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PubMed2000

Effects of prior heavy exercise on phase II pulmonary oxygen uptake kinetics during heavy exercise.

We tested the hypothesis that heavy-exercise phase II oxygen uptake (VO(2)) kinetics could be speeded by prior heavy exercise. Ten subjects performed four protocols involving 6-min exercise bouts on a cycle ergometer separated by 6 min of recovery: 1) moderate followed by moderate exercise; 2) moderate followed by heavy exercise; 3) heavy followed by moderate exercise; and 4) heavy followed by heavy exercise. The VO(2) responses were modeled using two (moderate exercise) or three (heavy exercise) independent exponential terms. Neither moderate- nor heavy-intensity exercise had an effect on the VO(2) kinetic response to subsequent moderate exercise. Although heavy-intensity exercise significantly reduced the mean response time in the second heavy exercise bout (from 65.2 +/- 4.1 to 47.0 +/- 3.1 s; P < 0.05), it had no significant effect on either the amplitude or the time constant (from 23.9 +/- 1.9 to 25.3 +/- 2.9 s) of the VO(2) response in phase II. Instead, this "speeding" was due to a significant reduction in the amplitude of the VO(2) slow component. These results suggest phase II VO(2) kinetics are not speeded by prior heavy exercise.

Adult↗
PubMedDate not supplied

Research and commentary: Change in exercise tolerance, activity and sleep patterns, and quality of life in patients with cancer participating in a structured exercise program.

PURPOSE/OBJECTIVES: To investigate the feasibility of an exercise program patterned after a phase II cardiac rehabilitation program to improve selected physiologic and psychological parameters of health in patients with cancer. DESIGN: Prospective, repeated measures study. SETTING: Two major military medical centers in the southwestern United States. SAMPLE: 62 patients diagnosed with cancer within the previous two years. Ages ranged from 24-83 (meanX = 59). Half of the participants were male and half were female. Minorities made up 29% of the sample. Participants had a wide range of cancer diagnoses and all stages of cancer. Fifteen subjects were undergoing treatment when they enrolled in the study. More than half of the subjects exercised prior to their cancer diagnoses, but fewer than half were able to resume an exercise routine following their cancer diagnoses. METHODS: Subjects met two days each week for 12 weeks for exercise and education. MAIN RESEARCH VARIABLES: Exercise tolerance as measured with a graded exercise test, activity and sleep patterns as measured with a wrist actigraph, and quality of life (QOL) as measured with the Cancer Rehabilitation Evaluation System-Short Form. FINDINGS: Significant improvements were observed over time in exercise tolerance, selected activity and sleep patterns, and QOL among the 46 (74%) subjects who completed the program. CONCLUSIONS: Patients with various types and stages of cancer can safely exercise using a cardiac rehabilitation model and can realize significant improvements in exercise tolerance, selected activity and sleep patterns, and QOL. IMPLICATIONS FOR NURSING: Most people are aware that regular exercise is part of a healthy lifestyle. After cancer diagnosis and treatment, patients experience uncertainty regarding how to resume exercise or how to begin an exercise program as part of their rehabilitation. Participation in a structured exercise program can provide patients with a safe environment within which to exercise at an intensity appropriate to their individual needs.

Adaptation, Psychological↗
PubMed2002

Relationship between resting parameters of the mitral valve and exercise capacity in patients with mitral stenosis: can the diastolic filling period predict exercise capacity?

