Alterations in blood volume following short-term supramaximal exercise

Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution on Athletes' Endurance Performance: A Systematic Review with Meta-analysis

BACKGROUND

Polarized training intensity distribution (POL) was recently suggested to be superior to other training intensity distribution (TID) regimens for endurance performance improvement.

OBJECTIVE

We aimed to systematically review and meta-analyze evidence comparing POL to other TIDs on endurance performance.

METHODS

PRISMA guidelines were followed. The protocol was registered at PROSPERO (CRD42022365117). PubMed, Scopus, and Web of Science were searched up to 20 October 2022 for studies in adults and young adults for ≥ 4 weeks comparing POL with other TID interventions regarding VO2peak, time-trial (TT), time to exhaustion (TTE) or speed or power at the second ventilatory or lactate threshold (V/P at VT2/LT2). Risk of bias was assessed with RoB-2 and ROBINS-I. Certainty of evidence was assessed with GRADE. Results were analyzed by random effects meta-analysis using standardized mean differences.

RESULTS

Seventeen studies met the inclusion criteria (n = 437 subjects). Pooled effect estimates suggest POL superiority for improving VO2peak (SMD = 0.24 [95% CI 0.01, 0.48]; z = 2.02 (p = 0.040); 11 studies, n = 284; I2 = 0%; high certainty of evidence). Superiority, however, only occurred in shorter interventions (< 12 weeks) (SMD = 0.40 [95% CI 0.08, 0.71; z = 2.49 (p = 0.01); n = 163; I2 = 0%) and for highly trained athletes (SMD = 0.46 [95% CI 0.10, 0.82]; z = 2.51 (p = 0.01); n = 125; I2 = 0%). The remaining endurance performance surrogates were similarly affected by POL and other TIDs: TT (SMD = - 0.01 [95% CI -0.28, 0.25]; z =  - 0.10 (p = 0.92); n = 221; I2 = 0%), TTE (SMD = 0.30 [95% CI - 0.20, 0.79]; z = 1.18 (p = 0.24); n = 66; I2 = 0%) and V/P VT2/LT2 (SMD = 0.04 [95% CI -0.21, 0.29]; z = 0.32 (p = 0.75); n = 253; I2 = 0%). Risk of bias for randomized controlled trials was rated as of some concern and for non-randomized controlled trials as low risk of bias (two studies) and some concerns (one study).

CONCLUSIONS

POL is superior to other TIDs for improving VO2peak, particularly in shorter duration interventions and highly trained athletes. However, the effect of POL was similar to that of other TIDs on the remaining surrogates of endurance performance. The results suggest that POL more effectively improves aerobic power but is similar to other TIDs for improving aerobic capacity.

The effect of chronic habitual exercise on oxygen carrying capacity and blood compartment volumes in older adults

Absolute total hemoglobin mass (tHbmass) and blood compartment volumes are often considered to be higher in endurance athletes compared with nonathletes, yet little data support a fitness effect in older age. Therefore, we measured tHbmass and blood compartment volumes (carbon monoxide rebreathing) in 77 healthy individuals (23% female; aged, 60-87 yr). Participants were recruited into groups based upon their lifelong (>25 yr) exercise "dose": 1) 15 sedentary individuals, <2 sessions/wk; 2) 25 casual exercisers, 2-3 sessions/wk; 3) 24 committed exercisers, 4-5 sessions/wk; and 4) 13 competitive Masters athletes, 6-7 sessions/wk, plus regular competitions. Absolute (L/min) and relative (mL/kg/min) V̇o2peak were higher with increasing exercise "dose" (P = 0.0005 and P < 0.0001, respectively). Hemoglobin concentration, hematocrit, and absolute tHbmass and blood compartment volumes were not significantly different between groups (all, P > 0.1328). When scaled to body mass, tHbmass (Sedentary, 9.2 ± 1.7 mL/kg; Casual, 9.2 ± 1.3; Committed, 10.2 ± 1.4; Competitive, 11.5 ± 1.4, ANOVA P < 0.0001) and blood volume were significantly different between groups [Sedentary, 63.4 (59.2-68.5) mL/kg; Casual, 67.3 (64.4-72.6); Committed, 73.5 (67.5-80.2); Competitive, 83.4 (78.9-88.6), ANOVA P < 0.0001], whereby all values were highest in Masters athletes. However, when scaled to fat-free mass (FFM), tHbmass and blood compartment volumes were greater in Competitive compared with Casual exercisers (all, P < 0.0340) and tHbmass and erythrocyte volume were also higher in Committed compared with Casual exercisers (both, P < 0.0134). In conclusion, absolute tHbmass and blood compartment volumes are not different between groups, with dose-dependent differences only among exercisers when scaled for FFM, with the highest tHbmass and blood compartment volumes in competitive Masters athletes.NEW & NOTEWORTHY We observed that absolute oxygen carrying capacity (total hemoglobin mass, tHbmass) and blood compartment volumes were not associated with lifelong exercise dose. However, hematological adaptations associated with lifelong habitual exercise are only present among exercisers, whereby competitive Masters athletes have a greater oxygen carrying capacity (tHbmass) and expanded blood compartment volumes when scaled to fat-free mass.

Exercise induces tissue-specific adaptations to enhance cardiometabolic health

The risk associated with multiple cancers, cardiovascular disease, diabetes, and all-cause mortality is decreased in individuals who meet the current recommendations for physical activity. Therefore, regular exercise remains a cornerstone in the prevention and treatment of non-communicable diseases. An acute bout of exercise results in the coordinated interaction between multiple tissues to meet the increased energy demand of exercise. Over time, the associated metabolic stress of each individual exercise bout provides the basis for long-term adaptations across tissues, including the cardiovascular system, skeletal muscle, adipose tissue, liver, pancreas, gut, and brain. Therefore, regular exercise is associated with a plethora of benefits throughout the whole body, including improved cardiorespiratory fitness, physical function, and glycemic control. Overall, we summarize the exercise-induced adaptations that occur within multiple tissues and how they converge to ultimately improve cardiometabolic health.

The influence of exercise volume and posture on exercise-induced plasma volume expansion

Acute high-intensity interval exercise is known to expand plasma volume 24 h after exercise. Upright exercise posture plays a role in expanding plasma volume by influencing lymphatic outflow and redistributing albumin while supine exercise does not. We examined if further upright and weight-bearing exercises could further promote plasma volume expansion. We also tested the volume of intervals needed to induce plasma volume expansion. To test the first hypothesis, 10 subjects performed intermittent high-intensity exercise (4 min at 85% V̇_O2max , 5 min at 40% V̇_O2max repeated 8 times) on separate days on the treadmill and cycle ergometer. For the second study, 10 subjects performed four, six, and eight intervals of the same interval protocol on separate days. Changes in plasma volume were calculated from changes in hematocrit and hemoglobin. Transthoracic impedance (Z₀ ) and plasma albumin were assessed while seated before and postexercise. Plasma volume increased 7.3% ± 4.4% and 6.3% ± 3.5% following treadmill and cycle ergometer exercise, respectively. For four, six, and eight intervals, plasma volume increased by 6.6% ± 4.0%, 4.7% ± 2.6%, and 4.2% ± 5.6%, respectively. The increases in plasma volume were similar for both exercise modes and all three exercise volumes. There were no differences in Z₀ or plasma albumin content between trials. In conclusion, rapid plasma volume expansion following eight bouts of high-intensity intervals appears to be independent of upright exercise posture (treadmill versus cycle ergometer). Meanwhile, plasma volume expansion was similar after four, six, and eight intervals of cycle ergometry.

