Dissociation of training effects on skeletal muscle mitochondrial enzymes and myoglobin in man

The effect of endurance training on skeletal muscle myoglobin concentration in man was investigated. 8 healthy sedentary males (20-31 yrs) trained on cycle ergometers 40 min/day, 4 days a week for 8 weeks. The work consisted of continuous exercise at a work load that during the last 5 weeks corresponded to 75% of the pretraining maximal oxygen uptake (VO2 max). The training program resulted in a 7% increase in VO2 max (p less than 0.01). The activities of the mitochondrial enzymes citrate synthase (CS), succinate dehydrogenase (SDH) and cytochrome c oxidase (Cyt-c-ox) in the quadriceps femoris muscle, as indicators of muscle respiratory capacity, increased by 62-82% (p less than 0.01). The metabolic adaptation of skeletal muscle was further indicated by a 17% increase in the work load corresponding to a blood lactate concentration of 4 mmol/l, as determined by a progressive exercise test (p less than 0.05). There was, however, no change in the myoglobin concentration of the thigh muscle with training (-1%, NS). It is suggested that endurance exercise in man at 75% of the maximal oxygen uptake does not severely tax the functions of myoglobin in skeletal muscle.     

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.     

Effects of high-intensity interval training on pulmonary function

To determine whether high-intensity interval training (HIT) would increase respiratory muscle strength and expiratory flow rates more than endurance training (ET), 15 physically active, healthy subjects (untrained) were randomly assigned to an ET group (n = 7) or a HIT group (n = 8). All subjects performed an incremental test to exhaustion (VO2max) on a cycle ergometer before and after training. Standard pulmonary function tests, maximum inspiratory pressure (PImax), maximum expiratory pressure (PEmax), and maximal flow volume loops were performed pre training and after each week of training. HIT subjects performed a 4-week training program, 3 days a week, on a cycle ergometer at 90% of their VO2max final workload, while the ET subjects performed exercise at 60-70% VO2max. The HIT group performed five 1-min bouts with 3-min recovery periods and the ET group cycled for 45 min continuously. A five-mile time trial (TT) was performed prior to, after 2 weeks, and after completion of training. Both groups showed improvements (P < 0.05) in VO2max (~8-10%) and TT (HIT 6.5 ± 1.3%, ET 4.4 ± 1.8%) following training with no difference (P > 0.05) between groups. Both groups increased (P < 0.05) PImax post training (ET ~ 25%, HIT ~ 43%) with values significantly higher for HIT than ET. There was no change (P > 0.05) in expiratory flow rates with training in either group. These data suggest that both whole-body exercise training and HIT are effective in increasing inspiratory muscle strength with HIT offering a time-efficient alternative to ET in improving aerobic capacity and performance.     

Endurance training decreases the non-linearity in the oxygen uptake-power output relationship in humans

In this study, we hypothesized that 5 weeks of cycling endurance training can decrease the magnitude of the non-proportional increase in oxygen uptake (V(O(2))) to power output relationship (V(O(2)) 'excess') at exercise intensities exceeding the lactate threshold (LT). Ten untrained, physically active men performed a bout of incremental cycling exercise until exhaustion before and after training. The mitochondrial DNA copy number, myosin heavy chain composition and content of uncoupling protein 3 and sarcoplasmic reticulum Ca(2+)-ATPases (SERCAs) were analysed in muscle biopsies taken from vastus lateralis before and after training. The training resulted in an enhancement of the power-generating capabilities at maximal oxygen uptake (V(O(2)max)) by ～7% (P = 0.002) despite there being no changes in V(O(2)max) (P = 0.49). This effect was due to a considerable reduction in the magnitude of the V(O(2)) 'excess' (P < 0.05) above the LT. A decrease in plasma ammonia concentration was found during exercise after training (P < 0.05). A downregulation of SERCA2 in vastus lateralis (P = 0.006) was observed after training. No changes in myosin heavy chain composition, selected electron transport chain proteins, uncoupling protein 3 or the mitochondrial DNA copy number (P > 0.05) were found after training. We conclude that the training-induced increase in power-generating capabilities at V(O(2)max) was due to attenuation of the V(O(2)) 'excess' above the LT. This adaptive response seems to be related to the improvement of muscle metabolic stability, as judged by a lowering of plasma ammonia concentration. The enhancement of muscle metabolic stability after training could be caused by a decrease in ATP usage at a given power output owing to downregulation of SERCA2 pumps.     

