Effects of general and local fatigue on postural control: A review

Postural Control and Stress Exposure in Young Men: Changes in Cortisol Awakening Response and Blood Lactate

BACKGROUND

It has recently been noticed that the quantity of stress affects postural stability in young women. The study was conducted with the goal of investigating whether increased stress may damagingly effect posture control in 90 young men (71 right-handed and 19 left-handed) while maintaining an upright bipedal posture, while keeping their eyes open or closed. Perceived Stress Scale (PSS) was administered and changes in free cortisol levels were monitored (Cortisol Awakening Response, CAR) in order to evaluate the amount of stress present during awakening, while the Profile of Mood States (POMS) was used to estimate distress on the whole. Posture control was evaluated with the use of a force platform, which, while computing a confidence ellipse area of 95%, was engaged by the Center of Pressure through five stability stations and was sustained for a minimum of 52 s, with and without visual input. Another goal of the experiment was to find out whether or not cortisol increases in CAR were linked with rises of blood lactate levels.

RESULTS

CAR, PSS and POMS were found to be extensively related. Furthermore, it has been observed that increases in salivary cortisol in CAR are associated with small but significant increases in blood lactate levels. As expected, stress levels did affect postural stability.

CONCLUSIONS

The results of the present study confirm that the level of stress can influence postural stability, and that this influence is principally obvious when visual information is not used in postural control.

Physical or Cognitive Exertion Does Not Influence Cortical Movement Preparation for Rapid Arm Movements

The contribution of central factors to movement preparation (e.g., the contingent negative variation [CNV]) and the influence of fatigue on such factors are still unclear, even though executive cognitive functions are regarded as key elements in motor control. Therefore, this study examined CNV amplitude with electroencephalography in 22 healthy humans during a rapid arm movement task prior to and following three experimental conditions: (a) a no exertion/control condition, (b) a physical exertion, and (c) a cognitive exertion. CNV amplitude was affected neither by a single bout of physical/cognitive exertion nor by the control condition. Furthermore, no time-on-task effects of the rapid arm movement task on the CNV were found. Exertion did not affect cortical movement preparation, which is in contrast to previous findings regarding time-on-task effects of exertion on CNV. Based on the current findings, the rapid arm movement task is deemed suitable to measure cortical movement preparation, without being affected by learning effects and physical/cognitive exertion.

Effects of Aerobic and Anaerobic Fatigue Exercises on Postural Control and Recovery Time in Female Soccer Players

Sixteen female soccer players (age = 20.19 ± 1.52 years; body mass = 56.52 ± 4.95 kg; body height = 164.81 ± 4.21 cm) with no history of lower extremity injury participated in the study. The Biodex SD Balance system was used to determine the non-dominant single-leg stability. In anaerobic exercise, each subject performed four maximal cycling efforts against a resistance equivalent to 0.075 kg/body mass for 30 s with three-minute rest intervals. In aerobic exercise, subjects performed the Bruce protocol on a motorized treadmill. After each exercise, subjects subsequently performed a single-leg stability test and then repeated the same test for four times with five-minute passive rest periods. In accordance with the results, it was found that the impairment observed right after the aerobic loading was higher (p < 0.001) compared to the anaerobic one. However, the time-related deterioration in both aerobic and anaerobic loadings was similar. The B-pre value was lower than B_post and B₅ (p < 0.01) and B₁₀ (p < 0.05) in both conditions. Subjects could reach the initial balance level at B₁₅ after aerobic and anaerobic loadings. The lactate level did not reach resting value even after 20 min of both fatigue protocols. Although the fatigue after aerobic and aerobic exercise negatively affects a single-leg dynamic balance level, single leg balance ability returns to the baseline status after 10 min of passive recovery duration.

Fatigue effects on the viscoelastic behavior of men and women in a landing task: a Mass-Spring-Damper modeling approach

The aim of this study was to compare the fatigue effect on the viscoelastic behavior of the musculoskeletal system between the two sexes in a landing task. Stiffness and shock absorption capacity were studied from ground reaction force data using a mass-spring-damper model. A parametric simulation was also performed to demonstrate the effect of different values of model parameters on the vertical ground reaction force. Following fatigue, the shock absorption capacity reduced in men. According to the parametric simulation, this reduction can result in lower rate of force development which may make men less susceptible to impact injuries than women.

The effects of general fatigue induced by incremental exercise test and active recovery modes on energy cost, gait variability and stability in male soccer players

The aerobic endurance is considered an important physiological capacity of soccer players which is examined by Incremental Exercise Test (IET). However, it is not clear how general fatigue induced by IET influences physiological and biomechanical gait features in soccer players and how players recover optimally at post-IET. Here, the effect of general fatigue induced by IET on energy cost, gait variability and stability in soccer players was investigated. To identify an optimal recovery mode, the effect of walking at Preferred Walking Speed (PWS), running at Individual Ventilation Threshold (IVT) (two active recovery modes), and Rest (a passive recovery mode) on aforementioned features were studied. Nine male players walked 4-min at PWS on a treadmill prior IET (PreT), which was followed by four 4-min walking trials (PosT-0, 1, 2, and 3) with three 4-min recovery intervals (PWS, IVT, or Rest) between them, in three sessions (one for each recovery mode) in a random order. Energy cost, gait variability and stability were examined at PreT (baseline), and at PosT-0, 1, 2, and 3 (intervals of respectively 0-4, 8-12, 16-20, 24-28 min at post-IET). Gait variability was assessed by the standard deviation of trunk angle and gait stability was assessed by the local dynamic stability of trunk angular velocity. Gait stability was not affected by IET, despite increases in gait variability and energy cost. Different from IVT, PWS and Rest recovery modes reduced energy cost at post-IET. Gait variability and energy cost recovered at PosT-1 and PosT-2, suggesting that 8-12 and 16-20 min recovery intervals, respectively, were required for returning to their baselines. No preference for active over passive recovery was found in terms of gait variability and energy cost.

