Keywords
Hand strength - Pinch strength - Muscle dynamometer - Korean population - Demographic
transition
INTRODUCTION
Grip and pinch strength are standard constructs of overall hand function. Testing
of such strength is simple and inexpensive and is frequently performed to evaluate
outcomes following upper extremity injuries [[1]
[2]]. In addition, hand strength levels provide validated assessments of a patient's
general functional index and the nutritional indices among inpatients receiving nutritional
intervention [[3]
[4]
[5]
[6]].
In most assessments of strength in hand injury patients, the contralateral non-injured
hand serves as a control [[7]]. Though such intra-individual comparisons are pragmatic, the interpretation of
such data could be questioned from a scientific point of view.
Even among healthy individuals, as might be expected, self-assessment of strength
varies from the dominant to non-dominant hand, which has been validated by Massy-Westropp
et al. [[8]], who have reported variations in intra-individual hand strengths to be great and
virtually universal. However, another study [[9]] on normative hand strength has revealed that hand dominance has varying correlations
with the types of strength measured.
Grip and pinch strength is generally influenced by the health status and level of
physical activity of a person [[10]
[11]]. The type of occupation appears to have a specific correlation to the degree of
strength exhibited [[12]], and a recent study in the Chinese population [[13]] has found a correlation between grip strength and anthropometric factors such as
forearm circumference, body height, and weight.
Presently, such normative data regarding hand strength is not available for the Korean
population. Evaluation of strength recovery in hand injury patients in this population
varies greatly in both intra- and inter-individual comparisons. Consequently, strength
assessments in postoperative hand patients are subjective at best. Thus, this study
was designed to characterize and establish baseline hand strength values and to determine
what patient-related factors might influence hand strength in the healthy Korean population.
METHODS
Subjects
The subjects in this study were recruited from patients who were visiting our institution
for normal health screening visits. The inclusion criteria were as follows: any Korean
person, of either sex, and older than 10 years of age. Exclusion criteria were any
history of 1) inflammatory disease or 2) neurologic disease or 3) traumatic event
to the upper extremity requiring medical management or leading to restrictions of
daily activity.
Study protocol
All surveys and hand strength assessments were administered by a single researcher.
Each potential research subject was given a paper survey to obtain demographic information,
hand dominance (i.e., the writing hand), and medical history. If a patient satisfied
the inclusion and exclusion criteria, the following anthropometric measurements were
taken as previously reported in an anthropometric study of a Caucasian population
[[14]]: 1) hand width (measured at the level of the distal palmar crease), 2) hand length
(distal wrist crease to the tip of the longest finger), 3) forearm length (lateral
humeral epicondyle to radial styloid process), and 4) forearm circumference (measured
to include the midpoint of the forearm length). Total body weight and height were
measured with standard scales.
Grip strength was measured with a Jamar hand dynamometer, and both of the pinch strengths
were measured with a Jamar hydraulic pinch gauge (Patterson Medical, Bolingbrook,
IL, USA). For each of the strength assessments, subjects were seated with the shoulder
adducted and neutrally rotated, elbow flexed at 90° with the forearm in neutral position,
and wrists between 0° and 30° of flexion and between 0° and 15° of ulnar deviation
[[15]]. Each test was performed three consecutive times at 1-minute intervals to reduce
measurement bias due to fatigue [[16]].
Data analysis
Descriptive statistics (mean and standard deviation) were performed for all direct
measurements and derived variables. An independent t-test was used for intra- and
inter-group comparisons between males and females. Data were analyzed using the SPSS
ver. 18.0 (SPSS, Inc., Chicago, IL, USA). A P-value of <0.01 was used to indicate
statistical significance. Correlations were determined using Pearson's correlation
coefficient test.
RESULTS
A total of 336 volunteers (199 women and 137 men) of 13 to 77 years of age were recruited
to this study. An intra-individual comparison showed a trend towards greater strength
in the right hand, though it was statistically insignificant. All of the mean strength
measurements were significantly greater in males than in females ([Table 1]).
Table 1 Average hand strength values in the Korean population
Values are presented as mean±standard deviation and were significantly different from
males to females (P<0.01).
Taking the teen group (10 to 19 years old) as baseline, hand strength showed the most
drastic increase into young adulthood (20 to 29 years old). This rise in hand strength
plateaued among the 30 to 39 year-old subjects and declined gradually back to the
baseline strength among the geriatric population. This pattern of hand strength across
the age groups is the most noticeable in the measure of gross motor function, which
is demonstrated by the grip strength ([Table 2]). For key and pulp pinch strength, the trend across age groups also appears to follow
the same pattern, though the differences appear to be smaller ([Tables 3], [4]). This is most likely a reflection of the fact that the pinch strength tests assess
fine motor functions, which would be expected to have small differences in strength.
Table 2 Grip strength by age
Table 3 Key pinch strength by age
Table 4 Pulp pinch strength by age
Hand dominance was found to have no significant correlation with measured variables,
though there was a trend towards the dominant hand having greater strength ([Table 5]). As mentioned above, anthropometric data such as total body weight, height, hand
width and length, and forearm length and circumference were obtained ([Table 6]). Among male participants, all metrics but the forearm lengths were found to correlate
with grip strength (r=0.4-0.5) but not so with pinch strengths, which are fine-motor
skills. Among female participants, no such statistically significant correlations
were found.
