Influence of Resistance Training on Gait & Balance Parameters in Older Adults: A Systematic Review

International Journal of Environmental Research and Public Health Systematic Review Influence of Resistance Training on Gait & Balance Parameters in Older Adults: A Systematic Review Christopher J. Keating 1,* , JoséCarlos Cabrera-Linares 1, Juan A. Párraga-Montilla 1, Pedro A. Latorre-Román1, Rafael Moreno del Castillo 1and Felipe García-Pinillos 2,3   Citation: Keating, C.J.; CabreraLinares, J.C.; Párraga-Montilla, J.A.; Latorre-Román, P.A.; del Castillo, R.M.; García-Pinillos, F. Influence of Resistance Training on Gait & Balance Parameters in Older Adults: A Systematic Review. Int. J. Environ. Res. Public Health 2021,18, 1759. https://doi.org/10.3390/ijerph 18041759 Academic Editor: Pantelis T. Nikolaidis Received: 20 January 2021 Accepted: 7 February 2021 Published: 11 February 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1Department of Didactics of Music, Plastic and Corporal Expression, University of Jaén, 23071 Jaén, Spain; [email protected] (J.C.C.-L.); [email protected] (J.A.P.-M.); [email protected] (P.A.L.-R.); [email protected] (R.M.d.C.) 2 Department of Physical Education and Sport, University of Granada, 18011 Granada, Spain; [email protected] 3 Department of Physical Education, Sport and Recreation, Universidad de La Frontera, Temuco 480011, Chile *Correspondence: [email protected] Abstract: In this work we aimed to perform a systematic review of randomized controlled trials within an aging population that investigated the general impacts of a resistance training (RT) protocol on key outcome measures relating to gait and/or balance. Following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement guidelines, two electronic databases (PubMed, and Scopus) were searched for randomized controlled trials that measured at least one key outcome measure focusing on gait and/or balance in older adults. 3794 studies were identified, and after duplicates were removed, 1913 studies remained. 1886 records were removed due to the abstract not meeting the inclusion criteria. 28 full-text articles were assessed further, and 20 of the articles were identified as meeting the criteria for inclusion. The remaining 20 studies were assessed for quality using the Physiotherapy Evidence Database (PEDro) scale; 12 studies remained and were included in this systematic review. Our review suggests that RT has a positive effect on both gait and balance in an elderly population. RT improves gait, specifically straight-line walking speed in older adults. RT is an adequate training method to improve balance in an aging population. Improvements in strength, attributed to RT, may allow for greater autonomy and independence to carry out activities of daily living as we age. Keywords: resistance training; strength training; aging; gait; balance; walking speed 1. Introduction The world’s population is aging and it is creating a unique situation in which the population over 65 years of age exceeds that of children under 5 years of age [ 1 ]. Currently, 11% of the world population is over 60 years of age. The population aging trend continues and it is projected that by 2050 this population will include more than 22% of the world population [ 2 ]. In light of these calculations, active aging is presented as one of the best options to allow the elderly to enjoy a higher quality of life and a higher level of health to be the protagonists of their own lives in advanced age. By doing so they can avoid spending excessive life years and money on costly medical care and treatment [3]. Physical activity (PA) is presented as an alternative to medicine in terms of improving quality of life since it has been proven to have positive physiological effects in an aging population (i.e., prevents chronic diseases and reduces the risk of non-communicable diseases) [ 4 ]. In this sense, the lack of physical activity is what causes the adverse effect, resulting in what is known as frailty. This is a syndrome that appears when 3 or more of the following criteria are present in a person who suffers from it: weight loss, weakness, slowness, exhaustion, and low levels of PA. Therefore, the term frailty encompasses various aspects such as gait, mobility, balance, muscle mass, motor processing, cognition, nutrition, endurance, and PA [ 5 ]. In those individuals over the age of 65, frailty causes a greater risk