Age and Gender Differences in Injuries and Risk Factors in Elite Junior and Professional Tennis Players

Abstract

Background:

Elite tennis athletes experience injuries throughout the entire body. Impairments in trunk stability, lower limb flexibility, and hip range of motion (ROM) are modifiable risk factors that can impact injuries and performance. Information on nonmodifiable risk factors such as age and gender is limited. The purpose of this investigation was to provide information on risk factors to direct clinical decision-making and injury prevention and rehab programming in this population.

Hypothesis:

Prevalence and location of injuries will differ by age group and gender. Trunk stability, lower limb flexibility, and hip ROM will differ by age group and gender.

Study Design:

Cross-sectional study.

Level of Evidence:

Level 3.

Methods:

A de-identified database (n = 237; females = 126) from the United States Tennis Association High Performance Profile (HPP) 2014-2015 was used for the analysis. Subjects were elite junior and professional tennis players (mean age 14.6 [range, 9-27] years). The HPP is a tennis-specific assessment and questionnaire that includes retrospective information on injury history. Subjects were categorized by injury, gender, and age. Injury locations were classified by region. Trunk stability measures included drop vertical jump (DVJ), single-leg squat, and prone and side planks. Lower limb measures included hamstring, quadriceps and hip flexor flexibility, and hip rotation ROM.

Results:

A total of 46% of athletes reported an injury. Significant differences were found for injury prevalence and location by age group. Adolescent athletes (age 13-17 years) had more trunk injuries, while adult athletes (age ≥18 years) had more lower limb injuries. Adolescent athletes performed worse on DVJ, dominant side plank, and hamstring flexibility compared with young (age ≤12 years) and adult athletes. Significant gender differences in hip ROM included internal rotation on both the dominant and nondominant sides.

Conclusion:

Impairments in trunk stability, lower limb flexibility, and hip rotation ROM may affect both health and performance outcomes in this population. Elite tennis athletes may benefit from additional off court programming to address trunk and lower limb impairments.

Clinical Relevance:

Adolescent elite tennis athletes may be at higher risk of trunk injuries. Age, gender, injury history, and impairments should be considered with all assessments and programming.

Tennis requires coordinated, repetitive, and forceful movements throughout the kinetic chain.^22,43,44,75 The physical demands are especially high at the elite levels and include strength, power, agility, and coordination to help produce maximal tennis stroke velocity.^25,61 As both an overhead and rotational sport, high forces and loads are generated, absorbed and transferred from the lower body to the upper body through the trunk.^{9,18,27,51,52} Sport or serve exposure may influence anatomic or functional sport-specific adaptations in elite tennis players.^13,78,79 Sport-specific adaptations have been documented in the dominant shoulders of elite players, but are not well understood in the trunk or lower limbs.^{3,13,20,48,55,74,76,79}

Tennis injuries occur throughout the entire body—upper limbs, trunk, and lower limbs.^{28,47,49,53,70,71,81,97} Acute injuries are more common in the lower limbs, while chronic or overuse injuries are seen more in the upper limbs.^{1,17,50,51,81} Previous tennis epidemiology studies have focused mainly on elite junior or professional players, but neglect to report on age and gender differences specific to injury type and location.

Risk of athletic injury is complicated and likely influenced by a combination of intrinsic (athlete related) and extrinsic (environmental) variables.^4,5 Since studies on risk factors are limited in tennis, oftentimes injury prevention programs are based on other sports or global perspectives. Nonmodifiable intrinsic risk factors such as age, gender, and previous injury are known to be related to athletic injuries.^{16,36,41,68,72,85-87} Impairments in foundational components of movement such as range of motion (ROM), flexibility, strength, and motor function are important to assess and address to reduce injury risk and maximize performance.^{8,11,24,25,29,31,35,38,46,56,63,88,91,93,97-99} To direct primary and secondary prevention programming, it is important to identify higher risk athletes such as youth and adolescent athletes, female athletes, and those with a previous injury history. The purpose of this study was to examine whether gender and age groups differed in the proportion (prevalence) of athletes reporting injuries at various locations or failing performance tests, to help guide clinical decision-making and injury prevention programming in the elite tennis population.

