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Hand strength as determinants for containeropening strategy in healthy adultsDaniel LemasterThe University of Toledo

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Strength Determinates 1

Hand Strength as Determinants for Container Opening

Strategy in Healthy Adults

Daniel Lemaster

Research Advisor: Martin S. Rice, Ph.D., OTR/L

Department of Occupational Therapy

Occupational Therapy Doctorate Program

The University of Toledo Health Science Campus

May 2010


Abstract

Objective: This study hypothesized that there would be a statistically significant

difference in pinch and grip strengths depending on the strategy employed to open

medicine bottle containers

Method: Sixty six healthy participants (19 male and 47 female) from the community

participated in this research study which examined strategies for opening small, medium,

and large medicine containers through video recordings. Hand grasp and finger

dynamometry were also obtained.

Results: There was a significant difference between the lateral pinch and gross grasp

when using the palm and hybrid bottle opening strategy for the large and small bottles.

Specifically, there was a significant difference in lateral pinch for the large bottle,

between the palm and hybrid strategies (p-value = .036), in gross grasp strength when

using palm and hybrid strategies when opening the large bottle (p-value = .030), in lateral

pinch when grasp using palm and hybrid opening the when opening the small bottle (p-

value = .007), and in gross grasp strength between palm and hybrid grasp strategies when

opening the small bottle (p-value = .025).

Conclusion: The results of the current study suggest the importance of educating clients

about the use of proper joint protection techniques when opening medicine bottles and

facilitating hand and finger strengthening occupations to increase daily task capabilities.

Further research is needed with participants with compromised orthopedic or

neurologically compromised hand function to determine the natural strategy for opening

containers based upon strength.


Introduction

On a day to day basis, individuals engage in occupations, such as brushing teeth

and donning clothing. In completing these tasks, people move in carefully coordinated

actions that generally require functional use of the hand and fingers. A wide variety of

movement patterns are influenced by hand and finger strength and size during an

occupation. That is, the comprised kinematic and kinetic variables involved in the

coordinated motions are often highly complex, although the specificity of the control

most often occurs at the subconscious level. Due to the highly complicated nature of

coordinated movements, any number of factors can interfere with the delivery of such

coordination; for instance size and strength of the hand and fingers for someone with

arthritis may limit function, and consequently, interrupt everyday occupations. It is also

possible that wrist and hand injuries such as carpal tunnel and joint deformities (e.g.,

swan neck deformity) can prohibit someone from have sufficient range of motion needed

in order to perform occupations. The objective of the current study is to investigate the

association between hand and finger strength and the motor strategies during the act of

opening medicine containers.

Background

A common daily task for many people is opening medicine containers for the

purpose of retrieving medications and nutritional supplements. Proper hand function can

help arbitrate personal drive towards something that has personal meaning and purpose.

Reilly (1962) proposed that “man through the use of his hands, as they are energized by

mind and will, can influence the state of his own health” (pg. 2). Therefore, a familiar


practice by occupational therapists is to focus treatment on improving hand function by

encouraging strength and coordination for the purpose of improving task aptitude.

Before an occupational therapist can begin treating in order to improve hand

dysfunction, they must first assess the individual’s current function. Functional

evaluation tests are one way an occupational therapist can assess hand performance.

McPhee (1987) studied the validity of 11 different hand evaluations, some of which

included Jebson’s Hand Function Test, MacBain’s Hand Function Test, Potvin’s

Activities of Daily Living Examination, and the Nine Hole Peg Test. McPhee found that

82% of the 11 tests used time to measure for hand function, and 55% of the assessments

tested bilateral hand use. Unfortunately, time and unilateral determinates, according to

McPhee, are not exclusively accurate portrayals of hand use. Therefore, McPhee

concluded that the therapist should assess a patient using several hand tests to

compensate for the fact that individual tests lack clear meaning and fail to be

comprehensive. Furthermore, functional hand tests should be synchronized with an

individual’s hand abilities, such as coordination, sensation, motivation, and strength

(McPhee, 1987). Consequently, matching hand function is specific to the person’s ability

and the goals the client wishes to achieve.

Data about an individual's grip strength do not provide enough information for the

therapist to determine complete hand function. It is critical for an occupational therapist

to see the hand in action (Conti, 1998). Developing efficient hand techniques may be a

more important technique for hand function than improving strength itself (Rice,

Leonard, & Carter, 1998). In addition, Conti (1998) explained that guided grasp

techniques may be more effective than standard strengthening techniques because any


given task may require different sequential muscle contractions by any of the 39 hand

muscles that contribute to task completion.

