Muscle Activity Determined by Cosine Tuning With a Nontrivial Preferred Direction During Isometric Force Exertion by Lower Limb

2005 ◽  
Vol 93 (5) ◽  
pp. 2614-2624 ◽  
Author(s):  
Daichi Nozaki ◽  
Kimitaka Nakazawa ◽  
Masami Akai
Keyword(s):  
Lower Limb ◽  
Muscle Activation ◽  
Isometric Force ◽  
Vastus Lateralis ◽  
Knee Extensor ◽  
Joint Torque ◽  
Emg Activity ◽  
Preferred Direction ◽  
Activation Level ◽  
Ankle Brace

We investigated how the CNS selects a unique muscle activation pattern under a redundant situation resulting from the existence of bi-articular muscles. Surface electromyographic (EMG) activity was recorded from eight lower limb muscles while 11 subjects were exerting isometric knee and hip joint torque simultaneously ( Tk and Th, respectively. Extension torque was defined as positive). The knee joint was kept at either 90 or 60°. Various combinations of torque were imposed on both joints by pulling a cable attached to an ankle brace with approximately three levels of isometric force in 16 directions. The distribution of the data in the three-dimensional plot (muscle activation level quantified by the root mean squared value of EMG vs. Tk and Th) demonstrates that the muscle activation level M can be approximated by a single model as M = ⌊ aTk + bTh⌋ where ⌊ x⌋ = max ( x,0) and a and b are constants. The percentage of variance explained by this model averaged over all muscles was 82.3 ± 14.0% (mean ± SD), indicating that the degree of fit of the data to the plane was high. This model suggests that the CNS uses a cosine tuning function on the torque plane ( Tk, Th) to recruit muscles. Interestingly, the muscle's preferred direction (PD) defined as the direction where it is maximally active on the torque plane deviated from its own mechanical pulling direction (MD). This deviation was apparent in the mono-articular knee extensor (MD = 0°, whereas PD = 14.1 ± 3.7° for vastus lateralis) and in the mono-articular hip extensor (MD = 90°, whereas PD = 53.4 ± 6.4° for gluteus maximus). Such misalignment between MD and PD indicates that the mono-articular muscle's activation level depends on the torque of the joint that it does not span. Practical implications of this observation for the motor control studies were discussed. We also demonstrated that the observed shift from the MD to the PD is plausible in the configuration of our musculo-skeletal system and that the experimental results are likely to be explained by the CNS process to minimize the variability of the endpoint force vector under the existence of signal-dependent noise.

Hindlimb muscle function in relation to speed and gait:in vivopatterns of strain and activation in a hip and knee extensor of the rat (Rattus norvegicus)

2001 ◽  
Vol 204 (15) ◽  
pp. 2717-2731 ◽  
Author(s):  
Gary B. Gillis ◽  
Andrew A. Biewener
Keyword(s):  
Muscle Activation ◽  
Stance Phase ◽  
Mechanical Performance ◽  
Vastus Lateralis ◽  
Knee Extensor ◽  
Metabolic Energy ◽  
Emg Activity ◽  
Muscle Strain ◽  
Step Cycle ◽  
Limb Muscles

