Evaluating tennis player performance based on different types of grip strength

Abstract

Grip strength is the concrete manifestation of the hand-wrist-forearm segment that links the body and the instrument at the end of the kinetic chain in events of handheld equipment. It plays a crucial role as a “gatekeeper” in transmission, control and coordination of force. A review of the literatures about the relationship between grip strength and tennis sports performance is provided to clarify the potential functions of grip strength within the kinetic chain, demonstrate more details of the performance of the hand-wrist-forearm segment in events of handheld implements, and enrich the theory of the kinetic chain. The “grip”, “grip strength”, “dynamic grip strength”, “static grip strength”, “grip endurance” and “tennis” as keywords are searched in internationally recognized databases (Web of Science, PubMed, Google Scholar, Scopus, and ProQuest, etc.). Relevant literatures are collected, screened, read, organized and analyzed. Here, grip strength is classified into specific and non-specific categories based on the differences in testing environment. By summarizing the functions of specific and non-specific grip strength, it is found that both kinds of grip strengths have significant intrinsic value. This review provides a new perspective for understanding the performance of the end of the kinetic chain and has great significance for enriching the theory of the kinetic chain.

Introduction

The evaluation of athletic performance has progressively shifted from macroscopic to microcosmic perspective, thereby providing more detailed diagnostics and feedback. Similarly, the biomechanical assessment of tennis players is conducted by macroscopic and microscopic investigations in field of the entire body, composite segments and individual segments [1–6]. In this approach, all states of the athlete’s kinetic chain are captured, the changes in the entire chain affected by single segment are also emphasized [2, 7–14]. Grip strength is one of the functional manifestations of the wrist and forearm [15–17]. It is also a part of the “resultant force” in the kinetic chain of tennis player’s stroke [18–21]. In addition, grip strength is the force generated by athletes through lower limb drive and rotation and then transmitted through the trunk and shoulders. Thus, grip strength is located at the terminal segment of the entire kinetic chain [22–26]. The wrist and forearm serve as critical nodes for tennis players, enabling grip strength and racket control. The function of grip strength as a “gateway mechanism” within the kinetic chain plays a vital role in the transmission, regulation and release of energy throughout the movement system [27, 28]. On the one hand, sports injury of single element within the kinetic chain can lead to alterations throughout the entire chain, resulting in suboptimal biomechanical adaptations [11, 29–33]. These sports injury may also increase the load on other joints in the movement sequence and trigger compensation mechanisms, thereby resulting in potential injuries [2, 11, 30, 32–36]. On the other hand, the high-intensity grip of the racket and the damping effect of grip strength in shock absorption along the upper limb represent two of the three primary injury mechanisms associated with “tennis elbow” [9, 37–40].

In previous literatures, grip strength was categorized into two forms, power grip and precision grip [1, 41]. For instance, power grip involves holding heavy barbells, grasping solid shot puts and so on. Precision grip includes pinching with the fingertips or the pads of the fingers, also known as hand grasping control. However, sports performance is not effectively demonstrated by this classification method in real sports scenarios.

For tennis players, grip strength is sustained during strokes and power grip corresponds to the hitting process [12, 42–46]. However, there is also a slight control grip between strokes, which is the overall contribution of the hand. This slight control grip is different from precision grip generated by the fingers and palm [47]. Therefore, grip strength is differentiated based on the testing environment in this review to analyze and discuss certain relationships between different types of grip strength clearly. In terms of presenting and evaluating the relationship between the performance of tennis player and grip strength, this strategy is superior to the previous classification method [11, 48–50].

Grip strength measured by a dynamometer to assess athlete’s upper-body strength is defined as non-specific grip strength (NSGS). Correspondingly, grip strength detected in specific hand areas of tennis players during strokes using devices (e.g., sensors [51, 52]) is referred to as specific grip strength (SGS). Obviously, NSGS and SGS are closely related. For example, Lucki et al. recorded grip strength generated by 4 male tennis players during serve using a force dynamometer attached to the handle of tennis rackets. The maximum grip force (150–250 N) produced during the serve was generally 31%-44% of the maximum grip strength of tennis player [44]. Clearly, NSGS is foundation for SGS.

The transformation from NSGS to SGS is fundamentally a complex process involving the optimization of neuromuscular regulation, the integration of multi-muscle coordination and the conversion of energy transfer modes [53–56]. Specifically, the nervous system is required to shift from a pattern of maximal voluntary contraction to the fine-tuned, temporally sequenced recruitment and reflex modulation of forearm and hand muscles [57].

Simultaneously, the function of grip strength is integrated into the full-body kinetic chain, and relies on the synergistic effect of intrinsic and extrinsic hand muscles to achieve efficient force transmission and precise control [58, 59]. Furthermore, the force production mode needs to adapt from an isometric contraction to utilizing the elastic energy of the stretch-shortening cycle and generating three-dimensional force vectors with specific directional and time-variant characteristics [60]. The fundamental distinction between NSGS as a “foundational potential” and SGS as a “functional performance” is elucidated by this pathway, thereby providing a solid theoretical basis for this classification and offering direct guidance for sport-specific training aimed at enhancing the efficiency of this transformation [61–63].

Given the application and foreseeable potential value of grip strength in evaluating tennis athletes’ performance, this study aims to provide a comprehensive summary of function of NSGS and SGS in evaluating tennis player performance. To our knowledge, this is the first review specifically focusing on grip strength in the context of tennis. In this review, the results and viewpoints of existing studies systematically are presented, additional research perspectives are elaborated, and valuable a reference for using grip strength are provided to evaluate sports performance in many handheld-implement events.

Method

The process of literature search and screening

The “grip”, “grip strength”, “dynamic grip strength”, “static grip strength”, “grip endurance” and “tennis” as keywords were searched in internationally recognized databases (Web of Science, PubMed, Google Scholar, Scopus, and ProQuest, etc.). Relevant literatures were collected, screened, read, organized, and analyzed and the representative literatures were selected for direct discussion and citation, as shown in Fig. 1. The function of NSGS and SGS in evaluating tennis player performance were summarized and discussed.

Fig. 1.

