A comparison of inspiratory muscle fatigue following maximal exercise in moderately trained males and females

Exercise-induced inspiratory muscle fatigue (IMF) has been reported in males but there are few reports of IMF in females. It is not known if a gender difference exists for inspiratory muscle strength following heavy exercise, as is reported in locomotor muscles. Therefore, the relationship between fatigue and subsequent recovery of maximal inspiratory pressure (MIP) following exercise to maximal oxygen consumption was examined in a group of moderately trained males and females. Eighteen males (23±3 years; mean ± SD) and 16 females (23±2 years) completed ten MIP and ten maximal handgrip (HG) strength maneuvers to establish baseline. Post-exercise MIP and HG were assessed successively immediately following a progressive intensity test on a cycle ergometer and at 1, 2, 3, 4, 5, 10, and 15 min. relative to fat-free mass was not statistically different between males (62±7 ml kg^–1 min^–1) and females (60±8 ml kg^–1 min^–1). Males had higher absolute MIP values than females at all time intervals (P<0.05). Immediately following exercise, MIP was significantly reduced in both genders (M=83±16%; F=78±15% of baseline) but HG values were not different than resting values. MIP values remained depressed for both males and females throughout the 15 min (P<0.05). Differences for MIP between males and females were not statistically significant at any measurement time (P>0.05). The findings in this study conclude that IMF, observed immediately following maximal exercise, demonstrated the same pattern of recovery for both genders.     

Plasma ghrelin responses to acute sculling exercises in elite male rowers

The regulatory effect of ghrelin on growth hormone (GH) is limited in describing ghrelin response to acute submaximal exercise intensities in elite athletes. We investigated the effects of a single sculling exercise performed above and below the individual anaerobic threshold (IAT) on total ghrelin concentration in highly trained male rowers. Nine elite male rowers (20.1 ± 3.7 years; 190.0 ± 5.2 cm; 89.6 ± 4.6 kg; %body fat: 9.9 ± 2.5%) volunteered for this study. Single scull rowing was performed below and above IAT using a mean of 5 bpm above and below the heart rate of the IAT during graded exercise test. Ghrelin, leptin, GH, insulin, and glucose were measured before, immediately after, and after 30 min of recovery. Plasma ghrelin concentration did not increase significantly in either exercise but was approaching significance after 30 min of recovery (P = 0.051) when the constant load sculling was performed at the intensity above the IAT. There were no changes in plasma leptin levels. GH increased significantly immediately after exercise and remained elevated during the 30 min of recovery in both exercise conditions, while insulin decreased significantly immediately after exercise and remained significantly lower after the 30 min of recovery in both exercise intensities. Baseline ghrelin was not correlated with the body composition, physical performance, or blood biochemical data. There was no significant relationship between plasma ghrelin and other blood variables immediately after the 30 min of recovery in both exercise tests and changes in ghrelin were not related to blood biochemical variables after the exercise tests. The acute constant load sculling exercise above or below IAT that increased GH concentrations did not significantly increase the circulating plasma ghrelin levels.     

Influence of L-carnitine administration on maximal physical exercise

Summary The effects of L-carnitine administration on maximal exercise capacity were studied in a double-blind, cross-over trial on ten moderately trained young men. A quantity of 2 g of L-carnitine or a placebo were administered orally in random order to these subjects 1 h before they began exercise on a cycle ergometer. Exercise intensity was increased by 50-W increments every 3 min until they became exhausted. After 72-h recovery, the same exercise regime was repeated but this time the subjects, who had previously received L-carnitine, were now given the placebo and vice versa. The results showed that at the maximal exercise intensity, treatment with L-carnitine significantly increased both maximal oxygen uptake, and power output. Moreover, at similar exercise intensities in the L-carnitine trial oxygen uptake, carbon dioxide production, pulmonary ventilation and plasma lactate were reduced. It is concluded that under these experimental conditions pretreatment with L-carnitine favoured aerobic processes resulting in a more efficient performance. Possible mechanisms producing this effect are discussed.     

