Showing papers in "Canadian Journal of Applied Physiology-revue Canadienne De Physiologie Appliquee in 1997"
TL;DR: Compared to single set (1S) versus multiple set (3S) heavy-resistance exercise protocols, higher volumes of total work produce significantly greater increases in circulating anabolic hormones during the recovery phase following exercise.
Abstract: 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...
206 citations
TL;DR: This brief review attempts to summarize a number of studies on the delineation, development, and distribution of human skeletal muscle fiber types.
Abstract: 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...
169 citations
TL;DR: The results of the present work indicate that MU behaviour during voluntary contractions is different in the tibialis anterior and in the adductor pollicis.
Abstract: The present work was carried out to analyse the properties and behaviour of Tibialis anterior motor units (MUs) during voluntary contractions in humans. A total of 528 single MU mechanical properties was recorded in 10 subjects by means of the spike-triggered averaging (STA) technique. MU recruitment thresholds and discharge frequencies were recorded during linearly increasing maximal voluntary contraction (MVC). The results indicate a mean (+/- SD) MU torque of 25.5 +/- 21.5 mN.m. and a mean time-to-peak of 45.6 +/- 13.6 ms. A comparison of the average MU twitch torque with that of the muscle allowed an estimate of about 300 MUs in the Tibialis anterior. A positive linear relationship was recorded between the MU twitch torque and the recruitment threshold. The mean minimal and maximal discharge frequencies of MUs were 8.4 +/- 3.0 Hz and 33.2 +/- 14.7 Hz, respectively. The results of the present work indicate that MU behaviour during voluntary contractions is different in the tibialis anterior and in the adductor pollicis.
122 citations
TL;DR: 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.
Abstract: 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 mal...
104 citations
TL;DR: It is suggested that isometric training atmaximum strength (100% Fmax) is a more effective form of supplementary training to increase power production than no load training at maximum velocity.
Abstract: 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 ...
93 citations
TL;DR: A new measurement of tissue capillarity, designed specifically for use on non-perfusion fixed muscle tissue (i.e., that obtained via needle biopsy), is presented that describes the capillary supply from this perspective.
Abstract: The surface area of contact between capillaries and muscle fibres has been suggested to be the site of greatest oxygen flux density in the movement of oxygen from the capillaries to the muscle fibres. A new measurement of tissue capillarity, designed specifically for use on non-perfusion fixed muscle tissue (i.e., that obtained via needle biopsy), is presented that describes the capillary supply from this perspective. The Capillary-to-Fibre Perimeter Exchange Index (the CFPE Index) is derived as the quotient of the individual capillary-to-fibre ratio (i.e., the capillary-to-fibre ratio calculated for each fibre individually) and the fibre perimeter. This method is suggested to provide a means of quantitating potential alterations in the capacity for oxygen flux (e.g., as may occur in response to a training intervention) and any carrier- or receptor-mediated aspect of blood-tissue exchange between the capillaries and muscle-fibres (e.g., insulin or glucose delivery).
84 citations
TL;DR: It is demonstrated 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.
Abstract: 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% VO2max. 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 +/- 0.34 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.
76 citations
TL;DR: The 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 cytokines response.
Abstract: 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-...
65 citations
TL;DR: This article illustrates how recent findings suggest a dual role of ROS generated during muscle contractions may be complemented by the synthesis of inducible heat-stress proteins (HSPs).
Abstract: Definitive characterization of the mechanisms of skeletal muscle fatigue is still an area of active investigation. One emerging theory concerns a role for the reactive oxygen species (ROS) produced primarily as a consequence of elevated rates of mitochondrial respiration. It has been theorized that the long-lasting effects of low-frequency fatigue (LFF) can be attributed to disruption of some stage of the excitation contraction coupling (ECC) process. Recent evidence suggests that ROS likely denature one or more proteins directly associated with the sarcoplasmic reticulum (SR) Ca2+ release mechanism. Given the potential of ROS to damage intracellular proteins during subsequent bouts of muscle contractions, the capacity of preexisting antioxidant pathways may be complemented by the synthesis of inducible heat-stress proteins (HSPs). HSPs collectively function to maintain cellular protein conformation during stressful proteotoxic insults. The goal of this article is to illustrate how recent findings suggest...
