摘要:

MOHR, T., F. DELA, A. HANDBERG, F. BIERING-SØRENSEN, H. GALBO, and M. KJÆR. Insulin action and long-term electrically induced training in individuals with spinal cord injuries.Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1247–1252.PurposeIndividuals with spinal cord injuries (SCI) have an increased prevalence of insulin resistance and type 2 diabetes mellitus. In able-bodied individuals, training with large muscle groups increases insulin sensitivity and may prevent type 2 diabetes mellitus. However, individuals with SCI cannot voluntarily recruit major muscle groups, but by functional electrical stimulation (FES) they can now perform ergometer bicycle training.MethodsTen subjects with SCI (35 ± 2 yr (mean ± SE), 73 ± 5 kg, level of lesion C6–Th4, time since injury: 12 ± 2 yr) performed 1 yr of FES cycling (30 min·d−1, 3 d·wk−1(intensive training)). Seven subjects continued 6 months with reduced training (1 d·wk−1(reduced training)). A sequential, hyperinsulinemic (50 mU·min−1·m−2(step 1) and 480 mU·min−1·m−2(step 2)), euglycemic clamp, an oral glucose tolerance test (OGTT), and determination of GLUT 4 transporter protein in muscle biopsies were performed before and after training.ResultsInsulin-stimulated glucose uptake rates increased after intensive training (from 4.9 ± 0.5 mg·min−1·kg−1to 6.2 ± 0.6 mg·min−1·kg−1(P< 0.008) (step 1) and from 9.0 ± 0.8 mg·min−1·kg−1to 10.6 ± 0.8 mg·min·kg−1(P= 0.103) (step 2)). With the reduction in training, insulin sensitivity decreased to a similar level as before training (P> 0.05). GLUT 4 increased by 105% after intense training and decreased again with the training reduction. The subjects had impaired glucose tolerance before and after training, and neither glucose tolerance nor insulin responses to OGTT were significantly altered by training.ConclusionsElectrically induced bicycle training, performed three times per week increases insulin sensitivity and GLUT 4 content in skeletal muscle in subjects with SCI. A reduction in training to once per week is not sufficient to maintain these effects. FES training may have a role in the prevention of the insulin resistance syndrome in persons with SCI.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

BIRMINGHAM, T. B., J. F. KRAMER, A. KIRKLEY, J. T. INGLIS, S. J. SPAULDING, and A. A. VANDERVOORT. Knee bracing after ACL reconstruction: effects on postural control and proprioception.Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1253–1258.PurposeTo evaluate the effects an anterior cruciate ligament (ACL) brace has on various measures of knee proprioception and postural control.MethodsThirty subjects (mean age 27 ± 11 yr) having undergone unilateral ACL reconstruction were tested with and without wearing their own custom-fit brace on their involved limb. Proprioception was assessed using joint angle replication tests completed on an isokinetic dynamometer. Postural control was assessed using a series of single-limb standing balance tests completed on a force platform. The balance tests included: 1) standing on the stable platform with eyes open, 2) standing on a foam mat placed over the platform with eyes open, 3) standing on the platform with eyes closed, and 4) standing on the platform after landing from a maximal single-limb forward hop.ResultsThe brace provided a small but statistically significant improvement in proprioception (mean reduction in error scores between target and reproduced angles = 0.64 ± 1.4°,P= 0.02). For the postural control tests, there was a significant brace condition by test situation interaction (P= 0.02), with the brace providing a small but statistically significant improvement during the test completed on the stable platform with eyes open (mean reduction in center of pressure path length = 4.2 ± 8.4 cm,P= 0.02) but not during the other more challenging test situations. Additionalpost hocanalyses indicated that the relationship between knee proprioception and postural control measures were low and not significant (r = 0.003 to 0.19,P> 0.32), consistent with the suggestion that changes in knee proprioception can occur in the absence of substantial changes in postural control. Also, standing balance tests that challenged the somatosensory contribution to postural control (i.e., those completed on foam, or with eyes closed) were significantly related to single-limb forward hop distances (r = −0.4,P< 0.05), whereas performance during the proprioception test was not (r = 0.1,P> 0.50).ConclusionsIn general, bracing appears to improve performance during tasks characterized by relatively limited somatosensory input but not during tasks characterized by increased somatosenory input. The small magnitude of the improvements, coupled with their apparent lack of carry over to more difficult and functionally relevant tasks, questions the clinical benefit of the present effects of bracing.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

POIRIER, P., S. MAWHINNEY, L. GRONDIN, A. TREMBLAY, T. BRODERICK, J. CLÉROUX, C. CATELLIER, G. TANCRÈDE, and A. NADEAU. Prior meal enhances the plasma glucose lowering effect of exercise in type 2 diabetes.Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1259–1264.PurposeTo compare the changes in plasma glucose and insulin levels in response to 1 h of exercise performed at 60% of &OV0312;O2peakeither in the fasted state or 2 h after a standardized breakfast in subjects with type 2 diabetes.MethodsTen sedentary men with type 2 diabetes treated with oral agents and not under strict metabolic control were tested on two occasions (fasted and fed state) in a random order at a 1-wk interval.ResultsPlasma glucose was slightly but not significantly higher at the beginning of exercise performed in the fed state versus the fasted state (12.4 ± 1.3 vs 11.1 ± 1.1 mmol·L−1respectively; mean ± SE,P= 0.06). However, after exercise, plasma glucose levels were much lower in the fed state (7.6 ± 1.1 mmol·L−1) compared with the fasted state (10.0 ± 1.0 mmol·L−1;P= 0.009). Insulin levels were higher at the beginning of the exercise bout performed in the fed state (177 ± 26 vs 108 ± 19 pmol·L−1;P< 0.05) and during exercise. Similar respiratory exchange ratio at identical workload indicated that the difference in glycemic response was not due to differences in whole body substrate utilization. Plasma concentrations of free fatty acids, glucagon, epinephrine, and norepinephrine were also similar during both experiments.ConclusionsOne hour of aerobic exercise has a minimal impact on plasma glucose level when performed in fasted moderately hyperglycemic men with type 2 diabetes but induces an important decrease in plasma glucose level when performed 2 h after breakfast. Because glucose utilization increased similarly during exercise in both conditions, the higher insulin levels after the meal might have blunted glucose production, creating an imbalance between total glucose production and total peripheral utilization in the fed state in contrast to the fasted state.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

McCOLE, S. D., A. M. DAVIS, and P. T. FUEGER. Is there a disassociation of maximal oxygen consumption and maximal cardiac output?Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1265–1269.PurposeThe purpose of the present study was to determine whether maximal cardiac output (&OV0422;) is affected by the duration of the maximal exercise test.MethodsNine healthy men (N= 6) and women (N= 3) performed three separate maximal treadmill exercise tests, separated by at least 24 h, and underwent a body composition assessment by hydrostatic weighing, all within a 2-wk period. A baseline maximal exercise test was performed to establish &OV0312;O2max. The second and third tests, assigned randomly, were designed to elicit the subjects’ predetermined &OV0312;O2maxin either 6 or 12 min. Heart rate (HR), blood pressure (BP), minutes of ventilation, and oxygen consumption (&OV0312;O2) were measured during all tests. At the end of the 6- and 12-min tests, &OV0422; was measured using an acetylene rebreathing technique. Stroke volume (SV), mean arterial pressure (MAP), total peripheral resistance (TPR), and arteriovenous O2difference were calculated using standard equations.ResultsRepeated-measures ANOVA indicated that there were no significant differences in HR and &OV0312;O2maxbetween the baseline, 6-min, and 12-min tests. Pairedt-tests revealed significantly greater &OV0422; (25.1 ± 5.6 vs 23.7 ± 5.2 L·min−1) and SV (138.3 ± 31.5 vs 130.5 ± 31.2 mL) in the 6- versus 12-min tests, respectively. There were no significant differences in systolic BP, diastolic BP, MAP, TPR, or arteriovenous O2difference.ConclusionsDespite there being no difference in &OV0312;O2maxbetween the two tests, the 6-min maximal exercise test resulted in a significantly greater &OV0422; than the 12-min test, because of a significantly greater SV. Thus, there was a disassociation between &OV0312;O2and &OV0422; during maximal exercise.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

LEIPER, J. B., N. P. BROAD, and R. J. MAUGHAN. Effect of intermittent high-intensity exercise on gastric emptying in man.Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1270–1278.PurposeThe effect on gastric emptying of brief intermittent high-intensity sprints and a moderate-intensity steady-state cycle exercise was studied.MethodsEight healthy male subjects were each studied at rest (R), during steady-state exercise at a constant power output corresponding to 66% of their &OV0312;O2max(C66), during intermittent high-intensity exercise at a power output averaging 66% of their &OV0312;O2max(I66), and during intermittent high-intensity exercise at a power output averaging 75% of their &OV0312;O2max(I75). Gastric emptying was measured using the double-sampling gastric aspiration technique. Subjects ingested 600 mL of a 6% carbohydrate-electrolyte solution immediately before exercise or seated rest.Results:The volume of test solution in the stomach was less at all time points on trial I66 than on trial I75 (P= 0.023). The rate of gastric emptying, expressed as the median (range) time (minutes) taken to empty half the test meal volume (t1/2), was not different on trials R (20 (7–30)) and C66 (21 (7–49)), and was faster than on trial I75 (62 (27-100);P= 0.003 andP= 0.005, respectively). Median t1/2was faster on trial R than on trial I66 (30 (15–74) min;P= 0.019), but no difference was detected between C66 and I66 or between I66 and I75. However, over the initial 30 min period after ingestion, the median (range) volume of test drink delivered to the duodenum was faster (P< 0.01) on trials R (387 (296–541) mL) and C66 (389 (165–584) mL) than on trials I66 (331 (191–494) mL) or I75 (249 (79–335) mL).Conclusion:The data demonstrate that gastric emptying of liquids is slowed during brief intermittent high-intensity exercise compared with rest or steady-state moderate exercise.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

GABBETT, T. J., G. C. GASS, L. THALIB, N. MORRIS, and E. M. GASS. Does endurance training affect orthostatic responses in healthy elderly men?Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1279–1286.PurposeTo investigate the effects and time course of endurance training on the regulation of heart rate (HR), arterial pressure (AP), norepinephrine (NE), and plasma volume (PV) during orthostatic stress in healthy elderly men.MethodsThirty-one healthy men (65–75 yr) were randomly allocated into endurance training (N= 20, EX) and control (N= 11, CON) groups. The EX group cycled 3 d·wk−1for 30 min at 70% &OV0312;O2peakfor 12 wk.&OV0312;O2peakwas determined on an electronically braked cycle ergometer, before training and after 4, 8, and 12 wk of endurance training. The immediate (initial 30 s), early steady-state (1 min), and prolonged (5, 10, 15 min) beat-by-beat HR and AP responses during 90° head-up tilt (HUT) were measured at least 3 d after each &OV0312;O2peaktest. Spontaneous baroreflex slopes were determined by application of linear regression to sequences of at least three cardiac cycles in which systolic blood pressure (SBP) and R-R interval changed in the same direction. Venous blood was collected during 90° HUT and analyzed for changes in plasma NE concentrations, as well as hematocrit and hemoglobin to determine changes in PV.ResultsEndurance training significantly (P< 0.01) increased &OV0312;O2peak(mL·kg−1·min−1) in EX by 10 ± 2%. The immediate, early steady-state, and prolonged HR and AP responses and spontaneous baroreflex slopes during 90° HUT were not significantly different (P> 0.05) between EX and CON groups before or after 4, 8, or 12 wk of endurance training. No significant differences (P> 0.05) were observed between EX and CON groups for peak changes in PV during orthostasis before (−15.0 ± 1.4% vs −11.9 ± 1.3%) or after 4 (−12.2 ± 1.0% vs −12.7 ± 1.4%), 8 (−13.7 ± 1.2% vs −12.4 ± 0.7%), and 12 wk (−10.8 ± 1.6% vs −10.6 ± 0.6%) of endurance training, suggesting a similar stimulus presented by 90° HUT in both groups. Peak changes in NE concentrations during HUT were similar (P> 0.05) between EX and CON groups before (119 ± 23 pg·mL−1vs 191 ± 36 pg·mL−1) and after 4 (139 ± 29 pg·mL−1vs 146 ± 25 pg·mL−1), 8 (114 ± 32 pg·mL−1vs 182 ± 41 pg·mL−1), and 12 wk (143 ± 35 pg·mL−1vs 206 ± 42 pg·mL−1) of endurance training.ConclusionsThese data indicate that in healthy elderly men, improvements in &OV0312;O2peakcan occur without compromising the regulation of HR, AP, NE, and PV during orthostatic stress.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

AMANO, M., T. KANDA, H. UE, and T. MORITANI. Exercise training and autonomic nervous system activity in obese individuals.Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1287–1291.PurposeThis study was designed to investigate the effects of 12 wk of exercise training on autonomic nervous system (ANS) in 18 obese middle-aged men (N= 9) and women (N= 9) (age: 41.6 ± 1.2 yr; BMI: 27.3 ± 0.4 kg·m−2; %fat: 29.6 ± 1.3%, mean ± SE).MethodsEach subject participated in an aerobic exercise training at anaerobic threshold (AT), consisting of 30 min/session, 3 times/wk, for 12 consecutive weeks. The ANS activities were assessed by means of power spectral analysis of heart rate variability (HRV) at resting condition before, at 5 wk, and after the exercise program.ResultsThe exercise training resulted in a significant decrease in body mass, BMI, and % fat (P< 0.01) but not in lean body mass (P> 0.05) together with a significant increase in the AT &OV0312;O2(P< 0.01). Our power spectral data indicated that there were significant increases in the low-frequency component associated with the sympathovagal activity (0.03–0.15 Hz, 348.5 ± 66.8 vs 694.7 ± 91.5 ms2,P< 0.01), the high-frequency vagal component (0.15-0.4 Hz, 146.3 ± 30.4 vs 347.7 ± 96.5 ms2,P< 0.05), and the overall autonomic activity as evaluated by total power (0.03-0.4 Hz, 494.8 ± 88.5 vs 1042.4 ± 180.9 ms2,P< 0.01) of HRV after the training.ConclusionsTwelve weeks of exercise training has significantly improved both the sympathetic and parasympathetic nervous activities of the obese individuals with markedly reduced ANS activity, suggesting a possible reversal effect of human ANS functions. These favorable changes may also have an influence on the thermoregulatory control over the obesity.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

McLEAN, J. A., S. I. BARR, and J. C. PRIOR. Dietary restraint, exercise, and bone density in young women: are they related?Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1292–1296.PurposeWomen with high scores for dietary restraint have been found to have higher 24-h urinary cortisol excretion and a higher prevalence of subclinical ovulatory disturbances, both of which may be risk factors for bone loss. The purpose of this study was to explore relationships between dietary restraint and bone health in regularly menstruating young women.Methods62 women (age: 21.7 ± 2.5 yr) had body composition and total body and lumbar spine bone mineral density (BMD) and content (BMC) assessed using dual-energy x-ray absorptiometry. Dietary restraint was assessed using the restraint subscale from the Three-Factor Eating Questionnaire: 29 women had low restraint (LR; restraint score 0–5), 33 had high restraint (HR; restraint score 13–21). Exercise (h·wk−1) was assessed by questionnaire on two occasions.ResultsLR and HR women were similar in age and body composition (fat mass = 15.0 ± 4.7 kg, lean mass = 40.9 ± 4.9 kg), but HR women exercised more (3.4 ± 1.7 vs 2.2 ± 1.8 h·wk−1,P< 0.05). Exercise was correlated with BMD and BMC, and when it was included as a covariate, total body BMC was significantly lower in HR than LR women. In multiple regression analysis, weekly hours of exercise and restraint score were significant predictors of total body BMD and BMC.ConclusionThe observations of this cross-sectional study suggest that high levels of cognitive dietary restraint, or associated factors such as higher cortisol, may attenuate the positive effects of exercise on bone in young women.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

MUJIKA, I., and S. PADILLA. Muscular characteristics of detraining in humans.Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1297–1303. Skeletal muscle is characterized by its ability to dynamically adapt to variable levels of functional demands. During periods of insufficient training stimulus, muscular detraining occurs. This may be characterized by a decreased capillary density, which could take place within 2–3 wk of inactivity. Arterial-venous oxygen difference declines if training stoppage continues beyond 3–8 wk. Rapid and progressive reductions in oxidative enzyme activities bring about a reduced mitochondrial ATP production. The above changes are related to the reduction in &OV0312;O2maxobserved during long-term training cessation. These muscular characteristics remain above sedentary values in the detrained athlete but usually return to baseline values in recently trained individuals. Glycolytic enzyme activities show nonsystematic changes during periods of training cessation. Fiber distribution remains unchanged during the initial weeks of inactivity, but oxidative fibers may decrease in endurance athletes and increase in strength-trained athletes within 8 wk of training stoppage. Muscle fiber cross-sectional area declines rapidly in strength and sprint athletes, and in recently endurance-trained subjects, whereas it may increase slightly in endurance athletes. Force production declines slowly and in relation to decreased EMG activity. Strength performance in general is readily maintained for up to 4 wk of inactivity, but highly trained athletes’ eccentric force and sport-specific power, and recently acquired isokinetic strength, may decline significantly.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

STEVENSON, S. W., and G. A. DUDLEY. Dietary creatine supplementation and muscular adaptation to resistive overload.Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1304–1310.PurposeThis study examined the influence of dietary creatine (CR) supplementation upon mechanical and hypertrophic responses to a well-defined conditioning stimulus provided by electromyostimulation (EMS).MethodsEighteen resistance-trained subjects were assigned CR or a placebo (PL) in a randomized, double-blind fashion. After CR loading (20 g·d−1for 7 d), CR supplementation (5 g·d−1) or PL was continued for 8 wk. During supplementation, EMS (3–5 sets of 10 coupled eccentric and concentric actions) was applied to the left m. quadriceps femoris (QF) twice weekly while subjects continued voluntary resistance training of both lower limbs unsupervised. Cross-sectional area (CSA) of each QF was assessed with magnetic resonance imaging (MRI). Torque during EMS was analyzed to assess muscle loading and fatigue resistance.ResultsMaximal torque and the torque time integral increased markedly over training (P≤ 0.0001). These responses reflected activation of more muscle as EMS current was increased (about 16%), greater recovery between sets (P≤ 0.0423), and less fatigue during sets over training (P= 0.0002). CR did not influence these responses (P= 0.8093). In accord with these results, the increase in CSA for the stimulated QF (11%) was comparable for CR and PL (P= 0.2190). CSA in the nonstimulated QF increased 5% in CR (P= 0.0091) but did not change in PL.ConclusionWe conclude that CR supplementation did not augment the mechanical or hypertrophic response to a precisely measured conditioning stimulus that attenuated but did not ameliorate fatigue. We suggest that enhanced fatigue resistance may not explain the apparent ergogenic effect of CR during voluntary training.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID