Training variables and autonomic nervous system adaption / 中国组织工程研究

BACKGROUND: Autonomic nervous system plays a critical role in mediating cardiovascular system to adapt the metabolic demands of the muscle activity, and is an important presenter and supporter of physical activity. OBJECTIVE: To systematically analyze the possible effects of exercise intensity, exercise modality, and exercise duration on autonomic nervous system regulation during and after exercise through reviewing the related literature on the autonomic nervous system and heart rate variability assessment of autonomic nervous system, so as to understand the mechanisms that meet the metabolic needs of physical activities. METHODS: PubMed and CNKI databases were searched using the keywords of “autonomic nerves system, heart rate variability, exercise intensity, exercise modality, exercise duration” in English and Chinese, respectively. The studies published from 1999 to 2018 were retrieved. RESULTS AND CONCLUSION: Cardiac autonomic neuromodulation is evaluated by heart rate variability index based on RR interval changes. Heart rate variability is a sensitive marker that reflects the co-regulation of cardiac function in sympathetic nerves and parasympathetic (vagal) nerves in the autonomic nervous system. In addition, the heart rate variability signals contain a large amount of regulatory information, including cardiovascular system, hormones and body fluids. Therefore, the mechanism of exercise-induced cardiac autonomic nervous system adaptation is still unclear. Exercise intensity may be the main factor affecting the regulation of cardiac autonomic nervous system during and after exercise. The training parameters such as exercise form and duration, as well as their interaction effects, may affect the adaptive process of cardiac autonomic nervous system.

Inflammation and oxidative stress in heart failure: effects of exercise intensity and duration

Although acute exercise is apparently pro-inflammatory and increases oxidative stress, it can promote the necessary stress stimulus to train chronic adaptations in patients with chronic heart failure (CHF). This study aimed to compare the effects of exercise intensity and duration on the inflammatory markers soluble tumor necrosis factor receptor (sTNFR1) and interleukin-6 (IL-6), and on oxidative stress [malondialdehyde (MDA) and antioxidant enzymes: catalase (CAT) and superoxide dismutase (SOD)] in individuals with CHF. Eighteen patients performed three exercise sessions: 30 min of moderate-intensity (M30) exercise, 30 min of low-intensity (L30) exercise, and 45 min of low-intensity (L45) exercise. Blood analysis was performed before exercise (baseline), immediately after each session (after), and 1 h after the end of each session (1h after). Thirty min of M30 exercise promoted a larger stressor stimulus, both pro-inflammatory and pro-oxidative, than that promoted by exercises L30 and L45. This was evidenced by increased sTNFR1 and MDA levels after exercise M30. In response to this stressor stimulus, 1 h after exercise, there was an increase in IL-6 and CAT levels, and a return of sTNFR1 to baseline levels. These findings suggest that compared with the duration of exercise, the exercise intensity was an important factor of physiologic adjustments.

A Comparative Study on Effects of Exercise Intensity and Duration on Left and Right Ventricular / 中国运动医学杂志

Objective To examine the effects of exercise intensity and duration on the structure,function and fibrosis of the left and right ventricular,and to discuss the potential mechanism in these processes.Methods Forty-eight male Sprague-Dawley rats were randomly divided into a sedentary(Sed)group,a moderate exercise(ME)group and an intensive exercise(IE) group,each of 16.Rats in Sed group were not given any training,while those in ME group and IE group run on treadmill at the speed of 15.2 m/min with the slope gradient of 5° and 28 m/min with the slope gradient of 10 degree 1 hour per day,5 days per week.Eight and 16 weeks after the training,we recorded the body weight and measure end-diastolic diameter,end-diastolic wall thickness,and ejection fraction of both ventriculars using the ultrasonic testing.All rats were then sacrificed after blood sampling.Elisa was used to measure serum cTnI concentration,and sirius red staining was applied to evaluate collagen volume fraction of both ventriculars.Results Eight or sixteen weeks after the training,the average bi-ventricular end-diastolic diameter of ME and IE rats was bigger than Sed group.There were no differences in end-diastolic diameter of both ventricular between ME group and IE group after sixteen-week training,but the left ventricular end-diastolic diameter of IE group was greater than ME group.As exercise intensive increased and time accumulated,the end-diastolic wall thickness of both ventriculars increased but without statistical significance.At sixteen-week intervention,the bi-ventricular ejection fraction of IE rats was significantly lower than Sed and ME groups,while there was a decreasing trend eight weeks earlier without significant differences.After 8 or 16 weeks of training,the serum cTnI was significantly higher in IE rats than Sed group or ME group,but there was no significant differences between ME group and Sed group.After 16 weeks' exercises,the average bi-ventricular collagen volume fraction of ME or IE group was greater than that after 8 weeks' exercises.The average collagen volume fraction of the right ventricular was greater than Sed group at the same time points,and after sixteenweek training the right ventricular collagen volume fraction in IE group was significantly greater than ME group.However,there were no significant differences in the measurement of the left side among different groups.The serum cTnI was negatively correlated with the left and right ventricular systolic function(r=-0.327,P=0.029 and r=-0.582,P=0.000).Moreover,it was positively correlated with the right ventricular collagen volume fraction moderately,but had no correlation with the left ventricular collagen volume fraction.Conclusion(1)Sixteen-week moderate and intensive exercise result in left ventricular dilation,and the dilation increases with the increase of the exercise intensity.Only 8 weeks' exercise at the same intensity can lead to right ventricular dilation,but exercise intensity has little influence on the right ventricular dilation.(2)Long-term moderate or intensive endurance exercises may cause bi-ventricular hypertrophy potentially.The left ventricular hypertrophy and dilation may not be synchronous with hypertrophy followed by dilation,while the right ventricular hypertrophy and dilation is synchronous.(3)The temporary decrease in bi-ventricular systolic function after intensive endurance exercise may be caused by ventricular injury,with more serious injury in the right ventricular than in the left.Moderate exercises don't cause ventricular injury,thus there is little or no influence on ejection fraction.(4) Long-term (8 or 16 weeks)moderate or intensive endurance exercises can increase the right ventricular collagen volume fraction,which may indicate cardiac fibrosis following right ventricular injury but not in the left ventricular.The bi-ventricular collagen volume fraction at sixteenth week in ME and IE rats are greater than corresponding rats at eighth week.It may result from the hypertrophy of bi-ventricular cardiomyocyte after 8-week training,followed by increase in the extracellular matrix but not cardiac fibrosis.