Methods

This cross-sectional study involved a de-identified database (n = 237) of the United States Tennis Association’s (USTA) High Performance Profile (HPP) on the top ranked and performing American elite junior and professional male and female tennis players. Players who consented and participated in the HPP testing were healthy, without injury, and participating in full training and competition at the time testing occurred during a USTA training camp. The HPP includes retrospective information on injury history (questionnaire) and a series of 10 musculoskeletal tests commonly used in the athletic population.^{14,20,34,46,96} This study focused on the trunk and lower quarter tests (7 of the 10 tests; Table 1) and injury history information. This study received institutional review board exemption since data had previously been collected.

Table 1.

Constructs of interest and High Performance Profile (HPP) trunk and lower quarter tests with cut points for pass/fail criteria

Tests From HPP	Construct	Level of Measurement	Pass/Fail Criteria
Drop vertical jump a	Motor function	Pass/fail (nominal)	Fail = presence of at least 1 compensation b
Single-leg squat	Motor function	Pass/fail (nominal)	Fail = presence of at least 1 compensation b
Plank tests Prone plank a Side plank	Trunk strength and endurance	Pass/fail (nominal)	Fail = unable to maintain position or hold test position for 30 seconds
Hip flexor (Thomas test)	Flexibility	Pass/fail (nominal)	Fail = unable to achieve neutral hip extension (touch table)
Hamstring	Flexibility	Pass/fail (nominal) at HPP cut point	Fail = <70°, pass = ≥70°
Quadriceps	Flexibility	Pass/fail (nominal) at HPP cut point	Fail = passive knee flexion <135°, pass = ≥135°
Hip range of motion (prone) Internal rotation (IR) External rotation (ER) Total (rotation) = IR + ER	Range of motion (hip)	Continuous (degrees)

^aBilateral tests, all other tests were tested unilaterally (dominant and nondominant sides).

^bCompensations = loss of balance, excessive knee valgus, forward knee translation/past toes, limited depth, excessive trunk flexion, foot-hyper pronation or eversion. Recorded with 2-dimensional video analysis then graded as pass/fail.

The database consisted of information collected from January 2014 to December 2015 on elite junior and professional players during participation in a USTA training camp by the same USTA staff members (a physical therapist [PT] and an athletic trainer [AT]). Both the PT and the AT were trained and experienced in administering the HPP. The PT had over 4 years of experience with the HPP and was in charge of data collection and management of the database in addition to providing players with corrective exercises based on the results of the HPP assessment. Before data were transferred in a Microsoft Excel spreadsheet for analysis, the database was de-identified by the PT. The HPP tests were administered, recorded, and scored by the PT/AT team.

Demographic Information

All demographic information in the HPP was self-reported and included age, gender, dominant arm, tennis experience (years), competitive tennis experience (years), height, and weight. Body mass index (BMI, kg/m²) was calculated. Competitive tennis experience is defined as the number of years playing competitive tournaments.

Injury Information

Injury history information from the HPP was retrospective and self-reported. Injured athletes (INJ) are those who answered “yes” to an injury in the previous year. Injured (INJ) was defined as “an event that forces a player to miss 3 or more consecutive days of tennis play, either practice or competition, or that requires medical attention from an athletic trainer, therapist, or doctor.” ⁹⁰ Noninjured athletes selected “no” to any injury in the previous year. If the player checked “injured” the following areas of injury were available for identification: location (neck, shoulder, elbow, wrist, back, abdominals, hip, knee, ankle, foot, other). Injuries were then subgrouped by region (upper quarter = shoulder/ elbow/ wrist, trunk = abdominal/low back, lower quarter = hip/knee/foot/ankle). ⁶⁹ Dominant side is the entire side a player serves from including the upper quarter, trunk, and lower quarter. Nondominant side is the opposite side of the body that a player serves from. This definition is consistent with previous tennis research. ²⁰