SUMMARYUnderstanding how animals actually use their muscles during locomotion is an important goal in the fields of locomotor physiology and biomechanics. Active muscles in vivo can shorten, lengthen or remain isometric, and their mechanical performance depends on the relative magnitude and timing of these patterns of fascicle strain and activation. It has recently been suggested that terrestrial animals may conserve metabolic energy during locomotion by minimizing limb extensor muscle strain during stance, when the muscle is active, facilitating more economical force generation and elastic energy recovery from limb muscle–tendon units. However, whereas the ankle extensors of running turkeys and hopping wallabies have been shown to generate force with little length change (<6% strain), similar muscles in cats appear to change length more substantially while active. Because previous work has tended to focus on the mechanical behavior of ankle extensors during animal movements, the actions of more proximal limb muscles are less well understood. To explore further the hypothesis of force economy and isometric behavior of limb muscles during terrestrial locomotion, we measured patterns of electromyographic (EMG) activity and fascicle strain (using sonomicrometry) in two of the largest muscles of the rat hindlimb, the biceps femoris (a hip extensor) and vastus lateralis (a knee extensor) during walking, trotting and galloping. Our results show that the biceps and vastus exhibit largely overlapping bursts of electrical activity during the stance phase of each step cycle in all gaits. During walking and trotting, this activity typically commences shortly before the hindlimb touches the ground, but during galloping the onset of activity depends on whether the limb is trailing (first limb down) or leading (second limb down), particularly in the vastus. In the trailing limb, the timing of the onset of vastus activity is slightly earlier than that observed during walking and trotting, but in the leading limb, this activity begins much later, well after the foot makes ground contact (mean 7% of the step cycle). In both muscles, EMG activity typically ceases approximately two-thirds of the way through the stance phase. While electrically active during stance, biceps fascicles shorten, although the extent of shortening differs significantly among gaits (P<0.01). Total average fascicle shortening strain in the biceps is greater during walking (23±3%) and trotting (27±5%) than during galloping (12±5% and 19±6% in the trailing and leading limbs, respectively). In contrast, vastus fascicles typically lengthen (by 8–16%, depending on gait) over the first half of stance, when the muscle is electrically active, before shortening slightly or remaining nearly isometric over much of the second half of stance. Interestingly, in the leading limb during galloping, vastus fascicles lengthen prior to muscle activation and exhibit substantial shortening (10±2%) during the period when EMG activity is recorded. Thus, patterns of muscle activation and/or muscle strain differ among gaits, between muscles and even within the same muscle of contralateral hindlimbs (as during galloping). In contrast to the minimal strain predicted by the force economy hypothesis, our results suggest that proximal limb muscles in rats operate over substantial length ranges during stance over various speeds and gaits and exhibit complex and changing activation and strain regimes, exemplifying the variable mechanical roles that muscles can play, even during level, steady-speed locomotion.

Lower limb skeletal muscle function after 6 wk of bed rest

1997 ◽  
Vol 82 (1) ◽  
pp. 182-188 ◽  
Author(s):  
H. E. Berg ◽  
L. Larsson ◽  
P. A. Tesch
Keyword(s):  
Skeletal Muscle ◽  
Lower Limb ◽  
Muscle Function ◽  
Fiber Type ◽  
Vastus Lateralis ◽  
Knee Extensor ◽  
Bed Rest ◽  
Emg Activity ◽  
Type I ◽  
Skeletal Muscle Function

Berg, H. E., L. Larsson, and P. A. Tesch. Lower limb skeletal muscle function after 6 wk of bed rest. J. Appl. Physiol. 82(1): 182–188, 1997.—Force, electromyographic (EMG) activity, muscle mass, and fiber characteristics were studied in seven healthy men before and after 6 wk of bed rest. Maximum voluntary isometric and concentric knee extensor torque decreased ( P < 0.05) uniformly across angular velocities by 25–30% after bed rest. Maximum quadricep rectified EMG decreased by 19 ± 23%, whereas submaximum (100-Nm isometric action) EMG increased by 44 ± 28%. Knee extensor muscle cross-sectional area (CSA), assessed by using magnetic resonance imaging, decreased by 14 ± 4%. Maximum torque per knee extensor CSA decreased by 13 ± 9%. Vastus lateralis fiber CSA decreased 18 ± 14%. Neither type I, IIA, and IIB fiber percentages nor their relative proportions of myosin heavy chain (MHC) isoforms were altered after bed rest. Because the decline in strength could not be entirely accounted for by decreased muscle CSA, it is suggested that the strength loss is also due to factors resulting in decreased neural input to muscle and/or reduced specific tension of muscle, as evidenced by a decreased torque/EMG ratio. Additionally, it is concluded that muscle unloading in humans does not induce important changes in fiber type or MHC composition or in vivo muscle contractile properties.