A task that requires hand function generally evokes people’s ability to use

assorted types of grasping techniques. Napier (1956) studied gripping techniques

including the power grip and precision grip, by examining people’s hands doing ordinary

tasks, such as holding a ball and gripping a wooden cylinder. The power grip technique

is when an object is held with partially flexed fingers, thumb, and the palm (e.g., holding

a wooden rod), whereas the precision grip is when an object is pinched between the

finger and thumb (e.g., holding a can of soda). He surmised that gripping consists of

dynamic or static movements. Dynamic gripping is the action required while producing a

grip, and static grip is the final state that indicates a grip. Landsmeer (1962) continued

Napier’s study by examining hand mechanics and determined that precision handling is

the dynamic phase of a gripping task. The author described that the dynamic phase is the

act of opening the hand, aligning the fingers, approaching the fingers to the object, and

static gripping of the object. This leads to the conclusion that after dynamic movements

of the fingers and hand contact with a particular entity, object manipulation can occur.

Occupational therapists test hand function in relation to typical gripping patterns

more realistic to daily occupations. Skerik, Weiss, and Flatt (1971) examined traditional

tests for hand function (i.e., range of motion, strength, etc.) performed by occupational

therapists, and concluded they were dissimilar and too precise to represent everyday hand

tasks. Therefore, Skerik et al. urged that testing should be relevant to hand functions in

relation to the five prehension patterns, which include power grip, lateral pinch, hook

grip, tip pinch, and palmer pinch (1971). These five terms describe dynamic and static


hand manipulation techniques commonly used when the palm, fingers, and thumb are

functioning jointly to perform an occupation. A lateral pinch is when an object, such as a

key, is held by the palmar surface of the distal phalanx of the thumb against the lateral

side intermediate and distal interphalangeal joint of the index finger (Skerik et al., 1971).

Skerik et al. (1971) defined the palmer pinch as using the pads of index and thumb with

the two digits forming a tapered oval from the radial view to hold and small object (e.g.,

needle). The tip pinch occurs when the tips of the index and thumb fingers are flexed in

order to hold or pick up an object (e.g., a tack). A person holding a bag with handles

with just the phalanges in a fixed flexed position is an example of a hook grip prehension

pattern. Skerik et al. (1971) do not define power grip due to their contention that

cylindrical and spherical grips patterns define the object being held rather than describing

the grip being used. They propose that depending on the item being held, a tennis ball or

a cup, power grip uses precision grip patterns already described. Holding a container

requires hand strength and range of motion, as well as a combination of other factors,

which include reliance upon sensation and motoric abilities. That is, they adapt to many

facets of an occupation, utilizing prehension patterns may be a more effective way of

improving a person’s ability to use his/her hand.

The dynamic and static manipulations (prehension patterns) of an object are based

on a person’s ability to perceive and comprehend the specific characteristics of the

occupational form. This is followed by a “mapping” of these perceptions to the body’s

specific potential movement strategies. Movement strategies are learned over time due to

the gaining of knowledge for action that acquires specific movement patterns in relation

to the task demands (Newell, 1991). The perceptual-motor workspace describes this


process in relation to a person’s environmental, organisimc, and task constraints (Turvey

and Kugler, 1984). This information is a method for which a person can locate task-

relevant solutions for the purpose of coordinating function (Newell, 1991). For example,

a patient with arthritic hands may learn to grasp a phone differently because previous

attempts caused a negative, painful reaction. Therefore, the patient may change the

previous movement based on learned strategy through the perceptual-motor workspace

constraints.

Newell (1986) also indicated that the arrangement of a specific occupation is

characterized by three types of constraints: environmental, task, and organisimc. These

constraints provide information for an individual’s boundaries, options, and

opportunities. Environmental constraints include everything that is external and

surrounds the persons, including lighting, air, temperature, and physical objects. Task

constraints are guidelines accompanied by the task; an example of a task constraint is

purpose. For example, playing soccer affords a task constraint of kicking the soccer ball

through a goal in order to score a point. The third constraint is an organisimc constraint,

which is internal to the person’s developmental structure. Examples of organisimc

constraints include memory, cognitive ability, coordination, size, and strength.

Successful task completion may have a direct relationship with constraints, as

well as affordances. Affordances are things in the environment that a person can

perceive and make a judgment about its utility; consciously or more frequently,

unconsciously. An affordance must also have meaning to the individual (Gibson, 1979).

