Reliability of assessments of ventilatory thresholds

Effects of exhaustive whole-body exercise and caffeine ingestion on muscle contractile properties in healthy men

BACKGROUND

The influence of exhaustive whole-body exercise and caffeine ingestion on electromechanical delay (EMD) has been underexplored. This study investigated the effect of exhaustive cycling exercise on EMD and other parameters of muscle contractile properties and the potential ability of caffeine to attenuate the exercise-induced impairments in EMD and muscle contractile properties.

METHODS

Ten healthy men cycled until exhaustion (88±2% of V̇O2max) on two separate days after ingesting caffeine (5 mg.kg-1 of body mass) or cellulose (placebo). Parameters of muscle contractile properties of the quadriceps muscles were assessed via volitional and electrically evoked isometric contractions, performed before and 50 minutes after ingestion of the capsules, and after exercise. Muscle recruitment during volitional contractions was determined via surface electromyography.

RESULTS

Exhaustive cycling exercise did not affect volitional and relaxation EMD (P>0.05) but increased evoked EMD. In addition, the exhaustive cycling exercise also increased muscle recruitment at the beginning of volitional isometric muscle contraction (P<0.05). The peak twitch force, maximal rate of twitch force development, and twitch contraction time were all compromised after exhaustive cycling exercise (P<0.05). Acute caffeine ingestion had no effect on muscle contractile properties (P>0.05), except that caffeine increased twitch contraction time at postexercise (P<0.05).

CONCLUSIONS

Exercise-induced decline in peripheral components of the EMD might be compensated by an increase in the muscle recruitment. In addition, acute caffeine ingestion had minimal influence on exercise-induced changes in muscle contractile proprieties.

Comparing the reliability of muscle oxygen saturation with common performance and physiological markers across cycling exercise intensity

Introduction

Wearable near-infrared spectroscopy (NIRS) measurements of muscle oxygen saturation (SmO2) demonstrated good test-retest reliability at rest. We hypothesized SmO2 measured with the Moxy monitor at the vastus lateralis (VL) would demonstrate good reliability across intensities. For relative reliability, SmO2 will be lower than volume of oxygen consumption (V̇O2) and heart rate (HR), higher than concentration of blood lactate accumulation ([BLa]) and rating of perceived exertion (RPE). We aimed to estimate the reliability of SmO2 and common physiological measures across exercise intensities, as well as to quantify within-participant agreement between sessions.

Methods

Twenty-one trained cyclists completed two trials of an incremental multi-stage cycling test with 5 min constant workload steps starting at 1.0 watt per kg bodyweight (W·kg-1) and increasing by 0.5 W kg-1 per step, separated by 1 min passive recovery intervals until maximal task tolerance. SmO2, HR, V̇O2, [BLa], and RPE were recorded for each stage. Continuous measures were averaged over the final 60 s of each stage. Relative reliability at the lowest, median, and highest work stages was quantified as intraclass correlation coefficient (ICC). Absolute reliability and within-subject agreement were quantified as standard error of the measurement (SEM) and minimum detectable change (MDC).

Results

Comparisons between trials showed no significant differences within each exercise intensity for all outcome variables. ICC for SmO2 was 0.81-0.90 across exercise intensity. ICC for HR, V̇O2, [BLa], and RPE were 0.87-0.92, 0.73-0.97, 0.44-0.74, 0.29-0.70, respectively. SEM (95% CI) for SmO2 was 5 (3-7), 6 (4-9), and 7 (5-10)%, and MDC was 12%, 16%, and 18%.

Discussion

Our results demonstrate good-to-excellent test-retest reliability for SmO2 across intensity during an incremental multi-stage cycling test. V̇O2 and HR had excellent reliability, higher than SmO2. [BLa] and RPE had lower reliability than SmO2. Muscle oxygen saturation measured by wearable NIRS was found to have similar reliability to V̇O2 and HR, and higher than [BLa] and RPE across exercise intensity, suggesting that it is appropriate for everyday use as a non-invasive method of monitoring internal load alongside other metrics.

