Effects of plantar-flexor muscle fatigue on the magnitude and regularity of center-of-pressure fluctuations

Effects of a Passive Back-Support Exosuit on Postural Control and Cognitive Performance During a Fatigue-Inducing Posture Maintenance Task

OBJECTIVE

To evaluate the effectiveness of passive back-support exosuit on postural control and cognitive performance during a fatigue-inducing posture maintenance task.

BACKGROUND

Wearable support systems (exoskeletons/exosuits) reduce physical demands but may also influence postural control and cognitive performance by reducing muscular fatigue.

METHOD

Eighteen participants visited on two different days to test an exosuit system and performed dual-task cognitive assessments based on human information processing (information acquisition, information integration, and action implementation) while maintaining a 35° trunk flexion posture for 16 minutes. Center-of-pressure (CoP), cognitive performance, and perceived workload were recorded, while erector spinae muscle activity was captured to quantify muscle fatigue.

RESULTS

The exosuit was effective in reducing erector spinae muscle fatigue during the static posture maintenance task (61% less in Δmedian frequency: -9.5 Hz (EXO-Off) versus -3.7 Hz (EXO-On)). The fatigue-inducing task increased CoP velocity as a function of time (29% greater: 9.3 mm/sec (pre) versus 12.0 mm/sec (post)), and exosuit use decreased CoP velocity (23% less: 12.1 mm/sec (EXO-Off) versus 9.4 mm/sec (EXO-On)). The exosuit was also effective at mitigating cognitive degradation, as evidenced by a higher hit-to-signal ratio (8% greater: 81.3 (EXO-Off) versus 87.9 (EXO-On)) in the information integration task and reducing perceived workload in all stages of human information processing.

CONCLUSION

Exosuit provided benefits of postural control and information integration processing during a 16-min static posture maintenance task.

APPLICATION

Torso exoskeletons/suits can have positive implications for occupations with concurrent physical and cognitive demands.

Effects of Anodal tDCS Applied Over the Cerebellum Combined with Physical Therapy on Center of Gravity Sway in a Patient with Cerebellar Ataxia: A Single-Case Study

Damage to the cerebellum results in dysfunctional standing postural control. Patients with cerebellar ataxia have a larger sway in the center of gravity (COG) while standing. Transcranial direct current stimulation (tDCS) has been applied in the rehabilitation of patients with central nervous system disorders; however, its effect on COG sway in patients with cerebellar ataxia remains unknown. We aimed to confirm the effects of anodal cerebellar tDCS (ctDCS) combined with physical therapy on COG sway in a patient with cerebellar ataxia using a retrospective ABA single-case study design. This study involved a patient with left cerebellar hemorrhage. Walking and postural balance rehabilitation were conducted in phase A. Anodal ctDCS was combined with the walking and postural balance rehabilitation in phase B. We measured COG sway in the open- and closed-eyes standing conditions daily throughout all the phases. In the open-eyes standing condition, there was no significant change in COG sway in phase B. Conversely, in the closed-eyes standing condition, the circumferential area, total sway path length, and anteroposterior sway path length decreased in phase B. No change was observed in the mediolateral sway path length. The combination of anodal ctDCS and physical therapy may decrease COG sway in patients with cerebellar ataxia in the closed-eyes standing condition, and its effect may be greater in the anteroposterior direction.

Effect of virtual reality training on standing balance in individuals with incomplete spinal cord injury

