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The wrist position between neutral and ulnar deviation that facilitates the maximum power grip strength
I Biomechsnrcs Vol. 13. pp. 50-511. Pergamon Press Ltd. 1980. Pnnted in Great
WZl-92WkIOKI601-0505
SO!.oOfl
Britain
THE WRIST POSITION BETWEEN NEUTRAL AND ULNAR DEVIATION THAT FACILITATES THE MAXIMUM POWER GRIP STRENGTH JAMES C. PRYCE 1002
MD 21227,
- The purpose of
to identify of neutral in volar powa grip strength. Thirty right hand dominant adults with normal right upper extremities participated as subjects in the study. The maximum grip strength was measured in each of nine wrist positions between neutral and ulnar deviation, and fifteen degrees each side of neutral in volar and dorsiflexioo by having the subject grip an adjustable isometric handle. The force data were subjected to an analysis of variance to determine that there was a significant diffcrcnce between ulnar deviation wrist positions and bctwccn volar-dorsiflcxioo wrist positions, and that there was significant iotaaction betwean ulnar deviation and volardorsiflaxion wrist positions. Further mating, using Duncan’s Multiple Range Test, revealed that the diffcrcocas in power grip strength means wm not significant for xcro degrees ulnar deviation and 15 degrees dorsiflexion, 15 degrees ulnar deviation and 15 degrees dorsiflexion, 15 degrees ulnar deviation and zero degrees volardorsiflexion, and zero dcgrccs ulnar deviation and zero degrees volar-dorsigexion wrist positions; however, tbcae means were significantly higher than the power grip strength means for the other five wrist positions tested. Finally, the differences between the five lowest grip strength means were not significant.
lNTRODUCTlON
8eixing an object and holding it partially or wholly within the compass of the hand has been defined as prehensile movement by Napier (1956). He further divided prehensile movements, based on the stability of the object in the hand, into power and precision grip. Power grip occurs when an object is held in a clamp formed by the partially flexed fingers and the palm. The thumb lies more or less in the plane of the palm and applies counterpressure during power grip. Precision grip takes place when an object is pinched between the flexor aspects of the fingers and the opposing thumb. Napier further stated that the grip is determined by the sixe and shape of the object and the nature of the intended use. Napier (1956), Landsmeer (1962), Flatt (1961), and Backhouse (1968) agree that in power grip the thumb is adducted at the metacarpalphalangeal (MP) and the carpo-metacarpal joints, while the fingers are flexed, laterally rotated, and ulnarly deviated as determined by the size of the object held. In contrast, for precision handling the thumb is abducted and rotated, while the fingers are flexed and abducted at the MP joints. Since the present study deals with power grip, precision grip will not be further discussed; however, it should be noted that the two grips are often combined in functional activities. Tying a shoe lace involves power grip on the ulnar side of the hand, and precision handling on the radial side of the hand. Bunnell (1942) stated that, in the position of function, the hand was at its best mechanical advantage when * Receiwd 26 July 1979; in revisedfirm 18 October 1979. 505
the wrist was slightly dorsiflexed and ulnarly deviated; the fingers were partially flexed; the thumb was forward from the hand, partially flexed, and in mild opposition ; and the metacarpal arches were maintained in a normal position. Mundak (1970) reported that when a handpiece is positioned with the subject’s third digit MP joint in 30 degrees of flexion and his proximal interphalangeal joint (PIP) in 70 degrees of flexion, the subject produces the maximum output for grip strength. The optimal angle for grip strength differed slightly for the MP, but quite significantly for the PIP functional position as quoted by Bunnell. Therefore, this author questions other functional hand position angles and how they are related to power grip strength. Does the wrist joint functional position of slight dorsiflexion and ulnar deviation offer the best mechanical advantage for power grip strength? Or, like the PIP, will the maximum power grip strength be produced when the wrist is positioned in other than the functional position? Anderson (1965), Skovly (1967), Kraft and Detels (1972), and Haxelton et al. (1975) found that the power grip strength is in8uenced by the wrist position. Anderson (1965) found the highest grip strength when the wrist was in neutral. Kraft and Detels (1972) stated that neutral and dorsiflexion were optimal while volarflexion produced the lower grip strength. Conversely, Skovly (1967), and Haxelton et 01. (1975) reported that the highest grip strength occurred when the wrist was in approximately 30 degrees of ulnar deviation. These authors, except Kra8 and Detels who used four positions near neutral used extremes of positioning to investigate the influence of wrist position on power grip strength. They did not, however, seek the optimal wrist position for power grip strength.
506
JAMFSC.
