- Email: [email protected]
Hand strength: Normative values
Hand Strength: Normative Values Carla A. Crosby, BS, Marwan A. Wehbk, MD, Bryn Mawr, PA We studied
normal
hands.
hundred
Two
at all five levels. hand
dominance,
hand
strength
fourteen
A pinch
and the difference
volunteers
were
tested
between with
gauge was used to assess key and pulp
and hobby
demands
were
predictive
dominant
a calibrated pinch.
of maximum
and nondominant Jamar dynamometer Height,
grip.
grip for women
was 81 lb. and for men was 137 lb. Key pinch
averaged
pinch
16% of maximum
had maximum
level
averaged
2. The majority
dominant
of right-handed
side. In left-handed
nant hand was stronger
grip.
subjects,
Only subjects
were
patients
10%
stronger
22%,
in grip
and Methods
Two hundred fourteen subjects were randomly selected. All subjects were in good physical health and claimed to have no previous hand injuries within the past 5 years. They had diverse occupational and recreational backgrounds that were assessed by a
From the Pennsylvania Hand Center. and Bryn Mawr Hospital. Bryn Mawr, and Thomas Jefferson University. Philadelphia. PA. Received for publication March 1-2. 1993: accepted in revised form Oct. 26. 1993. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Pennsylvania Hand Center, Reprints Department. PO Box 141. Bryn Mawr. PA 19010.
subjects.
(J Hand
Surg 1994;
sex,
maximum while
pulp
strengths
strength
mean grip was the same for both hands;
in 50% of left-handed
Few studies have used all five levels of the Jamar dynamometer (Asimow Engineering, Los Angeles. CA). These studies were undertaken to test reliability,‘.? fluctuations,’ or feigned weakness in grip testing.jwh Other studies have been performed to determine norms7-” and differences in strength between hands.‘l-‘? However. these studies did not test strength on all live levels. ‘-‘I Some of these studies included pinch strength measurements2.‘.Y.‘” but did not relate their findings extensively to demographics or grip strength. This study determined normal grip and pinch power with all five levels of the Jamar dynamometer, as well as pinch strength, using a pinch gauge (B & L Engineering, Santa Fe, CA). Materials
129 (60%)
weight,
Mean
at
on the
the nondomi-
19A:
665-670.1
physical demand scale as defined by the Dictionary of Occupational Titles (Table I ). The study included 214 subjects, 105 men and 109 women. Ages ranged between 16 and 63 years (mean, 32 years). There were 175 right-handed subjects (82%) and 39 left-handed subjects (18%). Subject body weight ranged from 45 to I I8 kg (mean, 71 kg), and height ranged from 150 to 198 cm (mean. 173 cm). A calibrated Jamar dynamometer was used by two hand therapists to assess grip strength at all five levels. The smallest grip was labeled as level I and the largest as level 5. A pinch gauge was used to assess key and pulp pinch. These instruments have been reported to be accurate for the measurement of strength with good inter-rater reliability.’ Time of day was not recorded since it has been shown to be of little significance.3 One trial was performed to assess grip strength using the standard arm position as recommended by the American Society of Hand Therapists: shoulder adducted and neutrally rotated, elbow at 90” flexion. and forearm in neutral.‘h.‘7 Wrist position was selfselected by each subject to allow for maximal gripping.lx Standard instructions were used: the subjects were asked to squeeze the gauge as hard as they possibly could with the extremity in the standard position.’ The dominant hand was tested at level 1 of the dynamometer: the other hand was tested next at the same level. Levels 2-5 were then tested in a similar fashion, alternating hands. Scores were recorded to The journal
of Hand
Surgery
665
666
Crosby and Wehbe I Hand Strength
Table 1. Physical Group
Physical Demand
1 2 3 4 5 6
Sedentary Light Medium Medium-heavy Heavy Very heavy
Level”
Demand
10 20 50 75 100 >I00
Use Sample
Sample Hobby
_____Occapation Receptionist Business executive Secretary Grocery checker Warehouse worker Steel worker
-Reading Swimming Tennis/golf Baseball
Hockey Weight lifting
subjects (26%). The increase was by 5-20 lb; decrease by 5-30 lb. Height, weight, sex, hand dominance, and hobby demand levels were predictive of maximum grip strength (adjusted R * = 75%; p = .OOOl). Hobbies had a stronger correlation (p = .0027) to maximum grip than occupational demands (p = .2806). The left-handed subjects had weaker grip strengths than the right-handed subjects when evaluated as a group, and women had weaker grip strengths than men. If grip strength is not known, weight, sex, hand dominance, and hobby demand (Table 1) can be used to predict it: Maximum dominant-hand grip strength = (height) (2.4) + (weight) (.14) - 100.2 + (sex [M = 1; F = 01) (33.5) - (handedness
[L = 1; R = 01) (9.6)
+ (hobby demand [A = 1, B = 2, C = 3, etc.]) (2.98).
Results The second trial of grip testing showed a decrease of maximum grip in 107 (50%) subjects; grip was increased in 51 subjects (24%) and unchanged in 56
n
Mean (lb.)
