Intermittent hypoxic training: fact and fancy

Intermittent hypoxic training (IHT) refers to the discontinuous use of normobaric or hypobaric hypoxia, in an attempt to reproduce some of the key features of altitude acclimatization, with the ultimate goal to improve sea-level athletic performance. In general, IHT can be divided into two different strategies: (1) providing hypoxia at rest with the primary goal being to stimulate altitude acclimatization or (2) providing hypoxia during exercise, with the primary goal being to enhance the training stimulus. Each approach has many different possible application strategies, with the essential variable among them being the "dose" of hypoxia necessary to achieve the desired effect. One approach, called living high-training low, has been shown to improve sea-level endurance performance. This strategy combines altitude acclimatization (2500 m) with low altitude training to ensure high-quality training. The opposite strategy, living low-training high, has also been proposed by some investigators. The primacy of the altitude acclimatization effect in IHT is demonstrated by the following facts: (1) living high-training low clearly improves performance in athletes of all abilities, (2) the mechanism of this improvement is primarily an increase in erythropoietin, leading to increased red cell mass, V(O2max), and running performance, and (3) rather than intensifying the training stimulus, training at altitude or under hypoxia leads to the opposite effect - reduced speeds, reduced power output, reduced oxygen flux - and therefore is not likely to provide any advantage for a well-trained athlete.     

Erythropoiesis and performance after two weeks of living high and training low in well trained triathletes

The purpose of our study was to evaluate hematologic acclimatization during 2 weeks of intensive normoxic training with regeneration at moderate altitude (living high-training low, LHTL) and its effects on sea-level performance in well trained athletes compared to another group of equally trained athletes under control conditions (living low - training low, CONTROL). Twenty-one triathletes were ascribed either to LHTL (n = 11; age: 23.0 +/- 4.3 yrs; VO 2 max: 62.5 +/- 9.7 [ml x min -1 x kg -1]) living at 1956 m of altitude or to CONTROL (n = 10; age: 18.7 +/- 5.6 yrs; VO 2 max: 60.5 +/- 6.7 ml x min -1 x kg -1) living at 800 m. Both groups performed an equal training schedule at 800 m. VO 2 max, endurance performance, erythropoietin in serum, hemoglobin mass (Hb tot, CO-rebreathing method) and hematological quantities were measured. A tendency to improved performance in LHTL after the camp was not significant (p < 0.07). Erythropoietin concentration increased temporarily in LHTL (Delta 14.3 +/- 8.7 mU x ml -1; p < 0.012). Hb tot remained unchanged in LHTL whereas was slightly decreased from 12.5 +/- 1.3 to 11.9 +/- 1.3g x kg -1 in CONTROL (p < 0.01). As the reticulocyte number tended to higher values in LHTL than in CONTROL, it seems that a moderate stimulation of erythropoiesis during regeneration at altitude served as a compensation for an exercise-induced destruction of red cells.     

Plasma nitrite/nitrate and erythropoietin levels in cross-country skiers during altitude training

BACKGROUND: The aim of this study was to evaluate the effects of training at altitude on plasma nitrite/nitrate and erythropoietin levels since previously it has been reported an interaction of the NO/cGMP system in erythropoietin production. METHODS: Nine physically trained cross-country male skiers, usually living at 800-1200 m altitude, underwent 6 days of intensive training at a moderate altitude of 3100 m preceeded by 2 days of acclimatisation. Six team-managers, selected as controls, did not undergo any regular physical activity in the last 5 years and during the altitude period. Haematological parameters, erythropoietin and nitrite/nitrate were measured prior to reach the place at altitude, at the end of the period at moderate altitude and 7 days after returning at home. RESULTS: Haematocrit significantly increased in controls after 8 days at altitude. Erythropoietin levels significantly increased after the intensive altitude training only in trained subjects (13.1+/-1.7 vs 6.7+/-1.7 mU x ml-1, p<0.001). Nitrite/nitrate baseline values were significantly higher in trained subjects compared to untrained (49.9+/-17.9 vs 25.4+/-2.8 micromol x l(-1), p<0.01); the altitude period significantly increased nitrite/nitrate levels, in untrained subjects, to the same values observed in trained subjects under control conditions (47.0+/-10.3 micromol x l(-1)). CONCLUSIONS: In our experimental conditions we demonstrated the influence of hypoxia on Epo levels in athletes sustaining a short-term training and the role of a regular physical activity (partly independent from altitude hypoxia) on NO production.     

不同负荷低氧训练对大鼠腓肠肌HIF-1α基因表达的影响

目的:探讨不同负荷低氧训练对大鼠腓肠肌HIF-1α基因表达的影响。方法:选用6周龄雄性SD大鼠90只,经2周适应性训练后,筛选出60只,随机分为6组,每组10只:恒定负荷低住低练组(S-LoLo)、恒定负荷高住高练组(S-HiHi)、恒定负荷高住低练组(S-HiLo)和递增负荷低住低练组(P-LoLo)、递增负荷高住高练组(P-HiHi)、递增负荷高住低练组(P-HiLo)。采用水平动物跑台进行耐力训练。恒定负荷常氧训练强度为35m/min,恒定负荷低氧训练强度为30m/min。递增负荷常氧训练以35m/min训练1周后,在第2周内分2次递增负荷强度到39m/min,然后以此强度进行训练。递增负荷低氧训练以30m/min训练1周后,在第2周内分2次递增负荷强度到34m/min,然后以此强度进行训练,持续4周,每周训练5 d。各组均在4周末最后一次训练结束恢复24h后取材。采用实时荧光定量PCR(RQ-PCR)技术检测腓肠肌HIF-1αmRNA水平。结果:S-HiLo组大鼠腓肠肌HIF-1αmRNA表达显著高于S-LoLo组和S-HiHi组(P<0.05,P<0.05);P-HiLo组大鼠腓肠肌HIF-1αmRNA显著低于S-HiLo组(P<0.05),P-HiHi组较S-HiHi组有所增加(+24%,P>0.05)。结论:恒定负荷高住低练比递增负荷高住低练更能促进大鼠腓肠肌HIF-1αmRNA表达;与恒定负荷高住高练相比,递增负荷高住高练对大鼠腓肠肌HIF-1αmRNA表达有一定的促进作用。     

Serum erythropoietin in cross-country skiers

Serum erythropoietin concentration and hemoglobin concentration were determined during the winter season in 41 male and 31 female well-trained, cross-country skiers. The athletes both lived and trained at low altitude (below 300 m above sea level). No significant differences in serum erythropoietin concentration were seen between male skiers (13.6 +/- 5.0 mU.ml-1), female skiers, (14.9 +/- 5.6 mU.ml-1), and normal controls (12.6 +/- 3.9 mU.ml-1) (mean +/- SD). In 18 of the skiers (12 males and 6 females), a second sample was taken after 2.3 +/- 0.18 months. No significant difference in either serum erythropoietin concentration or hemoglobin concentration was detected between the two samples in this combined group of skiers. The present study indicates that normal serum erythropoietin concentration is to be expected during the winter season at sea level in cross-country skiers living and training at low altitude.     

Athlete's heart in postmenopausal former elite endurance female athletes.

OBJECTIVE: To investigate cardiac structure and function and exercise capacity in senior former elite athlete women. DESIGN: Cross-sectional study. PARTICIPANTS: Twenty postmenopausal former elite endurance athletes and 19 age-matched sedentary controls. METHODS: All subjects underwent transthoracic Doppler echocardiography and maximal exercise test on a bicycle ergometer. MAIN OUTCOME MEASURES: Cardiac chamber dimensions, wall thickness, cardiac function, and exercise capacity. RESULTS: The athletes had a greater exercise capacity (183 +/- 26 vs. 144 +/- 36 W; P < 0.01) compared with controls. Three of 20 (15%) athletes and 9 of 19 (47%) controls exhibited ST depressions during exercise test (P < 0.05). Echocardiographic measurements demonstrated larger left ventricular diameter (2.9 +/- 0.3 vs. 2.6 +/- 0.2 cm/m; P < 0.01), left ventricular volume (64 +/- 14 vs. 54 +/- 8 mL/m; P < 0.05), right ventricular diameter (1.6 +/- 0.2 vs. 1.4 +/- 0.2 cm/m; P < 0.01), left atrial volume (20.8 +/- 6 vs. 16.6 +/- 3.6 mL/m; P < 0.05), and stroke volume (45 +/- 10 vs. 36 +/- 5 mL/m; P < 0.01) in athletes than controls, whereas interventricular septum (9.3 +/- 1.7 vs. 10.1 +/- 1.8 mm; P > 0.05) and posterior wall thickness (9.0 +/- 1.6 vs. 9.2 +/- 1.0 mm; P > 0.05) did not differ between the groups. CONCLUSIONS: This study demonstrates cardiac enlargement without increased wall thickness in postmenopausal former elite endurance athlete women. Our results also indicate that long-term training maintains a high level of cardiovascular fitness in the aging female athletes.     

Altitude negates the benefits of aerobic training on the vascular adaptations in rats

INTRODUCTION: This study questioned the effect of living and training at moderate altitude on aortic vasoreactivity. Considering that chronic hypoxia exposure and endurance training are able to generate opposite effects on the systemic vascular reactivity, it was hypothesized that endurance training benefits on the vascular function could be limited by chronic hypoxia. METHODS: Sea-level native rats were randomly assigned to N (living in normoxia), NT (living and training 5 d.wk for 5 wk in normoxia), CH (living in hypoxia, 2800 m), and CHT (living and training 5 d.wk for 5 wk in hypoxia, 2800 m) groups. Concentration response curves to epinephrine, norepinephrine, endothelin-1, acetylcholine, and sodium nitro-prusside were assessed on aortic isolated rings. Left ventricular resting and maximal (during Tyrode's infusion) stroke volumes were evaluated by Doppler-echocardiography and used as indexes of chronic aortic volume overload. RESULTS: The main finding was that favorable aortic vasoreactivity adaptations consecutive to sea-level training were not observed when training was conducted at altitude. An improvement in the endothelium-dependent vasorelaxation (maximal relaxation, R(max), N = 60.4 +/- 10.0 vs NT = 91.7 +/- 3.2%; P < 0.05) and a reduced sensitivity to ET-1 were observed in NT rats. Such an enhancement in endothelium-dependent vasorelaxation was not found in CHT rats (R(max): 48.4 +/- 7.8%). Moreover, a higher sensitivity to ET-1 was reported in this group. Altitude-induced limitation in aortic blood flow and shear stress could play a major role in the explanation of these specific altitude-training adaptations. CONCLUSION: If extrapolated to the peripheral vascular bed, our results have practical significance for aerobic performance as aortic vasoreactivity adaptations after altitude training could contribute to limit blood delivery to exercising muscles.     

Degree of arterial desaturation in normoxia influences VO2max decline in mild hypoxia.

PURPOSE: Elite endurance athletes display varying degrees of pulmonary gas exchange limitations during maximal normoxic exercise and many demonstrate reduced arterial O2 saturations (SaO2) at VO2max--a condition referred to as exercise induced arterial hypoxemia (EIH). We asked whether mild hypoxia would cause significant declines in SaO2 and VO2max in EIH athletes while non-EIH athletes would be unaffected. METHODS: Nineteen highly trained males were divided into EIH (N = 8) or Non-EIH (N = 6) groups based on SaO2 at VO2max (EIH <90%, Non-EIH >92%). Athletes with intermediate SaO2 values (N = 5) were only included in correlational analyses. Two randomized incremental treadmill tests to exhaustion were completed--one in normoxia, one in mild hypoxia (FIO2 = 0.187; approximately 1,000 m). RESULTS: EIH subjects demonstrated a significant decline in VO2max from normoxia to mild hypoxia (71.1+/-5.3 vs. 68.1+/-5.0 mL x kg(-1) min(-1), P<0.01), whereas the non-EIH group did not show a significant deltaVO2max (67.2+/-7.6 vs. 66.2+/-8.4 mL x kg(-1) x min(-1)). For all 19 athletes, SaO2 during maximal exercise in normoxia correlated with the change in VO2max from normoxia to mild hypoxia (r = -0.54, P<0.05). However, the change in SaO2 and arterial O2 content from normoxia to mild hypoxia was equal for both EIH and Non-EIH (deltaSaO2 = 5.2% for both groups), bringing into question the mechanism by which changes in SaO2 affect VO2max in mild hypoxia. CONCLUSIONS: We conclude that athletes who display reduced measures of SaO2 during maximal exercise in normoxia are more susceptible to declines in VO2max in mild hypoxia compared with normoxemic athletes.     

Individual variation in the erythropoietic response to altitude training in elite junior swimmers

Objectives: Inter-individual variations in sea level performance after altitude training have been attributed, at least in part, to an inter-individual variability in hypoxia induced erythropoiesis. The aim of the present study was to examine whether the variability in the increase in total haemoglobin mass after training at moderate altitude could be predicted by the erythropoietin response after 4 h exposure to normobaric hypoxia at an ambient Po₂ corresponding to the training altitude.

Methods: Erythropoietin levels were measured in 16 elite junior swimmers before and after 4 h exposure to normobaric hypoxia (Fio₂ 0.15, ~2500 m) as well as repeatedly during 3 week altitude training (2100–2300 m). Before and after the altitude training, total haemoglobin mass (CO rebreathing) and performance in a stepwise increasing swimming test were determined.

Results: The erythropoietin increase (10–185%) after 4 h exposure to normobaric hypoxia showed considerable inter-individual variation and was significantly (p<0.001) correlated with the acute erythropoietin increase during altitude training but not with the change in total haemoglobin mass (significant increase of ~6% on average). The change in sea level performance after altitude training was not related to the change in total haemoglobin mass.

Conclusions: The results of the present prospective study confirmed the wide inter-individual variability in erythropoietic response to altitude training in elite athletes. However, their erythropoietin response to acute altitude exposure might not identify those athletes who respond to altitude training with an increase in total haemoglobin mass.

     

Training and performance characteristics among Norwegian international rowers 1970-2001

This study quantified changes in training volume, organization, and physical capacity among Norwegian rowers winning international medals between 1970 and 2001. Twenty-eight athletes were identified (27 alive). Results of physiological testing and performance history were available for all athletes. Twenty-one of 27 athletes responded to a detailed questionnaire regarding their training during their internationally competitive years. Maximal oxygen uptake (VO2 max) increased 12% (6.5+/- 0.4 vs. 5.8+/-0.2 L min(-1)) from the 1970s to the 1990s. Similarly, 6-min ergometer rowing performance increased almost 10%. Three major changes in training characteristics were identified: (1) training at a low blood lactate (< 2 mM) increased from 30 to 50 h month(-1) and race pace and supra-maximal intensity training (approximately 8-14 mM lactate) decreased from 23 to approximately 7 h month(-1); (2) training volume increased by approximately 20%, from 924 to 1128 h yr(-1); (3) altitude training was used as a pre-competition peaking strategy, but it is now integrated into the winter preparation program as periodic 2-3-week altitude camps. The training organization trends are consistent with data collected on athletes from other sports, suggesting a "polarized" pattern of training organization where a high volume of low intensity training is balanced against regular application of training bouts utilizing 90%-95% of VO2 max.     

Arterial oxygen saturation and hemoglobin mass in postmenopausal untrained and trained altitude residents

Because of lacking ventilatory stimulation by sex hormones in postmenopausal women (PW), one might expect a lowered arterial oxygen saturation (S(O(2))) in hypoxia and therefore a stronger erythropoietic reaction than in young women (YW). Nine untrained (UTRPW) and 11 trained (TRPW) postmenopausal altitude residents (2600 m) were compared to 16 untrained (UTRYW) and 16 trained young women (TRYW) to check this hypothesis and to study the combined response to hypoxia and training. S(O(2)) was decreased in PW (89.2% +/- 2.2 vs. 93.6 +/- 0.7% in YW, p < 0.01). Hb mass, however, was similar in UT (UTRYW: 9.2 +/- 0.9 g/kg(1), UTRPW: 8.7 +/- 1.0 g/kg). But if body fat rise with age was excluded by relation to fat-free mass, Hb mass was increased in UTRPW (+1.2 g/kg, p < 0.05) compared to UTRYW. Training caused a similar rise of Hb mass in PW and YW (0.3 g/kg per mL/kg x min(1) rise in V(O(2peak))). There was no difference in erythropoietin among the groups. Ferritin was higher in PW than YW. The results show that female hormones and fitness level have to be considered in studies on erythropoiesis at altitude. The role of erythropoietin during chronic hypoxia still has to be clarified.     