Int. J. Environ. Res. Public Health 2021,18, 1759. https://doi.org/10.3390/ijerph18041759 https://www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2021,18, 1759 2 of 13 of falling, which is the second cause of death and injury in the world population and it is becoming a serious public health problem for the elderly [ 6 ]. One-third of the aging population falls at least once a year, and a fall in an elderly individual can have serious consequences such as life-threatening injury, hospitalization, fractures, and/or a loss of independence [ 7 ]. Falling or simply the fear of falling can result in a restriction of physical activity levels, and indirectly in the reduction of social interactions. This causes a paradox in which the fear of falling can increase the risk of future falls due to the deterioration of physical abilities from not participating in everyday life [8]. The physical inactivity derived from a fall can accentuate the loss of muscle mass and strength to a greater extent than that caused alone by age-associated loss. It is often reported that muscle mass decreases by roughly 2% each year after the age of 50 or, similarly, by 15% for every 10 years after the age of 50 [ 9 ]. This progressive loss of strength and muscle mass is known as Sarcopenia [ 10 ]. The term Dynapenia can also be used to further describe the age-related loss of muscle strength and power that is not caused by neurologic or muscular diseases [ 11 ]. Sarcopenia/Dynapenia and frailty cause a progressive deterioration of functional ability that is heightened in older ages. A gait speed greater than 1.20 m/s is associated with greater independence in older adults, while a speed less than 0.8 m/s is a predictor of future dependence that can lead to hospitalization, medical care, cognitive decline, and mortality at these ages [12]. Traditionally, aerobic training programs have been used to reverse the effects of the above-mentioned pathologies, as well as an improvement in the health status of the elderly [ 13 ]. This has been shown to improve cardiorespiratory function, decrease hypertension, and improve functional activities (e.g., muscle strength, physical performance, and decrease the risk of falls). In the same way, it can also improve cognitive function, while also having a positive impact on improving quality of life [ 14 ]. However, resistance training (RT) is also an appropriate exercise training method to improve health parameters and when used in combination with aerobic exercise it has been shown to improve functional capacity in an aging population [ 15 ]. In this regard, resistance training is defined as any exercise that causes the muscle to contract against resistance (weights, bands, external objects, body weight, etc.) with the intention of provoking physiological and/or morphological changes. Recent pilot data and theoretical reviews have suggested that RT in the elderly could be an effective and safe method of participating in PA that is capable of reversing the effects of sarcopenia [ 16 ], as well as an improvement in body posture, balance, and physical resistance [ 17 , 18 ]. Therefore, resistance training must be a key component to be introduced in training programs for the elderly since, in addition to the benefits mentioned, it may produce neuromuscular improvements such as increased muscle mass, strength, and functional capacity [ 19 ]. However, a large amount of this information is based upon outdated data sets. A systematic review from 2004 suggested that RT is a promising exercise regimen for older adults but more research was needed to determine its effectiveness [ 20 ]. Another systematic review and meta-analysis from 2010 found promising results, but concluded that further research is needed to provide more considerable conclusions regarding the effect that RT has on the functional performance of older adults [21]. Therefore, this work aimed to perform a systematic review of randomized controlled trials within an aging population that investigated the general impacts of a resistance training protocol on key outcome measures relating to gait and/or balance. 