10% rule is it valid

8/9/2019 10% rule is it valid

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Indian Journal of physiotherapy, Vol 45, No 2 (March): pp 116-121

Does the dominant hand possess 10% greater grip strength than the non dominant hand?

Rama Krishna Gedela, MSPT, Alanah Kirby, MSPT, Heini Huhtala, MSc

Background: The 10% rule states that the dominant hand possesses 10% more grip strength than the non domi-

nant hand. The 10% rule has been used for many years to plan out strength goals and rehabilitation programmes

in patients with hand injuries .The purpose of the study was to test the utility of the 10% rule in hand rehabilitation

and to verify whether the 10% rule applies to both left and right handed subjects. Sample size: The sample for the

study consisted of 40 healthy physiotherapy students. Methodology: Grip strength was measured using a standard

Jamar Dynamometer which was calibrated before and after data collection to ensure the data collected was accu-

rate. Standardised positioning (ASHT) and verbal instructions were used. Three trials were conducted for each arm,

with one minute rest periods to counteract fatigue. Results: Results showed an over all 10.02% grip strength differ-

ence between the dominant and non dominant hand there by proving the 10% rule as valid. However when sepa-

rate analysis of the right handed and left handed subjects was done, a 10.37% difference for right handed subjects

and a 8.16% difference for the left handed subjects was found. Conclusion: The study showed that the 10% rule

was valid for right handed persons alone. In the case of left handed persons the grip strength must be considered

equal in both hands.

The upper limb particularly the hand proves

paramount to daily life. The hand has a central

role in many activities of daily life like eating,

writing, typing, etc, the list is endless. Loss of

optimal hand function does not merely hamper

practical tasks such as personal hygiene it

affects other areas of the life 1. Grip strength

measurement is an important component of

hand rehabilitation because it assesses the

patient’s initial limitation as compared to the

norms 2. In cases of hand injury or disease,

clinicians commonly incorporate grip strength

in their assessment procedure to evaluate the

effectiveness of rehabilitation intervention. The

10% rule is often used by the clinicians in goal

setting.

Index words: grip strength; dominance; Jamar dynamometer; muscle strength; Dynamometry

This rule states that “ dominant hand has 10%

greater strength than the non dominant hand” 3.

In 1954, Betchol 3 observed that most patients

presented a difference of around 5 to 10%

between their dominant and non-dominant hands

on grip strength measurements. A number of

studies have since been conducted to establish

normative data for grip strength measurements to

be used as treatment guidelines in the

rehabilitation programmes. A study done by

Mathiowetz et al 4 revealed that the grip strength

of the right hand was stronger than the grip

strength in the left hand. Separate analysis of left

hand and right hand data revealed little functional

difference in the mean scores. This finding did

not support the 10% rule. Lunde et al 6 conducted

a three year study to examine the nutritional status

of 57 college women. Grip strength was one of

the many variables that were measured. The datafor the grip strength variable consisted of 107

measurements. The results indicated that there

From the Department of physiotherapy ,Queen Margaret University, Edinburgh.

Received February 7, 2008: accepted in revised form March 1, 2008. Online manuscript submission

and reviewshttp://indianjournalofphysiotherapy.net Address reprint requests to Rama Krishna Gedela, MSPT. E-mail: [email protected]

© 2008 by Indian Journal of physiotherapy


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was a 13% grip strength advantage in dominant hand when compared to non-dominant hand. However

a review of the data for each measurement revealed that 24% of the 107 measurements had showed

strength readings equal to or greater than the dominant hand.

Schmidt and Toews 7 in a larger study of 1,128 males and 80 females tested grip strength as a part of

the physical examination for employment at a large manufacturing firm. The results indicated a 10.3

strength advantage in dominant hand as compared to non-dominant hand, thus supporting the 10% rule.

When the individual scores were examined they found that 22.6% of the men were stronger in their

non-dominant hand and 5.4% had equal grip strength in their dominant and non-dominant hand. On

the basis Schmidt questioned the application of the 10% rule in such areas as workers compensa-

tion 7 .

Swason et al 8 conducted a study of 50 men and 50 women. The results indicated that the grip

strength of the non-dominant hand was equal to or greater than that of the dominant hand in 29% of the

subjects.

In the above three studies 24-29% of the subjects had grip strength readings in their non-dominant hand

that were equal to or greater than the grip strength readings of the dominant hand 6-8. On the basis of

this alone the utility of the 10% rule can be challenged. However none of these studies addressed right

or left hand grip strength differences in relation to the dominance6-8

. The aim of the present study is todetermine if there is a significant difference between grip strength of the dominant and non-dominant

hand, and to qualify if this difference agrees with the 10% rule. Further this study also aims to

investigate whether or not the 10% rule applies for both right and left handed individuals or does it need

to be modified.

METHOD

A convenient sample of 40 university physiotherapy students (12 females and 28 males) volunteered to

participate in this study. Ages ranged from 17 to 26 years (mean 21.9 years ± 0.57). Self report

established that six were left hand dominant (four males and two females). EHI10 was used to verify

the hand dominance. Subjects were not paid for their participation. The study was advertised through

the moderator in the college web mail and posters placed in location of high visibility. Some subjects

were also recruited through personal communication of the researchers.

A standard, adjustable hand held Jamar Hand Dynamometer (JHD) was used to measure grip strength.

The second position (of the 5 positions available) was used as recommended by Kellor et al 8.


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The dynamometer was reset to zero prior to each

reading of the grip strength. Suspended weight

calibration was performed before and after the

data collection process to ensure the accuracy of

the data collected. Linear correlation was used to

analyse the association between suspended

weights during calibration and the actual reading

on the JHD. The correlation between the two var-

iables was r=0.99, with p-value of p


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Results

The data collected was analysed using the SPSS (version 12) statistical package. All the data

was normal and ratio in nature thus parametric tests were used to assess if there was signifi-

cant difference between the dominant and non dominant hand. Mean grip strength values

obtained using JHD showed 15% of the subjects (n=6) showed greater grip strength in their

non-dominant hand in comparison to their dominant hand grip strength. A paired sample

t-test was used to assess if there was any significant difference between the dominant and

non-dominant hand. Paired samples t-test was also used to do separate analysis of left and

right handed subjects to assess if there was a significant difference between their dominant

and non-dominant hand. Values equal to or less than 0.01 were accepted as significant

(p


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according to sex right handed men had a mean percentage difference of 11.8% while right handed

women has a value of just 7.4%. A paired samples t-test was conducted to investigate if there was

any difference between the values for the left and right hands. A Pearson's correlation of r=0.98 was

achieved, thus illustrating that the variables are highly correlated. The paired samples t-test was sta-tistically significant(p


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of this attitude thereby leaving the left handed people with no option but to use their non dominant

hand far more than their dominant hand. As a result, the right hand of both the right and left handed

people is utilised in functional tasks more often than the left hand on daily may account for the re-

sults obtained.

References:

(1) Fisher MB, Birren JE. Age and hand strength. J Appl Psychol. 1947; 31(5): 54-57.

(2) Nalebuff E, Phillips C. The rheumatoid thumb. Clin Rheum Dis. 1984; 10(3): 589-607.

(3) Betchol CO. Grip test: The use of a dynamometer with adjustable handle spacings. J Bone Joint Surg Am. 1954; 36-a(4):

820-4.

(4) Mathiowetz V, Kashman N, Volland G. Grip and Pinch Strength: Normative data for adults. Arch Phys Med Rehabil.

1985;66(2): 69-74.

(5) Mathiowetz V, Rennells C, Donahoe L. Effect of elbow position on grip and key pinch strength. J Hand Surg. 1985; 10(5):

694-7.

(6) Lunde BK, Brewer WD, Garcia PA. Grip strength of college women. Arch Phys Med Rehabil. 1972; 53(10):491-3.

(7) Schmidt RT, Toews JV. Grip strength as measured by the Jamar dynamometer. Arch Phys Med Rehabil. 1970; 51(6): 321-7.

(8) Swason AB, Matev IB, De GrooT G. The strength of the hand. Bull Prosthet Res. 1970; 10(14):145-53.

(9) Kellor M, Frost J, Silberberg N, and others. Hand strength and dexterity. Am J Occup Ther. 1971; 25(2): 77-83.

(10) Fess EE, Moron CA. Clinical assessment recommendations. Philadelphia:American Society of Hand Therapists

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10% rule is it valid