Whole body vibration of different frequencies inhibits H-reflex but does not affect voluntary activation.

This study aimed to investigate the effects of whole-body vibration (WBV) at a frequency spectrum from 20 to 50 Hz on the Hoffmann (H) reflex and the voluntary motor output of ankle plantar-flexor muscles. A single-group (n: 8), repeated measures design was adopted with four conditions: standing (no vibration), 20, 35 and 50 Hz, each lasting one minute. H-reflex of the soleus muscle, maximal voluntary contraction (MVC) and central activation ratio (CAR) of the plantar-flexors were evaluated before, 1 and 5 min after each frequency condition. H-reflex decreased by 36.7% at 20 Hz, by 28% at 35 Hz, and by 34.8% at 50 Hz after one minute from WBV compared to baseline. Neither MVC nor CAR changed after WBV at all frequency conditions. The short-term, acute inhibition of the H-reflex after WBV at 20, 35 and 50 Hz suggested that decreased excitability of spinal motoneurons is not frequency dependent. On the other hand, the lack of vibration induced effects on MVC and CAR indicated that a 1-min WBV stimulus is not sufficient to affect the voluntary motor output.

Asymmetrical Lower Extremity Loading Early After Anterior Cruciate Ligament Reconstruction Is a Significant Predictor of Asymmetrical Loading at the Time of Return to Sport.

OBJECTIVES: The aim of this study was to examine whether asymmetrical lower limb loading early after anterior cruciate ligament reconstruction (1 mo) can predict asymmetrical lower limb loading at the time of return to sport (6 mos) and whether other early predictors as knee joint range of motion or maximal isometric strength affect this relationship. DESIGN: Ground reaction forces were measured during a sit-to-stand task 1 mo after anterior cruciate ligament reconstruction and a vertical countermovement jump 6 mos after anterior cruciate ligament reconstruction in 58 athletes. Other early postoperative measurements were knee joint range of motion (2 wks, 1 mo, and 2 mos after surgery) and maximal isometric strength of the knee extensor and flexor muscles (2 mos after surgery). Linear regression models were developed using side-to-side limb symmetry index (LSI) of countermovement jump as the dependent variable. RESULTS: LSI of sit-to-stand task 1 mo after surgery was a significant independent predictor of LSI of countermovement jump 6 mos after surgery. After accounting for deficits in knee joint range of motion and LSI of maximal isometric strength (ΔR² = 0.35, P < 0.01), LSI of sit-to-stand task predicted LSI of countermovement jump (ΔR² = 0.14 P < 0.01). CONCLUSIONS: Asymmetrical lower extremity loading 1 mo after anterior cruciate ligament reconstruction is an early predictor of asymmetrical lower extremity loading 6 mos after surgery.

Effects of rhythmical and extra-rhythmical qualities of music on heart rate during stationary bike activities.

BACKGORUND: The aim of this study was to evaluate the effects of rhythmical and extra-rhythmical qualities of music on the heart rate (HR) and rates of perceived exertion (RPE), during sub-maximal stationary bike activity. METHODS: HR of 28 female adult participants was monitored during 3 session of physical activity, performed under 3 different conditions: Hi-BPM (music with 150-170 BPM), RHYTHM (rhythmical qualities only of Hi-BPM condition) and control condition without music (CONTROL). Four parameters were analyzed: the highest HR value (High-HR), High-HR minus starting HR (∆HR), time to reach the 75% of Maximal HR (MHR) (TimeTo75%) and time over 75% MHR (TimeOver75%). HR trend analysis was performed to evaluate differences among the three conditions. OMNI-Cycle Scale was administered to evaluate RPE. RESULTS: MANOVA showed significant differences between the three conditions in TimeTo75%, ∆HR (P<0.01) and TimeOver75% (P<0.05). In RHYTHM and CONTROL conditions after reaching 75% MHR, the HR increase were significantly lower than Hi-BPM (P<0.01). No significant differences were found in OMNI-Cycle Scale scores of Hi-BPM and RHYTHM whereas RPE was significantly higher in CONTROL condition (P<0.05). CONCLUSIONS: Hi-BPM and RHYTHM music allowed a faster reaching of the aerobic training zone compared to CONTROL conditions. Nevertheless, after 75% MHR, extra-rhythmical qualities are necessary to maintain or to increase the working HR levels.

Activation of Neck and Low-Back Muscles Is Reduced with the Use of a Neck Balance System Together with a Lumbar Support in Urban Drivers.

