Effects of taper on endurance cycling capacity and single muscle fiber properties

PURPOSE: It was hypothesized that metabolic adaptations in single muscle cells after a taper period are fiber type (I and II) specific and protocol regimen dependent. METHODS: After 7-wk intensive endurance training, 22 male cyclists (VO2max=4.42 +/- 0.40 L.min(-1)) were randomly assigned to one of three 7-d taper groups: the control group (CON, N=7) continued weekly training, the first experimental group (INT) maintained training intensity but reduced duration (N=7), and the second experimental group (DUR) maintained training duration but reduced exercise intensity (N=8). Each cyclist completed a simulated 40-km time trial (40TT) before and after tapering on a set of wind-loaded rollers using their own bicycle. Muscle biopsies were taken immediately before the 40TT both before and after tapering, and analyzed for mATPase, succinate dehydrogenase (SDH), cyctochrome oxidase (CYTOX), alpha-glycerolphosphate dehydrogenase (alpha-GPD), and beta-hydroxyacyl CoA dehydrogenase (beta-HOAD) in Type I and II fibers, separately, using quantitative histochemistry. RESULTS: The results showed significant (P< or =0.05) increases in SDH (Type I) and mATPase, CYTOX, beta-HOAD, and SDH (Type II fibers) in the INT group, and significant increases in CYTOX (Type I) and beta-HOAD (Type I and II fibers) in the DUR group. Regression analysis showed that the change (posttaper minus pretaper) in simulated 40-km endurance time was correlated with the change in CYTOX and SDH activity for all groups combined (r2=0.62-0.72). CONCLUSION: These results demonstrated that the metabolic properties of different fiber types are altered with tapering, that the type of taper protocol used influences their physiological adaptation, and that improvements in simulated 40-km endurance time were related to changes in metabolic properties of the muscle at the single fiber level.     

Effect of sodium bicarbonate on muscle metabolism during intense endurance cycling

INTRODUCTION: Sodium bicarbonate (NaHCO3) ingestion has been shown to increase both muscle glycogenolysis and glycolysis during brief submaximal exercise. These changes may be detrimental to performance during more prolonged, exhaustive exercise. This study examined the effect of NaHCO3 ingestion on muscle metabolism and performance during intense endurance exercise of approximately 60 min in seven endurance-trained men. METHODS: Subjects ingested 0.3 g.kg-1 body mass of either NaHCO3 or CaCO3 (CON) 2 h before performing 30 min of cycling exercise at 77 +/- 1% .VO(2peak) followed by completion of 469 +/- 21 kJ as quickly as possible (approximately 30 min, approximately 80% .VO(2peak)). RESULTS: Immediately before, and throughout exercise, arterialized-venous plasma HCO3- concentrations were higher (P < 0.05) whereas plasma and muscle H+ concentrations were lower (P < 0.05) in NaHCO3 compared with CON. Blood lactate concentrations were higher (P < 0.05) during exercise in NaHCO3, but there was no difference between trials in muscle glycogen utilization or muscle lactate content during exercise. Reductions in PCr and ATP and increases in muscle Cr during exercise were also unaffected by NaHCO3 ingestion. Accordingly, exercise performance time was not different between treatments. CONCLUSION: NaHCO3 ingestion resulted in a small muscle alkalosis but had no effect on muscle metabolism or intense endurance exercise performance in well-trained men.     

