Treadmill Perturbation

DISCUSSION
Treadmill-perturbation training could effectively reduce falls upon an unannounced, novel slip resulting from the improvements in both proactive and reactive control of stability among community-dwelling older adults (lending support to Hypothesis One). Though merely walking on the treadmill could improve participants’ proactive control of stability, it could not improve their reactive control of stability nor effectively reduce their risk of falls (lending support to Hypothesis Two). Finally, pertaining to its ability to reduce rate of falls and to improve stability, treadmill-perturbation training was indeed significantly inferior to overground-perturbation training (lending support to Hypothesis Three).

Treadmill-perturbation
4 and 6a). The improvement in the reactive control of stability obtained after treadmill-perturbation training (Tt) was only about 40% of those resulted from overground-perturbation training (Ot) when using the difference between the reactive control of stability of Ot and Oc as the reference (Fig. 6a). This difference between these two groups could account for 13.9% more falls in the former than the latter group (Tt versus Ot, Fig. 4). The similarity between the training (from the 1st to the 23rd slip) and the generalization test (the 24th slip) in overground-perturbation training group might explain why its results were better in comparison to those of the treadmill-perturbation training group. During overground training, all slips occurred consistently under the right side (limb). During treadmill training, the device could not precisely control the onset timing of the perturbation with respect to the side (limb) or to the gait cycle, and hence subjects received slips under both sides or at different gait cycle (not always ~17 ms after right heel strike). Approximately half of perturbations occurred under the left side (11). In addition, subjects were not afforded the learning opportunity to change the relative relationship between the leading and the trailing limbs on treadmill as in comparison to the overground perturbation. Its belt speed was dictated by the computer profiles (Fig. 2c), and could not be actively controlled by the participant. In contrast, an individual control of the ground reaction force beneath each foot during the overground training allowed this subject to actively slow down the slip (BOS) velocity as well as to reduce the slip distance. These factors could also account for the differences found in the two training