the objectives of this study were to investigate the proportion of collegiate pitchers over one summer league season who demonstrated uptake and adherence among a novel biomechanical pitching sleeve and portable force plate for use as an injury prevention measure.
METHODS
Study Design
This feasibility study used a prospective (repeated measures) design and was conducted during a collegiate developmental league season from June 2023 to August 2023. Feasibility is defined as the extent to which a newly developed tool or intervention can be successfully used within the setting of interest.17 Feasibility outcomes were defined using the taxonomy proposed by Proctor et al. for implementation outcomes, specifically uptake and adherence for all combined pitcher activities (bullpen sessions, throwing, weighted ball training, and long toss) of the biomechanical devices.16 This study was approved by the Wake Forest School of Medicine Ethics Board (IRB00095826).
Patient and Public Involvement
Meetings were held prior to study design phase with clinicians, researchers, Major League Baseball (MLB) and USA Baseball, and the summer collegiate league representatives to discern project direction. These clinicians, baseball representatives, and researchers were further included in the creation of the study aims and research design. Biweekly meetings were held throughout the season with MLB and collegiate developmental league affiliates for study updates and quality management. Results from this study were presented to coaches and the MLB front office at the end of the study period for study implications and future recommendations of biomechanical device use.
Participant Eligibility Criteria
Participants were recruited from two teams that were engaged in a single collegiate summer league in the southeastern United States. Participant eligibility criteria consisted of 1) pitchers rostered on a collegiate summer league pitching staff; 2) ability to fully participate in all baseball related activities without restrictions at beginning of data collection; 3) consent to participate.
Description of Biomechanical Devices and Data Collection
Two Nextiles biomechanical devices were included in the study: 1) pitching sleeve and 2) portable force plate. The Nextiles (Nextiles Inc., Brooklyn, New York) pitching sleeve incorporates a fabric-based circuity sensor to track a range of biomechanical data, including arm speed, force, distance and direction, and pressure and can be utilized in both on and off-field settings to passively collect player movements. The Nextiles jump mat incorporates fabric-based circuity sensor into the mat to track ground reaction force, time from takeoff to landing, and pressure.
To collect pitching sleeve data, all throwing and pitching workouts were tracked. Data per outing were abstracted weekly from the data interface and stored in a de-identified player file by an assigned team data coordinator. Only non-game appearances were considered for the proportion of initial and continued use due to league wide policies on prohibiting single pitch or compression sleeve use in games. Uptake and adherence for in-game use could not be analyzed.
Game days, off-days, and days lost due to injury or leaving the team due to injury or reaching innings limit were excluded. The pitch sleeve data interface allowed selection of pitch related workout activities included pitching (bullpen), long toss, plyo or weighted ball training, and warm-up throws. Any pitching session could include one or a combination of these activities. If the sleeve was used for at least one of the pitch activities, the session was included in analysis.
Jump mat sessions consisted of weekly testing to perform a counter movement jump test (CMJ) using previously described methods,18 and as described in Supplemental File 1 as a measure of total body fatigue. Weeks where an athlete left the team due to injury or reaching innings limit were excluded.
Injury Definition, Athlete Exposure
Athlete exposure was defined as one athlete participating in one practice or competition where a player was at risk of sustaining an injury.8–10 An index injury was defined as an injury to a tendon, ligament, nerve, muscle, or bone that occurred during any baseball team sponsored activity or event.19 If a player was removed from the roster due to an injury or reaching the maximum number of innings, the time from removal to the end of season was not included as part of the calculation of the main outcomes. Injuries were extracted from managerial player status logs.
Participant Characteristics
Participant self-reported demographic information (sex, age, height, weight, hand dominance), sport characteristics (pitching role, team, collegiate division level), and injury history (current season, previous season, surgical history) were collected for all pitchers.
Main Outcomes
Uptake
Pitching sleeve uptake was defined as the proportion of pitchers who consented into the study that demonstrated pitch sleeve use during the first practice session they reported to the team. Portable force plate uptake was defined as use the portable force plate the first week of the season by a participant, or within one week that the athlete reported to the team.
Adherence
Adherence analyses were restricted to those who demonstrated initial uptake. For the biomechanical pitching sleeve, this was calculated as the proportion of the number of occurrences the sleeve was used divided by the total number of opportunities (practice only) to wear the sleeve over the entire study. For the portable force plate, adherence was calculated the proportion of the number of occurrences the force plate was used at least once per week divided by the total number of opportunities to jump on the portable force plate over the entire study.
