Full effort compared to partial effort performance of the tennis serve in collegiate tennis players

Introduction

Tennis is a sport played around the world at all levels of skill. Injury rates for collegiate tennis players are similar between men and women: 4.89/1000 athletic exposures for men and 4.88/1000 athletic exposures for women. ¹ An 8-year review of injury rates in Davis Cup players revealed 6.05/1000 injuries per playing hours and 6.64/1000 match hours. ² Shoulder and elbow injuries are common in elite level players including in elite junior players, ³ and professionals. ⁴

Following surgery or non-surgical conservative rehabilitation for injuries to the upper extremity, the use of interval tennis programs is common.^5,6 Following injury, rehabilitation programs for athletes consist of a gradual progression of increased range of motion, flexibility, muscular strengthening and muscular endurance training. Once motion, flexibility, strength and endurance have returned to near normal levels, an interval sports program can commence. The term “interval sports program” refers to a gradual and controlled return to full sports activities. Interval programs generally simulate or replicate the given sport with progressively applied forces and loads. ⁶ Sports physical therapists advocate interval tennis programs during the later stages of rehabilitation from shoulder and elbow surgeries or injuries.^5,7,8 An interval tennis rehabilitation program (ITRP) is typically divided into approximately 4 to 6 weeks of progressive participation based on injury severity and the subjective and objective tolerance of the player returning from injury. The early phases of the ITRP include the lowest level stressors (forehand and backhand groundstrokes) performed initially with low compression tennis balls. These exercises progress to the use of regular tennis balls once a tolerance to the low compression tennis balls are demonstrated. ⁹ The integration and tolerance of groundstroke (forehand and backhand) rallies from the baseline are followed by the introduction of volleys which involve hitting the ball prior to the ball bouncing and slowing down while positioned closer to the source of the oncoming ball. The rationale for this stroke progression is to prepare the athlete for a gradual return to the stressors inherent in the tennis volley or serve and ultimately for the upper extremity to gauge a tolerance for integration of the service motion. The present study did not test velocity of groundstrokes as that was not part of the study purpose. The serve places the greatest load on the shoulder and elbow based on an EMG study, ¹⁰ and also places the shoulder and elbow in ranges of motion that can create impingement and valgus overload to the shoulder and elbow, respectively.^9,11 A tennis player’s ability to estimate accurate serve velocity is unknown. Serving at higher intensities/velocities at earlier inappropriate timeframes may result in lost playing time due to re-injury, exacerbation of prior injury, or compromise a surgical repair.

Research on perceived effort and resultant ball velocity is sparse in the sports medicine and sport science literature. Baseball pitchers were required to throw at various intensities of effort while an objective measurement of throwing velocity measured the actual velocity of their performance. ¹² Skilled throwers, when asked to throw at the velocity they perceived to be 50% of their maximum speed, actually threw at approximately 85% velocity. When told to throw 75%, they threw at 90% normal velocity. ¹² Estimation of serving effort has not been studied in skilled tennis players. This information could provide rehabilitation professionals with valuable information to guide the progression of ITRP’s. Therefore, the purpose of this investigation, the first of its kind, was to determine actual tennis serve velocity in advanced level tennis players when asked to hit serves they perceive to be at 50% and 75% of their maximum velocity. The null hypothesis was that there would be no difference in the player’s perceived-effort velocity and actual-serve velocity.

Methods

Collegiate level tennis players were recruited from two Division I Universities and one Division 2 men’s (n = 22) and women’s (n = 17) tennis teams for this study. Volunteers (n = 41) completed a demographic cover page including player performance and training information which included height, weight and arm dominance. If the player answered that he/she was not at 100% physical capability, then he/she was excluded from the study. Prior to participation, each player read and signed a consent form approved by the institutions’ IRB committees.

Once cleared to participate in the study, each player proceeded to perform a standardized warm-up session. The warm-up session consisted of hitting groundstrokes for 2 minutes and 2 minutes of tennis serves at self-directed velocities. Following the warm-up, players were asked to hit 5 maximal effort tennis serves into the deuce side service box of the court. These serves were “first serves” hit flat with the primary goal of replicating the subjects’ maximal serve velocity and functioned as the 100% maximal effort serve for the purposes of this investigation. From the mean of the maximal serve effort, actual serve effort of 50% and 75% was calculated for statistical comparison. Researcher assumed that the subjects’ maximal perceived effort (100%) and the maximal velocity measured were the same. For data from the serve velocity to be included, serves had to land in the service box, consistent with a tennis serve according to International Tennis Federation rules. ¹³

Subjects were then directed to hit 5 serves at each of two randomly determined intensity levels, 50% and 75%. Which perceived level of intensity the player should attempt first was determined randomly. Each player hit 5 serves of the first selected level of intensity; then 5 of the other level of intensity. Players were instructed to “serve at an effort that you feel is either 50% or 75% of your maximum effort tennis serve.” The specific percent of intensity would have been inserted into the directions. Players were given no feedback during the data collection.

A radar gun (JUGS Professional Sports Radar Gun: JUGS Sports, Tualatin, OR) measured the service velocity. The examiner stood on a chair behind the server to best capture the serve’s post-impact ball velocity. Data related to the participants’ serves were recorded on a datasheet and transferred to SPSS for analysis.

