l-Carnitine and the recovery from exhaustive endurance exercise: a randomised, double-blind, placebo-controlled trial

We hypothesised that l-carnitine could accelerate recovery from exhaustive exercise since increased blood l-carnitine concentrations elicit a vasodilation in isolated animal vessels as well as in patients with peripheral vascular or coronary artery disease during exercise. Twelve subjects received either 2 g l-carnitine or a placebo in a study which was double-blind and crossover in design. Two hours after administration, the subjects performed a constant-load exercise test (CET₁) cycling at their individual anaerobic threshold to exhaustion. Three hours later this test was repeated (CET₂). After 4–14 days, each subject performed the same cycling tests after having taken the other substance. Exercise times of the 12 subjects were identical with l-carnitine (CET₁: 21.3±5.7 min; CET₂: 21.4±5.3 min) and placebo (CET₁: 21.9±6.2 min; CET₂: 20.4±4.8 min). Also, heart rate, oxygen consumption, respiratory exchange ratio, and blood lactate concentration were identical. In conclusion, 2 g of L-carnitine taken 2 h before a first of two constant-load exercise tests had no influence on the second tests performed 3 h after the first test compared with placebo.     

Acute effects of endurance exercise on mitochondrial distribution and skeletal muscle morphology

Summary Biopsies of vastus lateralis from seven well-trained males were studied 1 month before and 15–30 min after a 100-km race. The distribution of interfibrillar mitochondria was analyzed to determine whether a long bout of exercise induced a redistribution of mitochondria. Capillary densities and mean fiber areas were also estimated. Capillary density and mean interfibrillar mitochondrial volume density were found to be significantly correlated with running time in the race. An earlier study on these biopsies found that the mean volume densities of interfibrillar and subsarcolemmal mitochondria did not change after a race, but the volume densities of lipid droplets and interfibrillar glycogen decreased significantly. In the present study, volume density of interfibrillar mitochondria [V_v(mi, fim)] before the race was highest with a value of 0.098±0.007 near the fiber border, and decreased progressively with distance to 0.045±0.004 at the fiber center. After the race, V_v(mi, fim) was unchanged at the fiber border, but was significantly higher (0.062±0.005) in the center of the fiber. This increase in mitochondrial volume density was attributable to the shrinkage of the fibers from consumption of energy stores, which was relatively greater for interfibrillar glycogen than for subsarcolemmal glycogen. Thus the primary effect of this extended bout of endurance exercise on vastus lateralis was the nearly complete depletion of the interfibrillar glycogen and lipids, but there was no evidence of an acute redistribution of mitochondria.Supported by a Postdoctoral Fellowship from the Swiss National Science Foundation     

Effects of endurance training on hyperammonaemia during a 45-min constant exercise intensity

Summary Eleven laboratory-pretrained subjects (initial =54 ml·kg⁻¹·min⁻¹) took part in a study to evaluate the effect of a short endurance training programme [8–12 sessions, 1 h per session, with an intensity varying from 60% to 90% maximal oxygen consumption ] on the responses of blood ammonia (b[NH ₄ ⁺ ]) and lactate (b[la]) concentrations during progressive and constant exercise intensities. After training, during which did not increase, significant decreases in b[NH ₄ ⁺ ], b[la] and muscle proton concentration were observed at the end of the 80% constant exercise intensity, although b[NH ₄ ⁺ ] and b[la] during progressive exercise were unchanged. On the other hand, no correlations were found between muscle fibre composition and b[NH ₄ ⁺ ] in any of the exercise procedures. This study demonstrated that a constant exercise intensity was necessary to reveal the effect of training on muscle metabolic changes inducing the decrease in b[NH ₄ ⁺ ] and b[la]. At a relative power of exercise of 80% , there was no effect of muscle fibre composition on b[NH ₄ ⁺ ] accumulation.     

