Maximum Grip Strength in Normal Subjects from 20 to 64 Years of Age

Transcription

1 Maximum Grip Strength in Normal Subjects from to 64 Years of Age William P. Hanten, EdD, PT Professor School of Physical Therapy Texas Woman's University Houston, Texas Wen-Yin Chen, MS, PT Alicia Ann Austin, MS, PT Rebecca E. Brooks, MS, PT Harlan Clay Carter, MS, PT Carol Ann Law, MS, PT Melanie Kay Morgan, MS, PT Donna Jean Sanders, MS, PT Christe Ann Swan, MS, PT Amy Lorraine Vanderslice, MS, PT Graduate Students School of Physical Therapy Texas Woman's University Houston, Texas ABSTRACT: The purposes of this study were to develop normative maximum grip strength (GRIP) data for men and women aged to 64 years, separated into nine five-year age groups, and to develop prediction equations for GRIP using gender, age, height, weight, and hand dominance. A total of 1,182 volunteers (553 men and 629 women) participated in the study. Maximum hand grips were obtained using the Jamar dynamometer with standardized positioning and instructions. The hand to be tested first was chosen randomly. Each hand was then tested alternately. Three trials were performed on each hand. The highest GRIP for each hand was used for analysis. Two-way analyses of variance showed significant differences between the right and left hands and across the age groups for both genders. Follow-up analyses showed that significant decreases occurred between the age groups of and years in men and between the age groups of and years in women. The data also indicated that right and left GRIPs were highly correlated with each other (r = 0.93). Gender, height, and weight moderately correlated with both GRIPS (r = Age correlated weakly with both GRIPs (r = -0.). If either the right or the left GRIP was known, the other GRIP could be predicted easily from the known GRIP, with 87'Yo of variance accounted for. Without the knowledge of the other GRIP, either GRIP could be predicted through gender, height, weight, age, and hand dominance, with 61% to 62% of the explained variance. The norms and prediction equations of GRIP developed in this study for men and women aged to 64 years will help clinicians with decision making regarding grip strength. J HAND THER 12:193-0, G rip strength is an index of the power the hand can exert. 1 Maximum grip strength is an important predictor for hand function? It has been correlated with normal growth/ physical fitness/a and work capacity.4 Hand grip measurement can also be used as an assessment tool to indicate the degree of dysfunction of an injured or pathologic upper extremity. Determination of a patient's maximum grip strength is needed to establish not only treatment goals in hand rehabilitation but also compensation awards, which are often based on a person's pre-injury status. s Clinicians often reference the opposite uninjured hand for comparison. However, in cases of bilateral hand injuries, reliable normative data or prediction models are needed to determine the effectiveness of surgical or rehabilitation intervention. This paper was adapted from a poster presentation at the 11th Annual Krost Symposium and 1997 Annual Meeting of the Texas Regional Chapter of the American College of Sports Medicine, held at Seguin, Texas, on February 6, This study was supported in part by research grant 3P5002 from the National Institute on Disability and Rehabilitation of the U.S. Department of Education. Correspondence and reprint requests to William P. Hanten, EdD, PT, School of Physical Therapy, Texas Woman's University, 10 M. D. Anderson Boulevard, Houston, TX The lack of objective clinical norms for grip strength is emphasized in the literature.o 9 Several studies have attempted to set standards for grip strength. 6,8' Three main problems were found with these studies: The population used was too small or too specific;81s, standardized testing procedures were not used;8,1l-d., or instruments that are less commercially available than the Jamar dynamometer were used.1o,- When a sample size is too small, its capacity to represent the population mean is questionable. The importance of specific pretest instructions, uniform testing apparatus, and controlled subject positioning to enhance the credibility of the grip test and thus the significance of the result has been mentioned. 7 A change in the position of the arm and hand during testing can increase or decrease grip strength values.,19 The Jamar dynamometer, which measures the force produced by an isometric contraction, was reported in the mid-1950s to be the most effective instrument for measuring hand grip strength. When properly handled and calibrated, it continues to be used as an effective grip strength measurement device. 6 When a grip strength evaluation is administered by a clinician who is experienced in using dynamometers, the procedure is accurate and reliable.6,7,19 July-September

