Exercise training-induced alterations of cardiac morphology

Comparison of echocardiographic parameters of amputee football players with active football players and sedentary individuals

BACKGROUND

The purpose of this study is to compare the echocardiographic (ECHO) parameters of amputee football players (AF) with those of athletes without a disability (football players) (FP), and sedentary individuals (SI).

METHODS

A total of 37 male participants (nAF = 12, nFP = 12, nSI = 13) were included in the study. All participants underwent a transthoracic echocardiographic examination. Aortic diameter in systole (ADs), aortic diameter in diastole (ADd), isovolumic contraction time (IVCT), isovolumic relaxation time (IVRT), left ventricular ejection fraction (LVEF), early (E) and late (A) wave velocities, myocardial systolic (S), early diastolic (E'), and late diastolic (A') myocardial rates, interventricular septal thickness (IVS), left ventricular end-diastolic diameter (LVDd) and left ventricular end-systole diameter (LVDs), left ventricular posterior wall thickness (LVPWd), left atrial diameter (LAD), and ascending aortic diameter (AAD) were measured.

RESULTS

LVDd, E' were lower in AF than in FP. In contrast, LVDs, LVPWd, and A wave were higher in AF than in FP. When AF and SI groups were compared, ADs, LVPWd, A wave, IVRT, and S wave were higher in AF than in SI. ANOVA test showed a statistically significant difference between groups in LVPWd, A-wave, and E' wave. TTE data indicate that some parameters in AF differ from those observed in healthy individuals. The smaller LVEED diameter and higher PWT were found in AF.

CONCLUSIONS

Although within normal limits, some ECHO parameters in the AF group differed from those without disability. Future studies should further investigate these differences using different and detailed measurement methods.

When one says yes and the other says no; does calcineurin participate in physiologic cardiac hypertrophy?

Developing engaging activities that build skills for understanding and appreciating research is important for undergraduate and postgraduate science students. Comparing and contrasting opposing research studies does this, and more: it also appropriately for these cohorts challenges higher level cognitive processing. Here, we present and discuss one such scenario, that of calcineurin in the heart and its response to exercise training. This scenario is further accentuated by the existence of only two studies. The background is that regular aerobic endurance exercise training stimulates the heart to physiologically adapt to chronically increase its ability to produce a greater cardiac output to meet the increased demand for oxygenated blood in working muscles, and this happens by two main mechanisms: 1) increased cardiac contractile function and 2) physiologic hypertrophy. The major underlying mechanisms have been delineated over the last decades, but one aspect has not been resolved: the potential role of calcineurin in modulating physiologic hypertrophy. This is partly because the existing research has provided opposing and contrasting findings, one line showing that exercise training does activate cardiac calcineurin in conjunction with myocardial hypertrophy, but another line showing that exercise training does not activate cardiac calcineurin even if myocardial hypertrophy is blatantly occurring. Here, we review and present the current evidence in the field and discuss reasons for this controversy. We present real-life examples from physiology research and discuss how this may enhance student engagement and participation, widen the scope of learning, and thereby also further facilitate higher level cognitive processing.

High intensity interval training and molecular adaptive response of skeletal muscle

Increased cardiovascular fitness, V˙O_2max, is associated with enhanced endurance capacity and a decreased rate of mortality. High intensity interval training (HIIT) is one of the best methods to increase V˙O_2max and endurance capacity for top athletes and for the general public as well. Because of the high intensity of this type of training, the adaptive response is not restricted to Type I fibers, as found for moderate intensity exercise of long duration. Even with a short exercise duration, HIIT can induce activation of AMPK, PGC-1α, SIRT1 and ROS pathway as well as by the modulation of Ca²⁺ homeostasis, leading to enhanced mitochondrial biogenesis, and angiogenesis. The present review summarizes the current knowledge of the adaptive response of HIIT.

