Effect of multimodal exercise training on physical fitness indices, cognitive status, and depressive symptoms in Alzheimer's disease.

In Alzheimer's disease (AD) patients, low levels of physical fitness (PF) and cognitive status are associated with high rates of depression. However, this condition can be improved through physical training. Objective: The aim of the present study was to investigate the effect of multimodal exercise training (MET) on aerobic endurance, muscular strength, agility, dynamic balance, cognitive status, and depressive symptoms in men with mild-to-moderate AD. Methods: A total of 25 elderly men with a diagnosis of mild-to-moderate AD were randomly categorized into an MET or a control group. The subjects in the MET group participated in a 12-week, three sessions per week MET program that included resistance, balance, and aerobic exercises. While the participants in the control group did not perform any regular exercise training during this period. Patients' cognitive status and depressive symptoms were assessed by Mini-Mental State Examination and the Geriatric Depression Scale-15 (GDS-15) questionnaires. PF indicators such as aerobic endurance, muscular strength, agility, and dynamic balance, as well as cognitive status and depressive symptoms, were taken from all the subjects before and after MET. Results: The participants in the MET group improved handgrip, upper and lower body strength, agility, dynamic balance, and depressive symptoms (p<0.05). The intervention had no significant effect on aerobic endurance and cognitive status (p>0.05). Conclusions: MET is an effective strategy to improve muscular strength, agility, dynamic balance, and depressive symptoms in men with mild-to-moderate AD. It is recommended for AD patients to engage in this type of exercise to reduce AD complications.

Em pacientes com Alzheimer, baixos níveis de aptidão física (AF) e estado cognitivo estão associados a altas taxas de depressão. Essa condição, no entanto, pode ser melhorada através do treinamento físico. Objetivo: O objetivo do presente estudo foi investigar o efeito do treinamento multimodal (TMM) de resistência aeróbica, força muscular, agilidade, equilíbrio dinâmico, estado cognitivo e sintomas depressivos em homens com doença de Alzheimer (DA) leve a moderada. Métodos: 25 homens idosos com diagnóstico de DA leve a moderada foram divididos aleatoriamente em um grupo TMM ou controle. Os indivíduos do grupo TMM participaram de um programa de TMM de 12 semanas, três sessões/semana, que incluía exercícios de resistência, equilíbrio e aeróbicos, enquanto os participantes do grupo controle não realizaram nenhum treinamento regular de exercícios durante esse período. O estado cognitivo e os sintomas depressivos dos pacientes foram avaliados pelos questionários Mini-Mental State Examination (MMSE) e Geriatric Depression Scale-15 (GDS-15). Indicadores de AF, como resistência aeróbica, força muscular, agilidade e equilíbrio dinâmico, bem como estado cognitivo e sintomas depressivos, foram obtidos de todos os sujeitos antes e depois do TMM. Resultados: Os participantes do grupo TMM melhoraram a preensão manual e força de membros superiores e inferiores, agilidade, equilíbrio dinâmico e sintomas depressivos (p<0,05). A intervenção não teve efeito significativo na resistência aeróbica e no estado cognitivo (p>0,05). Conclusões: O TMM é uma estratégia eficaz para melhorar a força muscular, agilidade, equilíbrio dinâmico e sintomas depressivos em homens com DA leve a moderada. Recomenda-se que os pacientes com Alzheimer pratiquem esse tipo de exercício para reduzir as complicações da DA.

Enhanced corticospinal excitability in the tibialis anterior during static stretching of the soleus in young healthy individuals.

Corticospinal excitability is known to be affected by afferent inflow arising from the proprioceptors during active or passive muscle movements. Also during static stretching (SS) afferent activity is enhanced, but its effect on corticospinal excitability received limited attention and has only been investigated as a single average value spread over the entire stretching period. Using transcranial magnetic stimulation (TMS) the present study was conducted to explore the time course of corticospinal excitability during 30 seconds SS. Motor evoked potentials (MEPs) after TMS were recorded from soleus (SOL) and tibialis anterior (TA) muscles in 14 participants during: a passive dynamic ankle dorsiflexion (DF), at six different time points during maximal individual SS (3, 6, 9, 18, 21 and 25 seconds into stretching), during a passive dynamic ankle plantar flexion (PF) and following SS. To explore the time course of corticospinal excitability during the static lengthened phase of a muscle stretch, the stretching protocol was repeated several times so that it was possible to collect a sufficient number of stimulations at each specific time point into SS, as well as during DF and PF. During passive DF, MEPs amplitude was greater than baseline in both TA and SOL (p = .001 and p = .005 respectively). During SS, MEPs amplitude was greater than baseline in TA (p = .006), but not in SOL. No differences between the investigated time points were found and no trend was detected throughout the stretching time. No effect in either muscle was observed during passive PF and after SS. These results could suggest that an increased activity of secondary afferents from SOL muscle spindles exert a corticomotor facilitation on TA. The muscle-nonspecific response observed during passive DF could instead be attributed to an increased activation within the sensorimotor cortical areas as a result of the awareness of the foot passive displacements.

