Changes In Maximal Oxygen Uptake Research Articles

The changes in maximal oxygen uptake (V̊O2MAX) induced by physical exertion during an Antarctic expedition depend on the initial V̊O2MAX of the individuals: a case study of the Brazilian expedition

ABSTRACTAntarctic climate is challenging, since the cold, wind and sensory monotony are stressful stimuli to individuals. Moreover, camp activities and heavy clothes may contribute to increase physiological strain. Thus, we aimed to characterise the physiological demand of a 24-day period in the Antarctic field and then to evaluate the effect of this expedition on the aerobic fitness in individuals with heterogeneous initial aerobic fitness (as determined by estimating maximum oxygen consumption – V̊O2MAX). Before and after the 24-day period in Antarctica, 7 researchers and 2 mountaineers were subjected to incremental tests to estimate their V̊O2MAX. Field effort was characterised by measuring heart rate (HR). During the field trips, their HR remained 33.4% of the recording time between 50–60% HRMAX, 22.3% between 60–70% HRMAX, and only 1.4% between 80 and 90% HRMAX. The changes in estimated V̊O2MAX during the expedition depended on the pre-expedition aerobic fitness. The post-expedition V̊O2MAX increased by 5.9% and decreased by 14.3%in individuals with lower (researchers) and higher (mountaineers) initial V̊O2MAX, respectively. We concluded that physical effort in the Antarctic field is characterised as predominantly of low- to moderate-intensity. This effort represented an effective training load for individuals with lower initial V̊O2MAX, but not for those with higher V̊O2MAX.

Changes in maximal oxygen uptake during growth and development in girls who actively participate in basketball and in non-athletes girls: A longitudinal study

Background/Aim. It is well known that continuous engagement in physical activity is important for normal growth and development of children. Maximal oxygen uptake (VO2max), as a measure of functional state of the organism, is largely affected by level of physical activity, but it remains unclear to what extent it can be improved during childhood. The aim of the study was to evaluate dynamics of changes in aerobic capacity, anthropometric and body composition characteristics in active and non-active girls over a period of 3 years. Methods. A total of 48 young girls were included in the study. Girls were divided into 2 groups: training group consisted of 25 girls who played basketball (age 13.84 ? 0.94) and non-training group of 23 girls who were not involved in any organized sports (age 13.83 ? 0.98). Anthropometric and body composition characteristics were measured in order to monitor somatic growth during the study. VO2maxvalues were obtained by performing cardiopulmonary exercise testing on a treadmill. All parameters were measured every 6 months during 3-years period. Results. ANOVA analysis showed a significant time and group interaction effect on VO2max (p < 0.001), body mass index (BMI) (p < 0.001) and fat percentage (FAT%) (p < 0.01). Also, there was an obvious increase in VO2max within both groups due to growth and development itself (p < 0.001). Conclusion. The main finding of the study was an increase in VO2max due to growth and development. The girls who actively participated in basketball had higher level of aerobic capacity compared to non-active girls. Furthermore, continuous basketball training led to maintaining normal body composition in terms of FAT% and BMI, which altogether may imply that organized physical activity has a positive influence on evaluated characteristics.

Androgen receptor gene polymorphisms and maximal fat oxidation in healthy men. A longitudinal study.