Recovery of balance ability during standing is one of the primary and essential aims of rehabilitative programs in individuals with incomplete spinal cord injury (iSCI). A sample of ten participants (mean age: 35.7 years, range: 25-63 years) with traumatic or non-traumatic iSCI (AIS grade C or D) and were able to stand with or without the support of an assistive device for a minimum of 2 min were recruited from the rehabilitation department of the Indian Spinal Injuries Centre, New Delhi, India. The participants received Virtual Reality (VR) based balance training for one hour, three times a week for four weeks on the Nintendo Wii gaming console. Participants were assessed three times: pre-intervention, post-intervention and follow-up assessment for the total ellipse area (TEA), total sway perimeter (TSP), sway range (anterior-posterior/medio-lateral (AP/ML)) and limits of stability (LOS). At post-intervention assessment, significant increases in comparison with pre-intervention scores was found in LOS (P=0.00), TEA with eyes open (EO) (P=0.00) and eyes closed (EC) (P=0.00), TSP with EO (P=0.00) and EC (P=0.00), sway range in AP direction (SD-AP) with EO (P=0.01) and EC (P=0.02) and sway range in ML direction (SD-ML) with EO (P=0.02) and EC (P=0.01). At follow-up assessment, a significant improvement in comparison to post intervention scores was found in TEA measured both in EO (P=0.01) and EC conditions (P=0.02), TSP measured with EO (P=0.01) and SD-ML both with EO (P=0.04) and EC (P=0.01). No significant changes were found in LOS (P=0.89), TSP measured with EC (P=0.38) and SD-AP both with EO (P=0.50) and EC (P=1). However, significant improvement was seen on comparing follow-up assessment scores with pre-intervention scores for all variables, such as LOS (P=0.00), TEA in EO (P=0.00) and EC (P=0.00), TSP with EO (P=0.00) and EC (P=0.00), SD-AP with EO (P=0.01) and EC (P=0.02) and SD-ML with EO (P=0.01) and EC (P=0.00). VR-based balance training intervention was able to elicit improvements in balance ability and maintain it during follow-up despite a small training dosage suggesting that it is a promising intervention for standing balance rehabilitation among individuals with iSCI. The VR-based balance training challenges elements of balance, which physical therapists may want to consider when designing a comprehensive rehabilitation program.

Clinical Trials Registry-India: CTRI/2018/12/016814.

Effects of light finger touch on the regularity of center-of-pressure fluctuations during quiet bipedal and single-leg postural tasks

BACKGROUND

The use of extra sources of sensory information associated with light fingertip touch to enhance postural steadiness has been associated with increased attentional demands, whereas the regularity of center of pressure (COP) fluctuations has been interpreted as a marker of the amount of attention invested in posture control.

RESEARCH QUESTION

This study addressed whether increased attentional demands associated with postural tasks involving light finger touch might be reflected by measures of COP regularity.

METHODS

The experiments involved quiet bipedal stance (n = 8 participants) and single-legged stance (n = 14 participants). Each participant was instructed to stand as quietly as possible on a force plate, either touching an external rigid surface (applied force < 1 N, light touch condition), or not (no touch condition). Postural steadiness was assessed by traditional COP measurements (COP Area, RMS, and velocity), whereas the regularity of postural sway was based on estimates of the sample entropy (SaEn) of the COP time series.

RESULTS

Traditional parameters of postural sway and COP regularity (inversely related to SaEn COP measurements) were reduced during the touch conditions as compared to the no-touch conditions, for both bipedal quiet stance and single-legged stance. Decreased COP regularity with light touch was mainly reflected in the direction of the largest postural sway (i.e. in the sagittal plane for bipedal stance and in the frontal plane for single-legged stance).

SIGNIFICANCE

The present results suggest that actively touching an external surface with the fingertip, besides increasing postural steadiness, generated an externally oriented (presumably cognitive-dependent) focus of attention, so that participants invested less attention on the postural task per se (as suggested by increased SaEn), which might be associated with a more "automatic" control of posture.

Assessment of knee and ankle proprioception during the third trimester of pregnancy and postpartum period among primiparous women: An observational longitudinal study

BACKGROUND

Pregnant women experience falls, particularly in the third trimester. In this population, physiological changes, as well as ligament laxity, might influence joint proprioception and do not return to normal during the postpartum period. The prevalence of falls during pregnancy and postpartum periods imposes a need to study proprioception in pregnant women and the postpartum period.