Effect of multimodal exercise training on physical fitness indices, cognitive status, and depressive symptoms in Alzheimer's disease / O efeito do treinamento multimodal em índices de aptidão física, estado cognitivo e sintomas depressivos na doença de Alzheimer

ABSTRACT. In Alzheimer's disease (AD) patients, low levels of physical fitness (PF) and cognitive status are associated with high rates of depression. However, this condition can be improved through physical training. Objective: The aim of the present study was to investigate the effect of multimodal exercise training (MET) on aerobic endurance, muscular strength, agility, dynamic balance, cognitive status, and depressive symptoms in men with mild-to-moderate AD. Methods: A total of 25 elderly men with a diagnosis of mild-to-moderate AD were randomly categorized into an MET or a control group. The subjects in the MET group participated in a 12-week, three sessions per week MET program that included resistance, balance, and aerobic exercises. While the participants in the control group did not perform any regular exercise training during this period. Patients' cognitive status and depressive symptoms were assessed by Mini-Mental State Examination and the Geriatric Depression Scale-15 (GDS-15) questionnaires. PF indicators such as aerobic endurance, muscular strength, agility, and dynamic balance, as well as cognitive status and depressive symptoms, were taken from all the subjects before and after MET. Results: The participants in the MET group improved handgrip, upper and lower body strength, agility, dynamic balance, and depressive symptoms (p<0.05). The intervention had no significant effect on aerobic endurance and cognitive status (p>0.05). Conclusions: MET is an effective strategy to improve muscular strength, agility, dynamic balance, and depressive symptoms in men with mild-to-moderate AD. It is recommended for AD patients to engage in this type of exercise to reduce AD complications.

RESUMO. Em pacientes com Alzheimer, baixos níveis de aptidão física (AF) e estado cognitivo estão associados a altas taxas de depressão. Essa condição, no entanto, pode ser melhorada através do treinamento físico. Objetivo: O objetivo do presente estudo foi investigar o efeito do treinamento multimodal (TMM) de resistência aeróbica, força muscular, agilidade, equilíbrio dinâmico, estado cognitivo e sintomas depressivos em homens com doença de Alzheimer (DA) leve a moderada. Métodos: 25 homens idosos com diagnóstico de DA leve a moderada foram divididos aleatoriamente em um grupo TMM ou controle. Os indivíduos do grupo TMM participaram de um programa de TMM de 12 semanas, três sessões/semana, que incluía exercícios de resistência, equilíbrio e aeróbicos, enquanto os participantes do grupo controle não realizaram nenhum treinamento regular de exercícios durante esse período. O estado cognitivo e os sintomas depressivos dos pacientes foram avaliados pelos questionários Mini-Mental State Examination (MMSE) e Geriatric Depression Scale-15 (GDS-15). Indicadores de AF, como resistência aeróbica, força muscular, agilidade e equilíbrio dinâmico, bem como estado cognitivo e sintomas depressivos, foram obtidos de todos os sujeitos antes e depois do TMM. Resultados: Os participantes do grupo TMM melhoraram a preensão manual e força de membros superiores e inferiores, agilidade, equilíbrio dinâmico e sintomas depressivos (p<0,05). A intervenção não teve efeito significativo na resistência aeróbica e no estado cognitivo (p>0,05). Conclusões: O TMM é uma estratégia eficaz para melhorar a força muscular, agilidade, equilíbrio dinâmico e sintomas depressivos em homens com DA leve a moderada. Recomenda-se que os pacientes com Alzheimer pratiquem esse tipo de exercício para reduzir as complicações da DA.

Mental calculation increases physiological postural tremor, but does not influence physiological goal-directed kinetic tremor.

PURPOSE: During a cognitive effort, an increase in cortical electrical activity, functional alterations in the anterior cingulate cortex, and modifications in cortical inputs to the active motor units have been reported. In light of this, an increase in tremor could be anticipated as result of a mental task. In the present work, we tested this hypothesis. METHODS: In 25 individuals, tremor was measured with a three-axial accelerometer during 300 s of postural and goal-directed tasks performed simultaneously to mental calculation, or during control (same tasks without mental calculation). Hand and finger dexterity were also evaluated. Electromyographic (EMG) recordings from the extensor digitorum communis were collected during the postural task. RESULTS: Hand and finger dexterity was negatively affected by the mental task (p = .003 and p = .00005 respectively). During mental calculation, muscle tremor increased in the hand postural (+ 29%, p = .00005) but not in the goal-directed task (- 1.5%, p > .05). The amplitude of the main frequency peak also increased exclusively in the hand postural task (p = .028), whilst no shift in the position of the main frequency peak was observed. EMG was not affected. CONCLUSION: These results support the position of the contribution of a central component in the origin of physiological hand postural tremor. It is suggested that the different effect of mental calculation on hand postural and goal-directed tasks can be attributed to the different origins and characteristics of hand postural and goal-directed physiological tremor.

Tremor, finger and hand dexterity and force steadiness, do not change after mental fatigue in healthy humans.

The effects of mental fatigue have been studied in relation to specific percentages of maximal aerobic or anaerobic efforts, maximal voluntary contractions or the performance of sport specific skills. However, its effects on tremor, dexterity and force steadiness have been only marginally explored. The present work aimed at filling this gap. In twenty-nine young individuals, measurement of postural, kinetic and isometric tremor, pinch force steadiness and finger and hand dexterity were performed before and after either 100 min of mental fatigue or control tasks. During the interventions blood pressure, oxygen saturation and heart rate and perceived effort in continuing the task were recorded every 10 minutes. Tremor was analysed in both time (standard deviation) and frequency domain (position, amplitude and area of the dominant peak) of the acceleration signal. Finger dexterity was assessed by Purdue pegboard test and hand dexterity in terms of contact time in a buzz wire exercise. Force steadiness was quantified as coefficient of variation of the force signal. Postural, kinetic and isometric tremors, force steadiness and dexterity were not affected. Higher oxygen saturation values and higher variability of heart rate and blood pressure were found in the intervention group during the mental fatigue protocol (p < .001). The results provide no evidence that mental fatigue affects the neuromuscular parameters that influence postural, kinetic or isometric tremor, force steadiness and dexterity when measured in single-task conditions. Increased variability in heart rate may suggest that the volunteers in the intervention group altered their alert/stress state. Therefore, it is possible that the alterations that are commonly observed during mental fatigue, and that could have affected tremor, steadiness and dexterity only last for the duration of the cognitive task and are not detectable anymore soon after the mental task is terminated.

A Countermovement Jump for the Midterm Assessment of Force and Power Exertion After Anterior Cruciate Ligament Reconstruction.

OBJECTIVE: The aim of this study was to assess force and power exertion during a countermovement jump after anterior cruciate ligament reconstruction using either semitendinosus and gracilis or bone-patellar tendon-bone graft. DESIGN: One hundred-nineteen semitendinosus and gracilis and 146 bone-patellar tendon-bone participants performed a countermovement jump on two force platforms after 3 (T1) and 6-9 mos (T2) from surgery. Twenty-four healthy participants served as control group. Peak force of eccentric and concentric phases and peak power were obtained from the analysis of vertical components of the ground reaction forces. Asymmetry was quantified by means of limb symmetry index. RESULTS: Eccentric peak force was significantly ( P < 0.05) lower than concentric peak force in both bone-patellar tendon-bone and semitendinosus and gracilis at T1 and T2. At T1, bone-patellar tendon-bone showed higher peak power, but lower limb symmetry index in eccentric and concentric compared with semitendinosus and gracilis. At T2, bone-patellar tendon-bone showed higher peak power than semitendinosus and gracilis, although there were no differences in limb symmetry index between the two groups, which however was significantly ( P < 0.05) lower in both groups when compared with control group. CONCLUSIONS: Bone-patellar tendon-bone and semitendinosus and gracilis participants showed asymmetries in eccentric and concentric force during a countermovement jump. Bone-patellar tendon-bone showed greater asymmetries and a higher peak power respect to semitendinosus and gracilis participants.