Androgens play a major role in fat oxidation; however, the effects of androgens depend, among other factors, on the intrinsic characteristics of the androgen receptor (AR). Lower repetitions of CAG and GGN polymorphism appear to have a protective effect on fat accumulation in the transition from adolescent to mid-twenties. Whether a similar protective effect is present later in life remains unknown. The aims of this study were: a) to evaluate if extreme CAG and GGN repeat polymorphisms of the androgen receptors influence body fat mass, its regional distribution, resting metabolic rate (RMR), maximal fat oxidation capacity (MFO) and serum leptin, free testosterone and osteocalcin in healthy adult men; and b) to determine the longitudinal effects on fat tissue accumulation after 6.4 years of follow-up. CAG and GGN repeats length were measured in 319 healthy men (mean ± standard deviation [SD]: 28.3 ± 7.6 years). From these, we selected the subjects with extreme short (CAGS < or equal 19; n = 7) and long (CAGL > or equal 24; n = 10) CAG repeats, and the subjects with short (GGNS < or equal to 22; n = 9) and long (GGNL > or equal to 25; n = 10) GGN repeats. Body composition was assessed by DXA and serum levels of leptin, free testosterone and osteocalcin by ELISA. After 6.4 years of follow-up, DXA was repeated, and resting metabolic rate (RMR), MFO and VO2max determined by indirect calorimetry. CAGS and CAGL subjects had similar RMR and accumulated comparable amounts of fat tissue over 6.4 ± 1.0 years of follow-up. However, CAGL had higher MFO and total lean mass than CAGS(p < 0.05). Men with GGNSaccumulated greater amount of total fat mass than men with GGNL, particularly in the trunk region seven years later. This concurred with a greater MFO in the GGNLgroup (p < 0.05), who accumulated less fat mass. Free testosterone was associated with MFO in absolute values (r = 0.45; p < 0.05) and MFO per kg of lower extremity lean mass per height squared (r = 0.35; p < 0.05). CAG and GGN repeat polymorphisms may influence muscle fat oxidation capacity and may have a role in the accumulation of fat over the years.

Training-Induced Change in Aerobic Fitness and Anaerobic Power among Female College Basketball Players

PURPOSE: To examine training-induced changes in aerobic fitness and anaerobic power in a sample of division I, female college basketball players. METHODS: Aerobic fitness and anaerobic power were measured in a sample of female college basketball players before and after preseason training. Aerobic fitness was measured using a VO2 max test, and anaerobic power was measured using a Wingate test. Preseason training lasted one month and consisted of 8 hours per week of a combination of weight training, high-intensity interval sprint training, and skill workouts. Paired-sample t-tests were used to examine change pre- and post-intervention. Pearson correlations were conducted to examine potential associations among variables. RESULTS: A total of 13 female athletes completed this study. Maximal aerobic fitness significantly (p = .013) increased after preseason training, from 47.9 to 49.9 kg/ml/min. Relative peak power and relative mean power significantly increased after preseason training from 8.3 to 9.1 W/kg (p = .025) and from 6.7 to 7.6 W/kg (p < .001), respectively. Fatigue index did not significantly change as a result of preseason training. Despite these positive results, individual responses varied widely. Change in maximal aerobic fitness ranged from +0.2 to +6.1 ml/kg/min. Change in relative peak anaerobic power ranged from -1.0 to +3.0 W/kg, and change in relative mean anaerobic power ranged from +0.9 to +1.5 W/kg. Interestingly, change in maximal oxygen uptake and change in measures of anaerobic power were not significantly correlated with baseline levels of either of these variables. There were also no significant correlations between these changes in performance and age, year in school, or position played. There was, however, a significant, positive correlation (r = .77, p = .002) between change in relative peak anaerobic power and relative mean anaerobic power. CONCLUSIONS: Preseason training can have a positive effect on aerobic endurance and anaerobic power. These changes varied widely between athletes. However, this variation was not related to baseline fitness levels, age, year in school, or position played. This information may be useful for strength and conditioning coaches to design individualized training programs to maximize effects.

Cardiovascular exercise and burden of arrhythmia in patients with atrial fibrillation - A randomized controlled trial.

BackgroundPhysical activity at moderate-high intensity is recommended to prevent lifestyle diseases. Patients with atrial fibrillation are at risk of a sedentary lifestyle due to fear of exercise-induced episodes of atrial fibrillation. The burden of arrhythmia can be reduced by physical exercise. The effect of exercise intensity on burden of atrial fibrillation needs to be studied further.Methods and resultsIn a 12-week randomized controlled trial, 76 patients with paroxysmal/persistent atrial fibrillation were allocated to perform exercise at either low intensity or high intensity (50% and 80% of maximal perceived exertion, respectively). Primary outcome was burden of AF measured by daily electrocardiography-reporting during 12 weeks. Secondarily, change in maximal oxygen uptake (peak VO2) and 1-year hospitalization was compared between low and high intensity exercise. Sixty-three patients completed the follow-up. In the intention-to-treat analysis, we found no statistical difference in burden of atrial fibrillation between low and high intensity exercise (incidence rate ratio 0.742, 95% CI 0.29–1.91, P = 0.538). No serious adverse events were reported and there was no difference in hospitalization between the two exercise groups. Both exercise groups improved significantly in peak VO2 (low intensity: 3.62 mL O2/kg/min, SD 3.77; high intensity: 2.87 mL O2/kg/min, SD 4.98), with no statistical difference between-groups (mean difference: 0.76 mL O2/kg/min, 95% CI -3.22–1.7).ConclusionsHigh intensity physical exercise was not superior to low intensity physical exercise in reducing burden of atrial fibrillation. HI exercise was well tolerated; no evidence of an increased risk was found for HI compared to LI exercise. Larger studies are required to further prove our findings.Trial registrationClinicalTrials.gov NCT01817998

Exercise Training Reduces Liver Fat and Increases Rates of VLDL Clearance But Not VLDL Production in NAFLD.

Randomized controlled trials in nonalcoholic fatty liver disease (NAFLD) have shown that regular exercise, even without calorie restriction, reduces liver steatosis. A previous study has shown that 16 weeks of supervised exercise training in NAFLD did not affect total very low-density lipoprotein (VLDL) kinetics. The objective of the study was to determine the effect of exercise training on intrahepatocellular fat (IHCL) and the kinetics of large triglyceride (TG)-rich VLDL1 and smaller denser VLDL2, which has a lower TG content. This was a 16-week randomized controlled trial. A total of 27 sedentary patients with NAFLD participated in the trial. The intervention was composed of supervised exercise with moderate-intensity aerobic exercise or conventional lifestyle advice (control). VLDL1 and VLDL2-TG and apolipoprotein B (apoB) kinetics were investigated using stable isotopes before and after the intervention. In the exercise group, maximal oxygen uptake increased by 31% ± 6% (mean ± SEM) and IHCL decreased from 19.6% (14.8%, 30.0%) to 8.9% (5.4%, 17.3%) (median [interquartile range]) with no significant change in maximal oxygen uptake or IHCL in the control group (change between groups, P < .001 and P = .02, respectively). Exercise training increased VLDL1-TG and apoB fractional catabolic rates, a measure of clearance, (change between groups, P = .02 and P = .01, respectively), and VLDL1-apoB production rate (change between groups, P = .006), with no change in VLDL1-TG production rate. Plasma TG did not change in either group. An increased clearance of VLDL1 may contribute to the significant decrease in liver fat after 16 weeks of exercise in NAFLD. A longer duration or higher-intensity exercise interventions may be needed to lower the plasma TG and VLDL production rate.

Effect of Various Regimes of High Intensity Interval Training (HIIT) on Changes in Maximal Oxygen Uptake and Hemodynamic Function