Machine Learning Models for the Automatic Detection of Exercise Thresholds in Cardiopulmonary Exercising Tests: From Regression to Generation to Explanation

The cardiopulmonary exercise test (CPET) constitutes a gold standard for the assessment of an individual's cardiovascular fitness. A trend is emerging for the development of new machine-learning techniques applied to the automatic process of CPET data. Some of these focus on the precise task of detecting the exercise thresholds, which represent important physiological parameters. Three are the major challenges tackled by this contribution: (A) regression (i.e., the process of correctly identifying the exercise intensity domains and their crossing points); (B) generation (i.e., the process of artificially creating a CPET data file ex-novo); and (C) explanation (i.e., proving an interpretable explanation about the output of the machine learning model). The following methods were used for each challenge: (A) a convolutional neural network adapted for multi-variable time series; (B) a conditional generative adversarial neural network; and (C) visual explanations and calculations of model decisions have been conducted using cooperative game theory (Shapley's values). The results for the regression, generation, and explanatory techniques for AI-assisted CPET interpretation are presented here in a unique framework for the first time: (A) machine learning techniques reported an expert-level accuracy in the classification of exercise intensity domains; (B) experts are not able to substantially differentiate between a real vs an artificially generated CPET; and (C) Shapley's values can provide an explanation about the choices of the algorithms in terms of ventilatory variables. With the aim to increase their technology-readiness level, all the models discussed in this contribution have been incorporated into a free-to-use Python package called pyoxynet (ver. 12.1). This contribution should therefore be of interest to major players operating in the CPET device market and engineering.

Oxynet: A collective intelligence that detects ventilatory thresholds in cardiopulmonary exercise tests

The problem of the automatic determination of the first and second ventilatory thresholds (VT1 and VT2) from cardiopulmonary exercise test (CPET) still leads to controversy. The reliability of the gold standard methodology (i.e. expert visual inspection) feeds into the debate and several authors call for more objective automatic methods to be used in the clinical practice. In this study, we present a framework based on a collaborative approach, where a web-application was used to crowd-source a large number (1245) of CPET data of individuals with different aerobic fitness. The resulting database was used to train and test an artificial intelligence (i.e. a convolutional neural network) algorithm. This automatic classifier is currently implemented in another web-application and was used to detect the ventilatory thresholds in the available CPET. A total of 206 CPET were used to evaluate the accuracy of the estimations against the expert opinions. The neural network was able to detect the ventilatory thresholds with an average mean absolute error of 178 (198) mlO₂/min (11.1%, r = 0.97) and 144 (149) mlO₂/min (6.1%, r = 0.99), for VT1 and VT2 respectively. The performance of the neural network in detecting VT1 deteriorated in case of individuals with poor aerobic fitness. Our results suggest the potential for a collective intelligence system to outperform isolated experts in ventilatory thresholds detection. However, the inclusion of a larger number of VT1 examples certified by a community of experts will be likely needed before the abilities of this collective intelligence can be translated into the clinical use of CPET.

Validity and Reliability of Ventilatory and Blood Lactate Thresholds in Well-Trained Cyclists

PURPOSE

The purpose of this study was to determine, i) the reliability of blood lactate and ventilatory-based thresholds, ii) the lactate threshold that corresponds with each ventilatory threshold (VT1 and VT2) and with maximal lactate steady state test (MLSS) as a proxy of cycling performance.

METHODS

Fourteen aerobically-trained male cyclists ([Formula: see text] 62.1±4.6 ml·kg-1·min-1) performed two graded exercise tests (50 W warm-up followed by 25 W·min-1) to exhaustion. Blood lactate, [Formula: see text] and [Formula: see text] data were collected at every stage. Workloads at VT1 (rise in [Formula: see text];) and VT2 (rise in [Formula: see text]) were compared with workloads at lactate thresholds. Several continuous tests were needed to detect the MLSS workload. Agreement and differences among tests were assessed with ANOVA, ICC and Bland-Altman. Reliability of each test was evaluated using ICC, CV and Bland-Altman plots.

RESULTS

Workloads at lactate threshold (LT) and LT+2.0 mMol·L-1 matched the ones for VT1 and VT2, respectively (p = 0.147 and 0.539; r = 0.72 and 0.80; Bias = -13.6 and 2.8, respectively). Furthermore, workload at LT+0.5 mMol·L-1 coincided with MLSS workload (p = 0.449; r = 0.78; Bias = -4.5). Lactate threshold tests had high reliability (CV = 3.4-3.7%; r = 0.85-0.89; Bias = -2.1-3.0) except for DMAX method (CV = 10.3%; r = 0.57; Bias = 15.4). Ventilatory thresholds show high reliability (CV = 1.6%-3.5%; r = 0.90-0.96; Bias = -1.8-2.9) except for RER = 1 and V-Slope (CV = 5.0-6.4%; r = 0.79; Bias = -5.6-12.4).

CONCLUSIONS

Lactate threshold tests can be a valid and reliable alternative to ventilatory thresholds to identify the workloads at the transition from aerobic to anaerobic metabolism.