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

BACKGROUND: It is well known that different exercise intensities for the ankle muscles can impair postural stability. However, it remains unclear whether it is low-intensity exercises (which primarily induce central fatigue) or high-intensity exercises (which primarily induce peripheral fatigue) that have a greater effect on voluntary postural control. RESEARCH QUESTION: The aim of this study was to compare the effects of fatiguing exercises that induce either central or peripheral fatigue on voluntary postural stability. METHODS: Following isometric maximum voluntary contraction (IMVC) tests, 12 volunteers randomly performed submaximal (40% IMVC) and maximal (100% IMVC) fatiguing contractions of the plantar flexors on a dynamometer. Before and after the fatiguing protocols, postural stability was assessed by measuring the centre of pressure trajectory during voluntary sways on a force plate. The electromyography activity of the right gastrocnemius medialis was recorded. To assess central and peripheral fatigue, electrical stimulations were applied both during and after the IMVC. The effects of the fatiguing protocols and the differences between the protocols were tested with a two-way repeated measures ANOVA test (fatigue × time). RESULTS: Submaximal contractions induced a greater increase of sway area and medial-lateral sway cycle range than maximal contractions (P < 0.01). Voluntary activation decreased significantly more after submaximal contractions than maximal contractions (P < 0.01). Submaximal contractions induced a significantly greater reduction of IMVC than maximal contractions (P < 0.01). Resting twitch size was smaller after maximal contractions than submaximal contractions (P = 0.04). SIGNIFICANCE: The outcome of this study suggests that training programmes for patients with balance issues should be based on training with maximal rather than submaximal load, to avoid deficits that might compromise postural stability.

Tissue flossing of the thigh increases isometric strength acutely but has no effects on flexibility or jump height.

The purpose of this study was to investigate the effects of a single floss band treatment of the thigh on hip and knee range of motion (ROM), knee extensor passive resistive torque (PRT), knee extensor maximum voluntary contraction (MVC) torque, and countermovement jump (CMJ) height.Sixteen healthy male volunteers were tested before and after both the flossing treatment and the control condition, in random order. For the flossing treatment, the floss band was wound around both thighs for 120 s, and the subject was then asked to perform 20 squats. During the control treatment, only the 20 squats were performed. Before and after the treatments, knee and hip ROM were assessed using a Thomas test with 3D motion caption. The PRT and MVC of the knee extensors were measured with a dynamometer, and the electromyographic (EMG) signal was collected from the vastus lateralis. CMJs were performed on a force plate.Compared to the control condition, the flossing treatment showed a positive effect on the MVC of the knee extensors (P = 0.01); however, no effects on hip ROM (P = 0.58), knee ROM (P = 0.37), CMJ height (P = 0.75), or PRT (P = 0.22) were observed. Correlation analyses revealed that the increase in MVC was not significantly related to changes in the tension of the muscle-tendon unit (rP = -0.13; P = 0.64) or vastus lateralis EMG (rS = 0.44; P = 0.10). Since the increase in MVC cannot be explained by changes of the mechanical (PRT) or neuromuscular (EMG) properties, we speculate that an enhancement of growth hormone and norepinephrine levels following the compression release is instead responsible for the increase in MVC.

The Recovery of Muscle Spindle Sensitivity Following Stretching Is Promoted by Isometric but Not by Dynamic Muscle Contractions.

