Electromyographic patterns of lower limb muscles during apprehensive gait in younger and older female adults

ObjectiveInvestigate the influence of apprehensive gait on activation and cocontraction of lower limb muscles of younger and older female adults.MethodsData of 17 younger (21.47 ± 2.06 yr) and 18 older women (65.33 ± 3.14 yr) were considered for this study. Participants walked on the treadmill at two different conditions: normal gait and apprehensive gait. The surface electromyographic signals (EMG) were recorded during both conditions on: rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), tibialis anterior (TA), gastrocnemius lateralis (GL), and soleus (SO).ResultsApprehensive gait promoted greater activation of thigh muscles than normal gait (F = 5.34 and p = 0.007, for significant main effect of condition; RF, p = 0.002; VM, p < 0.001; VL, p = 0.003; and BF, p = 0.001). Older adults had greater cocontraction of knee and ankle stabilizer muscles than younger women (F = 4.05 and p = 0.019, for significant main effect of groups; VM/BF, p = 0.010; TA/GL, p = 0.007; and TA/SO, p = 0.002).ConclusionApprehensive gait promoted greater activation of thigh muscles and older adults had greater cocontraction of knee and ankle stabilizer muscles. Thus, apprehensive gait may leads to increased percentage of neuromuscular capacity, which is associated with greater cocontraction and contribute to the onset of fatigue and increased risk of falling in older people.     

Intra-session repeatability of lower limb muscles activation pattern during pedaling

Assessment of intra-session repeatability of muscle activation pattern is of considerable relevance for research settings, especially when used to determine changes over time. However, the repeatability of lower limb muscles activation pattern during pedaling is not fully established. Thus, we tested the intra-session repeatability of the activation pattern of 10 lower limb muscles during a sub-maximal cycling exercise.Eleven triathletes participated to this study. The experimental session consisted in a reference sub-maximal cycling exercise (i.e. 150 W) performed before and after a 53-min simulated training session (mean power output = 200 ± 12 W). Repeatability of EMG patterns was assessed in terms of muscle activity level (i.e. RMS of the mean pedaling cycle and burst) and muscle activation timing (i.e. onset and offset of the EMG burst) for the 10 following lower limb muscles: gluteus maximus (GMax), semimembranosus (SM), Biceps femoris (BF), vastus medialis (VM), rectus femoris (RF), vastus lateralis (VL), gastrocnemius medianus (GM) and lateralis (GL), soleus (SOL) and tibialis anterior (TA).No significant differences concerning the muscle activation level were found between test and retest for all the muscles investigated. Only VM, SOL and TA showed significant differences in muscle activation timing parameters. Whereas ICC and SEM values confirmed this weak repeatability, cross-correlation coefficients suggest a good repeatability of the activation timing parameters for all the studied muscles.Overall, the main finding of this work is the good repeatability of the EMG pattern during pedaling both in term of muscle activity level and muscle activation timing.     

Older adults show higher increases in lower-limb muscle activity during whole-body vibration exercise

The purpose of this study was to compare lower limb muscle activity during whole-body vibration (WBV) exercise between a young and an older study population. Thirty young (25.9±4.3 yrs) and thirty older (64.2±5.3 yrs) individuals stood on a side-alternating WBV platform while surface electromyography (sEMG) was measured for the tibialis anterior (TA), gastrocnemius medialis (GM), soleus (SOL), vastus lateralis (VL), vastus medialis (VM), and biceps femoris (BF). The WBV protocol included nine vibration settings consisting of three frequencies (6, 11, 16 Hz) x three amplitudes (0.9, 2.5, 4.0 mm), and three control trials without vibration (narrow, medium, wide stance). The vertical platform acceleration (peak values of maximal displacement from equilibrium) was quantified during each vibration exercise using an accelerometer. The outcomes of this study showed that WBV significantly increased muscle activity in both groups for most vibration conditions in the TA (averaged absolute increase: young: +3.9%, older: +18.4%), GM (young: +4.1%, older: +9.5%), VL (young: +6.3%, older: +12.6%) and VM (young: +5.4%, older: +8.0%), and for the high frequency-amplitude combinations in the SOL (young: +7.5%, older: +12.6%) and BF (young: +1.9%, older: +7.5%). The increases in sEMG activity were significantly higher in the older than the young adults for all muscles, i.e., TA (absolute difference: 13.8%, P<0.001), GM (4.6%, P=0.034), VL (7.6%, P=0.001), VM (6.7%, P=0.042), BF (6.4%, P<0.001), except for the SOL (0.3%, P=0.248). Finally, the vertical platform acceleration was a significant predictor of the averaged lower limb muscle activity in the young (r=0.917, P<0.001) and older adults (r=0.931, P<0.001). In conclusion, the older population showed greater increases in lower limb muscle activity during WBV exercise than their young counterparts, meaning that they might benefit more from WBV exercises. Additionally, training intensity can be increased by increasing the vertical acceleration load.     