Dynamic changes of deleted mitochondrial DNA in human leucocytes after endurance exercise

We examined the time course of the appearance and disappearance of deleted mitochondrial DNA (mtDNA) in human leucocytes after endurance exercise. Five untrained healthy females [aged 20.2 (0.4) years] exercised for 30 min at 50–60 W at 60 rpm on a cycle ergometer for 2 or 3 consecutive days. Blood samples were collected immediately before exercise, and on three occasions after the end of the last exercise bout. Levels of mtDNA were analyzed using the nested polymerase chain reaction method. Prior to exercise, a common mtDNA deletion was identified in all subjects. This common deletion was again identified in all subjects 1 day after completion of the exercise regime. However, mtDNA with this common deletion was found to have disappeared 2 days after exercise in three subjects, and after 4 days in the other two subjects. The deletion then reappeared 5 or 6 days after the final exercise bout in three of the five subjects. These findings demonstrate that a common deletion in leucocytes disappears over a period of several days after endurance exercise and reappears a number of days thereafter. Therefore, the status of the appearance and disappearance of common mtDNA deletion in leucocytes is highly dynamic. Electronic Publication     

Transfer effects of endurance training to exercise with untrained limbs

Summary There has been a controversy over whether the increases in maximal oxygen uptake ( O_{2 max}) and reductions in heart rate at a given submaximal workload after endurance training are limited to exercise with trained limbs or also may be observed during exercise with untrained limbs. In the present study five initially very sedentary young men trained by leg cycling (LT) and five by arm cranking (AT) 30 min per day on 4 days a week for 11 weeks at an intensity 75–80% O_{2 max}. Before and after training the subjects performed submaximal and maximal arm cranking and leg cycling tests. Leg cycling and arm cranking O_{2 max} increased 15% and 9% after LT and 12% and 35% after AT, respectively. Heart rate at a given submaximal workload was lower (p<0.05) during trained and untrained limb exercise following LT and AT. However, subjective ratings of perceived exertion (RPE) at a given submaximal workload were lower (p<0.01) only during exercise with trained limbs after LT and AT. In light of previous findings, the present increases in O_{2 max} and reductions in submaximal exercise heart rate with untrained limbs suggest that the initial fitness of the subjects as well as the intensity, frequency, and duration of training may be important factors in determining the extent to which transfer effects of endurance training can be observed. Although the present data suggest that reductions in RPE after endurance training may be the result of local changes in trained muscles, the possible contribution of central nervous adaptations cannot be excluded.Supported in part by Grant HL 18907 from The National Heart, Lung, and Blood Institute     

Comparison of incremental and steady state tests of endurance training

Summary To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditionning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70–80% . Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % , increased with training by 17% (p<0.01) and 9% (p<0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% ) to a blood lactate steady state (4.8±1.4 mmol·l^–1) whereas, after training, AeT intensity (73% ) led to a blood lactate accumulation of up to 6.6±1.7 mmol·l^–1 without significant modification of muscle lactate (7.6±3.1 and 8.2±2.8 mmol·kg^–1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise. Nevertheless, the results obtained at the end of the constant work load exercises were assumed to be independant of these changes, the occurrence of blood lactate accumulation being postulated to reflect a decreased removal from the blood linked to a higher relative work intensity. So, the use of incremental exercise is an incomplete procedure when evaluating endurance training effects.     

Uptake of 3H-leucine into different fractions of rat skeletal muscle following acute endurance and sprint exercise

Summary In order to study the specificity of the protein synthetic response to different acute exercise loads, 48 male rats served as non-exercised controls or ran at either 0.5 m·s^–1 for 1 h or 1.5 m·s^–1, 10 s20 s workrest, for 1h. Animals were killed and red and white vastus muscles excised from the controls or at 0, 2, 18, 24, or 48 h post-exercise. Muscle slices were incubated in a medium containing 10 Ci l-[4,5-³H]leucine for 30 min. Incorporation of the radionuclide was measured by liquid scintillation (dpm·mg^–1 protein) in the whole homogenate and in four subcellular fractions. The endurance exercise elicited increased uptakes into the mitochondrial fractions of both red and white vastus at 2 and 18 h respectively. However, the mitochondrial uptake was depressed at 24 h in the red and at 2 h in the white vastus. Only in red vastus was incorporation into the soluble protein elevated following endurance exercise. The sprint protocol elicited increased uptake into soluble protein at 2 and 18 h in both red and white vastus and into mitochondrial protein at 18 and 24 h in the white vastus. The shifts in uptake in white vastus occurred in conjunction with depressed uptakes in the total homogenate. These data indicate that both the changes in the type of protein and the time course of amino acid incorporation following acute exercise are related to both the metabolic characteristics of the muscle fibres and the intensity of the exercise.This study was supported by Grants from the Natural Sciences and Engineering Research Council (NSERC A0424 and NSERC A6436)     

Differential mobilization of leucocyte and lymphocyte subpopulations into the circulation during endurance exercise