Driving is associated with high activation of low-back and neck muscles due to the sitting position and perturbations imposed by the vehicle. The aim of this study was to investigate the use of a neck balance system together with a lumbar support on the activation of low-back and neck muscles during driving. Twelve healthy male subjects (age 32±6.71 years) were asked to drive in two conditions: 1) with devices; 2) without devices. During vehicle accelerations and decelerations root mean square (RMS) of surface electromyography (sEMG) was recorded from the erector spinae, semispinalis capitis and sternocleidomastoid muscles and expressed as a percentage of maximal voluntary contraction (MVC). The pitch of the head was obtained by means of an inertial sensor placed on the subjects' head. A visual analog scale (VAS) was used to assess the level of perceived comfort. RMS of the low back muscles was lower with than without devices during both acceleration and deceleration of the vehicle (1.40±0.93% vs 29 2.32±1.90% and 1.88±1.45% vs 2.91±2.33%, respectively), while RMS of neck extensor muscles was reduced only during acceleration (5.18±1.96% vs 5.91±2.16%). There were no differences between the two conditions in RMS of neck flexor muscles, the pitch of the head and the VAS score. The use of these two ergonomic devices is therefore effective in reducing the activation of low-back and neck muscles during driving with no changes in the level of perceived comfort, which is likely due to rebalancing weight on the neck and giving a neutral position to lumbar segments.

Early compensatory and anticipatory postural adjustments following anterior cruciate ligament reconstruction.

PURPOSE: Early identification of postoperative neuromuscular deficits has been advocated to prevent muscle weakness and maximize functional outcomes following anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to investigate neuromechanical changes in compensatory and anticipatory postural adjustments, which play a major role in minimizing unpredictable and predictable disturbances, respectively, as early as 2 months after ACLR. METHODS: Nine young male individuals who underwent ACLR with patellar tendon and nine age-matched healthy controls were exposed to two blocks of ten either unexpected or expected loading perturbations of the knee joint, while semi-reclined on a raised plinth. Amplitude and latency of postural responses in the vastus lateralis (VL), rectus femoris (RF) and biceps femoris (BF) muscles were determined by surface electromyography. RESULTS: Latency of compensatory responses was higher in patients with ACLR than in healthy participants for VL (82 ± 15 vs 68 ± 10 ms, P < 0.05) and RF (81 ± 21 vs 63 ± 10 ms, P < 0.05). Amplitude of compensatory responses was 54 % lower in patients with ACLR than in healthy participants for VL (P < 0.05). Onset of anticipatory responses occurred earlier in patients with ACLR than in healthy participants for VL (-83 ± 45 vs -26 ± 21 ms, P < 0.05), RF (-59 ± 48 vs -10 ± 13 ms, P < 0.05) and BF (-72 ± 42 vs -12 ± 14 ms, P < 0.01). CONCLUSION: Patients with ACLR showed early abnormalities in compensatory and anticipatory postural adjustments, which may reflect the inability to quickly detect sudden changes in muscle length or to completely activate muscles surrounding the knee, and may be addressed by specific training interventions.

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.

Comparison of walking energy cost between an anterior and a posterior ankle-foot orthosis in people with foot drop.

OBJECTIVE: To compare walking energy cost between an anterior and a posterior ankle-foot orthosis in people with foot drop. DESIGN: Within-group comparisons. PARTICIPANTS: Twenty-three adults (14 women, 9 men; mean age 56.8 years (standard deviation 15.4)) with foot drop. METHODS: PARTICIPANTS were asked to walk for 5 min at their self-selected walking speed under 3 conditions: (i) with shoes only; (ii) with a posterior ankle-foot orthosis; (iii) with an anterior ankle-foot orthosis. Spatio-temporal gait para-meters (speed, step length and step frequency) and walking energy cost per unit of distance were assessed for each walking condition. A visual analogue scale was used to quantify participants' level of perceived comfort for the 2 orthosis. RESULTS: Gait spatio-temporal parameters were higher with anterior ankle-foot orthoses than with posterior ankle-foot orthoses or shoes only. Walking energy cost per unit of distance was lower with anterior than posterior ankle-foot orthosis or shoes only ((mean ± standard error) 3.53 ± 1.00 vs 3.94 ± 1.27 and 3.98 ± 1.53 J·kg-1·m-1 respectively; p < 0.05) and level of perceived comfort was higher with anterior ((mean ± standard error) 8.00 ± 1.32) than with posterior ankle-foot orthosis ((mean ± standard error) 4.52 ± 2.57; p < 0.05). CONCLUSION: In people with foot drop the use of anterior ankle-foot orthoses resulted in lower energy costs of walking and higher levels of perceived comfort compared with posterior ankle-foot orthoses. Anterior ankle-foot orthoses may enable people with foot drop to walk further with less physical effort than posterior ankle-foot orthoses.

The role of the prefrontal cortex in the development of muscle fatigue in Charcot-Marie-Tooth 1A patients.

