Wk Of High-intensity Interval Training Research Articles

Genotype-Phenotype Models Predicting V̇O 2max Response to High-Intensity Interval Training in Physically Inactive Chinese.

This study aimed to analyze the interindividual differences of the maximal oxygen uptake (V̇O 2max ) response to 12 wk of high-intensity interval training (HIIT), and the genotype-phenotype models were constructed to predict the effect of HIIT on V̇O 2max . A total of 228 physically inactive adults who completed a 12-wk HIIT were analyzed. A genome-wide association study (GWAS) was conducted to identify genetic variants associated with the V̇O 2max response. Nonresponders, responders, and the highest training responders were defined as the effect sizes (ES) <0.2, ≥0.2, and ≥0.8, respectively. We generated polygenic predictor score (PPS) using lead variants and constructed a predictive model for V̇O 2max response based on a linear stepwise regression analysis. The V̇O 2max increased significantly after HIIT (~14%, P < 0.001), but with interindividual differences (-7.8 to 17.9 mL·kg -1 ·min -1 ). In 27% of participants, the V̇O 2max showed no improvement. We identified one genetic locus near the γ-aminobutyric acid type A receptor subunit beta 3 gene ( GABRB3 , rs17116985) associated with V̇O 2max response at the genome-wide significance level ( P < 5 × 10 -8 ), and an additional nine single nucleotide polymorphisms (SNPs) at the suggestive significance level ( P < 1 × 10 -5 ). The SNPs rs474377, rs9365605, and rs17116985, respectively, explained 11%, 9%, and 6.2% of variance in V̇O 2max response. The 13 SNPs ( P < 1 × 10 -5 ) were found on chromosome 6 (position: 148209316-148223568). Individuals with a PPS greater than 1.757 had the highest response, and those with a PPS lower than -3.712 were nonresponders. The PPS, baseline V̇O 2max , sex, and body mass explained 56.4% of the variance in the V̇O 2max response; the major predictor was the PPS, which explained 39.4% of the variance. The PPS, baseline V̇O 2max , sex, and body mass could explain the variance in V̇O 2max response. Individuals who had a PPS greater than 1.757 had the highest training response after 12 wk of HIIT. Genetic variants in a region on chromosome 6, especially the sterile alpha motif domain containing 5 gene ( SAMD5 ), which had been explored influencing angiogenesis, might have a potential role in the V̇O 2max response.

Altered intramuscular network of lipid droplets and mitochondria in type 2 diabetes.

Excessive storage of lipid droplets (LDs) in skeletal muscles is a hallmark of type 2 diabetes. However, LD morphology displays a high degree of subcellular heterogeneity and varies between single muscle fibers, which impedes the current understanding of lipid-induced insulin resistance. Using quantitative transmission electron microscopy (TEM), we conducted a comprehensive single-fiber morphological analysis to investigate the intramuscular network of LDs and mitochondria, and the effects of 8 wk of high-intensity interval training (HIIT) targeting major muscle groups, in patients with type 2 diabetes and nondiabetic obese and lean controls. We found that excessive storage of intramuscular lipids in patients with type 2 diabetes was exclusively explained by extremely large LDs situated in distinct muscle fibers with a location-specific deficiency in subsarcolemmal mitochondria. After HIIT, this intramuscular deficiency was improved by a remodeling of LD size and subcellular distribution and mitochondrial content. Analysis of LD morphology further revealed that individual organelles were better described as ellipsoids than spheres. Moreover, physical contact between LD and mitochondrial membranes indicated a dysfunctional interplay between organelles in the diabetic state. Taken together, type 2 diabetes should be recognized as a metabolic disease with high cellular heterogeneity in intramuscular lipid storage, underlining the relevance of single-cell technologies in clinical research. Furthermore, HIIT changed intramuscular LD storage toward nondiabetic characteristics.

Time course of changes in V̇o2peak and O2 extraction during ramp cycle exercise following HIIT versus moderate-intensity continuous training in type 2 diabetes.

