Muscle synergies for the control of single-limb stance with and without visual information in young individuals

Weighting of visual and auditory inputs in dancers with and without previous ankle injury

Elite dance requires highly controlled balance performance in dynamic visual and auditory environments characterized by the use of stage lighting and music. Perturbing visual input is known to influence balance in dancers, but the effects of sounds have not been clearly established. Ankle inversion injuries are common in dancers and may also play a role in dancers' ability to respond to sensory perturbations. The aims of this study were to identify changes in static balance in response to visual or auditory perturbation in elite collegiate dancers with and without a history of ankle injury, and to describe coupling of measurements obtained from the waist and head during balance. Thirty-seven dancers: 22 controls and 15 with a history of ankle sprain, performed single-leg balance under static and dynamic visual and auditory conditions. Dancers demonstrated increased waist sway when viewing a dynamic visual scene and when presented with moving sounds and increased head sway with dynamic visuals. These results did not vary by history of ankle sprain. While dancers appear to dampen the impact of waist sway on head motion during single leg stance, even highly trained dancers may experience challenges controlling balance under perturbing visual and auditory conditions like those present during stage performance.

Balance and Muscle Synergies During a Single-Limb Stance Task in Individuals With Chronic Ankle Instability

The aim of this study was to investigate balance performance and muscle synergies during a Single-Limb Stance (SLS) task in individuals with Chronic Ankle Instability (CAI) and a group of healthy controls. Twenty individuals with CAI and twenty healthy controls were asked to perform a 30-second SLS task in Open-Eyes (OE) and Closed-Eyes (CE) conditions while standing on a force platform with the injured or the dominant limb, respectively. The activation of 13 muscles of the lower limb, hip, and back was recorded by means of surface electromyography. Balance performance was assessed by identifying the number and the duration of SLS epochs, and the Root-Mean-Square (RMS) in Antero-Posterior (AP) and Medio-Lateral (ML) directions of the body-weight normalized ground reaction forces. The optimal number of synergies, weight vectors, and activation coefficients were also analyzed. CAI group showed a higher number and a shorter duration of SLS epochs and augmented ground reaction force RMS in both AP and ML directions compared to controls. Both groups showed an increase in the RMS in AP and ML forces in CE compared to OE. Both groups showed 4 optimal synergies in CE, while controls showed 5 synergies in OE. CAI showed a significantly higher weight of knee flexor muscles in both OE and CE. In conclusion, muscle synergies analysis provided an in-depth knowledge of motor control mechanisms in CAI individuals. They showed worse balance performance, a lower number of muscle synergies in a CE condition and abnormal knee flexor muscle activation compared to healthy controls.

The Influence of Knee Extensor and Ankle Plantar Flexor Strength on Single-Leg Standing Balance in Older Women

Impaired balance is a significant risk factor for falls among older adults. The precise impact of lower-extremity muscles, including the proportion of muscle strength, on the performance of single-leg standing balance tests in older individuals is very interesting. The aim of this study is to examine the correlation between the knee extensor (KE), ankle plantar flexor (AP) muscle strength, and performance in single-leg standing balance tests in older females. Additionally, it aims to evaluate the combined proportion of KE and AP muscle strength in maintaining balance during single-leg standing. A total of 90 older females (mean age 67.83 ± 8.00 years) were recruited. All participants underwent maximum voluntary isometric contraction (MVIC) testing of the KE and AP muscles, as well as single-leg standing balance tests with eyes open (SSEO) and eyes closed (SSEC). To examine the influence of KE and AP muscle strength on balance performance, multiple regression analysis was conducted. Low correlations were found between SSEO and MVIC of KE and AP muscles, but moderate correlations were found with percentage of MVIC to body weight ratio (%MVIC/BW). The best model for SSEO included 0.99 times of the %MVIC/BW of AP and 0.66 times that of KE muscles as independent predictor variables (r = 0.682). In conclusion, AP muscle strength was found to have a greater impact on single-leg standing balance compared with KE muscle strength.

Not only muscle mass but also muscle quality is associated with knee extension muscle strength in patients with hip fractures

Our results revealed that the decrease in isometric knee extension muscle strength on the operated and nonoperated sides in patients with hip fractures was associated with not only a decrease in skeletal muscle mass but also a decrease in muscle quality, characterized by a decreased PhA.

PURPOSE

This study aimed to assess the relationship between isometric knee extension muscle strength on the operated or nonoperated sides and PhA in patients with hip fractures at approximately 6 months postoperatively.

METHODS

This study was a cross-sectional study. Skeletal muscle index (SMI), PhA, knee extension muscle strength on the operated and nonoperated sides, and other physical function variables were assessed at approximately 6 months postoperatively. To identify predictors of knee extension muscle strength on the operated and nonoperated sides, hierarchical multiple regression analysis was performed.

