bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucagon Receptors: Effect of Exercise and Fasting
Authors: Lavoie Carole
Published: June 2009

One paradox of hormonal regulation during exercise is the maintenance of glucose homeostasis after endurance training despite a lower increase in plasma glucagon. One explanation could be that liver sensitivity to glucagon is increased by endurance training. Glucagon exerts its effect through a 62 KDa glycoprotein receptor, member of the G protein-coupled receptor. To determine whether changes with exercise in glucagon sensitivity occurred at the level of the glucagon receptor (GR), binding characteristics of hepatic glucagon receptors were ascertained in rat purified plasma membranes. Saturation kinetics indicated no difference in the dissociation constant or affinity of glucagon receptor, but a significantly higher glucagon receptor binding density in liver in endurance trained compared to untrained animals. Along with endurance training, it appears that fasting also changes GR binding characteristics. In animals fasting 24 hrs, a significant increase in glucagon receptor density was also reported. Although the exact mechanism remains unknown, there is no doubt that the liver can adapt to physiological stress through modulation of GR binding characteristics to enhance the hepatic glucose production responsiveness to glucagon. Key words: glucagon sensitivity, liver, endurance training, rats
Resistance Training: Cortical, Spinal, and Motor Unit Adaptations
Authors: Griffin Lisa , Cafarelli Enzo
Published: June 2009

During the first few weeks of isometric resistance training there is an increase in maximal muscle force output that cannot be accounted for by muscle hypertrophy. Early on, researchers postulated the existence of neural adaptations to training primarily through the use of surface electromyographic recordings. More recent evidence also suggests that increased excitation may occur at the cortical levels following short-term resistance training. Alterations in synergistic activation and reductions in antagonist activation are neural factors that have been identified as changing during the early stages of resistance training which could contribute to maximal force generation. Neural adaptations that occur during the ramp-up phase of isometric contraction include decreases in motor unit recruitment thresholds, increased motor unit discharge rates, and increases in double discharges. An increase in the maximal rate of force development also occurs during the early stages of resistance training, but whether the neural mechanisms associated with the increase in the rate of rise are also associated with the increase in maximal force has not been elucidated. More work is needed to examine the integration of changes in cortical and spinal excitability with single motor unit firing patterns during this simple form of exercise before we can extend our understanding to different types of training. Key words: strength training, neural adaptation, H-reflex, maximal voluntary contraction, cortical excitability
Comparaison inter-sexuelle des réponses thermique, cardiaque, et musculaire lors d'une course prolongée en ambiance chaude
Authors: Ftaiti Foued , Kacem Asma , Latiri Imed , Mdalla Samia Ben , Tabka Zouhair , Zouari Nouri , Ellouze Feriel , Grélot Laurent
Published: June 2009

The aim of this study was to compare male and female thermal, cardiac, and muscular responses induced by a prolonged run undertaken in a hot environment. Twelve volunteers participated in this study. The first group consisted of 6 men and the second one consisted of 6 women. After determination of their [Formula: see text] and maximal aerobic velocity (MAV), each athlete completed a 40-min run at 65% MAV in a hot and dry environment (temperature 31-33 °C, relative humidity 30%). Immediately before and after the run, each subject performed two different vertical jumps, i.e., a squat jump (SJ) and a counter-movement jump (CMJ) on a force platform. Force, velocity, power, and jump height were measured during each jump. The completion of the run was associated with a significant loss (p <  0.001) of body mass (BM) and significant increases (p <  0.001) in heart rate, tympanic temperature, and lactate concentration ([La]). Muscle power was significantly improved (+9%, p <  0.05) during the SJ only in the women. A significant enhancement of this parameter was also demonstrated during the CMJ in both groups (men: +10%, p <  0.05; women: +8%, p <  0.01). Surprisingly, a comparison of thermal, cardiac, and muscular responses did not reveal any significant differences between the sexes. Moderate dehydration (−2.0 to −2.3% of BM) and a rise in core temperature (above 39.2 °C) induced by the 40-min run led to an improvement of muscular strength in both men and women. However, the results of this study did not reveal any significant between-sex differences in thermal, cardiac, and muscular responses after exercising in the heat. Key words: exercise, dehydration, hyperthermia, tympanic temperature, fatigue, power
Vascular Nitric Oxide and Oxidative Stress: Determinants of Endothelial Adaptations to Cardiovascular Disease and to Physical Activity
Authors: Rush James W.E. , Denniss Steven G. , Graham Drew A.
Published: June 2009

