Wrestling is an intensive activity that requires high levels of upper-body strength and anaerobic power (23). Earlier reports from the Junior World Wrestling Championship suggested that these parameters tend to differentiate champions from unsuccessful wrestlers (23,34). Therefore, the development of upper-body strength through specific isometric actions is emphasized in a wrestling training program (17). Handgrip strength, in particular, is an important component to several wrestling holds because various take-down and defensive maneuvers rely on a strong grip (16,17). The evaluation of handgrip strength can assist coaches and athletic trainers to make appropriate professional decisions regarding performance enhancement, injury prevention, severity of hand dysfunction, and effectiveness of treatment strategies. Although previous studies have reported handgrip strength measurements in wrestlers (16,23,28,31), no reference data for handgrip strength across the developmental years are currently available in this population.
It is well known that strength increases with chronological age in boys (4,5,10). Previous results (19) suggested that there might be differences between athletes and nonathletes in the pattern of improvement in muscle strength across childhood. Maffulli et al. (19) showed that isometric leg strength was similar between athletes and nonathletes until the age of 15, whereas it was significantly higher in athletes at late puberty and adulthood, implying that there is an interaction between biological development and training responses. In the same context, Camic et al. (1) showed that the pattern of isokinetic leg strength development was different in wrestlers than in nonathletes. Whether their findings are limited to isokinetic strength of lower limb muscles or extent to other muscle groups and more specifically to handgrip muscles has not been investigated.
Strong correlations have been reported between grip strength and anthropometric measures (10) in prepubertal and adolescent untrained boys. However, the contribution of body size–related variables to the development of strength in these ages might be different between athletes and nonathletes (14,33). The relationship of anthropometric measures (such as body mass, body height, and hand dimensions) with the age-related changes in peak handgrip strength in wrestlers has not been explored, although this information could be of importance in talent detection in the sport of wrestling.
Moreover, previous studies that examined grip strength during the developmental years reported either no effect of hand preference in untrained participants (4) or hand-related differences in untrained children and adolescents (2,10), and young athletes, like tennis players and fencers (8,20). The hand-related differences in these athletes could possibly be attributed to the asymmetrical training of the preferred hand in these sports. Whether the intense upper limb training in wrestling results in symmetrical grip strength development in both hands has not been investigated. This information could be of importance in coaches and trainers, in the identification of muscle weaknesses, in injury prevention, and in the rehabilitation of the injured wrestler.
Therefore, the aims of this study were to examine (a) whether absolute and relative (normalized per unit of body mass) peak handgrip strength is similar in wrestlers and in nonathlete controls from childhood to adulthood (i.e., in children, young adolescents, late adolescents, and adults), (b) whether there are differences in grip strength between the hands in each age category, within the wrestling and the control groups, and (c) the relationship of anthropometrical characteristics with peak handgrip strength in wrestlers and in nonathlete controls. Based on the above studies, it has been hypothesized that wrestlers would demonstrate similar peak handgrip strength with nonathletes in preadolescent and early adolescent years; however, late adolescent and adult wrestlers would exhibit greater handgrip strength than the nonathletes of similar age. It was also hypothesized that wrestlers would produce similar peak handgrip strength in both hands.
Experimental Approach to the Problem
To investigate our first purpose, that is, whether peak handgrip strength development from childhood to adulthood follows a similar pattern in wrestlers and in nonathlete controls, male wrestlers (n = 122) and nonathlete controls (n = 122) were recruited for the study. For the purpose of this study, a nonathlete was defined as any subject who was not currently participating in competitive sports and had not been involved in any kind of systematic training of his upper extremities muscles in the past. A wrestler was defined as an athlete who trained in a wrestling team at least 3 times per week, for more than 18 months. Wrestlers were stratified into 4 groups according to their age: children (9–11 years), young adolescents (13–15 years), late adolescents (16–17 years), and adults (18–28 years). Nonathletes were also stratified into similar age groups (i.e., children, young adolescents, late adolescents, and adults). After assessment of anthropometric characteristics, participants underwent handgrip strength testing with a handgrip dynamometer. To investigate the second purpose of the study, that is, whether there are differences in grip strength between the hands in each age category, within the wrestling and the control group, handgrip testing was also performed with the contralateral hand. The preferred and the nonpreferred hand were tested in a random order. Finally, to determine the relationship of peak handgrip strength with anthropometric characteristics, body height, body mass, and hand dimensions (hand length, span, and width) were also measured.