105 109 175 39
137 81 109 103
+-24 ? 16 *35 232
105 109 175 39
27 20 24 22
c5 -t-5 +6 -c6
105 109 175 39 Y-P______
19 14 17 15
r4 +-4 r5 *4
____
Tables 2 and 3 show the results of the grip strength, key pinch, and pulp pinch tests for both the dominant and nondominant hand. Table 3. Strength of Nondominant
Table 2. Strength of Dominant Hand
Grip strength Men Women Right-handed Left-handed Key pinch Men Women Right-handed Left-handed Pulp pinch Men Women Right-handed Left-handed -_
for Hand
Maximam Weight Lifted (lb.) _____.-
the nearest 5 lb. The level with the best results for left and right grip strength was repeated immediately after the first trial; the highest result was recorded as the maximum grip. One trial was performed for key and pulp pinch. Each subject was allowed to assume the upper extremity position of most power. Usually, the forearm was held in neutral for key pinch and in pronation for pulp pinch. Scores were recorded to the closest pound. Data were statistically compared and evaluated using a computerized statistical package (Statistical Analysis System, Cary, NC). The significance of the categorical data, such as occupation, was assessed using the chi-square test for independence. Differences in means were tested by Student’s r-test for independent variables and analysis of variance. Correlation and regression coefficients were also calculated to examine the relationships between data that involved continuous values, such as grip and pinch strengths. Correlations were established between maximum grip strength and height, weight, sex, hand dominance, and hobbies.
--
Level
SD
Grip strength Men Women Right-handed Left-handed Key pinch Men Women Right-handed Left-handed Pulp pinch Men Women Right-handed Left-handed
Hand
n
Mean (lb.)
SD
105 109 175 39
129 75 101 104
*22 t 16 *33 232
105 109 175 39
26 19 22 22
*5 24 r6 r6
105 109 175 39
18 13 15 16
*4 *3 r4 24
The Journal
Table 4. Relation of Pinch to Grip Strength
in
of Hand
Surgery
/ Vol.
667
19A No. 4 July 1994
110 __
the Dominant Hand* (n = 214) Mrm
confidence
loo
SD
&5 t4
22 16 ~~~~~~~
Maximum key pinch Maximum pulp pinch * 9%
(5%of grip)
interval.
When maximum grip strength in the dominant hand is known, pinch power can be calculated as a percentage of grip (Table 4), and the reverse is also true. When key and pulp pinch are known, they can be used to predict maximum dominant hand grip strength:
__
90 __ P B .p 0 p f 4
50_.
70 __
80 t
40
Maximum dominant-hand grip strength
!
0
i
1
3
2
5
4
&mar laud
= (maximum dominant-hand
key pinch) (2.79)
+ (maximum dominant-hand
pulp pinch) (2.71)
Figure 1. Strength profile for maximum Jamar level in dominant hands. Notice that the bell-shaped curve applies only to levels 2, 3. and 4.
Level 2 of the Jamar dynamometer yielded the maximum grip strength for both the dominant and nondominant hand in the majority of the subjects (Table 5). There was, however, a significant number of subjects whose maximum grip strength in both the dominant and nondominant hand was at a level other than level 2. In fact, 83 (39%) subjects had their maximum dominant-hand grip strength at a level other than level 2, and 87 (41%) subjects had their highest nondominant-hand grip strength at a level other than level 2. It was also found that 37 (34%) women and 40 (38%) men had their maximum dominant-hand grip strength at levels 3. 4, and 5. For the nondominant hand, 36 (33%) women and 48 (46%) men had their maximum grip strengths at a level higher than level 2. When considering all five Jamar levels, the results tended to follow a bellshaped curve whenever the maximum grip strength was at levels 2, 3, or 4 (Fig. I). However, when
the maximum grip strength was at level I (7 (3%) subjects), the curve sloped downward from level 1 to level 5. Whenever the maximum grip strength was at level 5 (2 (1%) subjects), level 1 was drastically lower than all other levels on the curve. When considering the strength difference between the dominant and nondominant hand, there was a 6% difference for the entire study group (men, 5% and women, 7%). There was also a 3% difference in key pinch and a 5% difference in pulp pinch between the dominant and nondominant hand for the entire group (Table 6). Left-handed subjects had, on the average, a weaker pinch in their dominant hand for both key and pulp pinch, while right-handed subjects had 5-7% higher pinch strength in their dominant hand. The Jamar level of maximum grip strength in the nondominant hand was frequently different from that of the dominant hand (Table 7). This discrep-
-
1.63
Table 5. Jamar Dynamometer Le\lel
Dominant I 3 ;
Level of Maximum Grip Strength (%)
M
F
2 (2) 63 (60) 32 (30) 8 (8) 0 (0)
5 (5) 68 0 (62) (28) 4 (4) 2 (2)
2 (5) 31 (54) 15 (38) I (3) 0 (0)
5 (3) I IO (63) 47 (27) 1I (6) 2 (I)
l(I) 56 (53) 44 (42) 3 (3) l(I)
2 (2) 71 (65) 33 (30) 2 (2) l(I)
0 26 I2 0 I
3 I01 65 5 I
Left Dominant
Right
Dotnincrnt
All
Hand
4 5 Nondominant I 3 3 4 5
7 (3)
I31 63 I3 2
(61) (29) (6) (1)
Hand (0) (67) (31) (0) (?I
(2) (58) (37) (3) (I)
3 (I) I27 (59) 77 (361 5 (2) 2 (1)
668 Crosby and Wehbk I Hand Strength Table 6. Strength Difference of Dominant to Nondominant Hand’” Group
Maximum grip strength All Right-handed Left-handed Maximum key pinch All Right-handed Left-handed Maximum pulp pinch All Right-handed Left-handed
n
Mean (%)t
214 175 39
6 8 -2
* 10 *8 + 14
214 17.5 39
3 5 -5
2 14 ? 12 5 16
214 175 39
5 7 -7
‘- 18 * 16 -c22
SD
* 95% confidence intervals. 1-Percent difference of dominant to nondominant hand. ancy varied according to the level at which maximum grip strength was reached. The discrepancy was least for level 2 where nearly one third of the subjects did not have their maximum grip strength at the same level on the opposite hand. Discussion Grip strength and pinch power are important parameters of hand function. A knowledge of the potential and limitations of the instruments used is crucial to the interpretation of their results, especially since they are usually taken into consideration when deciding the treatment course and disposition of a patient. Our goal was to determine the strength of an individual, therefore maximum grip strength (rather than average grip strength) was recorded. Once the level of maximum grip strength was determined after testing at all five levels of the Jamar dynamometer, the level of highest grip was repeated. This demonstrated that repeat testing is unnecessary and can be even confusing, since half of the subjects had worse maximum grip strength when the test was repeated. If repeated testing is done, the best result should be taken, not the average. Table 7. Frequency of Discrepancy in Jamar Dynamometer Level For Maximum Grip Strength Between the Two Hands (%) Level
M (n = 105)_______. F (n = 109)
1 2 3 4 5
212 21163 12132 718 No subjects
* Four subjects.
