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| Mitochondria content and subcellular localization in distinct fiber types and at whole-muscle level of leg and arm muscles. There was a tendency (P = 0.095) toward a higher mitochondrial content in the intermyofibrillar (IMF) and subsarcolemmal (SS) regions, of arm muscle (open bars) compared with leg muscle (filled bars) (A). This tendency is also apparent when calculating total mitochondrial content (IMF + SS) (B). (C) Weighted mitochondrial volumes in the arm and leg muscle, estimated from a fiber type distribution of 57 and 37% MHC-I for the leg and arm (n = 9), respectively. These MHC weighted values of whole-muscle mitochondrial content in arm and leg muscles are similar. Values are means ± SE (n = 29-30 fibers from 10 subjects).
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As one of the most physically demanding sports in the Olympic Games, cross-country skiing poses considerable challenges with respect to both force generation and endurance during the combined upper- and lower-body effort of varying intensity and duration. The isoforms of myosin in skeletal muscle have long been considered not only to define the con...
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... line with this, Essén et al. (1975) reported an equally high SDH activity in the type 2 and type 1 muscle fibers in top endurance runners [with a maximal oxygen uptake ( ˙ VO 2max ) > 72 ml·kg −1 ·min −1 ], with untrained having a clear fiber type difference with only half the SDH activity in their type 2 muscle fibers. Also, the mitochondrial volume density is generally considered to be strongly fiber type-dependent. In untrained humans, the mitochondrial volume varies from 6% in type I fibers to 4.5% in type 2a and 2.3% in type 2x fibers (Howald et al., 1985), with a more pronounced difference in animal studies of oxidative and glycolytic muscle, i.e., 2.7 times higher in rabbits and 4.5 times higher in rats ( Saltin and Gollnick, 1983;Jackman and Willis, 1996). In the current study, we compared equally trained arm and leg muscle based on the same CS activity (Table 2), the same average capillarization (Table 3), and no difference in the mitochondrial content at whole-muscle level. Based on this, we state that arm and leg muscle are equally trained. In these endurance-trained humans, there is a twofold higher mitochondrial volume density between type 1 and 2 fibers (Figure 3). Furthermore, the volume density of the type 2 fibers from trained is equal to (Howald et al., 1985) or higher (Nielsen et al., 2010a) than in type 1 fibers from untrained individuals. Thus, fiber type mitochondrial content is extremely malleable with muscle activity and inactivity (Hoppeler, 1986;Nielsen et al., 2010b). These changes in fiber metabolic characteristics are clearly not fiber-type-dependent, and a considerable variation exists within each fiber type with a clear overlay between fiber types. In line with this, a recent study indicated that type 2a fibers can possess equally high or even higher mitochondrial respiration as type 1 fibers ( Boushel et al., 2014). The equal volume density of mitochondria and CS activity in different types of fibers suggest that the intrinsic characteristics of mitochondria are variable and not determined solely by fiber ...
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... the different fiber type distribution in leg and arm muscle, the mitochondrial volume fraction was equal in both ( Figure 3D). This suggests that arm muscles, despite lower fat oxidation capacity (Helge, 2010), HAD activity (present data), lower IMCL content ( Koh et al., 2017), and higher lactate release during exercise (Van Hall et al., 2003), still require a high mitochondrial oxidative capacity. Indeed, there was a tendency (P = 0.095) toward a 10% higher mitochondrial volume fraction in the fibers from the arms compared with the legs (Figure 3C), predominantly due to a tendency to higher volume fraction in type 2 fibers in the arms (Figure 3C). Thus, differences in leg and arm whole-muscle metabolic characteristics may not solely be explained by the dissimilar fiber type distribution in the limbs. The high mitochondrial content in type 2 fibers in arm could either be a consequence of the high metabolic demand in the upper body of these trained subjects or, possibly, due to a high demand for glycolytic flux in type 2 fibers. Thus, there is a clear necessity for being able to convert lactate to pyruvate within the mitochondrial intermembrane space with pyruvate subsequently taken into the mitochondrial matrix where it enters the TCA cycle and is ultimately oxidized ( Brooks et al., 1999;Hashimoto et al., 2006;Jacobs et al., 2013). Furthermore, peak arm blood flow and O 2 delivery per unit muscle mass during arm exercise is higher than that to leg muscle during leg cycling reflecting the proportional matching of oxygen delivery to oxidative capacity (Boushel et al., ...
