Effects of 4 h preexercise carbohydrate feedings on cycling performance

This study determined the effects of consuming three different amounts of liquid carbohydrate 4 h before exercise on the metabolic responses during exercise and on exercise performance. Four hours before exercise subjects consumed either 45 (L) or 156 (M) g of carbohydrate in isocaloric feedings and either 0 (P) or 312 (H) g of carbohydrate. Interval cycling was undertaken for 95 min, followed by a performance trial. Blood glucose had reached basal 1 h after all feedings; blood insulin had reached basal 3 h after ingestion of P, L, and M but was still 84% higher for H at the start of exercise. During exercise insulin averaged 48% higher for H than P. Blood glucose decreased 16% during exercise for P, L, and M, whereas for H there was a transient drop the first 15 min of exercise, after which glucose increased and remained constant throughout exercise. More carbohydrate oxidation occurred during exercise for H vs P, whereas results were similar for L and M. Ingestion of H improved performance by 15% as compared with P, whereas performance was similar for L and M. These results indicate that, despite elevated insulin at the start of and during exercise, consumption of 312 g of carbohydrate 4 h before moderately intense prolonged exercise can improve performance, perhaps via an enhancement of carbohydrate oxidation.     

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)     

Effects of preexercise carbohydrate ingestion on mountain bike performance

PURPOSE: This study examined the performance and metabolic effects of consuming 1.0 (LC) and 3.0 (HC) grams of carbohydrate (CHO) per kilogram body mass (BM), 3 h before a 93-min simulated mountain bike race. METHODS: After two familiarization trials, eight male subjects undertook two CHO trials in a double-blind counterbalanced fashion on a cycle ergometer. The HC meal was supplemented with maltodextrin while maintaining the same glycemic index and apparent volume of food as the LC meal. Stochastic cycling was undertaken for 93 min (4 x 22.50-min laps) with performance measured as the total work performed in 6 x 30-s periods each lap during the test. RESULTS: Performance in lap 1 was better with LC (P < 0.03) whereas performance in lap 4 was better with HC (P < 0.02). Overall performance was 3% greater in HC compared with LC (NS, P = 0.13). Serum glucose was significantly lower (P < 0.04) in HC immediately before the mountain bike test (180 min postprandial) and at 10 min into the test (P < 0.01). Gastrointestinal comfort decreased similarly for both trials over time (P < 0.05). CONCLUSION: These data suggest that ingestion of 3.0 g x kg(-1) BM of CHO 3 h before a 93-min mountain bike simulated race does not produce a statistically significant improvement in overall performance compared with 1.0 g x kg(-1) BM. However, in real terms, a 3% performance improvement may benefit athletes in a race situation. Differences in performance during the first and last laps indicate a variation in pacing strategies that may have resulted from differing blood glucose levels between trials.     

Effect of frequency of carbohydrate feedings on recovery and subsequent endurance run

PURPOSE: This study examined the effect of feeding pattern of a high glycemic index (GI) meal during a short-term recovery on subsequent endurance capacity. METHODS: Eight men ran at 70% .VO2max on a level treadmill for 90 min (T1) on two occasions, followed by 4-h recovery (R) and a further exhaustive run at the same speed (T2). During the R, subjects consumed a prescribed meal with a GI of 77 in either a "gorging" (GOR) or "nibbling" (NIB) intake pattern, providing 1.5 g carbohydrate (CHO) per kilogram body mass. In the GOR trial, the foods were consumed in a single bolus, 20 min after the end of T1. In the NIB trial, the same quantity of food was ingested in three equal portions; the first consumed 20 min after the end of T1 and the remainder at hourly intervals thereafter. RESULTS: The run time during T2 was similar between trials (GOR vs NIB: 68.1 +/- 8.2 vs 66.8 +/- 8.7 min, P > 0.05). However, CHO utilization was lower and fat utilization higher during T2 in the GOR trial compared with the NIB trial (GOR vs NIB: CHO: 94.4 +/- 11.4 vs 117.6 +/- 10.6 g, P < 0.05; FAT: 55.9 +/- 8.0 vs 44 +/- 8.6 g, P < 0.01). CONCLUSIONS: These results suggest that serial consumption of a high GI meal during a 4-h recovery increased the reliance on CHO oxidation for energy provision during a subsequent run when compared with a single feeding. However, there was no difference in the duration of the exhaustive run after the recovery between the GOR and NIB trials.     

Effects of acute cold exposure on submaximal endurance performance

The purposes of this study were to assess VO2max and submaximal endurance time to exhaustion (ET) during acute cold-air exposure. Eight male subjects (means age = 19.9 yr) were alternately exposed in groups of four to chamber temperatures of +20 degrees C and -20 degrees C for 30 h each. A week was allowed between exposures. Maximum oxygen uptake was measured using a mechanically-braked cycle ergometer, and ET was determined on the same ergometer using a 17-min/3-min exercise/rest schedule until the subject was unable to maintain pedal rate. Maximum oxygen uptake was not significantly different between conditions: 3.43 +/- 0.09 l X min-1 at +20 degrees C and 3.35 +/- 0.10 l X min-1 at -20 degrees C. During endurance exercise, intensities equaled 77.1 +/- 1.4% and 78.9 +/- 2.0% of VO2max at +20 degrees C and -20 degrees C, respectively. Heart rate and VO2 values obtained between 8 and 10 min of the endurance run were not significantly different (156 +/- 2 bpm and 2.63 +/- 0.08 l X min-1 at +20 degrees C and 158 +/- 3 bpm and 2.65 +/- 0.11 l X min-1 at -20 degrees C). Endurance time to exhaustion however, decreased 38% (P less than 0.05) from 111.9 +/- 22.8 min at +20 degrees C to 66.9 +/- 13.6 min at -20 degrees C. The data support the contention that aerobic capacity is not altered by cold exposure but suggest a marked decrease in submaximal endurance performance.     

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.     

Effects of submaximal and supramaximal interval training on determinants of endurance performance in endurance athletes

We compared the effects of submaximal and supramaximal cycling interval training on determinants of exercise performance in moderately endurance‐trained men. Maximal oxygen consumption (VO_2max), peak power output (P_peak), and peak and mean anaerobic power were measured before and after 6 weeks (3 sessions/week) of submaximal (85% maximal aerobic power [MP], HIIT₈₅, n = 8) or supramaximal (115% MP, HIIT₁₁₅, n = 9) interval training to exhaustion in moderately endurance‐trained men. High‐intensity training volume was 47% lower in HIIT₁₁₅ vs HIIT₈₅ (304 ± 77 vs 571 ± 200 min; P < 0.01). Exercise training was generally associated with increased VO_2max (HIIT₈₅: +3.3 ± 3.1 mL/kg/min; HIIT₁₁₅: +3.3 ± 3.6 ml/kg/min; Time effect P = 0.002; Group effect: P = 0.95), P_peak (HIIT₈₅: +18 ± 9 W; HIIT₁₁₅: +16 ± 27 W; Time effect P = 0.045; Group effect: P = 0.49), and mean anaerobic power (HIIT₈₅: +0.42 ± 0.69 W/kg; HIIT₁₁₅: +0.55 ± 0.65 W/kg; Time effect P = 0.01; Group effect: P = 0.18). Six weeks of submaximal and supramaximal interval training performed to exhaustion seems to equally improve VO_2max and anaerobic power in endurance‐trained men, despite half the accumulated time spent at the target intensity.     

Effects of strength training on lactate threshold and endurance performance

To determine the effects of 12 wk of strength training on lactate threshold (LT) and endurance performance, 18 healthy untrained males between 25 and 34 yr of age were randomly assigned to either strength training (N = 10) or control (N = 8) groups. Despite no changes in treadmill VO2max or cycle peak VO2, a 33 +/- 5% increase (P less than 0.001) in cycling time to exhaustion at 75% of peak VO2 was observed following training. No significant changes in cycling time were observed in the control group. There were significant reductions in plasma lactate concentration at all relative exercise intensities ranging between 55 and 75% of peak VO2 training. The improved endurance performance was associated with a 12% increase in LT (r = 0.78, P less than 0.001). The strength training program resulted in significant improvements (P less than 0.001) of 31 +/- 5% and 35 +/- 7% in isokinetic peak torque values for leg extension and flexion, respectively, at a velocity of 30 degrees.s-1. There were also significant increases in 1-RM values of 30 +/- 4% (P less than 0.001) for leg extension, 52 +/- 6% (P less than 0.001) for leg flexion, and 20 +/- 4% (P less than 0.001) for the bench press. These findings indicate that strength training improves cycle endurance performance independently of changes in VO2max. This improved performance appears to be related to increases in LT and leg strength.     

Effects of warm-up and precooling on endurance performance in the heat

Objective

To examine the effects of different thermoregulatory preparation procedures (warm‐up (WU), precooling (PC), control (C)) on endurance performance in the heat.

