bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Musculotendinous Stiffness on Drop Jump Performance
Authors: Walshe Andrew D. , Wilson Gregory J.
Published: June 2009

This study investigated the relationship between musculotendinous stiffness and the ability to perform dynamic stretch-shorten cycle actions involving a range of eccentric loads. Twenty trained male subjects performed a series of quasi-static muscular actions in a supine leg press position, during which a brief perturbation was applied. The resulting damped oscillations allowed the estimation of each subject's maximal musculotendinous stiffness (k) for the lower body musculature. All subjects also performed a countermovement jump (CMJ) and a series of drop jumps (DJs) from heights of 20, 40, 60, 80, and 100 cm. When the jump heights of the nine most compliant (mean k = 11.4 ± 2.7 kN•m−1) and nine stiffest (mean k = 20.5 ± 2.5 kN•m−1) subjects were compared, the stiff subjects demonstrated significantly poorer capacity to perform under the highest (DJ80 and DJ100) eccentric loading conditions. It was hypothesised that the relatively greater forces transmitted from the skeletal system to the musculature of the stiff subjects reduced their ability to attenuate the higher eccentric loads due to less effective contractile dynamics and greater levels of reflex induced inhibition. Key words: series elastic component, compliance, drop jump, muscle elasticity, eccentric contraction
Comparison of Sweat Rate Measured by a Pouch Collector and a Hygrometric Technique During Exercise
Authors: Boisvert Paul , Desruelle Anne-Virginie , Candas Victor
Published: June 2009

Measurements of local sweat rate (back) determined with a closed-pouch collector made of polyethylene (110 cm2) were compared with those obtained from a ventilated capsule using an infrared photometric hygrometer technique. Eight young male subjects underwent three exercise sessions each for 60 min at 45% [Formula: see text] on a cycle ergometer at an ambient temperature of 35 °C and 35% relative humidity. When the onset and transient sweating periods (0-20 min) are excluded from calculations, the difference between the mean values obtained by the collector and the sweat capsule during the 20-60 time period is only 0.06 ± 0.04 mg • cm−2 • min−1 (5%). Although a significant correlation (r = .74, p < .05) was obtained between methods, individual differences in sweat-rate measurements varied on average ±0.22 mg • cm−2 • min−1 (±19%). Designed more specifically for sweat-content analysis, the pouch collector may serve as a satisfactory field method to approximate the local sweat rate and excretion induced by prolonged exercise in a hot environment. Key words: sweating assessment, methodology, thermoregulation, skin temperature
Creatine Ingestion Increases Anaerobic Capacity and Maximum Accumulated Oxygen Deficit
Authors: Jacobs Ira , Bleue Scott , Goodman Jack
Published: June 2009

The purpose of this study was to test the hypothesis that ingestion of creatine monohydrate increases anaerobic exercise capacity, as reflected by the maximal accumulated oxygen deficit (MAOD). Subjects were assigned, double-blind, to placebo (PL, n = 12) or creatine (CR, n = 14) groups and ingested 5-g doses 4 times daily of artificial sweetener or artificially sweetened creatine monohydrate, respectively, for 5 days. On a separate day subjects exercised to exhaustion at 125%[Formula: see text]. After two familiarization trials, MAOD was again determined before treatment, after 5 days of PL or CR treatment, and 7 days later. MAOD increased after CR treatment from 4.04 ± 0.31 to 4.41 ± 034 L(p < .001) and remained elevated for another 7 days (4.31 ± 0.33, p < .001). Time to exhaustion also increased in CR from 130 ± 7 to 141 ± 7 s(p < .01) and remained increased for another 7 days (139 ± 8 s, p < .01). These data demonstrate that ingesting creatine monohydrate for 5 days increases the MAOD, and is likely to have an ergogenic effect on supramaximal exercise performance that persists for at least a week after treatment. Key words: metabolism, exercise, ergogenic, performance
Hormonal Responses of Multiset Versus Single-Set Heavy-Resistance Exercise Protocols
Authors: Gotshalk Lincoln Allan , Loebel Chad C , Nindl Bradley C , Putukian Margot , Sebastianelli Wayne J , Newton Robert U , Häkkinen Keijo , Kraemer William J
Published: June 2009

The purpose of this study was to compare serum growth hormone (GH), testosterone (T), cortisol (C) and whole blood lactate (L) responses to single set (1S) versus multiple set (3S) heavy-resistance exercise protocols. Eight recreationally weight-trained men completed two identical resistance exercise workouts (1S vs. 3S). Blood was obtained prexcerise (PRE), immediately postexercise (0P), and 5 min (5P), 15 min (15P), 30 min and 60 min (60P) postexercise and was analyzed for GH, T, C, and L levels. For 1S and 3S, GH, L, and T significantly increased from PRE to 0P and remained significantly elevated to 60P, except for 1S. For GH, T, and L, 3S showed significantly greater increases compared to 1S. For C, 3S and 1S were increased significantly from resting at 0P, 5P, and 15P; 3S increased compared to 1S at 5P, 15P and 30P. Higher volumes of total work produce significantly greater increases in circulating anabolic hormones during the recovery phase following exercise. Key words: growth hormone, testosterone, cortisol, lactate, strength
The Pattern of Breathing Following a 10-Breath Voluntary Hyperventilation During Hyperoxic Rebreathing
Authors: Chatha Deep , Duffin James
Published: June 2009