It is often suggested that stretching-related changes in performance can be partially attributed to stretching-induced neural alterations. Recent evidence though shows that neither spinal nor cortico-spinal excitability are susceptible of a long-lasting effect and only the amplitude of stretch or tap reflex (TR) is reduced up to several minutes. Since afferents from muscle spindles contribute to voluntary muscle contractions, muscle stretching could be detrimental to muscle performance. However, the inhibition of muscle spindle sensitivity should be reversed as soon as the stretched muscle contracts again, due to α-γ co-activation. The present work evaluated which type of muscle contraction (static or dynamic) promotes the best recovery from the inhibition in spindle sensitivity following static stretching. Fifteen students were tested for TR at baseline and after 30 s maximal individual static stretching of the ankle plantar flexors followed by one of three randomized interventions (isometric plantar flexor MVC, three counter movement jumps, and no contraction/control). Ten TRs before and 20 after the procedures were induced with intervals of 30 s up to 10 min after static stretching. The size of the evoked TRs (peak to peak amplitude of the EMG signal) following stretching without a subsequent contraction (control) was on average reduced by 20% throughout the 10 min following the intervention and did not show a recovery trend. Significant decrease in relation to baseline were observed at 9 of the 20 time points measured. After MVC of plantar flexors, TR recovered immediately showing no differences with baseline at none of the investigated time points. Following three counter movement jumps it was observed a significant 34.4% group average inhibition (p < 0.0001) at the first time point. This effect persisted for most of the participants for the next measurement (60 s after intervention) with an average reduction of 23.4% (p = 0.008). At the third measurement, 90 s after the procedure, the reflexes were on average still 21.4% smaller than baseline, although significant level was not reached (p = 0.053). From 120 s following the intervention, the reflex was fully recovered. This study suggests that not every type of muscle contraction promotes a prompt recovery of a stretch-induced inhibition of muscle spindle sensitivity.

Five minutes static stretching influences neural responses at spinal level in the background of unchanged corticospinal excitability.

OBJECTIVES: Corticospinal tract excitability and spinal reflex pathways are transiently affected by short applications of static stretching. However, it remains unclear whether the duration and magnitude of these neurophysiological responses can be increased with a longer duration of the applied stretch. The purpose of this study was to investigate alterations in cortical and spinal excitability following five minutes static stretching. METHODS: Seventeen participants (22.8±2.3 years old) were tested for the tendon tap reflex (T-reflex), Hoffman reflex (H-reflex) and motor-evoked potentials (MEPs) after transcranial magnetic stimulation (TMS) of the ankle flexor muscles in two separate occasions: before and after 5 minute static stretching or 5 minute control period, in a randomized order. RESULTS: No changes were observed following the control condition. H/M ratio increased by 16.2% after stretching (P=.036). Furthermore, immediately after stretching it was observed a strong inhibition of the T-reflex (57.6% inhibition, P=.003) that persisted up to five minutes after stretching (16.2% inhibition, P=.013) but returned to baseline following 10 minutes. MEPs were not affected by stretching. CONCLUSIONS: This study suggests that the neuromuscular responses that follow five minute of static stretching do not influence the excitability of the corticospinal tract and follow a different time course within spinal reflex pathways.

Soleus H-Reflex Inhibition Decreases During 30 s Static Stretching of Plantar Flexors, Showing Two Recovery Steps.

During the period when the ankle joint is kept in a dorsiflexed position, the soleus (SOL) H-reflex is inhibited. The nature of this inhibition is not fully understood. One hypothesis is that the decrease in spinal excitability could be attributed to post-activation depression of muscle spindle afferents due to their higher firing rate during the stretch-and-hold procedure. As the static stretching position is maintained though, a partial restoration of the neurotransmitter is expected and should mirror a decrease in H-reflex inhibition. In the present study, we explored the time course of spinal excitability during a period of stretching. SOL H-reflex was elicited during a passive dorsiflexion movement, at 3, 6, 9, 12, 18, 21, and 25 s during maximal ankle dorsiflexion, during plantar flexion (PF) and after stretching, in 12 healthy young individuals. Measurements during passive dorsiflexion, PF and after stretching were all performed with the ankle at 100° angle; measurements during static stretching were performed at individual maximal dorsiflexion. H-reflex was strongly inhibited during the dorsiflexion movement and at maximal dorsiflexion (p < 0.0001) but recovered during PF and after stretching. During stretching H-reflex showed a recovery pattern (r = 0.836, P = 0.019) with two distinct recovery steps at 6 and 21 s into stretching. It is hypothesized that the H-reflex inhibition observed until 18 s into stretching is the result of post-activation depression of Ia afferent caused by the passive dorsiflexion movement needed to move the ankle into testing position. From 21 s into stretching, the lower inhibition could be caused by a weaker post-activation depression, inhibition from secondary afferents or post-synaptic inhibitions.

Transient Increase in Cortical Excitability Following Static Stretching of Plantar Flexor Muscles.

