Absence of exercise-induced MRI enhancement of skeletal muscle in McArdle's disease

Fleckenstein, James L.; Haller, Ronald G.; Lewis, Steven F.; Archer, Branch T.; Barker, Bruce R.; Payne, Jerri; Parkey, Robert W.; Peshock, Ronald M.

doi:10.1152/jappl.1991.71.3.961

Cited by 82 publications

(78 citation statements)

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“…Second, following high-intensity resistance training, less muscle is required to lift a given absolute load, as documented by a reduction in magnetic resonance image contrast shift (29). Such a reduction in muscle recruitment is associated with an alteration in metabolic demand (1,11). Third, the kinetics of force development can also play a role in altering metabolic demand of the exercising muscle (36).…”

Section: Discussionmentioning

confidence: 99%

Maximal strength training and increased work efficiency: contribution from the trained muscle bed

Barrett-O’Keefe

Helgerud

Wagner

et al. 2012

Journal of Applied Physiology

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Maximal strength training (MST) reduces pulmonary oxygen uptake (V O2) at a given submaximal exercise work rate (i.e., efficiency). However, whether the increase in efficiency originates in the trained skeletal muscle, and therefore the impact of this adaptation on muscle blood flow and arterial-venous oxygen difference (a-vO 2diff), is unknown. Thus five trained subjects partook in an 8-wk MST intervention consisting of half-squats with an emphasis on the rate of force development during the concentric phase of the movement. Pre-and posttraining measurements of pulmonary V O2 (indirect calorimetry), single-leg blood flow (thermodilution), and single-leg a-vO2diff (blood gases) were performed, to allow the assessment of skeletal muscle V O2 during submaximal cycling [237 Ϯ 23 W; ϳ60% of their peak pulmonary V O2 (V O2peak)]. Pulmonary V O2peak (ϳ4.05 l/min) and peak work rate (ϳ355 W), assessed during a graded exercise test, were unaffected by MST. As expected, following MST there was a significant reduction in pulmonary V O2 during steady-state submaximal cycling (ϳ237 W: 3.2 Ϯ 0.1 to 2.9 Ϯ 0.1 l/min). This was accompanied by a significant reduction in single-leg V O2 (1,101 Ϯ 105 to 935 Ϯ 93 ml/min) and single-leg blood flow (6,670 Ϯ 700 to 5,649 Ϯ 641 ml/min), but no change in single-leg a-vO2diff (16.7 Ϯ 0.8 to 16.8 Ϯ0.4 ml/dl). These data confirm an MSTinduced reduction in pulmonary V O2 during submaximal exercise and identify that this change in efficiency originates solely in skeletal muscle, reducing muscle blood flow, but not altering muscle a-vO2diff. oxygen consumption; blood flow; work economy DURING CYCLE EXERCISE, at a given submaximal work rate (WR), pulmonary oxygen uptake (V O 2 ) is similar between individuals of varying aerobic capacities [peak V O 2 (V O 2peak )] (34). This is true despite the complex, systemwide metabolic costs of exercise, such as ventilatory and cardiac muscle work, ion transport, and exercise-induced alterations in thermoregulation and metabolism, each of which may influence the V O 2 /WR relationship (6,39,43). Thus work efficiency, measured as the ratio of pulmonary V O 2 to work accomplished during submaximal steady-state cycling, is a global assessment of metabolic demand and may be influenced by a change in any of these systems. Therefore, a perturbation or stressor, such as maximal strength training (MST), which has been determined to alter work efficiency (22,26,42), may not simply be attributed to a change in efficiency of the exercising muscle.For over a decade, studies have documented that the use of MST, which consists of high loads and few repetitions, with an emphasis on the maximal rate of force development, improves work efficiency in both sedentary (22) and aerobically trained individuals (26,42), and this MST-induced change is even more evident during high-intensity exercise (22). While it is reasonable to expect enhanced intramuscular efficiency to be a major contributor to this documented improvement in work efficiency, an attenuated O 2 cost, external ...

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Section: Discussionmentioning

confidence: 99%

Maximal strength training and increased work efficiency: contribution from the trained muscle bed

Barrett-O’Keefe

Helgerud

Wagner

et al. 2012

Journal of Applied Physiology

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“…This analysis revealed that pH i and % ⌬V i Ј changes both help to predict R 2i Ј changes (P Ͻ 0.05), but that V e Ј changes do not (P Ͼ 0.05). The equation resulting from this analysis is: [7] which indicates that 70% of the variance in R 2i Ј during exercise can be accounted for by intracellular pH and volume changes. None of the hypothesized physiological variables could explain the R 2e Ј changes.…”

Section: Exercise-inducedmentioning

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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“…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). Recently, Hu et al (12) showed through the injection of an extracellular contrast agent that postexercise hyperemia affects SI in T2-weighted images as well.…”

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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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Absence of exercise-induced MRI enhancement of skeletal muscle in McArdle's disease

Cited by 82 publications

References 0 publications

Maximal strength training and increased work efficiency: contribution from the trained muscle bed

Maximal strength training and increased work efficiency: contribution from the trained muscle bed

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle

Cluster analysis of muscle functional MRI data

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Absence of exercise-induced MRI enhancement of skeletal muscle in McArdle's disease

Cited by 82 publications

References 0 publications

Maximal strength training and increased work efficiency: contribution from the trained muscle bed

Maximal strength training and increased work efficiency: contribution from the trained muscle bed

Intracellular acidification and volume increases explain R2 decreases in exercising muscle

Cluster analysis of muscle functional MRI data

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About

Intracellular acidification and volume increases explain R₂ decreases in exercising muscle