2 Only one study, by Mathiowetz et al./ used the Jamar dynamometer with standardized testing procedures. These investigators had a sample of 310 men and 328 women aged to 94 years divided into 12 five-year age groups, with 21 to 31 subjects in each age-gender cell. 6 However, Mathiowetz et al. presented their grip data in terms of right/left hand, which was not consistent with earlier studies that used dominant/nondominant or major/minor hand. 1O,- Also, they had a relatively small percentage of subjects who were left-handed (less than 8%). Some of the age-gender cells in their study did not contain any subjects who were left-handed. 6 Previous studies have established the relationship of grip strength to gender, age, body height, and weight. In general, male subjects have stronger grips than female subjects and the dominant hand is stronger than the nondominant hand. Grip strength is reported to correlate positively with chronological age in subjects younger than years8,12 but negatively in adults.6.10,1l It has also been found to correlate l'ositively with body weight and height. 1O,,,,-22 Many studies presented grip strength data according to gender and age, without reference to other factors. Because body weight and height also correlated to grip strength, it appears reasonable to expect that a grip strength estimated from body height and weight in addition to age and gender would be more accurate. Grip prediction models incorporating factors such as age, gender, body height, and weight have been developed previously.j3, In a study by Schmidt and Toews, grip strength equations were derived from age, height, and weight data for the major and minor hands of 1,128 male subjects. They reported a rather wide range of errors (approximately :.t30 lbs.) for a predictive reliability of 95%? Grip strength prediction equations were not developed for female subjects in their study. A recent study done by Crosby et al. included height, weight, sex, hand dominance, and hobby-demand levels in developing a prediction equation of maximum dominant grip strength from 2 male and female subjects ( to 63 years of age). Although the determination of physical demand levels (on a scale from 1 to 5) for hobby was subjective, the five variables in their equations accounted for 75% of the variance in the maximum dominant grip measurement. However, they did not report the prediction equation for the nondominant grip. Grip data need to be collected from a larger sample that includes more left-handed subjects. Studies are also needed to determine whether normative grip strength should be presented in terms of right/left hand or dominant/nondominant hand. Also, physiological factors such as gender, age, body weight and height, and hand dominance need to be examined on a large sample to determine whether grip strength could be predicted by these factors. There were two purposes of this study. The first purpose was to develop normative data for maximum grip strength for men and women aged to 64 years separated into nine five-year age groups: -,25-29,30-34,35-39,40-44,45-49, 50-54, 55-59, and years. The second purpose was to develop prediction equations for maximum grip strength using values for gender, age, height, weight, and hand dominance. The grip data for right/left as well as dominant/nondominant hands are compared to determine how grip norms and prediction equations are better presented. MATERIALS AND METHODS Subjects A total of 1,3 subjects participated in the study. Twenty-one records showed missing data on hand dominance. These missing data seemed to be across both genders and all age groups without a specific pattern. Of the remaining 1,182 subjects, 553 were male and 629 were female. At least 49 male or female subjects (Table 1) were included in each five-year interval of ages through 64 years. This was a sample of convenience. Exclusion criteria included histories of recent upper extremity injury or any orthopedic, neurologic, or system pathology causing a function deficit or pain in the upper extremity. All subjects read and signed an institutionally approved consent form before participating in the study. Instrumentation Factory-calibrated Jamar dynamometers (Asimow Engineering Co., Los Angeles, California) were used in the study to assess grip strength. After factory calibration of the dynamometers, no further check of calibration was made. These dynamometers consisted of a sealed hydraulic system with five handle positions and a dial representing poundage. The dial reads the force of hand grip in pounds. The dynamometer handle was adjusted in the second position from the inside (1 1 h") throughout the study, because previous studies have established that maximum force is obtained at the second of the five possible handle positions., The' accuracy of the device has been documented to be ±3%.7 High interrater reliability (r = 0.99) and testretest reliabilities (r = ) using the dynamometer to test grip strength have also been reported. 7, Tester Reliability The data were collected, in less than a month, by eight testers using eight hand dynamometers. Most of the data were collected where the testers had access to large numbers of potential subjects, such as at sports stadiums, shopping malls, grocery stores, churches, universities, and office buildings. The eight testers were students at the end of their 194 JOURNAL OF HAND THERAPY

