RESUMEN
BACKGROUND/OBJECTIVES: Exercise performed shortly before (that is, within half a day of) a high-fat meal is beneficial for stimulating fat oxidation after the meal and reducing postprandial triglycerides (TG). This benefit of exercise is unfortunately negated if the after-exercise food choice to replace the calories expended during exercise is one containing high-glycemic index (HGI) carbohydrates. We determined the effect of consuming low-glycemic index (LGI) carbohydrates after an exercise session on fat oxidation and TG after a subsequent high-fat meal. SUBJECTS/METHODS: Using a randomized, counterbalanced crossover design, 23 overweight or obese individuals (body mass index ⩾25 kg m(-2)) performed: walking exercise (90 min) at 1800 h followed by no meal (EX); exercise followed by a meal with LGI carbohydrates (that is, lentils, EX-LGI); exercise followed by a meal with HGI carbohydrates (that is, instant potatoes, white bread, EX-HGI); and a control condition with no exercise or meal. After a 10-h overnight fast, participants were given a standardized high-fat meal. Fat oxidation was estimated before and for 6 h after this meal from respiratory gas measures and TG determined from blood samples. RESULTS: Fat oxidation (mean±s.d.) was higher with EX (6.9±1.7 g h(-1)) than EX-HGI (6.3±1.6 g h(-1); P=0.007) and Control (5.9±1.7 g h(-1); P=0.00002), and EX-LGI (6.6±1.7 g h(-1)) was higher than Control (P=0.002). TG total area under the curve was 18-32% lower with EX and EX-LGI compared with control (P=0.0005 and P=0.0001, respectively) and EX-HGI (P=0.05 and P=0.021, respectively). CONCLUSIONS: A meal containing HGI carbohydrates consumed after an evening exercise session cancels the beneficial effect of exercise for stimulating fat oxidation and lowering TG after a subsequent high-fat meal, whereas consuming a post-exercise meal with LGI carbohydrates retains the positive effect of exercise.
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Ejercicio Físico/fisiología , Índice Glucémico , Lípidos/sangre , Sobrepeso/fisiopatología , Periodo Posprandial/fisiología , Adulto , Estudios Cruzados , Carbohidratos de la Dieta , Grasas de la Dieta , Femenino , Humanos , Masculino , Comidas , Obesidad/sangre , Obesidad/fisiopatología , Sobrepeso/sangre , Adulto JovenRESUMEN
UNLABELLED: Muscle density is a risk factor for fractures in older adults; however, its association with falls is not well described. After adjusting for biologically relevant confounding factors, a unit decrease in muscle density was associated with a 17 % increase in odds of reporting a fall, independent of functional mobility. INTRODUCTION: Falls are the leading cause of injury, disability, and fractures in older adults. Low muscle density (i.e., caused by muscle adiposity) and functional mobility have been identified as risk factors for incident disability and fractures in older adults; however, it is not known if these are also independently associated with falls. The purpose of this study was to explore the associations of muscle density and functional mobility with fall status. METHODS: Cross-sectional observational study of 183 men and women aged 60-98 years. Descriptive data, including a 12-month fall recall, Timed Up and Go (TUG) test performance, lower leg muscle area, and density. Odds ratio (OR) of being a faller were calculated, adjusted for age, sex, body mass index, general health status, diabetes, and comorbidities. RESULTS: Every mg/cm(3) increase in muscle density (mean 70.2, SD 2.6 mg/cm(3)) independently reduced the odds of being a faller by 19 % (OR 0.81 [95 % CI 0.67 to 0.97]), and every 1 s longer TUG test time (mean 9.8, SD 2.6 s) independently increased the odds by 17 % (OR 1.17 [95 % CI 1.01 to 1.37]). When both muscle density and TUG test time were included in the same model, only age (OR 0.93 [95 % CI 0.87 to 0.99]) and muscle density (OR 0.83 [95 % CI 0.69 to 0.99]) were independently associated with fall status. CONCLUSIONS: Muscle density was associated with fall status, independent of functional mobility. Muscle density may compliment functional mobility tests as a biometric outcome for assessing fall risk in well-functioning older adults.
