Muscle Activation Sequence in Flywheel Squats

Background: Muscle coordination is important for rational and effective planning of therapeutic and exercise interventions using equipment that mimics functional movements. Our study was the first to assess muscle coordination during flywheel (FW) squats. Methods: Time-of-peak electromyographic activation order was assessed separately for 8, 4, and 3 leg muscles under four FW loads. A sequential rank agreement permutations tests (SRA) were conducted to assess activation order and Kendall’s tau was used to assess the concordance of activation order across subjects, loads and expected order of activation. Results: SRA revealed a latent muscle activation order at loads 0.05, 0.075, and 0.1, but not at 0.025 kg·m2. Kendall’s tau showed moderate-to-strong concordance between the expected (proximal-to-distal) and the observed muscle activation order only at a load 0.025 kg·m2, regardless of the number of muscles analyzed. Muscle activation order was highly concordant between loads 0.05, 0.075, and 0.1 kg·m2. Conclusions: The results show a specific role of each muscle during the FW squat that is load-dependent. While the lowest load follows the proximal-to-distal principle of muscle activation, higher loads lead to a reorganization of the underlying muscle coordination mechanisms. They require a specific and stable muscle coordination pattern that is not proximal-to-distal.

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Functional Roles of the Leg Muscles When Pedaling in the Recumbent Versus the Upright Position

Journal of Biomechanical Engineering ◽

10.1115/1.1865192 ◽

2004 ◽

Vol 127 (2) ◽

pp. 301-310 ◽

Cited By ~ 12

Author(s):

Nils A. Hakansson ◽

M. L. Hull

Keyword(s):

Gravity Field ◽

Muscle Activation ◽

Upright Position ◽

Knee Extensors ◽

Muscle Coordination ◽

Activation Patterns ◽

Functional Roles ◽

Leg Muscles ◽

Surface Electromyograms ◽

Pedaling Rate

An understanding of the coordination of the leg muscles in recumbent pedaling would be useful to the design of rehabilitative pedaling exercises. The objectives of this work were to (i) determine whether patterns of muscle activity while pedaling in the recumbent and upright positions are similar when the different orientation in the gravity field is considered, (ii) compare the functional roles of the leg muscles while pedaling in the recumbent position to the upright position to the upright position and (iii) determine whether leg muscle onset and offset timing for recumbent and upright pedaling respond similarly to changes in pedaling rate. To fulfill these objectives, surface electromyograms were recorded from 10 muscles of 15 subjects who pedaled in both the recumbent and upright positions at 75, 90, and 105rpm and at a constant workrate of 250W. Patterns of muscle activation were compared over the crank cycle. Functional roles of muscles in recumbent and upright pedaling were compared using the percent of integrated activation in crank cycle regions determined previously for upright pedaling. Muscle onset and offset timing were also compared. When the crank cycle was adjusted for orientation in the gravity field, the activation patterns for the two positions were similar. Functional roles of the muscles in the two positions were similar as well. In recumbent pedaling, the uniarticular hip and knee extensors functioned primarily to produce power during the extension region of the crank cycle, whereas the biarticular muscles crossing the hip and knee functioned to propel the leg through the transition regions of the crank cycle. The adaptations of the muscles to changes in pedaling rate were also similar for the two body positions with the uniarticular power producing muscles of the hip and knee advancing their activity to earlier in the crank cycle as the pedaling rate increased. This information on the functional roles of the leg muscles provides a basis by which to form functional groups, such as power-producing muscles and transition muscles, to aid in the development of rehabilitative pedaling exercises and recumbent pedaling simulations to further our understanding of task-dependent muscle coordination.

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On Minimal Copulas under the Concordance Order

Journal of Optimization Theory and Applications ◽

10.1007/s10957-019-01618-4 ◽

2019 ◽

Vol 184 (3) ◽

pp. 762-780 ◽

Cited By ~ 1

Author(s):

Jae Youn Ahn ◽

Sebastian Fuchs

Keyword(s):