Data (Burgomaster et al. 2008; Astorino et al. 2013) demonstrate improved maximal oxygen uptake (VO2max) after 6 and 12 wk of high intensity interval training (HIIT) which enhances exercise performance and health status. A few studies (Daussin et al. 2008; MacPherson et al. 2011) document changes in cardiac output (CO) in response to HIIT in which increases in VO2max occurred, and their results are equivocal. PURPOSE: To examine changes in VO2max and CO in response to various regimes of HIIT. METHODS: Fifty active men and women were randomized to control (CON, n = 24, age = 25.3 ± 4.7 yr) or one of three HIIT regimes, HIIT + sprint interval training (SIT) (n = 10, age = 22.8 ± 7.0 yr), HIIT + HIIT (n = 8, age = 21.8 ± 2.2 yr), or HIIT + periodized training (PER) (n = 8, age = 24.4 ± 6.8 yr). Training was performed 3 d/wk for 6 wk, with 10 sessions of HIIT (6 – 10 bouts of cycling for 60 s separated by 75 s recovery at 90 – 110 % peak power output) completed followed by randomization to one of three regimes for the ensuing 3 wk of the study. VO2max was measured pre- and post-training during progressive exercise, during which pulmonary gas exchange data were obtained. Cardiac output, heart rate (HR), and stroke volume (SV) were continuously estimated using thoracic impedance (Physioflow Enduro). Participants maintained their habitual physical activity during the study, and prior to all assessments, they abstained from exercise for 48 h. RESULTS: VO2max was unchanged in CON, yet a significant groupXtime interaction (p < 0.01) was demonstrated showing higher VO2max in HIIT + SIT (2.85 ± 0.47 L/min to 3.08 ± 0.34 L/min), HIIT + HIIT (2.81 ± 0.62 L/min to 3.02 ± 0.73 L/min), and HIIT + PER (2.64 ± 0.77 L/min to 2.92 ± 0.78 L/min). A significant groupXtime interaction (p = 0.038) was revealed for HR in that it was higher through HIIT. Stroke volume differed across time (p = 0.009) but no interaction occurred (p = 0.31). Cardiac output differed across time (p = 0.006) and a significant groupXtime interaction (p = 0.032) was shown. Compared to CON (20.9 ± 3.3 L/min to 20.8 ± 3.2 L/min), CO was increased in HIIT + SIT (19.9 ± 2.5 L/min to 21.4 ± 1.0 L/min), HIIT + HIIT (21.1 ± 4.0 L/min to 22.2 ± 2.7 L/min), and HIIT + PER (20.0 ± 3.7 L/min to 21.6 ± 4.4 L/min). CONCLUSION: Similar increases in VO2max occur in response to various regimes of HIIT, with greater CO explaining this outcome.

The Impact of Endurance Training on Functional Parameters During the Preparation Phase among Cross-Country Skiers

Summary In the study, we have tried to demonstrate the effect of endurance training on changes in functional parameters during the preparation phase (12-week mesocycle) among cross-country skiers. The group consisted of 10 male cross-country skiers (age: 21.4 ±5 year) who completed control (1st 6 week mesocycle) and experimental period (2nd 6 week mesocycle).We focused on the following time-varying parameters: changes in maximal oxygen uptake (VO2max), the level of aerobic (AeT) and anaerobic thresholds (AT), maximum heart rate (HRmax) and performance on the running treadmill. The intra-individual monitoring of each athlete revealed statistical significance of VO2max (mid_VO2max = 69.48 ± 5.72 l.kg-1.min-1, post_ VO2max = 70.96 ± 5.67 ml.kg-1.min-1; p≤0.05) and the level of AT (mid_AT = 86.2 ± 5.43 %, post_AT = 87.8 ± 5.59 %; p≤0.01) the performance on the running treadmill (mid_t = 14:54 ± 1:43 min., post_t = 15:30 ± 1:50 min.; p≤0.05).The significant changes were recorded in the AeT(pre_AeT = 70.3 ± 7.56 %, mid_AeT = 72.5 ± 7.59 %; p≤0.05) in theHRmax(pre_HRmax = 190 ± 8.04 bpm, mid_HRmax = 189 bpm, post_HRmax = 188 ± 7.34 bpm; p = n.s.) during control period. We assume that the significant differences occurred as a result of adaptation changes due to training stimuli, which were induced by changes in functional parameters. Increased training volume in zone lower level of oxygen regime (A1), upper level of oxygen regime (A2) and upper level of lactate tolerance(T2) during experimental period elicited changes which reflected the increase functional parameters and performance on the running treadmill compared to that of control period.

Changes in Endurance Performance in Young Athletes During Two Training Seasons.