Requirements and process for text the literature selection

Characteristics of the literature collection

During the literature collection and screening processes, the collected literature has the following characteristics: (i) Research literatures on tennis players’ grip strength were distributed across NSGS and SGS fields. Although their testing methods and functional orientations were different, the function and performance of the upper limb were reflected, especially the hand-wrist-forearm system for athletes (Fig. 2); (ii) In research papers, NSGS is often used as one of the indicators to evaluate the athletic performance of tennis players, rather than being studied entirely around it; (iii) In relevant studies, although SGS can be served as the focus of the entire paper, the instruments and indicators are different and the number of subjects is often relatively small; (iv) The distribution of literature is uneven, with more literature focusing on NSGS and less on SGS. And the distribution of literature on their respective subtopics is also uneven. For instance, many studies focused on the diagnosis and rehabilitation of upper limb injuries in tennis players. However, it was only one of the sub-themes rather than the central focus in most cases [6, 17, 64, 65].

Fig. 2.

The functional connection between NSGS and SGS

Supplementary explanation for method

Due to the aforementioned reasons, although a substantial number of research papers were initially collected (312 documents), they were not analyzed and cited each cases individually during the specific analysis. Instead, the representative studies were selected and discussed. Literatures screening was not strictly quantified as in systematic reviews, but rather conducted through more subjective methods. Nevertheless, several measures were implemented to enhance rigor, such as adopting independent screening and cross‑verification by multiple reviewers. Titles, abstracts and full texts were independently searched and selected by two reviewers. The search results were analyzed and compared, and any discrepancies were resolved by a third arbitrator. Although this approach has certain limitations, diverse subtopics is also achieved for improving content‑rich and comprehensive opinions in this review. For example, multiple themes (physical qualities, technical performance, sports fatigue, and sports injury, etc.) are articulated in this study. For example, the opinion evaluated for tennis player performance based on different types of grip strength comprehensively is explained from multiple themes mentioned above. Therefore, the representative literatures across these themes are particularly synthesized and cited. Moreover, due to the aforementioned reasons, a systematic review or Meta-analysis are unable to be directly conducted and a narrative review format is opted, which represented a methodological limitation in this review study. Nevertheless, the immense value inherent in the research presented is not shaken by these limitations. This review is a highly significant study for analyzing comprehensively the different types of grip strength (as the terminal segment of the kinetic chain) of tennis players.

Result and discussion

Grip strength assessment of physical qualities

NSGS, as a physical fitness indicator, is one of the metrics to assess tennis player performance [53, 54]. Its primary role is the assessment of upper-body strength in tennis players [54, 66–72]. Researches on NSGS mainly focus on investigating whether there are differences in NSGS among grades [44], age [42], gender [73] and the dominant or the non-dominant hands [74, 75] for tennis players, as shown in Table 1.

Table 1.

Detailed research on differences in NSGS among tennis players (representative study)

Study	Participants	Indicators	Sensor number	Result
Lucki and Nicolay, 2007 [44]	N = 83 participants, Female (42, aged 19-24yrs): 24 tennis players (aged 19-24yrs), height 164.8 ± 8.16 cm, weight 61.1 ± 7.48 kg; and 18 college students, height 161.6 ± 6.92 cm, weight 58.0 ± 5.07 kg. Male (41, aged 19-24yrs): Tennis players height 180.7 ± 7.48 cm and weight 76.8 ± 7.36 kg, and college students’ height 177.0 ± 4.23 cm and weight 75.6 ± 11.50 kg.	Maximum grip strength (MGS) 30-repetition intermittent test; 30-second sustained test	3	Tennis playersd, Tennis playerd Female(grade)d
Kramer and Knudson 1992 [79]	N = 16 participants, 16 players from two nationally ranked junior college tennis teams. 8 females (aged 18.9 ± 0.6yrs and weight 59.9 ± 8.6 kg) and 8 males (aged 20.3 ± 1.8yrs and weight 71.7 ± 7.2 kg)	30 MGS tests	30	Correlations between maximum voluntary contraction (MVC) and number for males and females (0.38 and 0.53).
Ulbricht et al., 2016 [53]	N = 912 participants, Male (N = 546; mean aged 13.14 ± 1.39yrs) and female (N = 366; mean aged 13.06 ± 1.29yrs).	MGS	2	U12b, U12a U16a
Pereira et al., 2011 [42]	N = 182 participants, including 137 male participants, and 45 female participants (aged 8-18yrs) were divided into 12, 14, 16, and 18 aged groups.	MGS	Not reported	Male (14–18)c Female players (18-)c
Fett, Ulbricht and Ferrauti 2020 [73]	N = 1019 participants, junior team tennis players from the German Tennis Federation (625 males and 394 females; aged range 9.4-17.9yrs).	MGS	2	Male tennis players U14d, U16d, and U18d Female players U12d.
Pion et al., 2010 [75]	N = 26 participants, expert group (height 176.8 ± 8.2 cm and weight 64.4 ± 7.6 kg), and the amateur group (height 177.4 ± 7.3 cm and weight 65.5 ± 6.7 kg).	MGS	Not reported	Femalea.
Armstrong and Oldham 1999 [77]	N = 88 participants, junior tennis players (44 males and 44 females, aged 12.4 ± 1.9yrs).	MGS	3	10–12 ageb,d U13-16 ageb U13-16 femalesd.
Sogut et al., 2019 [80]	N = 61 participants, female tennis players from Turkey, aged 10.4-13.2yrs.	MGS	2	Graded; Dominant and non-dominant sidec
Myburgh et al., 2016 [54]	N = 88 participants, British junior tennis players (44 males and 44 females), aged 12.4 ± 1.9yrs	MGS	3	U13-16 Graded; U13-16 Dominant and non-dominant sidec
Ducher et al., 2005 [81]	N = 52 participants, 52 tennis players (aged 24.2 ± 5.8yrs, with 16.2 ± 6.1yrs of training experience).	MGS	2	Maled Femaled
Sanchez-Pay et al., 2021 [82]	N = 15 participants, fifteen adult male tennis players (aged: 19.66 ± 1.63yrs): National (N = 8, height 176 ± 12 cm and weight 72.6 ± 11.4 kg), professional (N = 8, height 181 ± 5 cm and weight 77.8 ± 7.3 kg).	MGS	2	Grade

^aSignificant differences between levels, ^bsignificant differences between genders, ^csignificant differences between ages, ^dsignificant differences between dominant and non-dominant sides

Differences in training grades

The related previous studies of this area paid attention to whether there were differences in NSGS among tennis players of different levels. Ulbricht et al. suggested that there were horizontal differences in grades between male U12, female U12 and U16 players [53]. However, Pion et al. reached different conclusions and stated that no significant difference was found among male players, but a significant difference was found among female players [75]. Jung et al. pointed out that a significant difference was in right hand NSGS between elite female tennis players and non-elite female tennis players [76]. In addition, other researchers found that the differences between the same-side hands of untrained participants were relatively small [77, 78].

Differences between the dominant and non-dominant sides of arm

Due to the significant difference in using the dominant and the non-dominant sides by tennis players, assessment of the differences in NSGS between the two sides of arm was important [42]. Pereira et al. suggested that male athletes had higher NSGS values on the dominant side than on the non-dominant side starting from the age of 14. However, for females, non-specific asymmetry did not occur until the age of 18 [42]. Elliott pointed out that the average maximum grip strength on the dominant side of tennis players (51.19 kg) was significantly higher than that on the non-dominant side (45.03 kg) [74]. Other researchers also believed that tennis players had significantly greater NSGS on the dominant side compared with the non-dominant side [73, 77, 80, 81]. However, no difference was also obtained by some researchers in NSGS on both sides. Pion et al. suggested that there was no difference in NSGS on the dominant side among male tennis players of different grades [75], and Elliott and colleagues proposed that no significant difference was in the NSGS between tennis players and normal individuals on both arms [74].

Differences in age

As tennis players age, their NSGS increased gradually, which was beneficial for their ability to maintain consistent, accurate and powerful hitting abilities [83]. Under this trend, NSGS was also employed in some extent to predict tennis performance at each developmental stage [84]. From the analysis of age groups, significant differences were observed in NSGS between national and regional athletes in the U12. A significant difference was also found in grip strength among U12 female athletes selected from different countries and regions. Moreover, this phenomenon also existed among U16 athletes and older athletes had greater NSGS [80]. Therefore, the biological maturity had a positive impact on the NSGS for tennis players [54].

Differences between genders

Pereira et al. pointed out that NSGS increased significantly at the age of 11 for male tennis players and at the age of 10 for female tennis players [42[. NSGS of university-level tennis players (24 females, 24 males) and non-athlete college students (18 females, 17 males) were measured in Lucki and Nicolay’ research. Their results showed that female tennis players produced 25% more force on their dominant side than non-dominant side, while the difference between the two sides of male tennis players was 18% [44]. However, the ratio of the dominant side strength of female athletes to the non-dominant side was 0.97–1.71, and for male athletes the ratio was 0.88–1.51. In comparison, the ratios for non-athlete females and males were 0.78–1.39 and 0.82–1.54, respectively.

Differences in grip endurance

Lucki and Nicolay believed that compared to MGS there were no significant differences in dynamic endurance after 30 repetitions between tennis athlete and amateur, males and females, or any group of limbs [44]. It was worth noting that highly repetitive effort was essential for tennis players. No significant differences between limbs of tennis players were also found in similar studies about shoulder strength endurance [85, 86]. Lucki and Nicolay suggested that although grip strength decreased in all groups during the 30 repetitions, the level of the fatigue produced might not sufficient for causing significant statistical differences between limbs or groups [44]. Kramer and Knudson found that NSGS did not decrease after 30 repetitions with a 25 s rest interval between each repetition [79]. The grip endurance showed a minor change because the grip force exerted during tennis play remains submaximal. Players typically had a moderate level of effort rather than maximum voluntary contraction (MVC). Furthermore, athletes executed hundreds of strokes in each training session or competition, which further explained the observed endurance pattern [87]. Therefore, the result of 30 repetitions of NSGS test showed no decrease.

The observed discrepancies in related literatures are attributable to multiple factors, with the most obvious being that the measurement of NSGS is influenced by many variables [40, 67, 88–93]. The wrist position and the activation of the forearm extensor muscles are significant factors affecting grip strength [94, 95]. The wrist extension training leads to an increase in grip strength and alters the electromyographic activation balance between the forearm flexor and extensor muscles during gripping [94]. In addition, there are several factors that affect NSGS, such as gender [96], age [54, 88] occupation and training [45, 97], height, forearm circumference, wrist-phalangeal length, humeral width, and hand lean mass and bone mineral content. These are limiting factors that affect prepubescent [98]. It is also essential to consider the effects of lean body mass, bone area, bone mineral content [81], assessment time, wrist joint and body position [99, 100], sincerity of effort [101], anthropometric measurement characteristics [102, 103], and grip span on NSGS. Previous studies also reported a similar increase in MGS when the verbal encouragement was provided [104, 105].

Grip strength assessment of endurance: sports fatigue

Sports fatigue is divided into overall fatigue and local fatigue. NSGS is also used to assess overall and local fatigue [79, 106–108]. For example, NSGS is utilized to evaluate simultaneously muscle fatigue in the extensor and flexor muscle groups of the wrist, as it has been proven to activate both muscle groups [109–112]. And the fatigue level and risk of developing tennis elbow (lateral epicondylitis) are also evaluated by estimating the wrist and finger muscle capabilities of tennis players [89, 113–115]. To assess potential fatigue, the changes in NSGS of two groups of junior college tennis players over 30 trials were recorded in Kramer and Knudson’ study. 30 maximum grip strength tests with a 25 s rest between each trial were performed by 8 males and 8 females, respectively. A significant positive correlation was observed between the NSGS and the number of trials for both male and female athletes (0.38 and 0.53, respectively). In practical terms, NSGS of tennis players did not change during the 30 trials [79].

Grip strength of tennis players is used with hundreds of times when hitting the ball in a day, and the repeating 30 maximum grip strength (MGS) tests are not sufficient to trigger fatigue. There are limitations to using the fewer NSGS tests to determine whether tennis players experience fatigue in the hand-wrist-forearm area [116]. Since NSGS decreases after exercise but returns to baseline after a period of rest, there is a reorganization of motor unit strategies (recruiting more motor units). However, several studies on local fatigue are worth as reference. For example, Pitcher et al. induced that forearm muscle fatigue was achieved by requiring participants to maintain a grip strength of 80% of MVC on a dynamometer during a 5 s effort/5 s rest cycle, repeated 36 times [117, 118]. Forearm fatigue was considered to be reached when the MVC decreased by at least 20% of the MVC (corresponding to the fatigue induced by tennis matches) [48, 119].

