INTRODUCTION
Athletic injury is a major factor in diminished performance and strength. To prevent such injuries, various training programs have been developed and applied them. However, prior to establishing a training program, a test method capable of evaluating functional movement is needed (Cook et al., 2006a, 2006b).
The functional movement screen (FMS) is a way to pretest functional movement. FMS consists of the seven test items: deep squat, hurdle step, in-line lunge, shoulder mobility, active straight leg raise, trunk stability push-up, and rotary stability. The screen has a maximum of 21 points, with each item rated on a 3-point scale ranging from 0 (pain during the action) to 3 (action performed correctly) (Cook et al., 2006a, 2006b; Kiesel et al., 2007; Minick et al., 2010).
Kiesel et al. (2007) indicated that athletes whose total FMS scores are <14 points are more likely to get injured. Chorba et al. (2010) argued that a total score <14 points confers greater risk of injury than a score ≥14. Minick et al. (2010) opined that the FMS can help identify the risk of potential injury for an athlete. Training programs based on the FMS can improve the FMS score or lower the risk of injury (Kiesel et al., 2011; Peate et al., 2007). Thus, the FMS can be a good pretest to predict or prevent athletes’ injuries.
Good functional movement can make complete range of motion and the efficiency of power possible, emphasizing the Optimum Performance Pyramid (Cook, 2003). Stability and mobility, which can be checked by the FMS, are the basis of, and are relevant to, strength and flexibility (Cook et al., 2006a). This indicates that the FMS can contribute to improving strength and flexibility of athletes; however, this has not been directly studied. Rather, injury prediction or verification of reliability and validity has mainly been the subjects of study (Gulgin and Hoogenboom, 2014; Kiesel et al., 2007; Smith et al., 2013).
Accordingly, this study examined the effects of the FMS training program on the strength and flexibility of elite high school baseball players.
MATERIALS AND METHODS
Participants
The participants were 62 elite male high school baseball players (31 in the training group, 31 in the control group). All participants provide written informed consent. The features of the test participants are as shown in Table 1.
Body composition
After the test participants changed into comfortable clothes, an Inbody 720 bioelectrical impedance analysis device (BioSpace, Seoul, Korea) was used to determined body composition. For a more accurate measurement, the participants were instructed to fast overnight and were banned from making excessive movements and taking a long bath or sauna before the measurement.
FMS
Seven test items were selected based on prior results (Cook et al., 2006a, 2006b). The seven test items of FMS are shown in Fig. 1. According to Minick et al. (2010), a high level of reliability can be secured if the FMS movements are scored by image analysis or direct observation with the naked eye. In this study, two cameras were installed in front of and next to an athlete to monitor all movements. Three testers independently reviewed the filmed images and scored the movements of the athletes in accordance with prior scoring criteria (Cook et al., 2006a, 2006b).
Measurement of strength and flexibility
Participants were instructed to perform the hand grip strength, back muscle strength, bench-press and squat both for one-repetition maximum (1RM) to measure strength, and to perform trunk flexion, trunk extension and the splits to evaluate flexibility. Measurements were done in accordance with the Physical Fitness Test Manual of the Korea Institute of Sports Science (Kim et al., 2007).
FMS training programs
Scores ≤2 points were recorded for 27 participants for shoulder mobility, 23 for rotary stability, 16 for straight leg raise, 6 for deep squat, 13 for hurdle step, and 14 for in-line lung. No subjects scored ≤2 for trunk stability push-up. The FMS training program was developed based on these test results with reference to previous studies (Burkhart et al., 2003; Frederick and Frederick, 2006; Goldenberg and Twist, 2006; Kiesel et al., 2011; Peate et al., 2007) as well as the information available on the official website of the FMS (http://www.functionalmovement.com). The FMS training program consists of functional movements related with core stability and shoulder and hamstring flexibility improvement. As there was no one who scored <2 points in trunk stability push-up, related training were not included. Those who scored <2 points in certain test items were mandated to follow the training regimen customized to reinforce their shortcomings in these test items, while the form roller and core training were commonly applied to all test participants. The FMS training program was conducted three times per week for 16 weeks. The details of the FMS training program are shown in Table 2.
Statistics
SPSS ver. 18.0 was used to analyze the test results. The reliability test was performed to estimate the intraclass correlation coefficient (ICC) among the three testers, and repeated measure ANOVA was utilized to monitor changes in strength and flexibility due to the FMS training program. Statistical significance was set at 0.05.
RESULTS
Reliability
To boost the reliability of the FMS results about the FMS, inter-reliability testing among the three testers was done. The Kappa coefficient was 0.805, which indicates excellent reliability (Fleiss, 1986).
