PHYS THER
Vol. 87, No. 12, December 2007, pp. 1667-1668
DOI: 10.2522/ptj.20060378.ar
Author Response
Bruce Etnyre and
David Q Thomas
We were very pleased and honored to have Krebs comment on our work in an area of study that he, along with colleagues and friends, have studied extensively. Apparently, Krebs is an avid people watcher as we are, but rather than focusing on social or cultural aspects of appearance as most people do, we observe human movement patterns. Many physical therapists, who were trained to analyze gait by visual assessment, often find that they continue evaluating nearly every person's gait. Apparently, this is a similar phenomenon for those of us interested in the motion of rising from a sitting position. We also have observed the rich variety of body movements that people use to perform this relatively simple task. This wide variability of movements among and within individuals, however, creates problems for studying sit-to-stand (STS) movements in a scientifically acceptable way. It also makes defining "endpoints, commonalities, and demarcating events," similar to methods of gait analysis, particularly elusive (as Krebs correctly pointed out).
When we began conceiving this study,1 we initially developed a paradigm using a strictly scientific approach, similar to many previous studies, which included attempting to control the variability contributing to the STS movement (eg, adjusted seat height; fixed angles for the ankle, knee, hip, and trunk; arms crossed to reduce the influence of the arms on momentum; and others). Our quite astute and practical-minded physical therapist students who were recruited to conduct the study said they understood the need for scientific control, but the results would be relatively useless for their clinical practice because none of their patients (nor anyone else) would perform the STS movement in the manner that we originally prescribed for the study.
We began taking measurements of STS movements without any constraints other than the initial arm positions. Preliminary comparison of the force platform measurements showed remarkable, similarly occurring events among the STS methods and among the participants. Comparison with other STS studies with figures including tracings of STS movements using either force platforms or motion analysis showed similar event patterns.2–15 Krebs appropriately encouraged replication of our method by other researchers, and we welcome critical scientific challenges to the standardization system we proposed. Because of our study's relatively large number of participants, who were measured during varied STS arm-use conditions—and considering the previous studies that showed events remarkably similar to the events we proposed—we feel fairly confident of the outcome.
If the proposed standardization method for STS withstands scientific scrutiny, it may be possible to use the events to visually analyze STS movements, similar to methods used to evaluate gait. Some of the events may be too subtle to easily identify, such as the counter movement and rebound event, but we think that trained observers can learn to identify all of the events. If a force platform is unavailable, the events may be identifiable using videotape recordings, moving through frame by frame. From our observations, we found that initiation may occur from any body segment, but visual discrimination is sensitive to changes in movement and it should be apparent. The counter movement is usually the result of movement from ankle dorsiflexion, hip flexion, trunk extension, pelvic rotation, arm movement, or any combination of these variables. Seat-off is the most readily detectable movement, but it may occur over several frames. We chose seat-off as when the ischial tuberosity separated from the chair using a seat-switch, but a frame-by-frame analysis should show when the proximal end of the thigh separates from the seat. The peak force event is evident with full knee extension, and the rebound occurs with a subsequent slight knee flexion or hip extension/pelvic rotation, followed by steady standing.
We greatly appreciate Krebs' insightful commentary and encouragement, as well as his suggestion for others to challenge our findings.
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Copyright © 2007 by the American Physical Therapy Association.
