The effects of an ultra-endurance event on heart rate variability and cognitive performance during induced stress in Ironman triathletes

Includes abstract.Includes bibliographical references (leaves 55-79).The effects of long-term participation in ultra-endurance exercise on the cardiovascular system have recently been the subject of much interest. It is well known that HRV, a marker of autonomic activity, is enhanced with long-term aerobic exercise training. However, after acute exercise, HRV is reduced, but recovers over time depending on the intensity of the prior bout of exercise. A limitation of previous research is that exercise bouts of only up to 120 minutes have been studied. A modified Stroop Task is a laboratory stressor to assess executive cognitive function by means of reaction time and accuracy. The resting HRV is directly related to these prefrontal neural functions, but the effect of an altered HRV on cognitive function has never been investigated. We determined the effects of an ultra duration (10 – 15 hours) exercise event on parameters of HRV and cognitive function during a Modified Stroop Task, 60 – 200 minutes after the 2007 South African Ironman Triathlon event (3,6km swim; 180 Km cycle; 42,2 Km run). 1 Female and 13 male competing triathletes (IRON; ages 33.7±7.9) and 7 control subjects (CON; 2 female and 5 males aged 42 ±4.5) completed a Modified Stroop Task before and after the event. The individual HRV parameters, heart rate (HR), respiratory frequency (RF), reaction time (RT) and % of mistakes made were recorded via the Biopac MP150WSW System (Goletta, California, USA). Data was transformed by auto regressive analyses (Biomedical signal analysis group, University of Kuopio, Finland) into LF (0.04 - 0.15 Hz) and HF (0.15 - 0.5 Hz) components. Additional calculations included %LF and %HF as well as the central or peak frequencies in both the LF and HF bands

Acute and chronic effects of exercise in adults with Down syndrome

Doutoramento em Motricidade Humana na especialidade de Ciências da Motricidade.This thesis intended to explore both the acute and chronic physiological adaptations of persons with Down syndrome (DS) in response to exercise. Specifically, in terms of acute exercise responses, we aimed at investigating the submaximal exercise capacity and cardiac autonomic function of adults with and without DS. Subsequently, we determined whether 12 weeks of exercise training were effective in improving exercise capacity (economy and peak oxygen uptake – VO2peak) and autonomic function both in adults with and without DS. Overall, we found that the submaximal exercise capacity of adults with DS was characterized by poor walking economy, but appropriate VO2 kinetics. As importantly, these individuals demonstrated reduced cardiac responsiveness to changes in the sympathovagal balance resulting from submaximal dynamic exercise. Findings also indicated a breakdown in their fractal scaling properties of heart rate dynamics that was transversal to resting, exercise and post-exercise recovery conditions. Moreover, compared to nondisabled participants, adults with DS showed reduced cardiodeceleration during recovery from peak exercise intensities. Finally, in general terms, a combined exercise regimen resulted in gains of similar magnitude between participants with and without DS for submaximal exercise capacity and cardiac autonomic function. In conclusion, this thesis provides evidence that persons with DS have reduced submaximal exercise capacity and that this is paired by disturbed autonomic function. Nevertheless, these results also indicate that exercise training is an effective intervention for improving their physiological function in similar magnitude as in adults without DS.FCT - Fundação para a Ciência e a Tecnologia.PIDDAC, SFRH/BD/45896/200