Associations between physical fitness and HbA₁(c) in type 2 diabetes mellitus

AIM/HYPOTHESIS

In people with type 2 diabetes, exercise improves glucose control (as reflected in HbA₁(c)) and physical fitness, but it is not clear to what extent these exercise-induced improvements are correlated with one another. We hypothesised that reductions in HbA₁(c) would be related: (1) to increases in aerobic fitness and strength respectively in patients performing aerobic training or resistance training; and (2) to changes in strength and aerobic fitness in patients performing aerobic and resistance training.

METHODS

We randomly allocated 251 type 2 diabetes patients to aerobic, resistance, or aerobic plus resistance training, or to a sedentary control group. Peak oxygen consumption VO₂(peak), workload, treadmill time and ventilatory threshold measurements from maximal treadmill exercise testing were measured at baseline and 6 months. Muscular strength was measured as the maximum weight that could be lifted eight times on the leg press, bench press and seated row exercises.

RESULTS

With aerobic training, significant associations were found between changes in both VO₂(peak) (p = 0.040) and workload (p = 0.022), and changes in HbA₁(c.) With combined training, improvements in VO₂(peak) (p = 0.008), workload (p = 0.034) and ventilatory threshold (p = 0.003) were significantly associated with changes in HbA₁(c.) Increases in strength on the seated row (p = 0.006) and in mid-thigh muscle cross-sectional area (p = 0.030) were significantly associated with changes in HbA₁(c) after resistance exercise, whereas the association between increases in muscle cross-sectional area and HbA₁(c) in participants doing aerobic plus resistance exercise (p = 0.059) was of borderline significance.

CONCLUSIONS/INTERPRETATION

There appears to be a link between changes in fitness and HbA₁(c). The improvements in cardiorespiratory fitness with aerobic training may be a better predictor of changes in HbA₁(c) than improvements in strength.

Effect of exercise training on physical fitness in type II diabetes mellitus

Few studies have compared changes in cardiorespiratory fitness between aerobic training only or in combination with resistance training. In addition, no study to date has compared strength gains between resistance training and combined exercise training in type II diabetes mellitus (T2DM).

PURPOSE

We evaluated the effects of aerobic exercise training (A group), resistance exercise training (R group), combined aerobic and resistance training (A + R group), and sedentary lifestyle (C group) on cardiorespiratory fitness and muscular strength in individuals with T2DM.

METHODS

Two hundred and fifty-one participants in the Diabetes Aerobic and Resistance Exercise trial were randomly allocated to A, R, A + R, or C. Peak oxygen consumption (V O(2peak)), workload, and treadmill time were determined after maximal exercise testing at 0 and 6 months. Muscular strength was measured as the eight-repetition maximum on the leg press, bench press, and seated row. Responses were compared between younger (aged 39-54 yr) and older (aged 55-70 yr) adults and between sexes.

RESULTS

VO(2peak) improved by 1.73 and 1.93 mL O(2)*kg(-1)*min(-1) with A and A + R, respectively, compared with C (P < 0.05). Strength improvements were significant after A + R and R on the leg press (A + R: 48%, R: 65%), bench press (A + R: 38%, R: 57%), and seated row (A + R: 33%, R: 41%; P < 0.05). There was no main effect of age or sex on training performance outcomes. There was, however, a tendency for older participants to increase VO(2peak) more with A + R (+1.5 mL O(2)*kg(-1)*min(-1)) than with A only (+0.7 mL O(2)*kg(-1)*min(-1)).

CONCLUSIONS

Combined training did not provide additional benefits nor did it mitigate improvements in fitness in younger subjects compared with aerobic and resistance training alone. In older subjects, there was a trend to greater aerobic fitness gains with A + R versus A alone.

Metabolic and behavioral vulnerability related to weight regain in reduced-obese men might be prevented by an adequate diet–exercise intervention

The aim of this pilot study was to determine whether it was possible to prevent the metabolic and behavioral vulnerability related to weight regain generally observed in a reduced-obese state with a supervised diet-exercise clinical intervention. In this regard, the anthropometric and physiological effects of a body weight loss program were studied in 11 obese men and the impact of weight loss on appetite was measured by visual analogue scales (VAS) and by the use of a standardized buffet-type meal. All the measurements were assessed at the beginning of the intervention (baseline), after 5+/-1 kg body weight loss (Phase 1) and after 10+/-1 kg body weight loss (Phase 2). In Phase 1 and Phase 2, respectively, the diet-exercise intervention significantly reduced fat mass, waist circumference, fasting insulin and glucose, resting heart rate, and resting systolic and diastolic blood pressures. The diet-exercise intervention also preserved fat-free mass, resting metabolic rate, resting respiratory quotient, and immune function. No significant difference was observed in appetite sensations between the three time points, either measured with VAS in the fasting state or with the satiety quotient (SQ) calculation. Thus, this study provides evidence that obesity can be managed by adequate and specific lifestyle changes leading to clinical benefits while avoiding side effects potentially promoting an increase in energy intake and body weight relapse.

Psychobiological impact of a progressive weight loss program in obese men

Psychobiological effects associated with a progressive body weight loss may help to improve the understanding of psychological barriers to weight loss. We hypothesized that a moderate body weight loss (about 10% of initial body weight) is accompanied with some negative psychological impact. Four questionnaires [SF-36 Health Survey, Three-Factor Eating Questionnaire (TFEQ), Beck Depression Inventory (BDI) and Pittsburgh Sleep Quality Index (PSQI)] were administered at each phase of a body weight loss program that consisted of a supervised diet and exercise clinical intervention to 11 obese men (mean BMI = 33.4 kg/m(2), mean age = 38 yr). The three phases investigated were: 1) at the beginning of the intervention (baseline); 2) after 5 +/- 1 kg body weight loss (Phase 1); and 3) after 10 +/- 1 kg body weight loss (Phase 2). Using the SF-36 Health Survey, physical and mental health were shown to be significantly improved at Phase 1 (p < 0.05). The TFEQ showed that cognitive dietary restraint increased (p < 0.001), and both disinhibition (p < 0.05) and susceptibility to hunger (p < 0.05) were significantly reduced at both Phase 1 and 2 compared to baseline. Depression as measured by the BDI significantly increased at Phase 2 (p < 0.05) compared to baseline and Phase 1. However, the mean BDI scores observed remained below the cut-off point for likely clinical significance. Finally, the PSQI showed that sleep quality was significantly improved at Phase 1 compared to baseline (p < 0.01). Altogether, these results suggest that a substantial improvement in the psychobiological profile occurs with a 5-kg weight loss (Phase 1) but that with additional weight loss (Phase 2) a small, but significant increase in depression occurred and seems to be associated with the increase in rigid restraint of eating. However, prospective studies with a larger sample are needed to confirm and deepen these results.

Effects of exercise intensity on food intake and appetite in women

BACKGROUND

Increasing exercise intensity has been shown to reduce energy intake in men.

OBJECTIVE

The main objective of this study was to investigate the effects of exercise intensity on energy intake in women.

DESIGN

Thirteen moderately active (peak oxygen uptake: 44.0 +/- 4.7 mL . kg(-1) . min(-1)) women [body mass index (in kg/m(2)): 22.2 +/- 2.4; age: 22.2 +/- 2.0 y] were subjected to 3 experimental conditions: control with no exercise and 2 equicaloric (350 kcal) low- (LIE) and high- (HIE) intensity exercise sessions at 40% and 70% of peak oxygen uptake, respectively. After each session, the participants ate ad libitum from buffet-type meals at lunch and dinner and ate snacks during the afternoon and evening. Visual analogue scales were used to rate appetite.

RESULTS

More energy was ingested at lunchtime after the HIE session than after the control session (878 +/- 309 and 751 +/- 230 kcal, respectively; P = 0.02). Relative energy intake (postexercise energy intake corrected for the energy cost of exercise above the resting level) at lunch was lower after the LIE session than after the control session (530 +/- 233 and 751 +/- 230 kcal, respectively; P < 0.001) and was lower after the HIE session than after the control session (565 +/- 301 and 751 +/- 230 kcal, respectively; P < 0.01). Similarly, daily energy intake tended to increase during the HIE session relative to that during the control session. No treatment effect was found for appetite scores throughout the experiment.

CONCLUSION

The results suggest that HIE increases energy intake in women.

An Evaluation of the Predictive Validity and Reliability of Ventilatory Threshold

PURPOSE

To identify a valid and reliable method to determine 40-km time trial (40K) performance in a laboratory setting.

METHODS

Part 1: Ventilatory threshold (VT) and 40K performance were determined on two occasions (February/September) using two subsets of cyclists (N = 15 each; VO(2max) 67.6 +/- 4.2/71.5 +/- 3.0 mL x kg(-1) x min(-1)) to determine the predictive validity of VT assessments. Variables of interest were power output at VT, peak power output (MaxVT(w)), and average power output during 40K (40K(avgwatts)). For VT determination we used: breakpoint of VE/VO2; breakpoint of VE/VCO2; V-slope; RER = 1; and RER = 0.95. In part 2, test-retest reliability of VT and MaxVT(w) were examined in 20 subjects (VO(2max) 64.8 +/- 8.0 mL x kg(-1) x min(-1)) on two occasions, separated by 48 h.