HPP Testing

The HPP included tests for trunk stability, lower limb flexibility, and hip rotation ROM. All HPP test items are found in Table 1 with the constructs they represent. The trunk stability component of motor function was measured using the drop vertical jump (DVJ) and single-leg squat (SLS) tests.^14,94,95 Trunk stability is operationally defined as the ability of the musculoskeletal system to activate, respond, and maintain posture or positioning.^7,49,65,66 The SLS and DVJ are commonly used to identify impaired motor function in the athletic population.^{2,34,45,72,73} The inability to control and position the trunk during lower limb weightbearing activities can potentially place increased demands on the lower limbs.^14,33,34,98 The trunk stability components of trunk muscle strength and endurance were measured using the plank tests (prone plank and side plank). For all active and athletic populations, the trunk stability components of trunk strength and endurance are important foundational and functional measures to assess.^{6,15,19,46,54,84,95} Lower limb flexibility was measured by the hamstring, quadriceps, and hip flexor flexibility (Thomas test) tests. To assess for hip rotation restrictions, internal (IR) and external rotation (ER) was tested passively in the prone position.^20,31,55,90 All tests were performed on both dominant and nondominant sides, except the DVJ and prone plank, which are bilateral tests. The DVJ, SLS, plank, and lower limb flexibility tests were all graded as pass or fail based on specific grading criteria (Table 1). Both the DVJ and SLS were recorded with 2-dimensional video analysis to capture frontal and sagittal planes.

Motor Function

For DVJ testing, the subject started on top of a box 12 inches (31 cm) in height with feet positioned 14 inches (35 cm) apart. The examiner instructed the subject to drop directly down from the box, and immediately perform a maximal vertical jump raising both arms as if jumping for a basketball. Participants who demonstrated knee valgus, knee varus, forward trunk lean, and asymmetrical limb loading or excessive movement of knees forward over the toes were classified as having failed the test.

To perform the SLS, the subject began in an upright standing position with arms crossed over chest. The subject was instructed to bend the nonweightbearing knee to 90°, then descend into partial squat (approximately 30°-45°). The position was held briefly before the subject returned to the starting position. Participants who demonstrated good postural alignment, neutral spine position, a level pelvis, limb alignment, and singe limb balance during the movement were classified as a pass. Participants who failed the test demonstrated loss of balance, valgus position of the knee, Trendelenburg pattern or the dropping of the hip on opposite of the weightbearing limb, increased trunk flexion, and/or knee passing the toes of the weightbearing side. The test was performed on both the dominant and nondominant sides.

Trunk Strength and Endurance

For the prone plank test, the subject was positioned prone resting on elbows and toes. The examiner instructed the subject to maintain static hold of position and alignment for 30 seconds without wavering or compensation. After the prone plank, the side plank test was performed bilaterally. In the side plank, the subject was positioned on ipsilateral elbow with feet placed directly on top of each other. The contralateral arm was placed on the hip, while the examiner monitored the position during a 30-second hold for the presence of compensatory hip, pelvis, or trunk sagging or rotations. Inability to hold the 30-second test position or the presence of compensatory movements was scored as a fail. A pass was the ability to hold for 30 seconds.

Lower Limb Flexibility

For the hip flexor flexibility (Thomas test), the subject was supine toward the end of table so that the edge of the table lined up with the mid-femurs (mid-thighs). Both legs were brought up to chest, then one leg was held toward chest and other leg was lowered to test for neutral hip extension (achieved by the thigh touching table or dropping off the edge of the table.) The test was repeated on the opposite side. A failed test was inability to obtain neutral position.

