Specificity and reversibility of the training effects on the concentrationof Na+,K+-ATPase in foal skeletal muscle

The purpose of the present study was to determine whether training and detr aining affect the Na+,K+-ATPase concentration in horse skeletal muscles, an d whether these effects are specific for the muscles involved in the traini ng programme. Twenty-four Dutch Warmblood foals age 7 days were assigned ra ndomly to 3 groups: Box (box-rest without training), Training (box-rest wit h training: short-sprint) and Pasture (pasture without training), Exercise regimens were carried out for 5 months and were followed by 6 months of det raining, Fire of the foals in each group were subjected to euthanasia at ag e 5 months and the remaining foals at 11 months, Muscle samples were collec ted from the deep part of the gluteus medius, semitendinosus and masseter m uscles, The Na+,K+-ATPase concentration was quantified by [H-3]ouabain bind ing. In the Training group, the concentration of Na+,K+-ATPase in gluteus medius and semitendinosus muscle, but not in masseter muscle, showed a relative i ncrease of 20% (P <0.05) as compared to Box foals, After detraining for the subsequent 6 months, the concentration of Na+,K+-ATPase in semitendinosus muscle remained the same, while that in gluteus medius muscle was reduced b y 10%. It is concluded that: 1) short-sprint training for 5 months induced an incr ease of the Na+,K+-ATPase concentration in glutens medius and semitendinosu s muscles of the foal, Interestingly, this effect persisted during the 6 mo nths of the detraining period. Whether the higher Na+,K+-ATPase concentrati on due to training of young foals leads to a better athletic performance wh en they become mature still needs to be established; 2) the factors that in itiate an increase in Na+,K+-ATPase concentration following training are li kely to be located in the muscle itself and 3) the training effect may last for several months after returning to normal activity, especially in muscl es containing a high percentage of fast-twitch fibres.