Intent-Related Differences in Surface EMG of Maximum Eccentric and Concentric Contractions

2003 ◽  
Vol 19 (2) ◽  
pp. 99-105 ◽  
Author(s):  
Mark D. Grabiner ◽  
Tammy M. Owings
Keyword(s):  
Muscle Activation ◽  
Vastus Lateralis ◽  
Knee Extensor ◽  
Eccentric Contraction ◽  
Surface Emg ◽  
Vastus Lateralis Muscle ◽  
Concentric Contractions ◽  
Concentric Contraction ◽  
Contraction Condition ◽  
The Difference

For this study it was hypothesized that when participants intended to perform a maximum voluntary concentric (or eccentric) contraction but had an eccentric (or concentric) contraction imposed upon them, the initial EMG measured during the isometric phase preceding the onset of the dynamometer motion would reflect the intended contraction condition. The surface EMG of the vastus lateralis muscle was measured in 24 participants performing isokinetic concentric and eccentric maximum voluntary knee extensor contractions. The contractions were initiated from rest and from the same knee flexion angle and required the same level of external force to trigger the onset of dynamometer motion. Vastus lateralis EMG were quantified during the isometric phase preceding the onset of the dynamometer motion. When participants intended to perform a concentric contraction but had an eccentric contraction imposed upon them, the initial EMG resembled that of a concentric contraction. When they intended to perform an eccentric contraction but had a concentric contraction imposed upon them, the initial EMG resembled that of an eccentric contraction. Overall, the difference between concentric and eccentric contractions observed during the period of theinitialmuscle activation implies that descending signals include information that distinguishes between eccentric and concentric contractions.

THE EFFECT OF LEG PREFERENCE ON MECHANICAL EFFICIENCY DURING SINGLE-LEG EXTENSION EXERCISE

2021 ◽  
Author(s):  
Massimo Venturelli ◽  
Cantor Tarperi ◽  
Chiara Milanese ◽  
Luca Festa ◽  
Luana Toniolo ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Near Infrared ◽  
Isometric Force ◽  
Fiber Type ◽  
Vastus Lateralis ◽  
Critical Role ◽  
Inverse Correlation ◽  
Mechanical Efficiency ◽  
Peak Power Output ◽  
Leg Extension

To investigate how leg preference affects net efficiency (ηnet), we examined central and peripheral hemodynamics, muscle fiber type, activation and force of preferred (PL) and non-preferred (NPL) leg. Our hypothesis was that PL greater efficiency could be explained by adaptations and interactions between central, peripheral factors and force. Fifteen young participants performed single-leg extension exercise at absolute (35W) and relative (50%peak power-output (Wpeak)) workloads with PL and NPL. Oxygen uptake, photoplethysmography, Doppler ultrasound, near-infrared-spectroscopy deoxy-hemoglobin [HHb], integrated electromyography (iEMG), maximal isometric force (MVC), rate of force development (RFD50-100) and muscle biopsies of both vastus lateralis, were studied to assess central and peripheral determinants of ηnet. During exercise executed at 35W, ηnet was 17.5±5.1% and 11.9±2.1% (p<0.01) in NP and NPL respectively, while during exercise at the 50% of Wpeak, was in PL = 18.1±5.1% and in NPL = 12.5±1.9 (p<0.01). The only parameter correlated with ηnet was iEMG which showed an inverse correlation for absolute (r=-0.83 and -0.69 for PL and NPL) and relative workloads (r=-0.92 and -0.79 for PL and NPL). MVC and RFD50-100 were higher in PL than in NPL but not correlated to ηnet. This study identified a critical role of leg preference in the efficiency during single-leg extension exercise. The whole spectrum of the central and peripheral, circulatory and muscular determinants of ηnet did not explain the difference between PL and NPL efficiency. Therefore, the lower muscle activation exhibited by the PL is likely the primary determinant of this physiological phenomenon.