Changes in strength and flexibility
The changes in strength and flexibility after the 16-week FMS program are summarized in Table 3. Hand grip strength showed a significant level of interaction between time and group (P=0.011 and P=0.001, respectively), while back muscle strength did not have a significant interaction between time and group (P=0.660). Back muscle strength was not meaningfully different between groups (P=0.184) but was between times (P=0.001). Bench-press and squat both showed significant levels of interaction between time and group (P=0.001 and P=0.008, respectively). With respect to flexibility, trunk flexion did not show a significant level of interaction between time and group (P=0.983), between groups (P=0.754) and between times (P=0.754). In contrast, although the trunk extension did not reveal a significant interaction between time and group (P=0.073) meaningful differences were evident between groups (P=0.004) and between times (P=0.001). Splits showed a significant level of interaction between time and group (P=0.004).
DISCUSSION
Although the FMS has been utilized as an important pretest to predict injuries, its relation with strength and flexibility is unclear. This study analyzed the impact of the FMS training program on the strength and flexibility among high school baseball players. The FMS training program significantly improved strength and flexibility.
Strength is a crucial physical element for athletes. Traditional training programs designed to boost strength have focused on increasing muscle volume rather than on functional movements. More recently, a training program based on functional movements was reported to be more effective in improving strength (Cook, 2003). Presently, the 16-week FMS training program improved hand grip strength and bench-press by 12% and 9%, respectively, compared with pre-test levels. Cook (2003) argued that only when armed with functional movements, an athlete is expected to show an improvement in motion performance capability and techniques, and that if an athlete lacks functional movement patterns, it can deteriorate the efficiency and effectiveness of exercising power. Goss et al. (2009) reported significant levels of improvement in performing the single leg hop, kick-ups and vertical jump after applying a 6-week training program developed based on functional movements. Therefore, the reinforcement of functional movements is considered to be an important factor in improving strength; the present FMS results confirm this view.
Strength can be further increased when training is based on muscle stability (Shinkle et al., 2012), and the most representative training to boost the stability of muscles is core training. Core training actually contributes to enhanced strength in athletes (Segal et al., 2004; Sekendiz et al., 2010). Core stability enables stabilization of the body during movement, which is a crucial prerequisite to muscle development. Otherwise, a compensation effect will occur, which can increase body imbalance in the long-term. Ultimately, the imbalance of strength has a negative impact on athletic performance and increases the possibility of injuries (Askling et al., 2003). Core stability can be measured through functional movements (Leetun et al., 2004; Liemohn et al., 2005).
Presently, the functional movements of the baseball players were evaluated after performing the FMS training program developed based on the study (Cook et al., 2006a, 2006b). In general, participants lacked core stability. However, a 7-week training program developed in consideration of the FMS scores of American football players and which included core training reportedly improved FMS scores (Kiesel et al., 2011). Based on this fact, it is thought that the reinforcement of core stability can contribute to enhanced body balance and improved overall strength. However, in relation to strength, the training group actually displayed a significant decrease in the squat test compared with the control group. One of the possible (and unconfirmed) reasons for this result may be because physical strength deteriorated as they had to perform the training program and still play regular season games.
With regard to flexibility, all factors except for body flexion showed significant improvements after the 16-week FMS training program. The training program included many static stretching, which are effective in enhancing the mobility of joints. In particular, static stretching of the shoulder joints including the 90–90 stretch and sleeper stretch are effective in improving flexibility (Laudner et al., 2008). Also the self-myofascial release after using a foam roller seemed to have a positive influence and, indeed, has gained wide accepted by athletes as it can reduce adhesion of fascia and muscle spasm (Okamoto et al., 2013) and is usually included in a FMS training program (Cook et al., 2010). An athlete suffers from repeated micro-traumas during games or drills, and an inflammatory response can form scar tissues over time, which can in turn deteriorate flexibility (Cantu and Grodin, 2001). It is presumed that the self-myofascial release using the foam roller, which is part of the FMS training program, helps reduce scar tissue and so helps enhance flexibility (MacDonald et al., 2013).
The collective data indicate that the FMS training program positively contributed to altered strength and flexibility. In addition to the benefit of predicting injuries athletes reported by the previous FMS studies, this study indicates that the FMS training program may improve physical strength if the FMS results are utilized as basic data in formulating an training program. Strength and flexibility have long been considered to be essential in improving athletic performance and sports techniques, and especially flexibility is closely related to injuries (Bradley et al., 2007). In this regard, although an training program designed to improve strength and flexibility is extremely important, it can increase the risks of more severe injuries or overtraining, if it ignores the weakened functional movements or previous scar tissues. In the future, after functional movements are correctly evaluated, an training program must be developed based on the results. When developing an training program designed to boost strength and flexibility of athletes at a field site, their shortcomings in terms of functional movements need to be identified through the FMS, and if it includes appropriate training in consideration of these results, it can contribute to enhanced athletic performance.
Future studies should evaluate how much an improvement in strength and flexibility can actually contribute to reducing or preventing injuries and to enhancing athletic performance of a player during the season.
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