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... the different fiber type distribution in leg and arm muscle, the mitochondrial volume fraction was equal in both ( Figure 3D). This suggests that arm muscles, despite lower fat oxidation capacity (Helge, 2010), HAD activity (present data), lower IMCL content ( Koh et al., 2017), and higher lactate release during exercise (Van Hall et al., 2003), still require a high mitochondrial oxidative capacity. Indeed, there was a tendency (P = 0.095) toward a 10% higher mitochondrial volume fraction in the fibers from the arms compared with the legs (Figure 3C), predominantly due to a tendency to higher volume fraction in type 2 fibers in the arms (Figure 3C). Thus, differences in leg and arm whole-muscle metabolic characteristics may not solely be explained by the dissimilar fiber type distribution in the limbs. The high mitochondrial content in type 2 fibers in arm could either be a consequence of the high metabolic demand in the upper body of these trained subjects or, possibly, due to a high demand for glycolytic flux in type 2 fibers. Thus, there is a clear necessity for being able to convert lactate to pyruvate within the mitochondrial intermembrane space with pyruvate subsequently taken into the mitochondrial matrix where it enters the TCA cycle and is ultimately oxidized ( Brooks et al., 1999;Hashimoto et al., 2006;Jacobs et al., 2013). Furthermore, peak arm blood flow and O 2 delivery per unit muscle mass during arm exercise is higher than that to leg muscle during leg cycling reflecting the proportional matching of oxygen delivery to oxidative capacity (Boushel et al., ...
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... the different fiber type distribution in leg and arm muscle, the mitochondrial volume fraction was equal in both ( Figure 3D). This suggests that arm muscles, despite lower fat oxidation capacity (Helge, 2010), HAD activity (present data), lower IMCL content ( Koh et al., 2017), and higher lactate release during exercise (Van Hall et al., 2003), still require a high mitochondrial oxidative capacity. Indeed, there was a tendency (P = 0.095) toward a 10% higher mitochondrial volume fraction in the fibers from the arms compared with the legs (Figure 3C), predominantly due to a tendency to higher volume fraction in type 2 fibers in the arms (Figure 3C). Thus, differences in leg and arm whole-muscle metabolic characteristics may not solely be explained by the dissimilar fiber type distribution in the limbs. The high mitochondrial content in type 2 fibers in arm could either be a consequence of the high metabolic demand in the upper body of these trained subjects or, possibly, due to a high demand for glycolytic flux in type 2 fibers. Thus, there is a clear necessity for being able to convert lactate to pyruvate within the mitochondrial intermembrane space with pyruvate subsequently taken into the mitochondrial matrix where it enters the TCA cycle and is ultimately oxidized ( Brooks et al., 1999;Hashimoto et al., 2006;Jacobs et al., 2013). Furthermore, peak arm blood flow and O 2 delivery per unit muscle mass during arm exercise is higher than that to leg muscle during leg cycling reflecting the proportional matching of oxygen delivery to oxidative capacity (Boushel et al., ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... line with this, Essén et al. (1975) reported an equally high SDH activity in the type 2 and type 1 muscle fibers in top endurance runners [with a maximal oxygen uptake ( ˙ VO 2max ) > 72 ml·kg −1 ·min −1 ], with untrained having a clear fiber type difference with only half the SDH activity in their type 2 muscle fibers. Also, the mitochondrial volume density is generally considered to be strongly fiber type-dependent. In untrained humans, the mitochondrial volume varies from 6% in type I fibers to 4.5% in type 2a and 2.3% in type 2x fibers (Howald et al., 1985), with a more pronounced difference in animal studies of oxidative and glycolytic muscle, i.e., 2.7 times higher in rabbits and 4.5 times higher in rats ( Saltin and Gollnick, 1983;Jackman and Willis, 1996). In the current study, we compared equally trained arm and leg muscle based on the same CS activity (Table 2), the same average capillarization (Table 3), and no difference in the mitochondrial content at whole-muscle level. Based on this, we state that arm and leg muscle are equally trained. In these endurance-trained humans, there is a twofold higher mitochondrial volume density between type 1 and 2 fibers (Figure 3). Furthermore, the volume density of the type 2 fibers from trained is equal to (Howald et al., 1985) or higher (Nielsen et al., 2010a) than in type 1 fibers from untrained individuals. Thus, fiber type mitochondrial content is extremely malleable with muscle activity and inactivity (Hoppeler, 1986;Nielsen et al., 2010b). These changes in fiber metabolic characteristics are clearly not fiber-type-dependent, and a considerable variation exists within each fiber type with a clear overlay between fiber types. In line with this, a recent study indicated that type 2a fibers can possess equally high or even higher mitochondrial respiration as type 1 fibers ( Boushel et al., 2014). The equal volume density of mitochondria and CS activity in different types of fibers suggest that the intrinsic characteristics of mitochondria are variable and not determined solely by fiber ...