315 20168 19130 414 (loo)* 212 (loo)?
t Two subjects.
Group (n = 214)
517 41131 31162 1l/l2 212
It is generally agreed that men have greater strength than women,” and this trend is true irrespective of age. ‘K” This study also finds sex to be a predictor of maximum grip strength but, in addition, height and weight, as well as handedness and hobby demand, were found to be significant factors influencing maximum grip strength. Although hobby demand is the most subjective measurement in the prediction formula, its high correlation cannot be dismissed. Therefore, hobby demands should always be assessed in determining goals for strength. This will enhance patient satisfaction on discharge and return to work. Age was not found to be such an important factor, although a few previous studies concluded that grip strength was highest between 20 and 40 years.8-” These studies, however, tested only at level 2 of the Jamar dynamometer, thus, excluding 39% of the population (Table 5). Height and weight have been found previously to correlate with grip strength,” but handedness and work or hobby demands have not been taken into consideration. Studies are available on specific occupations and hobbies,l3.20.21 but not on physical demands as defined by the Dictionary of Occupational Titles. Many studies used homemade devices to measure strength rather than the Jamar dynamometer.“.“m’3 Normative values have been offered for each age group and sex. ‘.’ The standard deviation of these values in previous studies, as well as in this study, is so high (l&37%) that the normative values offer a false feeling of security. Sex is the most significant factor that should be taken into consideration, with the men in this study having a mean grip strength of 137 lb. and the women, 81 lb. Dominant hand grip strength, however, does depend on handedness since left-handed people, in general, had weaker grip strength than right-handed people (Table 2). A few studies have tabulated the normal values for pinch strength. *,’ Again, these were related to age, with standard deviations of 20-30% of the mean, making these detailed tables of little practical use. We agree with Young et al. that strength norms may be statistically accurate, but in view of the large fluctuations, they cannot be used to accurately predict a specific individual’s strength.3 Level 2 of the Jamar dynamometer was considered to be the best level for grip testing and has been adopted by the American Society of Hand Therapists for routine testing. Ih As a result, studies have been undertaken to evaluate strength using level 2 alone.’ Another study recommended using level 3 for men and level 2 for women, since these levels were thought to yield the maximum grip strength for each sex.’ As a result, other studies have limited their evaluation to levels 2 or 3, according to subject
The Journal
that such preference. I5 Our study demonstrated practice can be misleading. Sixty percent of men and 62% of women do have their maximum grip strength at level 2 but, overall, 39% of people do not. In addition, even when one hand has its maximum grip strength at one level, the other hand frequently has its maximum strength at a different level (Table 7). This may be due to varying hand sizes among people as well as in any one individual.24 The bell-shaped curve pattern of the Jamar dynamometer grip strength test has been touted as a standard for test reliability.4,5 Our results support the overall bell-shaped curve for Jamar dynamometer testing only when a subject’s maximum grip strength is reached at levels 2, 3, or 4. It should be noted, however, that in 9 (4%) of the subjects in our study. maximum grip strength was reached at level 1 or 5, and these do not have a bell-shaped curve (Fig. 1). This, indeed, is a small percentage and does not discredit the bell-shaped curve profile for the majority of the population. Another observation is that the curves were never horizontal, irrespective of which level yielded the highest strength. Other methods used to check the reliability of grip strength testing, such as the rapid exchange test, do not carry more reliability than the standard five-level test on the Jamar dynamometer.25 Studies that determine differences in strength between the two hands have results varying from 0% to 30%.’ Most of these studies, however, combined right- and left-hand dominant subjects and then determined the percent difference of the average grip. 7-9,11-14As a result, it was assumed for many years that the dominant hand is expected to be 10% stronger on average than the nondominant hand.‘.” This concept has been challenged by Petersen et al.” Our study supp orts Petersen et al.‘s findings in that the difference between the dominant and nondominant hand is 10% for the majority of people who are right-handed (Fig. 2). For left-handed people, there is usually no difference in grip strength between the two hands (Fig. 3). It should be noted, however, that this is true in less than 50% of the population, and these numbers should only be used as a guideline. In fact, 50% of left-handed people are weaker in their dominant hand, whereas only 9% of right-handed people are weaker in their dominant hand when compared with their nondominant hand. Similarly, for key pinch, 22% of right-handed people are weaker on their dominant side in contrast to 5 1% of left-handed subjects, and for pulp pinch, 19% of right-handed people are weaker on their dominant side compared to 44% of left-handed people who are weaker on their dominant side. These differences might be explained by the fact that it is a right-
of Hand
Surgery
/ Vol.
