Intensity and duration effects of exercise on heart cAMP, phosphorylase, and glycogen.

Glycogen, phosphorylase, and adenosine 3',5'-cyclic monophosphate (cAMP) were determined in rat heart following an acute exercise bout. Intensity and duration of exercise were varied to gain further insights into the mechanism regulating myocardial glycogenolysis during exercise. Groups of rats were run at either 15 or 30 m/min for 0, 5, 10, 15, or 30 min and immediately killed. Heart glycogen degradation was influenced by intensity and duration of exercise and was independent of cAMP levels and activation of phosphorylase to its a form. cAMP levels were increased in the heart, dependent on intensity and duration of exercise. Phosphorylase in the a form increased at the onset of exercise, independent of intensity, and remained elevated throughout the exercise despite little or no glycogenolysis. Absolute phosphorylase a activity was also increased with exercise and was independent of intensity of exercise. Compared with resting levels, total phosphorylase activity was decreased at all times at the lower exercise intensity, whereas total phosphorylase activity declined at the higher intensity only after glycogenolysis had occurred. These data suggest that myocardial glycogen degradation during exercise can occur independently of cAMP and that the percentage of phosphorylase in the a form is not a good indicator of glycogenolytic rate.

Intensity and duration of exercise effects on skeletal muscle cAMP, phosphorylase, and glycogen.

To gain further insights into the mechanisms regulating skeletal muscle glycogenolysis during exercise, glycogen, phosphorylase, and adenosine 3',5'-cyclic monophosphate (cAMP) were determined in fast-twitch white (FTW) and fast-twitch red (FTR) muscle from groups of rats that ran for 0, 5, 10, 15, or 30 min at either 15 or 30 m/min. Glycogen degradation demonstrated an intensity and duration response in both fiber types. cAMP increased in both fiber types by 5 min and remained elevated at all times measured. FTW muscle cAMP levels were independent of both intensity and duration of exercise. FTR muscle cAMP levels were higher from 10 to 30 min at the 30-m/min intensity compared with the 15-m/min intensity. The ratio of the activity of phosphorylase in the presence of 2 mM AMP X 100 (phosphorylase a%) remained elevated at 20-22% independent of intensity and duration in FTW muscle; however, phosphorylase a% demonstrated an intensity and duration effect in FTR muscle. Glycogenolytic rates decreased with time, even though both cAMP and phosphorylase a% remained elevated in both fiber types. These data suggest that cAMP and phosphorylase a activation can be maintained during exercise in skeletal muscle but indicate a dissociation of these factors from glycogenolysis.

Exercise in the treatment of obesity: effects of four interventions on body composition, resting energy expenditure, appetite, and mood.

This study investigated changes in body composition, resting energy expenditure (REE), appetite, and mood in 128 obese women who were randomly assigned to 1 of 4 treatment conditions: diet alone, diet plus aerobic training, diet plus strength training, or diet combined with aerobic and strength training (i.e., combined training). All women received the same 48-week group behavioral program and were prescribed the same diet. Exercising participants were provided 3 supervised exercise sessions per week for the first 28 weeks and 2 sessions weekly thereafter. Participants across the 4 conditions achieved a mean weight loss of 16.5 +/- 6.8 kg at Week 24, which decreased to 15.1 +/- 8.4 kg at Week 48. There were no significant differences among conditions at any time in changes in weight or body composition. Women who received aerobic training displayed significantly smaller reductions in REE at Week 24 than did those who received strength training. There were no other significant differences among conditions at any time on this variable or in changes in appetite and mood.

Response of patients with coronary artery disease stratified by ejection fraction following short-term training.

The purpose of this study was to investigate the response of patients with ischemic heart disease and varied left ventricular function following 6 weeks of exercise training. We studied the oxygen consumption (VO2), and central hemodynamic and metabolic responses of 14 patients with coronary artery disease (CAD) stratified by left ventricular ejection fraction (EF). There were two groups of patients: normal EF (NEF), EF = 64 +/- 9.9 (mean +/- S.E.M.); n = 7, and diminished EF (DEF), EF = 36 +/- 11.6; n = 7. The patients ranged in age from 42 to 72 years (54.9 +/- 2.2), and were evaluated prior to and then following training. Measures of VO2, cardiac output (Qt) stroke volume (SV), heart rate (HR), exercise duration (XTIME) and intensity (XI), as well as plasma lactate (LA), and the catecholamines epinephrine (E) and norepinephrine (NE) were obtained in response to maximal cycle ergometry. Subjects trained three times per week, 30 min per session, at an intensity equal to 70% of their peak oxygen consumption. Repeated measures analysis of variance (ANOVA) revealed no interaction between groups suggesting a similar training response. Significant post-training changes (P < 0.05) were observed in peak VO2 (VO2peak) NEF, 11.8% increase, (16.0 +/- 1.3 to 17.9 +/- 1.1 ml/kg/min) and DEF, 9.3% increase (15.1 +/- 1.6 to 16.5 +/- 1.2 ml/kg/min); submaximal HR, 4% decrease in the NEF (95.57 +/- 4.58 to 92 +/- 4.43 beats/min) and a 6% decrease in the DEF (107.29 +/- 7.44 to 101.43 +/- 6.77 beats/min); XTIME NEF, 11.2% increase (7.8 +/- 0.57 to 8.67 +/- 0.61 min) and DEF, 16.6% increase (7.3 +/- 0.91 to 8.51 +/- 0.69 min); and XI NEF, 19.2% increase (104.3 +/- 11.3 to 124.3 +/- 12.9 W) DEF, 21.2% increase (94.3 +/- 18.5 to 114.3 +/- 16.9 W), and a 15% decrease in resting NE (350 +/- 26 to 296.9 +/- 19 pg/ml). There were no changes in Qt, SV, LA, E, peak NE or peak HR for either group. These findings suggest short-term endurance training at 70% VO2peak provide the necessary stimulus for individuals with CAD and NEF or DEF to display an improvement in XI, XTIME, and VO2peak. The lack of a significant enhancement in Qt with short-term training may indicate that the mechanism by which both study groups were able to attain significantly higher levels of VO2peak may have been attributable to peripheral mechanisms rather than any alterations in Qt, a central mechanism.

