scholarly journals Functional and structural adaptations of skeletal muscle to microgravity

2001 ◽  
Vol 204 (18) ◽  
pp. 3201-3208 ◽  
Author(s):  
Robert H. Fitts ◽  
Danny R. Riley ◽  
Jeffrey J. Widrick
Keyword(s):  
Skeletal Muscle ◽  
Muscle Atrophy ◽  
Peak Force ◽  
Type I ◽  
Type Ii ◽  
Shortening Velocity ◽  
Slow Type ◽  
Fiber Atrophy ◽  
Type I Fibers ◽  
Type Ii Fibers

SUMMARY Our purpose is to summarize the major effects of space travel on skeletal muscle with particular emphasis on factors that alter function. The primary deleterious changes are muscle atrophy and the associated decline in peak force and power. Studies on both rats and humans demonstrate a rapid loss of cell mass with microgravity. In rats, a reduction in muscle mass of up to 37% was observed within 1 week. For both species, the antigravity soleus muscle showed greater atrophy than the fast-twitch gastrocnemius. However, in the rat, the slow type I fibers atrophied more than the fast type II fibers, while in humans, the fast type II fibers were at least as susceptible to space-induced atrophy as the slow fiber type. Space flight also resulted in a significant decline in peak force. For example, the maximal voluntary contraction of the human plantar flexor muscles declined by 20–48% following 6 months in space, while a 21% decline in the peak force of the soleus type I fibers was observed after a 17-day shuttle flight. The reduced force can be attributed both to muscle atrophy and to a selective loss of contractile protein. The former was the primary cause because, when force was expressed per cross-sectional area (kNm−2), the human fast type II and slow type I fibers of the soleus showed no change and a 4% decrease in force, respectively. Microgravity has been shown to increase the shortening velocity of the plantar flexors. This increase can be attributed both to an elevated maximal shortening velocity (V0) of the individual slow and fast fibers and to an increased expression of fibers containing fast myosin. Although the cause of the former is unknown, it might result from the selective loss of the thin filament actin and an associated decline in the internal drag during cross-bridge cycling. Despite the increase in fiber V0, peak power of the slow type I fiber was reduced following space flight. The decreased power was a direct result of the reduced force caused by the fiber atrophy. In addition to fiber atrophy and the loss of force and power, weightlessness reduces the ability of the slow soleus to oxidize fats and increases the utilization of muscle glycogen, at least in rats. This substrate change leads to an increased rate of fatigue. Finally, with return to the 1g environment of earth, rat studies have shown an increased occurrence of eccentric contraction-induced fiber damage. The damage occurs with re-loading and not in-flight, but the etiology has not been established.

scholarly journals Satellite cell content is specifically reduced in type II skeletal muscle fibers in the elderly

2007 ◽  
Vol 292 (1) ◽  
pp. E151-E157 ◽  
Author(s):  
Lex B. Verdijk ◽  
René Koopman ◽  
Gert Schaart ◽  
Kenneth Meijer ◽  
Hans H. C. M. Savelberg ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fiber ◽  
Fiber Type ◽  
The Elderly ◽  
Type I ◽  
Type Ii ◽  
Fiber Area ◽  
Muscle Fiber Atrophy ◽  
Fiber Atrophy ◽  
Type Ii Fibers

Satellite cells (SC) are essential for skeletal muscle growth and repair. Because sarcopenia is associated with type II muscle fiber atrophy, we hypothesized that SC content is specifically reduced in the type II fibers in the elderly. A total of eight elderly (E; 76 ± 1 yr) and eight young (Y; 20 ± 1 yr) healthy males were selected. Muscle biopsies were collected from the vastus lateralis in both legs. ATPase staining and a pax7-antibody were used to determine fiber type-specific SC content (i.e., pax7-positive SC) on serial muscle cross sections. In contrast to the type I fibers, the proportion and mean cross-sectional area of the type II fibers were substantially reduced in E vs. Y. The number of SC per type I fiber was similar in E and Y. However, the number of SC per type II fiber was substantially lower in E vs. Y (0.044 ± 0.003 vs. 0.080 ± 0.007; P < 0.01). In addition, in the type II fibers, the number of SC relative to the total number of nuclei and the number of SC per fiber area were also significantly lower in E. This study is the first to show type II fiber atrophy in the elderly to be associated with a fiber type-specific decline in SC content. The latter is evident when SC content is expressed per fiber or per fiber area. The decline in SC content might be an important factor in the etiology of type II muscle fiber atrophy, which accompanies the loss of skeletal muscle with aging.