Optimization Problems ◽

Sufficient Conditions ◽

Necessary Condition ◽

Negative Dependence ◽

Kendall’S Tau ◽

Kendall's Tau ◽

Minimal Elements ◽

Measures Of Concordance ◽

Concordance Order

AbstractIn the present paper, we study extreme negative dependence focussing on the concordance order for copulas. With the absence of a least element for dimensions $$d\ge 3$$d≥3, the set of all minimal elements in the collection of all copulas turns out to be a natural and quite important extreme negative dependence concept. We investigate several sufficient conditions, and we provide a necessary condition for a copula to be minimal. The sufficient conditions are related to the extreme negative dependence concept of d-countermonotonicity and the necessary condition is related to the collection of all copulas minimizing multivariate Kendall’s tau. The concept of minimal copulas has already been proved to be useful in various continuous and concordance order preserving optimization problems including variance minimization and the detection of lower bounds for certain measures of concordance. We substantiate this key role of minimal copulas by showing that every continuous and concordance order preserving functional on copulas is minimized by some minimal copula, and, in the case the continuous functional is even strictly concordance order preserving, it is minimized by minimal copulas only. Applying the above results, we may conclude that every minimizer of Spearman’s rho is also a minimizer of Kendall’s tau.

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New families of bivariate copulas via unit weibull distortion

Journal of Statistical Distributions and Applications ◽

10.1186/s40488-020-00110-z ◽

2020 ◽

Vol 7 (1) ◽

Author(s):

Fadal A.A. Aldhufairi ◽

Jungsywan H. Sepanski

Keyword(s):

Tail Dependence ◽

Copula Function ◽

Kendall’S Tau ◽

Kendall's Tau ◽

Density Distributions ◽

New Family ◽

Upper Tail Dependence ◽

Bivariate Copula

Abstract This paper introduces a new family of bivariate copulas constructed using a unit Weibull distortion. Existing copulas play the role of the base or initial copulas that are transformed or distorted into a new family of copulas with additional parameters, allowing more flexibility and better fit to data. We present a general form for the new bivariate copula function and its conditional and density distributions. The tail behaviors are investigated and indicate the unit Weibull distortion may result in new copulas with upper tail dependence when the base copula has no upper tail dependence. The concordance ordering and Kendall’s tau are derived for the cases when the base copulas are Archimedean, such as the Clayton and Frank copulas. The Loss-ALEA data are analyzed to evaluate the performance of the proposed new families of copulas.

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Merging of Healthy Motor Modules Predicts Reduced Locomotor Performance and Muscle Coordination Complexity Post-Stroke

Journal of Neurophysiology ◽

10.1152/jn.00825.2009 ◽

2010 ◽

Vol 103 (2) ◽

pp. 844-857 ◽

Cited By ~ 394

Author(s):

David J. Clark ◽

Lena H. Ting ◽

Felix E. Zajac ◽

Richard R. Neptune ◽

Steven A. Kautz

Keyword(s):

Nervous System ◽

Neural Control ◽

Muscle Activation ◽

Nonnegative Matrix ◽

Modular Organization ◽

Coordination Pattern ◽

Muscle Coordination ◽

Post Stroke ◽

Muscle Activation Patterns ◽

Flexion Extension

Evidence suggests that the nervous system controls motor tasks using a low-dimensional modular organization of muscle activation. However, it is not clear if such an organization applies to coordination of human walking, nor how nervous system injury may alter the organization of motor modules and their biomechanical outputs. We first tested the hypothesis that muscle activation patterns during walking are produced through the variable activation of a small set of motor modules. In 20 healthy control subjects, EMG signals from eight leg muscles were measured across a range of walking speeds. Four motor modules identified through nonnegative matrix factorization were sufficient to account for variability of muscle activation from step to step and across speeds. Next, consistent with the clinical notion of abnormal limb flexion-extension synergies post-stroke, we tested the hypothesis that subjects with post-stroke hemiparesis would have altered motor modules, leading to impaired walking performance. In post-stroke subjects ( n = 55), a less complex coordination pattern was shown. Fewer modules were needed to account for muscle activation during walking at preferred speed compared with controls. Fewer modules resulted from merging of the modules observed in healthy controls, suggesting reduced independence of neural control signals. The number of modules was correlated to preferred walking speed, speed modulation, step length asymmetry, and propulsive asymmetry. Our results suggest a common modular organization of muscle coordination underlying walking in both healthy and post-stroke subjects. Identification of motor modules may lead to new insight into impaired locomotor coordination and the underlying neural systems.

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Influence of Fatigue on Hand Muscle Coordination and EMG-EMG Coherence During Three-Digit Grasping

Journal of Neurophysiology ◽

10.1152/jn.00583.2010 ◽

2010 ◽

Vol 104 (6) ◽

pp. 3576-3587 ◽

Cited By ~ 51

Author(s):

Alessander Danna-Dos Santos ◽

Brach Poston ◽

Mark Jesunathadas ◽

Lisa R. Bobich ◽

Thomas M. Hamm ◽

...

