Effects of Ankle Muscle Fatigue and Visual Behavior on Postural Sway in Young Adults

Abstract

Ankle muscle fatigue has been shown to increase body sway. In addition, body sway in quiet upright standing is reduced when saccadic eye movements are performed. The purpose of this study was to investigate the effects of visual information manipulation on postural control during ankle muscle fatigue in young adults. Twenty young adults performed: (1) two 60-s trials in quiet bipedal standing with eyes open, eyes closed, and while performing saccadic eye movements; (2) maximum voluntary isometric contractions in a leg press device, custom-made to test ankle plantar flexion force; (3) a calf raise exercise on top of a step to induce ankle muscle fatigue; and (4) a repetition of items 1 and 2. Postural sway parameters were compared with two-way ANOVAs (vision condition × fatigue; p < 0.05). Ankle muscle fatigue increased anterior-posterior and medial-lateral displacement and RMS of sway, as well as sway area. Saccadic eye movements reduced anterior-posterior displacement and RMS of sway and area of sway compared to eyes open and eyes closed conditions. Both saccadic eye movements and eyes closed increased the frequency of AP sway compared to the eyes open condition. Finally, anterior-posterior displacement, anterior-posterior RMS, and both anterior-posterior and medial-lateral sway frequency were affected by an interaction of fatigue and vision condition. Without muscle fatigue, closing the eyes increased anterior-posterior displacement and RMS of sway, compared to eyes open, while during muscle fatigue closing the eyes closed reduced anterior-posterior displacement and had no significant effect on anterior-posterior RMS. In conclusion, body sway was increased after induction of ankle muscle fatigue. Saccadic eye movements consistently reduced postural sway in fatigued and unfatigued conditions. Surprisingly, closing the eyes increased sway in the unfatigued condition but reduced sway in the fatigued condition.

Motor strategy during postural control is not muscle fatigue joint-dependent, but muscle fatigue increases postural asymmetry

“…We found a reduction of approximately 18%; ii) the postural task proposed in our study did not threaten postural control to the point where changing strategies was required. The postural task, standing in a bipedal condition, can be considered an easier task for young adults even after muscle fatigue [ 1 ]. Therefore, even with impaired postural control after bilateral ankle muscle fatigue, the primary ankle motor strategy was performed by subjects, without performing the co-contraction.…”

“…Muscle fatigue is recognized as a serious social problem [ 1 , 2 ] affecting daily living activities. A relevant experimental framework has been indicated to investigate the capacity of the central nervous system to adapt in response to changes in muscle capacity [ 3 ].…”

“…Postural control asymmetry raises postural instability due to the increase in body mass over one lower limb [ 24 ], which can occur as a result of weight-bearing transfer from one leg to another [ 25 ], and has been used as a reliable measure to diagnose postural control impairments [ 25 , 26 ]. From the biomechanical point of view, maintaining greater symmetrical posture can lead to reduced body sway, which facilitates balance control [ 25 , 27 , 28 ], maintaining both the center of mass (CoM) and center of pressure (CoP) more distant from the limits of stability [ 1 , 21 ]. This improved postural control is especially interesting under muscle fatigue due to the negative effects of muscle fatigue on postural control.…”

Saccadic Eye Movements Attenuate Postural Sway but Less in Sleep-Deprived Young Adults

“…Mean trunk sway amplitude was reduced in the AP direction between 25 and 30% (Rodrigues et al, 2013 ) in adults. Additionally, saccadic eye movements consistently reduced postural sway in about the same percentage of young adults in fatigued and unfatigued conditions (Barbieri et al, 2019 ), in mildly affected people with multiple sclerosis (Santinelli et al, 2019 ), and even in children with dyslexia (Barela et al, 2020 ). Interestingly, our results show a similar amount of sway reduction comparing the respective visual conditions, fixation and saccade, to the sleep and sleep-deprived evaluations.…”

Prolonged Standing Task Affects Adaptability of Postural Control in People With Parkinson’s Disease

“…These changes increase the falling risk, but can also be understood as adjustments to deal with the task. Fatigue effects on postural control were observed in different populations, 61-63 although these studies induced fatigue by exercise and not by a standing task. Thus, the effects of fatigue on postural control may be interpreted according to the task.…”