Cardiovascular and respiratory responses to submaximal exercise training in the thoroughbred horse

Cardiovascular and respiratory responses to submaximal exercise training were investigated in 6 thoroughbred racehorses. Oxygen uptake, heart rate (HR) and arteriovenous oxygen content difference were measured during incremental treadmill exercise tests, before and after 7 weeks of treadmill training. Cardiac output during exercise was calculated by the direct Fick technique. Maximal oxygen uptake ( ) was increased by 23% after training, from 129.7 ml/kg/min to 160.0 ml/kg/min. The treadmill speed at which was attained increased by 19%. The increased aerobic power after training was associated with an increase in maximal cardiac output and stroke volume, a decrease in arteriovenous oxygen difference and no change in HR. There was no change in pulmonary ventilation during exercise at . Mean mixed venous oxygen content ( ) at before training was 2.8±1.0 ml/100 ml blood (mean ±SE). After training the value was 8.6±1.4 ml/100 ml blood. It is concluded that the increase in after training in the horse is dependant on augmented blood flow, and is not dependent on either increased arterial oxygen content or arteriovenous oxygen content difference. Cardiac capacity to pump blood is therefore of primary importance as a determinant of increases in due to training in the horse.     

The Nature of the Training Response; Peripheral and Central Adaptations to One-Legged Exercise

13 male subjects were studied and placed in 3 groups. Each group exercised one leg with sprint (S), or endurance (E) training and the other leg oppositely or not at all (NT). Oxygen uptake (Vo₂), heart rate and blood lactate were measured for each leg separately and for both legs together during submaximal and maximal bicycle work before and after 4 weeks of training with 4–5 sessions per week. Muscle samples were obtained from the quadriceps muscle and assayed for succinate dehydrogenase (SDH) activity, and stained for myofibrillar AT Pase. In addition eight of the subjects performed after the training two-legged exercise at 70% Vo₂ max for one hour. The measurements included muscle glycogen and lactate concentrations of the two legs as well as the blood flow and the a-v difference for O₂, glucose and lactate. The improvement in Vo₂ max, the lowered heart rate and blood lactate response at submaximal work levels were only found when exercising with a trained leg (E or S). Part of the variables studied were markedly more changed with E as compared with S-training. Although muscle fibre composition did not change a pronounced muscle adaptation took place with the training with enhancement of the SDH activity of the S and E legs while the NT-leg did not change. Blood flow and oxygen uptake were similar in NT and S–E legs while femoral vein oxygen content was slightly lower in the trained as compared to the NT-leg. Glycogen utilization was lowest in the trained leg with similar glucose uptake in all legs regardless of training status. Moreover, lactate was only continuously released from the NT-leg. It is concluded that training induces marked local adaptations which not only affects the metabolic response to exercise but also are of importance eliciting an improved cardiovascular function.     

Time course of adaptation to low intensity training in sedentary men: dissociation of central and local effects

The oxygen transporting capacity and the metabolic capacity of the vastus lateralis muscle were followed in parallel in 9 sedentary, overweighted men during a low intensity training program. Measurements were made at 0, 3, 6, 9, 12 and 30 weeks. Maximal oxygen uptake increased in an approximately linear fashion during the first 12 weeks (11%), but decreased a little (3%) during the following 18 weeks. Mean body weight decreased 8% (7.4 kg) during the training. The distribution of muscle fibre types, including the subgroups of type II fibres, did not change. Muscle enzyme activities remained essentially unchanged during the training. It was concluded that "central" och "local" adaptation need not occur in parallel, and that the leg oxygen utilization capacity probably does not limit the whole body's maximal oxygen uptake.     

