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LETTERS TO THE EDITOR
ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY
Copenhagen Muscle Research Centre, 1Institute of Exercise and Sport Sciences, Department of Human Physiology and 2Department of Molecular Biology, University of Copenhagen, Copenhagen, Denmark
REPLY: We thank Bishop and Schneiker (1) for their interest in our work and for raising some relevant questions.
The first issue is why the distance covered during training was different between the speed endurance training (SET) and sprint training (ST) groups. In preexperiments, it was observed that the group of untrained subjects in the present study (2) was not able to extend the number of sprints without having a significant decrease in the speed. Therefore, the total distance covered was less than for the SET group. Nevertheless, the training for the ST group was sufficient to stimulate an increase in a number of muscle transport proteins but not Na+/H+ exchanger isoform 1 (NHE1). It cannot be excluded that extending the number of sprints would have led to significant changes in NHE1, but it appears not likely. Thus, the observations that only the SET group increased their amount of NHE1 protein, as well as the rate of decrease in muscle pH in recovery from exercise, support the hypothesis that muscle H+ accumulation stimulates the synthesis of NHE1.
Bishop and Schneiker (1) are asking for a clarification of the data from the repeated sprint test. As written in our article (2) the peak 30-m sprint performance before the training period was the same in the ST and SET groups (4.66 ± 0.10 and 4.74 ± 0.11 s, respectively), and the same was the case for the fatigue index (5.0 ± 0.8 and 4.6 ± 1.0%, respectively). After the training period, the ST and SET groups had a 4.0% (not 5.8% as stated by Bishop and Schneiker) and 0.7% (P value not significant) improvement in peak 30-m sprint performance, respectively, and the fatigue index was improved by 12.6 ± 13.2% (P value not significant) in ST and by 53.8 ± 9.9% (P < 0.05) in SET. We agree that one always has to be careful when interpreting changes in the fatigue index, as it is depends on two variables that may both change. We did not find any relationship between the speed during the first sprint and the fatigue index for the subjects in the present study (2). Taken together with the information that the fatigue index was the same before the training period, it does not seem to explain that the SET group had a significant decrease in the fatigue index and the ST group had no significant change. These findings together with the observation that the SET group had a 29% improvement (larger than the 10% increase for the ST group) in the Yo-Yo IR2 test, which consists of high-intensity intermittent exercise, seems to validate the suggestion that the speed endurance training is useful in sports where the ability to carry out high-intensity intermittent exercise is essential for high-level performance.
Bishop and Schneiker (1) asked for clarification of a couple of points in our article. In the recovery period between sprints in the repeated sprint test and in the training, the subjects jogged back to the starting line. Furthermore, there was one dropout (for personal reasons) in the ST group and none in the SET group.
FOOTNOTES
Address for reprint requests and other correspondence: J. Bangsbo, Copenhagen Muscle Research Centre, Institute of Exercise and Sport Sciences, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark (e-mail: jbangsbo{at}aki.ku.dk)
REFERENCES
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