Showing papers in "Journal of Applied Physiology in 1998"
TL;DR: Findings strongly support the use of MRI and CT as reference methods for appendicular skeletal muscle, interstitial and subcutaneous adipose tissue measurement in vivo.
Abstract: Magnetic resonance imaging (MRI) and computerized tomography (CT) are promising reference methods for quantifying whole body and regional skeletal muscle mass. Earlier MRI and CT validation studies...
1,281 citations
TL;DR: Great training-induced gains in maximal and explosive strength in both middle-aged and elderly subjects were accompanied by large increases in the voluntary activation of the agonists, with significant reductions in the antagonist coactivation in the elderly subjects.
Abstract: Effects of 6 mo of heavy-resistance training combined with explosive exercises on neural activation of the agonist and antagonist leg extensors, muscle cross-sectional area (CSA) of the quadriceps femoris, as well as maximal and explosive strength were examined in 10 middle-aged men (M40; 42 ± 2 yr), 11 middle-aged women (W40; 39 ± 3 yr), 11 elderly men (M70; 72 ± 3 yr) and 10 elderly women (W70; 67 ± 3 yr). Maximal and explosive strength remained unaltered during a 1-mo control period with no strength training. After the 6 mo of training, maximal isometric and dynamic leg-extension strength increased by 36 ± 4 and 22 ± 2% (P < 0.001) in M40, by 36 ± 3 and 21 ± 3% (P < 0.001) in M70, by 66 ± 9 and 34 ± 4% (P < 0.001) in W40, and by 57 ± 10 and 30 ± 3% (P < 0.001) in W70, respectively. All groups showed large increases (P< 0.05–0.001) in the maximum integrated EMGs (iEMGs) of the agonist vastus lateralis and medialis. Significant (P < 0.05–0.001) increases occurred in the maximal rate of isometric force pr...
781 citations
TL;DR: It is concluded that a triaxial accelerometer provides the best assessment of activity and offers potential for large population studies.
Abstract: Eston, Roger G., Ann V. Rowlands, and David K. Ingledew.Validity of heart rate, pedometry, and accelerometry for predicting the energy cost of children’s activities.J. Appl. Physiol. 84(1): 362–371...
689 citations
TL;DR: Different lengths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses.
Abstract: Architectural properties of the triceps surae muscles were determined in vivo for six men. The ankle was positioned at 15° dorsiflexion (−15°) and 0, 15, and 30° plantar flexion, with the knee set ...
510 citations
TL;DR: A two-compartment model of the lungs is developed in an effort to explain several fundamental experimental observations of endogenous NO exchange and predicts that these relationships can be explained by significant contributions of NO in the exhaled breath from the nonexpansile airways and the expansile alveoli.
Abstract: The relatively recent detection of nitric oxide (NO) in the exhaled breath has prompted a great deal of experimentation in an effort to understand the pulmonary exchange dynamics. There has been very little progress in theoretical studies to assist in the interpretation of the experimental results. We have developed a two-compartment model of the lungs in an effort to explain several fundamental experimental observations. The model consists of a nonexpansile compartment representing the conducting airways and an expansile compartment representing the alveolar region of the lungs. Each compartment is surrounded by a layer of tissue that is capable of producing and consuming NO. Beyond the tissue barrier in each compartment is a layer of blood representing the bronchial circulation or the pulmonary circulation, which are both considered an infinite sink for NO. All parameters were estimated from data in the literature, including the production rates of NO in the tissue layers, which were estimated from expe...
478 citations
TL;DR: Results contradict the hypothesis that LH pulsatility is disrupted by exercise stress and suggest that luteinizing hormone pulsatility in women depends on energy availability.
Abstract: Loucks, A B, M Verdun, and E M Heath Low energy availability, not stress of exercise, alters LH pulsatility in exercising women J Appl Physiol84(1): 37–46, 1998—We tested two hypotheses
477 citations
TL;DR: It was concluded that relatively brief but intense sprint training can result in an increase in both glycolytic and oxidative enzyme activity, maximum short-term power output, and VO2 max.