Summary A total of 14 healthy subjects [means (SD): 27.6 (3.8) years; body mass 77.8 (6.6) kg; height 183 (6) cm] performed endurance exercise to exhaustion at 100% of the individual anaerobic threshold (Th_an) on a cycle ergometer (mean workload 207 (55) W; lactate concentrations 3.4 (1.2) mmol · l^–1; duration 83.8 (22.2) min, including 5 min at 50% of individual Th_an). Leucocyte subpopulations were measured by flow cytometry and catecholamines by radioimmunological methods. Blood samples were taken before and several times during exercise. Values were corrected for plasma volume changes and analysed using ANOVA for repeated measures. During the first 10 min of exercise, of all cell subpopulations the natural killer cells (CD3^–CD16/CD56+) increased the most (229%). Also CD3^÷CD16/CD56+ (84%), CD8^÷CD45RO^– (69%) cells, eosinophils (36%) and monocytes (62%) increased rapidly during thattime.CD3⁺, CD3⁺HLA-DR⁺, CD4⁺CD45RO⁺, CD4⁺CD45RO^–, CD8⁺CD45RO^÷ and CD19⁺ cells either did not increase or increased only slightly during exercise. Adrenaline and noradrenaline increased nearly linearly by 36% and 77% respectively at 10 min exercise. The increase of natural killer cells and heart rates between rest and 10 min of exercise correlated significantly (r=0.576,P=0.031). We conclude that natural killer cells, cytotoxic, non-MHC-restricted T-cells, monocytes and eosinophils are mobilized rapidly during the first minutes of endurance exercise. Both catecholamines and increased blood flow are likely to contribute this effect.     

Reduced plasma free fatty acid availability during exercise: effect on gene expression

Endurance exercise transiently increases the mRNA of key regulatory proteins involved in skeletal muscle metabolism. During prolonged exercise and subsequent recovery, circulating plasma fatty acid (FA) concentrations are elevated. The present study therefore aimed to determine the sensitivity of key metabolic genes to FA exposure, assessed in vitro using L6 myocytes and secondly, to measure the expression of these same set of genes in vivo, following a single exercise bout when the post-exercise rise in plasma FA is abolished by acipimox. Initial studies using L6 myotubes demonstrated dose responsive sensitivity for both PDK4 and PGC-1α mRNA to acute FA exposure in vitro. Nine active males performed two trials consisting of 2 h exercise, followed by 2 h of recovery. In one trial, plasma FA availability was reduced by the administration of acipimox (LFA), a pharmacological inhibitor of adipose tissue lipolysis, and in the second trial a placebo was provided (CON). During the exercise bout and during recovery, the rise in plasma FA and glycerol was abolished by acipimox treatment. Following exercise the mRNA abundance of PDK4 and PGC-1α were elevated and unaffected by either acipimox or placebo. Further analysis of skeletal muscle gene expression demonstrated that the CPT I gene was suppressed in both trials, whilst UCP-3 gene was only modestly regulated by exercise alone. Acipimox ingestion did not alter the response for both CPT I and UCP-3. Thus, this study demonstrates that the normal increase in circulating concentrations of FA during the later stages of exercise and subsequent recovery is not required to induce skeletal muscle mRNA expression of several proteins involved in regulating substrate metabolism.     

One-legged endurance training: leg blood flow and oxygen extraction during cycling exercise

Aim: As a consequence of enhanced local vascular conductance, perfusion of muscles increases with exercise intensity to suffice the oxygen demand. However, when maximal oxygen uptake (VO₂max) and cardiac output are approached, the increase in conductance is blunted. Endurance training increases muscle metabolic capacity, but to what extent that affects the regulation of muscle vascular conductance during exercise is unknown. Methods: Seven weeks of one‐legged endurance training was carried out by twelve subjects. Pulmonary VO₂ during cycling and one‐legged cycling was tested before and after training, while VO₂ of the trained leg (TL) and control leg (CL) during cycling was determined after training. Results: VO₂max for cycling was unaffected by training, although one‐legged VO₂max became 6.7 (2.3)% (mean ± SE) larger with TL than with CL. Also TL citrate synthase activity was higher [30 (12)%; P < 0.05]. With the two legs working at precisely the same power during cycling at high intensity (n = 8), leg oxygen uptake was 21 (8)% larger for TL than for CL (P < 0.05) with oxygen extraction being 3.5 (1.1)% higher (P < 0.05) and leg blood flow tended to be higher by 16.0 (7.0)% (P = 0.06). Conclusion: That enhanced VO₂max for the trained leg had no implication for cycling VO₂max supports that there is a central limitation to VO₂max during whole‐body exercise. However, the metabolic balance between the legs was changed during high‐intensity exercise as oxygen delivery and oxygen extraction were higher in the trained leg, suggesting that endurance training ameliorates blunting of leg blood flow and oxygen uptake during whole‐body exercise.     

