MEL415: BiomechanicsSubmitted on: 22-April-2013

ALTERNATE DESIGN FOR HAND-DYNAMOMETER

Abhishek Ghosh P2009ME1074

School of Mechanical Materials & Energy EngineeringIndian Institute of Technology RoparRupnagar – 140001, Punjab, INDIA

Mobile: (+91)95014-57087; E-mail: abhishekgh@iitrpr.ac.in

ABSTRACTReliable and valid evaluation of hand strength can provide an objective index of general upper body strength. Many models of hand dynamometers are present in the market. In this paper all the mainstream dynamometer types have been discussed, followed by some new ideas for hand grip measurement and finally the cost variation study of these devices.

INTRODUCTIONA dynamometer is a device for measuring force, moment of force (torque), or power (1). For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed (RPM). In the present case (Figure 1), this pertains to measuring the hand grip strength.

The power grip is the result of forceful flexion of all finger joints with the maximum voluntary force that the subject is able to exert under normal bio-kinetic conditions (2). The synergistic action of flexor and extensor muscles and the interplay of muscle groups is an important factor in the strength of the resulting grip. Many factors influence the strength of the grip, including muscle strength, hand dominance, fatigue, time of day, age, nutritional status, restricted motion, and pain.

HANDGRIP STRENGTH TESTINGThe purpose of this test is to measure the maximum isometric strength of the hand and forearm muscles. Handgrip strength is important for any sport in which the hands are used for catching, throwing or lifting. Also, as a general rule people with strong hands tend to be strong elsewhere, so this test is often used as a general test of strength.

It is also used to measure the grip strength of a person’s hands to monitor recovery rate of an injury (3).Procedure (4): The subject holds the dynamometer in the hand to be tested, with the arm at right angles and the elbow by the side of the body. The handle of the dynamometer is adjusted if required - the base should rest on first metacarpal (heel of

palm), while the handle should rest on middle of four fingers. When ready the subject squeezes the dynamometer with maximum isometric effort, which is maintained for about 5 seconds. No other body movement is allowed. The subject should be strongly encouraged to give a maximum effort.

Figure 1: A typical hand dynamometer

The average scores (averaged over all age groups) for the dominant hand is shown in Table 1 (4).

Table 1: Hand Grip Strength Scores

MALES FEMALES

rating (kg) (kg) excellent > 64 > 38very good 56-64 34-38

above average 52-55 30-33

average 48-51 26-29

below average 44-47 23-25

poor 40-43 20-22very poor < 40 < 20

1 Copyright © 2013 by Abhishek Ghosh

Advantages: This is a simple and commonly used test of general strength level, well researched and many norms are available.Disadvantages: The dynamometer must be adjusted for hand size, how successfully this is done will affect the accuracy of the measurement.

TYPES OF HAND DYNAMOMETERSThere are three (5) basic types of dynamometer, namely, a hydraulic gauge dynamometer, a pneumatic dynamometer, and myogrip (strain gauge type) dynamometer. Each of these dynamometers is used primarily in the health care industry to assist in evaluating and rehabilitating patients with regard to hand motion and strength.

1. One of the most common types of hydraulic dynamometers is called a JAMAR grip dynamometer (Fig.2). This instrument generally has a curved metal or plastic grip that a person holds in his or her hand and squeezes. The handle itself does not ordinarily move, but a hydraulic mechanism measures the pressure exerted by the grip, which is then displayed on a gauge located on the top of the instrument. Some models do not utilize a gauge but instead have a digital display. The JAMAR grip dynamometer is considered one of the most accurate and reliable models in the industry.

Figure 2: JAMAR grip dynamometer

2. Another type of dynamometer is known as a pneumatic hand dynamometer (Fig.3). This type of grip dynamometer utilizes a rubber squeeze ball on the end of a tube. The patient squeezes the ball, and the force exerted is then measured by a gauge at the other end of the tube. There are models available that utilize digital displays for this type of grip dynamometer as well. The most commonly used pneumatic dynamometer is called a Martin vigorimeter and is relied upon by many health care facilities for its ease of use and accuracy.

