Ergometric physical working capacity (PWC) testing has a long tradition in occupational medicine for assessing whether a sufficiently high level of physical performance for coping with the daily work requirements is given. Physical performance and stress resistance of the body are considered one of the main objects of influence of adaptogens. The stress-limiting effect of bioactive Naftussya water known. Data on the influence of Naftussya on the muscular performance are ambiguous. We set ourselves the goal of comparing balneotherapy-induced individual changes in PWC with changes in some parameters of the nervous and immune systems, as well as erythron, hemostasis, and metabolism. Material and methods. The object of observation were 19 men and 3 women (age 26÷61 years, body weight 78÷100 kg) with urate urolithiasis and chronic pyelonephritis. The survey was conducted twice: on admission and after two weeks of rehabilitation at the Truskavets’ Spa. Registered PWC150, parameters of HRV, EEG, immunity, phagocytosis, erythron, hemostasis and metabolism. Results. The analysis of individual changes revealed that in 45,5% patients reduced fitness was completely normalized, however, in 54,5% patients, the normal level of fitness fell to the lower zone of the norm. Discriminant analysis revealed 5 EEG parameters, VLF band HRV as well as plasma alanine aminotransferase and bactericidal capacity of monocytes of blood, the changes of which are characteristic (classification accuracy 100%) for alternative variants of actotropic effects of balneotherapy. Conclusion. The alternative response of fitness to balneofactors occurs within the framework of the functional-metabolic continuum and the neuro-immune complex. A decrease in fitness to the lower normal zone is accompanied by the normalization of the reduced bactericidal capacity of blood monocytes, so we interpret this decrease as a “physiological payment” for it.