Results

Thirty-nine players qualified for the study. Thirty players were needed for an effect size of .5 and a power of 77%. To have an effect size of 0.5 and a power of 84%, 35 tennis players were needed. Subject demographic information can be seen in Table 1.

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Table 1.

Subject demographics (n = 39).

Gender	Number of subjects	Hand dominance	Height cm Mean	SD	Weight kg Mean	SD	Age yrs	SD
Females	17	R = 17 (100%)	168.1	8.0	64.0	9.6	21.1 yrs	1.31
Males	22	R = 21 (95.5%)L = 1 (4.5%)	182.8	5.8	80.1	9.0	20.8 yrs	2.2

L: left; R: right; SD: standard deviation; Yrs: years.

The mean of the baseline service velocities at 100% effort was significantly different for males and females. Therefore, separate analyses were done by gender. Both males’ and females’ perceived velocities were significantly greater (p < .05) than the athletes’ computed velocities at 50% and 75%, respectively. Means and standard deviations for actual and perceived velocities for both male and females can be seen in Table 2.

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Table 2.

Mean (standard deviation) for actual and perceived velocities of male and female collegiate tennis players.

Gender	Computed 75% velocity*	Perceived 75% velocity	Computed 50% velocity*	Perceived 50% velocity
Female (n = 17)	64.92a	78.25 (7.02)a	43.28b	68.71 (6.92)b
Male (n = 22)	75.97a	83.25 (9.42)a	50.05b	72.84 (9.51)b

*Computed from mean of 100% velocity assumed to be 100% of perceived velocity.

^a,bSignificant difference between actual and perceived velocity ≤ 0.05.

Discussion

Forty one players volunteered to participate; 39 met the requirements. Two players did not meet requirements due to recent injury or treatment of shoulder pain.

The present study utilized healthy, non injured college level competitive tennis players who reported no discomfort during or after participation. In a population of injured tennis players, serving at significantly higher intensities/velocities than what they perceive to be a certain percent of effort may result in lost playing time due to re-injury, exacerbation of prior injury, or compromise of a surgical repair. These could have significant consequences for returning players. Lost time due to re-exacerbation or a failed surgery could cause not only a loss of match play, but also in some instances, the remainder of a collegiate season.

Recommendations from physicians, physical therapists, athletic trainers and coaches are to follow interval programs rigidly, to minimize the risk of re-injury. It is not uncommon for highly competitive individuals to increase intensity too soon, which may increase the risk of re-injury and a retarding of the rehabilitation process. ⁶ The results of this study indicate that a tennis player attempting to hit at 50% effort will more than likely hit at 75% of their maximal effort. It is presently unknown what effort of intensity is needed for the player to hit 50% of their maximal velocity. This study also shows that guidance is needed for collegiate level tennis players during the performance of the interval tennis rehabilitation program, as overestimation of effort producing higher ball velocities which has the potential to compromise rehabilitation.

Future research is needed to identify optimal effort levels for application of hitting and serving in interval tennis rehabilitation programs. Research that measures direct angular velocities of upper extremity body segments (shoulder and elbow) as a kinetic chain along with the trunk and hips in response to different perceived levels of exertion during the tennis serve may be the best way to perform a more specific future study. This would provide the ability to determine if the effort of the upper extremity remained at the desired level while the speed of the ball may be higher than expected due to hip and trunk rotation.

The present study is not without limitations. Only young, healthy, competitive college tennis players were evaluated. These results may be different for those recovering from injury. Therefore, caution should be taken when applying these results to other populations.

It was noted that during data collection, some players commented on difficulties maintaining a “first serve” effort during the 75% and 50% partial effort serves. When asked to decrease and hit at partial effort, some players responded that they naturally switched to a “second serve” and put more spin on the ball in an attempt to decrease the ball’s velocity. The present data were collected as a clinical study at tennis facilities with only a radar gun to measure velocities. Radar guns are common at tennis facilities to determine serve velocity. The study was designed to be replicated easily by tennis coaches, and researchers alike. We realize that velocity is just one potential indicator of an athlete’s ability to serve a tennis ball at perceived efforts and examining kinematics during serving may be a better indicator of the demands of serving at a certain percentage of perceived effort. More sophisticated kinetic data-capture devices to determine elbow extension or shoulder, trunk and hip rotation velocity may produce different findings. Similar findings as the present study have been reported in male baseball pitchers who consistently threw at velocities significantly higher than their perceived effort. ⁶ Future studies may include use of these types of devices to compare with our results. Follow up studies might allow tennis players to hit all serves without the need of concern of accuracy, as the need for accuracy might have limited the participants ability to serve at the requested velocity. As the present study only tested healthy collegiate level tennis players, generalizations to other levels of players or injured players should be done with caution. A healthy population was utilized as it was felt that asking injured players to hit at 100% effort, which may create more injury or prolong return to tennis would not be ethical.

Conclusion

Both male and female advanced level collegiate tennis players consistently and significantly overestimated their serve velocity when asked to hit tennis serves at 75% and 50% of maximal effort in this investigation. Serving at these levels early following musculoskeletal shoulder or elbow injury may increase the risk of re-injury or create a lack of therapeutic progression. Information from this study provides clinicians, coaches, athletic trainers, and strength and conditioning professionals with guidance for the progression of advanced tennis players during an interval-based tennis rehabilitation program.