Fiber type and temperature dependence of inorganic phosphate: implications for fatigue

2004 ◽  
Vol 287 (3) ◽  
pp. C673-C681 ◽  
Author(s):  
E. P. Debold ◽  
H. Dave ◽  
R. H. Fitts
Keyword(s):  
Contractile Function ◽  
Contractile Activity ◽  
Isometric Force ◽  
Fiber Type ◽  
Type I ◽  
Type Ii ◽  
Shortening Velocity ◽  
Single Fibers ◽  
Type I Fibers ◽  
Type Ii Fibers

Elevated levels of Pi are thought to cause a substantial proportion of the loss in muscular force and power output during fatigue from intense contractile activity. However, support for this hypothesis is based, in part, on data from skinned single fibers obtained at low temperatures (≤15°C). The effect of high (30 mM) Pi concentration on the contractile function of chemically skinned single fibers was examined at both low (15°C) and high (30°C) temperatures using fibers isolated from rat soleus (type I fibers) and gastrocnemius (type II fibers) muscles. Elevating Pi from 0 to 30 mM at saturating free Ca2+ levels depressed maximum isometric force (Po) by 54% at 15°C and by 19% at 30°C ( P < 0.05; significant interaction) in type I fibers. Similarly, the Po of type II fibers was significantly more sensitive to high levels of Pi at the lower (50% decrease) vs. higher temperature (5% decrease). The maximal shortening velocity of both type I and type II fibers was not significantly affected by elevated Pi at either temperature. However, peak fiber power was depressed by 49% at 15°C but by only 16% at 30°C in type I fibers. Similarly, in type II fibers, peak power was depressed by 40 and 18% at 15 and 30°C, respectively. These data suggest that near physiological temperatures and at saturating levels of intracellular Ca2+, elevated levels of Pi contribute less to fatigue than might be inferred from data obtained at lower temperatures.

scholarly journals Velocity, force, power, and Ca2+ sensitivity of fast and slow monkey skeletal muscle fibers

1998 ◽  
Vol 84 (5) ◽  
pp. 1776-1787 ◽  
Author(s):  
Robert H. Fitts ◽  
Sue C. Bodine ◽  
Janell G. Romatowski ◽  
Jeffrey J. Widrick
Keyword(s):  
Peak Power ◽  
Fiber Type ◽  
Medial Gastrocnemius ◽  
Type I ◽  
Fiber Types ◽  
Type Ii ◽  
Shortening Velocity ◽  
Hybrid Fibers ◽  
Slow Type ◽  
Type Ii Fibers

In this study, we determined the contractile properties of single chemically skinned fibers prepared from the medial gastrocnemius (MG) and soleus (Sol) muscles of adult male rhesus monkeys and assessed the effects of the spaceflight living facility known as the experiment support primate facility (ESOP). Muscle biopsies were obtained 4 wk before and immediately after an 18-day ESOP sit, and fiber type was determined by immunohistochemical techniques. The MG slow type I fiber was significantly smaller than the MG type II, Sol type I, and Sol type II fibers. The ESOP sit caused a significant reduction in the diameter of type I and type I/II (hybrid) fibers of Sol and MG type II and hybrid fibers but no shift in fiber type distribution. Single-fiber peak force (mN and kN/m2) was similar between fiber types and was not significantly different from values previously reported for other species. The ESOP sit significantly reduced the force (mN) of Sol type I and MG type II fibers. This decline was entirely explained by the atrophy of these fiber types because the force per cross-sectional area (kN/m2) was not altered. Peak power of Sol and MG fast type II fiber was 5 and 8.5 times that of slow type I fiber, respectively. The ESOP sit reduced peak power by 25 and 18% in Sol type I and MG type II fibers, respectively, and, for the former fiber type, shifted the force-pCa relationship to the right, increasing the Ca2+ activation threshold and the free Ca2+concentration, eliciting half-maximal activation. The ESOP sit had no effect on the maximal shortening velocity ( V o) of any fiber type. V o of the hybrid fibers was only slightly higher than that of slow type I fibers. This result supports the hypothesis that in hybrid fibers the slow myosin heavy chain would be expected to have a disproportionately greater influence on V o.

