Biomedical subjects

R A Robergs

Publications and source records attributed to R A Robergs.

At least 19 recordsLinked to original sources

PubMed1995

Changes in muscle proton transverse relaxation times and acidosis during exercise and recovery.

We studied changes in muscle proton (1H) transverse relaxation times (T2) by magnetic resonance imaging during exercise and compared these changes with alterations in muscle metabolism measured by phosphorus-31 magnetic resonance spectroscopy (31P-MRS). Eleven subjects completed two trials of intermittent incremental forearm wrist flexion exercise requiring 30 contractions/min for 5 min, 7 min of recovery between stages, and 5-N load increments/stage. Between stages of the first trial, T2 images of muscle 1H were obtained. Muscle T2 increased from 27.3 +/- 1.1 (SD) ms at rest to 35.8 +/- 3.6 ms after volitional fatigue (P < 0.05), whereas less active wrist extensor muscle T2 remained unchanged (26.8 +/- 0.9 to 28.8 +/- 1.6 ms; P > 0.05). After localizing the predominant muscle recruited from the T2 images, subjects completed an identical trial at least 1 wk later but involving surface coil 31P-MRS of the T2-enhanced muscle to measure the H+ concentration ([H+]). Intramuscular [H+] of T2-enhancing muscle increased from 1.1 +/- 0.1 x 10(-7) M at rest to 4.1 +/- 2.0 x 10(-7) M after volitional fatigue. Both muscle T2 and intramuscular [H+] increased in a bimodal manner, with T2 increasing before muscle [H+] (P < 0.05). The correlation coefficient between the percent change in T2 and muscle [H+] during exercise was +0.74 (range 0.48-0.98; P < 0.05) and +0.47 during recovery. After 12 min of recovery, muscle [H+] decreased to 1.4 +/- 0.3 x 10(-7) M (P < 0.05), and T2 remained close to postexercise values (32.2 +/- 3.1 ms, P > 0.05). The data indicate that 1) the T2 increases during increases in exercise intensity are nonlinear, 2) the T2 increases during exercise are significantly correlated with increases in [H+], and 3) the slow recovery of T2 compared with [H+] indicates that [H+] has a minor contribution to the recovery in T2.

Acidosis↗

PubMed1994

Effect of lordosis on the position of the nucleus pulposus in supine subjects. A study using magnetic resonance imaging.

STUDY DESIGN: Healthy young women (N = 20) underwent magnetic resonance imaging while supine with their hips and knees flexed (flexed position) and supine with a lumbar roll under the low back (extended position). The posterior and anterior margins of the nucleus pulposus (NP) relative to posterior and anterior margins of the adjacent vertebral bodies were calculated from mid-sagittal T2-weighted images to determine the position change of the NP as a function of two supine postures. OBJECTIVES: This study describes the effect of two commonly used supine postures on the position of the NP. SUMMARY OF BACKGROUND DATA: Management of patients with low back pain is often based on theorized positional changes of the NP during spinal extension and flexion. Data describing NP positional changes have not been reported for noninvasive measurements. RESULTS: The distance of the posterior margin of the NP to the posterior margins of the adjacent vertebral bodies was greater in the extended compared with the flexed position. There was no difference in the anterior distance. Eight of the 20 subjects had at least one degenerative disc in the lower lumbar spine. The NPs of the degenerative discs did not move the same as normal discs. CONCLUSIONS: The use of a lumbar roll under the low back when supine causes an increase in the distance from the posterior margin of the NP to the posterior portions of the vertebral bodies in normal discs of healthy young females. Degenerative discs deform differently from nondegenerative discs.

Adult↗

PubMed1994

Gender differences in substrate utilisation during exercise.

