Effects of resistance training and HIIT on physical function, body composition, and blood pressure in older adults with cardiometabolic risk: an analysis of interindividual variability and temporal adaptation dynamics

Physical inactivity is a critical risk factor in the development of multiple cardiometabolic conditions, including hypertension, type 2 diabetes, dyslipidemia, and obesity. At the muscular level, it promotes insulin resistance and ectopic fat accumulation, contributing to the age-related decline in physical fitness. In contrast, structured physical exercise is a non-pharmacological strategy capable of reversing these processes by improving body composition, muscular strength, and blood pressure. However, there is significant interindividual variability in response to exercise, which limits the effectiveness of generalized programs and underscores the need for personalized exercise prescriptions. Furthermore, physiological adaptations to exercise do not occur simultaneously or uniformly. Temporal dynamics of adaptation differ according to the biological system involved, training modality, and individual characteristics. Understanding how these responses vary over time and between individuals is essential for optimizing clinical interventions and promoting healthy aging, particularly among individuals with cardiometabolic risk. In this context, the present doctoral thesis includes two studies derived from a randomized controlled trial (NCT06201273), aimed at evaluating the effects of eight weeks of high-intensity interval training (HIIT) and resistance training (RT) using elastic bands in older adults with cardiometabolic risk factors. Changes in physiological and functional variables—such as blood pressure, body composition, isometric strength, and functional capacity—were analyzed, along with interindividual variability in response and the temporal evolution of these adaptations. Participants were classified as responders or non-responders based on individual response thresholds, enabling the characterization of both the magnitude and trajectory of exercise-induced effects. This thesis is based on two scientific studies that have been published in international peer-reviewed journals. In the first study (Chapter 1), the objective was to assess the effects of two low-volume exercise protocols—resistance training with elastic bands and high-intensity interval training using cycle ergometers—on systolic (SBP) and diastolic (DBP) blood pressure in hypertensive older adults undergoing pharmacological treatment. The intervention lasted eight weeks, with evaluations at baseline, week 4, and week 8. Specifically, the aims were to (1) evaluate the blood pressure-lowering effects of RT and HIIT at four and eight weeks, (2) compare the effectiveness of both modalities in reducing the proportion of non-responders (NRs), (3) examine the time-course adaptations in SBP and DBP among responders (Rs) and NRs, and (4) document changes in clinical blood pressure classification over the course of the intervention. In the second study (Chapter 2), the objective was to investigate the effects of two low-volume exercise protocols—RT and HIIT—on body composition, isometric muscle strength, and functional capacity (assessed using the six-minute walk test, 6MWT) in older women with impaired cardiometabolic health. Specifically, the study aimed to (1) assess outcomes after eight weeks of training, (2) compare the effectiveness of RT and HIIT in reducing the proportion of NRs between weeks four and eight, and (3) explore the temporal dynamics of physiological and functional adaptation among Rs and NRs.