Cross-Education Related to the Ipsilateral Limb Activity on Monopedal Postural Control of the Contralateral Limb: A Review

Cross-education is the effect whereby the ipsilateral limb training generates contralateral effects as part of motor tasks requiring strength and skills. However, it is not yet known if cross-education applies to postural control which could be essential as part of human motricity. Hence, this review addresses the possible effects of acute and chronic unilateral exercises (i.e., fatiguing exercises and regularly repeated/training exercises, respectively) on the contralateral monopedal postural control. Evidence suggests that fatiguing exercises disturb the contralateral monopedal postural control. This disturbance emanates from spinal and supra-spinal alterations which provokes changes to the motor function of the contralateral limb and degrades its postural control. Unilateral training produces cross-education related to postural control, especially when it includes balance exercises, but this remains to be tested when it includes resistance exercises. Mechanistic explanations are proposed to explain how neurophysiological changes operate in the disturbance or improvement of the contralateral monopedal postural control after unilateral fatiguing exercises or training exercises (respectively) of the lower-limb.

Bilateral Asymmetries Assessment in Elite and Sub-Elite Male Futsal Players

This study aimed to investigate morphological, functional, and neuromuscular asymmetries on futsal players’ lower limbs at different competitive levels. Sixteen male elite futsal players from the Spanish National Futsal League and thirteen male sub-elite futsal players from the third division participated in this study. Morphological asymmetry was assessed through bioelectrical impedance (fat-mass (g and %) and lean-mass (g)). Functional asymmetry was assessed by means of a 20-s static unipedal balance test. Finally, neuromuscular asymmetry was assessed using tensiomiography tests on both the rectus femoris (RF) and biceps femoris (BF) of each participant. The three tests conducted did not reveal significant bilateral asymmetries in elite players. On the other hand, sub-elite players showed significant bilateral asymmetry in fat-mass percentage between dominant and non-dominant limbs (+6%; CI95%: 1 to 11; ES: 0.88; p = 0.019). They also showed higher bilateral asymmetry in the delay time of the RF (+13%; CI95%: 7 to 21; ES: 1.3; p < 0.05). However, the static unipedal balance test (p > 0.05) did not evidence asymmetries regardless of the level of the participants. Elite futsal players do not develop bilateral asymmetries in lower limbs in the studied parameters. On the contrary, sub-elite players are likely to develop morphological and neuromuscular asymmetries between their dominant leg and non-dominant leg.

Lower limb muscle fatigability is not associated with changes in movement strategies for balance control in the upright stance

BACKGROUND

Fatigue is a distressing symptom inversely related to postural stability in adults with neuromuscular and systemic diseases. However, there is no information about the effects of lower limb muscles fatigability on the movement strategies for balance control in the upright standing.

METHODS

This study enrolled 41 healthy subjects (female/male: 22/19; age 23 ± 3 years; body mass index 25.4 ± 3.7 kg/m²). Participants underwent posturography and surface electromyography of the gastrocnemius medialis muscle during a sustained, fatiguing voluntary contraction of the gastrocnemius preceded and followed by quiet standing (120 s). Amplitude of electromyograms and fatigability were evaluated using the root mean square (RMS) value and both the RMS and spectral median frequency (f_med) slopes. Balance control was evaluated using the center-of-pressure elliptic area (Area) and average velocity (Vavg). Movement strategies for balance control were evaluated using the number of high-density regions (nHDR) and spatial patterns of the three-dimensional statokinesigram.

RESULTS

Mean time to muscle fatigability was 258 ± 190 s. Area and Vavg but not nHDR increased after the fatiguing task. Single-centered spatial patterns were predominant in both tasks (pre-fatigue: n = 22/41; post-fatigue: n = 19/41), with no evidence of an association between the spatial patterns and tasks (γ = 0.237, 95%CI = [-0.338; 0.542]).

CONCLUSIONS

Lower limb muscle fatigability increases postural instability, but it is not associated with changes in movement strategies for balance control in the upright stance.

The rapid recovery of vertical force propulsion production and postural sway after a specific fatigue protocol in female handball athletes

BACKGROUND

Muscle fatigue is characterized by a decrease in muscle performance, accompanied by an increase in perceived exertion to produce a desired amount of force. The duration of the fatigue effects is not completely clear regarding postural sway and force production in athletes.

RESEARCH QUESTION

What is the effect of a specific fatigue protocol in postural sway and force production in female handball athletes and the recovery time necessary for these variables?

METHODS

Twenty female handball athletes participated in this study. Specific handball actions composed the fatigue protocol in the format of a circuit with the gradual increment of laps. They stood upright in one-leg posture on a force plate. For the maximum propulsion force (FMAX), they performed a countermovement jump on the force plate. The center of pressure (COP) and the FMAX were obtained at baseline, immediately after the exhaustion due to the fatigue protocol and every minute during the first 10 min of the recovery phase.

RESULTS

The FMAX decreased ∼9.5% after the fatigue protocol, whereas de COP area increased 224%. During the recovery phase, the FMAX and the COP area returned to baseline values after five minutes.

SIGNIFICANCE

The first five minutes immediately after the fatigue protocol represent the time interval where the fatigue effects are still present. Future studies willing to investigate the effects of fatigue in athletes should perform the analysis within this short time-window.

