Influence of ankle plantarflexor fatigue on postural sway, lower limb articular angles, and postural strategies during unipedal quiet standing

Effects of triceps surae exercise-induced delayed onset muscle soreness on control of body stability in different postures

This research aimed to determine whether triceps surae delayed onset muscle soreness (DOMS) affects stability while performing different postural control tasks requiring upright and landing stabilization. Twenty-four participants who self-reported as healthy were recruited. Pre and 48 h after a protocol to induce DOMS in the triceps surae, participants were evaluated for DOMS perception, pressure pain threshold, and postural control (assessed by the center of pressure, CoP) during different standing and landing stabilization tasks. We found higher DOMS perception and lower pressure pain threshold 48 h after the exercise. Mediolateral CoP displacement was more sensitive to DOMS across different postural tasks, but no effects were found for bilateral standing. The landing time to stabilization elicited high individual variability in the presence of DOMS. Effects of DOMS in the performance of less challenging tasks, such as bipedal standing, were not found. We conclude that DOMS in the triceps surae impairs mediolateral postural control during challenging tasks such as unilateral standing and body forward lean. It highlights the need for caution and individualized approaches when incorporating movements requiring frontal plane control in training and rehabilitation sessions under the presence of DOMS.

Sex differences concerning the effects of ankle muscle fatigue on static postural control and spinal proprioceptive input at the ankle

Aims

The main aim of this study was to determine sex differences in postural control changes with ankle muscle fatigue during a standing forward leaning (FL) task under different vision conditions. The secondary aim was to examine sex differences in the effect of fatigue on soleus (SOL) H-reflex amplitude, a measure of motoneuron excitability with activation of Ia afferents.

Methods

Fifteen healthy young adult males (mean age: 28.0 years) and 16 healthy young adult females (mean age: 26.1 years) were asked to perform four consecutive FL tasks [30 s; two with eyes open (EO) and two with eyes closed (EC)] before, and immediately following a fatiguing exercise consisting of alternating ankle plantarflexion (6 s) and dorsiflexion (2 s) maximal isometric contractions, and at 5 and 10 min of recovery. Center of pressure (COP) sway variables (mean position, standard deviation, ellipse area, average velocity, and frequency), an ankle co-contraction index, and a ratio of SOL H-reflex to the maximum amplitude of the compound muscle action potential (M-max) were obtained during the FL tasks. A rating of perceived fatigue (RPF) was also documented at the different time points.

Results

Time to task failure (reduction of 50% in maximal voluntary isometric contraction torque of ankle plantar flexors) and the increase in RPF value were not significantly different between males and females. Both sex groups showed similar and significant increases (p < 0.05) in mean COP sway velocity with no significant changes in co-contraction indices. No significant effects of fatigue and related interactions were found for SOL H/M-max ratio.

Discussion

The absence of a significant sex difference in postural control change (sway and co-contraction) with fatigue could be explained by similar perceived (RPF) and performance fatigability (exercise duration) between males and females in the present study. Fatigue did not lead to significant changes in SOL spinal motoneuron excitability with activation of Ia afferents.

Early Changes in Postural Balance Following Inverted V-Shaped High Tibial Osteotomy in Patients With Knee Osteoarthritis

Patients with knee osteoarthritis and varus knee deformity have impaired postural balance, resulting in decreased walking performance and an increased risk of falls. This study aimed to investigate the early changes in the postural balance following inverted V-shaped high tibial osteotomy (HTO). Fifteen patients with medial knee osteoarthritis were recruited. Postural balance was assessed using the center-of-pressure (COP) data during single-leg standing before and 6 weeks after inverted V-shaped HTO. The maximum range, mean velocity, and area of COP movements in the anteroposterior and mediolateral directions were analyzed. Preoperative and postoperative visual analog scale for knee pain was assessed. The maximum range of COP in the mediolateral direction decreased (P = .017), whereas the mean velocity of COP in the anteroposterior direction increased 6 weeks postoperatively (P = .011). The visual analog scale score for knee pain significantly improved at 6 weeks postoperatively (P = .006). Valgus correction with inverted V-shaped HTO resulted in improved postural balance in the mediolateral direction and good short-term clinical outcomes early following surgery. Early rehabilitation after inverted V-shaped HTO should focus on postural balance in the anteroposterior direction.

Effects of an intermittent exercise protocol on ankle control during a single-legged landing

Purpose

To identify the effects of fatigue from an exercise protocol (similar to a soccer match) on ankle motion and forces during single-legged drop landing.

Methods

Seventeen males aged (mean ± SD) 22.2 ± 2.0 years participated in this repeated measures study. A 90-min intermittent exercise protocol with a 15-min rest at halftime was performed. Before, at halftime and after the exercise, participants were tested via a single-legged drop landing task onto a force platform whilst wearing a three-dimensional inertial measurement system (Xsens). Ankle angles (plantarflexion/dorsiflexion and inversion/eversion) were analysed before landing and at peak ground reaction force after landing, and center of pressure was analysed at peak ground reaction force.

