A comparison of two anesthetic techniques for the study of rat skeletal muscle high-energy phosphates in vivo using 31P-NMR.

31P-Nuclear magnetic resonance (NMR) spectroscopy was used to evaluate in vivo rat quadriceps ATP, phosphocreatine (PCr), inorganic phosphate (Pi) and tissue pH during anesthesia with ketamine/xylazine (K/X) or isoflurane (IS). A surface coil was used to receive signals from the quadriceps muscle of rats positioned in a wide-bore horizontal magnet. The PCr/beta-ATP ratios determined from the NMR spectra were 4.34 +/- 0.19 (K/X) and 4.40 +/- 0.28 (IS). Tissue pH was 7.09 +/- 0.05 (K/X) and 7.13 +/- 0.07 (IS). Metabolic stability of quadriceps PCr and ATP was demonstrated during both K/X and IS anesthesia, but the K/X-anesthetized animals had longer sleep time, lower food consumption, and lower body weight post-anesthesia than the IS-anesthetized animals. The PCr/beta-ATP ratio in quadriceps of repetitively IS-anesthetized rats did not fluctuate diurnally. In addition, the animals recovered rapidly and continued to gain weight following the multiple brief IS anesthetic procedures. These data indicate that serial in vivo investigations of high-energy-phosphate metabolism in small animals can be accomplished using 31P-NMR spectroscopy and IS anesthesia, which has several advantages over K/X anesthesia for these types of studies.

Chronic leptin administration increases insulin-stimulated skeletal muscle glucose uptake and transport.

Leptin, the product of the ob gene, has been shown to reduce fat mass, food intake, hyperglycemia, and hyperinsulinemia and to increase whole-body glucose disposal. However, it is unknown if leptin improves insulin action in skeletal muscle. Therefore, the purpose of this investigation was to determine if chronic leptin administration increases insulin-stimulated skeletal muscle glucose uptake and transport. Sixty-nine female Sprague-Dawley rats (240 to 250 g) were randomly assigned to one of three groups: (1) control, (2) pair-fed, and (3) leptin. All animals were subcutaneously implanted with miniosmotic pumps that delivered 0.5 mg leptin/kg/d to the leptin animals and vehicle to the control and pair-fed animals for 14 days. Following this 14-day period, all animals were subjected to hindlimb perfusion to determine the rates of skeletal muscle glucose uptake and 3-O-methyl-D-glucose (3-MG) transport under basal, submaximal (500 microU/mL), and maximal (10,000 microU/mL) insulin concentrations. Chronic leptin treatment significantly increased (P < .05) the rate of glucose uptake across the hindlimb by 27%, 32%, and 47% under basal, submaximal, and maximal insulin, respectively, compared with the control and pair-fed condition. However, when the submaximal rate of glucose uptake was expressed as a percentage of maximal insulin-stimulated glucose uptake, no differences existed among the groups, indicating that leptin treatment does not increase insulin sensitivity. Rates of 3-MG transport in the soleus, plantaris, and white and red portions of the gastrocnemius (WG and RG) were significantly increased (P < .05) in leptin animals under all perfusion conditions. 3-MG transport was not different between control and pair-fed animals. Collectively, these findings suggest that improvements in insulin-stimulated skeletal muscle glucose uptake and transport following chronic leptin treatment result from increased insulin responsiveness.

Effects of 24-hour fast on cycling endurance time at two different intensities.