Submaximal exercise cardiac output is increased by 4 weeks of sprint interval training in young healthy males with low initial Q̇-V̇O2: Importance of cardiac response phenotype

Cardiovascular adaptations to exercise, particularly at the individual level, remain poorly understood. Previous group level research suggests the relationship between cardiac output and oxygen consumption (Q˙-V˙O2) is unaffected by training as submaximal Q˙ is unchanged. We recently identified substantial inter-individual variation in the exercise Q˙-V˙O2 relationship that was correlated to stroke volume (SV) as opposed to arterial oxygen content. Therefore we explored the effects of sprint interval training (SIT) on modulating Q˙-V˙O2 given an individual’s specific Q˙-V˙O2 relationship. 22 (21±2 yrs) healthy, recreationally active males participated in a 4-week SIT (8, 20 second sprints; 4x/week, 170% of the work rate at V˙O2 peak) study with progressive exercise tests (PET) until exhaustion. Cardiac output (Q˙ L/min; inert gas rebreathe, Finometer Modelflow™), oxygen consumption (V˙O2 L/min; breath-by-breath pulmonary gas exchange), quadriceps oxygenation (near infrared spectroscopy) and exercise tolerance (6–20; Borg Scale RPE) were measured throughout PET both before and after training. Data are mean Δ from bsl±SD. Higher Q˙ (HQ˙) and lower Q˙ (LQ˙) responders were identified post hoc (n = 8/group). SIT increased the Q˙-V˙O2 post-training in LQ˙ (3.8±0.2 vs. 4.7±0.2; P = 0.02) while HQ˙ was unaffected (5.8±0.1 vs. 5.3±0.6; P = 0.5). ΔQ˙ was elevated beyond 80 watts in LQ˙ due to a greater increase in SV (all P<0.04). Peak V˙O2 (ml/kg/min) was increased in LQ˙ (39.7±6.7 vs. 44.5±7.3; P = 0.015) and HQ˙ (47.2±4.4 vs. 52.4±6.0; P = 0.009) following SIT, with HQ˙ having a greater peak V˙O2 both pre (P = 0.02) and post (P = 0.03) training. Quadriceps muscle oxygenation and RPE were not different between groups (all P>0.1). In contrast to HQ˙, LQ˙ responders are capable of improving submaximal Q˙-V˙O2 in response to SIT via increased SV. However, the increased submaximal exercise Q˙ does not benefit exercising muscle oxygenation.

The effect of exercises on left ventricular systolic and diastolic heart function in sedentary women: Step-aerobic vs core exercises

The purpose of this study is to investigate the effect of 16 weeks step-aerobic exercises and core exercises on left ventricular structure and function with some physiological parameters in sedentary women.

Methods

To achieve the purpose of this study, a total of 45 volunteers including (step-aerobic group (SAG, n = 25), core exercise group (CEG, n = 20) were selected as participants. Two different exercises were applied for 4 days a week, throughout 16 weeks, within 60 minutes for each exercise with the intensity of heart rate (HR) 60-70 percent. The HR was measured using a heart rate monitor for each subject. The physical, biochemical and echocardiographic characteristics of the women were measured before and after the exercise.

Results

During the exercise periods, there were a meaningful decrease in the body weight, BMI, value of waist region and hip circumference of the women in both intervention groups as well as in the values of HR, DBP, SBP (p < 0,05). In addition, serum homocysteine (Hcy) and high-sensitivity C-reactive protein (Hs-CRP) levels decreased and the VO_2max and left ventricular diastolic end-diastolic dimension increased in both SAG and CEG (p < 0.05). The left ventricular diastolic functions of the SAG improved more than CEG. Left ventricular systolic ejection time and fractional shortening meaningfully improved in both SAG and CEG (p < 0.01).

Conclusion

16 weeks of step-aerobic and core exercise showed significant changes of inflammatory and lipid markers with cardiac dimensions and had favorable effects on both left ventricular systolic function. Left ventricular diastolic function had more improved in SAG than the CEG.

Sedentary screen time and left ventricular structure and function: the CARDIA study

INTRODUCTION

Sedentary screen time (watching TV or using a computer) predicts cardiovascular outcomes independently from moderate and vigorous physical activity and could affect left ventricular structure and function through the adverse consequences of sedentary behavior.

PURPOSE

This study aimed to determine whether sedentary screen time is associated with measures of left ventricular structure and function.

METHODS

The Coronary Artery Risk Development in Young Adults Study measured screen time by questionnaire and left ventricular structure and function by echocardiography in 2854 black and white participants, age 43-55 yr, in 2010-2011. Generalized linear models evaluated cross-sectional trends for echocardiography measures across higher categories of screen time and adjusting for demographics, smoking, alcohol, and physical activity. Further models adjusted for potential intermediate factors (blood pressure, antihypertensive medication use, diabetes, and body mass index).