3 studies leading to a master's degree in physical therapy. All testers had previous coursework in force testing. To determine test-retest reliability over the eight testers, an intraclass correlation coefficient (3,1) model was used. This provided a reliability coefficient of Procedures Each subject's age, weight, height, sex, and hand dominance were recorded. Height and weight values were obtained by asking subjects for this information. People who said they didn't know or were unsure were not used as subjects. Hand dominance was determined by asking: "Are you righthanded or left-handed?/i If the subject was unsure, handedness was decided by the hand used to eat and write. The tester explained to each subject what the dynamometer was and how to use it. The standard dynamometer grip testing position as recommended by the American Society of Hand Therapists was followed, except that our subjects were standing and not seated. Each subject stood with the shoulder adducted and neutrally rotated, the elbow flexed to 90, and the forearm and wrist held in a neutral position. 7 Standardized instructions according to Mathiowetz et at? were used. Instructions were given to each subject as follows: "I want you to hold the handle like this and squeeze as hard as you can./i The examiner demonstrated this and then gave the dynamometer to the subject. After the subject was positioned appropriately, the examiner said, "Are you ready? Squeeze as hard as you can./i As the subject began to squeeze, the examiner said, "Harder!... Harder!... Stop./I TABLE 1. Maximum and Grip Strength (in Pounds) of Normal Men and Women Aged to 64 Years TABLE 2. Maximum and Grip Strength (in Pounds) of Normal Men and Women Aged to 64 Years Age Group Men Women (years) Hand No. Mean SD No. Mean SD Age Group (years) - Hand Men Women No. Mean SD No. Mean SD * 89* t * 88* t * 87* 49 56* 51*':j: *Significantly weaker than all age groups from to 54 years (p < 0.05). tsignificantly weaker than those aged 25-29, 30-34, and years (p < 0.05). :j:significantly weaker than those aged years (p < 0.05) * 86* 45 56* 51*':j: *Significantly weaker than all age groups from to 54 years (p < 0.05). tsignificantly weaker than those aged 25-29, 30-34, and years (p < 0.05). :j:significantly weaker than those aged years (p < 0.05). July-September

4 TABLE 3. Number (Percentage) of Subjects with a Stronger Maximum Grip Stregth (GRIP) According to Hand Dominance GRIP stronger GRIP stronger and left GRIPs equal Hand Dominance -handed 809 (76%) 1 (%) 87 (8%) -handed 59 (51%) 49 (43%) 7 (6%) TABLE 4. Two-way Analyses of Variance of the Maximum Grip Strength (GRIP) for the Effects of Age Group (Nine Five-year Groups) and Hand ( vs ) Men: Age group Within + residual Hand Age group X hand Within + residual Women: Age group Within + residual Hand Age group X hand Within + residual Sum of Squares df 83, , , , , , , , , Mean Squares F Ratio 10, , , , p Value Testing was preceded by one submaximal warm-up for each hand. Three trials were performed for each hand, alternating from one hand to the other. The hand to be tested first was chosen randomly. The subjects rested sec between each trial. The highest grip strength value (GRIP) for each hand was used for analysis. High test-retest reliability coefficients have been reported when grip strength was determined by the highest score over three trials (r = ). Data Analysis Means and standard deviations were calculated for men and women for each age group over right/left and dominant/nondominant hands. Two paired t-tests were used to determine whether the dominant hand was stronger than the nondominant hand in both right-handed and left-handed subjects. Grip data were then presented in terms of right/left or dominant/nondominant hands depending on these results. Two two-factor analyses of variance (ANOVAs) were used to compare differences between the GRIPs of the right and left hands and differences among the age groups for male and female subjects separately. One factor was a within-subject factor (hand) with two levels (right/left or dominant/nondominant); the other factor was a between-subject factor (age group) with nine levels. Follow-up analyses using the Tukey method were performed once the effect of age group was found significant.z s Pearson product moment correlation coefficients were calculated to investigate bivariate relationships between the variables. Multiple regression analyses were used to explore the multivariate relationship between the GRIP and gender, height, weight, age, and handedness and to determine prediction models for the GRIPs. All statistical analyses were performed using the SPSS computer software package. 