Spinal excitability in humans is inhibited by both passively holding a static position with the muscle lengthened (static stretching) and by a single non-active lengthening movement. However, whilst immediately after a passive lengthening movement the inhibition persists for several seconds, there seem to be an immediate recovery following static stretching. This result is counter intuitive and could be attributed to methodological procedures. Indeed, differently to what has been done until now, in order to study whether static stretching has a transient effect on the neuromuscular pathway, the procedure should be repeated many times and measurements collected at different time points after stretching. In the present study we repeated 60 times 30 s static stretching of ankle plantar flexors and measured tap reflex (T-reflex), Hoffman reflex (H-reflex), and motor evoked potentials (MEPs) from the Soleus muscle at several time points, starting from immediately after until 30 s following the procedure. T-reflex was strongly inhibited (range 31-91%, p = 0.005) and the inhibition persisted for 30 s showing a slow recovery (r = 0.541, p = 0.037). H-reflex was not affected by the procedure. Stretching increased the size of the MEPs (p < 0.0001), differences at times 0 and 2 s after stretching (p = 0.015 and p = 0.047, respectively). These results confirm that static stretching reduces muscle spindle sensitivity. Moreover it is suggested that post-activation depression of Ia afferents, which is commonly considered the cause of H-reflex depression during both dorsiflexion and static stretching, vanished immediately following stretching or is counteracted by an increased corticospinal excitability.

Local vibration inhibits H-reflex but does not compromise manual dexterity and does not increase tremor.

The present work aimed at investigating the effects of local vibration on upper limb postural and kinetic tremor, on manual dexterity and on spinal reflex excitability. Previous studies have demonstrated a decrease in spinal reflex excitability and in force fluctuations in the lower limb but an increase in force fluctuation in the upper limbs. As hand steadiness is of vital importance in many daily-based tasks, and local vibration may also be applied in movement disorders, we decided to further explore this phenomenon. Ten healthy volunteers (26±3years) were tested for H reflex, postural and kinetic tremor and manual dexterity through a Purdue test. EMG was recorded from flexor carpi radialis (FCR) and extensor digitorum communis (EDC). Measurements were repeated at baseline, after a control period during which no vibration was delivered and after vibration. Intervention consisted in holding for two minutes a vibrating handle (frequency 75Hz, displacement∼7mm), control consisted in holding for two minutes the same handle powered off. Reflex excitability decreased after vibration whilst postural tremor and manual dexterity were not affected. Peak kinetic tremor frequency increased from baseline to control measurements (P=0.002). Co-activation EDC/FCR increased from control to vibration (P=0.021). These results show that two minutes local vibration lead to a decrease in spinal excitability, did not compromise manual dexterity and did not increase tremor; however, in contrast with expectations, tremor did not decrease. It is suggested that vibration activated several mechanisms with opposite effects, which resulted in a neutral outcome on postural and kinetic tremor.

Acute effects of constant torque and constant angle stretching on the muscle and tendon tissue properties.

PURPOSE: Static stretching induces acute structural changes of the muscle-tendon unit (MTU) that are related to the intensity or duration of stretching. It has been reported that stretching with a constant torque (CT) leads to greater joint range of motion changes than stretching with a constant angle (CA). Whether or not this difference is due to different structural changes of the MTUs of the lower leg and ankle plantar flexors is not known. Therefore, the purpose of this study was to compare the acute effects of single CA and CT stretching on various muscle and tendon mechanical properties. METHOD: Seventeen young, healthy volunteers were tested on two separate days using either CT or CA stretching (4 × 30 s each). Before and after stretching, dorsiflexion range of motion (RoM), passive resistive torque (PRT), and maximum voluntary contraction (MVC) were measured with a dynamometer. Ultrasonography of the medial gastrocnemius (GM) muscle-tendon junction (MTJ) displacement allowed us to determine the length changes in the tendon and muscle, respectively, and hence to calculate their stiffness. RESULTS: Maximum dorsiflexion increased while PRT, muscle-tendon stiffness, and muscle stiffness decreased following both CA and CT stretching. There was a greater increase in RoM following CT stretching compared to CA stretching. Moreover, the decline in PRT was greater during CT stretching compared to CA stretching. As expected, several functional adaptations (RoM, PRT) were different between CT and CA stretching due to the higher intensity of CT stretching. However, no structural differences in the adaptations to the stretching modalities could be detected. CONCLUSION: We suggest that the different functional adaptations between CA and CT stretching are the consequence of different adaptations in the perception of stretch and pain.

