Increased co-contraction reaction during a surface perturbation is associated with unsuccessful postural control among older adults

Abstract

Background As a strategy to maintain postural control, the stiffening strategy (agonist-antagonist co-contractions) is often considered dysfunctional and associated with poor physical capacity. The aim was to investigate whether increased stiffening is associated with unsuccessful postural control during an unpredictable surface perturbation, and which sensory and motor variables that explain postural stiffening. Methods A sample of 34 older adults, 75.8 ± 3.8 years, was subjected to an unpredicted surface perturbation with the postural task to keep a feet-in-place strategy. The participants also completed a thorough sensory- and motor test protocol. During the surface perturbation, electromyography was measured from tibialis anterior and gastrocnemius to further calculate a co-contraction index during the feed-forward and feedback period. A binary logistic regression was done with the nominal variable, if the participant succeeded in the postural task or not, set as dependent variable and the co-contraction indexes set as independent variables. Further, the variables from the sensory and motor testing were set as independent variables in two separate Orthogonal Projections of Latent Structures (OPLS)-models, one with the feed-forward- and the other with the feedback co-contraction index as dependent variable. Results Higher levels of ankle joint stiffening during the feedback, but not the feed-forward period was associated with postural task failure. Feedback stiffening was explained by having slow non-postural reaction times, poor leg muscle strength and being female whereas feed-forward stiffening was not explained by sensory and motor variables. Conclusions When subjected to an unpredicted surface perturbation, individuals with higher feedback stiffening had poorer postural control outcome, which was explained by poorer physical capacity. The level of feed-forward stiffening prior the perturbation was not associated with postural control outcome nor the investigated sensory and motor variables. The intricate causal relationships between physical capacity, stiffening and postural task success remains subject for future research.

Older Fallers and Non-fallers’ Neuromuscular and Kinematic Alterations in Reactive Balance Control: Indicators of Balance Decline or Compensation?

“…Interestingly, our ndings differ from a prior study that reported no differences in postural sway timing or amplitude between fallers and non-fallers following lateral shoulder-impact perturbations, 18 suggesting that different body segment perturbations may elicit distinct reactive balance control strategies. Additionally, while previous research linked greater cocontraction to more joint stability and poorer balance control, 42,43 this study has observed that older fallers even with poorer balance performance than non-fallers (lower Mini-BEST scores) were able to reduce agonist-antagonist co-contractions of lower-limb muscles and achieve larger knee/hip exion for a suspensory strategy. On top of them, this study has observed fallers with the longer activation durations of ankle dorsi exor and hip abductor together with the longer ankle dorsi exion duration than non-fallers, which may be necessary for maintaining a knee bending posture during the suspensory strategy.…”

Different muscle strategy during head/knee level of functional reaching-transporting task to decrease falling probability in postmenopausal women with osteoporosis

“…Of course, it should be noted that the higher muscle activity in the osteoporotic participants, with weaker muscles, at both head and knee levels, may lead to excessive energy expenditure, resulting in fatigue and postural instability. On the other hand, excessive muscle coactivation increases postural rigidity and might restrict dynamic postural control, especially in daily activities with probable unpredictable perturbations [ 32 , 33 ]. Muscle fatigue was not assessed in this study.…”

Upper Limbs Muscle Co-Contraction Changes Correlate With The Physical Motor Impairments in CMT

“…In the light of this feature, i.e. the possibility of accounting both for the similarity and the magnitude of the EMG signals, and in consideration of its greater correlation with the joint stiffness, the Rudolph index is the one most used in the literature [15,20].…”