Effects of acute expansion of plasma volume on cardiovascular and thermal function during prolonged exercise

Exercise induced plasma volume expansion lowers cardiovascular strain during 15-km cycling time-trial in acute normobaric hypoxia

The purpose of our study was to assess the influence of a single high-intensity interval exercise (HIIE) bout in normoxia on plasma volume (PV) and consequent cycling performance in normobaric hypoxia (0.15 FiO2, simulating ~2,500 m). Eight males (VO2peak: 48.8 ± 3.4 mL/kg/min, 24.0 ± 1.6 years) completed a hypoxic 15 km cycling time trial (TT), followed by a crossover intervention of either HIIE (8x4 min cycling bouts at 85% of VO2peak) or CON (matched kJ production from HIIE at 50% of VO2peak). 48 hours post intervention, an identical TT was performed. Cardiovascular parameters were measured via impedance cardiography during each TT. Changes in PV was measured 24 and 48 hours post HIIE and CON. HIIE increased PV at 24 (4.1 ± 3.9%, P = 0.031) and 48 (6.7 ± 1.7, P = 0.006) hours post, while no difference was observed following the CON (1.3 ± 1.1% and 0.3 ± 2.8%). The higher PV led to an increased stroke volume (P = 0.03) and cardiac output (P = 0.02) during the hypoxic TT, while heart rate was not changed (P = 0.49). We observed no changes in time to completion (-0.63 ± 0.57 min, P = 0.054) and power output (7.37 ± 7.98 W, P = 0.078) between TTs. In the absence of environmental stress, a single bout of HIIE was an effective strategy to increase PV and reduce the cardiovascular strain during a cycling TT at moderate simulated altitude but did not impact hypoxic exercise performance. Trial registration: Clinical Trials ID: NCT05800808.

Durability is improved by both low and high intensity endurance training

Introduction: This is one of the first intervention studies to examine how low- (LIT) and high-intensity endurance training (HIT) affect durability, defined as 'time of onset and magnitude of deterioration in physiological-profiling characteristics over time during prolonged exercise'. Methods: Sedentary and recreationally active men (n = 16) and women (n = 19) completed either LIT (average weekly training time 6.8 ± 0.7 h) or HIT (1.6 ± 0.2 h) cycling for 10 weeks. Durability was analyzed before and after the training period from three factors during 3-h cycling at 48% of pretraining maximal oxygen uptake (VO_2max): 1) by the magnitude and 2) onset of drifts (i.e. gradual change in energy expenditure, heart rate, rate of perceived exertion, ventilation, left ventricular ejection time, and stroke volume), 3) by the 'physiological strain', defined to be the absolute responses of heart rate and its variability, lactate, and rate of perceived exertion. Results: When all three factors were averaged the durability was improved similarly (time x group p = 0.42) in both groups (LIT: p = 0.03, g = 0.49; HIT: p = 0.01, g = 0.62). In the LIT group, magnitude of average of drifts and their onset did not reach statistically significance level of p < 0.05 (magnitude: 7.7 ± 6.8% vs. 6.3 ± 6.0%, p = 0.09, g = 0.27; onset: 106 ± 57 min vs. 131 ± 59 min, p = 0.08, g = 0.58), while averaged physiological strain improved (p = 0.01, g = 0.60). In HIT, both magnitude and onset decreased (magnitude: 8.8 ± 7.9% vs. 5.4 ± 6.7%, p = 0.03, g = 0.49; onset: 108 ± 54 min vs. 137 ± 57 min, p = 0.03, g = 0.61), and physiological strain improved (p = 0.005, g = 0.78). VO_2max increased only after HIT (time x group p < 0.001, g = 1.51). Conclusion: Durability improved similarly by both LIT and HIT based on reduced physiological drifts, their postponed onsets, and changes in physiological strain. Despite durability enhanced among untrained people, a 10-week intervention did not alter drifts and their onsets in a large amount, even though it attenuated physiological strain.