Effects of carnosine on contractile apparatus Ca2+ sensitivity and sarcoplasmic reticulum Ca2+ release in human skeletal muscle fibers

2012 ◽  
Vol 112 (5) ◽  
pp. 728-736 ◽  
Author(s):  
T. L. Dutka ◽  
C. R. Lamboley ◽  
M. J. McKenna ◽  
R. M. Murphy ◽  
G. D. Lamb
Keyword(s):  
Skeletal Muscle ◽  
Human Muscle ◽  
Muscle Performance ◽  
Type I ◽  
Type Ii ◽  
Contractile Apparatus ◽  
Muscle Carnosine ◽  
Ec Coupling ◽  
Type I Fibers ◽  
Type Ii Fibers

There is considerable interest in potential ergogenic and therapeutic effects of increasing skeletal muscle carnosine content, although its effects on excitation-contraction (EC) coupling in human muscle have not been defined. Consequently, we sought to characterize what effects carnosine, at levels attained by supplementation, has on human muscle fiber function, using a preparation with all key EC coupling proteins in their in situ positions. Fiber segments, obtained from vastus lateralis muscle of human subjects by needle biopsy, were mechanically skinned, and their Ca2+ release and contractile apparatus properties were characterized. Ca2+ sensitivity of the contractile apparatus was significantly increased by 8 and 16 mM carnosine (increase in pCa50 of 0.073 ± 0.007 and 0.116 ± 0.006 pCa units, respectively, in six type I fibers, and 0.063 ± 0.018 and 0.103 ± 0.013 pCa units, respectively, in five type II fibers). Caffeine-induced force responses were potentiated by 8 mM carnosine in both type I and II fibers, with the potentiation in type II fibers being entirely explicable by the increase in Ca2+ sensitivity of the contractile apparatus caused by carnosine. However, the potentiation of caffeine-induced responses caused by carnosine in type I fibers was beyond that expected from the associated increase in Ca2+ sensitivity of the contractile apparatus and suggestive of increased Ca2+-induced Ca2+ release. Thus increasing muscle carnosine content likely confers benefits to muscle performance in both fiber types by increasing the Ca2+ sensitivity of the contractile apparatus and possibly also by aiding Ca2+ release in type I fibers, helping to lessen or slow the decline in muscle performance during fatiguing stimulation.

Effects of fiber type and training on beta-adrenoceptor density in human skeletal muscle

1989 ◽  
Vol 257 (5) ◽  
pp. E736-E742 ◽  
Author(s):  
W. H. Martin ◽  
A. R. Coggan ◽  
R. J. Spina ◽  
J. E. Saffitz
Keyword(s):  
Skeletal Muscle ◽  
Exercise Training ◽  
Fiber Type ◽  
Type I ◽  
Type Ii ◽  
Receptor Density ◽  
Beta Receptor ◽  
Type I Fibers ◽  
Total Tissue ◽  
Type Ii Fibers

The density and distribution of beta-adrenergic receptors in type I and II fibers of human gastrocnemius and quadriceps muscles were characterized in ten healthy sedentary subjects and in a subgroup of six subjects before and after 12 wk of endurance exercise training. Total tissue content of beta-receptors was measured in frozen sections of skeletal muscle biopsies incubated with 125I-labeled cyanopindolol in the presence and absence of 10(-5) M L-propranolol. The relative beta-receptor densities of type I and II fibers were delineated autoradiographically. Muscle fiber types were identified in adjacent serial sections by histochemical staining of myofibrillar adenosine-triphosphatase (ATPase) activity. Type I fibers had a threefold greater beta-receptor density than type II fibers of the same muscle [P less than 0.001; type I-to-type II fiber ratio of beta-receptor density was 3.06 +/- 0.43 (SD)]. Exercise training elicited a change in muscle fiber subtype composition (+34% type IIa and -42% type IIb; P less than 0.05 and P = 0.066, respectively), a 40% increase in citrate synthase activity of skeletal muscle (P = 0.01), and a 23% rise in peak oxygen uptake (P less than 0.001). However, no change in total tissue content of beta-receptors was observed after exercise training, even when receptor density was adjusted for preconditioning fiber type composition. Thus beta-receptor density of type I fibers of human skeletal muscle is threefold greater than that of type II fibers. Enhanced capacity for aerobic metabolism after endurance exercise training is not associated with upregulation of total beta-receptor density.