Effects of mental and physical orofacial training on pressure pain sensitivity and tongue strength: A single-blind randomized controlled trial

OBJECTIVES

The main objective of this study was to analyze differences on pain pressure thresholds, tongue strength and perceived effort between various orofacial motor exercise training dosages of mental representation training through motor imagery (MI) and action observation (AO), first in isolation and then in combination with real exercise performance.

METHODS

A single-blind randomized controlled trial was designed. 48 asymptomatic individuals were randomized into two groups: Intensive training group (IG) and Moderate training group (MG). Both groups performed a first session of MI and AO of orofacial exercises training and a second session of actual orofacial exercises combined with mental representation training, but with different dosage in terms of series and repetitions. Pain pressure thresholds (PPTs) in the masseter and temporal muscles and tongue muscle strength were the main variables.

RESULTS

Regarding the PPT, ANOVA revealed significant between-group differences, where MG showed a significantly higher PPT than IG at post-day2, with a medium effect size. Both groups showed with-in group differences between pre and post intervention measures in the first session, but only the IG showed differences in the second. Regarding tongue muscle strength, ANOVA revealed significant within-group differences only in MG between the pre-day and post-day first intervention.

CONCLUSION

The results of the present study suggest that movement representation training performed in isolation may have a positive effect on PPTs and tongue muscle strength. In addition, the combination with the actual execution of the exercises could be considered effective, but it is necessary to take into account the training dosage to avoid fatigue responses.

Shoes with active insoles mitigate declines in balance after fatigue

Fatigue can induce postural instability and even lead to falls. However, most current methods to delay or reduce fatigue require long preparatory time, or large and expensive equipment. We propose a convenient method to alleviate postural instability due to fatigue. We paid attention to that fatigue and aging share similar neurophysiological deterioration of sensory-motor function. Considering that stochastic resonance via sub-sensory mechanical vibration increases postural stability in the elderly, we propose that sub-sensory insole vibration reduces the negative effect of fatigue on postural control. We performed experiments with 21 young and healthy adult participants, and demonstrated that insole vibration compensates for the loss of balance ability due to fatigue. The sub-sensory insole vibration restored both the area of center of pressure and the complexity of the time series of the motor output after fatigue to the pre-fatigue levels. The insole units generating the vibration were completely concealed in shoes and controlled by a smart phone. This compact implementation contrasts with the cumbersome procedure of current solutions to fatigue-induced postural instability.

Effects of Soccer Training on Body Balance in Young Female Athletes Assessed Using Computerized Dynamic Posturography

The aim of this study was to determine the effect of regular soccer training on the balance system for young women. Computerized dynamic posturography of female footballers (n = 25) and control group (n = 50) was assessed during three tests: Sensory Organization Test, Motor Control Test, and Adaptation Test. Statistically significant differences between the groups was found in Composite Equilibrium Score with higher values, indicating better postural stability, for footballers. Regular trainees also showed better usefulness of vestibular system while maintaining balance. Weight symmetry of the lower limbs during Motor Control Test also showed statistically significant differences between the groups. This study shows that female footballers have better postural stability than their inactive peers and that regular workouts may improve the balance system.

The Influence of Dental Occlusion on Dynamic Balance and Muscular Tone

Excellent postural control is essential to improve the physical performance of athletes. Stability of the body during motor tasks depends on different physiological systems. The influence of dental occlusion on body balance has been widely investigated in the past few years. It has been suggested that this relationship is strengthened by disturbing environments for balance control (i.e., unstable platform, fatigue, development tasks.). Moreover, dental occlusion may influence the muscle tone of both masticatory and postural muscles, which are involved in the preservation of balance. Therefore, we attempted to determine whether (i) there are differences in dynamic balance assessed by the modified star excursion balance test between opposed dental occlusion conditions (dental contact: intercuspal position/no dental contact: cotton rolls mandibular position) and (ii) dental occlusion influences the biomechanical and viscoelastic properties of the masticatory and postural muscles assessed with MyotonPRO^®. Thirty physically active subjects were recruited for the study. The main findings were the following: (i) the Star Excursion Balance Test composite score was significantly higher for measurements made in cotton rolls mandibular position (p < 0.001) and also in subjects showing a correct occlusion (p = 0.04), and (ii) the biomechanic and viscolelastic properties of selected muscles showed different trend according to the presence of malocclusal traits. It is concluded that dental occlusion conditioned both dynamic stability and the biomechanic and viscoelastic properties of the analyzed muscles.

The fatigue-induced alteration in postural control is larger in hypobaric than in normobaric hypoxia

To test the hypothesis that postural control would be more affected by plantar flexors fatigue during acute exposure in hypobaric (HH) than in normobaric (NH) hypoxia or normobaric normoxia (NN). Twelve young male adults performed in a random order three experimental sessions (in HH and NH (F_iO₂ 0.139) at an altitude of 2950 m, and in NN at 500 m) composed of a bipedal postural control with eyes open on a posturographic platform before and after a plantar flexors fatiguing protocol. Center of pressure (CoP) trajectory and stabilogramm diffusion analyses (SDA) parameters were assessed. A two-way repeated measures analysis of variance was used to identify differences by examination of the group and time interaction. Surface of CoP trajectory analysis, increased at POST in HH (p < 0.001) and in NH (p < 0.01) compared to NN. SDA confirmed that PC was more altered in HH than in NH (p < 0.001) and NN (p < 0.05) at POST. The plantar flexor fatigue-induced alteration in postural control increased to a larger extent in HH than in NH or NN, suggesting an alleviating influence of the decreased barometric pressure per se and a mechanical influence of the higher breathing frequency in HH.

Effects of experimentally induced fatigue on healthy older adults' gait: A systematic review

Introduction

While fatigue is ubiquitous in old age and visibly interferes with mobility, studies have not yet examined the effects of self-reported fatigue on healthy older adults’ gait. As a model that simulates this daily phenomenon, we systematically reviewed eleven studies that compared the effects of experimentally induced muscle and mental performance fatigability on gait kinematics, variability, kinetics, and muscle activity in healthy older adults.

Methods

We searched for studies in databases (PubMed and Web of Science) using Fatigue, Gait, and Clinical conditions as the main terms and extracted the data only from studies that experimentally induced fatigue by sustained muscle or mental activities in healthy older adults.

Results

Eleven studies were included. After muscle performance fatigability, six of nine studies observed increases in stride length, width, gait velocity (Effect Size [ES] range: 0.30 to 1.22), inter-stride trunk acceleration variability (ES: 2.06), and ankle muscle coactivation during gait (ES: 0.59, n = 1 study). After sustained mental activity, the coefficient of variation of stride outcomes increased (ES: 0.59 to 0.67, n = 1 study) during dual-task but not single-task walking.

Conclusion

Muscle performance fatigability affects spatial and temporal features of gait and, mainly, inter-stride trunk acceleration variability. In contrast, sustained mental activity tends only to affect step variability during dual tasking. A critical and immediate step for future studies is to determine the effects of self-reported fatigue on gait biomechanics and variability in healthy older adults to verify the viability of experimentally induced fatigue as a model for the study of gait adaptability in old age.

Instantaneous interjoint rescaling and adaptation to balance perturbation under muscular fatigue

Adaptation of automatic postural responses (APR) to balance perturbations might be thought to be impaired by muscle fatigue, given the associated proprioceptive and effector deficits. In this investigation, we aimed to evaluate the effect of muscular fatigue on APR adaptation over repetitive balance perturbations through support base backward translations. APR adaptation was evaluated in three epochs: (a) pre-fatigue; (b) post-fatigue, immediately following fatigue of the plantiflexor muscles through isometric contractions and (c) post-recovery, 30 min after the end of fatiguing activity. Results showed the following: (a) Decreasing amplitudes of joints' maximum excursion over repetitive perturbations in the three fatigue-related epochs. (b) Modulation of joints' excursion was observed in the first trial in the post-fatigue epoch. (c) In the post-fatigue epoch, we found interjoint rescaling, with greater amplitude of hip rotation associated with reduced amplitude of ankles' rotation. (d) Amplitudes of ankles' rotation were similar between the post-fatigue and post-recovery epochs. These findings lead to the conclusions that adaptation of automatic postural responses over repetitive trials was effective under focal muscular fatigue; modulation of the postural response took place in the first perturbation under fatigue, and generalization of response characteristics from post-fatigue to post-recovery suggests that feedforward processes in APRs generation are affected by the recent history of postural responses to stance perturbations.

Influence of Running Phases on the Postural Balance of Modern Pentathlon Athletes in a Laser Run Event

Background: The Laser Run combined event is part of the modern pentathlon, consisting of successive shooting and running phases. The main factor hindering accurate and fast shooting is the increasing fatigue caused by running effort. The aim of this study was to assess the impact of the running phases on the postural balance in the shooting position of pentathletes in a Laser Run event. Methods: 25 modern pentathletes (18.6 ± 1.7 years), members of the Polish Association of Modern Pentathlon, completed a Laser Run event. During each shooting series, a Zebris dynamometric platform recorded the displacement of the centre of pressure (COP). Results: Significant changes in the average velocity of the COP (F = 3.43; p = 0.0223) and the width of the ellipse of the COP shifts area WoE (F = 3.30; p = 0.0259) between the first and the second shooting series were observed. The average velocity of the COP in series I was 72.6 m/s and increased to 84.3 m/s in series II. In turn, the average width of the ellipse of the COP in series I reached 29.1 mm and in series II, 34.1 mm. Conclusions: The fatigue caused by the running phases in the Laser Run affects the stability of the shooting position of pentathletes. Disturbances that occur after the first running phase are maintained at the same level during the subsequent shooting series. The fatigue level does not affect the magnitude of the disturbances of the postural balance in the shooting position.

Reweighting of the sensory inputs for postural control in patients with cervical spondylotic myelopathy after surgery

Background

Cervical spondylotic myelopathy (CSM) is a degenerative cervical disease in which the spinal cord is compressed. Patients with CSM experience balance disturbance because of impaired proprioception. The weighting of the sensory inputs for postural control in patients with CSM is unclear. Therefore, this study investigated the weighting of sensory systems in patients with CSM.

Method

Twenty-four individuals with CSM (CSM group) and 24 age-matched healthy adults (healthy control group) were analyzed in this observational study. The functional outcomes (modified Japanese Orthopaedic Association Scale [mJOA], Japanese Orthopaedic Association Cervical Myelopathy Questionnaire [JOACMEQ], Nurick scale) and static balance (eyes-open and eyes-closed conditions) were assessed for individuals with CSM before surgery, 3 and 6 months after surgery. Time-domain and time–frequency-domain variables of the center of pressure (COP) were analyzed to examine the weighting of the sensory systems.

Results

In the CSM group, lower extremity function of mJOA and Nurick scale significantly improved 3 and 6 months after surgery. Before surgery, the COP mean velocity and total energy were significantly higher in the CSM group than in the control group for both vision conditions. Compared with the control group, the CSM group exhibited lower energy content in the moderate-frequency band (i.e., proprioception) and higher energy content in the low-frequency band (i.e., cerebellar, vestibular, and visual systems) under the eyes-open condition. The COP mean velocity of the CSM group significantly decreased 3 months after surgery. The energy content in the low-frequency band (i.e., visual and vestibular systems) of the CSM group was closed to that of the control group 6 months after surgery under the eyes-open condition.

