摘要:

This randomized study compared the fibrinolytic circadian rhythm of healthy older men and older women (average age 66 ± 5), before and after 6 months of endurance training versus stretching controls. Compared with men, women at baseline had similar rhythms for tissue plasminogen activator (t-PA) activity and plasminogen activator inhibitor 1 (PAI-1) activity, but lower levels of total t-PA antigen. In men (N= 16), endurance training increased ˙VO2max15% (P< 0.001), while decreasing PAI-1 activity 37% (P= 0.034) and total t-PA antigen 18%(P= 0.0003) between midnight and 6 a.m., but did not affect t-PA activity. In women (N= 9), endurance training increased˙VO2max18% (P= 0.003), and increased t-PA activity 20%(P= 0.027) and total t-PA antigen 55% (P= 0.007) between 10 p.m. and 4 a.m., but had no effect on PAI-1 activity. After endurance training there were no significant differences in the fibrinolytic circadian rhythm of men versus women. Six months of nonaerobic stretching had no effect on ˙VO2maxor fibrinolysis in men (N= 11) or women(N= 8). This study indicates that potentially favorable changes occur in fibrinolytic factors after endurance training in older men and older women.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The purpose of this study was to determine whether patients with multiple sclerosis (MS) would show attenuated heart rate and/or pressor responses to isometric handgrip exercise. Patients with MS (30 males, 74 females, aged 23-61 yr) and control subjects (9 males, 16 females, aged 25-47 yr) performed isometric handgrip exercise at 30% of maximal voluntary contraction (MVC) to fatigue. Systolic, diastolic, and mean arterial pressure (MAP) increased linearly in both groups, but were significantly lower (P<0.05) in patients with MS at 20%, 40%, 60%, 80%, and 100% of exercise duration. Mean change in MAP at fatigue was +47.9 mm Hg for controls and +28.2 mm Hg for patients with MS, with 18 patients with MS between -6 mm Hg and +15 mm Hg. Heart rate increased normally in patients with MS. To predict change in MAP at fatigue in patients with MS, stepwise regression analysis using six variables yielded an R2of 0.26. These data suggest that in some patients MS lesions exist in areas of autonomic cardiovascular control that result in attenuated pressor responses to exercise. In 17% of patients tested, attenuation was profound. Data also suggest an abnormal dissociation between the heart rate and pressor response to static work in patients with MS.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We examined the electromyographic (EMG) activity of the supraspinatus and other rotator cuff muscles, the three portions of the deltoid muscle, and the pectoralis major muscle in two previously suggested positions for isolating the supraspinatus. The position suggested by Jobe and colleagues is with the elbow extended, the shoulder in full internal rotation, and the arm in the scapular plane. Blackburn and colleagues recommended the prone position, with the elbow extended and the arm abducted to 100° and externally rotated. Fine-wire EMG activity was obtained from the rotator cuff muscles and surface EMG from the other muscles in 17 subjects tested in these two positions. Both positions resulted in significant activity of the supraspinatus, but the difference between these two positions was not statistically significant. The Jobe position produced greater activation of the anterior deltoid and pectoralis major, whereas the Blackburn position caused greater activation of the posterior deltoid. Both positions produced significant activation of the middle deltoid. We conclude that either position can be used to strengthen the supraspinatus; however, neither position selectively isolates the supraspinatus during manual muscle testing.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Environmental stress can become so severe that athletes, in spite of proper training, heat acclimation, and hydration level, are unable to maintain thermal balance. Such incompensable conditions occur when air temperature exceeds 35°C and relative humidity becomes higher than 60%. At these high environmental temperatures, the heat liberated during exercise can only be lost by evaporation of sweat, and therefore water vapor pressure sets limits on the possible rate of evaporation. Calculations are presented for the required and the maximal possible sweat evaporation rate for high-intensity, long-duration events, using marathon racing as an example. The consequence of the environmental heat stress is that the athlete must reduce the speed of running considerably to prevent potential heat injury. In certain extreme environmental conditions, sporting events should be canceled or postponed.