Abstract: Our purpose was to examine the effects of sprint interval training on muscle glycolytic and oxidative enzyme activity and exercise performance. Twelve healthy men (22 +/- 2 yr of age) underwent intense interval training on a cycle ergometer for 7 wk. Training consisted of 30-s maximum sprint efforts (Wingate protocol) interspersed by 2-4 min of recovery, performed three times per week. The program began with four intervals with 4 min of recovery per session in week 1 and progressed to 10 intervals with 2.5 min of recovery per session by week 7. Peak power output and total work over repeated maximal 30-s efforts and maximal oxygen consumption (VO2 max) were measured before and after the training program. Needle biopsies were taken from vastus lateralis of nine subjects before and after the program and assayed for the maximal activity of hexokinase, total glycogen phosphorylase, phosphofructokinase, lactate dehydrogenase, citrate synthase, succinate dehydrogenase, malate dehydrogenase, and 3-hydroxyacyl-CoA dehydrogenase. The training program resulted in significant increases in peak power output, total work over 30 s, and VO2 max. Maximal enzyme activity of hexokinase, phosphofructokinase, citrate synthase, succinate dehydrogenase, and malate dehydrogenase was also significantly (P < 0.05) higher after training. It was concluded that relatively brief but intense sprint training can result in an increase in both glycolytic and oxidative enzyme activity, maximum short-term power output, and VO2 max.
463 citations
TL;DR: Both joint stiffness and limb geometry adjustments are important in adjusting leg stiffness to allow similar hopping on different surfaces, and a computer simulation was used to examine the sensitivity ofLeg stiffness to the observed changes in ankle stiffness and touchdown knee angle.
Abstract: When humans hop in place or run forward, leg stiffness is increased to offset reductions in surface stiffness, allowing the global kinematics and mechanics to remain the same on all surfaces. The purpose of the present study was to determine the mechanism for adjusting leg stiffness. Seven subjects hopped in place on surfaces of different stiffnesses (23-35,000 kN/m) while force platform, kinematic, and electromyographic data were collected. Leg stiffness approximately doubled between the most stiff surface and the least stiff surface. Over the same range of surfaces, ankle torsional stiffness increased 1.75-fold, and the knee became more extended at the time of touchdown (2.81 vs. 2.65 rad). We used a computer simulation to examine the sensitivity of leg stiffness to the observed changes in ankle stiffness and touchdown knee angle. Our model consisted of four segments (foot, shank, thigh, head-arms-trunk) interconnected by three torsional springs (ankle, knee, hip). In the model, an increase in ankle stiffness 1.75-fold caused leg stiffness to increase 1.7-fold. A change in touchdown knee angle as observed in the subjects caused leg stiffness to increase 1.3-fold. Thus both joint stiffness and limb geometry adjustments are important in adjusting leg stiffness to allow similar hopping on different surfaces.
447 citations
TL;DR: It is shown that the respiratory muscle work normally expended during maximal exercise has two significant effects on the cardiovascular system: up to 14-16% of the CO is directed to the respiratory muscles; and local reflex vasoconstriction significantly compromises blood flow to leg locomotor muscles.
Abstract: We have recently demonstrated that changes in the work of breathing during maximal exercise affect leg blood flow and leg vascular conductance (C. A. Harms, M. A. Babcock, S. R. McClaran, D. F. Peg...
441 citations
TL;DR: Results suggest that IGF-I may be acting to directly stimulate processes such as protein synthesis and satellite cell proliferation, which result in skeletal muscle hypertrophy.