Ten competitive cyclists were exercised to exhaustion to test the potential of a 24-h fast for increasing endurance. One group (n = 4) was tested at an initial intensity of 86% maximum O2 uptake (VO2max) (HI) and a second group (n = 6) at 79% VO2max (MI). Both groups repeated test rides in fasted and normal-diet conditions. Time to fatigue was designated at two points: fatigue 1 occurred when pedal frequency could not be maintained at the initial percent VO2max; fatigue 2 occurred when pedal frequency could not be maintained at a workload of approximately 65% VO2max. In both HI and MI the 24-h fast had no effect on resting muscle glycogen stores but significantly increased plasma free fatty acid (FFA) levels. Despite the increased FFA availability, time to fatigue was reduced in the fasted groups. Fatigue 1 and 2 times (mean +/- SE) for HI-fasted were 42.0 +/- 6.2 and 170.0 +/- 20.4 min, respectively, compared with those of the HI-normal diet of 115.3 +/- 25.6 and 201.0 +/- 14.8 min. Fatigue 1 and 2 times for MI-fasted were 142.0 +/- 19.6 and 167.5 +/- 10.5 min compared with those of the MI-normal diet of 191.3 +/- 25.0 and 214.3 +/- 18.9 min. The cause of fatigue at fatigue 1 was not readily apparent. Fatigue 2 in all groups seemed to be related to hypoglycemia as well as muscle glycogen depletion.

A physiological comparison of forward vs reverse wheelchair ergometry.

The purpose of this study was to compare metabolic and cardiopulmonary responses for forward wheelchair ergometry (FOR) and reverse wheelchair ergometry (REV) at equal power outputs (PO) levels. Moderately active able-bodies (N = 21) subjects exercised at 3-min stages at PO levels of 15, 20, 25, and 30 W for each mode of ergometry. Oxygen uptake (VO2), pulmonary ventilation (VE), respiratory exchange ratio (RER), heart rate (HR), percent net mechanical efficiency (ME), revolutions per minute (RPM) and strikes per minute (SPM) were determined at each PO level. With the exception of RER, all the physiological responses (VO2, VE, and HR) were higher for FOR exercise (P < 0.05) than REV exercise. ME increased with PO and was higher (P < 0.05) for REV than FOR at each PO level. SPM values for the REV were lower (P < 0.01) by almost half of that for the FOR exercise, although RPM remained constant between modes during all four stages. In general, these data suggest that reverse wheelchair ergometry is physiologically more efficient than conventional wheelchair ergometry and should be studied further as an alternative method for wheelchair ambulation.

Effects of stair-climbing vs run training on treadmill and track running performance.

Physically active college age women were evaluated to determine the effects of 9 wk of stair-climbing (Stairmaster Gauntlet) vs run training on 2414-m run time and treadmill measured aerobic capacity (VO2max) and submaximal physiological parameters. Subjects were randomly assigned to a stair-climbing (STAIR N = 11) (43.8 +/- 1.5 ml.kg-1.min-1) (mean +/- SEM) or run training (RUN N = 12) (44.2 +/- 1.8) group, training 4 d.wk-1 at 70-80% of maximum heart rate (MHR) for 30 min progressing to 85-90% MHR for 45 min. The STAIR group significantly increased (P < 0.01) their VO2max by 12% and decreased (P < 0.01) their 2414-m run time of 12.8 min by 8%. The RUN group increased (P < 0.01) their VO2max 16% and decreased run time (P < 0.01) 11% from 13.1 min. Submaximal treadmill runs at the same speed and grade demonstrated significant decreases in %VO2max and % MHR (P < 0.01) for both groups. The data support the use of stair-climbing exercise as an alternative mode to running with similar treadmill and running performance results subsequent to 9 wk of training.

Effect of run vs combined cycle/run training on VO2max and running performance.

The effects of 5 wk of equivalent intensity, 85-90% maximum heart rate (MHR), run-only (N = 6) vs cycle/run (N = 5) training were evaluated in moderately fit runners, mean VO2max of 55.2 ml.kg-1.min-1, 19-35 yr old, on maximal treadmill (TM) and cycle ergometer (CE) testing, 5000-m and 1609-m run performances, and submaximal measures while treadmill running. Subjects participated in either 4 d.wk-1 of run-only or alternating run and cycle training. Both groups significantly improved TM VO2max (P < 0.05), CE VO2peak (P < 0.01), and 5000-m (P < 0.01) and 1609-m (P < 0.05) run times with no significant differences between the groups. The TM VO2max pre/post values were 55.3 +/- 3.0 to 58.2 +/- 3.0 and 55.6 +/- 3.8 to 58.9 +/- 2.4 ml.kg-1.min-1 for the run group and cross-trained group, respectively. Posttraining submaximal treadmill running showed statistically significant pace increases of 18.7 (run) and 16.1 (cycle/run) m.min-1 with similar heart rate, blood lactate, and RQ values as pretraining. Results indicate that 5 wk of either mode of training can significantly improve aerobic capacity and run performance.

