1. Introduction
Tennis is the world’s second most popular sport. It is played in 195 countries and it has an estimated group of 87 million fans around the world, which represents 1.17% of the world’s population [
1,
2]. This sport has an intermittent character with repetitive high-intensity effort (i.e., acceleration, deceleration, changes of direction, and strokes) over a variable period of competition time (i.e., on average 90 min). It demands a high level of physical fitness concerning speed, agility, muscle strength and power, as well as cardiovascular fitness to achieve high performance level [
3]. Over the last few years, competitiveness in tennis has increased significantly, and players have devoted a significant time to improving their tennis skills through strength and conditioning, technical and tactical training, with an average of 15–20 h of training per week, even at a young age [
4].
Due to the high demands placed on the body during training and competition, tennis players are at increased risk of many injuries, including chronic overuse syndromes and acute traumatic injuries [
5]. Data from one of the most recent epidemiological studies on tennis injuries showed that upper limb injuries account for 28% of all injuries for male, adult players and 23% for female athletes, while the shoulder joint was reported to be the most frequently injured site of the upper limb [
6]. The most common overuse tennis-related injuries include: internal impingement and superior labrum anterior-to-posterior (SLAP) tears in the shoulder, medial or lateral elbow tendinopathy, tendinitis and subluxation of the extensor carpi ulnaris tendon at the wrist, as well as abdominal muscle strains, lumbar muscle strains and lumbar disc degenerative pathologies. The lower extremities are more prone to acute injuries such as ankle sprains, meniscal knee injuries, knee joint tendinopathy and hip injuries [
5].
There is still only limited evidence that total body and lower-extremity warm-up programs have the potential to significantly enhance performance and prevent injuries [
7,
8]. Correct fundamental movement patterns during sports and physical activities are very important for both athletic performance and injury prevention. The assessment of dysfunctional movement patterns can help healthcare professionals and coaches in implementing appropriate rehabilitation programs after injury, prescribing corrective exercise as well as developing injury-prevention training programs.
The Functional Movement Screen test (FMS™) has been described as a screening tool used to assess the quality of basic movement patterns and side-to-side limitation and movement asymmetries [
9]. The FMS was not intended to be a clinical, diagnostic tool. It was developed to evaluate movement performance in seven fundamental movement patterns in subjects with no current pain complaint or musculoskeletal injury. The seven tests in the FMS are: deep squat, hurdle step, in-line lunge, shoulder mobility, active straight-leg raise, trunk stability push-up, and rotary stability [
10]. These movement patterns are scored from 0 to 3 (with 3 points being the optimal score), based on individuals‘ performance with or without pain or compensation. The scores of each test are then summed up for a maximal composite score of 21. Low composite scores in this test (14 points or lower), as well as side-to-side functional asymmetries are reported as increased injury risk factors in male and female athletes and male military candidates [
11,
12,
13].
Previous studies have also evaluated the effects of different intervention programs focused on coordination, neuromuscular control, and/or strength training involved in FMS scores as a reliable measurement of movement skills and physical performance [
14,
15,
16]. However, these studies considered sporting disciplines other than tennis. To the best of the authors‘ knowledge, there is an absence of such studies considering the impact of core strengthening exercise programs on FMS results in adult tennis players. Thus the aim of this study was to evaluate whether the implementation of the six-week core stability training program could improve FMS test scores in adult male and female tennis players.
3. Results
Statistical analysis of the results in the first and second study (before and after introducing the core stability exercise program) revealed significant difference in FMS test results. The mean value of all the seven tests in FMS, as well as the FMS composite score, had significantly improved in both female and male tennis players (
Table 2). The mean value in the FMS total score in female athletes in the first study was 14.58 ± 2.91, and in the second study 17.20 ± 1.68 (
p < 0.001), while the scores were 14.44 ± 2.76 and 16.91 ± 1.36 (
p < 0.001) in the male group. Detailed results are presented in
Table 2.
Table 3 presents the results of the core stability tests before and after the core stability training program in the study group, sorted by the gender of the subjects. We observed a statistically significant increase in all test scores, in both women and men, although the average improvement after the six-week core stability exercise program was greater in male tennis players.
We observed a statistically significant improvement in all core stability tests results after the six-week training program in tennis players of both subgroups with regards to their training experience (1–3 years and 4 and more years) (
Table 4).
We also observed similar results in the FMS composite scores before and after the six-week core stability training program with regards to tennis players’ training experience. In the group with one to three years of training experience, the initial FMS composite score was 12.55 ± 2.55, while in the second study it was 16.32 ± 1.25 (
p < 0.001). In the the group with four or more years of training experience, the FMS composite score was 16.27 ± 1.67 in the first study, while it was 17.70 ± 1.45 (
p < 0.001) in the second study after the six-week training program. In both groups the average improvement of the FMS composite score was statistically significant (
Table 5).