Associations Between Heart Rate Variability and Metabolic Syndrome Risk Factors

Metabolic syndrome (MetS) is a clustering of risk factors for cardiovascular disease (CVD) and type 2 diabetes (T2D) – two major causes of morbidity and mortality worldwide. Heart rate variability (HRV) is a non-invasive measure of cardiac autonomic regulation that predicts mortality and morbidity. Additionally, HRV is reduced in CVD, T2D and MetS. As such, HRV has potential to be a novel cardiometabolic risk factor to be included in clinical risk assessment. Therefore, the purpose of this thesis was to examine the relationships between MetS and HRV. A systematic review of cross-sectional studies examining relationships between HRV and MetS was completed to consolidate existing evidence and to guide future studies. This was followed by a cross-sectional investigation of time and frequency domain and nonlinear HRV in a population with MetS risk factors to determine which MetS risk factors were associated with HRV parameters. A pilot study was then conducted to study the feasibility of conducting a mobile health (mHealth) and exercise intervention in a rural population, which was followed by a 24-week randomized clinical trial to examine the effects of the interactive mHealth exercise intervention compared to standard of care exercise in participants with MetS risk factors. Overall, HRV was reduced in women with MetS compared to those without, though there were no differences in men. Waist circumference and lipid profiles were most commonly related to HRV parameters when studied cross-sectionally. The changes in waist circumference and fasting plasma glucose were associated with the change in HRV parameters when studied longitudinally. Following the intervention period, waist circumference and blood pressure were improved with no other changes in MetS risk factors. HRV parameters indicative of vagal activity were reduced over the intervention period, but there were no changes in other HRV parameters. There were no differences in changes between the intervention and control groups. In conclusion, MetS and HRV are associated in women but not men. However, there were no clear associations between MetS and HRV to suggest that HRV would be a valuable clinical risk factor

The Effect of a Square-Stepping Exercise Intervention on Heart Rate Variability in Older Individuals with Type 2 Diabetes and Subjective Cognitive Complaints

Aging is associated with increased onset of diseases such as type 2 diabetes (T2D) and cognitive impairment. Heart rate variability (HRV), a measure of autonomic function, is reduced in T2D and may have the potential to indicate cognitive decline in this population. Square-stepping exercise (SSE) is a novel cognitive exercise recently implemented in cognitive research, which may have the potential to improve global cognitive function in T2D individuals. Participants with T2D (N=25, aged ≥ 50y) and self-reported cognitive complaints were randomized into either an SSE intervention or a wait-list (WL) control group for 24-weeks. HRV parameters (time and frequency domain) and GCF domains were assessed at baseline and 24-weeks. No significant differences were found in HRV parameters between groups at baseline and 24-weeks. However, heart rate was significantly reduced from baseline to 24-weeks in the SSE group, p = 0.046. Additionally, low and high frequency power were significantly decreased from baseline to 24-weeks in the WL group, p = 0.05 and p = 0.043 respectively. This study elucidates the impact of cognitive exercise training on HRV, however, it is inconclusive as to why a shift towards vagal modulation was observed in both the SSE and WL groups

The effects of aerobic interval training on heart rate recovery after cardiac resynchronization therapy

