Physical fitness indices and anthropometrics profiles in schoolchildren with sickle cell trait/disease

Endurance training and hydroxyurea have synergistic effects on muscle function and energetics in sickle cell disease mice

Sickle cell disease (SCD) is an hemoglobinopathy resulting in the production of an abnormal Hb (HbS) which can polymerize in deoxygenated conditions, leading to the sickling of red blood cells (RBC). These alterations can decrease the oxygen-carrying capacity leading to impaired function and energetics of skeletal muscle. Any strategy which could reverse the corresponding defects could be of interest. In SCD, endurance training is known to improve multiples muscle properties which restores patient's exercise capacity but present reduced effects in anemic patients. Hydroxyurea (HU) can increase fetal hemoglobin production which can reduce anemia in patients. The present study was conducted to determine whether HU can improve the effects of endurance training to improve muscle function and energetics. Twenty SCD Townes mice have been trained for 8 weeks with (n = 11) or without (n = 9) HU. SCD mice muscle function and energetics were analyzed during a standardized rest-exercise-recovery protocol, using Phosphorus-31 Magnetic resonance spectroscopy (31P-MRS) and transcutaneous stimulation. The combination of training and HU specifically decreased fatigue index and PCr consumption while muscle oxidative capacity was improved. These results illustrate the potential synergistic effects of endurance training and HU on muscle function and energetics in sickle cell disease.

Cardiac diastolic maladaptation is associated with the severity of exercise intolerance in sickle cell anemia patients

This pilot study focusing on Sickle Cell Anemia (SCA) patients offers a comprehensive and integrative evaluation of respiratory, cardiovascular, hemodynamic, and metabolic variables during exercise. Knowing that diastolic dysfunction is frequent in this population, we hypothesize that a lack of cardiac adaptation through exercise might lead to premature increase in blood lactate concentrations in SCA patients, a potential trigger for acute disease complication. SCA patients were prospectively included in PHYSIO-EXDRE study and underwent a comprehensive stress test with a standardized incremental exercise protocol up to 4 mmol L-1 blood lactate concentration (BL4). Gas exchange, capillary lactate concentration and echocardiography were performed at baseline, during stress test (at ∼ 2 mmol L-1) and BL4. The population was divided into two groups and compared according to the median value of percentage of theoretical peak oxygen uptake (%V ˙ O 2 p e a k t h ) at BL4. Twenty-nine patients were included (42 ± 12 years old, 48% of women). Most patients reached BL4 at low-intensity exercise [median value of predicted power output (W) was 37%], which corresponds to daily life activities. The median value of %V ˙ O 2 p e a k t h at BL4 was 39%. Interestingly, diastolic maladaptation using echocardiography during stress test along with hemoglobin concentration were independently associated to early occurrence of BL4. As BL4 occurs for low-intensity exercises, SCA patients may be subject to acidosis-related complications even during their daily life activities. Beyond assessing physical capacities, our study underlines that diastolic maladaptation during exercise is associated with an early increase in blood lactate concentration.

Muscle Properties, Gross Motor Performance, and Quality of Life in Children With Sickle Cell Disease

PURPOSE

To explore muscle properties, gross motor performance, and quality of life (QoL) in children with sickle cell disease (SCD) compared with controls and to assess relationships among these outcomes.

METHODS

A cross-sectional study of 24 children assessed muscle properties including: knee extension strength by dynamometry; vastus lateralis (VL) and rectus femoris (RF) muscle thickness by ultrasonography; and VL and RF neuromuscular activation (rate of muscle activation [RoA]) by electromyography (EMG). Gross motor performance and QoL were assessed by standardized tests and questionnaires.

RESULTS

Children with SCD had impaired knee extension strength, VL EMG RoA, gross motor performance, and QoL compared with children without SCD. Relationships among muscle properties, gross motor performance, and QoL were identified.

CONCLUSIONS

These findings indicate that comprehensive muscle properties, gross motor performance, and QoL assessments should be considered to support and develop individualized physical therapy plans for children with SCD.

Management of the Sickle Cell Trait: An Opinion by Expert Panel Members

The number of individuals with the sickle cell trait exceeds 300 million worldwide, making sickle cell disease one of the most common monogenetic diseases globally. Because of the high frequency of sickle cell disease, reproductive counseling is of crucial importance. In addition, unlike other carrier states, Sickle Cell Trait (SCT) seems to be a risk factor for several clinical complications, such as extreme exertional injury, chronic kidney disease, and complications during pregnancy and surgery. This expert panel believes that increasing knowledge about these clinical manifestations and their prevention and management can be a useful tool for all healthcare providers involved in this issue.

