PHYS THER
Vol. 86, No. 9, September 2006, p. 1264
DOI: 10.2522/ptj.20060034.bl
The Bottom Line
[Pua YH. Allometric analysis of physical performance in older adults. Phys Ther. 2006;86:1263–1270.]
The Bottom Line is a translation of study findings for application to clinical practice. It is not intended to substitute for a critical reading of the research article. Summaries are written by members of The Bottom Line Committee.
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What problems did the researcher set out to study, and why?
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A person's body mass can affect various performance measures. If we knew how much body mass affects the performance measure of interest, we could normalize the results appropriately and have more accurate reference standards. Using mathematical modeling that assumes body weight can be substituted for muscle mass, the author speculated that the correction factor is dependent on the type of physical performance test. The author presumed that tests that involve "rapid movements" (eg, jumping, running) would not be affected by body mass and used no correction factor, assuming that tests of "exertion of external forces" (eg, gripping, weight lifting) would be affected by mass.
The associated correction factor was 0.67 for forces and 1.0 for torques (force x lever arm). Preliminary work in athletes suggests that these theoretical values are accurate. The question of how mass affects physical performance in elderly people has not been examined. Therefore, the author was interested in whether the theoretical correction factors would hold true for physical performance variables known to be important in elders. The author hypothesized that handgrip strength and dorsiflexion force would be tasks that have a correction factor of 0.67; dorsiflexion torque, a correction factor of 1.0; and Timed "Up & Go" Test (TUG) speed, a correction factor closer to zero.
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Who participated in the study?
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131 older adults, of whom 75% were female, with an average age of 63 years. The participants were community dwelling and independent in all activities of daily living and instrumental activities of daily living, had a body mass index (BMI) of 21.9 kg/m2, and said they did not participate in any form of resistance training. The subjects were all healthy; over 50% exercised 3 or more times per week, and another 26.7% exercised 1 or 2 times per week.
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What new information does this study offer?
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The correction factor for handgrip force was 0.63, which was very close to the theoretical correction factor of 0.67. Thus, it may be more accurate to normalize handgrip measures using the scaling equations listed in the article. The correction factor for TUG time was close to zero (as predicted) and thus does not need to be "normalized." The dorsiflexion force and torque data were very variable and therefore did not support the theoretical correction factors. At this time, there is no reason to adjust dorsiflexion force or torque values.
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How did the researcher go about the study?
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The testing was performed in one session by 4 different physical therapists. Handgrip force was measured with a handgrip dynamometer and the elbow flexed to 90 degrees. Isometric dorsiflexion force was measured with a handheld dynamometer with the knee extended and the ankle in neutral position. Isometric torque was derived by multiplying the lever arm length (the distance from the lateral malleolus to the base of the fifth metatarsal) by the isometric force. Finally, TUG time was measured as the length of time it took for subjects to stand from a chair, walk 3 m, turn around, and return to sitting.
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How might the results of this study apply to patients who are treated by physical therapists from this point forward?
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These results may be useful to physical therapists who are developing a database of "normal" values for handgrip or TUG time. Similarly, when physical therapists perform health screens or fall risk screens for elderly people in the community, they may want to consider "normal" reference values that have been corrected for body mass versus uncorrected ones.
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What are the limitations of the study, and what further research is needed?
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The study sample was an elite group of "young" older adults who may not represent the typical elderly person in North America. The subjects were not overweight, exercised regularly, and had no chronic diseases. The ability to generalize the results from this sample to most elderly people in the United States, therefore, is questionable. The assumption that body weight can substitute for muscle mass is another key limitation; this substitution needs to be confirmed with older adults before the results can be used with confidence.
Related Article
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Allometric Analysis of Physical Performance Measures in Older Adults
- Yong-Hao Pua
Physical Therapy 2006 86: 1263-1270.
[Abstract]
[Full Text]
[PDF]
Copyright © 2006 by the American Physical Therapy Association.
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