Background: Heart failure is characterized by an autonomic nervous system dysfunction which leads to sympathetic overactivation and parasympathetic imbalance, culminating in central and peripheral dysfunction. In advanced HF, cardiac resynchronization therapy (CRT) and exercise training seem toimprove these conditions and result in improved functional and clinical parameters. A growing body of evidence supports the benefits of aerobic interval training (AIT) in other several HF populations, but less is known about its influence on autonomic function. Here we assessed the effects of AIT on the heart rate recovery (HRR), an indicator of parasympathetic activity. All participants had HF with a reduced ejection fraction, and six days before the intervention, underwent cardiac surgery. Our objective was to compare if the additive effect of AIT to CRT could indeed result in improved vagal reactivation, measured by the difference between the peak heart rate and the HRR at one minute (HRR1diff). Methods: Twenty-nine stable patients (aged 68.96 ± 9.92; VEF< 27 ; and a V O2Peak= 15 mL.kg-1.min-1) who were receiving optimal medical treatment, were randomized either to the control group, or the AIT group. The AIT group exercised twice a week, and began each session with a 10 minute warm-up (50-60% of the peak heart rate), followed by four intervals of 2-minutes (90-95% of the peak heart rate) and a 2-minute recovery (60-70% of the peak heart rate). After the first month, the 2-minute intervals were changed to 4-minute intervals and 3-minutes recovery. After cardiopulmonary exercise testing (CPET) to maximal volitional exertion, using the modified Bruce protocol, patients were seated and the HRR was immediately assessed. Results: After the six months of intervention our main effects were significant for V O2Peak (p= .010) and CPET duration (p= .025). Thus, after testing for simple main effects, only the AIT group depicted significant changes in the post-intervention for: V O2Peak (p= .013), CPET duration (p= .020), heart rate reserve (p= .035), peak pulse pressure (p= .036), and the HRR1diff (p= .025). Conclusions: After six months of intervention, the simple main effects suggest that AIT could improve vagal reactivation, assessed through HRR1diff, in patients that underwent CRT and were engaged in optimal medical treatment. Our findings also suggest that differences between groups in exercise capacity could be due to peripheral factors.Contexto: A insuficiência cardíaca (IC) é caraterizada por uma disfunção do sistema nervoso autónomo (SNA) que conduz a uma hiperativação simpática e desiquilíbrio parassimpático, culminando em disfunções centrais e periféricas. Nos casos mais avançados de IC, a terapêutica de ressincronização cardíaca (TRC) e o exercício parecem melhorar estas condições e, outros parâmetros clínicos e funcionais. O emergir de evidência robusta valoriza o treino intervalado aeróbio (TIA) em várias populações com IC, sabendo-se pouco acerca da sua influência sobre o SNA. Nesta análise, avaliámos os efeitos do TIA sobre a frequência cardíaca de recuperação (FCR), um indicador de ativação parasimpática. Todos os participantes possuíam uma fração de ejeção diminuída para ventrículo esquerdo, e colocaram o implante cardíaco seis dias antes do início da intervenção. O nosso objetivo foi o de avaliar se o TIA adicionado à TRC poderia melhorar a reativação vagal, medida pela diferença entre a frequência cardíaca pico e a FCR no primeiro minuto (FCR1dif). Métodos: Vinte e nove participantes idade 68 96 9 92; FEVE< 27 ; e o V O2Pico= 15 mL.kg-1.min-1) que estavam a receber tratamento médico otimizado (TMO), foram randomizados diferencialmente para os grupos de TIA e de controlo. O grupo de TIA realizou duas sessões de treino semanais, iniciando as mesmas com 10 minutos de aquecimento (50 a 60% da FC pico), seguido de quatro intervalos de 2 minutos (90 a 95% da FC pico) e 2 minutos de recuperação ativa (60 a 70% da FC pico). Depois de concluído o segundo mês, os intervalos de 2 minutos foram substituídos por intervalos de 4 minutos, enquanto os intervalos de recuperação por outros de 3 minutos. Recorrendo à prova de stress cardiopulmonar (PSCP), a qual foi efetuada até a capacidade volitiva máxima usando o protocolo de Bruce modificado, a FCR foi avaliada imediatamente a seguir ao mesmo. Resultados: A seguir aos seis meses de interven o, os efeitos principais foram significativos para V O2Pico (p= .010) e a duração da PSCP (p= .025). Contudo, depois de se testarem os simple main effects, apenas o grupo de TIA apresentou altera es significativas no per odo pós-interven o para: V O2Pico (p= .013), duração da PSCP (p= .020), frequência cardíaca de reserva (p= .035), pressão de pulso pico (p= .036), e FCR1dif (p= .025). Conclusões: Depois de seis meses de intervenção, os simple main effects sugerem-nos que o TIA pode melhorar a reativação vagal, medida pela FCR1dif a seguir ao exercício em pacientes que se encontram em TRC e TMO. Os resultados sugerem-nos ainda que as diferenças encontradas na capacidade funcional devem-se a fatores periféricos

Acute Effects of Exercise Modes on Arterial Stiffness and Cardiac Autonomic Function in Healthy Young and Middle-Aged Adults