Activation varies among the knee extensor muscles during a submaximal fatiguing contraction in the seated and supine postures

2003 ◽  
Vol 95 (4) ◽  
pp. 1515-1522 ◽  
Author(s):  
L Rochette ◽  
S. K. Hunter ◽  
N Place ◽  
R Lepers
Keyword(s):  
Vastus Lateralis ◽  
Maximum Voluntary Contraction ◽  
Knee Extensor ◽  
Voluntary Contraction ◽  
Emg Activity ◽  
Task Failure ◽  
Rate Of Increase ◽  
Extensor Muscles ◽  
Seated Posture ◽  
Knee Extensor Muscles

Ten young men sustained an isometric contraction of the knee extensor muscles at 20% of the maximum voluntary contraction (MVC) torque on three separate occasions in a seated posture. Subjects performed an isometric knee extension contraction on a fourth occasion in a supine posture. The time to task failure for the seated posture was similar across sessions (291 ± 84 s; P > 0.05), and the MVC torque was similarly reduced across sessions after the fatiguing contraction (42 ± 12%). The rate of increase in electromyograph (EMG) activity (%MVC) and torque fluctuations during the fatiguing contractions were similar across sessions. However, the rate of increase in EMG differed among the knee extensor muscles: the rectus femoris began at a greater amplitude (31.5 ± 11.0%) compared with the vastus lateralis and vastus medialis muscles (18.8 ± 5.3%), but it ended at a similar value (45.4 ± 3.1%). The time to task failure and increase in EMG activity were similar for the seated and supine tasks; however, the reduction in MVC torque was greater for the seated posture. These findings indicate that the time to task failure for the knee extensor muscles that have a common tendon insertion did not alter over repeat sessions as had been observed for the elbow flexor muscles (Hunter SK and Enoka RM. J Appl Physiol 94: 108-118, 2003).

The Association of Obesity With Quadriceps Activation During Sit-to-Stand

2020 ◽  
Vol 100 (12) ◽  
pp. 2134-2143
Author(s):  
Lance M Bollinger ◽  
Amanda L Ransom
Keyword(s):  
Vastus Lateralis ◽  
Knee Extensor ◽  
Quadriceps Muscle ◽  
Knee Extensors ◽  
Emg Activity ◽  
Vastus Medialis ◽  
Trunk Flexion ◽  
Maximal Voluntary Isometric Contraction ◽  
Sit To Stand ◽  
The Mean

Abstract Objective Obesity reduces voluntary recruitment of quadriceps during single-joint exercises, but the effects of obesity on quadriceps femoris muscle activation during dynamic daily living tasks, such as sit-to-stand (STS), are largely unknown. The purpose of this study was to determine how obesity affects quadriceps muscle recruitment during STS. Methods In this cross-sectional study, 10 women who were lean and 17 women who were obese completed STS from a chair with arms crossed over the chest. Three-dimensional motion analysis was used to define 3 distinct phases (I–III) of the STS cycle. The electromyographic (EMG) activity of the vastus medialis, vastus lateralis, and semitendinosus was measured. Results STS duration was greater (3.02 [SD = 0.75] seconds vs 1.67 [SD = 0.28] seconds) and peak trunk flexion angle was lower (28.9 degrees [SD = 10.4 degrees] vs 35.8 degrees [SD = 10.1 degrees]) in the women who were obese than in the women who were lean. The mean EMG activity of the knee extensors increased from phase I to phase II in both groups; however, the mean EMG activities of both the vastus medialis (32.1% [SD = 16.6%] vs 47.3% [SD = 19.6%] maximal voluntary isometric contraction) and the vastus lateralis (31.8% [SD = 19.4%] vs 47.5% [SD = 19.6%] maximal voluntary isometric contraction) were significantly lower during phase II in the women who were obese. The mean EMG activity of the semitendinosus increased throughout STS but was not significantly different between the 2 groups. Coactivation of the semitendinosus and knee extensors tended to be greater in the women who were obese but failed to reach statistical significance. Conclusions Knee extensor EMG amplitude was reduced in women who were obese during STS, despite reduced trunk flexion. Impact Reduced knee extensor recruitment during STS in obesity may redistribute forces needed to complete this task to other joints. Functional movement training may help improve knee extensor recruitment during STS in people who are obese. Lay Summary People with obesity often have low quadriceps muscle strength and impaired mobility during daily activities. This study shows that women who are obese have lower voluntary recruitment of quadriceps when rising from a chair than women who are lean do, which could increase workload on hip or ankle muscles during this important daily task. Quadriceps strengthening exercises might improve the ability to rise from sitting to standing.

Strength training counteracts motor performance losses during bed rest

2003 ◽  
Vol 95 (4) ◽  
pp. 1485-1492 ◽  
Author(s):  
Minoru Shinohara ◽  
Yasuhide Yoshitake ◽  
Motoki Kouzaki ◽  
Hideoki Fukuoka ◽  
Tetsuo Fukunaga
Keyword(s):  
Strength Training ◽  
Muscle Activation ◽  
Vastus Lateralis ◽  
Knee Extensor ◽  
Bed Rest ◽  
Training Group ◽  
Medial Gastrocnemius ◽  
Knee Extensors ◽  
Extensor Muscles ◽  
Muscle Groups

The purpose of the study was to determine the effect of bed rest with or without strength training on torque fluctuations and activation strategy of the muscles. Twelve young men participated in a 20-day bed rest study. Subjects were divided into a non-training group (BRCon) and a strength-training group (BRTr). The training comprised dynamic calf-raise and leg-press exercises. Before and after bed rest, subjects performed maximal contractions and steady submaximal isometric contractions of the ankle extensor muscles and of the knee extensor muscles (2.5-10% of maximal torque). Maximal torque decreased for both the ankle extensors (9%, P < 0.05) and knee extensors (16%, P < 0.05) in BRCon but not in BRTr. For the ankle extensors, the coefficient of variation (CV) for torque increased in both groups ( P < 0.05), with a greater amount ( P < 0.05) in BRCon (88%) compared with BRTr (41%). For the knee extensors, an increase in the CV for torque was observed only in BRCon (22%). The increase in the CV for torque in BRCon accompanied the greater changes in electromyogram amplitude of medial gastrocnemius (122%) and vastus lateralis (59%) compared with BRTr ( P < 0.05). The results indicate that fluctuations in torque during submaximal contractions of the extensor muscles in the leg increase after bed rest and that strength training counteracted the decline in performance. The response varied across muscle groups. Alterations in muscle activation may lead to an increase in fluctuations in motor output after bed rest.

scholarly journals Determining the optimal maximal and submaximal voluntary contraction tests for normalizing the erector spinae muscles

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7824
Author(s):  
Gemma Biviá-Roig ◽  
Juan Francisco Lisón ◽  
Daniel Sánchez-Zuriaga
Keyword(s):  
Muscle Activation ◽  
Individual Variability ◽  
Erector Spinae ◽  
Emg Activity ◽  
Horizontal Position ◽  
Maximum Voluntary Isometric Contraction ◽  
Emg Signal ◽  
Activation Level ◽  
Flexion Extension ◽  
Maximal Activation

Background This study aimed to identify which maximum voluntary isometric contraction (MVIC) and sub-MVIC tests produce the highest activation of the erector spinae muscles and the greatest reduction in inter-individual variability, to put them forward as reference normalization maneuvers for future studies. Methods Erector spinae EMG activity was recorded in 38 healthy women during five submaximal and three maximal exercises. Results None of the three MVIC tests generated the maximal activation level in all the participants. The maximal activation level was achieved in 68.4% of cases with the test performed on the roman chair in the horizontal position (96.3 ± 7.3; p < 0.01). Of the five submaximal maneuvers, the one in the horizontal position on the roman chair produced the highest percentage of activation (61.1 ± 16.7; p < 0.01), and one of the lowest inter-individual variability values in the normalized signal of a trunk flexion-extension task. Conclusions A modified Sorensen MVIC test in a horizontal position on a roman chair and against resistance produced the highest erector spinae activation, but not in 100% of participants, so the execution of several normalization maneuvers with the trunk at different inclinations should be considered to normalize the erector spinae EMG signal. A modified Sorensen test in a horizontal position without resistance is the submaximal maneuver that produces the highest muscle activation and the greatest reduction in inter-individual variability, and could be considered a good reference test for normalization.

Modularity of Motor Output Evoked By Intraspinal Microstimulation in Cats

2004 ◽  
Vol 91 (1) ◽  
pp. 502-514 ◽  
Author(s):  
Michel A. Lemay ◽  
Warren M. Grill
Keyword(s):  
Muscle Activation ◽  
Sagittal Plane ◽  
Force Fields ◽  
Isometric Force ◽  
Force Transducer ◽  
Spinal Reflexes ◽  
Lumbar Spinal Cord ◽  
Emg Activity ◽  
Active Force ◽  
Spinal Circuitry

We studied the forces produced at the cat's hindpaw by microstimulation of the ipsi- and contralateral lumbar spinal cord in spinal intact α-chloralose anesthetized ( n = 3) or decerebrate ( n = 3) animals. Isometric force and EMG responses were measured at 9-12 limb configurations, with the paw attached to a force transducer and with the hip and femur fixed. The active forces elicited at different limb configurations were summarized as force fields representing the sagittal plane component of the forces produced at the paw throughout the workspace. The forces varied in amplitude over time but the orientations were stable, and the pattern of an active force field was invariant through time. The active force fields divided into four distinct types, and a few of the fields showed convergence to an equilibrium point. The fields were generally produced by coactivation of the hindlimb muscles. In addition, some of the fields were consistent with known spinal reflexes and the stimulation sites producing them were in laminae where the interneurons associated with those reflexes are known to be located. Muscle activation produced by intraspinal stimulation, as assessed by intramuscular EMG activity, was modified with limb configuration, suggesting that the responses were not fixed, but were modified by position-dependent sensory feedback. The force responses may represent basic outputs of the spinal circuitry and may be related to similar spinal primitives found in the frog and rat.

An Anthropometrically Parameterized Assistive Lower-limb Exoskeleton

2021 ◽  
Author(s):  
Curt Laubscher ◽  
Ryan Farris ◽  
Antonie van den Bogert ◽  
Jerzy T. Sawicki
Keyword(s):  
Lower Limb ◽  
Muscle Activation ◽  
Vastus Lateralis ◽  
Mechanical Energy ◽  
Biceps Femoris ◽  
Knee Joints ◽  
Lower Limb Exoskeleton ◽  
Hip Abduction ◽  
The Subject ◽  
Muscle Activations

Abstract This paper presents a newly developed lower-limb exoskeleton tested for walking assistance. The novel exoskeleton design methodology uses additive manufacturing and a parametrized model based on user anthropometrics to give a person-specific custom fit. The process is applied to average children and a healthy adult, and a prototype device is fabricated for the adult to validate the feasibility of the approach. The developed prototype actuates the hip and knee joints without restricting hip abduction-adduction motion. To test usability of the device and evaluate walking assistance, user torque, mechanical energy generated, and muscle activation are analyzed in an assisted condition where the subject walks on a level treadmill with the exoskeleton powered. This is compared to an unassisted condition with the exoskeleton unpowered and a baseline condition with the subject not wearing the exoskeleton. Comparing assisted to baseline conditions, torque magnitudes increased at the hip and knee, mechanical energy generated increased at the hip but decreased at the knee, and muscle activations decreased in the Biceps Femoris and increased in the Vastus Lateralis. The presented preliminary results are inconclusive on whether the newly developed exoskeleton can assist in walking though show promise for basic usability of the device.

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