An investigation of the simultaneously recorded occlusal contact and surface electromyographic activity of jaw-closing muscles for patients with temporomandibular disorders and a scissors-bite relationship

Surface electromyographic (SEMG) activity of the masseter and anterior temporalis (TA) muscles has been reported to be associated with occlusion and orofacial pain. However, our recent report did not reveal an association between the side of orofacial pain and the side showing higher or lower level of SEMG activity of masseter or TA. The present purpose was to re-test this association in patients who had unilateral scissors-bite relationship. Thirty-two unilateral scissors-bite femalepatients complaining of unilateral orofacial pain (n = 15) or TMJ sounds (n = 17) were enrolled to simultaneously record contacts, force distribution of occlusion, and SEMG activity of masseter and TA during centric maximal voluntary clenching (MVC). The results indicated that neither orofacial pain nor the TMJ sounds had an association with the masseter’s SEMG values, while scissors-bite had (P < 0.05). A lower SEMG value for masseter was found on the scissors-bite side where there was a smaller number of contacts and a lower biting force distribution (P < 0.05). No such association was revealed in TA. In conclusion, in patients with unilateral TMD symptom(s) and scissors-bite, the jawclosing muscles’ SEMG activity during centric MVC was associated with the scissors-bite rather than the symptoms of orofacial pain or TMJ sounds.     

Reliability and interpretation of single leg stance and maximum voluntary isometric contraction methods of electromyography normalization

Normalization of electromyographic (EMG) amplitudes is necessary in the study of human motion. However, there is a lack of agreement on the most reliable and appropriate normalization method. This study evaluated the reliability of single leg stance (SLS) and maximal voluntary isometric contraction (MVIC) normalization methods and the relationship between these measures for the gluteus maximus (GMax), gluteus medius (GMed), rectus femoris (RF), vastus lateralis (VL), hip adductor group (ADD), and biceps femoris (BF). Surface EMG was recorded in 20 subjects during three 5 s trials of SLS and MVIC. SLS and MVIC methods both demonstrated good-to-excellent reliability in all muscles (ICCs > 0.80). Intrasubject coefficients of variation were lower for the MVIC method (9–36%) than for the SLS method (20–59%). EMG amplitudes during MVIC and SLS were significantly correlated for all muscles (Pearson r’s = 0.604–0.905, p < 0.005) except GMax (r = 0.250, p = 0.288). Use of SLS normalization for the RF, VL, and BF is not recommended due to a lack of measurement precision. However, this method is justified in the GMax, GMed, and ADD and may provide a better representation of coordinated muscle function during a functional task.     

Differences in neuromuscular control between impact and no impact roundhouse kick in athletes of different skill levels