All participants were healthy and had no previous injury of upper limbs. To avoid the potentially negative effects of severe rapid weight loss and dehydration on grip strength (16), testing in wrestlers was performed in the precompetition season. Participants were asked to follow their normal diet for 2 days before the study, to abstain from intense exercise activity for 16 hours before the study, and to have sufficient rest the night before the study. All measurements were performed at the same time of the day (i.e., during the morning hours) to prevent potential confounding effects of daily biorhythms (27).
Two hundred forty-four participants were recruited for the study. Wrestlers were stratified into 4 groups according to their age: children (9–11 years, Tanner stage 1; n = 31), young adolescents (13–15 years, Tanner stage 2–3; n = 30), late adolescents (16–17 years, Tanner stage 4–5; n = 31), and adults (18–28 years, n = 30). Nonathletes were also stratified into 4 age groups: children (9–11 years, Tanner stage 1; n = 31), young adolescents (13–15 years, Tanner stage 2–3; n = 30), late adolescents (16–17 years, Tanner stage 4–5; n = 31), and adults (18–28 years; n = 30). Wrestlers were volunteers from local wrestling teams. The training status of the wrestlers' group was 2.10 ± 0.40 years in children, 2.33 ± 0.76 years in young adolescents, 3.94 ± 2.45 years in late adolescents, and 9.07 ± 5.03 years in adults. The nonathletes, who served as controls, were male participants with no previous training experience in their upper extremities. In most cases, children/adolescents were physically active; however, none of the nonathlete participants had been involved in any kind of systematic training in the past. Children and adolescents in the control group were healthy and participated in physical education courses during the school year. The average values (mean ± SD) for the physical characteristics, that is, body mass (in kilograms), body height (in meters), and hand dimensions (hand length, hand span, and hand width [in centimeters]) of the participants are presented in Table 1. Wrestlers had wider (p < 0.05) hands than controls irrespective of age, whereas only adult wrestlers had longer hands than their control peers.
All our participants were normally nourished and were not on extensive dieting or hypohydration status at the time of the study. The study was approved by the University of Thessaly Review Board Committee, and written informed consent was obtained from the subjects and children's parents before testing.
Each participant reported to the exercise laboratory in the morning of the testing. After orientation and completion of a medical history form, the anthropometrical characteristics were assessed. First, body mass was measured to the nearest 0.1 kg using a calibrated physician's scale (Seca model 755; Seca, Hamburg, Germany). Body height was determined to the nearest 0.1 cm using telescopic height rod (Seca model 220; Seca). Next, the dimensions (length, span, and width) of the preferred hand were recorded with an ergonomic measuring tape (Seca model 201; Seca). Hand preference was determined by asking the participant which hand was used to hold a pencil. Hand length was measured with a Gulick measuring tape (Fitness Mart, Gay Mills, WI, USA) as the distance from the distal wrist crease to the end of the middle finger (2). Hand span was measured as the distance from the tip of the thumb to the tip of the little finger with the hand opened as wide as possible (29). Hand width was measured as the distance between the radial side of the second metacarpal joint to the ulnar side of the fifth metacarpal joint (2).
Next, the participant performed a standardized warm-up that included 3 preliminary trials for familiarization with the recording procedure and instrumentation. A portable hydraulic dynamometer (Jamar, 5030J1; Jamar Technologies, Horsham, PA, USA) was used for the handgrip strength measurement. The Jamar hand dynamometer has established test-retest, interrater and intrarater reliability in children and in adults (7,12,27). Handgrip testing was performed according to the recommendation of the American Society of Hand Therapists: the subject seated upright on a height-adjustable chair with feet supported, shoulders adducted and neutrally rotated, elbow flexed at 90°, with the forearm in neutral and wrist between 0° and 30° of dorsiflexion (21). The arm was positioned on a table to support the weight of the dynamometer. The set-up is shown in Figure 1.
