Exaggerated ANF response to exercise in middle-aged vs. young runners

Hormonal, electrolyte, and renal responses were measured before, during, and after a marathon (42.2 km) in 14 runners: 8 young (Y) (mean age 27.8 yr) and 6 middle aged (MA) (mean aged 46.7 yr). No differences between groups in prerun values for heart rate (HR), plasma osmolality (OSM), antidiuretic hormone (ADH), aldosterone (ALDO), atrial natriuretic factor (ANF), or plasma renin activity (PRA) were found. Renal and urinary measurements were also similar between groups before the marathon. After 10 km of running, both groups had significant increases in HR, ALDO, ANF, and PRA, while OSM, Na+, and ADH remained unchanged from prerun values. The increase in plasma ANF concentrations at this point was significantly greater in the MA subjects compared with the Y (mean increase 104.1 vs. 42.8 pg/ml, respectively; P less than 0.01). Immediate postmarathon values for OSM, ADH, and Na+ were significantly higher than initial values in both groups, while HR, PRA, and ALDO continued to increase above the elevated levels found at 10 km. ANF values immediately postmarathon remained higher than prerun concentrations but were significantly reduced from those obtained at 10 km. In contrast, HR continued to rise until the completion of the run. These data are consistent with recent reports of an exaggerated ANF response in older subjects in response to central blood volume expansion.     

Blood lactate vs. exhaustive exercise to evaluate aerobic fitness

This study compared the predictive power of a lactate-related index determined during submaximal cycle exercise to that of an exhaustive cycle ergometer test for evaluating the endurance exercise capacity of soldiers. The subjects (n = 48 males) performed a continuous exercise test to voluntary exhaustion on the cycle ergometer. Power output (PO) increased by 50 W steps each fourth min, with determinations of heart rate (HR), RPE and blood lactate concentrations (HLa) just prior to each PO increase. The PO at a 4 mmol L(-1) HLa concentration (WOBLA) was interpolated; based on the time to exhaustion the maximal PO that could be maintained for 6 min (Wmax6) was calculated from previously documented formulae. Subjects were timed during a 3000 m cross-country run. Both the cycle test and the run were performed again 3 months later, as was an additional 3000 m run with full military equipment weighing about 21 kg. All 3000 m times were significantly correlated (p less than 0.05) with both Wmax6 and WOBLA; similar predictive power was demonstrated for both Wmax6 and WOBLA, suggesting that accuracy in evaluation would not be sacrificed by substituting the submaximal for the exhaustive exercise test. HR and RPE-related indices showed markedly lower predictive power. The results extend the previously documented relationship between HLa during treadmill ergometry and running performance to include the use of cycle ergometry for the evaluation of running performance. The results also proved applicable to running performance while load carrying.     

Metabolic and performance responses to constant-load vs. variable-intensity exercise in trained cyclists.

We studied glucose oxidation (Glu(ox)) and glycogen degradation during 140 min of constant-load [steady-state (SS)] and variable-intensity (VI) cycling of the same average power output, immediately followed by a 20-km performance ride [time trial (TT)]. Six trained cyclists each performed four trials: two experimental bouts (SS and VI) in which muscle biopsies were taken before and after 140 min of exercise for determination of glycogen and periodic acid-Schiff's staining; and two similar trials without biopsies but incorporating the TT. During two of the experimental rides, subjects ingested a 5 g/100 ml [U-(14)C]glucose solution to determine rates of Glu(ox). Values were similar between SS and VI trials: O(2) consumption (3.08 +/- 0.02 vs. 3.15 +/- 0.03 l/min), energy expenditure (901 +/- 40 vs. 904 +/- 58 J x kg(-1) x min(-1)), heart rate (156 +/- 1 vs. 160 +/- 1 beats/min), and rating of perceived exertion (12.6 +/- 0.6 vs. 12.7 +/- 0.7). However, the area under the curve for plasma lactate concentration vs. time was significantly greater during VI than SS (29.1 +/- 3.9 vs. 24.6 +/- 3. 7 mM/140 min; P = 0.03). VI resulted in a 49% reduction in total muscle glycogen utilization vs. 65% for SS, while total Glu(ox) was higher (99.2 +/- 5.3 vs. 83.9 +/- 5.2 g/140 min; P < 0.05). The number of glycogen-depleted type I muscle fibers at the end of 140 min was 98% after SS but only 59% after VI. Conversely, the number of type II fibers that showed reduced periodic acid-Schiff's staining was 1% after SS vs. 10% after VI. Despite these metabolic differences, subsequent TT performance was similar (29.14 +/- 0.9 vs. 30.5 +/- 0.9 min for SS vs. VI). These results indicate that whole body metabolic and cardiovascular responses to 140 min of either SS or VI exercise at the same average intensity are similar, despite differences in skeletal muscle carbohydrate metabolism and recruitment.     

Sensory-mechanical relationships during high-intensity, constant-work-rate exercise in COPD.

During constant-work-rate exercise in chronic obstructive pulmonary disease, dyspnea increases steeply once inspiratory reserve volume (IRV) falls to a critical level that prevents further expansion of tidal volume (Vt). We studied the effects of this mechanical restriction on the quality and intensity of exertional dyspnea and examined the impact of an anticholinergic bronchodilator. In a randomized, double-blind, crossover study, 18 patients with chronic obstructive pulmonary disease (forced expiratory volume in 1 s = 40 +/- 3%predicted; mean +/- SE) inhaled tiotropium 18 mug or placebo once daily for 7-10 days each. Pulmonary function tests and symptom-limited cycle exercise at 75% of each patient's maximal work capacity were performed 2 h after dosing. Dyspnea intensity (Borg scale), operating lung volumes, breathing pattern, and esophageal pressure (n = 11) were measured during exercise. Dynamic hyperinflation reached its maximal value early in exercise and was associated with only mild increases in dyspnea intensity and the effort-displacement ratio, which is defined as the ratio between tidal swings of esophageal pressure (expressed relative to maximum inspiratory pressure) and Vt (expressed relative to predicted vital capacity). After a minimal IRV of 0.5 +/- 0.1 liter was reached, both dyspnea and the effort-displacement ratio rose steeply until an intolerable level was reached. Tiotropium did not alter dyspnea-IRV relationships, but the increase in resting and exercise inspiratory capacity was associated with an improved effort-displacement ratio throughout exercise. Once a critically low IRV was reached during exercise, dyspnea rose with the disparity between respiratory effort and the Vt response. Changes in dyspnea intensity after tiotropium were positively correlated with changes in this index of neuromechanical coupling.     

Hormonal responses to exercise during moderate cold exposure in young vs. middle-age subjects.

The influence of moderate cold exposure on the hormonal responses of atrial natriuretic factor (ANF), arginine vasopressin (AVP), catecholamines, and plasma renin activity (PRA) after exhaustive exercise was studied in 9 young and 10 middle-aged subjects. Exercise tests were randomly performed in temperate (30 degrees C) and cold (10 degrees C) environments. Heart rate, oxygen consumption, and peripheral arterial blood pressure were measured at regular intervals. Blood samples were collected before and immediately after exercise at 30 or 10 degrees C. Plasma sodium and potassium concentrations as well as hemoglobin and hematocrit were measured, and the change in plasma volume was calculated. At rest and during exercise, oxygen consumption was similar during exposure to both temperate and cold temperatures. During submaximal exercise intensities, the rise in heart rate was blunted while the increase in systolic blood pressure was significantly greater at 10 than at 30 degrees C. The increases in plasma sodium and potassium concentrations after exhaustion were similar between environments, as was the decrease in plasma volume. In both groups, all plasma hormones were significantly elevated postexercise, with the AVP response similar at 10 and 30 degrees C. However, the norepinephrine and ANF responses were significantly greater while the PRA response was significantly reduced at 10 degrees C. In the middle-aged subjects the epinephrine response to exercise was higher at 10 than at 30 degrees C. The greater ANF and reduced PRA responses to exercise in the cold may have resulted from central hemodynamic changes caused by cold-induced cutaneous vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Systemic vs. local cytokine and leukocyte responses to unilateral wrist flexion exercise.