Cardiovascular disease is the single leading cause of death and morbidity for Canadians. A universal feature of cardiovascular disease is dysfunction of the vascular endothelium, thus disrupting control of vasodilation, tissue perfusion, hemostasis, and thrombosis. Nitric oxide bioavailability, crucial for maintaining vascular endothelial health and function, depends on the processes controlling synthesis and destruction of nitric oxide as well as on the sensitivity of target tissue to nitric oxide. Evidence supports a major contribution by oxidative stress-induced destruction of nitric oxide to the endothelial dysfunction that accompanies a number of cardiovascular disease states including hypertension, diabetes, chronic heart failure, and atherosclerosis. Regular physical activity (exercise training) reduces cardiovascular disease risk. Numerous studies support the hypothesis that exercise training improves vascular endothelial function, especially when it has been impaired by preexisting risk factors. Evidence is emerging to support a role for improved nitric oxide bioavailability with training as a result of enhanced synthesis and reduced oxidative stress-mediated destruction. Molecular targets sensitive to the exercise training effect include the endothelial nitric oxide synthase and the antioxidant enzyme superoxide dismutase. However, many fundamental details of the cellular and molecular mechanisms linking exercise to altered molecular and functional endothelial phenotypes have yet to be discovered. The working hypothesis is that some of the cellular mechanisms contributing to endothelial dysfunction in cardiovascular disease can be targeted and reversed by signals associated with regular increases in physical activity. The capacity for exercise training to regulate vascular endothelial function, nitric oxide bioavailability, and oxidative stress is an example of how lifestyle can complement medicine and pharmacology in the prevention and management of cardiovascular disease. Key words: exercise, artery, reactive oxygen species, antioxidant, hypertension
An Investigation of the Bilateral Limb Deficit Phenomenon in Lower Limbs
Authors: Kuruganti Usha
Published: June 2009

not available
The Influence of the Self-Contained Breathing Apparatus (SCBA) on Ventilatory Function and Maximal Exercise
Authors: Eves Neil D. , Jones Richard L. , Petersen Stewart R.
Published: June 2009

Our previous work showed that breathing low density gases during exercise with the self-contained breathing apparatus (SCBA) improves maximal ventilation (VE) and maximal oxygen consumption [Formula: see text] This suggests that the SCBA limits exercise by adding a resistive load to breathing. In this study we compared [Formula: see text] with and without the various components comprising the SCBA to determine their impact on [Formula: see text] Twelve males performed 4 randomly ordered incremental exercise tests to exhaustion on a treadmill: (1) low-resistance breathing valve only (CON); (2) full SCBA (SCBA); (3) SCBA regulator only (REG); and (4) carrying the cylinder and harness assembly but breathing through a low-resistance breathing valve (PACK). Compared to CON, [Formula: see text] was reduced to a similar extent in the SCBA and REG trials (14.9% and 13.1%, respectively). The PACK condition also reduced [Formula: see text] but to a lesser extent (4.8 ± 5.3%). At [Formula: see text][Formula: see text] was decreased and expiratory mouth pressure and external breathing resistance (BR) were increased in both the SCBA and REG trials. There was a significant correlation between the change in maximal [Formula: see text] and [Formula: see text] with the SCBA. The results show that the SCBA reduces [Formula: see text] by limiting [Formula: see text] secondary to the increased BR of the SCBA regulator. Key words: ventilation, breathing resistance, expiratory flow limitation, [Formula: see text]
Effects of Strength Training and Nutritional Counseling on Metabolic Health Indicators in Aging Women
Authors: Sallinen Janne , Fogelholm Mikael , Pakarinen Arto , Juvonen Tuula , Volek Jeff S. , Kraemer William J. , Alen Markku , Häkkinen Keijo
Published: June 2009

Purpose: Effects of strength training (ST) and nutritional counseling (NC) on metabolic health indicators were examined in 50 aging women. Methods: Subjects performed ST for 21 weeks. NC was given to obtain sufficient energy and protein intake, and recommended intake of fat and fiber. Results: NC increased intake of protein and polyunsaturated fat by 4.5% and 10.7% and decreased intake of saturated fat by 18.3%. Serum concentrations of total cholesterol (TC), LDL-cholesterol (LDL-C), total and HDL-cholesterol (HDL-C) ratio and triacylglycerols (TAG) decreased, and serum HDL-C increased in all subjects after ST. Respectively, systolic and diastolic blood pressure and serum insulin concentration decreased in all subjects. NC contributed to the decreases in levels of serum LDL-C after the first half of ST and serum TC and HDL-C ratio during both ST periods. Changes in serum TAG concentrations correlated positively with intake of carbohydrates, and negatively with monounsaturated fat in all subjects. Respectively, changes in serum TC levels were related to protein intake, and changes in serum HDL-C to intake of fat, and inversely to carbohydrate and protein in all subjects. Relationships between serum TC and HDL-C levels and protein intake were only observable in the ST+NC group. Conclusions: The long-term ST had favorable effects on serum lipids, lipoproteins, insulin concentration, and blood pressure. However, NC further contributed to positive changes in serum lipids and lipoproteins. Key words: exercise, diet, elderly, cardiovascular diseases, diabetes
Estimation of the Parameters of the Relationship Between Power and Time to Exhaustion From a Single Ramp Test
Authors: Pouilly Jean-Pierre , Chatagnon Michel , Thomas Vincent , Busso Thierry
Published: June 2009

This study aimed to estimate the power/time relationship from a single ramp test (RT) assuming critical power (Pc) from ventilatory threshold (VT) and energy reserve (W') from total work during RT. These estimates from single RT were compared to those from a series of 4 constant power exercises (CPT) and from a series of 4 RT. Only W' from CPT was higher than from the series of RT and from single RT using VT (p <  0.05). Key words: exercise testing, critical power, anaerobic work capacity, cycle ergometry
Comparison of Aero-Bars Versus Traditional Cycling Postures on Physiological Parameters During Submaximal Cycling
Authors: Sheel A. William , Lama Iris , Potvin Patrick , Coutts Kenneth D. , McKenzie Donald C.
Published: June 2009