Furthermore, it is noted that local fatigue in the wrist and forearm of tennis players may be caused by the prolonged exposure to vibration in this region [74, 120–122]. SGS plays a crucial role in the damping effect within the wrist-forearm complex [123]. Features of SGS (onset and offset, duration, magnitude, and rhythm, etc.) can be employed by tennis players to directly control the shock absorption effect of the wrist and forearm [121, 124–135]. Therefore, conducting in-depth research on the SGS usage patterns of elite athletes can provide valuable insights and guidance for most athletes to reduce fatigue in their wrists and forearms.

Grip strength assessment skills

Assessment of tennis players skill using NSGS

The NSGS assessment of tennis players’ skill is primarily reflected through the correlation between NSGS and various performance metrics such as ball speed during hitting [73], international and domestic ranks or grades [136, 137]. On the one hand, Roetert suggested that the relationship between the tennis rank of junior male players and their NSGS was negligible 136. Pugh et al. showed that there was no significant relationship among the NSGS variables and ball speed [138]. Pion et al. argued that NSGS did not serve as a distinguishing factor between elite and sub-elite youth athletes. This conclusion was attribute to the observed similarity in weight and muscle mass between these two groups [53, 75, 138]. On the other hand, Ulbricht et al. demonstrated that elite tennis players had significantly higher NSGS and muscle mass than sub-elite athletes [53]. Girard and Millet pointed out that tennis rank was closely related to NSGS on the dominant side (correlation coefficient (r) = 0.67–0.80) [137], while grip strength on the non-dominant side was not related to athlete’s performance rank [53, 137].

In addition, the ball speed of serve was highly correlated with the NSGS on the dominant side [53, 83]. Turner and colleagues showed that 83.76% of the variation in groundstroke speed and accuracy index was also explained by the correlation between the NSGS strength of the dominant hand and rank [60]. Fett et al. considered that NSGS was an important indicator for assessment the upper body strength of tennis players, and the correlation between NSGS and serve speed was moderate with r = 0.43–0.59 for male and r = 0.27–0.37 for female, respectively [73]. Similarly, Sogut and coworkers indicated a significant correlation (r = 0.71) between the NSGS of young female tennis players on the dominant side and serve speed (p < 0.05) [139].

For the assessment of tennis player skill levels using NSGS, different results have been obtained by many researchers. After reviewing and analyzing relevant literatures, it is found that the grade, age, and gender of the subjects in researchers’ experiments are different, resulting in some discrepancies [140–145].

Assessment of tennis players skills using SGS

The specificity of tennis players’ SGS is evident in various aspects. In terms of scenario, as previously mentioned, the current detection of the SGS in tennis player hands refers to the changes in force at sensitive areas of hand in real stroke scenarios (computer simulations). In terms of muscle, SGS includes the transitional extension of the forearm extensor and followed by the contraction of the flexor muscles. The hand muscles exert the primary force when relaxed, and the forearm muscles exert the main force when hitting [43, 146–148]. The diagnosis of SGS is greatly improved by analyzing and interpreting the release characteristics of SGS (such as timing and peak grip force time) using precise pressure and force sensors during dynamic movements of specific actions, thereby optimizing exercise performance. The principle is that the timing and sequence of applying force with the hand to a tool (racket, stick, bat, rod, etc.) or object (e.g. a ball) in various stages of specific movement patterns are more crucial than the magnitude of the force applied [149, 150]. Therefore, it can be considered that SGS plays a “gatekeeper” role in the kinetic chain [64].

Current researches suggest that the dynamic behavior of a racket is not only determined by its mechanical properties but also highly dependent on the player’s SGS [47]. Moreover, athletes are able to fine-tune their SGS based on their stroke performance [151]. During the stroke, grip force on the handle is continuously adjusted by athletes in response to muscle fatigue. In actual tennis matches, this grip force directly governs the dynamic behavior of the racket [152]. Rossi et al. examined the influence of racket handle size on tennis elbow conditions and found that athletes finally adjusted their grip force based on the handle size [48, 153]. These results indicate that grip force serves as a key mechanism in driving the interaction between the hand and the racket. Therefore, the mechanical connection between the hand and the racket is directly determined by SGS of tennis players.

Research distribution of skills

The release of SGS in various tennis skills, including forehand [15, 16, 47, 108, 154, 159, 160], backhand [49, 161], serve [44, 155, 156], and volley [150] have been investigated in previous studies. Researches of tennis techniques focus on forehand and serve mainly, especially forehand, as shown in Table 2, because backhand is divided into two types, one-handed backhand and two-handed backhand. The one-handed backhand is easier to quantify for analysis. In contrast, the two-handed backhand shows variation in the way athletes use their both hands. There is no clear distinction between the phenomenon of relying mainly on the right hand, left hand or both hands among these the two-handed backhand players. Moreover, most researches focus on power-based skills, such as serve and forehand. For instance, Yang et al. analyzed the pressure waveforms of forehand in players of different grades, focusing mainly on the time domain of the pressure waveform and its maximum peak [15]. Lucki and Nicolay were also very concerned about the peak of SGS during the serve of 4 expert players [44].

Table 2.