Reliability of a high-intensity endurance cycling test

This study assessed the reproducibility of performance and selected metabolic variables during a variable high-intensity endurance cycling test. 8 trained male cyclists (age: 35.9 ± 7.7 years, maximal oxygen uptake: 54.3 ± 3.9 mL·kg?-?1·min?-?1) completed 4 high-intensity cycling tests, performed in consecutive weeks. The protocol comprised: 20 min of progressive incremental exercise, where the power output was increased by 5% maximal workload (Wmax) every 5 min from 70% Wmax to 85% Wmax; ten 90 s bouts at 90% Wmax, separated by 180 s at 55% Wmax; 90% Wmax until volitional exhaustion. Blood samples were drawn and heart rate was monitored throughout the protocol. There was no significant order effect between trials for time to exhaustion (mean: 4?113.0 ± 60.8 s) or total distance covered (mean: 4?6126.2 ± 1?968.7 m). Total time to exhaustion and total distance covered showed very high reliability with a mean coefficient of variation (CV) of 1.6% (95% Confidence Intervals (CI) 0.0 ± 124.3 s) and CV of 2.2% (95% CI 0.0 ± 1904.9 m), respectively. Variability in plasma glucose concentrations across the time points was very small (CV 0.46-4.3%, mean 95% CI 0.0 ± 0.33 to 0.0 ± 0.94 mmol·L?-?1). Plasma lactate concentrations showed no test order effect. The reliability of performance and metabolic variables makes this protocol a valid test to evaluate nutritional interventions in endurance cycling.     

Effect of exercise-induced muscle damage on endurance running performance in humans

Exercise-induced muscle damage (EIMD) is known to decrease muscle strength and power but its effect on endurance performance is unclear. Thirty moderately trained adult runners (24 men and six women) were randomly assigned to EIMD or control. The EIMD group jumped 100 times from a 35 cm bench, while controls did not perform any muscle-damaging exercise. Before and 48 h after treatment, subjects were tested on markers of EIMD, steady-state cardiorespiratory, metabolic and perceptual responses during a constant speed submaximal run; distance ran in 30 min on a treadmill. There were significant changes in muscle soreness, creatine kinase, and knee extensors strength (P<0.01). This EIMD significantly reduced self-paced time trial performance by 4% (P<0.01) because subjects reduced running speed (P=0.02), with no change in perceived exertion (P=0.31). No significant alterations in running economy and other physiological responses to submaximal running were found. However, there was a trend (P=0.08) for increased perceived exertion, which was correlated with decreased time trial performance (P<0.01). In conclusion, EIMD has a significant impact on endurance running performance in humans, and this effect seems to be mediated by alterations in the sense of effort.     

Effects of respiratory muscle endurance training on ventilatory and endurance performance of moderately trained cyclists

This study examined the effects of respiratory muscle endurance training (RMET) on ventilatory and endurance performance among moderately trained, male cyclists. Nine subjects initially completed two cycling VO2 max tests, two endurance cycling tests for time at 95% VO2 max, a 15-s MVV test, and an endurance breathing test for time at 100% MVV. Four subjects then underwent 3 weeks of strenuous RMET while five served as controls. Mean posttest 15-s MVV and endurance breathing time were significantly higher in the RMET group (243 +/- 14 l X min-1 and 804 +/- 94 s) than in the control group (205 +/- 6 l X min-1 and 48 +/- 8 s). No significant group differences in VO2 max or endurance cycling time at 95% VO2 max were observed following RMET. Results of this exploratory study indicated that RMET improved ventilatory power and endurance, but did not alter VO2 max or endurance cycling performance among moderately trained, male cyclists.     

Postexercise muscle glycogen recovery enhanced with a carbohydrate-protein supplement

PURPOSE: This study assessed whether liquid carbohydrate-protein (C+P) supplements, ingested early during recovery, enhance muscle glycogen resynthesis versus isoenergetic liquid carbohydrate (CHO) supplements, given early or an isoenergetic solid meal given later during recovery (PLB). METHODS: Two hours after breakfast (7.0 kcal.kg; 0.3 g.kg P, 1.2 g.kg C, 0.1 g.kg F), six male cyclists performed a 60-min time trial (AMex). Pre- and postexercise, vastus lateralis glycogen concentrations were determined using nMRS. Immediately, 1 h, and 2 h postexercise, participants ingested C+P (4.8 kcal.kg; 0.8 g.kg C, 0.4 g.kg P), CHO (4.8 kcal.kg; 1.2 g.kg C), or PLB (no energy). Four hours postexercise, a solid meal was ingested. At that time, C+P and CHO received a meal identical to breakfast, whereas PLB received 21 kcal.kg (1 g.kg P, 3.6 g.kg C, 0.3 g.kg F); energy intake during 6 h of recovery was identical among treatments. After 6 h of recovery, measurement and cycling protocols (PMex) were repeated. RESULTS: Absolute muscle glycogen utilization was 18% greater (P 相似文献   

The effects of cryotherapy on muscle damage in rats subjected to endurance training

Sixty 60-day-old Sprague-Dawley male rats were subjected to exhaustive and non-exhaustive exercise treatment over a period of 3, 5 and 7 weeks. Moderate exercise consisted of running on the treadmill at 10% grade at 10 m/min for 20 min for 5 days per week, while exhaustive running consisted of running at 10% grade at 15 m/min with an increase of 5 m/min every 5 min for 5 days per week. Half of the exercised rats were subjected to immersion in 4°C water for 5 min after each exercise bout. Histological analyses of the gastrocnemius showed that ultrastructural damage of myofibrils occurred after 5 weeks of exhaustive running and 7 weeks of moderate running. With post-exercise immersion in 4°C water for 5 min, the occurrence of ultrastructural damage advanced by 2 weeks in both treatments. It was concluded that the application of cryotherapy to the exercise groups was deleterious. Muscle damage occurred earlier in the treatment group and the degree of damage was also more serious over the same time period. This study supports the recommendation that the use of cryotherapy to reduce pain and haematoma formation should be coupled with rest for at least 48 hours.     

Effects of iron deficiency on endurance and muscle enzyme activity in man

The purpose of the present study was to evaluate the effects of iron deficiency on enzyme activities and endurance. Iron deficiency was induced in 9 healthy male subjects by repeated venesections. After a period of 9 wk (range, 8-11 wk) when the subjects had become iron deficient as defined by laboratory parameters, blood was retransfused to reestablish the control hemoglobin concentration. In this state it was possible to evaluate the effect of iron deficiency isolated from anemia. In samples secured by muscle biopsies, glycolytic, oxidative, and iron depending enzymes were analyzed in the control (C) and anemic (A) states and after retransfusion (R). There were no significant changes in the maximal activities of any of the enzymes studied. The capillary/fiber ratio remained unchanged between C (1.92) and R (1.94). Times to exhaustion on treadmill tests were 49 min, 11 s in C, 26 min, 33 s in A, and 52 min, 3 s in R. Vo2max was 4.55 1 X min-1 in C, 3.74 1 X min-1 in A, and 4.45 1 X min-1 in R. An artificially induced iron deficiency defined by conventional laboratory parameters did not affect endurance when transfusion of red blood cells was performed in order to exclude the influence of a low hemoglobin concentration. A 4-wk period of severely depleted or absent tissue iron stores did not affect the maximal activities of various enzymes in human skeletal muscle.     

Effects of short-term endurance training on muscle deoxygenation trends using NIRS

PURPOSE: This study examined changes in cardiorespiratory responses and muscle deoxygenation trends to test the hypothesis that both central and peripheral adaptations would contribute to the improvements in VO(2max) and simulated cycling performance after short-term high-intensity training. METHODS: Eight male cyclists performed an incremental cycle ergometer test to voluntary exhaustion, and a simulated 20-km time trial (20TT) on wind-loaded rollers before and after training (60 min x 5 d x wk(-1) x 3 wk at 85-90% VO(2max). Near-infrared spectroscopy (NIRS) was used to evaluate the trend in vastus medialis hemoglobin/myoglobin deoxygenation (Hb/Mb-O(2) during both tests pre- and post-training. RESULTS: Training induced significant increases (P 0.05) in the VO(2) (4.02 +/- 0.52 to 4.04 +/- 0.51), heart rate (176 +/- 9 to 173 +/- 8 beats x min ) or O pulse (22.4 +/- 3.2 to 23.5 +/- 2.8 mL O(2) x beat(-1)). However, mean muscle deoxygenation during the 20TT was significantly lower after training (-550 +/- 292 to -707 +/- 227 mV, P 相似文献   

Effect of pre-exercise carbohydrate feedings on endurance cycling performance

Six men were studied to compare the effects of pre-exercise carbohydrate feedings on endurance performance and muscle glycogen utilization during prolonged exercise. Trials consisted of a cycling ride to exhaustion at 75% maximal oxygen uptake preceded by the ingestion of either 75 g of glucose in 350 ml of water (GLU), 75 g of fructose in 350 ml of water (FRU), or 350 ml of an artificially sweetened and flavored placebo (CON). No differences were observed between trials for oxygen uptake, respiratory exchange ratio, heart rate, or exercise time to exhaustion (CON = 92.7 +/- 5.2 min, FRU = 90.6 +/- 12.4, and GLU = 92.8 +/- 11.3, mean +/- SE). Blood glucose was elevated as a result of the GLU feeding, but fell rapidly with the onset of exercise, reaching a low of 4.02 +/- 0.34 mmol X l-1 at 15 min of exercise. Serum insulin also increased following the GLU feeding but had returned to pre-drink levels by 30 min of exercise. No differences in blood glucose and insulin were observed between FRU and CON. Muscle glycogen utilization during the first 30 min of exercise (CON = 46.3 +/- 8.2 mmol X kg-1 wet weight, FRU = 56.3 +/- 3.0 mmol X kg-1 wet weight, GLU = 50.0 +/- 4.9 mmol X kg-1 wet weight) and total glycogen use (CON = 93.4 +/- 11.1, FRU = 118.8 +/- 10.9, and GLU = 99.5 +/- 4.3) were similar in the three trials.(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle damage and endurance events

Intensive training for and competition in endurance events like the marathon are accompanied by injury to fibres in the active skeletal muscles. Evidence for the injury comes from the increases in intramuscular enzymes and myoglobin found in the blood following the exercise, from the subjective sensation of soreness in the muscles in the post-exercise period, and from direct histological examination of samples of the damaged muscles. Histological studies demonstrate that some muscle fibres undergo degenerative changes following the exercise; the necrosis is accomplished by macrophages and other phagocytic cells that invade the injured cells and the adjacent interstitium. Following the degeneration the fibers appear to be regenerated so that there is not a net loss of fibres. Precisely what initiates the cellular damage is not known, but hypotheses suggested include, 'metabolic overload' and 'mechanical strain'. Eccentric contractions are known to cause the greater amount of damage in muscles, which suggests that high local tensions in fibres may be more important than metabolic considerations in the aetiology of the injury. Training reduces the magnitude of the damage that occurs in response to a given exercise task, although competitors in endurance events may demonstrate chronic muscle injury because of increasing training intensities. Other than training, there is no compelling evidence that any drug treatment or preventative measures will lessen this form of injury.     

Effects of creatine supplementation on muscle power, endurance, and sprint performance

PURPOSE: To determine the effects of creatine (Cr) supplementation (20 g x d(-1) during 5 d) on maximal strength, muscle power production during repetitive high-power-output exercise bouts (MRPB), repeated running sprints, and endurance in handball players. METHODS: Nineteen trained male handball players were randomly assigned in a double-blind fashion to either creatine (N = 9) or placebo (N = 10) group. Before and after supplementation, subjects performed one-repetition maximum half-squat (1RM(HS) and bench press (1RM(BP)), 2 sets of MRPB consisting of one set of 10 continuous repetitions (R10) followed by 1 set until exhaustion (R(max)), with exactly 2-min rest periods between each set, during bench-press and half-squat protocols with a resistance equal to 60 and 70% of the subjects' 1RM, respectively. In addition, a countermovement jumping test (CMJ) interspersed before and after the MRPB half-squat exercise bouts and a repeated sprint running test and a maximal multistage discontinuous incremental running test (MDRT) were performed. RESULTS: Cr supplementation significantly increased body mass (from 79.4 +/- 8 to 80 +/- 8 kg; P < 0.05), number of repetitions performed to fatigue, and total average power output values in the R(max) set of MRPB during bench press (21% and 17%, respectively) and half-squat (33% and 20%, respectively), the 1RM(HS) (11%), as well as the CMJ values after the MRPB half-squat (5%), and the average running times during the first 5 m of the six repeated 15-m sprints (3%). No changes were observed in the strength, running velocity, or body mass measures in the placebo group during the experimental period. CONCLUSION: Short-term Cr supplementation leads to significant improvements in lower-body maximal strength, maximal repetitive upper- and lower-body high-power exercise bouts, and total repetitions performed to fatigue in the R(max) set of MRPB, as well as enhanced repeated sprint performance and attenuated decline in jumping ability after MRPB in highly trained handball players. Cr supplementation did not result in any improvement in upper-body maximal strength and in endurance running performance.     