Improvement of $$\dot{V}\hbox{O}_{2 \max},$$ by cardiac output and oxygen extraction adaptation during intermittent versus continuous endurance training

Improvement of exercise capacity by continuous (CT) versus interval training (IT) remains debated. We tested the hypothesis that CT and IT might improve peripheral and/or central adaptations, respectively, by randomly assigning 10 healthy subjects to two periods of 24 trainings sessions over 8 weeks in a cross-over design, separated by 12 weeks of detraining. Maximal oxygen uptake (VO2max), cardiac output (Qmax) and maximal arteriovenous oxygen difference (Da-vO2max) were obtained during an exhaustive incremental test before and after each training period. VO2max and Qmax increased only after IT (from 26.3 +/- 1.6 to 35.2 +/- 3.8 ml min(-1) kg(-1) and from 17.5 +/- 1.3 to 19.5 +/- 1.8 l min(-1), respectively; P < 0.01). Da-vO2max increased after both protocols (from 11.0 +/- 0.8 to 12.7 +/- 1.0; P < 0.01 and from 11.0 +/- 0.8 to 12.1 +/- 1.0 ml 100 ml(-1), P < 0.05 in CT and IT, respectively). At submaximal intensity a significant rightward shift of the Q/Da-vO2 relationship appeared only after CT. These results suggest that in isoenergetic training, central and peripheral adaptations in oxygen transport and utilization are training-modality dependant. IT improves both central and peripheral components of Da-vO2max whereas CT is mainly associated with greater oxygen extraction.     

Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans

Low-volume 'sprint' interval training (SIT) stimulates rapid improvements in muscle oxidative capacity that are comparable to levels reached following traditional endurance training (ET) but no study has examined metabolic adaptations during exercise after these different training strategies. We hypothesized that SIT and ET would induce similar adaptations in markers of skeletal muscle carbohydrate (CHO) and lipid metabolism and metabolic control during exercise despite large differences in training volume and time commitment. Active but untrained subjects (23 +/- 1 years) performed a constant-load cycling challenge (1 h at 65% of peak oxygen uptake (.VO(2peak)) before and after 6 weeks of either SIT or ET (n = 5 men and 5 women per group). SIT consisted of four to six repeats of a 30 s 'all out' Wingate Test (mean power output approximately 500 W) with 4.5 min recovery between repeats, 3 days per week. ET consisted of 40-60 min of continuous cycling at a workload that elicited approximately 65% (mean power output approximately 150 W) per day, 5 days per week. Weekly time commitment (approximately 1.5 versus approximately 4.5 h) and total training volume (approximately 225 versus approximately 2250 kJ week(-1)) were substantially lower in SIT versus ET. Despite these differences, both protocols induced similar increases (P < 0.05) in mitochondrial markers for skeletal muscle CHO (pyruvate dehydrogenase E1alpha protein content) and lipid oxidation (3-hydroxyacyl CoA dehydrogenase maximal activity) and protein content of peroxisome proliferator-activated receptor-gamma coactivator-1alpha. Glycogen and phosphocreatine utilization during exercise were reduced after training, and calculated rates of whole-body CHO and lipid oxidation were decreased and increased, respectively, with no differences between groups (all main effects, P < 0.05). Given the markedly lower training volume in the SIT group, these data suggest that high-intensity interval training is a time-efficient strategy to increase skeletal muscle oxidative capacity and induce specific metabolic adaptations during exercise that are comparable to traditional ET.     

Exercise interval training: an improved stimulus for improving the physiology of pre-diabetes

Current reports estimate that type II diabetes (T2D) affects 5-8% of adults. Also recognized is a transitional group of patients whose fasting blood glucose is abnormal; yet, not considered high enough to be diagnosed as diabetes. Defined as "pre-diabetes" these individuals have impaired fasting glucose (IFG; fasting glucose 100-125 mg/dL), impaired glucose tolerance (IGT; 2 h glucose 140-199 mg/dL) or both. Two unifying features associated with IFG and IGT are their strong links to obesity and physical inactivity, which lead independently and collectively toward the erosion of various cellular processes affecting glucose control. In contrast, regular exercise positively influences IFG/IGT and obesity, thus representing an important therapy for preventing diabetes via the enhancement of several mechanisms of action. These include improved glucose metabolism, muscle respiratory capacity, mitochondrial respiratory chain activity and beta-oxidation. Contemporary exercise guidelines provided by various organizations recommend that exercise be performed at intensities ranging from 40% to 85% of maximal aerobic capacity. Unfortunately, little is known regarding the optimal intensity to best facilitate the physiological benefits associated with exercise. An evolving body of research shows that interval training produces greater changes in exercise capacity than traditional aerobic training. Interval training involves bouts of high exercise intensity (15s to 4 min; >90% VO(2max)) followed by a recovery period (40-50% VO(2max)) of equal or longer duration than the associated work interval. Though the net effect of interval training is aerobic, periodic excursions involving anaerobic energy pathways theoretically "push" the mitochondria to greater improvements in exercise capacity, mitochondrial biogenesis, enzymatic markers associated with glycolysis, aerobic metabolism and beta (beta)-oxidation. Though traditionally viewed as a training modality for athletes, a recent report has demonstrated that interval training is more effective than traditional aerobic exercise training in patients up to approximately 75 y of age and with low functional capacities (VO(2max) 13 ml/kg/min) by producing superior improvements in VO(2max), sub-maximal exercise tolerance, levels of peroxisome proliferator activator protein-gamma co-activator1alpha (PGC-1alpha), and quality of life indices more so than traditional aerobic exercise training. Erosion in these same markers is present in populations with pre-diabetes and T2D. The principal hypothesis of this paper is that interval training will provide a more powerful stimulus for improving insulin sensitivity than traditional low-to-moderate intensity aerobic conditioning. This theory further proposes that these affects will be due to greater changes in specific metabolic pathways associated with glycolysis, aerobic metabolism, beta-oxidation, and mitochondrial biogenesis.     

Central and Regional Circulatory Effects of Adding Arm Exercise to Leg Exercise

7 young, healthy, male subjects performed exercise on bicycle ergometers in two 20 min periods with an interval of 1 h. The first 10 min of each 20 min period consisted of arm exercise (38–62% of Vdot;o₂ max for arm exercise) or leg exercise (58–78% of Vdot;o₂ max for leg exercise). During the last 10 min the subjects performed combined arm and leg exercise (71–83% of Vdot;o₂ max for this type of exercise). The following variables were measured during each type of exercise: oxygen uptake, heart rate, mean arterial blood pressure, cardiac output, leg blood flow (only during leg exercise and combined exercise), arterio-venous concentration differences for O₂ and lactate at the levels of the axillary and the external iliac vessels. Superimposing a sufficiently strenuous arm exercise (oxygen uptake for arm exercise 40% of oxygen uptake for combined exercise) on leg exercise caused a reduction in blood flow and oxygen uptake in the exercising legs with unchanged mean arterial blood pressure. Superimposing leg exercise on arm exercise caused a decrease in mean arterial blood pressure and an increased axillary arterio-venous oxygen difference. These findings indicate that the oxygen supply to one large group of exercising muscles may be limited by vasoconstriction or by a fall in arterial pressure, when another large group of muscles is exercising simultaneously.     

Effects of maximal interval training on arterial oxygen desaturation and ventilation during heavy exercise

The purpose of the present study was to clarify longitudinally the effects of exercise training on arterial O(2) saturation (Sa(O(2))) and ventilation during heavy exercise. A group of six subjects (training group) volunteered to train four times a week for 12 weeks. Each training session consisted of five 3-min periods of exercise on a cycle ergometer at a power output of 100% maximal O(2) uptake (V(.)(O(2 max))), interspersed with 2-min recovery period cycling at 50% V(.)(O(2 max)). During the training, V(.)(O(2 max)), Sa(O(2)), the ventilatory equivalent for oxygen (V(.)E/V(.)(O(2))), and the end-tidal partial pressure of O(2) (PET(O(2))) during heavy exercise were measured periodically. The same parameters were measured simultaneously in another group of five subjects (control group) who led normal lives. Maximal interval training increases V(.)(O(2 max)), with little change in V(.)E(max) and pulmonary functions at rest. The training decreased PET(O(2)), V(.)E/V(.)(O(2)), and Sa(O(2)) during heavy exercise. Sa(O(2)) is significantly related to V(.)E/V(. )(O(2)) (r(2) = 0.49). These results suggest that less hyperventilatory response to exercise occurs with progress in physical training because the adaptability of ventilatory capacity is less than that of aerobic work capacity, which half induces arterial O(2) desaturation during heavy exercise. PET(O(2)) as well as V(.)E/V(.)(O(2)) and V(.)(O(2 max)) did not change anymore after the 6th week, nevertheless Sa(O(2)) kept decreasing up to the last 2 weeks. In addition, when the Sa(O(2))-V(.)E/V(.)(O(2)) plot was compared between the two groups, the regression line of the training group was steeper than that of the control groups; i.e., compared at a lower level of V(.)E/V(.)(O(2)) ( approximately 30 ml.ml(-1)), the Sa(O(2)) of the trained subjects exercising at a higher V(.)(O(2)) level was lower than that of the control subjects. Predominance of less hyperventilation and another factor, increased A-aDO(2), in the genesis of arterial hypoxemia and O(2) desaturation may be dependent upon V(.)(O(2)) levels in heavy exercise and the state of training.     

Linkage between oxygen uptake at ventilatory threshold and muscle strength in subjects with and without metabolic syndrome

We evaluated the linkage between oxygen uptake at the ventilatory threshold (VT) and muscle strength in subjects with and without metabolic syndrome. We used data of 226 Japanese men with metabolic syndrome and 265 Japanese men without the syndrome. Metabolic syndrome has recently been defined by a new criterion in Japan. Oxygen uptake at VT and muscle strength, i.e. grip strength and leg strength were measured. Oxygen uptake at VT and muscle strength/body weight were found to be significantly lower in subjects with metabolic syndrome than in those without the syndrome. However, the differences did not reach significant levels after adjusting for leg strength/body weight or oxygen uptake at VT. A combination of aerobic exercise and resistance training might be considered for preventing and improving metabolic syndrome.     

Effect of training intensity in adult females on aerobic power,related to lean body mass

Summary The aim of this study was to investigate the effect of training intensity on maximal aerobic power on the basis of the subjects lean body mass. Seven sedentary adult females aged 23–40 years participated in a 44-week training experiment. They trained on a bicycle ergometer at progressive intensities of 60, 75, and 90% VO₂ max for 13, 18, and 13 consecutive weeks, respectively. The total amount of work was between 9,000 and 12,000 kpm a day and frequency between 2 and 4 days a week, keeping both factors approximately constant for each subject throughout the 44-week training period. Mean VO₂ max increased significantly during 60 and 90% VO₂ max training. The increase during 75% VO₂ max training was not significant. The final values during the three training periods were not necessarily the highest ones. Keeping the effect of age statistically constant, a significant partial correlation developed between the initial values and the total gains (%) of VO₂ max, V _E, and O₂ pulse, expressed per lean body mass (LBM). The final attained values of VO₂ max per LBM were significantly correlated with age. Therefore, if training intensity is sufficiently effective, it might be assumed that everyone has the same capacity for the improvement of cardiorespiratory function corresponding to their lean body mass, which is related to the magnitude of muscle mass. Furthermore, it might be said that the attainable level of aerobic power is greatly limited by the effects of age.     