The pattern of breathing following a 10-breath voluntary hyperventilation period during hyperoxic rebreathing was compared to that without hyperventilation in 6 subjects (3 male and 3 female). The aim was to measure the posthyperventilation short-term potentiation of ventilation without changes in respiratory chemoreflex drives induced by the voluntary hyperventilation. Hyperoxia was used to reduce the peripheral chemoreflex drive, and rebreathing to prevent the decrease in arterial carbon dioxide tension normally produced by hyperventilation. There were significant differences between the male and female responses. However, in all subjects, ventilation and heart rate were increased during hyperventilation but end-tidal partial pressures of carbon dioxide and oxygen were unchanged. Following hyperventilation, ventilation immediately returned to the values observed when hyperventilation was omitted. Hyperventilation did not induce a short-term potentiation of ventilation under these conditions: changes in chemoreflex stimuli brought about by cardiovascular changes induced by hyperventilation may play a role in the short-term potentiation observed under other circumstances. Key words: rebreathing, hyperventilation, short-term potentiation
Preexercise Sugar Feeding Does Not Alter Prolonged Exercise Muscle Glycogen or Protein Catabolism
Authors: Van Zant R. Scott , Lemon Peter W. R.
Published: June 2009

The purpose of this study was to determine the effects of type of preexercise sugar feedings (glucose [GLU] or fructose [FRU]) on muscle glycogen and protein catabolism during prolonged exercise in fed men. Seven men cycled to exhaustion on three different occasions at 70% VO2max, 45 min of after ingestion (700 ml) of either a 0.476 mol • L−1 carbohydrate (CHO) solution or a sweetened placebo (PLA). With GLU, serum insulin was significantly increased prior to exercise. As a result, serum glucose was significantly lower at 15 and 30 min of exercise with GLU, but was similar to the other treatments thereafter. Time to fatigue was absolutely longer with the GLU feeding, and exercise muscle glycogen catabolism was absolutely lower during the FRU trial, but the observed differences did not attain statistical significance due to intersubject variability. Protein catabolism was similar for all treatments. These data indicate that a 60-g preexercise glucose or fructose feeding following CHO loading procedures has minimal effects on muscle glycogen or protein catabolism during prolonged exercise. Key words: fructose, glucose, endurance exercise, insulin, nitrogen, cycling
Effect of Exercise Intensity on Free Tryptophan to Branched-Chain Amino Acids Ratio and Plasma Prolactin During Endurance Exercise
Authors: Strüder Heiko K. , Hollmann Wildor , Platen Petra , Wöstmann Ronny , Ferrauti Alexander , Weber Karl
Published: June 2009

The potential of exercise-induced changes in peripheral amino acids to alter blood prolactin levels through a seratonergic system modification was investigated in 8 male athletes. In two trials, subjects (N = 8) exercised on a cycle ergometer for 5 hr. The intensity of exercise corresponded to 55% VO2max (T55) or 75% VO2max (T75) respectively. In each trial, each subject received a 25-g energy bar (111 kcal) every 60 min, as well as 300 ml of a 6% carbohydrate solution (90 kcal) every 30 min of exercise duration. Plasma glucose and insulin declined (p ≤.05) in both trials during exercise. Ammonia was augmented (p ≤.05) above the baseline concentration after 120 min in both trials. During the last 2 hr of exercise, plasma free fatty acids were higher (p ≤.05) in T75, than in T55. During this time, the plasma free TRP/BCAA ratio was also augmented (p ≤.05) in T75 while no change was induced in T55. Plasma prolactin did not change in T55, while an increase (p ≤.05) was found in T75. The findings may further support the hypothesis that during endurance exercise changes in peripheral amino acid concentration may influence prolactin response via serotonergic system modifications. Key words: blood-brain barrier, serotonin, neuroendocrine system, free fatty acids, ammonia
Human Skeletal Muscle Fiber Types: Delineation, Development, and Distribution
Authors: Staron Robert S.
Published: June 2009

This brief review attempts to summarize a number of studies on the delineation, development, and distribution of human skeletal muscle fiber types. A total of seven fiber types can be identified in human limb and trunk musculature based on the pH stability/ability of myofibrillar adenosine triphosphatase (mATPase). For most human muscles, mATPase-based fiber types correlate with the myosin heavy chain (MHC) content. Thus, each histochemically identified fiber has a specific MHC profile. Although this categorization is useful, it must be realized that muscle fibers are highly adaptable and that innumerable fiber type transients exist. Also, some muscles contain specific MHC isoforms and/or combinations that do not permit routine mATPase-based fiber typing. Although the major populations of fast and slow are, for the most part, established shortly after birth, subtle alterations take place throughout life. These changes appear to relate to alterations in activity and/or hormonal levels, and perhaps later in life, total fiber number. Because large variations in fiber type distribution can be found within a muscle and between individuals, interpretation of data gathered from human muscle is often difficult. Key words: aging, myosin heavy chains, myogenesis, myofibrillar adenosine triphosphate
Effects of Combined Training Loads on Relations Among Force, Velocity, and Power Development
Authors: Toji Hideki , Suei Kensaku , Kaneko Masahiro
Published: June 2009

The effects of different training programs on the force-velocity relation and the maximum power output from the elbow flexor muscles were examined in 12 male adults. The subjects were divided into two equal groups (G30 + 100 and G30 + 0), In the G30 + 100 group, training was performed with five, repetitions at 30% maximum strength (Fmax) and five isometric contractions (100% Fmax) and in the G30 + 0 group with five repetitions at 30% Fmax and five contractions with no load (0% Fmax). Training was performed 3 days a week for 11 weeks. Maximum power increased significantly in both groups after training. The power increase was significantly greater in the G30 + 100 group. Maximum strength was significantly higher only in the G30 + 100 group, while maximum velocity increased in both groups. No significant difference in strength or velocity gain was observed between the two groups. These results suggest that isometric training at maximum strength (100% Fmax) is a more effective form of supplementary training to increase power production than no load training at maximum velocity. Key words: muscle training, force-velocity relation, muscle power
Hemodynamic Strategies in Blood Pressure Regulation During Orthostatic Challenge in Women
Authors: Culham Tania L. , Savard Gabrielle K.
Published: June 2009

Several studies indicate that carotid baroreflex responsiveness is a good predictor of orthostatic tolerance. Two groups of healthy women with high (HI) and low (LO) carotid baroreflex responsiveness were studied (a) to determine any differences in the level of orthostatic tolerance of the two groups, and (b) to study the hemodynamic strategies used by HI and LO responders to regulate arterial pressure during the orthostatic challenge of lower body negative pressure (LBNP). Orthostatic tolerance was similar between the two groups, whereas the hemodynamic strategies recruited to maintain blood pressure at −40 mmHg LBNP differed: HI responders exhibited greater LBNP-induced decreases in stroke volume and cardiac output, as well as a greater increase in peripheral resistance compared to LO responders (p < .05). In addition, a significant increase in plasma renin activity during LBNP was found in the HI responders only. No significant between-group differences were found in arterial and cardiopulmonary control of vascular resistance or arterial haroreflex control of heart rate during LBNP. Key words: arterial pressure, carotid baroreceptor, lower body negative pressure, orthostatic tolerance, stroke volume
The Effects of Bicycle Crank Arm Length on Oxygen Consumption
Authors: Morris David M. , Londeree Ben R.
Published: June 2009

The purpose of this investigation was to determine the effects of various crank arm lengths on oxygen consumption for trained cyclists. Secondary purposes were, if optimal crank arm lengths existed, to determine if these lengths could be predicted based on an individual's leg length. Six trained cyclists completed four experimental protocols riding at a workload of approximately 68% of [Formula: see text] using crank arm lengths of 165, 170, and 175 mm. During each protocol, the cadence, oxygen consumption, and distance traveled were determined, and values were combined to give a [Formula: see text] value. The values then were placed in either a high, medium, or low efficiency category. Significant differences were found among the three protocols. No significant correlations were found between each subject's most efficient crank arm length and leg length. The results of the study suggest that each subject has a most efficient crank arm length, but it does not appear that optimal crank arm length can be predicted by leg length. Key words: optimal crank arm length, leg length, efficiency
Moderate Physical Activity Can Increase Dietary Protein Needs
Authors: Lemon Peter W. R. , Dolny Dennis G. , Yarasheski Kevin E.
Published: June 2009

Six healthy men completed three 1-hr bouts of treadmill Walk-jogging at low (L; 42 ± 3.9% VO2max), moderate (M; 55 ± 5.6%), and high (H; 67 ± 4.5%) exercise intensity in order to determine whether moderate physical activity affects dietary protein needs. Both sweat rate and sweat urea N loss were greater (p < .10) with increasing exercise intensity. Seventy-two hour postexercise urine urea N excretion was elevated (p < .05) over nonexercise control (26.6 ± 2.96 g) with both M (31.0 ± 3.65) and H (33.6 ± 4.39), but not L (26.3 ± 1.86), intensities. Total 72-hr postexercise urea N excretion (urine + sweat) for the. M and H exercise was greater than control by 4.6 and 7.2 g, respectively. This suggest that 1 hr of moderate exercrise increases protein oxidation by about 29-45 g, representing ∼16-25% of the current North American recommendations for daily protein intake. These data indicate that the type of exercise typically recommended for health/wellness can increase daily protein needs relative either to sedentary individuals or to those who exercise at lower intensities. Key words: dietary protein/amino acid requirements, exercise intensity, aerobic exercise, moderate exercise, health/wellness, nitrogen excretion, sweat, urine
Lactate Transport and Lactate Transporters in Skeletal Muscle
Authors: Bonen Arend , Baker Steven K. , Hatta Hideo
Published: June 2009

The study of lactate transport in skeletal muscle had until recently been hampered by the lack of suitable sarcolemmal vesicle preparations. Researchers are now at the threshold of developing some very new understandings about the movement of lactate into and out of skeletal muscle with (a) evidence for a lactate transport system in skeletal muscle, (b) the very recent cloning of several monocarboxylate transporter genes, (c) the expression of at least one monocarboxylate transporter protein that facilitates the transport of lactate in heart and skeletal muscle, and (d) the realization that lactate transport can be altered with changes in chronic muscle activity. The MCT1 expression patterns in metabolically heterogeneous skeletal suggest that a primary role of this lactate transporter is to take up lactate into the oxidative muscle fibers where it may be used as a fuel in mitochondrial oxidation. Increments in both MCT1 and lactate transport with training support this role. Key words: vesicles, MCT1, diffusion
A New Formula for Population-Based Estimation of Whole Body Muscle Mass in Males
Authors: Doupe Malcolm B. , Martin Alan D. , Searle Mark S. , Kriellaars Dean J. , Giesbrecht Gordon G.
Published: June 2009

