The older population is the least likely to engage in regular physical activity and to meet international recommendations for performing 150 minutes of moderate-intensity physical activity per week. Additionally, older adults living in care institutions tend to have even lower levels of physical activity compared to those living in the community. This physical inactivity among institutionalized older adults carries harmful consequences, such as the loss of muscle mass and strength, both of which are associated with decreased balance and an increased risk of falling, an adverse event with personal, physical, economic, social, and potentially fatal implications. Although this situation is well described in the literature, little is known about whether increasing physical activity levels from near-optimal (almost 150 minutes of physical activity per week) to optimal (more than 150 minutes per week) can influence muscle strength and balance in institutionalized older adults, and thereby reduce the burden related to falls.

This type of research is essential, as weekly frequency may be a variable to consider in the prescription of physical exercise for this population. The American College of Sports Medicine (ACSM) recommends using the FITT principle (Frequency, Intensity, Type, and Time) to guide exercise prescription. By adjusting these factors, individuals can tailor workouts to their specific goals and fitness levels. While attention has been given to the type of training, its intensity, and its duration, it is important to recognize that total weekly volume may be a determining factor for improvements in components of physical fitness.

Considering that this population tends to be physically inactive, incorporating physical activity two or three times per week may lead to different outcomes. While exercising twice per week may seem suboptimal, as it does not meet international guidelines, engaging in physical activity three times per week may be the minimum necessary to observe positive effects on muscle strength and balance.

Ageing is a universal experience. However, the physical ageing process occurs differently across individuals. When individuals remain physically active throughout life, their levels of physical fitness tend to be higher compared to those with low or no engagement in physical activity. Nevertheless, the literature shows that the general population does not meet the international recommendation of 150 minutes of moderate-intensity physical activity per week, and that the proportion of physically inactive individuals is higher among the older population compared to adults or children.

Given this scenario, marked by a lack of physical activity and the gradual loss of muscle mass inherent to ageing, which is exacerbated by the absence of muscular and cardiovascular stimulation, there is an increased risk of adverse outcomes, such as falls. It is well documented in the literature that physically inactive ageing is more pronounced in older adults living in institutions compared to those who remain in the community. This may be because community-dwelling older adults typically engage in behaviors considered physically active, such as household chores, social and recreational activities outside the home, gardening, or do-it-yourself tasks that promote movement. Conversely, older adults in institutional care, who are typically institutionalized due to a lack of autonomy and independence, tend to experience an accelerated physical ageing process, given the general lack of opportunities for physical activity. In such settings, household chores are not typically performed, opportunities to leave the premises for social or recreational activities are limited, and access to gardening spaces is often unavailable. Thus, institutionalized older adults are more vulnerable to the effects of physical inactivity, which further increases dependency on others.

The literature consistently highlights the beneficial effects of physical activity on the quality of life of older adults, including those living in institutions. Reducing the risk of falling is essential, as such events may result in total dependence, such as becoming bedridden or reliant on a wheelchair, and often involve a longer and more demanding recovery, both physically and psychologically. Falls also incur various costs: individual (e.g., medication), public (e.g., medical treatments), and institutional (e.g., hiring additional staff). Furthermore, fear of engaging in physically active behaviors, such as walking, due to the potential risk of falling again, can further discourage movement. Understanding that physical activity can play a protective role, by reducing fall risk, increasing confidence in physical activity, and gradually promoting independence and autonomy, may yield benefits both for the individual and for all parties involved in the care of institutionalized older adults.

In terms of international recommendations, the World Health Organization (WHO) and the American College of Sports Medicine (ACSM) advise that individuals perform at least 150 minutes of moderate-intensity physical activity per week, preferably 30 minutes per day. Additionally, strength training is recommended at least twice per week, at moderate intensity, involving 8-10 exercises and 10-15 repetitions per set. Flexibility and balance training are also advised twice per week, with each stretch lasting 15-30 seconds and repeated 2-4 times per muscle group, using static, dynamic, passive, or active exercises. However, despite being labelled as "recommendations," these guidelines present several practical limitations for the institutionalized older population. First, they imply approximately 60-90 minutes of regular physical activity per day, a significantly high volume for a population that is, by nature, physically inactive. Second, transitioning from inactivity to 60-90 minutes of daily exercise may be too abrupt, especially in the absence of appropriate adaptation and progression, and may increase the risk of adverse events associated with existing metabolic or cardiovascular conditions. Third, according to the ACSM, institutionalized older adults already present with at least one (or more) cardiovascular risk factor, requiring more cautious approaches than those applied to community-dwelling older adults or younger individuals. Lastly, not all institutions have access to resistance or cardio machines, free weights, transport to fitness facilities, or supervised professional guidance, which may limit the implementation of the strength training recommended by the WHO and ACSM.

Given this context, physical activity prescription for this population requires a tailored methodology suited to the institutional setting, namely, through multicomponent exercise programs. These programs integrate various components of physical fitness, including cardiovascular endurance, muscular strength, balance, agility, and flexibility. Sessions typically last 45-60 minutes and are conducted at light to moderate intensity, individualized based on each participant's subjective perception of effort, thereby allowing for self-regulation of intensity according to individual capabilities. According to the FITT framework, three of the four principles (Intensity, Type, and Time) are thereby addressed, with Frequency remaining as the variable to be further explored.

The variable of frequency is considered essential, as it can be pragmatically adjusted for populations residing in institutional settings. Multicomponent programs have traditionally been implemented two or three times per week, with a rest interval of one to two days between sessions. This schedule facilitates a cycle of physical stimulation followed by recovery. Furthermore, participation in two or three sessions per week, each lasting 45-60 minutes, presents a noteworthy distinction: two sessions fall short of the 150-minute weekly recommendation, while three sessions slightly exceed this threshold. Nevertheless, participation in such programs two or three times per week has demonstrated significant benefits across multiple domains of physical fitness, including cardiovascular endurance, muscular strength, balance, and agility. Thus, even without strict compliance with existing recommendations, substantial benefits are evident. The aim of the present investigation is to determine whether increased frequency yields greater benefits in this population, and whether greater emphasis should be placed not on rigid thresholds (e.g., the 150-minute guideline), but rather on identifying the minimum effective dose required to transition physically inactive institutionalized older adults to an "active" status during the initial stages of engagement in a multicomponent exercise program. The findings may support professionals in tailoring interventions to increase muscle mass and reduce fall risk among institutionalized older adults.

Inclusion criteria:

• 65 years to 90 years.
• Apparently healthy and without medical contraindications to exercise.
• Normal weight (BMI ≤ 24.99 kg/m2) or overweight (BMI > 25 ≤ 29.99 kg/m2)
• Being institutionalized for more than 6 months.
• Not having done any exercise regime for the last 6 months or any kind of structured sport activity.

Exclusion criteria

Before Enrollment:

• High risk of cardiovascular disease (ACSM, 2021)
• High blood pressure (≥ 140/90mmHg) in the pre-exercise evaluation (ESC, 2024)
• High risk of fall (more than 1 fall over the last 6 months).

During the intervention:

• Acquired injury.
• Acquired medical condition.
• Related or not related fall during intervention.
• Inability to perform 5 consecutive exercise sessions.
• Exercise adherence below 75% of total sessions (n = 24 or n = 36)

Primary and secondary data related to the study.

After publication.

University teachers and reseachers.