Changes in the relative contribution of each leg to the control of quiet two-legged stance following unilateral plantar-flexor muscles fatigue

Relationship between latent trigger points, lower limb asymmetry and muscle fatigue in elite short-track athletes

BACKGROUND

Short-track speed skating movement involves asymmetric overloading of the lower left side of the body. The gluteus maximus fatigue limits the physical and mental athletic capacity to perform set tasks. A possible link between the presence of latent trigger points (LTrPs) and muscle fatigue development/persistence has been posited. The aim of the study was to determine whether elite short-track speed skating can result in the impairment of the musculoskeletal system of the lower limbs.

METHODS

Elite short-track athletes as the experimental group (EXP) = 9, 19.5 ± 1.8 years, and healthy subjects as the control group (CON) = 18, 20.8 ± 1.2 years, were tested for: (i) lower limb loading asymmetry using ground reaction force (GRF) measurements during quiet standing, (ii) gluteus maximus fatigue measured with surface electromyography (sEMG) during the Biering-Sorensen test, and (iii) LTrPs presence in the 14 examined muscles of the pelvic girdle and lower limbs.

RESULTS

There were between-group differences in the number of LTrPs, with the EXP group (left lower limb (LLL) n = 18, right lower limb (RLL) n = 9) showing more LTrPs compared to the CON group (LLL n = 2, RLL n = 1), (p < 0.001), and within-group differences in the EXP group only (p < 0.001). There were also significant differences in muscle fatigue for the left side (p < 0.001) both between the groups and within the EXP group (p ≤ 0.001). The vertical ground reaction force (GRF) measurement showed a loading rate of 2% (p = 0.013) in the athletes' LLL exclusively.

CONCLUSIONS

The study confirmed an increased prevalence of LTrPs, increased muscle fatigue and left-sided limb load asymmetry in elite short-track athletes.

TRIAL REGISTRATION

The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of the Poznan University of Medical Sciences (Resolution No 110/22 of 10 March 2022).

TRIAL REGISTRATION

20/07/2022, Trial Id: ACTRN12622001016729.

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.

A smart insole system capable of identifying proper heel raise posture for chronic ankle instability rehabilitation

Heel raise is widely prescribed to patients with chronic ankle instability in order to strengthen the Peroneus Longus muscle (PL) which supports the weakened lateral collateral ligaments. While the exercise itself is intuitive, ankle orientation is of particular importance because heel raises performed with inversion do not well recruit the PL. This implies that proper execution is imperative and a means to assess heel raise training sessions is needed. In this study we present a smart insole system capable of identifying heel raise events and its corresponding rise, hold and drop phases, which allows for a more descriptive analysis. The results from our heel raise sessions, which consist of four different variants performed by five healthy subjects, suggest that medial–lateral foot pressure distribution and foot orientation are needed to differentiate heel raises performed with ankle eversion and inversion. We go further and substantiate that proper execution, detected by our system, indeed leads to increased PL activation by analyzing the electromyography signals. We believe that the proposed system may provide clinicians with invaluable information regarding onsite as well as at-home training and possibly, with biofeedback, serve as foundation for software as a medical device.

Effects of unilateral and bilateral lower extremity fatiguing exercises on postural control during quiet stance and self-initiated perturbation

Postural control can be more difficult during muscle fatigue. Anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs) are the two main postural strategies controlled by the central nervous system. Unchanged or early anticipatory onset together with altered activation magnitude during the APAs phase is observed in the trunk and thigh muscles following unilateral and bilateral fatiguing exercises. Thus far, no studies have compared the effect of such exercises on APAs and CPAs. This study compared the effects of these exercises performed at the same relative workload on center of pressure (COP)-based postural stability measures during quiet stance and electromyography (EMG)-based APAs and CPAs during self-initiated perturbation. Fifteen young male subjects completed the two separated fatiguing sessions; 50% of maximal voluntary contraction force obtained from the unilateral (dominant) and bilateral legs with five sets of 20 times lower limb exercise was respectively applied as unilateral and bilateral fatiguing protocols. Spatio-temporal COP parameters (sway velocity, total displacement, and envelope area) were used to evaluate postural stability, and spectral analysis was performed to estimate the distributions in COP power spectrum. EMG activities of transversus abdominis/internal oblique (TrA/IO) and lumbar multifidus (LMF) were recorded and analyzed during the APAs and CPAs phases. Increased sway velocity and total displacements occurred following both unilateral and bilateral fatiguing exercises; however, the envelope area was not affected. Further, early anticipatory onset of TrA/IO was found after bilateral than after unilateral fatiguing exercise. Co-activation index of the TrA/IO-LMF muscle pair during the CPAs phase increased following both fatiguing sessions. The results partly confirmed previously reported fatigue effects induced by unilateral and bilateral exercises on postural stability. It was observed that APAs onsets were altered differently following a unilateral or bilateral fatiguing exercise, whereas the alterations of CPAs were independent of fatigue conditions. Repetitive unilateral or bilateral fatiguing exercises in patients or athletes may differently alter the anticipatory component of postural control.

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.

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.

Compensatory control between the legs in automatic postural responses to stance perturbations under single-leg fatigue

In response to sudden perturbations of stance stability, muscles of both legs are activated for balance recovery. In conditions that one of the legs has a reduced capacity to respond, the opposite leg is predicted to compensate by responding more powerfully to restore stable upright stance. In this investigation, we aimed to evaluate between-leg compensatory control in automatic postural responses to sudden perturbations in a situation in which plantar flexor muscles of a single leg were fatigued. Young participants were evaluated in response to a series of perturbations inducing forward body sway, with a focus on activation of plantar flexor muscles: lateral and medial gastrocnemii and soleus. Muscular responses were analyzed through activation magnitude and latency of muscular activation onset. For evaluation of balance and postural stability, we also analyzed the center of pressure and upper trunk displacement and weight-bearing asymmetry between the legs. Responses were assessed in three conditions: pre-fatigue, under single-leg fatigue, and following the recovery of muscular function. Results showed (a) compensation of the non-fatigued leg through the increased magnitude of muscular activation in the first perturbation under fatigue; (b) adaptation in the non-fatigued leg over repetitive perturbations, with a progressive decrement of muscular activation over trials; and (c) maintenance of increased muscular activation of the non-fatigued leg following fatigue dissipation. These findings suggest that the central nervous system is able to modulate the descending motor drive individually for each leg's muscles apparently based on their potential contribution for the achievement of the behavioral aim of recovering stable body balance following stance perturbations.

Effect of local and general fatiguing exercises on disturbed and static postural control

This study compared the effect of local and general fatiguing exercise on disturbed and static postural control performances. Surface electromyography and center of pressure signals were respectively recorded during self-initiated perturbation test and static postural stability test from 7 young male subjects. Local fatiguing exercise was performed using intermittent isometric knee extensions at the level of 40% of maximal voluntary torques. General fatiguing exercise was implemented with rowing ergometer at a speed of 200 ± 5 m/min. Results of disturbed postural tests showed no significant change of anticipatory postural adjustment (APAs) organizations in individual muscles following both fatiguing exercises, but observed larger APAs coactivations in trunk and dorsal muscle pairs following local than general fatiguing exercise, and larger compensatory postural adjustments (CPAs) coactivation in dorsal muscle pair after both fatiguing exercises. In addition, the results of static postural tests indicated efficient static postural stability accompanying the down-weighting of visual input and the up-weighting of vestibular/somatosensory component following both fatiguing exercises. These findings evidenced a general compensation in the central nervous system in response to the neuromuscular deficiencies induced by local fatiguing exercise and put forward the function of sensory recalibration in maintaining postural stability under fatigue conditions.

Analysis of the Results of Heel-Rise Test with Sensors: A Systematic Review

Strokes are a constant concern for people and pose a major health concern. Tests that allow detection and the rehabilitation of patients have started to become more important and essential. There are several tests used by physiotherapists to speed up the recovery process of patients. This article presents a systematic review of existing studies using the Heel-Rise Test and sensors (i.e., accelerometers, gyroscopes, pressure and tilt sensors) to estimate the different levels and health statuses of individuals. It was found that the most measured parameter was related to the number of repetitions, and the maximum number of repetitions for a healthy adult is 25 repetitions. As for future work, the implementation of these methods with a simple mobile device will facilitate the different measurements on this subject.

Effects of body turn on postural sway during symmetrical and asymmetrical standing

Body sway has usually been studied during symmetrical standing while lower limbs equally contributed in upright posture. The present study aimed to examine the dynamics of body sway while turning during standing with symmetrical and asymmetrical weight distribution between the legs. Subjects performed a body turn of 30° to the right and left during quiet standing and standing with the right or left foot loaded with 70% of body weight. We found that body turn in the symmetrical posture induced weight increase on the foot contralateral to the turning direction and the common center of pressure (COP) velocity increase. Body turn in the asymmetrical posture induced further loading of the foot that was initially overloaded; also turning in the direction of the unloaded foot affects weight distribution more than turning in the direction of the overloaded foot. The posture transition from symmetrical to asymmetrical induced the common COP velocity increase and forward protraction of the unloaded foot COP. Turning in the asymmetrical posture produced further increase of the common COP velocity and further forward protraction of the unloaded foot COP. Moreover, when the left leg was unloaded this resulted not only in left leg's COP forward, but also in left leg's COP lateral protraction, and left leg's COP frontal velocity increase. These findings reveal that body position and weight distribution between the feet interact to stabilize upright posture and show the effect of footedness during turning in asymmetrical standing.

Unilateral Knee and Ankle Joint Fatigue Induce Similar Impairment to Bipedal Balance in Judo Athletes

The purpose of this study was to compare the effects of unilateral ankle fatigue versus the knee muscles with and without vision on bipedal postural control. Elite judo athletes who competed at the national level with at least 10 years of training experience, were randomised into KNEE (n = 10; 20 ± 2 years) and ANKLE (n = 9; 20 ± 3 years) groups, who performed dynamic isokinetic fatiguing contractions (force decreased to 50% of initial peak torque for three consecutive movements) of the knee flexors and extensors or ankle dorsiflexors and plantar flexors, respectively. Static bipedal postural control (French Posturology Association normative standards) with eyes open and eyes closed was examined before and immediately after the fatiguing task. Postural variables examined were the centre of pressure (CoP) sway in the medio-lateral and antero-posterior directions, total CoP area sway and CoP sway velocity. Although unilateral ankle and knee fatigue adversely affected all bipedal postural measures, with greater disturbances with eyes closed, there were no significant main group or interaction effects between KNEE and ANKLE groups. Unilateral lower limb fatigue adversely affected bipedal balance, with knee extension/flexion fatigue affecting bipedal postural control to a similar extent as unilateral ankle dorsiflexion/plantar flexion fatigue. Hence unilateral fatigue can affect subsequent bilateral performance or also have implications for rehabilitation exercise techniques. Our findings may be limited to judo athletes as other populations were not tested.

Effect of Bilateral and Unilateral Plantarflexor Muscle Fatigue on Blind Navigation Precision and Gait Parameters

The objective was to evaluate the impact of bilateral and unilateral fatigue of the plantarflexor muscles on blind navigation. Thirty-eight young adults walked 8-m without vision before fatigue (pre-fatigue), then fatigued either one or both of their plantarflexor muscles by performing isometric contractions. After each fatigue, two blind navigation trials were performed (post-fatigue trials 1 and 2). Results revealed no effect of bilateral muscle fatigue on navigation precision and gait parameters. Unilateral muscle fatigue led to longer linear distance travelled during post-fatigue trial 2 compared to pre-fatigue and to a change in angular deviation between pre- and post-fatigue. In general, results suggest that participants were able to make adaptive changes to counter muscle fatigue during blind navigation.

Exercise-induced muscle fatigue in the unaffected knee joint and its influence on postural control and lower limb kinematics in stroke patients

This study aimed to investigate the effects of exercise-induced muscle fatigue in the unaffected knee joint on postural control and kinematic changes in stroke patients. Forty participants (20 stroke patients, 20 age-matched healthy participants) were recruited. To induce fatigue, maximum voluntary isometric contractions were performed in the unaffected knee joint in a Leg Extension Rehab exercise machine using the pneumatic resistance. We measured static and dynamic balance and lower-limb kinematics during gait. Changes in postural control parameters anteroposterior sway speed and total center of pressure distance differed significantly between the stroke and control groups. In addition, changes in gait kinematic parameters knee and ankle angles of initial contact differed significantly between stroke (paretic and non-paretic) and control groups. Muscle fatigue in the unaffected knee and ankle impaired postural control and debilitates kinematic movement of ipsilateral and contralateral lower limbs, and may place the fatigued stroke patients at greater risk for falls.