The aim of the study was to assess changes in endurance performance in young runners (females and males) during two training seasons. It involved 19 male and 16 female athletes aged 15–17 specializing in track-and-field middle and long distances runs. The following parameters were measured three times during the training season: maximal oxygen uptake, running economy, and the level of the second ventilatory threshold. Training volume and intensity during each season were analyzed within an 8-week period prior to the exercise tests. The volume and intensity of training at various stages of preparation in both seasons were similar. During the first year of observation, significant improvements in relative volume of maximal oxygen uptake were reported both in female and male athletes. During the second training season, it was found that running economy improved both in women and men, with no changes in maximal oxygen uptake. The same (in terms of volume and intensity) endurance training carried out with young runners during two consecutive training seasons can result in different training effects.

Influência dos hormônios sexuais no consumo de oxigênio de ratos

Introdução: Achados da literatura sugerem que oscilações dos hormônios sexuais femininos podem alterar o consumo máximo de oxigênio (VO2max).Objetivo: Comparar o VO2max entre ratos machos (M, n=8), fêmeas nas fases ovulatórias (OV, n=8) ou não-ovulatórias (NOV, n=8) do ciclo estral e ooforectomizadas (OS, n=8).Métodos: A avaliação do consumo de oxigênio foi realizada em esteira rolante com caixa metabólica acoplada.Resultados: Em repouso, o VO2 foi semelhante entre os grupos estudados. O grupo M apresentou maior VO2max em relação ao grupo NOV, mas valores semelhantes ao do grupo OV. O VO2max foi menor no grupo ooforectomizado (OS: 62±3 ml.kg-1.min-1) quando comparado aos demais grupos (M: 92±2; NOV: 77±4; OV: 87±3 ml.kg-1.min-1).Conclusões: Esses achados evidenciam que a variação hormonal decorrente das diferentes fases do ciclo estral e da privação dos hormônios ovarianos pode induzir alterações no consumo máximo de oxigênio em ratos.

Reference values of maximal oxygen uptake for polish rowers.

The aim of this study was to characterize changes in maximal oxygen uptake over several years and to elaborate current reference values of this index based on determinations carried out in large and representative groups of top Polish rowers. For this study 81 female and 159 male rowers from the sub-junior to senior categories were recruited from the Polish National Team and its direct backup. All the subjects performed an incremental exercise test on a rowing ergometer. During the test maximal oxygen uptake was measured with the BxB method. The calculated reference values for elite Polish junior and U23 rowers allowed to evaluate the athletes’ fitness level against the respective reference group and may aid the coach in controlling the training process. Mean values of VO2max achieved by members of the top Polish rowing crews who over the last five years competed in the Olympic Games or World Championships were also presented. The results of the research on the “trainability” of the maximal oxygen uptake may lead to a conclusion that the growth rate of the index is larger in case of high-level athletes and that the index (in absolute values) increases significantly between the age of 19–22 years (U23 category).

An evaluation of upper-body muscle activation during coupled and uncoupled instability resistance training.

Recently, there has been a growth in the popularity of resistance exercises performed on unstable surfaces. However, the relationship between unstable surface training and load coupling on muscle activation is unclear. The purpose of this study was to evaluate changes in muscle activation during a barbell (BB) (coupled) and dumbbell (DB) (uncoupled) chest press exercise performed on an unstable surface. The 3 specific chest press conditions included 50% 1 repetition maximum (RM) with BB (50% BB), 50% 1RM with DBs (50% DB), and 25% 1RM with DBs (25% DB). Ten male subjects participated in the study (age, 23.9 ± 2.6 years; body weight, 82.8 ± 10.2 kg). During testing, mean electromyographic activity was assessed for pectoralis major (PM), triceps brachii, anterior deltoid (AD), and rectus abdominis (RA) and was presented as a percent change across the lifting conditions. It was observed that muscle activation increased by 15% in both the PM and RA from the 50% BB condition to the 50% DB condition. Also, the greatest percent difference in muscle activation between the 50 and 25% DB conditions occurred for PM and AD (+54% during 50% DB). These results suggest that demands on the core musculature to provide stability are increased with the use of DBs (uncoupled) as opposed to a BB (coupled). Where instability training provides a sufficient hypertrophy stimulus in prime mover muscle groups, there may be the added benefit of core stability training. Specifically, this type of training may benefit both untrained persons and those engaged in active rehabilitation.