Abstract: Insulin-like growth factor I (IGF-I) peptide levels have been shown to increase in overloaded skeletal muscles (G. R. Adams and F. Haddad. J. Appl. Physiol. 81: 2509-2516, 1996). In that study, the increase in IGF-I was found to precede measurable increases in muscle protein and was correlated with an increase in muscle DNA content. The present study was undertaken to test the hypothesis that direct IGF-I infusion would result in an increase in muscle DNA as well as in various measurements of muscle size. Either 0.9% saline or nonsystemic doses of IGF-I were infused directly into a non-weight-bearing muscle of rats, the tibialis anterior (TA), via a fenestrated catheter attached to a subcutaneous miniosmotic pump. Saline infusion had no effect on the mass, protein content, or DNA content of TA muscles. Local IGF-I infusion had no effect on body or heart weight. The absolute weight of the infused TA muscles was approximately 9% greater (P < 0.05) than that of the contralateral TA muscles. IGF-I infusion resulted in significant increases in the total protein and DNA content of TA muscles (P < 0.05). As a result of these coordinated changes, the DNA-to-protein ratio of the hypertrophied TA was similar to that of the contralateral muscles. These results suggest that IGF-I may be acting to directly stimulate processes such as protein synthesis and satellite cell proliferation, which result in skeletal muscle hypertrophy.
417 citations
TL;DR: It was concluded that exercise-heat tolerance in this uncompensable heat-stress environment is not influenced by short-term heat acclimation but is significantly improved by long-term aerobic fitness.
Abstract: The purpose of the present study was to determine the separate and combined effects of aerobic fitness, short-term heat acclimation, and hypohydration on tolerance during light exercise while wearing nuclear, biological, and chemical protective clothing in the heat (40 degrees C, 30% relative humidity). Men who were moderately fit [(MF); 55 ml . kg-1 . min-1 maximal O2 consumption; n = 8] were tested while they were euhydrated or hypohydrated by approximately 2.5% of body mass through exercise and fluid restriction the day preceding the trials. Tests were conducted before and after 2 wk of daily heat acclimation (1-h treadmill exercise at 40 degrees C, 30% relative humidity, while wearing the nuclear, biological, and chemical protective clothing). Heat acclimation increased sweat rate and decreased skin temperature and rectal temperature (Tre) in HF subjects but had no effect on tolerance time (TT). MF subjects increased sweat rate but did not alter heart rate, Tre, or TT. In both MF and HF groups, hypohydration significantly increased Tre and heart rate and decreased the respiratory exchange ratio and the TT regardless of acclimation state. Overall, the rate of rise of skin temperature was less, while DeltaTre, the rate of rise of Tre, and the TT were greater in HF than in MF subjects. It was concluded that exercise-heat tolerance in this uncompensable heat-stress environment is not influenced by short-term heat acclimation but is significantly improved by long-term aerobic fitness.
TL;DR: Current data indicate that major improvements in aerosol particle performance may also be achieved by lowering particle mass density and increasing particle size, since large, porous particles display less tendency to agglomerate than (conventional) small and nonporous particles.
Abstract: The ability to deliver proteins and peptides to the systemic circulation by inhalation has contributed to a rise in the number of inhalation therapies under investigation. For most of these therapi...
TL;DR: Changing changes in grip strength over a follow-up period of approximately 27 yr was described and the associations of rate of strength decline with weight change and chronic conditions were studied to help prevent steep strength decrease and poor absolute strength.
Abstract: The aim of this study was to describe changes in grip strength over a follow-up period of ∼27 yr and to study the associations of rate of strength decline with weight change and chronic conditions....
TL;DR: It is shown that Pennes used an inappropriate procedure to analyze his data and that, when the data are analyzed in a more rigorous manner, they support his theory.
Abstract: A paper published by Harry H. Pennes in Volume 1 of theJournal of Applied Physiology defined the theoretical basis for a considerable body of analysis performed by many investigators during the ens...
TL;DR: The muscle response after the short-lasting consecutive maximum jumps on the sledge apparatus may involve two distinct mechanisms acting in opposite directions, which indicates that the contractile mechanism seems to be potentiated through a shorter Ca2+ transient and faster cross-bridge cycling, as implied by twitch changes.
Abstract: Strojnik, V., and P. V. Komi. Neuromuscular fatigue after maximal stretch-shortening cycle exercise. J. Appl. Physiol. 84(1): 344–350, 1998.—To examine some possible sites of fatigue during short-l...
TL;DR: The view that different priorities are placed on lipid and carbohydrate oxidation during exercise in men and women is supported and that these gender-based differences extend to the catecholamine response to exercise.