Assessment of Changes in Physiological Markers in Different Body Fluids at Rest and after Exercise

Physiological and biological markers in different body fluids are used to measure the body’s physiological or pathological status. In the field of sports and exercise medicine, the use of these markers has recently become more popular for monitoring an athlete’s training response and assessing the immediate or long-term effects of exercise. Although the effect of exercise on different physiological markers using various body fluids is well substantiated, no article has undertaken a review across multiple body fluids such as blood, saliva, urine and sweat. This narrative review aims to assess various physiological markers in blood, urine and saliva, at rest and after exercise and examines physiological marker levels obtained across similar studies, with a focus on the population and study methodology used. Literature searches were conducted using PRISMA guidelines for keywords such as exercise, physical activity, serum, sweat, urine, and biomarkers, resulting in an analysis of 15 studies for this review paper. When comparing the effects of exercise on physiological markers across different body fluids (blood, urine, and saliva), the changes detected were generally in the same direction. However, the extent of the change varied, potentially as a result of the type and duration of exercise, the sample population and subject numbers, fitness levels, and/or dietary intake. In addition, none of the studies used solely female participants; instead, including males only or both male and female subjects together. The results of some physiological markers are sex-dependent. Therefore, to better understand how the levels of these biomarkers change in relation to exercise and performance, the sex of the participants should also be taken into consideration.

Four-Second Power Cycling Training Increases Maximal Anaerobic Power, Peak Oxygen Consumption, and Total Blood Volume

INTRODUCTION

High-intensity interval training (HIIT) is an effective tool to improve cardiovascular fitness and maximal anaerobic power. Different methods of HIIT have been studied but the effects of repeated maximal effort cycling with very short exercise time (i.e., 4-s) and short recovery time (15-30 s) might suit individuals with limited time to exercise.

PURPOSE

We examined the effects of training at near maximal anaerobic power during cycling (PC) on maximal anaerobic power, peak oxygen consumption (VO2peak), and total blood volume in 11 young healthy individuals (age: 21.3 ± 0.5 y) (6 men, 5 women).

METHODS

Participants trained three times a week for eight weeks performing a PC program consisting of 30 bouts of 4-s at an all-out intensity (i.e., 2 minutes of exercise per session). The cardiovascular stress progressively increased over the weeks by decreasing the recovery time between sprints (30 to 24 to 15-s) and thus total session time decreased from 17 to <10 min.

RESULTS

PC elicited a 13.2% increase in VO2peak (Pre: 2.86 ± 0.18 L/min, Post: 3.24 ± 0.21 L/min, (p = 0.003) and a 7.6% increase in total blood volume (Pre: 5,139 ± 199 ml, Post: 5,529 ± 342 ml, p < 0.05). Concurrently, maximal anaerobic power increased by 17.2% (Pre: 860 ± 53 watts, Post: 1,009 ± 71 watts; p < 0.001).

CONCLUSION

A Power Cycling training program employing 30 bouts of 4-s duration for a total of 2 min of exercise, resulting in a total session time of less than 10 min in the last weeks, is effective for improving total blood volume, VO2peak and maximal anaerobic power in young healthy individuals over 8 weeks. These observations require reconsideration of the minimal amount of exercise needed to significantly increase both maximal aerobic and anaerobic power.

Interval-induced metabolic perturbation determines tissue fluid shifts into skeletal muscle

Intense interval exercise has proven to be as effective as traditional endurance exercise in improving maximal oxygen uptake. Shared by these two exercise regimes is an acute reduction in plasma volume, which is a suggested stimulus behind exercise-induced increases in blood volume and maximal oxygen uptake. This study aimed to link exercise-induced metabolic perturbation with volume shifts into skeletal muscle tissue. Ten healthy subjects (mean age 33 ± 8 years, 5 males and 5 females) performed three 30 s all-out sprints on a cycle ergometer. Upon cessation of exercise magnetic resonance imaging, ³¹ Phosphorus magnetic resonance spectroscopy and blood samples were used to measure changes in muscle volume, intramuscular energy metabolites and plasma volume. Compared to pre-exercise, muscle volume increased from 1147.1 ± 35.6 ml to 1283.3 ± 11.0 ml 8 min post-exercise. At 30 min post-exercise, muscle volume was still higher than pre-exercise (1147.1 ± 35.6 vs. 1222.2 ± 6.8 ml). Plasma volume decreased by 16 ± 3% immediately post-exercise and recovered back to - 5 ± 6% after 30 min. Principal component analysis of exercise performance, muscle and plasma volume changes as well as changes in intramuscular energy metabolites showed generally strong correlations between metabolic and physiological variables. The strongest predictor for the volume shifts of muscle and plasma was the magnitude of glucose-6-phosphate accumulation post-exercise. Interval training leads to large metabolic and hemodynamic perturbations with accumulation of glucose-6-phosphate as a possible key event in the fluid flux between the vascular compartment and muscle tissue.

Heart Rate Variability Monitoring During Strength and High-Intensity Interval Training Overload Microcycles

Objective: In two independent study arms, we determine the effects of strength training (ST) and high-intensity interval training (HIIT) overload on cardiac autonomic modulation by measuring heart rate (HR) and vagal heart rate variability (HRV). Methods: In the study, 37 well-trained athletes (ST: 7 female, 12 male; HIIT: 9 female, 9 male) were subjected to orthostatic tests (HR and HRV recordings) each day during a 4-day baseline period, a 6-day overload microcycle, and a 4-day recovery period. Discipline-specific performance was assessed before and 1 and 4 days after training. Results: Following ST overload, supine HR, and vagal HRV (Ln RMSSD) were clearly increased and decreased (small effects), respectively, and the standing recordings remained unchanged. In contrast, HIIT overload resulted in decreased HR and increased Ln RMSSD in the standing position (small effects), whereas supine recordings remained unaltered. During the recovery period, these responses were reversed (ST: small effects, HIIT: trivial to small effects). The correlations between changes in HR, vagal HRV measures, and performance were weak or inconsistent. At the group and individual levels, moderate to strong negative correlations were found between HR and Ln RMSSD when analyzing changes between testing days (ST: supine and standing position, HIIT: standing position) and individual time series, respectively. Use of rolling 2-4-day averages enabled more precise estimation of mean changes with smaller confidence intervals compared to single-day values of HR or Ln RMSSD. However, the use of averaged values displayed unclear effects for evaluating associations between HR, vagal HRV measures, and performance changes, and have the potential to be detrimental for classification of individual short-term responses. Conclusion: Measures of HR and Ln RMSSD during an orthostatic test could reveal different autonomic responses following ST or HIIT which may not be discovered by supine or standing measures alone. However, these autonomic changes were not consistently related to short-term changes in performance and the use of rolling averages may alter these relationships differently on group and individual level.

Increase interval training intensity improves plasma volume variations and aerobic performances in response to intermittent exercise

PURPOSE

We studied the effect of two interval training programs of varying intensities (100% vs. 110% of maximal aerobic velocity [MAV]) on hematocrit (Ht), hemoglobin (Hb), and plasma volume variations (PVV) in young men.

METHODS

Thirty-nine male volunteered were assigned to two control groups (CG₁₀₀, n = 9 and CG₁₁₀, n = 10), and two training groups (one with 100% MAV [EG₁₀₀, n = 10] and one with 110% MAV [EG₁₁₀, n = 10]). All participants performed a maximal graded exercise test and an intermittent exercise (IE) protocol. Blood was collected at rest, at the end of the IE and after 15 min of recovery, before and after 8-weeks-training. Interval training (IT) sessions consist of 30s IE run at 100% or 110% MAV with 30s recovery at 50% MAV.

RESULTS

After training, time to exhaustion (TTE) was improved in EG₁₁₀ (+613.7) and EG₁₀₀ (+397.5). This improvement was greater in EG₁₁₀ than EG₁₀₀ (p < 0.005). After training, Hb deceased in EG₁₀₀ and EG₁₁₀ at rest (p < 0.01), at the end of IE (p = 0.000) and after 15 min of recovery (p = 0.01). This decrease was more slightly more substantial at rest in EG₁₀₀ (-0.6%) than EG₁₁₀ (-0.3%). After training, Ht decreased in EG₁₀₀ and EG₁₁₀ at rest (p = 0.001), at the end of IE (p = 0.000) and at 15 min of recovery (p = 0.01). This decrease was more important in EG₁₁₀ than EG₁₀₀ at rest (-2.7%), at the end of IE (-2.1%) and after 15 min recovery. After training, PVV_rest and PVV_end increased in EG₁₀₀ (+2.2%) and EG₁₁₀ (+3.2%). No significant difference between EG₁₀₀ and EG₁₁₀ was observed.

