Interactive effects of anemia and muscle oxidative capacity on exercise endurance

Cardiorespiratory fitness mediates cortisol and lactate responses to winter and summer marches

Background

The influence of homeostatically regulated physiological processes, including cardiorespiratory fitness (VO2max), on the response to physical stressors such as acclimatisation and marching, remains understudied. We aimed to investigate the effects of summer and winter acclimatisation and marching on cortisol levels and blood lactate, to gain insight into the role of these physiological processes in the stress response.

Methods

Two groups of young Europeans, classified as poor (PCF; n=9) and good physical condition (GCF; n=21), based on a VO2MAX threshold of 40 mL O2/ kg/min, underwent 2-h March (6-7 km/h) in winter (5˚C) and summer (32˚C). Commercial tests, UniCel DxI Access Cortisol assay and EKF Biosen Clinic/GP assay were used for cortisol and lactate blood measurements (morning samples and those taken immediately after marches), respectively.

Iron Status and Physical Performance in Athletes

Iron is an important mineral in the body, essential for muscle function and oxygen transport. Adequate levels of iron in the blood are necessary for athletes, as iron-deficiency anemia can reduce physical performance. Several studies have investigated iron status and supplementation in iron-deficient athletes, and determined how physical strain can change iron balance and markers related to iron status. The question of how to influence and optimize iron status, as well as other markers that can affect iron metabolism, has been less thoroughly investigated. Therefore, the aim of this review is to take a closer look at the importance of iron values, iron markers, and factors that can change iron metabolism for physical performance and the extent to which physical performance can be influenced in a positive or negative way. A systematic search of the PubMed database was performed, with the use of « iron» or «iron deficiency» or «hemoglobin» AND «athletes» AND «athletic performance» as a strategy of the search. After the search, 11 articles were included in the review after the application of inclusion and exclusion criteria. Major findings include that iron supplementation had the best effect in athletes with the lowest iron status, and effects on physical performance were mostly achieved in those who were originally in a deficit. Iron supplementation could be beneficial for optimal erythropoietic response during altitude training, even in athletes with normal iron stores at baseline, but should be performed with caution. Alteration of the hepcidin response can affect the use of existing iron stores for erythropoiesis. Energy intake, and the amount of carbohydrates available, may have an impact on the post-exercise hepcidin response. Optimal vitamin D and B12 levels can possibly contribute to improved iron status and, hence, the avoidance of anemia.

Skeletal muscle mitochondrial dysfunction and muscle and whole body functional deficits in cancer patients with weight loss

Reductions in skeletal muscle mass and function are often reported in patients with cancer-associated weight loss and are associated with reduced quality of life, impaired treatment tolerance, and increased mortality. Although cellular changes, including altered mitochondrial function, have been reported in animals, such changes have been incompletely characterized in humans with cancer. Whole body and skeletal muscle physical function, skeletal muscle mitochondrial function, and whole body protein turnover were assessed in eight patients with cancer-associated weight loss (10.1 ± 4.2% body weight over 6-12 mo) and 19 age-, sex-, and body mass index (BMI)-matched healthy controls to characterize skeletal muscle changes at the whole body, muscle, and cellular level. Potential pathways involved in cancer-induced alterations in metabolism and mitochondrial function were explored by interrogating skeletal muscle and plasma metabolomes. Despite similar lean mass compared with control participants, patients with cancer exhibited reduced habitual physical activity (57% fewer daily steps), cardiorespiratory fitness [22% lower V̇o_2peak (mL/kg/min)] and leg strength (35% lower isokinetic knee extensor strength), and greater leg neuromuscular fatigue (36% greater decline in knee extensor torque). Concomitant with these functional declines, patients with cancer had lower mitochondrial oxidative capacity [25% lower State 3 O₂ flux (pmol/s/mg tissue)] and ATP production [23% lower State 3 ATP production (pmol/s/mg tissue)] and alterations in phospholipid metabolite profiles indicative of mitochondrial abnormalities. Whole body protein turnover was unchanged. These findings demonstrate mitochondrial abnormalities concomitant with whole body and skeletal muscle functional derangements associated with human cancer, supporting future work studying the role of mitochondria in the muscle deficits associated with cancer.NEW & NOTEWORTHY To our knowledge, this is the first study to suggest that skeletal muscle mitochondrial deficits are associated with cancer-associated weight loss in humans. Mitochondrial deficits were concurrent with reductions in whole body and skeletal muscle functional capacity. Whether mitochondrial deficits are causal or secondary to cancer-associated weight loss and functional deficits remains to be determined, but this study supports further exploration of mitochondria as a driver of cancer-associated losses in muscle mass and function.

