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

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

Leptin reduction after endurance races differing in duration and energy expenditure

Serum leptin concentrations are reduced in the presence of a negative energy balance. It has been demonstrated, however, that strenuous and prolonged exercise, which induces a marked negative energy balance, is not always followed by a reduction in serum leptin levels. We therefore analysed serum leptin concentrations before and after three endurance races, which differed in duration and energy expenditure (EE), with the aim of clarifying the relationship between the level of EE and the reduction in leptin levels. Forty-five males participated in one of three competitive endurance races, a half-marathon run [21.097 km, estimated EE 1,400 kcal (5,852 kJ)], a ski-alpinism race [about 45 km, estimated EE 5,000 kcal (20,900 kJ)], and an ultramarathon race [100 km, estimated EE 7,000 kcal (29,269 kJ)]. Blood samples for analysis of serum leptin, and plasma free fatty acids (FFA) were collected before and after the races. Pre-race leptin values were significantly correlated with both body mass index and body fat mass (r=0.672 and r=0.699, respectively; P<0.0001). After exercise, serum leptin levels decreased significantly in the ultramarathon [from 4.15 (0.63) μg/l to 1.01 (0.15) μg/l; P<0.001] and in the ski-alpinism race [from 1.10 (0.28) μg/l to 0.62 (0.15) μg/l; P<0.01], but not in the half-marathon [from 1.38 (0.40) μg/l to 1.20 (0.36) μg/l]. Plasma FFA were found to have significantly increased in all three of the races, showing a negative correlation with the percent reduction in leptin (r=0.369, P<0.02). Our data indicate that only a prolonged endurance exercise involving a high EE can induce a marked reduction in circulating serum leptin levels. Electronic Publication     

Dynamics of changes in the cardiovascular response to submaximal exercise during low-intensity endurance training with particular reference to the systolic time intervals

Summary Eighteen male volunteers (aged 20–23 years), not involved in any sporting activities, were submitted to 13 weeks of training consisting of 30 min exercise [at 50%–75% maximal oxygen intake on a cycle ergometer, performed 3 times a week. Every 4 weeks cardiac function was evaluated by measuring the systolic time intervals at rest and during submaximal cycle exercise. Stroke volume (SV), heart rate (HR) and blood pressure (BP) responses to submaximal exercise, and anaerobic threshold (AT) were also determined. Significant increases in , increases in AT and SV at the submaximal exercise intensities, as well as decreases in HR and BP were found after 4 weeks of training. Resting systolic time intervals were not affected by training, but during the submaximal cycle exercise the values of the pre-ejection period (PEP) and isovolumic contraction time (ICT) corresponding to HR of 100 beats·min⁻¹ were significantly lowered after 13 weeks of training, whereas PEP, ICT and total electromechanical systole corresponding to HR of 130 beats·min⁻¹ were significantly shortened by the 4th week. The ratios of PEP:LVET (left ventricular ejection time) and ICT:LVET during submaximal exercise were significantly lowered by training starting from the 8th week. These changes might be interpreted as evidence of the training-induced enhancement of the “contractility reserve”, i.e. the ability to increase heart muscle contractility with increasing exercise intensity.     

Respiratory muscle endurance training in humans increases cycling endurance without affecting blood gas concentrations

Isolated respiratory muscle endurance training (RMT) can prolong constant-intensity cycling performance. We tested whether RMT affects O₂ supply during exercise, i.e. whether the partial pressure of oxygen in arterial blood (P _aO₂) and/or its oxygen saturation (S _aO₂) are higher during exercise after RMT than before. A group of 28 sedentary subjects were randomly assigned to either an RMT (n=13) or a control group (n=15). The RMT consisted of 40×30 min sessions of normocapnic hyperpnoea. The control group did not perform any training. Breathing and cycling endurance time as well as P _aO₂ and S _aO₂ during cycling at a constant intensity of 70% maximum power output were measured before and after the RMT or the control period. Mean breathing endurance increased significantly after RMT compared to control [RMT 5.2 (SD 2.9) vs 38.1 (SD 6.8) min, control 6.5 (SD 5.7) vs 6.4 (SD 7.6) min; P<0.01], as did mean cycling endurance [RMT 35.6 (SD 11.9) vs 44.0 (SD 17.2) min, control 32.8 (SD 11.6) vs 31.4 (SD 14.4) min; P<0.05]. The RMT did not affect P _aO₂ which ranged from 11.6 to 12.3 kPa (87–92 mmHg), and S _aO₂ which ranged from 96% to 98% throughout all tests. In conclusion, RMT substantially increased breathing and cycling endurance in sedentary subjects. These changes, however, cannot be attributed to increased O₂ supply, as neither P _aO₂ nor S _aO₂ were increased during exercise after RMT. Electronic Publication     