This study aimed at investigating two aspects of neuromuscular control around the hip and knee joint while executing the roundhouse kick (RK) using two techniques: Impact RK (IRK) at trunk level and No-Impact RK at face level (NIRK). The influence of technical skill level was also investigated by comparing two groups: elite Karateka and Amateurs. Surface electromyographic (sEMG) signals have been recorded from the Vastus Lateralis (VL), Biceps Femoris (BF), Rectus Femoris (RF), Gluteus Maximum (GM) and Gastrocnemious (GA) muscles of the kicking leg in six Karateka and six Amateurs performing the RKs. Hip and knee kinematics were also assessed. EMG data were rectified, filtered and normalized to the maximal value obtained for each muscle over all trials; co-activation (CI) indexes of antagonist vs. overall (agonist and antagonist) activity were computed for hip and knee flexion and extension. Muscle Fiber Conduction Velocity (CV) obtained from VL and BF muscles was assessed as well. The effect of group and kick on angular velocity, CIs, and CVs was tested through a two-way ANOVA (p < 0.05). An effect of group was showed in both kicks. Karateka presented higher knee and hip angular velocity; higher BF-CV (IRK: 5.1 ± 1.0 vs. 3.5 ± 0.5 m/s; NIRK: 5.7 ± 1.3 vs. 4.1 ± 0.5 m/s), higher CIs for hip movements and knee flexion and lower CI for knee extension. The results obtained suggest the presence of a skill-dependent activation strategy in the execution of the two kicks. CV results are suggestive of an improved ability of elite Karateka to recruit fast MUs as a part of training induced neuromuscular adaptation.     

Muscle activation patterns of knee flexors and extensors during passive and active movement of the spastic lower limb in chronic stroke patients

The aim of this study was to describe the characteristics of spasticity, quantified as muscle activity during stretch, during passive and active movement. For this cross sectional study 19 stroke patients with spasticity in the lower limb were recruited. Reflex activity was studied with surface electromyography of knee flexor and extensor muscles during passive and active movement of the lower leg.On both the affected and unaffected side, root mean square values of the knee extensor muscles, while stretched, were higher during active than during passive movement (p < 0.05). For the vastus lateralis (VL) the correlation was moderate (ρ = 0.54, p = 0.022), for the rectus femoris (RF) high (ρ = 0.83, p < 0.001). For the semitendinosus (ST) the correlation was low (ρ = 0.27) and not significant.During active movement the correlation between VL activity and activity of the antagonist ST, as an indicator for co-contraction of the affected muscles, was marked (ρ = 0.73, p = 0.001). A moderate negative correlation was found between reflex activity of RF during passive stretch and the active range of motion (ρ = ?0.51, p = 0.027).The results show that a passive stretch test alone is insufficient either as assessment method for spasticity during active motor tasks or as a measure for motor control.     

Electromyographic responses of erector spinae and lower limb’s muscles to dynamic postural perturbations in patients with adolescent idiopathic scoliosis

The aim of this study was to evaluate electromyographic (EMG) responses of erector spinae (ES) and lower limbs’ muscles to dynamic forward postural perturbation (FPP) and backward postural perturbation (BPP) in patients with adolescent idiopathic scoliosis (AIS) and in a healthy control group. Ten right thoracic AIS patients (Cobb = 21.6 ± 4.4°) and 10 control adolescents were studied. Using bipolar surface electrodes, EMG activities of ES muscle at T10 (ES_T10) and L3 (ES_L3) levels, biceps femoris (BF), gastrocnemius lateralis (G) and rectus femoris (RF) muscles in the right and the left sides during FPP and BPP were evaluated. Muscle responses were measured over a 1s time window after the onset of perturbation. In FPP test, the EMG responses of right ES_T10, ES_L3 and BF muscles in the scoliosis group were respectively about 1.40 (p = 0.035), 1.43 (p = 0.07) and 1.45 (p = 0.01) times greater than those in control group. Also, in BPP test, at right ES_L3 muscle of the scoliosis group the EMG activity was 1.64 times higher than that in the control group (p = 0.01). The scoliosis group during FPP displayed asymmetrical muscle responses in ES_T10 and BF muscles. This asymmetrical muscle activity in response to FPP is hypothesized to be a possible compensatory strategy rather than an inherent characteristic of scoliosis.     