Peak power output predicts maximal oxygen uptake and performance time in trained cyclists

Summary The purposes of this study were firstly to determine the relationship between the peak power output (W _peak) and maximal oxygen uptake (VO_2max) attained during a laboratory cycling test to exhaustion, and secondly to assess the relationship betweenW _peak and times in a 20-km cycling trial. One hundred trained cyclists (54 men, 46 women) participated in the first part of this investigation. Each cyclist performed a minimum of one maximal test during whichW _max andVO_2max were determined. For the second part of the study 19 cyclists completed a maximal test for the determination ofW _peak, and also a 20-km cycling time trial. Highly significant relationships were obtained betweenW _peak andVO_2max (r=0.97,P<0.0001) and betweenW _peak and 20-km cycle time (r= –0.91,P<0.001). Thus,W _peak explained 94% of the variance in measuredVO_2max and 82% of the variability in cycle time over 20 km. We concluded that for trained cyclists, theVO_2max can be accurately predicted fromW _peak, and thatW _peak is a valid predictor of 20-km cycle time.     

Physical work capacity in dynamic exercise with differing muscle masses in healthy young and older men

Ten young (aged 23–30 years) and nine older (aged 54–59 years) healthy men with similar estimated limb muscle volumes performed, in random order, three different types of ergometer exercise tests (one-arm cranking, two-arm cranking, and two-leg cycling) up to the maximal level. Values for work load (WL), peak oxygen consumption , peak heart rate (HR), peak ventilation , respiratory gas exchange ratio (R), recovery blood lactate concentration [La^–], and rating of perceived exertion (RPE) were compared between the age-groups in the given exercise modes. No significant age-related differences in WL, peak , peak HR, R, [La^–], or RPE were found in one-arm or two-arm cranking. During one-arm cranking the mean peak was 1.65 (SD 0.26)1 · min^–1 among the young men and 1.63 (SD 0.10)1 · min^–1 among the older men. Corresponding mean peak during two-arm cranking was 2.19 (SD 0.32)1 · min-1 and 2.09 (SD 0.18)1 · min^–1, respectively. During one-arm cranking peak was higher (P < 0.05) among the older men compared to the young men. During two-leg cycling the young men showed higher values in WL (P < 0.001), peak (P < 0.001), and peak HR (P < 0.001). The mean peak was 3.54 (SD 0.24)1 · min^–1 among the young men and 3.02 (SD 0.20)1 · min^–1 among the older men. Corresponding mean peak HR was 182 (SD 5) beats · min^–1 and 170 (SD 8) beats · min^–1, respectively. During two-leg cycling, peak , R, [La^–], and RPE did not differ between the two age-groups. In summary, the older men with similar sizes of estimated arm and leg muscle volumes as the young men had a reduced physical work capacity in two-leg cycling. In one-arm or two-arm cranking, no significant difference in work capacity was found between the age-groups. These results indicate, that in healthy men, age, at least up to the 6th decade of life, is not necessarily associated with a decline in physical work capacity in exercises using relatively small muscle groups, in which the limiting factors are more peripheral than central.     

Physiological comparisons among three maximal treadmill exercise protocols in trained and untrained individuals

The present investigation was undertaken to examine whether maximal oxygen uptake (VO2max) and anaerobic threshold (AT) measured during incremental treadmill exercise would be affected by the exercise protocol in trained and untrained individuals. Fifteen untrained men, 10 untrained women, and 12 trained individuals participated in this study. The Astrand, Bruce, and Costill/Fox protocols were selected for comparison. Each subject was tested using all three protocols and the three tests were conducted in a randomized counterbalanced order. During each test, oxygen uptake was measured every 30 s and the test was terminated according to the standard criteria. The VO2max was determined by averaging the two consecutive highest measurements, whereas AT was determined using ventilatory parameters following the V-slope technique. The Astrand, Bruce, and Costill/Fox protocols produced test durations of 9.8 (SEM 0.5), 12.4 (SEM 0.4), and 4.9 (SEM 0.3) min, respectively, in the untrained men, 9.0 (SEM 0.8), 11.0 (SEM 0.6), and 5.3 (SEM 0.6) min, respectively, in the untrained women, and 14.5 (SEM 0.5), 17.0 (SEM 0.5) and 10.4 (SEM 0.4) min, respectively, in the trained men. In the untrained men and women, no differences in VO2max were observed among the three different protocols, but AT was lower when using the Bruce compared to the Astrand protocol. In the trained men, VO2max and AT were lower when using the Bruce protocol than either the Astrand or Costill/Fox protocols. In conclusion, VO2max measured during treadmill exercise is not affected by the protocol of the test and using a running protocol of short duration (i.e. about 5 min) could be a time-efficient way of assessing VO2max in healthy untrained subjects. In trained subjects, however, a protocol consisting of running with small increments in gradient is effective in eliciting a higher VO2max. The lower AT associated with the Bruce protocol seen in both untrained and trained groups suggests this aerobic parameter is protocol dependent and this protocol dependency is not affected by training status.     

Respiratory responses of elite oarsmen,former oarsmen,and highly trained non-rowers during rowing,cycling and running

The position of the body and use of the respiratory muscles in the act of rowing may limit ventilation and thereby reduce maximal aerobic power relative to that achieved in cycling or running, in spite of the greater muscle mass involved in rowing. This hypothesis was investigated for three groups of male subjects: nine elite senior oarsmen, eight former senior oarsmen and eight highly trained athletes unskilled in rowing. The subjects performed graded exercise to maximal effort on a rowing ergometer, cycle ergometer and treadmill while respiratory minute volume and oxygen consumption were monitored continuously. The VE at a given during intense submaximal exercise (greater than 75% of maximal ) was not significantly lower in rowing compared with that in cycling and treadmill running for any group, which would suggest that submaximal rowing does not restrict ventilation. At maximal effort, and for rowing were less than those for the other types of exercise in all the groups, although the differences were not statistically significant in the elite oarsmen. These data are consistent with a ventilatory limitation to maximal performance in rowing that may have been partly overcome by training in the elite oarsmen. Alternatively, a lower maximal VE in rowing might have been an effect rather than a cause of a lower maximal if maximal was limited by the lower rate of muscle activation in rowing.     

Changes in erythrocyte 2,3 diphosphoglycerate in women following short term maximal exercise

15 untrained women were subjected to a walking treadmill test to determine the influence of maximal exercise upon synthesis of erythrocyte 2,3 DPG. Although there was a 9.8% increase in the 2,3 DPG content following exercise, there was a concomitant 9.4% increase in the hemoglobin level; therefore, when 2,3 DPG is expressed as a ratio to hemoglobin there was no significant change as a result of exercise stress. It was suggested that three additive factors produced during strenuous exercise: decreased pH; increased hemoglobin concentration; and increased CO₂ production result in by-product inhibition of 2,3 DPG synthesis. It is concluded that 2,3 DPG does not provide a physiologic benefit in the adaptation of the oxygen transport system to exercise.     

Sympathetic response to maximal bicycle exercise before and after leg strength training

Summary Plasma catecholamine concentrations at rest and in response to maximal exercise on the cycle ergometer (278±15 watts, 6 min duration) have been measured on seven young active male subjects (19±1 years old; 80±3 kg; 176±3 cm) prior to and after a eight week leg strength training program (5RM, squat and leg press exercise). Strength training resulted in a significant increase in performance on squat (103±3 to 140±5 kg) and leg press exercise (180±9 to 247±15 kg) associated with a small significant increase in lean body mass (64.5±2.2 to 66.3±2.1 kg) and no change in maximal oxygen consumption (47.5±1.3 to 46.9±1.2 ml · kg^–1 · min^–1). Plasma norepinephrine (NE) and epinephrine (E) concentrations (pg · mL^–1) were not significantly different before and after training at rest (NE: 172±19 vs 187±30; E: 33±10 vs 76±16) or in response to maximal exercise (NE: 3976±660 vs 4163±1081; E: 1072±322 vs 1321±508). Plasma lactate concentrations during recovery were similar before and after training (147±5 vs 147±15 mg · dL^–1). Under the assumption that the central command is reduced for a given absolute workload on the bicycle ergometer following leg strength training, these observations support the hypothesis that the sympathetic response to exercise is under the control of information from muscle chemoreceptors.Supported by grants from NSERC, Government of Canada and FRSQ, Government of Quebec     

Delayed reoxygenation after maximal isometric handgrip exercise in high oxidative capacity muscle

We hypothesized that after maximal short-term isometric exercise, when O₂ demand is still high and O₂ supply is not fully activated, higher oxidative capacity muscle may exhibit slower muscle reoxygenation after the exercise than low oxidative capacity muscle. Seven healthy male subjects performed a maximal voluntary isometric handgrip exercise for 10 s. The reoxygenation rate after the exercise (Reoxy-rate) in the finger flexor muscle was determined by near infrared continuous wave spectroscopy (NIRcws) while phosphocreatine (PCr) was measured simultaneously by ³¹P magnetic resonance spectroscopy. Muscle oxygen consumption (muscle V˙O₂) and muscle oxidative capacity were evaluated using the rate of PCr resynthesis post-exercise. The forearm blood flow (FBF) index at the end of exercise was measured using NIRcws. There was a significant positive correlation between the Reoxy-rate, which ranged between 0.53% s⁻¹ and 12.47% s⁻¹, and the time constant for PCr resynthesis, which ranged between 17.8 s and 38.3 s (r ²=0.939, P<0.001). At the end of the exercise, muscle V˙O₂ exceeded the resting level by approximately 25-fold, while the FBF index exceeded the resting level by only 3-fold on average. The Reoxy-rate closely correlated with muscle V˙O₂ (r ²=0.727, P<0.05), but not with the FBF index. Also, the estimated O₂ balance (muscle V˙O₂ index/FBF index) was negatively correlated with the Reoxy-rate (r ²=0.820, P<0.001). These results support our hypothesis that higher oxidative capacity muscle shows slower muscle reoxygenation after maximal short-term isometric exercise because the Reoxy-rate after this type of exercise may be influenced more by muscle V˙O₂ than by O₂ supply. Electronic Publication     