Effects of stairclimbing on VO2max and quadriceps strength in middle-aged females.

The purpose of this study was to determine the effect of 12 wk of stairclimbing with and without an external load on aerobic capacity and quadriceps strength of sedentary (initial VO2max 25.3 +/- 0.73 ml.kg-1.min-1) (mean +/- SEM) middle aged females (50-65 yr). Three groups, LOAD (stairclimbing with external load, N = 8), STAIR (no load, N = 9), and CONTROL (N = 7) were tested. By week 4, subjects warmed up 5 min on a cycle ergometer followed by 35 min on the stairclimber at 80-85% maximum heart rate (MHR) 4 d.wk-1. In week 6, the LOAD group carried an external load of 4% of body weight increasing to 8% for weeks 7-12. STAIR and LOAD group significantly increased (P < 0.01) VO2max by 11.1% and 9.6%, respectively. Isokinetic strength tests showed increased (P < 0.05) peak torque and total work for STAIR and LOAD at 120 and 180 degrees.s-1. For total work, a significant increase (P < 0.05) of 10.5% was observed at 60 degrees.s-1 for the LOAD group. The results indicate stairclimbing is an appropriate exercise for middle-aged females improving both aerobic capacity and strength following 12 wk of training.

Consequences of combining strength and endurance training regimens.

A common belief among many clinicians and trainers is that intensive simultaneous training for muscle strength and cardiovascular endurance is counterproductive. To test this premise, 14 healthy, untrained men trained four days per week for 20 weeks on a bicycle ergometer for endurance (END Group, n = 4), on an isokinetic device for increased torque production (ITP Group, n = 5), or on both devices (COMBO Group, n = 5). The ITP and COMBO groups had equal torque gains throughout the study (234 +/- 45 and 232 +/- 23 N.m, respectively). After 11 weeks, both END and COMBO groups had similar gains in maximal oxygen consumption (VO2max) (in milliliters per kilogram of body weight per minute). During the last half of the study, however, the END Group had a significant gain in VO2max (p less than .05) of 4.7 +/- 1.2 mL.kg-1.min-1, whereas the COMBO Group had a nonsignificant gain (p greater than .05) of 1.8 +/- 0.6 mL.kg-1.min-1. In harmony with this finding, the END Group showed a significant increase (p less than .05) in citrate synthase activity (15.5 +/- 7.9 mumol.g-1.min-1), whereas the COMBO Group had no significant increase. The authors concluded that simultaneous training may inhibit the normal adaptation to either training program when performed alone. The extent of the interference probably depends on the nature and intensity of the individual training program. [Nelson AG, Arnall DA, Loy SF, et al: Consequences of combining strength and endurance training regimens.

Relationship of Body Core Temperature and Warm-up to Knee Range of Motion.

This study examined the effects of submaximal, treadmill exercise-induced body core temperature (BCT) increase on selected knee range of motion (ROM). Twenty males, 18-35 years old, were tested (randomized crossover) for ROM, BCT, and heart rate (HR), followed by either Treatment I (20 minutes of rest) or Treatment II (20 minutes of submaximal running). The two treatments were subsequently followed by a two-minute passive stretch. Range of motion was assessed before and after passive stretch treatment intervention. Treatment means differed for BCT and HR (p < 0.001) but not for ROM after exercise intervention. It was concluded that 20 minutes of exercise increased BCT (>1 degrees C) but had no effect on knee ROM. J Orthop Sports Phys Ther 1991;13(3):126-131.

Effects of prior strength exercise on the heart rate oxygen uptake relationship during submaximal exercise.

Fourteen young males (mean age 26.7 yrs) were tested to determine if there was an alteration, in the heart rate-oxygen uptake relationship during submaximal cycle ergometer exercise following isokinetic strength training activity as has been documented following high intensity endurance activity. Results indicated that there was a significant increase rate without a concomitant increase in heart oxygen uptake during the first five minutes of submaximal cycle riding at 73% VO2max after heavy strength leg exercise, angular velocity of 30 degrees/second, when compared to no prior exercise. This alteration in the heart rate-oxygen uptake relation is not apparent by 20 minutes of the same submaximal exercise despite higher lactate values and greater ratings of perceived exertion. For individuals using heart rate as a guide to exercise intensity, the elevated heart rate at five minutes of submaximal exercise following heavy strength leg exercise does not exceed the 20 minute value which is an accurate reflection of energy cost and intensity.

Liver glycogenolysis during exercise in adrenodemedullated male and female rats.

Previous studies have shown that adrenodemedullation has no effect on the rate of liver glycogenolysis during exercise in male rats. Mature female rats have been reported to have a higher hepatic beta-adrenergic receptor activity than do male rats of the same age. The present study was undertaken to determine the role of plasma epinephrine in stimulating liver glycogenolysis during exercise in female rats. Both male and female rats were adrenodemedullated or sham operated. Three weeks later rats were run for 60 min at 21 m/min up a 15% grade. The rate of liver glycogenolysis during exercise was not affected by adrenodemedullation in either female rats or male rats. Hepatic adenosine 3',5'-cyclic monophosphate increased to approximately the same extent in sham operated as in adrenodemedullated female rats during exercise. Adrenodemedullation caused a significant reduction in the amount of glycogen utilized by the soleus muscle and in the degree of hyperglycemia during exercise. We conclude that epinephrine is unessential for stimulation of liver glycogenolysis during exercise in either male or female rats.

An epidemiological analysis of overuse injuries among recreational cyclists.

Two-hundred and ninety-four male and 224 female randomly selected recreational cyclists responded to a mail questionnaire. Significant differences were observed between male and female cyclists' training characteristics. Overall, 85% of the cyclists reported one or more overuse injury, with 36% requiring medical treatment. The most common anatomical sites for overuse injury/complaints reported by the male and female cyclists combined were the neck (48.8%), followed by the knees (41.7%), groin/buttocks (36.1%), hands (31.1%), and back (30.3%). For the male cyclists, effect upon back and groin/buttocks overuse injuries/complaints were miles/week, lower number of gears, and less years of cycling. For female cyclists, training characteristics which had the most significant effect upon groin/buttocks overuse injury/complaints were more non-competitive events/year and less stretching before cycling. The odds of female cyclists developing neck and shoulder overuse injury/complaints were 1.5 and 2.0 times more, respectively than their male counterparts.

Specificity effects of run versus cycle training on ventilatory threshold.

This study compared the effects of 9 weeks of run (RT) versus cycle (CT) training on ventilatory threshold (Thv) determined during treadmill (TM) and cycle ergometer (CE) graded exercise testing. Sixteen college age men were assigned to a RT or CT group and performed a TM and a CE test before and after training. Both training groups performed similar training protocols which initially consisted of continuous exercise 4 days.week-1 at 75-80% maximum heart rate (fc, max) for 45 min. Training intensity was later increased to 80-85% fc, max and interval training (90-95% fc, max) was incorporated 2 days.week-1 into the continuous training. Both groups showed significantly improved maximal oxygen consumption (VO2 max) on both TM and CE tests (P < 0.01) with no significant differences between the groups. Significant Thv increases (P < 0.05) were found on TM tests for RT (n = 8) and CT (n = 8) groups [mean (SD); 443 (438) and 373 (568) ml O2 x min-1, respectively] with no difference between the groups. Results from the CE tests revealed a significant Thv increase (P < 0.01) for the CT group [566 (663) ml O2 x min-1] with no change for the RT group. The Thv improvement noted for the RT group was significantly different (P < 0.05) comparing CE with TM tests but not for the CT group. The results indicate that CT and RT improvement in Thv for runners is dependent upon mode of training and testing, and there is an apparent dissociation of VO2 max and Thv specific to training.