This study intends to identify the wrist position between neutral and ulnar deviation, and 15 degrees each side of neutral in volar and dorsiflexion, that will produce the maximum power grip strength. The three null hypotheses state that there is no significant difference in power grip strength for three ulnar deviation, for three volardorsitkxion, and there is no interaction between ulnar deviation and volardorsifkxion wrist positions. METHODS Thirty right hand dominant adults with normal right upper extremities participated as subjects in this study. The subjects were between 20 and 40 years old, and were volunteers for the Medical College of Virginia, VCU. The person’s sex, age and the time of day tested were recorded. The major items of equipment used in this study ~nchuied: (1) a chair, (2) a forearm positioning table, (3) a Paciiic Scientific T-5166 grip device* connected to a Gould UL-4 200 lb load cell adaptert, (4) a Gould UC-3 transducer cell co~ected to a Gould SE 1105 Bridge Amplilkrt and a Data Precision Model 248 digital multimeter& The Gould UC-3 transducer cell’s sensingarmprovidesafullscalereadingwith0.12mm of movement, which is an isometric measurement of power grip strength. A dctaikd description of the grip device table is contained in a Master’s Thesis at Medical College of Vii Procedure Each day the msearcher calibrated the instrumentation by measuring the voltage change generated with known weights, repmsentative of the force produced by power grip. Voltage change produced by the five poundwdisht mcrements remail& constant throughout the study. The calibration chart was then utilixed to convert the voltage change to pounds of force. The equipment was turned on and allowed a fifteen minute warming period before testing each subject. The Wheatstone Bridge was balanced to the same zero point for every grip effort. The voltmeter was positioned so the subject was unable to see the output thereby negating the subject matching grip forces in different test positions. Next, the grip handle was wiped with an alcohol impregnated gauze pad and was wiped anytime the subject complained of slipperiness, or the researcher noticed the subject’s hand slipping during testing The subject read and initialed an instruction sheet, and signed a consent form. Details of the grip strength measurement procedure were explained and all questions were answered. Each subject was tested for two days prior to the experimental day in order to control the effects of motor learning. * pacificScientifCompany,Anaheim, CA. t Gould, Inc., 2230 Stat&am Blvd., Oxnard, CA. $ Data Precision Corp., Audubon Road, Wakefieid, Mass.
PRYCE
The subject was seated upright and strapped into a straight backed chair with his feet flat on the floor, his head in the midline, and the non-tested left (L) hand resting on the right (R) thigh (Fig. 1). The subject’s forearm was positioned in the splint while he grasped the grip device, and the table height was adjusted until the subject’sshoulders were even, and the ulnar surface of the forearm was resting securely against the splint. The subject’s forearm was then stabilized in the splint using Velcro closures. The right upper extremity was maintained at xero degrees of flexion, zero degrees of abduction, and fifteen degrees of external rotation at the shoulder, and the forearm was in a neutral position between supination and pronation. Next, the chair was positioned so the subject’s medial epicondyle was stabilixed against an orthoplast support, and the elbow was in ninety degrees of flexion. The grip device was then adjusted so the subject’ssecond digit MP was in 6fty degrees of fkxion and his PIP was in seventy degrees of flexion. The distal interphakngeal joint (DlP) was not controlled. This finger position was found to provide the most comfortable grip with the testing apparatus used in this experiment. Selection of a distinct wrist position sequence for each subject was made from a table of random numbers (Beyers, 1976). Each subject was tested in each of the nine positions listed in Table 1. Wrist measurements for ulnar deviation and volardorsifkxion were taken in the following manner. Ulnar deviation was determined by positioning the axis of the goniometer over the head of the capita@ and aligning the stable arm along the midline of the dorsum of the forearm and the moving arm along the dorsum of the third metacarpal shaft. In a similar manner volardorsifkxioa was determined by positioning the axis of the goniometer on the radial aspect of the wrist over the proximal tip of the scaphoid, and aligning the stable arm along the longitudinal axis of the radius, and the moving arm along the radial aspect of the second metacarpal shaft. The subject was reminded of the importance of his cooperation during the experiment. He was instructed to squeeze the grip device while maintaining his wrist position. One practice trial allowed the subject to become familiar with the equipment and the testing procedure. The subject was instructed to inhale and simultaneously to take up the slack in the cable of the grip device. He then squeexed the grip device with a Table 1. Wrist positions 1. 2. 3. 4. 5. 6. 7. 8. 9.
0” Ulnar deviation and 15” volar flexion 0” Ulnar deviation and 0” volar-dorsiflexion 0” Ulnar deviation and 15” dorsiflexion 15” Ulnar deviation and 15’ volar flexion 15” Ulnar deviation and 0’ volardorsiflexion 15” Ulnar deviation and 15” dorsiflexion 30” Ulnar deviation and 1P volar flexion 30” Ulnar deviation and 0” volar-dorsiflexion 30” Ulnar deviation and 15” dorsiflexion
Fig. 1. Wrist positioned in 15” ulnar deviation and 0” volar-dorsiflexion.