Effect of physostigmine on plasma lactate and pyruvate in untrained/trained rats.

Physostigmine (Phy) is metabolized to eseroline, a phenolic compound that appears to alter mitochondrial functions. The effect of Phy on recovery from exercise and on time course of plasma lactate and pyruvate levels following an acute bout of exercise (AE) was examined in untrained and trained (ET) rats. Phy alone elicited significantly higher plasma lactate and pyruvate levels than sedentary control. AE + Phy had a significantly higher plasma lactate and pyruvate levels compared to AE 2 min postadministration. From 5-30 min postexercise, lactate and pyruvate levels did not differ between these two acutely exercised groups. ET + Phy exhibited significantly lower levels of plasma lactate and pyruvate from 5-60 min postexercise compared to ET. The data show that the "additive" effect of Phy on postexercise plasma lactate and pyruvate levels can be attenuated by an enhanced fitness level in these rats.

Effect of concurrent exercise and physostigmine on lactate and pyruvate in plasma, muscle, and brain tissue of rats.

The purpose of this investigation was to determine the effect of physostigmine (Phy) and/or concurrent exercise on lactate, pyruvate, and L/P ratio in plasma, skeletal muscle, and brain tissue in male Sprague-Dawley rats. The Phy-dosed (Phy-D) and Phy-dosed + concurrent acute exercise (Phy-D + CAE) groups elicited significantly higher L/P ratios in plasma compared to the acutely exercised (AE) group at 30 min postexercise. Physostigmine dosing, with or without exercise, resulted in significantly lower muscle pyruvate levels, from 30 to 50 min postdrug administration, in Phy-D and Phy-D + CAE groups compared to the AE group. In the brain, lactate values were significantly elevated in the acutely exercised groups at 5 min postexercise with or without Phy dosing. However, at 15 to 30 min postexercise, lactate values were significantly elevated in the Phy-D + CAE compared to the AE group. These data suggest that when Phy is administered prior to a 20-min moderately intensive exercise bout, there is an accumulation of lactate for a prolonged period of time in recovery.

Flexibility and Strength Measures in Children Participating in a Cardiac Rehabilitation Exercise Program.

In brief: The purpose of this study was to evaluate the effects of a structured rehabilitation program on the strength and flexibility of children with surgically corrected congenital heart disease. Twelve children (eight boys, four girls) participated in one-hour exercise classes, two times per week for 12 weeks. Results showed minimal changes in upper extremity strength, but lower extremity strength improved 10% and 5% on the right and left sides, respectively. Flexibility improved about 25% in the lower extremities. Improvement was also noted in neck flexion, hip and oblique rotation, hamstring and low back stretch, and heel cord stretch. These findings indicate that this type of program can improve strength and flexibility in children who have undergone complex heart surgery and may help them achieve a more normal life-style.

Age-associated blood glucose levels during exercise in female swimmers.

The purpose of this study was to determine whether age-associated alterations in blood glucose levels occur during exercise. In addition, blood lactate and fitness levels (VO2max) were examined to ascertain if these factors influenced the age-related responses. Sixty-four female masters swimmers (25-75 years) were classified into either a well trained (WT) or recreational trained (RT) group and exercised on a treadmill to VO2max X VO2max data confirmed our classification of WT and RT swimmers based on activity levels. There were no differences in post-absorptive blood glucose and lactate levels across age and fitness. Significant age-related effects on blood glucose levels during exercise (p less than 0.01) but no fitness effect were revealed by ANOVA. Within the first or second exercise stage all age groups demonstrated a significant decline in blood glucose (6.3 to 14.1%). A hyperglycemic response was observed during recovery in all age groups with the exception of the over 60 (60+) group. The 60+ group exhibited lower blood glucose levels compared to all other age groups during exercise commencing with the second exercise stage. There were no significant differences in glucose levels among any of the other age groups during exercise or recovery. There were no age-related differences in maximal or recovery lactates. These data indicate that there is an alteration of blood glucose homeostasis during exercise in females over 60 years of age.

