Force coordination in static manipulation: Discerning the contribution of muscle synergies and cutaneous afferents

Abstract

Both an elaborate coordination of the hand grip force (G; normal component of force acting at the digits-object contact area) and load force (L; tangential component), and the role of cutaneous afferents in G-L coordination have been well documented in a variety of manipulation tasks. However, our recent studies revealed that G-L coordination deteriorates when L consecutively changes direction (bidirectional tasks; e.g., when vigorously shaking objects or using tools). The aim of the study was to distinguish between the possible role of the synergy of hand grip and arm muscles (exerting G and L, respectively) and the role of cutaneous afferent input in the observed phenomenon. Subjects (N=14) exerted sinusoidal L pattern in vertical direction against an externally fixed device in trials that gradually changed from uni-to fully bidirectional. In addition, a manipulation of an external arm support decoupled L measured by the device (and, therefore, recorded by the cutaneous receptors) from the action of arm muscles exerting L. The results revealed that switching from unito bidirectional tasks, no matter how low and brief L exertion was in the opposite direction, was associated with an abrupt decrease in G-L coordination. This coordination remained unaffected by the manipulation of external support. The first result corroborates our previous conclusion that the force coordination in uni-and bidirectional manipulation tasks could be based on partly different neural control mechanisms. However, the second finding suggests that the studied control mechanisms could depend more on the cutaneous afferent input, rather than on the synergy of the muscles exerting G and L.

The Force Synergy of Human Digits in Static and Dynamic Cylindrical Grasps

“…A previous study used different quantitative methods to explore mechanical and neural functions during various manipulation tasks [18], although the coordination parameters were not sufficiently precise to explain the process of hand coordination. Correlation coefficients and principal component analysis (PCA) are used to examine the synergy strength of performance variables, such as joint angles and finger forces.…”

Assessment of Hand Function Through the Coordination of Contact Forces in Manipulation Tasks

“…Therefore, the studies of GF-LF coordination have been seen as a promising approach for development of quantitative clinical tests of hand function (Jaric et al, 2005a; Nowak and Hermsdorfer, 2006; Krishnan and Jaric, 2008). Aside from the neurological populations, a deteriorated GF-LF coordination has been seen in healthy individuals during performance of presumably complex and demanding tasks, such as when the applied LF continuously changes its direction (Jaric et al, 2005b; de Freitas et al, 2007; Freitas et al, 2007; de Freitas et al, 2008b), when the frequency of LF change is particularly high (e.g., when shaking an object or producing an oscillatory LF against an external support (Flanagan and Wing, 1995; Jaric et al, 2006)), when the actions of two hands are dissimilar (Serrien and Wiesendanger, 2001; Krishnan and Jaric, 2010), or when the visual feedback (Danion et al, 2010) or gravitational field (White et al, 2005) is altered. Although most of these phenomena have been extensively studied, the role of a number of other potentially important mechanical and neural factors still remains largely unexplored.…”

Reprodutibilidade intra-avaliador do teste de discriminação de dois pontos na sola dos pés em idosos e jovens assintomáticos

“…In the upper limbs, changes of force direction are noticed by cutaneous receptors that help with the adjustment and control of fine motor responses 7 . In the lower limbs, more specifically on the sole of the feet, the perception of pressure contact with the ground have an important influence on the postural control during gait 3,4 consequently influencing the risk of falls.…”