Effects of short-term training on cardiac function during prolonged exercise

To determine the relationship between the training-induced increases in plasma volume (PV) and alterations in cardiac performance during prolonged submaximal cycle exercise, seven male subjects were studied prior to and following a short-term (3 d) training period (2 h.d-1 at 65% VO2max). Mean (range) VO2max was 3.42 l.min-1 (2.96-3.87). Training resulted in a 20% increase (P less than 0.05) in plasma volume (PV) and a 12% increase (P less than 0.05) in total blood volume (TBV). In contrast, training had no effect (P greater than 0.05) in altering exercise VO2, VCO2, VE BTPS, or RER. Cardiac output (Q) was higher (P less than 0.05) posttraining at all exercise sampling times (30, 60, 90, and 120 min). The elevations in Q were accompanied by an average decrease (P less than 0.05) in stroke volume (SV) of 22 ml. Arteriovenous O2 (a-v O2) difference was depressed (P less than 0.05) during exercise following the training. Although elevations (P less than 0.05) in core temperature (degrees C) occurred during the exercise, the training-induced PV increases did not affect thermoregulatory behavior. These results indicate that an early adaptive response to exercise training is an elevation in Q, an increase in SV, and a reduction in HR. These effects persist during prolonged exercise in spite of the progressive increase in body heat content. It is proposed that the increase in Q serves primarily to increase muscle blood flow and maintain arterial O2 delivery, while the altered cardiodynamic behavior serves to increase cardiac reserve, providing a greater tolerance to prolonged heavy exercise.     

Impact of repeated prolonged exercise bouts on cardiac function and biomarkers

PURPOSE: The present study examined the impact of repeated bouts of prolonged (< 60 min) exercise on left ventricular function and cardiac biomarkers. METHODS: Ten athletes completed a 15.3-mile hill run on three consecutive days and were assessed before, immediately after, 1 h after, and 20 h after each bout. Six of the athletes completed a fourth bout. Left ventricular (LV) function was examined echocardiographically using two-dimensional M-mode, Doppler, and flow propagation velocity (Vp). Venous blood samples were analyzed for cardiac biomarkers including cardiac troponin T (cTnT). RESULTS: Ejection fraction (EF) significantly decreased (P = 0.027) after the third exercise bout compared with baseline (mean +/- SD: 56.3 +/- 4.4 vs 51.3 +/- 5.9%), accompanied by a nonsignificant decrease in systolic blood pressure/end systolic volume (SBP/ESV) ratio. A sustained depression in systolic function 20 h after bout 3 also persisted in the subset who completed a fourth bout, yet this did not reach clinical levels. Significant (P < 0.01) reductions in early to late diastolic filling (E:A) ratio pre-to post-bout 1 (mean +/- SD: 1.9 +/- 0.5 vs 1.4 +/- 0.3) and pre- to post-bout 3(2.0 +/- 0.5 vs 1.3 +/- 0.4) normalized after each 20-h recovery period. A similar pattern of change was observed in Vp. Cardiac troponin T was elevated in four individuals 1 h after bout 1 (range: 0.013-0.125 microg.L(-1)) but was undetectable thereafter except in one athlete. CONCLUSION: Repeated bouts of prolonged exercise induce short-term reductions in diastolic filling and a cumulative decrease in systolic function, yet these alterations seem to have minimal clinical or functional impact. Elevated cTnT after the initial bout, but not thereafter, may represent an adaptive response to prolonged exercise.     

Effect of prolonged exercise in a hypoxic environment on cardiac function and cardiac troponin T

BACKGROUND: Exercise induced cardiac fatigue has recently been observed after prolonged exercise. A moderate to high altitude has been suggested as a possible stimulus in the genesis of such cardiac fatigue. OBJECTIVE: To investigate if exercise induced cardiac fatigue and or cardiac damage occurs after prolonged exercise in a hypoxic environment. METHODS: Eight trained male triathletes volunteered for the study. Each completed two 50 mile cycle trials, randomly assigned from normobaric normoxia and normobaric hypoxia (15% FIO(2)). Echocardiographic assessment and whole blood collection was completed before, immediately after, and 24 hours after exercise. Left ventricular systolic and diastolic functional variables were calculated, and serum was analysed for cardiac troponin T. Results were analysed using a two way repeated measures analysis of variance, with alpha set at 0.05. RESULTS: No significant differences were observed in either systolic or diastolic function across time or between trials. Cardiac troponin T was detected in one subject immediately after exercise in the normobaric hypoxic trial. CONCLUSIONS: A 50 mile cycle trial in either normobaric normoxia or normobaric hypoxia does not induce exercise induced cardiac fatigue. Some people, however, may exhibit minimal cardiac damage after exercise in normobaric hypoxia. The clinical significance of this is yet to be elucidated.     