CONCLUSION

Increasing IT intensity by 10% MAV increases PVV_rest and PVV_end. Despite the fact that EG₁₀₀ and EG₁₁₀ had the same PVV_end after training, greater performances were recorded in EG₁₁₀.

Left ventricular vascular and metabolic adaptations to high-intensity interval and moderate intensity continuous training: a randomized trial in healthy middle-aged men

KEY POINTS

High-intensity interval training (HIIT) has become popular, time-sparing alternative to moderate intensity continuous training (MICT), although the cardiac vascular and metabolic effects of HIIT are incompletely known. We compared the effects of 2-week interventions with HIIT and MICT on myocardial perfusion and free fatty acid and glucose uptake. Insulin-stimulated myocardial glucose uptake was decreased by training without any significantly different response between the groups, whereas free fatty acid uptake remained unchanged. Adenosine-stimulated myocardial perfusion responded differently to the training modes (change in mean HIIT: -19%; MICT: +9%; P = 0.03 for interaction) and was correlated with myocardial glucose uptake for the entire dataset and especially after HIIT training. HIIT and MICT induce similar metabolic and functional changes in the heart, although myocardial vascular hyperaemic reactivity is impaired after HIIT, and this should be considered when prescribing very intense HIIT for previously untrained subjects.

ABSTRACT

High-intensity interval training (HIIT) is a time-efficient way of obtaining the health benefits of exercise, although the cardiac effects of this training mode are incompletely known. We compared the effects of short-term HIIT and moderate intensity continuous training (MICT) interventions on myocardial perfusion and metabolism and cardiac function in healthy, sedentary, middle-aged men. Twenty-eight healthy, middle-aged men were randomized to either HIIT or MICT groups (n = 14 in both) and underwent six cycle ergometer training sessions within 2 weeks (HIIT session: 4-6 × 30 s all-out cycling/4 min recovery, MICT session 40-60 min at 60% V̇O2 peak ). Cardiac magnetic resonance imaging (CMRI) was performed to measure cardiac structure and function and positron emission tomography was used to measure myocardial perfusion at baseline and during adenosine stimulation, insulin-stimulated glucose uptake (MGU) and fasting free fatty acid uptake (MFFAU). End-diastolic and end-systolic volumes increased and ejection fraction slightly decreased with both training modes, although no other changes in CMRI were observed. MFFAU and basal myocardial perfusion remained unchanged. MGU was decreased by training (HIIT from 46.5 to 35.9; MICT from 47.4 to 44.4 mmol 100 g^-1  min^-1 , P = 0.007 for time, P = 0.11 for group × time). Adenosine-stimulated myocardial perfusion responded differently to the training modes (change in mean HIIT: -19%; MICT: +9%; P = 0.03 for group × time interaction). HIIT and MICT induce similar metabolic and functional changes in the heart, although myocardial vascular hyperaemic reactivity is impaired after HIIT. This should be taken into account when prescribing very intense HIIT for previously untrained subjects.

Right ventricular metabolic adaptations to high-intensity interval and moderate-intensity continuous training in healthy middle-aged men

Despite the recent studies on structural and functional adaptations of the right ventricle (RV) to exercise training, adaptations of its metabolism remain unknown. We investigated the effects of short-term, high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on RV glucose and fat metabolism. Twenty-eight untrained, healthy 40-55 yr-old-men were randomized into HIIT (n = 14) and MICT (n = 14) groups. Subjects performed six supervised cycle ergometer training sessions within 2 wk (HIIT session: 4-6 × 30 s all-out cycling/4-min recovery; MICT session: 40-60 min at 60% peak O2 uptake). Primary outcomes were insulin-stimulated RV glucose uptake (RVGU) and fasted state RV free fatty acid uptake (RVFFAU) measured by positron emission tomography. Secondary outcomes were changes in RV structure and function, determined by cardiac magnetic resonance. RVGU decreased after training (-22% HIIT, -12% MICT, P = 0.002 for training effect), but RVFFAU was not affected by the training (P = 0.74). RV end-diastolic and end-systolic volumes, respectively, increased +5 and +7% for HIIT and +4 and +8% for MICT (P = 0.002 and 0.005 for training effects, respectively), but ejection fraction mildly decreased (-2% HIIT, -4% MICT, P = 0.034 for training effect). RV mass and stroke volume remained unaltered. None of the observed changes differed between the training groups (P > 0.12 for group × training interaction). Only 2 wk of physical training in previously sedentary subjects induce changes in RV glucose metabolism, volumes, and ejection fraction, which precede exercise-induced hypertrophy of RV.

Iron Metabolism in Field Hockey Players During an Annual Training Cycle

Post-physical training changes in iron metabolism in the human body often occur. To fully describe these processes, fifteen male Polish National Team field hockey players (age 27.7 ± 5.2 years, body mass 72.8 ± 7.6 kg and body height 177.1 ± 5.7 cm) were examined in three phases of an annual training cycle: preparatory (T1), competitive (T2) and transition (T3). To assess aerobic fitness, maximal oxygen uptake (VO₂max) was evaluated. Based on the iron concentration, the changes in total iron binding capacity (TIBC), unsaturated iron binding capacity (UIBC) and other selected haematological indicators (haemoglobin, erythrocytes, mean corpuscular haemoglobin - MCH) in iron metabolism were estimated. The average values of maximum oxygen uptake increased from 54.97 ± 3.62 ml·kg⁻¹·min⁻¹ in T1 to 59.93 ± 3.55 ml·kg⁻¹·min⁻¹ in T2 (p<0.05) and then decreased to 56.21 ± 4.56 ml·kg⁻¹·min⁻¹ in T3 (p<0.05). No statistically significant changes in the erythrocyte count were noted. The MCH and haemoglobin concentration decreased between T1 and T2. The maximal exercise test caused a significant (p<0.05) increase in the plasma iron concentration during the competition and transition phases. Progressive but non-significant increases in resting iron concentration, TIBC and UIBC in the analysed annual training cycle were noted. To show global changes in iron metabolism in the human body, it is necessary to determine additional variables, i.e. UIBC, TIBC, haemoglobin, MCH or the erythrocyte count. The direction of changes in iron metabolism depends on both the duration and intensity of the physical activity and the fitness level of the subjects. Dietary intake of iron increases the level of this trace element and prevents anaemia associated with training overloads.

Effect of 3-week high-intensity interval training on VO2max, total haemoglobin mass, plasma and blood volume in well-trained athletes

PURPOSE

This study examined the haematological adaptations to high-intensity interval training (HIT), i.e. total haemoglobin mass (tHb-mass), blood volume (BV), and plasma volume (PV), and its effects on VO2max in well-trained athletes.

METHODS

Twenty-seven male and eight female well-trained (VO2max 63.7 ± 7.7 ml/min/kg) athletes were randomly assigned to the HIT (HITG, N = 19) or the control group (CG, N = 16). Over a 3-week period, the HITG performed 11 HIT sessions, consisting of four 4-min interval bouts at an exercise intensity of 90-95 % of the individual maximal heart rate (HRmax), separated by 4-min active recovery periods. Before and 5 ± 2 days after the intervention, tHb-mass, BV and PV were determined by the CO-rebreathing method. VO2max was assessed in a laboratory treadmill test.

RESULTS

tHb-mass (from 753 ± 124 to 760 ± 121 g), BV (from 5.6 ± 0.8 to 5.6 ± 0.9 l) and PV (from 3.2 ± 0.5 to 3.2 ± 0.5 l) remained unchanged after HIT and did not show an interaction (group × time). Within the HITG, VO2max improved from baseline by +3.5 % (p = 0.011), but remained unchanged in the CG. No interaction (group × time) was seen for VO2max. The HITG showed a significant reduction in HRmax compared to the baseline measurement (-2.3 %, p ≤ 0.001), but HRmax remained unchanged in the CG. There was a significant interaction (group × time) for HRmax (p = 0.006). Also, oxygen pulse significantly increased only in HITG from 22.9 ± 4.4 to 23.9 ± 4.2 ml/beat, with no interaction (p = 0.150).

CONCLUSIONS

Eleven HIT sessions added to usual training did neither improve VO2max nor haematological parameters compared to the CG.

Monitoring training status with HR measures: do all roads lead to Rome?