In the present study, we assessed the time course of adaptations in peak oxygen uptake (V̇o2peak) and muscle fractional oxygen (O2) extraction (using near-infrared spectroscopy) following 12 wk of low-volume high-intensity interval training (HIIT) versus moderate-intensity continuous endurance training (MICT) in adults with uncomplicated type 2 diabetes (T2D). Participants with T2D were randomly assigned to MICT (n = 12, 50 min of moderate-intensity cycling) or HIIT (n = 9, 10 × 1 min at ∼90% maximal heart rate) or to a nonexercising control group (n = 9). Exercising groups trained three times per week and measurements were taken every 3 wk. The rate of muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin concentration, Δ[HHb+Mb]) profiles of the vastus lateralis muscle were normalized to 100% of the response, plotted against % power output (PO), and fitted with a double linear regression model. V̇o2peak increased (P < 0.05) by week 3 of MICT (+17%) and HIIT (+8%), with no further significant changes thereafter. Total increases in V̇o2peak posttraining (P < 0.05) were 27% and 14%, respectively. The %Δ[HHb+Mb] versus %PO slope of the first linear segment (slope1) was reduced (P < 0.05) beyond 3 wk of HIIT and MICT, with no further significant changes thereafter. No changes in V̇o2peak or slope1 were observed in the control group. Low-volume HIIT and MICT induced improvements in V̇o2peak following a similar time course, and these improvements were likely, at least in part, due to an improved microvascular O2 delivery.

High-Intensity Training and Saffron: Effects on Breast Cancer-related Gene Expression.

Exercise training and some herbal components have an anticancer function and can suppress tumor growth. However, the role of these protective factors in altering breast cancer-related gene expression is still unknown. Thus, this study aimed to assess the effect of 4 wk of high-intensity interval training (HIIT) and saffron (Crocus sativus L.) aqueous extract (SAE) on Sirtuin-1 (SIRT1), human telomerase reverse transcriptase (hTERT), and p53 gene expression in female mice breast tumor tissue induced by 4T1 cell line. This study was performed on female BALB/c mice. The 4T1 breast cancer cells were subcutaneously implanted, and mice were randomly sorted into the following groups: control, HIIT, SAE, HIIT + SAE (n = 10 mice per group), and sham (n = 4 mice per group). Mice were sacrificed at the end of the intervention period, and the expression of SIRT-1, hTERT, and p53 was determined by real-time polymerase chain reaction. The mRNA level of SIRT1 was increased in the HIIT + SAE group compared with the HIIT and control groups (P = 0.007 and P = 0.03, respectively). Moreover, the amount of mRNA of p53 was increased after a 4-wk HIIT compared with the control and HIIT + SAE groups in tumor tissue (P = 0.03 and P = 0.02, respectively). No change was found in the mRNA expression of hTERT between groups (P = 0.92). These findings suggest that HIIT may reduce tumor burden through the upregulation of p53 associated with tumor suppression pathway. In contrast, the combination of HIIT and SAE did not alter p53 and SIRT1 expression levels and may suppress tumor growth by other mechanisms.

Effects of using high-intensity interval training and calorie restriction in different orders on metabolic syndrome: A randomized controlled trial.

Studies of the effectiveness of high-intensity interval training (HIIT) combined with calorie restriction (CR) are very limited, and the most effective order of intervention is unclear. Therefore, we investigated the impact of time-efficient HIIT with CR intervention on metabolic syndrome (MetS) and the impact of the intervention order on changes in MetS risk factors. Thirty-two participants with MetS underwent an 11-wk intervention program comprising 8 wk of HIIT and 3 wk of CR. Participants were randomly assigned to either the HIIT-then-CR or CR-then-HIIT groups. Thereafter, the CR-then-HIIT group performed a further 8 wk of training once per week after the initial intervention period. Risk factors for MetS and peak oxygen uptake (VO2peak) were assessed during the entire study period. During the 11-wk intervention period, body composition, MetS risk factors, and VO2peak significantly improved in both groups. No significant differences in these improvements were attributable to the intervention order; nonetheless, there was a tendency toward larger effect sizes in the CR-then-HIIT group. During the postintervention period (8 wk), a single weekly HIIT session prevented VO2peak reduction in the CR-then-HIIT group (-2.0 ± 7.2%; P=0.31). The time-efficient intervention program with HIIT and CR had a beneficial effect on MetS; however, the intervention order had no influence on the changes in risk factors.

Chronic effects of high-intensity interval training on postprandial lipemia in healthy men.