RESULTS

Regression analyses between power outputs at VTs and 40K(avgwatts) showed significant predictive validity for (February/September): V-slope (r = 0.79/0.84; SEE 155/13.3W), VE/VO2 (r = 0.80/0.81; SEE 15.2/14.2W), RER0.95 (r = 0.73/0.58; SEE 17.4/21.2W), RER1 (r = 0.75/0.74; SEE 16.8/16.7W), and MaxVT(w) (r = 0.81/0.73; SEE 15.0/17.1W). Paired t-tests between power outputs at VTs and the 40K(avgwatts) indicated that mean power outputs at VE/O2 (261 +/- 29W; P = 0.33) and RER0.95 (274 +/- 55W; P = 0.93) in February and VE/VO2 (274 +/- 37W; P = 0.79) in September were not significantly different from the respective 40K(avgwatts) (277 +/- 30W/281 +/- 30W). Test-retest reliability analysis yielded the following intraclass correlation and relative test-retest errors: V-slope: 0.98, 2.6%; VE/VO2: 0.95, 5.3%; RER0.95: 0.87, 9.8%; RER1: 0.94, 5.7%; VE/VCO2: 0.87, 12.1%; MaxVT(w): 0.98, 2.6%.

CONCLUSION

The high test-retest reliability and consistent ability to accurately predict athletes' 40K(avgwatts) across a competitive season indicated that VE/VO2 was superior to the other evaluated methods.

Is the relationship between adipose tissue and waist girth altered by weight loss in obese men?

OBJECTIVE

The aim of the present study was to examine whether the association of waist girth to visceral adipose tissue (AT) accumulation was altered by weight loss in abdominally obese men.

RESEARCH METHODS AND PROCEDURES

We studied 45 dyslipidemic abdominally obese men (45.4 +/- 6.2 years of age; body mass index [BMI], 31.3 +/- 3.0 kg/m(2); waist circumference, 103.4 +/- 7.6 cm; total cholesterol, <6.72 mM; triglycerides, > or =1.7 mM but < or =5.65 mM; high density lipoprotein cholesterol, < or =1.2 mM). Each of them followed nutritional recommendations combined with a prescription of gemfibrozil (1200 mg/d) or a placebo for 1 year. After 6 months, a training exercise program was added at a frequency of four sessions of 60 minutes per week at 50% of maximal oxygen uptake.

RESULTS

In response to the 1-year intervention program, men showed significant reductions in body weight, BMI, waist circumference, and in the partial volume of visceral and abdominal subcutaneous AT measured from two abdominal computed tomography scans performed at lumbar vertebra (L)2 to L3 and L4 to L5 levels. No change in waist-to-hip ratio was observed. Changes in visceral AT were strongly correlated with changes in body weight, BMI, and waist circumference (0.83 < r < 0.85; p < 0.001). However, a weak association was noted between waist-to-hip ratio and changes in visceral AT (r = 0.40; p < 0.05). There was no change in slopes or in intercepts before and after treatment in the relationships between volume or area of abdominal AT and anthropometric markers.

DISCUSSION

Despite a greater level of the partial volume of subcutaneous AT than of the partial volume of visceral AT at baseline (p < 0.001), the greater relative reduction in the visceral AT volume in comparison with the subcutaneous AT volume suggested a preferential mobilization of visceral AT with weight loss in these abdominally obese men. The close relationship between changes in the partial volume of visceral AT and changes in cross-sectional areas of visceral AT measured at L2 to L3 (r = 0.94; p < 0.001) or L4 to L5 (r = 0.88; p < 0.001) suggests that a single computed tomography scan performed at L2 to L3 or L4 to L5 could predict changes in the partial volume of visceral AT secondary to weight loss.

