Exercise-induced muscle modifications: study of healthy subjects and patients with metabolic myopathies with MR imaging and P-31 spectroscopy.

Kerviler, É. de; Leroy-Willig, A.; Jehenson, P.; Duboc, Denis; Eymard, B.; Syrota, A.

doi:10.1148/radiology.181.1.1887044

Cited by 63 publications

(29 citation statements)

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“…While changes in muscle volume as a factor involved in post-exercise T2 changes have been refuted on the basis of venous occlusion experiments [131], it has been clearly demonstrated that T2 changes were graded with exercise intensity during dorsiflexion exercises [130], thereby indicating that T2 changes during exercise are dependent on the force generated. Besides these observations, a direct relationship between changes in osmotically active metabolites such as lactate and P i has also been correlated with the extent of T2 changes [132,133], indicating that they are likely related to osmotically driven fluid shift. This relationship between the extent of T2 and pH changes in exercising muscle has been confirmed from a functionnal analysis of McArdle patients.…”

Section: T2 and Metabolic Changesmentioning

confidence: 82%

Functional investigations of exercising muscle: a noninvasive magnetic resonance spectroscopy-magnetic resonance imaging approach

Bendahan

Giannesini

Cozzone

2004

Cellular and Molecular Life Sciences (CMLS)

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Muscle fatigue, which is defined as the decline in muscle performance during exercise, may occur at different sites along the pathway from the central nervous system through to the intramuscular contractile machinery. Historically, both impairment of neuromuscular transmission and peripheral alterations within the muscle have been proposed as causative factors of fatigue development. However, according to more recent studies, muscle energetics play a key role in this process. Intramyoplasmic accumulation of inorganic phosphate (P(i)) and limitation in ATP availability have been frequently evoked as the main mechanisms leading to fatigue. Although attractive, these hypotheses have been elaborated on the basis of experimental results obtained in vitro, and their physiological relevance has never been clearly demonstrated in vivo. In that context, noninvasive methods such as 31-phosphorus magnetic resonance spectroscopy and surface electromyography have been employed to understand both metabolic and electrical aspects of muscle fatigue under physiological conditions. Mapping of muscles activated during exercise is another interesting issue which can be addressed using magnetic resonance imaging (MRI). Exercise-induced T2 changes have been used in order to locate activated muscles and also as a quantitative index of exercise intensity. The main results related to both issues, i.e. the metabolic and electrical aspects of fatigue and the MRI functional investigation of exercising muscle, are discussed in the present review.

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Section: T2 and Metabolic Changesmentioning

confidence: 82%

Functional investigations of exercising muscle: a noninvasive magnetic resonance spectroscopy-magnetic resonance imaging approach

Bendahan

Giannesini

Cozzone

2004

Cellular and Molecular Life Sciences (CMLS)

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“…The robust (up to ϳ30%; Ref. 16) changes in SI that occur during and after exercise are intensity dependent (14) and relate directly to electromyographic measures of motor unit activation (1). The inherent spatial localization capability of MRI means that muscle utilization can be evaluated in both superficial and deep muscles with in-plane resolutions of Ͻ10 mm 2 by using EPI or Ͻ5 mm 2 by using conventional spin-echo imaging.…”

Section: Discussionmentioning

confidence: 99%

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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“…T 2 is inversely related to intracellular pH (pH i ) in chemically-skinned rabbit psoas muscle (12) and in isolated rat liver (13). End-exercise pH i and T 2 are also correlated (2,14); however, during incremental arm ergometer exercise, pH i changes lag T 2 changes, and during recovery from this exercise, pH i recovers more quickly than T 2 (15). Together, these findings imply that pH i changes may contribute to, but cannot be the sole cause of, the T 2 increase during exercise.…”

mentioning

confidence: 99%

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Damon

Gregory

Hall

et al. 2001

Magnetic Resonance in Med

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Exercise-induced decreases in the 1 H transverse relaxation rate (R 2 ) of muscle have been well documented, but the mechanism remains unclear. In this study, the hypothesis was tested that R 2 decreases could be explained by pH decreases and apparent intracellular volume (V i ) increases. 31 P and 1 H spectroscopy, biexponential R 2 analysis, and imaging were performed prior to and following fatiguing exercise in iodoacetate-treated (IAA, to inhibit glycolysis), NaCN-treated (to inhibit oxidative phosphorylation), and untreated frog gastrocnemii. In all exercised muscles, the apparent intracellular R 2 (R 2i ) and pH decreased, while intracellular osmolytes and V i increased. These effects were larger in NaCN-treated and untreated muscles than in IAAtreated muscles. Multiple regression analysis showed that pH and V i changes explain 70% of the R 2i variance. Separate experiments in unexercised muscles demonstrated causal relationships between pH and R 2i and between V i and R 2i . These data indicate that the R 2 change of exercise is primarily an intracellular phenomenon caused by the accumulation of the end-products of anaerobic metabolism. In the NaCN-treated and untreated muscles, the R 2i change increased as field strength increased, suggesting a role for pH-modulated chemical exchange. Key words: skeletal muscle; exercise; hydrogen-ion concentration; osmolarity; nuclear magnetic resonance Exercise-induced increases in the apparent 1 H transverse relaxation time (T 2 ) of muscle water have been well documented. The amount of T 2 change increases as exercise intensity increases; T 2 plateaus 3-4 min after the onset of exercise (1). Following isometric leg extension to fatigue, T 2 recovery follows an approximately exponential time course and is complete after ϳ35 min. (2). The increase in signal intensity from active muscles in T 2 -weighted images allows muscle activity to be detected reliably and noninvasively, which may aid in the placement of regions of interest or surface coils in spectroscopic studies (2,3). With a full understanding of the mechanism(s) of the T 2 change, this phenomenon may also be useful in functional studies of muscle activation during exercise (e.g., Refs. 4 -6), noninvasive studies of pathologic conditions in which the T 2 response to exercise is altered (e.g., Refs. 7 and 8), and as a means of studying noninvasively those physiological changes that increase T 2 .The most universally offered and best-studied explanation for the T 2 increase during exercise is the concomitant increase in muscle volume. However, the mechanism of the T 2 increase is more complex than total water accumulation. For example, recovery of the muscle's anatomical cross-sectional area is faster than T 2 recovery (2), and enhancement of the extracellular fluid volume increase during exercise is not proportional to the T 2 increase (9). A further complication is that both ex vivo amphibian (10) and in vivo mammalian (11) studies suggest that exchange between the intra-and extracellular spaces in muscle is sl...

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Exercise-induced muscle modifications: study of healthy subjects and patients with metabolic myopathies with MR imaging and P-31 spectroscopy.

Cited by 63 publications

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Functional investigations of exercising muscle: a noninvasive magnetic resonance spectroscopy-magnetic resonance imaging approach

Functional investigations of exercising muscle: a noninvasive magnetic resonance spectroscopy-magnetic resonance imaging approach

Cluster analysis of muscle functional MRI data

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

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Exercise-induced muscle modifications: study of healthy subjects and patients with metabolic myopathies with MR imaging and P-31 spectroscopy.

Cited by 63 publications

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Functional investigations of exercising muscle: a noninvasive magnetic resonance spectroscopy-magnetic resonance imaging approach

Functional investigations of exercising muscle: a noninvasive magnetic resonance spectroscopy-magnetic resonance imaging approach

Cluster analysis of muscle functional MRI data

Intracellular acidification and volume increases explain R2 decreases in exercising muscle

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Intracellular acidification and volume increases explain R₂ decreases in exercising muscle