Reduced exercise capacity in patients with systemic sclerosis is associated with lower peak tissue oxygen extraction: a cardiovascular magnetic resonance-augmented cardiopulmonary exercise study

BACKGROUND

Exercise intolerance in systemic sclerosis (SSc) is typically attributed to cardiopulmonary limitations. However, problems with skeletal muscle oxygen extraction have not been fully investigated. This study used cardiovascular magnetic resonance (CMR)-augmented cardiopulmonary exercise testing (CMR-CPET) to simultaneously measure oxygen consumption and cardiac output. This allowed calculation of arteriovenous oxygen content gradient, a recognized marker of oxygen extraction. We performed CMR-CPET in 4 groups: systemic sclerosis (SSc); systemic sclerosis-associated pulmonary arterial hypertension (SSc-PAH); non-connective tissue disease pulmonary hypertension (NC-PAH); and healthy controls.

METHODS

We performed CMR-CPET in 60 subjects (15 in each group) using a supine ergometer following a ramped exercise protocol until exhaustion. Values for oxygen consumption, cardiac output and oxygen content gradient, as well as ventricular volumes, were obtained at rest and peak-exercise for all subjects. In addition, T1 and T2 maps were acquired at rest, and the most recent clinical measures (hemoglobin, lung function, 6-min walk, cardiac and catheterization) were collected.

RESULTS

All patient groups had reduced peak oxygen consumption compared to healthy controls (p < 0.022). The SSc and SSc-PAH groups had reduced peak oxygen content gradient compared to healthy controls (p < 0.03). Conversely, the SSc-PAH and NC-PH patients had reduced peak cardiac output compared to healthy controls and SSc patients (p < 0.006). Higher hemoglobin was associated with higher peak oxygen content gradient (p = 0.025) and higher myocardial T1 was associated with lower peak stroke volume (p = 0.011).

CONCLUSIONS

Reduced peak oxygen consumption in SSc patients is predominantly driven by reduced oxygen content gradient and in SSc-PAH patients this was amplified by reduced peak cardiac output. Trial registration The study is registered with ClinicalTrials.gov Protocol Registration and Results System (ClinicalTrials.gov ID: 100358).

Impact of Anemia on Exercise and Pharmacologic Stress Echocardiography

BACKGROUND

The safety and diagnostic accuracy of stress testing in anemic patients have not been well studied. Despite a lack of data, significant anemia may be considered a relative contraindication to stress testing because of safety concerns related to insufficient myocardial oxygen supply.

METHODS

The authors reviewed 28,829 consecutive patients with blood hemoglobin drawn within 48 hours of stress echocardiography (15,624 exercise and 13,205 dobutamine). The associations of blood hemoglobin concentration with arrhythmia and other stress echocardiographic findings were examined. Additionally, the effect of anemia on the positive predictive value of stress echocardiography for the detection of significant coronary artery stenosis (≥50%) was assessed in patients who subsequently underwent coronary angiography.

RESULTS

Anemia was present in 6,401 patients (22.2%) and was severe (hemoglobin < 8.0 g/dL) in 52. Stress testing with either exercise or dobutamine was safe, with no significant increase in serious arrhythmia events or need for hospitalization. In the exercise cohort, worsening anemia was associated with reduced treadmill exercise time, lower peak heart rate, peak rate-pressure product, and achieved workload. In the dobutamine stress cohort, worsening anemia was associated with higher resting heart rate, more use of atropine, and fewer patients attaining target heart rate. The positive predictive value of stress echocardiography was higher in patients with moderate anemia compared with those without anemia (71.8% vs 60.2%, P = .01).

