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arxiv: 1907.01649 · v1 · pith:3ULJAI5Xnew · submitted 2019-07-02 · 📡 eess.IV · cs.CV

Estimation of Absolute States of Human Skeletal Muscle via Standard B-Mode Ultrasound Imaging and Deep Convolutional Neural Networks

Pith reviewed 2026-05-25 10:16 UTC · model grok-4.3

classification 📡 eess.IV cs.CV
keywords ultrasound imagingdeep convolutional networksmuscle state estimationB-mode ultrasoundskeletal muscleelectromyographyjoint momentgeneralization
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The pith

Deep convolutional neural networks predict absolute muscle activity, joint angle and moment from standard 2D ultrasound images in held-out individuals.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tests whether 2D B-mode ultrasound images alone contain enough information for deep networks to recover the absolute activity-length-tension state of skeletal muscle. Synchronized ultrasound, EMG, joint angle and moment recordings were collected from the calf muscles of 32 participants while active contraction and passive stretch were varied independently. Segmented images of the medial gastrocnemius and soleus were used to train a convolutional network that outputs the three state variables. Cross-validation leaving out entire participants yielded mean accuracies of 55 percent for angle, 57 percent for EMG and 46 percent for moment. The result indicates that observation-only 2D ultrasound plus deep learning can supply a generalizable, drift-free readout of neural output, length and tension.

Core claim

With 2D US imaging, deep neural networks can encode in generalizable form the activity-length-tension state relationship of muscle. A convolutional network trained on segmented calf images predicts ankle joint angle, electromyography and joint moment to accuracies of 55±8 percent, 57±11 percent and 46±9 percent respectively across all 32 held-out participants under independent active and passive input variation, establishing that low-power 2D ultrasound can provide non-invasive estimation of neural output, length and tension.

What carries the argument

Deep convolutional neural network that maps segmented 2D ultrasound regions of interest directly to the three absolute state components (activity, joint angle, joint moment).

If this is right

  • Ultrasound could supply simultaneous, drift-free estimates of muscle activity, length and force where EMG and dynamometry are used separately today.
  • The activity-length-tension relationship could be measured non-invasively during natural movement.
  • The same imaging-plus-network approach could support diagnosis and monitoring in pain, injury, neurological conditions and ageing.
  • Real-time muscle-state feedback becomes feasible without implanted sensors or high-power imaging modalities.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same network architecture might generalize to other muscles if similar synchronized datasets are collected.
  • Accuracy could rise with larger training sets or 3D ultrasound volumes, moving the method closer to clinical thresholds.
  • Wearable ultrasound probes combined with the network could enable continuous muscle-state tracking outside the lab.
  • The encoding learned by the network may capture structural features that traditional image analysis misses.

Load-bearing premise

Data from 32 participants under controlled independent variation of active and passive inputs are sufficient to train a model that generalizes to completely new individuals.

What would settle it

Applying the trained network to a new cohort of participants and obtaining prediction accuracies indistinguishable from chance.

Figures

Figures reproduced from arXiv: 1907.01649 by Ian D. Loram, Ryan J. Cunningham.

Figure 1
Figure 1. Figure 1: Experimental setup. The participant stood upright on a foot pedal system (yellow), while strapped (red) at the chest to a backboard and observed an oscilloscope at eye level. An US probe (green) was attached to the left calf to image the gastrocnemius medialis (GM) and soleus (SO) muscles (right: grayscale). A wireless EMG sensor was attached to GM and to SO at standard locations (http://www.seniam.org/). … view at source ↗
read the original abstract

Objective: To test automated in vivo estimation of active and passive skeletal muscle states using ultrasonic imaging. Background: Current technology (electromyography, dynamometry, shear wave imaging) provides no general, non-invasive method for online estimation of skeletal intramuscular states. Ultrasound (US) allows non-invasive imaging of muscle, yet current computational approaches have never achieved simultaneous extraction nor generalisation of independently varying, active and passive states. We use deep learning to investigate the generalizable content of 2D US muscle images. Method: US data synchronized with electromyography of the calf muscles, with measures of joint moment/angle were recorded from 32 healthy participants (7 female, ages: 27.5, 19-65). We extracted a region of interest of medial gastrocnemius and soleus using our prior developed accurate segmentation algorithm. From the segmented images, a deep convolutional neural network was trained to predict three absolute, drift-free, components of the neurobiomechanical state (activity, joint angle, joint moment) during experimentally designed, simultaneous, independent variation of passive (joint angle) and active (electromyography) inputs. Results: For all 32 held-out participants (16-fold cross-validation) the ankle joint angle, electromyography, and joint moment were estimated to accuracy 55+-8%, 57+-11%, and 46+-9% respectively. Significance: With 2D US imaging, deep neural networks can encode in generalizable form, the activity-length-tension state relationship of muscle. Observation only, low power, 2D US imaging can provide a new category of technology for non-invasive estimation of neural output, length and tension in skeletal muscle. This proof of principle has value for personalised muscle diagnosis in pain, injury, neurological conditions, neuropathies, myopathies and ageing.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 1 minor

Summary. The manuscript reports a study using B-mode ultrasound images of the medial gastrocnemius and soleus from 32 participants. After applying a prior segmentation algorithm to extract ROIs, a CNN is trained to regress three absolute state variables (EMG activity, ankle joint angle, joint moment) under independent variation of active and passive inputs. In 16-fold cross-validation with held-out participants, the model achieves reported accuracies of 55±8% (angle), 57±11% (EMG), and 46±9% (moment). The central claim is that 2D US images contain generalizable information about the activity-length-tension relationship that can be extracted by deep networks.

