Skeletal muscle sorbitol levels in diabetic rats with and without insulin therapy and endurance exercise training.

Sorbitol accumulation is postulated to play a role in skeletal muscle dysfunction associated with diabetes. The purpose of this study was to determine the effects of insulin and of endurance exercise on skeletal muscle sorbitol levels in streptozotocin-induced diabetic rats. Rats were assigned to one experimental group (control sedentary, control exercise, diabetic sedentary, diabetic exercise, diabetic sedentary no-insulin). Diabetic rats received daily subcutaneous insulin. The exercise-trained rats ran on a treadmill (1 hour, 5X/wk, for 12 weeks). Skeletal muscle sorbitol levels were the highest in the diabetic sedentary no-insulin group. Diabetic sedentary rats receiving insulin had similar sorbitol levels to control sedentary rats. Endurance exercise did not significantly affect sorbitol levels. These results indicate that insulin treatment lowers sorbitol in skeletal muscle; therefore sorbitol accumulation is probably not related to muscle dysfunction in insulin-treated diabetic individuals. Endurance exercise did not influence intramuscular sorbitol values as strongly as insulin.

Sports and recreational injuries: regional rural injury study-II: impact on agricultural households and operations.

OBJECTIVES: To identify the incidence, severity, and potential risk factors for sports/recreational injuries incurred by children and adults in a five state, rural, Midwest, agricultural household population. METHODS: Computer assisted telephone interviews that included questions about all injuries were completed for eligible, participating households for 1999; 16,538 people participated, including 8488 children less than 20 years of age. Rates and 95% confidence intervals were calculated, and causal models guided multivariate models. RESULTS: Of a total of 2586 injuries, 1301 (50%) were not related to agricultural activity. Among these, 733 (28%) were associated with sports/recreational activities including multiple person sports (64%), general play activities (19%), and single person sports (14%). The overall rate was 46.4 injury events per 1000 persons per year. Rates for children were 99.4 for boys and 64.3 for girls. For adults (aged 20 and above), rates were 11.9 for men and 4.8 for women. For children, 93% received health care, 44% were restricted for seven or more days, and 18% lost agricultural work time of seven or more days; the respective proportions for adults were 88%, 45%, and 17%. Multivariate analysis for children showed increased risks for Nebraska residents, males, and those 10-14 or 15-19 years. For adults, increased risks were identified for males and those 20-24 years; decreased risks were observed for Nebraska residents and those 45-54 years. CONCLUSIONS: Sports/recreational activities are an important source of injury with relevant consequences for this population, including significant restricted daily activity and lost agricultural work time. Key findings provide a basis for further study to address these burdens.

Validity and reliability of combining three methods to determine ventilatory threshold.

PURPOSE: This research was undertaken to validate a combination of methodologies to determine ventilatory threshold (VT). METHODS: Three methods were used individually and then combined to determine VT as follows: 1) ventilatory equivalencies, 2) excess CO2 production, and 3) a modified V-slope method. Three groups of participants-endurance athletes (N = 132), healthy, aerobically active adults (N = 31), and healthy, sedentary/low-active adults (N = 22)-were independently evaluated for VT and compared with the criterion standard lactate threshold (LT) defined as the first rise in blood lactate with increasing intensity of exercise. RESULTS: VT and LT were significantly correlated using the combined VT method within each study group (r = 0.98, 0.97, and 0.95, respectively; P < 0.001). Mean VO2 values at VT and LT were not significantly different between the three groups (P > 0.20). The combined method improved the determination rate of VT and reduced the standard deviation of the LT - VT difference by 80-170% over the individual methods. During test-retest procedures VO2lt and VO2vt determined by the combined method met criteria demonstrating further reliability. CONCLUSION: The combined method to determine VT is valid and reliable across a wide fitness range in healthy individuals and improves the determination rate and accuracy of VT determination over the use of single methods.

Cardiac troponin T alterations in myocardium and serum of rats after stressful, prolonged intense exercise.