-20
-10
0
difference
Dam
669
19A No. 4 lulv 1994
-I %
30
20
10
to Non-h
Hand
Figure 2. Grip ratio for right-handed
subjects. Most righthanded subjects are 10% stronger on the right side.
handed world. Most tools and daily appliances were designed for the right hand. As a result, the right hand of both right- and left-handed people is exercised more often than the left on a daily basis. A comparison of the maximum grip strengths of various studies shows that the values given here are higher than those previously published (Table 8). This is explained by the methods used in each study. and again underlines the importance of testing subjects on all five levels of the Jamar dynamometer
d Y
36
.s 0 ;
30
5
25
3
20
;
15
rr 10 5 0 40
40
-20
-10
0
X Difference Dam to Non-bnI
10
20
Hend
Figure 3. Grip ratio for left-handed subjects. Most lefthanded subjects have no difference in strength between the two hands.
670
Crosby
and Wehbe
I Hand
Strength
Table 8. Maximum Grip Studies Comparison Hand
._
Schmidt and Toewes”*
Men Dominant Nondominant Women Dominant Nondominant
Lunde et al.9
113 110
-
-
67 59
MathioM*etz et al.“‘$
Current Study 3
104 103
137 129
63 63
81 75
* Dynamometer handles altered with sand-paint mixture. t Methods not standardized and unknown Jamar dynamometer level used. $ Only Jamar dynamometer level 2 used for all data. P All five Jamar dynamometer levels used with standardized method.
and allowing the patients to select their own wrist position during the test. The majority of right-handed individuals have a grip strength that is 10% higher in their dominant hand, and the majority of left-handed people have equal strength in both hands. Key pinch averaged 22% and pulp pinch averaged 16% of the maximum grip strength in most subjects. Maximum grip strengths followed a bell-shaped curve in over 95% of the subjects. Only 60% of the subjects had their maximum grip strength at level 2 of the Jamar dynamometer. References 1. Bechtol CO. Grip test: the use of a dynamometer with adjustable handle spacings. J Bone Joint Surg 1954: 36A:820-32. 2. Mathiowetz V, Weber K, Volland G, Kashman N. Reliability and validity of grip and pinch strength evaluations. J Hand Surg 1984;9A:222-6. 3. Young VL, Pin P, Kraemer BA, Gould RB, Nemergut L, Pellowski M. Fluctuation in grip and pinch strength among normal subjects. J Hand Surg 1989: 14A: 125-9. 4. Niebuhr BR, Marion R. Voluntary control of submaximal grip strength. Am J Phys Med Rehabil 1990;69: 96-101. 5. Stokes HM. The seriously uninjured hand: weakness of grip. J Occup Med 1983;25:683-4. WC, Lister GD, Hodges 6. Hildreth DH, Breidenbach AD. Detection of submaximal effort by use of the rapid exchange grip. J Hand Surg 1989;14A:742-5. 7. Kellor M, Frost J, Silberberg N, Iversen I, Cummings R. Hand strength and dexterity. Am J Occup Ther 1971;25:77-83. 8. Kellor M, Kondrasuk R, Iversen I, Frost J, Silberberg N, Hoglund M. Technical manual hand strength and dexterity tests. 1977. 9. Mathiowetz V, Kashman N, Volland G, Weber K, Dowe M, Rogers S. Grip and pinch strength: normative data for Adults. Arch Phys Med Rehabil 1985; 66:69-74. 10. Mathiowetz V, Wiemer DM, Federman SM. Grip and pinch strength: norms for 6- to lPyear-olds. Am J Occup Ther 1986;40:705-11.
11. Schmidt RT, Toews JV. Grip strength as measured by the Jamar dynamometer. Arch Phys Med Rehabil 1970;51:321-7. 12. Thorngren K-G, Werner CO. Normal grip strength. Acta Orthop Stand 1979;50:255-9. 13. Jarit P. Dominant-hand to nondominant-hand grip strength ratios of college baseball players. J Hand Ther 1991:4: 123-6. Lunde BK, Brewer WD, Garcia PA. Grip strength of college women. Arch Phys Med Rehabil 1972;491-3. Petersen P, Petrick M, Connor H. Conklin H. Grip strength and hand dominance: challenging the 10% rule. Am J Occup Ther 1989;43:444-7. Fess EE. Grip strength. In: Clinical assessment recommendations. 2nd ed. Chicago: American Society of Hand Therapists 1992;41-45. 17. Mathiowetz V. Rennells C, Donahoe L. Effect of elbow position on grip and key pinch strength. J Hand Surg 1985;lOA:694-7. 18. O’Driscoll SW. Horii E, Ness R, Cahalan TD. Richards RR, An K-N. The relationship between wrist position, grasp size, and grip strength. J Hand Surg 1992;17A: 169-77. 19. Agnew PJ, Maas F. Hand function related to age and sex. Arch Phys Med Rehabil 1982;63:269-71. 20. Nemethi CE. An evaluation of hand grip in industry. Ind Med Surg 1952;21:65-6. 21. Nygard C-H, Luopajarvi T, Cedercreutz G, Ilmarinen J. Musculoskeletal capacity of employees aged 44 to 58 years in physical, mental and mixed types of work. Eur J Appl Physiol 1987;56:555-61. 22. Kroll W. Reliability of a selected measure of human strength. Res Q 1963;33:410-7. 23. McGarvey SR. Morrey BF, Askew LJ, An K-N. Reliability of isometric strength testing. Clin Orthop 1984; 185:301-5. 24. Fess EE. The effects of Jaymar dynamometer handle position and test protocol on normal grip strength. J Hand Surg 1982;7:308-9. 25. Joughin K, Gulati P, Mackinnon SE, McCabe S, Murray JF, Griffiths S et al. An evaluation of rapid exchange and simultaneous grip test. J Hand Surg 1993; 18A:245-52. 26. US Department of Labor Employment and Training Administration, Washington DC. Dictionary of Occupational Titles. 4th ed. Vol. 2 1991;1013.