The purpose of this investigation was to quantify the difference in energy expenditure between traditional cycling handlebars and aero-bars during outdoor submaximal cycling. Eleven trained cyclists (age = 29.3 ± 1.9 years, weight = 69.4 ± 3.8 kg, VO2max = 58.1 ± 2.0 ml∙kg−1∙min−1) were randomly assigned a sequence of three hand positions: brake hoods (BH), drop-bars (DB), and aero-bars (AB). Subjects cycled at 30 km∙h−1 in one position for 5 minutes, then recovered until HR fell below 120 bpm. This was then repeated for the other hand positions. All cycling was completed on a standard racing bike fitted with aero-bars. Tire pressure was held constant for all trials. A portable telemetric system (Cosmed K-2) was used to measure VO2, VE and heart rate (HR) during the trials. No statistical differences were observed between AB and DB. Significant differences (p <.05) were found between BH (VE = 66.1 ± 2.7 L∙min−1; HR = 152 ± 4 bpm; VO2 = 1.56 ±.15 L∙min−1) and AB (VE = 61.3 ± 2.8 L∙min−1; HR = 146 ± 4 bpm; VO2 = 1.31 ±.10 L∙min−1). AB provides an energy savings over the traditional BH cycling posture. Key words: aerodynamic handlebars, oxygen consumption, field testing, portable telemetric system
Simultaneous Assessment of Isometric Forces in Fast- and Slow-Twitch Muscles of Single Rat Hindlimbs in Situ
Authors: Carvalho Andrew J. , McKee Nancy H.
Published: June 2009

An apparatus, consisting of a pair of small strain gauge transducers, was designed for the simultaneous assessment of isometric contractile function in two muscles, composed of a predominance of either fast- or slow-twitch fibers, and within a single rat hindlimb in situ. This facilitates assessment of mechanical performance of two separate muscles under identical conditions. In anesthetized rats (N = 10), the voltages and frequencies required to produce isometric twitch and tetanic forces from the soleus (SOL) and extensor digitorum longus (EDL) muscles were determined. The apparatus was then used to demonstrate the simultaneous assessment of forces produced by the SOL and EDL from the same hindlimbs (n = 5) during 30 min of fatigue and 30 min of recovery. With this apparatus, data collected were comparable to published data. The apparatus can be used for the simultaneous assessment of isometric contractile function and fatigue in both a fast- and a slow-twitch muscle of a single rat hindlimb in situ. Key words: model, fatigue, ischemia, soleus, extensor digitorum longus
Molecular Basis of Skeletal Muscle Regeneration
Authors: Chambers Rebecca L. , McDermott John C.
Published: June 2009

Skeletal muscle regeneration is a vital process with important implications for various muscle myopathies and adaptations to physiological overload. Few of the molecular regulatory proteins controlling this process have so far been identified. Several growth factors have defined effects on myogenic precursor cells and appear to also be involved during regeneration. In addition, factors that may be released by cells of the immune system may activate satellite cells during regeneration. Many of these growth factors are associated with signalling cascades which transmit information to the nucleus. The nuclear "receptors" that receive the incoming signals are transcription factors that interact with DNA regulatory sequences in order to modulate gene expression. Of the nuclear factors isolated so far, the immediate-early genes are associated with muscle precursor cell proliferation. This review aims to synthesize the extensive research on myogenic differentiation and relate this to research concerning the molecular regulation of skeletal muscle regeneration. Key words: satellite cells, growth factors, signal transduction, transcription factors, gene regulation, overload adaptation
Physiological Responses to Short-Duration High-Intensity Intermittent Rowing
Authors: Gullstrand Lennart
Published: June 2009

Six highly trained male elite rowers performed five sets of intermittent exercise on a rowing ergometer at competition intensity. Each set consisted of eight cycles of 15 s work and 15 s rest (15/15). Each set was repeated at 30-s intervals. Oxygen uptake and heart rate were continuously measured during each set. During the period between sets, microsamples of arterialized blood were obtained and later analyzed for lactate concentration. On two separate days, each subject also performed a 6-min bout of "all-out " exercise and a continuous incremental exercise test to fatigue on the rowing ergometer. During the intermittent rowing, no significant differences were detected in any of the measured variables between sets. Heart rate, oxygen uptake, and blood lactate averaged 89, 78, and 32%, respectively, of peak values measured during the continuous incremental exercise test. It is concluded that with rowing, the investigated 15/15 intermittent exercise model demands relatively high aerobic loading and low glycolytic activity. This exercise protocol may be considered an alternative model for training which allows rowers to work for prolonged periods of time at or slightly above competition intensity. Key words: Intermittent exercise, blood lactate, heart rate, oxygen uptake
Is Increased Voluntary Motor Activity Beneficial or Detrimental During the Period of Motor Nerve Regeneration/Reinnervation?
Authors: Soucy Martine , Seburn Kevin , Gardiner Phillip
Published: June 2009

A model of partial denervation of the rat lateral gastrocnemius was used to investigate the effects of daily activity (treadmill plus voluntary wheel exercise) on the regeneration/reinnervation of motoneurons recovering from nerve crush. It appears that increased activity has no effect on axon regeneration rate, but may be detrimental to the reinnervation process. Key words: exercise, training, denervation, motoneuron, axotomie
Peripheral Chemoreflex Drive in Moderate-Intensity Exercise
Authors: Croix Claudette M. St. , Cunningham David A. , Paterson Donald H. , Kowalchuk John M.
Published: June 2009