The goal of this study was to determine whether the stress of forced exercise would result in injury to the myocardium. Male rats with 8% of body weight attached to the tail were forced to swim 3.5 h (3.5S), forced to swim 5 h (5S), or pretrained for 8 days and then forced to swim 5 h (T5S). Rats were killed immediately after they swam (0 h PS) and at 3 h (3 h PS), 24 h (24 h PS), and 48 h after they swam (48 h PS). Tissue homogenates of the left ventricle were analyzed by Western blot analysis for cardiac troponin T (cTnT). Serum cTnT was quantified by immunoassay. Results indicated that, in the 3.5S, 5S, and T5S groups, serum cTnT was significantly (P < 0.01) increased at 0 and 3 h PS. The 5S group demonstrated a greater increase in serum cTnT than the 3.5S group (P < 0.01) and the T5S group (P < 0.01) at 0 h PS. Western blot analysis indicated significant decreases (P < 0. 01) in myocardial cTnT in the 5S group only at 0 h PS (P < 0.01) and 3 h PS (P < 0.05). Histological evidence of localized myocyte damage demonstrated by interstitial inflammatory infiltrates consisting of neutrophils, lymphocytes, and histiocytes, as well as vesicular nuclei-enlarged chromatin patterns, was observed in left ventricle specimens from the 5S group at 24 and 48 h PS. Our findings demonstrate that stressful, forced exercise induces alterations in myocardial cTnT and that training before exercise attenuates the exercise-induced heart damage.

Loss of myocardial CK-MB into the circulation following 3.5 hours of swimming in a rat model.

The purpose of this study was to document alterations of creatine kinase-B (CK-B) in the left and right ventricles of rats and CK-MB release into the circulation following a single bout of stressful prolonged intense exercise. Male Sprague-Dawley rats, with 8% bodyweight attached to each tail, were forced to swim 3.5 hours and were then sacrificed immediately (0 h PS), 3 hours (3 h PS), 24 hours (24 h PS), and 48 hours (48 h PS) post swimming, respectively. Sedentary (control) rats were sacrificed at rest. Serum CK-MB mass increased 2.1 times (8.9 microg/L; p < 0.01 vs. controls of 4.3 microg/L) and 1.4 times (6.0 microg/L; P < 0.01 vs. controls) at 0 h PS, and 3 h PS, respectively, and returned to baseline at 24 h PS. Western blot analysis indicated that CK-B of the right ventricle decreased 14% (p < 0.05), 20% (p < 0.01), and 12% (p < 0.05) at 3h PS, 24h PS and 48h PS, respectively. The CK-B of the left ventricles decreased 34% (p < 0.05) at 0 h PS, returned to baseline at 3 h PS, and was increased 39% (P < 0.01) at 48 h PS. Our findings demonstrate that a single bout of stressful, prolonged, intense exercise resulted in CK-B subunit loss from the myocardium, resulting in increased serum CK-MB concentrations, an indication of myocardial injury.

Alterations in the expression and activity of creatine kinase-M and mitochondrial creatine kinase subunits in skeletal muscle following prolonged intense exercise in rats.

Creatine kinase (CK) isoenzymes are important structural and energy metabolism components in skeletal muscle. In this study, CK isoenzyme alterations were examined in male rats, with an 8% body mass weight attached to their tail. The rats were either forced to swim for 5 h (5S, n = 51), or were pre-trained for 8 days and then forced to swim for 5 h (T5S, n = 48). Rats were sacrificed either immediately (0 h PS), 3 h (3 h PS), or 48 h post-swimming (48 h PS). Serum CK was increased significantly (P < 0.01) 6.2- and 2.0-fold at 0 h PS following the 5S and T5S protocols, respectively. However, training (T5S protocol) significantly (P < 0.01) decreased CK release. Soleus and white gastrocnemius (WG) CK activity was significantly decreased following the 5S protocol (P < 0.05), but not following the T5S protocol. The CK-M activity of the soleus muscle was significantly (P < 0.05) decreased at 0 h PS following both the 5S and T5S protocols, and returned to control values at 3 h PS. The CK-M activity of the WG was significantly (P < 0.05) decreased at 0 h PS following the 5S protocol. Sarcomeric mitochondrial CK (sCK-Mit) was decreased significantly (P < 0.01) at 0 h PS (20%), 3 h PS (14%), 24 h PS (22%), and 48 h PS (15%) following the 5S protocol. However, sCK-Mit was decreased significantly (P < 0.01) only at 0 h PS (7%) following the T5S. The results of this study demonstrate that prolonged intense exercise causes a loss of skeletal muscle CK-M and sCK-Mit activity and that training prior to the prolonged intense exercise attenuates the exercise-induced CK-M and sCK-Mit loss in both red and white skeletal muscles.