Os efeitos agudos do exercício na rigidez arterial (RA), variabilidade da frequência cardíaca (VFC) e sensibilidade barorreflexa (BRS) têm sido estudados nos últimos anos através de modelos laboratoriais de exercício. Atendendo ao facto de que a participação em aulas de ginástica em grupo é cada vez mais frequente de se manter fisicamente ativo, é importante examinar se os resultados são transferíveis entre modelos laboratoriais e ecológicos do exercício. O objetivo deste estudo foi comparar o período de tempo de reativação parassimpática pós-exercício do coração e alterações nos índices locais e regionais da RA para diferentes classes de condicionamento físico (Bike, Pump Power e Global Training). A intervenção incluiu 24 adultos jovens e de meia-idade (entre 24 e 55 anos). As medidas ocorreram 20 minutos antes de cada aula, com os participantes em posição supina para mensuração do GER por calorimetria indireta (K5, Cosmed, Roma, Itália), em intervalos de 10, 20 e 30 minutos após cada aula. Em conclusão, mudanças no pós-exercício foram dependentes da idade, segmento anatômico e o ponto de tempo medido. Nosso estudo sugere que as evidências de ambientes laboratoriais sobre os efeitos agudos do exercício em RA, VFC e BRS não podem ser totalmente transpostas para ambientes ecológicos.The acute effects of exercise on arterial stiffness (AS), heart rate variability (HRV), and baroreflex sensitivity (BRS) have been studied over the last few years in laboratorial models of exercise. In view of the fact that participation in group fitness classes is an increasingly popular way to stay physically active, it is important to examine whether findings are transferable between laboratorial and ecological models of exercise. The aim of this study was to compare time periods of post-exercise parasympathetic reactivation of the heart, and changes in local and regional indices of AS, between different fitness classes (Bike, Pump Power and Global Training), as prescribed for health and commercially available. The intervention included 24 young and middle-aged adults (from 24 to 55 years old). The measurements took place 20 minutes before each fitness class, with participants in supine rest for the measurement of the REE by indirect calorimetry (K5, Cosmed, Rome, Italy), in intervals of 10, 20, and 30 minutes after each fitness class. Overall, changes in post-exercise responses were found to be dependent on age, anatomical segments and time measurements. Our study suggests that evidence from laboratorial settings on the acute effects of exercise in AS, HRV and BRS cannot be fully transposed to more ecological settings

Methodological factors in measuring heart rate-based indices and effect of exercise-based cardiac rehabilitation on mortality predictors: from athletes to patients