Results

No significant differences were found for the outcomes between pre-, halftime and post-exercise (p > 0.05).

Conclusions

Findings suggest that exercises simulating a soccer match (regarding exertion) do not necessarily lead to significant changes in ankle motion or forces around the ankle.

Sex differences in the effect of muscle fatigue on static postural control under different vision and task conditions

The main aim of this study was to compare the effects of ankle plantar flexors fatigue on postural control between healthy young adult males and females. The secondary aim was to determine the effects of vision on the fatigue-induced postural changes. Ten healthy young males and nine females were asked to perform quiet standing (QS) and standing forward lean (FL) tasks with eyes open (EO) and closed (EC) before and immediately following exercise, and throughout a 15-min recovery period. A sustained isometric exercise of ankle plantar flexors was performed until participants were no longer able to maintain a target torque of 50% of maximal voluntary isometric contraction (MVIC). Mean anteroposterior (AP) and mediolateral (ML) positions of the center of pressure (COP), mean COP sway velocity, and 95% ellipse area of COP sway were measured. Ankle plantar flexors fatigue had significant effects on all dependent variables, except for sway area. A fatigue X sex interaction was found for sway velocity with the most challenging task condition (FL-EC), where males showed a significant increase in sway velocity up to 15 min following exercise, whereas females did not. Fatigue X vision interactions for AP position were also found, with the withdrawal of vision leading to a greater backward shift during recovery for both the QS (5 to 15 min) and FL (5 to 10 min) tasks. Our findings suggest the use of different postural control strategies with ankle fatigue between males and females, and also a contribution of vision to compensate for fatigue-induced instability that is not dependent on task difficulty.

Changes in postural control strategy during quiet standing in individuals with knee osteoarthritis

BACKGROUND

Knee osteoarthritis (OA) impairs postural control and may affect how the lower limb joints are used for postural control.

OBJECTIVE

To investigate how individuals with knee OA use lower limb joints for static postural control.

METHODS

Ten patients with knee OA and thirteen healthy controls performed quiet standing for 30 s. The standard deviation of the center of mass (COM) and lower limb joint motions in the anterior-posterior (AP) and medial-lateral (ML) planes were calculated from three-dimensional marker trajectories. Pearson's correlation analysis and independent t-tests were conducted to investigate the relationship between COM and lower limb joint motion and to compare group difference, respectively.

RESULTS

The AP hip angular velocity alone in the knee OA group and the AP hip and knee angular velocity in the control group were significantly correlated with the AP COM velocity. The ML hip angular velocity was significantly correlated with the ML COM velocity in both groups. The knee OA group exhibited a significantly larger standard deviation of AP COM velocity than the control group.

CONCLUSIONS

Individuals with knee OA depended solely on the contribution of the hip to the AP COM velocity, which could not be successfully controlled by the knee.

Contributions of Intrinsic and Extrinsic Foot Muscles during Functional Standing Postures

Purpose. Maintaining balance during static standing postures requires the coordination of many neuromuscular mechanisms. The role of the intrinsic and extrinsic foot muscles in this paradigm has yet to be clearly defined. The purpose of this study was to explore foot muscle activation during static phases on common weight-bearing tasks of varying loads and balance demands. Methods. Twenty healthy young adults performed 6 standing postures (single-limb and double-limb stand, squat, and heel raise) with one foot on a force plate. Muscle activity was recorded from the abductor hallucis, flexor hallucis longus and brevis, and tibialis posterior using intramuscular electrodes; surface electrodes were used to record activity from the peroneus longus and tibialis anterior. Two-way repeated measures ANOVA (2 loading conditions × 3 postures) were run to compare muscle activation and center of pressure velocity. Results. Intrinsic foot muscle activity increased as loading and postural demand increased; however, the specific effects varied for each of the extrinsic foot muscles. Conclusions. These results suggest that the intrinsic foot muscles play an important role in maintaining static balance. Strengthening intrinsic and extrinsic foot muscles may help increase stability in people who have weak toe flexors or who suffer from a variety of foot pathologies.

Submaximal fatiguing contractions reduce stability of voluntary postural control more than maximal fatiguing contractions

BACKGROUND

It is well known that different exercise intensities for the ankle muscles can impair postural stability. However, it remains unclear whether it is low-intensity exercises (which primarily induce central fatigue) or high-intensity exercises (which primarily induce peripheral fatigue) that have a greater effect on voluntary postural control.

RESEARCH QUESTION

The aim of this study was to compare the effects of fatiguing exercises that induce either central or peripheral fatigue on voluntary postural stability.