Effects of hydroxyurea on skeletal muscle energetics and force production in a sickle cell disease murine model

Hydroxyurea (HU) is commonly used as a treatment for patients with sickle cell disease (SCD) to enhance fetal hemoglobin production. This increased production is expected to reduce anemia (which depresses oxygen transport) and abnormal Hb content alleviating clinical symptoms such as vaso-occlusive crisis and acute chest syndrome. The effects of HU on skeletal muscle bioenergetics in vivo are still unknown. Due to the beneficial effects of HU upon oxygen delivery, improved skeletal muscle energetics and function in response to a HU treatment have been hypothesized. Muscle energetics and function were analyzed during a standardized rest-exercise-recovery protocol, using ³¹P-magnetic resonance spectroscopy in Townes SCD mice. Measurements were performed in three groups of mice: one group of 2-mo-old mice (SCD_2m, n = 8), another one of 4-mo-old mice (SCD_4m, n = 8), and a last group of 4-mo-old mice that have been treated from 2 mo of age with HU at 50 mg/kg/day (SCD_4m-HU, n = 8). As compared with SCD_2m mice, SCD_4m mice were heavier and displayed a lower acidosis. As lower specific forces were developed by SCD_4m compared with SCD_2m, greater force-normalized phosphocreatine consumption and oxidative and nonoxidative costs of contraction were also reported. HU-treated mice (SCD_4m-HU) displayed a significantly higher specific force production as compared with untreated mice (SCD_4m), whereas muscle energetics was unchanged. Overall, our results support a beneficial effect of HU on muscle function.NEW & NOTEWORTHY Our results highlighted that force production decreases between 2 and 4 mo of age in SCD mice thereby indicating a decrease of muscle function during this period. Of interest, HU treatment seemed to blunt the observed age effect given that SCD_4m-HU mice displayed a higher specific force production as compared with SCD_4m mice. In that respect, HU treatment would help to maintain a higher capacity of force production during aging in SCD.

Skeletal Muscle Measurements in Pediatric Hematology and Oncology: Essential Components to a Comprehensive Assessment

Children with hematologic and oncologic health conditions are at risk of impaired skeletal muscle strength, size, and neuromuscular activation that may limit gross motor performance. A comprehensive assessment of neuromuscular function of these children is essential to identify the trajectory of changes in skeletal muscle and to prescribe therapeutic exercise and monitor its impact. Therefore, this review aims to (a) define fundamental properties of skeletal muscle; (b) highlight methods to quantify muscle strength, size, and neuromuscular activation; (c) describe mechanisms that contribute to muscle strength and gross motor performance in children; (d) recommend clinical assessment measures; and (e) illustrate comprehensive muscle assessment in children using examples of sickle cell disease and musculoskeletal sarcoma.

Testes Ergométricos em Pacientes com Anemia Falciforme: Segurança, Viabilidade e Possíveis Implicações no Prognóstico

Fundamento

Pacientes com anemia falciforme (AF) têm risco aumentado de complicações cardiovasculares. O teste ergométrico é usado como marcador de prognóstico em uma série de doenças cardiovasculares. Entretanto, há uma escassez de evidências sobre exercícios em pacientes com AF, especialmente em relação à sua segurança, viabilidade e possível função prognóstica.

Objetivos

Usamos o teste em esteira máximo para determinar a segurança e a viabilidade do teste ergométrico em pacientes com AF. Além disso, os fatores associados à duração do exercício, bem como o impacto das alterações causadas pelo exercício em resultados clínicos, também foram avaliados.

Métodos

113 pacientes com AF que passaram pelo teste ergométrico e por uma avaliação cardiovascular abrangente incluindo um ecocardiograma e os níveis do peptídeo natriurético do tipo B (BNP). O desfecho de longo prazo foi uma combinação de eventos incluindo morte, crises álgicas graves, síndrome torácica aguda ou internações hospitalares por outras complicações associadas â doença falciforme. A análise de regressão de Cox foi realizada para identificar as variáveis associadas ao resultado. Um p valor <0,05 foi considerado estatisticamente significativo.

Resultados

A média de idade foi de 36 ± 12 anos (intervalo, 18-65 anos), e 62 pacientes eram do sexo feminino (52%). A presença de alterações isquêmicas ao esforço e resposta pressórica anormal ao exercício foram detectadas em 17% e 9 % da´população estudada respectivamente. Dois pacientes apresentaram crise álgica com necessidade de internação hospitalar no período de 48 horas da realização do exame. Fatores associados à duração do exercício foram idade, sexo, velocidade máxima de regurgitação tricúspide (RT), e relação E/e’, após a padronização quanto aos marcadores da gravidade da doença. Durante o período médio de acompanhamento de 10,1 meses (variando de 1,2 a 26), 27 pacientes (23%) apresentaram desfechos clínicos adversos. Preditores independentes de eventos adversos foram a concentração de hemoglobina, velocidade do fluxo transmitral tardio (onda A), e a resposta da PA ao exercício.

Conclusões

A realização de testes ergométricos em pacientes com AF, clinicamente estáveis, é viável. A duração do exercício estava associada à função diastólica e a pressão arterial pulmonar. A resposta anormal da PA foi um preditor independente de eventos adversos.

