Objective

The goal of this preliminary study is to analyze the biomechanical strategies of spine, pelvis and lower limbs (LL) with tridimensional motion analysis during stand-to-sit task, an understudied movement in the literature, however, source of questioning in clinical practice.

Observations

One female and one male, healthy participants, (respectively 28 and 48 years old) were included without history of pathology and with normal pelvic incidences. Participants performed stand-to-sit movements on a stool without using their hands. Once movement ended, participants’ thighs were parallel to the floor. The sensors were placed on the bony landmarks of LL and along the spinous processes from the middle of the sacrum to C7. The seven cameras of the Vicon ^® device recorded a total of three trials. The studied parameters were the evolution of kinematics curves of the spine, the pelvis and the LL in the different planes during the movement.

Results

Significant differences between the two subjects are particularly the amplitudes of variation in spinal curvatures and the intercondylar distance. Subject’s lumbar curvatures decreased during the movement: −39° for the female, −16° for the male. The thoracic curvatures move in the same direction: −36° for the female, −13° for the male. The intercondylar distance of the female increased by 4 cm, that of the male by 15 cm.

Discussion – conclusion

These results bring out two different biomechanical strategies for the same task. During stand-to-sit task, are solicited preferentially either the spine (in that case the female) or LL (in that case the male). What about the strategy used by patients with chronic low-back pain? These preliminary results provide new prospects in the understanding of the interaction between spine, pelvis and LL and must be confirmed by a cohort study.