Comparative analysis of serum zinc,copper, magnesium,calcium and iron level in acute and chronic patients of visceral leishmaniasis

ProjectChronic visceral leishmaniasis (VL) is an increasingly common problem in disease endemic states of India. Identification of prognosis risk factor in patients with VL may lead to preventive actions, toward decreasing its mortality in chronic individuals. Though serum Zinc levels are decreased in patients of VL, limited information is available regarding trace elements status in acute and chronic VL patients. The present study was undertaken to compare serum trace elements concentrations in acute and chronic VL patients.ProcedureAcute (mean age = 28.64 years), chronic (mean age = 23.68 years) VL patients and healthy controls (mean age = 23.05 years) who agreed to provide blood specimens for laboratory investigations participated in this study. Serum zinc (Zn), copper (Cu), iron (Fe), magnesium (Mg) and calcium (Ca) were measured spectrophotometrically using chemistry analyzer.ResultsSerum Zn concentration was comparatively much decreased in chronic VL than to acute ones (p = 0.007) while serum Mg was higher in chronic VL than acute (p = 0.002) ones. There was no statistically significant difference between acute and chronic VL in serum concentrations of Cu, Fe and Ca.ConclusionsSerum Zn levels were much decreased and serum Mg were increased in chronic VL as compared to acute cases. The serum concentrations of Fe and Ca did not show any difference between two groups. The serum Cu was increased in both groups but more in chronic ones. Serum Zn and Mg could be a potential prognosis factor for chronic VL patients. We hypothesize zinc supplementation as a chemo preventive agent for chronic VL cases, particularly in endemic areas.     

Influence of ankle functional instability on the ankle electromyography during landing after volleyball blocking

The purpose of this study was to describe, interpret and compare the EMG activation patterns of ankle muscles – tibialis anterior (TA), peroneus longus (PL) and gastrocnemius lateralis (GL) – in volleyball players with and without ankle functional instability (FI) during landing after the blocking movement. Twenty-one players with FI (IG) and 19 controls (CG) were studied. The cycle of movement analyzed was the time period between 200 ms before and 200 ms after the time of impact determined by ground reaction forces. The variables were analyzed for two different phases: pre-landing (200 ms before impact) and post-landing (200 ms after impact). The RMS values and the timing of onset activity were calculated for the three studied muscles, in both periods and for both groups. The co-activation index for TA and PL, TA and GL were also calculated. Individuals with FI presented a lower RMS value pre-landing for PL (CG = 43.0 ± 22.0; IG = 26.2 ± 8.4, p < 0.05) and higher RMS value post-landing (CG = 47.5 ± 13.3; IG = 55.8 ± 21.6, p < 0.10). Besides that, in control group PL and GL activated first and simultaneously, and TA presented a later activation, while in subjects with FI all the three muscles activated simultaneously. There were no significant differences between groups for co-activation index. Thus, the rate of contraction between agonist and antagonist muscles is similar for subjects with and without FI but the activation individually was different. Volleyball players with functional instability of the ankle showed altered patterns of the muscles that play an important role in the stabilization of the foot–ankle complex during the performance of the blocking movement, to the detriment of the ligament complex, and this fact could explain the usual complaints in these subjects.     

Approach run increases preactivation and eccentric phases muscle activity during drop jumps from different drop heights

The purpose of this study was to investigate the effects of a horizontal approach run and drop height on the activation of lower extremity muscles during drop jumps. Ten participants performed drop jumps from drop heights of 15, 30, 45 and 60 cm with zero (standing), one, two, and three approach run steps. The EMG activities of the Gluteus Maximus (GM), Rectus Femoris (RF), Biceps Femoris (BF), Vastus Lateralis (VL), Tibialis Anterior (TA), Gastrocnemius (GA) and Soleus (SO) were recorded, full-wave rectified, and averaged (aEMG) during the preactivation (50 ms before touchdown), downward, and push-off phases. Increasing drop height did not enhance the muscle activation level of any examined muscles except GA. During the preactivation phase, the aEMG of all muscles except TA increased with the number of approach run steps. The aEMG of RF, BF, VL, and SO also increased with the number of approach run steps during the downward phase, while no aEMG changes were observed during the push-off phase. These results suggest that a horizontal approach run preceding the drop jump is an effective strategy for increasing the muscle preactivation level, which contributes to a higher level of muscle activity during the eccentric contraction phase and could potentially contribute to the reported higher power output during the concentric contraction phase.     