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... the different fiber type distribution in leg and arm muscle, the mitochondrial volume fraction was equal in both ( Figure 3D). This suggests that arm muscles, despite lower fat oxidation capacity (Helge, 2010), HAD activity (present data), lower IMCL content ( Koh et al., 2017), and higher lactate release during exercise (Van Hall et al., 2003), still require a high mitochondrial oxidative capacity. Indeed, there was a tendency (P = 0.095) toward a 10% higher mitochondrial volume fraction in the fibers from the arms compared with the legs (Figure 3C), predominantly due to a tendency to higher volume fraction in type 2 fibers in the arms (Figure 3C). Thus, differences in leg and arm whole-muscle metabolic characteristics may not solely be explained by the dissimilar fiber type distribution in the limbs. The high mitochondrial content in type 2 fibers in arm could either be a consequence of the high metabolic demand in the upper body of these trained subjects or, possibly, due to a high demand for glycolytic flux in type 2 fibers. Thus, there is a clear necessity for being able to convert lactate to pyruvate within the mitochondrial intermembrane space with pyruvate subsequently taken into the mitochondrial matrix where it enters the TCA cycle and is ultimately oxidized ( Brooks et al., 1999;Hashimoto et al., 2006;Jacobs et al., 2013). Furthermore, peak arm blood flow and O 2 delivery per unit muscle mass during arm exercise is higher than that to leg muscle during leg cycling reflecting the proportional matching of oxygen delivery to oxidative capacity (Boushel et al., ...
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... the different fiber type distribution in leg and arm muscle, the mitochondrial volume fraction was equal in both ( Figure 3D). This suggests that arm muscles, despite lower fat oxidation capacity (Helge, 2010), HAD activity (present data), lower IMCL content ( Koh et al., 2017), and higher lactate release during exercise (Van Hall et al., 2003), still require a high mitochondrial oxidative capacity. Indeed, there was a tendency (P = 0.095) toward a 10% higher mitochondrial volume fraction in the fibers from the arms compared with the legs (Figure 3C), predominantly due to a tendency to higher volume fraction in type 2 fibers in the arms (Figure 3C). Thus, differences in leg and arm whole-muscle metabolic characteristics may not solely be explained by the dissimilar fiber type distribution in the limbs. The high mitochondrial content in type 2 fibers in arm could either be a consequence of the high metabolic demand in the upper body of these trained subjects or, possibly, due to a high demand for glycolytic flux in type 2 fibers. Thus, there is a clear necessity for being able to convert lactate to pyruvate within the mitochondrial intermembrane space with pyruvate subsequently taken into the mitochondrial matrix where it enters the TCA cycle and is ultimately oxidized ( Brooks et al., 1999;Hashimoto et al., 2006;Jacobs et al., 2013). Furthermore, peak arm blood flow and O 2 delivery per unit muscle mass during arm exercise is higher than that to leg muscle during leg cycling reflecting the proportional matching of oxygen delivery to oxidative capacity (Boushel et al., ...
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... the different fiber type distribution in leg and arm muscle, the mitochondrial volume fraction was equal in both ( Figure 3D). This suggests that arm muscles, despite lower fat oxidation capacity (Helge, 2010), HAD activity (present data), lower IMCL content ( Koh et al., 2017), and higher lactate release during exercise (Van Hall et al., 2003), still require a high mitochondrial oxidative capacity. Indeed, there was a tendency (P = 0.095) toward a 10% higher mitochondrial volume fraction in the fibers from the arms compared with the legs (Figure 3C), predominantly due to a tendency to higher volume fraction in type 2 fibers in the arms (Figure 3C). Thus, differences in leg and arm whole-muscle metabolic characteristics may not solely be explained by the dissimilar fiber type distribution in the limbs. The high mitochondrial content in type 2 fibers in arm could either be a consequence of the high metabolic demand in the upper body of these trained subjects or, possibly, due to a high demand for glycolytic flux in type 2 fibers. Thus, there is a clear necessity for being able to convert lactate to pyruvate within the mitochondrial intermembrane space with pyruvate subsequently taken into the mitochondrial matrix where it enters the TCA cycle and is ultimately oxidized ( Brooks et al., 1999;Hashimoto et al., 2006;Jacobs et al., 2013). Furthermore, peak arm blood flow and O 2 delivery per unit muscle mass during arm exercise is higher than that to leg muscle during leg cycling reflecting the proportional matching of oxygen delivery to oxidative capacity (Boushel et al., ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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... electron microscopy images showing the subcellular localization of skeletal muscle mitochondria in the highly trained cross-country skiers are shown in Figure 1, clearly demonstrating a very high mitochondrial volume in these trained muscles. The SS mitochondria were unevenly distributed below the sarcolemma, with a higher volume located near the capillaries and around the nuclei. The IMF mitochondria are wrapped around the myofibrils, mainly located on each side of the z-line. These mitochondria in the I-band are often connected to an adjacent mitochondrion in the same sarcomere through the A-band. Individual values for the total volume of mitochondria per volume of myofiber are given in Table 5. The total volume of mitochondria is a volume-weighted average of the superficial region and the central region of the myofiber as well as the SS space. The individual values are based on 8-12 myofibers from two different biopsies. The total mitochondrial volume averaged 8.6 ± 1.6 and 9.0 ± 2.0 µm 3 ·µm −3 , for the arm and leg, respectively. The relative distribution of the mitochondrial subcellular regions was estimated in a total of 29 or 30 fibers from the 10 participants. In these highly endurance-trained athletes, the skeletal muscle mitochondria had similar relative distribution between IMF and SS localizations in both leg and arm muscles and in type 1 and 2 fibers. Thus, 83-86% of the mitochondria are localized in the IMF region and 11-14% in the SS region. The mitochondrial content and subcellular localization in distinct fiber types and at the whole-muscle level of leg and arm muscles is shown in Figure 3. Intriguingly, there was a tendency toward (10-20%) a lower mitochondrial content in the IMF and SS regions of leg muscle fibers compared with arm muscle fibers ( Figure 3A, P = 0.095). This is also apparent when calculating a total (IMF + SS) mitochondrial content ( Figure 3B). By taking the different MHC composition of leg and arm muscles into account, the average fiber type-mitochondrial volume can be estimated, given a fiber type distribution of 57 and 37% MHC-1 in leg and arm, respectively. Weighting the fiber type distribution, the whole-muscle mitochondrial volume in leg and arm muscle was similar ( Figure 3C). Thus, at the whole-muscle level, the non-significantly higher mitochondrial content in the arms mediated, despite a relatively higher number of MHC-2 TABLE 2 | The profile of myosin heavy chains and enzyme activities in the arm (triceps brachii) and leg (vastus lateralis) muscles of elite cross-country skiers (n = 10). The maximal activities of 3-hydroxy-acyl-CoA-dehydrogenase (HAD) and citrate synthase (CS) are given in µmol/g dw/min. * Significantly different from the leg muscle. Capillary density was assessed immunohistochemically. Number of capillaries is given in: total number of capillaries per total number of fibers (#cap/fiber); total number of capillaries per muscle area (cap/mm 2 ), and number of capillaries around each fiber for each fiber type and average for all fibers. * Significantly different from the corresponding value for leg muscle; # significantly different from the corresponding values for the other fiber types. fibers, an equal whole-muscle mitochondrial content in the legs and arms ( Figure 3C). There was a significant correlation (P = 0.02) between the total mitochondrial content in arm muscle and whole body VO 2 max (L·min −1 ), which was not apparent in leg ...
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Clenbuterol induces a slow-to-fast fiber type transition in skeletal muscle. This muscle fiber transition decreased mitochondrial oxidative capacity and respiratory function. We hypothesized that the clenbuterol-mediated reduction in oxidative capacity is associated with the alteration in mitochondrial morphology. To verify this hypothesis, we exam...
Citations
... Subsequently, Helge 36 found that performing exercises with the upper limbs has a lower fat oxidation compared to those of the lower limbs, suggesting glycolytic predominance in the upper limbs compared to the lower limbs. Ørtenblad et al. 37 analyzed the metabolic differences and predominance of muscle fiber types in the triceps brachii and vastus lateralis thigh muscles in elite adult skiing athletes. It was suggested that the lower limbs pointed to a higher oxidative capacity due to the percentage of 3-hydroxy-acyl-CoA dehydrogenase capacity being higher in the leg muscles. ...