scholarly journals Phosphorylation of αB-crystallin and its cytoskeleton association differs in skeletal myofiber types depending on resistance exercise intensity and volume

2019 ◽  
Vol 126 (6) ◽  
pp. 1607-1618 ◽  
Author(s):  
Daniel Jacko ◽  
Käthe Bersiner ◽  
Jonas Hebchen ◽  
Markus de Marées ◽  
Wilhelm Bloch ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Resistance Exercise ◽  
Mechanical Stress ◽  
Fiber Type ◽  
Type I ◽  
Type Ii ◽  
Αb Crystallin ◽  
Serine 59 ◽  
Type I Fibers ◽  
Type Ii Fibers

αB-crystallin (CRYAB) is an important actor in the immediate cell stabilizing response following mechanical stress in skeletal muscle. Yet, only little is known regarding myofiber type-specific stress responses of CRYAB. We investigated whether the phosphorylation of CRYAB at serine 59 (pCRYABSer59) and its cytoskeleton association are influenced by varying load-intensity and -volume in a fiber type-specific manner. Male subjects were assigned to 1, 5, and 10 sets of different acute resistance exercise protocols: hypertrophy (HYP), maximum strength (MAX), strength endurance (SE), low intensity (LI), and three sets of maximum eccentric resistance exercise (ECC). Skeletal muscle biopsies were taken at baseline and 30 min after exercise. Western blot revealed an increase inpCRYABSer59only following 5 and 10 sets in groups HYP, MAX, SE, and LI as well as following 3 sets in the ECC group. In type I fibers, immunohistochemistry determined increasedpCRYABSer59in all groups. In type II fibers,pCRYABSer59only increased in MAX and ECC groups, with the increase in type II fibers exceeding that of type I fibers in ECC. Association of CRYAB andpCRYABSer59with the cytoskeleton reflected the fiber type-specific phosphorylation pattern. Phosphorylation of CRYAB and its association with the cytoskeleton in type I and II myofibers is highly specific in terms of loading intensity and volume. Most likely, this is based on specific recruitment patterns of the different myofiber entities due to the different resistance exercise loadings. We conclude thatpCRYABSer59indicates contraction-induced mechanical stress exposure of single myofibers in consequence of resistance exercise.NEW & NOTEWORTHY We determined that the phosphorylation of αB-crystallin at serine 59 (pCRYABSer59) after resistance exercise differs between myofiber types in a load- and intensity-dependent manner. The determination ofpCRYABSer59could serve as a marker indirectly indicating contractile involvement and applied mechanical stress on individual fibers. By that, it is possible to retrospectively assess the impact of resistance exercise loading on skeletal muscle fiber entities.

scholarly journals Dissociation between short-term unloading and resistance training effects on skeletal muscle Na+,K+-ATPase, muscle function, and fatigue in humans

2016 ◽  
Vol 121 (5) ◽  
pp. 1074-1086 ◽  
Author(s):  
Ben D. Perry ◽  
Victoria L. Wyckelsma ◽  
Robyn M. Murphy ◽  
Collene H. Steward ◽  
Mitchell Anderson ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Resistance Training ◽  
Muscle Function ◽  
Fiber Type ◽  
Peak Torque ◽  
Quadriceps Muscle ◽  
Type I ◽  
Type Ii ◽  
Type I Fibers ◽  
Type Ii Fibers