Measures of resting, exercise, and recovery heart rate are receiving increasing interest for monitoring fatigue, fitness and endurance performance responses, which has direct implications for adjusting training load (1) daily during specific training blocks and (2) throughout the competitive season. However, these measures are still not widely implemented to monitor athletes' responses to training load, probably because of apparent contradictory findings in the literature. In this review I contend that most of the contradictory findings are related to methodological inconsistencies and/or misinterpretation of the data rather than to limitations of heart rate measures to accurately inform on training status. I also provide evidence that measures derived from 5-min (almost daily) recordings of resting (indices capturing beat-to-beat changes in heart rate, reflecting cardiac parasympathetic activity) and submaximal exercise (30- to 60-s average) heart rate are likely the most useful monitoring tools. For appropriate interpretation at the individual level, changes in a given measure should be interpreted by taking into account the error of measurement and the smallest important change of the measure, as well as the training context (training phase, load, and intensity distribution). The decision to use a given measure should be based upon the level of information that is required by the athlete, the marker's sensitivity to changes in training status and the practical constrains required for the measurements. However, measures of heart rate cannot inform on all aspects of wellness, fatigue, and performance, so their use in combination with daily training logs, psychometric questionnaires and non-invasive, cost-effective performance tests such as a countermovement jump may offer a complete solution to monitor training status in athletes participating in aerobic-oriented sports.

Running Interval Training and Estimated Plasma-Volume Variation

The effect of endurance interval training (IT) on hematocrit (Ht), hemoglobin (Hb), and estimated plasma-volume variation (PVV) in response to maximal exercise was studied in 15 male subjects (21.1 ± 1.1 y; control group n = 6, and training group, n = 9). The training group participated in interval training 3 times a week for 7 wk. A maximal graded test (GXT) was performed to determine maximal aerobic power (MAP) and maximal aerobic speed (MAS) both before and after the training program. To determine Ht, Hb concentration, and lactate concentrations, blood was collected at rest, at the end of GXT, and after 10 and 30 min of recovery. MAP and MAS increased significantly (P < .05) after training only in training group. Hematocrit determined at rest was significantly lower in the training group than in the control group after the training period (P < .05). IT induced a significant increase of estimated PVV at rest for training group (P < .05), whereas there were no changes for control group. Hence, significant relationships were observed after training between PVV determined at the end of the maximal test and MAS (r = .60, P < .05) and MAP (r = .76, P < .05) only for training group. In conclusion, 7 wk of IT led to a significant increase in plasma volume that possibly contributed to the observed increase of aerobic fitness (MAP and MAS).

Higher serum 25-hydroxyvitamin D concentrations associate with a faster recovery of skeletal muscle strength after muscular injury

The primary purpose of this study was to identify if serum 25-hydroxyvitamin D (25(OH)D) concentrations predict muscular weakness after intense exercise. We hypothesized that pre-exercise serum 25(OH)D concentrations inversely predict exercise-induced muscular weakness. Fourteen recreationally active adults participated in this study. Each subject had one leg randomly assigned as a control. The other leg performed an intense exercise protocol. Single-leg peak isometric force and blood 25(OH)D, aspartate and alanine aminotransferases, albumin, interferon (IFN)-γ, and interleukin-4 were measured prior to and following intense exercise. Following exercise, serum 25(OH)D concentrations increased (p < 0.05) immediately, but within minutes, subsequently decreased (p < 0.05). Circulating albumin increases predicted (p < 0.005) serum 25(OH)D increases, while IFN-γ increases predicted (p < 0.001) serum 25(OH)D decreases. Muscular weakness persisted within the exercise leg (p < 0.05) and compared to the control leg (p < 0.05) after the exercise protocol. Serum 25(OH)D concentrations inversely predicted (p < 0.05) muscular weakness (i.e., control leg vs. exercise leg peak isometric force) immediately and days (i.e., 48-h and 72-h) after exercise, suggesting the attenuation of exercise-induced muscular weakness with increasing serum 25(OH)D prior to exercise. Based on these data, we conclude that pre-exercise serum 25(OH)D concentrations could influence the recovery of skeletal muscle strength after an acute bout of intense exercise.

Adaptations to high-intensity intermittent exercise in rodents

In humans, exercise-induced plasma volume (PV) expansion is typically associated with an increase in plasma albumin content, due in part to an increase in hepatic albumin synthesis. We tested the ability of a 12-day high-intensity intermittent exercise protocol to induce an increase in PV in rodents. Since albumin synthesis is transcriptionally regulated, we tested the hypothesis that exercise training would induce an increase in hepatic albumin gene expression. Fifty adult male Sprague-Dawley rats weighing between 245 and 350 g were randomly assigned to one of five groups: cage control (CC), sham exercise (sham), continuous moderate-intensity exercise training (MI), high-intensity intermittent exercise training (HI), or a single day of HI training (1-HI). Twenty-four hours after the last training session, rats were anesthetized. PV was determined, and the liver was removed, flash frozen, and stored for later analysis. Citrate synthase (CS) activity of the red quadriceps muscle, a marker of aerobic adaptation, increased with training (MI and HI) and in response to 1-HI (P < 0.05). We did not see a significant exercise-induced PV expansion as PV averaged 23.6 +/- 2.7 ml/kg body wt in the CC group and 26.6 +/- 1.3 ml/kg body wt in the HI group (P > 0.05). However, hepatic albumin mRNA expression, as determined by real-time PCR, increased 2.9 +/- 0.4- and 4.1 +/- 0.4-fold after MI and HI, respectively, compared with CC. A single bout of HI (1-HI) did not alter hepatic albumin mRNA expression. These data demonstrate an increase in both CS activity and hepatic albumin gene expression with 12 days of aerobic exercise training in the rodent with a rapid (within 24 h) adaptation in the skeletal muscle to high-intensity intermittent exercise.

Protein and carbohydrate supplementation after exercise increases plasma volume and albumin content in older and young men

This study examined whether increased plasma volume (PV) and albumin content (Alb(cont)) in plasma for 23 h after exercise were attenuated in older subjects compared with in young adult subjects, and if this attenuation abated by supplementation with protein and carbohydrate (CHO) immediately after exercise. Eight moderately active older (approximately 68 yr) and 8 young (approximately 21 yr) men performed two trials: control (CNT) and Pro-CHO in which subjects consumed placebo (0.5 kcal, 0 g protein, 0.5 mg Na(+) in 3.2 ml total fluid volume/kg body wt) or protein and CHO mixture (3.2 kcal, 0.18 g protein, 0.5 mg Na(+) in 3.2 ml total fluid volume/kg body wt) supplementations, respectively, immediately after high-intensity interval exercise for 72 min [8 sets of 4 min at 70-80% peak oxygen consumption rate (Vo(2peak)) intermitted by 5 min at 20% Vo(2peak)]. PV, Alb(cont), and plasma globulin content (Glb(cont)) were measured before exercise, at the end of exercise, every hour from the 1st to the 5th hour after exercise, and at the 23rd hour after exercise. From 12 h before the start to the end of experiment, food intake was controlled to the age-matched recommended dietary allowances. We found that during the first 4 h after exercise in CNT, Alb(cont) recovered less in the older than the young group by approximately 0.04 g/kg (P < 0.05), while it generally recovered more with Pro-CHO than CNT by approximately 0.09 and approximately 0.04 g/kg in the young and older group, respectively, accompanied by a greater increase in PV by approximately 1 and approximately 2 ml/kg, respectively, during the 23 h after exercise (P < 0.05). Glb(cont) remained constant throughout the experiment in both trials for both age groups. Thus the attenuated responses of Alb(cont) and PV after exercise in older subjects were restored by protein and CHO supplementation immediately after exercise, similarly to young subjects.