A new equation to estimate muscle mass in males was developed using parameters common to the 1981 Canada Fitness Survey and the male cadaver data of Martin et al. (1990b). The cadavers (N = 12) were randomly divided into two groups. The equation was developed on cadaver Group A and then validated on Group B. Once the equation with the most suitable variables was validated on Group B, it was redeveloped on combined data from Groups A and B. The final equation is as follows: muscle mass (gm) = Ht (0.031MUThG2 + 0.064CCG2 + 0.089CAG2) −3.006; adjusted R2 = .96, SEE = 1,488 gm, F = 87.5, p = .0001. Variables (in cm) were Ht, height; MUThG, modified upper thigh girth; CCG, corrected calf girth; and CAG, corrected arm girth. The predictive ability of this equation was comparable to the original equation of Martin et al. (1990b) and can be a valuable tool for muscle mass estimation of male subjects in the 1981 Canada Fitness Survey. Key words: equation, estimation, body composition, body fat, fat free mass, lean body mass, Canada Fitness Survey
Muscle Regionalization
Authors: Kernell Daniel
Published: June 2009

In this review, the term muscle fibre regionalization signifies the presence of regional intramuscular differences in fibre type composition. As is well known, highly regionalized muscles commonly have greater concentrations of slow fibres deep than superficially. However, the degree of regionalization varies markedly between muscles and is not confined to deep vs. superficial locations. Fibres of the same myosin type may show regionalized differences in their metabolic enzyme activity, even within single motor units (Larsson, 1992). Regionalization of fibre type composition occurs also within single neuromuscular partitions. The intraspinal position of motoneurones is often coarsely related to the intramuscular sites of their muscle units. Muscles with a marked fibre type regionalization tend to show a corresponding regionalization of activity; in several muscles, however, the activity regionalization may vary depending on the motor task. During early development, fibre type regionalization emerges even under aneural conditions. The mechanisms are still unknown; relevant aspects of early development are briefly reviewed. Key words: skeletal muscle, fiber type, topography, activity, development
Oxidative Stress, Antioxidant Status, and the Contracting Diaphragm
Authors: Lawler John M. , Powers Scott K.
Published: June 2009

Reactive oxygen species, including free radicals, are produced through a number of biochemical reactions, often as a consequence of aerobic metabolism. A system of antioxidant enzymes and scavenger substrates provides protection of membrane lipids, proteins, and DNA. An imbalance between production of reactive oxygen species and antioxidant protection results in "oxidative stress." Oxidative stress is believed to contribute to numerous pathological conditions including atherosclerosis, obstructive lung disease, aging, and fatigue of skeletal muscles including the diaphragm. Strenuous exercise, inflammation, infection, obstructive lung diseases, etc. increase exposure of the diaphragm to reactive oxygen species. Emerging data indicate that reactive oxygen species alter diaphragm contractions primarily in response to low-frequency stimulation. The response of the diaphragm is profoundly influenced by the degree of oxidative stress, fatigue state, glutathione status, and age. Exercise training results in an upregulation of antioxidant enzyme activities in the diaphragm and thus could provide additional protection against oxidative stress. Key words: aging, excitation-contraction coupling, exercise, fatigue, free radicals, glutathione peroxidase, oxidation/reduction, reactive oxygen species, respiratory muscles, skeletal muscle, superoxide dismutase
The Effect of Aerobic Exercise Training on the Distribution of Succinate Dehydrogenase Activity Throughout Muscle Fibres
Authors: Chilibeck Philip D. , Bell Gordon J. , Socha Teresa , Martin Tom
Published: June 2009

We evaluated the effect of endurance training (cycling 3 times per week for 12 weeks) on succinate dehydrogenase (SDH) activity in the subsarcolemmal (SS) and intermyofibrillar (IMF) regions of vastus lateralis muscle fibres in 7 individuals (4 females and 3 males). SDH activity of the SS region increased 9.4% and 12.8% in type I and II fibres, respectively (p < .05). SDH activity of the IMF region increased 4.7% and 6.7% in type I and II fibres, respectively (p < .05). This was less than the increase in the SS region (p < .O5). No significant changes were observed in a control group (4 females and 3 males). These data suggest that mitochondria in the SS and IMF regions of human vastus lateralis muscle fibres are sensitive to endurance training. The greater response in the SS region suggests that the metabolic requirements of SS mitochondria were stressed to a greater extent than IMF mitochondria with endurance training. Key words: subsarcolemmal mitochondria, intermyofibrillar mitochondria
Preface
Authors: Bhambhani Yagesh
Published: June 2009

not available
Molecular Mechanisms Mediating Synapse-Specific Gene Expression During Development of the Neuromuscular Junction
Authors: Goldman Daniel , Sapru Mohan K.
Published: June 2009

Adult skeletal muscle locally expresses nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction by selective induction of their subunit-encoding genes (αβεδ) in endplate-associated myonuclei. Neuregulin/ARIA is a nerve-derived factor that is thought to be largely responsible for this local gene induction, Neuregulin/ARIA activates a Ras/MAP kinase signalling cascade, which ultimately induces nAChR ε-subunit gene expression via a 15 bp sequence that harbors a core Ets transcription factor binding site (GGA). Interestingly, this same sequence also appears to participate in extrajunctional repression of the ε-subunit gene. Muscle Ets 2 overexpression induces nAChR ε-subunit gene promoter activity, whereas a dominant/negative Ets blocks neuregulin-dependent induction. These results suggest that Ets transcription factors play a role in mediating synapse-specific and neuregulin-mediated motor neuron control of nAChR gene expression. Key words: nicotinic acetylcholine receptor, Ras, MAP kinase. Ets transcription factors, neuregulin, protein tyrosine phosphatases
The Effect of Different Calculation Methods of Flywheel Parameters on the Wingate Anaerobic Test
Authors: Coleman Simon G. S.
Published: June 2009

Researchers compared different methods of calculating kinetic parameters of friction-braked cycle ergometers, and the subsequent effects on calculating power outputs in the Wingate Anaerobic Test (WAnT). Three methods of determining flywheel moment of inertia and frictional torque were investigated, requiring "run-down" tests and segmental geometry. Parameters were used to calculate corrected power outputs from 10 males in a 30-s WAnT against a load related to body mass (0.075 kg•kg−1). Wingate Indices of maximum (5 s) power, work, and fatigue index were also compared. Significant differences were found between uncorrected and corrected power outputs and between correction methods (p < .05). The same finding was evident for all Wingate Indices (p < .05). Results suggest that WAnT must be corrected to give true power outputs and that choosing an appropriate correction calculation is important. Determining flywheel moment of inertia and frictional torque using unloaded run-down tests is recommended. Key words: sprint ergometry, power output, moment of inertia
Association Between Aerobic Capacity and Carotid-Cardiac Baroreflex Responsiveness in Women
Authors: Culham Tania L. , Savard Gabrielle K.
Published: June 2009

The purpose of this study was to determine whether the positive correlation between carotid-cardiac baroreflex responsiveness and aerobic capacity [Formula: see text] that has been reported in men also occurs in women. Carotid-cardiac baroreflex responsiveness was tested in 40 healthy, normotensive women (age 18-35), using the variable neck pressure technique. Participants were subdivided into endurance-trained (ET; n = 11) and untrained (UT; n = 9) groups. No significant between-group difference was found in the range or gain of the carotid-cardiac baroreflex response despite a lower resting HR in the ET group. When participants were subdivided into high (HI: n = 13) and low (LO; n = 17) responders based on reflex RRI responses to CTP changes, no significant between-group differences were found in resting HR or [Formula: see text] levels. It was concluded that aerobic capacity [Formula: see text] is not a good predictor of cardiac-carotid baroreflex responsiveness in healthy women. Key words: blood pressure, endurance exercise training, aerobic capacity, carotid transmural pressure, arterial baroreflex
Mediation of Glucoregulation at Rest and During Exercise by the Glucose-Fatty Acid Cycle: In Vivo and In Vitro Studies
Authors: Rodgers Carol D. , Vranic Mladen
Published: June 2009

Himsworth (1934) demonstrated that increased fat consumption leads to decreased glucose tolerance due to decreased insulin sensitivity. Randle and colleagues (1964) named this interplay between fat and carbohydrate metabolism the glucose-fatty acid cycle (GFAC) and proposed a series of feedback mechanisms by which elevated levels of free fatty acids (FFAs) impair glucose uptake and oxidation in rat heart and diaphragm muscle. Numerous investigators have extended these studies to clarify the existence of GFAC and provide insight into the mechanisms and conditions under which it occurs. This paper reviews the literature and highlights other indirect means by which FFAs affect carbohydrate metabolism. Numerous in vitro studies are reviewed, emphasizing the importance of FFA concentration, carbon length, and degree of saturation. This article addresses evidence that the interplay between fat and carbohydrate metabolism is not a function of FFA concentration but a result of the impact that FFA levels have on insulin. Key words: glucose-fatty acid cycle, Randle cycle, carbohydrate metabolism, lipid metabolism, glucose uptake, glucose oxidation, fat oxidation
Gender and Fat Metabolism During Exercise: A Review
Authors: Tate Charlotte A. , Holtz Robert W.
Published: June 2009

We examined the evidence for greater fat utilization by women during exercise and the potential gender differences in specific cellular processes. Results from well-controlled studies show that, compared to men, women oxidize more fat during submaximal exercise, resulting in the relative sparing of muscle glycogen. Mature female rats use less muscle glycogen during running and can run longer than male counterparts. Circulating estrogen is critical to these observations, as shown by studies where male rats were treated with estrogen. Estrogen-treated male rats use less muscle glycogen during exercise and can run longer than untreated males. The cellular mechanisms and factors underlying these findings are unknown and certainly multifactorial. We offer some information that, unfortunately, does not lead to any natural conclusion. However, this area is certainly ripe for research. Key words: respiratory exchange ratio, fat metabolism, glycogen, estrogen, mitochondrion
Glucose Tolerance Is Improved After Low- and High-Intensity Exercise in Middle-Age Men and Women
Authors: Bonen Arend , Ball-Burnett Margaret , Russel Caryl
Published: June 2009