Physical Impairment and Function in Children and Adolescents With Sickle Cell Disease: A Systematic Review

OBJECTIVE

To examine physical impairments and physical function in children and adolescents with sickle cell disease (SCD).

DATA SOURCES

PubMed, Embase (embase.com), Cumulative Index to Nursing and Allied Health (EBSCO), Cochrane Central Register of Controlled Trials (Wiley), and Dissertations and Theses (ProQuest) were searched from January 1, 1990, to September 25, 2020. References retrieved were required to include a term for SCD and a term for physical impairments or physical function. Results were limited to articles with children and adolescents and in the English language.

STUDY SELECTION

A total of 3054 nonduplicate articles were independently screened by 2 reviewers, resulting in 240 articles for full-text review. The full-text review, performed by 2 independent reviewers, resulted in 67 articles.

DATA EXTRACTION

Data were extracted from each full text to a custom Excel document by a single reviewer and were verified by a secondary reviewer.

DATA SYNTHESIS

The studies identified in this systematic review offer evidence that children and adolescents with SCD demonstrate physical impairments and physical function limitations compared with control participants as noted by varying percentages in deficits up to 19%-58% in muscle and bone composition and/or symptoms, muscle strength, cardiopulmonary function, motor performance, physical activity, and physical function domains of quality of life questionnaires.

CONCLUSIONS

Children and adolescents with SCD present with physical impairments and physical function limitations. Scientists and clinicians should consider developing collaborative standards to define and objectively measure physical impairment and function in this population to comprehensively examine the underlying factors that contribute to physical impairments and function.

Is Skeletal Muscle Dysfunction a Limiting Factor of Exercise Functional Capacity in Patients with Sickle Cell Disease?

Patients with sickle cell disease (SCD) have reduced functional capacity due to anemia and cardio-respiratory abnormalities. Recent studies also suggest the presence of muscle dysfunction. However, the interaction between exercise capacity and muscle function is currently unknown in SCD. The aim of this study was to explore how muscle dysfunction may explain the reduced functional capacity. Nineteen African healthy subjects (AA), and 24 sickle cell anemia (SS) and 18 sickle cell hemoglobin C (SC) patients were recruited. Maximal isometric torque (Tmax) was measured before and after a self-paced 6-min walk test (6-MWT). Electromyographic activity of the Vastus Lateralis was recorded. The 6-MWT distance was reduced in SS (p < 0.05) and SC (p < 0.01) patients compared to AA subjects. However, Tmax and root mean square value were not modified by the 6-MWT, showing no skeletal muscle fatigue in all groups. In a multiple linear regression model, genotype, step frequency and hematocrit were independent predictors of the 6-MWT distance in SCD patients. Our results suggest that the 6-MWT performance might be primarily explained by anemia and the self-paced step frequency in SCD patients attempting to limit metabolic cost and fatigue, which could explain the absence of muscle fatigue.

Impact of a submaximal mono-articular exercise on the skeletal muscle function of patients with sickle cell disease

PURPOSE

Sickle cell disease (SCD) patients exhibit a limited exercise tolerance commonly attributed to anaemia, as well as hemorheological and cardio-respiratory abnormalities, but the functional status of skeletal muscle at exercise is unknown. Moreover, the effect of SCD genotype on exercise tolerance and skeletal muscle function has been poorly investigated. The aim of this study was to investigate skeletal muscle function and fatigue during a submaximal exercise in SCD patients.

METHODS

Nineteen healthy individuals (AA), 28 patients with sickle cell anaemia (SS) and 18 with sickle cell-haemoglobin C disease (SC) performed repeated knee extensions exercise (FAT). Maximal isometric torque (Tmax) was measured before and after the FAT to quantify muscle fatigability. Electromyographic activity and oxygenation by near-infrared spectroscopy of the Vastus Lateralis were recorded.

RESULTS

FAT caused a reduction in Tmax in SS (- 17.0 ± 12.1%, p < 0.001) and SC (- 21.5 ± 14.5%, p < 0.05) but not in AA (+ 0.58 ± 29.9%). Root-mean-squared value of EMG signal (RMS) decreased only in SS after FAT, while the median power frequency (MPF) was unchanged in all groups. Oxygenation kinetics were determined in SS and AA and were not different.

CONCLUSION

These results show skeletal muscle dysfunction during exercise in SCD patients, and suggest different fatigue aetiology between SS and SC. The changes in EMG signal and oxygenation kinetics during exercise suggest that the greater skeletal muscle fatigue occurring in SCD patients would be rather due to intramuscular alterations modifications than decreased tissue oxygenation. Moreover, SS patients exhibit greater muscle fatigability than SC.