Reproducibility of ventilation of thresholds in trained cyclists during ramp cycle exercise

The reproducibility of peak cardiopulmonary exercise responses and the first (VT1) and second [VT2) ventilation thresholds was studied in sixteen endurance-trained male cyclists (mean +/- SD peak oxygen uptake [VO2 peak] = 63.3 +/- 7.1 ml x kg(-1) x min(-1)) during duplicate 30 W x min(-1) ramp cycling protocols. Expired gas sampled from a mixing chamber was analysed on-line and VT1 and VT2 were determined by computerised V-slope analysis and visually by two evaluators (test-retest reliability) and again by one of the evaluators 12 months later (intra-evaluator reliability) from 20-s-average respiratory data. The results demonstrated high intra-evaluator reliability (r = 0.91-0.97, P < 0.0001) for repeat determinations of VO2, work rate (WR) and heart rate (HR) at VT1 and VT2. No significant differences were observed between Tests 1 and 2 for any of the measured variables (P > 0.05). Test-retest intraclass reliability coefficients ranged from 0.86 to 0.98 (P < 0.0001) for VO2 peak, peak pulmonary ventilation (VE), carbon dioxide output (VCO2), HR and WR values, and measurements of VO2 and WR at VT2, and from 0.67 to 0.80 (P < 0.01) for measurements of VO2 and WR at VT1. The reliability of VT1 and VT2 was reduced when the thresholds were expressed as relative (%VO2 peak) (r = 0.67-0.70, P<0.01) rather than absolute (l x min(-1)) (r = 0.77-0.93, P<0.001) VO2 values. It was concluded that VO2 peak, peak VE, VCO2. HR and WR values, and VT2 are highly reproducible in trained cyclists using a 30 W x min(-1) ramp exercise function. However, determinations of VT1 are less reliable. Additionally, ventilation thresholds are more reliably described using absolute rather than relative VO2 values.

Impact of high-intensity exercise on energy expenditure, lipid oxidation and body fatness

OBJECTIVE

Two studies were conducted to assess the potential of an increase in exercise intensity to alter energy and lipid metabolism and body fatness under conditions mimicking real life.

METHODS

Study 1 was based on the comparison of adiposity markers obtained in 352 male healthy adults who participated in the Québec Family Study who either regularly participated in high-intensity physical activities or did not. Study 2 was designed to determine the effects of high-intensity exercise on post-exercise post-prandial energy and lipid metabolism as well as the contribution of beta-adrenergic stimulation to such differences under a real-life setting.

RESULTS

Results from Study 1 showed that men who regularly take part in intense physical activities display lower fat percentage and subcutaneous adiposity than men who never perform such activities, and this was true even if the latter group reported a lower energy intake (917 kJ/day, P<0.05). In Study 2, the high-intensity exercise stimulus produced a greater post-exercise post-prandial oxygen consumption as well as fat oxidation than the resting session, an effect which disappeared with the addition of propranolol. In addition, the increase in post-prandial oxygen consumption observed after the high-intensity exercise session was also significantly greater than that promoted by the low-intensity exercise session.

CONCLUSION

These results suggest that high-intensity exercise favors a lesser body fat deposition which might be related to an increase in post-exercise energy metabolism that is mediated by beta-adrenergic stimulation.

Metabolic fitness in active reduced-obese individuals

OBJECTIVE

To verify whether a physical activity-low-fat diet follow-up could normalize the metabolic risk profile of reduced-obese men and women having undergone considerable weight loss through energy restriction and drug therapy.

RESEARCH METHODS AND PROCEDURES

Twenty obese individuals (12 men, 8 women) participated in a weight-reducing program that included two phases. In the first phase, a non-macronutrient-specific dietary restriction of about 700 kcal/day was prescribed to induce weight loss over 15 weeks, with either fenfluramine or placebo. The second phase consisted of a physical activity-low-fat diet follow-up that was maintained as long as subjects did not experience resistance to further body weight and fat loss. Resistance to lose fat occurred after a mean cumulative fat loss of 14 and 8 kg in men and women, respectively.

RESULTS

Despite this substantial decrease in body fat, subjects' adiposity remained much higher at the end of this protocol than values observed in lean control subjects. However, fasting plasma levels of insulin, cholesterol, high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol, and triglyceride as well as the response of insulin and glucose to oral glucose were normalized at the end of the physical activity-low-fat diet follow-up.

DISCUSSION

These results indicate that further weight and fat losses may not be justified when a moderate body weight loss resulting in a highly favorable improvement of metabolic risk profile is achieved in patients who would have still been diagnosed as overweight or obese on the basis of criteria currently promoted by public health agencies.

Physical activity and low-fat diet: is it enough to maintain weight stability in the reduced-obese individual following weight loss by drug therapy and energy restriction?

OBJECTIVE

The anthropometric and physiological effects of a physical activity (PA) and a mildly energy-restricted low-fat diet (LFD) follow-up program after a long-term dietary restriction were studied in 12 men and 8 women.