Background: Parasympathetic nervous system (PNS) activity can be indirectly assessed by heart rate (HR)-based indices (i.e., resting HR, resting vagal-related HR variability [HRV] indices, and post-exercise HR recovery 1 min [HRR 1 min]). Decreased PNS activity is considered an independent mortality predictor. In the same vein, cardiorespiratory fitness (CRF), assessed by peak oxygen uptake (V̇O2 peak), is also considered an independent mortality predictor. There is evidence showing the positive effect of exercise-based cardiac rehabilitation (CR) on mortality rates in patients with coronary artery disease (CAD). However, the results of previous studies of the effects of exercise-based CR on mortality predictors (i.e., HR-based indices and V̇O2 peak) are controversial. The sparse findings could be due to the influence of methodological factors (e.g., breathing pattern, use of averaged or isolated values, and assessment position) on the sensitivity of HR-based indices to detect PNS hyperactivity, which has mainly been investigated in endurance-trained athletes with functional overreaching (F-OR) symptoms. Moreover, controversial findings about the effects of exercise-based CR on mortality predictors could be explained by the influence of potential moderator variables (e.g., aerobic training method) on the training-induced effect. In this regard, previous systematic reviews with meta-analyses showed that high-intensity interval training (HIIT) enhances V̇O2 peak to a higher extent than moderate continuous training (MCT) in patients with CAD. Nonetheless, there is less evidence of the influence of other variables (e.g., training frequency) on the effect of exercise-based CR on CRF and PNS activity. Finally, high heterogeneity in the individual response to the same predefined training programme has also been previously reported. Therefore, the effects of individualised training programmes based on daily HRV measurements (i.e., HRV-guided training) have been tested in healthy people (i.e., sedentary or physically active people and endurance-trained athletes) and in patients with chronic heart failure, showing optimistic findings for improving CRF. However, the effects of HRV-guided training on HR-based indices have been less studied, and it has not been tested in patients with CAD. Therefore, the main objectives of this doctoral thesis were: a) to study the influence of methodological factors on the sensitivity of HR-based indices for inferring increased PNS activity; and b) to know the effect of exercise-based CR (i.e., predefined training and HRV-guided training) on mortality predictors (i.e., HR-based indices and V̇O2 peak) in patients with CAD. Methods: Systematic reviews with meta-analyses and experimental methods were used to address the aims of this doctoral thesis. Regarding the systematic reviews with meta-analyses, electronic searches were conducted in at least two databases. Selected terms were established based on the PICOS (participants, intervention, comparison, outcomes, and study design) guideline. Random-effects models of standardised mean difference or mean difference were estimated. On the other hand, in the experimental study, male and female adult patients diagnosed with CAD were randomly allocated to the HRV-guided training group (HRV-G = 11) or the predefined training group (PRED-G = 12). All the participants measured their HRV daily at home after waking up and trained three times a week for six weeks. Patients allocated to the HRV-G performed HIIT sessions based on their daily HRV measurements, while those patients allocated to the PRED-G followed a predefined training programme. HR-based indices and V̇O2 peak were assessed before and after the exercise-based CR programme. Regarding vagal-related HRV indices, isolated values were obtained in the time-domain (the root-mean-square difference of successive normal R-R intervals [RMSSD]) and frequency-domain (high frequency [HF]), as well as by using the Poincaré plot method (the standard deviation of the instantaneous beat-to-beat R-R interval variability [SD1]). In addition, daily RMSSD values measured at home across one week were pooled to obtain weekly averaged RMSSD before and after the intervention. Comparisons between the two groups were reported as difference in mean or median changes with 95% confidence interval. Moreover, the effect of exercise-based CR, regardless of the training group, on mortality predictors was also estimated if there was no difference between the two training prescription methods. Results: The first systematic review with meta-analysis showed an increase in averaged vagal-related HRV values (i.e., weekly averaged RMSSD) in F-OR athletes, while no changes in isolated vagal-related HRV indices were noticed. In addition, the results showed increased HRR 1 min in F-OR athletes. The second and third systematic review with meta-analysis showed that exercise-based CR enhances HRR 1 min and V̇O2 peak, respectively, in patients with CAD. The findings also confirmed that HIIT is more effective than MCT for improving V̇O2 peak. Regarding heterogeneity analyses, the training-induced effect on HRR 1 min was higher in studies which included younger patients. The improvement in V̇O2 peak after MCT was larger in studies which performed training sessions on a bicycle, as well as in studies which included patients with worse prognosis (e.g., increased risk of a new event) or lower CRF at baseline. In contrast, the results of the included studies of the effect of exercise-based CR programmes on vagal-related HRV indices (i.e., RMSSD or HF) were controversial. The findings showed an increase in RMSSD after an exercise-based CR programme. Nonetheless, there were no changes in HF, and the results of the included studies were sparse (i.e., high heterogeneity). In addition, no influence of potential moderator variables on the training-induced effect on HF was found. The fourth systematic review with meta-analysis showed that, accounting for methodological factors, HRV-guided training is more effective than predefined training for improving vagal-related HRV indices (i.e., RMSSD and SD1) in healthy people (i.e., sedentary or physically active people and endurance-trained athletes). Nonetheless, no differences were found between HRV-guided training and predefined training for improving CRF. In the same line, the fifth study showed that, taking methodological factors into account, HRV-guided training increases vagal-related HRV indices (i.e., weekly averaged RMSSD) to a greater extent than predefined training in patients with CAD. Regardless of the training prescription method used, the results showed that exercise-based CR enhances resting HR and V̇O2 peak, but not HRR 1 min, in patients with CAD. Conclusions: PNS hyperactivity found in F-OR athletes can be identified by means of HRR 1 min and weekly averaged RMSSD. On the other hand, exercise-based CR is effective for improving PNS tone (i.e., HRR 1 min) and CRF in patients with CAD. Nonetheless, the training-induced effect on PNS modulation is more controversial. Finally, accounting for methodological factors, HRV-guided training seems to be more effective than predefined training for enhancing PNS modulation (e.g., weekly averaged RMSSD) in patients with CAD, as well as in healthy people. The results of this doctoral thesis show the importance of considering methodological factors in measuring vagal-related HRV indices to detect increased PNS modulation, as well as the beneficial effect of exercise-based CR programmes on mortality predictors in patients with CAD.Antecedentes: La actividad parasimpática se puede estimar a partir de los índices basados en la frecuencia cardiaca (HR) (i.e., HR de reposo, índices vagales de la variabilidad de la HR [HRV] en reposo y recuperación de la HR durante