The effect of fatigue and habituation on the stretch reflex of the ankle musculature

Closed-Loop Reflex Responses of the Lateral Ankle Musculature From Various Thresholds During a Lateral Ankle Sprain Perturbation

CONTEXT

Latency is a reliable temporal metric used to evaluate sensorimotor integration of the fibularis longus (FL) and fibularis brevis (FB) during lateral ankle sprain perturbations. Currently, no clinical recommendations exist to select appropriate thresholds to evaluate the closed-loop reflex response of the lateral ankle musculature. The purpose of this study was to assess threshold value on latency of the FL and FB during an unanticipated inversion perturbation that simulates the mechanism of a lateral ankle sprain.

DESIGN

Descriptive laboratory study.

METHODS

Twenty healthy adults with no history of lateral ankle sprain injury completed an unanticipated single-leg drop landing onto a 25° laterally inclined force platform from a height of 30 cm. Surface electromyography recorded muscle activity data from the FL and FB during the inversion perturbation. Latency was identified at points where muscle activity exceeded 2, 5, and 10 SD above the average muscle activity 200 milliseconds prior to foot contact, and compared across threshold value using a 1-way analysis of variance (P < .05).

RESULTS

The 2 SD threshold was significantly shorter than both 5 SD and 10 SD thresholds for the FL (P < .01) and FB (P < .01). Likewise, the 5 SD threshold was significantly shorter than the 10 SD thresholds for FL (P = .004) and FB (P = .003).

CONCLUSIONS

More sensitive thresholds results in a shorter closed-loop reflexive response compared to the more rigorous thresholds. We recommend that selection of the appropriate threshold to identify latency of the lateral ankle musculature should be based on the device used to simulate a lateral ankle sprain and the ankle inversion velocity produced during the ankle inversion perturbation.

EVALUATION OF ANKLE MOVEMENTS ON A SUDDEN INVERSION PLATFORM

ABSTRACT Introduction: Ankle sprains are frequent in sports activities and can lead to joint instability with clinical and performance consequences. Sudden ankle inversion platforms have been used to study the mechanism of ankle sprain. Objectives: To test a static platform that simulates the movement of ankle sprain (sudden inversion) in soccer players. Methods: A platform was developed to perform the sudden movement of an ankle sprain dissociated in three axes: inversion, plantar flexion, and medial rotation. A computer program was also created to read the angular velocity and the time to reach the maximum amplitude of the three axes of movement, synchronized with the platform movements. Thirty soccer players without ankle sprains were evaluated on the sudden inversion platform. Each athlete performed 10 randomly initiated tests, with five per leg. Results: There was no statistical difference in angular velocity or time to reach maximum range of motion of plantar flexion and medial rotation between the tests. During the tests, the angular velocity of the inversion increased. Conclusion: The sudden static platform evaluated the movements performed by the ankle during the sprain reliably in the 10 tests with no difference in the mechanical behavior. Level of evidence I; Therapeutic studies - Investigation of treatment outcomes.

AVALIAÇÃO DOS MOVIMENTOS DO TORNOZELO NA PLATAFORMA DE INVERSÃO SÚBITA

RESUMO Introdução: A entorse do tornozelo é frequente nas atividades esportivas, podendo levar à instabilidade articular com consequências clínicas e de desempenho. As plataformas de inversão súbita do tornozelo têm sido usadas para estudar o mecanismo de entorse do tornozelo. Objetivos: Testar uma plataforma estática que simule o movimento de entorse do tornozelo (inversão súbita) em jogadores de futebol. Métodos: A plataforma foi desenvolvida para realizar o movimento súbito da entorse de tornozelo dissociado em três eixos: inversão, flexão plantar e rotação medial. Também foi criado um programa de computador para leitura da velocidade angular e do tempo para atingir a amplitude máxima dos três eixos de movimento, sincronizados com os movimentos da plataforma. Trinta jogadores de futebol sem entorse de tornozelo foram avaliados na plataforma súbita. Cada atleta fez 10 testes, iniciados de forma aleatória, sendo cinco em cada perna. Resultados: Entre os testes, não houve diferença estatística das velocidades angulares e tempo para atingir a amplitude máxima do movimento de flexão plantar e rotação medial. Durante os testes, a velocidade angular da inversão aumentou. Conclusão: A plataforma estática súbita, avaliada em 10 tentativas, foi confiável para avaliar os movimentos executados pelo tornozelo durante a entorse, e não houve diferença de comportamento mecânico. Nível de evidência I; Estudos terapêuticos - Investigação dos resultados do tratamento.