MATERIALS AND METHOD

An observational longitudinal study was conducted in June 2018 in outpatient clinic Chinchwad Pune. A total of 36 primiparous women were included in the study by using purposive sampling. The mean and standard deviation of the age was 25.92 (2.59). Proprioception was assessed for the knee joint and the ankle joint during the third trimester of pregnancy and 6^th and 12^th week postpartum. Outcomes included were the Joint Reposition Test for both knee and ankle joints using UTHSCSA Image Tool Software 3.0. Repeated-measure ANOVA was performed for the normally distributed data, and nonparametric test Friedman's test was performed for data that were not distributed normally. The data was statistically analyzed using the SPSS software version 26. The level of significance was set at 0.05, confidence intervals of 95% were used.

RESULT

The result revealed significant (P < 0.05) improvement in both knee and ankle proprioception during the third trimester of pregnancy and postpartum period 6^th and 12^th week.

CONCLUSION

Knee proprioception and ankle proprioception were found to improve significantly during the postpartum period 6^th and 12^th weeks compared to the third trimester of pregnancy but do not return to the prepregnancy state.

Balance control is impaired by mental fatigue due to the fulfilment of a continuous cognitive task or by the watching of a documentary

The aim of the present study was to evaluate the effects of mental fatigue (MF) induced by a 90-min continuous demanding cognitive task on balance control. Twenty healthy young participants were recruited. They had to perform three postural tasks (on a stable support with eyes open, with eyes closed and on a wobble board) while standing on a force platform before and after watching a documentary in a control condition or carrying out a prolonged continuous demanding cognitive task (AX-continuous performance test-AX-CPT) in a MF condition. Results showed that performing the AX-CPT generated MF since participants felt a higher subjective workload from the NASA Task Load Index after the AX-CPT than after viewing the documentary. Both the AX-CPT and the viewing of the documentary impaired balance control, mainly by affecting postural regulatory mechanisms which evolved towards a less automatic and less complex regulation mode with an increased participation of cognitive resources. MF generated by the AX-CPT affected balance control by compromising the attentional processing, while the deleterious influence of watching a documentary on postural control could stem from an adverse effect of prolonged sitting on balance control during subsequent standing.

Influence of transcutaneous electrical nerve stimulation on weight distribution in lower leg muscles

[Purpose] The purpose of this study was to compare the effects of transcutaneous electrical nerve stimulation (TENS), with and without visual input, on weight distribution following exercise-induced fatigue in the dorsiflexor and plantar flexor muscles of the ankle. [Subjects and Methods] This study had a cross-sectional design. Nineteen healthy adults (10 males, 9 females; mean age 21±0.8 years) were recruited to participate in a single group repeated measurements study lasting three days. On the first day, following exercise-induced fatigue, the standing position was maintained for 30 minutes, after which the postural sway was measured with eyes open (EO) and eyes closed (EC). On the second day, TENS was applied to the ankle dorsiflexors in the standing position for 30 minutes following exercise-induced fatigue. On the last day, TENS was applied to the plantar flexors, and the postural sway was measured with EO and EC following the same exercise-induced fatigue. [Results] On level terrain, with and without visual input, there was a significant difference between the baseline values and those following TENS on the tibialis anterior. On uneven terrain (simulated by a cushion), with and without visual input, there was a significant difference between the baseline values and those following TENS on the gastrocnemius. [Conclusion] Clinically, during walking on a flat surface for only a short period of time, TENS should be applied to the tibialis anterior. If walking training is performed on a variety of terrains for a longer time, TENS should be applied to the gastrocnemius.

New insights into neck-pain-related postural control using measures of signal frequency and complexity in older adults