Assessment sports skills of tennis players using SGS (representative study)

Study	Sensor Material	Number	Position	Indicator	Participants	Skills	Sensor calibration
Yang et al., 2023 [15]	Flexible piezoresistive pressure	5	Fingertips of 5 fingers	Peak value	N = 2 participants	forehand	Observe whether the pressure is linear through different stress tests
Rigozzi, Vio, and Poronnik,2023 [16]	Pressure sensor	1	Root of the index finger	Peak value	N = 40 participants, Expert group: 22, Aged 32.9 ± 10.6yrs, Height 180.6 ± 5.7 cm, Weight 81.6 ± 9.4 kg; Amateur group: 18, Aged 36.4 ± 12.8yrs, Height 178.5 ± 8.1 cm, Weight 78.2 ± 10.5 kg	forehand	Explain the stability of the sensor by citing references
Rigozzi et al., 2023 [154]	Pressure sensor	1	Root of the index finger	Peak value	N = 4 participants, 3 males and 1 female, Age 35.3 ± 8.5yrs, Height 172.5 ± 2.6 cm, Weight 77.0 ± 16.1 kg	forehand	Explain the stability of the sensor by citing references
Zhang et al., 2024[150]	Flexible piezoresistive pressure	5	Handle, N-type array	Peak value, Time domain and other 4 indicator	N = 20 participants, Expert Group 10, Height 176.8 ± 3.1 cm, Weight 66.3 ± 3.1 kg; Amateur Group, 10, Height 176.5 ± 4.4 cm, Weight 65.9 ± 3.0 kg; Age of all 20 participants 18-22yrs	forehand, backhand, serve, volley	Explain the stability of the sensor by citing references
Zhang et al., 2024and [28]	Flexible piezoresistive pressure	2	Root of the index finger	Peak value, time domain and other 4 indicator	N = 2 participants, 1 expert and 1 amateur, male	forehand, backhand, serve, volley	Explain the stability of the sensor by citing references
Lucki and Nicolay, 2007 [44]	Grip dynamometer	1	Handle	Peak value	N = 7 participants	serve	Label brand and place of origin
Knudson, 1991 [155]	Pressure sensor	2	Root of the index finger and the chin prominence	Peak value	N = 2 participants, 2 male NCAA players: Average aged 20.5yrs, Height 181 cm, Weight 72.6 kg	forehand	Label brand and place of origin
Knudson et al., 1989 [156]	Pressure sensor	2	Root of the index finger and the chin prominence	Peak value	N = 7 participants, 3 university and 4 professional tennis players	forehand	Label brand and place of origin
Hatze, 1976 [108]	Strain gauge	1	Root of the index finger	Peak value	N = 1 participant	forehand	Not reported
Hennig, 1992 [121]	Capacitive Pressure sensor	1	Handle	Peak value	N = 24 participants, Aged 32.9 ± 10.9yrs, Weight 75.3 ± 11.5 kg, Height 181.3 ± 8.4 cm	forehand backhand	Not reported
Christensen et al., 2016 [157]	Tekscan9811E	1	Handle	Peak value	N = 1 participant, 1 male, Aged 24yrs, Weight 63 kg, Height 183 cm	forehand	Label brand and place of origin
Rossi et al., 2014[153]	TekScan3200	1	Handle	Peak value and impulse	N = 8 participants, 8 male, Aged 21 ± 1yrs, Height 179 ± 7 cm, Weight 71 ± 9 kg, Arm Length 19.1 ± 0.5 cm	forehand	Label brand and place of origin
Xiao et al., 2025 [158]	Flexible piezoresistive pressure	3	Handle	Peak value average hand grip force	N = 30 participants, male: 15 nationally second-level athletes; aged 18.0 ± 1.7yrs, Height 177.1 ± 1.4 cm, Weight 67.3 ± 4.1 kg; 15 beginners aged 19.0 ± 1.1 yrs, Height 175.8 ± 3.1 cm, Weight 67.9 ± 2.4 kg	forehand, backhand, serve, volley	Explain the stability of the sensor by citing references

Additionally, there was few studies about the characteristic’s investigation of grip force release during skills such as volley, smashes, drop shots and slices in current researches. The conventional research perspectives of kinetics, kinematics and electromyography were mainly concerned to explore of these techniques for tennis players. And there was a scarcity of research literature for SGS [162]. The existed studies on the difference between standard volleys and drop volleys (drop shot volleys) lied in the differences in muscle relaxation of the wrist and elbow during impact moment. Current researches suggested that muscle activity for drop volleys with the forehand or backhand stroke style was lower than that of a standard volley. However, as the moment of impact approaches, muscle activity rises gradually instead of declining (relaxing) abruptly [163].

Although research on SGS in control-oriented techniques such as volleys and drop shots is limited, it also provides insight into the characteristics of SGS in these techniques and highlight differences compared to other strokes. Zhang et al.’s study involved continuous volleying techniques and placed volleys within the context of technical transitions [150]. The findings in this study revealed that compared to forehand, backhand, and serve techniques, elite athletes exhibited lower peak SGS values in volleying technique, coupled with high accuracy and well rhythm. In contrast, beginners showed smaller differences in peak grip strength between volleys and forehands, serves, or backhands, and demonstrated persistent SGS output between consecutive shots, indicating less proficient mastery of the volley technique. Furthermore, Xiao et al.’s study also examined grip force variations during volleys [158]. In the first and third scenarios of their experimental setup (involving movement and swing sequences), volleys were embedded within technical combinations, even though the scenarios were simulated swinging tasks without ball impact. Their study also increased task difficulty by placing athletes in the first and third scenarios within an alternating sequence of “power-oriented” and “control-oriented” techniques. Their results indicated similarly that athletes experienced lower difficulty than beginners in adapting grip force during technical transitions and movement-based swing changes, as reflected in their lower average and peak grip forces. In control-oriented tennis techniques, athletes were required to employ SGS with greater refinement. In real hitting scenarios, the contraction and relaxation of forearm and hand muscles were precisely controlled by tennis players with appropriate moments and durations through neuromuscular coordination to generate suitable grip force, thereby driving the racket to perform the expected action. Experimental research supports are provided by these two studies for understanding the differences of the use of SGS between control-oriented and power-oriented techniques in tennis, and offer more entry opinions for future research. Moreover, these experimental results can also be extended into the research of badminton and table tennis.