507
509
Wrist position between neutral and ulnar deviation effort for five seconds during a forced expiration (Chaffin, 1975). The expiration was to prevent a valsalva maneuver during the grip effort. The effect of the valsalva maneuver on grip strength has not been studied, therefore this researcher chose to standardize all subjects’ breathing techniques. The subject was encouraged during his five second effort with monotone verbal commands of squeeze, keep squeezing, and relax. The maximum voltage change was recorded and the test was repeated in the same wrist position within a ten second period. The second test should not match or exceed the initial voltage change if the first effort was maximal (Hislop, 1963; Schenck and Forward, 1965). If the first effort was maxima1 the wrist was stabilized in a new position and the angle of the wrist checked during a timed three minute rest period. The three minute rest following a five second contraction should control fatigue. If the second effort matched or exceeded the first, signifying that the first effort was not maximal, a timed three minute rest was permitted and the position retested. maximai
strength force means for each ulnar deviation wrist position (factor A) across volar-dorsiflexion wrist positions (factor B), and then compared grip strength means for each volardorsiflexion wrist position (fao tor B) across ulnar deviation wrist positions (factor A). Table 3 shows the differences in power grip strength means were not significant at the 0.01 level for 0” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and 0” volardorsiflexion, and 0” ulnar deviation and 0” volardorsiflexion. However, these power grip strength means were significantly higher than the power grip strength means from the other five wrist positions tested. The Duncan’s Test also showed that the differences in the five lowest grip strength means were not significant at the 0.01 level (i.e. 0” ulnar deviation and 15” volarllexion, 15” ulnar deviation and 15” volarflexion, 30” ulnar deviation and 15” volarflexion, 30” ulnar deviation and 0” volar-dorsiflexion, and 30” ulnar deviation and 15” dorsiflexion). DISCUSSION
RESULTS
The results of this study coincide with Anderson (1965) and Kraft and Detels (1972) who stated that the Table 2 shows the mean grip strength and standard deviation for each wrist position tested. An analysis of maximum power grip strength occurred with the wrist variance was performed using Barr et al.% SAS 76 in neutral; however, these results contrast with the (1976). The three levels of ulnar deviation (factor A) results of Skovly (1967) and Haxelton et al. (1975) who were 0’ ulnar deviation, 15” ulnar deviation, and 30” noted that the maximum power grip strength was achieved with the wrist in extreme ulnar deviation. ulnar deviation. The three levels of volar-dorsiflexion Anderson (1965), Skovly (1%7), &aft and Detels (factor B) were 15” volar flexion, 0” volar-dorsifkxion, (1972) and Hazelton et al. (1975) did not control the and 15” dorsiflexion. The F ratio of 13.79 for ulnar deviation (factor A) was significant at the 0.0001 level, use of reflexes, or the valsalva maneuver in their indicating that changing the ulnar deviation wrist studies. Neither Anderson (1965) nor Skovly (1967) stabilized the subject’s wrist position during testing. position resulted in significantly different grip strength Kraft and Detels (1972) and Haaelton et al. (1975) forces. The F ratio of 27.53 for volar-dorsiflexion stabilized the wrist position, but not the body position, (factor B) was significant at the 0.0001 level, indicating of each subject. The present study controlled the that changing the volardorsigexion wrist position resulted in significantly different grip strength forces. subject’s body and wrist position, the use of reflexes, and the valsalva maneuver. Three positions of volarThe F ratio of 3.55 for ulnar deviation and volardorsiflexion (AB) interaction was significant at the dorsiflexion at thirty degrees of ulnar deviation were tested and the grip strength of all three positions was 0.0078 level, indicating that there was significant not significantly different from the grip strength of the interaction between ulnar deviation and volarthree positions of ulnar deviation at fifteen degrees of dorsiflexion wrist positions during power grip. Kirk volarflexion. The wrist positions in thirty degrees of (1968) states if AB interaction is significant, attention should be directed to tests of simple main effects, that is ulnar deviation and tifteen degrees of volarflexion had each factor A must be analyzed across each factor B, grip strengths significantly lower than the other four and each factor B must be analyzed across each factor wrist positions tested. Furthermore, most of the subjects in this study stated that the thirty degrees of ulnar A. Duncan’s New Multiple Range Test, which tests deviation wrist positions felt uncomfortable compared simple main effects, was performed using Barr et al.‘s to the wrist positions near neutral when they squeezed SAS 76 (1976). The Duncan’s Test compared grip the isometric grip device.
Table 2. Power grip strength means and standard deviations (in pounds) for nine wrist positions (n = 30) 15” VolariIexion 0” Ulnar deviation 15” Ulnar deviation 30” Ulnar deviation
57.5 f 25.3 59.9 f 22.5 58.3 f 24.1
0” Volar-Dorsiflexion 65.1 f 20.9 65.0 f 23.9 59.1 f 24.1
15” Dorsiflexion 68.5 f 22.9 66.7 f 22.2 61.3 f 23.6
JAMESc. PRYCE
510
Table 3. Comparison of power grip streugth means (in pounds) by Ulnar Deviation and VoiarDorsiflcxion wrist positions using Duncan’s Multiple Range Test* 0” Ulnar deviation 15” Volarflexion MCMS
57.5
15” Volarflexion MMItS
59.9
0’ Volar-dorsiflexion
15” Dorsiflexion
685 . . . . . . . . . . . . 65 . . .1. . . . . . . . . . . . . . . . . . . . . . ..~............ 15” Ulnar deviation 0” Volar-dorsikion
15” Dorsiflcxion
. . . . . . . . . . . .659 . . . . . . . . . . . . . . . . . . . . . . . . . .667 .............. 30” Ulnar deviation
15” Vohrfiexion MUllS
l
30” Ulnar deviation
15” Ulnar deviation
30” Ulnar deviation
. . . . . . . . . . 65 . . . 1. . . . . . . . . . . . . . . . . . . . . . .659 . .. . . . . . . 15” Dorsitlexion
0” Ulnar deviation MC4lDS
15” Ulnar deviation
. . . . . . . . . . .575 . . . . . . . . . . . . . . . . . . . . . . . . . 598 . . . . . . ...*.. . . . . . . . . . . . . . .583 .............. 0” Volar-dorsiflexion 0” Ulnar deviation
MCiUlS
15” Dorsiflexion
. . . . . . . . . . 583 . . . . . . . . . . . . . . . . . . . . . . . . . . 59 . . .1. . . . . . . . . . . . . . . . . . . . . . .61.3 .............. 15” Volarlkxion 0“ Ulnar deviation
MCZUlS
0” Vohr-dorsiflexion
15”Ulnar deviation
59.1
30’ Ulnar deviation
. . . . . . . . . . 685 . . . . . . . . . . . . . . . . . . . . . . . . . .667 . .. . . . . . . . . . . . .
61.3
Means not connected by a dotted line differ significantly at the 0.01 level.
Clarke et UL(1950) stated that the optimal positionat which a muscle functions depended on the ability of the muscle to develop tension and the angk of pull at the insertion of the musck. The present study indicated that when the wrist was positioned near neutral the balance between tension of the finger flexors and their angle of pull was established. As noted in the present study, when the wrist deviated from neutral the power grip strength decreased. Perhaps the flexor tendons rubbing on the border of the carpal tunnel decreases the efficiency of the tendon pull (Armstrong and Chaffin, 1977), or possibly the length of the flexor muscles may be optimal for developing tension when the wrist is at neutral, and deviating from neutral takes the muscle away from its optimal length. Neutral wrist position may allow the maximum number of cross bridges in the finger flexor muscks, and deviating.from neutral may decrease the thick (myosin) and thin (actin) filament overlap (Mountcastk, 1968). The positions chosen in this study may not have isolated the optimum wrist position for power grip strength. The optimum wrist position for power grip strength may be located between the four positions which produced the highest grip strengths in this study (i.e. 0” ulnar deviation and 15” dorsitlexion, 15” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and
0” volardorsilkxion, and 0” ulnar deviation and 0” volardorsitlexion). Perhaps smaller increments of ulnar deviation and volardorsitlexion near neutral would eliminate the rubbing of the flexor tendons on the borders of the carpal tunnel while placing the muscle at its optimal length for developing tension, hence isolate the optimum wrist position for power grip strength. The results of this investigation indicate that it is essential to use the same wrist position in grip strength testing. Any further research correlating factors with power grip strength should control the subject’s positioning to ensure that the factor being studied is indeed the only variable acting in the study. Clinicians should control the patient’s wrist position during grip strength testing, otherwise changes in strength may be due to changes in wrist position rather than an exercise program. Perhaps the most sensible method of positioning a patient’s wrist, when he will perform predominantly power grip activities, is to evaluate the wrist function during the specific activities. Since the wrist position which facilitates maximum power grip strength is actually a range near neutral, any wrist position in that range could be chosen depending on the position needed for that patient’s activities.
Wrist position between neutral and ulnar deviation REVIEW OF THE ST&Y
Thirty normal right hand dominant adults were studied to determine which wrist position, between neutral and ulnar deviation and fifteen degrees each side of neutral in volardorsiflexion, facilitated maximum power grip strength. Each subject was tested for maximum power grip strength in nine wrist positions. An analysis of variance was used to determine that there was a significant difference in grip strength at the ulnar deviation wrist positions, at the volar-dorsiflexion wrist positions, and that there was significant interaction between ulnar deviation and volar-dorsiflexion wrist positions. The differences in mean grip strengths were not significant for 0” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and 0” volardorsiflexion, and 0” ulnar deviation and 0” volardorsiflexion ; however, these grip strength means were significantly higher than the grip strength means of the other five wrist positions tested. The differences in the five lowest grip strength means were not significant.
REFERENCES
Anderson, C. T. (1965) Wrist joint position tiuenccs normal hand function, Unpublished Master’s Thesis, University of Iowa. Armstrong, T. and Cbaffin, D. (1977) An investigation of the rehttionship between diapIacunents of the finger and wrist joints and the extrinsic flexor tendons. J. J3iomechanics 11, 119-128. Backhouse, K. M. (1968) The mechanics of normal digital control in the hand. Ann. R. CON Surg, England 43, 154-173.
511
Barr, A. J.,Goodnight, J. H., Sall, J. P. and Helwig, 1. T. (1976) A User’s Guide to SAS 76. Swrks Press. Raleinh. Beyer, W. H. (1976) Standard-Math Tabies. pp: 498-502, C.R.C. Press, Cleveland. Bunnell, S. (1942) Surgery of the intrinsic muscles of the hand other than producing opposition of the thumb. J. Bone Joint Surgery 24, l-32. Capener, N. (1956) The hand in surgery. J. Bone Jr Surg. 38-B. 128-151. ChafIin, D. (1975) Ergonomics guide for the assessment of human static strength. Am. Ind. Hyg. J. 36, 505-51 I. Clarke,H. H., E1kins.E. C., Ma&G. M. and Wakim, K. G. (1950) Relationship between body position and the application of muscle power to movements of the joints. Arch. _ Phys. Med. Rehobilitarion 31, 81-90. Flatt. A. F. (l%ll Kinesiolonv of the hand. Insrrcrional C&e Leit. 18,‘266-281. We Hazelton, F. T., Smidt, G. L., Flat& A. E. and Stephens, R. I. (1975) The influence of wrist position on the force produced by the finger flexors. J. Biomechanics g, 301-306. Hislop, H. J. (1963) Quantitative changes in human muscular strength during isometric exercise. J. Am. Phys. Ther. Assoc. 43, 21-38. Kirk, R. E. (1968) Experimental Design: Procedures for the Behavioral Sciences. Vol. 93, pp. 237-244, Wadsworth Publishing Co., California. Kraft, G. and Detels, P. (1972) Position of function of the wrist. Arch. Phys. Med. Rehabilitation 53, 272-275. Landsmccr, J. M. (1962) Power grip and precision handling. Ann. Rbeum. Dis. 22, 164-170. Mountcastle, V. B. (1%8) Medical Physiology. Vol. II, Chapter 55, Mosby, St. Louis. Mundak, M. 0. (1970) The relationship of intermittent isometric exercise to fatigue of hand grip. Arch. Phys. Med. Rehabilitation 51, 532-539. Napier, J. R. (1956) The prehensile movements of the human hand. J. Bone Jt kg. 3&B, 902-913. Schenk, J. M. and Forward, E. M. (1%5) Quantitative strength changes with test repetitions. Phys. Ther. 4S, 567-569.
Skovly, R. C. (1969) Power grip strength and how it is influenced by wrist joint position. Unpublished Masters Thesis, University of Iowa.
WZl-92WkIOKI601-0505
SO!.oOfl
Britain
THE WRIST POSITION BETWEEN NEUTRAL AND ULNAR DEVIATION THAT FACILITATES THE MAXIMUM POWER GRIP STRENGTH JAMES C. PRYCE 1002
MD 21227,
- The purpose of
to identify of neutral in volar powa grip strength. Thirty right hand dominant adults with normal right upper extremities participated as subjects in the study. The maximum grip strength was measured in each of nine wrist positions between neutral and ulnar deviation, and fifteen degrees each side of neutral in volar and dorsiflexioo by having the subject grip an adjustable isometric handle. The force data were subjected to an analysis of variance to determine that there was a significant diffcrcnce between ulnar deviation wrist positions and bctwccn volar-dorsiflcxioo wrist positions, and that there was significant iotaaction betwean ulnar deviation and volardorsiflaxion wrist positions. Further mating, using Duncan’s Multiple Range Test, revealed that the diffcrcocas in power grip strength means wm not significant for xcro degrees ulnar deviation and 15 degrees dorsiflexion, 15 degrees ulnar deviation and 15 degrees dorsiflexion, 15 degrees ulnar deviation and zero degrees volardorsiflexion, and zero dcgrccs ulnar deviation and zero degrees volar-dorsigexion wrist positions; however, tbcae means were significantly higher than the power grip strength means for the other five wrist positions tested. Finally, the differences between the five lowest grip strength means were not significant.
lNTRODUCTlON
8eixing an object and holding it partially or wholly within the compass of the hand has been defined as prehensile movement by Napier (1956). He further divided prehensile movements, based on the stability of the object in the hand, into power and precision grip. Power grip occurs when an object is held in a clamp formed by the partially flexed fingers and the palm. The thumb lies more or less in the plane of the palm and applies counterpressure during power grip. Precision grip takes place when an object is pinched between the flexor aspects of the fingers and the opposing thumb. Napier further stated that the grip is determined by the sixe and shape of the object and the nature of the intended use. Napier (1956), Landsmeer (1962), Flatt (1961), and Backhouse (1968) agree that in power grip the thumb is adducted at the metacarpalphalangeal (MP) and the carpo-metacarpal joints, while the fingers are flexed, laterally rotated, and ulnarly deviated as determined by the size of the object held. In contrast, for precision handling the thumb is abducted and rotated, while the fingers are flexed and abducted at the MP joints. Since the present study deals with power grip, precision grip will not be further discussed; however, it should be noted that the two grips are often combined in functional activities. Tying a shoe lace involves power grip on the ulnar side of the hand, and precision handling on the radial side of the hand. Bunnell (1942) stated that, in the position of function, the hand was at its best mechanical advantage when * Receiwd 26 July 1979; in revisedfirm 18 October 1979. 505
the wrist was slightly dorsiflexed and ulnarly deviated; the fingers were partially flexed; the thumb was forward from the hand, partially flexed, and in mild opposition ; and the metacarpal arches were maintained in a normal position. Mundak (1970) reported that when a handpiece is positioned with the subject’s third digit MP joint in 30 degrees of flexion and his proximal interphalangeal joint (PIP) in 70 degrees of flexion, the subject produces the maximum output for grip strength. The optimal angle for grip strength differed slightly for the MP, but quite significantly for the PIP functional position as quoted by Bunnell. Therefore, this author questions other functional hand position angles and how they are related to power grip strength. Does the wrist joint functional position of slight dorsiflexion and ulnar deviation offer the best mechanical advantage for power grip strength? Or, like the PIP, will the maximum power grip strength be produced when the wrist is positioned in other than the functional position? Anderson (1965), Skovly (1967), Kraft and Detels (1972), and Haxelton et al. (1975) found that the power grip strength is in8uenced by the wrist position. Anderson (1965) found the highest grip strength when the wrist was in neutral. Kraft and Detels (1972) stated that neutral and dorsiflexion were optimal while volarflexion produced the lower grip strength. Conversely, Skovly (1967), and Haxelton et 01. (1975) reported that the highest grip strength occurred when the wrist was in approximately 30 degrees of ulnar deviation. These authors, except Kra8 and Detels who used four positions near neutral used extremes of positioning to investigate the influence of wrist position on power grip strength. They did not, however, seek the optimal wrist position for power grip strength.
506
JAMFSC.
This study intends to identify the wrist position between neutral and ulnar deviation, and 15 degrees each side of neutral in volar and dorsiflexion, that will produce the maximum power grip strength. The three null hypotheses state that there is no significant difference in power grip strength for three ulnar deviation, for three volardorsitkxion, and there is no interaction between ulnar deviation and volardorsifkxion wrist positions. METHODS Thirty right hand dominant adults with normal right upper extremities participated as subjects in this study. The subjects were between 20 and 40 years old, and were volunteers for the Medical College of Virginia, VCU. The person’s sex, age and the time of day tested were recorded. The major items of equipment used in this study ~nchuied: (1) a chair, (2) a forearm positioning table, (3) a Paciiic Scientific T-5166 grip device* connected to a Gould UL-4 200 lb load cell adaptert, (4) a Gould UC-3 transducer cell co~ected to a Gould SE 1105 Bridge Amplilkrt and a Data Precision Model 248 digital multimeter& The Gould UC-3 transducer cell’s sensingarmprovidesafullscalereadingwith0.12mm of movement, which is an isometric measurement of power grip strength. A dctaikd description of the grip device table is contained in a Master’s Thesis at Medical College of Vii Procedure Each day the msearcher calibrated the instrumentation by measuring the voltage change generated with known weights, repmsentative of the force produced by power grip. Voltage change produced by the five poundwdisht mcrements remail& constant throughout the study. The calibration chart was then utilixed to convert the voltage change to pounds of force. The equipment was turned on and allowed a fifteen minute warming period before testing each subject. The Wheatstone Bridge was balanced to the same zero point for every grip effort. The voltmeter was positioned so the subject was unable to see the output thereby negating the subject matching grip forces in different test positions. Next, the grip handle was wiped with an alcohol impregnated gauze pad and was wiped anytime the subject complained of slipperiness, or the researcher noticed the subject’s hand slipping during testing The subject read and initialed an instruction sheet, and signed a consent form. Details of the grip strength measurement procedure were explained and all questions were answered. Each subject was tested for two days prior to the experimental day in order to control the effects of motor learning. * pacificScientifCompany,Anaheim, CA. t Gould, Inc., 2230 Stat&am Blvd., Oxnard, CA. $ Data Precision Corp., Audubon Road, Wakefieid, Mass.
PRYCE
The subject was seated upright and strapped into a straight backed chair with his feet flat on the floor, his head in the midline, and the non-tested left (L) hand resting on the right (R) thigh (Fig. 1). The subject’s forearm was positioned in the splint while he grasped the grip device, and the table height was adjusted until the subject’sshoulders were even, and the ulnar surface of the forearm was resting securely against the splint. The subject’s forearm was then stabilized in the splint using Velcro closures. The right upper extremity was maintained at xero degrees of flexion, zero degrees of abduction, and fifteen degrees of external rotation at the shoulder, and the forearm was in a neutral position between supination and pronation. Next, the chair was positioned so the subject’s medial epicondyle was stabilixed against an orthoplast support, and the elbow was in ninety degrees of flexion. The grip device was then adjusted so the subject’ssecond digit MP was in 6fty degrees of fkxion and his PIP was in seventy degrees of flexion. The distal interphakngeal joint (DlP) was not controlled. This finger position was found to provide the most comfortable grip with the testing apparatus used in this experiment. Selection of a distinct wrist position sequence for each subject was made from a table of random numbers (Beyers, 1976). Each subject was tested in each of the nine positions listed in Table 1. Wrist measurements for ulnar deviation and volardorsifkxion were taken in the following manner. Ulnar deviation was determined by positioning the axis of the goniometer over the head of the capita@ and aligning the stable arm along the midline of the dorsum of the forearm and the moving arm along the dorsum of the third metacarpal shaft. In a similar manner volardorsifkxioa was determined by positioning the axis of the goniometer on the radial aspect of the wrist over the proximal tip of the scaphoid, and aligning the stable arm along the longitudinal axis of the radius, and the moving arm along the radial aspect of the second metacarpal shaft. The subject was reminded of the importance of his cooperation during the experiment. He was instructed to squeeze the grip device while maintaining his wrist position. One practice trial allowed the subject to become familiar with the equipment and the testing procedure. The subject was instructed to inhale and simultaneously to take up the slack in the cable of the grip device. He then squeexed the grip device with a Table 1. Wrist positions 1. 2. 3. 4. 5. 6. 7. 8. 9.
0” Ulnar deviation and 15” volar flexion 0” Ulnar deviation and 0” volar-dorsiflexion 0” Ulnar deviation and 15” dorsiflexion 15” Ulnar deviation and 15’ volar flexion 15” Ulnar deviation and 0’ volardorsiflexion 15” Ulnar deviation and 15” dorsiflexion 30” Ulnar deviation and 1P volar flexion 30” Ulnar deviation and 0” volar-dorsiflexion 30” Ulnar deviation and 15” dorsiflexion
Fig. 1. Wrist positioned in 15” ulnar deviation and 0” volar-dorsiflexion.
507
509
Wrist position between neutral and ulnar deviation effort for five seconds during a forced expiration (Chaffin, 1975). The expiration was to prevent a valsalva maneuver during the grip effort. The effect of the valsalva maneuver on grip strength has not been studied, therefore this researcher chose to standardize all subjects’ breathing techniques. The subject was encouraged during his five second effort with monotone verbal commands of squeeze, keep squeezing, and relax. The maximum voltage change was recorded and the test was repeated in the same wrist position within a ten second period. The second test should not match or exceed the initial voltage change if the first effort was maximal (Hislop, 1963; Schenck and Forward, 1965). If the first effort was maxima1 the wrist was stabilized in a new position and the angle of the wrist checked during a timed three minute rest period. The three minute rest following a five second contraction should control fatigue. If the second effort matched or exceeded the first, signifying that the first effort was not maximal, a timed three minute rest was permitted and the position retested. maximai
strength force means for each ulnar deviation wrist position (factor A) across volar-dorsiflexion wrist positions (factor B), and then compared grip strength means for each volardorsiflexion wrist position (fao tor B) across ulnar deviation wrist positions (factor A). Table 3 shows the differences in power grip strength means were not significant at the 0.01 level for 0” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and 0” volardorsiflexion, and 0” ulnar deviation and 0” volardorsiflexion. However, these power grip strength means were significantly higher than the power grip strength means from the other five wrist positions tested. The Duncan’s Test also showed that the differences in the five lowest grip strength means were not significant at the 0.01 level (i.e. 0” ulnar deviation and 15” volarllexion, 15” ulnar deviation and 15” volarflexion, 30” ulnar deviation and 15” volarflexion, 30” ulnar deviation and 0” volar-dorsiflexion, and 30” ulnar deviation and 15” dorsiflexion). DISCUSSION