For example, an object such as knife may have many purposes to an individual; it can be


used to slice meat, carve wood, or be used as a weapon. Subsequently, an object’s

meaning is dependent on the intrinsic purpose of the individual.

Warren (1984) analyzed affordances in terms of the dynamics of the person-

environment. He examined two groups of male college students. One group had a mean

height of 5 feet, 4.4 inches and the other group had a mean height of 6 feet, 2.7 inches.

Warren also recorded each participant’s body measurements: standing height, sitting

height, eye height, and knee height (tibial notch). Before completing a bipedal stair

climbing occupation, the researcher instructed the students to observe stairways projected

upon a screen in order to judge them on whether they were “climbable” or

“unclimbable.” Warren (1984) hypothesized that if the person was able to perceive the

environment correctly by understanding the limits and best pathways, one might have

been able to predict appropriate actions. Warren compared the participant’s body-scaled

measures with his/her intrinsic perception between “climbable” and “unclimbable.” The

results were that an overall decrease in “climbable” judgments reached significance; and

tall participants compared to short participants gave significantly more “climbable”

judgments than did short ones. He concluded that the perceptual analysis between

“climbable” and “unclimbable” varied according to the height and mass of the

participant. Therefore, perceived environments were in direct proportion to each

participant’s body scaled measurements.

Mark (1987) extended Warren’s research by examining whether people’s

perceptual reasoning corresponded to particularized capacities by changing leg length by

means of applying blocks to each participant’s foot during a “sitting on” or “climbing on”

action boundary. The blocks created errors for the individual’s interpretation of the


boundaries, and the results indicated no statistical significance between study groups.

However, once the participants became familiar with the new leg lengths, their judgments

of the boundaries improved. Evidence from Mark (1987) and Warren (1984) indicate

that body-scaled attributes do perpetuate intrinsic perception of action boundaries.

Konczak, Meeuwsen, and Cress (1992) also extended the studies of Warren

(1984) and Mark (1987). Konczak et al. (1992) evaluated two groups of participants

consisting of healthy adults. The participants were asked to view and identify which of

eight different stairs (of increasing height) was the highest stair they could climb without

using their hands or knees. Participant’s anthropometric measures were recorded,

including standing height, sitting height, lower leg length, upper leg length, and trunk-

thigh angle. Leg strength and peak torque performance from the subjects preferred leg

were also recorded. Konczak et al. (1992) found that in both older and younger

participants, means of the perceptual boundaries were close to the action boundary. For

instance, young-tall observers had perceptual category boundary of 88%, whereas young-

short observers perceived maximum climbablility at 95% of leg length. Tall older adults

perceived a stair as unclimbable at 73% of total leg length while their shorter counterparts

perceived an unclimbable stair at 62%. Older adults were considerably more accurate

and made fewer mistakes with regard to perceptual ability. The researchers explained the

results given that older adults work in a smaller range of action boundaries due to their

decreased capabilities (Konczak, Meeuwsen, & Cress, 1992).

Cesari and Newell (1999) hypothesized that the qualitative properties of grip

configurations (number of hands and number of digits) could be predicted with a body-

scaled equation in which both the length and mass of both objects and the hand were


considered. They observed 10 adults between the ages of 22 and 49 years old utilizing

preferred human grip configurations to pick up and move cubes that varied in length,

mass, and density. In a series of trials, the participants were instructed to grasp and

displace cubes resting on a table and reposition them to a new final location. The results

illustrated that object length and mass of an object contributes to the scaling of the grip

style (Cesari & Newell, 1999). Therefore, one could conclude that hand strength and size

has great significance in determining grip configurations (power grip, lateral grip, hook

grip, tip pinch, and palmer pinch).

Cesari and Newell (2000) continued their previous study to research a precise test

of a dimensional relation between the object and the hand. The study examined two grip

configurations, five digits of one-hand grip and a two-hand grip, in two sets of

experiments. Experiment 1 included cubes with low density and small size; Experiment

2 included cubes with two fixed sizes and small increments in mass. The results

confirmed their previous findings that body-scaled information, such as anthropometric

measures, in relation to the object’s dimensions may predict the grip configurations used

to displace objects. Consequently, an object’s size may afford certain grip configurations

based on an individual’s anthropometric measures used in prehension patterns in order to

manipulate an object.

