Use of the MUNIX method to assess adaptation and maladaptation processes in middle-aged and older bodybuilders

Purpose. To determine the nature of changes in MUNIX and MUSIX parameters of the studied muscles in novice bodybuilders of middle-aged and older adults under conditions of using different load modes to assess adaptation and maladaptation processes. Materials & Methods. Ninety novice bodybuilders of middle-aged and older adults, who had a training experience in bodybuilding of only one year, were examined. Six groups of 15 participants each were formed: the first (A¹, A²) and second periods of middle age (B¹, B²); the older age (C¹, C²). Men in groups A¹, B¹, and C¹ utilized training model No. 1 for 90 days. Participants in groups A², B², and C² utilized training model No. 2. Electroneuromyography indicators (M-response, MUNIX, and MUSIX in the deltoid, triceps brachii, and biceps brachii muscles) were used to assess adaptation and maladaptation processes. Results. It was revealed that in the examined men of the second period of middle age, regardless of the features of the training models used, an increase in M-response amplitude was observed in the triceps brachii muscle (B¹: +20.8%; B²: +15.0%). At the same time, a similar significant increase was observed during the control of the changes in the MUNIX value (B¹: +20.1%; B²: +7.0%). However, the MUSIX parameter in this muscle demonstrates a decrease among the participants of groups B¹ (–7.3%) and B² (–9.2%). The results identified in the participants of groups A¹ and C², despite the significant difference in age, also demonstrate a significant increase in MUNIX parameters against the background of a decrease in MUSIX. It was established that it was among the representatives of the groups of the first period of middle-aged and older adults that a decrease in the parameters of the motor unit number estimation index of this muscle and a simultaneous increase in their size index were observed. Thus, in group A², which used training model No. 2 during the study, a decrease in MUNIX values (–12.3%) and an increase in MUSIX (+24.5%) were revealed. In group C¹, which used training model No. 1, the MUNIX parameter also decreased (–14.5%) and MUSIX increased (+8.1%). Concurrently, M-response amplitude decreased after 90 days of training compared with baseline values in representatives of groups A² (–10.4%) and C¹ (–27.5%). Conclusions. The research results indicate the necessity of using neurophysiological indices of the number and size of motor units in muscles to assess the processes of adaptation or the development of maladaptation during bodybuilding training. The findings indicated that in novice older bodybuilders, after a year of using the "classical" training model, the baseline MUNIX parameters in the muscles were significantly lower, and MUSIX parameters were higher compared to the data of middle-aged participants. It was revealed that in the examined men of the second period of middle age, regardless of the workload regimens of the experimental training models used, an increase in MUNIX in the muscles was observed during the study. However, among the participants of other age groups, depending on the training models used for 90 days, a completely different character of adaptive-compensatory responses was observed. Thus, in novice athletes of the first period of middle age, pronounced adaptation processes associated with an increase in the active motor unit number index in the studied muscles occur only under conditions of high-intensity workloads (Ra=0.78). At the same time, a similar character of increase in the level of intramuscular coordination in muscles that act as agonists in basic exercises occurs in older men only under conditions of low-intensity workloads (Ra=0.56). In other cases, a decrease in MUNIX parameters against the background of an increase in MUSIX was recorded, indicating pronounced manifestations of maladaptation in individual components of the neuromuscular system.