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Accidentes por Caídas , Músculo Esquelético/fisiología , Anciano , Anciano de 80 o más Años , Estudios Transversales , Femenino , Evaluación Geriátrica , Humanos , Vida Independiente , Masculino , Persona de Mediana Edad , Factores de RiesgoRESUMEN
UNLABELLED: Distal radius (wrist) fracture (DRF) in women over age 50 years is an early sign of bone fragility. Women with a recent DRF compared to women without DRF demonstrated lower bone strength, muscle density, and strength, but no difference in dual-energy x-ray absorptiometry (DXA) measures, suggesting DXA alone may not be a sufficient predictor for DRF risk. INTRODUCTION: The objective of this study was to investigate differences in bone and muscle properties between women with and without a recent DRF. METHODS: One hundred sixty-six postmenopausal women (50-78 years) were recruited. Participants were excluded if they had taken bone-altering medications in the past 6 months or had medical conditions that severely affected daily living or the upper extremity. Seventy-seven age-matched women with a fracture in the past 6-24 months (Fx, n = 32) and without fracture (NFx, n = 45) were measured for bone and muscle properties using the nondominant (NFx) or non-fractured limb (Fx). Peripheral quantitative computed tomography (pQCT) was used to estimate bone strength in compression (BSIc) at the distal radius and tibia, bone strength in torsion (SSIp) at the shaft sites, muscle density, and area at the forearm and lower leg. Areal bone mineral density at the ultradistal forearm, spine, and femoral neck was measured by DXA. Grip strength and the 30-s chair stand test were used as estimates of upper and lower extremity muscle strength. Limb-specific between-group differences were compared using multivariate analysis of variance (MANOVA). RESULTS: There was a significant group difference (p < 0.05) for the forearm and lower leg, with the Fx group demonstrating 16 and 19% lower BSIc, 3 and 6% lower muscle density, and 20 and 21% lower muscle strength at the upper and lower extremities, respectively. There were no differences between groups for DXA measures. CONCLUSIONS: Women with recent DRF had lower pQCT-derived estimated bone strength at the distal radius and tibia and lower muscle density and strength at both extremities.
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Densidad Ósea/fisiología , Músculo Esquelético/fisiopatología , Fracturas Osteoporóticas/fisiopatología , Fracturas del Radio/fisiopatología , Traumatismos de la Muñeca/fisiopatología , Absorciometría de Fotón/métodos , Anciano , Antropometría/métodos , Femenino , Cuello Femoral/fisiopatología , Humanos , Estilo de Vida , Vértebras Lumbares/fisiopatología , Persona de Mediana Edad , Músculo Esquelético/patología , Osteoporosis Posmenopáusica/patología , Osteoporosis Posmenopáusica/fisiopatología , Fracturas Osteoporóticas/patología , Posmenopausia/fisiología , Fracturas del Radio/patología , Tomografía Computarizada por Rayos X/métodos , Traumatismos de la Muñeca/patologíaRESUMEN
OBJECTIVES: Our objectives were to determine whether peripheral quantitative computed tomography (pQCT)-derived lower leg muscle density and area, and basic functional mobility differ between community-dwelling older women who do and do not report recent falls. DESIGN: Matched case-control comparison. SETTING: Academic biomedical imaging laboratory. PARTICIPANTS: 147 Women, 60 years or older (mean age 74.3 y, SD 7.7) recruited from a longitudinal, population-based cohort representing community-dwelling residents in the area of Saskatoon, Canada. MEASUREMENTS: A cross-sectional pQCT scan of the non-dominant lower leg was acquired to determine muscle density and area. Basic functional mobility (Timed Up and Go Test [TUG]) and SF36 health status were also measured. Fallers (one or more falls) and non-fallers (no falls) were grouped according to a 12-month retrospective survey and matched on measured covariates. RESULTS: The muscle density of fallers (n = 35) was a median of 2.1 mg/cm3 lower (P = 0.019, 95% C.I. -3.9 to -0.1) than non-fallers (n = 78) after matching and adjusting for age, body mass index, and SF36 general health scores. Muscle area and TUG did not differ between fallers and non-fallers. CONCLUSIONS: Muscle density may serve as a physiological marker in the assessment of lower leg muscular health and fall risk in community-dwelling elderly women. These results are limited to our study population who were mostly Caucasian. Prospective studies are required for verification.
