This report is a preparatory study for a new dynamic equilibrium examination, the “Foulage test”. Subjects step on the center of a stabilometer, keeping both toes constantly in contact with the plate, and lifting up only the heels alternately. Subjects had to accurately keep up a tempo of 120 beats per minute (BPM120) as set by an electric metronome. The examination time was 60 seconds, 120 steps, with eyes open and closed.
Sixteen healthy volunteers (8 men, 8 women, 24 to 55 years old, mean 36 years old) were tested with their eyes in the open and closed condition, changing the height of heels, from lower than 1 cm to almost 12 cm. 12 subjects were tested 5 times, 3 subjects were tested 6 times and also one volunteer, a 45-year-old healthy man, performed the test 16 times to get fine data. As the heels rose up, the locus was enlarged side to side and bent at the center like an inverted ‘V'rsquo; shape (Λ). The locus length was enlarged as the heels were raised higher, believed to reflect the activity of the subject. On the other hand the width of the locus band, front to back, was almost the same under conditions of stepping stably. However, if the subject swayed, this distance might increase. The total locus length (L) and the environed area (A) were investigated. The long length of the locus “Λ” shaped band was nearly the distance of one step. The subjects were stepping 120 times, therefore the mean distance of one step was almost L/120, and was nearly the length of the long axis of the locus band. The locus band was like a long square bent at the center, so the width, front to back, could be approximately presumed as A/(L/120)=120A/L.. Under stable stepping conditions, 400 cm<L<1400 cm, the width (120A/L) reached a plateau even when the height of the heels was changed. This could be a new parameter for the body sway, named FT.
Ninety-four data sets were sampled by all 16 volunteers. Under stable condition (400<L<1400), the FT value plateaued. The mean of 70 data sets with open-eye-FT was 2.92 cm (SD 0.42), and the mean of 72 data sets with closed-eye-FT was 3.87 cm (SD 0.57). FT increased significantly with the eyes closed (p<0.01 paired t-test), and the dynamic Romberg's rate was 1.37 in normal healthy subjects under stable conditions. Under the condition of 1400<L, the heels were too much high, some subjects began to sway and the FT value increased.
In conclusion, L (also L/120) reflects the height of stepping heels and it can be a parameter of activity: under the condition of 120 BPM, 60 seconds, 120 steps, 400<L<1400, FT=120A/L can possibly evaluate sway.