Upper body power comparison between groups of cross-country skiers and runners.

The purpose of this study was to evaluate relationships between upper body power (UBP) and cross-country ski skating race velocity (R) in a cross sectional representation of cross-country skiers. Additionally, cross-country skiers' UBP was compared to UBP of distance runners. Participants (n = 195) were tested on a Street Arm Ergometer for UBP using a ramped maximal UBP test simulating a double poling motion. A strong relationship (r = 0.89) between UBP and RV in skiers was determined. High school skiers were separated into slow and fast groups based on reported RV; significant differences (p < 0.05) in both UBP was found to be an effective partial predictor of RV, independent of gender. Mean UBP for the cross-country runners was 46% of mean UBP for the cross-country skiers. With UBP contributing so much to performance in cross-country ski racing, it is recommended that cross-country skiers focus a large portion of their training on the specific development of that fitness component.

Responses to training in cross-country skiers.

PURPOSE: This study evaluated whether cross-country skiers who did not respond positively to a training program consisting of high volume and low intensity would improve if high-intensity training volume was doubled during a subsequent training year. METHODS: During the first year of the study, cross-country skiers (N = 14) were evaluated for VO2max, VO2threshold, lactate response, max arm power, and competitive results after a standard training program. During the second year, the athletes were divided into a control group (athletes who had responded well to the training) and a treatment group (athletes who had responded poorly to the training). The control group (N = 7) repeated the previous year's training program. The treatment group (N = 7) was given a modified training program which increased high-intensity training time as a percentage of total training from < 17% to > 35% and decreased low-intensity training volume 22%. RESULTS: The treatment group, using the high-intensity training program, demonstrated significantly improved VO2max, VO2threshold, max arm power, and competitive results (P < 0.05). CONCLUSIONS: Increased volume of high-intensity training may improve competitive results in cross-country skiers who fail to respond to increased volume of low-intensity training.

Failure of 40 weeks of brisk walking to alter blood lipids in normolipemic women.

Sedentary, eumenorrheic women (N = 27) 22 to 40 years of age, with high baseline levels of plasma high-density lipoprotein cholesterol, were randomly assigned to a walking (n = 16) or a control group (n = 11). The training program involved treadmill walking 4.8 km (3.0 miles) four times a week for 40 weeks at a mean intensity of 72% maximal heart rate. Aerobic power (VO2max) was improved by 22%, but no training effect was observed in body composition variables or blood lipid/lipoprotein levels. Despite additional increments in exercise intensity over the final 20 weeks of training, most of the improvement in VO2max was observed over the first 20 weeks of the study. Exercising subjects' baseline levels of plasma HDL-C were found to be inversely associated with the change (delta) scores in the lipoprotein (r = -0.51, p < or = .05).

Effects of recovery duration and blood lactate level on power output during cycling.

This study identifies the quickest recovery between consecutive anaerobic tests to maintain power output (PO) on the repeated test. Sixteen male cyclists finished three sessions of max rpm initial and repeated 45-s cycling tests at 53.9 N. Tests were separated by 6, 9, or 12 min of recovery cycling (80 rpm, 9.8 N). Results showed no significant differences in PO between initial tests (M = 578.5 +/- 50 watts). PO was significantly less on the 6-min repeated test (M = 551.2 +/- 51) compared to the 9- (M = 575.1 +/- 53) and 12-min tests (M = 581.7 +/- 49.9) (p > 0.05). Net blood lactate [HLa] (repeated test-recovery) was significantly related to net PO (repeated test-initial test) on the 9- (r = 0.60, p < 0.05) and 12-min (r = 0.64, p < 0.001) trials, but not on the 6-min trial (r = 0.35, p = 0.19). In summary, at least 9 min of recovery cycling maintains PO on a repeated 45-s cycling test. Elevated [HLa] at the onset of high-intensity sprint exercise is moderately associated with PO on repeated cycle ergometer tests.

Cardiorespiratory responses to upper extremity aerobic training by postpolio subjects.