26 RESULTS Tables 1 and 2 show means and standard deviations of GRIP as grouped by gender and age in ranges of five years over right/left and dominant/ nondominant hands, respectively. These two tables appear identical. Approximately 89% of the male and 91% of the female participants were righthanded. For right-handed subjects, the dominant grip averaged 90.1 (±29.6) pounds and the nondominant grip averaged 82.7 (±27.5) pounds. The 0 1 : 100 : -;::::::=t:::::: - : FIGURE 1. Normative maximum grip 80 strength (GRIP), measured in pounds, by age group. Values for men are indicated by open 60 diamonds (right hands) and solid diamonds (left hands); values for women, by open circles 40 (right hands) and solid circles (left hands). O ~----~--~r---~----~---r--~ Age Group (years) 196 JOURNAL OF HAND THERAPY

5 difference was statistically significant (t =.61, df = 1,0, P < ). However, there was no statistical difference in the dominant and nondominant GRIPs (87.4 ± 29.0 vs ± 29.0; t = 1., df = 1, P =.2) in the left-handed subjects. Regardless of side of dominance, more subjects were stronger in their right hand than in their left (Table 3). This is the reason for presenting the grip norms by right/left rather than dominant/nondominant hand. The ANOVA results are presented in Table 4. A two-way ANOVA on the right and left GRIPs of the male subjects revealed significant main effects of age group (F = 11.92; df = 8, 552; P < ) and hand (F = ; df = 1, 552; P < ). A second two-way ANOVA on the right and left GRIPs of the female subjects revealed significant main effects of age group (F = 8.25; df = 8, 632; P < ) and hand (F = ; df = 1, 632; P < ). Follow-up analyses showed that the right and left GRIPs of male subjects in the age groups of and years were significantly different from those of male subjects in all the younger age groups (Table 1). There was no statistically significant difference of either GRIP for male subjects in age groups between and 54 years and between 55 and 64 years. For the female subjects, there was no significant difference in either the right or the left GRIP for those in age groups between and 54 years (Table 1). Tl1;e right GRIP of female subjects between 55 and 59 years of age was significantly weaker than that of female subjects in the age groups of 25-29, 30-34, and years, but not the other age groups; and their left GRIP differed only with those in the age group of years. The right GRIP of female subjects between 60 and 64 years of age was significantly weaker than that of female subjects in the age groups between and 54 years, but not between 55 and 59 years. On the other hand, the left GRIP of female subjects in the age group of years was significantly weaker than that of female subjects in every other age groups between and 59 years. Figure 1 presents the relationship of the GRIP with the age groups for both male and female subjects in this study. Stepwise multiple regression analyses showed that when either the right or the left GRIP was known, prediction of the other GRIP could be obtained by the combination of the known GRIP, gender, hand dominance, age, and body height and/ or weight (R = 0.93). A combination of all these predictor variables accounted for approximately 87% of the variance in GRIP measurements. If neither GRIP was available, estimation of the right or left GRIP could still be made through regression models that included predictor variables of gender, body height and weight, age, and/or hand dominance (R = ). The combination of these physiological factors accounted for more than 62% of the total variance in the right or left GRIP measurement. Table 5 summarizes these prediction models. Using dominance/nondominance GRIPs in analyzing the data TABLE 5. Prediction Equations for and Maximum Grip Strength (GRIP) One GRIP is known: Prediction Equations Rt = (Lt) (Ht) + 6.8(Hd) - 0.(Gn) (age) Lt = (Rt) (Gn) - 5.9(Hd) (Wt) (age) (Ht) Both GRIPS are unknown: Rt = (Gn) (Ht) + 0.0(Wt) (age) (Hd) R R Lt = (Gn) (Ht) + 0.(Wt) (Age) NOTE: Rt indicates right GRIP; Lt, left GRIP; Gn, gender (male = 0, female = 1); Ht, body height in inches; Wt, body weight in pounds; age, age in years, Hd, hand dominance (right-handed = 1, left-handed = 0). TABLE 6. Prediction Equations for and Maximum Grip Strength (GRIP) One GRIP is known: Prediction Equations Dom = (Non) (Ht) (Gn) (Wt) (age) Non = (Dom) (Gn) (age) (Wt) Both GRIPs are unknown: Dom = (Gn) (Ht) (age) + 0.(Wt) Non = (Gn) + 0.(Wt) (age) (Ht) R R NOTE: Dom indicates dominant GRIP; Non, nondominant GRIP; Rt, right GRIP; Lt, left GRIP; Gn, gender (male = 0, female = 1); Ht, body height in inches; Wt, body weight in pounds; age, age in years. TABLE 7. Bivariate Correlations Between and Maximum Grip Strength (GRIP), and GRIp, Gender, Height (in Inches), Weight (in Pounds), and Age (in Years) GRIP GRIP GRIP GRIP GRIP.1 GRIP GRIP GRIP Gender Height Weight Age produces similar regression models and coefficients (Table 6). The relationship of the right and left GRIPs and gender, body height and weight, and age is presented in a bivariate correlation matrix (Table 7). The results revealed that the GRIPs of the two hands were strongly correlated (r = 0.93). Gender and body height and weight were all highly cor- July-September