The aim of this study was to determine the chronic (≥72 h postexercise) effects of high-intensity interval training (HIIT) on postprandial lipemia and metabolic markers in healthy volunteers. Eight physically active young men (mean ± SD: age 22 ± 3 yr, height 1.77 ± 0.07 m, body mass 67.7 ± 6.2 kg) underwent two 6-h mixed-meal tolerance tests and resting vastus lateralis muscle biopsies before the first session and ≥72 h after the final session of 4 wk of HIIT [16 sessions in total; 10 × 60-s bouts of cycling at 90% maximal oxygen uptake (V̇o2max), interspersed with 60-s intervals at 45% V̇o2max]. Arterialized and deep venous blood samples from across the forearm, brachial artery blood flow measurements, and whole-body indirect calorimetry data were obtained before, and at regular intervals for 6 h after, consumption of a standardized mixed meal. The main findings revealed that, when assessed ≥72 h postexercise, postprandial free fatty acid (FFA) uptake across the forearm was increased in response to exercise training (P = 0.025). However, 4 wk of HIIT did not alter fasting or postprandial circulating triglyceride concentrations or their tissue uptake, despite a 10.2% ± 7.7% improvement in V̇o2max (P = 0.004). Protein content of adipose triglyceride lipase in the vastus lateralis at rest was reduced by 25% ± 21% (P = 0.01). Collectively, these findings suggest that 4 wk of HIIT enhances postprandial clearance of FFA when assessed ≥72 h postexercise but does not confer persisting (training) adaptations in postprandial triglyceridemia.NEW & NOTEWORTHY When assessed ≥72 h after the last exercise session, 4 wk of high-intensity interval training (HIIT) did not improve triglyceridemia but enhanced free fatty acid uptake into muscle with a concurrent reduction in skeletal muscle adipose triglyceride lipase protein content. This suggests that previously reported acute reductions in postprandial triglyceridemia following a single bout of HIIT do not translate to sustained improvements after 4 wk of HIIT, supporting the concept of frequent exercise for the maintenance of lipemic control.

Cardiac remodeling after six weeks of high-intensity interval training to exhaustion in endurance-trained men.

High-intensity interval training (HIIT) improves physical performance of endurance athletes, although studies examining its cardiovascular effects are sparse. We evaluated the impact of HIIT on blood pressure, heart rate, and cardiac cavities' size and function in endurance-trained adults. Seventeen endurance-trained men underwent 24-h ambulatory blood pressure monitoring and Doppler echocardiography at baseline and after 6 wk of HIIT. Participants were divided into 2 groups [85% maximal aerobic power (HIIT85), n = 8 and 115% maximal aerobic power (HIIT115), n = 9] to compare the impact of different HIIT intensities. Ambulatory blood pressure monitoring and cardiac chambers' size and function were similar between groups at baseline. HIIT reduced heart rate (55 ± 8 vs. 51 ± 7 beats/min; P = 0.003), systolic blood pressure (121 ± 11 vs. 118 ± 9 mmHg; P = 0.01), mean arterial pressure (90 ± 8 vs. 89 ± 6 mmHg; P = 0.03), and pulse pressure (52 ± 6 vs. 49 ± 5 mmHg; P = 0.01) irrespective of training intensity. Left atrium volumes increased after HIIT (maximal: 50 ± 14 vs. 54 ± 14 mL; P = 0.02; minimal: 15 ± 5 vs. 20 ± 8 mL; P = 0.01) in both groups. Right ventricle global longitudinal strain lowered after training in the HIIT85 group only (20 ± 4 vs. 17 ± 3%, P = 0.04). In endurance-trained men, 6 wk of HIIT reduced systolic blood pressure and mean arterial pressure and increased left atrium volumes irrespective of training intensity, whereas submaximal HIIT deteriorated right ventricle systolic function.NEW & NOTEWORTHY The novel findings of this study are that 6 wk of high-intensity interval training increases left atrial volumes irrespective of training intensity (85 or 115% maximal aerobic power), whereas the submaximal training decreases right ventricular systolic function in endurance-trained men. These results may help identify the exercise threshold for potential toxicity of intense exercise training for at-risk individuals and ideal exercise training regimens conferring optimal cardiovascular protection and adapted endurance training for athletes.

Exercise alters and β-alanine combined with exercise augments histidyl dipeptide levels and scavenges lipid peroxidation products in human skeletal muscle.