Moderate intensity cycling is better than running on recovery of eccentric exercise-induced muscle damage

ObjectiveTo compare the effects of moderate intensity running and cycling on markers of exercise-induced muscle damage in men.Study designRandomized controlled trial.SettingLaboratory.ParticipantsThirty volunteers were randomized in three groups [running (RG; n = 10), cycling (CG; n = 10) and control (CON; n = 10)] and were evaluated at baseline, post 24, 48 and 72 h of knee extensors’ muscle damage protocol. CON performed passive recovery, while RG and CG performed active recovery immediately after the protocol, as well as 24 h and 48 h afterwards.Main outcomes(i) maximal voluntary isometric contraction (MVIC); (ii) delayed-onset muscle soreness (DOMS); (iii) plasma creatine kinase (CK) and lactate dehydrogenase (LDH) levels.ResultsNo group-by-time interaction was found in any outcome evaluated (p > 0.05). All groups presented decreases in MVIC and increases in DOMS (p < 0.001), without differences in CK and LDH. Compared with CON, exercise groups presented likely beneficial effects for LDH, while only CG had a likely beneficial effect for DOMS. Lastly, CG presented likely/very likely beneficial effects for MVIC and DOMS compared to RG.ConclusionAlthough the null hypothesis analysis did not find differences, the magnitude-based inference analysis suggested that moderate intensity cycling have likely beneficial effects on knee extensor muscle recovery after eccentric exercise protocol.     

Effects of submaximal cycling and long-term endurance training on neutrophil phagocytic activity in middle aged men.

OBJECTIVE: To investigate the effects of long term (> 10 years) endurance training and submaximal exercise on the phagocytic activity of circulating neutrophil granulocytes. METHODS: The ability of stimulated blood neutrophils isolated from well trained cyclists [n = 8; VO2max 61.0(SD 8.8) ml.kg-1.min-1; age 38(4) years] and age matched sedentary controls [n = 8; VO2max 37.4 (6.6) ml.kg-1.min-1] to ingest nitroblue tetrazolium was assessed at rest and following a standardised submaximal bout of exercise on a cycle ergometer. RESULTS: Trained subjects had a lower resting blood neutrophil count (P < 0.01). Acute exercise caused a rise (P < 0.01) in the blood neutrophil count irrespective of training status, but the magnitude of the rise was smaller in the trained subjects (P < 0.05). The circulating neutrophil phagocytic capacity was approximately 70% lower in trained individuals at rest compared with the control subjects (P < 0.01). Acute submaximal exercise increased this variable in both groups, but phagocytic capacity remained substantially lower in the trained subjects compared with the controls (P < 0.05) despite the observation that a higher proportion of the circulating neutrophils were stimulated to undergo phagocytosis in the trained subjects [57(14)% v 32(7)%; P < 0.01). CONCLUSIONS: Although neutrophil phagocytic activity is only one variable that contributes to immunological status, prolonged periods of endurance training may lead to increased susceptibility to opportunistic infections by diminishing this activity at rest.     