Post-exercise hypotension and cardiovascular responses to moderate orthostatic stress in endurance-trained males

We tested the hypothesis that following an acute bout of exercise cardiovascular and cerebrovascular responses to lower-body negative pressure (LBNP) would be altered due to post-exercise hypotension (PEH). Ten healthy, male, endurance-trained athletes (mean age ± SD = 29.6 ± 5) were assessed for cardiovascular and cerebrovascular responses to LBNP following acute bouts of interval and continuous exercise. Mean arterial pressure (MAP), cardiac output, total peripheral resistance, heart rate variability, and total cerebral oxygen index were determined during a baseline LBNP session. These indices were also determined during two other LBNP sessions: following an acute bout of interval exercise, and following an acute bout of continuous exercise. Compared with baseline, MAP was reduced after both exercise conditions, similar to values previously reported (10 mmHg; p < 0.05 vs. pre-exercise). Total peripheral resistance was significantly reduced following both exercise bouts, and heart rate was significantly increased post-exercise (rest: 59.6 ± 11.2; interval: 77.8 ± 12.8; continuous: 80.3 ± 15.2 beats·min–1). Both cardiac output and stroke volume responses to LBNP following exercise were not altered when compared with baseline measurements. Tissue oxygenation during –40 mmHg (interval: 74.31% ± 7.82% vs. continuous: 69.13% ± 5.23%) was significantly lower than during normobaric pressure (interval: 77.14% ± 1.30% vs. continuous: 74.41% ± 0.94%). It appears from these observations that although young, endurance-trained males experience PEH following acute bouts of interval or continuous exercise, this hypotension does not alter the cardiovascular and cerebrovascular responses to a moderate orthostatic stress.

Blood Volume Response to Physical Activity and Inactivity

Data from both cross-sectional and longitudinal studies provide compelling evidence that circulating blood volume can be influenced by regular physical activity or inactivity. Expansion or contraction of plasma volume can account for most of the alteration in circulating blood volume during the initial 1 to 2 weeks of changing physical activity patterns; after this time, altered blood volume may be distributed equally between plasma and red cell volumes. Alterations in circulating blood volume that accompany changes in physical activity represent a net change in total body water and solutes that are associated with increased or decreased water intake and urine volume and solute output. The mechanism of altered urine output appears to be a modified renal tubular reabsorption of sodium. The expansion of blood volume that accompanies physical activity provides advantages of greater body fluid for heat dissipation (sweating) and thermoregulatory stability as well as larger vascular volume for greater cardiac filling and stroke volume and cardiovascular stability during exercise and orthostatic challenges. The opposite is true when blood volume is reduced during periods of relative physical inactivity. The observation that underlying mechanisms for alteration in blood volume with physical activity and inactivity are similar but respond directly opposite suggests that they are intricately related. These relations have implications as to a mechanism by which physical activity and fitness may be protective against reduced blood volume and subsequent development of cardiovascular disease associated with aging.

Physiological response to water immersion: a method for sport recovery?

Recovery from exercise can be an important factor in performance during repeated bouts of exercise. In a tournament situation, where athletes may compete numerous times over a few days, enhancing recovery may provide a competitive advantage. One method that is gaining popularity as a means to enhance post-game or post-training recovery is immersion in water. Much of the literature on the ability of water immersion as a means to improve athletic recovery appears to be based on anecdotal information, with limited research on actual performance change. Water immersion may cause physiological changes within the body that could improve recovery from exercise. These physiological changes include intracellular-intravascular fluid shifts, reduction of muscle oedema and increased cardiac output (without increasing energy expenditure), which increases blood flow and possible nutrient and waste transportation through the body. Also, there may be a psychological benefit to athletes with a reduced cessation of fatigue during immersion. Water temperature alters the physiological response to immersion and cool to thermoneutral temperatures may provide the best range for recovery. Further performance-orientated research is required to determine whether water immersion is beneficial to athletes.

Left ventricular adaptations following short-term endurance training

This study examined the effects of short-term endurance training (ET) on the left ventricular (LV) adaptation and functional response to a series of exercise challenges with increasing intensity. Eight untrained men, with a mean age of 19.4 +/- 0.5 (SE) yr, were studied before and after 6 days of ET consisting of cycling 2 h/day at 65% peak aerobic power (VO2max). LV ejection fraction and LV volumes were assessed by radionuclide angiography at rest and during exercise at three uninterrupted successive work rates corresponding to 53, 68, and 83% of VO2max, each lasting 20 min. ET produced a calculated plasma volume expansion of 11.4 +/- 2.2% (P < 0.05). The increase in plasma volume was accompanied by an increase in VO2max from 45.9 +/- 1.9 to 49.0 +/- 1.0 ml x kg(-1) x min(-1) (P < 0.01) and a decrease in maximal heart rate (197 +/- 2.3 to 188 +/- 1.0 beats/min; P < 0.01). Resting LV function was not changed, although there was a trend for higher stroke volumes (SVs) and improvement in the rapid filling phase of diastole (P = 0.08). Training induced an increase in exercise SV by 10.4, 10.2, and 7% at 53, 68, and 83% VO2max, respectively (P < 0.01). These changes were secondary to increases in end-diastolic volume, which increased significantly at each exercise work rate following training (139 +/- 6 to 154 +/- 6 ml at 53% VO2max, and from 136 +/- 5 to 156 +/- 5 ml at 83% VO2max; P < 0.01). End-systolic volumes were unchanged after ET. A significant bradycardia was observed both at rest (decreasing 7%) and exercise (decreasing 10.4%). LV ejection fraction during exercise was increased slightly by training, reaching significance at the highest work rate, after 60 min of exercise. (P < 0.05). Cardiac output was higher following training at the highest workload (20.8 +/- 2.2 vs. 22.9 +/- 3.1 l/min; P < 0.01). These data indicate that short-term training elicits rapid adaptation to the LV functional response exercise, with increases in SV being secondary to a Frank-Starling effect with minor changes in contractile performance. This produced a volume-induced bradycardia and increase in LV filling, which may be of benefit during prolonged exercise.

Blood volume expansion and cardiorespiratory function: effects of training modality

PURPOSE

To evaluate the effects of different modalities of aerobic (i.e., interval (INT) and continuous (CONT)) training on cardiorespiratory function and the importance of training-induced blood volume (BV) expansion on aerobic power and LV function. We hypothesized that if modality-mediated differences in cardiorespiratory function exist after INT and CONT, they would be related directly to differences in training-induced hypervolemia.

METHODS

We examined the effects of 12 wk of CONT and INT on BV, volume-regulatory hormones (angiotensin II, aldosterone, atrial natriuretic peptide), and cardiorespiratory function in 20 untrained males (mean age 30 +/- 4 (SD)). Participants were stratified (mass and VO2max) and randomly assigned to control, CONT, or INT.

RESULTS

There were no significant changes in cardiorespiratory function or BV in the control group. Twelve weeks of continuous and interval training, respectively, resulted in significant changes in VO2max (23 +/- 18 vs 21 +/- 10%), peak stroke volume (20 +/- 18 vs 11 +/- 18%), and BV (12 +/- 9 vs 10 +/- 6%). Changes in VO2max were directly related to changes in BV (r = 0.47). Angiotensin II significantly increased after 1 wk of CONT and INT and thereafter returned to baseline values. There was no significant difference between the CONT and INT groups with regard to changes in vascular volumes, volume-regulatory hormones, and/or cardiorespiratory function.

CONCLUSIONS

These data indicate that: 1) 12 wk of CONT and INT result in similar improvements in VO2max, and LV function and 2) training-induced hypervolemia accounts for approximately 47% of the changes in VO2max after CONT and INT.

Dehydration of football referees during a match

OBJECTIVES

To study hydration status in referees (main) and assistant referees (linesmen) during official football matches.

METHODS

Twelve male football referees were evaluated; all were volunteers. Before and after each match, the referee and one of the assistants were weighed without clothes and a blood sample was taken. Total water loss was determined for each subject from the change in body weight. The main haematological variables were analysed in the blood samples. Total plasma protein concentration and osmolarity were also determined. Variation in plasma volume was determined from changes in packed cell volume and a combination of changes in packed cell volume and haemoglobin concentrations.

RESULTS

During a match, total body water loss was 1.60 (0.13) litres, equivalent to 2.05 (0.18)% of body weight. Body weight was reduced by 1.55 (0.12)%, showing that water ingestion during the interval replaces only 24.4% of the body fluids lost during the match. The assistants lost 0.79 (0.19) litre of water, equivalent to 1.05 (0.25)% of body weight. The referees showed a significant decrease in plasma volume of 4.99 (1.33)%. The assistants showed a non-significant increase in plasma volume. The reduction in plasma volume observed in the referees correlated significantly with total body water loss (r = 0.9623). From these data, it is possible to predict that a dehydration of 1% reflects a reduction in plasma volume of nearly 2.5%.