BACKGROUND AND AIMS OF THE STUDY: In order to provide patients with better exercise capacity, interventional therapy to the mitral valve is often carried out in mitral stenosis (MS). Hence, it is crucial to determine exercise capacity before deciding on the time of intervention. The study aim was to demonstrate whether resting parameters of the mitral valve, notably left ventricular diastolic filling period (LVDFP) and mitral valve resistance (MVR), relate to restricted exercise capacity. METHODS: Forty-six patients (30 females, 16 males; mean age 44+/-11 years; range: 33-55 years) with rheumatic MS were enrolled. Exercise capacities of patients were grouped according to NYHA classification and maximal exercise tolerance values obtained using exercise testing. Exercise capacity in male patients was quantified. Relationships between patient variables and exercise capacity were evaluated using simple linear regression analysis. In order to identify determinants of exercise capacity, a discriminate multivariate analysis was performed with variables, which were found to correlate significantly in the univariate analysis. RESULTS: There were no correlations between echo score, MVR, planimetric mitral valve area (MVA), MVA obtained by the pressure half-time method or calculated by the continuity equation, and transmitral mean gradient and exercise capacity classes as defined by both NYHA and exercise testing. The only predictor of exercise capacity class determined by discriminate multivariate analysis using the significant parameters in the linear regression analysis was LVDFP. The quantified exercise capacity in male patients correlated only with LVDFP (r = 0.64, p = 0.008). CONCLUSION: Exercise capacity cannot be predicted using routine resting parameters of the mitral valve (including MVR) in patients with MS. In this respect, the LVDFP may be of value.

Adult↗
PubMed1998

The convective afterdrop component during hypothermic exercise decreases with delayed exercise onset.

HYPOTHESIS: Following cold water immersion, the post-cooling decrease in esophageal temperature (Tes) (i.e., afterdrop) is 3 times greater during exercise than during shivering, presumably due to increased muscular blood flow and convective core-to-periphery heat loss with exercise (J. Appl. Physiol. 63:2375, 1987). We felt that if exercise were to commence once the afterdrop period during shivering is complete, the threat of a further decrease in Tes (i.e., a second afterdrop) during the subsequent exercise would be minimized because much of the convective capacity for core cooling would already be dissipated. METHODS: Six subjects were each cooled three times in 8 degrees C water, until Tes decreased to 35.3 +/- 0.7 degrees C, and rewarmed by either shivering alone, exercise, or exercise commencing once a shivering afterdrop period was complete. RESULTS: The initial afterdrop was greater during Exercise only (1.1 +/- 0.4 degrees C) than Shivering only (0.35 +/- 0.3 degrees C) and Shivering-Exercise (0.45 +/- 0.2 degrees C) (p < 0.05). In contrast, exercise caused a secondary afterdrop of only 0.38 +/- 0.3 degrees C during Shivering-Exercise (p < 0.05). The initial rewarming rate during Exercise only (3.45 degrees C.h-1) was greater than the initial (2.7 degrees C.h-1) and second (2.4 degrees C.h-1) rewarming rates during Shivering-Exercise (p < 0.05), but not significantly greater than during Shivering only (2.99 degrees C.h-1) (p < 0.1). DISCUSSION: It is likely that during the Shivering-Exercise protocol, continued blood flow to shivering muscles: a) contributes to the initial afterdrop, and thus b) diminishes the convective capacity (or heat sink) available for further cooling during subsequent exercise.

Adult↗
PubMed2006

Perceived exercise barriers, enablers, and benefits among exercising and nonexercising adults with arthritis: results from a qualitative study.

OBJECTIVE: Rates of participation in regular exercise are lower among individuals with arthritis than those without arthritis. This study examined perceived exercise barriers, benefits, and enablers in exercising and nonexercising adults with arthritis. METHODS: Twelve focus groups were conducted with 68 adults with arthritis. Groups were segmented by exercise status, socioeconomic status, and race. Focus group discussions were transcribed verbatim and coded. NVivo software was used to extract themes for exercisers and nonexercisers. RESULTS: A wide range of physical, psychological, social, and environmental factors were perceived to influence exercise. Some of these factors were similar to those in general adult samples, whereas others were unique to individuals with chronic disease. Symptoms of arthritis were barriers to exercise, yet improvements in these outcomes were also seen as potential benefits of and motivations for exercise. Exercisers had experienced these benefits and were more likely to have adapted their exercise to accommodate the disease, whereas nonexercisers desired these benefits and were more likely to have stopped exercising since developing arthritis. Health care providers' advice to exercise and the availability of arthritis-specific programs were identified as needs. CONCLUSION: This study has implications for how to market exercise to individuals with arthritis and how communities and health care professionals can facilitate the uptake of exercise. These implications are discussed.

