1. Background Information

Authors: Smith, Doria A. and Lukens, Shirley A.

Title: Stress Effects of Isometric Contraction in Occupational Therapy

Source: The Occupational Therapy Journal of Research

Year: October, 1983, 3 (4), 222-242

2. Abstract

This study investigated the effects on blood pressure (BP) and pulse rate (PR) of four isometric activities with a sample of 40 S's (ages 19 to 30). The researchers' interest in this subject stems from the fact that isometric (or static) activities are used by occupational therapists and other health professionals to evaluate and treat clients. Since the medical literature reports that such muscle contraction, isometric rather than isotonic, can cause potentially harmful increases in BP and PR, the intent of this study was to identify a limited number of assessments and activities that require isometric muscle contraction (IMC) and suggest improved guidelines and treatment safeguards for such tasks.

Isometric muscle contraction, defined as muscle contraction where considerable effort is expended to perform a task, but there is little or no body movement. In contrast to IMC, isotonic muscle contraction produces obvious body movement, as in walking or swimming.

A repeated measures ANOVA of isometric activities (pinch, grasp, and push) for 3, 5, 10, and 30 seconds led to conclusions that there was a significant increase in BP and PR as time of contraction increased, and that the pushing activity had a significantly greater effect on BP and PR than did pinching and gripping.

Discussion by the researchers focused on suggestions for occupational therapists in all treatment areas who have clients potentially at risk from the effects of IMC. Possible treatment implications were cited.

3. Null hypotheses, alpha level, sample size per group

Three null hypotheses were tested in this research. For an adult (19 to 30 years old) with normal resting systolic blood pressure (SBP) and diastolic blood pressure (DBP) and resting PR as measured on the S/D Digital (electronic) Sphygmomanometer, it was postulated that there would be no significant difference between:

4. Independent and dependent variables

The two independent variables were:

1) Activity, which included 3 levels - pinch, grasp, and push.

2. Time, which included 4 levels - 3, 6, 10, and 30 second intervals with 3 minute rest periods between each IMC and 10 minute rests after each series of 4 IMC's before moving to the next type of activity.

1. Diastolic blood pressure
2. Systolic blood pressure
3. Pulse rate with 12 measures recorded on each resulting in a total of 36 dependent variables.

5. Instrument

The S/D 600 Digital Sphygmomanometer was used to measure BP and PR, and as an electronic instrument, is considered a standardized tool for such measurements. Both the Miller pinch gauge and the Jamar hand dynamometer for grip, used to measure two of the IMC activities, are considered reliable tools. However, a nonstandardized tool was used to measure pushing. It included the S's grasping a 1 and 1/8 inch stationary pole and pushing against an immovable metal frame.

6. Experimental Procedure

Of the 65 people between the ages of 19 and 30 years who volunteered for this study, 40 met the screening criteria (nine male and thirty-one female). This included having their SBP, DBP, and PR taken and comparing them with established norms. Precautions were taken by having the S's sign an informed consent form indicating that they had no contraindicated conditions for this study. Also, limits for BP and PR were approved by the Human Subjects Board at the university. Because of this safety restriction, 12 cases were discontinued from the study due to BP and PR readings exceeding the limits.

Initial testing included a pretest consisting of an average of 2 successive SBP, DBP, and PR readings. Each S did the pinch grasp for 3 seconds, then for 6, 10, and 30 seconds, with 3 minute rest periods between each IMC. The second and third activities (grip and push) were then done in consecutive order with the same times of IMC and rest. A ~MT was administered to each S following the above tests but this data were analyzed separately (See Appendix B).

7. Statistical Analysis and conclusion

The data on 3 measures (SBP, DBP, and PR) for 3 consecutive activities (pinch, grip, and push) for 4 time periods (3, 6, 10, and 30 second) were analyzed using an ANOVA for repeated measures. Where significance (p<.05) was reached or exceeded, other comparisons of the means were tested. Among these were 3 factor repeated measures to compare pinch to grip, to compare pinch to push and to compare grip to push, and in all 3 cases, against time and measures. Also, the data from the IMT were analyzed with a correlated t-test.

The 3 null hypotheses tested in this research were rejected. There were significant differences between pinch, grip, and push activities relative to their effects on increases on SBP, DBP, and PR. Further analysis indicated that the push activity caused a significantly greater effect on SBP, DBP, and PR than either the pinch or grip activities.

There were significant increases in SBP, DBP, and PR from 3 second tests of 7 muscle groups in a MMT.

Several recommendations for treatment application were offered by the researchers. These included:

1. that the therapist have a client stop pinching or gripping as soon as the gauge/set needle stops rising. There is no need to prolong the measure due to risk involved.
2. do not allow opportunities for practice or comparisons as this could result in an undue longer or greater IMC.
3. more research is needed in this area to identify effects of activities requiring high IMCís.
4. caution should be exercised when using isometric activities especially with clients with cardiovascular disease.
5. as a therapist, the need to be alert to signs or complaints of physical stress.

8. If you were the researcher, how would you improve the study?

On the whole, I felt this study was fairly accurate in its experimental procedure and stated results. The tables and result sections were well depicted. Great detail was given to the 12 S's who were eliminated from the study which I felt was an honest admission on the part of the researchers in describing their study.

However, I found some areas open to question. One deals with the kind of population from which the S's were drawn. Was it student, general public, and/or health fanatics? This was never actually identified. Also, male and female subjects were clumped together. I feel that these variables could have had a bearing on the results. In line with the type of population, I think that it would be helpful in future studies to use a patient population of mixed diagnoses, e.g., cardiovascular, pulmonary, and neurological. This would allow for a comparison of normal to sick groups.

Also, I'm not sure why they included the MI~T in the experiment. It was treated separately from the 3 factor ANOVA and not fully addressed in the discussion. I do feel that it could be treated as a factor in itself; since the majority of occupational therapists who specialize in physical disabilities will utilize this evaluation, its impact on physiological levels would be important to them. In addition, the measure for the push activity was not standardized as were the other 2 activities.

Another small point was that the authors tended to reiterate the results already described in the tables. This did become repetitious and did not add to the richness of the narrative.

One last remark is that I believe the title of the article could be misleading. Stress effects are never identified as related to BP and PR. Perhaps physiological effects or cardiovascular effects of IMC would be more specific to the actual factors studied in this research.

After studying this past week about the compound symmetry assumption associated with the repeated measures ANOVA design, I question whether or not it was applied to this study. No mention was made in the results and/or discussion about proving this assumption via variance-covariance matrices; and, if a violation was present, no strategies were identified to compensate for it.

Now, I am beginning to see how statistics can be interpreted to fit the data! It is interesting to observe that what is not reported in a study can be more enlightening than what is.