Bone metabolism in elite male rowers: adaptation to volume-extended training

We examined the effect of 6-month volume-extended training on bone metabolism in elite male rowers. Twelve elite male rowers (20.8±3.0 years; 192.9±4.7 cm; 91.9±5.3 kg; body fat 10.1±2.3%; 6.2±0.5 l min⁻¹) participated in this study. Bone biochemical markers, hormones, bone mineral content (BMC), and bone mineral density (BMD) were assessed before and after training. Average weekly training volume was significantly higher (P<0.05) during the 6 months of heavy training compared to relative rest (11.6±0.4 h week⁻¹ vs. 16.8±0.6 h week⁻¹), while intensity remained the same. At the end of training, only arm BMD was significantly increased by 5.7%. Osteocalcin (16.6%), insulin-like growth factor-1 (IGF-1) (20.2%) and the bioavailability IGF-1 index (17.9%) were significantly increased. Before heavy training, relationships were observed between the whole body BMD and growth hormone (r=0.64; P≤0.02), lumbar spine BMD and 1.25(OH)₂ vitamin D (r=0.69; P≤0.04), arm BMD and testosterone (r=0.59; P≤0.05), and arm BMD and adiponectin (r=0.59; P≤0.05). No relationship was found between BMC or BMD and blood biochemical measures 6 months later (r=0.56; P≥0.05). In addition, osteocalcin was related to IGF-1 (r>0.58; P<0.048) and bioavailability IGF-1 index (r>0.59; P≤0.055) before and after training. In summary, heavy training had a moderately favorable effect on BMD. Bone tissue at specific skeleton sites is sensitive to changes in training volume even in athletes with already high BMD values. Changes in BMD and bone formation may be caused by changes in specific hormones such as IGF-1 and adiponectin in male athletes.     

Physiological responses to maximal intensity intermittent exercise

Summary Physiological responses to repeated bouts of short duration maximal-intensity exercise were evaluated. Seven male subjects performed three exercise protocols, on separate days, with either 15 (S₁₅), 30 (S₃₀) or 40 (S₄₀) m sprints repeated every 30 s. Plasma hypoxanthine (HX) and uric acid (UA), and blood lactate concentrations were evaluated pre- and postexercise. Oxygen uptake was measured immediately after the last sprint in each protocol. Sprint times were recorded to analyse changes in performance over the trials. Mean plasma concentrations of HX and UA increased during S₃₀ and S₄₀ (P<0.05), HX increasing from 2.9 (SEM 1.0) and 4.1 (SEM 0.9), to 25.4 (SEM 7.8) and 42.7 (SEM 7.5) µmol · l^–1, and UA from 372.8 (SEM 19) and 382.8 (SEM 26), to 458.7 (SEM 40) and 534.6 (SEM 37) µmol · l^–1, respectively. Postexercise blood lactate concentrations were higher than pretest values in all three protocols (P<0.05), increasing to 6.8 (SEM 1.5), 13.9 (SEM 1.7) and 16.8 (SEM 1.1) mmol · l^–1 in S₁₅, S₃₀ and S₄₀, respectively. There was no significant difference between oxygen uptake immediately after S₃₀ [3.2 (SEM 0.1) l · min^–1] and S₄₀ [3.3 (SEM 0.4) l · min^–1], but a lower value [2.6 (SEM 0.1) l · min^–1] was found after S₁₅ (P<0.05). The time of the last sprint [2.63 (SEM 0.04) s] in S₁₅ was not significantly different from that of the first [2.62 (SEM 0.02) s]. However, in S₃₀ and S₄₀ sprint times increased from 4.46 (SEM 0.04) and 5.61 (SEM 0.07) s (first) to 4.66 (SEM 0.05) and 6.19 (SEM 0.09) s (last), respectively (P<0.05). These data showed that with a fixed 30-s intervening rest period, physiological and performance responses to repeated sprints were markedly influenced by sprint distance. While 15-m-sprints could be repeated every 30 s without decreases in performance, 40-m sprint times increased after the third sprint (P<0.05) and this exercise pattern was associated with a net loss to the adenine nucleotide pool.     

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.     

Influence of age on blood pressure recovery after maximal effort ergometer exercise in non-athletic adult males

This study investigated whether age influences blood pressure recovery after maximal exercise in adult males. Forty healthy, non-athletic adult males (20 young, aged 22 ± 3.46 years and 20 older, aged 48 ± 6.91 years) participated in the study. Subjects performed a maximal-effort ergometer exercise test. Peak oxygen uptake (VO_2max) was measured during the exercise protocol; heart rate (HR) and blood pressure (BP) were measured before exercise, during exercise (at 2-min intervals), and at the first minute of post-exercise recovery and subsequently at 2-min intervals until the recovery of BP. Results indicated that young adults had lower systolic blood pressure (SBP) recovery ratio (P < 0.05), lower SBP recovery time (P < 0.001), higher SBP% decline in 1, and 3 min (P < 0.001), and higher DBP% decline in 1, and 3 min (P < 0.05, <0.001) than the older adults, thus indicating faster BP recovery in young than older adults. A bivariate correlation test, revealed significant associations (P < 0.001, <0.01) between age and BP recovery parameters: percentage SBP decline in 1 and 3 min (27 and 39%), percentage DBP decline in 1 and 3 min (14 and 26%), third minute SBP ratio (22%), and SBP recovery time (72%). After controlling for factors affecting BP recovery such as resting SBP, percentage HR decline, VO_2max and delta SBP, the observed correlations reduced in SBP recovery time (29%; P < 0.002) but disappeared (P > 0.01) in the other BP recovery parameters. These data indicate the need to take into account, factors affecting BP recovery when interpreting the effect of age on BP responses after exercise in future investigations.     

Peak blood ammonia and lactate after submaximal,maximal and supramaximal exercise in sprinters and long-distance runners

Summary The purpose of this study was to elucidate the difference in peak blood ammonia concentration between sprinters and long-distance runners in submaximal, maximal and supramaximal exercise. Five sprinters and six long-distance runners performed cycle ergometer exercise at 50% maximal, 75% maximal, maximal and supramaximal heart rates. Blood ammonia and lactate were measured at 2.5, 5, 7.5, 10 and 12.5 min after each exercise. Peak blood ammonia concentration at an exercise intensity producing 50% maximal heart rate was found to be significantly higher compared to the basal level in sprinters (P < 0.01) and in long-distance runners (P < 0.01). The peak blood ammonia concentration of sprinters was greater in supramaximal exercise than in maximal exercise (P < 0.05), while there was no significant difference in long-distance runners. The peak blood ammonia content after supramaximal exercise was higher in sprinters compared with long-distance runners (P < 0.01). There was a significant relationship between peak blood ammonia and lactate after exercise in sprinters and in long-distance runners. These results suggest that peak blood ammonia concentration after supramaximal exercise may be increased by the recruitment of fast-twitch muscle fibres and/or by anaerobic training, and that the processes of blood ammonia and lactate production during exercise may be strongly linked in sprinters and long-distance runners.     

The validity of predicting maximal oxygen uptake from a perceptually-regulated graded exercise test

The purpose of this study was to assess the validity of predicting maximal oxygen uptake from sub-maximal values elicited during a perceptually-regulated exercise test. We hypothesised that the strong relationship between the ratings of perceived exertion (RPE) and would enable to be predicted and that this would improve with practice. Ten male volunteers performed a graded exercise test (GXT) to establish followed by three sub-maximal RPE production protocols on a cycle ergometer, each separated by a period of 48 h. The perceptually-regulated trials were conducted at intensities of 9, 11, 13, 15 and 17 on the RPE scale, in that order. and HR were measured continuously and recorded at the end of each 4 min stage. Individuals RPE values yielded correlations in the range 0.92–0.99 across the three production trials. There were no significant differences between measured (48.8 ml·kg^–1·min^–1) and predicted max values (47.3, 48.6 and 49.9 ml·kg^–1·min^–1, for trials 1, 2 and 3, respectively) when max was predicted from RPE values of 9–17. The same was observed when was predicted using RPE 9–15. Limits of agreement (LoA) analysis on actual and predicted values (from RPE 9–17) were (bias±1.96×SDdiff) 1.5±7.3, 0.2±4.9 and –1.2±5.8 ml·kg^–1·min^–1, for trials 1, 2 and 3, respectively. Corresponding LoA values for actual and predicted (from RPE 9–15) were 5.4±11.3, 4.4±8.7 and 2.3±8.4 ml·kg^–1·min^–1, respectively. The data suggest that a sub-maximal, perceptually-guided, graded exercise protocol can provide acceptable estimates of maximal aerobic power, which are further improved with practice in fit young males.     