To assess hamstring flexibility, the subject was positioned supine on table with a neutral spine. The nontest leg stayed straight/extended on the table. The examiner raised the test leg passively until motion was felt or observed at anterior superior iliac spine or contralateral limb moved as compensation. The hip flexion angle was measured with a goniometer. The test was performed bilaterally, measured in degrees. A hip flexion angle <70° was a failed test, and ≥70° was a pass. ⁹⁰

To assess quadriceps flexibility, the subject was lying prone with a neutral spine position. The limb not being tested was extended on the table. The examiner passively bent the test knee, trying to touch the heel to the buttock. A goniometer was used to measure the amount of knee flexion in degrees. The test was performed bilaterally, measured in degrees. Knee flexion <135° indicated a failed test, and ≥135° was a passed test. ⁹⁰

Hip ROM

To measure IR and ER hip ROM, the subject was positioned prone on his/her stomach. The hips were placed in a neutral adduction/abduction position. The starting position occurred with the knees flexed to 90°, from this position both hips were internally rotated, the measurement (with goniometer) was taken at the end-range position. After IR measurements were taken, one leg was extended fully while the other leg was externally rotated while the proximal hip and pelvis were stabilized during the movement to minimize compensation. The measurement was taken at the stable endpoint of ER. Then measurement of ER was repeated on other side (measured in degrees). Total hip ROM was calculated as the sum of IR and ER for each side, for both the dominant and nondominant sides (Total = IR + ER; Table 1).^20,90,92,97

Data Analysis

SAS University Edition (SAS Institute) was used for statistical analysis. The players were grouped by gender (male and female) and age (≤12 years = young players, 13-17 years = adolescent players, and ≥18 years = adult players). Descriptive statistics were used to summarize the data. Chi-square tests were used to examine differences in the prevalence and location of injuries (upper quarter, trunk, lower quarter) by age group and gender. To compare group differences in proportions of failed HPP tests, chi-square tests were used for the categorical variables. To compare group differences for the continuous variables, such as hip rotation ROM, t tests were used for the 2 group-gender comparison, while analysis of variance was used for the 3 age group comparison. A P value of less than 0.05 was considered statistically significant for this investigation.

Results

Women and men were well matched and had similar BMI (20.3 kg/m² for women vs 20.8 kg/m² for men) and years of tennis experience (8.9 years for women vs 9.0 years for men) (Table 2). Prevalence of injuries was reported at 46% (n = 111) with the highest proportion in the lower quarter (20%) followed by the trunk (15%) and upper quarter (11%) (Figure 1).

Table 2.

Demographics by gender (n = 237)

Variable	Whole Sample (n = 237)	Female (n = 126) 53.2%	Male (n = 111) 46.8%	P
Age, y, mean (SD) [range]	14.6 (3.7) [9-27]	14.9 (3.8)	14.3 (3.6)	0.18
Height, cm, mean (SD) [range]	167.4(13) [127-208]	165.6 (8.9)	169.7 (16.3)	0.02*
Weight, kg, mean (SD) [range]	56.5 (13.8) [27-94]	55.7 (11.9)	58.2 (15.7)	0.19
BMI, kg/m2, mean (SD) [range]	20.6 (3.6) [13-34]	20.3 (3.6) [13-34]	20.8 (3.6) [14-29]	0.31
Tennis experience, y mean (SD) [range]	8.9 (3.7) [2-22]	8.9 (3.8)	9.0 (3.6)	0.79
Competitive tennis experience, y, mean (SD) [range]	6.2 (3.2) [2-19]	6.2 (3.2)	6.2 (3.2)	0.98
Dominant hand, % right	87.3	91.0	83.0	0.05

^*Statistically significant (P < 0.05).

Figure 1.

Injury history of whole sample.

Age Group Comparison

Injuries differed among age groups in prevalence (P < 0.001) and location (P = 0.004) (Table 3). The adolescent and adult age groups had significantly higher proportions (57% and 59%, respectively) of injuries compared with the young age group (29%, P < 0.0001). Adolescent tennis players had the highest proportion of trunk injuries (39%), while the adult age group had the highest proportion of lower quarter injuries (54.2%, P = 0.0004).