normal
hands.
hundred
Two
at all five levels. hand
dominance,
hand
strength
fourteen
A pinch
and the difference
volunteers
were
tested
between with
gauge was used to assess key and pulp
and hobby
demands
were
predictive
dominant
a calibrated pinch.
of maximum
and nondominant Jamar dynamometer Height,
grip.
grip for women
was 81 lb. and for men was 137 lb. Key pinch
averaged
pinch
16% of maximum
had maximum
level
averaged
2. The majority
dominant
of right-handed
side. In left-handed
nant hand was stronger
grip.
subjects,
Only subjects
were
patients
10%
stronger
22%,
in grip
and Methods
Two hundred fourteen subjects were randomly selected. All subjects were in good physical health and claimed to have no previous hand injuries within the past 5 years. They had diverse occupational and recreational backgrounds that were assessed by a
From the Pennsylvania Hand Center. and Bryn Mawr Hospital. Bryn Mawr, and Thomas Jefferson University. Philadelphia. PA. Received for publication March 1-2. 1993: accepted in revised form Oct. 26. 1993. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Pennsylvania Hand Center, Reprints Department. PO Box 141. Bryn Mawr. PA 19010.
subjects.
(J Hand
Surg 1994;
sex,
maximum while
pulp
strengths
strength
mean grip was the same for both hands;
in 50% of left-handed
Few studies have used all five levels of the Jamar dynamometer (Asimow Engineering, Los Angeles. CA). These studies were undertaken to test reliability,‘.? fluctuations,’ or feigned weakness in grip testing.jwh Other studies have been performed to determine norms7-” and differences in strength between hands.‘l-‘? However. these studies did not test strength on all live levels. ‘-‘I Some of these studies included pinch strength measurements2.‘.Y.‘” but did not relate their findings extensively to demographics or grip strength. This study determined normal grip and pinch power with all five levels of the Jamar dynamometer, as well as pinch strength, using a pinch gauge (B & L Engineering, Santa Fe, CA). Materials
129 (60%)
weight,
Mean
at
on the
the nondomi-
19A:
665-670.1
physical demand scale as defined by the Dictionary of Occupational Titles (Table I ). The study included 214 subjects, 105 men and 109 women. Ages ranged between 16 and 63 years (mean, 32 years). There were 175 right-handed subjects (82%) and 39 left-handed subjects (18%). Subject body weight ranged from 45 to I I8 kg (mean, 71 kg), and height ranged from 150 to 198 cm (mean. 173 cm). A calibrated Jamar dynamometer was used by two hand therapists to assess grip strength at all five levels. The smallest grip was labeled as level I and the largest as level 5. A pinch gauge was used to assess key and pulp pinch. These instruments have been reported to be accurate for the measurement of strength with good inter-rater reliability.’ Time of day was not recorded since it has been shown to be of little significance.3 One trial was performed to assess grip strength using the standard arm position as recommended by the American Society of Hand Therapists: shoulder adducted and neutrally rotated, elbow at 90” flexion. and forearm in neutral.‘h.‘7 Wrist position was selfselected by each subject to allow for maximal gripping.lx Standard instructions were used: the subjects were asked to squeeze the gauge as hard as they possibly could with the extremity in the standard position.’ The dominant hand was tested at level 1 of the dynamometer: the other hand was tested next at the same level. Levels 2-5 were then tested in a similar fashion, alternating hands. Scores were recorded to The journal
of Hand
Surgery
665
666
Crosby and Wehbe I Hand Strength
Table 1. Physical Group
Physical Demand
1 2 3 4 5 6
Sedentary Light Medium Medium-heavy Heavy Very heavy
Level”
Demand
10 20 50 75 100 >I00
Use Sample
Sample Hobby
_____Occapation Receptionist Business executive Secretary Grocery checker Warehouse worker Steel worker
-Reading Swimming Tennis/golf Baseball
Hockey Weight lifting
subjects (26%). The increase was by 5-20 lb; decrease by 5-30 lb. Height, weight, sex, hand dominance, and hobby demand levels were predictive of maximum grip strength (adjusted R * = 75%; p = .OOOl). Hobbies had a stronger correlation (p = .0027) to maximum grip than occupational demands (p = .2806). The left-handed subjects had weaker grip strengths than the right-handed subjects when evaluated as a group, and women had weaker grip strengths than men. If grip strength is not known, weight, sex, hand dominance, and hobby demand (Table 1) can be used to predict it: Maximum dominant-hand grip strength = (height) (2.4) + (weight) (.14) - 100.2 + (sex [M = 1; F = 01) (33.5) - (handedness
[L = 1; R = 01) (9.6)
+ (hobby demand [A = 1, B = 2, C = 3, etc.]) (2.98).
Results The second trial of grip testing showed a decrease of maximum grip in 107 (50%) subjects; grip was increased in 51 subjects (24%) and unchanged in 56
n
Mean (lb.)
