Each year, professional baseball teams lose hundreds of millions of dollars when players become injured. The rate of shoulder and elbow injuries is especially high because of the excessive force and mechanics of pitching. Up to 50% of professional baseball pitchers have experienced elbow or shoulder pain at some point in their career, with >30% of these injuries being musculotendinous in nature (9).
Although a multitude of factors may contribute to the propensity of injuries in throwers, 1 concern is an ineffective warm-up (34). It is widely accepted that athletes should perform warm-up activities including resistance exercise before participating in a physically demanding activity (5,24,26). However, there has been conflicting evidence on whether warm-up is effective in both enhancing performance or preventing injuries (3,4,6,8,11,16,20,28). Several authors (5,7,13,29,34) have suggested that active warm-up routines reduce injury risk and increase the efficiency of complex tasks and prolong effective performance. Although the exact physiological processes contributing to the possible benefits of warm-up are not completely understood, increased body temperature, leading to increased rates of metabolic chemical reactions, reduced muscle viscosity, and increased sensitivity of nerve receptors are among the hypothesized mechanisms contributing to the altered post-warm-up function of the organism (26). Increasing the elasticity of the muscle fibers may enable the muscle to tolerate greater loads of stress, decreasing the chances of overloading and damaging the muscle.
Sling-based exercise (SE) is a novel form of exercise that allows an individual to use his or her body weight to provide resistance. The slings provide an unstable base of support that is suggested to increase muscle activation of the proximal musculature in an effort to maintain balance. The exercises can be performed in the closed kinetic chain and have been previously used to increase performance in softball players (23) and to effectively treat various musculoskeletal pathologies (31,33). Previous research has shown that similar exercises are effective in activating the stabilizing muscles of the core such as the transversus abdominis or the multifidus (15). Those core stabilizers may become inhibited or have a timing dysfunction and often contribute to injury (15). A similar mechanism may be present with the shoulder stabilizers, although the mechanism has not been examined. This novel exercise may provide a more functional method for training and warm-up. Closed chain exercise is often difficult for the upper extremity because there is a need to weight bear on the hands and wrists. Sling-based exercise has been proposed to provide a controlled unstable environment, which allows individuals to perform a myriad of exercises at various levels of difficulty. The slings also provide support and assistance with exercise, allowing for a more individualized progression to permit more comfortable exercise (19).
The core is an integral link between the upper and lower extremities. Deficiencies occurring in the core may cause a decrease in forces or inefficient transfer of forces through the accessory muscles of the extremities (14,17,19). With SE integration of the proximal stabilizing muscles and core during exercises, SE may be used as a functional warm-up for throwers. Proximal muscle function is essential for the throwing motion (30). Sling-based exercise training for softball players has been shown to increase throwing velocity (23), but its use for warm-up has not been evaluated.
Throwing velocity and accuracy can be used as measures of adequate warm-up because they are indicators of efficient and proper biomechanics and energy transfer through the kinetic chain (10). The purpose of this study was to compare the effects of SE and traditional warm-up methods on throwing velocity and accuracy in Division I collegiate baseball players. Because of the incorporation of the core with the SE, we hypothesized that subjects would demonstrate greater levels of velocity and accuracy after a SE warm-up compared to a traditional warm-up.
Experimental Approach to the Problem
A crossover design was used for this study and testing order was randomized. Testing sessions were performed approximately 72 hours apart. Main outcome measures were velocity of the throw, accuracy of the throw, subjective perceived shoulder, elbow and wrist pain.
Sixteen Division I collegiate baseball players between the ages of 18 and 23 (age = 19.6 ± 1.3 years, height = 184.2 ± 6.2 cm, and mass = 76.9 ± 19.2 kg) volunteered to participate in this study. Subjects were excluded from the study if they were younger than 18, exclusively a pitcher, or not medically cleared by a physician for competitive play. Approval from the Institutional Review Board and written informed consent were obtained before data collection.
Subjects were asked to fill out a Visual Analog Scale (VAS) for the shoulder, elbow and wrist to determine the current level of pain. The VAS consisted of a 10-cm line with the extremities labeled “no pain” and “worst pain imaginable.” The subjects rated this initial VAS score based on their perceived level of pain during general range of motion and movements at that moment, before any warm-up exercises. This procedure was designed to capture any discomfort that may be attributed to either warm-up condition or ongoing pathology that could affect throwing velocity or accuracy.
The Thrower's 10 consists of specific upper-extremity exercises using free weights and resistive tubing. The Thrower's 10 routine was specifically developed for the needs of the overhead thrower and is commonly used and regarded as a standard for specific active warm-up for pitchers (1,18,21). These exercises target the rotator cuff, biceps, triceps, and the wrist flexors, extensors, pronators, and supinators and are detailed in other publications (1,18,21). Each subject completed 1 set of 10 repetitions for each Thrower's 10 exercise using level 6 (black) Theraband Resistive Bands (The Hygenic Co. Akron, OH, USA) and 4-lb cuff weights. All exercises were performed under the supervision of a clinician versed on the proper form and execution for the Thrower's 10 exercises. Subjects completed a VAS to determine the level of pain in the shoulder, elbow, and wrist immediately after the traditional warm-up exercises.
In the SE condition, participants performed 5 exercises using the portable SE Training system (Redcord, Staubo, Norway): shoulder flexion, shoulder protraction, chest flies, push-up plus, and supine shoulder retraction (Figure 1). Each exercise was individually progressed to a level of difficulty determined by the subject's ability to execute the exercise comfortably and correctly. Each subject began the exercise in the most supported position and was progressed through the levels to decrease the amount of stability. Specifically, the degree of difficulty increased through changes in hand or body position, sling level, and/or the use of a Dynadisc balance pillow (Exertools, Rohnert Park, CA, USA). This assessment of exercise intensity was done with 1-2 repetitions with subject feedback and observation to determine the appropriate level of exercise. Once the subject was no longer able to perform the level using the proper form, the previous level was targeted as the exercise intensity to ensure that the subject was appropriately challenged by the exercise while still maintaining the correct form and proper execution. Each participant performed 1 set of 5 repetitions for each of the 5 SE exercises at the appropriate level. The clinician required approximately 7 minutes to find the appropriate level and execute each exercise 5 times under supervision. The level that the exercise was performed was noted and recorded for each of the 5 exercises. Upon completion of the SE exercises, the participant immediately completed a VAS of the shoulder, elbow, and wrist, to determine level of pain after the SE warm-up exercises.
After each warm-up condition, the subjects were escorted to an enclosed bullpen. All participants were then asked to loosen up within a 5-minute timeframe, and this number of practice throws was counted and recorded. Once the subject subjectively felt “loose,” a VAS battery was completed to determine level of pain in the shoulder, elbow, and wrist after the practice-up throws. Subjects were then taken to another enclosed bullpen for the throwing test. A custom-made accuracy frame (Figure 2) was placed at 1 end of the bullpen and a 15-in. line was marked with a tape at 60 ft 6 in. from the frame. The subjects were instructed to throw 10 times at maximal effort and accuracy, aiming at the 5-in. circle located in the center of the accuracy frame. A tester, who was blinded to the warm-up condition recorded the velocity for each throw with a cordless radar gun, the Jugs R1000 (JUGS Tualatin, OR, USA), located behind the frame. A second tester stood 30 ft away from the accuracy frame and following each throw, marked the location of where the ball hit the frame using a sticker marked with the pitch number and recorded velocity. If there were any questions on where the ball exactly hit the frame, it was verified by the ink impression left upon ball impact on the back of the paper. The subject was then offered ice after the completion of the testing. The procedure was then repeated within 72 hours with the alternate warm-up condition.
Accuracy was recorded by measuring the distance of the sticker from the center of the target in centimeters. Accuracy was not recorded, but the throws that did not hit the accuracy frame were noted. The accuracy score was obtained by the mean of the 3 most accurate throws for each session. If subjects did not hit the target 3 times, their data were not used in the study. Data from 2 of the 16 subjects were excluded because of insufficient accuracy scores. Velocity was recorded in miles per hour (mph) and was recorded for all throws.
A dependent t-test was used to determine differences in the number of warm-up throws following both the SE and Throwers' 10 intervention before accuracy and velocity testing. Two-way analysis of covariance (ANCOVA) was used to determine differences in throwing accuracy and velocity between the 2 warm-up conditions. Additionally, 2 × 4 repeated-measures ANOVAs were used to detect differences in self reported pain over time for the shoulder, elbow, and wrist. p ≤ 0.05 was set a priori. Data were analyzed using the Statistical Package for the Social Sciences (SPSS) V0.16 (SPSS Inc., Chicago, IL, USA).
Participants performed statistically more warm-up throws after the SE warm-up compared to the Throwers 10 warm-up before testing (14.9 vs. 10.4, t15 = 3.29, p = 0.005). Therefore, we decided to statistically control for this by performing ANCOVAs, with the covariates being the number of warm-up throws after both warm-up conditions.