The cardiorespiratory responses of ten postpolio subjects participating in a 16-week upper extremity aerobic exercise program were compared to ten non-exercised controls. The subjects trained three times a week for 20 minutes per session. Exercise intensity was prescribed at 70% to 75% of heart rate reserve plus resting heart rate. Dependent variables were resting heart rate, maximal heart rate, resting and immediate-post-exercise systolic and diastolic blood pressures, maximal oxygen consumption, maximal carbon dioxide production, minute ventilation, respiratory exchange ratio, power, and exercise time. After training, the exercise group was superior to the control group in oxygen consumption, carbon dioxide production, minute ventilation, power, and exercise time. There was no reported loss of muscle strength. It was concluded that postpolio subjects can safely achieve an increase in aerobic capacity with a properly modified upper extremity exercise program. This improvement is comparable to that demonstrated by able-bodied adults.

Health and metabolic responses of young calves housed at -30 degrees C to -8 degrees C.

Newborn, male, Holstein calves, were continuously housed for three weeks in calf hutches at 17 degrees C or in a thermal environment which varied rhythmically on a daily basis either between -20 degrees C and -8 degrees C (experiment A) or between -30 degrees C and -18 degrees C (experiment B). Compared to warm-housed calves, cold-housed calves in experiment A had metabolic rates which were significantly higher (p less than 0.001) in a standing position but which were not significantly different (p less than 0.05) in a recumbent position. Recumbent and standing cold-housed calves in experiment B had an increased (p less than 0.05) metabolic rate compared to warm-housed controls. Heat loss was less (p less than 0.05) for recumbent cold-housed calves in experiment B than for standing calves in a thermoneutral environment. Localized subcutaneous hemorrhages of hindlimbs were a consistent necropsy finding among all cold-housed calves. Average daily gains of cold-housed calves were not significantly different from warm-housed controls. Clinical, physiological and pathological findings indicated that cold treatments used in the present study did not cause serious harm to calves. It was concluded that calves housed in properly managed hutches are remarkably cold tolerant.

Professional ice hockey players: physiologic, anthropometric, and musculoskeletal characteristics.

Twenty-seven players from a National Hockey League (NHL) team were evaluated for maximal aerobic power, body composition, and muscle strength and flexibility upon reporting to training camp. Aerobic power was determined with a maximal treadmill exercise test. Body composition was determined by underwater weighing. Muscle strength of the internal and external shoulder rotator muscles and the knee flexors and extensors were determined isokinetically at 30 degrees/sec. Strength of the hip adductors was determined isometrically. The average (+/- standard error) maximal oxygen consumption (VO2max) for all players was 53.4 +/- 0.8 ml x kg-1 x min-1. When players were grouped by their usual playing positions (Goalies = G, n = 4; Forwards = F, n = 15; and Defensemen = D, n = 8) there were no differences in VO2 max, resting or maximal heart rate, and exercise test duration. Although G (77.7 +/- 3.2 kg) were significantly lighter than D (88.5 +/- 1.9 kg) and F (86.1 +/- 1.9 kg), there were no significant differences between player positions in height or percentage of body fat (9.2 +/- 0.9%). Measures of absolute muscle strength and muscle strength adjusted for body weight were similar for G, F, and D. Goalies, however, had significantly more flexibility in the hip and groin musculature than F and D. Although team averages for muscle strength and flexibility were normal and symmetric, ten players (37%) exhibited significant musculoskeletal strength and flexibility deficits.

Prognostic endpoint yield of high-level versus low-level graded exercise testing.

The prognostic endpoint yield (PEY) of a low-level (less than or equal to 4.6 METS) vs a high-level graded exercise test administered soon after myocardial infarction was evaluated with 184 patients. Test endpoints considered prognostically significant for future cardiac events were (1) ST segment depression greater than or equal to 1mm, (2) angina pectoris, and (3) complex ventricular beats. Test endpoints were assigned to both low-level and high-level tests if they occurred less than or equal to 4.6 METS; test endpoints greater than 4.6 METS were assigned to the high-level test only. Allowing the 145 patients who were asymptomatic during the low-level test to continue into the high-level protocol revealed a 2.5 times greater occurrence of angina pectoris (38 vs 15), a 3.4 times greater occurrence of ST segment depression (27 vs 8), and twice the occurrences of ventricular beats (4 vs 2). This substantial increase in prognostic endpoint yield was demonstrated in the presence of a significantly longer exercise time with the high-level test (9.0 vs 5.1 min), with no significant difference between protocols for peak heart rate or systolic blood pressure. Therefore, a high-level graded exercise test appears to increase the yield of test endpoints with known prognostic importance.