Methods

20 male subjects completed three treadmill runs to exhaustion (5 days apart). In each session, all subjects performed an incremental running test after WU (20 min at 70% maximum heart rate (HR)), after PC (wearing a cooling vest (0°C–5°C) for 20 min at rest) or without particular preparation (C). After a 5‐min break, the exercise protocol commenced at a workload of 9 km/h and was increased by 1 km/h every 5 min until the point of volitional fatigue. Running performance, HR, blood lactate concentration, tympanic temperature and skin temperature were measured in each trial.

Results

In the PC condition, the running performance (32.5 (5.1) min; mean (SD)) was significantly (p<0.05) higher than in WU (26.9 (4.6) min) and in C conditions (30.3 (4.3) min). During the first 30 min of testing, HR, tympanic temperature and skin temperature were significantly (p<0.05) lower after PC than after WU. There were no significant differences in lactate concentration; however, there was a trend to lower values after WU.

Conclusions

The use of an ice‐cooling vest for 20 min before exercising improved running performance, whereas the 20 min WU procedure had a distinctly detrimental effect. Cooling procedures including additional parts of the body such as the head and the neck might further enhance the effectiveness of PC measures.It is well established that high ambient temperatures have a detrimental effect on endurance performance.^1,2 Compared with temperate conditions (20°C), an ambient temperature of 30°C brought about a decrease of 2.3% in the performance of a 10 min exercise bout.² The question, however, as to what strategies could be applied to compensate for this heat‐induced decrease in performance has been left largely unanswered. Sufficient fluid intake is a possible answer, and application of cold provides another one.^3,4 In the context of endurance in heat a further question arises—namely, whether warm‐up (WU; including the concomitant increase in core temperature (CT)) is a sensible measure, taking into consideration the additional thermal stress.⁵For this reason, it is useful to compare the effects of WU and precooling (PC) to optimise endurance performance. The practical relevance of the objective lies in the fact that competitions—for example, the Olympic Games 2008 in Beijing—will be held in high ambient temperatures, exceeding 30°C at all times of day, and there is no coherent (systematically and experimentally tested) position in the literature on the implications of WU^6,7 for endurance performance in such temperatures. Although PC has been discussed more widely during the last two decades,^8,9,10 it has not yet been studied in comparison with active WU.     

Effects of Hemopure on maximal oxygen uptake and endurance performance in healthy humans

Haemoglobin-based oxygen carriers (HBOCs) such as Hemopure are touted as a tenable substitute for red blood cells and therefore potential doping agents, although the mechanisms of oxygen transport of HBOCs are incompletely understood. We investigated whether infusion of Hemopure increased maximal oxygen uptake (V.O 2max) and endurance performance in healthy subjects. Twelve male subjects performed two 4-minute submaximal exercise bouts equivalent to 60 % and 75 % of V.O (2max) on a cycle ergometer, followed by a ramped incremental protocol to elicit V.O (2max). A crossover design tested the effect of infusing either 30 g (6 subjects) or 45 g (6 subjects) of Hemopure versus a placebo. Under our study conditions, Hemopure did not increase V.O (2max) nor endurance performance. However, the infusion of Hemopure caused a decrease in heart rate of approximately 10 bpm (p=0.009) and an average increase in mean ( approximately 7 mmHg) and diastolic blood pressure ( approximately 8 mmHg) (p=0.046) at submaximal and maximal exercise intensities. Infusion of Hemopure did not bestow the same physiological advantages generally associated with infusion of red blood cells. It is conceivable that under exercise conditions, the hypertensive effects of Hemopure counter the performance-enhancing effect of improved blood oxygen carrying capacity.     

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.     

Effect of carbohydrate feedings on muscle glycogen utilization and exercise performance

Ten men were studied during 4 h of cycling to determine the effect of solid carbohydrate (CHO) feedings on muscle glycogen utilization and exercise performance. In the experimental trial (E) the subjects ingested 43 g of sucrose in solid form along with 400 ml of water at 0, 1, 2 and 3 h of exercise. During the control trial (C) they received 400 ml of an artificially sweetened drink without solid CHO. No differences in VO2, heart rate, or total energy expenditure were observed between trials; however, respiratory exchange ratios were significantly (P less than 0.05) higher during E. Blood glucose was significantly (P less than 0.05) elevated 20 min post-feeding in E; however, by 50 min no differences were observed between trials until 230 min (E = 4.5 +/- 0.2 mmol X l-1 vs C = 3.9 +/- 0.2, means +/- SE; P less than 0.05). Muscle glycogen utilization was significantly (P less than 0.05) lower during E (100.7 +/- 10.2 mmol X kg-1 w.w.) than C (126.2 +/- 5.5). During a sprint (100% VO2max) ride to exhaustion at the end of each trial, subjects performed 45% longer when fed CHO (E = 126.8 +/- 24.7 s vs C = 87.2 +/- 17.5; P less than 0.05). It was concluded that repeated solid CHO feedings maintain blood glucose levels, reduce muscle glycogen depletion during prolonged exercise, and enhance sprint performance at the end of such activity.     

Concurrent brain endurance training improves endurance exercise performance

ObjectivesMental fatigue impairs endurance exercise. Brain endurance training (BET) – engaging in cognitively fatiguing tasks during exercise - can develop resilience to mental fatigue and improve physical performance over physical training alone. The mechanism for this effect is unknown.This experiment examines if BET enhances performance over physical training and investigates potential underlying physiological mechanisms.DesignA mixed design randomised control trial.MethodsPre- and post-testing: 36 participants completed dynamic rhythmic muscular endurance handgrip tasks requiring generation of as much force as possible once a second for 300 s, performed under 3 counterbalanced conditions: following 600 s of a 2-back memory/attention task (subsequent); while performing a 2-back task (concurrent); and on its own (solo). Cardiac activity, electromyographic forearm activity, pre-frontal cerebral haemodynamics (near infrared spectroscopy), and force were recorded. Training: Participants (randomised to a Control or BET group) completed 24 (6 weeks) submaximal hand contractions sessions. The BET group also completed concurrent cognitive tasks (2-back, Stroop). Measures of motivation, physical and mental exertion and mental fatigue were collected throughout.ResultsEndurance performance, across the 3 tasks, improved more following BET (32%) than Control (12%) (p < 0.05). The better performance following BET occurred with a higher pre-frontal oxygenation during the post-training physical tasks over time relative to Control (p < 0.05).ConclusionsConcurrent BET improved endurance performance over physical training alone. This was accompanied by a training-induced maintenance of pre-frontal oxygenation, suggestive of reduced mental effort during physical activity.     

Caffeine and endurance performance

The belief among athletes that caffeine is an ergogenic aid is common, and several governing bodies of sport have barred use of the drug during competition. At the cellular level, caffeine has been implicated to affect the translocation of calcium in muscle, promote an increase in cellular levels of cyclic AMP and cause a blockade of adenosine receptors in the central nervous system. The general systemic effect of caffeine is to cause central nervous system arousal, mobilisation of free fatty acids and other metabolites, and possibly enhance the contractile status of muscle. At present, the scientific community remains divided as to whether caffeine ingestion will indeed produce an ergogenic effect upon sport performance. Some evidence suggests that caffeine may improve performance in events relying upon strength and power; however, the lack of in vivo research in humans makes it difficult to form firm conclusions. In addition, reports concerning caffeine's effect on VO2max and performance during incremental exercise are not in agreement. On the other hand, recent studies suggest that caffeine might indeed have ergogenic potential in endurance events (e.g. marathon running). It is hypothesised that the mechanism behind these findings is related to the increased availability of free fatty acids for muscle metabolism which has a glycogen-sparing effect.     

Effects of intra-session concurrent endurance and strength training sequence on aerobic performance and capacity

Aim: To examine the effects of the sequencing order of individualised intermittent endurance training combined with muscular strengthening on aerobic performance and capacity. Methods: Forty eight male sport students (mean (SD) age 21.4 (1.3) years) were divided into five homogeneous groups according to their maximal aerobic speeds (vV^·O₂MAX). Four groups participated in various training programmes for 12 weeks (two sessions a week) as follows: E (n = 10), running endurance training; S (n = 9), strength circuit training; E+S (n = 10) and S+E (n = 10) combined the two programmes in a different order during the same training session. Group C (n = 9) served as a control. All the subjects were evaluated before (T0) and after (T1) the training period using four tests: (1) a 4 km time trial running test; (2) an incremental track test to estimate vV^·O₂MAX; (3) a time to exhaustion test (t_lim) at 100% vV^·O₂MAX; (4) a maximal cycling laboratory test to assess V^·O₂MAX. Results: Training produced significant improvements in performance and aerobic capacity in the 4 km time trial with interaction effect (p<0.001). The improvements were significantly higher for the E+S group than for the E, S+E, and S groups: 8.6%, 5.7%, 4.7%, and 2.5% for the 4 km test (p<0.05); 10.4%, 8.3%, 8.2%, and 1.6% for vV^·O₂MAX (p<0.01); 13.7%, 10.1%, 11.0%, and 6.4% for V^·O₂MAX (ml/kg^0.75/min) (p<0.05) respectively. Similar significant results were observed for t_lim and the second ventilatory threshold (%V^·O₂MAX). Conclusions: Circuit training immediately after individualised endurance training in the same session (E+S) produced greater improvement in the 4 km time trial and aerobic capacity than the opposite order or each of the training programmes performed separately.     

Effect of mouth-rinsing carbohydrate solutions on endurance performance

Ingesting carbohydrate-electrolyte solutions during exercise has been reported to benefit self-paced time-trial performance. The mechanism responsible for this ergogenic effect is unclear. For example, during short duration (≤1 hour), intense (>70% maximal oxygen consumption) exercise, euglycaemia is rarely challenged and adequate muscle glycogen remains at the cessation of exercise. The absence of a clear metabolic explanation has led authors to speculate that ingesting carbohydrate solutions during exercise may have a 'non-metabolic' or 'central effect' on endurance performance. This hypothesis has been explored by studies investigating the performance responses of subjects when carbohydrate solutions are mouth rinsed during exercise. The solution is expectorated before ingestion, thus removing the provision of carbohydrate to the peripheral circulation. Studies using this method have reported that simply having carbohydrate in the mouth is associated with improvements in endurance performance. However, the performance response appears to be dependent upon the pre-exercise nutritional status of the subject. Furthermore, the ability to identify a central effect of a carbohydrate mouth rinse maybe affected by the protocol used to assess its impact on performance. Studies using functional MRI and transcranial stimulation have provided evidence that carbohydrate in the mouth stimulates reward centres in the brain and increases corticomotor excitability, respectively. However, further research is needed to determine whether the central effects of mouth-rinsing carbohydrates, which have been seen at rest and during fatiguing exercise, are responsible for improved endurance performance.     

Influence of endurance exercise on respiratory muscle performance

PURPOSE: During high-intensity, exhaustive, constant-load exercise above 85% of maximal oxygen consumption, the diaphragm of healthy subjects can fatigue. Although a decrease in trans-diaphragmatic pressure is the most objective measure of diaphragmatic fatigue, possible extra-diaphragmatic muscle fatigue would not be detected by this method. The aim of the present study was to investigate the impact of exhaustive, constant-load cycling exercise at different intensities on global respiratory performance determined by the time to exhaustion while breathing against a constant resistance. METHODS: Ten healthy, male subjects performed an exhaustive cycling endurance test at 65, 75, 85, and 95% of peak oxygen consumption (VO2peak). Before cycling (to) as well as at 10 min (t10) and 45 min (t45) after cycling, respiratory performance was determined. RESULTS: Breathing endurance was equivalently reduced after exhaustive cycling at either 65% (8.4 +/- 4.1 min [t0] vs 3.9 +/- 2.8 min [t10]), 75% (9.9 +/- 6.1 vs 4.4 +/- 2.8 min), 85% (9.3 +/- 6.0 vs 3.8 +/- 2.9 min), or 95% VO2peak (8.5 +/- 5.1 vs 4.0 +/- 2.5 min) and, therefore, was independent of exercise intensity. CONCLUSION: This result contradicts previous findings, possibly due to the fact that extra-diaphragmatic muscles are tested in addition to the diaphragm during resistive breathing.     

Effects of sucrose or caffeine ingestion on running performance and biochemical responses to endurance running

To elucidate the effects of sucrose or caffeine ingestion on metabolic responses to prolonged exercise and on performance of a finishing spurt after the prolonged exercise, seven male physical education students performed four sets of 30 min running (62%-67% VO2 max) followed by progressive exhaustive running on a treadmill. Before each set, they took 350 ml solution containing either sucrose 23.8 g (97.5 kcal), caffeine 200 mg, or a placebo. The duration of the exhaustive running after sucrose, caffeine, or placebo ingestion was not significantly different. Exhaustion would possibly be attained not by depletion of muscle glycogen but by a decrease in the capacity of muscle cells to produce high tension for anaerobic metabolism. Total energy and energy from carbohydrate combusted during four sets of running were estimated at 1255 kcal and 810 kcal in the sucrose trial, 1271 kcal and 624 kcal in the caffeine trial, and 1248 kcal and 649 kcal in the placebo trial. Judging from the figures above, glycogen sparing during prolonged running seemed to be attained by sucrose ingestion but not by caffeine ingestion. The latter finding would be caused by lower intensity and a larger amount of ingested caffeine. In conclusion, performance of progressive exhaustive running following endurance running for 2 h could not be improved either by sucrose or caffeine ingestion. Glycogen sparing in the muscle, however, was suggested by sucrose ingestion but not by caffeine ingestion.