Table 5 Strength ratio of the dominant to non-dominant hand
Table 6 Correlation between anthropometry and hand strength (R-value)
R, pearson correlation; r=0.1-0.3, no correlation; r=0.3-0.5, weak correlation; r=0.5-0.7,
strong correlation; F. circumference, forearm circumference.
DISCUSSION
The hand is not a fixed, static structure but a dynamic sensorimotor organ with an
incredible repertoire of motor functions. The primary aim of reconstruction of an
injured hand is to restore as much of these lost functions to the hand, and consequently,
much of the hand surgery literature has been dedicated to the recovery of sensory
and neuromuscular functions.
Table 7 Comparison to previously-published hand strength ratios
Objective assessment of both tactile resolution and passive ranges of motion are made
possible by the wide availability of normative data [[1]]. However, such normative data cannot be generalized for hand strength measurements
because of the wide range of demographic and physiologic factors influencing hand
strength.
The hand dynamometer and pinch gauges are inexpensive, easy to administer, and are
considered to provide repeatable measurements in clinical settings as well as for
research purposes [[9]]. Such strength measurements, however, are only useful in the presence of normative
data derived from the population of concern. Without a pre-existing cross-sectional
study providing such data, hand strength measurements can only provide a limited picture
of clinical progress in postoperative or medical patients.
In 1975, a study by Oh [[17]] provided normative values of grip strength among the South Korean population. Unfortunately,
the data from the study were reported in a publication that no longer exists, and
extant copies of the publication are not widely available, even among hand surgeons
living in Korea.
Additionally, anecdotal experiences of Korean hand surgeons who are familiar with
Oh's publication have suggested that the values reported in the study might be outdated.
During the ensuing decades since Oh's report, the population in South Korea has experienced
an exponential economic growth with a resultant demographic transition as well as
drastic improvements in nutrition and overall health outcome measures [[18]].
In this present study, grip strengths peaked in the young adult group (20 to 29),
and this outcome most obviously reflects the variations of muscular mass, which peaks
during this period, in the normal course of human development [[19]]. This result is consistent with the age-related patterns reported by Oh [[17]], Schmidt and Toews [[20]], and Lunde et al. [[21]].
The mean grip strength values in this study were greater than the values published
by Oh [[17]]. Taking the male group of 20 to 29 years age, a comparison can be made. In our
study, the grip strengths were 46.9 kg and 44.9 kg in the right and left hands. These
values are higher than the results reported 35 years ago by Oh [[17]], which were 42.1 kg and 38.6 kg, respectively.
It is worth noting that the 20- to 29-year-old participants in this study had all
been born after Oh's study [[17]]. The epidemiologic significance is that the increased hand strength appears to
reflect the dramatic nutritional and public health improvements that the South Korean
population has experienced in the past several decades [[18]].
In any given population, the hand strength ratios appear consistent. Among the male
participants in this study, the strength ratio between the dominant and non-dominant
hand was 1.05±0.08. This is similar to the ratio reported among Caucasian individuals
by Schmidt and Toews [[20]] (1.03±0.05) and also to the ratio reported earlier in the Korean population (1.02±0.14)
[[17]]. This overall similarity in strength ratios could also be observed among the female
populations from this study, from the study by Oh, and from those reported by Lunde
et al. [[21]] ([Table 7]).
Adjusting for sex and age group, however, the absolute normative values from this
study are different from those of the Korean population circa 1975 and, also, from
those of Caucasian populations [[14]]. Thus, we believe that our research data represents more valid and up-to-date normative
hand strength data for the population of interest.
An argument could be made as to whether this data holds any clinical utility. Of course,
objective measurements of hand strength are not routine parts of a primary-care exam,
and an individual who presents to a hand clinic most likely would not have had undergone
such measurements prior to an injury. Furthermore, certain types of hand injury do
not affect strength outcomes-especially those distal injuries that spare mechanical
components such as bones and tendons.
When an injury or a disease process does decrease hand strength, however, the consequent
result is a decrease in the overall function of the involved hand. Population-specific
normative data is useful in the management of such patients who experience declining
hand strength. The normative data validates the intra-individual standard of using
the non-injured hand as the control-with the understanding that a dominant hand is
only marginally stronger than the non-dominant one.
Normative hand strength data holds an even more significant utility in the management
of injuries or disease processes that involve both hands. When both hands are affected,
neither of them can serve as a control for the other. In such cases, hand strength
data provides the most useful standard for monitoring hand strength. At any point
in the management of such patients, a significant deviation from the expected range
of hand strengths would certainly warrant a clinical investigation for unrecognized
pathology and intervention, if necessary.
In summary, this study presents updated normative data on hand strengths in the South
Korean population. The characteristics of hand strength across demographic variables
and hand-dominance are consistent with previously published studies. Of special note
is that absolute hand strength measurements can neither be used across ethnicity nor
populations that have experienced rapid economic development. This is evidenced by
the change in hand strength among the South Korean population in the past four decades.
The hand dynamometer and pinch gauge used in this study are inexpensive and easy to
use. The measurements obtained from these instruments are reliable and objective.
Used in conjunction with available normative data, hand strength exams allow progressive
assessment of hand function in both post-surgical and medical patients. The authors
believe these strength tests to have a valid clinical and epidemiologic utility for
the population studied.