METHODS

Following isometric maximum voluntary contraction (IMVC) tests, 12 volunteers randomly performed submaximal (40% IMVC) and maximal (100% IMVC) fatiguing contractions of the plantar flexors on a dynamometer. Before and after the fatiguing protocols, postural stability was assessed by measuring the centre of pressure trajectory during voluntary sways on a force plate. The electromyography activity of the right gastrocnemius medialis was recorded. To assess central and peripheral fatigue, electrical stimulations were applied both during and after the IMVC. The effects of the fatiguing protocols and the differences between the protocols were tested with a two-way repeated measures ANOVA test (fatigue × time).

RESULTS

Submaximal contractions induced a greater increase of sway area and medial-lateral sway cycle range than maximal contractions (P < 0.01). Voluntary activation decreased significantly more after submaximal contractions than maximal contractions (P < 0.01). Submaximal contractions induced a significantly greater reduction of IMVC than maximal contractions (P < 0.01). Resting twitch size was smaller after maximal contractions than submaximal contractions (P = 0.04).

SIGNIFICANCE

The outcome of this study suggests that training programmes for patients with balance issues should be based on training with maximal rather than submaximal load, to avoid deficits that might compromise postural stability.

Ankle muscle fatigability impairs body sway for more than 24 h

This study aimed to investigate if the impairing in postural control, induced by ankle fatiguing exercise, remains after 24/48 h in young adults. Center of Pressure (CoP) was assessed in 16 participants (23 ± 3 years old) before, immediately after an ankle fatigability induction protocol (FI) and after 24 or 48 h of recovery using two 60-s trials with eyes open (EO) and closed (EC). The FI consisted of performing the ankle plantar flexion and dorsiflexion movement repeatedly (0.5 Hz). Ankle muscle fatigability increased CoP anterior-posterior (AP - p < 0.02) and medial-lateral (ML - p < 0.009) root mean square (RMS), and AP (p < 0.01) mean velocity immediately after compared to before FI. These effects remained after 24/48 h of recovery: higher CoP AP (p < 0.03) and ML (p < 0.009) RMS. No significant effects for detrend fluctuation analysis and entropy analysis among periods of postural evaluations was found. Fatigue*visual condition interaction revealed an increased AP median frequency (p < 0.001) during EC compared to EO only immediately after FI. Young adults' body sway remains impaired until 48 h, but not the postural control adaptability and complexity. Visual information may not attenuate the late deleterious ankle muscle fatigability effects. Individuals should be cautious during balance tasks and exercise after fatiguing exercise in the next 24/48 h, therefore avoiding unbalances and falls.

Rating of perceived exertion (RPE) in studies of fatigue-induced postural control alterations in healthy adults: Scoping review of quantitative evidence

BACKGROUND

Amongst the literature researching the effects of exercise-induced fatigue on postural control in healthy adults, many studies have used the Borg scales to document the rating of perceived exertion (RPE) and have shown a broad range of RPE values. Our main aim was to map fatigue-induced RPE values in included publications. Secondary aims were to summarize the preference and purpose for the use of Borg scales within the included publications and to explore the potential associations between fatigue-induced RPE values and postural control changes.

METHODS

Five databases (Ovid Medline, PubMed, CINAHL, Scopus, and SPORTDiscus) were systematically searched for synthesizing data among the publications that reported RPE values on the Borg RPE- and Category-Ratio (CR) 10 scales and also found fatigue effects on postural control in healthy adults. Spearman's rank correlations were conducted to assess potential associations between fatigue-induced RPE values and maximal postural control changes across the included publications (group data).

RESULTS

45 of 51 studies included in this review reported maximal RPE values following exercise and ranged from 10.4-20 (6-20 Borg RPE) or 0.9-10 (CR10) indicating "very light" or "very weak" to "maximal" exertions. The 6-20 Borg and CR10 scales were mainly used to assess cardiovascular and muscular exertion, respectively. The scales were used mostly to estimate fatigue levels (n = 45), and to a lesser extent to produce a specific exercise intensity (n = 5) and as the criterion for exercise termination (n = 1). In general, there was no significant association between RPE and postural control changes across studies.

CONCLUSION

The broad range of RPE values and weak correlations may suggest that various fatigue levels can lead to postural control changes. However, one should be careful in comparing the extent of fatigue from RPE values and its potential effect on postural control in the light of many confounding factors.