Correction: High Intensity Interval Training in a Real World Setting: A Randomized Controlled Feasibility Study in Overweight Inactive Adults, Measuring Change in Maximal Oxygen Uptake

Correction: High Intensity Interval Training in a Real World Setting: A Randomized Controlled Feasibility Study in Overweight Inactive Adults, Measuring Change in Maximal Oxygen Uptake

High Intensity Interval Training in a Real World Setting: A Randomized Controlled Feasibility Study in Overweight Inactive Adults, Measuring Change in Maximal Oxygen Uptake

BackgroundIn research clinic settings, overweight adults undertaking HIIT (high intensity interval training) improve their fitness as effectively as those undertaking conventional walking programs but can do so within a shorter time spent exercising. We undertook a randomized controlled feasibility (pilot) study aimed at extending HIIT into a real world setting by recruiting overweight/obese, inactive adults into a group based activity program, held in a community park.MethodsParticipants were allocated into one of three groups. The two interventions, aerobic interval training and maximal volitional interval training, were compared with an active control group undertaking walking based exercise. Supervised group sessions (36 per intervention) were held outdoors. Cardiorespiratory fitness was measured using VO2max (maximal oxygen uptake, results expressed in ml/min/kg), before and after the 12 week interventions.ResultsOn ITT (intention to treat) analyses, baseline (N = 49) and exit (N = 39) O2 was 25.3±4.5 and 25.3±3.9, respectively. Participant allocation and baseline/exit VO2max by group was as follows: Aerobic interval training N = 16, 24.2±4.8/25.6±4.8; maximal volitional interval training N = 16, 25.0±2.8/25.2±3.4; walking N = 17, 26.5±5.3/25.2±3.6. The post intervention change in VO2max was +1.01 in the aerobic interval training, −0.06 in the maximal volitional interval training and −1.03 in the walking subgroups. The aerobic interval training subgroup increased VO2max compared to walking (p = 0.03). The actual (observed, rather than prescribed) time spent exercising (minutes per week, ITT analysis) was 74 for aerobic interval training, 45 for maximal volitional interval training and 116 for walking (p = 0.001). On descriptive analysis, the walking subgroup had the fewest adverse events.ConclusionsIn contrast to earlier studies, the improvement in cardiorespiratory fitness in a cohort of overweight/obese participants undertaking aerobic interval training in a real world setting was modest. The most likely reason for this finding relates to reduced adherence to the exercise program, when moving beyond the research clinic setting.Trial RegistrationACTR.org.au ACTRN12610000295044

Lifestyle intervention involving calorie restriction with or without aerobic exercise training improves liver fat in adults with visceral adiposity.

Objective. To evaluate the effect of calorie restriction-induced weight loss with or without aerobic exercise on liver fat. Methods. Thirty-three adults with visceral adiposity were divided into calorie restriction (CR; n = 18) or CR and aerobic exercise (CR + Ex; n = 15) groups. Target energy intake was 25 kcal/kg of ideal body weight. The CR + Ex group had a targeted exercise time of 300 min/wk or more at lactate threshold intensity for 12 weeks. Results. Reductions in body weight (CR, −5.3 ± 0.8 kg; CR + Ex, −5.1 ± 0.7 kg), fat mass (CR, −4.9 ± 0.9 kg; CR + Ex, −4.4 ± 0.6 kg), and visceral fat (CR, −24 ± 5 cm2; CR + Ex, −37 ± 5 cm2) were not statistically different between groups. Liver fat decreased significantly in both groups, with no difference between groups. Change in maximal oxygen uptake was significantly greater in the CR + Ex group than in the CR group (CR, −0.7 ± 0.7 mL/kg/min; CR + Ex, 2.9 ± 1.0 mL/kg/min). Conclusion. Both CR and CR + Ex resulted in an improved reduction in liver fat; however, there was no additive effect of exercise training.

Prognostic Relevance of Changes in Exercise Test Variables in Pulmonary Arterial Hypertension

IntroductionExercise variables determined in patients with pulmonary arterial hypertension (PAH) at the time of diagnosis, predict survival. It is unknown whether upon treatment, subsequent changes in these exercise variables reflect improvements in survival. The aim of this study was to determine changes in exercise variables in PAH patients and to relate these changes to survival.MethodsBaseline cardiopulmonary exercise test (CPET) variables and six-minute-walk-distance (6MWD) were available from 65 idiopathic PAH patients (50 females; mean age 45±2yrs). The same variables were determined after treatment (13months) in a sub group of 43 patients. To estimate the association between changes in exercise variables and changes in cardiac function, right-ventricle ejection fraction (RVEF) was measured by cardiac MRI at baseline and after treatment in 34 patients. Mean follow-up time after the second CPET was 53 (range: 4-111) months. Kaplan-Meier analysis was used to relate survival to baseline and treatment-associated changes in exercise variables.ResultsSurvivors showed a significantly greater change in maximal oxygen uptake than non-survivors and this change in aerobic capacity was significantly related to changes in RVEF. From baseline until the end of the study period, two patients underwent a lung transplantation and 19 patients died. Survival analysis showed that baseline 6MWD (p<0.0001), maximal heart rate (p<0.0001) and the slope relating ventilation with carbon dioxide production (p≤0.05) were significant predictors of survival, whereas baseline oxygen uptake and oxygen pulse held no predictive value. Treatment associated changes in 6MWD (p<0.01), maximal heart rate (p<0.05), oxygen uptake (p<0.001) and oxygen pulse predicted survival (p<0.05), whereas changes in the slope relating ventilation with carbon dioxide production did not.ConclusionExercise variables with prognostic significance when determined at baseline, retain their prognostic relevance after treatment. However, when changes in exercise variables upon treatment are considered, a different set of variables provides prognostic information.

Magnitude and time course of changes in maximal oxygen uptake in response to distinct regimens of chronic interval training in sedentary women

This study aimed to compare changes in maximal oxygen uptake (VO2max) in response to two regimens of chronic interval training. Twenty healthy sedentary women (mean ± SD age and VO2max = 23.0 ± 5.7 years and 30.1 ± 4.4 mL kg(-1) min(-1), respectively) were randomized to complete 12 weeks of one of two interval training regimes, while an additional seven women served as controls. Training was performed 3 days week(-1) on a cycle ergometer and consisted of 6-10 bouts of 1 min duration at lower (60-80 % W max = LO, n = 10) or more intense (80-90 % W max = HI, n = 10) workloads separated by a brief recovery. Every 3 weeks, measures of VO2max and W max were repeated to assign new training intensities. Changes in blood pressure and body composition were also examined. Data revealed significant (p < 0.001) improvements in VO2max in LO (22.3 ± 6.9 %) and HI (21.9 ± 11.6 %) that were similar (p > 0.05) between groups. Approximately 60 % of the increase in VO2max in HI was observed in the initial 3 weeks, compared to only 20 % in LO. No change (p > 0.05) in body weight or body composition was revealed in response to training. Results demonstrate that a relatively prolonged regimen of moderate or more intense interval training induces similar improvements in cardiorespiratory fitness, although HI induced greater increases in VO2max early on in training than LO. Completion of more intense interval training may be an effective means to expedite increases in VO2max soon after initiation of exercise training.