The purpose of this study was to measure the contribution of the peripheral chemoreceptor (pRc) to [Formula: see text] during the steady-state of moderate-intensity cycle ergometer exercise using continuous hyperoxic suppression of pRc drive, while stabilizing the drive from the central chemoreceptor by clamping end-tidal PCO2 (PETCO2) at the peak level attained during the hyperoxic period of a poikilocapnic ride. In the isocapnic protocol, the PETCO2 was maintained at a constant level by a negative feedback, open loop system. Five subjects completed four repetitions of each of the poikilocapnic and isocapnic protocols. In the poikilocapnic protocol, [Formula: see text] declined following the step into hyperoxia and then began to increase, whereas the decline in [Formula: see text] was maintained in the isocapnic protocol. However, the mean decrease in [Formula: see text] was not significantly different between the poikilocapnic (16.1 ± 5.0%) and isocapnic (14.9 ± 4.4%) protocols. These results suggest that the declining phase of [Formula: see text] is fully complete before the secondary central stimulating actions of hyperoxia on [Formula: see text] and that the pRc contributes about 15% of the drive to breathe in moderate intensity exercise. Key words: ventilatory control, carotid bodies, hyperoxia
Influence of Velocity on Agonist and Antagonist Activation in Concentric Dorsiflexion Muscle Actions
Authors: Behm David G. , Sale Digby G.
Published: June 2009

Five women and 5 men performed maximal isometric and concentric dorsiflexion actions on an isokinetic dynamometer. The concentric actions were done at 10 preset velocities ranging from 0.26 to 5.23 rad∙s−1. Electromyographic (EMG) recordings were made from one agonist (tibialis anterior [TA]) and two antagonists (saleus [S], lateral gastrocnemius [LG]). The men produced greater absolute torque than the women, but there was no gender difference in the torque/body mass ratio. The shape of the torque-velocity relation was similar in men and women and approximated, but did not match, that obtained in animal preparations or in human studies using electrical stimulation. Agonist TA activation (integrated EMG/movement time) decreased with increasing velocity over the same range of velocities as torque. Antagonist S, but not LG, activation also decreased. The S/TA activation ratio was greater in men than women. In men the S/TA ratio tended to be greater than the LG/TA ratio, whereas the converse was true for women. These data indicate that velocity influences the relative activation of two antagonists in maximal dorsiflexion muscle actions, and that there is an apparent gender difference in the relative activation of two antagonists. Key words: torque-velocity relation, coactivation, electromyography
Plasma Catecholamine Response in Trained Rats Following Hemorrhage
Authors: Trudeau François , Milot Martin
Published: June 2009

The purpose of this study was to evaluate the effect of physical training on hemorrhage-induced catecholamine release in rats. The training program consisted of swimming 5 days a week, from 15 min in the first week to 2.5 hours in the 14th week. The rats were divided into four groups. Two groups (one trained and the other untrained) were studied during hemorrhage. The third and fourth groups (one trained and the other untrained) were not subjected to hemorrhage. After 14 weeks, trained rats had a lower heart rate than untrained animals at rest (311.86 ± 8.9 vs. 361.33 ± 12.13 bpm, p <.002) for a similar body weight. The trained and untrained groups had the same blood pressure, hematocrit, and norepinephrine responses following hemorrhage. However, plasma epinephrine concentration was lower in the trained rats 15 and 25 min following hemorrhage. These results suggest a decrease of the hemorrhage-induced epinephrine secretion in trained rats. An alteration of the relationship of arterial baroreflexes and of their hormonal effectors is a potential mechanism for the reduced plasma epinephrine level in trained hemorrhaged rats. Key words: epinephrine, norepinephrine, hypotension, physical training
A Review of Effects of Hypothyroidism on Vascular Transport in Skeletal Muscle During Exercise
Authors: McAllister Richard M. , Delp Michael D. , Laughlin M. Harold
Published: June 2009

Hypothyroidism is a common thyroid disease characterized by exercise intolerance. Both exercise capacity and endurance are compromised in the hypothyroid state. Studies involving rats performing treadmill running have shown that blood flows during exercise to high oxidative, extensor-type muscles are lower in hypothyroid rats compared with those in euthyroid rats. Abnormal cardiac and vascular function appear to contribute to this hxpoperfusion. Experiments involving isolated arterial vessel segments have demonstrated that potential for constriction is normal in vessels from hypothyroid animals; however, reduced vasodilator potential is associated with hypothyroidism. Dysfunction of both endothelium and vascular smooth muscle appear to contribute to blunted potential for vasodilation. Altered ability to generate vasodilatory substances and/or changes in responses to these vasodilators may account for vascular dysfunction. It appears that impaired vascular function interacts with other factors such as poor myocardial function and changes in energy metabolism to compromise exercise tolerance. Key words: blood flow, vasodilation, endothelium, smooth muscle, cGMP
Serum Lipid Levels and Steroidal Hormones in Women Runners With Irregular Menses
Authors: Thompson Dixie L. , Snead David B. , Seip Richard L. , Weltman Judy Y. , Rogol Alan D. , Weltman Arthur
Published: June 2009