el primer minuto post ejercicio [HRR 1 min]). La actividad parasimpática baja se considera un predictor independiente de mortalidad. Igualmente, el fitness cardiorrespiratorio (CRF), medido a través del consumo de oxígeno pico (V̇O2 pico), también se considera un predictor independiente de mortalidad. Existen evidencias acerca del efecto positivo de la rehabilitación cardiaca (CR) basada en el ejercicio físico sobre la mortalidad de pacientes con enfermedad arterial coronaria (CAD). Sin embargo, los resultados de estudios previos sobre el efecto de la CR basada en el ejercicio físico en los predictores de mortalidad (i.e., índices basados en la HR y V̇O2 pico) no son concluyentes. Los resultados contradictorios podrían ser debidos a la influencia de los factores metodológicos (p. ej., frecuencia respiratoria, utilización de valores promediados o puntuales, y posición en la que se lleva a cabo la valoración) sobre la sensibilidad de los índices basados en la HR para detectar los cambios de la actividad parasimpática, lo que ha sido estudiado principalmente en deportistas de resistencia con síntomas de sobrecarga funcional (F-OR). Además, la influencia de potenciales variables moderadoras (p. ej., método de entrenamiento aeróbico) sobre el efecto de la CR basada en el ejercicio físico en los predictores de mortalidad también podría explicar la falta de congruencia de los estudios previos. En relación con esto, revisiones sistemáticas y metaanálisis previos han mostrado que el entrenamiento interválico de alta intensidad (HIIT) es más efectivo que el entrenamiento continuo de moderada intensidad (MCT) para la mejora del V̇O2 pico en pacientes con CAD. Sin embargo, existen menos evidencias acerca de la influencia de otras variables de entrenamiento (p. ej., frecuencia de entrenamiento semanal) sobre el efecto de la CR basada en ejercicio físico en el CRF y la actividad parasimpática. Finalmente, debido a la alta heterogeneidad encontrada en la respuesta individual a un mismo programa de entrenamiento predefinido, estudios previos han analizado el efecto de programas de entrenamiento individualizados en función de los valores diarios de HRV (i.e., entrenamiento guiado por la HRV) en sujetos sanos y pacientes con insuficiencia cardiaca, mostrando resultados positivos para la mejora del V̇O2 pico. Sin embargo, el efecto del entrenamiento guiado por la HRV en los índices basados en la HR ha sido menos estudiado. Además, no se han llevado a cabo estudios que analicen el efecto del entrenamiento guiado por la HRV en los predictores de mortalidad en pacientes con CAD. Por tanto, los principales objetivos de esta tesis doctoral fueron: a) estudiar la influencia de los factores metodológicos sobre la sensibilidad de los índices basados en la HR para detectar los incrementos de actividad parasimpática; y b) conocer el efecto de los programas de CR basados en el ejercicio físico (i.e., entrenamiento predefinido y entrenamiento guiado por la HRV) en los predictores de mortalidad (i.e., índices basados en la HR y V̇O2 pico) en pacientes con CAD. Métodos: Para abordar los objetivos planteados en esta tesis doctoral se utilizaron métodos de revisiones sistemáticas con metaanálisis y métodos experimentales. Respecto a las revisiones sistemáticas con metaanálisis, las búsquedas electrónicas se llevaron a cabo en, al menos, dos bases de datos. Los términos utilizados para llevar a cabo las búsquedas se establecieron según la estrategia PICOS (participants, intervention, comparison, outcomes, and study design). Se utilizó un modelo de efectos aleatorios para la ponderación de la diferencia de medias estandarizada o la diferencia de medias. Respecto al estudio experimental, varones y hembras adultos que habían sido diagnósticos con CAD fueron distribuidos de forma aleatoria en el grupo de entrenamiento guiado por la HRV (HRV-G = 11) o en el grupo de entrenamiento predefinido (PRED-G = 12). Todos los pacientes registraron diariamente su HRV en casa al despertar y entrenaron tres días a la semana durante seis semanas. Los pacientes incluidos en el HRV-G realizaron sesiones de HIIT en función de sus valores diarios de HRV, mientras que aquellos que fueron asignados al PRED-G siguieron un programa de entrenamiento previamente establecido. Antes y después de la intervención se realizaron valoraciones de los índices basados en la HR y el V̇O2 pico. En cada una de las valoraciones se registraron valores puntuales (un registro) de los índices vagales de la HRV en el dominio del tiempo (raíz cuadrada de la media del cuadrado de las diferencias entre intervalos R-R adyacentes [RMSSD]) y de la frecuencia (alta frecuencia [HF]), así como por el método de Poincaré plot (desviación estándar instantánea de la variabilidad del intervalo R-R latido a latido [SD1]). Además, los valores diarios de RMSSD registrados en casa durante una semana se promediaron para obtener el promedio semanal de RMSSD antes y después de la intervención. Las comparaciones entre los dos grupos se reportaron como la diferencia de los cambios medios o medianos con un intervalo de confianza al 95%. Además, en el caso de no encontrar diferencias entre ambos grupos, se estimó el efecto de la CR basada en el ejercicio físico, independientemente del grupo de entrenamiento, en los predictores de mortalidad. Resultados: La primera revisión sistemática con metaanálisis mostró un incremento del promedio semanal de RMSSD en atletas con F-OR. Sin embargo, no se encontraron cambios de los valores puntuales de los índices vagales de la HRV. Además, los resultados de los estudios incluidos mostraron un incremento de la HRR 1 min en atletas con F-OR. La segunda y tercera revisión sistemática con metaanálisis mostraron que la CR basada en el ejercicio físico mejora la HRR 1 min y el V̇O2 pico, respectivamente, en pacientes con CAD. Los resultados confirmaron que el HIIT es más efectivo que el MCT para mejorar el V̇O2 pico. Respecto al análisis de la heterogeneidad, el efecto del entrenamiento sobre la HRR 1 min fue mayor en los estudios que incluyeron pacientes más jóvenes. Por otro lado, el efecto del MCT sobre el V̇O2 pico fue mayor en los estudios en los que las sesiones de entrenamiento se llevaron a cabo en bicicleta, así como en los estudios que incluyeron pacientes con peor pronóstico (p. ej., mayor riesgo de sufrir un nuevo evento) o menor CRF al inicio del estudio. Por el contrario, el efecto de la CR basada en el ejercicio físico sobre los índices vagales de la HRV (i.e., RMSSD o HF) es más controvertido. Los resultados mostraron un incremento de RMSSD tras un periodo de entrenamiento. Sin embargo, no se encontraron cambios en HF y los resultados de los estudios incluidos fueron contradictorios (i.e., alta heterogeneidad). Además, las variables moderadoras analizadas no mostraron influencia en el efecto inducido por el ejercicio físico en HF. La cuarta revisión sistemática con metaanálisis mostró que, considerando factores metodológicos, el entrenamiento guiado por la HRV es más efectivo que el entrenamiento predefinido para la mejora de los índices vagales de la HRV (i.e., RMSSD o SD1) en personas sanas (i.e., sujetos sedentarios, físicamente activos y atletas entrenados en resistencia). Sin embargo, no se encontraron diferencias entre ambos métodos de prescripción del entrenamiento en la mejora del CRF. En la misma línea, el quinto estudio mostró que, considerando factores metodológicos, el entrenamiento guiado por la HRV incrementa los índices vagales de la HRV (i.e., promedio semanal de RMSSD) en mayor medida que el entrenamiento predefinido en pacientes con CAD. Independientemente del método de prescripción del entrenamiento utilizado, los resultados mostraron que la CR basada en el ejercicio físico mejora la HR de reposo y el V̇O2 pico, pero no la HRR 1 min, en pacientes con CAD