The relationship between cardiac autonomic function and maximal oxygen uptake response to high-intensity intermittent-exercise training

Major individual differences in the maximal oxygen uptake response to aerobic training have been documented. Vagal influence on the heart has been shown to contribute to changes in aerobic fitness. Whether vagal influence on the heart also predicts maximal oxygen uptake response to interval-sprinting training, however, is undetermined. Thus, the relationship between baseline vagal activity and the maximal oxygen uptake response to interval-sprinting training was examined. Exercisers (n = 16) exercised three times a week for 12 weeks, whereas controls did no exercise (n = 16). Interval-sprinting consisted of 20 min of intermittent sprinting on a cycle ergometer (8 s sprint, 12 s recovery). Maximal oxygen uptake was assessed using open-circuit spirometry. Vagal influence was assessed through frequency analysis of heart rate variability. Participants were aged 22 ± 4.5 years and had a body mass of 72.7 ± 18.9 kg, a body mass index of 26.9 ± 3.9 kg · m−2, and a maximal oxygen uptake of 28 ± 7.4 ml · kg−1 · min−1. Overall increase in maximal oxygen uptake after the training programme, despite being anaerobic in nature, was 19 ± 1.2%. Change in maximal oxygen uptake was correlated with initial baseline heart rate variability high-frequency power in normalised units (r = 0.58; P < 0.05). Thus, cardiac vagal modulation of heart rate was associated with the aerobic training response after 12 weeks of high-intensity intermittent-exercise. The mechanisms underlying the relationship between the aerobic training response and resting heart rate variability need to be established before practical implications can be identified.

Cardiac autonomic function reveals adaptation to military training

The last 4 weeks of basic military training are very stressful. We tested the hypothesis that changes in cardiac autonomic function during this period are associated with changes in maximal oxygen uptake and/or serum hormonal concentrations in male conscripts (n=22). Cardiac vagal autonomic function was assessed by measuring the high-frequency (0.15–0.4 Hz) spectral power of R–R intervals. Maximal oxygen uptake ([Vdot]O2max) and basal serum testosterone concentration were measured at the beginning and end of the period. Individual changes in vagally mediated high-frequency power (range −15% to +25%) correlated (r=0.73, P=0.001) with changes in [Vdot]O2max (range −9% to +6%) and changes in testosterone concentration (range −52% to +43%; r=0.43, P=0.047). The mean values of [Vdot]O2max and testosterone concentration did not change during the study period. Measurements of autonomic function could be a useful tool for indicating adaptation to the highly stressful conditions associated with basic military training.

Variability in the magnitude of response of metabolic enzymes reveals patterns of co-ordinated expression following endurance training in women

Skeletal muscles improve their oxidative fatty acid and glucose metabolism following endurance training, but the magnitude of response varies considerably from person to person. In 20 untrained young women we examined interindividual variability in training responses of metabolic enzymes following 6 weeks of endurance training, sufficient to increase maximal oxygen uptake by 10 ± 8% (mean ± SD). Training led to increases in mitochondrial enzymes [succinate dehydrogenase (SDH; 47 ± 78%), cytochrome c oxidase (52 ± 70%) and ATP synthase (63 ± 69%)] and proteins involved in fatty acid metabolism [3-hydroxyacyl CoA dehydrogenase (69 ± 92%) and fatty acid transporter CD36 (86 ± 31%)]. Increases in enzymes of glucose metabolism [phosphofructokinase (29 ± 94%) and glucose transporter 4 (18 ± 65%)] were not significant. There was no relationship between changes in maximal oxygen uptake and the changes in the metabolic proteins. Considerable interindividual variability was seen in the magnitude of responses. The response of each enzyme was proportional to the change in SDH; individuals with a large increase in SDH also showed high gains in all other enzymes, and vice versa. Peroxisome proliferator-activated receptor γ coactivator 1α protein content increased after training, but was not correlated with changes in the metabolic proteins. In conclusion, the results revealed co-ordinated adaptation of several metabolic enzymes following endurance training, despite differences between people in the magnitude of response. Differences between individuals in the magnitude of response might reflect the influence of environmental and genetic factors that govern training adaptations.