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  • 1
    Digitale Medien
    Digitale Medien
    Oxygen uptake kinetics in trained athletes differing in $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ (1985)
    Springer
    European journal of applied physiology 54 (1985), S. 306-308 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Oxygen uptake kinetics ; $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ ; Exercise metabolism ; Trained athletes ; Gas exchange
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Previous work has shown that when $$\dot V_{{\text{O}}_{\text{2}} }$$ kinetics are compared for endurance trained athletes and untrained subjects, the highly trained athletes have a faster response time. However, it remains to be determined whether the more rapid adjustment of $$\dot V_{{\text{O}}_{\text{2}} }$$ toward steady state in athletes is due to $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ differences or training adaptation alone. One approach to this problem is to study the time course of $$\dot V_{{\text{O}}_{\text{2}} }$$ kinetics at the onset of work in athletes who differ in $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ but have similar training habits. Therefore, the purpose of these experiments was to compare the time course of $$\dot V_{{\text{O}}_{\text{2}} }$$ kinetics at the onset of exercise in athletes with similar training routines but who differ in $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ . Ten subjects ( $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ range 50–70 ml · kg−1 · min−1) performed 6-minutes of cycle ergometer exercise at ∼50% $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ . Ventilation and gas exchange were monitored by open circuit techniques. The data were modeled with a single component exponential function incorporating a time delay, (T D ); $$\Delta \dot V_{{\text{O}}_{{\text{2}}f} } = \Delta \dot V_{{\text{O}}_{2ss} } {\text{ (1}} - e^{ - t - T_D /_{\tau )} }$$ , where Τ is the time constant $$\Delta \dot V_{{\text{O}}_{{\text{2}}f} }$$ is the increase in $$\dot V_{{\text{O}}_{\text{2}} }$$ at time t and $$\Delta \dot V_{{\text{O}}_{{\text{2ss}}} }$$ is the steady-rate increment above resting $$\dot V_{{\text{O}}_{\text{2}} }$$ . Kinetic analysis revealed a range of $$\dot V_{{\text{O}}_{\text{2}} }$$ half times from 21.6 to 36.0 s across subjects with a correlation coefficient of r=−0.80 (p〈0.05) between $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ and $$\dot V_{{\text{O}}_{\text{2}} }$$ half time. These data suggest that in highly trained indicivuals with similar training habits, those with a higher $$\dot V_{{\text{O}}_{{\text{2max}}} }$$ achieve a more rapid $$\dot V_{{\text{O}}_{\text{2}} }$$ adjustment at the onset of work.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00426150
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  • 2
    Digitale Medien
    Digitale Medien
    Precision of ventilatory and gas exchange alterations as a predictor of the anaerobic threshold (1984)
    Springer
    European journal of applied physiology 52 (1984), S. 173-177 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Anaerobic threshold ; Ventilatory threshold ; Exercise ventilation ; Gas exchange ; Blood lactate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Anaerobic threshold has been defined as the oxygen uptake ( $$\dot V_{{\text{O}}_{\text{2}} }$$ ) at which blood lactate (La) begins to rise systematically during graded exercise (Davis et al. 1982). It has become common practice in the literature to estimate the anaerobic threshold by using ventilatory and/or gas exchange alterations. However, confusion exists as to the validity of this practice. The purpose of this study was to examine the precision with which ventilatory and gas exchange techniques for determining anaerobic threshold predicted the anaerobic threshold resolved by La criteria. The anaerobic threshold was chosen using three criteria: (1) systematic increase in blood La (ATLa), (2) systematic increase in ventilatory equivalent for O2 with no change in the ventilatory equivalent for CO2 ( $${\text{AT}}_{\dot V_{\text{E}} } /\dot V_{{\text{O}}_{\text{2}} }$$ ), and (3) non-linear increase in expired ventilation graphed as a function of $$\dot V_{{\text{O}}_{\text{2}} }$$ ( $${\text{AT}}_{\dot V_{\text{E}} }$$ ). Thirteen trained male subjects performed an incremental cycle ergometer test to exhaustion in which the load was increased by 30 W every 3 minutes. Ventilation, gas exchange measures, and blood samples for La analysis were obtained every 3rd min throughout the test. In five of the thirteen subjects tested the anaerobic threshold determined by ventilatory and gas exchange alterations did not occur at the same $$\dot V_{{\text{O}}_{\text{2}} }$$ as the ATLa. The highest correlation between a gas exchange anaerobic threshold and ATLa was found for $${\text{AT}}_{\dot V_{\text{E}} } /\dot V_{{\text{O}}_{\text{2}} }$$ and was r=0.63 (P〈0.05). These data provide evidence that the ATLa and $${\text{AT}}_{\dot V_{\text{E}} }$$ do not always occur simultaneously and suggest limitations in using ventilatory or gas exchange measures to estimate the ATla.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00433388
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  • 3
    Digitale Medien
    Digitale Medien
    Clenbuterol-induced fiber type transition in the soleus of adult rats (1996)
    Springer
    European journal of applied physiology 74 (1996), S. 391-396 
    Details
    ISSN: 1439-6327