All participants received the same “standardized” instructions as described by Mathiowetz et al. (21). Briefly, the standardized instructions (21) given were, “I want you to hold the handle like this and squeeze as hard as you can”. The examiner demonstrated and then gave the dynamometer to the participant. Next, the following instructions were given: “Are you ready? Squeeze as hard as you can.” As the participant commenced the handgrip contraction, the examiner said, “Harder! … Harder! … Relax.” Three maximal isometric contractions lasting 5 seconds each, in each hand, with a rest period of at least 60 seconds were performed. The highest reading was considered as the maximal handgrip strength and was included in the data analysis (21). Visual feedback was provided through a mirror. Relative handgrip strength per unit of body mass (i.e., kilograms of handgrip per kilograms of body mass) was calculated.
All data are presented as mean ± SD and were analyzed using SPSS 13.0 (SPSS, Inc., Chicago, IL, USA). Two-way analysis of variance (ANOVA) (group × age) was used to examine the effect of group (wrestlers and controls) and age (children, young adolescents, late adolescents, and adults) on absolute and relative (kilograms of handgrip per kilograms of body mass) peak handgrip strength. A 3-way ANOVA (group × age × hand) with repeated measures on the “hand” factor was used to analyze the effects of age and hand preference on handgrip strength within wrestlers and within controls. Significant ANOVAs were followed by Newman-Keuls post hoc tests to locate the significantly different means. Pearson correlations and linear regression analyses (y = a × x+ b) were used to determine the relationships of absolute peak handgrip strength with anthropometrical characteristics (body mass, body height, and hand dimensions) within each group. The statistical power in the manuscript for the n size used was 0.907. The reliability of the peak strength measurement using the Jamar Dynamometer was high (intraclass correlations ranged from 0.94 to 0.984 across ages in both groups). The test-retest reliability performed in separate days in a previous study in our laboratory using the Jamar handgrip dynamometer was 0.940 in children, 0.984 in adolescents, and 0.971 in adults (7). The level of significance was set at α = 0.05.
Peak Handgrip Strength
The pattern of increase in absolute handgrip strength values from childhood to adulthood, within the wrestlers and controls is depicted in Figure 2. Absolute peak handgrip strength increased (p < 0.05) during the developmental years in both groups; however, a significant “age × group” interaction was observed (p < 0.05). Within the wrestlers' group, children exhibited lower (p < 0.05) absolute peak handgrip than young adolescents, late adolescents, and adults. Young adolescent wrestlers exhibited lower absolute peak handgrip than late adolescent and adult wrestlers (p < 0.05); late adolescents exhibited lower peak handgrip than adults (p < 0.05). Within the control group, children exhibited lower (p < 0.05) absolute peak handgrip compared with the other groups, and young adolescents were significantly different (p < 0.05) than late adolescents and adults, whereas no differences were observed between late adolescents and adults. No significant differences in absolute handgrip strength were observed between wrestlers and controls in children and young adolescents, whereas late adolescent and adult wrestlers exhibited higher peak handgrip strength than their control peers (p < 0.05).
Next, the absolute peak handgrip strength values were adjusted per unit of body mass (relative handgrip strength; Figure 3). Significant effects of “age,” “group,” and an “age × group” interaction were observed (p < 0.05). Within the wrestlers' group, relative handgrip strength was significantly lower (p < 0.05) in children vs. young adolescents, late adolescents, and adults. Young adolescent wrestlers exhibited lower (p < 0.05) relative handgrip strength than late adolescents and adults, whereas no differences were observed between late adolescents and adults. Within the control group, relative handgrip strength was significantly lower (p < 0.05) in children compared with young adolescents, late adolescents, and adults, whereas no differences were observed among young adolescents, late adolescents, and adults. When wrestlers were compared with controls, no differences in relative handgrip strength were observed in children and in young adolescents, whereas late adolescent and adult wrestlers exhibited significantly higher relative handgrip strength than controls of similar age.