This study compared the lipid profile of women runners with menstrual cycle irregularities with their normally menstruating counterparts. Relationships among selected steroid hormones and serum lipid levels in 10 eumenorrheic (EU) and 8 oligo-/amenorrheic (O/A) women runners and 6 eumenorrheic controls (CON) were examined. Serum 17 β-estradiol (E2), progesterone (Prog), and dehydroepiandrosterone-sulfate (DHEAS) concentrations were determined in daily blood samples for 21 days, and integrated concentrations were calculated. Fasting blood samples were analyzed far total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), HDL2, HDL3, triglycerides (Trig), and apolipoproteins A-I, A-II, and B. The O/A group had significantly lower E2 and Prog than EU or CON groups. Women in the CON group had lower HDL-C and HDL3 than the runners. With all women grouped together, E2 was not significantly correlated with any measured blood lipid parameters. On the other hand, DHEAS was significantly correlated with HDL-C, HDL2, and apolipoprotein A-I. These data demonstrate that women runners, regardless of menstrual cycle status, exhibit higher HDL-C concentrations than CON and supports previous research reporting a positive association between DHEAS and HDL-C. Key words: estradiol, DHEAS, cholesterol, exercise, amenorrhea
Circulating Levels of Peripheral Blood Leucocytes and Cytokines Following Competitive Cycling
Authors: Gannon Greg A , Rhind Shawn G , Suzui Masatoshi , Sheck Pang N , Shephard Roy J.
Published: June 2009

The objective of the study was to determine if prolonged and strenuous cycling leads to a polarized cytokine response, and/or unique mobilization of circulating leucocyte populations. Resting venous blood samples were collected from 6 amateur cyclists, 24 hr before, and at 10-25 min and 150 min after completion of a 250-km road race (race time: 404 + 3.5 min). Total leucocyte counts were significantly elevated following competition. Cell counts of CD3+CD8bright+ lymphocytes were depressed by 50% 150 min after competition. A significant increase in CD4+ cells expressing the IL-2Rα chain was evident 150 min after competition IL-6 concentrations were greatly increased, both at 10-25 min and 150 min after competition. Resting TNF-a concentrations were approximately doubled at both time points after competition. Plasma levels of IFN-γ, IL-10 and IL-12 were below detection thresholds at all time points. These results suggest that performance of a 6.5 h competitive cycle-race does not induce a Type-1- or Type-2-dominated cytokine response, but one that is typical of a proinflammatory cytokine response. Key words: prolonged exercise, cyclists, immunity, cell recruitment and activation, interleukins, tumour necrosis factor, interferon
Morphological Adaptations of Neuromuscular Junctions Depend on Fiber Type
Authors: Sieck Gary C. , Prakash Y. S.
Published: June 2009

The neuromuscular junction (NMJ) forms the communicative types of motor units, which are recruited selectively to accomplish various link between motoneurons and muscle fibers. The properties of motoneurons and muscle fibers are matched in different motor behaviors. Motor units and muscle fibers can be classified based upon structural and functional properties, reflecting the essential match between motoneuron and muscle fiber. Using a three-color immunofluorescence technique combined with confocal microscopy, we examined the three-dimensional structure of pre- and postsynaptic elements of NMJs on different fiber types in the rat diaphragm muscle. On type I and IIa fibers, comprising slow-twitch and fast-twitch fatigue-resistant motor units, the structure of NMJs is far less complex than on type IIx and IIb fibers comprising fast-twitch fatigue-intermediate and fast-twitch fatigable motor units. We also found a greater extent of overlap between pre- and postsynaptic elements of NMJs on type I and IIa fibers. This review focuses on these normal phenotypic differences in NMJ properties and on the adaptations that occur under various conditions of altered use. Key words: nerve terminal, motor endplate, morphology, neuromuscular transmission, fatigue, plasticity
One-Mile Run-Walk Performance in Young Men and Women: Role of Anaerobic Metabolism
Authors: Sloniger Mark A. , Cureton Kirk J. , O'Bannon Patrice J.
Published: June 2009

The aim of this study was to evaluate the importance of anaerobic metabolism as a determinant of individual differences in performance of a 1-mile run-walk (MRW). Anaerobic capacity, percentage of anaerobic capacity used during the MRW, percentage of energy used during the MRW that was supplied through anaerobic processes, aerobic metabolic determinants of distance running performance, and MRW time were measured in 26 male and 29 female young adult nonathletes. Anaerobic processes averaged 7-8% of the energy used during the MRW. In multiple regression analyses, anaerobic capacity, and a linear combination of all three anaerobic variables contributed significantly to the prediction of MRW with the effects of gender and [Formula: see text] peak held constant, but the additional variance accounted for by the anaerobic variables was relatively small (2-7%). In conclusion, anaerobic metabolism supplies only a small portion of the energy used during the MRW, and anaerobic capacity and metabolism during the MRW do not confound its interpretation as an indicator of maximal aerobic power in a heterogeneous group of young men and women of moderate fitness level. Key words: energy metabolism, oxygen deficit, physical fitness, running performance
The Muscle Activation-Force Relationship Is Unaffected by Ischaemic Recovery
Authors: Behm David G. , St-Pierre Diane M. M.
Published: June 2009