Table 3.

Age group comparisons of injury groups (% injured)

Injury Region	Young Players, Age ≤12 y (n = 93)	Adolescent Players, Age 13-17 y (n = 104)	Adult Players, Age ≥18 y (n = 40)	P
Injured, % (n)	29 (26)	57 (61)	59 (24)	<0.0001*
Injured at each location, % (n)
Upper quarter	30.1 (8)	19.7 (12)	21 (5)
Trunk	23 (6)	39 (24)	21 (5)
Lower quarter	46 (12)	34.4 (21)	54.2 (13)	0.0004*

^*Statistically significant (P < 0.05).

The results of chi-square testing are found in Table 4 for the pass/fail tests, including the trunk stability components of motor function, trunk strength and endurance testing and hip flexor, hamstring, and quadriceps flexibility testing. In the HPP tests, a smaller proportion of the adult players failed the DVJ than did the young and adolescent players (P = 0.02). Results for the SLS tests were not statistically significant. For the dominant side plank, the adolescent age group had the highest proportion of failed tests (18.5%, P = 0.04). However, no statistically significant differences were found for prone plank or nondominant side plank tests. In flexibility, adult players had higher proportions of failed dominant hip flexor tests (P = 0.01). For the hamstring test, the adolescent and young age groups had higher proportions of failed tests compared with the adult age group with a statistically significant difference on the dominant side (P = 0.02). No significant differences were found in the proportions of failed quadriceps tests. For hip ROM differences among groups, see Table 5. The young age group had more mean ROM than the adolescent and adult age groups. Statistically significant differences were found among groups, especially in mean hip external rotation on the dominant side (P < 0.0001) and mean total ROM on both the dominant and nondominant sides (P < 0.0001) (Table 5).

Table 4.

Age group comparisons of tests (% failed)

Tests	Young, Age ≤12 y (n = 93)	Adolescent, Age 13-17 y (n = 103)	Adult, Age ≥18 y (n = 40)	P
Drop vertical jump	82.8	87.5	66.7	0.02*
Single-leg squat
Dominant	81.5	79.6	63.9	0.08
Nondominant	58.1	51.5	45.0	0.35
Plank tests
Prone	5.4	4.8	2.5	0.76
Dominant	12.9	18.5	2.5	0.04*
Nondominant	12.9	8.7	2.5	0.16
Hip flexor flexibility
Dominant	17.2	24.0	32.5	0.01*
Nondominant	16.1	21.2	27.5	0.31
Hamstring flexibility
Dominant	32.3	35.6	12.5	0.02*
Nondominant	27.9	30.8	12.5	0.07
Quadriceps flexibility
Dominant	9.7	9.6	20.0	0.17
Nondominant	11.8	4.8	15.0	0.09

^*Statistically significant (P < 0.05).

Table 5.

Age group comparison of hip range of motion (ROM) (in degrees)

Variable	Young, Age ≤12 y (n = 93)	Adolescent, Age 13-17 y (n = 103)	Adult, Age ≥18 y (n = 40)	P
Hip internal rotation, mean (SD) [range]
Dominant	41.7 (11.7) [12-66]a	40.0(12.4) [10-70] a,b	32.6(10.0) [12-50]b	0.0005*
Nondominant	42.2 (11.5) [4-68]a	38.3 (10.8) [10-62]b	34.1 (7.5) [20-50]b	0.0002*
Hip external rotation, mean (SD) [range]
Dominant	45.6 (10.5) [13-62]a	42.0 (9.4) [18-63]b	35.6 (9.7) [7-54]c	<0.0001*
Nondominant	42.9 (10.8) [15-65]a	40.4 (8.5) [17-64]a	32.6 (9.7) [12-60]b	<0.0001*
Hip total rotation, mean (SD) [range]
Dominant	87.3 (16.8) [30-123]a	81.0 (12.8) [35-115]b	68.9 (11.9) [44-89]c	<0.0001*
Nondominant	85.1 (16.8) [25-122]a	78.7 (13.2) [35-116]b	67.6(11.5) [38-89]c	<0.0001*

^a,bComparisons with the same letter are not statistically different.