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Accidentes por Caídas/estadística & datos numéricos , Pierna/anatomía & histología , Pierna/fisiología , Músculo Esquelético/anatomía & histología , Músculo Esquelético/fisiología , Anciano , Anciano de 80 o más Años , Estudios de Casos y Controles , Femenino , Humanos , Estudios Longitudinales , Persona de Mediana Edad , Osteoporosis Posmenopáusica , Equilibrio Postural , Características de la Residencia , Estudios Retrospectivos , SaskatchewanRESUMEN
OBJECTIVES: We sought to identify the variance in radius bone strength indices explained by forearm muscle cross sectional area (MCSA) and isometric (ISO), concentric (CON), or eccentric (ECC) grip torque in healthy men and postmenopausal women when gender and body size were controlled for. Additionally we assessed variance in various grip contractions explained by MCSA. METHODS: pQCT estimated bone strength of the radius and forearm MCSA were measured from 45 healthy adults (59.4-/+7.2 yrs). Isokinetic dynamometry was used to assess peak grip torque. Regressions were adjusted for gender and radius length. RESULTS: Peak grip torques were not independent predictors (p>0.05) of distal radius bone strength in compression (bone strength index; BSI(c)) when gender was included in the prediction model. Gender was not a contributor to any model that included MCSA (p>0.05). At the diaphysis all torque measures, MCSA, gender, and length, significantly contributed to predict similar portions (79-80%) of the stress strain index (SSI(p); strength in torsion). MCSA accounted for 68-76% of variance in grip torque (p<0.05). CONCLUSIONS: When estimating radius bone strength, forearm MCSA is a comparable predictor to CON, ISO, and ECC grip torques and is also a good surrogate of these contraction types.
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Densidad Ósea/fisiología , Huesos/fisiología , Fuerza de la Mano/fisiología , Músculo Esquelético/anatomía & histología , Músculo Esquelético/fisiología , Anciano , Femenino , Humanos , Masculino , Persona de Mediana Edad , Dinamómetro de Fuerza Muscular , Análisis de Regresión , TorqueRESUMEN
Aging subsequently results in bone and muscle loss which has a negative effect on strength, agility, and balance leading to increased risks of falls, injuries, and fractures. Resistance training is an effective strategy for maintaining bone mass, possibly by increasing activity of cells involved in bone formation and reducing activity of cells involved in bone resorption. However, bone loss is still evident in older adults who have maintained resistance training for most of their life, suggesting that other factors such as nutrition may be involved in the aging bone process. Emerging evidence suggests that creatine supplementation, with and without resistance training, has the potential to influence bone biology. However, research investigating the longer-term effects of creatine supplementation and resistance training on aging bone is limited.
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Envejecimiento/fisiología , Densidad Ósea/efectos de los fármacos , Creatina/uso terapéutico , Atrofia Muscular/tratamiento farmacológico , Entrenamiento de Fuerza , Anciano , Anciano de 80 o más Años , Densidad Ósea/fisiología , Creatina/administración & dosificación , Suplementos Dietéticos , Femenino , Humanos , Masculino , Persona de Mediana Edad , Factores de RiesgoRESUMEN
Sarcopenia, defined as the age-related loss of muscle mass, is a serious health concern. Contributing factors to sarcopenia include physical inactivity and undernutrition. Resistance training has a positive effect on muscle mass in the elderly. However, muscle loss is still observed in older adults who perform weight bearing exercise; suggesting that nutrition is important. Creatine supplementation has the potential to increase muscle accretion during resistance training, although the mechanism for its ergogenic effect is unclear. Creatine has the potential to increase cellular hydration and myogenic transcription factors and facilitate the up-regulation of muscle specific-genes such as myosin heavy chain possibly leading to muscle hypertrophy.