We hypothesized that brief exercise of a small muscle group would lead to local rather than systemic alterations in cytokines, peripheral blood mononuclear cells, and mediators of angiogenesis. Fifteen men and eight women (age range 22-36 yr old) performed 10 min of unilateral wrist flexion exercise. Blood was sampled from venous catheters in the resting and exercising arm at baseline, at the end of exercise, and at 10, 30, 60, and 120 min after exercise. Lactate was significantly elevated in the exercising arm (+276 +/- 35%; P < 0.0005) with no change in the resting arm. In contrast, increases in both arms were observed for interleukin-6 (+139 +/- 51%; P < 0.0005), growth hormone (+1,104 +/- 284%; P < 0.003), natural killer cells (+81 +/- 9%; P < 0.0005), and lymphocytes expressing CD62L, CD11a, and CD54. There were no significant differences in these increases between the resting and exercising arm. Catecholamines increased in both arms [epinephrine peak increase, +226 +/- 36% (P < 0.001); norepinephrine peak increase, +90 +/- 15% (P < 0.01)]. Fibroblast growth factor-2 initially decreased with exercise in both arms, and this was followed by a rebound increase. Vascular endothelial growth factor demonstrated a small but significant increase in both arms (+124 +/- 31%; P < 0.05). Brief, low-intensity exercise leads to a systemic rather than local response of mediators that could be involved in inflammation, repair, or angiogenic adaptation to physical activity.     

Isolated vs. complex exercise in strengthening the rotator cuff muscle group

The purpose of this study was to compare 2 different training modes in improving shoulder cuff muscular performance. Thirty-nine participants were randomly assigned into 3 groups: the isolated group exercised using 2-kg dumbbells; the complex group used a protocol with complex exercises; and the control group had no training. All participants trained for 6 weeks (3 times per week) and were evaluated isokinetically before (pretest) and after the training period (posttest). Results showed that the complex group significantly improved their muscular performance, but the isolated group did not, indicating that isolated exercises are only effective when the training goal is to strengthen the weaker muscle group, but they must be replaced by more complex and closed-kinetic exercises in order to obtain considerable improvement of the rotator cuff strength. The authors propose that a strengthening program should start with isolated movements for better stimulation of the weaker muscles and continue with complex exercise for more impressive strengthening.     

Ammonia production following maximal exercise: treadmill vs. bicycle testing.

From a population of 20 healthy male volunteers, half performed constant speed, incremental load maximal aerobic capacity (VO2max) tests on a motor-driven treadmill, while the other half performed similar VO2max tests on a bicycle ergometer. The two groups, matched for size and age, showed no significant differences in VO2max, maximum heart rate, or in post-exercise (4 min ) peripheral venous blood concentrations of lactete or pyruvate. However, post-exercise peripheral venous blood ammonia levels were significantly higher in the group tested on the bicycle ergometer than in the treadmill group.     

Glucose uptake is increased in trained vs. untrained muscle during heavy exercise.

Endurance training increases muscle content of glucose transporter proteins (GLUT-4) but decreases glucose utilization during exercise at a given absolute submaximal intensity. We hypothesized that glucose uptake might be higher in trained vs. untrained muscle during heavy exercise in the glycogen-depleted state. Eight untrained subjects endurance trained one thigh for 3 wk using a knee-extensor ergometer. The subjects then performed two-legged glycogen-depleting exercise and consumed a carbohydrate-free meal thereafter to keep muscle glycogen concentration low. The next morning, subjects performed dynamic knee extensions with both thighs simultaneously at 60, 80, and until exhaustion at 100% of each thigh's peak workload. Glucose uptake was similar in both thighs during exercise at 60% of thigh peak workload. At the end of 80 and at 100% of peak workload, glucose uptake was on average 33 and 22% higher, respectively, in trained compared with untrained muscle (P < 0.05). Training increased the muscle content of GLUT-4 by 66% (P < 0. 05). At exhaustion, glucose extraction correlated significantly (r = 0.61) with total muscle GLUT-4 protein. Thus, when working at a high load with low glycogen concentrations, muscle glucose uptake is significantly higher in trained than in untrained muscle. This may be due to the higher GLUT-4 protein concentration in trained muscle.     

Dynamic hyperinflation is associated with a poor cardiovascular response to exercise in COPD patients

Background

Pulmonary hyperinflation has the potential for significant adverse effects on cardiovascular function in COPD. The aim of this study was to investigate the relationship between dynamic hyperinflation and cardiovascular response to maximal exercise in COPD patients.

Methods

We studied 48 patients (16F; age 68 yrs ± 8; BMI 26 ± 4) with COPD. All patients performed spirometry, plethysmography, lung diffusion capacity for carbon monoxide (TLco) measurement, and symptom-limited cardiopulmonary exercise test (CPET). The end-expiratory lung volume (EELV) was evaluated during the CPET. Cardiovascular response was assessed by change during exercise in oxygen pulse (ΔO₂Pulse) and double product, i.e. the product of systolic blood pressure and heart rate (DP reserve), and by the oxygen uptake efficiency slope (OUES), i.e. the relation between oxygen uptake and ventilation.

Results

Patients with a peak exercise EELV (%TLC) ≥ 75% had a significantly lower resting FEV₁/VC, FEF₅₀/FIF₅₀ ratio and IC/TLC ratio, when compared to patients with a peak exercise EELV (%TLC) < 75%. Dynamic hyperinflation was strictly associated to a poor cardiovascular response to exercise: EELV (%TLC) showed a negative correlation with ΔO₂Pulse (r = - 0.476, p = 0.001), OUES (r = - 0.452, p = 0.001) and DP reserve (r = - 0.425, p = 0.004). Furthermore, according to the ROC curve method, ΔO₂Pulse and DP reserve cut-off points which maximized sensitivity and specificity, with respect to a EELV (% TLC) value ≥ 75% as a threshold value, were ≤ 5.5 mL/bpm (0.640 sensitivity and 0.696 specificity) and ≤ 10,000 Hg · bpm (0.720 sensitivity and 0.783 specificity), respectively.

Conclusion

The present study shows that COPD patients with dynamic hyperinflation have a poor cardiovascular response to exercise. This finding supports the view that in COPD patients, dynamic hyperinflation may affect exercise performance not only by affecting ventilation, but also cardiac function.     

慢性阻塞性肺疾病患者运动负荷时呼吸困难机理的研究

目的:探究慢性阻塞性肺疾病(COPD)患者呼吸困难与呼吸驱动及呼吸肌功能之间的关系.方法:对31例COPD患者和26例正常对照者分别检测静息常规肺功能、肺弥散功能(DLCO)、口腔阻断压(P0.1)、最大吸气压(PImax)及最大呼气压(PEmax),并进行运动负荷试验观测氧耗量(VO2)、二氧化碳产生量(VCO2)、分钟通气量(VE)、潮气量(VT)等气体代谢指标,受试者呼吸困难感的评价采用呼吸困难指数(BS)表示.运动负荷前、后检测动脉血气分析.结果:①COPD组患者PImax(5.33±1.95)kPa明显低于正常人组(7.02±2.53)kPa(P＜0.05),PEmax在两组中无明显差别(P＞0.05),COPD组患者P0 1(0.37±0.12)kPa明显高于正常人组(0.26±0.09)kPa(P＜0.05),P0.1/PImax(0.069±0.021)也明显高于正常人组(0.037±0.009)(P＜0.01).②COPD组患者极量负荷时BS与P0.1及PImax未发现明显的相关关系(P＞0.05),但与P0 1/PImax明显正相关(r=0.48,P＜0.05),且运动前后BS的变化(△BS)与P0.1/PImax亦明显正相关(r=0.44,P＜0.05).结论:COPD患者运动负荷时呼吸困难的产生除与残气的增加及弥散障碍等有关外,呼吸驱动调节异常及呼吸肌功能障碍也是引起其呼吸困难的重要因素.     

Detection of expiratory flow limitation during exercise in COPD patients

Koulouris, Nickolaos G., Ioanna Dimopoulou, PäiviValta, Richard Finkelstein, Manuel G. Cosio, and J. Milic-Emili.Detection of expiratory flow limitation during exercise in COPDpatients. J. Appl. Physiol. 82(3):723-731, 1997.The negative expiratory pressure (NEP) method wasused to detect expiratory flow limitation at rest and at differentexercise levels in 4 normal subjects and 14 patients with chronicobstructive pulmonary disease (COPD). This method does not requireperformance of forced expirations, nor does it require use of bodyplethysmography. It consists in applying negative pressure (5cmH₂O) at the mouth during early expiration and comparing the flow-volume curve of the ensuing expiration with that of the preceding control breath. Subjects in whomapplication of NEP does not elicit an increase in flow during part orall of the tidal expiration are considered flow limited. The fournormal subjects were not flow limited up to 90% of maximal exercisepower output(_max).Five COPD patients were flow limited at rest, 9 were flow limited atone-third _max, and 12 were flow limited at two-thirds_max. Whereasin all patients who were flow limited at rest the maximalO₂ uptake was below the normallimits, this was not the case in most of the other patients. Inconclusion, NEP provides a rapid and reliable method to detectexpiratory flow limitation at rest and during exercise.

     

Rectal and rectal vs. esophageal temperatures in paraplegic men during prolonged exercise

This study investigated the rectal (Tre), esophageal (Tes), and skin (Tsk) temperature changes in a group of trained traumatic paraplegic men pushing their own wheelchairs on a motor-driven treadmill for a prolonged period in a neutral environment. There were two experiments. The first experiment (Tre and Tsk) involved a homogeneous group (T10-T12/L3) of highly trained paraplegic men [maximum O2 uptake (VO2max) 47.5 +/- 1.8 ml.kg-1.min-1] exercising for 80 min at 60-65% VO2max.Tre and Tsk (head, arm, thigh, and calf) and heart rate (HR) were recorded throughout. O2 uptake (VO2), minute ventilation (VE), CO2 production (VCO2), and heart rate (HR) were recorded at four intervals. During experiment 1 significant changes in HR and insignificant changes in VCO2, VE, and VO2 occurred throughout prolonged exercise. Tre increased significantly from 37.1 +/- 0.1 degrees C (rest) to 37.8 +/- 0.1 degrees C after 80 min of exercise. There were only significant changes in arm Tsk. Experiment 2 involved a nonhomogeneous group (T5-T10/T11) of active paraplegics (VO2max 39.9 +/- 4.3 ml.kg-1.min-1) exercising at 60-65% VO2max for up to 45 min on the treadmill while Tre and Tes were simultaneously recorded. Tes rose significantly faster than Tre during exercise (dT/dt 20 min: Tes 0.050 +/- 0.003 degrees C/min and Tre 0.019 +/- 0.005 degrees C/min), and Tes declined significantly faster than Tre at the end of exercise. Tes was significantly higher than Tre at the end of exercise. Our results suggest that during wheelchair propulsion by paraplegics, Tes may be a better estimate of core temperature than Tre.