摘要:

ROCKWELL, J. A., J. WALBERG RANKIN, and B. TODERICO. Creatine supplementation affects muscle creatine during energy restriction.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 61–68.Introduction:Anaerobic performance and body protein may decrease with energy restriction practiced by some athletes for weight loss.Methods:This investigation examined the effects of creatine (Cr) supplementation during energy restriction on muscle Cr, exercise performance (10 sprints of 6 s, with 30-s rest), nitrogen balance, and body composition in male resistance trainers. Creatine supplemented (CrS, 20 g·d-1of Cr) and those given a placebo (Pl) consumed a formula diet of 75.3 kJ (18 kcal)·kg-1·d-1(54.7% C, 21.3% P, 24% F) for 4 d. A control group was unsupplemented and continued their normal diet. There were no changes in body composition or performance of the control group.Results:CrS and Pl demonstrated similar decreases in body weight and percent body fat. The percent change in fat-free mass was more for Pl (2.4 ± 0.3% reduction) than CrS (1.4 ± 0.4%), but urinary nitrogen losses were similar. Significant increases in muscle total Cr and CrP of 15–16% were demonstrated by CrS over the energy restriction period, whereas Pl had no changes in muscle Cr. Total work done during the sprints expressed per body weight tended to be 3.8% higher in CrS and 0.5% less in Pl after the energy restriction (P= 0.058).Conclusion:It was concluded that Cr supplementation increased muscle Cr during short-term energy restriction but did not affect body fat or protein loss. The change in muscle creatine was reflected in a tendency for higher total sprint work for the Cr group.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

BLANCHARD, M. A., G. JORDAN, B. DESBROW, L. T. MacKINNON, and D. G. JENKINS. The influence of diet and exercise on muscle and plasma glutamine concentrations.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 69–74.Purpose:This study examined the relationship between muscle glutamine, muscle glycogen, and plasma glutamine concentrations over 3 d of high-intensity exercise during which dietary carbohydrate (CHO) intake varied.Methods:Five endurance-trained men completed two exercise trials in randomized order, over a 14-d period. Each trial required subjects to perform 50 min of high-intensity continuous and interval exercise on three consecutive days while consuming a diet that provided 45% of the energy as CHO or a diet in which CHO provided 70% of the total energy. Four days of inactivity and consumption of a 55% CHO diet separated the two randomized trials. Menus and food were provided for the subjects and all food and drink consumed were weighed and recorded for later analysis. Before exercise on the first day of each trial, at the start of exercise on day 3 and on completion of exercise on day 3, muscle was biopsied from the vastus lateralis for the analysis of glutamine and glycogen concentrations. Venous blood was sampled before and twice after exercise on each day for the analysis of plasma glutamine and cortisol concentrations.Results:Mean plasma glutamine concentration was significantly higher during the 70% CHO exercise trial when compared with the 45% CHO trial (P< 0.05). Glycogen decreased by the same magnitude during both trials and there was no relationship between changes in plasma glutamine and changes in muscle glycogen concentration. Muscle glutamine concentration did not change in either trial.Conclusions:These data suggest that the influence of carbohydrate intake upon the concentration of plasma glutamine is not mediated through the concentration of intramuscular glycogen.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

MOORE, A. D. JR., S. M. C. LEE, J. B. CHARLES, M. C. GREENISEN, and S. M. SCHNEIDER. Maximal exercise as a countermeasure to orthostatic intolerance after spaceflight.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 75–80. Previous investigators have suggested that maximal exercise performed 24 h before the end of bed rest, a spaceflight analog, restores prebed rest plasma volume, baroreflex responses, and orthostatic tolerance.Purpose:In this case report, we examined the effect of a similar exercise protocol 24 h before a Shuttle landing on the orthostatic responses of four crewmembers (EX) after spaceflights of 8-14 d. Four additional crewmembers (CON) served as controls and did not perform exercise during the final day of the flight.Methods:Each crewmember performed a 10-min stand test approximately 10 d before launch (L-10) and within 1-2 h of landing (R+0). Cardiac stroke volume was measured (Doppler ultrasound) supine and during each min of standing for three EX and three CON subjects.Results:Preflight, all crewmembers completed the stand test and each group had similar heart rate and blood pressure responses. Postflight, all subjects also completed the 10-min stand test. Each group had similarly elevated supine and standing heart rates, elevated diastolic and mean arterial blood pressures, and reduced pulse pressures compared to L-10. However, postflight cardiac output, mean ± SEM, (EX: 4.5 ± 0.6 L·min-1; CON: 3.1 ± 0.3 L·min-1) and stroke volume (EX: 43 ± 7 mL·beat; CON: 30 ± 6 mL·beat) were higher after 10 min standing in the EX subjects compared to CON subjects.Conclusions:For these four crewmembers, maximal exercise performed 24 h before landing may have helped maintain stroke volume but did not maintain heart rate and blood pressure responses during standing compared to preflight.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