Myocardial dimensions and hemodynamics during 24-h ultraendurance ergometry

PURPOSE

This study aimed to evaluate cardiorespiratory and hemodynamic responses during 24 h of continuous cycle ergometry in ultraendurance athletes.

METHODS

Eight males (mean ± SD; age = 39 ± 8 yr, height = 179 ± 7 cm, body weight [Wt] = 77.1 ± 6.0 kg) were monitored during 24 h at a constant workload,∼25% below the first lactate turn point at 162 ± 23 W. Measurements included Wt, HR, oxygen consumption (V˙O2), cardiac output (Q), and stroke volume (SV) determined by a noninvasive rebreathing technique (Innocor; Innovision, Odense, Denmark). Myocardial dimensions were evaluated using a two-dimensional echocardiogram. [M-mode measurement]-left atrial (LAD), ventricular end-diastolic (LVEDD), and end-systolic diameters (LVESD) were obtained over the left parasternal area. Venous blood samples were analyzed for hematocrit (Hct%), albumin (g·L(-1)), aldosterone (pg·mL(-1)), CK, CK-MB (U·L(-1)), and N-terminal pro-brain natriuretic peptide (NT-proBNP) (pg·mL(-1)).

RESULTS

HR (bpm) significantly increased (P < 0.01) from 1 h (132 ± 11) to 6 h (143 ± 10) and significantly decreased (P < 0.001) from 6 to 24 h (116 ± 10). V˙O2 and (Q were unchanged during the 24 h. Wt (76.6 ± 5.6 vs 78.7 ± 5.4), SV (117 ± 13 vs 148 ± 19), LVEDD (4.9 ± 0.3 vs 5.6 ± 0.2), and LAD (3.6 ± 0.5 vs 4.3 ± 0.7) significantly increased between 6 and 24 h (P < 0.001). No significant changes were observed for LVESD. Hct (45.1 ± 1.3 vs 41.3 ± 1.2) significantly decreased (P < 0.05) and CK (181 ± 60/877 ± 515), aldosterone (48 ± 17 vs 661 ± 172), and NT-proBNP (23 ± 13 vs 583 ± 449) significantly increased (P < 0.05). The increase in SV (ΔSV) was significantly related to changes in Wt (ΔWt), and HR (ΔHR) and ΔWt were significantly related to ΔLAD and ΔLVEDD.

CONCLUSION

Our findings suggest that the decrease in HR during 24 h of ultraendurance exercise was due to hypervolemia and the associated ventricular loading, increasing left ventricular diastolic dimensions because of increased SV and LVEDD, resulting in an increase in NT-proBNP.

Encapsulated environment

In many occupational settings, clothing must be worn to protect individuals from hazards in their work environment. However, personal protective clothing (PPC) restricts heat exchange with the environment due to high thermal resistance and low water vapor permeability. As a consequence, individuals who wear PPC often work in uncompensable heat stress conditions where body heat storage continues to rise and the risk of heat injury is greatly enhanced. Tolerance time while wearing PPC is influenced by three factors: (i) initial core temperature (Tc), affected by heat acclimation, precooling, hydration, aerobic fitness, circadian rhythm, and menstrual cycle (ii) Tc tolerated at exhaustion, influenced by state of encapsulation, hydration, and aerobic fitness; and (iii) the rate of increase in Tc from beginning to end of the heat-stress exposure, which is dependent on the clothing characteristics, thermal environment, work rate, and individual factors like body composition and economy of movement. Methods to reduce heat strain in PPC include increasing clothing permeability for air, adjusting pacing strategy, including work/rest schedules, physical training, and cooling interventions, although the additional weight and bulk of some personal cooling systems offset their intended advantage. Individuals with low body fatness who perform regular aerobic exercise have tolerance times in PPC that exceed those of their sedentary counterparts by as much as 100% due to lower resting Tc, the higher Tc tolerated at exhaustion and a slower increase in Tc during exercise. However, questions remain about the importance of activity levels, exercise intensity, cold water ingestion, and plasma volume expansion for thermotolerance.