This study aimed at comparing both peripheral and central mechanisms of muscle fatigue between Charcot-Marie-Tooth 1A patients and healthy individuals during a fatiguing voluntary task by simultaneous electromyographic and electroencephalographic recordings. Six Charcot-Marie-Tooth 1A patients (3 females, 40±11 years) and 6-matched healthy individuals performed four blocks of sub-maximal isometric knee extensions. At the beginning of the session and after each block, electrically-evoked maximal single-twitch, maximal voluntary contraction and surface-electromyography of the vastus lateralis muscle were measured. The movement-related-cortical potentials were averaged in early (block 1-2) and late (block 3-4) stages of fatigue. The effect of fatigue was demonstrated at peripheral level by the decline of maximal voluntary contraction, maximal twitch and surface electromyography amplitude and at central level by the larger amplitude of movement-related-cortical-potentials during late than early stage of fatiguing sub-maximal contractions. Charcot-Marie-Tooth 1A patients showed lower motor cortex activity during motor planning, with earlier onset and larger prefrontal cortex activity during the late stage of the fatiguing task than healthy controls. These data demonstrate the key role of the prefrontal cortex in the development of fatigue in Charcot-Marie-Tooth 1A patients, which may be activated as a compensatory mechanism for the low motor cortex activation, thus reflecting high awareness of movement complexity.

Amount and intensity of daily living activities in Charcot-Marie-Tooth 1A patients.

BACKGROUND: Charcot-Marie-Tooth 1A (CMT1A) patients show a reduction of spontaneous activities of daily living measured by means of questionnaires or pedometers, which are quite inaccurate compared to recent measurement techniques. AIM: The study aimed at quantifying daily living activities in CMT1A patients by means of inertial sensors, which give information not only on the amount but also on the intensity of these activities. MATERIALS AND METHODS: Time and count (amount), and velocity and power (intensity) of 24 h daily living activities were measured in eight patients (20-48 years; Barthel >90; Tinetti >20) and eight healthy individuals, matched for age and gender, by means of a wearable inertial sensor device. RESULTS: There were no differences between patients and controls in the 24-h distance covered and count of steps. However, count of step climbing and sit to stand were lower in patients than in controls (139.93 ± 141.66 vs. 341.06 ± 164.07 n and 58.23 ± 7.82 vs. 65.81 ± 4.75 n, respectively; P < 0.05) as well as mean daily step-climbing and walking velocities (1.07 ± 0.17 vs. 1.21 ± 0.10 m/sec and 1.16 ± 0.31 vs. 1.87 ± 0.50 m/sec, respectively; P < 0.05). In CMT1A patients there was a positive correlation between strength of the knee extensor muscles and both count of steps climbed (R = 0.80) and sit to stand (R = 0.79). DISCUSSION AND CONCLUSION: The reduced ability of CMT1A patients to carry out activities at high intensity, which was correlated with strength, suggests that strength training might be a rehabilitation tool for improving the 1 ability to carry out these activities.

An anterior ankle-foot orthosis improves walking economy in Charcot-Marie-Tooth type 1A patients.

BACKGROUND: Ankle-foot orthoses are commonly prescribed in Charcot-Marie-Tooth type 1A disease to improve quality of walking and reduce the risk of falling due to the foot drop. OBJECTIVES: This study aimed at assessing the effect of an anterior ankle-foot orthosis on walking economy in a group of Charcot-Marie-Tooth type 1A patients. STUDY DESIGN: Within-group comparisons. METHODS: 7 Charcot-Marie-Tooth type 1A patients (four women and three men; 37 ± 11 years; age range = 22-53 years) were asked to walk on a circuit at their self-selected speeds ('slow', 'comfortable' and 'fast') in two walking conditions: (1) with shoes only and (2) with Taloelast(®) anterior elastic ankle-foot orthoses. Speed of walking and metabolic cost of walking energy cost per unit of distance were assessed at the three self-selected speeds of walking for both walking conditions. RESULTS: Speed of walking at the three self-selected speeds did not differ between shoes only and anterior elastic ankle-foot orthoses, whereas walking energy cost per unit of distance at comfortable speed was lower in patients using anterior elastic ankle-foot orthoses with respect to shoes only (2.39 ± 0.22 vs 2.70 ± 0.19 J kg(-1) m(-1); P < 0.05). CONCLUSIONS: In Charcot-Marie-Tooth type 1A patients, the use of anterior elastic ankle-foot orthoses improved walking economy by reducing the energy cost of walking per unit of distance, thus reflecting a lower level of metabolic effort and improved mechanical efficiency in comparison with shoes only. CLINICAL RELEVANCE: From a practical perspective, Charcot-Marie-Tooth type 1A patients with anterior elastic ankle-foot orthoses can walk for a longer duration with a lower level of physical effort. Improvements in walking economy due to ankle-foot orthoses are likely a consequence of the reduction in steppage gait.

