The invention relates to medical technology, to non-medicinal means for improving physical health and enhancing physical capabilities by means of a breathing system, and specifically relates to devices which are intended for inhaling hypoxic/hypercapnic mixtures having various compositions, and which have an adjustable resistance to inhalation/exhalation. According to a first variant, a breathing exerciser contains a first chamber, which is connected to means for connecting the exerciser to a user's respiratory tract； a second chamber, communicating with the first chamber； a third chamber, communicating with the second chamber； means for adjusting the composition of a breathing mixture； and means for adjusting the resistance to inhalation/exhalation, installed in a channel through which the first chamber and the second chamber communicate. The second chamber communicates with the atmosphere； the third chamber is elastic； means for regulating the composition of a breathing mixture are in the form of adjustable throttling devices installed in the channels through which the second chamber communicates with the third chamber and with the atmosphere； the means for adjusting the resistance to inhalation/exhalation are capable of separately and independently adjusting resistance to inhalation and resistance to exhalation. A second variant is characterized in that a first chamber communicates with a second chamber by means of two parallel channels, in that means for adjusting the resistance to inhalation/exhalation are installed in the parallel channels, and in that a breathing mixture is capable of passing through said channels in mutually opposite directions.