Adult↗
PubMed1991

Effects of supramaximal exercise on blood glucose levels during a subsequent exercise.

The purpose of the present investigation was to examine the effects of hyperglycemia induced by supramaximal exercise on blood glucose homeostasis during submaximal exercise following immediately after. Six men were subjected to three experimental situations; in two of these situations, 3 min of high-intensity exercise (corresponding to 112, SD 1% VO2max) was immediately followed by either a 60-min period of submaximal exercise (68, SD 2% VO2max) or a 60-min resting period. In the third situation, subjects performed a 63-min period of submaximal exercise only. There were no significant differences between the heart rates, oxygen uptakes, and respiratory exchange ratios during the two submaximal exercise bouts (greater than 15 min) whether or not preceded by supramaximal exercise. The supramaximal exercise was associated within 10 min of the start increases (P less than 0.05) in blood glucose, insulin, and lactate concentrations. This hyperglycemia was more pronounced when subjects continued to exercise submaximally than when they rested (at 7.5 min; P less than 0.05). There was a more rapid return to normal exercise blood glucose and insulin values during submaximal exercise compared with rest. The data show that the hyperinsulinemia following supramaximal exercise is corrected in between 10-30 min during submaximal exercise following immediately, suggesting that this exercise combination does not lead to premature hypoglycemia.

Adult↗
PubMed2003

Exercise, hormones, and body temperature. regulation and action of GH during exercise.

UNLABELLED: That physical exercise stimulates pituitary GH secretion has been known for forty years, but the underlying mechanisms as well as the physiological significance remain elusive. We have previously shown that the concomitant increase in core temperature is essential for the exercise-induced GH release, inasmuch as exercise performed at 4 C results in a suppression of GH secretion, whereas passive heating constitutes a potent stimulus for GH release. Moreover, studies in normal subjects show that GH stimulates sweat production and evaporative heat loss during heat exposure with and without exercise, whereas GH-deficiency is associated with reduced sweat secretion and increased heat storage during similar conditions. The neurotransmitters involved in GH secretion during exercise remain uncertain; we therefore investigated the putative role of ghrelin, which is a gut-derived endogenous ligand for the GHS receptor. We measured circulating ghrelin levels before during and after submaximal aerobic exercise in healthy subjects and GH-deficient patients. The circulating ghrelin levels were unchanged during and after exercise in all subjects. Growth hormone stimulates lipolysis and lipid oxidation during basal and fasting conditions and we recently investigated whether GH also regulates substrate metabolism during exercise. The design involved GH-deficient patients studied during exercise with and without GH administration as compared to untreated healthy subjects. Growth hormone predominantly stimulated the turnover of free fatty acids in the recovery phase after exercise. CONCLUSIONS: 1) the increase in GH release during exercise is associated with the concomitant increase in body temperature, 2) GH stimulates sweat secretion and heat evaporation during exercise, which seems to be of distinct physiological significance, 3) ghrelin is not involved in exercise-induced GH release, 4) the impact of GH on substrate metabolism during exercise includes increased FFA turnover.

Body Temperature↗
PubMed2002

The effect of exercise intensity on the post-exercise esophageal temperature response.