Conclusion

Before surgery, the patients with CSM may have had compensatory sensory weighting for postural control, with decreased weighting on proprioception and increased weighting on the other three sensory inputs. After surgery, the postural control of the patients with CSM improved, with decreased compensation for the proprioceptive system from the visual and vestibular inputs. However, the improvement remained insufficient because the patients with CSM still had lower weighting on proprioception than the healthy adults did. Therefore, patients with CSM may require balance training and posture education after surgery.

Trial registration

Trial Registration number: NCT03396055

Name of the registry: ClinicalTrials.gov

Date of registration: January 10, 2018 - Retrospectively registered

Date of enrolment of the first participant to the trial: October 19, 2015

The effect of trunk muscle fatigue on postural control of upright stance: A systematic review

BACKGROUND

Fatigability and postural control deficits are both serious concerns in a variety of chronic musculoskeletal conditions. Research has shown that muscle fatigue may adversely affect postural control. This is while the evidence on the relevance of fatigue to postural control has never been summarized nor critically appraised.

RESEARCH QUESTION

Is there sufficient and strong enough evidence to accept trunk muscle fatigue as a contributing factor to postural control alterations during upright standing posture?.

METHODS

EMBASE, Scopus, ELSEVIER, PubMed, ProQuest, Google scholar and reference lists of the relevant articles were searched through April 2018. Studies having investigated the trunk muscle fatigue effect on postural control in asymptomatic individuals were included in the study. Only those studies having assessed postural control in terms of center of pressure driven variables were included.

RESULTS

Twelve studies (218 asymptomatic participants) matched the inclusion criteria of this systematic review. Their results supported the hypothesis that fatigue has a significant effect on postural control in terms of the time domain variables. Sway velocity was consistently found to be affected by fatigue. The results were inconsistent in the frequency domain. The only study on the structural dynamics of center of pressure displacements also confirmed such a relationship.

SIGNIFICANCE

The present review indicates that postural control is altered in asymptomatic individuals following trunk muscle fatigue. This may suggest that trunk muscle endurance training is crucial to address postural impairment in chronic spine musculoskeletal conditions.

Feasibility of Ski Mountaineering for Patients Following a Total Knee Arthroplasty: A Descriptive Field Study

Background: Total knee arthroplasty (TKA) is socially relevant due to its high prevalence, high incidence and the affected population. A subpopulation of TKA patients exists that strives to be active and also return to sports after total joint replacement. In this context, a further group of TKA patients is interested in high-impact physical activities and want to proceed with such activities even after surgery. Focusing on winter sports, there is still a lack of evidence on whether ski mountaineering is feasible for this subgroup of patients. Therefore, this feasibility study examines the effects of moderate ski mountaineering on strength, balance, functional abilities and mental health in persons following a TKA. Methods: Eight patients (six males, two females; median age, 63 ± Interquartile range 9 years) with TKA were included in this study. The volunteers, who were pre-selected for a 7-day holiday in Sankt Johann (Tyrol, Austria), participated in five guided ski mountaineering tours. Statistical analyses of non-parametric longitudinal data were performed using analysis of variance. For gait parameters and the Feeling Scale, one-factor longitudinal models were used. Statistical significance was set at the level of p < 0.05. Results: A significant decrease in the S3-Check MFT stability index (p = 0.04), a significant increase in general well-being (p = 0.05), and a trend towards a decrease in general stress (p = 0.1) were detected, while all other parameters were unaffected. Conclusion: A 7-day recreational ski mountaineering holiday had no negative effects on ski-experienced patients with TKA and seemed to increase well-being. Further studies should focus on larger groups and use controlled designs. Additionally, long-term effects should be evaluated.

Monitoring residual 36 h post-match neuromuscular fatigue in rugby union; a role for postural control?

The present study investigated single-leg balance and landing measures, respectively, at the beginning of a weekly micro-cycle 36 h after a match compared to 48 h rest without any match load. Twenty-seven professional rugby union players performed balance and landing tests on a 1000 Hz force plate across three in-season micro-cycles either with or without match loads in the prior 36 h. Participants were further sub-divided into higher and lower match load groups to investigate changes in balance and landing variables. Differences between rested and 36 h post-match single-leg balance sway velocity were trivial in all cases, except for the higher-load group on the dominant leg, which were possibly impaired 36 h post-match (ES ± 90% CL = 0.68 ± 0.66). Differences between rested and 36 h post-match single-leg landing measures of relative impulse on the non-dominant leg were possibly lower (0.36 ± 0.34), with possible impairment observed on both legs in the higher load group 36 h post-match (0.39 ± 0.33; 0.49 ± 0.42). Differences in landing measures of peak force and time to stabilisation were mainly trivial (ES < 0.20). Postural control measures at 36 h post-match are comparable to a rested state; though impairment of sway velocity on the dominant leg and landing impulse may indicate residual neuromuscular fatigue resulting from increased match exposure.

Evaluation of 18-Week Whole-Body Vibration Training in Normobaric Hypoxia on Lower Extremity Muscle Strength in an Elderly Population

Therapeutic benefits of hypoxic training have been suggested for clinical populations, such as elderly who could suffer loss of lower limb muscle strength and higher risk of falling. This study investigated the effects of 18 weeks of whole-body vibration (WBV) training in normobaric hypoxia on the strength parameters of an elderly population. Thirty-one healthy elderly participants were randomly assigned to a hypoxic whole-body vibration group (HWBV; n = 10), normoxic whole-body vibration group (NWBV; n = 11), or control group (n = 10). The experimental groups received the same vibration treatment in a hypoxia chamber (HWBV: 16.1% fraction of inspired oxygen [FiO₂]; NWBV: 21.0% FiO₂). Isokinetic leg muscle strength was evaluated using a Biodex System-3 isokinetic dynamometer. Body composition was obtained with dual-energy X-ray absorptiometry. There were no significant differences between groups in either strength or body composition parameters. The NWBV group showed statistically significant improvements in the maximal strength of knee extensors, with a small effect size (p = 0.004; d = 0.54). No significant differences were found in any variable of the HWBV group. The combination of WBV training and exposure to normobaric cyclic hypoxia carried out in the present study did not have an effect on strength parameters in healthy elderly subjects.