The Effect of Fatigue on Single-Leg Postural Sway and Its Transient Characteristics in Healthy Young Adults

Neuromuscular fatigue is known to impair balance ability, which is reflected in increased postural sway during quiet standing tasks. Recently, quantifying transient characteristics of postural sway has been suggested as an approach to obtain additional information regarding postural control. However, this approach is currently vastly unexplored. The purpose of this study was to investigate the effects of fatigue (induced by a repeated change of direction task) on postural sway and its transient characteristics during single-leg standing, including whole-trial estimates and indexes of transient behavior in young healthy active adults. The study involved 28 physically active students (14 females). Single-leg postural sway was recorded for 30s before and after a fatiguing protocol, which consisted of a repeated change of direction tasks. We calculated the traditional whole-trial estimates of postural sway [center-of-pressure (CoP) velocity and amplitude in anterior-posterior (AP) and medial-lateral (ML) directions] and corresponding transient behavior indexes, based on three 10-s intervals. Statistically significant sex×fatigue interaction with medium effect sizes was found for whole-trial CoP velocity in AP (p=0.028; η²=0.17) and ML directions (p=0.019; η²=0.19). Post-hoc test showed that both variables substantially decreased in female participants (p=0.041–0.045; d=0.54–0.56), but remained similar in males (p=0.194–0.294). There were small to medium statistically significant main effects of fatigue on transient index for CoP amplitude in both directions (p=0.042–0.049; η²=0.02–0.14). Notably, CoP AP amplitude increased in the first 10-s interval for males (before fatigue: 5.6±1.3mm; after fatigue: 6.3±1.6mm), while the CoP AP amplitude in the third interval remained similar after fatigue (before fatigue: 5.5±1.4mm; after fatigue: 5.1±1.2mm). In conclusion, the responses to fatigue in terms of postural sway were time interval specific, and there were certain sex-differences in responses to fatigue, which could be related to better ability to adapt balance strategies in females. Moreover, our results demonstrate that the indexes of transient behavior could perhaps detect smaller fatigue-induced changes in postural sway that are seen in whole-trial estimates.

The Influence of Kinesio Tape and an Ankle Brace on the Lower Extremity Joint Motion in Fatigued, Unstable Ankles during a Lateral Drop Landing

BACKGROUND

An unstable ankle along with plantar flexor muscle fatigue may exacerbate landing performance. External support may be an option to control the ankle motion and protect joints from injuries. Research goal: To investigate the immediate changes in the joint motion of a lower extremity under ankle plantar flexors fatigue conditions in athletes with unstable ankles using different external supports.

METHODS

A total of 44 participants were allocated to a control (Cn) group, an ankle brace (AB) group, and a kinesio tape (KT) group, and were asked to perform a lateral drop landing before and after a fatigue protocol. The outcome measures were fatigue-induced changes in the maximal joint angle and changes in the angle ranges of the hip, knee, and ankle.

RESULTS

Smaller changes in the maximal hip abduction were found in the AB group (p = 0.025), and the KT group exhibited smaller changes in the maximal ankle dorsiflexion (p = 0.009). The AB group landed with a smaller change in the range of hip flexion and knee flexion (p = 0.008 and 0.006). The Cn group had greater fatigue-induced changes in the COM range than AB and KT group (p = 0.002 and 0.028).

SIGNIFICANCE

Despite the beneficial effect in the postural control in the frontal plane, the use of AB might constrain the distal joint motion which might lead to an extended knee landing posture resulting in secondary injuries to the knee joint. Therefore, the use of AB in conjunction with an additional training of landing strategy might be recommended from the injury prevention perspective.

Relationship between ankle strength and range of motion and postural stability during single-leg quiet stance in trained athletes

The aim of this study was to determine the relationship between strength of ankle plantar and dorsal flexors and range of motion (RoM), and body sway variables during single-leg quiet stance, in highly trained athletes. The participants for this study were young athletes from 9 disciplines (n = 655). Center of pressure (CoP) velocity, amplitude, and frequency were measured during single-leg quiet stance. Moreover, athletes were measured for passive ankle plantar flexion (PF) and dorsal flexion (DF) RoM, and for rate of torque development (RTD) in the 0–50 (RTD50) and 0–200 ms time windows (RTD200). Ankle strength and RoM could not predict CoP velocity total, anterior–posterior (AP), and medial–lateral (ML) (p > 0.05). However, PF_RTD50 and PF_RoM and PF_RoM positively influenced CoP amplitude in ML direction (p < 0.001, R² = 0.10). Moreover, CoP frequency in ML direction significantly increased with lower PF_RTD50, DF_RTD50, DF_RTD200, PF_RoM, and DF_RoM (p < 0.05). We have demonstrated that ankle strength and RoM were related to single-leg quiet stance postural balance in trained athletes. The ankle RoM showed the greatest influence on CoP variables in ML directions.

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

The aim of this study was to investigate the effects of ankle and hip muscle fatigue on motor adjustments (experiment 1) and symmetry (experiment 2) of postural control during a quiet standing task. Twenty-three young adults performed a bipedal postural task on separate force platforms, before and after a bilateral ankle and hip muscle fatigue protocol (randomized). Ankle and hip muscles were fatigued separately using a standing calf raise protocol (ankle fatigue) on a step and flexion and extension of the hip (hip fatigue) sitting on a chair, at a controlled movement frequency (0.5Hz), respectively. In both experiments, force, center of pressure, and electromyography parameters were measured. The symmetry index was used in experiment 2 to analyze the postural asymmetry in the parameters. Our main findings showed that muscle fatigue impaired postural stability, regardless of the fatigued muscle region (i.e., ankle or hip). In addition, young adults used an ankle motor strategy (experiment 1) before and after both the ankle and hip muscle fatigue protocols. Moreover, we found increased asymmetry between the lower limbs (experiment 2) during the quiet standing task after muscle fatigue. Thus, we can conclude that the postural motor strategy is not muscle fatigue joint-dependent and a fatigue task increases postural asymmetry, regardless of the fatigued region (hip or ankle). These findings could be applied in sports training and rehabilitation programs with the objective of reducing the fatigue effects on asymmetry and improving balance.

Repeatability and Reproducibility of Postural Variables by Photogrammetry

OBJECTIVE

This study aimed to examine the reliability of postural variables analyzed by photogrammetry obtained at different instances on the same day and between 2 different days.

METHODS

A sample composed of 24 healthy adult individuals of both sexes was submitted to photogrammetric postural assessment. From 35 seconds of filming, 7 photographs (of time instance at 0 second, 05 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, and 30 seconds) were extracted and digitalized on digital image-based postural assessment software. One factor repeated-measures analysis of variance quantified the alterations in the magnitude of the variables within and between sessions (factor time and factor day, respectively). The intraclass correlation coefficient (ICC), standard error of measurement (SEM), and minimal detectable change (MDC) were calculated to verify the repeatability and reproducibility.

RESULTS

The repeatability shows that postural variables did not present significant differences in the comparison among the 7 instances; all the variables had excellent and significant ICCs, and SEM and MDC values indicated measurement errors lower than 5%. The intrarater reproducibility shows that postural variables did not present significant differences between 2 days of evaluation; most of the variables had excellent and significant ICCs, and SEM and MDC values were between 0.9% and 12.5%.

CONCLUSION

The results for repeatability and reproducibility show that most of the variables have excellent and significant ICCs. Postural evaluation by photogrammetry can be performed at any time within a 30-second interval counting from the positioning of the participant for assessment. Therefore, we conclude that a single photograph can represent the static posture of an individual in the postural evaluation, which is reliable enough and useful to determine the effects of an intervention either in clinical practice or in research.

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

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.

Positive verbal suggestion optimizes postural control

Balance is a very important function that allows maintaining a stable stance needed for many daily life activities and for preventing falls. We investigated whether balance control could be improved by a placebo procedure consisting of verbal suggestion. Thirty healthy volunteers were randomized in two groups (placebo and control) and asked to perform a single-leg stance task in which they had to stand as steadily as possible on the dominant leg. The task was repeated in three sessions (T0, T1, T2). At T1 and T2 an inert treatment was applied on the leg, by informing the placebo group that it was effective in improving balance. The control group was overtly told that treatment was inert. An accelerometer applied on participants’ leg allowed to measure body sways in different directions. Subjective parameters, like perception of stability, were also collected. Results showed that the placebo group had less body sways than the control group at T2, both in the three-dimensional space and in the anterior-posterior direction. Furthermore, the placebo group perceived to be more stable than the control group. This study represents the first evidence that placebo effect optimizes posture, with a potential translational impact in patients with postural and gait disturbances.

Effects of Plantar Flexor Muscles Fatigue on Postural Control during Quiet Stance and External Perturbation in Healthy Subjects

BACKGROUND

The maintenance of postural control is a key component in dynamic physical activity, especially during muscle fatigue and against external forces. Despite many studies in this field, there is no consensus regarding the effects of plantar flexor muscles fatigue on postural control during different postural tasks.

OBJECTIVE

To evaluate the effects of plantar flexor muscles fatigue on postural control during quiet stance and external perturbation in healthy subjects.

MATERIAL AND METHODS

Twenty four healthy individuals (20-35 years) participated this interventional study. The foot center of pressure data was measured using a single force platform, and then the postural control parameters, including the center of pressure displacement and velocity in the anterior-posterior and medial-lateral direction and also path length calculated under two conditions; quiet and perturbed stance, before and after plantar flexor muscles fatigue.

RESULTS

The statistical analysis demonstrated that mean displacement and velocity of the center of pressure in the anterior-posterior direction and also path length increased after the fatigue protocol in the perturbed condition. However, fatigue had no significant effects on postural control parameters in the quiet standing condition.

CONCLUSION

These results indicated that the effects of muscle fatigue on postural control depend on the difficulty of the task and the relevance of proprioceptive information. The postural control system appears to use distinct control strategies in different situations such as quiet and perturbed stance conditions, and these strategies may be differentially altered by fatigue. In conclusion, due to the potential risk of loss of balance, it is important to take the role of plantar flexor muscle fatigue into account during more difficult postural tasks.