Loading and knee flexion after stroke: Less does not equal more

It is believed that force feedback can modulate lower extremity extensor activity during gait. The purpose of this research was to determine the role of limb loading on knee extensor excitability during the late stance/early swing phase of gait in persons post-stroke. Ten subjects with chronic hemiparesis post-stroke participated in (1) seated isolated quadriceps reflex testing with ankle loads of 0–0.4N m/kg and (2) gait analysis on a treadmill with 0%, 20% or 40% body weight support. Muscle reflex responses were recorded from vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) during seated testing. Knee kinematics and quadriceps activity during late stance/early swing phase of gait were compared across loading conditions. Although isolated loading of the ankle plantarflexors at 0.2 N m/kg reduced VM prolonged response (p = 0.04), loading did not alter any other measure of quadriceps excitability (all p > 0.08). During gait, the use of BWS did not influence knee kinematics (p = 0.18) or muscle activity (all p > 0.17) during late stance/early swing phase. This information suggests that load sensed at the ankle has minimal effect on the ipsilateral quadriceps of individuals post-stroke during late stance. It appears that adjusting limb loading during rehabilitation may not be an effective tool to address stiff-knee gait following stroke.     

Multichannel EMG-based estimation of fiber conduction velocity during isometric contraction of patients with different stages of diabetic neuropathy

This study compares muscle fiber conduction velocities estimated using surface electromyography during isometric maximal voluntary contraction in different stages of diabetic neuropathy. Eighty-five adults were studied: 16 non-diabetic individuals and 69 diabetic patients classified into four neuropathy stages, defined by a fuzzy expert system: absent (n = 26), mild (n = 21), moderate (n = 11) and severe (n = 11). Average muscle fiber conduction velocities of gastrocnemius medialis, tibialis anterior, vastus lateralis and biceps femoris were assessed using linear array electrodes, and were compared by ANOVA. Conduction velocities were significantly decreased in the moderate neuropathy group for the vastus lateralis compared to other groups (from 18% to 21% decrease), and were also decreased in all diabetic groups for the tibialis anterior (from 15% to 20% from control group). Not only the distal anatomical localization of the muscle affects the conduction velocity, but also the proportion of muscle fiber type, where the tibialis anterior with greater type I fiber proportion is affected earlier while the vastus lateralis with greater type II fiber proportion is affected in later stages of the disease. Generally, the muscles of the lower limb have different responsiveness to the effects of diabetes mellitus and show a reduction in the conduction velocity as neuropathy progresses.     

Altered EMG patterns in diabetic neuropathic and not neuropathic patients during step ascending and descending

Diabetic peripheral neuropathy (DPN) causes motor control alterations during daily life activities. Tripping during walking or stair climbing is the predominant cause of falls in the elderly subjects with DPN and without (NoDPN). Surface Electromyography (sEMG) has been shown to be a valid tool for detecting alterations of motor functions in subjects with DPN. This study aims at investigating the presence of functional alterations in diabetic subjects during stair climbing and at exploring the relationship between altered muscle activation and temporal parameter. Lower limb muscle activities, temporal parameters and speed were evaluated in 50 subjects (10 controls, 20 with DPN, 20 without DPN), while climbing up and down a stair, using sEMG, three-dimentional motion capture and force plates. Magnitude and timing of sEMG linear envelopes peaks were extracted. Level walking was used as reference condition for the comparison with step negotiation. sEMG, speed and temporal parameters revealed significant differences among all groups of patients. Results showed an association between earlier activation of lower limb muscles and reduced speed in subjects with DPN. Speed and temporal parameters significantly correlated with sEMG (p < 0.05). The findings of this study are encouraging and could be used to improve rehabilitation programs aiming at reducing falls risk in diabetic subjects.     