On 2 separate days, nine volunteers aged 23.8 (2.0) years performed 15-min bouts of treadmill running in a temperature-controlled chamber at 29 degrees C at a power output that elicited either 70% (moderate) or 93% (intense) of maximum oxygen consumption. Exercise was followed by a 45-min recovery period. End-exercise esophageal temperature (Tes) was elevated by 0.97 degrees C and 2.17 degrees C above baseline for the moderate and intense exercise trials, respectively. Post-exercise Tes achieved a sustained elevated value of 0.38 degrees C and 0.79 degrees C within 15 min of exercise cessation. Systolic blood pressure (SBP) for both exercise trials became hypotensive for the full recovery period, with the magnitude of the reduction being greater for the intense exercise (P < 0.05). Diastolic blood pressure (DBP) was unaffected by exercise intensity and values were lower than baseline between 15 min and 30 min post-exercise (P < 0.05). Mean arterial pressure (MAP) was reduced from baseline for both exercise trials, with intense exercise showing a greater decrement (P < 0.05). It was shown that the increase in the post-exercise hypotensive response, induced by exercise of increasing intensity, was paralleled by an increase in the magnitude of the post-exercise elevation in Tes (i.e., a difference of 0.41 degrees C between conditions).

Adult↗
PubMed2005

Prior endurance exercise attenuates growth hormone response to subsequent resistance exercise.

This study examined the influence of prior endurance exercise on hormonal responses to subsequent resistance exercise. Ten males exercised on a cycle ergometer at 50% of maximal oxygen uptake for 60 min and subsequently completed a resistance exercise (bench and leg press, four sets at ten repetitions maximum with an interset rest period of 90 s). Alternatively, the subjects performed the protocol on a separate day with prior endurance exercise limited to 5 min. Blood was obtained before and after the endurance exercise, and 10, 20, and 30 min after the resistance exercise. Maximal isometric torque measured before and after endurance and resistance exercises showed no significant difference between trials. No significant difference was seen in the concentrations of glucose, lactate, testosterone, and cortisol between the trials, but free fatty acids (FFA) and growth hormone (GH) increased (P<0.01 and P<0.05, respectively) after 60 min of endurance exercise. Conversely, after the resistance exercise, GH was attenuated by 60 min of prior exercise (P<0.05). These results indicate that the GH response to resistance exercise is attenuated by prior endurance exercise. This effect might be caused by the increase in blood FFA concentration at the beginning of resistance exercise.

Adult↗
PubMed1994

Comparison of exercise echocardiography with an exercise score to diagnose coronary artery disease in women.

This study compares the accuracy of the routine exercise electrocardiogram, exercise score, and exercise echocardiography for the diagnosis of coronary artery disease (CAD) in women. Seventy women with a pretest probability of 53 +/- 30% for CAD were stressed using a maximal symptom-limited bicycle exercise protocol. Significant ST-segment change was defined by a depression of > 0.1 mV 0.06 second after the J point. The exercise score was calculated from ST response, heart rate, and workload using an equation derived from a multivariate model. A positive stress echocardiogram was defined by development of a new or worsening wall motion abnormality. The results were compared with the presence or absence of significant (> 50% diameter) stenoses at angiography. Exercise echocardiography identified 29 of the 33 patients (88%) with CAD, compared with 22 (67%) using ST analysis alone, and 20 (61%) using the exercise score (both p < 0.05 vs exercise echocardiography). The specificity of exercise echocardiography (84%) and the multivariate score (73%) were comparable, and exceeded that of the ST analysis (51%) in 37 patients without CAD (p < 0.01). The accuracy of exercise echocardiography (86%) exceeded that of the exercise score (67%, p = 0.01) and ST analysis (59%, p < 0.01). Among all 70 patients, an intermediate (20% to 80%) probability of coronary disease was identified in 21 patients on the basis of exercise echocardiography, in 38 based on the multivariate score, and in 38 based on the ST analysis alone. Exercise echocardiography is more sensitive than the exercise score, and more sensitive and specific than ST-segment analysis for the diagnosis of CAD in women.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed2000

Superiority of endothelin-1 over norepinephrine in exercise-induced alterations of the conduit artery tone of the non-exercised arm in patients with chronic heart failure.