Carnosine and anserine are dipeptides synthesized from histidine and β-alanine by carnosine synthase (ATPGD1). These dipeptides, present in high concentration in the skeletal muscle, form conjugates with lipid peroxidation products such as 4-hydroxy trans-2-nonenal (HNE). Although skeletal muscle levels of these dipeptides could be elevated by feeding β-alanine, it is unclear how these dipeptides and their conjugates are affected by exercise training with or without β-alanine supplementation. We recruited 20 physically active men, who were allocated to either β-alanine or placebo-feeding group matched for peak oxygen consumption, lactate threshold, and maximal power. Participants completed 2 wk of a conditioning phase followed by 1 wk of exercise training, a single session of high-intensity interval training (HIIT), followed by 6 wk of HIIT. Analysis of muscle biopsies showed that the levels of carnosine and ATPGD1 expression were increased after CPET and decreased following a single session and 6 wk of HIIT. Expression of ATPGD1 and levels of carnosine were increased upon β-alanine-feeding after CPET, whereas ATPGD1 expression decreased following a single session of HIIT. The expression of fiber type markers myosin heavy chain I and IIa remained unchanged after CPET. Levels of carnosine, anserine, carnosine-HNE, carnosine-propanal, and carnosine-propanol were further increased after 9 wk of β-alanine supplementation and exercise training but remained unchanged in the placebo-fed group. These results suggest that carnosine levels and ATPGD1 expression fluctuates with different phases of training. Enhancing carnosine levels by β-alanine feeding could facilitate the detoxification of lipid peroxidation products in the human skeletal muscle.NEW & NOTEWORTHY Carnosine synthase expression and carnosine levels are altered in the human skeletal muscle during different phases of training. During high-intensity interval training, β-alanine feeding promotes detoxification of lipid peroxidation products and increases anserine levels in the skeletal muscle.

Two weeks of moderate-intensity continuous training, but not high-intensity interval training, increases insulin-stimulated intestinal glucose uptake.

Similar to muscles, the intestine is also insulin resistant in obese subjects and subjects with impaired glucose tolerance. Exercise training improves muscle insulin sensitivity, but its effects on intestinal metabolism are not known. We studied the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on intestinal glucose and free fatty acid uptake from circulation in humans. Twenty-eight healthy, middle-aged, sedentary men were randomized for 2 wk of HIIT or MICT. Intestinal insulin-stimulated glucose uptake and fasting free fatty acid uptake from circulation were measured using positron emission tomography and [18F]FDG and [18F]FTHA. In addition, effects of HIIT and MICT on intestinal GLUT2 and CD36 protein expression were studied in rats. Training improved aerobic capacity (P = 0.001) and whole body insulin sensitivity (P = 0.04), but not differently between HIIT and MICT. Insulin-stimulated glucose uptake increased only after the MICT in the colon (HIIT = 0%; MICT = 37%) (P = 0.02 for time × training) and tended to increase in the jejunum (HIIT = -4%; MICT = 13%) (P = 0.08 for time × training). Fasting free fatty acid uptake decreased in the duodenum in both groups (HIIT = -6%; MICT = -48%) (P = 0.001 time) and tended to decrease in the colon in the MICT group (HIIT = 0%; MICT = -38%) (P = 0.08 for time × training). In rats, both training groups had higher GLUT2 and CD36 expression compared with control animals. This study shows that already 2 wk of MICT enhances insulin-stimulated glucose uptake, while both training modes reduce fasting free fatty acid uptake in the intestine in healthy, middle-aged men, providing an additional mechanism by which exercise training can improve whole body metabolism.NEW & NOTEWORTHY This is the first study where the effects of exercise training on the intestinal substrate uptake have been investigated using the most advanced techniques available. We also show the importance of exercise intensity in inducing these changes.

Low-Active Male Adolescents: A Dose Response to High-Intensity Interval Training.

High-intensity interval training (HIIT) is a potential alternative to traditionally recommended steady state exercise for providing health benefits in adolescents, yet its dose-response relationship in this cohort remains unclear, as does its translatability to real-world, nonclinical settings. The present study adopts a novel dose-response design to investigate the effects of undertaking 8 wk of HIIT on the cardiometabolic health of low-active male adolescents. Twenty-six male adolescents (age 16 ± 1 yr), identified as low active by nonparticipation in structured sport and physical education classes, were randomly assigned to one of five treatment groups. Corresponding with their group numbers (1-5), participants completed a number of HIIT "sets," which consisted of 4 repeated bouts of 20-s near-maximal exertion interspersed with 10-s passive recovery. Participants performed two HIIT sessions and one resistance training session each week for 8 wk. Baseline and follow-up health measures consisted of peak oxygen uptake (V˙O2peak) with an incremental ramp test to volitional exhaustion; body composition (including visceral fat mass, body fat, and lean tissue mass) with dual-energy x-ray absorptiometry; and lipid profile, glucose, insulin, and interleukin-6 from blood analysis. All health outcomes were analyzed as percentage changes, and data were modeled using a quadratic function to explore dose-response relationships. Significant improvements were observed for V˙O2peak (∼6%), body fat percentage (∼4%), visceral fat mass (∼10%), and waist circumference-to-height ratio (∼3%), but there was no clear effect of dose across groups. Low-active adolescent males performing a single HIIT set twice weekly, in addition to one resistance training session, gained meaningful improvements in fitness and body composition. Performing additional HIIT sets provided no additional improvements to those of the lowest dose in this study.

The Effects of Chronic Sodium Bicarbonate Ingestion and Interval Training in Highly Trained Rowers

Recent research has reported performance improvements after chronic NaHCO3 ingestion in conjunction with high-intensity interval training (HIT) in moderately trained athletes. The purpose of the current study was to determine the effects of altering plasma H+ concentration during HIT through NaHCO3 ingestion over 4 wk (2 HIT sessions/wk) in 12 Australian representative rowers (M ± SD; age 22 ± 3 yr, mass 76.4 ± 4.2 kg, VO(2peak) 65.50 ± 2.74 ml · kg(-1) · min(-1)). Baseline testing included a 2,000-m time trial and an incremental exercise test. After baseline testing, rowers were allocated to either a chronic NaHCO3 (ALK) or placebo (PLA) group. Starting 90 min before each HIT session, subjects ingested a 0.3-g/kg body mass dose of NaHCO3 or a placebo substance. Fingertip blood samples were taken throughout the study to analyze bicarbonate and pH levels. The ALK group did not produce any additional improvements in 2,000-m rowing performance time compared with PLA (p > .05). Magnitude-based inferential analysis indicated an unclear or trivial effect on 2,000-m power, 2,000-m time, peak power output, and power at 4 mmol/L lactate threshold in the ALK group compared with the PLA group. Although there was no difference between groups, during the study there was a significant mean (± SD) 2,000-m power improvement in both the ALK and PLA groups of 17.8 ± 14.5 and 15.2 ± 18.3 W, respectively. In conclusion, despite overall improvements in rowing performance after 4 wk of HIT, the addition of chronic NaHCO3 supplementation during the training period did not significantly enhance performance further.

Exercise training increases sarcolemmal and mitochondrial fatty acid transport proteins in human skeletal muscle

Fatty acid oxidation is highly regulated in skeletal muscle and involves several sites of regulation, including the transport of fatty acids across both the plasma and mitochondrial membranes. Transport across these membranes is recognized to be primarily protein mediated, limited by the abundance of fatty acid transport proteins on the respective membranes. In recent years, evidence has shown that fatty acid transport proteins move in response to acute and chronic perturbations; however, in human skeletal muscle the localization of fatty acid transport proteins in response to training has not been examined. Therefore, we determined whether high-intensity interval training (HIIT) increased total skeletal muscle, sarcolemmal, and mitochondrial membrane fatty acid transport protein contents. Ten untrained females (22 +/- 1 yr, 65 +/- 2 kg; .VO(2peak): 2.8 +/- 0.1 l/min) completed 6 wk of HIIT, and biopsies from the vastus lateralis muscle were taken before training, and following 2 and 6 wk of HIIT. Training significantly increased maximal oxygen uptake at 2 and 6 wk (3.1 +/- 0.1, 3.3 +/- 0.1 l/min). Training for 6 wk increased FAT/CD36 at the whole muscle (10%) and mitochondrial levels (51%) without alterations in sarcolemmal content. Whole muscle plasma membrane fatty acid binding protein (FABPpm) also increased (48%) after 6 wk of training, but in contrast to FAT/CD36, sarcolemmal FABPpm increased (23%), whereas mitochondrial FABPpm was unaltered. The changes on sarcolemmal and mitochondrial membranes occurred rapidly, since differences (< or =2 wk) were not observed between 2 and 6 wk. This is the first study to demonstrate that exercise training increases fatty acid transport protein content in whole muscle (FAT/CD36 and FABPpm) and sarcolemmal (FABPpm) and mitochondrial (FAT/CD36) membranes in human skeletal muscle of females. These results suggest that increases in skeletal muscle fatty acid oxidation following training are related in part to changes in fatty acid transport protein content and localization.

Seven High-Intensity Interval Training Sessions Increases Aerobic Capacity and Blunts the Metabolic and Hormonal Responses to Intense Exercise

Numerous studies have shown that traditional endurance exercise (∼55–70% VO2peak) improves aerobic capacity. Alternately, a recent study reported that 2 wk of sprint interval training (>100% VO2peak) also improved aerobic capacity and exercise performance. Interval training at an intermediate, but still intense power output (∼90% VO2peak), may offer a more practical training protocol to improve aerobic capacity and high intensity performance for the general population. PURPOSE: Our aim was to investigate the effects of a short term, high intensity interval training (HIT) program on aerobic capacity and to quantify the short-term changes in the cardiovascular, metabolic and hormonal responses to exercise at ∼90% VO2peakM METHODS: Eight females participated in the study (mean ± SE: 22.1 ± 0.2 yrs, 65.0 ±0.8 kg, 2.36 ± 0.17 VO2peak). Subjects performed a VO2peak test prior and following training. Training consisted of 7 HIT sessions over 2 wk. Subjects trained every other day performing ten 4 min bouts at 90% VO2peak with 2 min of rest between bouts. On the 2nd and 7th training session, heart rate (HR) and respiratory and blood samples were collected before and after bouts 1, 3, 5 and 10. The 7th training session was at the same absolute power output as the 2nd session. RESULTS: On average, subjects reached 90% VO2peak by the end of each exercise bout (session 2 (S2): 90.3 ± 3.6, session 7 (S7): 90.5 ± 4.0% VO2peak). Exercising workloads increased throughout training, with an average increase of 10% from the 1 * to 6th training session. VO2peak significantly increased (p < 0.05) following training (2.36 ± 0.17 to 2.66 ± 021 l/min). Lactate decreased with training following the 3rd bout (S2: 3.37 ± 0.08 vs. S7: 2.96 ± 0.18 mM) and following the 5th bout (S2: 3.63 ±0.12 vs. S7: 3.27 ± 0.18 mM). Plasma epinephrine significantly decreased with training following the 3rd bout (S2: 1.80 ±0.08 vs. S7: 0.95 ± 0.06 nM) and the 10th bout (S2: 3.11 ±0.24 vs. S7: 1.39 ±0.03 nM). The highest HR reached during exercise significantly decreased following training (S2: 179.6 ± 1.4, S7: 173.9 ± 1.7 beats/min). HR recovery during rest periods decreased on average from 128.1 ± 3.0 to 122.8 ± 3.5 beats/min. Plasma free fatty acids (S2: 0.38 ±011 vs. S7: 0.27 ± 0.03 mM) and glycerol(S2: 127.7 ± 13.5 vs. S7: 97.6 ± 5.9 mM) following bout 10 were significantly decreased following training. CONCLUSION: Aerobic capacity was increased and cardiovascular, hormonal and metabolic responses to high intensity exercise were blunted with 2 wk of HIT. HIT at ∼90% VO2peak may offer a realistic and practical training protocol to improve aerobic capacity and high intensity performance for the general population.

Increases in maximal accumulated oxygen deficit after high-intensity interval training are not gender dependent

Gender differences in maximal accumulated oxygen deficit (MAOD) were examined before and after 4 and 8 wk of high-intensity interval training. Untrained men (n = 7) and women (n = 7) cycled at 120% of pretraining peak oxygen uptake (VO2 peak) to exhaustion (MAOD test) pre-, mid-, and posttraining. A posttraining timed test was also completed at the MAOD test power output, but this test was stopped at the time to exhaustion achieved during the pretraining MAOD test. The 14.3 +/- 5.2% increase in MAOD observed in men after 4 wk of training was not different from the 14.0 +/- 3.0% increase seen in women (P > 0.05). MAOD increased by a further 6.6 +/- 1.9% in men, and this change was not different from the additional 5.1 +/- 2.3% increase observed in women after the final 4 wk of training. VO2 peak measured during incremental cycling increased significantly (P < 0.01) in male but not in female subjects after 8 wk of training. Moreover, the accumulated oxygen (AO2) uptake was higher in men during the posttraining timed test compared with the pretraining MAOD test (P < 0.01). In contrast, the AO2 uptake was unchanged from pre- to posttraining in female subjects. The increase in MAOD with training was not different between men and women, suggesting an enhanced ability to produce ATP anaerobically in both groups. However, the increase in VO2 peak and AO2 uptake obtained in male subjects after training indicates improved oxidative metabolism in men but not in women. We conclude that there are basic gender differences that may predispose men and women to specific metabolic adaptations after a period of intense interval training.