The effects of creatine and glycerol hyperhydration on running economy in well trained endurance runners

Background

Ingestion of creatine (Cr) and glycerol (Gly) has been reported to be an effective method in expanding water compartments within the human body, attenuating the rise in heart rate (HR) and core temperature (T_core) during exercise in the heat. Despite these positive effects, a substantial water retention could potentially impair endurance performance through increasing body mass (BM) and consequently impacting negatively on running economy (RE). The objective of the present study was to investigate the effects of a combined Cr and Gly supplementation on thermoregulatory and cardiovascular responses and RE during running for 30 min at speed corresponding to 60% of maximal oxygen uptake (V˙O2max) in hot and cool conditions.

Methods

Cr·H₂O (11.4 g), Gly (1 g·kg^-1 BM) and Glucose polymer (75 g) were administered twice daily to 15 male endurance runners during a 7-day period. Exercise trials were conducted pre- and post-supplementation at 10 and 35°C and 70% relative humidity.

Results

BM and total body water increased by 0.90 ± 0.40 kg (P < 0.01; mean ± SD) and 0.71 ± 0.42 L (P < 0.01), respectively following supplementation. Despite the significant increase in BM, supplementation had no effect on V˙O2 and therefore RE. Both HR and T_core were attenuated significantly after supplementation (P < 0.05, for both). Nevertheless, thermal comfort and rating of perceived exertion was not significantly different between pre- and post-supplementation. Similarly, no significant differences were found in sweat loss, serum osmolality, blood lactate and in plasma volume changes between pre- and post-supplementation.

Conclusions

Combining Cr and Gly is effective in reducing thermal and cardiovascular strain during exercise in the heat without negatively impacting on RE.

Hypervolemia and Blood Alkalinity: Effect on Physiological Strain in a Warm Environment

Purpose:

To evaluate the influence of acute hypervolemia, achieved through the ingestion of a sodium citrate-rich beverage, on cardiovascular strain and thermoregulatory function, during moderate-intensity aerobic exercise in a warm environment. Sodium citrate’s ability to increase buffering capacity was also assessed.

Methods:

Twelve endurance-trained athletes completed two blind randomized treatment trials, separated by a minimum of seven days, on a cycle ergometer under heat stress (30.9°C, 64% RH). The subjects ingested 12 mL·kg−1of (1) Gatorade, the control (CNT), or (2) sodium-citrate plus Gatorade (NaCIT: 170 mmol Na+L−1) before cycling at 15% below ventilatory threshold (VT) for 62 minutes. Core and skin temperature, expired gas samples, heart rate, and perceived exertion were measured throughout exercise. Blood samples were taken before drinking each beverage, before commencing exercise, and throughout the exercise bout.

Results:

Plasma volume (PV) was significantly expanded in the NaCIT trial (3.6 ± 5.5%) and remained significantly higher throughout exercise in the NaCIT trial compared with the CNT trial (P ≤ .05). No significant differences were found in heart rate, in core and skin temperature, or in the metabolic data between the treatment groups. NaCIT significantly increased [HCO3−], base excess, and pH throughout the trial.

Conclusion:

Acute oral ingestion of high-sodium citrate beverages before moderate exercise induces mild levels of hypervolemia and improves blood-buffering capacity in humans; however, mild hypervolemia during 62 minutes of moderate exercise does not reduce physiological strain or improve thermoregulation.

Effects of creatine supplementation on aerobic power and cardiovascular structure and function