^*Statistically significant (P < 0.05).

Gender Group Comparisons

Injury prevalence, classified by gender is presented in Table 6. Women had a higher proportion of injuries compared to men (51% vs 44%, P = 0.4). By location, female athletes had a higher proportion of injuries in the upper quarter (12% vs 9%) and lower quarter (23% vs 17%) compared with male athletes (P = 0.6) (Table 6).

Table 6.

Gender comparison of injury prevalence (% injured)

	Female (n = 126)	Male (n = 111)	P
Injured, % (n)	51 (61)	44 (45)	0.4
Injured at each location, % (n)
Upper quarter	25 (15)	22 (10)
Trunk	30 (18)	38 (17)
Lower quarter	45 (28)	40 (18)	0.6

Differences in the proportion of male and female athletes who failed the trunk stability components of motor function, strength and endurance, and lower limb flexibility are found in Table 7, and differences in hip ROM are found in Table 8. In trunk strength (plank tests), female athletes had higher proportions of failed tests than male athletes, with a close to statistically significant difference on the nondominant side test (P = 0.05) (Table 6). Proportions of failed SLS tests were significantly different on the dominant side (71.4% female vs 84.6% male, P = 0.02) but not on the nondominant side (55.7% female vs 50% male, P = 0.39). Patterns of lower limb flexibility differed between men and women. Women had higher proportions of failed hip flexor tests, while men had a larger proportion of failed tests on the hamstring (P < 0.0001) and quadriceps tests. In hip ROM, men had less mean hip IR on both the dominant (P < 0.0001) and nondominant (P < 0.003) sides compared with women (Table 8).

Table 7.

Gender comparisons of tests (% failed)

	Whole Sample (n = 237)	Female (n = 126)	Male (n = 111)	P
Drop vertical jump	82.0	80.7	83.5	0.60
Single-leg squat
Dominant	77.8	71.4	84.6	0.02*
Nondominant	53.0	55.7	50	0.39
Plank tests
Prone	4.6	6.4	2.7	0.18
Dominant	13.6	14.4	12.6	0.69
Nondominant	9.3	12.8	5.4	0.05*
Hip flexor flexibility
Dominant	22.8	26.2	18.9	0.18
Nondominant	20.3	24.6	15.3	0.08
Hamstring flexibility
Dominant	30.4	17.5	45.1	<0.0001*
Nondominant	26.6	15.9	38.7	<0.0001*
Quadriceps flexibility
Dominant	11.4	7.9	15.3	0.07
Nondominant	9.3	7.1	11.7	0.22

^*Statistically significant (P < 0.05).

Table 8.

Gender comparison of hip range of motion (ROM) (in degrees)

Variable	Male (n = 111)	Female (n = 126)	P
Hip internal rotation, mean (SD) [range]
Dominant	35.2 (11.0) [10-60]	42.3 (12.1) [12-70]	<0.0001*
Nondominant	36.4 (10.9) [4-56]	41.6 (10.7) [10-68]	<0.0003*
Hip external rotation
Dominant	43.0 (9.7) [13-63]	41.8 (10.9) [7-62]	0.38
Nondominant	40.9 (9.9) [13-64]	39.8 (10.5) [12-65]	0.50
Hip total rotation
Dominant	78.3 (15.5) [35-115]	81.3 (15.3) [30-123]	0.004*
Nondominant	77.1 (15.9) [28-115]	84.2 (15.2) [25-122]	0.04*

^*Statistically significant (P < 0.05).

Discussion

A key element of injury prevention programming is understanding injury prevalence, or the magnitude and distribution of injuries within a population. ⁵ Previous authors have recognized the need for more injury prevention programming in tennis based on injury data.^36,40,69-71 By including both male and female players across a wide age range (9-27 years), this study addresses several research gaps. Higher risk groups and impairments in modifiable risk factors were identified, which can be used to direct future research and programming in this population.