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

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

Transfer effects in endurance exercise

Summary The effects of 8 weeks of bicycle endurance training (5 x /week for 30 min) on maximal oxygen uptake capacity ( ) during arm and leg ergometry, and on the ultrastructure of an untrained arm muscle (m. deltoideus), and a trained leg muscle (m. vastus lateralis) were studied. With the training, leg- for bicycling increased by +13%, while the capillary per fiber ratio and the volume density of mitochondria in m. vastus lateralis increased by +15% and +40%, respectively. In contrast, the untrained m. deltoideus showed an unchanged capillary per fiber ratio and a decreased mitochondrial volume density (−17%). Despite this decrease of mitochondrial volume arm- increased by +9%. It seems unlikely that the observed discrepancy can be explained by cardiovascular adaptations, since arm cranking did not fully tax the cardiovascular system (arm- /leg- : 0.74 and 0.71 before and after training, respectively). Thus neither cardiovascular adaptations nor local structural changes in the untrained muscles could explain the increased arm- . However, the enhanced capacity for lactate clearance after endurance training could be sufficient to account for the larger during arm cranking. We propose that an increased net oxidation of lactate might be responsible for the increased arm- found after bicycle endurance training. This work was supported by grant 3.128.81 from the Swiss National Science Foundation, and by Cilo S.A., Bicycles, Romanel/Switzerland     

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

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

Atrial natriuretic peptide response to endurance physical training in the rat

Summary The effect of an endurance physical training programme on the plasma and atrial natriuretic peptides (ANP) and on renal glomerular ANP receptors was evaluated in male normotensive Wistar rats. Maximal O₂ uptake was significantly greater in the endurance trained (117.1 Ml O₂ · kg^–1 · min^–1, SEM 6.18 versus the control rats 84.2 ml O₂ · kg^–1 · min^–1, SEM 4.88, P<0.01. In addition, various muscle oxidative enzymes were also significantly higher in endurance trained animals. An increase in resting plasma [ANP] was observed after 11 weeks of physical training (40.02 pg · ml^–1, SEM 7.07 vs 22.8 pg.ml^–1, SEM 3.83, P<0.05). Glomerular ANP receptor density was lower in trained rats (272 fmol · mg^–1 protein, SEM 3.1 vs 380 fmol · mg^–1 protein, SEM 6.1, P < 0.05), whereas atrial tissue [ANP] was not significantly different between controls and trained animals. However, in trained rats, circulating [ANP] was closely correlated with left atrial [ANP] (r = –0.92, P<0.05). Resting systolic blood pressure had not changed at the end of this physical training programme. It is considered that under physiological conditions ANP may be involved in long-term extracellular fluid volume homeostasis through the regulation of renal glomerular ANP receptors, and that the left atrium might play a significant role in this long term fluid volume control.     

The effect of endurance training on the ventilatory response to exercise in elite cyclists

The purpose of this study was to investigate the effects of endurance training on the ventilatory response to acute incremental exercise in elite cyclists. Fifteen male elite cyclists [mean (SD) age 24.3 (3.3) years, height 179 (6) cm, body mass 71.1 (7.6) kg, maximal oxygen consumption (V˙O_2max) 69 (7) ml · min⁻¹ · kg⁻¹] underwent two exercise tests on a cycle ergometer. The first test was assessed in December, 6 weeks before the beginning of the cycling season. The second test was performed in June, in the middle of the season. During this period the subjects were expected to be in a highly endurance-trained state. The ventilatory response was assessed during an incremental exercise test (20 W · min⁻¹). Oxygen consumption (V˙O₂), carbon dioxide production (V˙CO₂), minute ventilation (V˙ _E), and heart rate (HR) were assessed at the following points during the test: at workloads of 200 W, 250 W, 300 W, 350 W, 400 W and at the subject's maximal workload, at a respiratory exchange ratio (R) of 1, and at the ventilatory threshold (Th_vent) determined using the V-slope-method. Post-training, the mean (SD) V˙O_2max was increased from the pre-training level of 69 (7) ml · min⁻¹ · kg⁻¹ (range 61.4–78.6) to 78 (6) ml · min⁻¹ · kg⁻¹ (range 70.5–86.3). The mean post-training V˙O₂ was significantly higher than the pre training value (P < 0.01) at all work rates, at Th_vent and at R=1. V˙O₂ was also higher at all work rates except for 200 W and 250 W. V˙ _E was significantly higher at Th_vent and R=1. Training had no effect on HR at all workloads examined. An explanation for the higher V˙O₂ cost for the same work rate may be that in the endurance-trained state, the adaptation to an exercise stimulus with higher intensity is faster than for the less-trained state. Another explanation may be that at the same work rate, in the less-endurance-trained state power is generated using a significantly higher anaerobic input. The results of this study suggest the following practical recommendations for training management in elite cyclists: (1) the V˙O₂ for a subject at the same work rate may be an indicator of the endurance-trained state (i.e., the higher the V˙O₂, the higher the endurance-trained capacity), and (2) the need for multiple exercise tests for determining the HR at Th_vent during a cycling season is doubtful since at Th_vent this parameter does not differ much following endurance training. Accepted: 19 October 1999     