Preventive measures for the critical postexercise period in sickle cell trait and disease

The immediate postexercise/physical activity period is critical for sickle cell trait (SCT) carriers and disease (SCD) patients. Exercise-related blood acidosis is known to trigger the cascade of HbS deoxygenation and polymerization, leading to red blood cell sickling and subsequent complications. Unfortunately, two facts worsen exercise-related blood acidosis during the initial postexercise period: First, blood lactate and H⁺ concentrations continue to increase for several minutes after exercise completion, exacerbating blood acidosis. Second, blood lactate concentration remains elevated and pH altered for 20-45 min during inactivity after intense exercise, keeping acid/base balance disturbed for a long period after exercise. Therefore, the risk of complications (including vasoocclusive crises and even sudden death) persists and even worsens several minutes after intense exercise completion in SCT carriers or SCD patients. Light physical activity following intense exercise (namely, active recovery) may, by accelerating lactate removal and acid/base balance restoration, reduce the risk of complications. Scientific evidence suggests that light exercise at or below the first lactate threshold is an appropriate strategy.

In vivo muscle function and energetics in women with sickle cell anemia or trait: a 31P-magnetic resonance spectroscopy study

Sickle cell anemia (SCA) is a genetic hemoglobinopathy associated with an impaired oxygen delivery to skeletal muscle that could alter ATP production processes and increase intramuscular acidosis. These alterations have been already reported in the Townes mouse model of SCA but the corresponding changes in humans have not been documented. In the present study, we used 31-phosphorus magnetic resonance spectroscopy to investigate in vivo the metabolic changes induced by a moderate-intensity exercise in twelve SCA patients, eight sickle cell trait (SCT) carriers, and twelve controls women. The rest-exercise-recovery protocol disclosed slight differences regarding phosphocreatine (PCr) consumption and lactate accumulation between SCA patients and controls but these differences did not reach a statistical significance. On that basis, the in vivo metabolic changes associated with a moderate-intensity muscle exercise were slightly altered in SCA patients and SCT carriers but within a normal range. The present results strongly support the fact that a moderate-intensity exercise is safe and could be recommended in stable SCA patients and SCT subjects.NEW & NOTEWORTHY The main finding of the present study was that the metabolic changes associated with a moderate-intensity muscle exercise were slightly modified in stable sickle cell anemia patients and sickle cell trait carriers as compared to controls but still in the normal range. The present results strongly support the safety of a moderate-intensity exercise for stable sickle cell anemia patients and sickle cell trait carriers.

How Sickle Cell Disease Impairs Skeletal Muscle Function: Implications in Daily Life

Sickle cell disease (SCD) is the most frequent life-threatening genetic hemoglobinopathy in the world and occurs due to the synthesis of abnormal hemoglobin S (HbS). hemoglobin S-containing red blood cells (RBC) are fragile, leading to hemolysis and anemia, and adhere to the endothelium, leading to hemorheological and hemodynamical disturbances. In its deoxygenated form, HbS may polymerize, leading to sickling of red blood cells and potentially to vasoocclusive crises. Recent findings observed that SCD patients demonstrate significant skeletal muscle remodeling and display reduced muscle functional capacities, contributing to exercise intolerance and poor quality of life. Although acute high-intensity exercise is not recommended for SCD patients because it may increase the risk of sickling, regular moderate-intensity physical activity could have beneficial effects on skeletal muscle and more generally on the well-being of SCD patients. This article reviews the literature regarding the impact of the disease on muscular tissue characteristics and function, as well as the corresponding implications for SCD patients' quality of life.

Effect of acute exercise on RBC deformability and RBC nitric oxide synthase signalling pathway in young sickle cell anaemia patients

Sickle cell anaemia (SCA) is characterized by reduced red blood cell (RBC) deformability and nitric oxide (NO) bioavailability. The aim of the study was to investigate whether exercise might affect these parameters in SCA. SCA patients and healthy controls (AA) performed an acute submaximal exercise test until subjects reached the first ventilatory threshold (VT 1). Blood was sampled at rest and at VT 1. At rest, free haemoglobin level was higher and RBC count, haemoglobin and haematocrit were lower in SCA compared to AA. RBC deformability was lower in SCA. Exercise had no effect on the tested parameters. RBC NO level was higher in SCA compared to AA at rest and significantly decreased after exercise in SCA. This might be related to a reduction in RBC-NO synthase (RBC-NOS) activation which was only observed in SCA after exercise. Free radical levels were higher in SCA at rest but concentration was not affected by exercise. Marker for lipid peroxidation and antioxidative capacity were similar in SCA and AA and not affected by exercise. In conclusion, a single acute submaximal bout of exercise has no deleterious effects on RBC deformability or oxidative stress markers in SCA, and seems to modulate RBC-NOS signalling pathway.

