## 4 Discussion  
The aim of this study was to understand the effect of age on force production and symmetry according to upper limbs and different music cadences. Young adults and older women showed different kinetic behavior when performing horizontal adduction at different music cadences, but symmetry was similar between both. The cadences of 105-120 and 120-135 b-min\({}_{-1}\) lead to the different in-water force of the dominant limb in young adults and older women, while the force of the non-dominant limb showed mix-findings. Young adult women applied around 43-67 N of force while older women applied around 31-55 N during the incremental protocol of music cadences. The previous literature has reported slightly lower values than those found in the present study. For instance, [PERSON] et al. [16] found that older women applied around 31 N at the cadence of 150 b-min\({}^{-1}\) while performing horizontal adduction of upper limbs. Despite this, [PERSON] et al. [10] found that young adult participants (men and women) were able to apply around 50 N at the same cadence, but only the dominant limb was reported. [PERSON] et al. [24] noted in a clinical population values near 45 and 60 N for the right and left hand, respectively, during horizontal arm addiction at maximum velocity. Although arms act as a fundamental lever, the hand and finger positions may influence kinetic behavior. As seen previously, a higher drag force can be reached when hands are positioned perpendicular to the flow [25] and when fingers adopt a small spread [26]. Even though intermittent verbal and visual feedback was given, the kinematic behavior was not controlled for further analysis. So, one can be argued that the perception of correct body segmental alignment and orientation (i.e., the expertise level of the participants) could influence the kinematics and, therefore, the kinetic behavior. Another explanation from diverse results may be related to data computation and analysis when considering the hand surface area. So, this should be kept in mind when comparing data in further studies. The motion patterns in the water have been analyzed over the years in different basic exercises, e.g., [12], with different strategies while using the limb (e.g., alternating vs. simultaneous) [14] and adding resistive or fluctuating material, e.g., [27]. Nonetheless, water fitness instructors face heterogeneous groups in their daily water fitness sessions. So, providing proper knowledge about acute responses, namely from a kinetic point and according to the age of participants, could help them to design a proper program to achieve the desired level of exertion for all. To the best of our knowledge, this is the first study to  
Figure 3: Comparison of music cadences and limbs according to young adult (Panel (**A**)) and older women (Panel (**B**)). Blue bars represent the resultant peak force (FPEAK) of the dominant upper limb (D), while green bars represent the non-dominant upper limb (ND). *, \(p\leq 0.05\); **, \(p\leq 0.01\). provide data about kinetic behavior according to different age groups. As expected, young adult women were able to apply a greater amount of force than their older counterparts. Differences were around 7-8 N for the dominant limb and ranged between 8 and 17 N for the non-dominant limb. It is well-documented that the aging process leads to a natural loss of muscle mass with an increase in body fat [17]. This happens mostly above 60 years old accompanied by a decline in the neuromuscular system [28]. So, the ability to generate force tends to rapidly decline within advancing age when compared with maximum strength [29]. Due to the atrophy of type II muscle fibers [30], physiological responses (i.e., blood lactate) also tend to be lower in such cohort [16]. Thus, instructors should give special attention to the effect of age as different behaviors can arise within the same water fitness session. Our hypothesis was only partially confirmed, as both groups were similar in the symmetry index throughout all music cadences.