Asymmetries in Gait and Balance Control After Ankle Arthrodesis

Previous gait analysis studies of patients with an ankle arthrodesis have reported increased motion in the adjacent joints. However, of similar importance are the forces that act on the ipsi- and contralateral joints and the effect of ankle arthrodesis with regard to balance control. The purpose of the present study was to determine the joint moments and the amount of asymmetrical loading of the ankle and joints adjacent to the ankle in patients after successful ankle arthrodesis. Therefore, 8 patients with a painless ankle fusion were included and assessed using 4 functional tests: preferred and fast speed walking, a sit-to-stand test, and a balance test. The ground reaction force and ankle joint moment were smaller in the fused ankle. During the balance on foam test, the velocity of the center of pressure was significantly larger on the contralateral extremity. In conclusion, ankle arthrodesis leads to small asymmetries in joint moments during gait, indicating greater loading of the contralateral ankle. In addition, the unaffected leg compensates for the operated leg in balance control. Because of the small alterations, overuse of the contralateral ankle is not expected after ankle arthrodesis.

The effects of shoulder stabilization exercises and pectoralis minor stretching on balance and maximal shoulder muscle strength of healthy young adults with round shoulder posture

[Purpose] The purpose of this study was to analyze the effects of pectoralis minor stretching and shoulder strengthening with an elastic band on balance and maximal shoulder muscle strength in young adults with rounded shoulder posture. [Subjects and Methods] Nineteen subjects with rounded shoulder posture were randomly divided into 2 groups: a shoulder stabilization exercise group and a stretching exercise group. The groups performed each exercise for 40 minutes, 3 times a week, for 4 weeks. Static balance (eyes open and closed), dynamic balance (the limits of stability in 4 directions) and shoulder muscle strength in 5 directions were measure before and after the exercises. [Results] The stretching exercise demonstrated a significant difference between the pre- and post-exercise in the static balance with eyes closed and extension and horizontal abduction strength while the stabilization exercise demonstrated significant difference in the left and right directions between the pre- and post-exercise of the dynamic balance and flexion strength. The stabilization exercise demonstrated significant differences shown in the flexion between the pre- and post-test. [Conclusion] The shoulder stabilization and stretching exercises improved the static balance, dynamic balance, and muscle strength.

Does corrective spine surgery improve the standing balance in patients with adult spinal deformity?

BACKGROUND CONTEXT

The effect of corrective spine surgery on standing stability in adult spinal deformity (ASD) has not been fully documented.

PURPOSE

To compare pre- and postoperative standing balance and posture in patients with ASD.

STUDY DESIGN/SETTING

This study is a prospective case series.

PATIENT SAMPLE

Standing balance before and after corrective spine surgery was compared in 35 consecutive female patients with ASD (65.6±6.9 years, body mass index 22.3±2.7 kg/m², Cobb angle 50.2±19.2°, C7 plumb line 9.3±5.6 cm, and pelvic incidence-lumbar lordosis mismatch 40.8±23.3°).

OUTCOME MEASURES

The Scoliosis Research Society Patient Questionnaire, the Oswestry Disability Index, and force-plate analysis were used to evaluate the patient outcomes.

MATERIALS AND METHODS

We reviewed patient charts and X-rays and compared standing balance before and after corrective spine surgery. All subjects were assessed by force-plate analysis using optical markers while standing naturally on a custom-built force platform. The spinal tilt, pelvic obliquity, pelvic tilt, and joint angle were calculated. The lower leg lean volume was obtained by whole-body dual X-ray absorptiometry to assess muscle strength.

RESULTS

ASD patients showed significant differences between the left and right sides in ground reaction force (dGRFs), hip (dHip), and knee angle (dKnee) while standing (dGRF 15.1±8.7%, dHip 7.1±6.6°, dKnee 5.9±5.5°). The recorded center-of-gravity (CoG) area was not improved after surgery, whereas the dGRF, dHip, and dKnee all decreased. The spinal tilt, pelvic obliquity, and pelvic tilt were all significantly improved after surgery. We found significant correlations between the radiographic trunk shift and the postoperative coronal CoG distance and recorded CoG area, and between the sagittal CoG distance and the age and the lean volume of the lower extremities (trunk shift R=0.33, 0.45; age R=0.32; lean volume R=0.31).

CONCLUSIONS

Corrective spinal surgery improved the spinal alignment and joint angles in patients with ASD but did not improve the standing stability. A correlation found between the sagittal CoG distance and the lean volume of the lower extremities indicated the importance of the leg muscles for stability when standing, whereas a correlation found between the coronal CoG distance and trunk shift reflected the attenuated postural response in the ASD patients.