Exercise Testing of Adolescents and Young Adults With Sickle Cell Disease: Perceptual Responses and the Gas Exchange Threshold

For individuals with sickle cell disease (SCD), mild to moderate exercise is advised, but self-regulation of these intensities is difficult. To regulate intensity, one SCD recommendation is to stop exercising at the first perception of fatigue. However, perceived effort and affect (how one feels) are perceptual cues that are commonly used to guide exercise intensity. This study (a) examined perceived effort, affect, and fatigue in relation to metabolic state (gas exchange) in adolescents and young adults (AYAs) with SCD, (b) explored guidelines AYAs use to self-regulate exercise, and (c) compared perceived effort and affect at gas exchange threshold (GET) with healthy counterparts. Twenty-two AYAs with SCD completed an incremental cycle test. Perceived effort, affect, and fatigue were assessed every 2 minutes. A mixed-effects linear model was conducted to model changes in effort, affect, and fatigue across time. Mean scores of effort and affect at GET were compared with published data of healthy counterparts. Participants were queried about self-regulation exercise strategies. Findings indicated that both perceived fatigue and effort at GET was lower than expected. Perceived effort was lower (p < .0001), and perceived affect was significantly higher (p = .0009) than healthy counterparts. Interviews revealed that most participants (95%) do not stop exercising until fatigue is moderate to severe, and many (73%) do not stop until symptoms are severe (chest tightness, blurry vision). Nurses should review guidelines for safe exercise with AYAs with SCD. Exercise training may be beneficial to AYAs with SCD for learning how to interpret bodily responses to exercise to improve self-regulation.

Dietary intakes and nutritional status of children with sickle cell disease at the Princess Marie Louise Hospital, Accra - a survey

Background

Sickle cell disease (SCD) is a chronic genetic blood disorder common among people of African descent, which places nutritional burden among affected individuals. The aim of the study was to determine the dietary intake and nutritional status of children with SCD.

Method

This was a cross sectional study that involved 120 children with SCD aged 3-12 years at the paediatric outpatient department of Princess Marie Louise Hospital (PML) in Accra. A semi-structured questionnaire was used to take information on participant's demographic characteristics and clinical data were obtained from their medical records. Dietary data were obtained using 24-h dietary recall and food frequency questionnaire. Height and weight were measured for participants and their haemoglobin levels were determined to assess their anaemia status.

Results

Intakes of participants were below recommendations for most nutrients, particularly for calcium and antioxidant vitamins (vitamin C and E). Adequacy of nutrient intake declined with age and children with genotype HbSS had a lower tendency to meet dietary recommendations (aOR = 0.45, 95% CI: 0.18, 1.10; p = 0.084). More than a third of the study children (38%) were malnourished, with older children having a tendency to be malnourished compared to the younger ones. Children with the SS genotype were more likely to be stunted (aOR = 3.48, 95% CI: 1.10, 11.01), compared to other genotypes.

Conclusion

Malnutrition is prevalent among children with SCD and hence there is the need to develop comprehensive management coupling nutritional therapy to medical care to improve their nutritional status. Nutritional management should focus much on calcium-rich foods and antioxidants nutrients particularly vitamin C and E to reduce rapid erythrocyte haemolysis and chronic anaemia.

Muscle Strength, Power, and Torque Deficits in Children With Type SS Sickle Cell Disease

In African-American children aged 5 to 17 years with and without type SS sickle cell disease (SCD-SS), dominant hand maximal handgrip strength, peak power, and plantar flexion isometric maximal voluntary contraction (MVC) torque were compared with adjustments for body size and composition. Children with SCD-SS (n=21; age, 11±1 y) compared with healthy control children (n=23; 10±1 y) did not differ by age, sex, or maturation stage, but had significantly lower Z scores for height, weight, body mass index, arm circumference, upper arm muscle area, and lean mass-for-height. Children with SCD-SS had significantly lower unadjusted handgrip strength (16±2 vs. 23±2 kg, P<0.01), peak power (1054±107 vs. 1488±169 W, P<0.04) and MVC torques at 2 angles (10 degrees: 27±3 vs. 42±5 Nm; 20 degrees: 21±3 vs. 34±4 Nm; all P<0.05). Performance decrements persisted when handgrip strength was adjusted for lean body mass and fat mass explaining 66% of the variance; peak power adjusted for age, lean body mass, fat mass, and height explaining 91% of the variance; and the highest MVC torque (10-degree angle) adjusted for left leg length, lean mass-for-height, and fat mass-for-height Z scores explaining 65% of the variance. This suggests additional factors contribute to the attenuated anaerobic performance.

The role of nutrition in the pathophysiology and management of sickle cell disease among children: A review of literature

Sickle cell disease (SCD) is one of the common inherited blood disorders in humans and has been associated with decreased dietary intake which results in poor nutritional status and impaired growth. Nutrition is one of the most important but often forgotten aspect of care of patients with chronic disorders and there have been emerging concern in literature on increased nutritional needs of SCD patients. This paper sought to review the available literature on the roles of individual nutrients in the pathophysiology and management of SCD among children. Children with SCD have been shown to exhibit suboptimal status with respect to both macronutrients and micronutrients. Thus, nutrition could play an important role in the management of SCD. However, there is paucity of evidence coming from trials with large sample sizes to support the suggestion that supplementation with various nutrients that have been considered in this review will be helpful.