Statistical Analyses
Participant characteristics were reported as mean (standard deviation) for continuous variables, and as a count (percentage) for categorical variables. Potential non-response bias (i.e., exploration of a lack of uptake or adherence that could introduce response bias in a larger effectiveness trial) than could occur in a hypothetical study using these measures) was analyzed descriptively to compare pitchers that demonstrated initial uptake and adherence after the first session for the Nextiles sleeve (≤ 1 day pitch sleeve use, >1 day pitch sleeve use) and force plate (≤ 1 week force plate use, >1 week force plate use). Variables considered in the potential non-response bias analysis included demographic characteristics, (i.e., age, BMI, hand dominance, athlete year, collegiate division, pitching role, orthopaedic surgery history, injury history previous season, upper extremity function), clinical measures (i.e., shoulder range of motion, humeral torsion, shoulder strength), athlete game and pitch exposures. A full description of these variables is available in Supplemental File 1.
The proportions of uptake and adherence for the pitch sleeve and force plate, and the proportion of pitch sleeve activities (bull-pen session, long-toss, plyo ball work, and warm up throws) were reported with 95% confidence intervals (95% CI) calculated using the Clopper-Pearson method. Lasagna plots were created to visualize all recorded uses of device to discern patterns of use throughout the season for the pitch sleeve and the force plate.20
All analyses were performed in R 4.12 R Core Team (2021). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/. The GenBinomAppa package was used to calculate the Clopper-Pearson confidence intervals. All analysis code is available in Supplemental File 2.
RESULTS
A total of thirty-four pitchers were eligible but twelve pitchers did not consent to participate in the study, resulting in twenty-two baseball pitchers who were included in the analysis. Most pitchers were right-handed (19, 86%), Division I (15, 68%), and reported performing both starter and reliever roles (10, 45%) (Table 1). For the exploration of potential non-response bias, pitchers that did not continue to use the Nextiles pitch sleeve after initial testing reported a higher proportion of injuries the previous season (8 injured pitchers, 50.0%) compared to pitchers who demonstrated use after the initial session (0 injured pitchers, 0.0%) (Table 1). Pitchers that demonstrated pitch sleeve use beyond the first session reported a higher mean season pitch count volume compared to pitchers who did not report use beyond the first session (432.7 versus 271.9 pitches) (Supplemental File 3). Clinical variables were generally similar between sleeve use groups (Supplemental File 4). No notable differences were observed comparing use and non-use groups for the force plate (Supplemental Files 5-7).
Uptake and Adherence of Pitch Sleeve
For all teams combined, uptake of the pitching sleeve was 0.55 (95% CI: 0.32, 0.76). Among the athletes that demonstrated initial uptake of the pitch sleeve, adherence of the pitch sleeve was 0.13 (95% CI: 0.10, 0.17). Of 52 pitch sleeve uses recorded, the most performed activity was bullpen sessions (n=22, 43.1%, 95% CI: 29.3%, 57.8%) and long toss (n=18, 35.3%, 95% CI: 22.4, 49.9), followed by warm up throws (n=8, 15.7%, 95% CI: 7.0%, 28.6%), and plyo or weighted ball throws (n=3 5.9%, 95% CI: 1.6, 16.2%). Figure 1 demonstrates use of the pitch sleeve throughout the season for all recorded sessions. Of the athletes that used the pitch sleeve beyond the first recorded session, an observed pattern of use one to two times per week was observed. A total of 60% (95% CI: 36%, 81%) of athletes did not continue use of the pitch sleeve after the first recorded session.
Pitcher Initiated and Continued Nextiles Force Plate Use
The proportion of athletes that initiated use of the force plate during the first week was 0.32 (95% CI: 0.14, 0.55). Among athletes that demonstrated initial uptake of the force plate, the proportion of athletes that continued to use the force plate was 0.46 (95% CI: 0.31, 0.70). Figure 2 provides visual evidence of force plate use over the duration of the season with 33% (95% CI: 18%, 52%) of athletes demonstrating weekly use through the duration of the study time frame, or prior to right censoring (i.e., reached innings limit, loss to injury).