RESULTS

The relationship between screen time and left ventricular mass (LVM) differed in blacks versus whites. Among whites, higher screen time was associated with larger LVM (P < 0.001), after adjustment for height, demographics, and lifestyle variables. Associations between screen time and LVM persisted when adjusting for blood pressure, antihypertensive medication use, and diabetes (P = 0.008) but not with additional adjustment for body mass index (P = 0.503). Similar relationships were observed for screen time with LVM indexed to height, relative wall thickness, and mass-to-volume ratio. Screen time was not associated with left ventricular structure among blacks or left ventricular function in either race group.

CONCLUSIONS

Sedentary screen time is associated with greater LVM in white adults, and this relationship was largely explained by higher overall adiposity. The lack of association in blacks supports a potential qualitative difference in the cardiovascular consequences of sedentary screen-based behavior.

Modeling of Longitudinal Changes in Left Ventricular Dimensions among Female Adolescent Runners

PURPOSE

Left ventricular (LV) enlargement has been linked to sudden cardiac death among young athletes. This study aimed to model the effect of long-term incessant endurance training on LV dimensions in female adolescent runners.

METHODS

Japanese female adolescent competitive distance runners (n = 36, age: 15 years, height: 158.1 ± 4.6 cm, weight: 44.7 ± 6.1 kg, percent body fat: 17.0 ± 5.2%) underwent echocardiography and underwater weighing every 6 months for 3 years. Since the measurement occasions varied across subjects, multilevel analysis was used for curvilinear modeling of changes in running performance (velocities in 1500 m and 3000 m track race), maximal oxygen uptake (VO2max), body composition, and LV dimensions.

RESULTS

Initially, LV end-diastolic dimension (LVEDd) and LV mass were 47.0 ± 3.0 mm and 122.6 ± 15.7 g, respectively. Running performance and VO2max improved along with the training duration. The trends of changes in fat-free mass (FFM) and LVEDd were similarly best described by quadratic polynomials. LVEDd did not change over time in the model including FFM as a covariate. Increases in LV wall thicknesses were minimal and independent of FFM. LV mass increased according to a quadratic polynomial trend even after adjusting for FFM.

CONCLUSIONS

FFM was an important factor determining changes in LVEDd and LV mass. Although running performance and VO2max were improved by continued endurance training, further LV cavity enlargement hardly occurred beyond FFM gain in these adolescent female runners, who already demonstrated a large LVEDd.

Low-frequency severe-intensity interval training improves cardiorespiratory functions

PURPOSE

The present study investigated the effects of severe-intensity interval training at a frequency of once a week on cardiorespiratory function at rest and during exercise.

METHODS

Fourteen young healthy males were randomly assigned to either an interval training group or control group. Cardiorespiratory function was investigated by incremental maximal exercise test and constant work rate submaximal exercise test before and after the intervention period in all subjects. Submaximal exercise test was conducted at two work rates (80% ventilatory threshold (VT) level and 100% VT level plus 50% of the difference between VT and peak oxygen consumption (V˙O2)) for 8 min; the same work rates and duration were used before and after training. Left ventricular adaptations were assessed by echocardiography under supine resting conditions before and after training. In the interval training group, seven subjects performed cycle ergometer training once per week for 3 months. The training consisted of three bouts of exercises to volitional fatigue at 80% maximum work rate.

RESULTS

Increased V˙O2max (+13%, P = 0.015), VT (+21%, P = 0.001), and left ventricular posterior wall thickness (+18%, P = 0.002) and reduced minute ventilation (-12%, P = 0.032) and blood lactate concentration (-16%, P = 0.025) during high-intensity exercise were observed after the training program compared with baseline. Although not significant, V˙O2 and cycling economy (V˙O2 per work rate) during high-intensity exercise decreased slightly after training.

CONCLUSION

The present results indicate that severe-intensity interval training, even when performed at a low frequency, markedly improves cardiorespiratory function as well as induces cardiac morphological adaptations involving left ventricular hypertrophy and cardiorespiratory metabolic response during submaximal exercise. The present findings may provide new insights for low-frequency, severe-intensity interval training in the field of sports science.

Real-time core body temperature estimation from heart rate for first responders wearing different levels of personal protective equipment

First responders often wear personal protective equipment (PPE) for protection from on-the-job hazards. While PPE ensembles offer individuals protection, they limit one's ability to thermoregulate, and can place the wearer in danger of heat exhaustion and higher cardiac stress. Automatically monitoring thermal-work strain is one means to manage these risks, but measuring core body temperature (Tc) has proved problematic. An algorithm that estimates Tc from sequential measures of heart rate (HR) was compared to the observed Tc from 27 US soldiers participating in three different chemical/biological training events (45-90 min duration) while wearing PPE. Hotter participants (higher Tc) averaged (HRs) of 140 bpm and reached Tc around 39 °C. Overall the algorithm had a small bias (0.02 °C) and root mean square error (0.21 °C). Limits of agreement (LoA ± 0.48 °C) were similar to comparisons of Tc measured by oesophageal and rectal probes. The algorithm shows promise for use in real-time monitoring of encapsulated first responders.