CONCLUSIONS

This study demonstrates that stress testing is safe in patients with mild and moderately anemia, albeit with a small increase in mild supraventricular arrhythmias with exercise. However, worsening anemia was associated with a significant reduction in exercise capacity. Additionally, worsening anemia was associated with an improvement in the positive predictive value of stress echocardiography. Extrapolation of these data to patients with severe anemia should be performed with caution given the limited number of patients with severe anemia in this study.

Erythropoietin and the use of a transgenic model of erythropoietin-deficient mice

Despite its well-known role in red blood cell production, it is now accepted that erythropoietin (Epo) has other physiological functions. Epo and its receptors are expressed in many tissues, such as the brain and heart. The presence of Epo/Epo receptors in these organs suggests other roles than those usually assigned to this protein. Thus, the aim of this review is to describe the effects of Epo deficiency on adaptation to normoxic and hypoxic environments and to suggest a key role of Epo on main physiological adaptive functions. Our original model of Epo-deficient (Epo-TAg^h) mice allowed us to improve our knowledge of the possible role of Epo in O₂ homeostasis. The use of anemic transgenic mice revealed Epo as a crucial component of adaptation to hypoxia. Epo-TAg^h mice survive well in hypoxic conditions despite low hematocrit. Furthermore, Epo plays a key role in neural control of ventilatory acclimatization and response to hypoxia, in deformability of red blood cells, in cerebral and cardiac angiogenesis, and in neuro- and cardioprotection.

Effects of arms-only swimming training on performance, movement economy, and aerobic power

CONTEXT

Forward propulsion in freestyle swimming is predominantly achieved through arm action. Few studies have assessed the effects of arm training on arm power and swimming performance, yet there have not been any investigations on the effects of arms-only swimming training on swimming performance and physiological responses to arm exercise.

PURPOSE

To investigate the changes in arms-only and full-stroke swimming performance, movement economy and aerobic power after an arms-only swimming training program.

METHODS

Fifteen male county level swimmers were assigned either to an experimental (ES, n = 8) or control group (CS, n = 7). For six weeks ES performed arms-only freestyle swimming exercises for 20% of their weekly training distance three times per week, whereas CS performed their usual swimming training. Before and after the training program, both groups performed a) two time trials, 186 m using arms-only (186ARMS) and 372 m using full-stroke (372FULL) freestyle swimming, and b) an incremental arm-pulling exercise test. The time to complete the trials was recorded. Peak oxygen uptake (VO2peak), peak exercise intensity (EIpeak) submaximal oxygen uptake at 60 W (VO2-60) and exercise intensity at ventilatory threshold (VTW) were determined from the exercise test.

RESULTS

After training, ES had improved in 186ARMS (-14.2 +/- 3.6%, P = .03), VO2-60 (-22.5 +/- 2.3%, P = .04), EIpeak (+17.8 +/- 4.2%, P = .03), and VTW (+18.9 +/- 2.3%, P = .02), but not in VO2peak (P = .09) or in 372FULL (P = .07). None of the measures changed in CS (P > .05).

CONCLUSION

Arms-only swimming training at 20% of the weekly training distance is an effective method to improve arm conditioning during the preparatory phase of the annual training cycle.

Endurance exercise performance: the physiology of champions

Efforts to understand human physiology through the study of champion athletes and record performances have been ongoing for about a century. For endurance sports three main factors--maximal oxygen consumption (.VO(2,max)), the so-called 'lactate threshold' and efficiency (i.e. the oxygen cost to generate a given running speed or cycling power output)--appear to play key roles in endurance performance. and lactate threshold interact to determine the 'performance .VO(2)' which is the oxygen consumption that can be sustained for a given period of time. Efficiency interacts with the performance .VO(2) to establish the speed or power that can be generated at this oxygen consumption. This review focuses on what is currently known about how these factors interact, their utility as predictors of elite performance, and areas where there is relatively less information to guide current thinking. In this context, definitive ideas about the physiological determinants of running and cycling efficiency is relatively lacking in comparison with .VO(2,max) and the lactate threshold, and there is surprisingly limited and clear information about the genetic factors that might pre-dispose for elite performance. It should also be cautioned that complex motivational and sociological factors also play important roles in who does or does not become a champion and these factors go far beyond simple physiological explanations. Therefore, the performance of elite athletes is likely to defy the types of easy explanations sought by scientific reductionism and remain an important puzzle for those interested in physiological integration well into the future.

Characterisation of the ventilatory response to hypoxia in a model of transgenic anemic mice

Both polycythemia and the increase in hypoxic ventilatory response (HVR) are considered as important factors of acclimatization to hypoxia. The objective of this study was to characterise the ventilation pattern at different inspired oxygen fraction in a model of chronic anemic mice. These mice have a targeted disruption in the 5' untranslated region of the Epo gene that reduces Epo expression such that the homozygous animal is severely anemic. Ventilation in normoxia in Epo-TAg(h) mice was significantly greater than in wild type, and the difference was mainly due to a higher tidal volume. HVR was higher in Epo-TAg(h) mice at every FIO2 suggesting a higher chemosensitivity. Resting oxygen consumption was maintained in anemic mice. Maximal oxygen consumption was 30% lower while hemoglobin was 60% lower in anemic mice compared to wild type. This small decrease in maximal oxygen consumption is probably due a greater cardiac output and/or a better tissue oxygen extraction and would allow these anemic mice to acclimatize to hypoxia in spite of low oxygen carrying capacity. In conclusion, Epo-TAg(h) anemic mice showed increased ventilation and hypoxic ventilatory response. However, whether these adaptations will contribute to acclimatization in chronic hypoxia remains to be determined.

Effects of Nandrolone Decanoate on &OV0312;O2max, Running Economy, and Endurance in Rats

PURPOSE

The aim of the present study was to determine the effects of treatment with an anabolic androgenic steroid (AAS), nandrolone decanoate, on the submaximal running endurance (SRE), maximum oxygen consumption (VO2max), running economy (VO2submax), and blood oxygen carrying capacity of endurance trained rats.

METHODS

Forty male Wistar rats were randomly allocated into two groups: a sedentary group and an exercising group training on treadmill for 8 wk. Half of the trained and half of the sedentary rats received weekly either nandrolone decanoate (10 mg x kg(-1)) or placebo (Pl) for the last 6 wk of experiment. SRE and VO2max tests were performed several times for all four groups (N = 10 each).Red blood cells parameters were measured at the end of the experiment.

RESULTS

The trained rats had increased their SRE compared with sedentary rats throughout the experiment. At the end of the trial, the trained rats receiving nandrolone decanoate ran 46% longer than trained rats receiving Pl during the SRE test (P < 0.05). At the end of the experiment, trained rats had greater maximal time to exhaustion and higher VO2max than those of the sedentary rats but there were no differences in VO2max, VO2submax, and red blood cells parameters between the trained rats receiving nandrolone decanoate and those receiving Pl.

CONCLUSIONS

Nandrolone decanoate has no effect on the SRE, VO2max and VO2submax of untrained rats. AAS treatment combined with submaximal training enhances SRE more than training alone but exerts no additive effects on VO2max, running economy, and oxygen carrying capacity of blood. The results suggest that this improvement in SRE of trained rats is due to the impact of AAS on other factors involved in exercise adaptation.

The effects of endurance training and exhaustive exercise on mitochondrial enzymes in tissues of the rat (Rattus norvegicus)

The aim of the present study was to ascertain the effects of training and exhaustive exercise on mitochondrial capacities to oxidize pyruvate, 2-oxoglutarate, palmitoylcarnitine, succinate and ferrocytochrome c in various tissues of the rat. Endurance capacity was significantly increased (P<0.01) by an endurance training program over a period of 5-6 weeks. The average run time to exhaustion was 214.2+/-23.8 min for trained rats in comparison with 54.5+/-11.7 min for their untrained counterparts. Oxidative capacities were reduced in liver (P<0.05) and brown adipose tissue (P<0.05) as a result of endurance training. On the contrary, the oxidative capacity of skeletal muscle was slightly increased and that of heart almost unaffected except for the oxidation of palmitoylcarnitine, which was significantly reduced (P<0.05) as a result of training.