The acute and chronic effects of isometric exercise on haemodynamic, autonomic and cardiac function in a pre-hypertensive population

Raised blood pressure (BP) remains the leading modifiable risk factor for cardiovascular disease morbidity and mortality globally. As such, primary prevention strategies are required to improve risk factors to prevent the development of hypertension (HTN). Isometric exercise training (IET) is becoming an established intervention for reducing resting BP. However, few studies have investigated the effects of IET in a population at increased risk of developing HTN. Therefore, this thesis examined the effects of IET, using a novel home-based wall squat intervention, in a pre-hypertensive male population. Specifically, the thesis aimed to explore the potential mechanism/s responsible for improved BP control using an acute isometric exercise (IE) stimuli and a four-week IET intervention. Firstly, acute IE was shown to elicit a step-wise increase in BP, heart rate and cardiac output and associated increase in sympathetic activity. In the immediate recovery period, there was a hypotensiveresponse, which was associated with parasympathetic activation, increased baroreceptor reflex control and reduced peripheral vascular resistance. The hypotensive response was also associated with improved indices of cardiac function, including a reduced estimated filling pressure. Four weeks of IET was shown to significantly reduce resting and ambulatory BP. Improved autonomic cardiovascular control, with increased parasympathetic over sympathetic activity, greater baroreceptor reflex sensitivity and reduced peripheral vascular resistance potentially mediated the decreased BP. A reduction in plasma interleukin-6 and asymmetric dimethylarginine suggests an anti-inflammatory response and improved vascular function, respectively, following IET. Finally, improved myocardial diastolic function suggests positive cardiac adaptations in response to BP reductions. Collectively, the findings of this thesis highlight potential mechanistic pathways for improved BP control in a prehypertensive population and demonstrates wider cardiovascular benefits of IET beyond BP reductions, which are important observations for risk reduction in this population