Strategies for equilibrium maintenance during single leg standing on a wobble board

The aim of this study was to identify and compare movement strategies used to maintain balance while single leg standing on either a firm surface (FS) or on a wobble board (WB). In 17 healthy men, retroreflective markers were positioned on the xiphoid process and nondominant lateral malleolus to calculate trunk and contralateral-leg excursion (EXC) and velocity (VEL), and center of pressure (CoP) EXC and VEL during FS on a force platform. From the WB test, standing time (WBTIME) was determined and the board's angular EXC and VEL were calculated from four markers on the WB as surrogate measures for CoP dynamics. Electromyographic average rectified values (ARV) from eight leg and thigh muscles of the supporting limb were calculated for both tasks. WB ARV amplitudes were normalized with respect to the value of FS ARV and presented significantly higher peroneus longus and biceps femoris activity (p<0.05). WB standing time was correlated to trunk sagittal plane velocity (r=-0.73 at p=0.016) and excursion (r=-0.67 at p=0.03). CoP and WB angular movement measures were weakly and not significantly correlated between tasks. This lack of correlation indicates that WB balance maintenance requires movement beyond the ankle strategy as described for the FS task. WB standing likely demands different biomechanical and neuromuscular control strategies, which has immediate implications for the significance of WB tests in contrast to FS balance tests. Differences in control strategies will also have implications for the understanding of mechanisms for rehabilitation training using such devices.

[The investigation of kinematic features of gait in healthy subjects and patients with post-stroke atactic disorders]

AIM

To study spatial/temporal parameters of gait in post-stroke vestibular-atactic syndrome.

MATERIAL AND METHODS

Authors investigated the speed, rhythmic and angle parameters of the gait in healthy subjects (n=15) and in patients with atactic disorders in the recovery period of vertebrobasillar ischemic stroke (n=15). Physical examination with elements of anthropometry, clinical assessment of gait function with the Dynamic Gait Index, objective assessment of gait parameters using the system for 3D movement video analysis VICON Motion Capture Systems were used.

RESULTS

There were a statistically significant decrease in the speed and pace of the gait, increase in the step duration and duration of the double support phase. The speed and rhythmic parameters of the left and right lower limb differed significantly. A delay of the moments of foot lifting from the surface was observed. Authors also revealed a decrease in the amplitude of flexion and extension in all segments of the lower limbs in the double step phase.

CONCLUSION

These characteristics represent the activation of the «sitting» strategy and facilitate the objective assessment of the hyperfunction of the reactive postural synergies in patients with post-stroke atactic disorders.

Effects of different types of exercise on muscle activity and balance control

[Purpose] This study analyzed the effects of isotonic, isokinetic, and isometric exercises of ankle joint muscles on lower extremity muscle activity and balance control. [Subjects and Methods] The subjects were 30 healthy adults (15 males) in their 20s who were randomly assigned to three different exercise method groups of 10 people each. The isokinetic exercise group performed three sets at an angular velocity of 60°/sec, including a single rest period after every set of 10 repetitions. The isometric exercise group performed three sets consisting of three 15 repetitions of a 15-second exercise followed by a 5-second rest. [Results] Multivariate analysis of variance revealed that depending on the exercise method, the non-dominant tibialis anterior, gastrocnemius muscle, and peroneus longus showed significant differences in muscle activity for weight-bearing non-dominant sides; when the dominant side was weight-bearing, the dominant gastrocnemius and peroneus longus showed significant differences in muscle activity; and the non-dominant and dominant sides showed significant differences in balance control depending on the duration of support in the area. [Conclusion] Muscle fatigue from the three exercise methods produced a decline in muscle activity and balance control; due to the fatigue before exercise, the side that did not perform the exercises was affected.

Effect of isotonic and isokinetic exercise on muscle activity and balance of the ankle joint

[Purpose] This study was performed to examine how the balance of lower limbs and the muscle activities of the tibialis anterior (TA), the medial gastrocnemius (GCM), and the peroneus longus (PL) are influenced by isotonic and isokinetic exercise of the ankle joint. [Subjects] The subjects of this study were healthy adults (n=20), and they were divided into two groups (isotonic=10, isokinetic=10). [Methods] Isotonic group performed 3 sets of 10 contractions at 50% of MVIC and Isokinetic group performed 3 sets of 60°/sec. Muscle activity was measured by EMG and balance was measured by one-leg standing test. [Results] For muscle activity, a main effect of group was found in the non-dominant TA, and the dominant TA, GCM and PL. For balance, a main effect of time was found in both groups for the sway area measured support was provided by the non-dominant side. [Conclusion] In terms of muscle activity, the two groups showed a significant difference, and the isokinetic group showed higher muscle activities. In terms of balance, there was a significant difference between the pre-test and the post-test. The results of this study may help in the selection of exercises for physical therapy, because they show that muscle activity and balance vary according to the type of exercise.

Temporal dependency of sway during single leg stance changes with age

BACKGROUND

Balance deteriorates with age and fall related injuries are often linked to long-term disability and loss of independence in older adults. This study focuses on the task of establishing single leg stance, which requires the ability to shift the center of mass onto the supporting leg.