We compared the effects of low- and high-intensity exercise on oral glucose tolerance immediately and 24 hr after each exercise bout. Participants were 5 male and 5 female individuals (age 40-48). A fasted, oral glucose tolerance test (OGTT) was conducted several days before the first exercise bout. Glucose and insulin concentrations were determined every 15 min throughout a 2 hr, 75 g OGTT. Immediately after low-intensity exercise, the incremental glucose area under the curve was reduced by 16%, compared to the fasting OGTT (p < .05). This was reduced further (−30%) 24 hr postexercise (p < .05). After high-intensity exercise, similar results were observed, with the incremental glucose area reduced by 14 and 35% immediately and 24 hr postexercise, respectively (p < .05). In conclusion, exercise improves glucose tolerance, this effect is more pronounced 24 hr postexercise, and low-and high-intensity exercise provide similar beneficial effects on glucose tolerance. Key words: cycle ergometry, insulin
Glutamine: A Potentially Useful Supplement for Athletes
Authors: Antonio Jose , Street Chris
Published: June 2009

The role of glutamine as a possible ergogenic aid has not been posited in the scientific literature. Although there is an abundance of clinical evidence supporting the need for exogenous glutamine in the maintenance of muscle protein mass and immune system function in critically ill patients, little work has been done that examines the potential utility of glutamine for athletes engaged in heavy exercise training. This brief review will describe a number of studies on the effects of glutamine supplementation on muscle protein mass, immune system function, and glucose regulation. Based on the available clinical evidence, we would speculate that glutamine has potential utility as a dietary supplement for athletes engaged in heavy exercise training. Key words: amino acid, protein, muscle, exercise, nutrition
From Molecules to Marathons: The Wisdom of Our Past Presidents. Introduction to the Symposium
Authors: Shephard Roy J.
Published: June 2009

not available
Identifying Bottlenecks in Endurance Performance: The Conductance Theorem
Authors: Shephard Roy J.
Published: June 2009

The various transport processes that contribute to human endurance performance, such as oxygen intake, elimination of carbon dioxide, lactate and heat, and the delivery of metabolic fuels, can all be represented by conductance analogues. The use of such models is helpful in identifying bottlenecks within each of these systems, and in comparing parallel systems such as the intake of oxygen and the elimination of carbon dioxide. However, in order to make the models manageable, many simplifications are necessary, and corresponding caution is needed in drawing inferences from conductance analogues. Key words: carbon dioxide transport, electrical analogues, heat elimination, lactate gradients
The Gas Transporting Systems: Limits and Modifications With Age and Training
Authors: Paterson Donald H. , Cunningham David A.
Published: June 2009

The interplay of cardiovascular and cellular oxygen uptake determinants of aerobic performance and the system adaptations to training in different population samples are examined in order to describe the limitation. With [Formula: see text] a central limitation following myocardial infarction and ageing is modified with training. Peripheral adaptations occur and stroke volume may be increased primarily through improved diastolic filling. In submaximal perturbations, control of the increase in O2 uptake at exercise onset (O2 kinetics) is most often under peripheral metabolic control, but in exceptions may also be limited by central factors. In young and old the peripheral machinery is matched to the growth (puberty) and loss (ageing) of muscle mass. Cardiac stroke volume capacity may adjust following the changes in muscle mass. Submaximal endurance is closely influenced by the anaerobic threshold (θan) and peripheral factors of oxidative metabolism. Relative to [Formula: see text] the θan is low in children and high in older adults, perhaps reflecting a slow time course in full development and loss of peripheral adaptations. Remarkable increases in endurance performance are related to relatively small changes in the maximal capacity and the relative intensity of performance. Key words: cardiorespiratory, [Formula: see text] anaerobic threshold, oxygen kinetics, endurance
The Effects of Endurance Training on Muscle Fibre Types and Enzyme Activities
Authors: Taylor Albert W. , Bachman Lori
Published: June 2009

Practitioners and scientists have demonstrated great interest in the physiological and biochemical effects of endurance training on the results of the marathon run. It is well documented that athletes with a large proportion of slow twitch and fast twitch aerobic skeletal muscle fibre, high metabolic enzyme activities and concentrations, large mitochondria concentration and, of course, the ability to increase the power output generated for a given rate of oxygen consumption and energy expenditure, are generally highly successful distance runners. Aerobic and endurance training have been shown to bring about sgnificant adaptations to the skeletal muscle and its inclusions as well as to the delivery system. In particular, enzyme activity levels are readily mutable, mitochondrial concentrations increase, and some evidence suggests that the fibre distribution is changed. This article briefly reports on changes in skeletal muscle brought about by endurance training and those changes that appear most effective in yielding success in endurance events. Key words: muscle metabolism, glycogen, substrates, training
Haemoglobin, Blood Volume, Cardiac Function, and Aerobic Power
Authors: Gledhill Norman , Warburton Darren , Jamnik Veronica
Published: June 2009

