Ryosuke Ando

Validity of fascicle length estimation in the vastus lateralis and vastus intermedius using ultrasonography

The purpose of this study was to determine the validity of fascicle length estimation in the vastus lateralis (VL) and vastus intermedius (VI) using ultrasonography. The fascicle lengths of the VL and VI muscles were measured directly (dFL) using calipers, and were estimated (estmFL) using ultrasonography, in 10 legs from five Thiels embalmed cadavers. To determine the validity of the estmFLs, FL was estimated using five previously published models and compared with dFL. The intraclass correlation coefficients (ICCs) of two of the five models were>0.75, indicating that these estimates were valid. Both of these models combined measurement of the length of the visible part of the fascicle with linear extrapolation of the length of the part of the fascicle that was not visible on the sonographic image. The ICCs and absolute% difference were best in models that used appropriate pennation angles. These results suggest that two of the five previously published models are valid for obtaining estmFL of the VL and VI using ultrasonography.

Local architecture of the vastus intermedius is a better predictor of knee extension force than that of the other quadriceps femoris muscle heads

The purpose of this study was to determine whether the muscle architecture of each head of the quadriceps femoris (QF) at multiple regions can be used to predict knee extension force. Muscle thickness and pennation angle were measured using sonographic images from multiple regions on each muscle of the QF with the knee flexed to 90°. The fascicle lengths of the rectus femoris (RF), vastus lateralis (VL) and vastus intermedius (VI) muscles were estimated based on sonographic images taken along the length of the thigh. The muscle architecture of the vastus intermedius was determined in two separate locations using sonographic images of the anterior (ant‐VI) and lateral portions (lat‐VI). The maximal voluntary contraction (MVC) was measured during isometric knee extension at a knee joint angle of 90°. The relationship between MVC force and muscle architecture was examined using a stepwise linear regression analysis with MVC force as the dependent variable. The muscle thickness of the ant‐VI was selected as an independent variable in the first step of the linear regression analysis (R2 = 0·66, P<0·01). In the second step, pennation angle of the lat‐VI was added to the model (R2 = 0·91, P<0·01). These results suggest that among the four muscles that make up the QF, the muscle architecture of the VI is the best predictor of knee extension force.

Difference in fascicle behaviors between superficial and deep quadriceps muscles during isometric contractions

In this study we examined changes in fascicle length and pennation of vastus intermedius (VI) and vastus lateralis (VL) from rest to isometric contraction.

Non-uniform recruitment along human rectus femoris muscle during transcutaneous electrical nerve stimulation

PurposeTo test the hypothesis that motor units with different axonal excitability levels are localized in specific portions of the rectus femoris (RF) muscle using transcutaneous electrical nerve stimulation.MethodsM-waves were elicited by transcutaneous electrical nerve stimulation and detected from 24 sites along longitudinal line of the muscle. The stimulation was applied to the femoral nerve, and the current level was gradually increased.ResultsThe central locus activation, which is calculated from the spatial distribution of M-waves, appeared at the proximal regions at low stimulation level and then moved to the middle site of the muscle with an increase in the stimulation level. The results reveal that groups of motor units activated at different stimulation levels are located in different positions in the proximal–distal muscle direction.ConclusionOur results suggest that motor unit properties in proximal and other regions are not uniform within the RF muscle.

Effects of prolonged vibration to vastus intermedius muscle on force steadiness of knee extensor muscles during isometric force-matching task.

Afferent inputs from Ia fibers in muscle spindles are essential for the control of force and prolonged vibration has been applied to muscle-tendon units to manipulate the synaptic input from Ia afferents onto α-motor neurons. The vastus intermedius (VI) reportedly provides the highest contribution to the low-level knee extension torque among the individual synergists of quadriceps femoris (QF). The purpose of the present study was to examine the effect of prolonged vibration to the VI on force steadiness of the QF. Nine healthy men (25.1±4.3years) performed submaximal force-matching task of isometric knee extension for 15s before and after mechanical vibration to the superficial region of VI for 30min. Target forces were 2.5%, 10%, and 30% of maximal voluntary contraction (MVC), and force steadiness was determined by the coefficient of variation (CV) of force. After the prolonged VI vibration, the CV of force at 2.5%MVC was significantly increased, but CVs at 10% and 30%MVCs were not significantly changed. The present study concluded that application of prolonged vibration to the VI increased force fluctuations of the QF during a very low-level force-matching task.