2. Methods This review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement guidelines [ 22 ]. Two electronic databases (PubMed, and Scopus) were searched for randomized controlled trials that measured at least one key outcome measure focusing on gait and/or balance in older adults. Search terms used included: resistance training OR strength training AND balance OR gait. The search terms were limited to TITLE/ABSTRACT/KEYWORDS. The search was further Int. J. Environ. Res. Public Health 2021,18, 1759 3 of 13 limited to “clinical trials”, in “humans”, published in “the last ten (10) years” (January 2010 to June 2020), “adult: 65+ years” of age, and published in “English”. 2.1. Study Selection—Inclusion Criteria The inclusion criteria for this systematic review were full-length research articles published in peer-reviewed academic journals in the English language. Only randomized controlled trials published from January 2010 up to June 2020 were eligible. Studies that included participants with a median age of 60+ years. Resistance training interventions that measured at least one variable relating to gait and/or balance were included. 2.2. Study Selection—Exclusion Criteria Abstracts, conference presentations, poster presentations, letters to the editor, books or book chapters, unpublished papers, proposed protocols, validation studies, or retrospective designs were excluded. Studies were also excluded if the participants were taking supplements, or if the average age of participants was ≤ 60 years. Also, studies that met the inclusion criteria yet later did not achieve a score of 5 or greater on the PEDro scale were also excluded from the review. 3. Results The initial search resulted in 3794 studies; after duplicates were removed, 1913 studies remained, and the abstracts were reviewed for meeting the inclusion criteria. Following the initial screening process, 1886 records were removed due to the abstract not meeting the inclusion criteria. 28 full-text articles were assessed further and 20 of the articles were identified as meeting the criteria for inclusion. The remaining 20 studies were assessed for quality using the Physiotherapy Evidence Database (PEDro) scale, 8 of the studies did not score 5 or greater and were consequently removed. 12 studies remained, and all were included in the systematic review. (Figure 1) The Physiotherapy Evidence Database (PEDro) scale is an 11-item scale that rates randomized controlled trials from 0 to 10. One item (eligibility criteria) is included in the scale because it influences external validity but not the internal or statistical validity of the trial, thus it is not counted toward the final score. Therefore, the PEDro score is generated from an 11-item scale resulting in a final score of 0 to 10. Seventeen of the twenty studies were scored directly from the Physiotherapy Evidence Database [ 23 ]. The remaining three studies were not included in the database and were scored separately by 2 authors (CJK and JCCL); there was full consensus amongst the authors’ scores. (Table 1) Table 1. PEDro—Quality Assessment. Authors 1 * 2 3 4 5 6 7 8 9 10 11 Total Score Alfieri et al., (2012) 1 1010000111 5 Cancela Carral et al., (2019) 1 1010001011 5 De Sousa et al., (2013) n1 1000000011 3 Fahlman et al., (2011) 1 1010011011 6 Forte et al., (2013) 1 1000000011 3 Gonzalez et al., (2014) n1 1010001111 6 Hewitt et al., 2018 1 1110011111 8 Iuliano et al., (2015) 0 1010000011 4 Marques et al., (2011) 1 1110010111 7 Martins R, et al. (2011) 1 1010001011 5 Nicholson et al., (2015) 1 1010000011 4 Nicklas et al., (2016) n1 1110011111 8 Pamukoff et al., 2014 1 1010000011 4 Ramirez-Campillo, Rodrigo, et al. (2016) 0 1010011011 6 Int. J. Environ. Res. Public Health 2021,18, 1759 4 of 13 Table 1. Cont. Authors 1 * 2 3 4 5 6 7 8 9 10 11 Total Score Roma et al., (2013) 1 1010000011 4 Sahin et al., (2018) 1 1010000011 4 Shiotsu & Yanagita, (2018) 1 1010001011 5 Sparrow et al., (2011) 1 1010011111 7 Sylliaas et al., (2011) 1 1110011111 8 Yoon et al., (2018) 0 1010000011 4 * Not counted toward total score; n Scored by reviewers; Bolded Total Score ≤ 4 and therefore not included in this review. Figure 1. Article selection flow-chart. Study Characteristics Twelve studies were included in the review, and all were published in the English language. The randomized controlled trials were conducted in the following countries: USA = 4 [ 24 – 27 ], Portugal = 2 [ 28 , 29 ], Australia = 1 [ 30 ], Brazil = 1 [ 31 ], Chile = 1 [ 32 ], Japan = 1 [ 33 ], Norway = 1 [ 34 ], and Spain = 1 [ 35 ]. The total number of participants analyzed in all studies was 499 (only including resistance-trained participants). Eleven of the twelve studies had reported the gender of the participants and approximately 60% of Int. J. Environ. Res. Public Health 2021,18, 1759 5 of 13 them were female (149 males to 304 females). Three studies reported mean ages of ≥ 65–69.9 years [ 27 , 28 , 33 ], 6 studies reported mean ages between 70–79.9 years [ 24 – 26 , 29 , 31 , 32 ], two studies reported mean ages between 80–89.9 years [ 30 , 34 ], and one study reporting a mean age of >90 years [35]. Nine of the twelve studies recruited participants that were community-dwelling [24–28,31–34], whereas three studies recruited participants from residential care facilities [ 29 , 30 , 35 ]. Of those studies that had recruited participants from the community, only two had reported further underlying conditions; Nicklas et al. included participants that were overweight or obese and Sylliaas et al. investigated hip fracture patients [ 27 , 34 ]. Only one study with participants from residential care facilities reported further underlying conditions, and they reported on “frail” nonagenarians [35]. (Table 2) Table 2. Participant characteristics. Authors Population Population (Cont.) Age n= Male Female Alfieri et al., (2012) Communitydwelling 70.18 ±4.8 23 1 22 Cancela Carral et al., (2019) Residential care Frail 90.8 ±4.02 13 0 13 Fahlman et al., (2011) Communitydwelling 74.8 ±1 46 NR NR Gonzalez et al., (2014) Communitydwelling 71.1 ±6.1 23 12 11 Hewitt et al., 2018 Residential care 86 ±7 113 42 71 Marques et al., (2011) Communitydwelling 67.3 ±5.2 23 0 23 Martins et al. (2011) Residential care 73.4 ±6.4 23 10 13 Nicklas et al., (2016) Communitydwelling Overweight/Obese 69.4 ±3.6 63 34 29 Ramirez-Campillo et al., (2016) Communitydwelling 70 ±6.9 8 0 8 Shiotsu & Yanagita, (2018) Communitydwelling 69.0 ±4.1 12 0 12 Sparrow et al., (2011) Communitydwelling Vets & Spouses * 70.3 ±7.5 52 35 17 Sylliaas et al., (2011) Communitydwelling Hip Fracture 82.1 ±6.5 100 15 85 * US Military Veterans and Spouses, NR = not reported. Resistance training intervention duration ranged greatly from 6 to 32 weeks, with one study reporting data for 6 weeks [ 25 ], one study reporting for 10 weeks [ 33 ], four studies reporting for 12 weeks [ 31 , 32 , 34 , 35 ], two studies reporting for 16 weeks [ 24 , 29 ], one study reporting for 20 weeks [ 27 ], one study reporting for 25 weeks [ 30 ], one study reporting for 26 weeks [ 26 ], and one study reporting for 32 weeks [ 28 ]. All twelve studies described the frequency of training in “days/week”; the studies were split evenly with six studies conducting the intervention 2 days/week [ 25 , 30 – 33 , 35 ] and six studies conducting the interventions 3 days/week [24,26–29,34]. Regarding the number of sets and repetitions used in the RT interventions, the research appears to be relatively diverse. The number of sets used in the interventions included three interventions using 2 sets [ 24 , 26 , 28 ], six interventions using 3 sets [ 25 , 27 , 31 – 34 ], one study using 2–3 sets [ 30 ], and two studies simply using a “varied” use of sets [ 29 , 35 ]. The number of repetitions used per set of exercise in the respective interventions included one study using 6 to 8 [ 28 ], two studies using 8 to 12 [ 33 , 34 ], one study using 8 to 15 [ 25 ], one study using 10 to 15 [ 30 ], one study only using 10 [ 27 ], two studies only using 12 [ 24 , 26 ], one study using a fixed 12, 10, and 8 repetitions model [ 31 ], and three studies using “varied” repetitions [32,35,36]. All studies reported the type of resistance modalities used during the training sessions. Of which, four studies reported using resistance machines [ 27 , 28 , 31 , 33 ], two studies utilizing elastic bands [ 24 , 35 ], two studies utilizing both body weight and machines [ 25 , 34 ], Int. J. Environ. Res. Public Health 2021,18, 1759 6 of 13 one study utilizing high-speed resistance training with free weights [32], one study utilizing a combination of pneumatic machines and balance training [ 30 ], one study utilizing a combination of calisthenics and elastic bands [ 29 ], and one study utilizing both body weight and free weights [26]. (Table 3) Table 3. Resistance training intervention details. Authors Exercise Modality Days/Week Weeks Sets Reps Rest-time Load Total Time Alfieri et al., (2012) Machines 2 12 3 12,10,8 NR 50%, 75%, MTL 60 Cancela Carral et al., (2019) Elastic Bands 2 12 varied varied 30–60 sec progressive 60 Fahlman et al., (2011) Elastic Bands 3 16 2 12 NR progressive NR Gonzalez et al., (2014) Body