RESULTS
The results of this study coincide with Anderson (1965) and Kraft and Detels (1972) who stated that the Table 2 shows the mean grip strength and standard deviation for each wrist position tested. An analysis of maximum power grip strength occurred with the wrist variance was performed using Barr et al.% SAS 76 in neutral; however, these results contrast with the (1976). The three levels of ulnar deviation (factor A) results of Skovly (1967) and Haxelton et al. (1975) who were 0’ ulnar deviation, 15” ulnar deviation, and 30” noted that the maximum power grip strength was achieved with the wrist in extreme ulnar deviation. ulnar deviation. The three levels of volar-dorsiflexion Anderson (1965), Skovly (1%7), &aft and Detels (factor B) were 15” volar flexion, 0” volar-dorsifkxion, (1972) and Hazelton et al. (1975) did not control the and 15” dorsiflexion. The F ratio of 13.79 for ulnar deviation (factor A) was significant at the 0.0001 level, use of reflexes, or the valsalva maneuver in their indicating that changing the ulnar deviation wrist studies. Neither Anderson (1965) nor Skovly (1967) stabilized the subject’s wrist position during testing. position resulted in significantly different grip strength Kraft and Detels (1972) and Haaelton et al. (1975) forces. The F ratio of 27.53 for volar-dorsiflexion stabilized the wrist position, but not the body position, (factor B) was significant at the 0.0001 level, indicating of each subject. The present study controlled the that changing the volardorsigexion wrist position resulted in significantly different grip strength forces. subject’s body and wrist position, the use of reflexes, and the valsalva maneuver. Three positions of volarThe F ratio of 3.55 for ulnar deviation and volardorsiflexion (AB) interaction was significant at the dorsiflexion at thirty degrees of ulnar deviation were tested and the grip strength of all three positions was 0.0078 level, indicating that there was significant not significantly different from the grip strength of the interaction between ulnar deviation and volarthree positions of ulnar deviation at fifteen degrees of dorsiflexion wrist positions during power grip. Kirk volarflexion. The wrist positions in thirty degrees of (1968) states if AB interaction is significant, attention should be directed to tests of simple main effects, that is ulnar deviation and tifteen degrees of volarflexion had each factor A must be analyzed across each factor B, grip strengths significantly lower than the other four and each factor B must be analyzed across each factor wrist positions tested. Furthermore, most of the subjects in this study stated that the thirty degrees of ulnar A. Duncan’s New Multiple Range Test, which tests deviation wrist positions felt uncomfortable compared simple main effects, was performed using Barr et al.‘s to the wrist positions near neutral when they squeezed SAS 76 (1976). The Duncan’s Test compared grip the isometric grip device.
Table 2. Power grip strength means and standard deviations (in pounds) for nine wrist positions (n = 30) 15” VolariIexion 0” Ulnar deviation 15” Ulnar deviation 30” Ulnar deviation
57.5 f 25.3 59.9 f 22.5 58.3 f 24.1
0” Volar-Dorsiflexion 65.1 f 20.9 65.0 f 23.9 59.1 f 24.1
15” Dorsiflexion 68.5 f 22.9 66.7 f 22.2 61.3 f 23.6
JAMESc. PRYCE
510
Table 3. Comparison of power grip streugth means (in pounds) by Ulnar Deviation and VoiarDorsiflcxion wrist positions using Duncan’s Multiple Range Test* 0” Ulnar deviation 15” Volarflexion MCMS
57.5
15” Volarflexion MMItS
59.9
0’ Volar-dorsiflexion
15” Dorsiflexion
685 . . . . . . . . . . . . 65 . . .1. . . . . . . . . . . . . . . . . . . . . . ..~............ 15” Ulnar deviation 0” Volar-dorsikion
15” Dorsiflcxion
. . . . . . . . . . . .659 . . . . . . . . . . . . . . . . . . . . . . . . . .667 .............. 30” Ulnar deviation
15” Vohrfiexion MUllS
l
30” Ulnar deviation
15” Ulnar deviation
30” Ulnar deviation
. . . . . . . . . . 65 . . . 1. . . . . . . . . . . . . . . . . . . . . . .659 . .. . . . . . . 15” Dorsitlexion
0” Ulnar deviation MC4lDS
15” Ulnar deviation
. . . . . . . . . . .575 . . . . . . . . . . . . . . . . . . . . . . . . . 598 . . . . . . ...*.. . . . . . . . . . . . . . .583 .............. 0” Volar-dorsiflexion 0” Ulnar deviation
MCiUlS
15” Dorsiflexion
. . . . . . . . . . 583 . . . . . . . . . . . . . . . . . . . . . . . . . . 59 . . .1. . . . . . . . . . . . . . . . . . . . . . .61.3 .............. 15” Volarlkxion 0“ Ulnar deviation
MCZUlS
0” Vohr-dorsiflexion
15”Ulnar deviation
59.1
30’ Ulnar deviation
. . . . . . . . . . 685 . . . . . . . . . . . . . . . . . . . . . . . . . .667 . .. . . . . . . . . . . . .
61.3
Means not connected by a dotted line differ significantly at the 0.01 level.