Red beetroot extract accelerates recovery of nonlinear dynamics of heart rate variability following exercise: A randomized trial

Introduction: Studying the behavior on nonlinear HRV indexes in situations mediated by exercise may reveal other ways to analyze HRV recovery after stress situations. To investigate the acute effects of beet extract on autonomic recovery following an acute resistance exercise session. Methods: This is a randomized, crossover, double-blind and placebo-controlled trial. We assessed 12 healthy male adults who participated in two protocols in randomized days: Beetroot extract (600mg in capsule) and Placebo (600mg in capsule). Both protocols were applied 120 minutes prior to an exercise resistance session (75% 1RM). Nonlinear dynamics of HRV (Symbolic analysis, SampEn, DFA and HR fragmentation) were studied before, during exercise and during recovery from strength exercise. Results: Beetroot extract protocol intensified the recovery of the symbolic analysis of HRV via index 0V% (zero opposite variations) and 2UV% (two unlike variations); accelerating the recovery of fractal analysis (DFA); nevertheless, it was unable to trigger changes during recovery in SampEn and HR fragmentation. Conclusion: Ingestion of beetroot extract prior to resistance exercise improves nonlinear HRV dynamical autonomic recovery following physical effort

Red beetroot extract accelerates recovery of nonlinear dynamics of heart rate variability following exercise : a randomized trial

Introduction: Studying the behavior on nonlinear HRV indexes in situations mediated by exercise may reveal other ways to analyze HRV recovery after stress situations. To investigate the acute effects of beet extract on autonomic recovery following an acute resistance exercise session. Methods: This is a randomized, crossover, double-blind and placebo-controlled trial. We assessed 12 healthy male adults who participated in two protocols in randomized days: Beetroot extract (600mg in capsule) and Placebo (600mg in capsule). Both protocols were applied 120 minutes prior to an exercise resistance session (75% 1RM). Nonlinear dynamics of HRV (Symbolic analysis, SampEn, DFA and HR fragmentation) were studied before, during exercise and during recovery from strength exercise. Results: Beetroot extract protocol intensified the recovery of the symbolic analysis of HRV via index 0V% (zero opposite variations) and 2UV% (two unlike variations); accelerating the recovery of fractal analysis (DFA); nevertheless, it was unable to trigger changes during recovery in SampEn and HR fragmentation. Conclusion: Ingestion of beetroot extract prior to resistance exercise improves nonlinear HRV dynamical autonomic recovery following physical effort