Different neurophysiological circuits underlie the various frequencies of the body sway for the regulation of human upright posture. Servo-controlled platforms allowed experimental studies about latency responses after a sudden external disturbance but power frequency repartition during spontaneous dynamic equilibrium has rarely been examined. The purpose of the present study was to examine the zone of sway frequency assigned to proprioceptive afferences from muscular, articular and tendinous receptors in healthy and injured subjects standing on an unstable and minimal area. Dynamic balance conditions were realized by asking athletes to stand up on a seesaw (stabilometer). The recordings (stabilograms) were monitored by means of an accelerometer. Their power spectra were obtained by a fast Fourier transform process. A first study was conducted in order to specify the contribution of articular receptors of the ankle in the regulation of spontaneous dynamic equilibrium of five soccer players with unilateral injured ankle (IA). The balance parameters in lateral sways were measured in monopodal stance on the healthy ankle (HA) comparatively to IA. The stabilogram was longer (P < 0.05), the total energy of 2-20 Hz band (P < 0.01) higher in the IA (1074 +/- 111 mm and 53 +/- 8 V2) than in the HA (836 +/- 150 mm and 36 +/- 8 V2). A second study analyzed the contribution of knee articular receptors involved in the reflexes of antigravity extension. We assessed during bipodal stance the anteroposterior sways of five basketball players with injured knee (IK) and 3 with healthy knee (HK) in eyes-open and eyes-closed situations.(ABSTRACT TRUNCATED AT 250 WORDS)