AlgunSos de los cambios más sme of the most significativos a los que se enfrenta la población mundial son el aumento del número y lant changes facing the world population are the increase in the number and proporción de personas mayorestion of older people [ 1 ] yand lathe progresión de la esperanza de vida a edades más avanzadas sion of life expectancy to older ages [ 2 ]. El deteriCoro cognitivo es una pose impairment is a possible consecuencia delquence of the aging proceso de envejecimiento, ya que a partir de la tercera década de la vida el cerebro comienza a atrofiarse, disminuyendo su riego sanguíneo y su pesoss, since from the third decade of life the brain begins to atrophy, reducing its blood flow and weight [ 3 ]. EThisto afecta en gran medida el funcionamiento del sistema nervioso central greatly affects the functioning of the central nervous system [ 1 ], produciendo pérdida de memoria, atencióg loss of memory, attention, reducción de laed learning capacidad de aprendizaje y ty and deterioro de las funcionesation of cognitivae functions [ 4 , 5]. EThista disminución se asocia con un mayor riesgo de demenc decline is associated with an increased risk of dementia, así como con resultado well as adversos para la salud, como limitacionee health outcomes such as funcionales y discapacidadtional limitations and disability [ 6 ].

The burden on health systems caused by dementia and other adverse cognitive outcomes has become a major social challenge with great added financial costs [7]. New methods are required in order to prevent losses and even improve cognitive performance, functionality, autonomy, and quality of life in general [6]. For this reason, over the last decades interest has grown concerning the influence of lifestyle factors such as physical exercise on the prevention of cognitive impairment among older people [6].

Today, physical activity is deemed to be a highly protective factor of cognitive functions in normal brain aging, as well as in several stages of pathology-related cognitive deterioration [8,9]. Regular physical exercise has been associated with an increased brain volume of regions related to cognitive functions, which normally decline with age [10].

ÚltimLamente, el entrenamiento de tely, high-intensity intervalos de alta intensidad training (HIIT, por sus siglas en inglés) ha llamado la atención como una buena opción de ejercicio tanto para la población joven como para la adulta. Este tipo de ejercicio se c) has gained attention as a good exercise option for both the young and adult population. This type of exercise is characteriza por sesiones breves e ed by short, intermitentes de actividad de altattent sessions of high intensidadty activity alternadas conted with periodos de descanso o de baja s of rest or low intensidad. El número de estudios que ty. The number of studies investigan este tipo de entrenamiento en la población mayor se hating this type of training in the elderly population has incrementado en los últimos añoased in recent years [ 2 , 11 , 12 ]. UAna alternativa ale to HIIT es el entrenamiento funcional de alta intensidadis high-intensity functional training (HIFT, por sus siglas en inglés), una ), a relatively new training modalidad de entrenamiento relativamente nueva que enfatiza los movimientos funcionales de múltiples articulaciones que se pueden adaptar a cualquier nivel de condición física y conducen a un mayor reclutamiento muscular que las formas de ejercicio más tradicionales. Las sesiones de HIFT pueden durar desde dosty that emphasizes multi-joint functional movements that can be adapted to any fitness level and lead to greater muscle recruitment than more traditional forms of exercise. HIFT sessions can last anywhere from two minutos hasta más de una horaes to over an hour [ 13 ]. SeIt diferencia delffers from HIIT en el uso de ejercicios funcionales constantemente variados y in the use of constantly varied functional exercises and actividades dties of adaptable duración adaptable que pueden o notion that may or may not incorporar pausaste breaks. [ 14 ]. HIFT empleaoys múultiples vías de energía a través de la utilización de ejercicio energy pathways through the use of multimodal exercise [ 15]. Duebido a los mú to the multiples esquemas de prescripción relacionados con las tion schemes related to repeticiones y duraciones de los ejercicios etions and exercise durations in HIFT, los programas pueden variar desde ejercicios de peso corporal realizados es can range from bodyweight exercises performed in circuitos o is or timed intervalos cronometrados hasta esquemas más s to more complicados queted schemes involucran levantamientos olímpicos, con un número determinado de ving Olympic lifts, with a set number of repeticionetions [ 13 ]. Although HIIT AND HIFT share many similarities, they differ in that HIIT uses only aerobic exercises performed at very high intensity without variation [16], whereas HIFT uses constantly varied high-intensity functional and muscle-strengthening exercises of varying durations that may or may not incorporate breaks [14]. Similarly, studies suggest that HIFT is more effective than HIIT in increasing strength [17] and adherence to exercise [15,18], and strength training increases brain-derived neurotrophic factor [19] and IGF-1, [20] myokines important in cognition to a greater extent.