This study is aimed at examining the relative importance of norepinephrine and endothelin-1 in treadmill exercise-induced changes in brachial arterial tone of the non-exercised arm in patients with chronic heart failure (CHF). Brachial artery diameter and blood flow were measured before and after exercise in eight healthy volunteers and 18 patients with stable chronic heart failure by high-resolution ultrasound. Maximal exercise resulted in brachial artery dilatation in controls (4.42+/-0.39 vs. 4.77+/-0.39 mm; P<0. 0001) in contrast to constriction seen in the patients (5.27+/-0.67 vs. 5.12+/-0.66 mm; P=0.07). Both groups demonstrated a significant increase in blood flow after exercise. The pre-exercise (2.83+/-0.76 vs. 1.69+/-0.15 pmol/l; P=0.0004), post-exercise (4.15+/-1.5 vs. 2. 02+/-0.34 pmol/l; P=0.0004) and the percent increase (47.15+/-32.5 vs. 19.0+/-10.5%; P=0.02) in endothelin-1 levels were significantly greater in patients than in controls. In contrast to endothelin-1, the exercise-induced percent increase in norepinephrine was greater in controls than patients (100.7+/-51.8 vs. 49.8+/-43.4%; P=0.01). The percent change in the diameter of the brachial artery in response to maximal exercise was significantly correlated to pre- (r=0.634; P=0.003) and post-exercise (r=0.467; P=0.05) endothelin-1 levels in patients but not in controls [pre-exercise (r=0.07; P=0. 86), post-exercise (r=0.310; P=0.47)]. The change in the diameter of the brachial artery did not correlate with pre- or post-exercise plasma norepinephrine levels in either group. These findings suggest that endothelin-1 is potentially more important than norepinephrine in contributing exercise-induced brachial artery constriction in patients with chronic heart failure.

Brachial Artery↗
PubMed2003

Clinical and economic impact of exercise electrocardiography and exercise echocardiography in clinical practice.

BACKGROUND: Patients with known or suspected coronary disease are often investigated to facilitate risk assessment. We sought to examine the cost-effectiveness of strategies based on exercise echocardiography and exercise electrocardiography. METHODS AND RESULTS: We studied 7656 patients undergoing exercise testing; of whom half underwent exercise echocardiography. Risk was defined with the Duke treadmill score for those undergoing exercise electrocardiography alone, and by the extent of ischaemia by exercise echocardiography. Cox proportional hazards models, risk adjusted for pretest likelihood of coronary artery disease, were used to estimate time to cardiac death or myocardial infarction. Costs (including diagnostic and revascularisation procedures, hospitalisations, and events) were calculated, inflation-corrected to year 2000 using Medicare trust fund rates and discounted at a rate of 5%. A decision model was employed to assess the marginal cost effectiveness (cost/life year saved) of exercise echo compared with exercise electrocardiography. Exercise echocardiography identified more patients as low-risk (51% vs 24%, p<0.001), and fewer as intermediate- (27% vs 51%, p<0.001) and high-risk (22% vs 4%); survival was greater in low- and intermediate-risk and less in high-risk patients. Although initial procedural costs and revascularisation costs (in intermediate-high risk patients) were greater, exercise echocardiography was associated with a greater incremental life expectancy (0.2 years) and a lower use of additional diagnostic procedures when compared with exercise electrocardiography (especially in lower risk patients). Using decision analysis, exercise echocardiography ( in 2615/life year saved) was more cost effective than exercise electrocardiography. CONCLUSION: Exercise echocardiography may enhance cost-effectiveness for the detection and management of at risk patients with known or suspected coronary disease.

Coronary Artery Disease↗
PubMed2003

Can primary care doctors prescribe exercise to improve fitness? The Step Test Exercise Prescription (STEP) project.

