How Does Lower Limb Respond to Unexpected Balance Perturbations? New Insights from Synchronized Human Kinetics, Kinematics, Muscle Electromyography (EMG) and Mechanomyography (MMG) Data

Abstract

Making rapid and proper compensatory postural adjustments is vital to prevent falls and fall-related injuries. This study aimed to investigate how, especially how rapidly, the multiple lower-limb muscles and joints would respond to the unexpected standing balance perturbations. Unexpected waist-pull perturbations with small, medium and large magnitudes were delivered to twelve healthy young adults from the anterior, posterior, medial and lateral directions. Electromyographical (EMG) and mechanomyographical (MMG) responses of eight dominant-leg muscles (i.e., hip abductor/adductors, hip flexor/extensor, knee flexor/extensor, and ankle dorsiflexor/plantarflexors) together with the lower-limb joint angle, moment, and power data were recorded. The onset latencies, time to peak, peak values, and/or rate of change of these signals were analyzed. Statistical analysis revealed that: (1) agonist muscles resisting the delivered perturbation had faster activation than the antagonist muscles; (2) ankle muscles showed the largest rate of activation among eight muscles following both anteroposterior and mediolateral perturbations; (3) lower-limb joint moments that complied with the perturbation had faster increase; and (4) larger perturbation magnitude tended to evoke a faster response in muscle activities, but not necessarily in joint kinetics/kinematics. These findings provided insights regarding the underlying mechanism and lower-limb muscle activities to maintain reactive standing balance in healthy young adults.

Trend change analysis in the assessment of body balance during posture adjustment in reaction to anterior-posterior ground perturbation

“…e ., where the test participant knew when the moment of unbalance would take place). It would seem that increased Vcop and TCI_dV values should result in a different TCI number as a reaction of the nervous system aimed to coordinate the activity of individual muscles [ 26 – 29 ]. Additional analysis of TCI_dS and TCI_dT revealed that the observed increase in both velocities was primarily due to the extension of the path of momentary leaps of COP (TCI_dS) while maintaining constant times between leaps (TCI_dT) and consequently the same number of TCI.…”

Peroneal muscle response to single-leg drop-jump and unexpected leg-drop in young and middle-aged adults before and after one session of neuromuscular training

“…In addition, previous studies have found an increase in time to peak activation of various ankle muscles (with the exception of PL, which has not been studied) in the elderly compared with young adults. A longer time to peak activation of a muscle correlates with a lower rate of force generation and a reduction in sufficient postural responses [ 50 , 52 ]. Possible reasons for the difference in results are the muscles tested, because different muscles may be affected differently, and the type, direction, or speed of the perturbation performed in each study, which may also affect muscle response [ 53 ].…”

Editorial: Balance-controlling mechanism and fall-prevention strategy

“…By comparing healthy walking, functional electrical stimulation (FES)-assisted walking, and non-FES walking, they have observed some asymmetric activation patterns in the investigated cortical areas for stroke survivors. Regarding the motor output pathway, recent studies have investigated the speed of multiple major lower-limb muscles' activation in maintaining reactive standing balance by analyzing the timing and rising rate of electromyographic (EMG) signals, revealing that ankle muscles have the faster response ( 2 , 3 ). In addition to EMG, with the advancing of wearable technologies, some techniques, such as the ultrasound imaging of muscles, have been available to detect the muscle morphological changes in dynamic situations and assess balance performance ( 4 , 5 ).…”