6 related to the GRIPs (r = -0., 0.64, 0.53, respectively). Age correlated negatively but weakly with each GRIP (r = 0.). The correlation pattern was the same when the data were presented in terms of dominant/nondominant GRIPs. DISCUSSION Normative data for men and women aged to 64 years collected in this study were similar to those reported by Mathiowetz et a1. 6 Differences in the mean grip strength for each age-gender group between the two studies were between 0 and pounds. Because standard deviations for each agegender group varied between and 26 pounds in this study (Table 1) and between 8 and 27 pounds in their study/ most differences between the two studies appear to be insignificant due to subject variations. However, the test position used in this study was not entirely standard. The standard is to sit. A clinician who decides to use the prediction equations developed in this study should keep this in mind. The large sample size in this study lends credibility to the results of the study. Some previous reports have indicated that grip strength peaks in early adult life and declines progressively after the second or third decade of life. 6,10,11,, However, none of the previous studies had determined whether the decline was statistically significant or had attempted to show between which age groups the significant decline in grip strength occurred. The present study shows that in the and year age groups of men the right and the left GRIPs are significantly weaker than those of men in the younger age groups, between and 54 years (Table 1). On the other hand, no significant difference was observed between the age groups of and years. In other words, there might be a significant GRIP decline in men between the age groups of years and years. This significant age effect of declining grip strength, however, is not apparent in women until after years. The right and left GRIP scores of women in this study were not different between the age groups from to 54 years. The women in the age group of years showed no significant difference in the right grip strength compared with those in the two adjacent age groups (50-54 and years), and their left GRIP scores were not significantly different from those in the younger groups, from to 54 years, although they are stronger than those in the older group (60-64 years). The right and left GRIPs in women aged years, nonetheless, were significantly weaker than those in the other younger age groups ( to 54 years). The reason female subjects did not show GRIP decline as early as their male counterparts is not clear. The regression models shown in Table 5 offer a very strong prediction for maximal grip strength, especially when one of the two GRIPs is known. This is evident in the high regression coefficients and the explained variances determined by the regression model (R = 0.93 and R2 = 0.87). When none of the GRIPs is known, however, the regression coefficients drop to , and the combination of factors of gender, body height and weight, and age explain only 61 % or 62% of the total variance in the GRIP measurement. From the data analyzed in this study, it is interesting to note that when one GRIP is known, prediction of the other GRIP from the known one provides almost as strong a prediction model as the full model, which includes all significant predictors (Tables 5 and 6). The combination of gender, handedness, age, and body height and/or weight explains only an additional 1% of the total variance in the GRIP after the other GRIP value has entered the regression equations. This is because the right and left GRIPs are highly correlated (r = 0.93) (Table 7). Therefore, the simplified prediction equations presented in Table 8 may be used by the clinician with only the known GRIp, without losing much accuracy. The incidence of left-handedness is 9% to 11% in the present study, which agrees with previous reports 6,,27 that the incidence is approximately 6% to %. Although the dominant hand is stronger in most right-handed subjects, the dominant-handstronger pattern is not seen in the left-handed subjects in this study. On the contrary, more than 50% o.f left-handed persons in this study a stronger nght-hand GRIP (Table 3). This is in agreement with the findings of Mathiowetz et a1./ who believed that presenting grip data in terms of right/ left hand by combining the data for right- or for left-hand-dorninant subjects was justified because the mean right-hand strength scores in their lefthanded subjects were greater than the mean lefthand scores. It is difficult to explain why most lefthanded subjects are not stronger in their dominant hand, as this and previous studies indicate their right-handed counterparts are. Speculation is that the right hand is stronger either because they have to cope with a world organized for the righthanded or because they have a more symmetric functional organization of the two hemispheres of the brain, in contrast to the cerebral lateralization (or unequal functional organization) commonly recognized in right-handed persons. 