Alterations in [Hb], which are mediated through changes in arterial oxygen content, and alterations in BV, which are mediated through changes in cardiac output [Formula: see text] have a significant effect on both [Formula: see text] and aerobic performance. If BV is held constant, a decrease in [Hb] (anaemia) causes a decrease in [Formula: see text] and aerobic performance, while an increase in [Hb] (blood doping) causes an increase in [Formula: see text] and aerobic performance. If [Hb] is held constant, an increase in BV can cause an increase in both [Formula: see text] and aerobic performance, while a decrease in BV can cause a decrease in both [Formula: see text] and aerobic performance. In addition, an increase in BV can compensate for moderate reductions in [Hb] through increases in [Formula: see text], allowing [Formula: see text] to remain unchanged or even increase. Also, a large portion of the difference in the enhanced cardiovascular function of endurance athletes is due to their high BV and the resultant enhancement of diastolic function. Hence, optimizing both [Hb] and BV is a very important consideration for endurance performance. Key words: blood doping, sport anemia, stroke volume
Motor Unit Double Discharges: Statistical Anomaly or Functional Entity?
Authors: Garland S. Jayne , Griffin Lisa
Published: June 2009

Motor unit double discharges, or doublets, have been described as two consecutive motor unit discharges that occur with a short interspike interval of 2.5-20 ms (Simpson, 1969). Double discharges have been reported in the literature for over 70 years. For instance, Eccles and Hoff(1932) found that double discharges were elicited occasionally at the onset of a crossed extension reflex in the soleus muscle of the anaesthetized cat. With the use of electrical stimulation protocols, short interspike intervals inserted at the beginning of a stimulation train have been shown to increase both the peak force and the rate of rise of force production, and also decrease the rate of fatigue. The extent to which double discharges occur in naturally-occurring voluntary behaviours remains relatively unexplored. This review examines the issue of whether double discharges occur solely because of an intrinsic property of motoneurones, thereby representing a "statistical anomaly," or whether they may result from a neural control strategy to augment force production, i.e., a "functional entity." Key words: doublet, fatigue, muscle
Exercise in the Heat: Limitations to Performance and the Impact of Fluid Replacement Strategies. Introduction to the Symposium
Authors: Maughan Ron J.
Published: June 2009

The cause of fatigue during prolonged exercise in the heat has not been clearly established, but performance appears to be limited by thermoregulatory and fluid balance factors. Both dehydration and hyperthermia separately impair performance. Prior acclimation reduces the impact of heat, and ingestion of fluids also improves performance. Ingested fluids should contain carbohydrate and some electrolytes, primarily sodium, but many factors will dictate the choice of fluids. These include the relative need for carbohydrate to supplement endogenous stores, the need for fluid replacement, the limitations on replacement imposed by the nature of the event, and the athlete's own requirements and preferences. Key words: fatigue, thermoregulation, hyperthermia, dehydration, fluid balance
Limitations to Fluid Replacement During Exercise
Authors: Maughan Ron J. , Leiper John B.
Published: June 2009

Fluid replacement during exercise is essential for endurance exercise performance and reducing the risk of heat illness. Fluids supply water, which ameliorates dehydration, and also substrate for the working muscles. Absorption of water and nutrients occurs in the upper part of the small intestine, and replacement may be limited by the rate at which fluid is emptied from the stomach or absorbed in the intestine. Gastric emptying of liquids is influenced primarily by the volume of fluid in the stomach and by its energy density. Increasing the volume will speed emptying, but increasing the nutrient content will slow emptying. Osmolality, temperature, and pH of drinks, as well as exercise intensity, are of minor importance. Intestinal water absorption is a passive process: water follows osmotic gradients but will also follow the active absorption of nutrients, especially glucose, which is actively co-transported with sodium. Water transport is maximised by the presence in the intestine of hypotonic solutions of glucose and sodium. Hypertonic solutions promote net water secretion into the intestinal lumen, resulting in a temporary net loss of water from the body. The amount of fluid ingested by athletes is normally much less than can be tolerated, therefore issues such as palatability and practising drinking during training are important. Key words: dehydration, rehydration, gastric emptying, intestinal absorption
Dehydration, Rehydration, and Exercise in the Heat: Rehydration Strategies for Athletic Competition
Authors: Galloway Stuart D.R.
Published: June 2009

Exercise capacity and exercise performance are reduced when the ambient temperature is high. This has mainly been attributed to the large sweat losses which lead to hypohydration, a failure of thermoregulation, and eventually circulatory collapse. Exercising athletes rarely drink enough before or during exercise to replace the ongoing fluid losses, especially in hot conditions. In order to combat dehydration, hyperthermia, and impending circulatory collapse, athletes should drink fluids before, during, and after exercise. Preexercise strategies include attempts to maintain euhydration but also to hyperhydrate. Hyperhydration is relatively easy to achieve, but thermoregulatory benefits during prolonged exercise have not been observed in comparison to euhydration. In prolonged continuous exercise, fluid and carbohydrate (CHO) ingestion has clearly been shown to improve performance, but the evidence is not so clear for high-intensity intermittent exercise over a prolonged period. The general consensus is that fluid ingestion should match sweat losses during exercise and that the drink should contain CHO and electrolytes to assist water transport in the intestine and to improve palatability. Postexercise rehydration is essential when the strategies adopted before or during exercise have not been effective. The best postexercise rehydration strategy would be to ingest a large volume of a beverage that contains a CHO source and a high sodium content. Key words: hyperhydration, euhydration, fluid replacement
Muscle Substrate Utilization and Lactate Production During Weightlifting
Authors: Macdougall J. Duncan , Ray Slavko , Sale Digby G. , Mccartney Neil , Lee Perry , Garner Scott
Published: June 2009