Abstract: This study aimed to determine gender-based differences in fuel metabolism in response to long-duration exercise. Fuel oxidation and the metabolic response to exercise were compared in men (n = 14) ...
TL;DR: After a 28-day altitude training camp, a significant improvement in 5,000-m run performance is, in part, dependent on living at a highenough altitude to achieve a large acute increase in Epo, sufficient to increase the total red cell volume and V(O2)max, and training at a low enough altitude to maintain interval training velocity and O2 flux near sea-level values.
Abstract: Moderate-altitude living (2,500 m), combined with low-altitude training (1,250 m) (i.e., live high-train low), results in a significantly greater improvement in maximal O2 uptake (V˙o 2 max) and pe...
TL;DR: Female hormones (possibly progesterone) have a substantial impact on upper airway dilator muscle activity and there was a significant increase in EMGgg in the postmenopausal group restudied after hormone therapy.
Abstract: Obstructive sleep apnea is a disorder with a strong male predominance. One possible explanation could be an effect of female hormones on pharyngeal dilator muscle activity. Therefore, we determined the level of awake genioglossus electromyogram (EMGgg) and upper airway resistance in 12 pre- and 12 postmenopausal women under basal conditions and during the application of an inspiratory resistive load (25 cmH2O . l-1 . s). In addition, a subgroup of eight postmenopausal women were studied a second time after 2 wk of combined estrogen and progesterone replacement in standard doses. Peak phasic and tonic genioglossus activity, expressed as a percentage of maximum, were highest in the luteal phase of the menstrual cycle (phasic 23.9 +/- 3.8%, tonic 10.2 +/- 1.0%), followed by the follicular phase (phasic 15.5 +/- 2.2%, tonic 7.3 +/- 0.8%), and were lowest in the postmenopausal group (phasic 11.3 +/- 1.6%, tonic of 5.0 +/- 0.6), whereas upper airway resistance did not differ. There was a weak but significant positive correlation between progesterone levels and both peak phasic (P < 0.05) and tonic (P < 0.01) EMGgg. Finally, there was a significant increase in EMGgg in the postmenopausal group restudied after hormone therapy. In conclusion, female hormones (possibly progesterone) have a substantial impact on upper airway dilator muscle activity.
TL;DR: It is demonstrated that this sigmoidal equation can fit with excellent precision inflation and deflation P-V curves of normal lungs and of lungs with alveolar derecruitment and/or a region of gas trapping while yielding robust and physiologically useful parameters.
Abstract: Venegas, Jose G., R. Scott Harris, and Brett A. Simon.A comprehensive equation for the pulmonary pressure-volume curve.J. Appl. Physiol. 84(1): 389–395, 1998.—Quantification of pulmonary pressure-v...
TL;DR: Cutaneous active vasodilation requires functional NO synthase to achieve full expression as achieved by perfusion with the NO donor nitroprusside through the microdialysis probes, and L-NAME had no effect on sweat rate.
Abstract: Whether nitric oxide (NO) is involved in cutaneous active vasodilation during hyperthermia in humans is unclear. We tested for a role of NO in this process during heat stress (water-perfused suits)...
TL;DR: It is concluded that physiological factors, particularly age and gender, have significant impact on BRS in healthy subjects and values that have been proposed to be useful in identifying postinfarction patients at high risk of sudden death are frequently found inhealthy subjects.
Abstract: Laitinen, Tomi, Juha Hartikainen, Esko Vanninen, Leo Niskanen, Ghislaine Geelen, and Esko Lansimies. Age and gender dependency of baroreflex sensitivity in healthy subjects.J. Appl. Physiol. 84(2):...
TL;DR: It is demonstrated that the large variation in individual internal fat content cannot be predicted from either indirect methods or direct imaging techniques, such as MRI or computed tomography, on the basis of a single-slice sampling strategy.
Abstract: In this study we assessed different magnetic resonance imaging (MRI) scanning regimes and examined some of the assumptions commonly made for measuring body fat content by MRI. Whole body MRI was used to quantify and study different body fat depots in 67 women. The whole body MRI results showed that there was a significant variation in the percentage of total internal, as well as visceral, adipose tissue across a range of adiposity, which could not be predicted from total body fat and/or subcutaneous fat. Furthermore, variation in the amount of total, subcutaneous, and visceral adipose tissue was not related to standard anthropometric measurements such as skinfold measurements, body mass index, and waist-to-hip ratio. Finally, we show for the first time subjects with a percent body fat close to the theoretical maximum (68%). This study demonstrates that the large variation in individual internal fat content cannot be predicted from either indirect methods or direct imaging techniques, such as MRI or computed tomography, on the basis of a single-slice sampling strategy.
TL;DR: One cannot extrapolate the effects of Caf to Cof; there must be a component(s) of Cof that moderates the actions of Caf.
Abstract: Caffeine (Caf) ingestion increases plasma epinephrine (Epi) and exercise endurance; these results are frequently transferred to coffee (Cof) consumption. We examined the impact of ingestion of the ...
TL;DR: Comparable reductions in Po and K+-induced force, and minor reductions in the maximal SR Ca2+ release rate, suggest that the E-C coupling defect site is located at the t tubule-SR interface immediately after injury.
Abstract: The objectives of this research were to determine the contribution of excitation-contraction (E-C) coupling failure to the decrement in maximal isometric tetanic force (Po) in mouse extensor digitorum longus (EDL) muscles after eccentric contractions and to elucidate possible mechanisms. The left anterior crural muscles of female ICR mice (n = 164) were injured in vivo with 150 eccentric contractions. Po, caffeine-, 4-chloro-m-cresol-, and K+-induced contracture forces, sarcoplasmic reticulum (SR) Ca2+ release and uptake rates, and intracellular Ca2+ concentration ([Ca2+]i) were then measured in vitro in injured and contralateral control EDL muscles at various times after injury up to 14 days. On the basis of the disproportional reduction in Po (approximately 51%) compared with caffeine-induced force (approximately 11-21%), we estimate that E-C coupling failure can explain 57-75% of the Po decrement from 0 to 5 days postinjury. Comparable reductions in Po and K+-induced force (51%), and minor reductions (0-6%) in the maximal SR Ca2+ release rate, suggest that the E-C coupling defect site is located at the t tubule-SR interface immediately after injury. Confocal laser scanning microscopy indicated that resting [Ca2+]i was elevated and peak tetanic [Ca2+]i was reduced, whereas peak 4-chloro-m-cresol-induced [Ca2+]i was unchanged immediately after injury. By 3 days postinjury, 4-chloro-m-cresol-induced [Ca2+]i became depressed, probably because of decreased SR Ca2+ release and uptake rates (17-31%). These data indicate that the decrease in Po during the first several days after injury primarily stems from a failure in the E-C coupling process.
TL;DR: It is concluded that addition of relatively low amounts of Caf to CES improves performance and that postexercise urinary Caf concentration remained low.
Abstract: The effect of addition of different dosages of caffeine (Caf) to a carbohydrate-electrolyte solution (CES) on metabolism, Caf excretion, and performance was examined. Subjects (n = 15) ingested 8 m...
TL;DR: In the present experimental model, elimination of any delay in O2 delivery during the rest-to-contraction transition did not affect muscle V(O2) kinetics, which suggests that this kinetics was mainly set by an intrinsic inertia of oxidative metabolism.
Abstract: The mechanism(s) limiting muscle O2 uptake (V˙o 2) kinetics was investigated in isolated canine gastrocnemius muscles (n = 7) during transitions from rest to 3 min of electrically stimulated isomet...
TL;DR: Results indicate that REx prevented BRU-induced myofiber atrophy and also maintained training-specific strength, and may prove useful in prescribing exercise for astronauts in microgravity.
Abstract: Because resistance exercise (REx) and bed-rest unloading (BRU) are associated with opposing adaptations, our purpose was to test the efficacy of REx against the effects of 14 days of BRU on the knee-extensor muscle group. Sixteen healthy men were randomly assigned to no exercise (NoEx; n = 8) or REx (n = 8). REx performed five sets of leg press exercise with 80-85% of one repetition maximum (1 RM) every other day during BRU. Muscle samples were removed from the vastus lateralis muscle by percutaneous needle biopsy. Myofiber distribution was determined immunohistochemically with three monoclonal antibodies against myosin heavy chain (MHC) isoforms (I, IIa, IIx). MHC distribution was further assessed by quantitative gel electrophoresis. Dynamic 1-RM leg press and unilateral maximum voluntary isometric contraction (MVC) were determined. Maximal neural activation (root mean squared electromyogram) and rate of torque development (RTD) were measured during MVC. Reductions (P < 0.05) in type I (15%) and type II (17%) myofiber cross-sectional areas were found in NoEx but not in REx. Electrophoresis revealed no changes in MHC isoform distribution. The percentage of type IIx myofibers decreased (P < 0.05) in REx from 9 to 2% and did not change in NoEx. 1 RM was reduced (P < 0.05) by 9% in NoEx but was unchanged in REx. MVC fell by 15 and 13% in NoEx and REx, respectively. The agonist-to-antagonist root mean squared electromyogram ratio decreased (P < 0.05) 19% in REx. RTD slowed (P < 0.05) by 54% in NoEx only. Results indicate that REx prevented BRU-induced myofiber atrophy and also maintained training-specific strength. Unlike spaceflight, BRU did not induce shifts in myosin phenotype. The reported benefits of REx may prove useful in prescribing exercise for astronauts in microgravity.
TL;DR: It can be concluded that, in isometric contractions of a human muscle, mechanical work, some of which is absorbed by the tendinous tissue, is generated by the shortening of muscle fibers and that ultrasonography can be used to determine the stiffness and Young's modulus for human tendons.
Abstract: Fascicle length, pennation angle, and tendon elongation of the human tibialis anterior were measured in vivo by ultrasonography. Subjects (n = 9) were requested to develop isometric dorsiflexion to...
TL;DR: A force treadmill was constructed to measure the vertical, horizontal and lateral components of the ground-reaction forces and moments exerted by walking and running humans and it indicated that the force treadmill recorded Fz, Fy, Mx and My ground- Reaction Forces and moments accurately.
Abstract: We constructed a force treadmill to measure the vertical, horizontal and lateral components of the ground-reaction forces (F z , F y , F x , respectively) and the ground-reaction force moments (M z...
TL;DR: It is indicated that leg blood flow and vascular conductance during cycle ergometer exercise are significantly lower in older endurance-trained men in comparison to their younger counterparts.
Abstract: It is currently unclear whether aging alters the perfusion of active muscles during large-muscle dynamic exercise in humans. To study this issue, direct measurements of leg blood flow (femoral vein thermodilution) and systemic arterial pressure during submaximal cycle ergometry (70, 140, and 210 W) were compared between six younger (Y; 22-30 yr) and six older (O; 55-68 yr) chronically endurance-trained men. Whole body O2 uptake, ventilation, and arterial and femoral venous samples for blood-gas, catecholamine, and lactate determinations were also obtained. Training duration (min/day), estimated leg muscle mass (dual-energy X-ray absorptiometry; Y, 21.5 +/- 1.2 vs. O, 19.9 +/- 0.9 kg), and blood hemoglobin concentration (Y, 14.9 +/- 0.4 vs. O, 14.7 +/- 0.2 g/dl) did not significantly differ (P > 0.05) between groups. Leg blood flow, leg vascular conductance, and femoral venous O2 saturation were approximately 20-30% lower in the older men at each work rate (all P < 0.05), despite similar levels of whole body O2 uptake. At 210 W, leg norepinephrine spillover rates and femoral venous lactate concentrations were more than twofold higher in the older men. Pulmonary ventilation was also higher in the older men at 140 (+24%) and 210 (+39%) W. These results indicate that leg blood flow and vascular conductance during cycle ergometer exercise are significantly lower in older endurance-trained men in comparison to their younger counterparts. The mechanisms responsible for this phenomenon and the extent to which they operate in other groups of older subjects deserve further attention.