Showing papers in "Journal of Applied Physiology in 1999"
TL;DR: It is demonstrated that high internal body temperature per se causes fatigue in trained subjects during prolonged exercise in uncompensable hot environments and time to exhaustion in hot environments is inversely related to the initial temperature and directly related toThe rate of heat storage.
Abstract: We investigated whether fatigue during prolonged exercise in uncompensable hot environments occurred at the same critical level of hyperthermia when the initial value and the rate of increase in bo...
1,093 citations
TL;DR: The trainability of VO(2max) is highly familial and includes a significant genetic component, and the most parsimonious models yielded a maximal heritability estimate of 47%.
Abstract: The aim of this study was to test the hypothesis that individual differences in the response of maximal O2 uptake (V˙o 2 max) to a standardized training program are characterized by familial aggreg...
796 citations
TL;DR: A dynamic model predicting human thermal responses in cold, cool, neutral, warm, and hot environments is presented in a two-part study.
Abstract: A dynamic model predicting human thermal responses in cold, cool, neutral, warm, and hot environments is presented in a two-part study. This, the first paper, is concerned with aspects of the passi...
690 citations
TL;DR: It is suggested that mild EIAH be defined as an arterial O(2) saturation of 93-95% (or 3-4% 25-30 Torr) and inadequate compensatory hyperventilatory response, as do acid- and temperature-induced shifts in O( 2) dissociation at any given arterial PO(2).
Abstract: Exercise-induced arterial hypoxemia (EIAH) at or near sea level is now recognized to occur in a significant number of fit, healthy subjects of both genders and of varying ages. Our review aims to d...
646 citations
TL;DR: Regression analysis showed that MQ, defined as PT per unit of MM, was significantly higher in the arm than in the leg across age in both genders, and the magnitude of this effect depends on the muscle group studied and the type of muscle action used to assess strength.
Abstract: To determine the differences between arm and leg muscle quality (MQ) across the adult life span in men and women, concentric (Con) and eccentric (Ecc) peak torque (PT) were measured in 703 subjects...
621 citations
TL;DR: To investigate the effects of simultaneous explosive-strength and endurance training on physical performance characteristics, 10 experimental (E) and 8 control (C) endurance athletes trained for 9 months to improve their explosive strength and endurance performance.
Abstract: To investigate the effects of simultaneous explosive-strength and endurance training on physical performance characteristics, 10 experimental (E) and 8 control (C) endurance athletes trained for 9 ...
590 citations
TL;DR: Evidence is presented that the mechanism that decreases the sensitivity of short-latency reflexes can be activated because of RPS, and the origin of this system seems to be a reduction in the activity of the large-diameter afferents, resulting from the reduced sensitivity of the muscle spindles to repeated stretch.
Abstract: Experiments were carried out to test the effect of prolonged and repeated passive stretching (RPS) of the triceps surae muscle on reflex sensitivity. The results demonstrated a clear deterioration ...
535 citations
TL;DR: Chronic chemical activation of AMPK results in increases in GLUT-4 protein, hexokinase activity, and glycogen, similarly to those induced by endurance training.
Abstract: This study was designed to determine whether chronic chemical activation of AMP-activated protein kinase (AMPK) would increase glucose transporter GLUT-4 and hexokinase in muscles similarly to peri...
514 citations
TL;DR: The data indicate that older men do respond with an enhanced hormonal profile in the early phase of a resistance training program, but the response is different from that of younger men.
Abstract: To examine the adaptations of the endocrine system to heavy-resistance training in younger vs. older men, two groups of men (30 and 62 yr old) participated in a 10-wk periodized strength-power training program. Blood was obtained before, immediately after, and 5, 15, and 30 min after exercise at rest before and after training and at rest at -3, 0, 6, and 10 wk for analysis of total testosterone, free testosterone, cortisol, growth hormone, lactate, and ACTH analysis. Resting values for insulin-like growth factor (IGF)-I and IGF-binding protein-3 were determined before and after training. A heavy-resistance exercise test was used to evaluate the exercise-induced responses (4 sets of 10-repetition maximum squats with 90 s of rest between sets). Squat strength and thigh muscle cross-sectional area increased for both groups. The younger group demonstrated higher total and free testosterone and IGF-I than the older men, training-induced increases in free testosterone at rest and with exercise, and increases in resting IGF-binding protein-3. With training the older group demonstrated a significant increase in total testosterone in response to exercise stress along with significant decreases in resting cortisol. These data indicate that older men do respond with an enhanced hormonal profile in the early phase of a resistance training program, but the response is different from that of younger men.
487 citations
TL;DR: The sliding filament and cross-bridge theories of muscle contraction provide discrete predictions of the tetanic force- length relationship of skeletal muscle that have been tested experimentally and suggest that muscles that operate on the ascending limb of the force-length relationship typically function in stretch-shortening cycle contractions.
Abstract: The sliding filament and cross-bridge theories of muscle contraction provide discrete predictions of the tetanic force-length relationship of skeletal muscle that have been tested experimentally. The active force generated by a maximally activated single fiber (with sarcomere length control) is maximal when the filament overlap is optimized and is proportionally decreased when overlap is diminished. The force-length relationship is a static property of skeletal muscle and, therefore, it does not predict the consequences of dynamic contractions. Changes in sarcomere length during muscle contraction result in modulation of the active force that is not necessarily predicted by the cross-bridge theory. The results of in vivo studies of the force-length relationship suggest that muscles that operate on the ascending limb of the force-length relationship typically function in stretch-shortening cycle contractions, and muscles that operate on the descending limb typically function in shorten-stretch cycle contractions. The joint moments produced by a muscle depend on the moment arm and the sarcomere length of the muscle. Moment arm magnitude also affects the excursion (length change) of a muscle for a given change in joint angle, and the number of sarcomeres arranged in series within a muscle fiber determines the sarcomere length change associated with a given excursion.
460 citations
TL;DR: The mechanism of cutaneous vasodilation by local warming requires NOS generation of NO, and effects of NO synthase (NOS) inhibition with NG-nitro-L-arginine methyl ester (L-NAME) on Vasodilation induced byLocal warming of skin in six subjects were examined.
Abstract: Local warming of skin induces vasodilation by unknown mechanisms. To test whether nitric oxide (NO) is involved, we examined effects of NO synthase (NOS) inhibition with NG-nitro-L-arginine methyl ester (L-NAME) on vasodilation induced by local warming of skin in six subjects. Two adjacent sites on the forearm were instrumented with intradermal microdialysis probes for delivery of L-NAME and sodium nitroprusside. Skin blood flow was monitored by laser-Doppler flowmetry (LDF) at microdialysis sites. Local temperature (Tloc) of the skin at both sites was controlled with special LDF probe holders. Mean arterial pressure (MAP; Finapres) was measured and cutaneous vascular conductance calculated (CVC = LDF/MAP = mV/mmHg). Data collection began with a control period (Tloc at both sites = 34 degrees C). One site was then warmed to 41 degrees C while the second was maintained at 34 degrees C. Local warming increased CVC from 1.44 +/- 0.41 to 4.28 +/- 0.60 mV/mmHg (P < 0.05). Subsequent L-NAME administration reduced CVC to 2.28 +/- 0.47 mV/mmHg (P < 0.05 vs. heating), despite the continued elevation of Tloc. At a Tloc of 34 degrees C, L-NAME reduced CVC from 1.17 +/- 0.23 to 0.75 +/- 0.11 mV/mmHg (P < 0.05). Administration of sodium nitroprusside increased CVC to levels no different from those induced by local warming. Thus NOS inhibition attenuated, and sodium nitroprusside restored, the cutaneous vasodilation induced by elevation of Tloc; therefore, the mechanism of cutaneous vasodilation by local warming requires NOS generation of NO.
TL;DR: Direct evidence is provided that oxidant production in skeletal muscle is increased in old age and during prolonged exercise, with both mitochondrial respiratory chain and NADPH oxidase as potential sources.
Abstract: Reactive oxygen species (ROS) are implicated in the mechanism of biological aging and exercise-induced oxidative damage. The present study examined the effect of an acute bout of exercise on intrac...
TL;DR: The results of this study suggest that fan-beam DEXA offers considerable promise for the measurement of total body FFM and leg MM in elderly persons.
Abstract: The aim of the study was to examine the accuracy of fan-beam dual-energy X-ray absorptiometry (DEXA) for measuring total body fat-free mass (FFM) and leg muscle mass (MM) in elderly persons. Partic...
TL;DR: The findings indicate that mature stride dynamics may not be completely developed even in healthy 7-yr-old children and that different aspects of stride dynamics mature at different ages.
Abstract: In very young children, immature control of posture and gait results in unsteady locomotion. In children of ∼3 yr of age, gait appears relatively mature; however, it is unknown whether the dynamics...
TL;DR: A positive association of the I allele with elite endurance performance is supported in 91 British Olympic-standard runners and among 404 Olympic- standard athletes from 19 other mixed sporting disciplines.
Abstract: Human physical performance is strongly influenced by genetic factors. A variation in the structure of the human angiotensin I-converting enzyme (ACE) gene has been reported in which the insertion (...