Similarity of muscle synergies extracted from the lower limb including the deep muscles between level and uphill treadmill walking

This study aimed to examine muscle synergies involving the deeper muscles of the lower limb during level and uphill treadmill walking. Seven men and five women walked on a treadmill at three speeds (60, 80, and 100m/min) and two grades (level and 10% grade). Surface electromyographic (EMG) signals were recorded from 10 muscles of the lower limb, including vastus intermedius, adductor magnus, and adductor longus. Muscle synergies were extracted applying non-negative matrix factorization, and the relative co-activation across muscles and the temporal information of synergy recruitment were identified by the muscle synergy vector and synergy activation coefficient, respectively. Correlation coefficients between a pair of synergy vectors during level and uphill walking were analyzed as a similarity index, with the similarity criterion at r=0.76. Changes in synergy activation coefficients between the walking conditions were evaluated by cross-correlation analysis. The mean number of synergies ranged from 3.8 to 4.0 across all conditions, and they were not significantly different between level and uphill walking conditions. Similarity between walking conditions was high (r>0.76) for three muscle synergies, but not for one synergy that mainly consisted of the quadriceps femoris. The inter-condition similarity of the synergy activation coefficients was high for the four synergies, and a significant lag time for synergy 2, which consisted mainly of the activity of medial gastrocnemius, was found at 60 and 80m/min. The muscle synergies extracted from the lower limb involving the deeper muscles appear to be consistent during level and uphill treadmill walking.

Muscle synergies are consistent across level and uphill treadmill running

This study aimed to identify muscle synergies of the lower limb during treadmill running on level and inclined ground. Eight subjects ran on a treadmill at three speeds (2.5, 3.3, and 4.1 m/s) and two grades (level and 10% grade). Surface electromyographic (EMG) signals were recorded from 10 muscles of the lower limb, including deeper muscles such as vastus intermedius, adductor magnus, and adductor longus. Muscle synergies were extracted applying a non-negative matrix factorization algorithm, and relative co-activations across muscles and the temporal recruitment pattern were identified by muscle synergy vector and synergy activation coefficient, respectively. The scalar product between pairs of synergy vectors and synergy activation coefficients during level and uphill running conditions were analyzed as a similarity index, with values above 0.8 recognized as similar. Approximately 4 muscle synergies controlled the majority of variability in 10 EMGs during running, and were common between level and uphill conditions. At each running speed, inter-condition similarity was observed in synergy vector (r > 0.83) and synergy activation coefficients (r > 0.84) at each type of synergy. These results suggest that types of synergy are consistent between level and uphill running.

Vastus intermedius vs vastus lateralis fascicle behaviors during maximal concentric and eccentric contractions

Vastus intermedius (VI) plays a major role in knee extension, but its fascicle behaviors during dynamic contractions are not well understood. This study aimed to compare VI and vastus lateralis (VL) fascicle behaviors during singular maximal concentric and eccentric contractions. Thirteen men (27.1 ± 3.4 years) performed maximal isokinetic concentric contractions through knee joint angles of 105° to 35° (0° = full extension) and eccentric contractions from 35° to 105° at an angular velocity of 30°/s. Longitudinal VI and VL sonographic images were simultaneously recorded at 30 Hz, and muscle fascicle lengths at the knee joint angles of 40° and 100° were measured to compare the magnitudes of fascicle length change between the muscles. During concentric contractions, VI and VL fascicle lengths at 100° were 108 ± 12 mm and 104 ± 12 mm, respectively, and shortened by 36 ± 12 mm for VI and 28 ± 13 mm for VL (not statistically different; P = .13) at 40°. During eccentric contractions, VI and VL fascicle lengths at 40° were 72 ± 7 mm and 75 ± 8 mm, respectively, but lengthened by 35 ± 9 mm for VI and 24 ± 5 mm for VL at 100°, with a significant difference between the muscles (P = .01). These results indicate that VI fascicles are lengthened 1.4 times more than VL fascicles during eccentric contractions, whereas VI and VL fascicles shorten similarly during concentric contractions. This suggests a possibility that a greater mechanical strain is imposed to VI than VL during eccentric contractions.

Knee joint angle and vasti muscle electromyograms during fatiguing contractions

We compared vasti muscle electromyograms for two knee joint angles during fatiguing tetanic contractions. Tetanic contraction of the knee extensors was evoked for 70 s by electrical stimulation of the femoral nerve at knee joint angles of 60° (extended, with 0° indicating full extension) and 110° (flexed) in eight healthy men. Surface electromyography was recorded from the vastus intermedius (VI), vastus lateralis (VL) and vastus medialis (VM) muscles. Knee extension force and M‐wave amplitudes and durations were calculated every 7 s, which were normalized by the initial value. Normalized knee extension force was decreased at the flexed knee joint angle compared with that of the extended knee joint angle (P<0·05). Decreased normalized M‐wave amplitude and increased normalized M‐wave duration of the VI were greater at the flexed knee joint angle than the extended knee joint angle (P<0·05), whereas those for the VL and VM were similar (P>0·05). These results suggest that peripheral fatigue profiles of the VI might be greater at the flexed than the extended knee joint angles, but that of VL and VM might be similar in the tested range of knee joint angles (i.e. 60°–110°) during continuous tetanic contraction induced by electrical stimulation. Therefore, greater reduction of knee extension force at the flexed knee joint angle than the extended knee joint angle may reflect fatigue development of the VI more than other quadriceps femoris components.

Oxygenation and neuromuscular activation of the quadriceps femoris including the vastus intermedius during a fatiguing contraction

The purpose of this study was to assess oxygenation and neuromuscular activation of the quadriceps femoris muscle group, including the vastus intermedius (VI), during a fatiguing contraction.