Jordan and Newell (2004) studied whether or not task goal affected the control of

isometric force output in a precision grip task and how the process was influenced by the

size and mass of the object. They examined participants targeting and holding an

apparatus that contained force and torque sensors. The holding condition was told to

hold the apparatus between opposed distal pads of their thumb and index finger in a


precision grip for 30 sec. Participants in the manipulating conditions were told to move

the apparatus toward a target fixed to a computer screen. The results were that force

production was similar for the target and holding conditions. Furthermore, the mass and

size of an object during a goal directed task influenced the variability structure for the

same mean force output of the digits acting on the object (Jordan & Newell, 2004).

Based on these findings, Jordan, Pataky, and Newell (2005) surmised that when an object

is grasped between the index finger and thumb, the mean and standard deviations of grip

force will increase with increasing grip width, independent of the mass object. The

researchers observed adults manipulate the width and mass of a grasping apparatus using

two and three grip configuration techniques to determine force production. The results

were that there was a significant increase in average normal force and the regularity of

force production decreased with increased grip width. Subsequently, force output may be

influenced by normal grip configurations that people use to modulate objects of different

size and mass.

There is limited research that links hand strength and coordination to functional

success in occupations of daily living. However, there are two studies which include

explorations on the relationship of hand strength and “accessing” containers. Rice,

Leonard, and Carter (1998) investigated whether hand strength is fundamental for

opening common household containers. This study recruited 49 college students and

investigated the relationship between hand and finger grip performances with the forces

required to open six common household containers. The researchers found a weak

correlation between grip, pinch strength, and forces exerted while opening and

manipulating the containers.


Rahman, Thomas, and Rice (2002) also examined the relationship between grip

and pinch strength and the forces produced while accessing common household

containers, but with a different population. Rahman et al. (2002) investigated 51 healthy

elderly adults; results were consistent with those of Rice et al. (1998). The researchers

concluded that greater hand strength did not correlate with superior hand functioning

when opening common household containers. However, Rice et al. (1998) and Rahman

et al. (2002) also reported that personal strategy appeared to be largely determined by

how well a person opened containers. Therefore, future studies that show how grip

strength and hand proportions are used during motor control occupations may help

provide evidence on strategies that are taken by individuals during accessing a container.

Arcaro (2006) investigated hand size and strength in order to determine methods

for effectively accessing containers. Her study included 56 adults (14 healthy males and

42 healthy females) opening containers. In the first phase of opening containers, Arcaro

measured the participant’s overall hand strength, (e.g., tip pinch, lateral grasp pinch, 3-

jaw chuck pinch, and gross grasp), as well as hand anthropometric measures (e.g., hand

length, hand mass, and body height). The second phase consisted of the participants

opening a medicine container. The results indicated no statistical significance for the

anthropometric variables; however, there was a significant difference related to the tip-

pinch strength. Specifically, participants with weak finger strength opened medicine

containers using finger manipulation based on prior memory, whereas other participants

with normal finger strength generally used the whole hand (Arcaro, 2006). The

researcher delineated the importance of occupational therapists teaching better hand

mechanics to patients with weak finger strength.


The current study is designed to investigate the association between hand strength

and movement strategy when accessing a container. The theoretical implications of a

relationship between anthropometric characteristics and mechanical technique include the

need for increased awareness, education, and intervention strategies to address

individuals who may be at increased risk for physical injuries (Shivers et al, 2002).

Identification of factors affecting body mechanics can increase awareness of individuals

who are at risk and prompt further research regarding ways to address this issue.

Accessing containers can have an important role in a person’s everyday occupations;

therefore, a person’s strategy for opening a container has considerable application.

Determining contributions to the improvement of this occupation, such as strength, could

help occupational therapists utilize more appropriate and effective evaluations and

exercises with patients. Current literature regarding hand strategies for the purpose of

accessing containers is inconclusive. Therefore, the purpose of this study is to investigate

the association of hand dynamometry on healthy adults upon the strategies used when

accessing containers. Our primary hypothesis states that there will be a statistically

significant difference in pinch and grip strengths depending on the strategy employed to

open medicine bottle containers.

Method

Participants:

The sample consisted of 66 healthy adult subjects (19 males and 47 females),

aged 18 to 45 years (mean age of 25.32). Ethnicity, hand dominance, and gender were

recorded. Participants were recruited through word of mouth, posters, and email from the

Midwest region of the United States. All participants had self-reported to be in good health


with no neuromuscular or orthopedic conditions that would adversely affect their ability to

open containers.