105 109 175 39
137 81 109 103
+-24 ? 16 *35 232
105 109 175 39
27 20 24 22
c5 -t-5 +6 -c6
105 109 175 39 Y-P______
19 14 17 15
r4 +-4 r5 *4
____
Tables 2 and 3 show the results of the grip strength, key pinch, and pulp pinch tests for both the dominant and nondominant hand. Table 3. Strength of Nondominant
Table 2. Strength of Dominant Hand
Grip strength Men Women Right-handed Left-handed Key pinch Men Women Right-handed Left-handed Pulp pinch Men Women Right-handed Left-handed -_
for Hand
Maximam Weight Lifted (lb.) _____.-
the nearest 5 lb. The level with the best results for left and right grip strength was repeated immediately after the first trial; the highest result was recorded as the maximum grip. One trial was performed for key and pulp pinch. Each subject was allowed to assume the upper extremity position of most power. Usually, the forearm was held in neutral for key pinch and in pronation for pulp pinch. Scores were recorded to the closest pound. Data were statistically compared and evaluated using a computerized statistical package (Statistical Analysis System, Cary, NC). The significance of the categorical data, such as occupation, was assessed using the chi-square test for independence. Differences in means were tested by Student’s r-test for independent variables and analysis of variance. Correlation and regression coefficients were also calculated to examine the relationships between data that involved continuous values, such as grip and pinch strengths. Correlations were established between maximum grip strength and height, weight, sex, hand dominance, and hobbies.
--
Level
SD
Grip strength Men Women Right-handed Left-handed Key pinch Men Women Right-handed Left-handed Pulp pinch Men Women Right-handed Left-handed
Hand
n
Mean (lb.)
SD
105 109 175 39
129 75 101 104
*22 t 16 *33 232
105 109 175 39
26 19 22 22
*5 24 r6 r6
105 109 175 39
18 13 15 16
*4 *3 r4 24
The Journal
Table 4. Relation of Pinch to Grip Strength
in
of Hand
Surgery
/ Vol.
667
19A No. 4 July 1994
110 __
the Dominant Hand* (n = 214) Mrm
confidence
loo
SD
&5 t4
22 16 ~~~~~~~
Maximum key pinch Maximum pulp pinch * 9%
(5%of grip)
interval.
When maximum grip strength in the dominant hand is known, pinch power can be calculated as a percentage of grip (Table 4), and the reverse is also true. When key and pulp pinch are known, they can be used to predict maximum dominant hand grip strength:
__
90 __ P B .p 0 p f 4
50_.
70 __
80 t
40
Maximum dominant-hand grip strength
!
0
i
1
3
2
5
4
&mar laud
= (maximum dominant-hand
key pinch) (2.79)
+ (maximum dominant-hand
pulp pinch) (2.71)
Figure 1. Strength profile for maximum Jamar level in dominant hands. Notice that the bell-shaped curve applies only to levels 2, 3. and 4.
Level 2 of the Jamar dynamometer yielded the maximum grip strength for both the dominant and nondominant hand in the majority of the subjects (Table 5). There was, however, a significant number of subjects whose maximum grip strength in both the dominant and nondominant hand was at a level other than level 2. In fact, 83 (39%) subjects had their maximum dominant-hand grip strength at a level other than level 2, and 87 (41%) subjects had their highest nondominant-hand grip strength at a level other than level 2. It was also found that 37 (34%) women and 40 (38%) men had their maximum dominant-hand grip strength at levels 3. 4, and 5. For the nondominant hand, 36 (33%) women and 48 (46%) men had their maximum grip strengths at a level higher than level 2. When considering all five Jamar levels, the results tended to follow a bellshaped curve whenever the maximum grip strength was at levels 2, 3, or 4 (Fig. I). However, when
the maximum grip strength was at level I (7 (3%) subjects), the curve sloped downward from level 1 to level 5. Whenever the maximum grip strength was at level 5 (2 (1%) subjects), level 1 was drastically lower than all other levels on the curve. When considering the strength difference between the dominant and nondominant hand, there was a 6% difference for the entire study group (men, 5% and women, 7%). There was also a 3% difference in key pinch and a 5% difference in pulp pinch between the dominant and nondominant hand for the entire group (Table 6). Left-handed subjects had, on the average, a weaker pinch in their dominant hand for both key and pulp pinch, while right-handed subjects had 5-7% higher pinch strength in their dominant hand. The Jamar level of maximum grip strength in the nondominant hand was frequently different from that of the dominant hand (Table 7). This discrep-
-
1.63
Table 5. Jamar Dynamometer Le\lel
Dominant I 3 ;
Level of Maximum Grip Strength (%)
M
F
2 (2) 63 (60) 32 (30) 8 (8) 0 (0)
5 (5) 68 0 (62) (28) 4 (4) 2 (2)
2 (5) 31 (54) 15 (38) I (3) 0 (0)
5 (3) I IO (63) 47 (27) 1I (6) 2 (I)
l(I) 56 (53) 44 (42) 3 (3) l(I)
2 (2) 71 (65) 33 (30) 2 (2) l(I)
0 26 I2 0 I
3 I01 65 5 I
Left Dominant
Right
Dotnincrnt
All
Hand
4 5 Nondominant I 3 3 4 5
7 (3)
I31 63 I3 2
(61) (29) (6) (1)
Hand (0) (67) (31) (0) (?I
(2) (58) (37) (3) (I)
3 (I) I27 (59) 77 (361 5 (2) 2 (1)
668 Crosby and Wehbk I Hand Strength Table 6. Strength Difference of Dominant to Nondominant Hand’” Group
Maximum grip strength All Right-handed Left-handed Maximum key pinch All Right-handed Left-handed Maximum pulp pinch All Right-handed Left-handed
n
Mean (%)t
214 175 39
6 8 -2
* 10 *8 + 14
214 17.5 39
3 5 -5
2 14 ? 12 5 16
214 175 39
5 7 -7
‘- 18 * 16 -c22
SD
* 95% confidence intervals. 1-Percent difference of dominant to nondominant hand. ancy varied according to the level at which maximum grip strength was reached. The discrepancy was least for level 2 where nearly one third of the subjects did not have their maximum grip strength at the same level on the opposite hand. Discussion Grip strength and pinch power are important parameters of hand function. A knowledge of the potential and limitations of the instruments used is crucial to the interpretation of their results, especially since they are usually taken into consideration when deciding the treatment course and disposition of a patient. Our goal was to determine the strength of an individual, therefore maximum grip strength (rather than average grip strength) was recorded. Once the level of maximum grip strength was determined after testing at all five levels of the Jamar dynamometer, the level of highest grip was repeated. This demonstrated that repeat testing is unnecessary and can be even confusing, since half of the subjects had worse maximum grip strength when the test was repeated. If repeated testing is done, the best result should be taken, not the average. Table 7. Frequency of Discrepancy in Jamar Dynamometer Level For Maximum Grip Strength Between the Two Hands (%) Level
M (n = 105)_______. F (n = 109)
1 2 3 4 5
212 21163 12132 718 No subjects
* Four subjects.