Means and SDs for VAS are provided in Table 1 and those for velocity and accuracy are provided in Table 2. After adjusting for the number of warm-up throws, there was no difference in throwing velocity (p = 0.874, Figure 3) or throwing accuracy (p = 0.136, Figure 4) between SE and the Thrower's 10 warm-up sessions. Additionally, there was no statistical difference between the VAS for the shoulder, elbow, and wrist for either group over time (p > 0.05) after taking the number of warm-up throws into account.
The major finding of the present study was that SE warm-up had similar effects on velocity and accuracy compared to the traditional Throwers 10 warm-up. Although several studies have shown a lack of beneficial effects of warm-up on immediate sports performance (3,4,6,8,11,12,16,20,26,28,32), it should be noted that the definition of warm-up has been vague and can be loosely used to describe any period of activity preparation before competition or training performance (12). The term warm-up has been used to describe active warm-up, passive warm-up, and various forms of stretching (34). Active warm-up involves some form of physical activity, whether it is general (with nonspecific body movements, such as biking or jogging) (24) or a sports-specific warm-up. Sports-specific warm-up uses activities that are consistent with the planned sport (26), such as arm biking or push-ups (25,26) for overhead throwing activity. Faigenbaum et al. (11) suggested that a specific warm-up is more effective on performance because it mimics the activity to be later performed. The general warm-up, however, has greater implications on complex tasks that incorporate multijoint activities such as the vertical jump (16). We chose the Thrower's 10 exercises as a traditional, specific warm-up that is commonly used for baseball players. The SE was used as a combined general and specific warm-up because it incorporated both targeted and core muscles.
The core and proximal musculature contributes to delayed fatigue and to the forces applied when throwing (30). Sling-based exercise training has been shown to increase performance in softball players when used in an off-season strengthening program (23). Furthermore, the facilitation of the musculature has been observed immediately after the application of the SE (31). The exercises are supported in a pain-free position while the movements are performed. The exercise progression decreases both the amount of support and stability provided by the slings and surface. These factors lessen the possibility of compensating for the appropriate stabilizing musculature to perform the task. This combination of general and specific muscle activation led to the hypothesis that SE might be a more effective warm-up procedure compared to the Throwers 10.
To minimize injury risk that might occur from throwing maximally during the testing, we used a 5-minute period of progressively increasing throwing speed to allow our participants to “loosen up” before collecting data. Bast et al. (2) found a 33% increase from baseline measurement in arterial and venous volume blood flow in the arm after a warm-up throwing session consisting of 20 throws. Peak blood flow volume was measured at 60 throws (2). Therefore, the warm-up throws may have had an effect on overall performance. However, when the number of warm-up throws was accounted for, there was no difference in performance for either condition. All of the participants had no previous experience with the sling exercise program, but were currently using the Thrower's 10 in their own warm-up procedures. The participant's familiarity and confidence in the traditional program coupled with the novel nature of the sling exercise may have affected the outcome measures. It is possible that as individuals become habituated to SE warm-up performance might improve. However, it should be noted that there was no difference in the performance after either the SE or Thrower's 10 warm-ups. This suggests that a single session of SE is as efficient at warming up for throwing as the established Thrower's 10 regimen and likely achieved desired physiological effects. The desired intensity of warm-up exercises should be ∼40-60% of o2max (maximal oxygen uptake) because adequate muscle temperature will be achieved without depleting high-energy phosphates levels (5). Although no tools or instruments were used to measure temperature increases during this study, it is of general consensus that light to mild sweating without fatigue is a reliable indicator of an adequate increase in muscle temperature (25,26). Upon observation of the subjects during both warm-up sessions, both the SE and Thrower's 10 warm-up exercises produced light sweating with no fatigue.
We measured pain in the upper-extremity joints using a VAS, and there were no significant differences between warm-up conditions. Our subjects were healthy, but we wanted to account for any discomfort associated with either warm-up. We theorized that the SE warm-up might decrease pain through neuromuscular activation. Because the participants were not in pain before the procedure, any affect was negligible.
A benefit of using SE for warm-up is in the incorporation the proximal stabilizing muscles. Sling-based exercise simultaneously involves the core and the arm at the same time during warm-up, similar to the actual act of throwing. The athlete can also customize the warm-up exercises to continuously challenge their physical limits or to continue effectively and painlessly exercising when injured. Although we did not observe immediate effects, the program may require a consistent training program to show results on performance, as previously described (23).
The study demonstrates equivalent performance effects observed in throwing accuracy and throwing velocity between the SE warm-up and Thrower's 10 warm-up. There were also no differences observed in shoulder, elbow, and wrist pain between the SE and Thrower's 10 warm-up. The SE program provides an alternative to the traditional warm-up procedure in baseball players.
The study was supported in part by an unrestricted grant from RedCord, AS, Staubo, Norway.
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