耐力运动对青年与老年小鼠股骨组织微结构变化的影响

目的　应用原子力显微镜（atomic force microscope,AFM）观察中等强度耐力运动后青年与老年小鼠股骨组织微结构的变化,并探讨耐力运动对预防和改善骨质疏松的适宜年龄阶段。 方法　不同月龄清洁级雄性C57小鼠40只,平均分为3月龄青年组和16月龄老年组,每组再平均分为对照组和运动组。青年及老年运动组使用转棒仪跑步运动12周,运动参数15 r/min,25 min/日。对照组正常饲养。实验结束后处死各组小鼠取股骨,石蜡包埋切片后通过AFM观察小鼠股骨皮质骨组织微结构。 结果　青年对照组可见骨陷窝环绕哈弗系统排列规则,有骨小管与其相沟通,钙磷晶体部分呈小柱状,部分呈团状分布;与青年对照组相比青年运动组可见骨陷窝数量及大小变化,表面粗糙度显著降低（P＜0.05）,提示骨组织表面平滑度增加,骨量增加;与青年对照组相比老年对照组可见骨陷窝数量大小变化,钙磷晶体数量减少,表面粗糙度显著增高（P＜0.05）,提示存在骨质疏松;与老年对照组相比老年运动组可见骨陷窝及钙磷晶体数量及大小无明显改变,表面粗糙度改变无统计学意义。 结论　中等强度耐力运动可以改善青年小鼠骨组织微结构,提高骨质量,但对已经发生骨质疏松的老年小鼠骨微结构无明显改善。提示老年骨质疏松的运动预防可能需要从成年开始。     

Extracellular fluid volume and central circulation after long lasting exercise and dehydration in conscious dogs

Summary Two aspects of the recovery period after endurance exercise were investigated: a) the fluid distribution between the intra- and extravascular parts of the extracellular fluid volume (ECFV) induced by exercise dehydration, b) the cardiovascular response pattern [blood pressure (BP), heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), and central venous pressure (CVP)] to the heat load which results from the preceding exercise.Seven conscious dogs performed endurance exercise in a cool environment (16°C) on a horizontal treadmill till 4% of the body weight was lost. It was found that about 70% of the total fluid loss of the body came from intracellular water. During exercise sodium and chloride concentrations rose by 6 mMol and 7 mMol respectively (P<0.005) and remained elevated throughout the early recovery period indicating a fluid loss of about 100–200 ml out of the ECFV. Direct measurements of the ECFV as sulfate space confirmed these values. Since the plasma volume remained unchanged, this fluid loss was carried totally by the interstitial fluid volume.Immediately after exercise body temperature was elevated by 1.5°C and returned towards control within 90 min. Cardiac output was above control level for 2 h after the end of exercise, at first due to an increased HR and thereafter to an elevated stroke volume (SV) (P<0.02). CVP and TPR were below control levels for at least 2 h (P<0.01). A linear correlation was found between CVP and TPR.A close correlation existed between the body temperature and the cardiovascular parameters. It can be concluded that even long after exercise the cardiovascular system has to serve thermoregulatory needs.This study was supported by the Bundesinstitut für Sportwissenschaften Köln andthe Deutsche Forschungsgemeinschaft     

Factors in maximal power production and in exercise endurance relative to maximal power

