Muscular adaptation which occurs following eccentric exercise-induced muscle damage has been associated with changes in the mechanical properties of muscle manifested as a shift in the length-tension relationship towards longer muscle lengths. However, it is not clear whether this shift is a long term adaptation to eccentric exercise. The purpose of this study was to investigate functional adaptations to skeletal muscle damage in humans, tracking such responses several days into muscle recovery. Ten healthy young men performed an eccentric exercise protocol involving the quadriceps muscle and functional measurements were performed before and on days 1, 2, 5, 8, 12 and 16 post-exercise. Blood samples were also withdrawn before and at 6 h, and 2 days, 5 days and 16 days post-exercise. The exercise protocol resulted in muscle damage, indicated by changes in clinical markers including increased serum creatine kinase activity and muscle soreness compared to pre-exercise levels (p<0.05-0.001). An acute, but not sustained shift in the quadriceps isokinetic and isometric angle-torque curves towards longer muscle lengths was observed post-exercise (p<0.05). It was speculated that the functional adaptations following eccentric exercise might be affected by the short resting and functional length of the quadriceps muscle, relative to its optimum. More studies are needed to confirm the hypothesis that a sustained shift in the muscle's length-tension relationship, as an adaptation after lengthening contraction-induced damage, is muscle specific.

Different insulin-like growth factor-1 (IGF-1) isoforms, namely IGF-1Ea, IGF-1Eb and IGF-1Ec (MGF), have been proposed to have various functions in muscle repair and growth. To gain insight into the potentially differential actions of IGF-1 isoforms in the regulation of muscle regeneration, we assessed the time course of their expressions at both mRNA and protein levels after exercise-induced muscle damage in humans. In addition, we characterized mature IGF-1 and synthetic MGF E peptide signalling in C2C12 myoblast-like cells in vitro. Ten healthy male volunteers were subjected to exercise-induced muscle damage and biopsy samples were taken from the exercised muscles before and 6 h, 2, 5 and 16 days post exercise. Muscle damage was documented by specific functional and biochemical responses post exercise. PCR-based analyses of muscle biopsy samples revealed a rapid and transient up-regulation of MGF mRNA expression which was followed by a prolonged increase of IGF-1Ea and IGF-1Eb mRNA expression (p<0.05). Patterns similar to those for mRNA expression were detected for MGF and IGF-1Ea expression at the protein level. The action of synthetic MGF E peptide differed from that of mature IGF-1 since its proliferative effect on C2C12 myoblast-like cells was not blocked by an anti-IGF-1 receptor neutralizing antibody and it did not phosphorylate Akt. Therefore, we conclude that the differential expression profile of IGF-1 isoforms in vivo and the possible IGF-1R - independent MGF E peptide signalling in skeletal muscle-like cells in vitro support the notion that tissue-specific mRNA expression of MGF isoform produces mature IGF-1 and MGF E peptides which possibly act as distinct mitogens in skeletal muscle regeneration.

Background: Muscle adaptation which occurs following eccentric exercise-induced muscle damage has been associated with an acute inflammatory response. The purpose of this study was to investigate serum interleukin-6 (IL-6), osteoprotegerin and receptor activator of nuclear factor kB ligand (OPG/RANKL) concentrations following muscle damage. We measured changes for several days following muscle damage. Methods: Ten healthy young males performed an eccentric exercise protocol using their quadriceps. Blood samples were withdrawn before and at 6 h, 2 days, 5 days and 16 days post-exercise. Functional and clinical measurements were performed before, and on days 1, 2, 5, 8, 12 and 16 post-exercise. Results: The exercise protocol resulted in muscle damage, indicated by changes in biochemical markers. An increase in IL-6 and OPG, and a decrease in RANKL concentrations were seen at 6 h and on day 2 post-exercise; the OPG:RANKL ratio was increased at 6 h post-exercise (p<0.05). Conclusions: Changes in IL-6 and OPG/RANKL system may represent systemic responses in muscle inflammation and repair processes. However, further studies are needed to elucidate a potential systemic and/or local role of the OPG/RANKL system in skeletal muscle repair. © 2009 by Walter de Gruyter.

PURPOSE: There is evidence to suggest that muscle damage caused by resistance exercise (RE) may increase postprandial lipemia (PPL). This study examined PPL for two consecutive days after a protocol of low-volume eccentric RE that caused muscle damage. METHODS: Nine healthy, untrained male volunteers aged 27.2 ± 1.1 yr performed a session of eccentric RE consisting of eight sets of inclined leg presses at six repetition maximum with 3-min rest intervals. A high-fat meal (1.2 g fat, 1.2 g carbohydrate, 0.22 g protein, and 68.6 kJ•kg -1 body mass) was administered 16 h (day 1) and 40 h (day 2) after exercise as well as after an overnight fast with no prior exercise (control condition [C]). Venous blood samples were obtained before and hourly for 6 h after each meal. RESULTS: The duration of the exercise session (including rest intervals) was 25.6 ± 0.2 min, whereas net exercise time was 4.6 ± 0.2 min. Total energy expenditure was 0.64 ± 0.04 MJ. Serum creatine kinase and ratings of perceived muscle soreness were significantly elevated on day 1 and peaked on day 2. Triacylglycerol total area under the curve was 12.1% lower on day 1 compared with C (7.51 ± 0.99 vs. 8.54 ± 1.07 mmol•L -1•6 h -1, P < 0.02), whereas no difference existed between C and day 2. Serum insulin incremental area under the curve was significantly elevated on day 2 compared with C, indicating transient insulin resistance. CONCLUSION: These results show that low-volume eccentric RE is effective in reducing postprandial triacylglycerol concentration despite the low energy expenditure. Muscle damage does not have a detrimental effect on PPL. © 2009 by the American College of Sports Medicine.

Muscular adaptation which occurs following eccentric exercise-induced muscle damage has been associated with changes in the mechanical properties of muscle manifested as a shift in the length-tension relationship towards longer muscle lengths. However, it is not clear whether this shift is a long term adaptation to eccentric exercise. The purpose of this study was to investigate functional adaptations to skeletal muscle damage in humans, tracking such responses several days into muscle recovery. Ten healthy young men performed an eccentric exercise protocol involving the quadriceps muscle and functional measurements were performed before and on days 1, 2, 5, 8, 12 and 16 post-exercise. Blood samples were also withdrawn before and at 6 h, and 2 days, 5 days and 16 days post-exercise. The exercise protocol resulted in muscle damage, indicated by changes in clinical markers including increased serum creatine kinase activity and muscle soreness compared to pre-exercise levels (p<0.05-0.001). An acute, but not sustained shift in the quadriceps isokinetic and isometric angle-torque curves towards longer muscle lengths was observed post-exercise (p<0.05). It was speculated that the functional adaptations following eccentric exercise might be affected by the short resting and functional length of the quadriceps muscle, relative to its optimum. More studies are needed to confirm the hypothesis that a sustained shift in the muscle's length-tension relationship, as an adaptation after lengthening contraction-induced damage, is muscle specific.

Different insulin-like growth factor-1 (IGF-1) isoforms, namely IGF-1Ea, IGF-1Eb and IGF-1Ec (MGF), have been proposed to have various functions in muscle repair and growth. To gain insight into the potentially differential actions of IGF-1 isoforms in the regulation of muscle regeneration, we assessed the time course of their expressions at both mRNA and protein levels after exercise-induced muscle damage in humans. In addition, we characterized mature IGF-1 and synthetic MGF E peptide signalling in C2C12 myoblast-like cells in vitro. Ten healthy male volunteers were subjected to exercise-induced muscle damage and biopsy samples were taken from the exercised muscles before and 6 h, 2, 5 and 16 days post exercise. Muscle damage was documented by specific functional and biochemical responses post exercise. PCR-based analyses of muscle biopsy samples revealed a rapid and transient up-regulation of MGF mRNA expression which was followed by a prolonged increase of IGF-1Ea and IGF-1Eb mRNA expression (p<0.05). Patterns similar to those for mRNA expression were detected for MGF and IGF-1Ea expression at the protein level. The action of synthetic MGF E peptide differed from that of mature IGF-1 since its proliferative effect on C2C12 myoblast-like cells was not blocked by an anti-IGF-1 receptor neutralizing antibody and it did not phosphorylate Akt. Therefore, we conclude that the differential expression profile of IGF-1 isoforms in vivo and the possible IGF-1R - independent MGF E peptide signalling in skeletal muscle-like cells in vitro support the notion that tissue-specific mRNA expression of MGF isoform produces mature IGF-1 and MGF E peptides which possibly act as distinct mitogens in skeletal muscle regeneration.