This project aimed to determine 1) whether creatine (Cr) supplementation affects cardiovascular structure and function and 2) to examine its effect on aerobic power. Eighteen males undertook aerobic testing on a cycle ergometer and echocardiographic assessment of the heart. The experimental group (N = 9) ingested 20g x day(-1) of Cr for seven days followed by l0g x day(-1) for a further 21 days. The control group (N = 9) followed an identical protocol ingesting a placebo for the same period. Assessment was performed pre-, mid- (seven days) and post-testing (28 days). A MANOVA with repeated measures was used to test for group differences before and after supplementation. The Cr group demonstrated a significant increase in body mass for the pre-mid (1.0 +/- 0.6 kg) and the pre-post (1.5 +/- 0.7 kg) testing occasions. Submaximal VO2 decreased significantly from the pre-mid and pre-post testing occasions by between 4.8% to 11.4% with Cr supplementation at workloads of 75 W and 150 W. Other oxygen consumption measures and exercise time to exhaustion, for the Cr group, showed decreasing trends that approached significance. Additionally, there was a significant pre-post decrease in maximum heart rate of 3.7%. There were no changes in any of the echocardiographic or blood pressure measures for either group. The present results suggest short term Cr supplementation has no detectable negative effect on cardiac structure or function. Additionally, Cr ingestion improves submaximal cycling efficiency. These results suggest that the increase in efficiency may be related to peripheral factors such an increase in muscle phosphocreatine, rather than central changes.

Training Principles and Issues for Ultra-endurance Athletes

Ultra-endurance competition is defined as events that exceed than 6 hours in duration. The longer events rely on long-term preparation, sufficient nutrition, accommodation of environmental stressors, and psychologic toughness. Successful ultra-endurance performance is characterized by the ability to sustain a higher absolute speed for a given distance than other competitors. This can be achieved through a periodized training plan and by following key principles of training. Periodization is an organization of training into large, medium and small training blocks which are referred to as macro-, meso-, and microcycles, respectively. When the sequencing of training is correctly applied, athletes can achieve a high state of competition readiness and during the months of hard training, avoid the overtraining syndrome. A plan is executed in accordance with the following principles of training: all-around development, overload, specificity, individualization, consistent training, and structural tolerance. Training relies heavily on the athlete's tolerance to repetitive strain. Today's ultra-endurance athlete must also follow appropriate nutritional practices in order to recover and prepare for daily training and remain injury free and healthy. Rehydration after exercise, together with the timing and method of increased food intake to cope with heavy training, are essential for optimal performance. Furthermore, the treatment of soft tissue after training or racing is necessary to control inflammation.

Effect of ultramarathon cycling on the heart rate in elite cyclists

OBJECTIVES

To analyse the heart rate (HR) response and estimate the ultraendurance threshold-the optimum maintainable exercise intensity of ultraendurance cycling-in ultraendurance elite cyclists competing in the Race across the Alps.

METHODS

HR monitoring was performed in 10 male elite cyclists during the first Race across the Alps in 2001 (distance: 525 km; cumulative altitude difference: 12 600 m) to investigate the exercise intensity of a cycle ultramarathon and the cardiopulmonary strains involved. Four different exercise intensities were defined as percentages of maximal HR (HR(max)) as follows: recovery HR (HR(re)), <70% of HR(max); moderate aerobic HR (HR(ma)), 70-80%; intense aerobic HR (HR(ia)), 80-90%; and high intensity HR (HR(hi)), >90%.

RESULTS

All athletes investigated finished the competition. The mean racing time was 27 hours and 25 minutes, and the average speed was 18.6 km/h. The mean HR(max) was 186 beats/min, and the average value of measured HRs (HR(average)) was 126 beats/min resulting in a mean HR(average)/HR(max) ratio of 0.68, which probably corresponds to the ultraendurance threshold. The athletes spent 53% (14 hours 32 minutes) of total race time within HR(re), 25% (6 hours 51 minutes) within HR(ma), 19% (5 hours 13 minutes) within HR(ia), and only 3% (49 minutes) within HR(hi), which shows the exercise intensity to be predominantly moderate (HR(re) + HR(ma) = 78% or 21 hours 23 minutes). The HR response was influenced by the course profile as well as the duration. In all subjects, exercise intensity declined significantly during the race, as indicated by a decrease in HR(average)/HR(max) of 23% from 0.86 at the start to 0.66 at the end.

CONCLUSIONS

A substantial decrease (10% every 10 hours) in the HR response is a general cardiovascular feature of ultramarathon cycling, suggesting that the ultraendurance threshold lies at about 70% of HR(max) in elite ultramarathon cyclists.

