ISSN:0112-1642    

DOI:10.2165/00007256-199111040-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryRegular physical activity can improve cardiovascular fitness and may reduce the likelihood and debilitating effects of cardiovascular disease.Weight-training has generally been believed to have limited value in modifying risks of cardiovascular disease. Effects shown of resistance training on parameters associated with cardiovascular fitness and disease include: heart rate decreases for maximal work and recovery from short term weight-training, increased ventricular mass, and increased ventricular wall and septum thickness. Studies suggest that myocardial hypertrophy resulting from resistive training can be accompanied by positive myocardial adaptations.Blood pressure response considerations to resistive training include: similarity of resistive exercise peak response to other forms of high intensity exercise, highest blood pressures occur at or near exhaustion during maximum lifts, training appears to reduce the exercise blood pressure. Given the blood pressure responses caution is required for individuals with cardiovascular disease.Studies of high-volume weight-training indicate that small to moderate increases in aerobic power can occur in relatively short periods of time. The mechanisms by which weight-training increases V̇O2maxis unclear.Resistive training may produce positive changes in serum lipids with the volume of training being the dependent factor.Cross-sectional and longitudinal studies of bodybuilders suggest that weight-training may beneficially alter glucose tolerance and insulin sensitivity. It appears that weight-training can increase short term high intensity endurance without a concomitant loss in performance. Resistive training increases power output and performance.Body composition has important relationships to cardiovascular fitness, strength and flexibility. It is likely that it can be affected and controlled by use of large body mass during exercise depending on training volume.

ISSN:0112-1642    

DOI:10.2165/00007256-199111040-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryWith the cessation of exercise, glycogen repletion begins to take place rapidly in skeletal muscle and can result in glycogen levels higher than those present before exercise. Understanding the rate-limiting steps that regulate glycogen synthesis will provide us with strategies to increase the resynthesis of glycogen during recovery from exercise, and thus improve performance.Given the importance of muscle glycogen to endurance performance, various factors which may optimise glycogen resynthesis rate and insure complete restoration have been of interest to both the scientist and athlete. The time required for complete muscle glycogen resynthesis after prolonged moderate intensity exercise is generally considered to be 24 hours provided ≈500 to 700g of carbohydrate is ingested. Muscle glycogen synthesis rate is highest during the first 2 hours after exercise. Ingestion of 0.70g glucose/kg bodyweight every 2 hours appears to maximise glycogen resynthesis rate at approximately 5 to 6 µmol/g wet weight/h during the first 4 to 6 hours after exhaustive exercise. Further enhancement of glycogen resynthesis rate with ingestion of greater than 0.70g glucose/kg bodyweight appears to be limited by the constraints imposed by gastric emptying. Ingestion of glucose or sucrose results in similar muscle glycogen resynthesis rates while glycogen synthesis in liver is better served with the ingestion of fructose. Also, increases in muscle glycogen content during the first 4 to 6 hours after exercise are greater with ingestion of simple as compared with complex carbohydrate.Glycogen synthase activity is a key component in the regulation of glycogen resynthesis. Glycogen synthase enzyme exists in 2 states: the less active, more phosphorylated (D) form which is under allosteric control of glucose-6-phosphate, and the more active, less phosphorylated (I) form which is independent of glucose-6-phosphate. There is generally an inverse relationship between glycogen content in muscle and the percentage synthase in the activated (I) form. Exercise and insulin by themselves activate glycogen synthase by conversion to glycogen synthase I. Although small changes in the activity ratio (% I form) can lead to large changes in the rate of glycogen synthesis, glycogen synthase I appears to increase very little (≈25%) in response to glycogen depletion and returns to pre-exercise levels as glycogen levels return to normal. Thus glycogen resynthesis, which may increase 3- to 5-fold, may also be influenced by glucose-6-phosphate, which can activate glycogen synthase in the D form.There is considerable evidence that glucose transport across the cell membrane is the rate limiting step in the synthesis of muscle glycogen. Thus, regulation of glucose transport may ‘set the pace’ for glycogen resynthesis after exercise. Contractile activity increases the permeability of muscle to glucose even in the absence of insulin and this increase in glucose transport persists for several hours after cessation of exercise. Increased glucose transport into muscle may persist for 16 to 20 hours following exercise in rats if carbohydrate intake is restricted. This suggests that glucose transport may be regulated by glycogen concentration. However, the rate of glucose transport is not increased when muscle glycogen concentration is reduced by an overnight fast, suggesting that contractile activity provides an important stimulus linking glucose transport and the resynthesis of muscle glycogen. The changes in glucose transport suggest that ingestion of carbohydrate immediately after cessation of exercise should result in the most rapid resynthesis of muscle glycogen.Muscle possesses a unique tissue specific glucose transporter protein, termed GLUT4, which regulates glucose transport across the muscle cell membrane. Exercise training increases the synthesis of GLUT4 glucose transporters in skeletal muscle. This adaptation, along with a similar increase in glycogen synthase enzyme with training, suggests the ability to increase glycogen stores in the trained state may in part be due to increased numbers of glucose transporters.

ISSN:0112-1642    

DOI:10.2165/00007256-199111040-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryResearch demonstrates a positive and graded relationship between handweighted exercise energy costs, the distance through which handweights are swung and the weight used. The energy costs of handweighted exercise when swinging 0.45 to 1.36kg handweights have been shown to be 3 to 155% greater than costs of unweighted exercise at any pace. The upper limit of such increases is unknown. Moreover, the use of handweighted arm swings can convert walking, benchstepping or running from leg dominated endurance training modalities to exercises that simultaneously challenge muscles of both the upper and lower body.The use of handweights may induce a pressor response characterised by elevated heart rate and blood pressure responses at a given exercise intensity. However, such elevations have not been consistently reproduced and when they occurred, were on average small and of little physiological concern. Individual blood pressure responses may vary more widely between hand-weighted and unweighted walking, with some exhibiting higher and others lower blood pressures when using handweights. Taken together, research suggests that the prescription of handweighted exercise is safe for most individuals. However, it should be prescribed using precautions similar to those used when implementing new exercise regimens, particularly among those with cardiovascular complications. Potential strength and endurance training adaptations to handweighted exercise that incorporates large arm and leg range of motion movement patterns have yet to be determined.

ISSN:0112-1642    

DOI:10.2165/00007256-199111040-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummarySatisfactory results following knee surgery can be obtained only through the combined efforts of the surgeon, patient and therapist. A rehabilitative plan is based upon consideration of the effects of disuse and immobility on musculoskeletal tissues, and knowledge of the healing requirements following injury and specific surgical procedures. A balance must be made between simultaneous demands for protection against undue stress to facilitate healing and the need for stress to retard atrophy of musculoskeletal tissue. A thorough review of these concepts forms the basis for a rational approach to rehabilitation after specific surgical procedures.The phasic approach to knee rehabilitation is based upon progression in a logical fashion through the chronology of immobility, range of motion, progressive weight bearing and strengthening exercises. The latter category can be subdivided into its own progression from isometrics, isotonics, functional exercises through isokinetics. The ultimate goal and final phase is a safe return to full activity.By integrating a thorough knowledge of the healing parameters of musculoskeletal tissues and the simultaneous coexisting needs for protection and controlled stress, specific rehabilitative programmes can then be designed for the most common surgical procedures including: anterior and posterior cruciate ligament reconstruction, meniscal repair and meniscectomy, lateral release and hyaline cartilage procedures.

ISSN:0112-1642    

DOI:10.2165/00007256-199111040-00005

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS