SAlgunome of the mosts de los cambios más significant changes facing the world population are the increase in the number andtivos a los que se enfrenta la población mundial son el aumento del número y la proportion of older people ^[1]ción de personas mayores [ 1 ] y land the progression of life expectancy to older agesión de la esperanza de vida a edades más avanzadas [ 2 ^[1]]. El Cdeterioro cognitive impairment is a poso es una posible consequence of the aging cuencia del process, since from the third decade of life the brain begins to atrophy, reducing its bloodo de envejecimiento, ya que a partir de la tercera década de la vida el cerebro comienza a atrofiarse, disminuyendo su riego sanguíneo y su peso [ 3 ]. flEstow and weight afecta ^[2].en This greatly affects the functioning of the central nervous systeman medida el funcionamiento del sistema nervioso central [ 1 ^[1]], producieng loss ofdo pérdida de memory, attentioia, atención, reduced learningcción de la capacity and dad de aprendizaje y deterioration of o de las funciones cognitiveas [ 4 functions, ^[3][4]5]. ThiEs decline is associated with an increased risk ofta disminución se asocia con un mayor riesgo de dementcia, as well aí como con resultados adverse health outcomes such asos para la salud, como limitaciones functional limitations and disabilityionales y discapacidad [ 6 ^[5]].

The burden on health systems caused by dementia and other adverse cognitive outcomes has become a major social challenge with great added financial costs ^[6][7]. New methods are required in order to prevent losses and even improve cognitive performance, functionality, autonomy, and quality of life in general ^[5][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 ^[5][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 ^[7][8][8,9]. Regular physical exercise has been associated with an increased brain volume of regions related to cognitive functions, which normally decline with age ^[9][10].

LÚltimately, high-intensitymente, el entrenamiento de interval trainingos de alta intensidad (HIIT) has gained attention as a good exercise option for both the young and, por sus siglas en inglés) ha llamado la atención como una buena opción de ejercicio tanto para la población joven como para la adult population. This type of exercise is cha. Este tipo de ejercicio se caracterized by short,a por sesiones breves e intermittent sessions of hightentes de actividad de alta intensity activitydad alternated withdas con periods of rest or lowos de descanso o de baja intensity. The number of studiesdad. El número de estudios que investigating this type of training in the elderly population hasn este tipo de entrenamiento en la población mayor se ha increased in recent yearmentado en los últimos años ^[10][11][12][ 2 , 11 , 12 ]. AUna alternative toa al HIIT is high-intensity functes el entrenamiento funcional trainingde alta intensidad (HIFT), a relatively new training, por sus siglas en inglés), una modality that emphasizes multi-joint functional movements that can bedad de entrenamiento relativamente nueva que enfatiza los movimientos funcionales de múltiples articulaciones que se pueden adapted to any fitness level and lead to greater muscle recruitment than more traditional forms of exercise. HIFT sessions can last anywhere from two minutes to over an hourar 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 dos minutos hasta más de una hora ^[13][ 13 ]. ItSe differs fromerencia del HIIT in the use ofen el uso de ejercicios funcionales constantly varied functional exercises and activities of emente variados y actividades de duración adaptable duration that may or may notque pueden o no incorporate breaks.r pausas [ 14 ^[14]]. HIFT employsea muúltiple energy pathways through the use ofs vías de energía a través de la utilización de ejercicio multimodal exercise ^[15][ 15]. Due to the mubido a los múltiple s esquemas de prescription schemes related to ción relacionados con las repetitions and exercise durations iciones y duraciones de los ejercicios en HIFT, los programs can range from bodyweight exercises performed ias pueden variar desde ejercicios de peso corporal realizados en circuits or timed ios o intervals to moreos cronometrados hasta esquemas más complicated schemesdos que involving Olympic lifts, with a set number ofucran levantamientos olímpicos, con un número determinado de repetitionsciones [ 13 ^[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][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 woarkticles 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. ^[21][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 woarkticles ^[22][23][34,37] used intensity-based prescription (%1 RM), while the remaining five woarkticles ^{[24][25][26][27]}[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 ^[28][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 ^[29][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 ^[30][47], the predominance of the eccentric or concentric phase ^[31][48], and speed of execution ^[32][49]. These variations influence force production and other hormonal ^[32][49] and neuromuscular responses ^[33][50]. In addition, there is evidence for a positive association between movement speed and cognition in older adults ^[34][51], and it has been reported that a greater cognitive load is required in eccentric-predominant exercises compared to concentric-predominant ones ^[35][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 ^[36][53]. In the strategy used by Gbiri et al. ^[22][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.  OnPor the other hand, although the otro lado, aunque los benefits of exercise ocios del ejercicio sobre la función cognitive function are well a están bien documentedados [ 54 ^[37][38][39], 55 , 56 ], una recent work revealed no bevisión reciente y un metanálisis revelaron que no hubo un efecto beneficial effect of HIIT-onlyoso de las interventions on cognitive functioning in people withciones basadas exclusivamente en HIIT sobre el funcionamiento cognitivo de personas con dementiacia [ ^[40]57 ]. InPor el contrast, functional exercise-basedrio, se ha informado que los programs have been reported to have some positive effects on cognitive function in olderas basados ​​en ejercicio funcional pueden tener ciertos efectos positivos sobre la función cognitiva en adults with mildos mayores con deterioro cognitive impairment (MCIo leve (DCL) ^[41][ 58]. In aAdditionemás, HIFT has been sido administered to olderrado a adults withos mayores con demencia moderate toada a severe dementia in nursing homea en hogares de ancianos, generating in this population joy and rediscovery of bodily skills, as well as a safendo en esta población alegría y redescubrimiento de competencias corporales, así como una adherence toia segura a las activities and understanding of the objectives of the exercisesdades y comprensión de los objetivos de los ejercicios [ 59 ^[42]]. LAsikewise, the apmismo, la aplicability of this type of dad de este tipo de intervention has been successfullyciones se ha evaluated ido con éxito en relation to theción con la intensity of exercise achieveddad del ejercicio alcanzado [ ^[43]60 ]. HowSin ever, thembargo, los results on the effect ofados sobre el efecto de HIFT onen la cognición general cognition are varied and in some caseson variados y en algunos casos contradictoryios. It iEs important to emphasize that more studies are still needed to better monitor the activities in the e recalcar que aún se necesitan más estudios que realicen un mejor seguimiento de las actividades en el grupo control group, as well as the , así como la estandardization of aización de un instrument used to assess generalo utilizado para evaluar la cognition and a more rigorous design of the ción general y un diseño más riguroso de la intervention. This design mustción. Dicho diseño debe consider, for example, the speed of execution of the exercise, the type of ar, por ejemplo, la velocidad de ejecución del ejercicio, el tipo de contractiocción (concentric or eccentric) and the recovery period betweenéntrica o excéntrica) y el período de recuperación entre series. Only in this way would it be possible to knowSolo así sería posible conocer con precisely the possible effectión los posibles efectos induced by theidos por la intervention and their duration over time. Ución y su duración en el tiempo. Se requiere la unification ofción de concepts in bothos tanto en la intervention and measurementción como en la medición de las variables in RCTs is required to een los ECA para dilucidate the effects ofr los efectos del HIFT on generalsobre la cognition in olderción general en adults with mild to moderateos mayores con deterioro cognitive impairmento leve a moderado.