RESEARCH METHODS AND PROCEDURES

The dietary restriction (approximately 700 kcal/day) was accompanied by a fenfluramine (60 mg/day) or placebo treatment for 15 weeks, whereas the mean duration of the PA-LFD follow-up was 18 weeks.

RESULTS

The long-term dietary restriction reduced body weight (-11.9 and -7.6 kg, p<.001), fat mass (FM) (-10.6 and -5.8 kg, p<0.01), resting metabolic rate (RMR) (-304 kcal/day, p<0.01 and -148 kcal/day, NS) in men and women, respectively. A decrease in fat-free mass (FFM) was also observed in women (-1.8 kg, p<0.05). The PA-LFD follow-up preserved weight stability at a reduced body weight and caused an additional significant decrease in FM for men (-3.4 kg, p<0.05). This part of the intervention also caused an increase in daily RMR for men (134 kcal/day, NS) to the point where this value no longer differed from the pre-energy restriction value. In contrast, RMR was further reduced in women (-200 kcal/day) to the point where it significantly differed from initial values (p<0.01). Resting seated heart rate was reduced by the PA-LFD follow-up in men leading it to differ significantly from both pre- and post-energy restriction values (-8.5 and -5.5 bpm, p<0.01).

DISCUSSION

In conclusion, these results suggest that a PA-LFD follow-up has the potential to permit body weight stability and may even accentuate fat loss in the reduced-obese state. Moreover, resting energy expenditure is increased under such conditions in men. These stimulating effects seem to be specific to energy metabolism since seated heart rate was either further reduced or remained stable in response to the PA-LFD follow-up.

Postexercise macronutrient oxidation: a factor dependent on postexercise macronutrient intake

BACKGROUND

It has been widely shown that exercise increases postexercise fat oxidation and energy expenditure.

OBJECTIVE

The aim of this study was to investigate the effect of exercise on postexercise substrate oxidation and energy expenditure when the exercise-induced expenditure of energy and macronutrients oxidized is compensated by an equivalent intake immediately after exercise.

DESIGN

Twenty-four-hour energy expenditure (24EE) and macronutrient oxidation of 8 young men were measured in a whole-body indirect calorimeter under the 2 following, randomly assigned conditions: 1) a control session of sedentary activities in the calorimeter for 61 h and 2) a similar session preceded by 60 min of exercise at 50% of maximal oxygen consumption. Immediately after exercising, subjects ingested a milk shake containing the same amount of energy (above resting metabolic rate) expended during exercise and with a food quotient corresponding to the mean exercise respiratory quotient. 24EE and substrate oxidation were compared between conditions on a day-to-day basis (days 1, 2, and 3) and for the 61-h observation period.

RESULTS

There was no difference in 24EE between the 2 conditions. Moreover, the composition of the postexercise fuel mix oxidized, as reflected by the respiratory quotient, was strictly the same under the 2 conditions.

CONCLUSION

Voluntary postexercise compensations in energy and macronutrient intakes play a major role in the ability of exercise to alter postexercise substrate utilization.

Monitoring high-intensity endurance exercise with heart rate and thresholds

Ventilatory and lactate thresholds have been proposed as tools to establish the highest steady-state intensity sustainable during prolonged physical exercise. The purposes of this study were to clarify whether the intensity at the ventilatory threshold could be sustained during prolonged high-intensity exercise and if the corresponding work rate, pulmonary ventilation, and blood lactate concentration could also be maintained. Fifteen young and healthy male subjects were submitted to a VO2max test on ergocycle and a 90-min high-intensity ergocycle endurance exercise test. During the 90-min exercise test, subjects were able to maintain an intensity corresponding to a heart rate 5 beats.min-1 lower than that predetermined from the ventilatory threshold. Heart rate, FeO2, and FeCO2 were stable during the period from 20 to 80 min, VO2 was constant from 30 to 80 min, while work output, pulmonary ventilation, blood lactate, and VCO2 decreased significantly over the 90-min performance. These results show that physiological parameters near the ventilatory threshold are not interchangeable and that some cannot be used to monitor high-intensity long term exercise. Moreover, they clearly demonstrate that the blood lactate concentration fluctuates substantially during a 90-min endurance performance and cannot predict the highest work intensity that can be sustained during prolonged exercise without fatigue. However, heart rate and VO2 at the ventilatory threshold seem to be more suitable markers for that purpose.