    Schlagwort(e): β(2)-Adrenoceptor agonist ; Skeletal muscle ; Fiber type ; Myosin heavy chain isoforms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract This study examined the effects of 6 weeks of treatment with theβ (2)-adrenoceptor agonist, clenbuterol, on the soleus muscle of adult female Sprague-Dawley rats. Animals (4 months old) were divided into two groups: clenbuterol treated (CL,n=7) (2 mg kg−1 body mass injected subcutaneously every other day), and control (CON,n=7) (injected with isotonic saline). Post-treatment body weights were ≈ 5% greater in the CL group compared to CON (P〈0.05). Polyacrylamide gel electrophoresis (SDS-PAGE) of soleus myofibrillar protein indicated a clenbuterol-induced decrease (P〈0.05) in the relative percentage of type I myosin heavy chain (MHC) with a concomitant increase (P〈0.05) in type IIdx MHC, while the proportion of type IIa MHC was unaffected. ATPase fiber typing revealed increases (P〈0.05) in the proportion of type II fibers expressed both as a percentage of total fiber number and total cross-sectional area (CSA). Finally, mean type II fiber CSA was ≈25% greater (P〈0.05) in the CL groups as compared to the CON group. These data indicate that clenbuterol treatment results in alterations in the MHC phenotype and an increased proportion of type II fiber CSA in the soleus of adult rats. These observations were due to an increase in the total number of type II fibers, as well as hypertrophy of these fibers. Thus, the relative increase in the number of histochemically determined type II fibers and the emergence of the normally unexpressed type IIdx MHC isoform in the soleus suggest a clenbuterol-induced transition of muscle fiber phenotype as well as selective hypertrophy of the type 11 fibers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02337718
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  • 4
    Digitale Medien
    Digitale Medien
    Clenbuterol-induced fiber type transition in the soleus of adult rats (1996)
    Springer
    European journal of applied physiology 74 (1996), S. 391-396 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Key words β(2)-Adrenoceptor agonist ; Skeletal muscle ; Fiber type ; Myosin heavy chain isoforms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  This study examined the effects of 6 weeks of treatment with the β(2)-adrenoceptor agonist, clenbuterol, on the soleus muscle of adult female Sprague-Dawley rats. Animals (4 months old) were divided into two groups: clenbuterol treated (CL, n=7) (2 mg·kg–1 body mass injected subcutaneously every other day), and control (CON, n=7) (injected with isotonic saline). Post-treatment body weights were ≈5% greater in the CL group compared to CON (P〈0.05). Polyacrylamide gel electrophoresis (SDS-PAGE) of soleus myofibrillar protein indicated a clenbuterol-induced decrease (P〈0.05) in the relative percentage of type I myosin heavy chain (MHC) with a concomitant increase (P〈0.05) in type IIdx MHC, while the proportion of type IIa MHC was unaffected. ATPase fiber typing revealed increases (P〈0.05) in the proportion of type II fibers expressed both as a percentage of total fiber number and total cross-sectional area (CSA). Finally, mean type II fiber CSA was ≈25% greater (P〈0.05) in the CL groups as compared to the CON group. These data indicate that clenbuterol treatment results in alterations in the MHC phenotype and an increased proportion of type II fiber CSA in the soleus of adult rats. These observations were due to an increase in the total number of type II fibers, as well as hypertrophy of these fibers. Thus, the relative increase in the number of histochemically determined type II fibers and the emergence of the normally unexpressed type IIdx MHC isoform in the soleus suggest a clenbuterol-induced transition of muscle fiber phenotype as well as selective hypertrophy of the type II fibers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004210050091
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  • 5
    Digitale Medien
    Digitale Medien
    Short-term exercise training improves diaphragm antioxidant capacity and endurance (2000)
    Springer
    European journal of applied physiology 81 (2000), S. 67-74 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Key words Diaphragm ; Oxidative stress ; Fatigue ; Lipid peroxidation ; Antioxidants
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract These experiments tested the hypothesis that short-term endurance exercise training would rapidly improve (within 5 days) the diaphragm oxidative/antioxidant capacity and protect the diaphragm against contraction-induced oxidative stress. To test this postulate, male Sprague-Dawley rats (6 weeks old) ran on a motorized treadmill for 5 consecutive days (40–60 min · day−1) at approximately 65% maximal oxygen uptake. Costal diaphragm strips were excised from both sedentary control (CON, n=14) and trained (TR, n=13) animals 24 h after the last exercise session, for measurement of in vitro contraction properties and selected biochemical parameters of oxidative/antioxidant capacity. Training did not alter diaphragm force-frequency characteristics over a full range of submaximal and maximal stimulation frequencies (P 〉 0.05). In contrast, training improved diaphragm resistance to fatigue as contraction forces were better-maintained by the diaphragms of the TR animals during a submaximal 60-min fatigue protocol (P 〈 0.05). Following the fatigue protocol, diaphragm strips from the TR animals contained 30% lower concentrations of lipid hydroperoxides compared to CON (P 〈 0.05). Biochemical analysis revealed that exercise training increased diaphragm oxidative and antioxidant capacity (citrate synthase activity +18%, catalase activity +24%, total superoxide dismutase activity +20%, glutathione concentration +10%) (P 〈 0.05). These data indicate that short-term exercise training can rapidly elevate oxidative capacity as well as enzymatic and non-enzymatic antioxidant defenses in the diaphragm. Furthermore, this up-regulation in antioxidant defenses would be accompanied by a reduction in contraction-induced lipid peroxidation and an increased fatigue resistance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00013799
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