... [10][11][12][13] However, there was restricted data about RTS on neuromuscular performance among athletes after ARinf and most available studies also focus on the lower-body. [14][15][16] Upper-body strength and power were of particular importance to some sports, like kayaking, cross-country skiing, rowing, etc. 17,18 Furthermore, the effects of RTS during the pandemic on maintaining body composition in athletes remain mixed results. [19][20][21] Given above, it is necessary to elucidate the influences of ARinf and RTS in athletes who demand high-level neuromuscular function and optimum body composition, such as kayakers. ...
... 3,20,41 Furthermore, the effects of ARinf on the upper and lower-body neuromuscular function may differ due to the relatively small muscle mass and differences in muscle fiber type, oxygen uptake, glucose and fat oxidation ability compared to the lowerbody. 17,18 Regarding the upper-body function was crucial for many other exercises (e.g., rowing, kayaking, water-polo, cross-country skiing, etc), 18,22 it may be useful in future studies to refine the RTS strategy according to the importance of different body parts of the athletes for performance. ...
... 3,20,41 Furthermore, the effects of ARinf on the upper and lower-body neuromuscular function may differ due to the relatively small muscle mass and differences in muscle fiber type, oxygen uptake, glucose and fat oxidation ability compared to the lowerbody. 17,18 Regarding the upper-body function was crucial for many other exercises (e.g., rowing, kayaking, water-polo, cross-country skiing, etc), 18,22 it may be useful in future studies to refine the RTS strategy according to the importance of different body parts of the athletes for performance. ...
Purpose: This study aimed to examine the short-term effects of SARS-CoV-2 infection and return to sport (RTS) on neuromuscular performance, body composition, and mental health in well-trained young kayakers. Methods: 17 vaccinated kayakers (8 male, 9 female) underwent body composition assessment, peak power output bench press (BP), and 40-s maximum repetition BP tests 23.9 ± 1.6 days before and 22.5 ± 1.6 days after a SARS-CoV-2 infection. A linear transducer was used to examine the BP performance. The perception of training load and mental health were quantified with Borg's CR-10 scale and the Hooper questionnaire before and after infection. The difference and relationship of variables were used Wilcoxon test, Student t-test, Pearson's, and Spearman's r correlation coefficients. Results: There was a significant increase in body mass, fat-free mass, and skeletal muscle mass, but no significant changes in body fat, fat mass, and all BP performance after infection (p < 0.05). There was a significant reduction in training hours per week, session rating of perceived exertion (sRPE), internal training load (sRPE-TL), fatigue, muscle soreness levels, and Hooper index, but no changes in sleep quality and stress levels after infection (p < 0.05). The training and mental health during the RTS period were significantly correlated (r = −0.85 to 0.70) with physical performance after infection. Conclusion: A SARS-CoV-2 infection did not appear to impair the upper-body neuromuscular performance and mental health of vaccinated well-trained young kayakers after a short-term RTS period. These findings can assist coaches, and medical and club staff when guiding RTS strategies after other acute infections or similar restrictions.
... We observed that there was no influence of an acute dose of NO 3 − on flight time, peak force, or propulsion during kneeling explosive push-ups. It has previously been suggested that NO 3 − could be more efficacious in upper-body exercise given that upper body musculature could be comprised of a greater proportion of type II muscle fibers (61), and that NO 3 − favorably influences type II muscle fibers. To date, few studies have examined the potential effects of NO 3 − during upper-body resistance-type exercise, with conflicting results reported (9,11,13). ...
This study tested the hypothesis that co-ingesting nitrate (NO3-)-rich beetroot juice (BR) and pomegranate powder (POM) would enhance neuromuscular performance during vertical countermovement jumps, explosive kneeling countermovement push-ups, and back squats compared to BR ingestion alone. Fifteen recreationally-active males were assigned in a double-blind, randomised, crossover design, to supplement in 3 conditions: 1) NO3--depleted beetroot juice (PL; 0.10 mmol NO3-) with two empty gelatin capsules; 2) NO3--rich beetroot juice (BR; 11.8 mmol NO3-) with two empty gelatin capsules, and 3) BR with 1000 mg of POM powder in two capsules (BR+POM). Participants completed 5 countermovement jumps and 5 kneeling countermovement push-ups interspersed by 1 min of recovery. Subsequently, participants performed 2 sets of 2 x 70% one-repetition maximum back squats, interspersed by 2 min of recovery. Plasma [NO3-] and nitrite ([NO2-]) were elevated following BR and BR+POM compared with PL and POM (P<0.001) with no differences between BR and BR+POM (P>0.05) or PL and POM (P>0.05). Peak power during countermovement jumps increased by 3% following BR compared to BR+POM (88.50 ± 11.46 vs. 85.80 ± 10.14 W/Kg0.67, P=0.009) but not PL (88.50 ± 11.46 vs. 85.58 ± 10.05 W/Kg0.67, P=0.07). Neuromuscular performance was not different between conditions during explosive kneeling push-ups and back squats (P>0.05). These data provide insight into the efficacy of NO3- to modulate explosive resistance exercise performance and indicate that supplementing with BR alone or combined with POM has limited ergogenic potential on resistance exercise. Furthermore, caution is required when combining BR with POM, as this could compromise aspects of resistance exercise performance, at least when compared to BR ingested independently.