Increases in muscle MCT are associated with reductions in muscle lactate after a single exercise session in humans

To investigate the effects of a single session of prolonged cycle exercise [60% peak O2 uptake (VO2 peak) for 5-6 h] on metabolic adaptations in working vastus lateralis muscle, nine untrained males (peak O2 uptake = 47.2 +/- 1.1 ml x kg(-1) x min(-1), means +/- SE) were examined before (Pre) and at 2 (Post-2), 4 (Post-4), and 6 (Post-6) days after the training session. On the basis of 15 min of cycle exercise at 59% VO2 peak, it was found that training reduced (P < 0.05) exercise muscle lactate (mM) at Post-2 (6.65 +/- 0.69), Post-4 (7.74 +/- 0.63), and Post-6 (7.78 +/- 1.2) compared with Pre (10.9 +/- 1.3). No effect of training was observed on exercise ATP, phosphocreatine, and glycogen levels. After the single session of training, plasma volumes were elevated (P < 0.05) at Post-2 (6.7 +/- 1.7%), Post-4 (5.86 +/- 1.9), and Post-6 (5.13 +/- 2.5). The single exercise session also resulted in elevations (P < 0.05) in the monocarboxylate transporters MCT1 and MCT4 throughout the 6 days after exercise. Although epinephrine and norepinephrine both increased with exercise, only norepinephrine was reduced (P < 0.05) with training and only at Post-4. These results indicate that regulation of cellular lactate levels occurs rapidly and independently of other metabolic adaptations. It is proposed that increases in MCT and plasma volume are at least partly involved in the lower muscle lactate content observed after the training session by increasing lactate membrane transport and removal, respectively.

Factors affecting performance in an ultraendurance triathlon

In the recent past, researchers have found many key physiological variables that correlate highly with endurance performance. These include maximal oxygen uptake (VO2max), anaerobic threshold (AT), economy of motion and the fractional utilisation of oxygen uptake (VO2). However, beyond typical endurance events such as the marathon, termed 'ultraendurance' (i.e. >4 hours), performance becomes harder to predict. The ultraendurance triathlon (UET) is a 3-sport event consisting of a 3.8 km swim and a 180 km cycle, followed by a 42.2 km marathon run. It has been hypothesised that these triathletes ride at approximately their ventilatory threshold (Tvent) during the UET cycling phase. However, laboratory assessments of cycling time to exhaustion at a subject's AT peak at 255 minutes. This suggests that the AT is too great an intensity to be maintained during a UET, and that other factors cause detriments in prolonged performance. Potential defeating factors include the provision of fuels and fluids due to finite gastric emptying rates causing changes in substrate utilisation, as well as fluid and electrolyte imbalances. Thus, an optimum ultraendurance intensity that may be relative to the AT intensity is needed to establish ultraendurance intensity guidelines. This optimal UET intensity could be referred to as the ultraendurance threshold.

Altitude acclimatization, training and performance

Exposure to altitude results in a reduction in partial pressure of oxygen in the arterial blood and a reduction in oxygen content. In an attempt to maintain aerobic metabolism during increased effort, a series of acclimatization responses occur. Among the most conspicuous of these responses is an increase in hemoglobin (Hb) concentration. The increase in Hb has been construed as the fundamental adaptation enabling increases in aerobic power and performance to occur on return to sea-level. However, the use of altitude to boost training adaptations and improve elite sea-level performance, although tantalizing, is largely unproven. The reasons appear to be many, ranging from the poor experimental designs employed, to the numerous strategies designed to manipulate the altitude experience and the large inter-individual differences in response patterns. However, other factors may also be important. Acclimatization has also been shown to induce alteration in selected properties of the muscle cell, some of which may be counterproductive. The processes involved in cation cycling, as an example, appear to be down-regulated. Changes in these processes could impair certain types of performance.

Effect of acute plasma volume expansion on thermoregulation and exercise performance in the heat

PURPOSE

We investigated the effects of acute plasma volume expansion on exercise performance in the heat.