The selection and utilisation of metabolic substrates during endurance exercise are regulated by a complex array of effectors. These factors include, but are not limited to, endurance training and cardiorespiratory fitness, exercise intensity and duration, muscle morphology and histology, hormonal factors and diet. Although the effects of these factors on substrate utilisation patterns are well understood, the variation in substrate utilisation during endurance exercise between males and females is not. Because of the extreme heterogeneity in exercise protocols and individuals studied, the differences in substrate utilisation between males and females remain somewhat inconclusive. Regardless of heterogeneity, if the results from studies are interpreted collectively, an apparent gender difference in the selection and metabolism of substrates can be seen in sedentary individuals. However, this difference between genders diminishes as the level of cardiorespiratory fitness is increased to that of highly trained individuals. During rest and lower intensity exercise, the preferential metabolism of lipid occurs with a concomitant sparing of muscle glycogen. However, as the intensity of exercise is increased, the relative contribution of carbohydrate also increases. The exercise intensity at which the shift from lipid to carbohydrate is determined and regulated by the previously mentioned factors. Because the intensity and duration of exercise play a predominant role, the variation in exercise protocols poses a methodological concern when interpreting previous research. When attempting to compare the metabolism of substrates during endurance exercise, appropriate selection and interpretation of measurement techniques are necessary. Measurement techniques include the nonprotein respiratory exchange ratio, muscle and fat biopsies and the measurement of various blood metabolites, such as free fatty acids and glycerol. Similarly, in vitro analysis of lipolytic activity has also been demonstrated in males and females in response to varying levels of female gonadotrophic hormones. When comparing the substrate utilisation patterns between males and females, the area of hormonal regulation has received less attention. Often the catecholamine response to endurance exercise is measured; however, the gonadotrophic hormones, particularly those of the female, have received less attention when comparing genders. Indeed, the regulatory nature of the female gonadotrophic hormones has been demonstrated. Collectively, the effects of elevated estrogen, as in the luteal phase of menstruation, appear to promote lipolytic activity. Estrogen-mediated lipolytic activation occurs by apparently altering the sensitivity to lipoprotein lipase and by increasing the levels of human growth hormone (somatotropin), an activator of lipolysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Increased endothelin and creatine kinase after electrical stimulation of paraplegic muscle.

The purpose of this study was to assess changes in creatine kinase (CK) and endothelin (ET) in individuals with spinal cord injury (SCI) after computerized functional electrical stimulation leg ergometry (CFES LE). Eight subjects (7 male and 1 female) with complete spinal cord lesions (C7 to L1) completed zero-loaded CFES LE tests at baseline, after 3, 6, and 12 wk of CFES LE training (30 min, 3 times/wk), and also after detraining (DT) (n = 5). Venous blood samples were drawn 24, 48, and 72 h after CFES LE for measurement of ET and CK. The CK response was largest (peak CK) 72 h after baseline tests (28.2 +/- 6.0 to 895.7 +/- 345.9 ktals/l) and was no different from baseline by weeks 3, 6, and 12. After DT, CK was similar before and after CFES LE (153.8 +/- 19.0 and 189.7 +/- 34.5 ktals/l, respectively). CFES LE also significantly increased peak ET after baseline (from 11.7 +/- 1.5 to 18.0 +/- 2.5 pg/ml). During the subsequent training, peak ET remained significantly higher than the baseline value at weeks 3, 6, and 12 (20.2 +/- 1.8, 18.0 +/- 1.1, and 16.9 +/- 2.2 pg/ml, respectively). After DT, peak ET increased significant relationship (r = 0.44) existed between ln peak CK activity and peak ET. In summary, the increase in circulating ET in spinal cord-injured individuals may have implications for baroreceptor function and therefore blood pressure control in SCI. Further research into CFES LE, ET, and baroreceptor function in SCI is warranted.

Adult↗

PubMed1993

Effects of electrical stimulation and upper body training after spinal cord injury.