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We investigated the effects of clenbuterol on the muscle mass, contractile properties, myosin phenotype, and bioenergetic enzyme activity in the gastrocnemius (GS)-plantaris (PL)-soleus (SO) muscle complex. Rats were sham-injected or treated with clenbuterol (2 mg·kg-1, subcutaneously) for 14 d. Clenbuterol increased (P< 0.05) body weight and muscle complex weight. Also, clenbuterol treatment resulted in an increase in total muscle force production and maximal shortening velocity(P< 0.05). No difference (P> 0.05) in relative force production (force·g-1muscle) existed between experimental groups. However, muscle fatigue increased with clenbuterol treatment. Myosin heavy chain (MHC) composition was not altered in the GS or PL muscles, but shifted toward the fast Type II MHC in the SO. Myosin light chain (MLC) composition was not altered in any of the muscles. Clenbuterol caused a decrease in oxidative and glycolytic enzyme activity in the GS and PL, but not the SO. These data suggest that the clenbuterol-induced increase in muscle mass and maximal force generation is due to hypertrophy of both fast and slow fibers. Furthermore, these findings support the notion that beta-agonists may be beneficial in combating conditions that result in muscle wasting and dysfunction.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We hypothesized that lumbar sympathetic nerve activity (LSNA) increases at the onset of whole-body dynamic exercise in the rat. To test this hypothesis, we recorded LSNA, heart rate (HR), and arterial pressure (AP) at rest and during a graded exercise test in six adult rats. Rats were instrumented with arterial and venous catheters and recording electrodes around the lumbar sympathetic trunk. Following recovery, each rat ran continuously on a hand-driven or motorized treadmill at 6 m·min-1, 12 m·min-1, and 18 m·min-1on a 10% grade for approximately 3 min at each workload. Before exercise, mean arterial pressure(MAP), HR, and LSNA averaged 108 ± 4 mm Hg, 385 ± 20 bpm, and 100%, respectively. As hypothesized, all variables increased abruptly and dramatically at the onset of treadmill exercise. For example, MAP (117± 5 mm Hg), HR (450 ± 15 bpm), and LSNA (225 ± 19%) all increased significantly within the first 25 s of treadmill running at 6 m·min-1. As the exercise continued, there was a progressive increase in HR; however, MAP plateaued at 6 m·min-1and LSNA plateaued at 12 m·min-1. Since LSNA increased at the onset of whole-body dynamic exercise in the rat, we suggest that the increase in LSNA at the onset of exercise is mediated by a central (feed forward) mechanism.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Endurance training reduces the ventilatory response to a given level if work, and there is evidence that endurance athletes possess attenuated chemosensitivity at rest; but it is unclear whether attenuation persists during exercise. We compared the carbon dioxide sensitivity (S) of endurance-trained (ETG), sprint-trained (STG), and control subjects (CG), at rest and during cycle ergometry. Steady-state carbon dioxide (CO2) inhalation was employed; ventilatory parameters were measured using an ultrasonic flowmeter linked to a computer. CO2concentrations were measured at the mouth using an infrared CO2analyzer or mass spectrometer. Mean resting CO2sensitivity of the ETG was significantly lower than that of the STG (P< 0.05), but not the CG(P< 0.058). S increased from rest to exercise in all endurance-trained subjects, but the responses of the STG and CG were varied. Compared to rest, mean S was significantly higher during exercise for the ETG, but not for the STG or CG. S was the same in all groups during exercise. During air breathing exercise all subjects were mildly hypercapnic. The ETG showed the greatest rise in mean alveolar PCO2, but this could not be attributed to attenuated chemosensitivity since responsiveness during exercise was identical in all three groups.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We investigated NaHCO3infusion effects on plasma lactate removal by forearm muscles and performance during intensive leg exercise. Seven subjects performed the force-velocity (FV) test with placebo and NaHCO3(2 mEq·min-1) with a double-blind crossover protocol. Blood samples for arterial ([LA]A) and venous ([LA]V) lactate determinations were taken 1) at rest before infusion, and 2, 6, 10, 14, 18, and 22 min following its start; and 2) at the end of each exercise bout. The arteriovenous difference ([LA]A-V) was determined for each sampling. NaHCO3significantly increased arterial bicarbonate concentration and pH during rest (P< 0.001;P< 0.001) and the FV test (P< 0.001;P< 0.05). During the test,[LA]Aand [LA]Vwere significantly higher with NaHCO3(P< 0.05,P< 0.001). At test onset, [LA]A-Vbecame positive and increased until the braking force of 6 kg, with NaHCO3and placebo, with values significantly lower for NaHCO3(P< 0.001). Peak anaerobic power (Wanae, peak) and the corresponding braking force (Fmax) were also determined. Fmaxwas significantly increased with NaHCO3(P< 0.001). In conclusion, the increasing rise in [LA]Aand [LA]Vinduced by NaHCO3may be partly explained by a decreased rate of lactate uptake by forearm skeletal muscles. NaHCO3did not improve Wanae, peak, but improved Fmax, thus increasing FV duration.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We sought to evaluate the effects of exercise and aspirin on gastroduodenal and intestinal permeability. Seven volunteers (age = 29 ± 3 yr;˙VO2max= 56.8 ± 4.1 ml·kg-1·min-1) rested or performed treadmill exercise (60 min at ≈68% ˙VO2max), with or without aspirin ingestion. Placebo (glucose) or aspirin (1.3 g) was taken the night before and prior to rest or exercise (total 2.6 g). A permeability test solution (≈ 1300 mOsm·kg-1), containing 10 g lactulose (L), 5 g mannitol(M), and 10 g sucrose (S), was ingested prior to rest or exercise. Urinary excretion rates (6·h-1), expressed as a percentage of ingested dose, were used to quantify intestinal (L/M ratio) or gastroduodenal (S) permeability. Ingestion of aspirin before running increased (P< 0.05) intestinal permeability compared to placebo + running and placebo + rest, but not compared to aspirin + rest; mean (±SE) values for the L/M ratio were 0.248 ± 0.046, 0.029 ± 0.012, 0.012 ± 0.004, and 0.104 ± 0.057, respectively. Gastroduodenal permeability following aspirin + running (3.25 ± 1.21%) was also elevated (P< 0.05) compared to placebo + running (0.43 ± 0.15%) and placebo + rest(0.24 ± 0.11%), but not compared to aspirin + rest (0.66 ± 0.27%). Neither running nor aspirin ingestion was associated with gastrointestinal (GI) complaints. Thus, GI permeability while running can be markedly elevated by aspirin ingestion.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

National policy for increasing leisure physical activity in the United States is impeded by a poor understanding of interventions that can be implemented by community and clinical medicine. To clarify the literature in this area, we conducted a quantitative, meta-analysis of 127 studies that examined the efficacy of interventions for increasing physical activity among≈131,000 subjects in community, worksite, school, home, and health care settings; 445 effects were expressed as a Pearson correlation coefficient (r) and examined as they varied according to moderating variables important for community and clinical intervention. The mean effect was moderately large, r = 0.34, approximating three-fourths of a standard deviation or an increase in binomial success rate from 50% to 67%. The estimated population effect weighted by sample size was larger, r = 0.75, approximating 2 standard deviations or increased success to 88%. Contrasts between levels of independent moderating variables indicated that effects weighted by sample size were larger when the interventions: 1) employed the principles of behavior modification, 2) used a mediated delivery, 3) targeted groups, 4) of combined ages, 5) sampled apparently healthy people, or 6) measured active leisure, of 7) low intensity, 8) by observation. Independently of sample size, effects were larger when interventions 1) used behavior modification, 2) employed a pre-or quasi-experimental design, or 3) were of short duration, regardless of features of the people, setting, or physical activity. Our results show that physical activity can be increased by intervention. The optimal ways for selecting intervention components, settings, and population segments to maintain increases in physical activity and the relative contributions by community and clinical medicine toward successful physical activity intervention require experimental confirmation, warranting accelerated attention in clinical trials.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID