Sex differences in cardiac function after prolonged strenuous exercise.

OBJECTIVE: To evaluate sex differences in left ventricular (LV) function after an ultramarathon, and the association of vascular and training indices with the magnitude of exercise-induced cardiac fatigue. DESIGN: Descriptive field study. SETTING: Fat Dog 100 Ultramarathon Trail Race, Canada. PARTICIPANTS: Thirty-four (13 women) recreational runners (aged 28-56 years). INTERVENTIONS: A 100-km or 160-km mountain marathon. MAIN OUTCOME MEASURES: Baseline baroreceptor sensitivity, heart rate variability, and arterial compliance; Pre-exercise and postexercise echocardiographic evaluations of LV dimensions, volumes, Doppler flow velocities, tissue velocities, strain, and strain rate. RESULTS: Finishers represented 17 men (44.8 ± 6.6 years) and 8 women (45.9 ± 10.2 years; P = 0.758). After ultraendurance exercise, significant reductions (P < 0.05) in fractional shortening (men: 40.9 ± 6.9 to 34.1 ± 7.6%; women: 42.5 ± 6.5 to 34.6 ± 7.9%) diastolic filling (E/A, men: 1.28 ± 0.68 to 1.26 ± 0.33; women: 1.55 ± 0.51 to 1.30 ± 0.27), septal and lateral tissue velocities (E'), and longitudinal strain (men: -21.02 ± 1.98 to -18.44 ± 0.34; women: -20.28 ± 1.90 to -18.44 ± 2.34) were observed. Sex differences were found for baseline cardiac structure and global function, peak late transmitral flow velocity, and estimates of LV filling pressures (P < 0.05). Regression analysis found that higher baseline arterial compliance was associated with lower reductions in cardiac function postexercise, to which sex was a significant factor for E' of the lateral wall. Faster race pace and greater lifetime ultramarathons were associated with lower reductions in LV longitudinal strain (P < 0.05). CONCLUSIONS: Cardiac responses after an ultramarathon were similar between men and women. Greater evidence of exercise-induced cardiac fatigue was found to be associated with lower baseline arterial compliance and training status/experience. CLINICAL RELEVANCE: These findings suggest that vascular health is an important contributor to the degree of cardiovascular strain incurred as the result of an acute bout of prolonged strenuous exercise.

Exercise volume and intensity: a dose-response relationship with health benefits.

INTRODUCTION: The health benefits of exercise are well established. However, the relationship between exercise volume and intensity and health benefits remains unclear, particularly the benefits of low-volume and intensity exercise. PURPOSE: The primary purpose of this investigation was, therefore, to examine the dose-response relationship between exercise volume and intensity with derived health benefits including volumes and intensity of activity well below international recommendations. METHODS: Generally healthy, active participants (n = 72; age = 44 ± 13 years) were assigned randomly to control (n = 10) or one of five 13-week exercise programs: (1) 10-min brisk walking 1×/week (n = 10), (2) 10-min brisk walking 3×/week (n = 10), (3) 30-min brisk walking 3×/week (n = 18), (4) 60-min brisk walking 3×/week (n = 10), and (5) 30-min running 3×/week (n = 14), in addition to their regular physical activity. Health measures evaluated pre- and post-training including blood pressure, body composition, fasting lipids and glucose, and maximal aerobic power (VO2max). RESULTS: Health improvements were observed among programs at least 30 min in duration, including body composition and VO2max: 30-min walking 28.8-34.5 mL kg(-1) min(-1), 60-min walking 25.1-28.9 mL kg(-1) min(-1), and 30-min running 32.4-36.4 mL kg(-1) min(-1). The greater intensity running program also demonstrated improvements in triglycerides. CONCLUSION: In healthy active individuals, a physical activity program of at least 30 min in duration for three sessions/per week is associated with consistent improvements in health status.

Using aerobic exercise to improve health outcomes and quality of life in stroke: evidence-based exercise prescription recommendations.

BACKGROUND: Stroke patients often suffer from poor cardiovascular health and deficits in physical, psychosocial and cognitive functioning. Aerobic exercise training may be a viable treatment approach to address these health issues. The objective of this systematic review was to determine the effects of aerobic exercise on various indicators of health, functioning and quality of life in stroke patients. It was hypothesized that the systematic review would reveal compelling support for the effectiveness of aerobic exercise in stroke patients, such that detailed evidence-based exercise prescription recommendations could be derived. METHODS: Major electronic databases were searched systematically to identify randomized controlled studies that examined the effects of aerobic exercise in stroke patients (last search performed in January 2012). The methodological quality of each study was evaluated using the PEDro scale (9-10 = excellent; 6-8 = good; 4-5 = fair; <4 = poor). Based on the methodological quality and sample size used, the level of evidence was determined for each study (level 1: PEDro ≥6 and sample size >50; level 2: PEDro ≤5 or sample size ≤50). Meta-analysis was performed on a given outcome when appropriate. RESULTS: Twenty-five trials fulfilled the selection criteria, of which 8 were level 1 studies. Treadmill and cycle ergometer were the two most popular modalities used to provide aerobic training. The most commonly adopted exercise session duration and frequency was 21-40 min and 3-5 days per week, respectively. The duration of the training programme varied, ranging from 3 weeks to 6 months. Over 60% of the trials used a high training intensity [60-80% heart rate reserve (HRR)]. Meta-analysis showed a significant effect on peak oxygen consumption (p < 0.001), peak workload (p < 0.001), maximal gait speed (p = 0.003) and walking endurance (p < 0.001) in favour of aerobic exercise. Meta-analysis revealed no significant effect on self-selected gait speed, Berg balance score and Functional Independence Measure score. The efficacy of aerobic exercise in improving other health outcomes in physical, psychosocial and cognitive domains as well as quality of life was inconclusive. The health risk associated with engaging in such exercise is small. CONCLUSIONS: There is strong evidence that aerobic exercise (40-50% HRR progressing to 60-80%) conducted 20-40 min and 3-5 days per week is beneficial for enhancing aerobic fitness, walking speed and walking endurance in people who have had mild to moderate stroke and are deemed to have low cardiovascular risk with exercise after proper screening assessments (grade A recommendation). The effects of aerobic exercise on other health outcomes require further study.

Characterisation of baroreflex sensitivity of recreational ultra-endurance athletes.

Altered autonomic function has been identified following ultra-endurance event participation among elite world-class athletes. Despite dramatic increases in recreational athlete participation in these ultra-endurance events, the physiological effects on these athletes are less known. This investigation sought to characterise changes in surrogate measures of autonomic function: heart rate variability (HRV), blood pressure variability (BPV) and baroreceptor sensitivity (BRS) following ultra-endurance race participation. Further, we sought to compare baseline measures among ultra-endurance athletes and recreationally active controls not participating in the ultra-endurance race. Recreational ultra-endurance athletes (n = 25, 44.6 ± 8.2 years, 8 females) and recreationally active age, sex and body mass index matched controls (n = 25) were evaluated. Measurements of HRV, BPV and BRS were collected pre- and post-race for recreational ultra-endurance athletes and at baseline, for recreationally active controls. Post-race, ultra-endurance athletes demonstrated significantly greater sympathetic modulation [low frequency (LF) power HRV: 50.3 ± 21.6 normalised units (n.u.) to 65.9 ± 20.4 n.u., p = 0.01] and significantly lower parasympathetic modulation [high frequency (HF) power HRV: 45.0 ± 22.4 n.u. to 23.9 ± 13.1 n.u., p < 0.001] and BRS. Baseline measurements BRS (spectral: 13.96 ± 10.82 ms·mmHg(-1) vs. 11.39 ± 5.33 ms·mmHg(-1)) were similar among recreational ultra-endurance athletes and recreationally active controls, though recreational ultra-endurance athletes demonstrated greater parasympathetic modulation of some HRV and BPV measures. Recreational ultra-endurance athletes experienced increased sympathetic tone and declines in BRS post-race, similar to previously reported elite world-class ultra-endurance athletes, though still within normal population ranges.