PRACTITIONER SUMMARY

An algorithm to estimate core temperature (Tc) from non-invasive measures of HR was validated. Three independent studies (n = 27) compared the estimated Tc to the observed Tc in humans participating in chemical/ biological hazard training. The algorithm’s bias and variance to observed data were similar to that found from comparisons of oesophageal and rectal measurements.

VO2max trainability and high intensity interval training in humans: a meta-analysis

Endurance exercise training studies frequently show modest changes in VO₂max with training and very limited responses in some subjects. By contrast, studies using interval training (IT) or combined IT and continuous training (CT) have reported mean increases in VO₂max of up to ∼1.0 L · min⁻¹. This raises questions about the role of exercise intensity and the trainability of VO₂max. To address this topic we analyzed IT and IT/CT studies published in English from 1965–2012. Inclusion criteria were: 1)≥3 healthy sedentary/recreationally active humans <45 yrs old, 2) training duration 6–13 weeks, 3) ≥3 days/week, 4) ≥10 minutes of high intensity work, 5) ≥1∶1 work/rest ratio, and 6) results reported as mean ± SD or SE, ranges of change, or individual data. Due to heterogeneity (I² value of 70), statistical synthesis of the data used a random effects model. The summary statistic of interest was the change in VO₂max. A total of 334 subjects (120 women) from 37 studies were identified. Participants were grouped into 40 distinct training groups, so the unit of analysis was 40 rather than 37. An increase in VO₂max of 0.51 L ·min⁻¹ (95% CI: 0.43 to 0.60 L · min⁻¹) was observed. A subset of 9 studies, with 72 subjects, that featured longer intervals showed even larger (∼0.8–0.9 L · min⁻¹) changes in VO₂max with evidence of a marked response in all subjects. These results suggest that ideas about trainability and VO₂max should be further evaluated with standardized IT or IT/CT training programs.

The effect of creatine supplementation on myocardial function, mitochondrial respiration and susceptibility to ischaemia/reperfusion injury in sedentary and exercised rats

AIM

To investigate the effects of dietary creatine supplementation alone and in combination with exercise on basal cardiac function, susceptibility to ischaemia/reperfusion injury and mitochondrial oxidative function. There has been an increase in the use of creatine supplementation among sports enthusiasts, and by clinicians as a therapeutic agent in muscular and neurological diseases. The effects of creatine have been studied extensively in skeletal muscle, but not in the myocardium.

METHODS

Male Wistar rats were swim-trained for 8 weeks, 5 days per week. Hearts were excised and either freeze-clamped for biochemical analysis or perfused on the isolated heart perfusion system to assess function and ischaemia/reperfusion tolerance. Mechanical function was documented in working heart and retrograde mode. The left coronary artery was ligated and infarct size determined. Mitochondrial oxidative capacity was quantified.

RESULTS

Aortic output recovery of hearts from the sedentary controls (CSed) was significantly higher than those from creatine-supplemented sedentary (CrSed), creatine-supplemented exercised (CrEx) as well as control exercised (CEx) groups. Ischaemic contracture of hearts from CrEx was significantly higher than that of CSed. There were no differences in infarct size and mitochondrial oxygen consumption.

CONCLUSION

This study suggests that creatine supplementation has no effects on basal cardiac function but reduces myocardial tolerance to ischaemia in hearts from exercise-trained animals, by increasing the ischaemic contracture and decreasing reperfusion aortic output. Exercise training alone also significantly decreased aortic output recovery. However, the exact mechanisms for these adverse myocardial effects are unknown and need further investigation.

Changes in ventricular twist and untwisting with orthostatic stress: endurance athletes versus normally active individuals

Endurance-trained individuals exhibit larger reductions in left ventricular (LV) end-diastolic volume in response to lower body negative pressure (LBNP) compared with normally active individuals. However, the relationship between LV torsion and untwisting and the LV volume response to LBNP in endurance athletes is unknown. Eight endurance-trained athletes [maximal oxygen consumption (V̇o2max): 66.4 ± 7.2 ml·kg−1·min−1] and eight normally active individuals (V̇o2max: 41.9 ± 9.0 ml·kg−1·min−1) (all men) underwent two cardiac magnetic resonance imaging (MRI) assessments, the first during supine rest and the second during −30 mmHg LBNP. Right ventricular (RV) and LV volumes were assessed, myocardial tagging was applied in order to quantify LV peak torsion and peak untwisting rate, and filling rates were measured with phase-contrast MRI. In response to LBNP, endurance-trained individuals had greater reductions in RV and LV end-diastolic volume and stroke volume ( P < 0.05). Endurance athletes had reduced untwisting rates (20.3 ± 8.7°/s), while normally active individuals had increased untwisting rates (−16.2 ± 32.1°/s) in response to LBNP ( P < 0.05). Changes in peak untwisting rate were significantly correlated with change in peak torsion ( R = −0.87, P < 0.05), with the change in early filling rate and V̇o2max, but not with changes in end-diastolic or end-systolic volume ( P > 0.05). We conclude that increased untwisting rates in normally active subjects may mitigate the drop in early filling rate with LBNP and thus may be a compensatory mechanism for the reduction in stroke volume with volume unloading. The opposite response in athletes, who showed a decreased untwisting rate, may contribute to their larger reductions in LV end-diastolic and stroke volumes with volume unloading and their orthostatic intolerance.

Improvement of systolic and diastolic heart function after physical training in sedentary women

The present study examined the cardiac effects of football training and running for inactive pre-menopausal women by standard echocardiography and tissue Doppler imaging. Thirty-seven subjects were randomized to two training groups (football: FG; n=19; running; RG; n=18) training 1 h with equal average heart rates twice a week for 16 weeks and compared with a matched inactive control group (CG; n=10). During the training period, left ventricular end-diastolic volume increased by 13% in FG and 11% in RG (P<0.05). Left ventricular posterior wall thickness increased in FG from 8.5+/-1.4 to 9.0+/-1.3 mm (P<0.05). Right ventricle diameter increased by 12% in FG and 10% in RG (P<0.05). Tissue Doppler imaging demonstrated increased left ventricular systolic and diastolic performances in both training groups. Peak systolic velocity increased by 26% in FG and 17% in RG (P<0.05) and left ventricular longitudinal displacement increased in both groups by 13% (P<0.05). Isovolumetric relaxation time decreased significantly more in FG than in RG (26% vs 14%, respectively P<0.05). In conclusion, 16 weeks of football and running exercise training induced significant changes of cardiac dimensions and had favorable effects on both left ventricular systolic and diastolic function. These training-induced cardiac adaptations appeared to be more consistent after football training compared with running.

Bioenergetic provision of energy for muscular activity

A complex series of metabolic pathways are present in human muscle that break down substrates from nutritional sources to produce energy for different types of muscular activity. However, depending on the activity in which an individual is engaged, the body will make use of different energy systems that have been adapted for the particular activity. More specifically, utilization of bioenergetic substrates depends on the type, intensity, and duration of the exercise. The aerobic oxidative system is used for longer duration activities of low to moderate intensity, the anaerobic glycolytic system is used for short to moderate duration activities of higher intensity, and the high energy phosphagen system is used for short duration activities of high intensity. The efficiency and effectiveness of these pathways can be enhanced through physical activity and training. It is these bioenergetic pathways that are the focus of this review.

Concentric myocardial hypertrophy after one year of increased training volume in experienced distance runners

OBJECTIVES

As evidence on the predominant type of cardiac hypertrophy due to endurance running training is inconsistent, the aim of this study was to investigate the effect of increased training volume on echocardiographic variables of distance runners.

METHODS

Twenty three adult, experienced, male distance runners underwent standard two dimensionally guided M mode and Doppler echocardiography before and after a one year period during which they were randomly allocated to either control (n = 11) or intervention (n = 12) groups. The intervention group increased their training volume from (mean (SD)) 8.0 (3.0) to 12.5 (3.9) hours/week without increasing the intensity, and the controls changed neither training parameter.

