Aging leads to substantial alterations in the nervous and skeletal muscle systems that ultimately lead to a reduction in "neural drive" and motor performance. While maximal strength starts declining as early as 50 years of age, aging brings even greater reductions in rate of force development and muscle power, that has been shown to be a stronger predictor of functional independence and balance impairments.

Falls are a major health concern as one third of adults over 65 years loses balance and falls every year, and based on a published report, the estimated health care costs associated with falls in the European Union is €25 billion.

The ability to recover balance declines with aging, where older individuals often recover balance with a greater number of balance recovery steps and non-optimal stepping strategies. In addition, older adults have more difficulty recovering balance in the medio-lateral direction. The hip abductors are fundamental in controlling the motion of the body centre of mass in this direction during weight transfers of standing, stepping, and walking.

Furthermore, these muscles appear to be more susceptible to age-related composition and performance declines than other muscles of the lower limbs, especially in individuals at a higher risk for falls.

Unfortunately, common balance interventions, such as, functional balance training, Tai-Chi, or dance, have a very limited capacity to reduce the risk of falls in older adults. Interestingly, resistance training is relatively better than the mentioned interventions at reducing this problem. This may come about through mitigating the agerelated neuromuscular performance deficits. However, traditional resistance training lacks the emphasis in high velocity movements required for adequate fall prevention protective stepping strategies. Muscle power training is a safe and effective alternative to traditional resistance training. By emphasizing in maximum speed of execution, its results are often better than with traditional resistance training, especially in functional outcomes, with the potential to enhance balance recovery. However, there is little and inconsistent evidence on the optimal exercise parameters (such as velocity) for prevention of falls.

Community-based multi-component exercise programs are often used to promote health and functional benefits in the older adult population. These programs not only have a positive impact in a larger number of communitydwelling individuals, but can also lead to significant improvements. Nonetheless, these programs limited in reducing the risk for falls. Considering the robust effects of muscle power training in the older population, it is conceivable that a multi-component community-based exercise intervention, that focuses on developing muscle power and reduce fall risk, can improve the older individuals' ability to recover balance and consequently, bring greater benefits to the older adult community. However, there is no information on the feasibility of conducting an exercise program to develop muscle power and reduce fall risk in a community-based setting. Furthermore, it is generally unknown if such an exercise intervention can improve function, balance, and reduce the occurrence of falls in older adults especially, among those that have fallen in the past- which are the most relevant target population for both clinical studies and practice.

This study will adopt a randomized controlled trial design comparing a community-based multi-component exercise program focused on muscle power (MCP) with a traditional community-based multi-component exercise program (TMC). Equal numbers of older adults with and without a history of falls will be allocated to each intervention group.

1. Participants

   Based on the effect size calculated (0.55-1.75), to achieve a statistical power of 80% with a significance of p smaller than 0.05, this study would need to recruit approximately 22 subjects per group. Anticipating 20% dropout and attrition, and considering this study will propose four different groups, a total of 120 community-dwelling older adults will be recruited from the greater Porto area through existing partnerships with Maia's municipality. Retrospective falls incidence during the 12 months prior to enrollment will be used to classify participants as fallers (n=60) or non-fallers (n=60). Using stratified randomization, participants will be allocated to one of four groups: TMC non-fallers (n=30), TMC fallers (n=30), MCP non-fallers (n=30), or MCP fallers (n=30).

   The study will be conducted in accordance with the Declaration of Helsinki of 1975, revised in 2013 and General Data Protection Regulation (GDPR) requirements. Ethical approval will be obtained from the Ethics Committee of the University of Maia prior to participant enrollment. Written informed consent will be obtained from all participants before participation.

2. Procedures

   2.1.Screening

   An initial screening will ascertain if participants meet the inclusion/exclusion criteria. Additionally, the International Physical Activity Questionnaire will be applied to control for physical activity as confounding factor.

   2.2.Assessments

   Pre_Control, Pre_Intervention, Post_Intervention and Ret sessions will be identical and will consist of functional mobility and balance tests, including gait speed, mini-BESTest, Four Square Step Test (FSST) and five time Sit-to-Stand (5STS) test. Neuromuscular assessments, consisting of isometric maximal voluntary contractions (IMVC) of the handgrip (Gripwisetech, PT), knee extensors, hip extensors and hip abductors (DESMOTEC, IT), at a collection frequency of 100Hz. Participants will be instructed to "push as hard and as fast as possible" for 15 seconds.

   A questionnaire assessing participant perspectives on the exercise intervention will be used at week 13. Adverse events and falls incidence will be assessed monthly via questionnaire from Pre_Control-Ret.

3. Interventions

   TMC and MCP interventions will be applied for 12 weeks, 3 times per week. Both interventions will be composed by aerobic exercises, such as walking overground and/or on a treadmill at the preferred speed, balance exercises involving stepping and manipulation of the center of mass over the base of support and resistance training. In the resistance training, participants will perform knee extension, hip extension and hip abduction exercises, in a regimen of 3 sets of 10 repetitions at 60-75% of the participant's 1 repetition maximum (1RM), with weights and/or weight machines. 1RM estimation will be done through a 10RM protocol and apply Brzycki's equation. 1RM assessment will be conducted on the first training session and re-done every 3 weeks to progressively adjust resistance training loads.

   While in TMC participants will be instructed to perform the repetitions of the resistance exercises at a cadence of 2s concentric and 2s eccentric, participants in the MCP will be instructed to perform every repetition as fast as possible. To maintain high velocity in this group, 50% of 1RM training load will used.

4. Statistical Analyses

   A linear mixed effects model will test the main effects of intervention, group and time, and their interactions, for a significance level of p less than 0.05.

5. Expected outcomes

   The interventions are expected to be feasible and safe and it will have a positive adherence.Therefore, the application of muscle power training within a community-based multi-component setting is expected to be feasible.

   The muscle power-focused multi-component exercise program (MCP) is expected to produce greater improvements in neuromuscular performance and functional mobility when compared to the traditional multi-component exercise program (TMC).

   Participants with a history of falls are expected to demonstrate larger relative improvements in neuromuscular and functional outcomes compared to non-fallers, due to greater baseline impairments.

   Improvements achieved following the MCP intervention are expected to be maintained over time and associated with a reduction in falls incidence during the post-intervention follow-up period.

6. Potential risks and contingency plans

Multi-component exercise programs, including muscle power-oriented training, have been previously applied safely in community-dwelling older adults. Therefore, the risk of adverse effects associated with the TMC and MCP interventions is considered low.

Participant safety will be monitored throughout the study, and any adverse symptoms or events will be documented and addressed accordingly.

There is a possibility that the interventions may not result in statistically significant improvements. In the event that observed effect sizes are smaller than anticipated, the lack of significant differences may be attributable to sample size limitations. In such cases, recruitment may be extended to increase the study sample.

Inclusion Criteria:

• Age between 65-85 years;
• Fall history over the 12 months prior to enrollment (fallers group).

Exclusion Criteria:

• Any existing medical conditions or injuries which would affect the ability or safety to perform exercise;
• Taking medication affecting balance (such as sedatives, anti-depressives);
• Regular (more than 1d/week) participation in resistance training with loading greater than bodyweight during the last year;
• BMI greater than 32 kg/m2.