Peak Handgrip Strength and Hand Preference
The effects of hand preference on peak handgrip strength in wrestlers and controls are presented in Table 2. A significant (p < 0.05) main effect of “hand preference” was observed in wrestlers and in controls. A “hand × group” interaction was observed (p = 0.056). Neuman-Keuls post hoc comparisons revealed that children in both groups (i.e., wrestlers and nonathlete controls) did not exhibit any differences in grip strength between the preferred and the nonpreferred hand; however, young adolescent wrestlers and nonathletes exerted higher peak strength (p < 0.05) with the preferred hand than the nonpreferred hand. Wrestlers in late adolescence and adulthood exhibited similar peak strength values with both hands. In contrast, nonathlete controls of similar age exhibited higher handgrip strength with the preferred hand than the nonpreferred hand (p < 0.05).
Handgrip Strength and Anthropometrical Characteristics
Τhe relationships of handgrip strength with anthropometrical characteristics were examined within each group. In the control group, significant strong correlations (p < 0.01) of body height (r = 0.824), body mass (r = 0.733), and hand dimensions (hand length: r = 0.818; hand span: r = 0.747; and hand width: r = 0.796) with peak handgrip strength were observed. Similarly, in wrestlers, body height (r = 0.867), body mass (r = 0.796), and hand dimensions (hand length: r = 0.850; hand span: r = 0.792; and hand width: r = 0.781) exhibited significant strong correlations (p < 0.01) with handgrip strength. The linear fit of handgrip strength with body mass and body height in wrestlers and in controls is depicted in Figure 4.
The main findings of this study were (a) wrestlers exhibited a different pattern in the age-related increase in absolute and relative handgrip strength than nonathletes during the developmental years; (b) wrestling training attenuated the asymmetry in handgrip strength between the preferred and the nonpreferred hand that was observed in late adolescence and adulthood; (c) body height and hand length exhibited the strongest correlations with handgrip strength during the developmental years, in wrestlers and in controls. More specifically, handgrip strength was similar in wrestlers and in controls in the younger age groups (i.e., in children and young adolescents), whereas late adolescent and adult wrestlers exhibited significantly greater peak handgrip strength than their control peers. Nonathletes older than 15 years demonstrated an approximately 10% greater peak handgrip strength with their preferred hand compared with the nonpreferred hand. In contrast, wrestling training resulted in symmetrical grip strength development in late adolescence and adulthood. Peak handgrip strength exhibited a significant linear correlation with all the anthropometric measures examined; however, a higher percentage in the variation in peak handgrip strength during the developmental years was explained by body height and hand length than the other anthropometric variables.
Children and young adolescents in this study exhibited peak handgrip strength values, which are relatively similar to those previously reported in the general population (4,13); however, they are slightly higher than normative data recently reported in English (3) and Canadian children (32). Several methodological factors could potentially affect the handgrip strength measurement, such as the type of dynamometer used (Jamar vs. Takei), the position of the elbow joint (90° flexion vs. fully extended) (6), the number of trials performed (3 test trials vs. 2) (3,27,32), and whether the mean or the maximum value is considered as peak strength. Reporting the average of the 3 trials (although reliable) results in lower (18) peak handgrip strength values. In our study, handgrip strength was evaluated using the Jamar dynamometer, a widely used instrument (30) with established reliability (27) and excellent concurrent validity with known weights (22). The Jamar dynamometer has the most extensive normative data (27) and has been considered as a gold standard for grip strength assessments (27).
Children and young adolescent wrestlers in this study exhibited relatively similar peak handgrip strength to controls, whereas late adolescent and adult wrestlers exhibited higher peak handgrip strength values than controls. This is consistent with previous findings (11,19) comparing strength development in the lower limbs between athletes and nonathletes. The mechanisms by which the mechanical stress imposed by wrestling resulted in the greater adaptations in grip strength in late adolescence cannot be directly answered by this study. However, it is generally agreed that the increased humoral milieu in puberty plays an anabolic role on the handgrip muscles. During adolescence, testosterone, growth hormone, and insulin growth factors result in skeletal muscle growth. Exercise training stimulates mechanisms affecting whole body growth. In addition, resistance training and isometric maneuvers, as the ones used in wrestling (24), affect local mechanisms that stimulate specific tissue growth in the hand muscles. Therefore, wrestling training possibly augmented the high anabolic profile observed during late adolescence, resulting in greater adaptations in grip strength. Increases in motor skill coordination (34), and altered activation of muscle sensory receptors (9) that arise in response to wrestling training, could also contribute to the higher adaptations in grip strength observed during these ages (11).
