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Sphygmomanometer vs. Dynamometer

The article by Hamilton et al pro- vides useful information for the cli- nician considering use of the modified sphygmomanometer ( M S ) in lieu of the Jamar dynamometer to measure hand grip strength ( 2 ) . The purpose of this letter is to relate the authors' work to findings presented previously by other investigators. The correlation ( r , = .75) reported by Hamilton et al between measurements obtained with the MS and Jamar is less than the correlation ( r = .841) reported by Balogun et al between measurements obtained with a MS and Harpenden dynamometer ( 1 ) . The correlation reported by Hamilton et al is substan- tially higher in magnitude than the correlations reported by Lusardi and Bohannon (3). The Pearson correlations between the MS and Jamar measurements in their study were .417 and .509 when the MS was in- flated to 20 and 3 0 mm Hg, respec- tively. Based on their findings and the grip configurations their subjects used with the different devices, they concluded that "either device may be acceptable for measuring grip strength, but the devices may be measuring different types of grip strength and should not be used in- terchangeably." Richard \Ir. Bohannon, EdD, PT, NCS Associate Professor University of Connecticut Storrs, CT

REFERENCES 1. Balogun /A, Akomolafe CT, Amusa LO:

Reproducibility and criterion-related validity of a modified sphygmomanometer for isometric testing of grip strength. Physiother Can 42:290-295, 1990

2. Hamilton CF, McDonald C, Chenier TC: Measurement of grip strength: Va- lidity and reliability of the sphygmo-

R S T O T H E E

manometer and lamar grip dynamometer. I Orthop Sport Phys Ther 16:2 15- 219, 1992

3. Lusardi MM, Bohannon RW: Handgrip strength: Comparability of measurements obtained with a lamar dynamometer and a modified sphygmomanometer. I Hand Ther 4: 1 17- 122, 1991

Author's response: We appreciate Dr. Bohannon's critical review and comments on our study (2). He has identified differences in the correlation values between three studies which have compared the modified sphygmomanometer (MS) at 20 mm Hg against mechanical grip dynamometers (1 -3). Balogun et a1 found high correlation (.84 1) between the MS at 20 mm Hg baseline pressure and a Harpenden (mechanical) dynamometer. Our findings (.75) were similar to those of Balogun when we compared the MS against the lamar (mechanical) grip dynamometer. Both studies provided support for intratester reliability and construct validity of the MS as a grip strength measurement device. We feel the device is particularly valuable when testing hand impaired subjects unable to tolerate harsh surface contact and who have relatively poor strength. Both Balogun et a1 and Hamilton et a1 reported formulae for conversion from MS values to the respective mechanical dynamometer values. While Lusardi and Bohannon's findings support intrarater reliability of the MS for grip strength measurement, they did not find high correlation (.4 17 with MS at 20 mm Hg) between the MS and the lamar device, a factor which produces diverging information as to the relationship between MS-based and mechanical-based (lamar) grip measurement devices. Upon examination, we found that neither the Balogun et a1 estimate of .84 1 nor the Lusardi and Bohannon estimate (.4 17) are statistically different from our estimate (.75) at the .05 level of significance. Part of the problem lies with the relatively small samples used

D I T O R

in estimating these correlation coefficients.

Secondly, methodology may have contributed to the differences reported. Balogun's use of a single maximum trial should inflate the estimate of reliability by eliminating intertrial variability. All three investigators utilized college-age subjects, all of whom were females, except in Balogun's study. Measurement methods were similar, with Balogun subjects performing grip tests with an extended elbow in a standing position while lusardi and Bohannon and our subjects performed grip tests with the elbow Nexed and in a seated position. The studies provided meanlstandard deviation values for MS grip strength measurements (at 20 mm Hg) of 18 119 by Balogun et al, 215130 by Lusardi and Bohannon, and 20312 1 by Hamilton et al. Similarity in mean MS-measured values across the three studies added support for the utilization of the MS procedure for grip measurements. Mean values for the lamar measurements were 28.913.9 by Lusardi and Bohannon and 64.919 by Hamilton et a/; Balogun et a1 did not report mean values for the Harpenden dynamometer. Substantial difference in lamar measurements could be a function of different grip size settings and may have impacted upon the differences in relationship reported between the two methods of measurement.