Biopsies (biceps) were examined in 8 bodybuilders across a typical arm-curl training session (80% 1-RM). [PCr] and [glycogen] decreased 62 and 12% after 1 set (n = 4), and 50 and 24% after 3 sets (n = 4). [Lactate] was 91 and 118 mm kg−1, respectively, after 1 and 3 sets. Fatigue was probably partially caused by decreased [PCr] and increased [H+] (first set) and by increased [H+] in subsequent sets. Key words: phosphagen utilization, glycogen depletion, biceps brachii
Nutritional Antioxidants as Therapeutic and Preventive Modalities in Exercise-Induced Muscle Damage
Authors: Goldfarb Allan H.
Published: June 2009

Several mechanisms have been forwarded to explain the etiology of exercise-induced muscle damage. Free-radical mediated processes appear to be an important component of the inflammatory mediated response. Free radicals have also been demonstrated to be a contributing factor in the loss of calcium homeostasis within the cell. Therefore, one of the proposed treatments for preventing or reducing the extent of this damage is the intervention of free-radical mediated processes. Antioxidants are agents that typically work to prevent free-radical mediated alterations within cells by quenching free radicals. The traditional dietary antioxidants most commonly investigated to inhibit free-radical damage are vitamin E, vitamin C, and beta carotene. Other nutritional agents have also been noted to posses antioxidant properties. Isoflavonoids and some phytochemicals have been proposed to contain antioxidant properties. This paper briefly reviews some aspects of these agents and their role, either proven or proposed, in the prevention of oxidative stress and muscle damage. Key words: vitamin E, vitamin C, beta carotene, genistein, oxidative stress
Gaining Weight: The Scientific Basis of Increasing Skeletal Muscle Mass
Authors: Houston Michael E.
Published: June 2009

Most athletes today tend to have a larger muscle mass than their predecessors. Better training and nutrition practices are responsible for much of this difference, but whatever the mechanism, the balance between muscle protein synthesis and breakdown must be in favor of increased muscle protein. Applying new techniques for measuring whole body and muscle protein synthesis to resistance exercise has led to some interesting results. In the recovery period following resistance exercise, both muscle protein synthesis and breakdown are accelerated in the fasted state. Ingestion of carbohydrate or carbohydrate and protein during recovery further increases muscle protein synthesis, due in part to an improved anabolic hormone environment. In addition, the anabolic effect of a resistance training bout may last well beyond 48 hours. Using information obtained from research studies, better training and dietary practices can optimize the benefits from resistance training, Key words: protein synthesis, protein breakdown, anabolic hormones, nutrition, resistance training
Leptin and Reproduction: Is it a Critical Link Between Adipose Tissue, Nutrition, and Reproduction?
Authors: Thong Farah S.L. , Graham Terry E.
Published: June 2009

Exercise-associated reproductive disorders are frequently reported among recreationally active and elite female athletes. Although an association between exercise and menstrual disorders has been established, the mechanism by which exercise disrupts reproductive function remains unknown. Recent findings suggest that low energy availability rather than inadequate body fatness or exercise stress is likely the mechanism by which exercise impinges negatively on the hypothalamic-pituitary-ovarian axis in female athletes. The peripheral signal that informs the neural network of energy availability remains unknown. The identification of the adipocyte-derived ob gene product, leptin, and subsequent findings of its association with reproduction in both rodents and humans, led to speculations that it may be involved in the interactions between nutrition and reproduction. This review article focuses on leptin's role in modulating reproduction, and in particular, as a peripheral signal of nutritional status that integrates adipose tissue, nutrition, and reproduction in female athletes. Key words: female athletes, ob gene, exercise, energy balance, amenorrhea
Reproducibility of Resting Heart Rate Variability With Short Sampling Periods
Authors: Marks Bonita L. , Lightfoot J. Timothy
Published: June 2009

The purpose of this study was to determine whether resting heart rate variability (HRV) is reproducible with short sampling measurement periods using an office-based personal computer measurement system. Eight healthy active women participated in ECG analyses on 2 days within 1 week under controlled environmental and physiological conditions. After they rested for 10 minutes, a 10-min ECG was recorded. HRV was determined from a 2.5- and 5-min sample period using both time domain variables (meanRR and SDNN) and frequency domain variables (LF, HF, LF:HF). Repeated measures ANOVA found no significant differences between Day 1 and Day 2 for either sampling period (p >= 0.23). For both the 2.5- and 5-min sampling periods, the intraclass correlations between days for the time domain variables showed good reproducibility (R = 0.86-0.90). The reproducibility of the frequency domain variables was only average (R = 0.67-0.96), with the LF:HF ratio yielding the higher R values. Key words: fast Fourier transformation, frequency domain, spectral analysis, time domain, women
Fatty Acid Transporters (FABPpm, FAT, FATP) in Human Muscle
Authors: Bonen Arend , Miskovic Dragana , Kiens Bente
Published: June 2009

Recently, a number of putative LCFA transporters have been identified: fatty acid binding protein (FABPpm), fatty acid translocase (FAT/CD36), and fatty acid transport protein (FATP). We have demonstrated, for the first time, that transcripts of all three putative LCFA transporters (FAT mRNA, FATP mRNA, and mAspAT/FABPpm mRNA) are present in human skeletal muscle. Key words: mRNA, membrane