高住高练和高住低练对大鼠血脂及腓肠肌脂肪酸氧化的影响

目的:从血脂和脂肪酸氧化的角度研究高住高练和高住低练对大鼠脂代谢的影响。方法:经适应性训练筛选30只雄性SD大鼠,采用双盲法分成低住低练组(LoLo)、高住高练组(HiHi)和高住低练组(HiLo)。采用水平动物跑台进行耐力训练,运动强度为常氧下35m/min、低氧下30m/min,1h/d,6d/周,持续训练4周。最后一次训练后恢复24h取血和腓肠肌。全自动生化分析仪检测血脂4项,ELISA法检测血清脂蛋白酯酶(LPL)、瘦素(Leptin)、脂联素(AD),荧光定量PCR测试腓肠肌PPARα和CPT-1 mRNA表达。结果:高住高练组大鼠血清TC和TG水平较低住低练组显著下降(P<0.05),LPL、AD水平显著升高(P<0.01);腓肠肌PPARαmRNA和CPT-1 mRNA表达均显著升高(P<0.05),其它指标无显著性差异。高住低练组大鼠血清HDL较低住低练组显著降低(P<0.05);腓肠肌CPT-1 mRNA相对表达量显著降低(P<0.01);其余指标无显著性变化。高住高练组大鼠血清HDL较高住低练组显著升高(P<0.05);LPL、AD水平和腓肠肌CPT-1 mRNA显著升高(P<0.01),其余指标无显著性差异。结论:(1)高住高练调节血脂变化的作用优于常氧训练,可能与提高血清LPL水平有关,高住高练较常氧训练更能促进腓肠肌脂肪酸氧化,可能与提高血清AD和腓肠肌PPARαmRNA、CPT-1 mRNA表达关系密切;(2)高住低练较常氧训练对血脂代谢无有利影响,对腓肠肌脂肪酸氧化起抑制作用;(3)高住高练对血清HDL影响优于高住低练,可能与提高血清LPL有关,高住高练较高住低练更能促进腓肠肌脂肪酸氧化,可能与提高血清AD和腓肠肌CPT-1mRNA表达关系密切。     

高住低练对大鼠心肌线粒体活性氧的影响

目的:探讨常压不同低氧(14.5%、12.6%氧含量)环境下(相当于模拟海拔3000m和4000m)高住低练对大鼠心肌线粒体活性氧(ROS)的影响,为运动与低氧适应的应用研究提供参考。方法:120只SD大鼠,随机分为12组,分别为低住安静组、低住低练组、急性高住安静组、急性高住运动组、急性高住低练组、高住安静组和高住低练组,5个高住组又分为常压14.5%氧含量和12.6%含氧量2个亚组。采用二氯荧光素双醋酸盐(DCFH-DA)荧光探针观察线粒体ROS的变化。结果:急性低氧应激后,大鼠心肌线粒体ROS呈上升趋势。与低住安静组相比,模拟海拔3000m和4000m急性高住安静组和急性高住运动组线粒体ROS均显著升高(P<0.05,P<0.01);与低住低练组相比,急性高住运动组均显著升高(P<0.01),模拟海拔4000m高住低练组显著升高(P<0.05);与急性高住运动组相比,模拟海拔3000m急性高住低练组和高住低练组均显著下降(P<0.05),可见模拟海拔3000m高住低练能使ROS生成减少。结果提示:心肌线粒体ROS可能参与低氧适应的形成和发展,高住低练有利于缺氧耐受性的形成。     

不同低氧训练模式对大鼠腓肠肌有氧代谢酶活性的影响

目的:探讨三种低氧训练模式对大鼠腓肠肌有氧代谢酶活性的影响。方法:经过适应性训练和力竭实验筛选出40只雄性SD大鼠,采用双盲法平均分成4组:低住低练组、高住高练组、高住低练组和低住高练组。采用水平动物跑台进行耐力训练,运动强度为常氧下35m/min、低氧下30m/min,1h/d,5d/周,持续训练6周。低住低练组大鼠在常氧环境下生活训练;高住高练组大鼠在低氧环境(氧浓度为13.6%,约相当于海拔3500m高度)生活训练;高住低练组大鼠低氧环境生活12h,常氧环境训练;低住高练组大鼠在常氧环境生活,低氧环境训练。最后一次训练后恢复48h取腓肠肌,检测柠檬酸合成酶(CS)、琥珀酸脱氢酶(SDH)和苹果酸脱氢酶(MDH)活性。结果:与低住低练组比较,高住高练组大鼠腓肠肌CS、SDH和MDH活性分别升高11.7%(P<0.01)、8.7%(P<0.05)和12.5%(P<0.01);高住低练组、低住高练组较低住低练组增加,但无统计学意义。结论:3500米三种低氧训练模式就提高机体有氧代谢酶活性而言,高住高练优于高住低练和低住高练。     