Delayed onset of electromyographic activity of the vastus medialis relative to the vastus lateralis may be related to physical activity levels in females with patellofemoral pain

The aims of this study were to examine group differences in muscle activation onset of the vastus medialis (VM) in relation to the vastus lateralis (VL) and pain level during stair ascent in females with patellofemoral pain (PFP) who maintain high and moderate levels of physical activity; to determine the association between physical activity level and muscle activation onset. Forty-three females with PFP and thirty-eight pain-free females were recruited and divided into four groups based on their level of physical activity: females with PFP (n = 26) and pain-free females (n = 26) who practiced a moderate level of physical activity and females with PFP (n = 17) and pain-free females (n = 12) who practiced an intense amount of physical activity. Participants were asked to ascend a seven-step staircase and the VM and VL activation onset was determined. Females with PFP who practiced high level of physical activity demonstrated delayed onset of VM (4.06 ms) compared to healthy females (−14.4 ms). Conversely, females with PFP who practiced moderate level of physical activity did not present VM delay (−2.48 ms) in comparison to healthy females (−9.89 ms). Furthermore, physical activity significantly correlated to the muscle activation onset difference (p = 0.005; R = 0.60). These findings may explain why controversial results regarding VM and VL muscle activation onset have been found.     

Muscle architecture variations along the human semitendinosus and biceps femoris (long head) length

The purpose of this study was to examine whether muscle architecture of the long head of biceps femoris (BF) and semitendinosus (ST) muscles varies along their length. The ST and BF muscles were dissected and removed from their origins in eight cadaveric specimens (age range 67.8–73.4 years). One-way analysis of variance designs were used to compare fascicle length (FL), pennation angle (PA) and muscle thickness (MT) between proximal, mid-belly and distal positions. Tendon and muscle length properties were also quantified. For the BF muscle, one-way analysis of variance tests showed a higher PA (23.96 ± 3.82°) and FL (7.12 ± 0.48 cm) proximally than distal positions (PA = 17.78 ± 1.95° and FL = 6.35 ± 0.89 cm, respectively). For the ST, there was a significantly (p < 0.05) lower PA (8.81 ± 1.22°) and FL (13.10 ± 1.54 cm) proximally than distally (PA = 14.69 ± 1.09° and FL = 15.49 ± 2.30 cm, respectively). Muscle thickness significantly increased from distal to more proximal positions (p < 0.05). These data suggest that the ST and BF architecture is not uniform and that measurement of these parameters largely depends on the measurement site. Modeling these muscles by assuming a uniform architecture along muscle length may yield less accurate representation of human hamstring muscle function.     

Myoelectric manifestations of fatigue in vastus lateralis,medialis obliquus and medialis longus muscles

The purpose of this study was to determine whether surface electromyography (EMG) assessment of myoelectric manifestations of muscle fatigue is capable of detecting differences between the vastus lateralis and medialis muscles which are consistent with the results of previous biopsy studies. Surface EMG signals were recorded from the vastus medialis longus (VML), vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during isometric knee extension contractions at 60% and 80% of the maximum voluntary contraction (MVC) for 10 s and 60 s, respectively. Initial values and rate of change of mean frequency (MNF), average rectified value (ARV) and conduction velocity (CV) of the EMG signal were calculated. Comparisons between the two force levels revealed that the initial values of MNF for the VL muscle were greater at 80% MVC compared to 60% MVC (P < 0.01). Comparisons between the vasti muscles demonstrated lower initial values of CV for VMO compared to VL at 60% MVC (P < 0.01) and lower than VML and VL at 80% MVC (P < 0.01). In addition, initial values of MNF were higher for VL with respect to both VML and VMO at 80% MVC (P < 0.01) and initial estimates of ARV were higher for VMO compared to VML at both force levels (P < 0.01 at 60% MVC and P < 0.05 at 80% MVC). For the sustained contraction at 80% MVC, VL demonstrated a greater decrease in CV over time compared to VMO (P < 0.05).These findings suggest that surface EMG signals and their time course during sustained isometric contractions may be useful to non-invasively describe functional differences between the vasti muscles.     