Significance. If the reported generalization holds without leakage from the segmentation step and with a clearly defined performance metric, the work would demonstrate a non-invasive, drift-free estimator of intramuscular states from standard imaging. This could open a new category of technology for clinical monitoring in neuromuscular conditions. The use of held-out participants and synchronized multi-modal ground truth are positive design elements.

major comments (3)
  1. [Abstract] Abstract: the performance metric called 'accuracy' for continuous regression outputs (55±8%, 57±11%, 46±9%) is non-standard and its exact definition is never supplied. Without this, the numerical claims cannot be interpreted or compared to conventional regression metrics such as R², normalized MAE, or correlation coefficient.
  2. [Methods] Methods (ROI extraction paragraph): the pipeline first applies a prior segmentation algorithm to produce the input images for the CNN. Because joint angle is directly encoded in the geometric length and boundary positions of the segmented muscle, angle prediction can succeed from boundary geometry alone rather than from learned texture-to-state mappings. No ablation on raw (unsegmented) images, no held-out validation of the segmentation algorithm itself, and no quantitative check that segmentation accuracy does not leak length cues are provided.
  3. [Results] Results (cross-validation paragraph): the reported 55±8% accuracy on joint angle is only modestly above a trivial baseline for a continuous variable; combined with the segmentation step, this raises the possibility that the EMG and moment results (57±11%, 46±9%) partly reflect residual correlations rather than extraction of the claimed activity-length-tension relationship.
minor comments (1)
  1. [Abstract] Abstract: notation '55+-8%' should be standardized to '55 ± 8%'.

Simulated Author's Rebuttal

3 responses · 1 unresolved

We thank the referee for the detailed and constructive review. We address each major comment below with point-by-point responses. Where the manuscript requires clarification or additional analysis, we indicate planned revisions. We have been careful not to overstate what the original experiments demonstrate.

read point-by-point responses
  1. Referee: [Abstract] Abstract: the performance metric called 'accuracy' for continuous regression outputs (55±8%, 57±11%, 46±9%) is non-standard and its exact definition is never supplied. Without this, the numerical claims cannot be interpreted or compared to conventional regression metrics such as R², normalized MAE, or correlation coefficient.

    Authors: We agree that the term 'accuracy' is non-standard for regression and that its precise definition was not supplied in the manuscript. In the revised version we will replace the reported figures with standard metrics (R², normalized MAE, and Pearson r) computed on the held-out participants and will update both the abstract and results sections accordingly. This change will allow direct comparison with conventional regression performance. revision: yes

  2. Referee: [Methods] Methods (ROI extraction paragraph): the pipeline first applies a prior segmentation algorithm to produce the input images for the CNN. Because joint angle is directly encoded in the geometric length and boundary positions of the segmented muscle, angle prediction can succeed from boundary geometry alone rather than from learned texture-to-state mappings. No ablation on raw (unsegmented) images, no held-out validation of the segmentation algorithm itself, and no quantitative check that segmentation accuracy does not leak length cues are provided.

    Authors: The segmentation step was introduced to restrict the network input to the muscle tissue of interest. We acknowledge that boundary geometry could contribute to angle prediction and that the absence of an ablation on raw images leaves open the possibility of leakage. In the revision we will add an explicit discussion of this limitation, including the fact that EMG and moment predictions are less directly supported by geometry. We cannot, however, supply new ablation results on raw images because those experiments were not performed. revision: partial

  3. Referee: [Results] Results (cross-validation paragraph): the reported 55±8% accuracy on joint angle is only modestly above a trivial baseline for a continuous variable; combined with the segmentation step, this raises the possibility that the EMG and moment results (57±11%, 46±9%) partly reflect residual correlations rather than extraction of the claimed activity-length-tension relationship.

    Authors: We accept that the angle result is modest and that residual correlations cannot be ruled out without further controls. In the revised manuscript we will add explicit baseline comparisons (mean predictor and linear regression on segmented length) and will discuss the extent to which the EMG and moment results can be attributed to learned textural features versus geometric cues. These additions will be placed in the results and discussion sections. revision: yes

standing simulated objections not resolved
  • Absence of ablation experiments on raw (unsegmented) ultrasound images and held-out validation of the segmentation algorithm, neither of which were conducted in the original study.

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper describes an empirical supervised learning pipeline: synchronized US, EMG, angle and moment data are collected from 32 participants under controlled variation of active and passive inputs; a prior segmentation algorithm extracts an ROI; a CNN is trained to regress the three state variables; performance is reported via 16-fold cross-validation on completely held-out participants. No mathematical derivation chain exists. The single self-reference to the authors' earlier segmentation work is a preprocessing detail whose validity is not required to establish the held-out prediction numbers. Those numbers are measured against independently recorded target variables on unseen subjects and therefore do not reduce to the training inputs by construction. No self-definitional loop, fitted-parameter-as-prediction, or load-bearing uniqueness theorem is present.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claim rests on the CNN learning a mapping from segmented images to three continuous state variables; the dominant fitted elements are the network weights, and the approach inherits the accuracy of a prior segmentation algorithm.

free parameters (1)
  • CNN weights
    Network parameters are optimized on the ultrasound image dataset to regress the three target variables.
axioms (2)
  • domain assumption Prior segmentation algorithm accurately isolates medial gastrocnemius and soleus regions of interest
    All subsequent feature learning depends on the ROI extracted by the earlier segmentation method.
  • domain assumption Experimental protocol produces independent variation of passive (angle) and active (EMG) inputs across participants
    The training objective requires that the three targets can be disentangled from the images.

pith-pipeline@v0.9.0 · 5874 in / 1099 out tokens · 36328 ms · 2026-05-25T10:16:59.400888+00:00 · methodology

discussion (0)

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Reference graph

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