LAUGHLIN, M. H., and D. H. KORZICK. Vascular smooth muscle: integrator of vasoactive signals during exercise hyperemia.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 81–91. The primary focus of this review is to discuss the importance of vascular smooth muscle function in mechanisms underlying exercise hyperemia in skeletal muscle. Important features of exercise hyperemia are presented and include: 1) the large magnitude of increase in blood flow, 2) the pattern of increased blood flow within and among skeletal muscle during exercise, 3) exercise hyperemia results from increases in vascular conductance produced by relaxation of vascular smooth muscle, 4) the increased blood flow is linked to the oxidative metabolism of the muscle, and 5) the increased blood flow occurs very rapidly with the initiation of exercise. A prevailing theme throughout this review is that vascular smooth muscle is a primary integrator of vasoactive signals that, in turn, regulate vascular resistance and muscle blood flow. Signal transduction pathways involved in vascular smooth muscle contraction and relaxation are discussed, with particular emphasis on the role of multiple and redundant signaling pathways for initiating a given contractile/relaxation response. We emphasize the concept that exercise hyperemia is a local phenomenon and that, during maximal exercise when most signals for vasoconstriction are still present, three primary control mechanisms are thought to regulate vasodilation and subsequent increases in vascular conductance: myogenic vascular control, metabolic vascular control, and endothelium-mediated vascular control. Experimental paradigms to test the relative importance of the predominant mechanisms thought to underlie exercise hyperemia are discussed and evaluated in light of the multiple and redundant control systems now known to contribute to control of blood flow in striated muscle tissue.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

STUEWE, S. R., P. A. GWIRTZ, and R. T. MALLET. Exercise training increases creatine kinase capacity in canine myocardium.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 92–98.Introduction:The creatine kinase (CK) energy shuttle of cardiomyocytes channels metabolic energy from the mitochondria to sites of energy utilization at contracting myofibrils and sarcolemmal and sarcoplasmic reticular ion pumps. Although plasticity of the myocardial CK system in response to hemodynamic overload has been repeatedly demonstrated, the effects of aerobic exercise training on myocardial CK are less well understood. This investigation tested the hypothesis that aerobic exercise training increases the capacity of the CK system in canine myocardium.Methods:Mongrel dogs were conditioned by a 9-wk treadmill running program or cage-rested for 4 wk. Total CK activity was measured colorimetrically; CKMBwas separated from other CK isoforms and measured by electrophoresis.Results:Relative to sedentary controls, training increased left ventricular total CK activity 46% (P< 0.05) but did not alter total CK activity in right ventricular myocardium. Also in left ventricular myocardium, training increased CKMBisoenzyme activity 4.5-fold and the CKMBfraction of total CK threefold from 1.1 ± 0.4 to 3.4 ± 0.8% (P< 0.05). In contrast to left ventricle, CKMBactivity and its fraction of total CK activity were not altered by training in right ventricular myocardium.Conclusions:Aerobic exercise training increases total myocardial CK activity and CKMBcontent in canine left ventricular myocardium, although CKMBremains a minor component of the myocardial CK system. The right ventricular CK system was not affected by training.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

WILMORE, J. H., P. R. STANFORTH, J. GAGNON, T. RICE, S. MANDEL, A. S. LEON, D. C. RAO, J. S. SKINNER, and C. BOUCHARD. Cardiac output and stroke volume changes with endurance training: The HERITAGE Family Study.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 99–106.Purpose:The purpose of this study was to determine the magnitude of changes in cardiac output (Qc), stroke volume (SV), and arterial-mixed venous oxygen difference (a-&OV0456;O2diff) during submaximal exercise following a 20-wk endurance training program, with the primary focus on identifying differences in response by race, sex, and age.Methods:The participants in this study (N= 631) were healthy and previously sedentary men (N= 277) and women (N= 354) of varying age (17–65 yr) and race (blacks,N= 217; whites,N= 414) who had completed the HERITAGE Family Study protocol. After baseline measurements, participants trained on cycle ergometers 3 d·wk-1for a total of 60 exercise sessions starting at the HR associated with 55% of maximal oxygen uptake (O2max) for 30 min/session and building to the HR associated with 75% of O2maxfor 50 min/session, which was maintained during the last 6 wk. HR, Qc (CO2rebreathing), and SV (Qc/HR) were determined in duplicate at 50 W and at 60% of O2maxon two different days both before and after training.Results:After training, there were significant decreases in HR and Qc, and significant increases in SV and a-&OV0456;O2diff at 50 W (except for no change in a-&OV0456;O2diff in black men). The changes in HR differed by sex and age, and the changes in SV, Qc, and a-&OV0456;O2diff differed by race. Qc decreased by 0.6 L·min-1at 50 W for the total sample, consistent with the decrease in O2at this power output. At 60% of O2max, HR decreased, and SV, Q, and a-&OV0456;O2diff increased. There were small differences in response by sex (HR and SV), race (HR), and age (HR and Qc).Conclusion:It is concluded that the cardiovascular systems of men and women, blacks and whites, and younger and older subjects are not limited in their ability to adapt to endurance training.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

WILMORE, J. H., P. R. STANFORTH, J. GAGNON, T. RICE, S. MANDEL, A. S. LEON, D. C. RAO, J. S. SKINNER, and C. BOUCHARD. Heart rate and blood pressure changes with endurance training: The HERITAGE Family Study.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 107–116.Purpose:The purpose of this study was to determine the magnitude of change in resting and exercise heart rate (HR) and blood pressure (BP), by race, sex, and age, after a 20-wk endurance training program in 507 healthy and previously sedentary subjects from the HERITAGE Family Study.Methods:After baseline measurements, subjects exercised on cycle ergometers 3 d·wk-1for a total of 60 exercise sessions starting at 55% of O2maxfor 30 min·session−1and building to 75% of O2maxfor 50 min·session−1for the last 6 wk. HR and BP at rest and during exercise (50 W, 60% of O2max, maximal exercise) were each determined in duplicate on two different days both before and after training (resting values at 24-h and 72-h posttraining).Results:After the period of training, there was a small decrease in resting HR (−2.7 to −4.6 beats·min-1across groups at 72-h posttraining), and small changes (i.e., < 3 mm Hg) in resting systolic (SBP), diastolic (DBP), and calculated mean BP (MBP), which varied by race, sex, and age. During exercise at the same absolute work rate (50 W), HR, SBP, DBP, and MBP were all significantly reduced, with greater reductions in HR in women compared with men, and greater reductions in BP in blacks and older subjects compared with whites and younger subjects, respectively. At the same relative work rate (60% O2max), HR, DBP, and MBP were reduced, but SBP remained unchanged. Blacks had a greater reduction in DBP, but whites had a greater reduction in HR. Finally, at maximal exercise, there was a small decrease in HR, with men and whites decreasing more than women and blacks; an 8 mm Hg increase in SBP, with men increasing more than women; a 4 mm Hg decrease in DBP, with blacks decreasing more than whites; and no change in MBP.Conclusion:In conclusion, the reductions in resting HR and BP with training were generally small, but the reductions during exercise were substantial and clinically important, with the older and the black populations experiencing greater reductions.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

DAMIANO, D. L., T. L. MARTELLOTTA, J. M. QUINLIVIN, and M. F. ABEL. Deficits in eccentric versus concentric torque in children with spastic cerebral palsy.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 117–122.Purpose:The purposes of this study were to determine whether ambulatory children with spastic cerebral palsy (CP) had abnormal isokinetic eccentric peak torque values at the knee and ankle, and to gain further insights on the influence of spasticity on voluntary force production in this population.Methods:Twenty-four children with spastic CP (mean = 11.1 ± 2.6 yr) and twenty children of comparable age with no neuromotor pathology (mean = 10.3 ± 2.6 yr) participated in an isokinetic testing protocol on a Biodex dynamometer that measured eccentric and concentric peak torques of the knee extensors, knee flexors, ankle dorsiflexors, and ankle plantarflexors. Angular velocity of the eccentric trials was 30°·s-1and of the concentric trials was 30°·s-1, 60°·s-1, and 120°·s-1. Peak torque values were normalized by body weight and compared across groups by using ANOVA procedures. Eccentric to concentric (E/C) peak torque ratios at 30°·s-1were computed for each muscle and compared across groups. The torque values in CP were also expressed as a percent of the mean normalized value of the comparison group and compared across conditions using repeated measures ANOVA (P< 0.05).Results:Children with CP demonstrated decreased eccentric and concentric peak torques for all muscle groups tested. The relative deficit in eccentric torque was less than the concentric torque and the decrement in concentric torque across speeds was greater in CP for all muscle groups except the ankle dorsiflexors. The E/C ratios for the knee extensors and flexors were also greater in CP.Conclusions:Children with CP have diminished eccentric as well as concentric peak torques at the knee and ankle. The influence of spasticity on voluntary force production can be inferred from the bias toward greater eccentric torque and the greater decrement in concentric torque across speeds in children with spastic CP.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

HOPKINS, J. T., C. D. INGERSOLL, B. A. KRAUSE, J. E. EDWARDS, and M. L. CORDOVA. Effect of knee joint effusion on quadriceps and soleus motoneuron pool excitability.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 123–126.Purpose:To examine changes in quadriceps and soleus MN pool activity resulting from knee joint effusion over a 4-h period and assess the relationship between the muscles.Methods:A repeated measures before-after trial design was used for this study. Eight, neurologically sound volunteers (age 23.3 ± 2.1 yr, height 171.8 ± 15.9 cm, mass 65.5 ± 17.7 kg) participated in this study. An area superomedial to the patella was cleaned and anesthetized, and 30 mL of sterile saline was injected into the knee joint capsule to mimic mechanical joint effusion. The Hoffman reflex (H-reflex) was elicited by applying a percutaneous stimulus to the appropriate nerve and recording the response through surface electromyography. Soleus and vastus medialis H-reflex measures were collected from each volunteer before, at 30 min, 90 min, 150 min, and 210 min intervals over a 4-h period after knee effusion.Results:All soleus H-reflex measures after effusion (30 min 5.89 ± 0.92 V; 90 min 6.16 ± 0.48 V; 150 min 6.59 ± 0.50 V; 210 min 6.70 ± 0.56 V) were increased in relation to the preeffusion measure (5.01 ± 0.79 V). All vastus medialis H-reflex measures after effusion (30 min 4.23 ± 0.94 V; 90 min 4.15 ± 1.11 V; 150 min 4.16 ± 0.57 V; and 210 min 4.99 ± 1.23) were decreased in relation to the preeffusion measure (5.88 ± 1.44 V;P≤ 0.05).Conclusions:Afferent activity from the knee joint capsule resulted in an inhibitory effect on the vastus medialis and a facilitatory effect on the soleus. Facilitation of the soleus in cooperation with other lower extremity musculature could be a mechanism for compensation of the inhibited quadriceps to maintain lower kinetic chain function.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

ESCAMILLA, R. F. Knee biomechanics of the dynamic squat exercise.Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 127–141.Purpose:Because a strong and stable knee is paramount to an athlete’s or patient’s success, an understanding of knee biomechanics while performing the squat is helpful to therapists, trainers, sports medicine physicians, researchers, coaches, and athletes who are interested in closed kinetic chain exercises, knee rehabilitation, and training for sport. The purpose of this review was to examine knee biomechanics during the dynamic squat exercise.Methods:Tibiofemoral shear and compressive forces, patellofemoral compressive force, knee muscle activity, and knee stability were reviewed and discussed relative to athletic performance, injury potential, and rehabilitation.Results:Low to moderate posterior shear forces, restrained primarily by the posterior cruciate ligament (PCL), were generated throughout the squat for all knee flexion angles. Low anterior shear forces, restrained primarily by the anterior cruciate ligament (ACL), were generated between 0 and 60° knee flexion. Patellofemoral compressive forces and tibiofemoral compressive and shear forces progressively increased as the knees flexed and decreased as the knees extended, reaching peak values near maximum knee flexion. Hence, training the squat in the functional range between 0 and 50° knee flexion may be appropriate for many knee rehabilitation patients, because knee forces were minimum in the functional range. Quadriceps, hamstrings, and gastrocnemius activity generally increased as knee flexion increased, which supports athletes with healthy knees performing the parallel squat (thighs parallel to ground at maximum knee flexion) between 0 and 100° knee flexion. Furthermore, it was demonstrated that the parallel squat was not injurious to the healthy knee.Conclusions:The squat was shown to be an effective exercise to employ during cruciate ligament or patellofemoral rehabilitation. For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligaments may increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat.

ISSN:0195-9131    

出版商:OVID    

年代:2001

数据来源: OVID