... Similarly, skeletal muscle citrate synthase (CS) activity was significantly higher in EG than both other groups, a consequence of longterm endurance training 11 . Skeletal muscle type 1 fiber proportion was significantly higher in EG compared with both other groups (Table 1, Figure S1), a difference that has been observed before 12,13 . ...
Life-long high-level exercise training leads to improvements in physical performance and multi-tissue adaptation following changes in molecular pathways. While skeletal muscle baseline differences between exercise-trained and untrained individuals have been previously investigated, it remains unclear how acute exercise multi-omics are influenced by training history. We recruited and extensively characterized 24 individuals categorized as endurance athletes, strength athletes or control subjects. Multi-omics profiling was performed from skeletal muscle before and at three time-points after endurance or resistance exercise sessions. Timeseries multi-omics analysis revealed distinct differences in molecular processes such as fatty- and amino acid metabolism and for transcription factors such as HIF1A and the MYF-family between both exercise history and acute form of exercise. Furthermore, we found a "transcriptional specialization effect" by transcriptional narrowing and intensification. Finally, we performed multi-omics network analysis and clustering, providing a novel resource of skeletal muscle transcriptomic and metabolomic profiling in highly trained and untrained individuals.
... Fast-twitch fibers can be further differentiated into intermediate (ie, type IIa) and fastglycolytic fibers (ie, type IIx). 1 There appears to be similar maximal force capability between fiber types 2 and seemingly negligible differences in mitochondria, at least in the muscle of well-trained endurance athletes. 3 Fibers likely differ with respect to myoglobin content and capillary density, and type II fibers have a much higher maximal shortening velocity and therefore peak power. 1 MFT describes the proportion of type I and type II muscle fibers an individual possesses, which is primarily determined hereditarily. [4][5][6] MFT may be deterministic with regard to performance level within specific disciplines, whereby elite athletes in a given discipline (ie, sprint or endurance) possess a higher predominance of one fiber type (ie, more type II or I fibers, respectively) compared with their subelite counterparts. ...
Purpose:
The aim of this systematic review was to (1) determine the muscle fiber-type composition (or muscle fiber typology [MFT]) of team-sport athletes and (2) examine associations between MFT and the physical characteristics and performance tasks in team-sport athletes.
Methods:
Searches were conducted across numerous databases-PubMed, SPORTDiscus, MEDLINE, and Google Scholar-using consistent search terms. Studies were included if they examined the MFT of team-sport athletes. Included studies underwent critical appraisal using the McMasters University critical appraisal tool for quantitative research.
Results:
A total of 10 studies were included in the present review, wherein the MFT of athletes was measured from 5 different team sports (soccer, rugby union, rugby league, handball, and volleyball). There was large variability in the MFT of team-sport athletes both within (up to 27.5%) and between sports (24.0% relative difference). Male football players with a higher proportion of type II fibers had faster 10- and 30-m sprint times, achieved a greater total distance sprinting (distance at >6.67 m·s-1), and a greater peak 1-minute sprint distance.
Conclusions:
MFT varies considerably between athletes both within and between different team sports. The results from some studies suggest that variation in MFT is associated with high-intensity running performance in a football match, as well as 10- and 30-m sprint times. Further experimental studies should focus on how determination of the MFT of team-sport athletes could be utilized to influence talent identification, team selection, and the individualization of training.
... Using these criteria, skeletal muscle fibers can be divided into three main types: fasttwitch glycolytic fibers, slow-twitch oxidative fibers, and fast-twitch oxidative fibers. Fasttwitch glycolytic fibers have a lower mitochondrial content, rapid contraction kinetics, less dependence on oxidative phosphorylation (OXPHOS), and low fatigue resistance [15,16]. In the fast fibers, the hydrolysis of ATP occurs approximately twice as fast as in the slow fibers, which explains the faster kinetics of contraction. ...
