title: Sprint-interval training-induced alterations of Myosin heavy chain isoforms and enzyme activities in rat diaphragm: effect of normobaric hypoxia.
abstract: The purpose of this study was twofold: (i) to investigate if sprint-interval training (SIT) alters myosin heavy chain (MyHC) isoform composition and bioenergetic properties within the rat diaphragm, and (ii) to determine if mild normobaric hypoxia would enhance the effects of SIT-induced diaphragmatic adaptation. Male Wistar rats (8 weeks old) were randomly assigned to one of four groups (n = 7/group): (i) normoxic control (NC); (ii) normoxic training (NT); (iii) hypoxic control (HC); or (iv) hypoxic training (HT). The NT and HT groups were engaged in SIT (1 min sprint and 2-5 min rest, 6-10 sets/day, 5-6 days/week) on a treadmill for 9 weeks. Animals in the HC and HT groups were exposed to normobaric hypoxia (14.5% O(2)) during an SIT program from the 4th week of the training period. After completion of the training program, MyHC composition, citrate synthase (CS) activity, and lactate dehydrogenase (LDH) activity in the diaphragm and plantaris muscle were analyzed. An analysis of diaphragmatic MyHC composition demonstrated increased type IIa and decreased type IId/x for both training groups (P < 0.05), with the HT group producing greater changes than the NT group (P < 0.05). The plantaris muscle, however, showed increased Type IIa and IId/x and decreased Type IIb for both the NT and HT groups (P < 0.05). CS activity increased only for the training groups (P < 0.05), and this change was greater for the HT group in the diaphragm and for the NT group in the plantaris muscle (P < 0.05). Further, diaphragmatic LDH activity in HT was significantly lower (P < 0.05) than in HC and NT. These findings demonstrated that SIT could induce alterations in MyHC composition from fast to slow within type II isoforms and also improve the oxidative capacity in the diaphragm and plantaris muscles. It is of importance that our data revealed that SIT-induced diaphragmatic adaptations were enhanced when SIT was performed in normobaric hypoxia.
authors.affiliation: Department of Exercise Physiology, School of Health and Sports Science, Juntendo University, Chiba, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ogura
authors.forename: Hisashi
authors.initials: H
authors.lastname: Naito
authors.forename: Junichiro
authors.initials: J
authors.lastname: Aoki
authors.forename: Jin
authors.initials: J
authors.lastname: Uchimaru
authors.forename: Takao
authors.initials: T
authors.lastname: Sugiura
authors.forename: Shizuo
authors.initials: S
authors.lastname: Katamoto
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D001835:Body Weight / Q000502:physiology; D002950:Citrate (si)-Synthase / Q000032:analysis; D003964:Diaphragm / Q000737:chemistry / Q000201:enzymology*; D004591:Electrophoresis, Polyacrylamide Gel; D004734:Energy Metabolism; D000860:Hypoxia / Q000503:physiopathology*; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D007773:Lactates / Q000097:blood; D008124:Locomotion / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000737:chemistry / Q000201:enzymology; D018995:Myosin Heavy Chains / Q000032:analysis / Q000737:chemistry*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D020033:Protein Isoforms / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D012132:Respiratory Muscles / Q000737:chemistry / Q000201:enzymology
chemical_list: D007773:Lactates; D020033:Protein Isoforms; D007770:L-Lactate Dehydrogenase; D002950:Citrate (si)-Synthase; D018995:Myosin Heavy Chains