Since reported changes in muscle activation following fatigue could be affected by alterations in muscle contractile properties, the plantar flexors' activation-force relationship was investigated before and following an isometric, intermittent, submaximal, fatigue protocol. Voluntary and evoked force and muscle activation was tested pre- and postfatigue with ischaemic and nonischaemic recovery. The muscle activation-force relationship of ischaemic and nonischaemic groups was best described by a second-order polynomial equation with similar y intercepts, slopes, and curvature of the slopes. A significantly increased muscle activation-force slope during recovery may be attributed to decreased muscle activation and not impaired muscle kinetics. The index of muscle activation immediately postfatigue was not significantly different between ischaemic and nonischaemic groups (88.5% vs. 92.7%). No significant difference in the estimate of muscle activation postfatigue with polynomials and interpolated twitch (IT) ratios (superimposed/potentiated doublets) suggested that IT ratios can be used as a general estimate of muscle inactivation following fatigue. Key words: fatigue, interpolated twitch technique, second-order polynomial, ischaemia
Temperature of Ingested Water and Thermoregulation During Moderate-Intensity Exercise
Authors: Wimer Gregory S. , Lamb David R. , Sherman William M. , Swanson Scott C.
Published: June 2009

The effect of the temperature of ingested water on the rise in core temperature (TCO) during exercise is not clear. Seven trained subjects were recruited to complete 2 hr of recumbent cycling at 51% VO2 peak in a temperate environment (Ta = 26 °C, relative humidity = 40%) on four occasions, while ingesting either no fluid (trial NF26), cold water (0.5 °C; trial CD26), cool water (19 °C; trial CL26), or warm water (38 °C; trial WA26) during the second hour of exercise. A fifth trial was conducted during which convective and radiative heat loss were reduced by raising Ta to 31 °C. During this trial, subjects ingested cold water (0.5 °C; trial CD31). When compared to WA26, over the second hour of exercise, CD26 attenuated the time-averaged changes in (TCO) and forearm blood flow and decreased whole-body sweat rate and forearm sweat rate (p < .05). Similarly, relative to WA26, the CL26 trial attenuated the time-averaged changes in TCO and reduced whole-body sweat rate (p < .05) during the second hour of exercise, but CL26 had no significant effect on forearm sweat rate or blood flow. Finally, regardless of beverage temperature, water ingestion (vs. NF26) reduced the time-averaged changes in TCO and in heat storage during the second hour of exercise (p < .05). Key words: exertion, temperature regulation, skin blood flow, body temperatures, fluid replacement
Mechanisms by Which Insulin and Muscle Contraction Stimulate Glucose Transport
Authors: Cortright Ronald N. , Dohm G. Lynis
Published: June 2009

Insulin binding to its receptor activates a tyrosine kinase that initiates a cascade of signaling events, the initial step being the tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1). Subsequent IRS-1 association and activation of phosphatidylinositiol 3-kinase (PI 3-kinase) is believed to be involved in the events leading to the translocation of glucose transporters (GLUT4) to the plasma membrane resulting in uptake of glucose into the cell. Muscle contractions increase insulin sensitivity, but also stimulate muscle glucose uptake independent of insulin. The contraction signaling pathway is distinct from the insulin pathway because the effect of insulin and contractions on glucose uptake are additive, and contractions do not increase insulin receptor kinase or PI 3-kinase activity. In contrast, studies indicating that contractions cause the translocation of GLUT4 and that both contractions and insulin-stimulated glucose transport can be blocked by calcium channel blockers suggest that the two pathways may converge. However, the possibility that two distinct GLUT4 pools may be targeted, one by insulin the other by contractions, indicates that additional research is needed to better define the mechanisms by which glucose transport is stimulated in muscle. Key words: insulin signaling, exercise
Musculoskeletal and Neurological Disabilities: Implications for Fitness Appraisal, Programming, and Counselling
Authors: Steadward Robert
Published: June 2009

not available
Nerve-Derived Trophic Factors and DNA Elements Controlling Expression of Genes Encoding Synaptic Proteins in Skeletal Muscle Fibers
Authors: Jasmin Bernard J. , Gramolini Anthony O. , Adatia Feisal A. , Angus Lindsay , Boudreau-Larivière Céline , Chan Roxanne Y.Y. , Krupa Andrea M. , Lunde John A. , Mankal Fawzi A. , Wu Jun
Published: June 2009

The neuromuscular junction represents an excellent model system for studying various critical issues in neurobiology at the molecular, cellular, and physiological levels. Our understanding of the basic events underlying synpase formation, maintenance, and plasticity has progressed considerably over the last few years primarily because of the numerous studies that have focused on this synapse and used sophisticated recombinant DNA technology. Recent data indicate that myonuclei located in the vicinity of the postsynaptic membrane are in a differential state of transcription compared to nuclei of the extrasynaptic sarcoplasm. Thus, renewal of postsynaptic membrane proteins appears to occur via a mechanism involving the local transcriptional activation of genes encoding these specialized proteins and extracellular cues originating from motoneurons. Such interaction between presynaptic nerve terminals and the postsynaptic sarcoplasm indicates that the entire signal transduction pathway is compartmentalized at the level of the neuromuscular junction. Expression of these genes appears less coregulated than originally anticipated, indicating that maintenance of the postsynaptic membrane requires the contribution of multiple extracellular signals, which ultimately urge target transcription factors to distinct DNA regulatory elements via various second messenger systems. Key words: neuromuscular junction, synapse, acetylcholinesterase, utrophin, agrin, CGRP, promoter, mRNA
Induction of S100β in Myocardium: An Intrinsic Inhibitor of Cardiac Hypertrophy
Authors: Parker Thomas G. , Tsoporis James N.
Published: June 2009