One minute static stretch of plantar flexors transiently increases H reflex excitability and exerts no effect on corticospinal pathways.

NEW FINDINGS: What is the central question of this study? What mediates neural responses following static stretching, and how long do these influences last? What is the main finding and its importance? This study shows that 1 min of static stretching inhibits the tendon tap reflex and facilitates the H reflex without influencing motor-evoked potentials. The results indicate that at least two different mechanisms mediate neural responses after static stretching. The purpose of this study was to determine whether the neural responses observed after static stretching are mediated by sensitivity of muscle spindles, spinal excitability or cortical excitability and how long these influences last. Nineteen volunteers (25.7 ± 5.6 years old) were tested for the tendon tap reflex (T-reflex), H reflex and motor-evoked potentials on ankle flexors and extensors immediately, 5 and 10 min after 1 min static stretching applied at individual maximal ankle dorsiflexion, as well as immediately, 5 and 10 min after a control period of the same duration. Comparison of measurements collected immediately after stretching or control conditions revealed that the T-reflex was weaker after stretching than after control (-59.2% P = 0.000). The T-reflex showed a slow recovery rate within the first 150 s after stretching, but 5 min after the inhibition had disappeared. The H reflex increased immediately after stretching (+18.3%, P = 0.036), showed a quick tendency to recover and returned to control values within 5 min from stretching. Motor-evoked potentials were not affected by the procedure. These results suggest that 1 min of static stretching primarily decreases muscle spindle sensitivity and facilitates the H reflex, whereas effects on the motor cortex can be excluded.

Changes in H-reflex amplitude to muscle stretch and lengthening in humans.

Spinal reflex excitability is traditionally assessed to investigate neural adjustments that occur during human movement. Different experimental procedures are known to condition spinal reflex excitability. Among these, lengthening movements and static stretching the human triceps have been investigated over the last 50 years. The purpose of this review is to shed light on several apparent incongruities in terms of magnitude and duration of the reported results. In the present review dissimilarities in neuro-spinal changes are examined in relation to the methodologies applied to condition and measure them. Literature that investigated three different conditioning procedures was reviewed: passive dorsiflexion, active dorsiflexion through antagonists shortening and eccentric plantar-flexors contractions. Measurements were obtained before, during and after lengthening or stretching. Stimulation intensities and time delays between conditioning procedures and stimuli varied considerably. H-reflex decreases immediately as static stretching is applied and in proportion to the stretch degree. During dorsiflexions the inhibition is stronger with greater dorsiflexion angular velocity and at lower nerve stimulation intensities, while it is weaker if any concomitant muscle contraction is performed. Within 2 s after a single passive dorsiflexion movement, H-reflex is strongly inhibited, and this effect disappears within 15 s. Dorsiflexions repeated over 1 h and prolonged static stretching training induce long-lasting inhibition. This review highlights that the apparent disagreement between studies is ascribable to small methodological differences. Lengthening movements and stretching can strongly influence spinal neural pathways. Results interpretation, however, needs careful consideration of the methodology applied.

Alpha band cortico-muscular coherence occurs in healthy individuals during mechanically-induced tremor.

The present work aimed at investigating the effects of mechanically amplified tremor on cortico-muscular coherence (CMC) in the alpha band. The study of CMC in this specific band is of particular interest because this coherence is usually absent in healthy individuals and it is an aberrant feature in patients affected by pathological tremors; understanding its mechanisms is therefore important. Thirteen healthy volunteers (23±4 years) performed elbow flexor sustained contractions both against a spring load and in isometric conditions at 20% of maximal voluntary isometric contraction (MVC). Spring stiffness was selected to induce instability in the stretch reflex servo loop. 64 EEG channels, surface EMG from the biceps brachii muscle and force were simultaneously recorded. Contractions against the spring resulted in greater fluctuations of the force signal and EMG amplitude compared to isometric conditions (p<.05). During isometric contractions CMC was systematically found in the beta band and sporadically observed in the alpha band. However, during the contractions against the spring load, CMC in the alpha band was observed in 12 out of 13 volunteers. Partial directed coherence (PDC) revealed an increased information flow in the EMG to EEG direction in the alpha band (p<.05). Therefore, coherence in the alpha band between the sensory-motor cortex and the biceps brachii muscle can be systematically induced in healthy individuals by mechanically amplifying tremor. The increased information flow in the EMG to EEG direction may reflect enhanced afferent activity from the muscle spindles. These results may contribute to the understanding of the presence of alpha band CMC in tremor related pathologies by suggesting that the origin of this phenomenon may not only be at cortical level but may also be affected by spinal circuit loops.

Effect of mental fatigue on induced tremor in human knee extensors.

In this study, the effects of mental fatigue on mechanically induced tremor at both a low (3-6Hz) and high (8-12Hz) frequency were investigated. The two distinct tremor frequencies were evoked using two springs of different stiffness, during 20s sustained contractions of the knee extensor muscles at 30% maximum voluntary contraction (MVC) before and after 100min of a mental fatigue task, in 12 healthy (29±3.7years) participants. Mental fatigue resulted in a 6.9% decrease in MVC and in a 9.4% decrease in the amplitude of the agonist muscle EMG during sustained 30% MVC contractions in the induced high frequency only. Following the mental fatigue task, the coefficient of variation and standard deviation of the force signal decreased at 8-12Hz induced tremor by 31.7% and 35.2% respectively, but not at 3-6Hz induced tremor. Similarly, the maximum value and area underneath the peak in the power spectrum of the force signal decreased by 55.5% and 53.1% respectively in the 8-12Hz range only. In conclusion, mental fatigue decreased mechanically induced 8-12Hz tremor and had no effect on induced 3-6Hz tremor. We suggest that the reduction could be attributed to the decreased activation of the agonist muscles.

Dexterity training improves manual precision in patients affected by essential tremor.

OBJECTIVE: To evaluate the effect of a short-term dexterity-training program on muscle tremor and the performance of hand precision tasks in patients with essential tremor (ET). DESIGN: Three testing sessions: baseline, after 4 weeks without any interventions (control), and after 4 weeks of dexterity-training carried out 3 times per week. SETTING: Biomechanics research laboratory. PARTICIPANTS: Patients (N=8) with a diagnosis of ET. INTERVENTION: Training program consisted of 12 dexterity training sessions where each session comprised 4 tasks involving both goal-directed manual movements and hand postural exercises. MAIN OUTCOME MEASURES: Testing included an ET-specific quality of life questionnaire and postural and kinetic tremor assessments. Each training session was scored to evaluate the performance. RESULTS: After training, improvements were observed in the performance of the 2 goal-directed tasks (P<.01); however, postural and kinetic tremor did not change. CONCLUSIONS: This study suggests that dexterity training could be effective in increasing fine manual control during goal-directed movements, which are known to be the most compromised in this pathology. The absence of a decrease in tremor severity highlights the necessity for developing this novel training technique further, perhaps over a longer period of time. This study could provide guidelines for the prescription of self-directed and personalized home-based exercises and will offer clinicians a treatment that might be used as an adjuvant or an alternative to the classical pharmacotherapy.

The effects of isometric resistance training on stretch reflex induced tremor in the knee extensor muscles.

This study examines the effect of 4 wk of high-intensity isometric resistance training on induced tremor in knee extensor muscles. Fourteen healthy volunteers were assigned to either the training group (n = 7) or the nontraining control group (n = 7). Induced tremor was assessed by measuring force fluctuations during anisometric contractions against spring loading, whose compliance was varied to allow for preferential activation of the short or long latency stretch reflex components. Effects of high-intensity isometric resistance training on induced tremor was assessed under two contraction conditions: relative force matching, where the relative level of activity was equal for both pre- and post-training sessions, set at 30% maximum voluntary contraction (MVC), and absolute force matching, where the level of activity was set to 30% pretrained MVC. The training group experienced a 26.5% increase in MVC in contrast to the 0.8% for the control group. For relative force-matching contractions, induced tremor amplitude and frequency did not change in either the training or control group. During absolute force-matching contractions, induced tremor amplitude was decreased by 37.5% and 31.6% for the short and long components, respectively, with no accompanying change in frequency, for the training group. No change in either measure was observed in the control group for absolute force-matching contractions. The results are consistent with high-intensity isometric resistance training induced neural changes leading to increased strength, coupled with realignment of stretch reflex automatic gain compensation to the new maximal force output. Also, previous reported reductions in anisometric tremor following strength training may partly be due to changed stretch reflex behavior.