Keyword(s):

Muscle Fatigue ◽

Muscle Activation ◽

Maximum Voluntary Contraction ◽

Voluntary Contraction ◽

Coordination Pattern ◽

Muscle Coordination ◽

Heterogeneous Distribution ◽

Hand Muscles ◽

Emg Amplitude ◽

Vector Orientation

Fingertip force control requires fine coordination of multiple hand muscles within and across the digits. While the modulation of neural drive to hand muscles as a function of force has been extensively studied, much less is known about the effects of fatigue on the coordination of simultaneously active hand muscles. We asked eight subjects to perform a fatiguing contraction by gripping a manipulandum with thumb, index, and middle fingers while matching an isometric target force (40% maximal voluntary force) for as long as possible. The coordination of 12 hand muscles was quantified as electromyographic (EMG) muscle activation pattern (MAP) vector and EMG-EMG coherence. We hypothesized that muscle fatigue would cause uniform changes in EMG amplitude across all muscles and an increase in EMG-EMG coherence in the higher frequency bands but with an invariant heterogeneous distribution across muscles. Muscle fatigue caused a 12.5% drop in the maximum voluntary contraction force ( P < 0.05) at task failure and an increase in the SD of force ( P < 0.01). Although EMG amplitude of all muscles increased during the fatiguing contraction ( P < 0.001), the MAP vector orientation did not change, indicating that a similar muscle coordination pattern was used throughout the fatiguing contraction. Last, EMG-EMG coherence (0–35 Hz) was significantly greater at the end than at the beginning of the fatiguing contraction ( P < 0.01) but was heterogeneously distributed across hand muscles. These findings suggest that similar mechanisms are involved for modulating and sustaining digit forces in nonfatiguing and fatiguing contractions, respectively.

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Faculty Opinions recommendation of Predictive modulation of muscle coordination pattern magnitude scales fingertip force magnitude over the voluntary range.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1009807.135658 ◽

2002 ◽

Author(s):

Emanuel Todorov

Keyword(s):

Coordination Pattern ◽

Muscle Coordination ◽

Fingertip Force ◽

Force Magnitude ◽

Magnitude Scales

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Characterizing Asymptotic Dependence via Conditional Kendall's Tau

SSRN Electronic Journal ◽

10.2139/ssrn.2376288 ◽

2014 ◽

Cited By ~ 2

Author(s):

Alexandru V. Asimit ◽

Yanxi Hou ◽

Liang Peng

Keyword(s):

Asymptotic Dependence ◽

Kendall’S Tau ◽

Kendall's Tau

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Workload for radiologists during on-call hours: dramatic increase in the past 15 years

Insights into Imaging ◽

10.1186/s13244-020-00925-z ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

R. J. M. Bruls ◽

R. M. Kwee

Keyword(s):

Western Europe ◽

Kendall Test ◽

Kendall’S Tau ◽

Kendall's Tau ◽

X Ray ◽

The Past ◽

Relative Value ◽

Burn Out ◽

Picture Archiving And Communication ◽

Ct Studies

Abstract Background The objective of this study is to investigate the workload for radiologists during on-call hours and to quantify the 15-year trend in a large general hospital in Western Europe. Methods Data regarding the number of X-ray, ultrasound and computed tomography (CT) studies during on-call hours (weekdays between 6.00 p.m. and 7.00 a.m., weekends, and national holidays) between 2006 and 2020 were extracted from the picture archiving and communication system. All studies were converted into relative value units (RVUs) to estimate the on-call workload. The Mann–Kendall test was performed to assess the temporal trend. Results The total RVUs during on-call hours showed a significant increase between 2006 and 2020 (Kendall's tau-b = 0.657, p = 0.001). The overall workload in terms of RVUs during on-call hours has quadrupled. The number of X-ray studies significantly decreased (Kendall's tau-b = − 0.433, p = 0.026), whereas the number of CT studies significantly increased (Kendall's tau-b = 0.875, p < 0.001) between 2006 and 2020. CT studies which increased by more than 500% between 2006 and 2020 are CT for head trauma, brain CTA, brain CTV, chest CT (for suspected pulmonary embolism), spinal CT, neck CT, pelvic CT, and CT for suspected aortic dissection. The number of ultrasound studies did not change significantly (Kendall's tau-b = 0.202, p = 0.298). Conclusions The workload for radiologists during on-call hours increased dramatically in the past 15 years. The growing amount of CT studies is responsible for this increase. Radiologist and technician workforce should be matched to this ongoing increasing trend to avoid potential burn-out and to maintain quality and safety of radiological care.

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