Moderate and intense muscular exercises induce marked intramyocellular metabolic acidosis in sickle cell disease mice

Sickle cell disease (SCD) is associated with an impaired oxygen delivery to skeletal muscle that could alter ATP production processes. The present study aimed to determine the effects of sickle hemoglobin (HbS) on muscle pH homeostasis in response to exercise in homozygous (HbSS, n = 9) and heterozygous (HbAS, n = 10) SCD (Townes) mice in comparison to control (HbAA, n = 10) littermates. Magnetic resonance spectroscopy of phosphorus 31 enabled to measure intramuscular pH and phosphocreatine (PCr) concentration during rest-stimulation-recovery protocols at two different intensities. Maximal activity of some enzymes involved in muscle energetics and content of proteins involved in pH regulation were also investigated. HbSS mice presented a more pronounced exercise-induced intramuscular acidosis, whatever the intensity of exercise. Moreover, the depletion of PCr was also exacerbated in HbSS mice in response to intense exercise as compared with both HbAA and HbAS mice ( P < 0.01). While no difference was observed concerning proteins involved in muscle pH regulation, the activity of enolase (a glycolytic enzyme) was higher in both HbSS and HbAS mice as compared with controls ( P < 0.05). Interestingly, HbAS mice presented also metabolic impairments as compared with their control counterparts. This study has identified for the first time an exacerbated exercise-induced intramuscular acidosis in SCD mice.

NEW & NOTEWORTHY The main finding of the present study was that the exercise-induced intramuscular acidosis was systematically more pronounced in sickle cell disease (SCD) mice as compared with their control counterparts. This result is important since it has been demonstrated in vitro that acidosis can trigger hemoglobin polymerization. From that point of view, our results tend to support the idea that high-intensity exercise may increase the risk of hemoglobin polymerization in SCD.

Role of Exercise-Induced Oxidative Stress in Sickle Cell Trait and Disease

Sickle cell disease is a class of hemoglobinopathy in humans, which is the most common inherited disease in the world. Although complications of sickle cell disease start from polymerization of red blood cells during its deoxygenating phase, the oxidative stress resulting from the biological processes associated with this disease (ischaemic and hypoxic injuries, hemolysis and inflammation) has been shown to contribute to its pathophysiology. It is widely known that chronic exercise reduces oxidative stress in healthy people, mainly via improvement of antioxidant enzyme efficiency. In addition, recent studies in other diseases, as well as in sickle cell trait carriers and in a mouse model of sickle cell disease, have shown that regular physical activity could decrease oxidative stress. The purpose of this review is to summarize the role of oxidative stress in sickle cell disease and the effects of acute and chronic exercise on the pro-oxidant/antioxidant balance in sickle cell trait and sickle cell disease.

Impaired muscle force production and higher fatigability in a mouse model of sickle cell disease

Skeletal muscle function has been scarcely investigated in sickle cell disease (SCD) so that the corresponding impact of sickle hemoglobin is still a matter of debate. The purpose of this study was to investigate muscle force production and fatigability in SCD and to identify whether exercise intensity could have a modulatory effect. Ten homozygous sickle cell (HbSS), ten control (HbAA) and ten heterozygous (HbAS) mice were submitted to two stimulation protocols (moderate and intense) to assess force production and fatigability. We showed that specific maximal tetanic force was lower in HbSS mice as compared to other groups. At the onset of the stimulation period, peak force was reduced in HbSS and HbAS mice as compared to HbAA mice. Contrary to the moderate protocol, the intense stimulation protocol was associated with a larger decrease in peak force and rate of force development in HbSS mice as compared to HbAA and HbAS mice. These findings provide in vivo evidence of impaired muscle force production and resistance to fatigue in SCD. These changes are independent of muscle mass. Moreover, SCD is associated with muscle fatigability when exercise intensity is high.

Acute moderate exercise does not further alter the autonomic nervous system activity in patients with sickle cell anemia

A decreased global autonomic nervous system (ANS) activity and increased sympathetic activation in patients with sickle cell anemia (SCA) seem to worsen the clinical severity and could play a role in the pathophysiology of the disease, notably by triggering vaso-occlusive crises. Because exercise challenges the ANS activity in the general population, we sought to determine whether a short (<15 min) and progressive moderate exercise session conducted until the first ventilatory threshold had an effect on the ANS activity of a group of SCA patients and a group of healthy individuals (CONT group). Temporal and spectral analyses of the nocturnal heart rate variability were performed before and on the 3 nights following the exercise session. Standard deviation of all normal RR intervals (SDNN), total power, low frequencies (LF) and high frequencies powers (HF) were lower but LF/HF was higher in SCA patients than in the CONT group. Moderate exercise did not modify ANS activity in both groups. In addition, no adverse clinical events occurred during the entire protocol. These results imply that this kind of short and moderate exercise is not detrimental for SCA patients.

Hematological and hemorheological determinants of the six-minute walk test performance in children with sickle cell anemia

The six-minute walk test is a well-established submaximal exercise reflecting the functional status and the clinical severity of sickle cell patients. The aim of the present cross-sectional study was to investigate the biological determinants of the six-minute walk test performance in children with sickle cell anemia. Hematological and hemorheological parameters, pulmonary function and the six-minute walk test performance were determined in 42 children with sickle cell anemia at steady state. The performance during the six-minute walk test was normalized for age, sex and height and expressed as percentage of the predicted six-minute walk distance. We showed that a high level of anemia, a low fetal hemoglobin expression and low red blood cell deformability were independent predictors of a low six-minute walk test performance. This study describes for the first time the impact of blood rheology in the six-minute walk test performance in children with sickle cell anemia.

Sickle-Cell Trait and Atopic and Inflammatory Disease in Children

Roughly 9% of African-Americans carry 1 copy of the sickle β-globin allele [sickle-cell trait (SCT)]. The sickle allele may affect the host responses in a way that protects against sequelae of malaria. Besides the association with sporadic episodes of erythrocyte sickling, acute chest syndrome, and sudden death, the SCT is generally regarded as asymptomatic. Separately, and for unclear reasons, the African-Americans have an elevated risk compared to whites for several immune-mediated diseases, including asthma, eczema, and other respiratory conditions. We propose to determine whether the SCT contributes to the elevated risk of these inflammatory conditions. We performed a retrospective cohort study of children with and without the sickle trait to assess the risk for common immune-mediated conditions. The cohorts were individually matched, and multiple logistic regression was used with variables selected using a backward stepwise approach. A second approach (case-control design) assessed the odds of the SCT among African-Americans with and without asthma. We found 2,481 children with and 4,962 matched patients without the SCT in the cohort design. The sickle trait was associated with greater odds for several immune-mediated conditions in a multivariable analysis, but not associated with asthma (odds ratio, OR=1.10, P=0.212). In an adjusted case-control analysis (n=20,000), the sickle trait was weakly associated with asthma [adjusted odds ratio (aOR)=1.46, 1.01-2.13]. In both the designs and in all statistical models used, we found that the SCT was associated with bronchitis (aOR=1.71, 1.09-2.67) and eczema (aOR=1.74, 1.23-2.46). The SCT may contribute to an increased risk for eczema and asthma-like symptoms in the African-American children.

Mild haemorheological changes induced by a moderate endurance exercise in patients with sickle cell anaemia

The levels and duration of physical activity that can be considered as completely safe in patients with sickle cell anaemia (SCA) is unknown. The present study compared the haemorheological and haematological profile, cell density distribution and basic biochemistry between a group of 17 patients with SCA and 21 healthy subjects before and after a 20 min duration submaximal cycling exercise at the same absolute workload. Blood was sampled at rest and 3 min after the end of exercise for measurement of biological parameters. Exercise did not affect the haematocrit and blood viscosity in the two groups. Plasma viscosity was not different between the two groups at rest and similarly increased with exercise. The proportion of intermediary dense cells (with density between 1·11 and 1·12 g/ml) decreased with exercise in the SCA group resulting in an increase in the proportion of red blood cells with a density >1·12 g/ml. No change was observed in the control group. The present study suggests that mild-moderate exercise is not very harmful for SCA patients. The haemorheological and haematological changes were very mild, except for the formation of dense cells but no clinically significant signs of medical complication were present in any of the patients.

Attenuated maximal muscle strength and peak power in children with sickle cell disease

Dominant hand maximal handgrip strength evaluated with a handgrip dynamometer and peak power evaluated with a force plate, adjusted for body size and composition, were compared in African-American children aged 5 to 13 years, with and without type SS sickle cell disease (SCD-SS). Children with SCD-SS (n = 35; age, 9.0 ± 2.0 y) compared with healthy control children (n = 103; age, 8.6 ± 1.8 y) did not differ by age, sex, or pubertal status, yet had significantly lower Z scores for height, weight, body mass index, upper arm muscle area, upper arm fat area, fat mass-for-height and lean mass-for-height. Children with SCD-SS had significantly lower handgrip strength (12.7 ± 3.3 vs. 15.2 ± 5.1 kg, P < 0.008), peak power (882 ± 298 vs. 1167 ± 384 W, P < 0.001), and growth and body composition adjusted Z scores for handgrip strength (0.6 ± 1.3 standard deviations, P < 0.004) and peak power (male children = 1.0 ± 0.8 standard deviations, P < 0.0002; female children = 1.0 ± 1.7 standard deviations, P < 0.006). Maximal muscle strength and peak power are attenuated in children with SCD-SS compared with healthy control children beyond expectation for growth and body composition deficits suggesting that additional factors contribute to attenuation in anaerobic performance.