We agree with Lusardi and Bohannon's recommendation that interchanging methods of grip strength measurement is not a good practice. However, we believe that the outcome of Balogun et al's study and our study provide support for the validity of the MS as a grip measurement device and for extrapolation of MS readings when one is required to conform with mechanical- based grip strength standards. When doing so, we would recommend the conversion formulae be shown in the report.

We believe the MS grip dynamometer is a reasonable tool for

Volume 17 Number 6-June 1993 *JOSPT

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use in reporting and researching hand therapeutics, that further research data is needed to fully understand the reliability and validity of methods for measuring grip strength, and that clinical studies that utilize grip strength measurements should include repeated trials and report the reliability of the measurement technique.

George F. Hamilton, MS, PT, OCS Professor East Carolina University Greenville, NC

REFERENCES I. Balogun IA, Akomolafe CT, Amusa LO:

Reproducibility and criterion-related validity of a modified sphygmomanometer for isometric testing of grip strength. Physiother Can 42:290-295, 1990

2. Hamilton CF, McDonald C, Chenier TC: Measurement of grip strength: Va- lidity and reliability of the sphygmomanometer and lamar grip dynamometer. I Orthop Sport Phys Ther 16:2 15- 219, 1992

3. Lusardi MM, Bohannon RW: Handgrip strength: Comparability of measurements obtained with a lamar dynamometer and a modified sphygmomanometer. I Hand Ther 4: 1 17- 122, 1991

Sympathetic Effect of Stretching: Only Neurogenic?

T h e paper by Kornberg and McCarthy (2) reported on the thermographic effect bilaterally a t four locations on each lower extremity after the hamstring muscles of one side were placed on full stretch for 7 seconds in the seated position. At the same time, tension was added to the muscles and fascia of the back by forcefully flexing the head and neck (the Kornberg "slump test"). At all four sites measured, the skin temperature increased on the side of the muscle being stretched and decreased on the side not stretched compared

with the temperature recorded pre- ceding the procedure.

T h e authors cite a study by Korn- berg and Lew (3) that showed that 16 players who received only "tradi- tional" treatment that included "hamstring stretches" did not respond as well as 12 players who received the same treatment plus the slump stretching technique. Kornberg and Lew concluded that a neurogenic ele- ment was responsible for the difference. There is also the possibility that the additional stabilization of the pelvis by upper spinal flexion could have improved the effectiveness of the hamstring stretch in those players.

T h e slump test was presented as a means of assessing grade 1 hamstring injury. All three of the criteria required for a positive test-local pain and tenderness of the muscle, weakness with pain on isometric contraction, and decreased muscle length-are characteristic of a muscle that has one o r more myofascial trigger points (6).

Kornberg and McCarthy (2) concluded that, together, the results of the Kornberg and Lew study (3) and their own study indicate a neurogenic mechanism for musculoskeletal symptoms that focus on the hamstring muscle group. However, the interpreta- tion of the Kornberg and McCarthy study is not consistent with the facts. T h e thermographic response was highly specific and consistent in show- ing a strong lateralization: an increase of temperature on the side of the stressed hamstring muscle and very nearly an equal decrease on the un- stressed side. T h e stress induced in neurological structures above the pelvis in this experimental situation should be bilaterally symmetrical. Therefore, thermographic response to that stress should be bilaterally symmetrical, which it emphatically was not. Why not look to the structure of interest that was subjected to vig- orous unilateral stimulation, the ham-

string muscle group, for the source of the temperature change?

It is now known that muscles are well supplied with afferents capable of strongly modulating central nervous system transmission (5). More spe- cifically, trigger points have been shown to modulate skin temperature by producing a hot spot near the lo- cation of an active T r P (1) and that pressure on a T r P modulates the skin temperature distally (4).

It would be most interesting to see the results of the other experi- ment, where upper spinal flexion is introduced as a constant, and the thermograms are taken before and after placing the hamstring muscle under stretch. How much of the response is attributable just to stretch of the muscle?