Physical training increases skeletal muscle Na+,K+-ATPase content (NKA) and improves exercise performance, but the effects of inactivity per se on NKA content and isoform abundance in human muscle are unknown. We investigated the effects of 23-day unilateral lower limb suspension (ULLS) and subsequent 4-wk resistance training (RT) on muscle function and NKA in 6 healthy adults, measuring quadriceps muscle peak torque; fatigue and venous [K+] during intense one-legged cycling exercise; and skeletal muscle NKA content ([3H]ouabain binding) and NKA isoform abundances (immunoblotting) in muscle homogenates (α1-3, β1–2) and in single fibers (α1–3, β1). In the unloaded leg after ULLS, quadriceps peak torque and cycling time to fatigue declined by 22 and 23%, respectively, which were restored with RT. Whole muscle NKA content and homogenate NKA α1–3 and β1–2 isoform abundances were unchanged with ULLS or RT. However, in single muscle fibers, NKA α3 in type I (−66%, P = 0.006) and β1 in type II fibers (−40%, P = 0.016) decreased after ULLS, with other NKA isoforms unchanged. After RT, NKA α1 (79%, P = 0.004) and β1 (35%, P = 0.01) increased in type II fibers, while α2 (76%, P = 0.028) and α3 (142%, P = 0.004) increased in type I fibers compared with post-ULLS. Despite considerably impaired muscle function and earlier fatigue onset, muscle NKA content and homogenate α1 and α2 abundances were unchanged, thus being resilient to inactivity induced by ULLS. Nonetheless, fiber type-specific downregulation with inactivity and upregulation with RT of several NKA isoforms indicate complex regulation of muscle NKA expression in humans.

scholarly journals Myoglobin concentration in skeletal muscle fibers of chronic heart failure patients

2009 ◽  
Vol 107 (4) ◽  
pp. 1138-1143 ◽  
Author(s):  
Martijn A. Bekedam ◽  
Brechje J. van Beek-Harmsen ◽  
Willem van Mechelen ◽  
Anco Boonstra ◽  
Willem J. van der Laarse
Keyword(s):  
Heart Failure ◽  
Skeletal Muscle ◽  
Chronic Heart Failure ◽  
Muscle Fibers ◽  
Type I ◽  
Fiber Types ◽  
Type Ii ◽  
Skeletal Muscle Fibers ◽  
Type I Fibers ◽  
Type Ii Fibers

The purpose of this study was to determine the myoglobin concentration in skeletal muscle fibers of chronic heart failure (CHF) patients and to calculate the effect of myoglobin on oxygen buffering and facilitated diffusion. Myoglobin concentration, succinate dehydrogenase (SDH) activity, and cross-sectional area of individual muscle fibers from the vastus lateralis of five control and nine CHF patients were determined using calibrated histochemistry. CHF patients compared with control subjects were similar with respect to myoglobin concentration: type I fibers 0.69 ± 0.11 mM (mean ± SD), type II fibers 0.52 ± 0.07 mM in CHF vs. type I fibers 0.70 ± 0.09 mM, type II fibers 0.49 ± 0.07 mM in control, whereas SDH activity was significantly lower in CHF in both fiber types ( P < 0.01). The myoglobin concentration in type I fibers was higher than in type II fibers ( P < 0.01). Consequently, the oxygen buffering capacity, calculated from myoglobin concentration/SDH activity was increased in CHF: type I fibers 11.4 ± 2.1 s, type II fibers 13.6 ± 3.9 s in CHF vs. type I fibers 7.8 ± 0.9 s, type II fibers 7.5 ± 1.0 s in control, all P < 0.01). The calculated extracellular oxygen tension required to prevent core anoxia (Po2crit) in muscle fibers was similar when controls were compared with patients in type I fibers 10.3 ± 0.9 Torr in CHF and 11.5 ± 3.3 Torr in control, but was lower in type II fibers of patients 6.1 ± 2.8 Torr in CHF and 14.7 ± 6.2 Torr in control, P < 0.01. The lower Po2crit of type II fibers may facilitate oxygen extraction from capillaries. Reduced exercise tolerance in CHF is not due to myoglobin deficiency.

scholarly journals Effect of 23-day muscle disuse on sarcoplasmic reticulum Ca2+ properties and contractility in human type I and type II skeletal muscle fibers

2016 ◽  
Vol 121 (2) ◽  
pp. 483-492 ◽  
Author(s):  
C. R. Lamboley ◽  
V. L. Wyckelsma ◽  
B. D. Perry ◽  
M. J. McKenna ◽  
G. D. Lamb
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Muscle Fibers ◽  
Type I ◽  
Fiber Types ◽  
Specific Force ◽  
Type Ii ◽  
Muscle Disuse ◽  
Type I Fibers ◽  
Type Ii Fibers

