## 1 Introduction  
Water fitness programs have become one of the most popular physical activities within the health primary and tertiary prevention systems mainly due to their benefits for health, such as reducing weight [1] or improving older peoples' balance [2]. The water proprieties arise as being accountable for the popularity achieved in this type of physical activity [3]. The reduced effect of body weight (weight-bearing) due to buoyancy and multidirectional load linked to the drag force acts favorably in adherence to this type of program [4, 5]. These often include muscular conditioning as some part of the sessions aiming to improve participants' strength and conditioning, as well as, to help in the rehabilitation from an injury episode [6]. Those programs are widely chosen by participants of different age groups, gender, fitness levels, and/or health conditions. Although attendance prevails in older women, water exercise also promotes several health-related benefits in young adults and middle-aged participants, e.g., [7, 8]. Water fitness exercises are commonly reported as \"head-out aquatic exercises\" and can be coupled into six main groups [9] with distinct variants (i.e., number of limbs, added material) being employed for the session diversification. Within this, music cadence is essential to achieve the desired level of exertion and to obtain synchronization with a specific movement [10]. Acute physiological and biomechanical responses derived from increases in music cadence have become widely reported in the water fitness literature [4; 11]. Within the biomechanics domain, the effect of music cadence in movement kinematics has taken most of the attention, and just a small amount of research has been directed to movement kinetics. The previous literature has reported that an increase in music cadence led to an increase in segmental velocity [12] and therefore in drag force [4]. The same behavior seems to occur with the in-water forces, as an increase in music cadence promotes a consequential increase in the in-water force of the upper limbs during basic water exercises [13; 14]. Still, a paucity of information remains about in-water forces, mostly when searching for a comparison between different groups. The available literature has given special attention to particular target groups (e.g., older women), but most water fitness sessions are heterogeneous. Men and women of different ages, fitness levels, or social backgrounds can be found in a single session. At least from a sex comparison point of view, young adult men showed higher in-water forces when compared with women from the same age range [15]. However, it remains unclear if participants from the same sex, but with different ages, show different in-water kinetic behaviors. At least in the physiological domain, different acute responses should be expected while performing a basic water exercise. [PERSON] et al. [16] found that an increase in effort seemed to trigger different physiological responses in young and older women, with the lower values being detected for the older group. It is well known that the aging process is associated with a decline in muscle mass and therefore in strength [17] and with changes in motor control affecting coordination [18]. Older women seem not able to reach symmetric motion while exercising at different music cadences [19], but young adults tend to be more symmetric at the cadence of 135 b\(\cdot\)min\({}^{-1}\)[13] while performing horizontal adduction of upper limbs. So, understanding kinetic behavior in a broad range of ages (young vs. older) and through a larger spectrum of music cadences could help water fitness instructors design and plan programs according to the target groups, even if they belong to the same class or are part of the same session. The aim of this study was to understand the effect of age on force production and symmetry during the horizontal adduction performed at different music cadences. A comparison according to upper limbs and different music cadences was also run.