Summary The relationship of muscle fiber type and mass to maximal power production and the maintenance of power (endurance time to exhaustion) at 36%, 55%, and 73% of maximal power was investigated in 18 untrained but physically active men. Power output was determined at constant pedalling rate (60 rev · min^–1) on a cycle ergometer instrumented with force transducers and interfaced with a computer. Maximal power was determined for each subject as the highest one-revolution average power. Fat-free mass was determined by hydrostatic weighing, fat-free thigh volume by water displacement and skinfold measurement, and percent age and area of type 11 fibers from biopsy specimens taken from the vastus lateralis. Maximal power averaged 771 ± 149 W with a range of 527–1125 W. No significant correlations were found among percentage of type II fibers, relative area of type II fibers, or fat-free thigh volume and maximal power or endurance times to exhaustion at any percentage of maximal power. Weak but significant relationships were found for fat free mass with both maximal power (r=0.57) and endurance time at 73% of maximal power (r= -0.47). These results show maximal power to be more dependent on factors related to body size than muscle-fiber characteristics. The low correlations for so many of the relationships, however, suggest that individuals employ either different combinations of these factors or utilize other strategies for the generation of high power.Human subjects participated in these studies after giving their free and informed voluntary consent. Investigators adhered to AR 70-25 and USAMRDC regulation 70-25 on Use of Volunteers in Research.The views, opinions, and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by other official documentation.     

Comparison of muscle sympathetic nerve activity during exercise in dominant and nondominant forearm

Summary To determine whether or not muscle endurance training alters exercise-induced sympathetic nerve response, we recorded muscle sympathetic nerve activity (MSNA) microneurographically during forearm exercise and compared MSNA between dominant (D) and nondominant (ND) forearms of players of racket sports. Three kinds of forearm exercise were conducted on each side; static (SHG) and dynamic (DHG, at a rate of 1 Hz) handgrip exercise at a loading of 25°10 of maximal voluntary contraction until exhaustion, and 10-min submaximal dynamic handgrip (at a rate of 1 Hz) at an intensity of 0.9 W. Heart rate, ventilation and blood pressure were also monitored at rest and during SHG and DHG exercises. During the last minute of SHG exercise, MSNA burst rate had increased on average by 290 (SEM 46) % in D and 330 (SEM 46) % in ND, while during DHG it increased by 288 (SEM 38) % in D and 344 (SEM 36) % in ND, respectively. There were no significant differences in the MSNA responses between D and ND forearms in either exercise modes. Significant increases in heart rate, ventilation and blood pressure during the last minute of fatiguing SHG and DHG were observed, but there were no significant differences between the two forearms. During submaximal DHG, while MSNA increased significantly above control values in both D and ND, the MSNA response was less in D than that in ND forearm. The results would suggest that exercise-induced MSNA responsiveness is influenced little by muscle endurance training but the intensity of response may be due to the magnitude of metaboreceptor stimulation in the exercising muscle.     

Effect of acute exercise on glucose tolerance following post-exercise feeding

It is well documented that a single bout of endurance exercise (EE) can improve insulin sensitivity, whereas relatively little is known about the acute effects of resistance exercise (RE) in humans. The objective of this study is to investigate the insulin and glucose responses to an oral glucose tolerance test (OGTT) following a high intensity bout of either EE or RE followed by post-exercise carbohydrate-protein hydrolysate ingestion. Eighteen participants were divided into two groups: a group in which nine participants completed 1 h of EE (cycle ergometry at 75% W (max)) and a RE group in which nine participants completed a RE circuit (3 sets of 10 repetitions). Participants ingested 1.5 l of a carbohydrate (200 g)-protein hydrolysate (50 g) beverage within 1 h of exercise completion. An OGTT was performed 6 h post-exercise. On the control day the endurance and resistance groups performed the above protocol without the prior exercise (CEE or CRE). The control and exercise days were counterbalanced. RE reduced plasma glucose AUC (822 +/- 68 vs. 694 +/- 23 mmol l(-1).120 min; CRE vs. RE, respectively; P < 0.05) but EE did not lead to a change (784 +/- 40 vs. 835 +/- 59 mmol l(-1).120 min; CEE vs. EE, respectively). Plasma insulin AUC remained unchanged compared to the control in both the RE and EE groups. The results suggest that the benefit of RE on glucose tolerance following CHO intake remains for 6 h even when a carbohydrate-protein hydrolysate beverage was ingested within 1 h after exercise, while the well documented benefit of EE was not observed.     