Background: Muscle adaptation which occurs following eccentric exercise-induced muscle damage has been associated with an acute inflammatory response. The purpose of this study was to investigate serum interleukin-6 (IL-6), osteoprotegerin and receptor activator of nuclear factor kB ligand (OPG/RANKL) concentrations following muscle damage. We measured changes for several days following muscle damage. Methods: Ten healthy young males performed an eccentric exercise protocol using their quadriceps. Blood samples were withdrawn before and at 6 h, 2 days, 5 days and 16 days post-exercise. Functional and clinical measurements were performed before, and on days 1, 2, 5, 8, 12 and 16 post-exercise. Results: The exercise protocol resulted in muscle damage, indicated by changes in biochemical markers. An increase in IL-6 and OPG, and a decrease in RANKL concentrations were seen at 6 h and on day 2 post-exercise; the OPG:RANKL ratio was increased at 6 h post-exercise (p<0.05). Conclusions: Changes in IL-6 and OPG/RANKL system may represent systemic responses in muscle inflammation and repair processes. However, further studies are needed to elucidate a potential systemic and/or local role of the OPG/RANKL system in skeletal muscle repair. © 2009 by Walter de Gruyter.

PURPOSE: There is evidence to suggest that muscle damage caused by resistance exercise (RE) may increase postprandial lipemia (PPL). This study examined PPL for two consecutive days after a protocol of low-volume eccentric RE that caused muscle damage. METHODS: Nine healthy, untrained male volunteers aged 27.2 ± 1.1 yr performed a session of eccentric RE consisting of eight sets of inclined leg presses at six repetition maximum with 3-min rest intervals. A high-fat meal (1.2 g fat, 1.2 g carbohydrate, 0.22 g protein, and 68.6 kJ•kg -1 body mass) was administered 16 h (day 1) and 40 h (day 2) after exercise as well as after an overnight fast with no prior exercise (control condition [C]). Venous blood samples were obtained before and hourly for 6 h after each meal. RESULTS: The duration of the exercise session (including rest intervals) was 25.6 ± 0.2 min, whereas net exercise time was 4.6 ± 0.2 min. Total energy expenditure was 0.64 ± 0.04 MJ. Serum creatine kinase and ratings of perceived muscle soreness were significantly elevated on day 1 and peaked on day 2. Triacylglycerol total area under the curve was 12.1% lower on day 1 compared with C (7.51 ± 0.99 vs. 8.54 ± 1.07 mmol•L -1•6 h -1, P < 0.02), whereas no difference existed between C and day 2. Serum insulin incremental area under the curve was significantly elevated on day 2 compared with C, indicating transient insulin resistance. CONCLUSION: These results show that low-volume eccentric RE is effective in reducing postprandial triacylglycerol concentration despite the low energy expenditure. Muscle damage does not have a detrimental effect on PPL. © 2009 by the American College of Sports Medicine.

Muscular adaptation which occurs following eccentric exercise-induced muscle damage has been associated with changes in the mechanical properties of muscle manifested as a shift in the length-tension relationship towards longer muscle lengths. However, it is not clear whether this shift is a long term adaptation to eccentric exercise. The purpose of this study was to investigate functional adaptations to skeletal muscle damage in humans, tracking such responses several days into muscle recovery. Ten healthy young men performed an eccentric exercise protocol involving the quadriceps muscle and functional measurements were performed before and on days 1, 2, 5, 8, 12 and 16 post-exercise. Blood samples were also withdrawn before and at 6 h, and 2 days, 5 days and 16 days post-exercise. The exercise protocol resulted in muscle damage, indicated by changes in clinical markers including increased serum creatine kinase activity and muscle soreness compared to pre-exercise levels (p<0.05-0.001). An acute, but not sustained shift in the quadriceps isokinetic and isometric angle-torque curves towards longer muscle lengths was observed post-exercise (p<0.05). It was speculated that the functional adaptations following eccentric exercise might be affected by the short resting and functional length of the quadriceps muscle, relative to its optimum. More studies are needed to confirm the hypothesis that a sustained shift in the muscle's length-tension relationship, as an adaptation after lengthening contraction-induced damage, is muscle specific.