高强度间歇运动可改善大鼠的心肺耐力

背景:最大摄氧量(VO2max)是评定心肺耐力及运动能力最直接有效的客观指标,但目前研究中反映大鼠较长时间最大摄氧量变化数据的文章较少,尚未见有关高强度间歇训练对大鼠增龄过程中心肺耐力持续变化影响的相关报道。目的:探讨16周高强度间歇训练对大鼠心肺耐力的改善作用,并通过对29周龄大鼠最大摄氧量持续16周测定,为实验动物训练强度的量化提供数据参考。方法:将28只29周龄雄性Wistar大鼠分为2组:安静对照组大鼠正常饮食生活,无训练;高强度间歇训练组大鼠进行高强度(90%最大摄氧量)、低强度(50%最大摄氧量)的间歇运动,为期16周,每周5次,平均每2周测定最大摄氧量、完成最大摄氧量测试对应的最大跑速变化,并针对2组大鼠最大摄氧量和最大跑速值进行对比及相关分析。实验经北京体育大学运动科学实验伦理委员会批准(2015025)。结果与结论:①29-45周龄增龄过程中最大摄氧量出现下降-上升-下降波动,16周后,高强度间歇训练组大鼠最大摄氧量下降了31.6%,安静对照组大鼠最大摄氧量下降了47.9%,高强度间歇训练组大鼠最大摄氧量显著高于安静对照组(P<0.01);②干预6,8,16周时高强度间歇训练组最大摄氧量下降幅度显著低于安静对照组(P<0.05或P<0.01);③干预4,8周时高强度间歇训练组最大跑速值显著高于安静对照组(P<0.05或P<0.01);④最大摄氧量与最大跑速的相对值呈正相关;⑤结果说明,年龄的增加是大鼠心肺耐力下降的不可逆因素,但高强度间歇训练可延缓心肺耐力下降趋势;高强度间歇训练干预6周后可明显降低大鼠因增龄导致的心肺耐力下降幅度,8周后可有效延缓大鼠因增龄导致的心肺耐力下降;高强度间歇训练干预4周后大鼠最大跑速提高,运动能力增强。     

Comparison of muscle hypertrophy following 6-month of continuous and periodic strength training

To compare the effects of a periodic resistance training (PTR) program with those of a continuous resistance training (CTR) program on muscle size and function, 14 young men were randomly divided into a CTR group and a PTR group. Both groups performed high-intensity bench press exercise training [75 % of one repetition maximum (1-RM); 3 sets of 10 reps] for 3 days per week. The CTR group trained continuously over a 24-week period, whereas the PTR group performed three cycles of 6-week training (or retraining), with 3-week detraining periods between training cycles. After an initial 6 weeks of training, increases in cross-sectional area (CSA) of the triceps brachii and pectoralis major muscles and maximum isometric voluntary contraction of the elbow extensors and 1-RM were similar between the two groups. In the CTR group, muscle CSA and strength gradually increased during the initial 6 weeks of training. However, the rate of increase in muscle CSA and 1-RM decreased gradually after that. In the PTR group, increase in muscle CSA and strength during the first 3-week detraining/6-week retraining cycle were similar to that in the CTR group during the corresponding period. However, increase in muscle CSA and strength during the second 3-week detraining/6-week retraining cycle were significantly higher in the PTR group than in the CTR group. Thus, overall improvements in muscle CSA and strength were similar between the groups. The results indicate that 3-week detraining/6-week retraining cycles result in muscle hypertrophy similar to that occurring with continuous resistance training after 24 weeks.     

Atrial natriuretic factor during exercise in male endurance athletes: effect of training

Nine male endurance runners were evaluated with bicycle exercise testing before a training break of 3 weeks duration, and 0, 2 and 4 weeks after resumption of training to assess the effects of training on resting and exercise plasma atrial natriuretic factor (ANF) measured at 50% and 100% of predetermined maximal workload. Maximal oxygen uptake and lean body mass (LBM) were calculated at each time point. Maximal oxygen uptake decreased during training break, but rose 4 weeks after resumption of training (P less than 0.01). LBM was unchanged after inactivity, but rose after resumption of training (P less than 0.01). Plasma ANF at rest did not change throughout the experiment. ANF levels rose after training break at maximal workload (P less than 0.05), and decreased 4 weeks after resumption of training, but only at submaximal workload (P less than 0.05). No correlations between systolic blood pressure, mean blood pressure or heart rate and ANF could be demonstrated. These results indicate that the haemodynamic changes associated with endurance training are reflected in plasma ANF levels during exercise, but not at rest. The full adaptation of ANF release to training probably requires more time than the 4 weeks reported for the haemodynamic adjustments.     