RESULTS

In the intervention group, training induced an increase in left ventricular (LV) mass (from 240.4 (53.8) to 279.5 (60.6) g, p<0.001) and LV mass index (from 126.7 (28.2) to 147.6 (32.3) g/m2, p<0.001) mainly due to an increase in end diastolic interventricular septum (from 10.4 (1.8) to 11.5 (1.7) mm, p<0.01) and LV posterior wall thickness (from 10.4 (1.6) to 11.5 (1.6) mm, p<0.001). No significant changes in LV internal diameter or measured indices of LV function occurred (p>0.05). The sum of the right ventricular diameter and wall thickness was greater after the increased volume training (p<0.05). None of the variables changed significantly in the control group (p>0.05).

CONCLUSIONS

In experienced, subelite distance runners, further increasing the training volume results in concentric cardiac hypertrophy.

Adaptation of left ventricular morphology to long−term training in sprint− and endurance−trained elite runners

Long-term studies on left ventricular (LV) adaptation have not been reported. The echocardiograms of 41 top-class runners (8 males and 6 females sprint-trained, 15 males and 12 females endurance-trained) were recorded at the beginning and after 1, 2, and 3 years of training. A one-way ANOVA and a linear regression analysis were conducted to determine changes and association between performance and LV values. Training resulted in an increase in performance and LV internal diameter at end-diastole (LVIDd) and decreases in end-diastolic interventricular septal wall thickness, and posterior wall thickness (PWTd). There were no significant differences in LV mass and LV ejection fraction (LVEF, %). The changes in PWTd were linked to enlargement of the LV. In athletes with unusual LV dilatation (>60 mm), LVIDd was related to performance and LVEF was >50%. Maximal wall thickness was <13 mm in all athletes. LV adaptations were independent of sex and type of training and related to the initial level of performance. We believe that LV enlargement in elite runners is a physiological adaptation and that the LVIDd is a predictor of running performance.

Atrioventricular Plane Displacement in Untrained and Trained Females

PURPOSE

Female athletes often demonstrate changes in cardiac dimensions that are less prominent than in male athletes, and results from longitudinal studies are conflicting. The atrioventricular plane displacement (AVPD) in the heart is used as an index of left ventricular systolic function with the assumption that it is a more sensitive method for measuring myocardial contractility compared with left ventricular ejection fraction. The aim of the present study was to determine the effect of a short period of endurance training on cardiac dimensions in sedentary female subjects and to measure the AVPD at rest and during submaximal workload.

METHODS

Twelve sedentary female subjects (21.9 +/- 1.3 yr, 168.8 +/- 3.5 cm, 64.0 +/- 6.6 kg, and 42.6 +/- 2.9 mL x kg(-1) x min(-1) in maximal oxygen uptake) were examined with echocardiography before and after a period of interval training (varying from 2 to 5 min at 90-95% of maximal heart rate, 3 d x wk(-1), 8 wk).

RESULTS

Maximal oxygen uptake increased by 18% to 50.4 +/- 3.1 mL x kg(-1) x min(-1) (P < 0.001). Left ventricular mass increased from 123.9 to 139.2 g (P = 0.007). There was a significant increase in posterior wall thickness but no change in cavity size. The AVPD did not change at rest but increased significantly from 15.6 to 17.6 mm (P < 0.001) during exercise at 85-90% of maximal heart rate.

CONCLUSION

This study shows that a short period of aerobic endurance training induces changes in the female heart, both in cardiac dimensions at rest and in left ventricular systolic function at submaximal workload. AVPD during submaximal exercise discriminate well between the untrained and trained healthy heart.

Reduced submaximal leg blood flow after high-intensity aerobic training

This study evaluated the hypothesis that active muscle blood flow is lower during exercise at a given submaximal power output after aerobic conditioning as a result of unchanged cardiac output and blunted splanchnic vasoconstriction. Eight untrained subjects (4 men, 4 women, 23-31 yr) performed high-intensity aerobic training for 9-12 wk. Leg blood flow (femoral vein thermodilution), splanchnic blood flow (indocyanine green clearance), cardiac output (acetylene rebreathing), whole body O(2) uptake (VO(2)), and arterial-venous blood gases were measured before and after training at identical submaximal power outputs (70 and 140 W; upright 2-leg cycling). Training increased (P < 0.05) peak VO(2) (12-36%) but did not significantly change submaximal VO(2) or cardiac output. Leg blood flow during both submaximal power outputs averaged 18% lower after training (P = 0.001; n = 7), but these reductions were not correlated with changes in splanchnic vasoconstriction. Submaximal leg VO(2) was also lower after training. These findings support the hypothesis that aerobic training reduces active muscle blood flow at a given submaximal power output. However, changes in leg and splanchnic blood flow resulting from high-intensity training may not be causally linked.