Research on indicators of SGS for assessment sports skills

SGS, as the end of the “kinematic chain” generated by tennis players during stroke, acts as a “gatekeeper”. Evaluating sports performance from a microeconomic perspective using the release patterns of SGS can provide researchers with more referable details. Certainly, the SGS curves produced within each stroke contain enormous information, such as the magnitude of the peak SGS [49]. The indicators used for peak including the sequence of the peak was related to the moment of the maximum value (Fig. 3a and 3c) [16, 44] time domain (Fig. 3a and 3d) [28, 156] and impact (Fig. 3e) [44, 156]. the maximum and average grip pressure (I_max and I_ave) curves were used by Xiao et al.’ study (Fig. 3f) [158]. To avoid the limitations of single channel data, a data vector consisting of the maximum values of 5 channels was used in Yang et. al ’ paper for evaluating the grip strength curve of tennis players (Fig. 3e) [15]. Some researchers not only quantified the grip strength change curves during the hitting, but also emphasized the use of grip strength between consecutive hits. And low values indicated that the well hand relaxation was maintained between consecutive hits by athletes (Fig. 3d) [28]. These indicators were relatively common, but assessing the skills proficiency of tennis players based on a single indicator is one-sided. Particularly, Zhang et al.’s study was very interesting, as 4 kinds of indicators to quantify was developed and SGS of tennis players was compared. Both the peak of SGS and the relationship between beginning (or end) of the movement and emergence (or disappearance) of SGS were also addressed. As shown in (Fig. 3b), the indicators included T₁ (s): the time difference between the time of grip strength occurrence and the start time of the backswing; T₂ (s): the time difference between the time at grip pressure disappearance and the end time of the follow-through; T₃ (s): the consecutive time is from the appearance of grip strength to its disappearance; and Current peak I (A): the maximum current value that occurs during the stroke process [28, 150]. In addition, the maximum grip pressure (I_max) and its correlation with grip strength impulse were also used by Rossi et. al (Fig. 3i and 3j) [153, 155]. And an intriguing direction was showed in their approach for future assessments in the field.

Fig. 3.

a The SGS change curve during forehand stroke indicators [16]. b The change curve of pressure-current values during a single stroke, indicators: T₁, T₂, T₃, and I [150]. c The MGS during the serving technique [44]. d Changes in the forehand grip strength curve and its maximum value [156]. e The data vector composed of the maximum values of the five channel pressure current during the hitting process of various techniques [15]. f The maximum and average grip pressure (I_max and I_ave) curves during multi-directional swing and alternating forehand and backhand strokes [158]. g Extreme grip strength for forehand hitting [48]. h The grip strength between consecutive shots [28]. i Different techniques for grip strength, impulse, and maximum value [153]. j during forehand hitting process, grip strength, impulse, and maximum value [155]

SGS release patterns of tennis players

Although the core elements of tennis players’ skill movements are consistent, there is currently a controversy over the consistency of SGS application patterns during strokes. Due to the fact that the racket relies on the grip of the player hand to attach it to the players kinetic chain, the dynamic behavior of the racket is highly dependent on SGS of the player [164]. Some researchers have found that athletes have unique SGS patterns throughout the entire stroke process [16, 48, 154]. King et al. believed that the mechanical coupling between the handle and the athlete’s body changed with each grip force change due to the constantly changing of grip force on the handle by the forearm muscles [49]. However, as shown in Figs. 3 and 4 some scholars argued that all same grade athletes exhibited similar grip strength levels during strokes [15, 150]. Athletes had similar rhythmic grip patterns in Knudson and White’s researches [155, 156]. The research data recorded at the bottom of the index finger demonstrated that the grip force during serve process was very consistent for each player. The coefficient of variation of the peak grip force was 5% or less during serve, which was usually smaller than the coefficient of variation of serve speed. Interestingly, although there was a significant decrease in the speed of the second serve, no significant change was in SGS between the first and second serves. The consistency of net grip force detected by Knudson was contrasted with the high variability of post-impact (rather than pre-impact) force recorded by sensors placed at specific points on the hand [155, 156]. Although the force at specific points may be highly variable, the SGS applied to the racket appears to be a highly consistent parameter in the current research [3–6].

Fig. 4.

a Variation curves of strokes during technical transitions for elite tennis players versus amateurs [150]. b Elite athletes, intermediate athletes, and beginners continuous hitting pressure current value change curve [15]. c Changes in grip strength during the forehand stroke process for elite players versus amateurs, and its relationship with the time of relevant muscle activation [154]

Current study about the grip strength change patterns of tennis players has gradually deepened. According to the studies of single strokes, the focus has shifted to continuous strokes and technical transitions (Fig. 4a). Grip strength is utilized by elite athletes with greater precision, concentration and rhythm. Their hands are relatively relaxed between each stroke, and there is no the “clutter” in the pressure waveform [150]. Attention of the grip strength change patterns has also been extended to the phases between consecutive strokes. For example, some researchers aim to evaluate how players relax and utilize grip strength with precision and rhythm (Fig. 4b) [15]. Concurrently, the correlation between grip strength change and the activation patterns of forearm prime movers is also investigated (Fig. 4c) [154]. The K-nearest neighbors (KNN) algorithm is applied to a mixed sample of 4 kinds of tennis strokes (forehand, backhand, serve and volley). an Accuracy of 95.0% is achieved by professional athletes, while 84.6% is reached by amateur players (Fig. 5a and 5b) [28]. The accuracy of the training set and its corresponding confusion matrix are also evaluated (Fig. 5c and 5d).

Fig. 5.

a The accuracy and confusion matrix of the KNN training set for a mixed sample of 4 strokes (forehand, backhand, serve, and volley), with professional athletes achieving 95.0% and (b) amateur players achieving 84.6%. c The accuracy of the training set and its corresponding confusion matrix with professional athletes. d The accuracy of the training set and its corresponding confusion matrix with amateur players [28]

The impact of SGS for racket head and ball speed

Racket head and ball speed are commonly used indicators to assess the skills of tennis players [157, 165]. The relationship between SGS and ball speed was categorized into two situations in current studies. On the one hand, Lucki and Nicolay suggested that the degree of SGS applied was unrelated to the speed and placement of serves [44]. Similarly, Watanabe and colleagues demonstrated that SGS was independent of the post-impact ball speed for any given impact velocity [166]. Liu pointed out that SGS did not affect the rebound speed, and the recovery coefficient between the tennis ball and racket had a greater impact on the rebound speed [167]. Grabiner and co-works suggested that variations in grip firmness did not lead to a significant difference in rebound ball speed [122]. However, Grabiner and co-works’ study also found that gripping the racket tightly after a ball impact had a potential positive impact on racket control. Hennig also supported that the speed of the outgoing ball was not affected by the magnitude of the grip force [168].