Instruments

A Baseline hydraulic digital dynamometer was used to measure grip strength, and

a Baseline digital pinch gauge was used to measure pinch strength. Both the

dynamometer and the pinch meter were calibrated before initiation of the study. A

Detecto eye-level beam scale with height rod was used to obtain participant mass and

height. A finger circumference gauge was used to measure the middle finger proximal

phalange circumference. A flexible tape measure was used to measure the length of the

hand. Videotaping (VHS) was used to record the strategy employed for opening the

container. Medicine bottles of three different sizes (e.g., Owens Illinois T-8, T16, and

T30, Perrysburg, Ohio, USA) each with a ‘push down and turn lid’ were used for all

participants (See Figure 1).

------------------------------ Insert Figure 1 Here

------------------------------ Procedure

This study was approved by the Biomedical institutional review board of the

University of Toledo (IRB # 106082). Informed consent was obtained from all

participants. Demographics of age, gender, height, weight, limb dominance, and ethnicity

were collected. Data collection occurred from September 10, 2008 to February 13, 2009,

with each participant participating in one session. This study involved three phases. The

first phase involved opening a container, the second phase involved taking

anthropometrical and dynamometrical measurements, and the third phase involved

categorizing strategies used to open the containers through video tape recordings. The


anthropometric portion of this study was under the auspices of another research project

occurring in conjunction with this current study.

The participants were videotaped during the first phase. Participants were

randomly assigned to one of three order of presentation groups (e.g., small-medium-

large, medium-large-small, large-small-medium) to control for order effects.

Randomization occurred using a custom software computerized random number

generator using permutated blocks of 8 blocks of 3 participants, 4 blocks of 6 participants

and two blocks of 9 participants. After informed consent was obtained, the investigator

entered the participant’s identification number into a custom computer software program

which then assigned the order of presentation group for that participant.

During the container-opening process, the participant sat at an adjustable-height

table whose height was adjusted so that the participant’s elbow was flexed at 90° with the

forearms resting on the table. The medicine bottle was placed directly in front of the

participant on a tray so that the investigator would not demonstrate any type of handling

technique or hand positioning with the container. The medicine bottle was 30cm away

from the edge of the table.

The participant was given the following verbal instructions: “When I say ‘Begin,’

I want you to pick up and open the container and then place the lid and the open container

back onto the table.” Once the participant acknowledged he or she understood the

instructions, the investigator said “Begin.”

Hand grip and pinch (i.e., lateral, tip-to-tip, three jaw chuck) measurements for

both limbs were obtained following the American Society of Hand Therapists


standardized procedures as reported by Mathiowetz et al. (1984). A 30-sec rest period

was provided between each of the three trials of dynamometry.

Anthropometry of the hand was obtained using a standardized protocol (Snyder,

et al., 1977). Specifically, the length of the hand was measured from the wrist crease to

the tip of the middle finger, parallel to fingers and with the metacarpal and

interphalangeal joints extended. Additionally, the length of the palm was obtained by

measuring the distance from the wrist crease to the metacarpal crease of the middle

finger. The circumference of the proximal phalange of the middle finger was obtained

using a finger circumference gauge. Lastly, the mass and height of the patient were

obtained by using the Detecto eye-level beam scale with height rod.

Statistical Analyses

For grip and each type of pinch, the mean of the three trials was calculated for

each hand. In addition to the investigator, a research assistant who was blind to the study

reviewed the videotape of each participant. The purpose of the videotape was to

categorize the type of grip strategy used to open the container. Hybrid, palm, and finger

grasps were the three grip strategies the researchers categorized for opening medicine

containers (See Table & Figure 1). Dependent variables included variables of hand and

finger strength (e.g., tip pinch, lateral grasp pinch, 3-jaw chuck pinch, and gross grasp).

The independent variable is the hand grip strategy used to access/open the containers. A

Kappa statistic was calculated between the videotape viewers to determine their

agreement of categorization. A multivariate analysis of variance (MANOVA) was used

to analyze the right hand pinch and grip strengths across the container opening strategies.

For those factors in the between-subject ANOVA that had a p-value of <.05, a follow-up


Bonforroni Post-Hoc pairwise comparison was performed. This was done to determine

any statistically significant hand/finger strength between any two finger/grip strategies

used by the participants.

------------------------------ Insert Table 1 Here

------------------------------

Results

A total of 66 (19 male and 47 female) participants, aged 18 to 36 years, were

recruited to participate in the study. Unfortunately, one participant was not included in

the statistical analysis because of a video camera malfunction during the medicine bottle

opening procedure.