CONCLUSIONS

Referees are moderately dehydrated after a football match (2%), whereas assistants show a non-significant dehydration of 1% of their body weight.

Short-term training effects on left ventricular diastolic function and oxygen uptake in older and younger men

OBJECTIVE

To determine the effect of plasma volume change with short-term training and diuresis on left ventricular diastolic filling and exercise oxygen uptake (VO(2)) in older versus younger men.

METHODS

Eleven older (68 +/- 5 y) physically active (maximal oxygen uptake [VO(2max)] = 25.9 +/- 3.6 mL. kg-1. min-1) and 10 younger sedentary males (24 +/- 5 y, VO(2max) 40.5 +/- 5.0 mL. kg-1. min-1) were randomly assigned to 5 consecutive days of (1) 1 h/d high intensity stationary cycling (EXER); (2) 100 mg/d spironolactone (DIUR); and (3) exercise and diuretic (EXDI). Each treatment was separated by a 21-day washout. Doppler echocardiographic indices of left ventricular diastolic filling including peak early and atrial transmitral flow velocity and isovolumic relaxation time; percent change in plasma volume; submaximal VO(2) kinetics; and VO(2max) were determined at baseline and 48 hours after each treatment.

RESULTS

Plasma volume was increased more in the young following EXER (8.92 +/- 7.6 vs. 6.2%, P = 0.038) and decreased more in the older group following DIUR (-11.5% vs. -3.54 +/- 9.0, P < 0.001). There was no significant difference between groups after EXDI. Significant changes in peak early flow velocity with EXER in older subjects were not reflected in any other changes in left ventricular diastolic filling across conditions. No changes in left ventricular diastolic filling were observed in the young group with any condition. VO(2max) and VO(2) kinetics were unchanged under all conditions from baseline in both groups.

CONCLUSIONS

These results suggest that exercise VO(2) responses either at maximal or submaximal workrates are not limited by alterations in left ventricular pump function in physically fit older adults.

Water intake and fluid shifts in horses: effects of hydration status during two exercise tests

In the present study, the main objective was to study factors affecting postexercise voluntary water intake in horses. Four Standardbred horses (mean +/- s.e. bwt 500 +/- 8 kg) were used to study water intake and effects of altering hydration status before an incremental exercise test (INCR) and a 40 min constant velocity exercise test (CONST) on a treadmill. Exercise was performed during normohydration (N), after dehydration for 24 h (DEH) and after hyperhydration with 12 l water 30 min before exercise (HH). DEH resulted in a bodyweight loss of 3% and there were signs of some fluid uptake prior to exercise in both HH trials. By the end of the INCR, the calculated change in plasma volume (PVcalc) was -13 +/- 1, -21 +/- 1 and -11 +/- 3% in the N, DEH and HH trials, respectively. During the highest exercise velocities a hypotonic shift of fluid was seen in all INCR trials. There was a greater accumulation of plasma lactate (pLA) in HH-than in N-INCR, probably caused by the extra weight to be carried. CONST induced a similar fluid loss (3%) in all trials, but the decrease in PVcalc at the end of exercise was significantly smaller in HH (-7 +/- 2%) than in N (-14 +/- 1%) and DEH (-19 +/- 2%). In DEH-INCR and DEH-CONST, plasma sodium concentration (pNa) was higher than in N until drinking water was offered 1 h postexercise. In the presence of both an increased pNa and a decrease in PVcalc when dehydrated, the horses drank immediately when offered water postexercise. In N-CONST, there was a significant decrease in calculated PVcalc (-10 +/- 2%) but no increase in pNa when water was given and in this trial the horses rehydrated less rapidly. Plasma aldosterone concentration (PAC) had increased to the same magnitude in all trials after about 10 min, irrespective of type of exercise or hydration status. It was concluded that when both an osmotic and hypovolemic thirst stimulus was present, the horses rehydrated more rapidly postexercise.

Influence of microgravity on astronauts' sympathetic and vagal responses to Valsalva's manoeuvre

When astronauts return to Earth and stand, their heart rates may speed inordinately, their blood pressures may fall, and some may experience frank syncope. We studied brief autonomic and haemodynamic transients provoked by graded Valsalva manoeuvres in astronauts on Earth and in space, and tested the hypothesis that exposure to microgravity impairs sympathetic as well as vagal baroreflex responses. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, respiration and peroneal nerve muscle sympathetic activity in four healthy male astronauts (aged 38-44 years) before, during and after the 16 day Neurolab space shuttle mission. Astronauts performed two 15 s Valsalva manoeuvres at each pressure, 15 and 30 mmHg, in random order. Although no astronaut experienced presyncope after the mission, microgravity provoked major changes. For example, the average systolic pressure reduction during 30 mmHg straining was 27 mmHg pre-flight and 49 mmHg in flight. Increases in muscle sympathetic nerve activity during straining were also much greater in space than on Earth. For example, mean normalized sympathetic activity increased 445% during 30 mmHg straining on earth and 792% in space. However, sympathetic baroreflex gain, taken as the integrated sympathetic response divided by the maximum diastolic pressure reduction during straining, was the same in space and on Earth. In contrast, vagal baroreflex gain, particularly during arterial pressure reductions, was diminished in space. This and earlier research suggest that exposure of healthy humans to microgravity augments arterial pressure and sympathetic responses to Valsalva straining and differentially reduces vagal, but not sympathetic baroreflex gain.

Enhanced synthesis of albumin and fibrinogen at high altitude

The acute effects of active and passive ascent to high altitude on plasma volume (PV) and rates of synthesis of albumin and fibrinogen have been examined. Measurements were made in two groups of healthy volunteers, initially at low altitude (550 m) and again on the day after ascent to high altitude (4,559 m). One group ascended by helicopter (air group, n = 8), whereas the other group climbed (foot group, n = 9), so that the separate contribution of physical exertion to the response could be delineated. PV was measured by dilution of (125)I-labeled albumin, whereas synthesis rates of albumin and fibrinogen were determined from the incorporation of isotope into protein after injection of [ring-(2)H(5)]phenylalanine. In the air group, there was no change in PV at high altitude, whereas, in the foot group, there was a 10% increase in PV (P < 0.01). Albumin synthesis (mg. kg(-1). day(-1)) increased by 13% in the air group (P = 0.058) and by 32% in the foot group (P < 0.001). Fibrinogen synthesis (mg. kg(-1). day(-1)) increased by 40% in the air group (P = 0.068) and by 100% in the foot group (P < 0.001). Hypoxia and alkalosis at high altitude did not differ between the groups. Plasma interleukin-6 was increased modestly in both groups but C-reactive protein was not changed in either group. It is concluded that increases in PV and plasma protein synthesis at high altitude result mainly from the physical exercise associated with climbing. However, a small stimulation of albumin and fibrinogen synthesis may be attributable to hypobaric hypoxia alone.

Importance of post-exercise hypotension in plasma volume restoration

The aim of this study was to test the hypothesis that post-exercise hypotension was the mechanism for the plasma volume and albumin gain during recovery. Seven healthy young men completed two experiments (> or =1 week apart) to exercise continuously at 65% of peak aerobic capacity for 60 min followed by the recovery without (experiment 1) or with phenylephrine infusion (experiment 2) to counteract post-exercise hypotension. Heart rate, arterial pressure (Finapres), plasma volume (PV, Evans blue dye dilution), haematocrit, haemoglobin, plasma total solutes (refractometer), albumin, total proteins (colorimetric method), [Na+] and [K+] were not different prior to the experiments. Exercise decreased PV -13.7% (-521 mL) and -14.2% (-566 mL) at the end of 60 min in experiments 1 and 2, respectively, associated with increases in the concentrations of plasma albumin, total protein and solutes. These changes were similar between the two experiments. Following 30 min recovery in experiment 1 the decreased PV was not significantly different from the baseline. Although the volume restoration was complete at the end of 90 min recovery, the change in the albumin concentration was still above zero, indicating a gain of 11 g albumin (P < 0.05). When phenylephrine was infused during recovery, there was no gain in intravascular albumin associated with a sustained decrease in PV (-7% or -280 mL, P < 0.05) observed at the end of experiment 2. These data suggest that post-exercise hypotension may be the mechanism for a gain of intravascular albumin via the lymph return, which enhances plasma water retention and PV restoration during recovery from exercise induced hypovolaemia, even without rehydration.

The thermophysiology of uncompensable heat stress. Physiological manipulations and individual characteristics

In many athletic and occupational settings, the wearing of protective clothing in warm or hot environments creates conditions of uncompensable heat stress where the body is unable to maintain a thermal steady state. Therefore, special precautions must be taken to minimise the threat of thermal injury. Assuming that manipulations known to reduce thermoregulatory strain during compensable heat stress would be equally effective in an uncompensable heat stress environment is not valid. In this review, we discuss the impact of hydration status, aerobic fitness, endurance training, heat acclimation, gender, menstrual cycle, oral contraceptive use, body composition and circadian rhythm on heat tolerance while wearing protective clothing in hot environments. The most effective countermeasure is ensuring that the individual is adequately hydrated both before and throughout the exercise or work session. In contrast, neither short term aerobic training or heat acclimation significantly improve exercise-heat tolerance during uncompensable heat stress. While short term aerobic training is relatively ineffective, long term improvements in physical fitness appear to provide some degree of protection. Individuals with higher proportions of body fat have a lower heat tolerance because of a reduced capacity to store heat. Women not using oral contraceptives are at a thermoregulatory disadvantage during the luteal phase of the menstrual cycle. The use of oral contraceptives eliminates any differences in heat tolerance throughout the menstrual cycle but tolerance is reduced during the quasi-follicular phase compared with non-users. Diurnal variations in resting core temperature do not appear to influence tolerance to uncompensable heat stress.

Blood volume, aerobic power, and endurance performance: potential ergogenic effect of volume loading

OBJECTIVE

Blood volume (BV) and hemoglobin concentration ([Hb]) play important roles in oxygen transport. Manipulation of both BV and [Hb] can markedly affect systemic oxygen transport and maximal aerobic capacity (VO2max). However, the role of BV in oxygen transport and aerobic performance is not well understood. It has recently been postulated that an acute expansion of BV using plasma volume (PV), independent of changes in [Hb], may represent a potential ergogenic property. Therefore, the primary objective of this review was to determine the potential ergogenic properties of volume loading.

DATA SOURCES

An extensive research of Medline and Sport-Discus along with cross-referencing was conducted. Articles were included on the basis of their relevancy to the purpose of this review. Only articles published in English were included in the analysis.

STUDY SELECTION

All study designs using human participants were reviewed.

DATA EXTRACTION

A systematic analysis of data regarding the effect of BV on the determination of oxygen transport, aerobic capacity, and endurance performance was conducted. Particular emphasis was given to articles that examined BV as the key independent variable. Articles relevant to the evaluation of the impact of BV on aerobic capacity and endurance performance were reviewed according to the strengths of the individual study designs.

RESULTS

Seven investigations evaluated the impact of acute changes in BV, independent of changes in [Hb], on VO2max. Of these investigations, three revealed that acute manipulations of BV result in no change or a slight reduction in VO2max. Three investigations revealed a significant improvement in VO2max after acute PV expansion. One investigation revealed a nonsignificant increase in VO2max after acute PV expansion. Seven investigations evaluated the impact of acute changes in BV, independent of changes in [Hb], on endurance performance: two revealed a significant improvement in endurance performance after acute PV expansion, and five revealed an unchanged or reduced endurance performance after acute PV expansion. The majority of investigations showing an improvement in VO2max and/or endurance performance after acute PV expansion were conducted using untrained individuals.

CONCLUSION

Volume loading does not result in an improvement in VO2max and/or endurance performance in endurance athletes. Volume loading in untrained individuals may improve VO2max, but does not bring these individuals to the aerobic capacity of endurance-trained athletes. Also, volume loading generally does not lead to improvement in endurance performance, irrespective of its effects on VO2max.

Mechanism for the posture-specific plasma volume increase after a single intense exercise protocol

To test the hypothesis that exercise-induced hypervolemia is a posture-dependent process, we measured plasma volume, plasma albumin content, and renal function in seven healthy subjects for 22 h after single upright (Up) or supine (Sup) intense (85% peak oxygen consumption rate) exercise. This posture was maintained for 5 h after exercise. Plasma volume decreased during exercise but returned to control levels by 5 h of recovery in both postures. By 22 h of recovery, plasma volume increased 2.4 +/- 0.8 ml/kg in Up but decreased 2.1 +/- 0.8 ml/kg in Sup. The plasma volume expansion in Up was accompanied by an increase in plasma albumin content (0.11 +/- 0.04 g/kg; P < 0.05). Plasma albumin content was unchanged in Sup. Urine volume and sodium clearance were lower in Up than Sup (P < 0.05) by 5 h of recovery. These data suggest that increased plasma albumin content contributes to the acute phase of exercise-induced hypervolemia. More importantly, the mechanism by which exercise influences the distribution of albumin between extra- and intravascular stores after exercise is altered by posture and is unknown. We speculate that factors associated with postural changes (e.g., central venous pressure) modify the increase in plasma albumin content and the plasma volume expansion after exercise.

The influence of exercise-induced plasma volume changes on the interpretation of biochemical parameters used for monitoring exercise, training and sport

A number of studies have demonstrated considerable plasma volume changes during and after exposure to different environmental and physiological conditions. These changes are thought to result from transient fluid shifts into (haemodilution) and out of (haemoconcentration) the intravascular space. If the levels of plasma constituents are to be routinely measured for research purposes or used as indicators of training adaptation or the health of an athlete, then it is important to consider the dynamic nature of plasma volume. Controversy still exists over the relevance of plasma volume interactions with plasma constituent levels, and while some investigators have taken plasma volume shifts into account, others have chosen to ignore these changes. Bouts of acute exercise have been shown to produce a transient haemoconcentration immediately after long distance running, bicycle ergometry and both maximal and submaximal swimming exercise. While these changes are transient, lasting only a few hours, other studies have reported a longer term haemodilution following acute exercise. In addition, endurance training has been shown to cause long term expansion of the plasma volume. It would, therefore, seem important to consider the influence of plasma volume changes on plasma solutes routinely measured for research, and as markers of training adaptation, prior to arriving at conclusions and recommendations based purely on their measured plasma level. To further confound this issue, plasma volume changes are known to be associated with heat acclimatisation, hydration state, physical training and postural changes, all of which may differ from one experiment or exercise bout to the next, and should thus be taken into account.

Albumin synthesis after intense intermittent exercise in human subjects

We measured hepatic albumin synthesis in five volunteers (4 men and 1 woman) at 3 and 6 h after recovery from intense exercise. A primed-constant infusion of a stable isotopic tracer of phenylalanine was used to determine hepatic fractional synthetic rate (FSR) and absolute synthetic rate (ASR) of albumin from the enrichment of phenylalanine in albumin. The infusion of the stable isotope tracer began 2 h after upright exercise or upright rest. Albumin FSR and ASR were 6.39 +/- 0.48%/day and 120 +/- 9 mg.kg body wt-1.day-1, respectively, 3-6 h after recovery from exercise; the FSR and ASR on the time control study day were 5.94 +/- 0.47%/day and 104 +/- 9 mg.kg body wt-1.day-1, respectively. The 6 and 16% increases (P < 0.05) in FSR and ASR after exercise were associated with an elevated plasma albumin content at 5 and 6 h of recovery (P < 0.05), an increased total protein content throughout recovery (P < 0.05), and a negative free water clearance (P < 0.05) at 2, 3, and 6.5 h of recovery compared with baseline values; these variables were unchanged from their baselines on the time control study day. Increased albumin content and reduced free water clearance contribute to a retention of fluid within the circulation after intense exercise. The measured increase in albumin synthesis could not account for the entire increase in albumin content at 6 h of recovery from exercise. However, we estimate that if the increased activity was maintained for the next 18 h, it could account for the expected increase in albumin content at 24 h of recovery.

