Forward and backward axial synergies in man

Abstract

Upper trunk and head forward and backward movements were analyzed in human subjects standing on a force platform. EMG of several flexor and extensor muscles was recorded together with the kinematics of the movement (EL.I.TE. system). It was found that upper trunk movements are accompanied by movements of hip and knees in the opposite direction, resulting in a slight displacement of the center of gravity projection on the ground. In fast movements, all the body segments were displaced at the same time, which suggests a feedforward control, whereas in slow movements, onset of displacement of the body segments was found to take place sequentially in a cranio-caudal direction. EMG analysis during fast movements revealed two different types of control, utilized in forward and backward movements. With forward bending movements the action of two sets of muscles could be recognized: the prime mover (R. Abd.), the activation of which was not correlated with that of the other muscles and preceded the onset of movement with a fairly constant lead, and a group of postural muscles, the activation (VM, TA) and inhibition (Sol) of which were closely correlated. By contrast, with backward movements, the prime mover (Er.S.) and the postural leg muscles (Hamstrings, Sol) were activated simultaneously. In both cases, a feedforward type of control is evident. Performance of the fast forward movements was accompanied by an initial forward displacement of the knee. The function of this phenomenon is discussed in term of a destabilizing action favouring the forward bending of the body or a prestretching of the knee extensor muscles increasing the strength of their subsequent contraction.

Combining modules for movement

“…The studies mentioned above as well as many others (see Macpherson, 1991) are not in agreement with other reports claiming that human postural responses are indeed organized synergistically (Nashner (1977), Crenna et al (1987), Mc Collum et al(1984 Nashner and McCollum (1985)). However, the synergies described by these investigators were present only in restricted set of movements such as postural sways in the sagittal plane, and further examination by others of more complex postural responses showed different and richer combinations of muscle activations.…”

A motor programme for the initiation of forward‐oriented movements in humans.

“…For instance, at the initiation of walking, anticipatory commands directed to muscles acting on the sagittal plane are associated with anticipatory commands to muscles acting on the frontal plane (Carlsoo, 1966). A similar phenomenon can be observed in forward bending (Crenna et al 1987) and in raising the upper limb (Gurfinkel et al 1988).…”

“…tibialis anterior and soleus) remained fixed, in that their recruitment or derecruitment latencies co-varied predictably according to a linear function. Such a close correlation was not observed for other muscles examined (Crenna et al 1987). The presence of a temporally invariant pattern of recruitment indicates that two or several muscles involved in the anticipatory adjustment can be brought into action together as a single functional entity, i.e.…”

Postural Synergies and Their Development

“…Van der Fits et al, 1999)nthe (C) (Horak & Nashner, 1986), a multi-link strategy and muscle amplitude synergies (Allum et al, 1989. Allum & Honneger, 1993, the ankle, knee, and hip eigenmovements (Alexandrov et al, 1998), axial synergies (Crenna et al, 1987), and reciprocal and co-contraction strategies (Slijper & Latash, 2000). All (Turvey, 1990.…”