Cardiac hypertrophy induced by pressure overload and following myocardial infarction entails regulation of myocardial gene expression, recapitulating an embryonic phenotype, including activation of fetal β-myosin heavy chain and skeletal α-actin. Progressive hypertrophy and alterations in gene expression may contribute to myocardial failure. Although signaling pathways that contribute to hypertrophy development have been identified, intrinsic cardiac regulators that limit hypertrophic response have not been determined. The β subunit of S100 protein is induced in the myocardium of human subjects and an experimental rat model following myocardial infarction. Forced S100β expression in neonatal rat cardiac myocyte cultures and high level expression of S100β in transgenic mice hearts inhibit cardiac hypertrophy and the associated phenotype by modulating protein kinase C-dependent pathways. S100β expression is probably a component of the myocyte response to trophic stimulation that serves as a negative feedback mechanism to limit cellular growth and the associated alterations in gene expression. Key words: gene expression, cardiac myocytes, growth factors, heart failure, calcium-binding proteins
Reliability of Noninvasive Methods to Measure Cardiac Autonomic Function
Authors: Amara Catherine E. , Wolfe Larry A.
Published: June 2009

Cardiac autonomic modulation was examined in 10 healthy subjects (mean age = 27.8 ± 1.7) at rest (paced breathing at 12 and 16 breaths/min) and during a submaximal cycle ergometer exercise test. Heart rate variability (HRV) spectral parameters and spontaneous baroreflex (SBR) function variables showed no significant differences between mean values for any of the testing conditions. Spectral parameters and SBR function did not differ significantly between the resting conditions. Significant reliability coefficients (r = 0.59-0.73) were observed for all spectral parameters except low frequency power (r = 0.22) during 12 breaths/min, with moderately lower values during 16 breaths/min (r = 0.10-0.75) and exercise (r = 0.20-0.89). Significant reliability coefficients were observed for baroreflex sensitivity at 12 (r = 0.83) and 16 (r = 0.92) breaths/min. It was concluded that at rest. HRV spectral and SBR analyses are reliable methods for studying cardiac autonomic balance. Key words: heart rate variability, spontaneous baroreflex function, exercise
Determination of Critical Power by Pulmonary Gas Exchange
Authors: Hill David W. , Smith Jimmy C.
Published: June 2009

Although the physiological underpinnings of critical power (CP) have yet to be fully elucidated, it has been proposed that CP demarcates the heavy and severe exercise intensity domains and that each domain is associated with a different pattern of metabolic response and mechanism of fatigue. Severe intensity has been defined such that, during exercise at intensities above CP, the slow component of the [Formula: see text] response will drive [Formula: see text] to [Formula: see text] at the point of fatigue. In this Study, two parameters were derived for each of 8 participants: (a) CP, the asymptote of the relationship between power and time to exhaustion, and (b) a related parameter, CP′, the asymptote of the relationship between power and time to [Formula: see text] CP′ theoretically represents the threshold intensity above which [Formula: see text] will be elicited during exercise of sufficient duration. Participants performed two exhaustive tests at CP. There were three important findings: First, there was a practice effect on time to exhaustion at CP, and times increased 27% in the second test. Second, both CP and CP′ could be obtained with good precision. Third, and most important, CP was equal to CP′, thereby providing a physiological description of the mathematically derived CP parameter. It was concluded that [Formula: see text] cannot be elicited at intensities equal to or less than CP. Key words: cycle ergometry, endurance, exercise
Exercise in the Heat: Thermoregulatory Limitations to Performance in Humans and Horses
Authors: Lindinger Michael I.
Published: June 2009

This paper reviews the limits to exercise imposed by increases in ambient, hypothalamic, and contracting skeletal muscle temperature in humans and horses. Like humans, horses frequently compete in hot environments, yet their high mass-specific rate of heat production and low mass-specific surface area for heat dissipation places them at a great disadvantage compared to humans. Exercise in hot conditions increases the rate of body heat storage and reduces the time required to reach a critical hypothalamic temperature that results in voluntary fatigue. This critical temperature appears to be associated with dysfunction of the brain's motor control centres. The ensuing voluntary cessation of exercise appears to coincide with temperature-induced alterations in skeletal muscle function with increased requirement for anaerobic ATP provision. The duration of exercise that can be performed before this critical temperature is reached can be increased by ingesting fluids, of a volume at least equal to that lost in sweat, within 60 min prior to and during exercise. Emerging research in the area of skeletal muscle heat dissipative mechanisms involves heat-induced increases in muscle sympathetic nerve activity, producing stimulation of CIII and CIV afferent nerve stimulation, and heat-induced release of nitric oxide within skeletal muscle and skin, producing muscle and skin vasodilation. Key words: equine, skeletal muscle, cardiovascular, blood volume, fluid shift
Tissue Oxygenation by Near-Infrared Spectroscopy and Muscle Blood Flow During Isometric Contractions of the Forearm
Authors: Hicks Andrew , Mcgill Stuart , Hughson Richard L.
Published: June 2009

