Changes in magnetic resonance images of muscle depend on exercise intensity and duration, not work

Jenner, G.; Foley, Jeanne M.; Cooper, Tim F.; Potchen, E. James; Meyer, Ronald A.

doi:10.1152/jappl.1994.76.5.2119

Cited by 92 publications

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“…Jenner et al (14) reported an approximately exponential rise in SI during isotonic dorsiflexion exercise. Others (2,19) have shown a more complex pattern to the SI changes during and after exercise, with (sometimes) an abrupt initial rise, a dip (possibly below baseline), a secondary rise, and continued increases after exercise.…”

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“…Any of these possible explanations, acting alone or in concert with the others, suggests that the intracellular T2 increase results from changes in the chemical behavior of water resulting from increased flux through energy metabolism pathways. In keeping with the long time required for flux through these pathways to reach a steady rate (ϳ2-3 min), these changes make up a slowly evolving, large-magnitude component of the mfMRI response (14).Changes in the extracellular space also affect the SI in mfMRI. Increases in interstitial volume [such as those caused by exercise (24) or leg negative pressure (18)] increase SI in T2-weighted images (6, 18), although the low interstitial volume fraction diminishes the importance of these changes (4, 18).…”

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“…Exercise-induced changes in energy metabolism, intracellular and interstitial volumes, and blood volume and oxygenation have different time courses; the result is a complex temporal pattern of SI changes in serially obtained echo-planar images (2,14,19). Jenner et al (14) reported an approximately exponential rise in SI during isotonic dorsiflexion exercise.…”

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Cluster analysis of muscle functional MRI data

Damon¹,

Wigmore²,

Ding³

et al. 2003

Journal of Applied Physiology

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magnetic resonance imaging (mfMRI) is frequently used to determine spatial patterns of muscle involvement in exercising humans. A frequent finding in mfMRI is that, even within synergistic muscle groups, signal intensity (SI) data from individual voxels can be quite heterogeneous. The purpose of this study was to develop a novel method for organizing heterogeneous mfMRI data into clusters whose members behave similarly to each other but distinctly from members of other clusters and apply it in studies of functional compartmentalization in the anterior compartment of the leg. An algorithm was developed that compared the SI time courses of adjacent voxels and grouped together voxels that were sufficiently similar. The algorithm's performance was verified by using simulated data sets with known regional differences in SI time courses that were then applied to experimental mfMRI data acquired from six male subjects (age 22.6 Ϯ 0.9 yr, mean Ϯ SE) who sustained isometric contractions of the dorsiflexors at 40% of maximum voluntary contraction. The experimental data were also characterized by using a traditional analysis (userspecified regions of interest from a single image), in which the relative change in SI and the contrast-to-noise ratio [CNR; 100%ϫ(SI RESTING Ϫ SIACTIVE)/(noise standard deviation)] were measured. In general, clusters were found in areas in which the CNR exceeded 5. Cluster analysis made functional distinctions between regions of muscle that were not seen with traditional analysis. In conclusion, cluster analysis's use of the full SI time course provides more sensitivity to muscle functional compartmentation than traditional analysis.transverse relaxation time constant; image processing; time series; exercise; dorsiflexors DURING THE PAST 15 YEARS, muscle functional magnetic resonance imaging (mfMRI) has emerged as a promising tool for studying muscle involvement during exercise because it is sensitive to the spatial pattern and extent of muscle utilization. For example, mfMRI has been used to identify different muscle utilization patterns in novice and elite rowers (9) and in uphill and horizontal running (25). It has also been used to detect changes in muscle function consequent to clinical conditions such as peripheral vascular disease (31). The interpretation of these data, however, is limited by the absence of a full theoretical understanding of which physiological variables produce the mfMRI response and how their contributions may differ during and after exercise.Multiexponential relaxation analysis has shown that the major contribution to signal intensity (SI) changes in mfMRI is made by the increase in the transverse relaxation time constant (T2) of intracellular water protons (4,22,23). Proposed explanations for intracellular T2 increases include the accumulation of end products of cellular energy metabolism, which cause water to move into the cell (4, 21), decreased intracellular pH (4, 8), and water shifts from an intracellular compartment possessing a short T2 (ϳ20 ms) to a second int...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Cluster analysis of muscle functional MRI data

Damon¹,

Wigmore²,

Ding³

et al. 2003

Journal of Applied Physiology

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“…Whereas magnetic resonance (MR) imaging (MRI) has been used to acquire anatomical information (4,5,22), use of human skeletal muscle has also been assessed with exercise-induced contrast shift in transverse relaxation time (T2) of MR images (1-3, 6, 7, 14, 21, 33-35, 42). It has been demonstrated that this contrast shift is correlated with integrated EMG activity (1), related to isometric torque induced by electromyostimulation (EMS) (2), increases with exercise intensity (1,2,21,26,30,33,36) and the metabolic state of skeletal muscle (37,40,42), and can discriminate use among relatively small synergistic muscles (13,14) and neuromuscular compartments (3). Thus exerciseinduced contrast shift in MR images seemed ideal to assess neuromuscular plasticity among synergists.…”

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Vastus lateralis fatigue alters recruitment of musculus quadriceps femoris in humans

Akima

Foley

Prior³

et al. 2002

Journal of Applied Physiology

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. Vastus lateralis fatigue alters recruitment of musculus quadriceps femoris in humans. J Appl Physiol 92: 679-684, 2002; 10.1152/ japplphysiol.00267.2001.-This study tested the hypothesis that fatigue of a single member of musculus quadriceps femoris (QF) would alter use of the other three muscles during knee extension exercise (KEE). Six men performed KEE with the left QF at a load equal to 50% of the 4 ϫ 10 repetitions maximum. Subsequently, electromyostimulation (EMS), intended to stimulate and fatigue the left m. vastus lateralis (VL), was applied for 30 min. Immediately after EMS, subjects repeated the KEE. Transverse relaxation time (T2)-weighted magnetic resonance images were taken before and after each bout of KEE and at 3 and 30 min of EMS to assess use and stimulation, respectively, of the QF. T2 of each of the QF muscles was increased 8-13% after the first KEE. During EMS, T2 increased (P Ͻ 0.05) even more in VL (10%), whereas it decreased (P Ͻ 0.05) to pre-KEE levels in m. vastus medials (VM) and m. rectus femoris (RF). The VL and, to some extent, the m. vastus intermedius were stimulated, whereas the VM and RF were not, thereby recovering from the first bout of KEE. Isometric torque, initially 30% of maximal voluntary, was reduced to 13% at 3 min and 7% at 30 min. T2 was greater (P Ͻ 0.05) after the second than the first bout of KEE, especially the increase for the VM and RF. These results suggest that subjects were able to perform the second bout with little contribution of the VL by greater use of the other QF muscles. The simplest explanation is increased central command to the QF such that the intended act could be accomplished despite acute fatigue of one of its synergists.

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An image processing strategy for the quantification and visualization of exercise-induced muscle MRI signal enhancement

Warfield

Mulkern

Winalski

et al. 2000

J. Magn. Reson. Imaging

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Exercise increases the skeletal muscle water signal in T2-weighted images. Potential medical applications of MR studies of exercise induced muscle signal intensity changes are the assessment of myopathies, sport training regimens, and physical therapy approaches following surgeries. We developed an automated image processing technique which provides volumetric analysis and visualization of exercise related T2-weighted image intensity changes. The image processing was applied to the segmentation and quantification of activated muscle volumes. Qualitative assessment of muscle activation is demonstrated with 3D surface rendering. Quantitative determination of active muscle volume, signal intensity and change over time is demonstrated. Visualization of the activated muscles allows functional anatomical assessment of exercise which in turn allows detection of muscle utilization.

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Changes in magnetic resonance images of muscle depend on exercise intensity and duration, not work

Cited by 92 publications

References 0 publications

Cluster analysis of muscle functional MRI data

Cluster analysis of muscle functional MRI data

Vastus lateralis fatigue alters recruitment of musculus quadriceps femoris in humans

An image processing strategy for the quantification and visualization of exercise-induced muscle MRI signal enhancement

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