Table 6 presents the differences in the FMS composite score and core stability test results, comparingtennis players with shorter and longer training experience in the first and second study. During the initial study the FMS composite score was significantly lower in the group of tennis players with shorter training experience compared to the group with four or more years of training experience (12.55 ± 2.55 and 16.27 ± 1.67,
p < 0.001). There were no significant differences between these two groups in core stabilility test scores before the six week training program. However, statistical analysis revealed a significant differences in all test results (FMS composite score and core stability test results) after the training program.
In the second study the average results of all tests improved in both groups of athletes, although by analysing the average improvement in the core stability tests results, we observed that improvement was greater in the group of athletes with longer training experience. This may suggest that they “responded“ better to the training program.
Table 7 provides data concerning correlations between the FMS composite score and each of the core stability tests during the second study, which was undertaken after the six-week training program. All the correlations were statistically significant, though moderate, with the correlation between the FMS composite score and the trunk extensors muscle endurance test results being the most significant of them all (R = 0.690).
4. Discussion
The FMS test and core stability tests are commonly used to assess an athlete‘s functional performance and injury risk [
9,
28]. In our research we used the FMS test and core stability tests to assess the effects of a six-week training program focused mainly on strengthening and stabilising of the lumbo-pelvic complex muscles in a group of athletes aged 18–23 (20.27 ± 1.68 years) practising tennis. The shortest training experience in our group ranged from one to three years (47.50% of the study group), with the rest of the group having four or more years of training experience (52.50% of the study group).
In numerous studies the researchers assessed the effects of various forms of training and prevention exercises on functional movement patterns and sports injury risk in many sports disciplines [
29,
30]. Šćepanović et al. [
31] evaluated the effects of a six-week core strengthening exercise in a group of 36 female, untrained students, randomly assigned to two groups. In a specific, core strengthening exercise training group, they observed higher results in the FMS test, compared with a group of female students participating in a traditional exercise program.
Bonazza et al. [
32] performed a scientific review of the literature concerning the effectiveness of FMS for assessing injury risk in athletes and individuals in military service. The authors suggested that FMS was a reliable, valid, and injury predictive tool, with lower scores on the test indicating increased injury risk in this group. Asgari et al. [
33] presented a similar systematic review on the FMS test injury predictive value in the active, female groups. The authors confirmed the validity of the FMS test in scientific practice, although they emphasised that due to the insufficient number of studies among active females, there is still a need to perform such studies on a larger female, athletic population. In the authors’ own research, the results of statistical analysis revealed a significant improvement of all FMS test scores in the second study after a six-week core stability exercise program, both in male and female athletes.
Šiupšinskas et al. [
34] assessed the association of pre-season musculoskeletal screening and functional test results (including FMS) with sports injuries in elite female basketball players. Researchers showed that impaired functional movement patterns (FMS test) as well as poor jump landing biomechanics (Landing Error Scoring System test-LESS) during pre-season screening tests were associated with an increased risk of lower limb injuries in female basketball players during the following season. The injured group had a lower composite FMS score (
p = 0.0001) and a higher total LESS score (
p = 0.028) than the non-injured group. However, the impairments of dynamic stability in the lower limbs (Y Balance test) were not associated with a higher injury rate in their study. The authors suggested that due to the fact that many different factors may contribute to increased injury risk in sport, a combination of the functional tests and performance-oriented tests should be used in pre-season injury risk assessment. They also indicated that systematic, specific functional training, including core stability exercises, may reduce the injury risk in female basketball players [
34]. In our study we also observed a significant improvement in core stability tests results after the six-week training program, which may have a positive impact on reducing injury risk.
Xio et al. [
35] presented results of the systematic review concerning the effects of exercise on physical fitness characteristics in young tennis players. The results of their review indicated that specific exercise training could significantly increase the physical fitness of young tennis players in terms of speed and agility, although there was a lack of evidence or conflicting evidence about strength and flexibility, as well as power, in this group. The results of our study indicated that a specific, functional exercise program could improve functional movement patterns (as assessed with the FMS test) and core stability test results. The FMS composite score and core stability test results were significantly higher after the six-week training program in our study group.