There is evidence to implicate the role of the cervical spine in influencing postural control, however the underlying mechanisms are unknown. The aim of this study was to explore standing postural control mechanisms in older adults with neck pain (NP) using measures of signal frequency (wavelet analysis) and complexity (entropy). This cross-sectional study compared balance performance of twenty older adults with (age=70.3±4.0 years) and without (age=71.4±5.1 years) NP when standing on a force platform with eyes open and closed. Anterior-posterior centre-of-pressure data were processed using wavelet analysis and sample entropy. Performance-based balance was assessed using the Timed Up-and-Go (TUG) and Dynamic Gait Index (DGI). The NP group demonstrated poorer functional performance (TUG and DGI, p<0.01) than the healthy controls. Wavelet analysis revealed that standing postural sway in the NP group was positively skewed towards the lower frequency movement (very-low [0.10-0.39Hz] frequency content, p<0.01) and negatively skewed towards moderate frequency movement (moderate [1.56-6.25Hz] frequency content, p=0.012). Sample entropy showed no significant differences between groups (p>0.05). Our results demonstrate that older adults with NP have poorer balance than controls. Furthermore, wavelet analysis may reveal unique insights into postural control mechanisms. Given that centre-of-pressure signal movements in the very-low and moderate frequencies are postulated to be associated with vestibular and muscular proprioceptive input respectively, we speculated that, because NP demonstrate a diminished ability to recruit the muscular proprioceptive system compared to controls, they rely more on the vestibular system for postural stability.

Center-of-pressure total trajectory length is a complementary measure to maximum excursion to better differentiate multidirectional standing limits of stability between individuals with incomplete spinal cord injury and able-bodied individuals

Background

Sensorimotor impairments secondary to a spinal cord injury affect standing postural balance. While quasi-static postural balance impairments have been documented, little information is known about dynamic postural balance in this population. The aim of this study was to quantify and characterize dynamic postural balance while standing among individuals with a spinal cord injury using the comfortable multidirectional limits of stability test and to explore its association with the quasi-static standing postural balance test.

Methods

Sixteen individuals with an incomplete spinal cord injury and sixteen able-bodied individuals participated in this study. For the comfortable multidirectional limits of stability test, participants were instructed to lean as far as possible in 8 directions, separated by 45° while standing with each foot on a forceplate and real-time COP visual feedback provided. Measures computed using the center of pressure (COP), such as the absolute maximal distance reached (COP_max) and the total length travelled by the COP to reach the maximal distance (COP_length), were used to characterize performance in each direction. Quasi-static standing postural balance with eyes open was evaluated using time-domain measures of the COP. The difference between the groups and the association between the dynamic and quasi-static test were analyzed.

Results

The COP_length of individuals with SCI was significantly greater (p ≤ 0.001) than that of able-bodied individuals in all tested directions except in the anterior and posterior directions (p ≤ 0.039), indicating an increased COP trajectory while progressing towards their maximal distance. The COP_max in the anterior direction was significantly smaller for individuals with SCI. Little association was found between the comfortable multidirectional limits of stability test and the quasi-static postural balance test (r ≥ −0.658).

Conclusion

Standing dynamic postural balance performance in individuals with an incomplete spinal cord injury can be differentiated from that of able-bodied individuals with the comfortable limits of stability test. Performance among individuals with an incomplete spinal cord injury is characterized by lack of precision when reaching. The comfortable limits of stability test provides supplementary information and could serve as an adjunct to the quasi-static test when evaluating postural balance in an incomplete spinal cord injury population.

Measuring regularity of human postural sway using approximate entropy and sample entropy in patients with Ehlers-Danlos syndrome hypermobility type

Ligament laxity in Ehlers-Danlos syndrome hypermobility type (EDS-HT) patients can influence the intrinsic information about posture and movement and can have a negative effect on the appropriateness of postural reactions. Several measures have been proposed in literature to describe the planar migration of CoP over the base of support, and the most used in clinical field are the CoP excursions in antero-posterior and medio-lateral direction. In recent years a growing number of studies have been designed to explore the complexity of the COP trajectories during quiet standing. We assessed 13 adults with EDS-HT (EDSG) and 20 healthy adults (CG) during static posture, evaluating the CoP using time and frequency domain analysis and entropy analysis (SampEn and ApEn parameters). Higher values of CoP displacements in medio-lateral and anterior-posterior directions for EDSG than CG were found; no differences were observed in CoP frequency. The entropy analysis showed lower value for EDSG than CG, pointing out the needing of EDSG to concentrate more attention on postural control, loosing complexity and reflecting a less automatized postural control.