ECSS Paris 2023: CP-PN09
INTRODUCTION: Current guidelines for exercise include recommendations about Frequency, Intensity, Time (duration), and Type of exercise (FITT), but not for time of the day. This is surprising considering the well-known impact of the circadian timing system on human health [1] and the well-documented diurnal variations in peak oxygen uptake (VO2peak) [2] as well as many other physiological outcomes. A recent meta-analysis [3] showed that to this date no study has investigated the effect of exercising around noon or the late evening on VO2peak. While some studies have investigated the effect of exercising in the morning or afternoon, they show several methodological limitations. The aim of this study was to investigate the effect of exercising at different times of the day on VO2peak. METHODS: Participants completed cardiopulmonary exercise tests using a ramp protocol on a cycle ergometer to determine VO2peak before being randomly allocated to an exercise time at which they exercised three times a week for 12 weeks. Exercise times were 8:00, 12:00, 16:00 or 20:00. Nutrition, sleep and physical activity were closely monitored during the intervention period to control for confounding factors. The same exercise test was done after the intervention to compare post-intervention VO2peak values between the four groups adjusted for baseline values using analysis of covariance. VO2peak was confirmed using pre-specified verified criteria for RERmax in those participants that did not show a VO2-plateau. RESULTS: Participants’ (n=59, 42% female) mean (standard deviation – SD) age was 68.3 (4.9) years and body mass index was 24.2 (2.9) kg/m2. Baseline VO2peak (mL/kg/min) values of the groups were 29.4 (6.9) for 8:00, 32.3 (5.2) for 12:00, 29.2 (5.6) for 16:00, and 32.5 (5.8) for 20:00, respectively. The observed mean differences (mL/kg/min) (95% confidence interval [95%CI]) for exercising at 8:00 compared to 12:00, 16:00, and 20:00, were -1.1 (-4.7; 2.5), -0.2 (-4.4; 4.0), and 0.3 (-3.3; 3.9), respectively. For the comparison of 12:00 compared to 16:00 and 20:00 it was 0.9 (-3.3; 5.2) and 1.4 (-2.0; 4.9), and for 16:00 compared to 20:00 it was 0.5 (-3.7; 4.7). CONCLUSION: In contrast to our hypothesis, we found no evidence that the timing of exercise impacted the changes in VO2peak during the exercise intervention period. The well-known diurnal variation in physical performance, thus might not affect long-term adaptations to physical exercise. REFERENCES [1] Mason I, et al. (2020) Impact of circadian disruption on glucose metabolism: implications for type 2 diabetes. Diabetologia 63(3):462-472. [2] Knaier R, et al. (2022). Diurnal Variation in Maximum Endurance and Maximum Strength Performance: A Systematic Review and Meta-analysis. Med Sci Sports Exerc 54(1):169–180. [3] Bruggisser F, et al. (2023). Best Time of Day for Strength and Endurance Training to Improve Health and Performance? A Systematic Review with Meta-analysis. Sports Med Open 9(1):34.
Read CV Raphael KnaierECSS Paris 2023: CP-PN09
INTRODUCTION: Long-duration space missions are characterized by prolonged isolation and confinement in extreme environments. In these living conditions, astronauts face desynchronisation of the circadian rhythms with relevant consequences of physical and mental health [1]. In Antarctica, crew members of Concordia station are exposed to environmental conditions (hypobaric hypoxia, absence of sunlight) and lifestyle changes (isolation, confinement, modification of daily physical activity) similar to astronauts, resulting an ideal experimental setting to test human physiological adaptations and circadian rhythms alteration [2,3]. As physical activity levels and changes in cardiorespiratory fitness seem to play a pivotal role on circadian rhythms [4], we aimed to evaluate how prolonged exposure to Antarctic extreme environment affects cardiorespiratory fitness of crew members living at Concordia station for eleven months. METHODS: Twenty-four male subjects (age: 39±11 ys, height: 177±8 cm, weight: 79±10 kg) were recruited. Before flying to Concordia (BDC), participants performed i) a ramp incremental cardiopulmonary test (CPET) up to exhaustion on a cyclo-ergometer and ii) two constant work rate (CWR) exercise at 40% (MOD) and 70% (HVY) of peak work rate (Wpeak). At Concordia station, participants performed MOD and HVY tests on monthly base. Pulmonary ventilation (V’E), oxygen consumption (V’O2) and carbon dioxide production (V’CO2) were monitored. Heart rate (HR) was recorded. Rate of perceived exertion (RPE) using 6-20 Borg Scale and blood lactate were collected before and at the end of exercise. Two-way ANOVA for repeated measures was used to evaluate changes in cardiorespiratory fitness, using time and intensity (MOD vs HVY). RESULTS: At BDC, Wpeak and V’O2peak were 244±38 W and 35.8±5.4 ml*min-1*kg-1, respectively. Peak values of HR (174±14 bpm), RER (1.40±0.11), RPE (16±2) and lactate (10.6±1.7 mM) confirmed exhaustion. MOD was performed at 101±16 W. HR was 123±11 bpm and RPE was 10±2. HVY was performed at 173±25 W. HR was 155±38 bpm and RPE was 14±2. At Concordia, MOD and HVY work rate were reduced of about 25% due to hypoxic environment. HR and RPE were higher in HVY vs MOD at all time points (p<0.05). No time effect or time x intensity interaction were observed (p>0,05) for both HR and RPE. In MOD, HR (109±14 bpm) and RPE (9±2) were not affected between visits. Also for HVY, HR (131±15 bpm) and RPE (13±2) were not affected among visits. CONCLUSION: Cardiovascular and perceptual responses to MOD and HVY exercises were not affected by eleven months at Concordia station. Thus, cardiorespiratory functions seems unaltered during prolonged confinement and hypoxia suggesting that other environmental stressors may alter circadian rhythms. REFERENCES [1] Albornoz-Miranda, 2023 [2] Steinach, 2016 [3] Porcelli, 2017 [4] Sha, 2023
Read CV Marianna NeriECSS Paris 2023: CP-PN09
INTRODUCTION: Regular aerobic exercise plays a pivotal role in improving cardiorespiratory fitness (CRF) and preventing cardiovascular morbidity and mortality. Despite the clear health benefit of regular aerobic exercise of 150 minutes or more per week, many adults do not perform recommended amount of aerobic exercise due to time constraints. Recently, reduced-exertion high-intensity interval training (ReHIT) has been proposed as a time-efficient alternative. The effects of ReHIT on CRF remain inconclusive due to the limited number of studies with small sample sizes conducted to date. Without comprehensive analyses, it is difficult to determine the effects of ReHIT on CRF and cardiovascular disease (CVD) risk factors, and the minimum required amount of exercise. Therefore, the aim of this meta-analysis was to evaluate the effects of ReHIT on changes in CRF, a CVD risk factor, in sedentary adults. METHODS: The literature search was performed using two electronic databases including the PubMed and Web of Science from Oct 10 2024 to Dec 5 2024. We included the studies that focus on: (a) sedentary adults, (b) ReHIT, (c) comparison with control (CONT) group or moderate-intensity continuous training (MICT) group, (d) CRF, and (e) randomized controlled trials (RCT). The criteria for ReHIT were as follows: (a) total duration of session: ≤10 minutes, (b) mode of exercise: Cycling, (c) minimum period ≥ 4 weeks. RESULTS: Total eight studies were included in this meta-analysis. The random effects meta-analysis revealed that ReHIT group demonstrated significantly higher VO2peak, a marker of cardiorespiratory fitness, than untrained CONT group (effects size = 0.972; 95% CI= 0.185-1.759, p = 0.015; I2 =74%). However, there was no significant difference in VO2peak in comparison with MICT group (effect size = 0.110; 95% CI = -0.518 to 0.737, p = 0.731; I2 = 61%). Additionally, there were no significant effects on body weight reduction in either CONT (effects size = -0.525; 95% CI= -1.387-0.337, p = 0.337; I2 =79%) or MICT group (effects size = -0.237; 95% CI= -0.915-0.441, p = 0.493; I2 =65%). CONCLUSION: The findings of this meta-analysis indicates that ReHIT can be an effective alternative for the typical moderate-intensity aerobic exercise with 150 minutes or more per week for improving CRF and reducing CVD risk in habitually sedentary adults. However, it seems difficult to expect additional health benefits through weight loss since the absolute amount of exercise in ReHIT is relatively low.
Read CV Moon-Hyon HwangECSS Paris 2023: CP-PN09