Figure 1.

Representation of the proposed methods and strategies for reconditioning motor output (antigravity muscles) and postural balance in frail older subjects prone to falls. At first, for each increase in muscle strength, postural balance is improved-curve and threshold on the left side of the figure (First stage). Once this increase reaches the threshold beyond which postural balance is no longer improved, it seems appropriate to implement exercises aimed at concomitantly improving motor output and postural balance in order to counteract or even reverse the involution process of the postural balance system (Second stage). This is a global theoretical strategy since frail older subjects are only able to achieve the first stage and the first step of the second stage. Regarding the last steps of the second stage, older subjects must no longer be fragile in order to undertake them. Only after completing the preconditioning training can initial frail older subjects continue the proposed process. For the global theoretical strategy, only preconditioned older subjects would be able to apply it completely at the motor and postural levels. ① Motor training – Firstly, muscle power/rate of force development (RFD), coordination and movement control should be progressively developed under ecological conditions by carrying, moving, throwing, and controlling objects. Secondly, all these physiological qualities (including aerobic and flexibility qualities) should be mobilized under stimulating conditions. ② Postural training – Based on different postural positions and conditions, the relevant reconditioning in frail older subjects requires postural balance tasks from easy to difficult. These tasks include different postures (bipedal and monopedal), bases of support (static-dynamic; large-narrow; and firm-foam), shoeing condition (dress shoes, sports shoes, shoes with textured insoles, and barefoot), visual condition (eyes open, eyes closed, and visual manipulations), nature of tasks (balance task alone, combined with cognitive tasks, i.e., dual-task), temporal constraints (with or without reaction time requirements, responses to sound and visual signals), and variation of postural constraints (no disturbance, expected or unexpected disturbances). For most of postural balance tasks, a multitude of variants can be suggested related to feet position (close feet, semi-tandem, and tandem stances), body segmental position or movement (e.g., arm crossed, hip and knee flexed, different head placements, and heel or toe contact with the ground), and light and acoustic environments (very or not enough light, without any noise or with music) etc. The overall strategy (first and second stages) is based first on analytical/static tasks, then on local/dynamic tasks, and finally on global/dynamic tasks for motor and postural training.