Postural balance and rifle stability in a standing shooting position after specific physical effort in biathletes

The aim of the study was to evaluate the effect of maximal specific physical effort on postural balance and rifle stability in biathletes in a standing shooting position. The study included 10 junior elite biathletes. The measurements were taken with the Vicon system and AMTI force platform. Postural balance and rifle stability characteristics were determined at rest as well as 1 and 5 min post maximal specific physical effort which was performed on a ski ergometer and continued until exhaustion. Maximal physical effort exerted a significant effect on all examined postural sway and rifle sway characteristics. The duration of the post-exercise changes was longer than 5 minutes. Higher post-effort rifle sway was observed in the vertical direction than in the across the shooting line direction. Post-effort postural balance impairment in the shooting line was much greater than in the across the shooting line direction. Moreover, a strong correlation was found between postural balance and rifle stability. Maximal physical effort influenced postural balance and rifle stability during aiming. Rifle sway during aiming in a standing shooting position seems to be coordinated with the postural sway of the biathlete's body. Thus, an increase in postural sway contributes to greater sway and lesser stability of the rifle.

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.

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.

Moderate treadmill run worsened static but not dynamic postural stability of healthy individuals

PURPOSE

Running has been demonstrated to be one of the most relevant exercise in altering static postural stability, while limiting attention has been paid to its effects on dynamic postural stability. The aim of the present study was to investigate if 25 min of moderate running on a treadmill altered static and dynamic postural stability in healthy subjects.

METHODS

Eight female and six male participants (age 27.7 ± 8.3 years, height 170.9 ± 12.2 cm, weight 63.9 ± 15.6 kg) took part in the study. Before and after the run static postural stability was evaluated on a stabilometric platform (10 trials of 30 s each), while dynamic postural stability was assessed on an instrumented unstable platform (2 trials of 30 s each).

RESULTS

After the treadmill run the area of the confident ellipse (from 67.97 ± 34.56 to 93.08 ± 50.00 mm²), sway path velocity (from 6.92 ± 1.85 to 7.83 ± 2.57 mm/s), sway area velocity (from 6.88 ± 3.27 to 9.54 ± 5.36 mm²/s), and medio-lateral maximal oscillation (from 9.48 ± 2.80 to 11.44 ± 3.64 mm) significantly increased. Stabilogram diffusion analysis showed no statistically significant difference in the diffusion coefficients, both short and long term. No statistically significant differences were reported in all the parameters of the dynamic postural stability test.

CONCLUSION

The contrasting results of the static and dynamic postural stability tests raise the question of which are the more selective tests to assess the acute effect of physical exercise on postural stability among healthy individuals. The proper interaction of both static and dynamic postural evaluations could represent the next challenge in the postural stability assessment.

Postural Control Follows a Bi-Phasic Alteration Pattern During Mountain Ultra-Marathon

It is well knows that postural control (PC) is deteriorated with neuromuscular fatigue, altitude or sleep deprivation induced by a mountain ultra-marathon (MUM). Several regulatory mechanisms have also been reported during this type of event and the changes in PC at different points of MUM remain unknown. The purpose of this study was to investigate the time course of PC during an extreme MUM. We tested the hypothesis that PC alteration would not increase linearly.

Methods: 16 participants (age 45.1 ± 9.6 years) were tested bipedaly on a posturographic platform for 51.2 s with eyes open every ∼50 km. Both traditional and stabilogram diffusion analyses (SDA) were performed. A visual analog scale (VAS) was used for a subjective evaluation of global fatigue, sleep feeling and pain.

Results: The main parameters (center of pressure trajectory analysis) increased significantly (p < 0.001, d = 1.56, very large) until km 100. This was confirmed by SDA in the antero-posterior plane. Short term effective diffusion coefficient significantly increased (p < 0.001, d = 1.07, very large) as critical point (p < 0.01, d = 1.57, very large). From km 100 to 200, a different response was observed with a continuous decrease in most of the PC parameters. This was confirmed by SDA in the antero-posterior plane. Short term effective diffusion coefficient significantly increased (p < 0.001, d = 1.39, very large) as critical point (p < 0.01, d = 1.51, very large).

Conclusion: Posture alteration is progressively increased until 100 km. After this point, compensatory mechanisms appear to limit the posture degradation. This bi-phasic response is of interest for better understanding the coping with extreme fatigue.

Small Molecule Oligopeptides Isolated from Walnut (Juglans regia L.) and Their Anti-Fatigue Effects in Mice

Walnut (Juglans regia L.) is unique for its extensive biological activities and pharmaceutical properties. There are few studies on walnut oligopeptides (WOPs), which are small molecule peptides extracted from walnuts. This study aimed to evaluate the anti-fatigue effects of WOPs on ICR mice and explore the possible underlying mechanism. Mice were randomly divided into four experimental sets and each set of mice were then randomly divided into four groups. The vehicle group was administered distilled water, and the three WOP intervention groups were orally administered WOP solution at a dose of 110, 220, and 440 mg/kg of body weight, respectively. After 30 days of WOP intervention, the anti-fatigue activity of WOPs were evaluated using the weight-loaded swimming test and by measuring the change of biochemical parameters, glycogen storage and energy metabolism enzymes, anti-oxidative capacity and mitochondrial function. It was observed that WOPs could significantly prolong the swimming time, decrease the accumulation of lactate dehydrogenase (LDH), creatine kinase (CK), blood urea nitrogen (BUN) and blood lactic acid (BLA), and increased the glycogen storage of liver and gastrocnemius muscle. WOPs also markedly inhibited fatigue induced oxidative stress by increasing the activity of superoxide dismutase (SOD), glutathione peroxidase (GPX) and decreasing the content malondialdehyde (MDA). Notably, WOPs improved the activity of pyruvate kinase (PK), succinate dehydrogenase (SDH), Na+-K+-ATPase, and enhanced the mRNA expression of mitochondrial biogenesis factors and mitochondrial DNA content in skeletal muscles of mice. These results suggest that WOPs have beneficial anti-fatigue effects, which may be attributed to their positive effects on increasing glycogen storage, improving energy metabolism, inhibiting oxidative stress, enhancing mitochondrial function in skeletal muscle, and ameliorating the cell damage and the muscular injury.

Effects of Recreational Ski Mountaineering on Cumulative Muscle Fatigue - A Longitudinal Trial

Sport is known to have many positive effects on mental and physical health. High-intensity exercise is considered to decrease muscle strength and induce muscle fatigue, which is associated with a higher risk of injury. In recreational alpine skiers, a decrease of eccentric peak hamstring torque, as an indication of muscle fatigue, occurs even after 1 day of skiing. The popularity of ski mountaineering is increasing enormously, but no studies are available on its effects on muscle strength. Therefore, the present study examined the consequences of ski mountaineering on muscle fatigue of the concentric/eccentric quadriceps and/or hamstrings. In addition, a possible role of myofascial foam rolling in reducing muscle fatigue was evaluated. Fifty recreational ski mountaineers (27 males, 23 females) completed five consecutive tours of ski mountaineering within 1 week. After each day of skiing, participants underwent an isokinetic muscle test assessing the concentric and eccentric muscle strength of both thighs. One group completed an additional session of myofascial foam rolling. Right and left concentric quadriceps peak torque, left hamstrings peak torque, left eccentric quadriceps peak torque, as well as right and left hamstring peak torque, were reduced after a single day of ski mountaineering (p ≤ 0.016 for all). However, no cumulative muscle fatigue was detected and we could not demonstrate any effect of myofascial foam rolling. The results show conclusively that a single day of ski mountaineering leads to a significant decrease of concentric and eccentric quadriceps and hamstring strength. Therefore, in order to improve muscle strength for the ski mountaineering season, a physical training program including concentric and eccentric methods can be recommended.

The influence of physical exercise on the relation between the phase of cardiac cycle and shooting accuracy in biathlon

This study examined the influence of physical exercise on the relation between shooting accuracy and the phase of the cardiac cycle in which the shot is fired. Thirteen experienced biathletes (8 females, mean age 17 years) fired from the standing position at rest and right after a submaximal exercise on a bicycle ergometer. Shooting accuracy and the timing of each shot relative to the R-waves of the electrocardiogram (ECG) were recorded. Best shots (with greatest accuracy) and worst shots (with lowest accuracy) were fired prevalently in different phases of the cardiac cycle. In the rest condition, best shots were fired less frequently from 200 to 300 ms and more frequently from 500 to 600 ms after the R-wave, compared to worst shots. In the exercise condition, best shots were fired less frequently from 100 to 200 ms after the R-wave and from 20% to 30% of the R-R interval, compared to worst shots. These findings support the hypothesis that shooting accuracy is influenced by the cardiac cycle phase due to the ballistocardiac recoil generated at each heartbeat. To achieve best results athletes could be trained (e.g. through biofeedback) to fire within a specific phase of the cardiac cycle.

The influence of knee extensor fatigue on lower extremity muscle activity during chair rise in young and older adults

PURPOSE

The purpose of this investigation was to evaluate alterations in muscular effort and temporal characteristics of their activity during the sit-to-stand (STS) due to isolated fatiguing of the knee extensors, as indicated by declines in torque output.

METHODS

Surface electromyography of the lower extremity was recorded in healthy young (n = 11) and older (n = 11) adults as they ascended from a seated position, before and after dynamic knee extension exercise.

RESULTS

Knee extensor fatigue caused significant increases in soleus, gastrocnemius, and gluteus maximus relative effort (%MVC) in both age groups during the STS task. Rectus femoris %MVCs in both young and older adults significantly increased to similar extents throughout the STS movement, whereas vastus lateralis amplitudes only increased in preparation for seat-off. Muscle temporal characteristics appeared to generally be invariant with fatigue, except for earlier activation onset for the ankle musculature in older adult participants.

CONCLUSIONS

These findings demonstrate that isolated knee extension fatiguing exercise caused compensatory changes in muscle activation patterns and increased reliance of non-fatigued muscles at the ankle and hip as well as increased activity of synergist muscles during the STS. Moreover, this occurred to similar extents in older adults who had lower knee extensor strengths and greater quadriceps %MVCs in comparison to their younger counterparts, regardless of fatigue condition.

The influence of physiobiomechanical parameters, technical aspects of shooting, and psychophysiological factors on biathlon performance: A review

The biathlon, an Olympic sporting discipline that combines cross-country skiing with rifle marksmanship, entails considerable physiological demands, as well as fine motor control while shooting after intense exercise and under mental pressure. Although much of our knowledge about cross-country skiing is probably also applicable to the biathlon, carrying the rifle and shooting under stress make this discipline somewhat unique. The present review summarizes and examines the scientific literature related to biathlon performance, with a focus on physiological and biomechanical factors and shooting technique, as well as psychophysiological aspects of shooting performance. We conclude with suggestions for future research designed to extend our knowledge about the biathlon, which is presently quite limited.