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Envejecimiento/fisiología , Creatina/farmacología , Músculo Esquelético/efectos de los fármacos , Levantamiento de Peso/fisiología , Anciano , Suplementos Dietéticos , Ejercicio Físico , Humanos , Contracción Isométrica/efectos de los fármacos , Contracción Isométrica/fisiología , Músculo Esquelético/crecimiento & desarrollo , Músculo Esquelético/fisiología , Atrofia Muscular/prevención & controlRESUMEN
AIM: Creatine monohydrate supplementation is beneficial for enhancing high-intensity exercise performance, especially activities that involve repeated sprints. Creatine monohydrate supplementation is common in ice-hockey players. The purpose of this study was to determine the effect of creatine monohydrate supplementation on sprint skating performance in Junior B and collegiate ice-hockey players. METHODS: Seventeen ice-hockey players were randomly assigned to receive creatine (0.3 g/kg body mass/day for 5 days) or placebo. Before and after supplementation players performed repeated sprints to exhaustion on a skating treadmill (repeated 10-s sprints; 30-s rest between sprints) while blood lactate was simultaneously collected. The time to exhaustion on the treadmill test was calculated as total amount of time, including partial intervals, before the player reached exhaustion. Players were also tested for peak torque and average power during knee extension/flexion (3 sets of 10 reps; 60-s rest between sets) on an isokinetic dynamometer at 60 degrees/s. RESULTS: The change in time to exhaustion from before to after supplementation averaged 20.6+/-7 s in the creatine group and 21.9+/-13 s in the placebo group, with no differences between groups. Likewise, there were no differences between groups for changes in isokinetic peak torque and average power. There were no differences between groups over time for blood lactate changes during the repeated sprints on the treadmill. CONCLUSIONS: We conclude that creatine was not effective for improving performance in these ice-hockey players.
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Creatina/farmacología , Suplementos Dietéticos , Hockey/fisiología , Esfuerzo Físico/efectos de los fármacos , Patinación/fisiología , Adolescente , Creatina/administración & dosificación , Método Doble Ciego , Humanos , Articulación de la Rodilla/fisiología , Ácido Láctico/sangre , Masculino , Rango del Movimiento Articular , TorqueRESUMEN
Our purpose was to determine the effects of creatine supplementation combined with resistance training on bone mineral content and density in older men. Twenty-nine older men (age 71 y) were randomized (double blind) to receive creatine (0.3 g/kg creatine for 5 d and 0.07 g/kg thereafter) or placebo while participating in resistance training (12 weeks). Bone mineral content and density were determined by dual energy X-ray absorptiometry before and after training. There was a time main effect for whole-body and leg bone mineral density (p < or = 0.05) with these measures increasing by approximately 0.5%, and 1%, respectively in the combined groups. There was a group by time interaction for arms bone mineral content, with the group receiving creatine increasing by 3.2% (p < 0.01) and the group receiving placebo decreasing by 1.0% (not significant). Changes in lean tissue mass of the arms correlated with changes in bone mineral content of the arms (r = 0.67; p < 0.01). Resistance training of 12 weeks increases bone mineral density in older men and creatine supplementation may provide an additional benefit for increasing regional bone mineral content. The increase in bone mineral content may be due to an enhanced muscle mass with creatine, with potentially greater tension on bone at sites of muscle attachment.
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Densidad Ósea/efectos de los fármacos , Creatina/farmacología , Músculo Esquelético/metabolismo , Levantamiento de Peso/fisiología , Absorciometría de Fotón/métodos , Adaptación Fisiológica , Anciano , Envejecimiento , Análisis de Varianza , Densidad Ósea/fisiología , Suplementos Dietéticos , Relación Dosis-Respuesta a Droga , Método Doble Ciego , Humanos , Masculino , Soporte de Peso/fisiologíaRESUMEN
Energy restriction affects the hypothalamus, leading to a decrease in production of reproductive and thyroid hormones. A decrease in reproductive hormones affects fertility and a decrease in thyroid hormones affects muscle metabolism. A pig model has been used to determine that reproductive function is negatively affected if the normal practice of overfeeding is limited during the late luteal phase of the estrous cycle. We used a sub-set of pigs from this study to examine effects of limiting overfeeding on thyroid hormones and skeletal muscle (i.e. maximal enzyme activities, and muscle fibre characteristics). Eighteen rapidly growing gilts were randomized into three groups: 1) feeding a high plane of nutrition throughout the first 15 days of the estrous cycle; 2) limited overfeeding (25% below the first group) for first 7 days of the estrous cycle (early luteal phase), followed by a high plane of nutrition for days 8-15 (late luteal phase); and 3) high plane of nutrition throughout the first 7 days of the estrous cycle, followed by 8 days of limited overfeeding. Muscle biopsies were collected from the triceps brachii, and blood samples were collected for assessment of thyroid hormones at days 0 (baseline), 8 and 16. There was no effect of limited overfeeding on thyroid hormones, maximal enzyme activities, muscle fibre area or muscle fibre type. Limited overfeeding in rapidly growing pigs does not affect thyroid hormone status or muscle characteristics.
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Fenómenos Fisiológicos Nutricionales de los Animales , Ciclo Estral/metabolismo , Desarrollo de Músculos/fisiología , Alimentación Animal , Animales , Peso Corporal , Femenino , Modelos Animales , Fibras Musculares Esqueléticas/fisiología , Porcinos , Hormonas Tiroideas/metabolismoRESUMEN
BACKGROUND: The optimal intake of calcium and vitamin D for postmenopausal women not taking estrogen is not known. Further, there are indications that excess vitamin A as retinol might be detrimental to bone. OBJECTIVE: We determined whether dietary intakes of calcium and vitamin D were important for maintaining cortical and trabecular bone mineral density (BMD). We also determined whether nutrient supplements increased retinol intake to a level that would reduce BMD. DESIGN: This was a cross-sectional study of 58 women, age 45-75 years. Dietary intakes and lifestyle factors were assessed by retrospective questionnaires. BMD at the whole body, lumbar spine, and proximal femur (including neck, trochanter, and Wards) was measured using dual energy x-ray absorptiometry (DXA) bone densitometry. RESULTS: There were significant (p < 0.05) positive correlations between total calcium intake and BMD at all sites except spine. At the trochanter, the correlation between total vitamin D and BMD was significant while that between total retinol and BMD showed a trend (p < 0.10). In a stepwise multiple regression, a significant proportion of variance of BMD was accounted for by years since menopause (8.0 to 36.2 %) and body weight (14.5 to 27.1%) at most bone sites. Adding total calcium intake (food + supplements) into the model further accounted for a significant proportion of variance of BMD at cortical bone sites such as hip, femoral neck, Wards, and total body ( 5.2 - 8.4 %). There was no dietary calcium effect on BMD at the spine. CONCLUSION: The positive effect of total calcium intake on cortical BMD of postmenopausal women not taking estrogen suggests that supplemental calcium use is critical for maintaining bone mass. Increased retinol intake from nutrient supplements had no adverse effect on BMD.
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Densidad Ósea/efectos de los fármacos , Calcio de la Dieta/administración & dosificación , Osteoporosis Posmenopáusica/etiología , Vitamina A/administración & dosificación , Vitamina D/administración & dosificación , Anciano , Peso Corporal/fisiología , Densidad Ósea/fisiología , Estudios de Cohortes , Estudios Transversales , Suplementos Dietéticos , Estrógenos/administración & dosificación , Femenino , Humanos , Estilo de Vida , Persona de Mediana Edad , Osteoporosis Posmenopáusica/prevención & control , Posmenopausia , Encuestas y Cuestionarios , Factores de Tiempo , Vitamina A/efectos adversosRESUMEN
The combined and separate effects of exercise training and bisphosphonate (etidronate) therapy on bone mineral in postmenopausal women were compared. Forty-eight postmenopausal women were randomly assigned (double blind) to groups that took intermittent cyclical etidronate; performed strength training (3 d/week) and received matched placebo; combined strength training with etidronate; or took placebo and served as nonexercising controls. Bone mineral, lean tissue, and fat mass were assessed by dual-energy X-ray absorptiometry before and after 12 months of intervention. After removal of outlier results, changes in bone mineral density (BMD) of the lumbar spine and bone mineral content (BMC) of the whole body were greater in the subjects given etidronate (+2.5 and +1.4%, respectively) compared with placebo (-0.32 and 0%, respectively) (p < 0.05), while exercise had no effect. There was no effect of etidronate or exercise on the proximal femur and there was no interaction between exercise and etidronate at any bone site. Exercise training resulted in significantly greater increases in muscular strength and lean tissue mass and greater loss of fat mass compared with controls. We conclude that etidronate significantly increases lumbar spine BMD and whole-body BMC and that strength training has no additional effect. Strength training favourably affects body composition and muscular strength, which may be important for prevention of falls.
