FEV1 can be associated with reduced values after vigorous exercise in healthy adolescents.

Abstract

To the Editor: I read with great interest the study “Vigorous exercise can cause abnormal pulmonary function in healthy adolescents,” recently published by Abosaida and colleagues (1). The study considered more than 50 healthy adolescents who underwent a constant and progressively increasing work rate exercise testing protocol on a cycle ergometer. The study was designed so that participants had at least 2 weeks between the test protocols to allow for complete recovery, but not more than a month, to reduce chances of participants showing a change in respiratory tests’ outcomes unrelated to the experimental design, and in accordance with the American Thoracic Society guidelines (2). The main result of the study was that 10 participants had a decrease in FEV1 after vigorous exercise testing. Of these participants, three showed a decrease only after the constant work rate test, five only following the ramp test, and two after each testing protocol. The article concludes that healthy adolescents demonstrate subtle bronchoconstriction after exercise. I think that the effect of fatigue, and especially central command, could have been overlooked in this study. Also, this study shows association between vigorous exercise and decreased FEV1, not causality, as the title suggests. It is possible that the cause of the observed FEV1 reduction after vigorous exercise is not exercise-induced bronchoconstriction. Table 2 in the article shows that participants with abnormal FEV1 had a (not significant) reduction in exercise capacity in terms of work rate that they could sustain for a given heart rate. No significant difference was detected in any of the other physiological variables measured; this may depend on the complex nature of the cardiac and respiratory parameters measured such as heart rate and ventilation, especially at heart rates of 80–90% peak heart rate. These results could suggest that a greater fatigue may be experienced by participants presented in the abnormal FEV1 group, irrespective of FEV1 itself. For example, it is possible that different baseline fitness levels, not taken into account or not detectable by the exercise testing protocols used, may be associated with the reduced exercise capacity. For example, accumulation of blood lactate could help show whether this may be the case (3). Most important, the FEV1 test requires participants’ collaboration and volitional effort, which could be reduced after vigorous exercise (4), as is briefly mentioned in the discussion of this study (1). It is possible that central fatigue after vigorous exercise has reduced some participants’ capacity to obtain an FEV1 result comparable with the preexercise values; this effect could be entirely unrelated to exercise-induced bronchoconstriction. Central fatigue was essentially not controlled for in this study, and it is difficult to exclude it as a factor determining reduced FEV1 after vigorous exercise in some participants. The concept that “The bronchoconstrictive effect found after exercise depends on the individual reaching near their limit of physiologic response to exercise,” and the reported observation that “the flow-volume loops before and after exercise did not reveal any limitation of the inspiratory flow in any responder” could support the alternative explanation proposed here. In conclusion, I think we need additional evidence to support the conclusion that vigorous exercise per se can cause abnormal pulmonary function in healthy adolescents.