6,7,27 Presenting GRIP data in terms of the right/left hand rather than the dominant/nondominant hand appears to be more advantageous based on the facts that the mean right GRIP is stronger than the left, regardless of handedness pattern (Table 1); using dominant/ n~m~ominant GRIP data did not improve the prediction model, in terms of regression coefficients or explained variance, compared with using right/left GRIP data (Tables 4 and 5); and using right/left TABLE 8. Simplified Maximum Grip Strength (GRIP) Prediction Equations When One GRIP Is Known Prediction Equations GRIP = (left GRIP) GRIP = (right GRIP) R R , JOURNAL OF HAND THERAPY

7 GRIP avoided the issue of choosing sides for those who consider themselves ambidextrous, or equalhanded. 28 The fact that adult male subjects have a stronger grip than female subjects has generally been accepted 6,1l,,, and is also confirmed in this study with this population. Data in this study also show that gender is the most important factor in predicting GRIP and explained more than 50% of the variance in GRIP measurement when information of the other GRIP is not available. Body mass, especially the percentage of the lean body mass, has been suggested as a possible factor causing strength difference between the two genders after maturity is reached. 29 Body height and weight are directly related to grip strength (Table 7). In the present study, the bivariate correlation coefficients between grip and height ranged from 0.63 to 0.. The coefficients between grip and weight ranged from 0.52 to The results of this study agree with previous findings.,,22 Schmidt and Toews reported that grip strength is in direct relationship with height up to 75" and weight up to 2 pounds. Lunde et al. reported correlation coefficients of 0.22 to 0. between grip strength and height and 0. to 0.31 between grip strength and weight in 57 college women. Vitasalo et a1. 22 reported a correlation coefficient of 0.52 between dominant grip and height and 0. between dominant grip and weight in 180 men in three age groups. The present study demonstrates a much stronger relationship between GRIPs and weight as well as between GRIPs and height. The much larger sample size would lend a higher credibility to the results in the present study. Age has been reported as an important factor for grip strength in previous studies that showed a negative relationship between age and the grip strength for adults. 6,1O,1l,,,22 Higher negative correlations between the grip strength and age were reported by Mathiowetz et al./ who studied grip data for adults aged to 94 years. The correlation coefficients between age and right and left grip strength ranged between and in their male and female subjects. In the present study, however, age is found to be only weakly correlated to GRIP (r = -0.). This agrees with other reports that age did not seem to be an important factor in the grip measure for adults younger than 65 years., The discrepancy between our results and those of Mathiowetz et at? could be attributed to the greater age range in their study and also to the difference in the sizes of the populations, which could have influenced the effect size. Further analyses change in GRIP with age shed some light on the low correlation between GRIP and age in the present study. Although the mean score fluctuates, subjects between the age groups of - and years in the present study show no statistically significant differences in their GRIPS, regardless of gender or dominant side. The age factor becomes more important for those in the age group of years in this study, as the correlation coefficient increased more negatively to in a separate analysis. It would not be difficult to imagine that the correlation would continue to grow negatively with age if subjects older than 65 years were included in the study. CONCLUSION Normative grip data were established on the basis of gender and age groups at five-year intervals between and 64 years. Results of this study supported the presentation of data on normative grip strength in terms of right/left hand instead of dominant/nondominant hand. 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