Influence of age on caloric expenditure during exercise.

Young (147 +/- 2 g) and adult (322 +/- 7 g) male Sprague Dawley rats were subjected to an incremental treadmill protocol and assessed via the Oxyscan Metabolic System in order to determine if differences exist relative to oxygen consumption (VO2, expressed in ml/kg/min), respiratory exchange ratio (RER) and caloric expenditure of two different age groups. The young rats attained a higher VO2 (81.55 +/- 1.22) compared to adult rats (68.97 +/- 2.05) at a maximal level of exercise. The adult rats became dependent upon carbohydrates as the primary source of energy until reaching 52% VO2 max, whereas the young rats did not resort to carbohydrate utilization as a primary fuel source until reaching 87% VO2max. At peak exercise, the adult animals burned only 15% less kcal/kg/h than the young rats, but the adult rats burned 37% more carbohydrate than the young animals. These data suggest that as exercise intensity increases, younger rats can more readily maintain a higher level of oxygen consumption accompanied by a more efficient use of fat as an energy source compared to adult rats. The clinical implication of this finding suggests that during the growth and development years of life, fat plays a significant role in energy expenditure needs and may therefore be more important than currently believed in young children's nutritional intake.

Contemporary cardiac rehabilitation: patient characteristics and temporal trends over the past decade.

BACKGROUND: Recent and dramatic therapeutic advances, aggressive care of the elderly, and a heightened awareness of secondary prevention have had a significant, albeit incompletely described, impact on cardiac rehabilitation (CR) programs. The authors did a retrospective analysis on 1,848 patients from their phase II CR program that were treated over the past decade. The authors sought to identify and analyze how advances in cardiovascular care might be related to temporal changes in demographics, medical comorbidities, coronary artery disease risk factors, and cardiovascular history among individuals with cardiac disease who have completed the phase II CR program over a 10-year period. METHODS: Cardiac rehabilitation records were reviewed from 1986 to 1996 at Akron City Hospital. The data were compiled prospectively by nurses and exercise physiologists and were subsequently analyzed. The charts reviewed were from 1,848 patients who completed outpatient phase II CR. RESULTS: The program began in 1986 with 53 patients completing CR and evolved to 309 in 1996. There has been an increase in the number of elderly patients referred to and completing the program. The number of participants older than 65 years of age increased from 28.3% in 1986 to 52.1% in 1996. Cardiac rehabilitation participants reflect the known demographics of patients with clinical coronary artery disease. Men outnumber women and, on average, the female participants are older than the male participants. There has been a statistically significant increase in medical comorbidities over the course of the study. Although the absolute number of patients entering CR after coronary artery bypass graft survey has remained fairly constant, there has been a dramatic increase in the absolute number of patients entering CR after percutaneous tansluminal coronary angioplasty (with the latter recently comprising a majority of CR participants). CONCLUSION: There is a significant trend in the attendance and completion of CR programs by older individuals, which suggests a greater awareness of patients and their physicians. The growth of the program is fueled by high-risk patients with more comorbidities who potentially are the group of patients able to obtain the greatest absolute benefit from CR.

Endurance training, not acute exercise, differentially alters beta-receptors and cyclase in skeletal fiber types.

beta-Adrenergic receptor binding characteristics and adenylate cyclase activity were examined in rat skeletal muscle membranes to determine if acute exercise or endurance training altered beta-receptors or adenylate cyclase activity in different muscle fiber types. Binding characteristics and adenylate cyclase activity were examined in type IIA [red fast-twitch, red vastus (RV)], type IIB [white fast-twitch, white vastus (WV)], and type I [red slow-twitch, soleus (S)] muscles. Acute exercise involved a 20-min run on a treadmill at 20 m/min and did not alter beta-receptor density or adenylate cyclase activity in any of the fiber types examined. Endurance training consisted of a progressive treadmill protocol that involved increasing intensity and duration of exercise for 18 wk. beta-Adrenergic receptor density increased in skeletal muscle fiber types primarily recruited during submaximal training (types I and IIA), whereas nonreceptor-mediated adenylate cyclase activity was altered in the three fiber types. Endurance training significantly increased beta-receptor density in RV by 25% and in S by 19% (P less than 0.05), whereas in WV beta-receptor density was not altered. Basal adenylate cyclase activity in RV was increased approximately 2.5 fold by endurance training. Nonreceptor-mediated adenylate cyclase activity, stimulated by NaF and forskolin, increased by approximately twofold in both RV and WV as a result of endurance training. The data support and extend previous observations to show greater effects of endurance training in types I and IIA fibers with respect to alterations in beta-receptor density and alterations in adenylate cyclase activity in each fiber type. Acute exercise did not alter these parameters either in trained or untrained rats.