The findings related to injury prevalence and distribution of injuries by location is consistent with previous tennis epidemiology studies^{36,47,53,70,71,81} that a majority of injuries occur in the lower limbs, followed by either the trunk or upper limbs. The finding that female tennis athletes had a higher proportion of lower limb injuries is also consistent with injuries reported at the collegiate and professional level.^47,53

One of the main hypotheses and findings of this study was that there were differences in the prevalence of injuries and location of injuries among age groups. Adolescent tennis athletes (13-17 years old) had the highest proportion of trunk injuries (39% vs 23% young, 21% adult), while the adult age group had more lower limb injuries (54.2% vs 34.9% adolescent, 46% young). Lower limb injuries in elite tennis (acute and overuse) are among the most common and likely influenced by the increase in physical and extrinsic demands (competition and training) at higher levels of tennis.

Adolescent tennis athletes in this study had a higher proportion of trunk injuries, with more trunk stability impairments in trunk strength and endurance (dominant side), and motor function (DVJ). Together these findings are consistent with sports medicine research, that adolescent athletic injuries may be influenced by stage of development, where puberty, growth spurts, and muscular imbalances may contribute to trunk injuries.^26,32 Injury location and rates may be affected not only by the physiological changes during puberty and periods of rapid growth but also by sport-specific and biomechanical factors such as large, repetitive, end-range spinal movements and forces seen in tennis, baseball, gymnastics and diving.^{10,26,68,80,86} A magnetic resonance imaging (MRI) study by Alyas et al ³ reported abnormal findings and pars lesions were relatively common in the lumbar spines of asymptomatic elite adolescent tennis players, where 84% of the adolescent players had abnormal MRI findings, with 32% of those presenting as pars lesions. Back pain and trunk injuries in the youth or adolescent athlete can vary by type such as minor (muscle strains) or severe (spondylolysis). Selhorst et al ⁸⁰ reported a prevalence of spondylolysis at 30% in a group of adolescent athletes with low back pain, which was most common in baseball for men and gymnastics for women.

Additional motor function and injury prevention training has been recommended for youth athletes, especially early sport specializers. ^56,58 Tennis is known for early sport specialization, where athletes participate in only one sport and play more than 8 months a year, similar to other highly skilled and individual sports such as diving and gymnastics. ⁶⁷ All elite tennis athletes in this study, but especially the young and adolescent players, had high proportions of failed trunk stability tests related to motor function (DVJ and SLS). There is evidence that additional motor function programming can not only prevent and reduce injuries but also improve performance.^{23,25,35,56,77,83} For example, the inclusion of a motor function program before tennis training for a group of young tennis athletes had a positive change in performance variables compared with after tennis training over a 5-week period. ²⁵ A reduction in lower limb injuries in team sports (incidence rate ratio = 0.64; 95% CI 0.49-0.84) was found in a systematic review by Emery et al ²³ on the preventative effect of neuromuscular programming. All elite tennis players may benefit from additional trunk stability related to motor function programming, but especially young elite junior players since they primarily participate in only tennis and have less of an opportunity to develop diversity of motor skills and trunk stability through other sports and play.^39,57,58

Gender

Some gender differences in musculoskeletal performance were found in this study. Female tennis athletes had higher proportions of failed tests on trunk strength and endurance (plank) tests, while male athletes had higher proportions of failed flexibility tests (hamstring and quadriceps). For hip rotation ROM, men had less mean hip IR ROM compared with women. Similar to previous studies by Ellenbecker et al ²⁰ and Moreno-Perez et al ⁵⁵ on of hip rotation ROM, this research adds to the descriptive profiles for elite male and female tennis players. However, it also expands on the understanding of the descriptive profile in tennis by including additional musculoskeletal tests of the trunk and lower limbs. The gender-specific information from this study can be used to direct programming, where women may benefit from additional trunk stability exercises, while more focused flexibility exercises for men can help address muscular imbalances. Lower limb flexibility and muscular imbalances can affect lower limb function, as well as the ability to transfer forces from the lower body into the trunk and upper body. Previous research has reported relationships between hip impairments and trunk injuries for men and women.^91,93,97 Young et al ⁹⁷ found impairments in hip flexor flexibility (the Thomas test) were related to abdominal muscle injuries in female professional tennis players.

Although there is limited information in the tennis population, gender differences in movement patterns, modifiable risk factors, and injuries are well established in the sports medicine literature.^{30,37,41,46,62,85,86,98,99} A greater incidence of knee and anterior cruciate ligament injuries, as well as overuse injuries has been reported for female athletes compared with male athletes.^85,86 Injured female athletes have also been found to have more trunk and hip impairments.^46,63,98 For example, prospective studies by Zazulak et al^98,99 found injured female athletes had more trunk impairments, measured by postural sway and proprioception, than noninjured female athletes or injured male athletes. The collective evidence regarding gender differences in athletic injuries has helped guide injury prevention programming and research, especially in team and field sports such as soccer and basketball. However, gender-specific information and programming is still limited in tennis.

The physical requirements of elite tennis place high demands on the entire body, but especially the trunk. The ability of the trunk to absorb, generate, and transfer force from the lower limbs to the upper body, is a key component for tennis and overhead athletes.^{18,42,43,76,82} During the tennis serve, the trunk must have the ability to withstand large, end-range forces and loads.^10,12,27,89 Therefore, trunk stability, or the ability to activate, respond, maintain posture and/or position is as essential component for all tennis athletes to maximize health and performance. Trunk stability and its components of motor function, strength and endurance are not only foundational components of function but also necessary to perform higher level athletic performance variables such as speed and power.^12,24,88 Therefore, trunk impairments can potentially have both health and performance implications. A prospective study by Martin et al ⁵¹ on male professional tennis players found that the uninjured players had a better quality of energy transfer or energy flow, from the trunk to upper limb with lower upper body joint forces (in shoulder, elbow, wrist), fewer upper body overuse injuries, and higher ball velocity compared with the injured players during the serve. The authors found higher amounts of energy absorbed instead of transferred into the shoulder, elbow, and wrist of the injured compared with the uninjured players, which they hypothesized contributed to the reported overuse injuries (in 57.8%, 11 of 19 players). ⁵¹

For overall health and performance, all tennis players can benefit from the protective effects of enhanced trunk stability through focused off court programming. This may be especially important for female and adolescent elite tennis players, who demonstrated more impairments in trunk stability related to trunk strength and endurance during the plank tests.

Lower body and trunk muscle imbalances are important to assess during preseason examinations, and throughout the playing season. This study focused on the trunk and lower body impairments since this is an area of limited information in elite tennis. Previous tennis studies on the trunk have primarily focused on serve performance, highlighting the important role of the trunk and use of the lower body or leg drive, which is related to higher velocity or performing serves.^12,27,59,75

Strengths and Limitations

Strengths of this study include the size and variability of the sample. Both male and female tennis athletes were represented in similar proportions compared to previous tennis studies.^{28,55,79,91,97} Limitations include possible recall and information bias (errors during data collection or categorization) as a cross-sectional study. Injury data were self-reported and limited. Data did not include injury type (acute or overuse) or a formal diagnosis. Additional limitations include the HPP tests, many of which were pass/fail and are not the best measures of the constructs of interest. For example, the plank test, a measure of trunk strength and endurance, had a possible ceiling effect in this study with a 30-second hold. Finally, this study did not address test reliability, exposure volume, or biomechanics. Lack of adequate test reliability would negatively affect the validity of these measures. Elite players all generally have high intense training volumes and specialization based on prior studies.^60,67

Conclusion

Impairments in trunk stability, hip rotation ROM, and lower limb flexibility may affect both health and performance outcomes in this population.