Evidence-based risk recommendations for best practices in the training of qualified exercise professionals working with clinical populations.

This systematic review examines critically "best practices" in the training of qualified exercise professionals. Particular attention is given to the core competencies and educational requirements needed for working with clinical populations. Relevant information was obtained by a systematic search of 6 electronic databases, cross-referencing, and through the authors' knowledge of the area. The level and grade of the available evidence was established. A total of 52 articles relating to best practices and (or) core competencies in clinical exercise physiology met our eligibility criteria. Overall, current literature supports the need for qualified exercise professionals to possess advanced certification and education in the exercise sciences, particularly when dealing with "at-risk" populations. Current literature also substantiates the safety and effectiveness of exercise physiologist supervised stress testing and training in clinical populations.

Physicochemical analysis of acid-base responses to prolonged moderate exercise in late gestation.

Stewart's physicochemical approach was employed to investigate the safety of an average recreational and occupational activity (prolonged moderate exercise) on maternal acid-base homeostasis. The responses of 10 healthy, physically active pregnant women (PG, gestational age 34-38 weeks) were compared with those of 10 non-pregnant female controls (CG). Subjects cycled for 40 min at 85% of their measured ventilatory threshold (VT). During the transition from rest to exercise, hydrogen ion concentration ([H+]) increased significantly and bicarbonate concentration ([HCO3-]) decreased significantly in both groups. Total weak acid ([Atot]) increased significantly with exercise in both groups, whereas the strong ion difference ([SID]) and CO2 tension (PaCO2) did not change significantly with exercise. Values for [H+], [HCO3-], PaCO2, [Atot] and [SID] were significantly lower in the PG vs. CG under all experimental conditions. Acid-base responses to prolonged moderate exercise are quantitatively similar in the pregnant vs. non-pregnant state. However, pregnant women maintain a lower plasma [H+] (approximately 3 neq/L (1 neq/L=1 nmol/L)) throughout rest, exercise, and recovery, as a result of lower values for PaCO2 and [Atot], which is partly offset by a lower [SID]. The results indicate that prolonged moderate exercise appears to be well tolerated by healthy recreationally and occupationally active pregnant women.

Effects of pregnancy on maternal work tolerance.

This review summarizes current information on the tolerance of healthy pregnant women and their fetuses to acute strenuous exertion. Maximal aerobic power, expressed in L x min(-1), is not significantly affected in women who maintain an active lifestyle, whereas values expressed in ml x kg(-1) x min(-1) decline with advancing gestational age in relation to maternal/fetal weight gain. Efficiency during standard exercise testing and the ventilatory anaerobic threshold (Tvent) also appear to be unaffected by pregnancy, but the ability to utilize carbohydrate and exercise anaerobically during brief strenuous exercise may be reduced. Fetal responses to short strenuous exercise are usually moderate and revert to baseline values within approximately 30 min postexercise. Future studies should examine alveolar gas exchange kinetics at the start of exercise and during recovery from both moderate and strenuous exertion. Existing studies of the responses of pregnant women to prolonged exercise have focused primarily on substrate utilization and glucose homeostasis. Other maternal responses to prolonged exercise that should be examined include acid-base regulation, temperature regulation, fluid and electrolyte balance, and perception of effort. Fetal reactions should also be examined in relation to maternal responses. Until evidence-based, occupation-specific guidelines become available, it is recommended that pregnant women use the Joint SOGC/CSEP Clinical Practice Guideline: Exercise in Pregnancy and the Postpartum Period, published by the Society of Obstetricians and Gynaecologists of Canada and the Canadian Society for Exercise Physiology (2003).