Physiological and biochemical adaptations to training in Rana pipiens

Fifteen Rana pipiens were trained on a treadmill thrice weekly for 6.5 weeks to assess the effects of training on an animal that supports activity primarily through anaerobiosis. Endurance for activity increased 35% in these frogs as a result of training ( P =0.006, Fig. 1). This increased performance was not due to enhanced anaerobiosis. Total lactate produced during exercise did not differ significantly for the trained or untrained animals in either gastrocnemius muscle (2.77±0.21 and 2.82±0.13 mg/g, respectively) or whole body (1.32±0.10 and 1.47±0.06 mg/g, respectively). Glycogen depletion also did not differ between the two groups (Fig. 2c). The primary response to training appeared to involve augmentation of aerobic metabolism, a response similar to that reported for mammals. Gastrocnemius muscles of trained frogs underwent a 38% increase over those of untrained individuals in the maximum activity of citrate synthase (14.5±1.0 and 10.5±0.9 μmoles/(g wet wt·min); P =0.008). This enzyme was also positively correlated with the level of maximum performance for all animals tested ( r =0.61, P <0.01) and with the degree of improvement in the trained animals ( r =0.72, P <0.05). In addition to an increased aerobic capacity, the trained animals demonstrated a greater removal of lactate from the muscle 15 min after fatigue (Fig. 2b).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47124/1/360_2004_Article_BF00710002.pd

Mitochondrial efficiency in rat skeletal muscle: influence of respiration rate, substrate and muscle type.

Aim: To investigate the hypothesis that mitochondrial efficiency (i.e. P/O ratio) is higher in type I than in type II fibres during submaximal rates of respiration. Methods: Mitochondria were isolated from rat soleus and extensor digitorum longus (EDL) muscles, representing type I and type II fibres, respectively. Mitochondrial efficiency (P/O ratio) was determined with pyruvate (Pyr) or palmitoyl-L-carnitine (PC) during submaximal (constant rate of ADP infusion) and maximal (Vmax, state 3) rates of respiration and fitted to monoexponential functions. Results: There was no difference in Vmax between PC and Pyr in soleus but in EDL Vmax with PC was only 58% of that with Pyr. The activity of 3-hydroxyacyl-CoA dehydrogenase (HAD) was 3-fold higher in soleus than in EDL. P/O ratio at Vmax was 8-9% lower with PC (2.33±0.02 (soleus) and 2.30±0.02 (EDL)) than with Pyr (2.52±0.03 (soleus) and 2.54±0.03 (EDL)) but not different between the two muscles (P&gt;0.05). P/O ratio was low at low rates of respiration and increased exponentially when the rate of respiration increased. The asymptotes of the curves were similar to P/O ratio at Vmax. P/O ratio at submaximal respirations was not different between soleus and EDL neither with Pyr nor with PC. Conclusion: Mitochondrial efficiency, as determined in vitro, was not significantly different in the two fibre types neither at Vmax nor at submaximal rates of respiration. The low Vmax for PC oxidation in EDL may relate to low activity of β-oxidation.The definitive version is available at www.blackwell-synergy.co