Postural Steadiness in Cancer Survivors Based on Time Domain Measures of Center of Pressure

Abstract

A common side-effect of cancer treatments is a loss of balance. Unfortunately, the literature related to balance in cancer patients is very descriptive with limited quantitative assessments of posture and balance in this population. PURPOSE: To determine whether time-domain measures of center of pressure (COP) during quiet standing were sensitive to changes in surface conditions and visual input in cancer survivors. METHODS: Quiet standing in cancer survivors (n=11; mass = 75.6 ± 22.1 kg; height = 1.60 ± 0.05 m; age = 56 ± 14 yr) was assessed while survivors stood on a: a) rigid surface with eyes open, b) rigid surface with eyes closed, c) compliant surface with eyes open, and d) compliant surface with eyes closed. COP data were collected for 30 s (1000 Hz). Based on previous literature focusing on postural steadiness in young and old populations, these time-domain measures were included: root-mean squares (RMS) of the resultant distance (RD), anterior-posterior (AP), and medial-lateral (ML) COP; total excursions of the RD, AP, and ML COP; mean velocities of RD, AP, and ML COP; and total sway area. Two-way ANOVAs (p<0.05) with repeated measures were used to test main effects and interactions of surface and vision conditions. RESULTS: RMS values of RD and AP COP increased with eyes closed (4.6 to 6.5 and 3.9 to 6.0 mm, respectively; p<0.01). RMS values of ML COP increased with the compliant surface (1.7 to 3.1 mm; p<0.01). Total excursions of RD and AP COP increased with eyes closed (22.5 to 33.4 and 19.6 to 30.8 mm, respectively; p<0.01), and total excursions of RD and ML COP were increased with the compliant surface (24.1 to 31.9 and 8.7 to 14.4 mm, respectively; p<0.05). Mean velocity of RD, AP, and ML COP increased with eyes closed (10.6 to 20.0, 9.0 to 18.0, and 3.9 to 6.1 mm/s, respectively; p<0.05). Total sway area of AP COP increased with eyes closed (13.7 to 30.8 mm2/s; p<0.05). No interaction effects were found. CONCLUSION: AP COP measures increased when survivors stood with eyes closed, but AP COP measures were not altered by changes in surface. AP COP measures might be beneficial in initial assessments of cancer survivors. Surface changes may be a useful perturbation in cancer survivors so that lateral stability problems may be detected, given the sensitivity of ML COP measures to surface changes.