Normalizing peak handgrip values per unit of body mass showed a lower handgrip to body mass ratio in children compared with the older age groups. This finding suggests that recruitment and firing rate of motor units is not optimal in pre-adolescents compared with the older groups. In the control group, relative handgrip strength increased from childhood to young adolescence and exhibited a plateau thereafter, whereas in the wrestlers' group, relative grip strength continued to rise until late adolescence. These results suggest that the wrestling training stimuli postponed the development of the plateau in relative handgrip strength. In close proximity to our results, Terbizan and Seljevold (31) reported that relative handgrip strength was not different between 16- and 17-year-old wrestlers.
The effect of handedness of handgrip strength has been a matter of debate because some studies reported that the preferred hand was about 10% stronger than the nonpreferred hand and others reported no differences (8,9,18,20). In this study, prepubertal children (wrestlers controls) did not exhibit asymmetry in grip strength between the preferred and the nonpreferred hand. Similar findings were reported by Newman et al. (25) in untrained children. However, beyond the age of 13, the preferred hand in the control group was approximately 10% stronger than the nonpreferred hand. In contrast, wrestling training abolished the asymmetry in grip strength between the 2 hands in late adolescence and adulthood. Evidently, the isometric actions performed by both hands during grasping maneuvers in wrestling training (16) explain our findings.
These results are of clinical significance because hand and wrist injuries account for a large percentage of injuries during training and competition in wrestling. Coaches and athletic trainers often need to evaluate their athletes' grip strength to make appropriate professional decisions to set realistic training goals and prevent further injury. The 10% rule used by therapists treating patients with injured hands states that the dominant hand has a 10% stronger grip than the nondominant hand. Our results indicate that comparisons with the contralateral/unaffected hand should be performed and the failure to achieve similar grip strength to the contralateral hand may indicate partial rehabilitation.
Our data showed a high correlation between muscle handgrip strength and body height during the developmental years in wrestlers and control male participants, supporting previous findings in adults (18). Hand size can modify the gripping biomechanics and consequently the ability to produce strength (26). Therefore, we also examined the relationship of hand dimensions with handgrip strength. Hand length exhibited the strongest correlation with peak handgrip strength than hand span and hand width. Other anthropometrical measures, such as forearm girth, midstylion-dactylion, and acromiale-radiale length and hand lean body mass, have also been proposed to influence handgrip strength in prepubertal children (15).
In conclusion, the ability to produce handgrip strength in both absolute and relative terms exhibited a different pattern of increase in wrestlers than nonathlete controls during the developmental years. Children and young adolescent wrestlers did not exhibit differences in handgrip strength than their nonathletic peers; therefore, coaches may consider using normative values from the general population in these ages. However, the adaptations in handgrip strength after wrestling training are evident in late adolescence and in adulthood and are possibly attributed to increases in lean body mass, hypertrophy, and the improvements in motor skills. Wrestling training eliminates the handedness asymmetry observed during late adolescence and adulthood in nonathletes.
Coaches and trainers often need to evaluate handgrip strength in their athletes because previous studies have shown that it is an important parameter for succeeding in this sport. We report that wrestlers exhibit a sport-specific pattern of handgrip strength changes during the developmental years. The data presented in this study (average and 95% confidence intervals) serve to provide a descriptive profile of grip strength in wrestlers to assist both coaches and health professionals for talent selection and/or development of training programs for performance enhancement and rehabilitation. Coaches could consult normative data from the general population in the prepubertal years; however, in late adolescence and adulthood, when the training adaptations are clearly evident, the use of sport-specific reference data is recommended.
This study was supported by internal university funding.
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