Inactivity negatively impacts on skeletal muscle function mainly through muscle atrophy. However, recent evidence suggests that the quality of individual muscle fibers is also altered. This study examined the effects of 23 days of unilateral lower limb suspension (ULLS) on specific force and sarcoplasmic reticulum (SR) Ca2+ content in individual skinned muscle fibers. Muscle biopsies of the vastus lateralis were taken from six young healthy adults prior to and following ULLS. After disuse, the endogenous SR Ca2+ content was ∼8% lower in type I fibers and maximal SR Ca2+ capacity was lower in both type I and type II fibers (−11 and −5%, respectively). The specific force, measured in single skinned fibers from three subjects, decreased significantly after ULLS in type II fibers (−23%) but not in type I fibers (−9%). Western blot analyses showed no significant change in the amounts of myosin heavy chain (MHC) I and MHC IIa following the disuse, whereas the amounts of sarco(endo)plasmic reticulum Ca2+-ATPase 1 (SERCA1) and calsequestrin increased by ∼120 and ∼20%, respectively, and the amount of troponin I decreased by ∼21%. These findings suggest that the decline in force and power occurring with muscle disuse is likely to be exacerbated in part by reductions in maximum specific force in type II fibers, and in the amount of releasable SR Ca2+ in both fiber types, the latter not being attributable to a reduced calsequestrin level. Furthermore, the ∼3-wk disuse in human elicits change in SR properties, in particular a more than twofold upregulation in SERCA1 density, before any fiber-type shift.

scholarly journals Resistance exercise training promotes fiber type-specific myonuclear adaptations in older adults

2020 ◽  
Vol 128 (4) ◽  
pp. 795-804 ◽  
Author(s):  
Tatiana Moro ◽  
Camille R. Brightwell ◽  
Elena Volpi ◽  
Blake B. Rasmussen ◽  
Christopher S. Fry
Keyword(s):  
Older Adults ◽  
Skeletal Muscle ◽  
Exercise Training ◽  
Fiber Type ◽  
Type I ◽  
Type Ii ◽  
Resistance Exercise Training ◽  
Myonuclear Domain ◽  
Type I Fibers ◽  
Type Ii Fibers

Aging induces physiological decline in human skeletal muscle function and morphology, including type II fiber atrophy and an increase in type I fiber frequency. Resistance exercise training (RET) is an effective strategy to overcome muscle mass loss and improve strength, with a stronger effect on type II fibers. In the present study, we sought to determine the effect of a 12-wk progressive RET program on the fiber type-specific skeletal muscle hypertrophic response in older adults. Nineteen subjects [10 men and 9 women (71.1 ± 4.3 yr)] were studied before and after the 12-wk program. Immunohistochemical analysis was used to quantify myosin heavy chain (MyHC) isoform expression, cross-sectional area (CSA), satellite cell abundance, myonuclear content, and lipid droplet density. RET induced an increase in MyHC type II fiber frequency and a concomitant decrease in MyHC type I fiber frequency. Mean CSA increased significantly only in MyHC type II fibers (+23.3%, P < 0.05), but myonuclear content increased only in MyHC type I fibers ( P < 0.05), with no change in MyHC type II fibers. Satellite cell content increased ~40% in both fiber types ( P > 0.05). RET induced adaptations to the capillary supply to satellite cells, with the distance between satellite cells and the nearest capillary increasing in type I fibers and decreasing in type II fibers. Both fiber types showed similar decrements in intramuscular lipid density with training ( P < 0.05). Our data provide intriguing evidence for a fiber type-specific response to RET in older adults and suggest flexibility in the myonuclear domain of type II fibers during a hypertrophic stimulus. NEW & NOTEWORTHY In older adults, progressive resistance exercise training (RET) increased skeletal muscle fiber volume and cross-sectional area independently of myonuclear accretion, leading to an expansion of the myonuclear domain. Fiber type-specific analyses illuminated differential adaptation; type II fibers underwent hypertrophy and exhibited myonuclear domain plasticity, whereas myonuclear accretion occurred in type I fibers in the absence of a robust hypertrophic response. RET also augmented satellite cell-capillary interaction and reduced intramyocellular lipid density to improve muscle quality.

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