On the other hand, many researchers consider that SGS can directly affect racket head speed and ball speed. Elliot studied the impact of grip strength on ball speed and reactive force after impact, but contrary to Watanabe. And the experimental results indicated that an increase in SGS led to an increase in reactive force and rebound speed, especially in off-center impacts [107]. Chadefaux et al. found that the dynamic behavior of the racket was highly dependent on the grip strength of player [164]. Hatze indicated that a tight grip increased the impulse on the ball, thus increasing the power and speed of the hitting [108]. In Christensen et al.’ study, an elite male tennis player was recruited, and firm or normal grip conditions were chosen in the laboratory environment [157]. Each grip condition involved 50 forehand topspin shots and the ball was stroked after bounce. The point of impact was achieved as consistently as possible. The results showed that compared to the normal grip condition, the firm grip condition led to a significant (p < 0.001) increase in the average speed of the racket head. And the normal grip condition resulted in a significant (p < 0.001) increase in the average racket head speed for grip size 2 compared to grip size 4. This study is the first time to quantified the kinematic contribution of angular velocity of an elite male tennis player regarding grip strength and its changes during performing topspin forehand [157]. Choppin et al. found that the angular deviation for all impact positions along the racket’s transverse axis was reduced by applying a torque about the handle [169]. In a standard forehand shot, both the flight time and the trajectory angle of the ball after impact were reduced by a firm grip. These results suggested that employing a firm grip were beneficial during competitive play.

The conclusion of the above studies is that SGS does not affect ball speed or racket head speed. Grip is only a small part of the large kinematic chain of coordinated forces and movements that occur during a serve [170–172]. Kibler offered the hip and trunk together produced up to 54% of the force, while the shoulder, elbow, and wrist only produced 25% of the force with the forearm contributing about 5% during a serve [173]. Furthermore, the ground reaction force generated through the extension and propulsion of the lower limbs serves as a crucial energy source for producing ball speed during a tennis stroke. Consequently, the generation of ball speed is caused by the integrated contribution of lower‑limb drive, force transmission through the hips, trunk, and shoulders, and the supplementary input from the upper limbs and hands [2, 10, 30, 50, 153]. Therefore, it is reasonable that grip strength has no effect on ball speed. However, some researchers conclude that there is another reason for the correlation between SGS and ball speed. In sports, the timing and sequence of applying force with the hand to a tool (e.g. racket, stick, club and shaft) or object (such as a ball) are more important than the magnitude of the force applied [48, 50, 146, 153, 174–177]. The contradiction between these two perspectives may stem from their distinct analytical focuses. The former argument posits no significant effect based on the extreme values of SGS. And the latter conclusion is likely drawn from the timing sequence of peak force relative to the moment of ball impact. Regarding the relationship between the SGS and ball speed and racket head speed, Knudson offered a unique viewpoint. And Knudson’s study showed that grip strength had a negligible effect on the speed of hitting the center ball, while excessive gripping actually limited the movement and had a negative impact on ball speed [178].

Research on the effects of SGS on racket head speed and ball speed has produced contradictory findings. These discrepancies are mainly attributed to methodological differences, which fall into 4 categories [43, 179]. Firstly, different observations regarding the correlation between SGS and speed indicators are caused by variations in subjects’ characteristics such as motor skill level and physiological traits [82, 180]. Secondly, the lack of unified standards for measuring equipment, indicators, and grip strength definitions has compromised comparability between different studies [181, 182]. Thirdly, the controlled laboratory settings and isolated movement tasks fail to replicate real-match conditions, and there are inconsistencies in the task design [64, 183, 184]. Fourthly, the role of SGS depends on the biomechanical context of hitting and it acts as a “terminal regulator” with its effects varying according to force transmission efficiency and hitting scenarios [179]. Essentially, the context-dependent nature of SGS is highlighted by these contradictions. Standardized measurement schemes, stratify subjects based on skill levels, and design tasks with high ecological validity should be adopted in future researches to clarify whether, when, and how SGS has a substantial impact on speed indicators in tennis.

Peak value of SGS and the impact moment of ball

The relationship between the peak value of SGS and the moment of ball impact is an intriguing field. Coaches and athletes are very concerned about this relationship. But this is a challenging detection that requires extremely high precision in the detection technique [156]. However, there is also controversy over the chronological relationship between the peak value of SGS and the moment of impact. Some researchers argued that experienced athletes gripped the racket tightest during the acceleration phase (exceeding 96% MVC), while amateur athletes gripped the racket tightest after impact (exceeding 93% MVC) [16, 154]. From the perspective of the whole-body coordination mechanisms, the influence of other segments in the kinetic chain cannot be overlooked [60, 185, 186]. The performance of a local segment within the kinetic chain is also affected by other segments [36, 187]. For example, the driving role of the lower limbs and the force transmission and stabilization function can also affect the use of grip strength by athletes and beginners [188]. Hennig et al. compared the grip strength of professional and recreational athletes during forehand strokes [121]. Their results showed that professional athletes released their peak grip force significantly earlier than recreational athletes before impact. Additionally, professionals experienced significantly lower peak acceleration loads at the wrist. The results of Rigozzi,, and colleagues’ study were contrary to these findings, indicating no significant differences between experienced and recreational players [16]. Similarly, Lucki and Nicolay believed that there were no significant differences in grip strength around the moment of impact between experienced athletes and amateur athletes [44]. There was uncertainty in the research results regarding the moment of impact in Schnabel and Hennig’ study. And the speed and rotation of ball as well as the sample size were not recorded in their results.

The aforementioned research controversies can be attributed to the following two reasons. Firstly, there is a lack of large-sample and long-term evaluation. The conclusions drawn from the above studies may be influenced by the limited sample of shots analyzed in each instance. The limited sample size is not sufficient to clearly reveal the differences in performance amplitude. Furthermore, the physical demands of actual tennis matches are not accurately represented in the controlled conditions. The potential impact of fatigue is not taken into account in these studies. However, the effect of fatigue is considered significant for performance, as grip strength capacity is reduced by 20% [119, 152, 153], thereby decreasing skills stability [189]. The precision of the detection techniques is not yet adequate. According to Table 1, the detection components (sensors) used for detecting SGS in tennis players’ hands are mostly rigid or directly modified with grip dynamometers on the racket handle. And the frequency of data collection has not yet reached the interval between the moment of impact and the peak grip force of tennis players.