Clarke et UL(1950) stated that the optimal positionat which a muscle functions depended on the ability of the muscle to develop tension and the angk of pull at the insertion of the musck. The present study indicated that when the wrist was positioned near neutral the balance between tension of the finger flexors and their angle of pull was established. As noted in the present study, when the wrist deviated from neutral the power grip strength decreased. Perhaps the flexor tendons rubbing on the border of the carpal tunnel decreases the efficiency of the tendon pull (Armstrong and Chaffin, 1977), or possibly the length of the flexor muscles may be optimal for developing tension when the wrist is at neutral, and deviating from neutral takes the muscle away from its optimal length. Neutral wrist position may allow the maximum number of cross bridges in the finger flexor muscks, and deviating.from neutral may decrease the thick (myosin) and thin (actin) filament overlap (Mountcastk, 1968). The positions chosen in this study may not have isolated the optimum wrist position for power grip strength. The optimum wrist position for power grip strength may be located between the four positions which produced the highest grip strengths in this study (i.e. 0” ulnar deviation and 15” dorsitlexion, 15” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and
0” volardorsilkxion, and 0” ulnar deviation and 0” volardorsitlexion). Perhaps smaller increments of ulnar deviation and volardorsitlexion near neutral would eliminate the rubbing of the flexor tendons on the borders of the carpal tunnel while placing the muscle at its optimal length for developing tension, hence isolate the optimum wrist position for power grip strength. The results of this investigation indicate that it is essential to use the same wrist position in grip strength testing. Any further research correlating factors with power grip strength should control the subject’s positioning to ensure that the factor being studied is indeed the only variable acting in the study. Clinicians should control the patient’s wrist position during grip strength testing, otherwise changes in strength may be due to changes in wrist position rather than an exercise program. Perhaps the most sensible method of positioning a patient’s wrist, when he will perform predominantly power grip activities, is to evaluate the wrist function during the specific activities. Since the wrist position which facilitates maximum power grip strength is actually a range near neutral, any wrist position in that range could be chosen depending on the position needed for that patient’s activities.
Wrist position between neutral and ulnar deviation REVIEW OF THE ST&Y
Thirty normal right hand dominant adults were studied to determine which wrist position, between neutral and ulnar deviation and fifteen degrees each side of neutral in volardorsiflexion, facilitated maximum power grip strength. Each subject was tested for maximum power grip strength in nine wrist positions. An analysis of variance was used to determine that there was a significant difference in grip strength at the ulnar deviation wrist positions, at the volar-dorsiflexion wrist positions, and that there was significant interaction between ulnar deviation and volar-dorsiflexion wrist positions. The differences in mean grip strengths were not significant for 0” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and 15” dorsiflexion, 15” ulnar deviation and 0” volardorsiflexion, and 0” ulnar deviation and 0” volardorsiflexion ; however, these grip strength means were significantly higher than the grip strength means of the other five wrist positions tested. The differences in the five lowest grip strength means were not significant.
REFERENCES
Anderson, C. T. (1965) Wrist joint position tiuenccs normal hand function, Unpublished Master’s Thesis, University of Iowa. Armstrong, T. and Cbaffin, D. (1977) An investigation of the rehttionship between diapIacunents of the finger and wrist joints and the extrinsic flexor tendons. J. J3iomechanics 11, 119-128. Backhouse, K. M. (1968) The mechanics of normal digital control in the hand. Ann. R. CON Surg, England 43, 154-173.
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Barr, A. J.,Goodnight, J. H., Sall, J. P. and Helwig, 1. T. (1976) A User’s Guide to SAS 76. Swrks Press. Raleinh. Beyer, W. H. (1976) Standard-Math Tabies. pp: 498-502, C.R.C. Press, Cleveland. Bunnell, S. (1942) Surgery of the intrinsic muscles of the hand other than producing opposition of the thumb. J. Bone Joint Surgery 24, l-32. Capener, N. (1956) The hand in surgery. J. Bone Jr Surg. 38-B. 128-151. ChafIin, D. (1975) Ergonomics guide for the assessment of human static strength. Am. Ind. Hyg. J. 36, 505-51 I. Clarke,H. H., E1kins.E. C., Ma&G. M. and Wakim, K. G. (1950) Relationship between body position and the application of muscle power to movements of the joints. Arch. _ Phys. Med. Rehobilitarion 31, 81-90. Flatt. A. F. (l%ll Kinesiolonv of the hand. Insrrcrional C&e Leit. 18,‘266-281. We Hazelton, F. T., Smidt, G. L., Flat& A. E. and Stephens, R. I. (1975) The influence of wrist position on the force produced by the finger flexors. J. Biomechanics g, 301-306. Hislop, H. J. (1963) Quantitative changes in human muscular strength during isometric exercise. J. Am. Phys. Ther. Assoc. 43, 21-38. Kirk, R. E. (1968) Experimental Design: Procedures for the Behavioral Sciences. Vol. 93, pp. 237-244, Wadsworth Publishing Co., California. Kraft, G. and Detels, P. (1972) Position of function of the wrist. Arch. Phys. Med. Rehabilitation 53, 272-275. Landsmccr, J. M. (1962) Power grip and precision handling. Ann. Rbeum. Dis. 22, 164-170. Mountcastle, V. B. (1%8) Medical Physiology. Vol. II, Chapter 55, Mosby, St. Louis. Mundak, M. 0. (1970) The relationship of intermittent isometric exercise to fatigue of hand grip. Arch. Phys. Med. Rehabilitation 51, 532-539. Napier, J. R. (1956) The prehensile movements of the human hand. J. Bone Jt kg. 3&B, 902-913. Schenk, J. M. and Forward, E. M. (1%5) Quantitative strength changes with test repetitions. Phys. Ther. 4S, 567-569.
Skovly, R. C. (1969) Power grip strength and how it is influenced by wrist joint position. Unpublished Masters Thesis, University of Iowa.