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

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

Comparison of incremental and steady state tests of endurance training

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

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

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

The response of runners to arduous triathlon competition

Summary As very few of the competitors in a triathlon are truly specialist in more than one of the three disciplines, high levels of physical (and mental) stress may result during the course of the event. We investigated some of the physiological responses occurring in runners participating in an Iron Man triathlon consisting of canoeing (20 km), cycling (90 km) and running (42 km), in that sequence.Twenty-one male entrants volunteered as subjects for the study. Prior to the competition, maximal oxygen consumption ( ) was determined. Basal venous blood samples were collected on the day prior to the competition and post-exercise venous blood samples were collected within 5 minutes of completion of the race.Serum iron was significantly reduced from a mean basal value of 20.6 mol · l^–1 to a mean value of 8.4 mol · l^–1 after the race. Cortisol levels showed a 3 fold increase after the race. Gross (l · min^–1) and mass standardised (ml · min^–1 · kg^–1) were both negatively correlated to cortisol levels after the race (p<0.05). Total performance time was not related to gross (l · min^–1) but was well correlated to mass corrected (ml · min^–1 · kg^–1).The marked fall in serum iron may have been related to heavy sweating or prelatent iron deficiency. Chronic iron deficiency (without frank anaemia) can impair physical performance, although we were unable to show any significant correlation between serum iron level after the race and time taken to complete the event. The subjects with a lower (ml · min^–1 · kg^–1) had a higher cortisol concentration. In spite of a longer performance time, these subjects were apparently still exposed to greater physiological strain.     

耐力运动对青年与老年小鼠股骨组织微结构变化的影响

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

Sex differences in endurance capacity and metabolic response to prolonged,heavy exercise

Summary In order to test for possible sex differences in endurance capacity, groups of young, physically active women (n=6) and men (n=7) performed bicycle ergometer exercise at 80% and 90% of their maximal oxygen uptakes ( ). The groups were matched for age and physical activity habits. At 80% the women performed significantly longer (P<0.05), 53.8±12.7 min vs 36.8±12.2 min, respectively (means ± SD). Mid-exercise and terminal respiratory exchange ratio (R) values were significantly lower in women, suggesting a later occurrence of muscle glycogen depletion as a factor in their enhanced endurance. At 90% the endurance times were similar for men and women, 21.2±10.3 min and 22.0±5.0 min, respectively. The blood lactate levels reached in these experiments were only marginally lower (mean differences 1.5 to 2 mmol·l^–1) than those obtained at , suggesting high lactate levels as a factor in exhaustion. The changes in body weight during the 80% experiments and the degree of hemoconcentration were not significantly different between men and women.     

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

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

Respiratory muscle training increases cycling endurance without affecting cardiovascular responses to exercise

We tested whether the increased cycling endurance observed after respiratory muscle training (RMT) in healthy sedentary humans was associated with a training-induced increase in cardiac stroke volume (SV) during exercise, similar to the known effect of endurance training. Thirteen subjects underwent RMT by normocapnic hyperpnea, nine underwent aerobic endurance training (cycling and/or running) and fifteen served as non-training controls. Training comprised 40 sessions performed within 15 weeks, where each session lasted 30 min. RMT increased cycling endurance at 70% maximal aerobic power ( ) by 24% [mean (SD) 35.6 (11.9) min vs 44.2 (17.6) min, P<0.05], but SV at 60% was unchanged [94 (21) ml vs 93 (20) ml]. Aerobic endurance training increased both SV [89 (24) ml vs 104 (32) ml, P<0.01] and cycling endurance [37.4 (12.8) min vs 52.6 (16.9) min, P<0.01]. In the control group, no changes were observed in any of these variables. It is concluded that the increased cycling endurance that is observed after RMT is not due to cardiovascular adaptations, and that the results provide evidence for the role of the respiratory system as an exercise-limitingfactor. Electronic Publication     

The significance of the aerobic-anaerobic transition for the determination of work load intensities during endurance training

Summary Anaerobic and aerobic-anaerobic threshold (4 mmol/l lactate), as well as maximal capacity, were determined in seven cross country skiers of national level. All of them ran in a treadmill exercise for at least 30 min at constant heart rates as well as at constant running speed, both as previously determined for the aerobic-anaerobic threshold. During the exercise performed with a constant speed, lactate concentration initially rose to values of nearly 4 mmol/l and then remained essentially constant during the rest of the exercise. Heart rate displayed a slight but permanent increase and was on the average above 170 beats/min. A new arrangement of concepts for the anaerobic and aerobic-anaerobic threshold (as derived from energy metabolism) is suggested, that will make possible the determination of optimal work load intensities during endurance training by regulating heart rate.With support of Bundesinstitut für Sportwissenschaft, Köln-Lövenich