Clinical significance of cardiac damage and changes in function after exercise

Acute bouts of ultraendurance exercise may result in the appearance of biomarkers of cardiac cell damage and a transient reduction in left ventricular function. The clinical significance of these changes is not fully understood. There seems to be two competing issues to be resolved. First, could prolonged endurance exercise produce a degree of cardiac stress and/or damage that results, during the short or long term, in deleterious consequences for cardiac health. Second, there is a clear need to educate those responsible for the medical care of endurance athletes about the possibility of a transient reduction in cardiac function and the appearance of cTnT/cTnI after an exercise. Minor elevations in cardiac troponins are commonplace after an endurance exercise in elite and recreational athletes and may occur alongside exercise-associated collapse. Misdiagnosis of myocardial injury and subsequent mismanagement can be unnecessarily expensive and psychologically damaging to the athlete. Diagnosis of myocardial injury after prolonged exercise should be made on the basis of all available information and not blood tests alone. The clinical significance of chronic exposure to endurance exercise is unknown. The development of myocardial fibrosis has been suggested as a long-term outcome to chronic exposure to repetitive bouts of endurance exercise and has been linked to an exercise-induced inflammatory process observed in an animal model. This hypothesis is supported by a limited number of studies reporting postmortem studies in athletes and an increased prevalence of complex arrhythmia in veteran athletes. Care is warranted in promoting this hypothesis without further detailed work, given the unequivocal link between exercise and mortality and morbidity. It would seem erroneous, however, to assume that a linear relationship exists between exercise volume and cardiac health.     

Influence of exercise duration and hydration status on cognitive function during prolonged cycling exercise

The purpose of the present study was to examine the influence of submaximal aerobic exercise duration on simple and complex cognitive performance. Eight well-trained male subjects agreed to participate in this study (trial group). A control group of eight regularly trained male subjects was included for comparative purposes. For the trial group, the experiment involved a critical flicker fusion test (CFF) and a map recognition task performed before, every 20 min during, and immediately after, a 3-h cycling task at an intensity corresponding to approximately 60 % of VO2max. Data were obtained over two experimental sessions with fluid ingestion (F) or no fluid (NF) ingestion. For the control group the experiment was the same but without exercise and fluid ingestion. In the trial group, a significant effect of hydration status was observed on physiological parameters (p <0.05). No effect was found on cognitive performance. A significant decrease in CFF performance was observed after 120 min of exercise when compared with the first 20 min (respectively for CFFmdi: 2.6 vs. 3.8 Hz), irrespective of experimental condition. A significant improvement in speed of response (respectively: 3291 vs. 3062 msec for 20 and 120 min, respectively) and a decrease in error number (21.5 % vs. 6.0 % for 20 and 120 min, respectively) during the map recognition task were recorded between 80 min and 120 min when compared with the first 20 min of exercise. After 120 min the number of recorded errors was significantly greater indicating a shift in the accuracy-speed trade-off (6.0 % vs. 14.1 % for 120 and 180 min, respectively). These results provide some evidence for exercise-induced facilitation of cognitive function. However this positive effect disappears during prolonged exercise--as evidenced within our study by an increase in errors during the complex task and an alteration in perceptual response (i.e. the appearance of symptoms of central fatigue).     

Depressed systolic and diastolic cardiac function after prolonged aerobic exercise in healthy subjects.

We studied 11 healthy untrained volunteers (aged 28.9 +/- 4.6 years) during 60 minutes of aerobic ergometric exercise with constant heart rates of 130 to 140 beats/minute. We found a continuous and significant decrease in systolic and diastolic pressure from 175 +/- 18/77 +/- 7 mmHg in the 5th minute to 144 +/- 14/68 +/- 6 mmHg in the 60th minute of exercise. Cardiac function and structure were assessed by M-mode echocardiography before exercise, after 5 minutes and after 60 minutes of exercise at comparable heart rates. The results demonstrated significant decreases in cardiac output, ejection fraction, and diastolic posterior wall velocity and an increase in total peripheral resistance after 60 minutes of exercise. We conclude that the decrease in blood pressure during long-term aerobic exercise in healthy untrained subjects might be at least influenced by a decrease in left ventricular filling and contractility, possibly indicating cardiac fatigue.     

Effect of fluid ingestion on neuromuscular function during prolonged cycling exercise

Objectives: To investigate the effects of fluid ingestion on neuromuscular function during prolonged cycling exercise.

Methods: Eight well trained subjects exercised for 180 minutes in a moderate environment at a workload requiring ~60% maximal oxygen uptake. Two conditions, fluid (F) and no fluid (NF) ingestion, were investigated.

Results: During maximal voluntary isometric contraction (MVC), prolonged cycling exercise reduced (p<0.05) the maximal force generating capacity of quadriceps muscles (after three hours of cycling) and root mean square (RMS) values (after two hours of cycling) with no difference between the two conditions despite greater body weight loss (p<0.05) in NF. The mean power frequency (MPF) for vastus lateralis muscle was reduced (p<0.05) and the rate of force development (RFD) was increased (p<0.05) only during NF. During cycling exercise, integrated electromyographic activity and perceived exertion were increased in both conditions (p<0.05) with no significant effect of fluid ingestion.

Conclusions: The results suggest that fluid ingestion did not prevent the previously reported decrease in maximal force with exercise duration, but seems to have a positive effect on some indicators of neuromuscular fatigue such as mean power frequency and rate of force development during maximal voluntary contraction. Further investigations are needed to assess the effect of change in hydration on neural mechanisms linked to the development of muscular fatigue during prolonged exercise.

     

Cardiovascular drift during prolonged exercise: new perspectives

We propose that cardiovascular drift, characterized by a progressive decline in stroke volume after 10-20 min of exercise, is primarily due to increased heart rate rather tahn a progressive increase in cutaneous blood flow as body temperature rises.     

The incidence of hyponatremia during prolonged ultraendurance exercise

Recent studies have shown that potentially fatal hyponatremia can develop during prolonged exercise. To determine the incidence of hyponatremia in athletes competing in ultradistance events, we measured serum sodium levels in 315 of 626 (50%) runners who were treated for collapse after two 90 km ultramarathon footraces (total starters 20,335; total finishers 18,031) and in 101 of 147 (69%) finishers in a 186 km ultratriathlon. In both races the athletes drank fluids with low sodium chloride content (less than 6.8 mmol.l-1). Hyponatremia (serum sodium level less than 130 mmol.l-1) was identified in 27 of 315 (9%) collapsed runners in the 90 km races and in none of the triathletes. In response to diuretic therapy, the runner with the most severe hyponatremia (serum sodium level = 112 mmol.l-1) excreted in excess of 7.5 l dilute urine during the first 17 h of hospitalization. These data suggest that, although symptomatic hyponatremia occurs in less than 0.3% of competitors during prolonged exercise even when they ingest little sodium chloride, it is found in a significant proportion (9%) of collapsed runners. A regulated contraction of the extracellular fluid volume would explain why the majority of athletes maintain normal serum sodium levels even though they develop a significant sodium chloride deficit during prolonged exercise. Alternatively, sodium chloride losses during prolonged exercise may be substantially less than are currently believed. Physicians treating collapsed ultradistance athletes need to be aware that as many as 10% or more of such patients may be hyponatremic.     

Sex differences in fitness and cardiac function during exercise in adolescents with chronic fatigue

Females demonstrate less robust Frank‐Starling mechanism with respect to cardiac preload than males at rest. We asked whether this phenomenon would also affect cardiac performance during exercise. We hypothesized that stroke volume (SV ) response to exercise would be more limited in deconditioned females such that cardiac output would be mainly rate dependent, compared with males. We conducted a chart audit of clinical exercise tests performed by adolescents with chronic fatigue. Oxygen uptake () was measured breath‐by‐breath at rest and during cycle ergometry, while cardiac output was measured by acetylene rebreathing at rest plus 2‐3 subthreshold workloads. SV response was analyzed in two ways: after normalization for body surface area (SV index, SVI ) and as percentage change from resting values. Among 304 adolescents (78% females) with chronic fatigue, 189 (80%) of 236 females and 52 (76%) of 68 males were deconditioned (peakO₂ <90% predicted). Heart rate trajectory during exercise was steeper for unfit than fit females, 70 vs 61 beat·min⁻¹ per L·min⁻¹ , (P =.003); but not for males, 47 vs 42 beat·min⁻¹ per L·min⁻¹ (P =.23). The highest measured SVI did not differ between unfit vs fit females (42.8 vs 41.5 mL·m⁻², P =.39) while fit males showed larger SV during exercise than their unfit peers (highest SVI 55.9 vs 48.0 mL·m⁻², P =.014). Both qualitative and quantitative sex differences exist in SV responses to exercise among chronically fatigued adolescents, suggesting volume loading may be more efficacious in girls.     

Protein and energy metabolism during prolonged exercise in trained athletes

Eight elite triathlon athletes participated in a laboratory study of the effects of endurance exercise on protein and energy metabolism. The study consisted of 3 h of cycling and 5 h of treadmill running; 3.5 h before beginning the exercise, a primed constant infusion of 1-13C leucine and 6,6(-2)H glucose was begun. Serial blood samples were collected during the rest and exercise periods for isotopic analysis. Respiratory gas exchange was determined every half hour. Results: the subjects exercised at an average of 53% +/- 3% of peak VO2. During the 8-h exercise period there was a decline in glucose utilization and an increase in lipid oxidation. For the first part of the exercise, most of the glucose oxidized was of muscle origin. Hepatic glucose production increased with exercise from 20 g/h to a maximum of about 60 g/h after 4 h of exercise and then decreased toward the pre-exercise rate. The plasma urea concentration was unchanged during the study. The leucine flux decreased during the first 4 h of exercise and then attained a new plateau about 20% lower than the pre-exercise value indicating an adaptive reduction in protein turnover.     

Cardiovascular fitness and thermoregulation during prolonged exercise in man.

Nine healthy male subjects differing in their training status (VO2 max 54 +/- 7 ml.min-1.kg-1, mean +/- SD; 43-64 ml.min-1 kg-1, range) exercised on two occasions separated by one week. On each occasion, having fasted overnight, subjects exercised for 1 h on an electrically braked cycle ergometer at a workload equivalent to 70 per cent VO2 max (test A) or at a fixed workload of 140 W (test B). Each test was assigned in a randomized manner and was performed at an ambient temperature of 22.5 +/- 0.0 degrees C and a relative humidity of 85 +/- 0 per cent. Absolute exercise workload was the most successful predictor of sweat loss during test A (r = 0.82, p less than 0.01). Sweat loss was also related to VO2 max tests A (r = 0.67, p less than 0.05) and B (r = 0.67, p less than 0.05). There was no relationship between resting pre-exercise core temperature and VO2 max. However, core temperature recorded during the final min of exercise in test B was inversely related to VO2 max (r = -0.86, p less than 0.01). As a consequence, core temperature during the final minute of exercise was also related to the relative exercise intensity (% VO2 max) performed (r = 0.82, p less than 0.01). The heart rate response during test B was inversely related to VO2 max (r = -0.71, p less than 0.05) and was positively related to the relative exercise intensity performed (r = 0.68, p less than 0.05). No relationship was found between weighted mean skin temperature during the final minute of exercise and the relative (r = 0.26) or absolute (r = 0.03) workloads performed during exercise. The results of the present experiment suggest that cardiovascular fitness (as indicated by VO2 max) will have a significant influence upon the thermoregulatory responses of Man during exercise.     

Serial assessment of cardiac function during and after exercise by an ambulatory ventricular function monitor (VEST)

Cardiac function was serially assessed during and after exercise by an ambulatory ventricular function monitor (VEST) in 31 patients who received coronary angiography. Based on the study of fluctuation during the baseline recording, greater than or equal to 6% change in ejection fraction (EF) was considered significant. The serial changes in EF during exercise was divided into 5 types, including continuous increase (type A), initial increase but return to the baseline (type B), no change (type C), initial increase but later decrease below the baseline (type D), and continuous decrease (type E). Among 8 normal subjects, their EF changes during exercise showed type A in 3, type B in 2, type C in 2, and type D in 1. Among 21 patients with coronary artery disease, the EF changes showed type A in 5, type B in 4, type C in 4, type D in 5 and type E in 3. Thus, there was a significant overlap in EF response between normal and coronary patients. However, every patient showing type A and B had single-vessel disease, and 63% of them had persistent thallium defect without redistribution. After the exercise, 29 patients showed rapid increase in EF. The time to the peak EF was significantly longer in coronary patients (1.88 +/- 1.24 min) than that in normal cases (0.88 +/- 0.55 min) (p less than 0.05) particularly in patients with multi-vessel disease (2.22 +/- 1.29 min). In addition, those showing type C, D or E tended to have a longer time to peak EF and more increase in EF after exercise than those showing type A or B. These data suggest that VEST is suitable for continuous measurement of cardiac function during and after exercise which provided valuable indices for assessment of severity of ischemia in coronary artery disease.     

Gastric emptying during prolonged cycling exercise in the heat

Eight trained male cyclists (age 20-33 yr) completed four 3-h bouts of cycling at 60% peak VO2 in the heat (33 degrees C) drinking either water (W), 5% glucose (G), 5% glucose polymer (GP), or 3.2% glucose polymer + 1.8% fructose (GP/F) at a rate of 350 ml every 20 min (3.15 l total volume). Similar changes in heart rate, sweat rate, rectal and mean skin temperatures, and plasma [Na+], [K+], and osmolality were observed during all trials. Mean changes in plasma volume, although not significantly different between trials, were lowest for the GP/F drink (-2.6%) and greatest for the G (-8.1%) drink. Plasma volume decreased (P less than 0.05) below pre-exercise control values during the W, G, and GP trails but was maintained at control values during the GP/F trials. In contrast to water ingestion, G, GP, and GP/F ingestion maintained plasma glucose and respiratory exchange ratios throughout the 3-h exercise bouts. Gastric residual volume (GRV) obtained at the end of exercise was similar for the W, GP, and GP/F trials. The G trials yielded greater (P less than 0.05) GRV than W trials. For all drinks ingested, over 90% of the 3.15 l consumed was emptied from the stomach during the 3-h exercise bouts. At a mean sweat rate of 1.2 l.h-1, cyclists replaced 73% of fluid lost and experienced only a 1.6% loss in body weight. This study demonstrates that, during prolonged (3-h) cycling exercise in the heat, large volumes of W and 5% carbohydrate can be emptied from the stomach to help minimize the effects of dehydration.     

Left ventricular function immediately following prolonged exercise: A meta-analysis

PURPOSE: Evidence supporting cardiac fatigue following prolonged endurance exercise remains equivocal. The purpose of this meta-analysis was to quantify all data fulfilling the specified inclusion criteria, examining the short-term effect of prolonged endurance exercise on left ventricular function. METHODS: A random effects meta-analysis of the weighted mean change in ejection fraction (EF), systolic blood pressure/end systolic volume (SBP/ESV) ratio, and early-to-late diastolic filling (E/A) was conducted on 23 studies using the SE of the between-subjects SD. HR, SBP, and left ventricular internal diameter during diastole (LVIDd) were also analyzed. Studies were coded according to exercise duration and training status: moderate duration trained (MDt) and untrained (MDu), 60-150 min; long duration (LD), 166-430 min; and ultra duration (UD), 640-1440 min. Relationships were assessed via Pearson's product-moment correlation. RESULTS: A significant (P < 0.05) overall decrease in EF (mean, confidence interval (CI): -1.95%, -1.03 to -2.88%), SBP/ESV (mean, CI: -0.8, -0.63 to -0.97), and E/A (mean, CI: -0.45, -0.39 to -0.51) was observed. Only UD and MDu subgroups demonstrated a reduction in EF. All subgroups demonstrated significant (P < 0.05) decreases in E/A. Alterations in LVIDd and SBP were related to respective decreases in EF and SBP/ESV, but not to E/A. CONCLUSION: The decrease in EF and SBP/ESV observed in UD and MDu indicates a reduction in systolic function, partially explained by altered cardiac loading. A decrease in E/A in all subgroups, unrelated to changes in loading, suggests an intrinsic impairment of left ventricular relaxation. Future investigators should employ load-independent indices of cardiac function and attempt to uncover the mechanisms of this phenomenon.     

Sex difference in fluid balance responses during prolonged exercise

Maintaining a proper fluid balance is important during exercise as athletes are prone to develop dehydration during exercise. Although several factors may regulate the fluid balance, little is known about the role of sex during prolonged moderate‐intensity exercise. Therefore, we compared body mass changes and fluid balance parameters in men vs women in a large heterogeneous group of participants during prolonged exercise. Ninety‐eight volunteers walked 30–50 km at a self‐selected pace. Exercise duration (8 h, 32 min) and intensity (69% HR_max) were comparable between groups. Men demonstrated a significantly larger change in body mass than women (?1.6% vs ?0.9%, respectively, P < 0.001) and a higher incidence of dehydration (defined as ≥2% body mass loss) compared with women (34% vs 12%, respectively, odds ratio = 4.2, 95% CI = 1.1–16.7). Changes in blood sodium levels were significantly different between men (+1.5 mmol/L) and women (?0.4 mmol/L), while 27% of the men vs 0% of the women showed postexercise hypernatremia (sodium levels ≥ 145 mmol/L). Moreover, men demonstrated a significantly lower fluid intake (2.9 mL/kg/h) and higher fluid loss (5.0 mL/kg/h) compared with women (3.7 and 4.8 mL/kg/h, respectively). Taken together, our data suggest that men and women demonstrate different changes in fluid balance in response to a similar bout of exercise.