Impact of different sports and training on cardiac structure and function

There is overwhelming evidence, particularly from echocardiography, that the heart of competitive athletes may differ from that of nonathletes, matched for age, gender, and body size. A larger left ventricular mass has been shown in athletes performing predominantly dynamic aerobic and anaerobic sports, in athletes engaged in static training, and in players of ball sports. Enlargement of the left ventricular internal diameter was most pronounced and reached about 10% in athletes performing predominantly dynamic sports; mainly strength training athletes had a lesser increase of the internal dimension, which was limited to 2.5%. Also the left ventricular wall appeared to be thickened in all types of athletes compared with controls. In sports with high dynamic and low static demands, wall thickness was proportionate or slightly disproportionate to the size of the internal diameter so that relative wall thickness was not different from controls or slightly increased (predominantly eccentric hypertrophy). In strength athletes, the disproportionate increase of wall thickness averaged about 12% (predominantly concentric hypertrophy). In sports with high dynamic and high static demands and requiring prolonged training, such as cycling, the increases of absolute and relative wall thickness reached 29% and 19% and were more pronounced than in runners (mixed hypertrophy). A plausible interpretation of these results is that the development of so-called eccentric or concentric left ventricular hypertrophy according to the type of sports cannot be regarded as an absolute or dichotomous concept because training regimens and sports activities are not exclusively dynamic or static and because the load on the heart is not purely of the volume or the pressure type. Most studies agree that left ventricular systolic and diastolic function is normal in the athlete at rest, whereas diastolic function seems to be enhanced in the exercising endurance athlete. The consistency of the results of studies on athletes in the competitive and the resting season, of training of sedentary subjects, and of spinal cord-injured patients suggests that variations in physical activity can alter left ventricular structure; genetic factors do not seem to be involved in the size of the left ventricular internal diameter but have to be taken into account to interpret wall thickness.

Exercise training in patients with severe congestive heart failure: enhancing peak aerobic capacity while minimizing the increase in ventricular wall stress

OBJECTIVES

The aims of the study were to 1) assess the effects of 12 weeks of exercise training at low work loads (i.e., corresponding to < or = 50% of peak oxygen consumption [Vo2]) on peak Vo2 and hyperemic calf blood flow in patients with severe congestive heart failure; and 2) evaluate left ventricular diastolic pressure and wall stress during exercise performed at work loads corresponding to < or = 50% and 70% to 80% of peak Vo2.

BACKGROUND

Whether the benefits of exercise training can be achieved at work loads that result in lower left ventricular diastolic wall stress than those associated with conventional work loads is unknown in patients with severe congestive heart failure.

METHODS

Sixteen patients with severe congestive heart failure trained at low work loads for 1 h/day, four times a week, for 12 weeks. Peak Vo2 and calf and forearm reactive hyperemia were measured before and during training. Nine of the 16 patients underwent right heart catheterization and echocardiography during bicycle exercise at low and conventional work loads (i.e., 50% and 70% to 80% of peak Vo2, respectively).

RESULTS

The increase in left ventricular diastolic wall stress was substantially lower during exercise at low work loads than during exercise at conventional work loads, (i.e., [mean +/- SEM] 23.3 +/- 7.4 vs. 69.6 +/- 8.1 dynes/cm2 (p < 0.001). After 6 and 12 weeks of training, peak Vo2 increased from 11.5 +/- 0.4 to 14.0 +/- 0.5 and 15.0 +/- 0.5 ml/kg per min, respectively (p < 0.0001 vs. baseline for both). Peak reactive hyperemia significantly increased in the calf but not in the forearm. The increases in peak Vo2 and calf peak reactive hyperemia correlated closely (r = 0.61, p < 0.02).

CONCLUSIONS

In patients with severe congestive heart failure, peak Vo2 is enhanced by exercise training at work loads that result in smaller increases in left ventricular diastolic wall stress than those observed at conventional work loads.