TL;DR: Although older men appear to have a greater capacity for absolute strength and muscle mass gains than older women in response to ST, the relative contribution of neuromuscular and hypertrophic factors to the increase in strength appears to be similar between genders.
Abstract: To determine the effects of strength training (ST) on muscle quality (MQ, strength/muscle volume of the trained muscle group), 12 healthy older men (69 ± 3 yr, range 65–75 yr) and 11 healthy older ...
TL;DR: It is concluded that sarcomere length instabilities provide the most comprehensive explanation of the early consequences of eccentric exercise.
Abstract: Unaccustomed exercise involving stretch of active muscle at long length causes an immediate loss of tension-generating capacity, a shift of optimum length, and changes in excitation-contraction cou...
TL;DR: The results indicate that stress-induced systemic release of bioactive substances may determine neutrophil mobilization and functional status, which then may affect local tissue damage of susceptible organs.
Abstract: We analyzed adaptation mechanisms regulating systemic inflammatory response of the stressed body by using an experimental challenge of repeated exercise bouts and accompanying muscle inflammation. ...
TL;DR: The results suggested that the stiffness of tendon structures has a favorable effect on stretch-shortening cycle exercise, possibly due to adequate storage and recoil of elastic energy.
Abstract: The purpose of this study was to quantify the elastic properties of tendon structures in vivo and to investigate the influence of the tendon properties on jump performance with and without countermovement. Elongation of the tendon and aponeurosis of vastus lateralis muscle (dL) was directly measured by ultrasonography while subjects (n = 31) performed ramp isometric knee extension up to the voluntary maximum (MVC). The relationship between muscle force and dL was fitted to a linear regression above 50% MVC, the slope of which was defined as stiffness of the tendon structures. Statistical analysis revealed no significant difference between duplicated measurements of stiffness, with an interday reliability of r = 0.88 and a coefficient of variance of 6.1%. Although the stiffness was not significantly related to absolute jump height in either vertical jump, it was inversely correlated with the difference in jump height between the vertical jumps performed with and without countermovement. The results suggested that the stiffness of tendon structures has a favorable effect on stretch-shortening cycle exercise, possibly due to adequate storage and recoil of elastic energy.
TL;DR: The results indicate that vastus lateralis muscle shows marked fiber atrophy, no change in the proportion of type I fibers, and a relative independence of metabolic enzyme levels from activation during the first 24 wk after clinically complete SCI.
Abstract: This study examined the influence of spinal cord injury (SCI) on affected skeletal muscle. The right vastus lateralis muscle was biopsied in 12 patients as soon as they were clinically stable (aver...
TL;DR: The effects of aging on motoneuron firing rates and muscle contractile properties were studied in tibialis anterior muscle by comparing results from six young and six old men, and relatively higher firing rates were matched with shorter contraction times from the young men, indirectly supports the neuromuscular age-related remodeling principle.
Abstract: The effects of aging on motoneuron firing rates and muscle contractile properties were studied in tibialis anterior muscle by comparing results from six young (20.8 +/- 0.8 yr) and six old men (82.0 +/- 1.7 yr). For each subject, data were collected from repeated tests over a 2-wk period. Contractile tests included maximal voluntary contraction (MVC) with twitch interpolation and stimulated twitch contractions. The old men had 26% lower MVC torque (P < 0.01) than did the young men, but percent activation was not different (99.1 and 99.3%, respectively). Twitch contraction durations were 23% longer (P < 0.01) in the old compared with the young men. During a series of repeated brief steady-state contractions at 10, 25, 50, 75, and 100% MVC, motor unit firing rates were recorded. Results from approximately 950 motor unit trains in each subject group indicated that at all relative torque levels mean firing rates were 30-35% lower (P < 0.01) in the old subjects. Comparisons between young and old subjects' mean firing rates at each of 10%, 50%, and MVC torques and their corresponding mean twitch contraction duration yielded a range of moderate-to-high correlations (r = -0.67 to -0.84). That lower firing rates were matched to longer twitch contraction durations in the muscle of old men, and relatively higher firing rates were matched with shorter contraction times from the young men, indirectly supports the neuromuscular age-related remodeling principle.
TL;DR: A positive relationship between activity and fitness and a negative relationship between fatness and activity are supported and HR is misleading as a measure of activity are suggested.
Abstract: The relationships between children's activity, aerobic fitness, and fatness are unclear. Indirect estimates of activity, e.g., heart rate (HR) and recall, may mask any associations. The purpose of this study was to assess these relationships by using the Tritrac-R3D, a pedometer, and heart rate. Thirty-four children, ages 8-10 yr, participated in the study. The Tritrac and pedometer were worn for up to 6 days. HR was measured for 1 day. Activity measured by Tritrac or pedometer correlated positively to fitness in the whole group (Tritrac, r = 0.66; pedometer, r = 0.59; P 139 beats/min correlated positively to fatness in girls (r = 0.64, P < 0.05). This suggests that HR is misleading as a measure of activity. This study supports a positive relationship between activity and fitness and suggests a negative relationship between fatness and activity.
TL;DR: Tc and Tsk contribute about equally toward thermal comfort, whereas Tc predominates in regulation of the autonomic and metabolic responses.
Abstract: Subjective thermal comfort plays a critical role in body temperature regulation since this represents the primary stimulus for behavioral thermoregulation. Although both core (Tc) and skin-surface ...
TL;DR: It is suggested that, after submaximal exercise, PCr recovery, under normoxic conditions, is limited by O2 availability, which is significantly altered by FIO2.
Abstract: In skeletal muscle, phosphocreatine (PCr) recovery from submaximal exercise has become a reliable and accepted measure of muscle oxidative capacity. During exercise, O2 availability plays a role in...
TL;DR: A three-dimensional (3D) model of the human airway tree is proposed using a deterministic algorithm that can generate a branching duct system in an organ and its morphometric characteristics are in good agreement with those reported in the literature.
Abstract: A three-dimensional (3D) model of the human airway tree is proposed using a deterministic algorithm that can generate a branching duct system in an organ. The algorithm is based on two principles: ...
TL;DR: The results suggest that isometric specific strength and the ability to fully and rapidly activate the dorsiflexor muscles during a single isometric contraction were unimpaired by aging, however, there was an age-related deficit in the able to perform rapid repetitive dynamic contractions.
Abstract: The extents to which decreased muscle size or activation are responsible for the decrease in strength commonly observed with aging remain unclear. Our purpose was to compare muscle isometric strength [maximum voluntary contraction (MVC)], cross-sectional area (CSA), specific strength (MVC/CSA), and voluntary activation in the ankle dorsiflexor muscles of 24 young (32 ± 1 yr) and 24 elderly (72 ± 1 yr) healthy men and women of similar physical activity level. Three measures of voluntary muscle activation were used: the central activation ratio [MVC/(MVC + superimposed force)], the maximal rate of voluntary isometric force development, and foot tap speed. Men had higher MVC and CSA than did women. Young men had higher MVC compared with elderly men [262 ± 19 (SE) vs. 197 ± 22 N, respectively], whereas MVC was similar in young and elderly women (136 ± 15 vs. 149 ± 16 N, respectively). CSA was greater in young compared with elderly subjects. There was no age-related impairment of specific strength, central activation ratio, or the rate of voluntary force development. Foot tap speed was reduced in elderly (34 ± 1 taps/10 s) compared with young subjects (47 ± 1 taps/10 s). These results suggest that isometric specific strength and the ability to fully and rapidly activate the dorsiflexor muscles during a single isometric contraction were unimpaired by aging. However, there was an age-related deficit in the ability to perform rapid repetitive dynamic contractions.
TL;DR: It is demonstrated that exhaustion during all FIO2 occurred when a particular intracellular environment was achieved and suggested that during the lowest Fio2 condition, the greater PCr hydrolysis and intrace cellular acidosis at submaximal workloads may have contributed to the significantly earlier time to exhaustion.
Abstract: The purpose of this study was to use31P-magnetic resonance spectroscopy to examine the relationships among muscle PCr hydrolysis, intracellular H+ concentration accumulation, and muscle performance...
TL;DR: The accuracy and precision of seven previously published BIA models for the measurement of change in body water compartmentalization among individuals infused with lactated Ringer solution or administered a diuretic agent are investigated and it is concluded that the multifrequency Cole-Cole model is superior under conditions in which body water compartments is altered from the normal state.
Abstract: The 1994 National Institutes of Health Technology Conference on bioelectrical impedance analysis (BIA) did not support the use of BIA under conditions that alter the normal relationship between the...
TL;DR: This technique, when combined with blood flow studies in human subjects, will enable the study of retinal O2 utilization under experimental and various disease conditions.
Abstract: A method for noninvasive measurement of Hb O2 saturation (So 2) in retinal blood vessels by digital imaging was developed and tested. Images of vessels were recorded at O2-sensitive and O2-insensit...
TL;DR: It is demonstrated that fatigue during prolonged exercise in hot conditions is not related to carbohydrate availability, and the increased endurance in CT compared with NT is probably due to a reduced glycogenolytic rate.
Abstract: To examine the effect of ambient temperature on metabolism during fatiguing submaximal exercise, eight men cycled to exhaustion at a workload requiring 70% peak pulmonary oxygen uptake on three sep...