## 4 Discussion  
In the context of health promotion, the evaluation of health parameters constitutes a fundamental component for the identification of determinants and the formulation of evidence-based interventions. Many methods of assessing the response of the CVS to workload are presented in the scientific literature [22], and cyclical exercise tests are commonly described [23]; however, CVS responses to intermittent workload for the back muscles are not sufficiently investigated. Strengthening the back muscles is an integral part of physical health, and the connection between active working muscles and the CVS is complex. This complexity results from the fact that the muscles do not work in isolation but together with other muscle groups, internal organs, and all other physiological systems [24; 25]. Therefore, in our study, two different workloads helped us to monitor CVS responses to back muscle exercises and differences in this dynamic response by age. HR and ABP are well-known and well-studied indicators of CVS responses to workload [26]. An increase in HR during physical exertion is linked to a reduction in parasympathetic influence and a simultaneous rise in sympathetic nervous system activity [27]. In our study, the dynamic changes in HR during the ergometer testing were consistent with the findings of previous research. It is notable that although the differences between age groups were not statistically significant, HR values in the over-45 group remained consistently higher throughout the test. This result may be associated with age-related changes in the autonomic nervous system, slower recovery of parasympathetic tone, and decreased physical fitness in older adults [28]. During intermittent workloads applied to the back muscles, HR increased more during the recovery phases than during exercise repetitions. Throughout the testing procedure, participants' postural changes from supine  
Figure 5: The \(\mathsf{StO}_{2}\) dynamic during (**A**) the bicycle ergometer test while the workload increased stepwise every minute and (**B**) the intermittent workloads applied to back muscles. _Note. \(\mathsf{StO}_{2}\), muscle oxygen saturation; mmHg, millimetres of mercury; W, watts; min, minute; REP, repetition. *_p < 0.05._to standing positions could be related to the HR and ST-segment depression responses to workload. HR changes caused by postural provocations are widely described in the literature [29]. Increased HR immediately after a repetition could also be attributed to the calf muscle pump activation during exercise; in the literature, this mechanism has been referred to as the body's'second heart' due to its role in enhancing systemic blood circulation [30]. Notably, age-related differences were observed: participants aged 45 and older exhibited a more pronounced HR response to the workload, with HR increasing more noticeably during the testing procedure compared with younger individuals. ABP is one of the most extensively used haemodynamic variables studied following exercise. In this study, ABP data confirm the well-known hypothesis [31] that during exercise, sBP increases and dBP decreases at the same moment. In this study, ABP returned to initial values after the intermittent workloads applied to back muscles. After ergometer exercise, 3 min was too short a time for ABP values to return to baseline values. Similar results were found by other investigators [26]. However, dBP responses varied with age. Participants over the age of 45 demonstrated more stable diastolic values throughout the ergometer test, while younger individuals showed a statistically significant decrease in dBP. This age-related difference may be attributed to reduced arterial elasticity in older adults, which limits the ability of blood vessels to accommodate increased cardiac output [32]. Similar results were observed when evaluating dBP dynamics during back muscle exercises, with older individuals exhibiting smaller fluctuations in this parameter.