不同低氧训练模式对大鼠脑组织线粒体呼吸链酶复合体活性的影响

目的:探讨不同低氧训练模式对大鼠脑线粒体呼吸链功能的影响。方法:40只健康2月龄雄性Wistar大鼠随机均分为5组:常氧训练组(LoLo)、高住高练组(HiHi)、高住低训组(HiLo)、低住高练组(LoHi)和高住高练低训组(HiHiLo),每组8只。依实验方案,各组大鼠分别在常氧(模拟海拔1500m,大气压为632mmHg)或/和低氧(模拟海拔3500m,大气压为493mmHg)环境中居住及递增负荷训练5周,每周训练6天。最后一次训练后在常氧环境恢复72h,力竭运动后即刻取样。差速离心提取线粒体。分光光度法测定呼吸链酶复合体(CⅠ～CⅢ)活性。结果:4个低氧训练组大鼠脑组织线粒体呼吸链CⅠ活性与LoLo组相比均无显著性差异。LoHi组CⅡ活性显著下降(P<0.01),降低76.199%,其余各组无显著性差异。HiHi组、HiLo组和LoHi组CⅢ活性均显著下降(P<0.01),分别降低71.496%、65.240%和87.838%,HiHiLo组显著性上升(P<0.01),提高170.145%。结论:在模拟海拔3500m的4种低氧训练中,髙住高练低训提高大鼠脑组织线粒体呼吸链功能的作用优于髙住高练、高住低训和低住高练。     

A three-week traditional altitude training increases hemoglobin mass and red cell volume in elite biathlon athletes

It is well known that altitude training stimulates erythropoiesis, but only few data are available concerning the direct altitude effect on red blood cell volume (RCV) in world class endurance athletes during exposure to continued hypoxia. The purpose of this study was to evaluate the impact of three weeks of traditional altitude training at 2050 m on total hemoglobin mass (tHb), RCV and erythropoietic activity in highly-trained endurance athletes. Total hemoglobin mass, RCV, plasma volume (PV), and blood volume (BV) from 6 males and 4 females, all members of a world class biathlon team, were determined on days 1 and 20 during their stay at altitude as well as 16 days after returning to sea-level conditions (800 m, only males) by using the CO-rebreathing method. In males tHb (14.0 +/- 0.2 to 15.3 +/- 1.0 g/kg, p < 0.05) and RCV (38.9 +/- 1.5 to 43.5 +/- 3.9 ml/kg, p < 0.05) increased at altitude and returned to near sea-level values 16 days after descent. Similarly in females, tHb (13.0 +/- 1.0 to 14.2 +/- 1.3 g/kg, p < 0.05) and RCV (37.3 +/- 3.3 to 42.2 +/- 4.1 ml/kg, p < 0.05) increased. Compared to their sea-level values, the BV of male and female athletes showed a tendency to increase at the end of the altitude training period, whereas PV was not altered. In male athletes, plasma erythropoietin concentration increased up to day 4 at altitude (11.8 +/- 5.0 to 20.8 +/- 6.0 mU/ml, p < 0.05) and the plasma concentration of the soluble transferrin receptor was elevated by about 11 % during the second part of the altitude training period, both parameters indicating enhanced erythropoietic activity. In conclusion, we show for the first time that a three-week traditional altitude training increases erythropoietic activity even in world class endurance athletes leading to elevated tHb and RCV. Considering the relatively fast return of tHb and RCV to sea-level values after hypoxic exposure, our data suggest to precisely schedule training at altitude and competition at sea level.     

Effect of intense training on plasma leptin in male and female swimmers

PURPOSE: The purpose of this study was to determine whether fasting plasma leptin concentration was altered with an increase in training volume in competitive male and female athletes. METHODS: Intercollegiate male (N = 9) and female (N = 12) swimmers were examined during the preseason and at two times during the mid-season (mid-season 1 and mid-season 2) when training volume was relatively high (33,000 m.wk(-1)). Body composition (hydrostatic weighing), energy intake and expenditure, and fasting plasma leptin concentration were measured. RESULTS: In the women, there was a significant (P < 0.05) decline in fat mass (2 kg) with the increase in training volume, which was not accompanied by a reduction in fasting leptin (12.8 +/- 1.5 vs 11.0 +/- 1.2 vs 11.0 +/- 1.5 ng.mL(-1) for preseason, mid-season 1, and mid-season 2, respectively). In the men, there were no significant changes in body composition, body mass, or fasting leptin (4.4 +/- 0.8 vs 4.3 +/- 0.8 vs 4.6 +/- 0.8 ng.mL(-1), respectively). CONCLUSION: These findings suggest 1) plasma leptin is not sensitive to an increase in training volume and 2) leptin may not be indicative of changes in fat mass with an increase in training volume in female athletes. These data suggest that leptin may not be useful in monitoring relative training stress in athletes.