Assessment of Fatigue and Recovery in Sport: Narrative Review

Fatigue is a phenomenon associated with decreases in both physical and cognitive performances and increases in injury occurrence. Competitive athletes are required to complete demanding training programs with high workloads to elicit the physiological and musculoskeletal adaptations plus skill acquisition necessary for performance. High workloads, especially sudden rapid increases in training loads, are associated with the occurrence of fatigue. At present, there is limited evidence elucidating the underlying mechanisms associating the fatigue generated by higher workloads and with an increase in injury risk. The multidimensional nature and manifestation of fatigue have led to differing definitions and dichotomies of the term. Consequently, a plethora of physiological, biochemical, psychological and performance markers have been proposed to measure fatigue and recovery. Those include self-reported scales, countermovement jump performance, heart rate variability, and saliva and serum biomarker analyses. The purpose of this review is to provide an overview of fatigue and recovery plus methods of assessments.

Effect of laterality and fatigue in peroneal electromechanical delay

Introduction: Extremity dominance is one of the intrinsic factors that have been identified for ankle sprains. Electromechanical delay (EMD) is an integral part of the peroneal motor response and, therefore, substantial in preventing ankle sprains. This study aimed to investigate the effect of laterality on EMD times before and after fatigue. Methods: Fifteen healthy male volunteers participated in the study. Measurements were taken with the ankle in a neutral (0°) position, and all subjects followed an isokinetic fatigue protocol. Repeated ANOVA was used for statistical analysis, and the α level was set a priori at p ≤ 0.05. Results: No significant difference was noted in EMD times between the dominant and non-dominant legs of the volunteers (p = 0.940). Fatigue caused a significant increase in EMD by 10–15 ms (p = 0.003), while the leg × fatigue interaction was not significant (p = 0.893). Conclusions: In a non-injured athlete, both ankles seem to be under the same protection of the reactive response of the peroneal muscles. Therefore, athletes should be aware that both their extremities are equally exposed to the danger of an ankle injury. Also, fatigued ankles demonstrate longer EMD times, implying that improving resistance to fatigue may add another layer of protection that has the potential to prevent ankle sprain recurrence.

Can Low-Dose of Dietary Vitamin E Supplementation Reduce Exercise-Induced Muscle Damage and Oxidative Stress? A Meta-Analysis of Randomized Controlled Trials

Vitamin E plays an important role in attenuating muscle damage caused by oxidative stress and inflammation. Despites of beneficial effects from antioxidant supplementation, effects of antioxidants on exercise-induced muscle damage are still unclear. The aim of this meta-analysis was to investigate the effects of dietary vitamin E supplementation on exercise-induced muscle damage, oxidative stress, and inflammation in randomized controlled trials (RCTs). The literature search was conducted through PubMed, Medline, Science Direct, Scopus, SPORTDiscuss, EBSCO, Google Scholar database up to February 2022. A total of 44 RCTs were selected, quality was assessed according to the Cochrane collaboration risk of bias tool (CCRBT), and they were analyzed by Revman 5.3. Dietary vitamin E supplementation had a protective effect on muscle damage represented by creatine kinase (CK; SMD −1.00, 95% CI: −1.95, −0.06) and lactate dehydrogenase (SMD −1.80, 95% CI: −3.21, −0.39). Muscle damage was more reduced when CK was measured immediately after exercise (SMD −1.89, 95% CI: −3.39, −0.39) and subjects were athletes (SMD −5.15, 95% CI: −9.92, −0.39). Especially vitamin E supplementation lower than 500 IU had more beneficial effects on exercise-induced muscle damage as measured by CK (SMD −1.94, 95% CI: −2.99, −0.89). In conclusion, dietary vitamin E supplementation lower than 500 IU could prevent exercise-induced muscle damage and had greater impact on athletes