Incidence of upper respiratory tract infection and duration of weekly training among Japanese collegiate male and female athlete / 体力科学

Strenuous exercise induces upper respiratory tract infection (URTI), whereas moderate exercise prevents URTI. This study aimed to assess the incidence of URTI and the association between URTI episodes and exercise duration in Japanese collegiate athletes. A cross-sectional survey was conducted with 1,740 participants; 1,235 responses were eligible for analysis. Participants were classified into three groups: control group (weekly total exercise duration <60 min, n=405), exercise group (weekly total exercise duration >60 min, n=193), and athlete group (joined a sports club and weekly exercise frequency >5 days, n=637). We requested the following information from participants: basic characteristics, incidence of URTI symptoms (fever, runny or plugged nose, sore throat, and cough) or influenza for each month over the past year, day of the week exercise is typically performed, and duration of exercise per week. The incidence of URTI episodes per year was significantly lower in the athlete group (2.0 ± 2.4 episodes) compared to the control group (2.6 ± 2.4 episodes, p<0.001). The incidence of URTI episodes did not significantly differ between the control group and exercise group (2.9 ± 2.9 episodes, p=0.607). Although the frequency of URTI episodes and exercise duration were not significantly associated among male athletes (p=0.209), they were positively associated in female athletes (p=0.027). These results indicate that Japanese collegiate athletes experience fewer URTI episodes than non-athletes, but athletes who exercise for long durations may frequently experience URTI, particularly female athletes.

CHANGES IN BRACHIAL AND FEMORAL ARTERY VASCULAR CONDUCTANCE IN NON-EXERCISING LIMBS DURING HANDGRIP EXERCISE / 体力科学

The purpose of this study was to determine the difference in vascular conductance changes in brachial and femoral artery (BVC, FVC) of non-exercising limbs during handgrip exercise at different intensities. Six subjects performed rhythmic handgrip exercise, which consisted of 2-second contraction and 2-second relaxation at the intensities of 15%, 30%, and 45% of maximal voluntary contraction (MVC). Brachial and femoral artery blood flow (Doppler ultrasound method) of non-exercising limbs, blood pressure, and heart rate were measured. The BVC during exercise at lower intensities (15% and 30%MVC) and FVC during exercise at any of three intensities did not change significantly. However, BVC significantly decreased at 45%MVC when the exercise was continued to longer than 60% of maximal endurance time (P<0.05). These results suggest that FVC of the non-exercising limb dose not change during handgrip exercise at the intensity lower than 45%MVC, but BVC of the non-exercising limb change during handgrip exercise depending on the exercise intensity and duration.

Minimum duration of exercise for improving aerobic capacity in middle-aged and elderly female patients with coronary heart disease and/or hypertension / 体力科学

To determine the minimum duration of exercise for improving the aerobic capacity of patients with coronary heart disease (CHD), 23 female patients with CHD and/or hypertension, aged 52.8±8.7 years, were studied. After pre-testing, all the patients were conditioned for 4 months in order to elicit improvements in their aerobic capacity and other healthrelated factors. Duration and contents of daily activities were recorded by each patient. After 4 months, oxygen uptake at lactate threshold (VO<SUB>2LT</SUB>) and VO<SUB>2peak</SUB> were increased significantly from 12.9±2.6 to 16.0±3.4m<I>l</I>/kg/min and from 18.5±4.2 to 22.3±5.6m<I>l</I>/kg/min, respectively. Duration of exercise conditioning for the 4 months averaged 23.8±12.2min per day, ranging from 4.6 to 49.7min. Correlational analyses were applied in order to determine the extent to which the improvement in aerobic capacity was associated with the individual mean duration of exercise conditioning. As a result, changes in VO<SUB>2LT</SUB> and VO<SUB>2peak</SUB> correlated significantly with the exercise duration (Pearson's r=0.51, Spearman's rho=0.47 for VO<SUB>2LT</SUB>; Spearman's rho=0.58 for VO<SUB>2peak</SUB>) . Both VO<SUB>2LT</SUB> and VO<SUB>2peak</SUB> tended to improve markedly when daliy exercise duration was 20 min or longer. Furthermore, it was shown that the improvement in aerobic capacity remained almost the same within a range of exercise duration of 20 to 60min. We suggest that the minimum exercise duration for improving the aerobic capacity of cardiac patients is 20 to 30min per day or 140min or more per week.

Relationship between sympathetic and adrenomedullary activities during exercise. With reference to duration of exercise / 体力科学

This study was designed to evaluate the effect of exercise duration on the relation between sympathetic and adrenomedullary activities. Six trained subjects completed the following two exercise protocols ; six 2-min exercise sessions at 100% maximal O<SUB>2</SUB>uptake (VO<SUB>2</SUB>max) interspersed with 10-min recovery periods, and three 10-min exercise sessions at 80%VO<SUB>2</SUB>max interspersed with 10-min recovery periods. Plasma noradrenaline (NA), plasma adrenaline (A), NA/A ratio (NA/A), heart rate (HR), coefficient of variation of R-R intervals (CVRR) and blood lactate (La) were measured. With repetition of exercise sessions in both protocols, HR, NA and A gradually increased. CVRR rapidly decreased at the first exercise session and remained unchanged thereafter. NA/A increased by the first exercise session, but decreased by the following exercise sessions. NA in the second exercise session at 100%VO<SUB>2</SUB>max was significantly lower than that in the first. We conclude that, at the beginning of exercise, the increase of sympathetic activity is more dominant than that of adrenomedullary activity, whereas, with prolongation of exercise duration, the increase of adrenomedullary activity becomes more dominant than that of sympathetic activity,

Exercise-induced bone hypertrophy in growing rats / 体力科学

The effects of exercise training on bone development in growing rats were studied using the photon-absorption method and histomorophological analyses. Thirty-seven male Wistar strain rats at 4 wks of age were divided into five groups : sedentary control (C; N=7), 15 min/day training (T 15 ; N=6), 30 min/day training (T 30 ; N=8), 60 min/day training (T 60 ; N=8) and 120 min/day training (T 120 ; N=8) . All rats in these training groups were subjected to a treadmill running at a speed of 30 m/min, 5 days/wk for 11 wks. The results of our study were summarized as follows :<BR>1) Fat-free dry weight of the tibia was significantly heavier in T 30, T 60 and T 120 than C and T 15, respectively.<BR>2) Bone mineral content (mg/cm) of tibial midshaft in all T groups was significantly higher than that in C group, respectively, while no differences were found between any of the training groups.<BR>3) On histological parameters of cross-sectional samples from tibia, such as cortical area, total area and appositional growth rate on periosteum, higher values were observed in T groups compared with C group.<BR>These results suggest that physical training induce markedly facilitative girth growth associated with elevated bone formation of periosteum in the tibia, and moreover, the daily exercise duration does not change the degree of bone hypertrophy.

Effects of exercise duration on post-exercise glucose metabolism / 体力科学

Effects of bicycle exercise duration (i. e., 20, 40 and 60 min) on post-exercise glucose metabolism was studied in four healthy untrained men (19.8±0.4 yr), who were previously considered normal on a resting oral glucose tolerance test (OGTT) . These three exercises were performed on different days. The intensity of exercise corresponded to approximately 60% of VO<SUB>2</SUB>max. A glucose sample of 100-g/300 ml was orally administered on 20 min after the completion of each exercise. Blood samples were obtained from a forearm vein before exercise, immediately after and on 20 min after the cessation of exercise, and on 30, 60, 90, 120 and 180 min after glucose ingestion. The following results were obtained. 1) Blood glucose concentrations observed on 60, 90, 120 and 180 min after glucose ingestion following 60 min exercise appeared to be higher than OGTT levels, indicating the time delay to return to the resting level. 2) Serum insulin concentrations after glucose ingestion following 20 and 40 min exercise were lower than OGTT levels. Changes in serum insulin concentrations following 60 min exercise were similar to those on OGTT levels with the exception of the level on 30 min after glucose ingestion. Serum C-peptide response curves were similar to serum insulin response curves after each exercise. 3) Serum free fatty acids (FFA) increased during each exercise as compared to a resting level and increased further after each exercise. The degree of changes in FFA was most significant during a recovery period following 60 min exercise, however, it decreased abruptly after glucose ingestion as a case after 20 and 40 min exercise. 4) Plasma cyclic-AMP concentrations increased most profoundly during 60 min exercise. Plasma cyclic-AMP level before glucose ingestion was also higher following 60 min exercise. These results suggested that postexercise glucose metabolism after glucose ingestion tended to be decreased with elevated rates of serum FFA during a recovery period following 60 min exercise.