63 citations
TL;DR: Regardless of beverage temperature, water ingestion reduced the time-averaged changes in Tco and in heat storage during the second hour of exercise, but CL26 had no significant effect on forearm sweat rate or blood flow.
Abstract: 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% VO2peak in a temperate environment (Ta = 26 degrees C, relative humidity = 40%) on four occasions, while ingesting either no fluid (trial NF26), cold water (0.5 degree C; trial CD26), cool water (19 degrees C; trial CL26), or warm water (38 degrees 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 degrees C. During this trial, subjects ingested cold water (0.5 degree 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).
61 citations
TL;DR: 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.
Abstract: 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.
TL;DR: Creatine supplementation had no effect on subjects' ability to reproduce or maintain a high percentage of PP during the second bout of exercise and the absolute time to fatigue (TTF) was compared pre- versus postsupplementation.
Abstract: The purpose of this study was to determine the effects of creatine supplementation on the ability to reproduce and maintain a high percentage of peak power output during the second of two bouts of ...
TL;DR: 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.
Abstract: 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.
TL;DR: 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.
Abstract: 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 ...
TL;DR: The analysis of amylase concentration in total saliva during exercise might be used as a valid new method for determining anaerobic threshold, and there existed a high correlation between AT and Tsa.
Abstract: The purpose of this study was to determine the anaerobic threshold from analysis of amylase concentration in total saliva during a laboratory exercise test. Each of 20 healthy young men performed b...
TL;DR: Hypoxia does not stimulate ventilation when carbon dioxide is below its peripheral-chemoreflex threshold, and ventilation did not increase, despite a progressive fall in end-tidal oxygen partial pressure.
Abstract: The ventilatory response to acute progressive hypoxia below the carbon dioxide threshold using rebreathing was investigated. Nine subjects rebreathed after 5 min of hyperventilation to lower carbon...
TL;DR: Normal phenotypic differences in NMJ properties and on the adaptations that occur under various conditions of altered use are focused on.
Abstract: 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 mo...
TL;DR: The study of lactate transport in skeletal muscle had until recently been hampered by the lack of suitable sarcolemmal vesicle preparations, but the MCT1 expression patterns in metabolically heterogeneous skeletal suggests 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.
Abstract: 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 suggests 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.
TL;DR: The 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, suggesting that 1 hr of moderate exercise increases protein oxidation by about 29-45 g.
Abstract: 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 suggests that 1 hr of moderate exercise increases protein oxidation by about 29-45 g, representing approximately 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.
TL;DR: Pulmonary function did not limit performance based on the very slow decline in VEmax and the normal FEV1.0, and the decay in HRmax was better described by a linear model, resulting in an extremely slow tau.
Abstract: The purpose of the present investigation was to describe, for a subset of a large random survey of men and women, restricted to the ages of 55 to 85 years, the physiological decay pattern for aerobic fitness and contributing factors of cardiovascular and pulmonary function. The time course of the age-related changes in maximal oxygen uptake (VO2max), ventilatory threshold (TVE), maximal ventilation (VEmax), maximal heart rate (HRmax), and O2 pulse (VO2max/HRmax) were examined by fitting the data to a decaying exponential model by use of a least-squares parameter estimation technique. The time constant (tau) was used to describe the rate of decline. The women showed a much slower decline in VO2max (tau = 47.4 years) and TVE (tau = 83.3 years) than the men (tau = 20.8 and 15.4 years, respectively). There was a significant age-related decrease in body weight (0.45 kg.yr-1) in the men, whereas the women showed no change. Pulmonary function did not limit performance based on the very slow decline in VEmax and the normal FEV1.0. The decay in HRmax was better described by a linear model, resulting in an extremely slow tau. Maximal O2 pulse clearly exhibited an exponential decay, with a shorter tau (tau men = 13.5 years; tau women = 28.5 years) than any other variable.
TL;DR: A mathematical model that evaluates the Conconi test and predicts 10-km race time and heart rate deflection determined from a laboratory test is validated and is closely related to traditional laboratory measures.
Abstract: The purpose of this study was to validate a mathematical model (MM) that evaluates the Conconi test and predicts 10-km race time. In addition, the relationship between ventilatory threshold (Tvent) determined from a laboratory test and heart rate deflection (HRd) from the Conconi test were examined. Seventeen trained runners performed the Conconi test, and performance times were predicted using a MM based on a logistics function. A correlational analysis indicated a highly significant relationship (r = .98, p < .01) between MM predicted time and actual time. Significant relationships were found between velocity at Tvent and HRd (r = .95, p < .01), and predicted times from each method (r = .96, p < .01). Heart rates from Tvent and HRd were also related (r = .79, p < .01). These results suggest that a MM of the Conconi test is a valid method of predicting 10-km performance and is closely related to traditional laboratory measures.
TL;DR: The magnitude of variation is such that it is vital to obtain experimental and control data at identical time points in both acute and chronic studies of exercise and immune function.
Abstract: Biological rhythms can influence both exercise tolerance and immune function. Most studies have focussed upon circadian rhythms, but some circaseptan, circatrigintan, and circannual cycles have also been described. Rhythms may have an endogenous or an exogenous basis. Endogenous rhythms originate in the cells of the suprachiasmatic nucleus. Impulses from this region pass to the pineal gland, where they regulate the production of melatonin, a compound that modulates the sleep/wakefulness cycle. Endocrine, physiological, and psychological parameters all show evidence of periodicity. Most components of the immune system, both cellular and humoral, also show large rhythmic changes. It is not yet clear how far such periodicity is secondary to changes in other body systems. Nevertheless, the magnitude of variation is such that it is vital to obtain experimental and control data at identical time points in both acute and chronic studies of exercise and immune function. Disturbance of the sleep/wakefulness cycle can constitute a form of stress, with adverse consequence for immune function.
TL;DR: The data indicate that aerobic fitness assessments do not indicate the ability to recover after intermittent, high-intensity exercise in endurance-trained cyclists.
Abstract: This investigation examined the relationship between several different aerobic fitness test results and measurements of metabolic recovery from intermittent, high-intensity exercise in 16 male cycl...
TL;DR: The results of the study suggest that each subject has a most efficient crank arm length, but it does not appear that optimal crank armlength can be predicted by leg length.
Abstract: 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...
TL;DR: It is demonstrated that in older men, the ventilatory responses to CO2 in euoxia and hyperoxia are similar to younger men, while in hypoxia the ventILatory responses are characterised by smaller gain terms.
Abstract: The purpose of this study was to examine the ventilatory response to carbon dioxide (CO2) in young and older men. Six square-wave steps of end-tidal CO2 (PETCO2) were administered in euoxia (PETO2 = 100 torr), hyperoxia (PETO2 = 500 torr), and mild hypoxia (PETO2 = 60 torr) The peripheral and central chemoreflex loops were described by three parameters including a gain (gp and gc), time constant of the response(τp, τc), and a time delay (Tp, Tc), respectively. The young and older men showed similar characteristics for Tp and Tc, with Tp, being 3 to 5 s shorter than Tc. In hypoxia, the ventilatory responses of the old group were characterised by a significantly smaller gc and a smaller gp. In hypoxia, τc was significantly shortened from its euoxic value in the young group, but not in the old group. Thus, this study demonstrated that in older men, the ventilatory responses to CO2 in euoxia and hyperoxia are similar to younger men, while in hypoxia the ventilatory responses are characterised by smaller gain ...
TL;DR: It is demonstrated 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.
Abstract: 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 beta-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 for total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), HDL2, HDL3, triglycerides (Trig), and apolipoproteins A-1, 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.
TL;DR: It was concluded that short-term, high-intensity exercise training improves LVDF and is tolerated well in older subjects, and that the calculated changes in PV and aerobic power are similar to those observed previously in a younger population.
Abstract: We evaluated the effects of short-term, high-intensity exercise training and detraining on resting left ventricular diastolic function (LVDF) and maximal aerobic power (VO2max) in 7 sedentary older (age = 68 +/- 4 years) men (n = 5) and women (n = 2). Training consisted of cycling for 60 min with power output set at 70% (Day 1), 80% (Day 2), and 90% (Days 3-5) of the pretraining peak work rate. Detraining consisted of a return to regular exercise habits. LVDF increased 10% in the early (E) flow velocity, decreased 18% in the late (A) flow velocity wave, and decreased 31% in the isovolumic relaxation time. VO2max was increased 12% while plasma volume (PV) increased 10% following training and returned to baseline after detraining. The exercise-induced change in VO2max was directly related to the change in E/A (r = .52) and indirectly related to the change in IVRT (r = -.62). It was concluded that short-term, high-intensity exercise training improves LVDF and is tolerated well in older subjects, and that the calculated changes in PV and aerobic power are similar to those observed previously in a younger population.
TL;DR: The plantar flexors' activation-force relationship was investigated before and following an isometric, intermittent, submaximal fatigue protocol and no significant difference in the estimate of muscle activation postfatigue with polynomials and interpolated twitch (IT) ratios suggested that IT ratios can be used as a general estimate of Muscle inactivation following fatigue.
Abstract: Les modifications de l'activation d'un muscle epuise peuvent etre affectees, semble-t-il, par la variation des proprietes contractiles; des lors, le but de cette etude est d'etablir la relation activation-force des flechisseurs plantaires avant et apres un effort isometrique sous-maximal intermittent jusqu'a epuisement. La relation activation-force est analysee dans des conditions d'activation volontaire et electrique, avant et apres l'effort et durant la periode de recuperation, avec et sans ischemie. La relation activation-force du groupe sous ischemie et de celui sans ischemie est bien decrite par une equation quadratique polynomiale aux ordonnees a l'origine, pentes et courbures respectives similaires. Durant la recuperation, l'augmentation significative de la pente semble attribuable a une reduction de l'activation plutot qu'a une defaillance de la cinetique. Immediatement apres l'effort, l'index d 'activation musculaire ne differe statistiquement pas d'un groupe a l'autre (88,5% vs. 92,7%). Les estimations post-effort de l'activation musculaire au moyen des equations et des ratios (superposees/doublets potenties) de secousse interpolee (IT) ne sont significativement pas differentes ; les ratios IT peuvent donc servir d'estimateur global de l'inactivation d'un muscle epuise.
TL;DR: 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.
Abstract: 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...
TL;DR: The variation in physiological and subjective responses to lifting with menstrual cycle phase did not reach statistical significance, however, the HR response to lifting was elevated by approximately 10 beats x min-1 in the postovulatory phases of the cycle.
Abstract: Cyclic variations in physiological and endocrinological baselines are known to be consistent with the eumenorrheic (healthy) menstrual cycle. The aim of this study was to examine the interaction of these variations with the physiological responses to repeated lifting. Sixteen females visited the laboratory in each of five phases of their menstrual cycle. During each visit, subjects performed a repetitive lifting task, lifting a weighted box, from knee to shoulder height, at six repetitions per minute for 10 min. Oxygen consumption, minute ventilation, heart rate (HR), and perceived exertion were monitored throughout the task. The variation in physiological and subjective responses to lifting with menstrual cycle phase did not reach statistical significance (p > .05). However, the HR response to lifting was elevated by approximately 10 beats x min-1 in the postovulatory phases of the cycle (effect size > 0.61). Although the impact of the menstrual cycle upon lifting performance is minimal, alterations in HR must be taken into account in determining new international standards for manual handling.