When dealing with musculoskeletal pain, it is wise to first consider the contribution of the muscular com- ponent. It is the most likely culprit and is where the least research has been directed but is most urgently needed. David G. Simons, MD Clinical Professor Department of Physical Medicine and

Rehabilitation University of California, Iruine Iruine, C A

REFERENCES I . Fischer AA: Documentation of myofas-

cia1 trigger points. Arch Phys Med Re- habil69:286-29 1, 1988

2. Kornberg C, McCarthy T: The effect of neural stretching technique on sympathetic outflow to the lower limbs. I Orthop Sports Phys Ther 16:269-274, 1992

3. Kornberg C, Lew P: The effect of stretching neural structures on grade one hamstring injuries. I Orthop Sports Phys Ther 1 O:48 1-487, 1989

4. Kruse RA lr, Christiansen /A: Thermo- graphic imaging of myofascial trigger points: A follow-up study. Arch Phys Med Rehabil73:8 19-823, 1992

5. Mense 5: Considerations concerning

JOSPT Volume 17 Number 6 June 1993

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the neurobiological basis of muscle pain. Can / Physiol Pharmacol69:6 10- 616, 1991

6. Travel1 /C, Simons DC: Myobscial Pain and Dysfunction: The Trigger Point Manual (Vol I ) , pp 18-1 9. 15altimore: Williams R Wilkinc, 1983

Author's response: We thank Dr. Simons for his letter and take this opportunity to respond to some points that he has raised. Firstly, although a small point, Kornherg cannot take credit for the slump test. Maitland (5) first described the test in 1979. Secondly, Dr. Simons has confused Kornherg and Lew's (3) description of grade 1 hamstring strain with that of the definition of a positive slump test. The definition of positive slump test was described as reproduction of the symptoms, namely the "hamstring" pain, with alleviation of symptoms with release of cervical flexion (3, p 482). We agree that the symptoms that Dr. Simons describes can he characteristic of a muscle that has one or more myofascial trigger points, but the symptoms he descrihed were definitely not the criteria for a positive slump test. Kornberg and Lew were, in fact, trying to show that these signs and symptoms were indicative of many different pathologies and not just grade 1 hamstring strain.

There may also he some confusion regarding the term neurogenic. for the purpose of our study, neurogenic implied that neural mechanisms were the underlying

mediators of the response. As we discussed in the paper (4, p 273) "The exact nature of the afferent stimulation accompanying the slump stretch is uncertain. . . .Muscle and nociceptor afferents must nlso he taken into account."

In concluding that the source of the response seen in this study is the stretched hamstring muscle, Dr. Simons contends that the stress induced in neurological structures ahove the pelvis should he symmetrical in the test. However, there is evidence to the contrary. Coddard and Reid (2) have found that with unilateral straight leg raise technique, there is between 1.5 and 4 mm of movement of the nerve roots, on that side, up to the level of L4. Breig (I) showed that the mechanics of the "crossed straight leg raising test" involved movement of the dura and contralateral nerve roots medially and distally when the unaffected limb was raised, ie., toward the side of the straight leg raise. Based on this, the asymmetrical autonomic response may be explained by a nerve stretching mechanism and, hence, we cannot concur that the stretch of the hamstring muscle was the only possible source of the temperature change.

finally, while there may he evidence that manipulation of trigger points is capahle of modulating sympathetic outflow, we emphasize that our study was carried out on asymptomatic, elite track and field athletes. The fundamental conclusion

that we came to was that, although the exact nature of the afferent stimulation was unknown, a physical technique was capahle of producing a sympatholytic, neurogenic response.

Charlip Kornhprg, ,\lAP:\, .\I.\IPA/\ Tim ,\lcCa rthv, ,\ IRRS, FF;\ Ri\ CS ,\I~tropolitan Spinal Clinic Prahan, \'I(,', :\tlstralia

REFERENCES I . Breig A: Adverse Mechanical Tension

in the Central Nervous System: An Analysis of Cause and Effect, Relief hy functional Neurosurgery, Stockholm: Almquist R Wiksell, International Pub- lishers, 1978

2. Coddard MD, Reid ID: Movements induced by straight leg raising in the lumho-sacral roots, nerves and plexus, and the intrapelvic section of the sciatic nerve. / Neurol Neurosurg Psy- chiatry 28: 12, 1965

3. Kornberg C, Lew P: The effect of stretching neural structures on grade one hamstring injuries. / Orthop Sports Phys Ther lO:48 I -487, 1989

4. Kornherg C, McCarthy T: The effect of neural stretching technique on sympathetic outflow to the lower limbs. / Orthop Sports Phys Ther 16:269-274, 1992

5. Maitland CD: Movement of pain sen- sitive structures in the vertebral canal in a group of physiotherapy students. In: Proceedings of the inaugural Con- gress Manipulative Therapists' Associ- ation of Australia, pp 37-50. Sydney, Austrdia, 1979

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