METHODS

Fifteen younger adults and eight older adults participated in the study. Subjects performed a step with self-selected step length onto the force plate to establish a single leg stance (SLS) on their dominant leg. The first four seconds of SLS were analyzed to investigate age related temporal dependencies of sway area, sway velocity, anterior-posterior sway, and medio-lateral sway.

FINDINGS

Younger adults show a rapid decrease of sway area, anterior-posterior sway, medio-lateral sway, and sway velocity within the first four seconds while older adults show elevated initial values in anterior-posterior sway and sway velocity and less decrease over time.

INTERPRETATION

Older adults have not only diminished initial sway, but also less ability to control sway during the initial phase of single leg stance. The early phase of single leg stance is rather dynamic in older adults compared to younger adults who maintain their balance after three seconds with small adjustments.

Ankle muscle strength discriminates fallers from non-fallers

It is well known that center of pressure (CoP) displacement correlates negatively with the maximal isometric torque (MIT) of ankle muscles. This relationship has never been investigated in elderly fallers (EF). The purpose of this study was thus to analyze the relationship between the MIT of ankle muscles and CoP displacement in upright stance in a sample aged between 18 and 90 years old that included EF. The aim was to identify a threshold of torque below which balance is compromised. The MIT of Plantar flexors (PFs) and dorsal flexors (DFs) and CoP were measured in 90 volunteers: 21 healthy young adults (YA) (age: 24.1 ± 5.0), 12 healthy middle-aged adults (MAA) (age: 50.2 ± 4.5), 27 healthy elderly non-fallers (ENF) (age: 75.5 ± 7.0) and 30 EF (age: 78.8 ± 6.7). The MIT of PF and DF were summed to obtain the overall maximal ankle muscle strength. Body weight and height were used to normalize MIT (nMIT) and CoP (nCoP), respectively. nCoP correlated negatively with nMIT. 90% of EF generated an nMIT <3.1 N·m·kg⁻¹, whereas 85% of non-fallers generated an nMIT >3.1 N·m·kg⁻¹. The relationship between nMIT and nCoP implies that ankle muscle weakness contributes to increased postural instability and the risk of falling. We observed that below the threshold of 3.1 N·m·kg⁻¹, postural stability was dramatically diminished and balance was compromised. Our results suggest that measuring ankle torque could be used in routine clinical practice to identify potential fallers.

Alterations in postural control during the world's most challenging mountain ultra-marathon

We investigated postural control (PC) effects of a mountain ultra-marathon (MUM): a 330-km trail run with 24000 m of positive and negative change in elevation. PC was assessed prior to (PRE), during (MID) and after (POST) the MUM in experienced ultra-marathon runners (n = 18; finish time = 126 ± 16 h) and in a control group (n = 8) with a similar level of sleep deprivation. Subjects were instructed to stand upright on a posturographic platform over a period of 51.2 seconds using a double-leg stance under two test conditions: eyes open (EO) and eyes closed (EC). Traditional measures of postural stability (center of pressure trajectory analysis) and stabilogram-diffusion analysis (SDA) parameters were analysed. For the SDA, a significantly greater short-term effective diffusion was found at POST compared with PRE in the medio-lateral (ML; Dxs) and antero-posterior (AP) directions (Dys) in runners (p<0.05) The critical time interval (Ctx) in the ML direction was significantly higher at MID (p<0.001) and POST (p<0.05) than at PRE in runners. At MID (p<0.001) and POST (p<0.05), there was a significant difference between the two groups. The critical displacement (Cdx) in the ML was significantly higher at MID and at POST (p<0.001) compared with PRE for runners. A significant difference in Cdx was observed between groups in EO at MID (p<0.05) and POST (p<0.005) in the ML direction and in EC at POST in the ML and AP directions (p<0.05). Our findings revealed significant effects of fatigue on PC in runners, including, a significant increase in Ctx (critical time in ML plan) in EO and EC conditions. Thus, runners take longer to stabilise their body at POST than at MID. It is likely that the mountainous characteristics of MUM (unstable ground, primarily uphill/downhill running, and altitude) increase this fatigue, leading to difficulty in maintaining balance.

Changes in posture associated with postural control impairment induced by ankle plantarflexor fatigue during unipedal quiet standing

The aim of the present study was to investigate changes in joint angles and limb positions accompanying postural control impairments induced by fatigue of the ankle plantarflexor muscles and vision removal. Thirteen subjects performed unipedal standing tasks with and without vision before and after isometric fatigue of the plantarflexor muscles. Results indicated that to compensate for the negative effects of fatigue and vision removal on postural control, participants increased flexion at the ankle, knee and back while the free lower limb and the pelvis moved backward and the upper limbs forward. These strategies could be performed to increase the role of non-fatigued muscles and optimize the use of all the joints implicated in unipedal standing.