Weight/Machines 2 6 3 8 to 15 NR NR NR Hewitt et al., 2018 Pneumatic/Balance 2 25 2 to 3 10 to 15 NR Moderate (CR10) 60 Marques et al., (2011) Machines 3 32 2 6 to 8 ≥2 min 75–85% 1RM 60 Martins et al. (2011) Calesthetics/Elastic Bands 3 16 varied varied 3 min progressive 45 Nicklas et al., (2016) Machines 3 20 3 10 ±1 min 70% 1RM NR RamirezCampillo et al., (2016) High-speed RT 2 12 3 varied ±1 min 75% 1RM 50 to 70 Shiotsu & Yanagita, (2018) Machines 2 10 3 8 to 12 NR 60–70% 1RM NR Sparrow et al., (2011) Body Weight/Free Weights 3 26 2 12 NR varied 60 Sylliaas et al., (2011) Body Weight/Machines 3 12 3 8 to 12 NR 80% 1RM 45 to 60 NR = not reported, progressive = article only stated progressive resistance training when referring to the load applied, 1RM = 1 repetition maximum, CR10 = Borg rating of perceived exertion CR10, MTL = maximum tolerated load. All twelve studies reported the dropout rates of their respective participants; three of the studies reported that no participants had dropped out of the resistance training group [ 25 , 29 , 32 ], two studies reported its dropouts but did not provide explanation [ 24 , 26 ], and seven studies had reported the dropout rate of its resistance training participants with explanations [ 27 , 28 , 30 , 31 , 33 – 35 ]. On the other hand, only three studies reported on adverse events related to the resistance exercise intervention [ 26 , 27 , 30 ]. Of those three studies that reported adverse events, there was a total of fourteen individual events; thirteen of those events were related to musculoskeletal aches and pains and only 1 event was related to a non-injurious fall [30]. (Table 4) Seven of the twelve studies reported on variables related to balance alone [ 25 , 26 , 28 , 29 , 31 , 32 , 35 ], whereas only one study reported on gait alone [ 24 ]; the remaining four studies reported on both gait and balance variables [ 27 , 30 , 33 , 34 ]. The most common test used to assess balance was the Timed Up and Go (TUG) or the 8 foot Timed Up and GO (8ftTUG) variation; other tests included the single-leg stance, tandem or bilateral stance, as well as the body’s center of oscillation. Tests assessing gait alone included velocity (m/min), step time (seconds), and step length (cm). Tests in the studies that provided measures for both gait and balance were mixed and included assessments such as the Short Physical Performance Battery (SPPB), 10-m walk speed, Functional Reach Test (FRT), Berg Balance Scale (BBS), the center of oscillation, and the 400-m walk test for time (Table 5). Int. J. Environ. Res. Public Health 2021,18, 1759 7 of 13 Table 4. Reported dropouts & adverse events. Authors Drop-outs Explanation Adverse Events Explanation Alfieri et al., (2012) 5 1 ankle fracture, 1 rib fracture, 1 uncontrolled HF, 1 knee pain, 1 gave up NR Cancela Carral et al., (2019) 2 death NR Fahlman et al., (2011) 4 NR NR Gonzalez et al., (2014) 0 0 Hewitt et al., 2018 16 15 deceased, 1 moved away 4 3 musculoskeletal aches/pains, 1 noninjurious fall. Marques et al., (2011) 8 Medical issues unrelated (n= 3) Disinterest (n= 3) Personal reasons (n= 2) 0 Martins et al. (2011) 0 NR Nicklas et al., (2016) 7 3 personal health issues, 2 caretaking, 1 changed mind, 1 lost to follow-up 22 musculoskeletal complaints Ramirez-Campillo et al., (2016) 0 0 Shiotsu & Yanagita, (2018) 3 3 private reasons NR Sparrow et al., (2011) 3 NR 8 8 musculoskeletal Sylliaas et al., (2011) 5 1 nursing home, 1 died, 3 illness NR NR = not reported. Table 5. Study conclusions. Authors Variable Tools Conclusion Alfieri et al., (2012) Balance Timed Up and Go (TUG); Berg; Oscillation of the body’s center of pressure Both multisensory and RT interventions improved static and dynamic mobility in healthy elderly subjects. Cancela Carral et al., (2019) Balance TUG Muscle strength intervention programs may help promote healthy lifestyles by maintaining autonomy, improving function, and balance. Fahlman et al., (2011) Gait Velocity (m/min), step time (seconds), step length (cm): GAITRite mat Eight weeks of RT increased the parameters of velocity and step length. Additional emphasis on gait training could improve gains even further. Gonzalez et al., (2014) Balance Single leg balance These findings support the use of progressive resistance training for untrained older adults to improve balance. Hewitt et al., 2018 Gait & Balance Short Physical Performance Battery (SPPB) Moderate-intensity PRT and high-level balance exercise significantly reduced falls and improved SPPB performance. Marques et al., (2011) Balance 8-foot Up and Go (8-ft UG) 8-month RT, but not AT, can induce significant bone adaptation in older women and both regimens elicited significant gains in balance. Martins et al., (2011) Balance 8-ft UG Both AT and RT interventions improved functional fitness. Int. J. Environ. Res. Public Health 2021,18, 1759 8 of 13 Table 5. Cont. Authors Variable Tools Conclusion Nicklas et al., (2016) Gait & Balance gait speed; SPPB; chair rise Both RT and RT + Calorie Restriction groups increased in gait speed, SPPB score, and chair rise time. Ramirez-Campillo et al., (2016) Balance 8-ft UG; Bilateral balance w/Bertec BP5050 balance plate platform 2 or 3 training sessions/week of RT (equated for volume and intensity) are equally effective for improving physical performance and quality of life of older women. Shiotsu & Yanagita, (2018) Gait & Balance 10-m walk speed; TUG; single-leg balance with eyes open; Functional Reach Test (FRT) 10-m walk speed significantly increased in all training groups; Combined AT & moderate-intensity RT resulted in significant improvements in dynamic balance capacity. Sparrow et al., (2011) Balance Single leg balance (eyes open) and Tandem stance A home-based RT program for older adults resulted in significant improvements in muscular strength and balance. Sylliaas et al., (2011) Gait & Balance Berg; TUG; 10-m walk speed Significant improvements in BBS, sit-to-stand, TUG, and 10 m walk speed. All twelve studies observed a positive effect of the RT intervention in at least one of the studies’ outcome measures; none of the studies reported a negative effect due to the RT intervention. All eleven studies that analyzed balance specified an improvement in either static and/or dynamic balance. All five studies reporting on gait measures reported a positive effect of the RT intervention, and particularly an improvement in gait speed. 4. Discussion The main objective of this work was to examine the general impact that an RT program has on key outcome measures relating to gait and balance. According to the studies included in this review, it is evident that RT has a positive effect on both gait and balance in an elderly population. Regarding gait, only five studies were found to investigate gait parameters. All five of those studies used some form of a timed walking test, four of which evaluated the 10-m walking test, whereas the other measured gait as part of the SPPB (3/4-m walking test). This may be due to the common belief that gait speed itself is the best indicator of gait function, which does fall in line with the findings from Guralnik et al. that suggest that gait speed could be the best predictor of frailty and disability in older adults [ 37 ]. However, unidirectional walking speed is simply one of the many methods to analyze gait. This sentiment is echoed by M.W. Whittle, who indicates that walking is only one of the many functions of the musculoskeletal system and that we should “broaden our horizons and use the power of the modern measurement systems to study a wide range of other activities” [ 38 ]. Although the authors of this review believe that unidirectional gait assessment is an essential measurement, we also suggest that further research needs to include multidirectional and/or double task scenarios to better understand their utility in analyzing gait in older adults. It is interesting to note that only one study examined the effects of RT on gait parameters alone and they concluded that eight weeks of resistance training improved the measures of velocity and step length; however, there was no significant increase in step time measured in seconds. Those authors also indicated that it could be possible to see additional gains if an emphasis were placed specifically on gait training and that it is necessary to design programs with a specific objective centered on the target population and/or individual rather than a standardized or “one size fits all” model [ 24 ]. The other four studies analyzing gait measured the time of a 10-m walking test, and all of them found significant improvements from baseline to post RT intervention. Int. J. Environ. Res. Public Health 2021,18, 1759 9 of 13 According to the findings included in this review, resistance training undoubtedly improves gait parameters in older adults, but specifically unidirectional