Grip strength and the diagnosis of the tennis elbow

Although sports injuries are not performance metrics for tennis player performance, but their occurrence affects the outcome of an athlete performance and is also another manifestation of athletic performance [190–192]. Grip strength is often used as a diagnostic tool for the incidence and recovery status of disease such as the tennis elbow (lateral epicondylitis) and the golfer elbow (internal epicondylitis) [190, 193–195]. In addition, as the tennis elbow is not exclusive to tennis players, some researches demonstrate that 40%-50% of tennis players experience elbow injury symptoms throughout their career [160, 196]. The repetitive overload of forearm muscle tissue caused by repeatedly hitting, namely the repetitive use of grip strength [197] and vibration frequencies in the range of 80–200 Hz [121] are considered as the reason of elbow tendonitis in tennis players. The diagnosis of the tennis elbow using grip strength (pain-free grip strength) is generally based on the principle of imbalanced activation of the patient forearm extensor and flexor muscles [27, 89, 198]. In tennis, the forearm extensor muscles are more prone to injury and the lateral epicondylitis is more destructive than internal epicondylitis [99, 198, 199]. Some forearm injuries, such as the lateral epicondylitis, occur due to an imbalance in the activation of the forearm flexor and extensor muscles [81, 133, 200, 201]. Alizadehkhaiyat et al. indicated that compared to healthy males, individuals with lateral epicondylitis had weaker extensor carpi radialis activation during gripping and exhibited compensatory activation of other muscles [109].

Limitations

• i).Limitations inherent to the research methodology: some subjective biases are introduced into the literature selection process due to the use of narrative description instead of systematic review and quantification with Mate-analysis (specific reasons are elaborated in the Methods section).
• ii).Limitations of uneven distribution of existing the literature: There are substantial research cases on NSGS, while studies focusing specifically on SGS are relatively scarce. Furthermore, within SGS research, studies on the serve and forehand (power-oriented strokes) are more common, whereas research on volleys and drop shots (control-oriented strokes) is limited. The imbalance in these research directions has raised doubts about the applicability of grip strength functionality across all techniques, which hinders a comprehensive exploration of the relationship between the NSGS and SGS.
• iii).Limitations in methodological heterogeneity: the interpretation of results can also be influenced by the variations in the equipment, metrics, and participant characteristics (such as skill level, age, gender, and sample size) across these studies. For example, it is noteworthy that most SGS studies involve small sample sizes (N < 20, Table 2).

Future outlook

• i).The application of grip endurance and control should be valued in future research. Non-specific tests are quite convenient, and the assessment of upper limb strength tennis players using NSGS has been widely recognized. However, the current studies show that the correlation is no significance between NSGS and sports performance of tennis players, such as rank and ball speed. This is related to most of studies adopted mostly the method of collecting the maximum value of NSGS three times, which neglects the fact that tennis is a continuous and repetitive swinging sport. And it is necessary to accurately use grip strength with fit size at the appropriate moment. Grip endurance and control can overcome this limitation.
• ii).In future research, multi-modal concurrent measurement should be increased. The current studies focus on the SGS release of tennis players in various skills and scenarios. However, the methods such as kinematics and dynamics for simultaneous detection are insufficient. The information embedded in SGS can be fully extracted by the simultaneous detection of multiple detection techniques for demonstrating the relationship between grip force and other aspects clearer.
• iii).Future research should delve deeper into the aspects of continuous hitting, long durations of intermittent activity and real match scenarios in tennis. Meanwhile, the correlation between SGS and NSGS across various sports and techniques should be enhanced and the relationship of two types of grip strength should be clearly clarified. Then training methods that enhance the functions of both NSGS and SGS are improved based on this relationship, thereby serving coaches and athletes in their training.
• iv).In the future, grip force should be placed within the context of the entire movement chain and the full process of release for investigating. The current studies on SGS only focus on the changes in grip force during the athlete’s stroke, and the influence of the entire kinematic chain on the release of SGS is ignored in the wrist and forearm. The exploration on the relationship between SGS and downstream factors such as racket head speed, ball speed, rotation, stability and precision is insufficient.
• v).In the future, more detailed research should be conducted on amateur athletes, and the relationship between off-center impact, skills, strength, and elbow pain deserves special attention.

Conclusions

Through literatures review and analysis, the current application status of two types of grip strength is presented in the performance evaluation fields of physical qualities, technical performance, sports fatigue and sports injury for tennis players. Specific and non‑specific grip strength (SGS and NSGS) represent two distinct forms of grip capacity. By measuring and evaluating tennis players’ SGS during stroke execution, a local perspective is obtained on the details and ways in which athletes utilize grip strength. And higher‑performing athletes employ grip strength with greater precision, efficiency, and rhythm. Correspondingly, NSGS is primarily used in the assessment, diagnosis and evaluation of tennis elbow upper‑limb strength, and the monitoring of training status and fatigue levels. Although this review has advantages as an indicator, it also has inherent limitations. Given ongoing debates surrounding both types of grip strength, the aforementioned issues should be addressed and necessary studies based on practical needs should be conducted in future research for highlighting the potential role of grip strength in evaluating athletic performance.

Abbreviations

NSGS

Non-specific grip strength

SGS

Specific grip strength

MGS

Maximum grip strength

KNN

K-nearest neighbors algorithm

MVC

Maximum voluntary contraction

Authors’ contributions

Kebao Zhang: Conceptualization, methodology, formal analysis, investigation, writing-original draft. Jianing Cui: Conceptualization, visualization. Yi Jia: Conceptualization, methodology, visualization, writing-review and editing. Liu Wang: Conceptualization, writing-review and editing, supervision.

Funding

This project is funded by Zhiyuan Laboratory (No. ZYL2025014).

Data availability

The datasets used and analysed during the current study available from the authors (20180051@nuc.edu.cn, Kebao Zhang) on reasonable request.

Declarations

Ethics approval and consent to participate

The procedures were conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of North University of China (Application No. 202505018). And signed informed consent forms were obtained from all participants.

Consent for publication

All participants have consented to the publication of this manuscript, including data, information and images in an online publication.

Competing interests

The authors declare no competing interests.