Effects of endurance training on left ventricular performance: a study in anaesthetized rabbits

Endurance training is known to increase ventricular performance during exercise and to decrease resting heart rate. The aim of this study was to evaluate a model for endurance training in rabbits and to study the effects of endurance training on local myocardial performance in the left ventricle during resting conditions. One group of rabbits underwent a 10-week exercise training programme. The rabbits trained 5 days a week on a treadmill. Training periods increased gradually from 15 min to 1 h with increments in speed from 0.5 to 1.2 km h-1. After the training programme the rabbits were anaesthetized and studied as acute open-chest preparations. A micro-tip pressure transducer was introduced via apex to the left ventricle and two pairs of ultrasonic crystals were implanted in the left anterior wall to measure segment lengths. One pair measured shortening in the circumferential direction whereas the other pair measured shortening in the longitudinal direction. Heart rate was lower in the trained group (n = 5), 172 +/- 9 beats min-1 (mean +/- SEM), compared with 235 +/- 19 beats min-1 in the control group (n = 8) (P < 0.02). Stroke volume, measured by radio-nuclidelabelled microspheres, was greater in the trained rabbits compared with controls (P < 0.03). Shortening in both segments was of similar magnitude for the trained and control groups. End-systolic pressure-length relations (ESPLR) obtained by occlusion of the descending aorta (balloon catheter) showed reduced slopes for longitudinal segments in the trained group compared with the control group (P < 0.05). We conclude that this endurance training programme in rabbits can be used to study myocardial effects of endurance training. Furthermore, the less steep slope of ESPLRs for the longitudinal segment in the trained animals might indicate a structural myocardial remodelling and increased contractile reserve that might be recruited during adrenergic stimulation in the trained group.

Characterization of sports by the VO2 dynamics of athletes in response to sinusoidal work load

The purpose of this study was to evaluate the specificity of maximal oxygen uptake (VO2max) and the dynamic response of oxygen uptake (VO2) to sinusoidal work load in distance runners and in American-football players. Sinusoidal work load during ergometer cycling was carried from 30 W to 60% to VO2max (60% VO2max) for a 2 min period. VO2 was measured by the breath-by-breath method. The subjects were 10 distance runners (DRs), 10 American-football players (AFPs), and 11 untrained men (UTM). Mean VO2max was 64.4 mL kg-1 min-1 in the DRs, 53.1 mL kg-1 min-1 in the AFPs and 47.3 mL kg-1 min-1 in the UTM. The fundamental amplitudes of the VO2 response, normalized by dividing by steady state VO2 at 60% VO2max, were similar in the AFPs (20.3%) and the UTM (19.5%), and both were significantly less than in the DRs (25.5%). Phase shift to work load expressed in degrees was similar in the AFPs (87.7 degrees) and UTM (88.0 degrees), but significantly greater than in the DRs (80.4 degrees). HR dynamics in all three groups were similar to a dynamic VO2 response. These findings suggest that development of the dynamic VO2 response and higher VO2max is achieved in the DRs. They also suggest that despite the higher VO2max in the AFPs there is no improvement in the dynamic VO2 response. The results of the present study demonstrate that athletes participating in different sports have characteristic dynamic VO2 responses during cycling exercise.

Physical fitness as a predictor of cardiovascular mortality in asymptomatic North American men. The Lipid Research Clinics Mortality Follow-up Study

Limited data are available on the relation between physical fitness and mortality from cardiovascular disease. We examined this question in a study of 4276 men, 30 to 69 years of age, whom we followed for an average of 8.5 years. Examinations at base line included assessment of conventional coronary risk factors and treadmill exercise testing. The heart rate during submaximal exercise (stage 2 of the exercise test) and the duration of exercise were used as measures of physical fitness. Men with incomplete data (n = 308) or who were using cardiovascular drugs (n = 213) were excluded from the analysis. Men who had clinical evidence of cardiovascular disease at base line (n = 649) were analyzed separately. Forty-five deaths from cardiovascular causes occurred among the remaining 3106 men. A lower level of physical fitness was associated with a higher risk of death from cardiovascular and coronary heart disease, after adjustment for age and cardiovascular risk factors. The relative risk of death from cardiovascular causes was 2.7 (95 percent confidence interval, 1.4 to 5.1; P = 0.003) for healthy men with an increment of 35 beats per minute in the heart rate during stage 2, and 3.0 (95 percent confidence interval, 1.6 to 5.5; P = 0.0004) for those with a decrement of 4.4 minutes in the exercise time spent on the treadmill. The corresponding values for death from coronary heart disease were 3.2 (95 percent confidence interval, 1.5 to 6.7; P = 0.003) and 2.8 (95 percent confidence interval, 1.3 to 6.1; P = 0.007), respectively. We conclude that a lower level of physical fitness is associated with a higher risk of death from coronary heart disease and cardiovascular disease in clinically healthy men, independent of conventional coronary risk factors.