A Kappa statistic was calculated between two videotape viewers to determine

their agreement of categorization. In and effort to increase reliability, one viewer was

independent of the study’s hypothesis. The viewers determined what type of grip

strategies (i.e., phalanges, hybrid, and palm) were used while opening the medicine

bottles. The measure of agreement between the two viewers were at levels considered to

be “excellent” (Streiner & Norman, 1994). For instance, the measure of agreement for

the large bottle opening strategy was .956, for the medium it was .914, and for the small

it was 1.000.

A Pearson Correlation was used to determine the correlations between the

different dependant variables, in particular the left hand versus the right hand. For

instance, the left and right grasp measurements for the tip-pinch was .86, the left and right

three-jaw chuck pinch was .88, for the lateral pinch it was .94, and the gross hand grasp


was .97, all of which have a p-value of < .001. Due to the high correlation between the

two hands, only the right hand/finger strength was included in the analyses.

The means and standard deviations for each dependent variable across the three

different grasp configurations can be seen in Table 2. The between-subject analysis of

variance revealed that in the large bottle opening strategies, there was no significant

difference in the tip pinch or the three-jaw chuck pinch strength across the strategies.

However, there was a difference in lateral pinch and gross grasp across the container

opening strategies. In the medium bottle opening strategies, there was no sign of

significant difference in strength for either gross grasp strengths or the pinch strengths for

any of the strategies for opening containers. Also, there was no significant difference

during the small opening strategies, between the tip-pinch or three-jaw chuck pinches.

However, there was a statistically significant difference between lateral pinch and gross

grasp across all three strategies (See Table 3).

------------------------------ Insert Tables 2 and 3 Here ------------------------------

Because there was a significant difference in the overall ANOVAs for lateral

pinch and gross grasp for the large and small bottles, a Bonforroni Post-Hoc multi-

comparison test was performed for the pinch and gross grasp strategies on the bottles.

However, because there was only one person who demonstrated the finger strategy, it

was removed from the Bonforroni Post-Hoc analyses. The aforementioned test results

demonstrated a significant difference in lateral pinch, for the large bottle, between the

palm and hybrid strategies (p-value = .036) (See Table 3 and Figure 2). In addition, the

palm and hybrid strategies when opening the large bottle showed that the gross grasp


strength had a statistical difference (p-value = .030) (See Figure 2). When opening the

small bottle there was a significant difference between the palm and hybrid grasp for the

lateral pinch (p-value = .007) (See Figure 3). Likewise, there was a significant difference

in gross grasp strength between palm and hybrid grasp strategies when opening the small

bottle (p-value = .025) (See Figure 3). As mentioned above, the Bonforroni Post-Hoc

multi-comparison did not include the finger strategy due to an n=1 for that comparison

strategy.

Discussion

The purpose of the current study was to investigate the association of hand

dynamometry on healthy adults upon the strategies used when accessing medicine

bottles. The hypothesis was that there would be a significant difference in pinch and grip

strengths depending on the method by which the participants used to open medicine

bottles. Based on the analysis performed there was a significant difference between the

lateral pinch and gross grasp when using the palm and hybrid bottle opening strategy for

the large and small bottles. However, none of the other strength variables reached

significance.

These results suggest that a person’s lateral pinch and gross grasp strength may

determine the method by which he/she utilizes when accessing large and small sized

medicine bottles. This may be based upon the developmental structure’s unconscious

knowledge of the current possible strength and endurance of the lateral pinch and gross

grasp biomechanical and muscle potential. Before accessing a medicine bottle, this

information is considered during the motor planning process. The perception of opening

a medicine bottle undoubtedly evoked some past experience opening the exact or similar


object. Given both the memory and the viable strength and endurance of the lateral pinch

and gross grasp, the perceptual motor workspace maps this information together to form a

motor plan or motor solution to open the medicine bottle. Based upon the results of the

study, the data suggest that people with stronger lateral pinch and gross grasp are more

likely to use a palm opening strategy when opening large medicine bottles. However,

those same participants are more likely to use a hybrid strategy when opening small

medicine bottles.

Rice et al. (1998) found little to no relationship between grip and pinch strengths

and forces generated in accessing the majority of containers. However, Arcaro (2006)

examined strength performance for each grasp type and found that the greatest magnitude

of strength occurred when a mixed hybrid type strategy was used. This current study

examined strength magnitude across different grasp strategies used when accessing

containers and found that the palm and phalanges strategy was used most often. Conti

(1998) stated that an occupational therapist must assess the hand in action, performing

meaningful and functional tasks. Both, Rice et al. (1998) and Rahman et al. (2002) did

not control for hand placement while participants opened containers during their research.

However, the current study followed Arcaro (2006), by controlling hand placement

through categorizing each hand placement into three categories, hybrid, palm, and finger

grasp.

Gibson (1979) declared that an object may “afford” a certain type of handling or

manipulation based upon the objects characteristics. Warren (1984) also analyzed

affordances and found that the absolute measure of the perceptual boundary of stairs

being “climbable” and “not climbable” varied according to the participant’s size and


mass. In a similar vein, it is possible that this current study’s participants' grasp

performance was based upon their hand strength. That is, individuals who demonstrate a

high level of lateral pinch and gross grasp muscle strength are afforded using the palm

and hybrid strategies upon perceiving the small and large sized medicine bottles.

Arcaro (2006) found that participants with weak finger strength opened medicine

bottles using finger manipulation, whereas other participants with normal finger strength

generally used the whole hand. Her research delineated the importance of occupational

therapists teaching better hand mechanics to patients with weak finger strength.

Conversely, this current study found that participants with strong lateral pinch and gross

grasp muscle strength used the palm or hybrid strategy to access the bottle.

Implications of this study to the practice of occupational therapy include the

suggestions that occupational therapists should deliver therapeutic applications that

encourage an increase in both pinch and grasp strength and teach better hand mechanics

to patients with weak gross grasp and pinch strength. This current study found that

participants with strong lateral pinch and gross grasp muscle strength opened medicine

bottles using the palm or hybrid strategy. Therefore, an implication would be for

occupational therapists to support the increase of grip and lateral pinch strength with

patients who access containers (e.g., medicine, food jars, etc.) on a daily basis.

Additionally, the results of the current study support the notion that patient

education is imperative to occupational therapy practice. According to Arcaro (2006),

the joint protection strategy in occupational therapy espouses the use of more proximal

joints and larger muscle groups when interacting with objects that require significant

force of torque to access. The joint protection strategy relieves greater forces that would


otherwise be applied to smaller, more fragile joints. Although not statistically significant,

the current study’s findings also suggest that the intuitive logic of weaker participants

accessed medicine bottles incongruously to the joint protection theory; participants who

did not demonstrate strong grasp and pinch strength were not as likely to use palm and

hybrid opening strategies. Therefore, occupational therapists should focus on educating

patients who have weak grip strength, especially those persons at risk (e.g., with arthritis,

decreased strength, or neurological problems) about proper joint protection strategies.

Interestingly, in addition to hand strength, performance may also be influenced by

the specific verbal instruction. For instance, a study examining an external-focus

condition versus an internal-focus condition during a reaching task, Fasoli, Trombly,

Degnen-Tickle, and Verfaellie (2002) found that patients who had had a cerebrovasular

accident exhibited shorter movement time and greater peak velocity in the external-focus

condition. These findings suggest that instructions from occupational therapists

describing an object (e.g., the cup is round), versus (e.g., move your arm this way) may

facilitate better movement from clients. Therefore, based on Fasoli et al. (2002) the

current study may have facilitated proper movement patterns since participants were

externally instructed to “open” the medicine bottle, rather than relying on internal-focus

coaching (e.g., open bottle with specific grip technique).

The fact that the investigators knew the hypothesis and could have inadvertently

been biased to the study is one of the study’s limitations. However, strict controls were

set in place to diminish any potential bias (e.g., a precise research protocol and a blind

research assistant who categorized the grasps). It is also possible that the sample size

may have been small demonstrating small effect sizes. Therefore, a Type II error may


have occurred. It may be important for future researchers to incorporate a larger sample

size in order to decrease the likelihood of a Type II error.

Conclusion

The results of the current study suggest that hand and finger strength had an effect

on the manner in which participants accessed large and small medicine containers.

Specifically, participants with stronger lateral pinch and gross grasp tended to open the

medicine bottles using a palm opening strategy when they accessed large medicine

bottles. In addition, participants with stronger lateral pinch and gross grasp were more

likely to use a hybrid strategy when opening small medicine bottles.