Carrying heavy asymmetrical loads increases postural sway during quiet standing in older adults

Holding asymmetrical loads in the hands is common during many daily and occupational activities which, depending on the load mass, may alter postural stability. The purpose of this study was to determine the effect of load magnitude held asymmetrically in the hand on postural sway in older people. Eighteen healthy older adults (age 65.9 ± 5.7 years) were assessed in the following conditions; (1) standing without an external load (0%), (2) standing while holding a grocery bag containing 5%, (3) 10% and (4) 20% body mass in the dominant hand. The total displacement of the centre of pressure (COP) in the anteroposterior and mediolateral directions (cm), mean COP velocity (cm s^-1) and COP area (cm²) were used to indirectly assess postural sway. The COP area (R ² = 0.96), anteroposterior (R ² = 0.85) and mediolateral (R ² = 0.84) COP displacement increased linearly with additional load. The 20% load condition elicited the greatest increase in postural sway (d = 2.1-3.6) compared to 0%, while the 5% load had no effects on sway (P ≥ 0.05). In contrast, the mean COP velocity decreased by similar amounts when holding a load at 5% (d = 1.6), 10% (d = 1.4) and 20% (d = 1.5) body mass, compared to 0% (all P < 0.001). The slower COP velocity, combined with greater COP displacements may suggest that postural reactions were restricted and/or delayed. From a fall-prevention perspective, it is advised that older people avoid holding asymmetrical external loads greater than 5% of body mass.

Effects of motor fatigue on walking stability and variability during concurrent cognitive challenges

Cognitive-motor interference, a negative influence on the performance of one or both tasks, is manifested when simultaneously performing a cognitive and a motor task. Motor fatigue reduces the ability of generating a required force level. However, little is known about the effects of motor fatigue on the cognitive-motor dual-tasking performance, an important capability during our daily lives. This study investigated how motor fatigue affects dual-task walking performance. Eighteen healthy younger adults walked on a treadmill under three different conditions: walking only, walking while receiving the Paced Auditory Serial Addition Test (PASAT) or a modified Stroop test before and after a lower-extremity fatiguing exercise. We computed dynamic margins of stability (MOS), step and joint kinematic variability, and short-term local divergence exponent (LDE) of the trunk motion. We found that subjects had similar values of short-term LDE during all conditions, indicating that local stability was not affected by the motor fatigue or dual-task conditions. Compared to the baseline, subjects had significantly greater mean MOS after the fatiguing exercise by walking with greater step length and width while having significantly greater gait variability. In contrast, subjects walked with similar mean MOS but significantly less gait variability during the dual-task conditions, indicating that subjects used different adaptive strategies when walking with motor fatigue and during dual-task conditions. There were no significant differences in the number of errors for the two cognitive tests before and after the fatiguing exercise. The current findings demonstrate that motor fatigue does not affect cognitive but motor performance in younger adults.

Effect of Gastrocnemius Kinesio Taping on Countermovement Jump Performance and Vertical Stiffness Following Muscle Fatigue

Context: Kinesio tape (KT) is a widely used intervention in the fields of sports and rehabilitation. However, its effects on lower-extremity behavior during functional activities are not entirely known. Objective: To test the hypothesis that application of KT can change performance and vertical stiffness (VS) during the countermovement jump (CMJ) before and after a fatigue protocol. Design: A predesign and postdesign to study the effect of KT in 2 situations, prefatigue and postfatigue. In each fatiguing condition, there were 2 conditions with and without KT application on the gastrocnemius muscle. Setting: Biomechanics laboratory. Participants: Fifty healthy, nonathlete participants (26 females and 24 males). Interventions: KT application on the gastrocnemius muscle and a fatigue protocol to induce fatigue in plantar flexor muscles. Main Outcome Measures: Various jumping parameters, including jump height, maximum force, maximum power, rate of force development, eccentric lower-limb stiffness, and VS, were calculated using the vertical ground reaction force data. Eccentric lower-limb stiffness and VS were calculated using a mass-spring model. The studied variables can present lower-extremity elastic behavior and performance during CMJ. Results: The results of a 2-way repeated-measures analysis of variance showed no significant effect for KT application. Fatigue resulted in lower values of jump height, maximum power, and VS. Moreover, male subjects showed greater values of jump height, maximum force, and maximum power than did females. Conclusions: The main finding of this study was that gastrocnemius KT has no effect on performance or elastic behavior of the lower-extremity during CMJ. Moreover, KT cannot reduce the adverse effect of fatigue in a functional activity such as CMJ. It seems that gastrocnemius KT is not effective for demanding activities.

The Use of the Anchor System Reduces Postural Sway During Upright Standing Irrespective of Plantar Flexors Muscle Fatigue in Young and Older Adults

Our purpose was to verify the effects of the use of the anchors on postural control after the fatigue of the plantar flexor muscles in young and older adults. They stood barefoot, with their eyes closed in four conditions combining the use of the anchors and the fatigue. When using the anchors, participants held one cable in each hand and kept the cable taut without removing the loads (125 g) from the ground. The fatigue protocol consisted of performing a single series of bilateral plantar flexion movements. The fatigue protocol increased postural sway in both groups. Both groups reduced postural sway with the anchors, but this effect was independent of fatigue. We conclude that the anchors contributed to the reduction of postural sway in young and older adults, but they were unable to compensate for the disturbing effect in postural control created by fatigue of the plantar flexor muscles.