Time course of the cross-over effect of fatigue on the contralateral muscle after unilateral exercise

We investigated the cross-over effect of muscle fatigue and its time course on the non-exercising contralateral limb (NEL) after unilateral fatiguing contractions of the ipsilateral exercising limb (EL). For this purpose, 15 males performed two bouts of 100-second maximal isometric knee extensions with the exercising limb, and neuromuscular function of both the EL and NEL was assessed before (PRE), after a first fatiguing exercise (MID) and after a second fatiguing exercise (POST). Maximal voluntary isometric torque production declined in the EL after the first bout of exercise (-9.6%; p<0.001) while in the NEL, the decrease occurred after the second bout of exercise (-10.6%; p<0.001). At MID, torque decline of the EL was strictly associated to an alteration of the mechanical twitch properties evoked by neurostimulation of the femoral nerve (i.e., peak twitch torque, maximal rate of twitch development). According to these markers, we suggest that peripheral fatigue occurred. At POST, after the second bout of exercise, the voluntary activation level of the knee extensor muscles was altered from PRE (-9.1%; p<0.001), indicating an overall central failure in both the EL and NEL. These findings indicate that two bouts of unilateral fatiguing exercise were needed to induce a cross-over effect of muscle fatigue on the non-exercising contralateral limb. Differential adjustments of the motor pathway (peripheral fatigue vs. central fatigue) might contribute to the respective torque decline in the EL and the NEL. Given that our unilateral fatiguing exercise induced immediate maximal torque reduction in the EL and postponed the loss of torque production in the NEL, it is also concluded that the time course of muscle fatigue differed between limbs.

Effects of unilateral knee extensor muscle fatigue induced by stimulated and voluntary contractions on postural control during bipedal stance

OBJECTIVE

This study aim was to compare the effects of unilateral knee extensor fatigue induced by electrically stimulated (ES) and voluntary (VOL) contractions on postural control during bipedal stance.

METHODS

Seventeen healthy active males (21.5±2 years) completed these two fatiguing exercises of the quadriceps femoris muscle. Both exercises were of equal duration (130 repetitions of 5 seconds, each separated by a rest period of 2 seconds) and intensity (20% isometric maximal voluntary contraction [MVC]). Both MVC and postural control were recorded using an ergometer and a force platform that registered the centre of foot pressure (COP). We analyzed the spatiotemporal COP parameters (in eyes closed condition) and the spectral power density given by the wavelet transform. Recordings were performed before (PRE condition) and after the completion of each fatiguing task (immediately: POST condition; and after a 5-minute recovery: POST 5 condition).

RESULTS

In the POST and POST 5 conditions, the ES exercise affected MVC more than the VOL exercise but the bipedal postural control was similarly deteriorated for both exercises.

CONCLUSIONS

The disturbance of the bipedal postural control after unilateral knee muscle fatigue is not only related to a reduction in muscle strength but also (especially) to an impairment of the effectiveness of sensory inputs. Unilateral knee muscle fatigue induced by ES similarly degrades the bipedal postural control as that induced by VOL, and the duration of the recovery of postural control did not differ between both fatiguing exercises.

Contribution of each leg to the control of unperturbed bipedal stance in lower limb amputees: new insights using entropy

The present study was designed to assess the relative contribution of each leg to unperturbed bipedal posture in lower limb amputees. To achieve this goal, eight unilateral traumatic trans-femoral amputees (TFA) were asked to stand as still as possible on a plantar pressure data acquisition system with their eyes closed. Four dependent variables were computed to describe the subject's postural behavior: (1) body weight distribution, (2) amplitude, (3) velocity and (4) regularity of centre of foot pressure (CoP) trajectories under the amputated (A) leg and the non-amputated (NA) leg. Results showed a larger body weight distribution applied to the NA leg than to the A leg and a more regular CoP profiles (lower sample entropy values) with greater amplitude and velocity under the NA leg than under the A leg. Taken together, these findings suggest that the NA leg and the A leg do not equally contribute to the control of unperturbed bipedal posture in TFA. The observation that TFA do actively control unperturbed bipedal posture with their NA leg could be viewed as an adaptive process to the loss of the lower leg afferents and efferents because of the unilateral lower-limb amputation. From a methodological point of view, these results demonstrate the suitability of computing bilateral CoP trajectories regularity for the assessment of lateralized postural control under pathological conditions.