Enhanced heat loss responses induced by short-term endurance training in exercising women

We investigated the effects of short-term endurance training and detraining on sweating and cutaneous vasodilatation during exercise in young women, taking into account changes in maximal oxygen uptake (VO2max) and the phase of the menstrual cycle. Eleven untrained women participated in endurance training; cycle exercise at approximately 60% VO2max for 60 min day(-1), 4-5 days week(-1) (30 degrees C, 45% relative humidity) for three complete menstrual cycles. The standard exercise test consisted of exercise at 50% VO2max for 30 min (25 degrees C, 45% relative humidity), and was conducted before training (Pre), during training sessions (T1, T2 and T3) and after cessation of training (D1 and D2). Values of VO2max increased significantly from 32.7 +/- 1.2 to 37.8 +/- 1.2 ml min(-1) kg(-1) at the end of the training. Local sweat rate in the chest and thigh, but not in the back and forearm, were significantly greater during T1 and T2 only in women who started training from the midfollicular phase. Cutaneous blood flow did not change with training. The threshold oesophageal temperatures for heat loss responses were significantly decreased during T1 versus Pre (averaged values for each body site: sweating, 37.49 +/- 0.08 versus 37.22 +/- 0.12 degrees C; and cutaneous vasodilatation, 37.40 +/- 0.07 versus 37.17 +/- 0.10 degrees C) and maintained through T3; the sensitivities of heat loss responses were not altered. These changes returned to the Pre level by D1. Our data indicate that physical training improves heat loss responses by decreasing the threshold temperatures and that these effects occur within a month of training and disappear within a month after cessation of training. The degree of increase in sweating with training differs among body sites and might be affected by the phase of the menstrual cycle.     

Skeletal muscle fiber area alterations in two opposing modes of resistance-exercise training in the same individual

Summary The purpose of this study was to observe fiber area changes that might occur in the same subject from two opposing resistance-exercise training regimes isolating the quadriceps muscle group. Twelve college-age men divided into two groups participated in each of two 7.5-week regimens; one performed a muscular strength program (high-resistance, low-repetition) 4 days a week on a resistance-exercise apparatus, while the other performed a muscular endurance (low-resistance, high-repetition) program. After a 5.5-week hiatus, the groups changed regimens for the second 7.5 weeks. Closed-needle biopsies of the dominant vastus lateralis and isokinetic dynamometer evaluations were made before and at the end of each training period. The muscle samples were analyzed for area changes. In both groups the initial exercise stimulus, whether for strength or endurance, increased the area of fibers of all three major types (I, IIA, and IIB). Subjects doing strength exercises as their second treatment showed a further increase in the area of type I and IIB fibers, whereas those doing endurance exercises showed a decrease in all fiber types. From the first to the last biopsy all fiber areas were decreased (P<0.05) in the control-strength-endurance group and increased (P<0.05) in the control-endurance-strength group. These results suggested that endurance exercise preceding strength exercise in an isolated muscle group maximized fiber area adaptations to exercise stress. Consideration should thus be given in exercise and rehabilitation programs to the muscle cellular adaptations evidenced in different orders of training, particularly if muscular strength is considered important.     

Effects of fatigue and sprint training on electromechanical delay of knee extensor muscles

Electromechanical delay (EMD) of knee extensors in isometric contraction was investigated in six healthy men before and after four periods of 30-s all-out sprint cycling exercise, conducted pre and post a 7-week sprint cycling training programme. The EMD was lengthened from 40.4 (SEM 3.46) ms at rest to 63.4 (SEM 7.80) ms after the fatiguing exercise (P 0.05) in the pre-training test. During maximal voluntary contractions (MVC) conducted after the fatiguing exercise, the peak contraction force (F _peak) and peak rate of force development (RFD_peak) were reduced by 51%–56% and 38%–50%, respectively (both P 0.05). The mechanisms of EMD lengthening during fatigue could have been due to the deterioration in muscle conductive, contractile or elastic properties and require further study. The training programme increased the total work performed during the four periods of sprint exercise (P 0.05). However, no significant training effects were found in the resting or postexercise EMD, F _peak and RFD_peak during isometric MVC. These unchanged isometric contraction variables but enhanced dynamic performance suggest that isometric tests of muscle are insensitive to the neuromuscular adaptations to sprint training.