315 20168 19130 414 (loo)* 212 (loo)?
t Two subjects.
Group (n = 214)
517 41131 31162 1l/l2 212
It is generally agreed that men have greater strength than women,” and this trend is true irrespective of age. ‘K” This study also finds sex to be a predictor of maximum grip strength but, in addition, height and weight, as well as handedness and hobby demand, were found to be significant factors influencing maximum grip strength. Although hobby demand is the most subjective measurement in the prediction formula, its high correlation cannot be dismissed. Therefore, hobby demands should always be assessed in determining goals for strength. This will enhance patient satisfaction on discharge and return to work. Age was not found to be such an important factor, although a few previous studies concluded that grip strength was highest between 20 and 40 years.8-” These studies, however, tested only at level 2 of the Jamar dynamometer, thus, excluding 39% of the population (Table 5). Height and weight have been found previously to correlate with grip strength,” but handedness and work or hobby demands have not been taken into consideration. Studies are available on specific occupations and hobbies,l3.20.21 but not on physical demands as defined by the Dictionary of Occupational Titles. Many studies used homemade devices to measure strength rather than the Jamar dynamometer.“.“m’3 Normative values have been offered for each age group and sex. ‘.’ The standard deviation of these values in previous studies, as well as in this study, is so high (l&37%) that the normative values offer a false feeling of security. Sex is the most significant factor that should be taken into consideration, with the men in this study having a mean grip strength of 137 lb. and the women, 81 lb. Dominant hand grip strength, however, does depend on handedness since left-handed people, in general, had weaker grip strength than right-handed people (Table 2). A few studies have tabulated the normal values for pinch strength. *,’ Again, these were related to age, with standard deviations of 20-30% of the mean, making these detailed tables of little practical use. We agree with Young et al. that strength norms may be statistically accurate, but in view of the large fluctuations, they cannot be used to accurately predict a specific individual’s strength.3 Level 2 of the Jamar dynamometer was considered to be the best level for grip testing and has been adopted by the American Society of Hand Therapists for routine testing. Ih As a result, studies have been undertaken to evaluate strength using level 2 alone.’ Another study recommended using level 3 for men and level 2 for women, since these levels were thought to yield the maximum grip strength for each sex.’ As a result, other studies have limited their evaluation to levels 2 or 3, according to subject
The Journal
that such preference. I5 Our study demonstrated practice can be misleading. Sixty percent of men and 62% of women do have their maximum grip strength at level 2 but, overall, 39% of people do not. In addition, even when one hand has its maximum grip strength at one level, the other hand frequently has its maximum strength at a different level (Table 7). This may be due to varying hand sizes among people as well as in any one individual.24 The bell-shaped curve pattern of the Jamar dynamometer grip strength test has been touted as a standard for test reliability.4,5 Our results support the overall bell-shaped curve for Jamar dynamometer testing only when a subject’s maximum grip strength is reached at levels 2, 3, or 4. It should be noted, however, that in 9 (4%) of the subjects in our study. maximum grip strength was reached at level 1 or 5, and these do not have a bell-shaped curve (Fig. 1). This, indeed, is a small percentage and does not discredit the bell-shaped curve profile for the majority of the population. Another observation is that the curves were never horizontal, irrespective of which level yielded the highest strength. Other methods used to check the reliability of grip strength testing, such as the rapid exchange test, do not carry more reliability than the standard five-level test on the Jamar dynamometer.25 Studies that determine differences in strength between the two hands have results varying from 0% to 30%.’ Most of these studies, however, combined right- and left-hand dominant subjects and then determined the percent difference of the average grip. 7-9,11-14As a result, it was assumed for many years that the dominant hand is expected to be 10% stronger on average than the nondominant hand.‘.” This concept has been challenged by Petersen et al.” Our study supp orts Petersen et al.‘s findings in that the difference between the dominant and nondominant hand is 10% for the majority of people who are right-handed (Fig. 2). For left-handed people, there is usually no difference in grip strength between the two hands (Fig. 3). It should be noted, however, that this is true in less than 50% of the population, and these numbers should only be used as a guideline. In fact, 50% of left-handed people are weaker in their dominant hand, whereas only 9% of right-handed people are weaker in their dominant hand when compared with their nondominant hand. Similarly, for key pinch, 22% of right-handed people are weaker on their dominant side in contrast to 5 1% of left-handed subjects, and for pulp pinch, 19% of right-handed people are weaker on their dominant side compared to 44% of left-handed people who are weaker on their dominant side. These differences might be explained by the fact that it is a right-
of Hand
Surgery
/ Vol.