BACKGROUND: Sedentary lifestyle is associated with adverse health outcomes. Available evidence suggests that, despite positive attitudes toward regular exercise in promoting a healthy lifestyle, few physicians actually prescribe exercise for their patients. Barriers include lack of skills and standard office instruments. Because primary care physicians have regular contact with a large proportion of the population, the impact of preventive health interventions may be great. OBJECTIVES: To determine the effect of an exercise prescription instrument (i.e., Step Test Exercise Prescription [STEP]), compared to usual-care exercise counseling delivered by primary care doctors on fitness and exercise self-efficacy among elderly community-dwelling patients. DESIGN: Randomized controlled trial; baseline assessment and intervention delivery with postintervention follow-up at 3, 6, and 12 months. SETTING: Four large (>5000 active patient files) academic, primary care practices: three in urban settings and one in a rural setting, each with four primary care physicians; two clinics provided the STEP intervention and two provided usual care control. PARTICIPANTS: A total of 284 healthy community-dwelling patients (72 per clinic) aged >65 years were recruited in 1998-1999. INTERVENTION: STEP included exercise counseling and prescription of an exercise training heart rate. MAIN OUTCOME MEASURES: The primary outcome measure was aerobic fitness (VO(2max)). Secondary outcomes included predicted VO(2max) from the STEP test, exercise self-efficacy (ESE), and clinical anthropometric parameters. RESULTS: A total of 241 subjects (131 intervention, 110 control) completed the trial. VO(2max) was significantly increased in the STEP intervention group (11%; 21.3 to 24ml/kg/min) compared to the control group (4%; 22 to 23ml/kg/min) over 6 months (p <0.001), and 14% (21.3 to 24.9ml/kg/min) and 3% (22.1 to 22.8ml/kg/min), respectively, at 12 months (p <0.001). A similar significant increase in ESE (32%; 4.6 vs 6.8) was observed for the STEP group compared to the control group (22%; 4.2 vs 5.4) at 12 months (p < 0.001). Systolic blood pressure decreased 7.3% and body mass index decreased 7.4% in the STEP group, with no significant change in the control group (p <0.05). Exercise counseling time was significantly (p <0.02) longer in the STEP (11.7+/-3.0 min) compared to the control group (7.1+/-7.0 min), but more (p <0.05) subjects completed > or =80% of available exercise opportunities in the STEP group. CONCLUSIONS: Primary care physicians can improve fitness and exercise confidence of their elderly patients using a tailored exercise prescription (e.g., STEP). Further, STEP appears to maintain benefits to 12 months and may improve exercise adherence. Future study should determine the impact of combining cognitive/behavior change strategies with STEP.

Aged↗
PubMedDate not supplied

Comparison of echocardiography at peak exercise and after bicycle exercise in evaluation of patients with known or suspected coronary artery disease.

To determine if echocardiography done immediately after bicycle exercise provides the same information as imaging at peak exercise, we evaluated 104 consecutive patients being studied for coronary artery disease. Interpretable exercise echocardiograms were obtained in 96 patients (92%), 29 of whom had a new wall motion abnormality detected with exercise echocardiography. Of these 29 patients, 10 had a wall motion abnormality detected in apical views obtained during peak exercise that resolved by the time apical imaging was performed after exercise. Three of these 10 patients, however, had wall motion abnormalities in parasternal views taken after exercise in areas adjacent to the wall motion abnormality imaged at peak exercise. The sensitivity of exercise-induced wall motion abnormality for the detection of significant coronary artery disease in those patients undergoing coronary arteriography was 70% for imaging done after exercise versus 100% for imaging done at peak exercise. Six patients' conditions would have been misclassified as normal if only imaging done after exercise had been performed. We conclude that the addition of echocardiographic imaging at peak exercise on a bicycle enhances the sensitivity for the detection of coronary artery disease with exercise echocardiography.

Adult↗
PubMed2006

Effects of exercise intensity and duration on the excess post-exercise oxygen consumption.

