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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: kishangedela@yahoo.com
© 2008 by Indian Journal of physiotherapy
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Indian Journal of physiotherapy, Vol 45, No 2 (March): pp 116-121
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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Indian Journal of physiotherapy, Vol 45, No 2 (March): pp 116-121
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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Indian Journal of physiotherapy, Vol 45, No 2 (March): pp 116-121
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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Indian Journal of physiotherapy, Vol 45, No 2 (March): pp 116-121
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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Indian Journal of physiotherapy, Vol 45, No 2 (March): pp 116-121
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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