DISCUSSION
This is the first study to report feasibility outcomes for wearable and portable technological devices among baseball players, addressing a major gap in discerning use patterns in technology commonly used in this target population. This study found 55% volitional uptake of the pitch sleeve, only 40% of whom used it more than once, and with reduced continued adherence throughout the season. Notably, results from the potential non-response bias analysis demonstrated that pitchers that did not continue to use the Nextiles pitching sleeve after initial testing reported a higher proportion of injuries the previous season (47%) compared to those who continued to use the Nextiles pitching sleeve (14%). Among pitchers that continued to wear the pitch sleeve during the season, specific use patterns were observed, with an average of two uses between pitching appearances and an activity preference for bullpen sessions and long toss. In contrast, there was only 10% force plate volitional uptake, with 56% adherence observed among participants that demonstrated initial uptake.
Use of wearable and portable biomechanical pitch sleeves may play an important role in understanding how to prevent upper extremity injuries by tracking important training load variables and proxy measures for fatigue in order to establish their potential causal role. Although a moderate uptake was observed, the pitch sleeve was utilized in only 13% of the potential use opportunities among players that initially used the pitch sleeve (uptake). Compared to the pitch sleeve, a lower initial uptake was observed for the force plate with 32% of athletes demonstrating initial use during the first week. However, a higher adherence was observed, with 56% of these athletes demonstrating continued use for all potential use opportunities. Prior literature on feasibility or implementation outcomes among wearable and portable technology in throwing sports is nonexistent; in other widely studied interventions such as neuromuscular training programs, injury reductions have been observed, but the magnitude of the effect differs based on adherence, demonstrating a dose-response relationship.22–25 Given the low to moderate levels of uptake and continued adherence observed, studies using these devices to investigate causal relations or for prognostic and diagnostic research may not be feasible (e.g., high risk of potential non-response bias and high proportion of missing data) until solutions to improve adherence are identified.
Uptake and adherence of wearable and portable biomechanical devices are likely informed by athlete behaviors influenced by team environments, personal knowledge of the device, athlete motivation, and potential for health promoting behavior that are dynamic as training situations change.26,27 In this study, pitchers that reported use of the pitching sleeve beyond the first opportunity were less likely to report an injury the prior season (14.3% vs 46.7%). This finding may be indicative of pitchers that present with ‘health promoting behaviors’ such as a regimented training routine or regular engagement in arm care programs, and thus have a propensity for adapting training devices that may further inform these training practices.21,28 In contrast, athletes with an injury history may display hesitancy in engaging in wearable technology due to fear of underperformance that the data may demonstrate (i.e., lower velocity). Specific to the force plate, higher adherence observed compared to the pitch sleeve may be due to decreased athlete burden (i.e., less technology use sessions required), or team training environment allowing for easy incorporation of weekly jump test sessions.27 Training optimization strategies that incorporate wearable and portable technology may need to align with team schedules, and ensure that health promoting behavior is encouraged while providing education that minimizes potential for fear avoidance behaviors to improve adherence and hence athletes’ buy-in.27,29
Lasagna plots revealed patterns for pitch sleeve use among users who demonstrated initial uptake, with a pitch sleeve use pattern of twice per week. A majority of sessions captured were bullpen sessions (43.1%) or long toss (35.3%). Understanding biomechanical device use patterns and frequency may help form recommendations that are feasible for the athlete and for implementation in larger studies. Prior research among neuromuscular training programs have demonstrated potential variability in program frequency and intervention activities, highlighting the importance of the need for subcomponent analysis of intervention strategies.30 However, further qualitative research is needed to highlight specific barriers or facilitators that may inform this pattern of use, such as environmental constraints, or user knowledge.31
Limitations
This study is not without limitations. First, these data were collected on a small sample, resulting in wide 95% CI for adherence, uptake, and activity specific proportion measures. While these results provide some preliminary information about the feasibility of these technologies, caution is needed in generalizing the findings league wide within a summer league season or among other levels of play. Similarly, inferences on discerning differences between users and non-users of the devices need to be further confirmed among larger studies or qualitative studies to discern barriers and facilitators for device use. Third, due to league wide restrictions in sleeve use among players in games, adherence and uptake for in-game use could not be analyzed.
CONCLUSION
Understanding the feasibility of technologies in real scenarios is important to investigate whether these can be successfully implemented in baseball athletes for large scale studies or for routine monitoring. This study showed only 55% uptake with 13% adherence for the pitch sleeve, and only 32% uptake with 46% adherence for the force plate. For the pitch sleeve, players that demonstrated continued use had a pattern of two times per week use for long toss and bullpen sessions. Future research will need to identify specific barriers and facilitators to use of each device to better inform their implementation in research and practice.