Recovery from a bout of exercise is associated with an elevation in metabolism referred to as the excess post-exercise oxygen consumption (EPOC). A number of investigators in the first half of the last century reported prolonged EPOC durations and that the EPOC was a major component of the thermic effect of activity. It was therefore thought that the EPOC was a major contributor to total daily energy expenditure and hence the maintenance of body mass. Investigations conducted over the last two or three decades have improved the experimental protocols used in the pioneering studies and therefore have more accurately characterized the EPOC. Evidence has accumulated to suggest an exponential relationship between exercise intensity and the magnitude of the EPOC for specific exercise durations. Furthermore, work at exercise intensities >or=50-60% VO2max stimulate a linear increase in EPOC as exercise duration increases. The existence of these relationships with resistance exercise at this stage remains unclear because of the limited number of studies and problems with quantification of work intensity for this type of exercise. Although the more recent studies do not support the extended EPOC durations reported by some of the pioneering investigators, it is now apparent that a prolonged EPOC (3-24 h) may result from an appropriate exercise stimulus (submaximal: >or=50 min at >or=70% VO2max; supramaximal: >or=6 min at >or=105% VO2max). However, even those studies incorporating exercise stimuli resulting in prolonged EPOC durations have identified that the EPOC comprises only 6-15% of the net total oxygen cost of the exercise. But this figure may need to be increased when studies utilizing intermittent work bouts are designed to allow the determination of rest interval EPOCs, which should logically contribute to the EPOC determined following the cessation of the last work bout. Notwithstanding the aforementioned, the earlier research optimism regarding an important role for the EPOC in weight loss is generally unfounded. This is further reinforced by acknowledging that the exercise stimuli required to promote a prolonged EPOC are unlikely to be tolerated by non-athletic individuals. The role of exercise in the maintenance of body mass is therefore predominantly mediated via the cumulative effect of the energy expenditure during the actual exercise.

Adaptation, Physiological↗
PubMed1998

Exercise metabolism in human skeletal muscle exposed to prior eccentric exercise.

1. The effects of unaccustomed eccentric exercise on exercise metabolism during a subsequent bout of graded concentric exercise were investigated in seven healthy male subjects. Arterial and bilateral femoral venous catheters were inserted 2 days after eccentric exercise of one thigh (eccentric thigh) and blood samples were taken before and during graded two-legged concentric knee-extensor exercise. Muscle biopsies were obtained from the eccentric and control vastus lateralis before (rest) and after (post) the concentric exercise bout. 2. Maximal knee-extensor concentric exercise capacity was decreased by an average of 23 % (P < 0.05) in the eccentric compared with the control thigh. 3. The resting muscle glycogen content was lower in the eccentric thigh than in the control thigh (402 +/- 30 mmol (kg dry wt)-1 vs. 515 +/- 26 mmol (kg dry wt)-1, means +/- s.e.m., P < 0.05), and following the two-legged concentric exercise this difference substantially increased (190 +/- 46 mmol (kg dry wt)-1 vs. 379 +/- 58 mmol (kg dry wt)-1, P < 0.05) despite identical power and duration of exercise with the two thighs. 4. There was no measurable difference in glucose uptake between the eccentric and control thigh before or during the graded two-legged concentric exercise. Lactate release was higher from the eccentric thigh at rest and, just before termination of the exercise bout, release of lactate decreased from this thigh (suggesting decreased glycogenolysis), whereas no decrease was found from the contralateral control thigh. Lower glycerol release from the eccentric thigh during the first, lighter part of the exercise (P < 0.05) suggested impaired triacylglycerol breakdown. 5. At rest, sarcolemmal GLUT4 glucose transporter content and glucose transport were similar in the two thighs, and concentric exercise increased sarcolemmal GLUT4 content and glucose transport capacity similarly in the two thighs. 6. It is concluded that in muscle exposed to prior eccentric contractions, exercise at a given power output requires a higher relative workload than in undamaged muscle. This increases utilization of the decreased muscle glycogen stores, contributing to decreased endurance.