The neurophysiology of central and peripheral fatigue during sub-maximal lower limb isometric contractions.

Fatigue has been defined as an exercise-induced decline in force generation capacity because of changes at both the peripheral and central levels. Movement is preceded and accompanied by brain activities related to the preparation and execution of movement (movement related cortical potentials, MRCP), which have been correlated with the perception of effort (RPE). We combined force measurements, surface electromyography (sEMG), peripheral electrical stimulation (maximal twitch, MT) and MRCP analysis to further our understanding of the neural correlates of peripheral and central changes during a fatiguing task involving the lower limbs. Eighteen healthy volunteers performed 4 blocks of isometric knee extensions at 40% of the maximal voluntary contraction (MVC) for a total of 240 2-s contractions. At the baseline and after each block, we measured RPE, MT and MVC. We simultaneously recorded the force of the knee extensor muscles, root mean square (RMS) of the sEMG of the vastus lateralis muscle, and electroencephalography (EEG) from 64 channels. The MRCPs were extracted from the EEG recordings and averaged in the early (Block 1-2) and late (Block 3-4) blocks. Two cohorts were obtained by cluster analysis based on the RPE (i.e., perception of effort) and MT (i.e., peripheral fatigue). We observed a significant decline in both the MVC (-13%) and RMS (-25%) of the sEMG signal over the course of the task; thus, muscle fatigue had occurred in all of the participants regardless of the cohort. The MRCP amplitude was larger in the fatigued than the non-fatigued MT cohort in the supplementary and premotor areas, whereas the MRCP amplitude was larger in the fatigued than the non-fatigued RPE cohort in the aforementioned areas, and also in the primary motor and prefrontal cortices (PFC). The increase in the positive activity of the PFC, along with the perception of effort, represents a novel result, suggesting that it is modulated more by the perception of effort than peripheral fatigue.

Neuromuscular function after muscle fatigue in Charcot-Marie-Tooth type 1A patients.

INTRODUCTION: The effect of recovery time on neuromuscular function after a fatiguing task was compared in both the upper and lower limbs between patients with Charcot-Marie-Tooth type 1A (CMT1A) and healthy individuals. METHODS: Torque of elbow flexors and knee extensors and surface electromyography (sEMG) data of biceps brachii and vastus lateralis were recorded from 8 CMT1A patients and 8 matched, healthy individuals during maximal voluntary contraction (MVC) before (pre-fatigue MVC), 10 s after (10-s post-fatigue MVC), and 10 min after (10-min post-fatigue MVC) a fatiguing task at 80% MVC until exhaustion. RESULTS: Only in the lower limb, torque and root mean square of sEMG (RMS) during pre-fatigue MVC were lower (P < 0.05) in patients (91.93 ± 45.95 Nm, 0.11 ± 0.07 mV) than in controls (161.06 ± 75.5 Nm, 0.24 ± 0.16 mV). In the 10-min post-fatigue MVC, muscle-fiber conduction velocity (MFCV) and RMS, expressed as a percentage of pre-fatigue MVC, were lower (P < 0.05) in patients (MFCV 90.3 ± 6.91%, RMS 84.50 ± 9.89%) than in controls (MFCV 100.87 ± 5.1%, RMS 92.71 ± 11.84%). CONCLUSIONS: CMT1A patients are not only weaker than healthy individuals in the knee extensors, but they also have impaired neuromuscular recovery after fatigue.

Charcot-Marie-Tooth 1A patients with low level of impairment have a higher energy cost of walking than healthy individuals.

The study aimed at quantifying the walking energy cost of a group of Charcot-Marie-Tooth 1A patients (CMT1A), with low severity of walking impairment, in comparison with healthy individuals. Oxygen uptake was measured in 8 patients (age-range 20-48 years; Barthel >90; Tinetti >20) and 8 healthy individuals, matched for age and gender, when walking on a circuit for 5-min at their self-selected speeds ("slow", "comfortable" and "fast"). Both comfortable and fast speeds were lower in patients than in the control group (0.92±0.16 vs 1.16±0.22 and 1.27±0.27 vs 1.61±0.22 m s⁻¹, respectively; P<0.05), whereas walking energy cost per unit of distance was higher in patients than in the control group (P<0.05) at both "comfortable" (2.27±0.35 vs 1.92±0.21 J kg⁻¹m⁻¹) and "fast" speed (3.05±0.35 vs 2.37±0.42 J kg⁻¹m⁻¹). CMT1A patients, therefore, choose to walk slower but with higher metabolic cost compared to healthy individuals, despite no clinically evident walking impairment, which is likely due to altered walking patterns.