The relationship between tissue oxygenation measured by near-infrared spectroscopy (NIRS) and forearm muscle blood flow (FBF) measured by Doppler ultrasound was tested during isometric contractions at 10 and 30% maximal voluntary contraction (MVC) under conditions of normoxia and hypoxia (14% inspired O2). Six subjects maintained contractions at 10% MVCfor 5 min and at 30% for 2 min in both gas conditions. FBF was elevated during exercise at 10% MVC in hypoxia compared to normoxia, but there was no further increase in flow at 30% MVC. Median power frequency calculations from electromyographic recordings suggested progressive development of fatigue throughout both 10 and 30% MVC contractions. NIRS indicated no change in muscle oxygenation at 10% MVC, but deep venous blood O2 saturation was reduced in normoxia and more so in hypoxia. At 30% MVC, both NIRS and venous O2 saturation were reduced, with no effect of hypoxia on the NIRS signal. While NIRS might provide an indication of muscle oxygenation during isometric exercise, the conflicting findings for NIRS and direct venous blood sampling at 10 vs. 30% MVC suggest caution in the application of this noninvasive technique. Key words: exercise, Doppler ultrasound, venous blood. O2 saturation, hemoglobin
Etiology of Exercise-Induced Muscle Damage
Authors: Clarkson Priscilla M. , Sayers Stephen P.
Published: June 2009

Muscle damage is caused by strenuous and unaccustomed exercise, especially exercise involving eccentric muscle contractions, where muscles lengthen as they exert force. Damage can be observed both directly at the cellular level and indirectly from changes in various indices of muscle function. Several mechanisms have been offered to explain the etiology of the damage/repair process, including mechanical factors such as tension and strain, disturbances in calcium homeostasis. the inflammatory response, and the synthesis of stress proteins (heat shock proteins). Changes in muscle function following eccentric exercise have been observed at the cellular level as an impairment in the amount and action of transport proteins for glucose and lactate/H+, and at the systems level as an increase in muscle stiffness and a prolonged loss in the muscle's ability to generate force. This paper will briefly review factors involved in the damage/repair process and alterations in muscle function following eccentric exercise. Key words: eccentric exercise, inflammation, stress proteins, muscle function
Massage and Ultrasound as Therapeutic Modalities in Exercise-Induced Muscle Damage
Authors: Tiidus Peter M.
Published: June 2009

Although both massage and ultrasound treatment are used in clinical settings to enhance muscle functional recovery following exercise-induced muscle damage, there is a paucity of experimental evidence for their efficacy. Theoretically both massage and ultrasound could affect some physiological factors associated with enhancement of postexercise muscle recovery. However, the actual physiological mechanisms by which massage or ultrasound could influence postexercise muscle damage and repair are unknown. Most experimental evidence suggests that massage has little influence on muscle blood flow, clearance of "noxious" substances, recovery of postexercise muscle strength, or delayed soreness sensation. However, more data is needed before conclusions can be drawn as to the ability of massage to influence postexercise inflammatory response or various other physiological changes that characterize exercise-induced muscle damage and repair. There is even less information on the ability of ultrasound to influence physiological or functional factors associated with postexercise muscle damage. The few experiments that have been done tend to be contradictory and have yet to consider the range of ultrasound treatment parameters for therapeutic effectiveness in treating postexercise damage and influencing repair processes. Much more research is needed to determine whether either treatment modality can have any therapeutic effect on exercise-induced muscle damage and recovery of postexercise muscle function. Key words: muscle repair, inflammation, muscle soreness, muscle blood flow
Chiropractic Intervention in the Treatment of Joint and Soft Tissue Disorders
Authors: Crawford John P.
Published: June 2009

The concept of manual therapy, specifically manipulation of the bodily joints as in the practice of chiropractic, can no longer be deemed an invalid system of health care. Practiced for over 2,000 years by a variety of ancient civilizations, the art of manipulation for the purpose of correcting and restoring joint function has continued to fluorish, despite opposition. The climate, however, is changing. The art of chiropractic is increasingly being seen as a uniquely devised and administered technique whereby high velocity, low amplitude thrusting maneuvers are specifically directed by the skilled practitioner toward spinal segments and peripheral articulations in an effort to correct aberrant mechanical function. The corrections are effected while utilizing the transverse and spinal processes of individual vertebrae as contacting levers. Hippocrates is credited with the advice to, "Look well to the spine for the cause of disease," as displaced or degenerative vertebrae may irritate spinal nerve roots while exiting the intervertebral foramina and, consequently, interfere with normal nerve function. Similarly, it is a fundamental precept of chiropractic philosophy that irritation of the nervous system by mechanical, chemical, or psychogenic means is considered as causative in the development of disease. The scientific evidence associated with chiropractic intervention in the treatment and management of musculoskeletal disorders and visceral diseases is growing. This paper discusses the history, philosophy, and efficacy of joint manipulation and its influence on the development of chiropractic treatment. Key words: manipulation, mobilization, manual therapy