The purpose of this study was to measure the cardiorespiratory improvements during the initial weeks of training in individuals with spinal cord injury (SCI). Eight adult volunteers (ages 23-41) with paraplegia (T4-L1, N = 7) and low levels of quadriplegia (C7, N = 1) participated in a 12-wk training program consisting of 6 wk of computerized functional electrical stimulation leg ergometry (CFES LE) followed by 6 wk of combined arm ergometry and CFES LE (hybrid ergometry; HE). Measures of peak oxygen consumption (pV02) and immediate post-exercise blood lactate (La-) were collected during an intermittent CFES LE graded exercise test (3-min stages; 1/8-kp increments) prior to training (0T), following 6 wk of CFES LE training (6T) and following 6 wk of HE training (12T). Voluntary arm ergometry (AE) graded exercise tests were also completed at each of 0T, 6T, and 12T, and an intermittent graded HE test was also given at 6T and 12T. Following the 6 wk of CFES LE, AE pVO2 increased from 1.14 +/- 0.09 l.min-1 to 1.39 +/- 0.172 l.min-1 (P < 0.05), and CFES LE pVO2 increased from 0.51 +/- 0.05 l.min-1 to 0.83 +/- 0.06 l.min-1 (P < 0.05). Following the 6 wk of HE, HE pVO2 increased from 1.31 +/- 0.15 l.min-1 to 1.49 +/- 0.14 l.min-1 (P < 0.05). HE pVO2 was 58%-60% higher than CFES LE pVO2 at the mid- and post-testing periods. HE pVO2 was 14% higher than AE pVO2 at the post-testing period.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Glycogen resynthesis in skeletal muscle following resistive exercise.

The purpose of this investigation was to determine the influence of post-exercise carbohydrate (CHO) intake on the rate of muscle glycogen resynthesis after high intensity weight resistance exercise in subjects not currently weight training. In a cross-over design, eight male subjects performed sets (mean = 8.8) of six single leg knee extensions at 70% of one repetition max until 50% of full knee extension was no longer possible. Total force application was equated between trials using a strain gauge interfaced to a computer. The subjects exercised in the fasted state. Post-exercise feedings were administered at 0 and 1 h consisting of either a 23% CHO solution (1.5 g.kg-1) or an equal volume of water (H2O). Total force production, preexercise muscle glycogen content, and degree of depletion (-40.6 and -44.3 mmol.kg-1 wet weight) were not significantly different between H2O and CHO trials. As anticipated during the initial 2-h recovery, the CHO trial had a significantly greater rate of muscle glycogen resynthesis as compared with the H2O trial. The muscle glycogen content was restored to 91% and 75% of preexercise levels when water and CHO were provided after 6 h, respectively.

Adult↗

PubMed1992

Fluid replacement after dehydration: influence of beverage carbonation and carbohydrate content.

This investigation evaluated the effects of beverage carbonation and carbohydrate (CHO) content on fluid replacement following exercise/thermal dehydration. On four occasions separated by at least 7 days, eight healthy men cycled at 50% of VO2max in a hot environmental chamber (40 degrees C, 40% relative humidity) until a weight loss of 4.12 +/- 0.22% was attained. In the subsequent four hours, subjects ingested one of four solutions at 15-min intervals. The total volume ingested equalled that lost during dehydration. The solutions were administered in randomized order and varied in their carbonation and carbohydrate (CHO) content: 1. CK: carbonated 10% glucose-fructose solution, 2. NCK: non-carbonated 10% glucose-fructose solution, 3. CNK: carbonated non-caloric solution, and 4. NCNK: non-carbonated non-caloric solution. Plasma volume changes, total plasma protein concentration, plasma osmolality, and the plasma glucose concentration were determined at rest before and after dehydration, and at 30, 90, 150, and 240 min of recovery. Plasma volume changes and the plasma protein concentration were not different (p greater than 0.05) between treatments. Values for the plasma glucose concentration and the change in plasma osmolality were significantly elevated when CHO beverages were ingested when compared with non-CHO beverage ingestion. Five-min cycling bouts were performed at 70% of VO2max before and after dehydration and at 60, 120, 180, and 240 min of rehydration. The respiratory exchange ratio was elevated in both of the CHO treatments when compared with both of the non-CHO treatments at 60, 120, 180 and 240 min of rehydration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

The effects of a carbonated carbohydrate drink on gastric emptying, gastrointestinal distress, and exercise performance.

To determine the effect of a carbonated carbohydrate (CHO) drink on gastric function and exercise performance, eight male cyclists completed four 120-min bouts of cycling. Each bout consisted of a 105-min ride at 70% VO2max followed by a 15-min self-paced performance ride. During each trial, one of four test solutions was ingested: carbonated CHO (C-10%), noncarbonated CHO (NC-10%), carbonated non-CHO (C), and noncarbonated non-CHO (NC). Following the performance ride, the subjects had their stomach contents removed by aspiration. There were no significant differences in gastric emptying (GE) except for Trial C-10%, which averaged 13.3% less than NC. However, there was no difference in the perception of gastrointestinal comfort between this trial and any other. Average power output during the performance ride was not significantly different between carbonated and noncarbonated trials, or between CHO-fed and no-CHO trials; however, the subjects worked at a greater intensity when fed CHO. Finally, acid base status did not change when a carbonated drink was ingested. This indicates that adding carbonation to a sport drink does not significantly alter gastric function, the perception of GI comfort, or exercise performance.

Adult↗

PubMed1991

Nutrition and exercise determinants of postexercise glycogen synthesis.

During the initial hours of recovery from prolonged exhaustive lower body exercise, muscle glycogen synthesis occurs at rates approximating 1-2 mmol.kg-1 wet wt.hr-1 if no carbohydrate is consumed. When carbohydrate is consumed during the recovery, the maximal rate of glycogen synthesis approximates 7-10 mmol.kg-1 wet wt.hr-1. The rate of post-exercise glycogen synthesis is lower if the magnitude of glycogen degradation is small, if less than 0.7 gm glucose.kg-1 body wt.hr-1 is ingested, when the recovery is active, and when the carbohydrate feeding is delayed. The rate of postexercise glycogen synthesis is not reduced during the initial hours (< 4) after eccentric exercise. For studies evaluating muscle glycogen synthesis in excess of 12 hours of recovery, average rates of glycogen synthesis are below 4 mmol.kg-1 wet wt.hr-1. Glycogen synthesis is known to be impaired for time periods in excess of 24 hours following exercise causing eccentric muscle damage. Following intense exercise resulting in high concentrations of muscle lactate, muscle glycogen synthesis occurs at between 15-25 mmol.kg-1 wet wt.hr-1. These synthesis rates occur without ingested carbohydrate during the recovery period and are maintained when a low intensity active recovery is performed.

Dietary Carbohydrates↗

PubMed1991

Muscle glycogenolysis during differing intensities of weight-resistance exercise.

Skeletal muscle glycogen metabolism was investigated in eight male subjects during and after six sets of 70% one repetition maximum (1 RM, I-70) and 35% 1 RM (I-35) intensity weight-resistance leg extension exercise. Total force application to the machine lever arm was determined via a strain gauge and computer interfaced system and was equated between trials. Compared with the I-70 trial, the I-35 trial was characterized by almost double the repetitions (13 +/- 1 vs. 6 +/- 0) and half the peak concentric torque for each repetition (12.4 +/- 0.5 vs. 24.2 +/- 1.0 Nm). After the sixth set, muscle glycogen degradation was similar between I-70 and I-35 trials (47.0 +/- 6.6 and 46.6 +/- 6.0 mmol/kg wet wt, respectively), as was muscle lactate accumulation (13.8 +/- 0.7 and 16.7 +/- 4.2 mmol/kg wet wt, respectively). After 2 h of passive recovery without caloric intake, muscle glycogen increased by 22.2 +/- 6.8 and 14.2 +/- 2.5 mmol/kg wet wt in the I-70 and I-35 trials, respectively. Optical absorbance measurement of periodic acid-Schiff-stained muscle sections after the 2 h of recovery revealed larger absorbance increases in fast-twitch than in slow-twitch fibers (0.119 +/- 0.024 and 0.055 +/- 0.024, P = 0.02). Data indicated that when external work was constant, the absolute amount of muscle glycogenolysis was the same regardless of the intensity of resistance exercise. Nevertheless the rate of glycogenolysis during the I-70 trial was approximately double that of the I-35 trial.

Adult↗

PubMed1991

Influence of muscle glycogen depletion on the rate of resynthesis.

In an effort to determine what effect the degree of muscle glycogen depletion has on the rate of resynthesis, six male cyclists completed an exercise protocol that involved both one- and two-legged cycling. One leg completed 30 min of single-leg cycling, ten one-min sprints, and 30 min cycling with both legs. This resulted in a large degree of depletion (LD). The contralateral leg completed only 30 min of double-leg cycling and experienced a small amount of depletion (SD). Following the exercise, the subjects rested quietly for 6 h and were fed a 24% carbohydrate (CHO) solution every 20 min in order to achieve a CHO intake of 0.7 g.kg-1.h-1. Biopsies taken from the vastus lateralis muscle immediately after exercise revealed that the glycogen content of the LD leg decreased 93.9 (+/- 11.6) mmol.kg-1 w.w., whereas the SD leg used 49.3 (+/- 5.7) mmol.kg-1 w.w. (P less than 0.01). Subsequent biopsies taken at 2 and 6 h of recovery demonstrated that the rate of muscle glycogen resynthesis was significantly greater in the LD leg, averaging 8.8 (+/- 2.4) mmol.kg-1.h1 w.w, while the SD leg restored glycogen at a rate of 3.0 (+/- 1.0) mmol.kg-1.h-1 w.w. (P less than 0.05). Glycogen synthase activity, expressed as its activity ratio (I/D), was also greater (P less than 0.01) in the LD leg both immediately after exercise (0.45 +/- 0.05 vs 0.24 +/- 0.04) and at 2 h of recovery (0.54 +/- 0.06 vs 0.27 +/- 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Effects of warm-up on muscle glycogenolysis during intense exercise.

This study investigated the effects of preliminary exercise (warm-up) on glycogen degradation and energy metabolism during intense cycle ergometer exercise. After determination of VO2max, six male subjects were randomly assigned to perform warm-up (WU) and no warm-up (NWU) trials incorporating a 2 min standardized sprint ride (SR) at 120% of the power output attained at VO2max (POmax). Muscle biopsies and temperature (Tm) recordings were obtained from the vastus lateralis muscle. Tm was elevated above the resting level prior to the SR during the WU trial (37.7 +/- 0.1 vs 35.4 +/- 0.4 degrees C; P less than 0.05) and remained higher than the NWU trial after the SR (38.6 +/- 0.2 vs 37.1 +/- 0.4 degrees C; P less than 0.05). Similar trends existed for rectal temperature (Tr). The increases in Tm and Tr during the SR were both greater in the NWU trial (P less than 0.05). Muscle glycogen degradation was similar for the WU and NWU trials (30.8 +/- 3.7 vs 25.6 +/- 3.7 mmol.kg-1, respectively). When blood and muscle lactate concentrations after the SR were expressed relative to values before the SR, the WU trial resulted in a lower accumulation of blood lactate (6.5 +/- 0.9 vs 10.7 +/- 0.8 mEq.l-1; P less than 0.01) and muscle lactate (20.1 +/- 0.1 vs 23.4 +/- 2.2 mEq.kg-1 wet wt.; P less than 0.05). Furthermore, oxygen consumption during the 1st min of the SR was higher in the WU trial (2.3 +/- 0.2 vs 1.9 +/- 0.2 l.min-1; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Adaptations to swimming training: influence of training volume.

In an effort to assess the contributions of a period of increased training volume on swimming performance, two matched groups of collegiate male swimmers were studied before and during 25 wk of training. For the first 4 wk of this study, the two groups trained together in one session per day for approximately 1.5 h.d-1. During the following 6 wk (weeks 5-11), one group (LONG) trained two sessions per day, 1.5 h in the morning and 1.5 h in the afternoon. The other group (SHORT) continued to train once each day, in the afternoon with the LONG group. Over the final 14 wk of the study, both groups trained together in one session per day (1.5 h.d-1). Although the swimmers experienced significant improvements in swimming power, endurance, and performance throughout the 25 wk study, there were no differences between the groups. However, during the 6 wk period of increased training, the LONG group experienced a decline in sprinting velocity, whereas the SHORT group showed a significant increase in sprinting performance. The test results suggest that a 6 wk period of two 1.5 h training sessions per day does not enhance performance above that experienced with a single training session of 1.5 h each day. It was also noted that both groups showed little change in swimming endurance and power after the first 8 wk of training, though their performances improved significantly after each taper period.

Analysis of Variance↗

PubMed1990

Effects of warm-up on blood gases, lactate and acid-base status during sprint swimming.

A standardized 200-m front crawl sprint swim (SpS) was used to evaluate the effects of warm-up on pH, blood gases, and the concentrations of lactate ([La-]) and bicarbonate ([HCO3-]) in arterialized and venous blood. Eight trained male swimmers performed two randomly assigned 200-m front crawl swims at previously determined intensities corresponding to 120% VO2max. One swim was preceded by a warm-up (WU trial) which consisted of a 400-m front crawl swim (82% VO2max), 400-m flutter kicking (45% VO2max), and 4 x 50-m front crawl sprints (111% VO2max). The second was performed without warm-up (NWU trial). Blood was sampled from a hyperemized earlobe and an antecubital vein before the warm-up, 9 min after the warm-up (1 min before the swim), immediately following the SpS, and at 2, 5, 10, and 20 min after the SpS. The warm-up exercise resulted in a higher pre-SpS [La-] in arterialized blood (3.1 +/- 0.4 and 1.7 +/- 0.4 mmol x l-1, p less than 0.05), a higher hydrogen ion concentration ([H+]) in venous blood (45.9 +/- 0.9 and 42.2 +/- 0.8 nmol x l-1, p less than 0.001), and a lower arterialized blood [HCO3-] (25.1 +/- 0.9 and 22.2 +/- 0.8 mmol x l-1, p less than 0.05). The SpS was accompanied with higher heart rates during the WU trial (178 +/- 3 and 169 +/- 3 bpm; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Blood lactate threshold differences between arterialized and venous blood.

The purpose of this study was to investigate the differences between lactate thresholds determined from venous and arterialized blood. Seven endurance-trained college males performed an incremental bicycle ergometer exercise test until exhaustion. At the end of each 3 min stage, blood was sampled simultaneously from a hyperemized ear-lobe and an antecubital vein for the measurement of blood lactate (La-). Two-minute rest intervals separated each stage. Arterialized blood La-concentrations ([La-]) were significantly higher than venous blood at 350 W (14.5 and 9.7 mmol.l-1), maximal exercise (15.5 and 11.39 mmol.l-1), and throughout recovery. Arterialized [La-] was significantly higher than venous blood at the onset of blood La- accumulation (OBLA) (4.0 and 2.8 +/- 0.1 mmol.l-1), the individual anaerobic threshold (IAT) (3.4 +/- 0.3 and 2.1 +/- 0.1 mmol.l-1), and the ventilatory threshold (VT) (4.7 +/- 0.9 and 3.2 +/- 0.6 mmol.l-1). No significant differences were found between either La-threshold for arterialized or venous blood. The oxygen consumption (VO2) at OBLA was significantly lower when determined from arterialized blood La (2.3 +/- 0.2 and 2.8 +/- 0.2 l.min-1). No significant differences existed between the LT, OBLA, and IAT threshold-VO2 determinations from arterialized blood; however, significant differences were found between IAT-OBLA (2.1 +/- 0.2 and 2.8 +/- 0.2 l.min-1) and LT (2.2 +/- 0.2 l.min-1)-OBLA from venous blood. These results indicate that differences between venous and arterialized blood [La-] need to be considered when comparing different anaerobic threshold determinations.

Adult↗

PubMed1990

Impaired muscle glycogen resynthesis after eccentric exercise.

Eight men performed 10 sets of 10 eccentric contractions of the knee extensor muscles with one leg [eccentrically exercised leg (EL)]. The weight used for this exercise was 120% of the maximal extension strength. After 30 min of rest the subjects performed two-legged cycling [concentrically exercised leg (CL)] at 74% of maximal O2 uptake for 1 h. In the 3 days after this exercise four subjects consumed diets containing 4.25 g CHO/kg body wt, and the remainder were fed 8.5 g CHO/kg. All subjects experienced severe muscle soreness and edema in the quadriceps muscles of the eccentrically exercised leg. Mean (+/- SE) resting serum creatine kinase increased from a preexercise level of 57 +/- 3 to 6,988 +/- 1,913 U/l on the 3rd day of recovery. The glycogen content (mmol/kg dry wt) in the vastus lateralis of CL muscles averaged 90, 395, and 592 mmol/kg dry wt at 0, 24, and 72 h of recovery. The EL muscle, on the other hand, averaged 168, 329, and 435 mmol/kg dry wt at these same intervals. Subjects receiving 8.5 g CHO/kg stored significantly more glycogen than those who were fed 4.3 g CHO/kg. In both groups, however, significantly less glycogen was stored in the EL than in the CL.

Adult↗

PubMed1990

Effects of exercise mode on muscle glycogen restorage during repeated days of exercise.

The purpose of this study was to examine differences in muscle glycogen storage during three successive days of running or cycling. In a crossover design, seven male subjects performed two 3-d trials of either running (trial R) or cycling (trial C) for 60 min at 75% VO2max. Biopsy samples were obtained before and after each day's exercise from the gastrocnemius (trial R) or vastus lateralis (trial C) muscle. Diets in the 2 d preceding and during each trial contained 5 g carbohydrate.kg-1.d-1 and 14,475 +/- 402 kJ.d-1. Mean pre-exercise glycogen content (mmol.kg-1 wet wt.) was significantly reduced in both trials on day 3 (103.4 +/- 6.0) when compared to day 1 and day 2 (119.9 +/- 6.8 and 116.4 +/- 5.7, respectively). Day 1 glycogen reduction was significantly greater in trial C (P less than 0.03), and glycogen restorage was greater (P less than 0.02) only in trial C between the 1st and 2nd d. On day 3, spectrophotometric analysis of PAS strains showed that pre-exercise glycogen content in either muscle group was significantly (P less than 0.01) less in Type I as compared to Type II fibers. This difference in fiber glycogen storage did not appear to be attributable to muscle damage as negligible leukocyte infiltration and low blood CK levels were obtained. No difference between modes were observed for CK values throughout the trials. These data suggest that the depressed glycogen storage before the 3rd d of exercise was due to the moderate carbohydrate intake.

Adult↗

PubMed1990

The influence of exercise intensity on heat acclimation in trained subjects.

Low-intensity exercise (less than or equal to 50% VO2max) has been demonstrated to produce heat acclimation (HA) in trained subjects. The purpose of this study was to determine whether shorter-duration, moderate-intensity exercise would also result in HA. Nine trained runners performed two 9-d exercise heat-stress protocols. Each protocol consisted of a 90-min heat tolerance test on days 1 (HTT1) and 9 (HTT2). On days 2-8 the subjects exercised at 50% VO2max for 60 min.d-1 (T50) or at 75% VO2max for 30-35 min.d-1 (T75). Final HTT2 heart rate and rectal temperature (Tr) were significantly (P less than 0.001) reduced, as compared to HTT1, with no differences between T50 and T75. Both protocols resulted in significant (P less than 0.05) reductions in HTT2 pre-exercise Tr and total exercising caloric expenditure, both of which are known to contribute to HA. No changes in resting plasma volume, osmolality, protein, post-HTT aldosterone, and exercising sweat rate were observed. These results demonstrate that equal levels of HA were obtained with T50 and T75, which suggests that moderate-intensity, short-duration exercise in the heat can produce HA in trained subjects.

Acclimatization↗