One implication for occupational therapy is the importance of educating clients

about the use of proper joint protection techniques when opening medicine bottles that

require a push and turn to open. Another implication of the current study is the

importance of increasing clients’ strength to reduce injury and increase function. The

results of the current study indicated statistical significance, which suggests the need to

extend this research to populations with inherent orthopedic or neurological pathologies

that interfere with hand function to determine the quality of bottle opening strategies in

terms of joint protection, energy conservation, and hand and finger strength.


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Table 1 Coding Determinates Utilized by Video Reviewers Type of Grasp Description of Grasp Finger Only the phalanges or fingers. No metacarpal or palm contribution

Palm Only the metacarpal or palm of hand. Phalanges and fingers used only to pull off cap.

Hybrid Uses the metacarpal, phalanges, and/or fingers.


Table 2 Means and Standard Deviation of Finger and Hand Strength when using finger,palm, and hybrid strategies Fingers Palm Hybrid Fingers Palm Hybrid Mean in pounds Standard Deviation Large Bottle R Tip Pinch 4.67 6.00 6.13 n/a 1.16 1.37L Tip Pinch 4.33 5.40 5.53 n/a 1.45 1.47R 3-Jaw Chuck 8.00 8.64 8.05 n/a 2.72 2.72L 3-Jaw Chuck 6.00 8.14 7.49 n/a 2.15 2.05R Lateral Pinch 7.33 9.43 8.92 n/a 2.59 2.14L Lateral Pinch 6.33 9.00 8.41 n/a 2.53 2.06R Gross Grasp 32.33 41.14 38.60 n/a 12.04 12.38L Gross Grasp 29.33 38.19 35.45 n/a 12.63 12.00Medium Bottle R Tip Pinch 6.13 6.13 6.05 1.91 1.13 1.36L Tip Pinch 5.33 5.48 5.51 1.70 1.53 1.42R 3-Jaw Chuck 8.80 8.19 8.10 2.43 2.39 2.31L 3-Jaw Chuck 7.87 7.85 7.47 2.06 2.03 2.12R Lateral Pinch 9.27 9.20 8.89 2.75 2.29 2.19L Lateral Pinch 8.53 8.69 8.42 2.29 2.57 2.00R Gross Grasp 43.33 38.20 38.90 14.18 11.90 12.29L Gross Grasp 40.53 35.65 35.53 12.71 12.91 11.75Small Bottle R Tip Pinch 6.50 5.70 6.13 2.00 1.12 1.32L Tip Pinch 5.58 5.15 5.55 1.85 1.39 1.45R 3-Jaw Chuck 9.00 7.70 8.21 2.76 2.27 2.31L 3-Jaw Chuck 8.33 7.48 7.57 2.06 1.79 2.15R Lateral Pinch 9.75 8.12 9.14 2.92 1.96 2.22L Lateral Pinch 9.08 7.75 8.62 2.23 1.87 2.22R Gross Grasp 46.08 34.70 39.45 14.75 8.92 12.50L Gross Grasp 43.33 31.58 36.32 12.77 8.77 12.42note: n= 1 for Finger, n= 14 for Palm, n= 50 for Hybrid


Table 3 Analysis of variance for dynamometry performance on the factor of grasp/ pinch strength Dynamometry

Source Grasp/ Pinch

Sum of Squares df

Mean Square F p

Large Tip 0.25 1 0.25 0.14 0.711 3-Jaw 17.26 1 17.26 3.21 0.078 Lateral 21.37 1 21.37 4.62 0.036 Gross 701.85 1 701.85 4.97 0.030

Medium Tip 0.64 1 0.64 0.35 0.554 3-Jaw 0.05 1 0.05 0.01 0.927 Lateral 1.54 1 1.54 0.33 0.567 Gross 15.59 1 15.59 0.11 0.741

Small Tip 2.79 1 2.79 1.55 0.218 3-Jaw 15.18 1 15.18 2.82 0.098 Lateral 35.58 1 35.58 7.69 0.007 Gross 748.36 1 748.36 5.30 0.025

Error Tip 106.31 59 1.80 3-Jaw 317.48 59 5.38 Lateral 273.16 59 4.63 Gross 8326.37 59 141.13

Total Tip 2152.56 65 3-Jaw 4684.67 65 Lateral 5588.44 65 Gross 108639.00 65

note: n= 65


Figure 1: Research set-up with video camera and three medicine bottles.


Figure 2: Srength values for large bottle across grasp strategies.


Figure 3: Strength values for small bottle across grasp strategies.

hand strength as determinants for container opening ... · medicine bottle containers method: sixty...

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