TSH,T3, rT3 and fT4 in maximal and submaximal physical exercise

Summary The response of various thyroid hormone parameters to maximal physical exercise (MPE) was investigated in 14 medium and long distance runners and 13 divers. The effect of submaximal long time physical exercise (SMPE) was examined in seven divers. The TSH-level decreases significantly during MPE and slightly rises again after the end of the exercise. In SMPE, however, TSH continuously rises until 15 min after the end of the exercise. The T₃ level rises significantly in MPE and falls below the initial value 15 min after the exercise finishes, during SMPE it remains practically unchanged and slightly decreases after the finish. In MPE, the rT₃ level does not change and slightly decreases after termination, while the fT₄ level continuously decreases from the beginning till 15 min after the exercise period. The latter two parameters do not show any change in SMPE. As possible reasons for the changes of TSH levels a decrease (MPE) or an increase (SMPE) of pituitary secretion might play a role. Furthermore, in MPE the rise in T₃ level might be related to hemoconcentration, and the decrease in fT₄ level to an elevated cellular utilization.     

Differences in cardio-respiratory responses to exhaustive exercise between athletes and non-athletes

Summary To study the factors limiting the O₂ supply in heavy exercise, O₂ uptake at exhaustion was determined by progressive loading method with a bicycle ergometer in 33 well-trained male runners and 34 male sedentary adults. Pulmonary ventilation, oxygen removal, respiratory rate, tidal volume, pulmonary diffusing capacity, alveolar-capillary oxygen difference, cardiac output, arterial-venous oxygen difference, stroke volume and heart rate were measured. It was found that pulmonary diffusing capacity, cardiac output and stroke volume were correlated with the difference in O₂ uptake at exhaustion between athletes and non-athletes.     

Changes in lipid profile variables in response to submaximal and maximal exercise in trained cyclists

This study examined the effect of prolonged submaximal exercise followed by a self-paced maximal performance test on cholesterol (T-Chol), triglycerides (TG), and high-density lipoprotein cholesterol (HDLC). Nine trained male athletes cycled at 70% of maximal oxygen consumption for 60 min, followed by a selfpaced maximal ride for 10 min. Venous blood samples were obtained at rest, at 30 and 60 min during submaximal exercise, and immediately after the performance test. Lactic acid, haematocrit (Hct), haemoglobin (Hb), T-Chol and TG were measured in the blood, while plasma was assayed for HDL-C. Plasma volume changes in response to exercise were calculated from Hct and Hb values and all lipid measurements were corrected accordingly. In order to ascertain the repeatability of lipid responses to exercise, all subjects were re-tested under identical testing conditions and experimental protocols. When data obtained during the two exercise trials were analysed by two-way ANOVA no significant differences (P > 0.05) between tests were observed. Consequently the data obtained during the two testing trials were pooled and analysed by one-way ANOVA. Blood lactic acid increased non-significantly (P > 0.05) during the prolonged submaximal test, but rose markedly (P < 0.05) following the performance ride. Lipid variables ascertained at rest were within the normal range for healthy subjects. ANOVA showed that blood T-Chol and TG were unchanged (P > 0.05), whereas HDL-C rose significantly (P < 0.05) in response to exercise. Post hoc analyses indicated that the latter change was due to a significant rise in HDL-C after the performance ride. It is concluded that apparent favourable changes in lipid profile variables occur in response to prolonged submaximal exercise followed by maximal effort, and these changes showed a good level of agreement over the two testing occasions.     

Muscle function during brief maximal exercise: accurate measurements on a friction-loaded cycle ergometer

A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N·kg^–1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137–180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17–214 rpm). Thus, the individual's muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (v _opt) and individual maximal power output (P _max) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since v _opt has been demonstrated to be related to human fibre type composition both v _opt, P _max and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.