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Composición Corporal/efectos de los fármacos , Densidad Ósea/efectos de los fármacos , Ácido Etidrónico/uso terapéutico , Ejercicio Físico , Posmenopausia , Ingestión de Energía/efectos de los fármacos , Femenino , Humanos , Persona de Mediana EdadRESUMEN
We examined the effect of combined strength and endurance training on quantitative estimates of mitochondria in subsarcolemmal and intermyofibrillar regions of muscle fibers. Ten subjects (five males, five females) participated in a 12 week program of combined strength and endurance training. Seven subjects (three males and four females) served as controls. Biopsy samples from the vastus lateralis were obtained before and after training in both groups and also at the mid-point of training in the exercise group. Measurement of succinate dehydrogenase activity throughout muscle fibers, as a quantitative estimate of mitochondrial subpopulations, revealed no differences between exercise and control groups before and after training. Within the exercise group, there was a significant increase in succinate dehydrogenase activity in all regions of muscle fibers from before to after training. There was also a significant increase in succinate dehydrogenase activity in the subsarcolemmal, relative to the intermyofibrillar region from mid-(six weeks) to after-training ( regional distribution x time; p < 0.05). This may have been associated with an oxidative shift in fiber types, as type I fiber percentage was increased in the exercise, compared to the control group (group x time; p < 0.05). We conclude that mitochondrial populations undergo differential changes throughout training. IMF mitochondria increase in a linear manner throughout training, while SS mitochondria undergo a preferential increase late in training. This increase late in training may be related to an increase in proportion of type I fibers.
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Mitocondrias Musculares/enzimología , Músculo Esquelético/enzimología , Educación y Entrenamiento Físico/métodos , Resistencia Física/fisiología , Succinato Deshidrogenasa/metabolismo , Adaptación Fisiológica/fisiología , Adulto , Biopsia , Femenino , Humanos , Masculino , Mitocondrias Musculares/ultraestructura , Músculo Esquelético/citología , Miofibrillas/enzimología , Consumo de Oxígeno/fisiología , Sarcolema/enzimología , Factores de TiempoRESUMEN
PURPOSE: To study the effect of creatine (Cr) supplementation combined with resistance training on muscular performance and body composition in older men. METHODS: Thirty men were randomized to receive creatine supplementation (CRE, N = 16, age = 70.4 +/- 1.6 yr) or placebo (PLA, N = 14, age = 71.1 +/- 1.8 yr), using a double blind procedure. Cr supplementation consisted of 0.3-g Cr.kg(-1) body weight for the first 5 d (loading phase) and 0.07-g Cr.kg(-1) body weight thereafter. Both groups participated in resistance training (36 sessions, 3 times per week, 3 sets of 10 repetitions, 12 exercises). Muscular strength was assessed by 1-repetition maximum (1-RM) for leg press (LP), knee extension (KE), and bench press (BP). Muscular endurance was assessed by the maximum number of repetitions over 3 sets (separated by 1-min rest intervals) at an intensity corresponding to 70% baseline 1-RM for BP and 80% baseline 1-RM for the KE and LP. Average power (AP) was assessed using a Biodex isokinetic knee extension/flexion exercise (3 sets of 10 repetitions at 60 degrees.s(-1) separated by 1-min rest). Lean tissue (LTM) and fat mass were assessed using dual energy x-ray absorptiometry. RESULTS: Compared with PLA, the CRE group had significantly greater increases in LTM (CRE, +3.3 kg; PLA, +1.3 kg), LP 1-RM (CRE, +50.1 kg; PLA +31.3 kg), KE 1-RM (CRE, +14.9 kg; PLA, +10.7 kg), LP endurance (CRE, +47 reps; PLA, +32 reps), KE endurance (CRE, +21 reps; PLA +14 reps), and AP (CRE, +26.7 W; PLA, +18 W). Changes in fat mass, fat percentage, BP 1-RM, and BP endurance were similar between groups. CONCLUSION: Creatine supplementation, when combined with resistance training, increases lean tissue mass and improves leg strength, endurance, and average power in men of mean age 70 yr.
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Composición Corporal/efectos de los fármacos , Creatina/farmacología , Músculo Esquelético/efectos de los fármacos , Resistencia Física/efectos de los fármacos , Levantamiento de Peso/fisiología , Anciano , Anciano de 80 o más Años , Creatina/efectos adversos , Diarrea/inducido químicamente , Método Doble Ciego , Ejercicio Físico/fisiología , Humanos , Masculino , Persona de Mediana Edad , Calambre Muscular/inducido químicamente , Análisis y Desempeño de TareasRESUMEN
Since the discovery that oral ingestion of creatine leads to an increase in intramuscular creatine, its supplementation has become widespread. However, the dosage necessary to maximize retention and create significant increases in intramuscular creatine is poorly understood. In this study, 24-hour urinary creatine and creatinine levels of 20 university men's football players and 20 university men's hockey players involved in a resistance-exercise program and supplementing with creatine were collected and analyzed. In a double-blind, randomized design, 10 football players and 10 hockey players were randomly assigned to either the supplement or placebo group. Subjects provided a 24-hour urine sample twice during the study: once prior to supplementation (baseline) and the second 7 days after daily supplementation and resistance exercise. Creatine dosage was 0.1 g x kg(-1) lean body mass. The quantity of creatine ingested was compared with the amount excreted in the urine of those subjects supplementing with creatine and with placebo. Creatinine levels were compared between the first and second urine collection and between groups. Creatine and creatinine concentrations were determined using high-performance liquid chromatography. In 24-hours, 46% of the ingested creatine was excreted. There was no change in creatine levels for placebo subjects. Creatinine levels remained the same within groups at the first and second collection times (p < 0.05). Our findings indicate that when supplementing with dosages of 0.1 g x kg(-1) lean body mass or between 6 and 8 g at a time, approximately half of the ingested creatine gets excreted. Because there was no change in urinary creatinine, it can be assumed that enhanced degradation of creatine did not occur.
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Creatina/administración & dosificación , Creatina/orina , Suplementos Dietéticos , Ejercicio Físico/fisiología , Administración Oral , Adolescente , Adulto , Constitución Corporal , Creatinina/orina , Relación Dosis-Respuesta a Droga , Humanos , MasculinoRESUMEN
Our purpose was to assess muscular adaptations during 6 weeks of resistance training in 36 males randomly assigned to supplementation with whey protein (W; 1.2 g/kg/day), whey protein and creatine monohydrate (WC; 0.1 g/kg/day), or placebo (P; 1.2 g/kg/day maltodextrin). Measures included lean tissue mass by dual energy x-ray absorptiometry, bench press and squat strength (1-repetition maximum), and knee extension/flexion peak torque. Lean tissue mass increased to a greater extent with training in WC compared to the other groups, and in the W compared to the P group (p < .05). Bench press strength increased to a greater extent for WC compared to W and P (p < .05). Knee extension peak torque increased with training for WC and W (p < .05), but not for P. All other measures increased to a similar extent across groups. Continued training without supplementation for an additional 6 weeks resulted in maintenance of strength and lean tissue mass in all groups. Males that supplemented with whey protein while resistance training demonstrated greater improvement in knee extension peak torque and lean tissue mass than males engaged in training alone. Males that supplemented with a combination of whey protein and creatine had greater increases in lean tissue mass and bench press than those who supplemented with only whey protein or placebo. However, not all strength measures were improved with supplementation, since subjects who supplemented with creatine and/or whey protein had similar increases in squat strength and knee flexion peak torque compared to subjects who received placebo.
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Composición Corporal/efectos de los fármacos , Creatina/uso terapéutico , Suplementos Dietéticos , Ejercicio Físico , Proteínas de la Leche/uso terapéutico , Contracción Muscular/efectos de los fármacos , Absorciometría de Fotón , Adulto , Humanos , Articulación de la Rodilla , Masculino , Cooperación del Paciente , Educación y Entrenamiento Físico/métodos , Postura , Torque , Proteína de Suero de LecheRESUMEN
The issue of whether there is a difference in the amount of force produced from a simultaneous two-limb maximal contraction compared to the sum of individual one-limb contractions has received considerable debate in the literature. A bilateral deficit (BLD) is when the resultant force from bilateral homonymous limb contractions is less than the summed force of individual limb contractions. Determining whether differences exist between one- and two-limb movements may provide insight into complex neuromuscular control patterns. Many dynamic two-limb studies report a BLD, whereas isometric studies are more numerous and controversial. It is important to categorize the movements studied in order to establish consistency. This paper purports that the BLD is an unstable phenomenon, and its presence should be considered in the context of the movement studied. Most likely, this phenomenon is dependent upon some minor deviation in descending drive between the cortical level and peripheral motor neuron
