Fractal behavior of the trajectories of the foot centers of pressure during pregnancy

Abstract

The equilibrium of pregnant women is compromised because the falling risk increases as pregnancy progresses. The trajectories of the centers of pressure are related to equilibrium, gait and posture. The purpose of this work was to investigate the fractal behavior of the trajectories of the center of pressure of both feet in standing and walking pregnant women and how they evolve during pregnancy. By using instrumented insoles (F-Scan ® system working at 40 Hz), the trajectories of the center of pressure of both feet were obtained for 71 women in the three trimesters of their pregnancy. The 'detrended fluctuation analysis', a technique designed to extract the fractal properties of a signal, was used to analyze the fractal behavior of both the x and y components of the measured trajectories. Specifically, the fractal characteristic exponents corresponding to the small and large end regions of the corresponding scaling functions were obtained and compared. No differences were found between the characteristic exponents obtained for x and y components nor from the signals found for left and right feet within the statistical uncertainties. In standing conditions all the exponents obtained remained almost constant, regardless of the elapsed pregnancy time, taking values around 0.5. In walking conditions, the small end exponents did not change with respect to those found in static conditions; on the contrary, the large-end exponents reduced as pregnancy progressed, reaching values of the order of −0.6 in the third trimester. The multi-scaling character of the walking signals could be related to the anteroposterior and medio-lateral displacement observed in previous experiments and that could be on the root of the development of musculoskeletal discomfort and a falling risk that increases with the pregnancy time.

Assessment of physical fitness during pregnancy: validity and reliability of fitness tests, and relationship with maternal and neonatal health – a systematic review

“… 141 151 Moreover, one article used a triaxial accelerometer 146 ; another article assessed balance through recording (without specification of camera type) 145 and another using instrumented insoles. 176 All three of these articles used walking protocols.…”

Assessing physical fitness during pregnancy: validity and reliability of fitness tests, and relationship with maternal and neonatal health-related outcomes. A systematic review

“…With regard to static balance, 18 were laboratory tests of which 12 assessed balance through stabilometry tests on force platform [35,140,149,150,[141][142][143][144][145][146][147][148], one on pressures platform [143] and another on Equitest® platform [151]. Four articles did not mention the type of platform used (40,150,176,177).…”

“…Moreover, 1 article used a triaxial accelerometer [175]; another article assessed balance through recording (without specification of camera type) [176], and another using instrumented insoles [177]. All three articles used walking protocols.…”

“…Baena-Garcia et al [13] found increased flexibility associated with a more alkaline arterial pH (r = 0.220, p<0.05), higher arterial PO 2 (r = 0.237, p<0.05) and lower arterial PCO 2 (r =-0.331, p<0.01) in the umbilical cord blood. Moreover, 1 article used a triaxial accelerometer [175]; another article assessed balance through recording (without specification of camera type) [176], and another using instrumented insoles [177]. All three articles used walking protocols.…”

“…[35,140,149,150,[141][142][143][144][145][146][147][148], one on pressures platform[143] and another on Equitest® platform[151]. Four articles did not mention the type of platform used(40,150,176,177). platform, which was used in two articles[157,158].…”