walking speed. It is interesting to note that there are other forms of gait parameter tests that are not simply straight-line walking tests [ 39 ]. The authors suggest that more research needs to be done on the effects of an RT program on a complex gait or a dual-task scenario. Research has found an association between gait variables and cognitive function in older adults [ 39 ]. In this regard, a complex gait test when measuring the time to completion would allow researchers to get a better understanding of the relationship between the functional and cognitive state of the individual. Furthermore, a complex gait test would be a more accurate representation of a real-life scenario, and therefore a better predictor of future adverse events. However, irrespective of straight-line walking speed, more research is needed to determine if RT can enhance the various aspects of gait in older adults. Regarding balance, 11 studies analyzed at least one balance variable and all of them reported that RT had a significant effect on improving balance; only 1 of the studies analyzed advised concern regarding the improvements from the RT group. That study, by Alfieri et al., could not determine which of the programs included in their research (a multisensory or RT intervention) was more suitable for improving balance control [ 31 ]. They further state that although there was no significant between-group difference, the multisensory group showed better improvements in the dorsiflexor and plantar flexor muscles of the ankle which have been demonstrated to be important for the maintenance of static balance. In any case, RT did induce a significant change in measures such as TUG, BBS, and the body’s center of oscillation. Numerous variables need to be controlled and/or modified to achieve the desired objectives of improving balance. For that very reason, RT can be difficult to program and prescribe to such a diverse population base [ 40 , 41 ]. Considering that there are many variables requiring attention to develop an effective RT program, it is promising to report that all studies included in this review obtained significant improvements in balance across a wide variety of RT programs. The duration of the interventions varied widely from 6 to 32 weeks, with 12 weeks being the most common. It is important to highlight that Gonzalez et al., obtained improvements in balance with a basic RT program consisting of 2 days/week for 6 weeks. This indicates that an RT program with a specific objective (in this case, improved balance) can achieve significant improvements in a relatively short intervention time. This reduction in intervention time could prevent the abandonment of the program by participants, since lack of adherence due to interest is one of the main reasons why subjects cease training [ 42 , 43 ]. This short training time could allow the exercise specialist to include well-deserved breaks for the participants within the macro/mesocycle, as well as changing the program accordingly to make it more desirable for the participants. Regarding the number of sets used (2–3) and the number of repetitions (between 8–15), 11 of the articles analyzed used a methodology following the American College of Sports Medicine Position Stand on Progression Models in Resistance Training for Healthy Adults in order to increase muscle mass through hypertrophy [ 44 ]. Five of the twelve studies used the 1-repetition maximum (1-RM) method to prescribe training loads [ 21 , 22 , 26 – 28 ]. Despite its widespread use, this method has some disadvantages that must be considered. Among others, this can be unsafe and harmful for the performer when the subject does not have prior training and/or their performance technique is not correct [ 45 ]. The intense efforts of a 1-RM may produce unnecessary musculoskeletal loading that may not be recommended for certain populations such as the elderly. For this population, an alternative method would be to include one of the many 1-RM prediction equations which have been shown to be a good predictor of an individual’s true 1-RM [46]. Several studies analyzed in this review included a variety of rest times between sets from 1 min, 2 min, and 3 min. However, many of the studies analyzed did not report the rest time between sets. The rest time between sets is an important variable to consider when planning an RT program and, surprisingly, more studies did not plan or at least