METHODS

Six moderately trained men cycled for 40 min at 64 +/- 2% peak pulmonary oxygen uptake (VO2peak) followed by an individual performance time trial, where subjects completed a set amount of work (267 +/- 15 kJ) in as little time as possible. Exercise trials were performed at 35 degrees C with a relative humidity of 40%. Subjects performed two exercise trials: one after 13.1 +/- 1% acute plasma volume expansion (PVE), which was achieved by the intravenous infusion of 8 mL x kg(-1) body weight of Hemaccel (35 g x L(-1) polygeline, 145 mmol x L(-1) Na+, and 145 mmol x L(-1) Cl-) and the other without prior treatment (CON).

RESULTS

Core temperature, skin blood flow, and heart rate progressively increased (P < 0.05) during exercise, but no differences were observed between trials. Plasma glucose and lactate were similar at rest and during exercise, as was VO2 during exercise. Exercise performance was not influenced by plasma volume expansion (CON 17.5 +/- 0.4 min and PVE 17.1 +/- 0.2 min).

CONCLUSION

These data suggest that, in moderately trained men, plasma volume expansion alone does not enhance thermoregulatory function and exercise performance during moderate intensity exercise in the heat.

Acute plasma volume expansion alters cardiovascular but not thermal function during moderate intensity prolonged exercise

To investigate the hypothesis that the increase in plasma volume (PV) that typically occurs with training results in improved cardiovascular and thermal regulation during prolonged exercise, eight untrained males (Vo2peak = 3.52 ± 0.12 L·min-1) performed 90 min of cycle ergometry at 62% Vo2peak before and after acute PV expansion. Subjects were infused with a PV-expanding solution (dextran (6%) or Pentaspan (10%)) equivalent to 6.7 mL·kg-1 body mass (PVX) or acted as their own control (CON) in a randomized order. PVX resulted in a calculated 15.8% increase in resting PV, which relative to CON, was maintained throughout the exercise (P < 0.05). During PVX, heart rate was lower (P < 0.05) and stroke volume and cardiac output were higher (P < 0.05) during the exercise. Mean arterial pressure and total peripheral resistance, although altered by exercise (P < 0.05), were not different between the two conditions. Core temperature, which was progressively increased by the exercise (P < 0.01), was not affected by PVX. A similar decrease in body weight was observed between the conditions as a result of the exercise (P < 0.01). These results indicate that acute PVX alters cardiovascular performance without affecting the thermoregulatory response to prolonged cycle exercise.Key words: cardiovascular, prolonged exercise, acute plasma volume expansion, thermoregulation, hypervolemia.

Blood volume: importance and adaptations to exercise training, environmental stresses, and trauma/sickness

This paper reviews the influence of several perturbations (physical exercise, heat stress, terrestrial altitude, microgravity, and trauma/sickness) on adaptations of blood volume (BV), erythrocyte volume (EV), and plasma volume (PV). Exercise training can induce BV expansion: PV expansion usually occurs immediately, but EV expansion takes weeks. EV and PV expansion contribute to aerobic power improvements associated with exercise training. Repeated heat exposure induces PV expansion but does not alter EV. PV expansion does not improve thermoregulation, but EV expansion improves thermoregulation during exercise in the heat. Dehydration decreases PV (and increases plasma tonicity) which elevates heat strain and reduces exercise performance. High altitude exposure causes rapid (hours) plasma loss. During initial weeks at altitude, EV is unaffected, but a gradual expansion occurs with extended acclimatization. BV adjustments contribute, but are not key, to altitude acclimatization. Microgravity decreases PV and EV which contribute to orthostatic intolerance and decreased exercise capacity in astronauts. PV decreases may result from lower set points for total body water and central venous pressure, while EV decreases may result from increased erythrocyte destruction. Trauma, renal disease, and chronic diseases cause anemia from hemorrhage and immune activation which suppresses erythropoiesis. The re-establishment of EV is associated with healing, improved life quality, and exercise capabilities for these injured/sick persons.