Skeletal muscle is the most abundant tissue in the body and requires high levels of energy to function properly. Skeletal muscle allows voluntary movement and body posture, which require different types of fiber, innervation, energy, and metabolism. Here, we summarize the contribution received at the time of publication of this Introductory Issue for the Special Issue dedicated to “Skeletal Muscle Atrophy: Mechanisms at a Cellular Level”. The Special Issue is divided into three sections. The first is dedicated to skeletal muscle pathophysiology, the second to disease mechanisms, and the third to therapeutic development.
... In obese individuals with diabetes, the activity of slow muscles is reduced compared to that of fast muscles, similar to the effect of a shift in fiber type from type I and 2A fibers to type 2X fibers. [48,49]. Similarly, our current data showed that atrophy in the GA muscle of db/db mice increased with a fiber-type shift from type 1 to type 2B. ...
Type 2 diabetes reduces muscle mass and function. Chronic inflammation and mitochondrial dysfunction play critical roles in muscle atrophy pathogenesis. Here, we investigated the effects of bavachin and corylifol A from Psoralea corylifolia L. seeds on muscle atrophy in dexamethasone-treated mice and in db/db mice. Bavachin and corylifol A enhanced muscle strength and muscle mass in dexamethasone-treated mice. In diabetic mice, they enhanced muscle strength and cross-sectional areas. Bavachin and corylifol A suppressed inflammatory cytokine (interleukin-6 and tumor necrosis factor-α) expression levels by downregulating nuclear factor-κB phosphorylation. They decreased the muscle atrophic factor (myostatin, atrogin-1, and muscle RING finger-1) expression levels. They activated the AKT synthetic signaling pathway and induced a switch from fast-type glycolytic fibers (type 2B) to slow-type oxidative fibers (types I and 2A). They increased mitochondrial biogenesis and dynamic factor (optic atrophy-1, mitofusin-1/2, fission, mitochondrial 1, and dynamin 1-like) expression levels via the AMP-activated protein kinase–peroxisome proliferator-activated receptor gamma coactivator 1-alpha signaling pathway. They also improved mitochondrial quality by upregulating the mitophagy factor (p62, parkin, PTEN-induced kinase-1, and BCL2-interacting protein-3) expression levels. Therefore, bavachin and corylifol A exert potential therapeutic effects on muscle atrophy by suppressing inflammation and improving mitochondrial function.
... Furthermore, studies examining arm-cycling RSE BFR until exhaustion either report no significant reductions in performance (59,60) or a shorter exercise time during RSE in systemic hypoxia (46%) and RSE BFR (26%) compared with unrestricted RSE (43). The lesser performance decrements during armcycling compared with leg-cycling RSE BFR are likely explained by faster muscle reoxygenation rates increasing phosphocreatine resynthesis (22,59) and greater size and proportion of type 2a muscle fibers and myosin heavy chain-2 fibers in arms, respectively (41). Although adding BFR to RSE seems detrimental to acute performance, this is expected of any training approach attempting to stress a physiological capability. ...
... In contrast to endurance running, sprint kayaking imposes high demands on the upper-body endurance capacity of the athlete, as the athlete propels the boatbody-system against water resistance involving his/her relatively small upper-body muscles [10]. Differences in muscle mass, muscle fibre spectrum, oxygen extraction [11] as well as glucose and lipid oxidative capacity [11][12][13] between upper and lower body require different qualitative and quantitative training stimuli for distinct adaptation. From this perspective, the TID in kayak sprinting when compared to other leg-dominated sports should be different. ...
... In contrast, sprint kayaking imposes high demands on the endurance capacity of the athletes' upper body, as the athlete propels the boat-body-system against water resistance involving relatively small upper-body muscles [10]. Differences in muscle mass, muscle fibre spectrum, oxygen extraction [11] as well as glucose and lipid oxidative capacity [11][12][13] between upper and lower body require different qualitative and quantitative training stimuli for distinct adaptation. Recent studies in elite cross-country skiers investigated upper and lower-body muscles and found upper-body muscles to be less capable to oxidize fat and to rely more on carbohydrate oxidation than lower-body muscles [11,12]. ...
... Differences in muscle mass, muscle fibre spectrum, oxygen extraction [11] as well as glucose and lipid oxidative capacity [11][12][13] between upper and lower body require different qualitative and quantitative training stimuli for distinct adaptation. Recent studies in elite cross-country skiers investigated upper and lower-body muscles and found upper-body muscles to be less capable to oxidize fat and to rely more on carbohydrate oxidation than lower-body muscles [11,12]. Thus, it may seem plausible to assume that kayakers may not be able to perform as much volume in the higher intensity zones (Z2, Z3), as arm-glucose storages depleted earlier and therefore kayakers (have to) implement more time in Z1 compared to whole-body and/or lower-body sports. ...