Adult↗
PubMed2001

Effects of exercise pressor reflex activation on carotid baroreflex function during exercise in humans.

1. This investigation was designed to determine the contribution of the exercise pressor reflex to the resetting of the carotid baroreflex during exercise. 2. Ten subjects performed 3.5 min of static one-legged exercise (20 % maximal voluntary contraction) and 7 min dynamic cycling (20 % maximal oxygen uptake) under two conditions: control (no intervention) and with the application of medical anti-shock (MAS) trousers inflated to 100 mmHg (to activate the exercise pressor reflex). Carotid baroreflex function was determined at rest and during exercise using a rapid neck pressure/neck suction technique. 3. During exercise, the application of MAS trousers (MAS condition) increased mean arterial pressure (MAP), plasma noradrenaline concentration (dynamic exercise only) and perceived exertion (dynamic exercise only) when compared to control (P < 0.05). No effect of the MAS condition was evident at rest. The MAS condition had no effect on heart rate (HR), plasma lactate and adrenaline concentrations or oxygen uptake at rest and during exercise. The carotid baroreflex stimulus-response curve was reset upward on the response arm and rightward to a higher operating pressure by control exercise without alterations in gain. Activation of the exercise pressor reflex by MAS trousers further reset carotid baroreflex control of MAP, as indicated by the upward and rightward relocation of the curve. However, carotid baroreflex control of HR was only shifted rightward to higher operating pressures by MAS trousers. The sensitivity of the carotid baroreflex was unaltered by exercise pressor reflex activation. 4. These findings suggest that during dynamic and static exercise the exercise pressor reflex is capable of actively resetting carotid baroreflex control of mean arterial pressure; however, it would appear only to modulate carotid baroreflex control of heart rate.

Adult↗
PubMed2002

Influence of pre-exercise muscle glycogen content on exercise-induced transcriptional regulation of metabolic genes.

Transcription of metabolic genes is transiently induced during recovery from exercise in skeletal muscle of humans. To determine whether pre-exercise muscle glycogen content influences the magnitude and/or duration of this adaptive response, six male subjects performed one-legged cycling exercise to lower muscle glycogen content in one leg and then, the following day, completed 2.5 h low intensity two-legged cycling exercise. Nuclei and mRNA were isolated from biopsies obtained from the vastus lateralis muscle of the control and reduced glycogen (pre-exercise glycogen = 609 +/- 47 and 337 +/- 33 mmol kg(-1) dry weight, respectively) legs before and after 0, 2 and 5 h of recovery. Exercise induced a significant (P < 0.05) increase (2- to 3-fold) in transcription of the pyruvate dehydrogenase kinase 4 (PDK4) and uncoupling protein 3 (UCP3) genes in the reduced glycogen leg only. Although PDK4, lipoprotein lipase (LPL) and hexokinase II (HKII) mRNA were elevated in the reduced glycogen leg before exercise, no consistent difference was found between the two legs in response to exercise. In a second study, six subjects completed two trials (separated by 2 weeks) consisting of 3 h of two-legged knee extensor exercise with either control (398 +/- 52 mmol kg(-1) dry weight) or low (240 +/- 38 mmol kg(-1) dry weight) pre-exercise muscle glycogen. Exercise induced a significantly greater increase in PDK4 transcription in the low glycogen (> 6-fold) than in the control (< 3-fold) trial. Induction of PDK4 and UCP3 mRNA in response to exercise was also significantly higher in the low glycogen (11.4- and 3.5-fold, respectively) than in the control (5.0- and 1.7-fold, respectively) trial. These data indicate that low muscle glycogen content enhances the transcriptional activation of some metabolic genes in response to exercise, raising the possibility that signalling mechanisms sensitive to glycogen content and/or FFA availability may be linked to the transcriptional control of exercise-responsive genes.

Adult↗