Effects of muscle damage induced by eccentric exercise on muscle fatigue

PURPOSE: The present study was designed to determine to what extent muscle damage induced by repetitive eccentric exercise with maximal voluntary effort (ECC) affects the time course of central and peripheral fatigue during sustained maximal voluntary contraction (MVC). METHODS: Ten healthy male volunteers were asked to perform brief (control MVC) and sustained MVC (fatigue test of 60 s in duration) with elbow flexion before and 2 and 4 d after ECC. Transcranial magnetic stimulation (TMS) was applied to the motor cortex to determine changes in voluntary activation (VA), the size of the motor evoked potential (MEP), and length of electromyographic (EMG) silencing. The ratio of the root mean square value for the surface EMG of the biceps brachii and exerted force within 50 ms before TMS was also calculated (RMS/F). RESULTS: In two subjects, no significant changes in MVC and muscle soreness were seen after ECC so that their data was excluded from further analysis. Control MVC and muscle soreness was significantly decreased and increased, respectively, 2 and 4 d after ECC compared with that before ECC (P < 0.001). During the fatigue test, VA, which was determined by a phasic increase in the twitch force after TMS, significantly decreased 2 and 4 d after ECC compared with that beforehand (P < 0.01). In addition, the RMS/F was significantly increased 2 and 4 d after ECC (P < 0.001). Although the degree of facilitation of the MEP was significantly increased (P < 0.05), the length of EMG silencing was less affected by ECC. CONCLUSIONS: Muscle damage and/or muscle soreness induced by repetitive eccentric exercise with maximal effort may be a strong modifier of central and peripheral fatigue during sustained MVC.     

Effects of a 7-day eccentric training period on muscle damage and inflammation

PURPOSE: This study examined the effects of a 7-d repeated maximal isokinetic eccentric training period on the indicators of muscle damage and inflammatory response. METHODS: Twenty-two college-age males were randomly assigned to eccentric training (ET) (N = 12) and control groups (CON) (N = 10). The initial exercise was 30 repetitions of maximal voluntary isokinetic eccentric contraction (ECC1) on nondominant elbow flexors with Cybex 6000 at 60 degrees.s-1 angular velocity. The ET group performed the same exercise for the following 6 consecutive days (referred to as ECC2 to ECC7) after ECC1. Upper arm circumference (CIR), range of motion (ROM), and maximal isometric force (MIF) were measured before, immediately after, and every 24 h for 7 consecutive days after ECC1. Plasma creatine kinase (CK), lactate dehydrogenase (LDH), glutamic oxaloacetate transaminase (GOT), leukocyte counts, and serum interleukin-1beta and -6 (IL-1beta, IL-6) levels were assessed before; at 2 h; and at 1, 3, 4, 6, and 7 d after ECC1. Muscle soreness was measured before and for 7 consecutive days after ECC1. RESULTS: The ECC1 produced significant changes in most of the measures for both groups (P < 0.05), with the exception of leukocyte counts (P > 0.05). No indicators of increased damage (P > 0.05) were found from ECC2 to ECC7 for the ET group. CONCLUSION: Continuous intensive isokinetic eccentric training performed with damaged muscles did not exacerbate muscle damage and inflammation after ECC1. In addition, a muscular "adaptation effect" may occur as early as 24 h after ECC1, as shown by the ET group's performance for 6 consecutive days after ECC1.     

Effects of ibuprofen on exercise-induced muscle soreness and indices of muscle damage.

Thirty-two volunteers participated in a two-period crossover study in which ibuprofen was tested against an identical placebo for its effectiveness in reducing muscle soreness and damage after two bouts of downhill running. Subjective soreness, quadriceps isometric strength and isometric endurance time at 50 percent of maximum strength, serum activities of creatine kinase, lactate dehydrogenase and aspartate transaminase and serum levels of creatinine and urea were recorded at intervals up to 72 hours after exercise. Each downhill run produced muscle soreness, and a decline in muscle strength and 50 percent endurance time, although these parameters were unaffected by ibuprofen treatment. All serum parameters measured increased after both runs, but for the three enzymes this increase was smaller after the second run. Serum creatine kinase and urea levels were higher in the ibuprofen group after both runs. These results indicate that ibuprofen is not an appropriate treatment for delayed onset muscle soreness and damage.