The acute effects of exercise and glucose ingestion on circulating angiotensin-converting enzyme in humans

Angiotensin-converting enzyme (ACE) activity has been suggested as a determinant of some exercise phenotypes via some studies that have associated the ACE gene with exercise performance, although several studies provide conflicting evidence regarding the influence of the ACE gene. The relationships between ACE phenotype (ACE activity) and various exercise parameters should also be examined. An early step in this process is to determine whether common environmental stimuli such as exercise and diet have acute effects on ACE activity. In this study, the acute effects of aerobic exercise, resistance exercise and glucose ingestion on circulating ACE activity were examined. On three separate occasions, 20 healthy adult volunteers (9 female and 11 male) performed 20 min of submaximal cycle exercise at 70–80% of maximal heart rate, four sets of ten repetitions of unilateral leg extension resistance exercise at ten-repetition maximum load, or ingested 1 g kg^–1 glucose. Circulating ACE activity was assessed for 1 h after each intervention using a modified fluorometric method. Pre-intervention ACE activity remained remarkably stable across test days (difference 1.8%). Furthermore, there was no significant change in circulating ACE activity following any of the interventions (difference from pre-intervention values 6.8% when unadjusted for plasma volume changes, 4.5% when adjusted for plasma volume changes). These results suggest that acute exercise and glucose ingestion interventions as used here do not affect circulating ACE activity. These findings are an early step in illuminating the relationships between ACE activity and various exercise parameters.     

Exercise-induced muscle damage: effects of light exercise on damaged muscle

Summary The effects of performing light eccentric exercise (LB) during the period of recovery from a heavy eccentric exercise bout (HB) were studied. An experimental and a control group, each consisting of nine college age volunteers (seven women, two men) performed two HB - HB1 and HB2 - 14 days apart, using the elbow flexor and extensor muscles of one arm. The experimental group performed an additional LB on the day following the first HB. HB 1 resulted in muscle soreness, muscle weakness, changes in elbow joint flexibility, and large delayed increases in serum creatine kinase (CK) activity. The HB2 produced smaller changes in all parameters, indicating that adaptation to the effects of eccentric exercise had occurred in the muscle. The LB did not alter muscle soreness, strength or elbow flexibility, but did reduce or delay CK activity increase after HB1. The LB had no apparent effect on adaptation to HB2.     

The effects of a reduced exercise duration taper programme on performance and muscle enzymes of endurance cyclists

Summary The influence of tapering on the metabolic and performance parameters in endurance cyclists was investigated. Cyclists (n = 25) trained 5 days · week^–1, 60 min·day^–1, at 75–85% maximal oxygen consumption (VO_2max) for 8 weeks and were then randomly assigned to a taper group: 4D (4 days;n = 7), 8D (8 days;n = 6), CON (control, 4 days rest;n = 6), NOTAPER (non-taper, continued training;n = 6). Muscle biopsy specimens taken before and after training and tapering were analysed for carnitine palmityltransferase (CPT), citrate synthase, ß-hydroxyacyl CoA dehydrogenase (HOAD), cytochrome oxidase (CYTOX), lactate dehydrogenase, glycogen and protein. Significant increases inVO_2max (6%), a 60-min endurance cycle test (34.5%), oxidative enzymes (77–178%), glycogen (35%) and protein (34%) occurred following training. After the taper, HOAD and CPT decreased 25 % (P<0.05) and 26% respectively, in the CON. Post-taper CYTOX values were different (P<0.05) for 4D and 8D compared with CON. Muscle glycogen levels were increased (P<0.05) after tapering in the 4D, 8D and CON, but decreased in NOTAPER. Similarly, power output at ventilation threshold was significantly increased in the 4D (27.4 W) and 8D (27 W) groups, but decreased (22 W) in the NOTAPER. These findings suggest that tapering elicited a physiological adaptation by altering oxidative enzymes and muscle glycogen levels. Such an adaptation may influence endurance cycling during a laboratory performance test.     

人参二醇组皂甙及游泳训练对大鼠股四头肌α-肌动蛋白mRNA表达的影响

目的 :观察大鼠 7周大负荷游泳训练及人参二醇组皂甙 (PDS)对大鼠股四头肌α -肌动蛋白mRNA表达的影响。方法 :采用Northernblot分析 7周大负荷游泳训练后恢复期大鼠股四头肌α -肌动蛋白mRNA表达水平及PDS对其影响。结果 :α-肌动蛋白mRNA杂交信号的扫描积分光密度值 (A) ,运动·盐水组较安静组略强 ;运动·PDS,扫描积分光密度值 (A)显著强于运动·盐水组和安静组 ,运动·甲睾组与运动·盐水组表达无明显差异。结论 :PDS可提高长期耐力运动大鼠股四头肌α -肌动蛋白mRNA表达 ,从而提高耐力运动能力 ;长期应用外源性雄激素对耐力训练大鼠股四头肌α -肌动蛋白无明显提高 ,这可能与外源睾酮对内源性睾酮分泌的抑制有关。