Test-Retest reliability of the internal shoulder rotator muscles' stretch reflex in healthy men

Until now the reproducibility of the short latency stretch reflex of the internal rotator muscles of the glenohumeral joint has not been identified. Twenty-three healthy male participants performed three sets of external shoulder rotation stretches with various pre-activation levels on two different dates of measurement to assess test-retest reliability. All stretches were applied with a dynamometer acceleration of 10⁴°/s² and a velocity of 150°/s. Electromyographical response was measured via surface EMG. Reflex latencies showed a pre-activation effect (ƞ² = 0,355). ICC ranged from 0,735 to 0,909 indicating an overall "good" relative reliability. SRD 95% lay between ±7,0 to ±12,3 ms. The reflex gain showed overall poor test-retest reproducibility. The chosen methodological approach presented a suitable test protocol for shoulder muscles stretch reflex latency evaluation. A proof-of-concept study to validate the presented methodical approach in shoulder involvement including subjects with clinically relevant conditions is recommended.

Delayed peroneal muscle reaction time in male amateur footballers during a simulated prolonged football protocol

Peroneal muscle fatigue could result in ankle inversion sprain injuries. This study investigated the peroneal muscle reaction time during a simulated prolonged football protocol. Nine male footballers completed a 105-minute simulated prolonged football protocol. The peroneal muscle reaction time to an ankle inversion perturbation was measured every 15 minutes by a surface electromyography system sampling at 1000 Hz. One-way repeated ANOVA with post-hoc paired t-test showed a steady upward trend starting from 48.9 ms at baseline to 57.1 ms at the end of the first half, followed by a recovery back to 50.9 ms at the start of the second half and a further delay in the last 30 minutes to 60.2 ms at the end of the protocol. Delayed peroneal muscle reaction was found after 30 minutes of the first half and 15 minutes of the second half of a football match. The risk of ankle sprain could increase in the latter minutes in each half protocol. Thus, prevention injury training strategies should focus on these specific durations in football matches.

Delayed ankle muscle reaction time in female amateur footballers after the first 15 min of a simulated prolonged football protocol

PURPOSE

Ankle sprain injury rate is reported to be higher towards the end of a football match. Muscle fatigue may contribute to the delayed muscle reaction and subsequent injury. This study investigated the ankle muscle reaction time during a simulated, prolonged football protocol.

METHODS

Seven amateur female football players participated in a 105-min simulated, prolonged football protocol. An ankle muscle reaction test was conducted with a pair of ankle sprain simulators at a scheduled interval every 15-min. The reaction times of peroneus longus, tibialis anterior, and lateral gastrocnemius were collected using an electromyography system sampling at 1000 Hz. Repeated measures one-way multivariate analysis of variance with post-hoc paired t-tests were conducted to evaluate if the reaction time at each time point significantly differed from baseline. Statistical significance was set at p < 0.05 level.

RESULTS

Reaction times started from 40.5-47.7 ms at baseline and increased to 48.6-55.7 ms at the end. Reaction times significantly increased in all muscles after the first 15 min except for the dominant lateral gastrocnemius. Increased reaction times were seen in the non-dominant limb after 60 min for tibialis anterior, after 75 min for peroneus longus, and after 90 min for the lateral gastrocnemius.

CONCLUSIONS

Delayed reaction time of the ankle muscles were found after the first 15 min and in the final 45 min of a simulated prolonged football protocol. Strategies for injury prevention should also focus on tackling the delayed ankle muscle reaction time in the acute phase (the first 15 min), in addition to the latter minutes in the second half.

LEVEL OF EVIDENCE

Controlled laboratory study, Level V.

The influence of fatigue in evertor muscles during lateral ankle sprain

Ankle sprain in plantarflexion and inversion is one of the most common injuries occurring in daily activities and sports. Although acute symptoms may resolve quickly, many individuals have reported persistent pain and instability. Thus, understanding the factors that contribute to the occurrence of this type of injury is extremely important. Although sprains are multifactorial, a relationship can be established between sprain and fatigue. Therefore, the present study examined the latency and intensity of activation of the peroneus longus and brevis muscles under conditions of fatigue. Twenty-three women participated in the study, including 12 with functional instability of the ankle and 11 without a history of sprain. To induce fatigue, the volunteers maintained the force of eversion and plantarflexion at 70% of the maximum voluntary isometric contraction for as long as possible until a 10% decline in the rated force occurred. Ten simulations of ankle sprains were performed before and after fatigue at random for each side, with simultaneous recordings of the electromyographic signals, using a simulator platform for inversion sprain and plantarflexion. As a result, after fatigue, no change in latency was observed. However, a reduction in the intensity of contraction of the muscles analyzed in both groups was observed. Neuromuscular control was concluded to be compromised in situations of fatigue, while differences in muscle behavior were not observed between stable and unstable ankles.

The Effect of Static Stretching of Peroneal and Tibialis Anterior Muscles on Reaction Time: A Randomized Controlled Study

OBJECTIVE

The aim of this study was to investigate the acute and chronic effects of static stretching on peroneal and tibialis anterior reaction characteristics.

DESIGN

All 23 participants who volunteered for this study were randomly divided into static (n = 12) and control (n = 11) groups. The subjects in the static stretching group performed stretching exercises for the ankle evertor and dorsiflexor muscles 5 days a week for 6 wks. Peroneal and tibialis anterior muscle reaction characteristics were evaluated at the beginning (2 times for acute effect) and end of this period. Electromyographic activity parameters of the muscles were measured using an ankle inversion tilting platform that simulated a sudden ankle inversion. The following were the four different ankle inversion conditions: (a) ankle-neutral, 15-degree inversion; (b) ankle-neutral, 30-degree inversion; (c) ankle-20-degree plantarflexion, 15-degree inversion; and (d) ankle-20-degree plantarflexion, 30-degree inversion.

RESULTS

Either in terms of acute or chronic effects, no significant differences were found after static stretching exercises for peroneal and tibialis anterior muscle reaction time, reaction duration, and muscle activity evaluated in four positions on the ankle inversion simulation platform (P > 0.05).

CONCLUSIONS

In light of these results, it is possible to state that the short duration of static stretching exercises can still be applied before sports activities.

Decrease of the electrical potentials measured on the surface of the knee and produced by cartilage compression during successive loading cycles

Electroarthrography (EAG) is a new technique for measuring electrical potentials appearing on the knee surface during loading that reflects cartilage quality and joint contact force. Our objective was to investigate the evolution of EAG signals during successive loading cycles. The study was conducted on 20 standing subjects who shifted their body weight to achieve knee loading. Their EAG signals were recorded during 10 successive loading cycles, and during a subsequent sequence of 10 cycles recorded after a 15min exercise period. Multiple linear regression models estimated the electro-mechanical ratio (EMR) interpreting the ability of cartilage to generate a certain potential for a given ground reaction force by taking into account this force and the center of pressure displacements during unipedal stance. The results showed that the EMR values slowly decreased with successive cycles: during the initial sequence, the correlation coefficients between EMR values and sequence numbers were significant at 3 of the 4 electrode sites (p<0.05); for the post-exercise sequence, the EMR values still decreased and were significantly lower than during the initial sequence (p<0.001). The reduction of EMR values could arise from muscle activity and habituation of the stretch reflex, and also from the time dependent electromechanical properties of cartilage. In conclusion, refraining from physical activity before the EAG measurements is important to improve measurement repeatability because of the EMR decrease. The electromechanical model confirmed the role of EAG as a natural sensor of the changes in the knee contact force and also improved EAG measurement accuracy.

The influence of a medio-lateral unstable sole on invertor and evertor activation while descending stairs

[Purpose] This study examined the effects of a medio-lateral unstable sole on invertor and evertor activation while descending stairs. [Subjects and Methods] The subjects were 30 university students with no history of ankle sprain. They descended stairs while wearing the medio-lateral unstable sole or with bare feet. Electromyography was used to record the activity of the tibialis anterior and peroneus longus and brevis muscles and paired t-tests were used to assess statistical significance. [Results] The medio-lateral unstable sole group showed increased tibialis anterior and peroneus longus and brevis muscle activation compared to the barefoot group. [Conclusion] Medio-lateral unstable sole can be used with exercises to prevent further ankle damage by activating both the inversion and eversion muscles.

The effect of repetitive ankle perturbations on muscle reaction time and muscle activity

The use of a tilt platform to simulate a lateral ankle sprain and record muscle reaction time is a well-established procedure. However, a potential caveat is that repetitive ankle perturbation may cause a natural attenuation of the reflex latency and amplitude. This is an important area to investigate as many researchers examine the effect of an intervention on muscle reaction time. Muscle reaction time, peak and average amplitude of the peroneus longus and tibialis anterior in response to a simulated lateral ankle sprain (combined inversion and plantar flexion movement) were calculated in twenty-two physically active participants. The 40 perturbations were divided into 4 even groups of 10 dominant limb perturbations. Within-participants repeated measures analysis of variance (ANOVA) tests were conducted to assess the effect of habituation over time for each variable. There was a significant reduction in the peroneus longus average amplitude between the aggregated first and last 10 consecutive ankle perturbations (F2.15,45.09=3.90, P=0.03, ɳp(2)=0.16). Authors should implement no more than a maximum of 30 consecutive ankle perturbations (inclusive of practice perturbations) in future protocols simulating a lateral ankle sprain in an effort to avoid significant attenuation of muscle activity.

The Effects of Temporal and Spatial Predictions on Stretch Reflexes of Ankle Flexor and Extensor Muscles While Standing

The purpose of the present study was to investigate how stretch reflex (SR) responses in the ankle extensor (soleus: SOL) and flexor (tibialis anterior: TA) muscles would be modulated with temporal and/or spatial predictions of external perturbations and whether their effects are specific to the standing posture. SR responses in the SOL/TA were elicited by imposing quick ankle toes-up/toes-down rotations while standing upright and in the supine position. We designed four experimental conditions based on pre-information about perturbations: no information (No Cue), the timing of the perturbation onset (TIM), the direction of the perturbation (DIR), and both the timing and direction of the perturbation (TIM/DIR). Each condition was separated and its order was counterbalanced. In the SR of TA evoked by toes-down rotation, integrated electromyography activities of the late component were significantly reduced in the TIM and TIM/DIR conditions as compared with those in the No Cue and DIR conditions. The occurrence rate of late SR components that reflects how often the reflex response was observed was also lower in the TIM and TIM/DIR conditions as compared with that in the No Cue and DIR conditions. On the other hand, no significant changes were seen among the four conditions in the early SR component in the TA and both SR components in the SOL. The same results in the occurrence rate were found in the supine position. The present results suggest (1) only temporal predictions have a remarkable effect on the SR excitability of the TA, and (2) this effect is independent of posture.

A fadiga influencia a resposta dos músculos eversores após a simulação de uma entorse do tornozelo?

INTRODUÇÃO: a entorse em inversão do tornozelo, uma das lesões mais comuns do esporte, muitas vezes ocorre na fase final de um treino ou competição. Mesmo sabendo que a entorse é multifatorial, tal característica gera a hipótese que a fadiga muscular possa ser um fator predisponente para o desenvolvimento da lesão.OBJETIVO: a presente investigação propõe o estudo da resposta reflexa dos músculos fibular curto e longo em condições de fadiga.MÉTODOS: participaram do estudo 10 voluntárias do sexo feminino, sem histórico de entorse do tornozelo, fisicamente ativas. Utilizou-se uma plataforma simuladora da entorse em inversão do tornozelo, na qual ambos os pés das voluntárias foram fixados e somente abaixo do fixador do pé direito encontrava-se um transdutor de força. Para a indução da fadiga, inicialmente foi registrada a contração isométrica voluntária máxima (CIVM) em eversão. Durante a indução, as voluntárias foram orientadas a manter 70% da CIVM. No momento em que a força aplicada era menor que 60% da CIVM o protocolo era interrompido e as voluntárias imediatamente posicionadas sobre a plataforma simuladora. Antes e após a fadiga foram realizadas 10 simulações da entorse em ambos os tornozelos, de forma aleatória, e simultaneamente, o sinal eletromiográfico foi registrado. A análise, no domínio do tempo, contemplou o estudo da latência e da amplitude do sinal.RESULTADOS: após a fadiga não houve alteração da latência, no entanto, ocorreu uma redução da amplitude do sinal. A queda da amplitude do sinal pode ser considerada uma resposta ao processo de fadiga. Esse decréscimo é um indicativo da diminuição da capacidade de recrutamento das unidades motoras decorrentes das alterações do input neural que chega ao músculo.CONCLUSÃO: a fadiga muscular diminui a amplitude da resposta dos músculos eversores após a entorse do tornozelo.

Longer reaction time of the fibularis longus muscle and reduced postural control in basketball players with functional ankle instability: A pilot study

BACKGROUND

Motor control evaluation in subjects with functional ankle instability is questionable when both ankles of the same subject are compared (affected vs non-affected).

OBJECTIVE

To compare the postural control and reaction time of ankle muscles among: basketball players with FAI (instability group), basketball players without FAI (non-instability group) and healthy non-basketball-playing participants (control group).

DESIGN

Case-control study.

SETTING

Laboratory.

PARTICIPANTS

Instability (n = 10), non-instability (n = 10), and control groups (n = 11).

MAIN OUTCOME MEASURES

Centre of pressure variables (area, velocity and sway) were measured with a force platform. Reaction time of ankle muscles was measured via electromyography.

RESULTS

A one-way ANOVA demonstrated that there were significant differences between the instability and non-instability groups in the fibularis longus (p < 0.001), fibularis brevis (p = 0.031) and tibialis anterior (p = 0.049) muscles. Repeated-measures ANOVA and post hoc analysis determined significant differences for the area between the instability and non-instability groups (p = 0.001).

CONCLUSION

Basketball players with FAI have reduced postural control and longer reaction time of the fibularis and tibialis anterior muscles.

Effects of quadriceps muscle fatigue on stiff-knee gait in patients with hemiparesis

The relationship between neuromuscular fatigue and locomotion has never been investigated in hemiparetic patients despite the fact that, in the clinical context, patients report to be more spastic or stiffer after walking a long distance or after a rehabilitation session. The aim of this study was to evaluate the effects of quadriceps muscle fatigue on the biomechanical gait parameters of patients with a stiff-knee gait (SKG). Thirteen patients and eleven healthy controls performed one gait analysis before a protocol of isokinetic quadriceps fatigue and two after (immediately after and after 10 minutes of rest). Spatiotemporal parameters, sagittal knee and hip kinematics, rectus femoris (RF) and vastus lateralis (VL) kinematics and electromyographic (EMG) activity were analyzed. The results showed that quadriceps muscle weakness, produced by repetitive concentric contractions of the knee extensors, induced an improvement of spatiotemporal parameters for patients and healthy subjects. For the patient group, the increase in gait velocity and step length was associated with i) an increase of sagittal hip and knee flexion during the swing phase, ii) an increase of the maximal normalized length of the RF and VL and of the maximal VL lengthening velocity during the pre-swing and swing phases, and iii) a decrease in EMG activity of the RF muscle during the initial pre-swing phase and during the latter 2/3 of the initial swing phase. These results suggest that quadriceps fatigue did not alter the gait of patients with hemiparesis walking with a SKG and that neuromuscular fatigue may play the same functional role as an anti-spastic treatment such as botulinum toxin-A injection. Strength training of knee extensors, although commonly performed in rehabilitation, does not seem to be a priority to improve gait of these patients.

Eccentric/concentric training of ankle evertor and dorsiflexors in recreational athletes: muscle latency and strength

The aim of this study was to investigate the effects of a combined eccentric-concentric exercise program of the ankle evertors and dorsiflexors on the latency time of the peroneus longus and tibialis anterior muscles. Twenty-four healthy male recreational athletes were admitted to this study and were randomly assigned to either the exercise group (n = 12) or the control group (n = 12). Subjects in the exercise group performed an isokinetic exercise program of the ankle evertors and dorsiflexors in a combined eccentric-concentric mode for 3 days per week for 6 weeks. Before and after the exercise program, muscle reaction times of the peroneus longus and tibialis anterior muscles to sudden supinating maneuvers on a tilting platform, and isokinetic strength of the ankle joint musculature were evaluated. The peroneus longus and tibialis anterior reaction times showed significant (P < 0.01-0.05) reductions following six weeks of intervention in the exercise group. Additionally, eccentric peak torques for the ankle evertor and dorsiflexors represented significant (P < 0.05) increases in the exercise group compared with the control group. The results of this study suggest that it is possible to reduce peroneal and anterior tibial reaction times following a six week eccentric/concentric isokinetic training program in healthy ankles.