RESULTS

A total of 90 patients with hip fractures were included (mean age, 80.1 ± 6.9 years). SMI (0.45) and PhA on the operated side (0.27) were the significant associated factors extracted for isometric knee extension muscle strength on the operated side (standardized partial regression coefficients), independent of age, sex, and body mass index (BMI). Movement control during one-leg standing on the nonoperated side (0.26), SMI (0.32), and PhA on the nonoperated side (0.40) were the significant associated factors extracted for isometric knee extension muscle strength on the nonoperated side, independent of age, sex and BMI.

CONCLUSIONS

Our results revealed that the decrease in isometric knee extension muscle strength on the operated and nonoperated sides in patients with hip fractures at approximately 6 months postoperatively was associated with not only a decrease in skeletal muscle mass but also a decrease in muscle quality, characterized by a decreased PhA.

Characteristics of the postural stability of the lower limb in different visual states of undergraduate students with moderate myopia

Objective: To explore the characteristics of lower limb postural stability in undergraduates with moderate myopia in three different visual states. Methods: Twenty male undergraduate students were recruited to complete respectively the static and dynamic postural stability tests under eyes-closed, myopia (taking off their glasses immediately) and corrected vision conditions. A three-dimensional force platform (Bertec, United States) was used to test static postural stability, which calculated the total path length of the Center of Pressure (COP), path length in the antero-posterior (A/P) and medio-lateral (M/L) directions, COP area, SampleEntropy (SampEn), and low-, medium-, and high-frequency spectrum energies. Dynamic postural stability was tested using the Y-balance test, and the Y-balance test scores were calculated. The Vicon three-dimensional motion capture system (Oxford, United Kingdom) measured the maximum flexion angles of the ankle, knee, and hip joints. The electromyography (EMG) root mean square (RMS) and integral EMG (iEMG) of the tibialis anterior and lateral gastrocnemius of the lower extremity were simultaneously measured using wireless surface electromyography (Noraxon, United States). Results: The SampEn-A/P and SampEn-M/L of corrected vision state higher than myopia and eyes-closed states, and myopia state larger than eyes-closed state (χ² = 51.631, p < .001). The original and standard scores of the anterior, postero-medial and comprehensive values of the three visual states had significant differences (F = 32.125, p < .001). The original and standard values of postero-lateral corrected vision and myopia were larger than those of eyes-closed states (F = 37.972, p < .001). The maximum flexion angles of the ankle and knee joints were in the following order: corrected vision, myopia and eyes-closed (F = 10.93, p < .001). The iEMG and RMS had significant differences in the three different states (χ² = 12.700, p < .001) in the all directions of YBT. Conclusion: Compared with corrected vision, the stability of static posture in the state of myopia was decreased, and the postural regularity was more regular. The dynamic postural stability in the state of myopia was also lower than that corrected vision, and the activation and work of ankle muscles were also increased.

The impact of unexpected platform perturbation on ankle proprioception ability in static and dynamic starting positions

AIMS

To examine the relationship between ankle proprioception and the ability to maintain balance with increased magnitudes of unexpected perturbations; and to compare the participants' ability to maintain balance following perturbations when starting from static and dynamic positions.

METHODS

Sixty physical education students (average 24.6 years) were tested for proprioception ability (AUC scores) and balance challenges presented on a perturbation treadmill. The degree at which participants lost postural balance was recorded in seven starting positions: standing-eyes-open (SO), standing-eyes-closed (SC), tandem-dominant (TD), tandem non-dominant, (TND) single-leg lateral side perturbation (SLP), single-leg medial side perturbation (SMP), and walking. Perturbation scores were analysed divided by tertiles. Multidimensional Unfolding SPSS Statistics 25 (PREFSCAL) was used to examine the relationships between data sets.

RESULTS

AUC scores of both dominant and non-dominant legs were significantly correlated with SO (r = 0.316; r = 0.445), SC (r = 0.364; r = 0.413), TD (r = 0.346; r = 0.308), and walking (r = 0.265; r = 0.439), respectively. In the dominant-leg, AUC scores of individuals with below-median SO scores were significantly worse compared to those with median SO scores (p = .046). In the non-dominant leg, individuals with above-median SC had significantly better AUC scores compared to those with lower-than-median SC (p = .008). Those with median and above-median SO and walking achieved better AUC scores than those with below-median (SO: p = .049, p = .004; walking: p = .016, p < .001, respectively). In dimension I, the SLP and SMP were located opposite one another; in dimension II, the TD and TND were located at the upper side, whereas SC, SO and walking were at the lowest side.

CONCLUSIONS

AUC scores were significantly correlated with the level at which postural balance was lost, whereby the better the proprioception ability, the better the ability to maintain balance. As such, the ability to maintain balance is harder in tandem positions than in standing and walking positions. This ability differed when perturbations were to the lateral or medial sides.