Fernandez et al. [
36] have assessed the effects of a five-week training program including specific neuromuscular exercises on physical performance in a group of young, elite tennis players. The study group consisted of 18 young, male tennis players (mean age 15.09 ± 1.16 years). They were randomly assigned to two groups. The first group performed specific, neuromuscular training as a part of their warm-up before tennis training sessions, while the other group performed the same training program after their tennis training sessions. The inclusion of neuromuscular training before regular tennis training had a positive effect on most physical fittnes measures in the second study, after completing the training program (i.e., jump, sprint, change of direction-agility, as well as upper-body power). Interestingly, performing the same exercise after the regular tennis training was not associated with the same improvement in physical performance test results. The authors also emphasised the importance of specific core stability training as well as trunk and shoulder exercises in combination with neuromuscular training as a part of a regular warm-up routine, in order to improve tennis-related physical performance variables. These results were similar to our study, where we observed significant improvement in functional movement patterns and core stability test results, after the six-week core stability exercise program.
Rey et al. [
37] presented slightly different conclusions in their research. The aim of their study was to assess the effect of the structured warm-up program (FIFA 11+), compared to a standard warm-up. on fundamental movement patterns in the FMS test in a group of amateur, male footballers. The 11+ warm-up routine in the intervention group lasted for around 25 min and it was performed three times a week for a six week period, instead of the regular, basic warm-up in the control group. The FMS total score improved significantly in both the intervention and control group, although there were no significant differences in overall performance beetwen the two groups. These results may suggest that specific and structured warm-up programs (i.e., 11+) may not result in additional, significant improvements in fundamental movement patterns, other than those achieved using a standard, sport discipline specific warm-up in soccer players.
Hoover et al. [
38] performed research concerning the injury predictive validity of the FMS test in a group of 32 male and female professional basketball players. The aim of the study was to assess the risk of non-contact injuries in professional basketball players based on FMS scores. The basketball players were initially assessed using FMS during a pre-season training camp. Each athlete was then monitored throughout the season with number and type of injury and time lost due to injury recorded. The authors of the study used linear regression models to analyse predictive ability of the FMS score. In all models the total FMS score did not turn out to be a significant injury predictor (
p > 0.05). In contrast to much other research, the results of their study did not confirm FMS test injury predictive validity in this sample of professional basketball players.
Two Polish authors, Koźlenia and Domaradzki [
39], evaluated in their study the association between physical performance test results and the quality of fundamental movement patterns assessed with the FMS test among young female Physical Education students. The authors suggested that there were still some conflicting results concerning the association between physical performance and quality of movement. However, both these factors could affect injury risk. In their study physical performance tests evaluated strength, power and flexibility. The main findings indicated that flexibility had the strongest and most statistically significant impact on the FMS composite score (ß = 0.25,
p = 0.0106) and asymmetries in the test (ß = −0.30,
p = 0.0014). Additionally, a significant, negative correlation of abdominal muscle strength and FMS asymmetries were observed (ß = −0.29,
p = 0.0027).
There are some other studies which use FMS to evaluate the effectiveness of different training and intervention programs in athletic populations. [
14,
15,
16]. Our study results have also revealed a significant improvement in FMS results following the six-week training program in a group of tennis players with different training experience (one to three years as well as four or more years of training experience). The recent study of Fernandez et al. [
40] assessed the effect of different types of warm-up exercises (neuromuscular vs. dynamic warm-up) on physical performance measures in young tennis players. The results showed that both warm-up routines significantly improved some of the physical performance test scores in the both study groups (sprinting performance, bilateral and unilateral counter movement jump, overhead medicine ball throw and some shoulder strength and ROM values). However, the neuromuscular warm-up produced greater gains in most of the performance-oriented test results (i.e., 5–10 m sprint, counter movement jump, overhead medicine ball throw and serve speed). The results of their study may indicate that a systematic, neuromuscular warm-up routine (including mobility, core stability, and shoulder strength exercises, combined with neuromuscular-related exercises, e.g., plyometric, acceleration/deceleration, and change of direction agility drills) can be recommended in young tennis players [
40].
The results of our study showed positive effects of the six-week core stability training program in a homogeneous group of adult tennis players. We observed significant improvement in functional movement patterns measured with the FMS test, as well as improved core stability (trunk muscle endurance test results), both in male and female athletes. According to some other studies results, this may have a positive impact on tennis-related physical performance and reduced injury risk. However, due to the lack of strong evidence and some conflicting results, the relationship between the quality of movement patterns, core stability and injury risk as well as tennis-specific physical performance requires further research in this study group.
There are some limitations in our study that need to be addressed in the future research. The major limitations of our study concern the lack of a control group that had not participated in the six-week core stability exercise program. Moreover, our study was performed in a particular group of amateur, adult tennis players. Therefore future studies should include different age groups (including youth tennis players) and ability level.