Background
Research results on the training intensity distribution (TID) in endurance athletes are equivocal. This non-uniformity appears to be partially founded in the different quantification methods that are implemented. So far, TID research has solely focused on sports involving the lower-body muscles as prime movers (e.g. running). Sprint kayaking imposes high demands on the upper-body endurance capacity of the athlete. As there are structural and physiological differences between upper- and lower-body musculature, TID in kayaking should be different to lower-body dominant sports. Therefore, we aimed to compare the training intensity distribution during an 8-wk macrocycle in a group of highly trained sprint kayakers employing three different methods of training intensity quantification.
Methods
Heart rate (HR) and velocity during on-water training of nine highly trained German sprint kayakers were recorded during the final 8 weeks of a competition period leading to the national championships. The fractional analysis of TID was based on three zones (Z) derived from either HR (TIDBla-HR) or velocity (TIDBla-V) based on blood lactate (Bla) concentrations (Z1 ≤ 2.5 mmol L⁻¹ Bla, Z2 = 2.5–4.0 mmol L⁻¹ Bla, Z3 ≥ 4.0 mmol L⁻¹ Bla) of an incremental test or the 1000-m race pace (TIDRace): Z1 ≤ 85% of race pace, Z2 = 86–95% and Z3 ≥ 95%.
Results
TIDBla-V (Z1: 68%, Z2: 14%, Z3: 18%) differed from TIDBla-HR (Z1: 91%, Z2: 6%, Z3: 3%) in each zone (all p < 0.01). TIDRace (Z1: 73%, Z2: 20%, Z3: 7%) differed to Z3 in TIDBla-V (p < 0.01) and all three TIDBla-HR zones (all p < 0.01). Individual analysis revealed ranges of Z1, Z2, Z3 fractions for TIDBla-HR of 85–98%, 2–11% and 0.1–6%. For TIDBla-V, the individual ranges were 41–82% (Z1), 6–30% (Z2) and 8–30% (Z3) and for TIDRace 64–81% (Z1), 14–29% (Z2) and 4–10% (Z3).
Conclusion
The results show that the method of training intensity quantification substantially affects the fraction of TID in well-trained sprint kayakers. TIDRace determination shows low interindividual variation compared to the physiologically based TIDBla-HR and TIDBla-V. Depending on the aim of the analysis TIDRace, TIDBla-HR and TIDBla-V have advantages as well as drawbacks and may be implemented in conjunction to maximize adaptation.
... For example biceps brachii have been reported to contain a higher proportion of type 2 fibres [37], while the knee extensors are known to have higher proportion of type 1 fibres [38]. Broadly speaking, upper body appendicular skeletal muscle has a higher proportion of type 2 fibres with a higher proportion of type 1 fibres found in human lower body appendicular muscle [36,39]. A recent study by Srikuea et al. reported higher levels of the VDR in predominantly type 2 muscles (plantaris) compared to predominantly type 1 muscles (soleus) in a mouse model [40]. ...
... Additionally, there are a number of metabolic differences between these upper and lower body muscle groups, particularly related to fat utilization. Specifically, compared to legs, arm muscles have been reported to display lower fat oxidation capacity [51], lower 3-hydroxy-acyl-CoAdehydrogenase (HAD) activity (necessary for fatty acid oxidation) [39], lower intramyocellular lipid (IMCL) content [52], and higher exercise-induced lactate release [53]. While these factors are not directly related to fat-free mass, they highlight some considerable differences in upper and lower body skeletal muscle metabolism, which could have implications for the effects of vitamin D status on muscle size in the upper and lower extremities. ...
Vitamin D insufficiency is a global health concern and low vitamin D status is regularly associated with reduced muscle mass and sarcopenia in observational research. Recent research using Mendelian randomization (MR) has highlighted the potentially causal positive effect of serum vitamin D (25(OH)D) on total, trunk and upper body appendicular fat-free mass (FFM). However, no such effect was found in lower body FFM, a result that mirrors the outcomes of some vitamin D intervention studies. Here we review the current literature on vitamin D, muscle mass and strength and discuss some potential mechanisms for the differing effects of vitamin D on upper and lower body FFM. In particular, differences in distribution of the vitamin D receptor as well as androgen receptors, in the upper and lower body musculature, will be discussed.