-20
-10
0
difference
Dam
669
19A No. 4 lulv 1994
-I %
30
20
10
to Non-h
Hand
Figure 2. Grip ratio for right-handed
subjects. Most righthanded subjects are 10% stronger on the right side.
handed world. Most tools and daily appliances were designed for the right hand. As a result, the right hand of both right- and left-handed people is exercised more often than the left on a daily basis. A comparison of the maximum grip strengths of various studies shows that the values given here are higher than those previously published (Table 8). This is explained by the methods used in each study. and again underlines the importance of testing subjects on all five levels of the Jamar dynamometer
d Y
36
.s 0 ;
30
5
25
3
20
;
15
rr 10 5 0 40
40
-20
-10
0
X Difference Dam to Non-bnI
10
20
Hend
Figure 3. Grip ratio for left-handed subjects. Most lefthanded subjects have no difference in strength between the two hands.
670
Crosby
and Wehbe
I Hand
Strength
Table 8. Maximum Grip Studies Comparison Hand
._
Schmidt and Toewes”*
Men Dominant Nondominant Women Dominant Nondominant
Lunde et al.9
113 110
-
-
67 59
MathioM*etz et al.“‘$
Current Study 3
104 103
137 129
63 63
81 75
* Dynamometer handles altered with sand-paint mixture. t Methods not standardized and unknown Jamar dynamometer level used. $ Only Jamar dynamometer level 2 used for all data. P All five Jamar dynamometer levels used with standardized method.
and allowing the patients to select their own wrist position during the test. The majority of right-handed individuals have a grip strength that is 10% higher in their dominant hand, and the majority of left-handed people have equal strength in both hands. Key pinch averaged 22% and pulp pinch averaged 16% of the maximum grip strength in most subjects. Maximum grip strengths followed a bell-shaped curve in over 95% of the subjects. Only 60% of the subjects had their maximum grip strength at level 2 of the Jamar dynamometer. References 1. Bechtol CO. Grip test: the use of a dynamometer with adjustable handle spacings. J Bone Joint Surg 1954: 36A:820-32. 2. Mathiowetz V, Weber K, Volland G, Kashman N. Reliability and validity of grip and pinch strength evaluations. J Hand Surg 1984;9A:222-6. 3. Young VL, Pin P, Kraemer BA, Gould RB, Nemergut L, Pellowski M. Fluctuation in grip and pinch strength among normal subjects. J Hand Surg 1989: 14A: 125-9. 4. Niebuhr BR, Marion R. Voluntary control of submaximal grip strength. Am J Phys Med Rehabil 1990;69: 96-101. 5. Stokes HM. The seriously uninjured hand: weakness of grip. J Occup Med 1983;25:683-4. WC, Lister GD, Hodges 6. Hildreth DH, Breidenbach AD. Detection of submaximal effort by use of the rapid exchange grip. J Hand Surg 1989;14A:742-5. 7. Kellor M, Frost J, Silberberg N, Iversen I, Cummings R. Hand strength and dexterity. Am J Occup Ther 1971;25:77-83. 8. Kellor M, Kondrasuk R, Iversen I, Frost J, Silberberg N, Hoglund M. Technical manual hand strength and dexterity tests. 1977. 9. Mathiowetz V, Kashman N, Volland G, Weber K, Dowe M, Rogers S. Grip and pinch strength: normative data for Adults. Arch Phys Med Rehabil 1985; 66:69-74. 10. Mathiowetz V, Wiemer DM, Federman SM. Grip and pinch strength: norms for 6- to lPyear-olds. Am J Occup Ther 1986;40:705-11.
11. Schmidt RT, Toews JV. Grip strength as measured by the Jamar dynamometer. Arch Phys Med Rehabil 1970;51:321-7. 12. Thorngren K-G, Werner CO. Normal grip strength. Acta Orthop Stand 1979;50:255-9. 13. Jarit P. Dominant-hand to nondominant-hand grip strength ratios of college baseball players. J Hand Ther 1991:4: 123-6. Lunde BK, Brewer WD, Garcia PA. Grip strength of college women. Arch Phys Med Rehabil 1972;491-3. Petersen P, Petrick M, Connor H. Conklin H. Grip strength and hand dominance: challenging the 10% rule. Am J Occup Ther 1989;43:444-7. Fess EE. Grip strength. In: Clinical assessment recommendations. 2nd ed. Chicago: American Society of Hand Therapists 1992;41-45. 17. Mathiowetz V. Rennells C, Donahoe L. Effect of elbow position on grip and key pinch strength. J Hand Surg 1985;lOA:694-7. 18. O’Driscoll SW. Horii E, Ness R, Cahalan TD. Richards RR, An K-N. The relationship between wrist position, grasp size, and grip strength. J Hand Surg 1992;17A: 169-77. 19. Agnew PJ, Maas F. Hand function related to age and sex. Arch Phys Med Rehabil 1982;63:269-71. 20. Nemethi CE. An evaluation of hand grip in industry. Ind Med Surg 1952;21:65-6. 21. Nygard C-H, Luopajarvi T, Cedercreutz G, Ilmarinen J. Musculoskeletal capacity of employees aged 44 to 58 years in physical, mental and mixed types of work. Eur J Appl Physiol 1987;56:555-61. 22. Kroll W. Reliability of a selected measure of human strength. Res Q 1963;33:410-7. 23. McGarvey SR. Morrey BF, Askew LJ, An K-N. Reliability of isometric strength testing. Clin Orthop 1984; 185:301-5. 24. Fess EE. The effects of Jaymar dynamometer handle position and test protocol on normal grip strength. J Hand Surg 1982;7:308-9. 25. Joughin K, Gulati P, Mackinnon SE, McCabe S, Murray JF, Griffiths S et al. An evaluation of rapid exchange and simultaneous grip test. J Hand Surg 1993; 18A:245-52. 26. US Department of Labor Employment and Training Administration, Washington DC. Dictionary of Occupational Titles. 4th ed. Vol. 2 1991;1013.