Asunto(s)
Contracción Muscular/fisiología , Músculo Esquelético/fisiología , Brazo , Humanos , Contracción Isométrica/fisiología , PiernaRESUMEN
The purpose of this study was to assess the effect of oral glutamine supplementation combined with resistance training in young adults. A group of 31 subjects, aged 18-24 years, were randomly allocated to groups (double blind) to receive either glutamine (0.9 g x kg lean tissue mass(-1) x day(-1); n = 17) or a placebo (0.9 g maltodextrin x kg lean tissue mass(-1) x day(-1); n = 14 during 6 weeks of total body resistance training. Exercises were performed for four to five sets of 6-12 repetitions at intensities ranging from 60% to 90% 1 repetition maximum (1 RM). Before and after training, measurements were taken of 1 RM squat and bench press strength, peak knee extension torque (using an isokinetic dynamometer), lean tissue mass (dual energy X-ray absorptiometry) and muscle protein degradation (urinary 3-methylhistidine by high performance liquid chromatography). Repeated measures ANOVA showed that strength, torque, lean tissue mass and 3-methylhistidine increased with training (P < 0.05), with no significant difference between groups. Both groups increased their 1 RM squat by approximately 30% and 1 RM bench press by approximately 14%. The glutamine group showed increases of 6% for knee extension torque, 2% for lean tissue mass and 41% for urinary levels of 3-methylhistidine. The placebo group increased knee extension torque by 5%, lean tissue mass by 1.7% and 3-methylhistidine by 56%. We conclude that glutamine supplementation during resistance training has no significant effect on muscle performance, body composition or muscle protein degradation in young healthy adults.
Asunto(s)
Glutamina/farmacología , Educación y Entrenamiento Físico , Levantamiento de Peso/fisiología , Adulto , Método Doble Ciego , Femenino , Humanos , Rodilla/fisiología , Masculino , Metilhistidinas/orina , Proteínas Musculares/metabolismo , Delgadez , Factores de Tiempo , TorqueRESUMEN
Dietary supplementation (SUP) has become a significant part of athletic training. Studies indicate that creatine (Cr) can enhance short-duration, high-intensity activities. This study examined the effect of 21 days of low dose Cr SUP ( approximately 7.7 g/day) and resistance training on force output, power output, duration of mean peak power output, and total work performed until fatigue. A double-blind protocol was used, where an individual, who was not part of any other aspect of the study, randomly assigned subjects to creatine and placebo groups. Forty-one male university athletes were randomly assigned to either Cr (n = 20) or placebo (n = 21) SUP. On the first and last day of the study, subjects were required to perform concentric bench press movements until exhaustion on an isokinetic dynamometer. The dynamometer was hard-wired to a personal computer, which provided force, velocity, and duration measures. Force and power output until fatigue, were used to determine total work, force-time, and power-time relationships. ANOVA results revealed that the Cr subjects performed more total work until fatigue, experienced significantly greater improvements in peak force and peak power, and maintained elevated mean peak power for a longer period of time. These results indicate that Cr SUP can significantly improve factors associated with short-duration, high-intensity activity.
Asunto(s)
Creatina/farmacología , Fatiga Muscular/efectos de los fármacos , Esfuerzo Físico/efectos de los fármacos , Adulto , Análisis de Varianza , Creatina/administración & dosificación , Suplementos Dietéticos , Método Doble Ciego , Ejercicio Físico/fisiología , Prueba de Esfuerzo , Humanos , Masculino , Resistencia Física/efectos de los fármacosRESUMEN
The study purpose was to determine the effect of functional electrical stimulation (FES)-leg cycle ergometer training (30 minutes on 3 d/wk for 8 weeks) on the GLUT-1 and GLUT-4 content of paralyzed skeletal muscle. Biopsy samples of vastus lateralis muscle were obtained pre- and post-training from five individuals with motor-complete spinal cord injury ([SCI] four men and one woman aged 31 to 50 years, 3 to 25 years postinjury involving C5-T8). Western blot analysis indicated that GLUT-1 increased by 52% and GLUT-4 increased by 72% with training (P < .05). This coincided with an increase in the muscle oxidative capacity as indicated by a 56% increase in citrate synthase (CS) activity (P < .05) and an improvement in the insulin sensitivity index as determined from oral glucose tolerance tests (P < .05). It is concluded that FES endurance training is effective to increase glucose transporter protein levels in paralyzed skeletal muscle of individuals with SCI.