Disturbance and recovery of trunk mechanical and neuromuscular behaviours following repetitive lifting: influences of flexion angle and lift rate on creep-induced effects

Repetitive lifting is associated with an increased risk of occupational low back disorders, yet potential adverse effects of such exposure on trunk mechanical and neuromuscular behaviours were not well described. Here, 12 participants, gender balanced, completed 40 min of repetitive lifting in all combinations of three flexion angles (33, 66, and 100% of each participant's full flexion angle) and two lift rates (2 and 4 lifts/min). Trunk behaviours were obtained pre- and post-exposure and during recovery using sudden perturbations. Intrinsic trunk stiffness and reflexive responses were compromised after lifting exposures, with larger decreases in stiffness and reflexive force caused by larger flexion angles, which also delayed reflexive responses. Consistent effects of lift rate were not found. Except for reflex delay no measures returned to pre-exposure values after 20 min of recovery. Simultaneous changes in both trunk stiffness and neuromuscular behaviours may impose an increased risk of trunk instability and low back injury.

PRACTITIONER SUMMARY

An elevated risk of low back disorders is attributed to repetitive lifting. Here, the effects of flexion angle and lift rate on trunk mechanical and neuromuscular behaviours were investigated. Increasing flexion angle had adverse effects on these outcomes, although lift rate had inconsistent effects and recovery time was more than 20 min.

Effects of previous lateral ankle sprain and taping on the latency of the peroneus longus

The latency of the peroneus longus may be a key factor in the prevention of lateral ankle sprains (LASs). In addition, ankle taping is often applied to help prevent LASs. The purpose of this study was to determine the effects of a previous LAS and ankle taping on the latency of the peroneus longus after an inversion perturbation. Twenty-six participants, including 13 participants with no previous history of a LAS and 13 participants with a history of a single LAS completed the testing. Ankle taping was applied in a closed basket weave technique on one of the two testing days. The latency of the peroneus longus was determined by the onset of muscle activity exceeding 10 SD from baseline activity, after initiation of the 25 degrees inversion perturbation. A significant main effect (p < 0.05) was present for the ankle support condition, with ankle taping causing a significant reduction in latency of the peroneus longus (65.04 +/- 10.81 to 57.70 +/- 9.39 ms). There was no difference (p > 0.05) in latency between the injury groups. Ankle taping, immediately after application, reduces the latency of the peroneus longus among participants with and without a history of a LAS.

Effects of Inversion Perturbation After Step-Down on the Latency of the Peroneus Longus and Peroneus Brevis

The purpose of this investigation was to determine the effect of different types of ankle sprains on the response latency of the peroneus longus and peroneus brevis to an inversion perturbation, as well as the time to complete the perturbation (time to maximum inversion). To create a forced inversion moment of the ankle, an outer sole with fulcrum was used to cause 25 degrees of inversion at the ankle upon landing from a 27 cm step-down task. Forty participants completed the study: 15 participants had no history of any ankle sprain, 15 participants had a history of a lateral ankle sprain, and 10 participants had a history of a high ankle sprain. There was not a significant difference between the injury groups for the latency measurements or the time to maximum inversion. These findings indicate that a previous lateral ankle sprain or high ankle sprain does not affect the latency of the peroneal muscles or the time to complete the inversion range of motion.

Effects of ankle fatigue on functional reflex activity during gait perturbations in young and elderly men

There is growing evidence that aging and muscle fatigue result in impaired postural reflexes in humans. Therefore, the objective of this study was to examine the effects of ankle fatigue on functional reflex activity (FRA) during gait perturbations in young and elderly men. Twenty-eight young (27.0+/-3.1 years, n=14) and old (67.2+/-3.7 years, n=14) healthy active men participated in this study. Fatigue of the plantarflexors and dorsiflexors was induced by isokinetic contractions. Pre and post-fatigue, subjects were tested for their ability to compensate for decelerating gait perturbations while walking on a treadmill. Latency, FRA of lower extremity muscles and angular velocity of the ankle joint complex were analysed by means of surface electromyography and goniometry. After the fatigue protocol, no significant main and interaction effects were detected for the parameter latency in m. tibialis anterior (TA). For both groups, a significant pre to post-test decrease in FRA in TA (p<.001) was observed coming along with increases in antagonist coactivity (p=.013) and maximal angular velocity of the ankle joint (p=.007). However, no significant groupxtest interactions were found for the three parameters. Ankle fatigue has an impact on the ability to compensate for gait perturbations in young and elderly adults. However, no significant differences in all analysed parameters were detected between young and elderly subjects. These results may imply that age-related deteriorations in the postural control system do not specifically affect the ability to compensate for gait perturbations under fatigued condition.

A novel dynamic ankle-supinating device

Lateral ankle sprains (LAS) are among the most common joint injuries, and although most are resolved with conservative treatment, others develop chronic ankle instability (AI). Considerable attention has been directed toward understanding the underlying causes of this pathology; however, little is known concerning the neuromuscular mechanisms behind AI. A biomechanical analysis of the landing phase of a drop jump onto a device that simulates the mechanism of a LAS may give insight into the dynamic restraint mechanisms of the ankle by individuals with AI. Furthermore, work evaluating subjects who have a history of at least one lateral ankle sprain, yet did not develop AI, may help elucidate compensatory mechanisms following a LAS event. Identifying proper neuromuscular control strategies is crucial in reducing the incidence of AI.

Timing-specific transfer of adapted muscle activity after walking in an elastic force field

Human locomotion results from interactions between feedforward (central commands from voluntary and automatic drive) and feedback (peripheral commands from sensory inputs) mechanisms. Recent studies have shown that locomotion can be adapted when an external force is applied to the lower limb. To better understand the neural control of this adaptation, the present study investigated gait modifications resulting from exposure to a position-dependent force field. Ten subjects walked on a treadmill before, during, and after exposure to a force field generated by elastic tubing that pulled the foot forward and up during swing. Lower limb kinematics and electromyographic (EMG) activity were recorded during each walking period. During force field exposure, peak foot velocity was initially increased by 38%. As subjects adapted, peak foot velocity gradually returned to baseline in <or=125 strides. In the adapted state, hamstring EMG activity started earlier (16% before toe off) and remained elevated throughout swing. After force field exposure, foot velocity was initially reduced by 22% and returned to baseline in 9-51 strides. Aftereffects in hamstring EMGs consisted of increased activity around toe off. Contrary to the adapted state, this increase was not maintained during the rest of swing. Together, these results suggest that while the neural control of human locomotion can adapt to force field exposure, the mechanisms underlying this adaptation may vary according to the timing in the gait cycle. Adapted hamstring EMG activity may rely more on feedforward mechanisms around toe off and more on feedback mechanisms during the rest of swing.

Reorganization of multidigit physiological tremors after repetitive contractions of a single finger

In light of the interplay among physiological finger tremors, this study was undertaken to investigate the transfer effect of fatigue on coordinative strategies of multiple fingers. Fourteen volunteers performed prolonged position tracking with a loaded middle finger while measures of neuromuscular function, including electromyographic activities of the extensor digitorum (ED)/flexor digitorum superficialis (FDS) and physiological tremors of the index, middle, ring, and little fingers, were monitored. The subjects exhibited inferior tracking congruence and an increase in ED activity at the end of the tracking. Fatigue spread was manifested in a remarkable increase in tremor across fingers, in association with enhanced involuntary tremor coupling among fingers that was topologically organized in relation to the distance of the digits from the middle finger. Principal component analysis suggested that an enhanced 8- to 12-Hz central rhythm contributed primarily to the tremor restructure following fatigue spread. The observed tremor reorganization validated the hypothesis that the effect of fatigue was not limited to the instructed finger and that fatigue functionally decreased independence of the digits. The spreading of fatigue weakens neural inputs that diverge to motor units acting on various digits because of fatigue-related enhancement of common drive at the supraspinal level.