Effect of hydroxyurea on physical fitness indices in children with sickle cell anemia

The current studies aimed at determining physical fitness indices and anthropometrics profiles of children with sickle cell anemia (SCA) after the use of hydroxyurea (HU). Ninety-three male schoolchildren--who participated previously in a similar study before the introduction of HU--comprising 2 groups participated in the studies. Group 1 was 41 children who were suffering from sickle cell disease (SCD) and were on HU for a minimum of 2 years, whereas group 2 was 50 normal healthy controls. Anthropometrics measurement and parameters of physical fitness were assessed in all subjects. All children were also subjected to a minimum of 6-minute running exercise test on a flat motorized treadmill at speed corresponding to 5 km/h. Throughout the test heart rate was monitored and recorded during exercise and for 10 minutes during recovery. Blood hemoglobin (Hb) and HbF% were measured after the use of HU. The mean values of weight, height, and lean body mass were still lower in the SCD children (P < .05) compared with the healthy subjects. However, they had significant decrease in the mean heart rate values and they spent longer time on the treadmill before they got tired compared to their previous performance and were just below the normal controls. Hydroxyurea treatment improved the aerobic exercise tolerance and most of the physical fitness parameters in children with SCD.

Fracture prevalence and relationship to endocrinopathy in iron overloaded patients with sickle cell disease and thalassemia

Transfusional iron overload leads to gonadal failure and low bone mass in patients with thalassemia (Thal). However, gonadal failure is rarely reported in transfused patients with sickle cell disease (SCD) and the literature regarding fracture prevalence in SCD is limited. The objective of this study was to assess self-reported fracture prevalence and its relationship to endocrinopathy in transfused Thal or SCD subjects and compare to non-transfused subjects with SCD (NonTxSCD). Eligibility was based on age> or =12 years and liver iron concentration> or =10 mg/g dry wt or serum ferritin> or =2000 ng/mL (Thal or TxSCD) or for NonTxSCD, ferritin<500 ng/mL. Data were collected by patient interview and chart review at 31 clinical centers in the U.S., Canada and the U.K. 152 subjects with Thal (52% Male; 25.6+/-0.7 years), 203 subjects with TxSCD (44% Male, 24.7+/-0.9 years: Mean+/-SE), and 65 NonTxSCD (50% Male, 22.2+/-1.3 years) were enrolled. Overall, male subjects with Thal were more likely to have sustained a fracture in their lifetime (51%) compared to TxSCD (28%) or NonTxSCD (32%) (p=0.005). There was no difference in fracture prevalence among women (Thal: 26%, TxSCD 17%, NonTxSCD: 16%). Fracture was most frequently reported in the upper extremities (53.3% of all fractures) while spine and pelvic fractures were relatively common for such a young cohort: 10.6%. Though overall fracture prevalence was not distinctly different from published healthy cohorts, fewer fractures occurred during the adolescent years. In multivariate analysis, the significant predictors of fracture prevalence were Thal diagnosis (Odds Ratio: 2.3; 1.2-4.6; 95%CI), male gender (OR: 2.6; 1.5-4.5), hypothyroidism (OR: 3.3; 1.1-9.8) and age (OR: 1.1; 1.03-1.08). These data suggest that despite similar iron burden, transfused patients with Thal are at greater risk for fracture than subjects with SCD. Male subjects with Thal and hypothyroidism are at particular risk for fracture, in contrast, transfused subjects with SCD had no greater risk of fracture compared to non-transfused SCD. Though ethnic differences in fracture risk cannot be ignored, endocrinopathy is rare in TxSCD which may also provide some protection from fracture.

Cardiopulmonary stress testing in children with sickle cell disease who are on long-term erythrocytapheresis

The purpose of the study was to assess the feasibility and safety of symptom-limited cardiopulmonary stress testing (CPST) in children with sickle cell disease (SCD), who are on long-term erythrocytapheresis. Maximal symptom-limited CPST was performed in 16 children with SCD who were maintained on long-term erythrocytapheresis and the exercise response in this patient cohort was compared with those of a healthy control population. All patients completed the CPST without any complications. Twelve patients with SCD had significant reduction in aerobic capacity [peak oxygen consumption (VO2) <80% predicted]. No patient demonstrated evidence of myocardial ischemia. In summary, symptom-limited CPST can be performed safely in a subgroup of children with SCD and can yield valuable clinical information.

Physical activity for youth with disabilities: a critical need in an underserved population

The recommended amount of daily physical activity for youth is 60 minutes a day, most days of the week. Youth with disabilities are not achieving this target and are significantly less active and more obese than their non-disabled peers. The combination of the health risks associated with physical inactivity and obesity presents a serious health concern in this population. While there is a small amount of research on interventions aimed at improving fitness among youth with disabilities, the majority of these studies were conducted in clinical settings where most or all of the common barriers to participation were eliminated (e.g. transportation, lack of knowledgeable staff, adaptation of programmes and/or facilities to child's needs). One of the most important challenges for paediatric rehabilitation and healthcare professionals is finding ways to increase physical activity and fitness among youth with disabilities in community-based settings. The use of information technology (IT) to customize physical activity programmes for youth with disabilities offers a promising approach to addressing this important health issue in the future.