Different insulin-like growth factor-1 (IGF-1) isoforms, namely IGF-1Ea, IGF-1Eb and IGF-1Ec (MGF), have been proposed to have various functions in muscle repair and growth. To gain insight into the potentially differential actions of IGF-1 isoforms in the regulation of muscle regeneration, we assessed the time course of their expressions at both mRNA and protein levels after exercise-induced muscle damage in humans. In addition, we characterized mature IGF-1 and synthetic MGF E peptide signalling in C2C12 myoblast-like cells in vitro. Ten healthy male volunteers were subjected to exercise-induced muscle damage and biopsy samples were taken from the exercised muscles before and 6 h, 2, 5 and 16 days post exercise. Muscle damage was documented by specific functional and biochemical responses post exercise. PCR-based analyses of muscle biopsy samples revealed a rapid and transient up-regulation of MGF mRNA expression which was followed by a prolonged increase of IGF-1Ea and IGF-1Eb mRNA expression (p<0.05). Patterns similar to those for mRNA expression were detected for MGF and IGF-1Ea expression at the protein level. The action of synthetic MGF E peptide differed from that of mature IGF-1 since its proliferative effect on C2C12 myoblast-like cells was not blocked by an anti-IGF-1 receptor neutralizing antibody and it did not phosphorylate Akt. Therefore, we conclude that the differential expression profile of IGF-1 isoforms in vivo and the possible IGF-1R - independent MGF E peptide signalling in skeletal muscle-like cells in vitro support the notion that tissue-specific mRNA expression of MGF isoform produces mature IGF-1 and MGF E peptides which possibly act as distinct mitogens in skeletal muscle regeneration.

Background: Muscle adaptation which occurs following eccentric exercise-induced muscle damage has been associated with an acute inflammatory response. The purpose of this study was to investigate serum interleukin-6 (IL-6), osteoprotegerin and receptor activator of nuclear factor kB ligand (OPG/RANKL) concentrations following muscle damage. We measured changes for several days following muscle damage. Methods: Ten healthy young males performed an eccentric exercise protocol using their quadriceps. Blood samples were withdrawn before and at 6 h, 2 days, 5 days and 16 days post-exercise. Functional and clinical measurements were performed before, and on days 1, 2, 5, 8, 12 and 16 post-exercise. Results: The exercise protocol resulted in muscle damage, indicated by changes in biochemical markers. An increase in IL-6 and OPG, and a decrease in RANKL concentrations were seen at 6 h and on day 2 post-exercise; the OPG:RANKL ratio was increased at 6 h post-exercise (p<0.05). Conclusions: Changes in IL-6 and OPG/RANKL system may represent systemic responses in muscle inflammation and repair processes. However, further studies are needed to elucidate a potential systemic and/or local role of the OPG/RANKL system in skeletal muscle repair. © 2009 by Walter de Gruyter.

PURPOSE: There is evidence to suggest that muscle damage caused by resistance exercise (RE) may increase postprandial lipemia (PPL). This study examined PPL for two consecutive days after a protocol of low-volume eccentric RE that caused muscle damage. METHODS: Nine healthy, untrained male volunteers aged 27.2 ± 1.1 yr performed a session of eccentric RE consisting of eight sets of inclined leg presses at six repetition maximum with 3-min rest intervals. A high-fat meal (1.2 g fat, 1.2 g carbohydrate, 0.22 g protein, and 68.6 kJ•kg -1 body mass) was administered 16 h (day 1) and 40 h (day 2) after exercise as well as after an overnight fast with no prior exercise (control condition [C]). Venous blood samples were obtained before and hourly for 6 h after each meal. RESULTS: The duration of the exercise session (including rest intervals) was 25.6 ± 0.2 min, whereas net exercise time was 4.6 ± 0.2 min. Total energy expenditure was 0.64 ± 0.04 MJ. Serum creatine kinase and ratings of perceived muscle soreness were significantly elevated on day 1 and peaked on day 2. Triacylglycerol total area under the curve was 12.1% lower on day 1 compared with C (7.51 ± 0.99 vs. 8.54 ± 1.07 mmol•L -1•6 h -1, P < 0.02), whereas no difference existed between C and day 2. Serum insulin incremental area under the curve was significantly elevated on day 2 compared with C, indicating transient insulin resistance. CONCLUSION: These results show that low-volume eccentric RE is effective in reducing postprandial triacylglycerol concentration despite the low energy expenditure. Muscle damage does not have a detrimental effect on PPL. © 2009 by the American College of Sports Medicine.