Non-invasive assessment of muscle fiber conduction velocity during an incremental maximal cycling test

Muscle fiber conduction velocity (MFCV) gives critical information on neuromuscular control and can be considered a size principle parameter, being suggestive of motor unit recruitment strategies. MFCV has been recently measured during constant-load sub-maximal cycling exercise and was found to correlate positively with percentage of type I myosin heavy chain.The aim of this study was to test the hypothesis that MFCV measured during an incremental cycling test using surface electromyography (sEMG), can be sensitive to the different metabolic requests elicited by the exercise. In particular, the relationship between ventilatory threshold (T-vent), V^′O_2max and MFCV was explored.Eleven male physically active subjects (age 30 ± 9 years) undertook a 1-min incremental cycling test to exhaustion. T-vent and V^′O_2max were measured using an open circuit breath by breath gas analyzer. The sEMG was recorded from the vastus lateralis muscle with an adhesive 4-electrodes array, and the MFCV was computed on each sEMG burst over the last 30-s of each step.The mean V^′O_2max obtained during the maximal test was 53.32 ± 2.33 ml kg^?1 min^?1, and the T-vent was reached at 80.77 ± 3.49% of V^′O_2max. In all subjects reliable measures of MFCV were obtained at every exercise intensity (cross correlation values >0.8). MFCV increased linearly with the mechanical load, reaching a maximum value of 4.28 ± 0.67 m s^?1 at an intensity corresponding to the T-vent. Thereafter, MFCV declined until maximal work intensities. This study demonstrates that MFCV can be used as non-invasive tool to infer MUs recruitment/derecruitment strategies even during dynamic exercise from low to maximal intensities.     

Muscle fibre conduction velocity and cardiorespiratory response during incremental cycling exercise in young and older individuals with different training status

We investigated the effect of ageing and training on muscle fibre conduction velocity (MFCV) and cardiorespiratory response during incremental cycling exercise. Eight young (YT; 24 ± 5 yrs) and eight older (OT; 64 ± 3 yrs) cyclists, together with eight young (YU; 27 ± 4 yrs) and eight older (OU; 63 ± 2 yrs) untrained individuals underwent to an incremental maximal test on a cycle ergometer. Ventilatory threshold (VT), respiratory compensation point (RCP) and maximal oxygen uptake (VO₂max) were identified and MFCV recorded from the vastus lateralis muscle using surface electromyography with linear arrays electrodes.In YT MFCV increased with the exercise intensity, reaching a peak of 4.99 ± 1.02 [m/s] at VT. Thereafter, and up to VO₂max, MFCV declined. In YU MFCV showed a similar trend although the peak [4.55 ± 0.53 m/s] was observed, at 75% of VO₂max an intensity higher than VT (66% of VO₂max). In both YT and YU MFCV did not decline until RPC, which occurred at 78% VO₂max in YU and at 92% VO₂max (P < 0.01) in YT. Differently from young individuals, MFCV in older subjects did not increase with exercise intensity. Moreover, maximal MFCV in OU was significantly lower [3.53 ± 0.40 m/s;] than that of YT (P < 0.005) and YU (P < 0.05).The present study shows that, especially in young individuals, MFCV reflects cardiorespiratory response during incremental dynamic cyclic exercise and hence can be used to investigate motor unit recruitment strategies.     

Ultrasonographic quantification of architectural response in tibialis anterior to neuromuscular electrical stimulation

While muscle contraction in voluntary efforts has been widely investigated, little is known about contraction during neuromuscular electrical stimulation (NMES). The aim of this study was to quantify in vivo muscle architecture of agonist and antagonist muscles at the ankle joint during NMES. Muscle fascicle lengths and pennation angles of the tibialis anterior (TA) and lateral gastrocnemius muscles were assessed via ultrasonography in 8 healthy young males. Measures were obtained during maximal NMES and torque-matched voluntary dorsiflexion contractions. In the TA, NMES induced a shorter fascicle length (67.2 ± 8.1 mm vs 74.6 ± 11.4 mm; p = 0.04) and a greater pennation angle (11.0 ± 2.4° vs 9.3 ± 2.5°; p = 0.03) compared with voluntary torque-matched dorsiflexion contractions. Architectural responses in the antagonist lateral gastrocnemius muscle did not significantly differ from rest or between voluntary and electrically induced contractions (p > 0.05). Contraction of the antagonist muscle was not a contributing factor to a greater fascicle shortening and increased pennation angle in the TA during NMES. TA architectural response during NMES likely arose from the contribution of muscle synergists during voluntary contractions coupled with a potentially localized contractile activity under the stimulation electrodes during NMES induced contractions.