Figure 3: Pneumatic hand dynamometer

3. The Myogrip dynamometer (Fig.4) is a type of grip dynamometer that utilizes a strain gauge. This type of dynamometer is smaller than either the JAMAR or the Martin vigorimeter. It is also much more sensitive and is used primarily with patients who are frail, weak, or who otherwise have very poor grip strength. Due to its nature, the Myogrip dynamometer is used almost exclusively in the health care industry.

Figure 4: Myogrip dynamometer

There are other, more specialized, ones to do grip strength tests of your pinch strength (your thumb pinching towards your other 4 fingers).

ALTERNATE DESIGNMany of the techniques which I brainstormed were already in practice. However, some of the new ideas include:

1. Using a crush hand gripper (Fig.5) and attaching a dial to the torsion spring.

Figure 5: A crush hand gripper

Thus, the gripping of the hands would result in a change in the dial readings and the dial can be calibrated to show the force readings.

2 Copyright © 2013 by Abhishek Ghosh

2. Attaching a linear scale to the front of the hand exerciser (Fig.6), allows individual finger grip strength measurements. (Research interest)

Figure 6: Hand exerciser

ALTERNATE MECHANISMSSome alternate ways of measuring grip strength apart from the conventional dynamometer:

1. Cable tensiometers are another type of measuring device, used to measure force in other body parts mostly, but you can use them for your hand. They use a cable attached to a stationary object, and you contract your muscles and pull against it. Sort of like pulling on a scale you might find in the produce section of your grocery store.

2. Grip Strength Test With A Bathroom ScaleIt needs a scale, a bar or, and a stopwatch (6). The method includes the following steps:

Stand on the scale and measure your bodyweight. Then, grab the bar and, without bending your elbows

and not using any part of your body other than your hands, tense your hands and pull yourself up for 5 sec-onds.

Record what the scale says for the 5 seconds you're tensing your hands.

How much you weigh - how much you weigh while tensing your hands = your grip strength.

COST VARIATION The market cost of a good quality dynamometer goes to $150+, the price variation is also too high. Starting from as low as $3 (Rs 200/-) (Chinese product- Fig.7), the price can go as high as $200 (Fig.2).

As the costs are pretty low (Chinese products), no cheaper version of a standard hand dynamometer is possible.

Figure 7: Cheap Dynamometer (under $3)

3 Copyright © 2013 by Abhishek Ghosh

REFERENCE1. en.wikipedia.org. Dynamometer. [Online] http://en.wikipedia.org/wiki/Dynamometer.2. Hand Grip Strength PROTOCOL. cdaar.tufts.edu. [Online] 3. Biomechanics. www.stem.neu.edu. [Online] http://www.stem.neu.edu/programs/k-12-school-field-trips/biomechanics/.4. Fitness Testing. www.topendsports.com. [Online] http://www.topendsports.com/testing/tests/handgrip.htm.5. www.wisegeek.com. [Online] http://www.wisegeek.com/what-are-the-different-types-of-grip-dynamometer.htm.6. Sagar, Heather Reynolds. Climbing Your Best: Training to Maximize Your Performance. Mechanicsburg : Stackpole Books, 2001.

IMAGE COURTESYFigure 1(http://www.topendsports.com/testing/tests/handgrip.htm)2(http://www.complete-strength-training.com/grip-strength-test.html)3(http://www.amazon.com/Baseline-12-0297-Pneumatic-Dynamometer-Pinch/dp/B001RQ0K1K)4(http://www.complete-strength-training.com/grip-strength-test.html)5(http://chicshaping.com/exercise-of-the-week/hand-grip-exercises/)6(http://www.amazon.com/Gripmaster-Hand-Exerciser/dp/B0085MX3SG/ref=pd_sim_hpc_4)7(http://www.dhgate.com/store/product/hand-dynamometer-grip-strength-power-force/14378528-155748835.html)

4 Copyright © 2013 by Abhishek Ghosh