Short- and long-term prognostic value of graded exercise testing soon after myocardial infarction.

We attempted to determine whether graded exercise testing (GXT) soon after a myocardial infarction (MI) using an unlimited metabolic equivalent (MET) level and target heart rate (HR) of 90% of the age-predicted maximal HR is a safe procedure and yields prognostic results different from tests that use lower level end points. We administered GXT to a random sample of 85 patients at a mean of 14.8 days post-MI. End points that included ST-segment depression (STD), angina pectoris (AP), ventricular ectopic activity, and achieved MET level during testing were evaluated as predictors of cardiac events that include death, recurrent nonfatal MI, and coronary artery bypass graft surgery. We conducted short-term follow-up monitoring for one year after the initial MI and long-term follow-up monitoring for a mean of 864.7 days. No serious complications occurred during testing. Angina pectoris, STD accompanied by AP, and achieved MET level were predictive (p less than .05) of future fatal and nonfatal cardiac events during the first year of follow-up monitoring. Fifty-nine percent of the patients with AP suffered a subsequent cardiac event within one year, whereas only 17% of those without AP experienced another cardiac event. Sixty-seven percent of the patients with both STD and AP had a subsequent cardiac event within one year, but only 22% of those without AP and STD had a subsequent cardiac event. For the long-term follow-up monitoring, the presence of AP and a low achieved MET level during testing were associated with subsequent cardiac events.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of wearing the complete Lenox Hill Derotation Brace on energy expenditure during horizontal treadmill running at 161 meters per minute.

Ten volunteer subjects (means age = 26.6 +/- 4.9 years, means height = 177.9 +/- 5.6 cm, and means weight = 76.9 +/- 11.2 kg) who had been wearing the Lenox Hill Derotation Brace (LHB) for a mean time of 23.9 +/- 28.0 months were familiarized with horizontal treadmill running at 161 m/min with and without the LHB. They were then tested randomly for four runs, two with the LHB and two without the LHB. Metabolic measurements using a device that counted footstrikes on the treadmill were taken during the 3rd and 6th minutes of each run. Regardless of sampling time, wearing the LHB produced significantly higher values for VO2 (4.58%, P less than 0.025) and heart rate (5.10%, P less than 0.004) compared to the no brace condition. Regardless of whether or not the subjects were wearing the LHB, 6 minute values were significantly higher than 3 minute values for VO2 (5.89%, P less than 0.0004), VE (10.8%, P less than 0.004), heart rate (5.35%, P less than 0.0000), and R (2.17%, P less than 0.038). The mean 6 minute values of VO2 with (37.42 +/- 3.55 ml/kg/min) and without (35.54 +/- 2.17 ml/kg/min) the brace fall within the range of expected values of 28.1 to 39.3 ml/kg/min derived from regression equations from the literature which predict VO2 response to horizontal treadmill running. Mean stride lengths while wearing the LHB (97.85 cm) were not significantly different from mean stride lengths without the LHB (98.56 cm). It is concluded that wearing the LHB produces a 4.58% increase in energy expenditure during horizontal treadmill running at 161 m/min which cannot be attributed to changes in stride length or to time of sampling during the run.

Exercise for optimal health: strategies and motivational considerations.

It appears that most people who engage in exercise for 20-60 min per day, 3 days per week, at an intensity level of 70-80% of maximal heart rate will derive at least some health-related benefits associated with improved cardiorespiratory fitness and optimal body weight. Individuals exhibiting extremely low cardiorespiratory fitness can probably derive benefits from even less exercise, while higher intensity and/or longer duration may be required to optimize some desired changes, particularly in areas associated with metabolic adaptation relative to blood lipids, diabetes, and psychological affect. While there is some evidence that it may take less exercise to maintain fitness levels already attained, a lifelong pattern of regular physical activity is recommended to optimize health-related benefits. Strategies which have been successful in combating high attrition rates in exercise programs include educational efforts to increase the participants' awareness pf exercise benefits; assessment procedures which determine the participants' needs, provide continuous motivational reinforcement, and accurately record improvement; and written contracts which hold participants accountable for reaching realistic goals within specified time periods.