Effect of acute plasma volume expansion on substrate turnover during prolonged low-intensity exercise

We investigated the effect of acute, graded increases in plasma volume (PV) by use of dextran on substrate turnover and oxidation during exercise. Eight untrained males [peak aerobic power (VO2peak) = 45.2 +/- 2.2 (SE) ml.kg-1.min-1] performed 2 h of cycle ergometry at 46 +/- 4% of VO2peak on three occasions in a randomized order: 0% PV expansion (CON) and after 14% (LOW) and 21% (HIGH) PV expansion. Glucose and glycerol turnover were measured using primed continuous infusions of [6,6-2H2]glucose and [2H5]glycerol, respectively. Glycerol rate of appearance (Ra) was taken as a relative index of whole body lipolysis. Increases in PV had no effect on glucose Ra or disappearance (Rd) either at rest or during exercise. At the onset of exercise, both glucose Ra and Rd increased approximately 100% (P < 0.01). Glucose Ra and Rd continued to increase with exercise duration (P < 0.05) so that, at 120 min of exercise, they were > 330% higher than at rest (P < 0.01). Glycerol Ra also increased with exercise duration (P < 0.05). Total lipolysis during exercise, calculated as the area under the glycerol Ra vs. time curve, was reduced during LOW vs. CON (P < 0.01). Further expansion of PV (HIGH) had no additional effect on whole body lipolysis. No effect of hypervolemia was observed on whole body fat or carbohydrate oxidation. These results indicate that acute PV expansion can alter whole body lipolysis, possibly via a reduction in catecholamine secretion.

The interaction between short-term exercise training and a diuretic-induced hypovolemic stimulus

Nine healthy untrained males [mean (SEM) age, 20.2 (1) years; peak oxygen uptake (VO2max, 48.2 (2) ml.kg-1.min-1] took part in a study to examine whether short-term exercise training (cycle exercise 2 h.day-1 for 3 days at 60% VO2max), which normally results in an expansion of plasma volume (PV), can counteract a diuretic-induced hypovolemic stimulus (100 mg triamterene + 50 mg hydrochlorothiazide.day-1 for 5 days concurrent with exercise training) and restore PV to control levels. Resting and exercise responses (90 min, 60% VO2max) in the diuretic plus exercise training condition (D+E) were compared to a control (C) and a diuretic (D) condition in which no exercise was performed. Following the short-term training, PV was still decreased (P < 0.05) below C by -8.3 (3)% in D+E and was similar (P > 0.05) to the reduction in D [-12.4 (2)%]. The reduced PV in response to the diuretic was associated with similar (P > 0.05) elevations in resting aldosterone (ALDO) and norepinephrine (NOREPI) levels (ng.100 ml-1) in D [101 (12), 61 (4)] and D+E [85 (16), 60 (10)] above (P < 0.05) C [22 (5), 37 (4)]. During exercise, ALDO levels were increased (P < 0.05) by 66 (5) and 70 (10) ng.100 ml-1 in D and D+E, respectively, and the increase was greater (P < 0.05) than C [44 (8) ng.100 ml-1]. The rise in NOREPI during exercise was lower (P < 0.05) in D+E [164 (44) ng.100 ml-1] than in D [244 (24) ng.100 ml-1] with levels similar to C [176 (25) ng.100 ml-1]. Thus, the ALDO response to the diuretic was heightened at rest and during exercise but was not additionally affected by the short-term training session. Results suggest that 3 days of exercise training are unable to counteract the hypovolemic effects of a diuretic and restore PV to control levels despite chronic elevations in NOREPI and ALDO.

Effects of high volume and/or intense exercise on selected blood chemistry parameters

The goal of athletic training is to provide the body with a stimulus to adapt, increasing the capacity of the various systems to perform increased work loads. However, the magnitude of the stress must be large enough to induce the synthesis of new enzymes, tissues, and yet not so large that the biochemical and physiological processes of recovery are depressed. As each individual undergoes this process at a different rate, objective evaluation of the level of fatigue and adaptation is of enormous value in directing the training program of an athlete. The role of iron in the body is such that this element can be used as a marker of both adaptation to training and as an indicator of an acute inflammatory response to exercise. The various clinical measurements of iron in transport, storage, and in hematological parameters are discussed in this paper, relative to athletic populations. In addition expected changes in the level of the acute inflammatory protein, alpha 1-antitrypsin are also discussed relative to acute and chronic training protocols. Data is presented indicating that measurement of serum iron, transferrin, serum ferritin, and alpha 1-antitrypsin can be used to differentiate between an inflammatory response to tissue damage and infection. These parameters can also provide information as to the state of recovery, or lack thereof, experienced by an athlete to both acute and chronic training programs. The use of biochemical markers can help to avoid an overstress situation.

Comparing the effects of two in-flight aerobic exercise protocols on standing heart rates and VO(2peak) before and after space flight

The effects of regular aerobic exercise on orthostatic tolerance have been the subject of a long-standing controversy that will influence the use of exercise during space flight. To examine these effects, astronauts performed continuous (CE) aerobic exercise (n = 8), interval (IE) aerobic exercise (n = 4), or no (NE) exercise (n = 5) during flights of 7 to 11 days. Heart rate (HR) responses to an orthostatic challenge (stand test) were measured 10 days before flight and on landing day. VO(2peak) (graded treadmill exercise) was measured 7 to 21 days before and 2 days after flight. No significant differences across the groups were observed in standing HRs before or after flight. However, the within-group mean HRs significantly increased in the NE (71-89 beats/min) and CE (60-85 beats/min) groups after space flight. The HRs for the IE group did not significantly increase (75-86 beats/min) after space flight. VO(2peak) decreased (P < .05) in the NE (-9.5%) group, but did not change in the CE (-2.4%) and IE (1%) groups. The relationship (r = 0.237) between the delta HR and delta VO(2peak) was not significant. These preliminary results indicate that: (1) continuous exercise does not affect the orthostatic HR response after space flight; (2) interval exercise may minimize an increase in the postflight orthostatic HR; and (3) both exercise protocols can maintain VO(2peak).

Changes in plasma volume and baroreflex function following resistance exercise

The dynamics of change in plasma volume (PV) and baroreflex responses have been reported over 24 h immediately following maximal cycle exercise. The purpose of this study was to determine if PV and baroreflex showed similar changes for 24 h after resistance exercise. Eight men were studied on 2 test days, 1 week apart. On 1 day, per cent change (% delta) in PV was estimated at 0,3, and 6 h after resistance exercise using haematocrit and haemoglobin. Baseline PV was measured 24 h after exercise using Evans blue dye. The carotid baroreceptor-cardiac reflex response was measured before, and 3, 6, 9, 12, and 24 h post-exercise. Each subject performed six sets of the bench press and leg press with 10 repetitions per set with a load that induced failure within each set. On a control day, the protocol was used without exercise. Plasma volume did not change during the control day. There was a 20% decrease in PV immediately post-exercise; the recovery of the PV was rapid and complete within 3 h. PV was 20% greater 24 h post-exercise than on the control day. There were no differences in any of the baroreflex measurements. Therefore, it is suggested that PV shifts may occur without altering baroreflex sensitivity.

Alterations in plasma volume, plasma constituents, renin activity and aldosterone induced by maximal exercise in the horse

Plasma volume (PV) decreased by 13 per cent following the completion of 1,000 m of maximal exercise in the horse. This study demonstrated that the critical reduction in PV following maximal exercise occurred within 10 mins of completion of exercise, as previously reported in man. Total plasma protein (TPP) increased by 23 per cent at 2 and 5 mins, and by 21 per cent at 10 mins post exercise. Therefore, it does not appear to be an accurate measurement to assess the degree of PV contraction in the horse. Protein was apparently added to the intravascular space either during or following exercise. The changes in osmolality correlated strongly with those in sodium, which is the primary determinant of alterations in plasma tonicity. The increase in osmolality (12 per cent) was similar to the reduction in PV (13 per cent) concluding that a transient hypotonic fluid loss had occurred. The increase in plasma renin activity (PRA) following maximal exercise was followed by an increase in aldosterone (ALD) concentration in both magnitude and time course. Alterations in PV should be considered when interpreting electrolyte and serum enzyme activity data collected following maximal exercise.