2. High-Intensity Functional Training in Elderly with Cognitive Impairment

Evidence exists of the benefits of HIFT on general cognition in older adults with cognitive impairment, assessed using the MMSE, the ADAS-cog, or both. Two articles that showed improvement in cognitive function used progressive HIFT with 80% RM at 6, 12, and 18 weeks; on the other hand, studies with HIFT interventions at intensities of 12 RM find no significant differences at 3, 4, 6, 7 or at 12 months. However, due to the heterogeneity of intervention protocols, measurement time points, and control group activities, divergent results were evidenced. It is still necessary to determine the modality (load and duration) that guarantees the effectiveness of the intervention. Khandker et al. [43], evaluated the comparability of ADAS-cog and MMSE, finding a significant association between MMSE and ADAS-cog (p < 0.001, R2 = 0.561, in 813 patients and 1520 MMSE/ADAS-cog paired measurements) where increases by 2.01 points (95% CI [1.90, 2.11]) of ADAS-cog were associated with decreases by one point for MMSE. Furthermore, variability in the HIFT protocols were identified, which was expected because this training modality uses constantly varied, multi-joint exercises of varying duration, with or without rest periods [14]. Two articles [34,37] used intensity-based prescription (%1 RM), while the remaining five articles [35,36,38,39] used a volume measure (the number of repetitions). Despite these two measures usually being correlated, recent research has raised doubts about the accuracy of this correlation [45]. It has been reported that the amount of muscle mass used during exercise influences the number of repetitions performed at a given percentage of 1 RM [46]. Likewise, intensity (expressed as %1 RM) and volume (expressed as the number of repetitions), when used as the only measures of training load control, are insufficient to correctly prescribe this type of training, as it is necessary to control variables such as inter-set recovery duration [47], the predominance of the eccentric or concentric phase [48], and speed of execution [49]. These variations influence force production and other hormonal [49] and neuromuscular responses [50]. In addition, there is evidence for a positive association between movement speed and cognition in older adults [51], and it has been reported that a greater cognitive load is required in eccentric-predominant exercises compared to concentric-predominant ones [52]. On the other hand, some differences found in the load progression strategies should be pointed out, which could induce different adaptations with respect to load volume [53]. In the strategy used by Gbiri et al. [34] the rate of execution of the exercises was monitored, increasing by 10% every 2 weeks. Additionally, the same authors reported an initial measure of the load equal to 80% RM, with no progressions in this regard.  PorOn the otro lado, aunque los her hand, although the beneficios del ejercicio sobre la funciónts of exercise on cognitiva están biene function are well documentadosed [ 54 , 55 , 56 ], una revisión reciente y un metanálicent review and meta-analysis revelaron que no hubo un efecto beneficioso de lasaled no beneficial effect of HIIT-only intervenciones basadas exclusivamente en HIIT sobre el funcionamiento cognitivo de personas contions on cognitive functioning in people with demenctia [ 57 ]. Por elIn contrario, se ha informado que losst, functional exercise-based programas basados ​​en ejercicio funcional pueden tener ciertos efectos positivos sobre la función cognitiva ens have been reported to have some positive effects on cognitive function in older adultos mayores con deterioros with mild cognitivo leve (DCLe impairment (MCI) [ 58]. AIn addemásition, HIFT ha sidos been administrado aered to older adultos mayores con demencias with moderada ate to severa en hogares de ancianoe dementia in nursing homes, generando en esta población alegría y redescubrimiento de competencias corporales, así como unating in this population joy and rediscovery of bodily skills, as well as a safe adherencia segura a las actividades y comprensión de los objetivos de los ejercicioe to activities and understanding of the objectives of the exercises [ 59 ]. AsLimismo, la akewise, the applicabilidad de este tipo de ty of this type of intervenciones se ha tion has been successfully evaluado con éxito eted in relación con lation to the intensidad del ejercicio alcanzadoty of exercise achieved [ 60 ]. Sin Howevembargo, losr, the resultados sobre el efecto des on the effect of HIFT en laon general cognición general son variados y en algunos casotion are varied and in some cases contradictoriosy. EIt is importante recalcar que aún se necesitan más estudios que realicen un mejor seguimiento de las actividades en el grupo to emphasize that more studies are still needed to better monitor the activities in the control, así como la e group, as well as the standarización de udization of an instrumento utilizado para evaluar la used to assess general cognición general y un diseño más riguroso de lation and a more rigorous design of the intervención. Dicho diseño debetion. This design must considerar, por ejemplo, la velocidad de ejecución del ejercicio, el tipo de , for example, the speed of execution of the exercise, the type of contracciótion (concéntrica o excéntrica) y el período de recuperación entreentric or eccentric) and the recovery period between series. Solo así sería poOnly in this way would it be possible conocer con to know precisión los posibles efectoely the possible effects inducidos por laed by the intervención y su duración en el tiempo. Se requiere la ution and their duration over time. Unificación detion of conceptos tanto en las in both intervención como en la medición de lastion and measurement variables en los ECA para diin RCTs is required to elucidar los efectos delte the effects of HIFT sobre laon general cognición general en adultos mayores con deteriorotion in older adults with mild to moderate cognitivo leve a moderadoe impairment.