Specificity effects of run versus cycle training on ventilatory threshold

This study compared the effects of 9 weeks of run (RT) versus cycle (CT) training on ventilatory threshold (Thv) determined during treadmill (TM) and cycle ergometer (CE) graded exercise testing. Sixteen college age men were assigned to a RT or CT group and performed a TM and a CE test before and after training. Both training groups performed similar training protocols which initially consisted of continuous exercise 4 days.week-1 at 75-80% maximum heart rate (fc, max) for 45 min. Training intensity was later increased to 80-85% fc, max and interval training (90-95% fc, max) was incorporated 2 days.week-1 into the continuous training. Both groups showed significantly improved maximal oxygen consumption (VO2 max) on both TM and CE tests (P < 0.01) with no significant differences between the groups. Significant Thv increases (P < 0.05) were found on TM tests for RT (n = 8) and CT (n = 8) groups [mean (SD); 443 (438) and 373 (568) ml O2 x min-1, respectively] with no difference between the groups. Results from the CE tests revealed a significant Thv increase (P < 0.01) for the CT group [566 (663) ml O2 x min-1] with no change for the RT group. The Thv improvement noted for the RT group was significantly different (P < 0.05) comparing CE with TM tests but not for the CT group. The results indicate that CT and RT improvement in Thv for runners is dependent upon mode of training and testing, and there is an apparent dissociation of VO2 max and Thv specific to training.

The ventilatory threshold gives maximal lactate steady state

The purpose of this study was to examine whether the ventilatory threshold (Thv) would give the maximal lactate steady state ([la]ss, max), which was defined as the highest work rate (W) attained by a subject without a progressive increase in blood lactate concentration [la]b at constant intensity exercise. Firstly, 8 healthy men repeated ramp-work tests (20 W.min-1) on an electrically braked cycle ergometer on different days. During the tests, alveolar gas exchange was measured breath-by-breath, and the W at Thv (WThv) was determined. The results of two-way ANOVA showed that the coefficient of variation of a single WThv determination was 2.6%. Secondly, 13 men performed 30-min exercise at WThv (Thv trial) and at 4.9% above WThv (Thv + trial), which corresponded to the 95% confidence interval of the single determination. The [la]b was measured at 15 and 30 min from the onset of exercise. The [la]b at 15 min (3.15 mmol.l-1, SEM 0.14) and at 30 min (2.95 mmol.l-1, SEM 0.18) were not significantly different in Thv trial. However, the [la]b of Thv + trial significantly increased (P less than 0.05) from 15 min (3.62 mmol.l-1, SEM 0.36) to 30 min (3.91 mmol.l-1, SEM 0.40). These results indicate that Thv gives the [la]ss, max, at which one can perform sustained exercise without continuous [la]b accumulation.

Heredity and changes in body composition and adipose tissue metabolism after short-term exercise-training

The purpose of the experiment was to investigate the genotype dependency of body composition and adipose tissue metabolism following short-term exercise-training. Six pairs of male, sedentary monozygotic twins took part in a 22 day ergocycle training program at 58% VO2max, with a mean exercise duration of 116 min x day-1. Body weight, fat mass, percent body fat and VO2max, were evaluated before and after the training program. From a suprailiac region fat biopsy, the following adipose tissue metabolic variables were evaluated: fat cell diameter, basal and epinephrine stimulated lipolysis, basal and insulin stimulated lipogenesis from glucose and heparin releasable lipoprotein lipase activity. The exercise-training program increased (p less than 0.01) VO2max and decreased (p less than 0.01) body weight, fat mass and percent body fat. Variation in response within twin pairs was not significantly different than response between pairs in the aforementioned variables. However, a significant within pair resemblance (p less than 0.01) for changes in fat free mass was observed. Adipose tissue metabolic indicators exhibited a large interindividual variation in response to exercise-training. Significant within twin pair resemblance was observed only for basal lipogenesis. Moreover, the non significant within twin pair resemblance for changes in body fat and adipose tissue metabolic indicators suggests that heredity is not a major factor influencing changes in body fat and adipose tissue indicators to short-term training resulting in negative energy balance. Changes in fat free mass were, however, closely coupled to the genotype.

Heredity and changes in hormones and metabolic rates with short-term training

The purpose of this experiment was to assess the effects of a 22-day training program on resting metabolic rate (RMR), thermic effect of a meal (TEM), and associated hormonal changes. Six pairs of male monozygotic twins were submitted to a 22-day ergocycle exercise program designed to induce a deficit in energy balance of 4.2 MJ per day. RMR and TEM after a 4.2-MJ meal challenge were measured before and after training. Results indicated that RMR and TEM did not change significantly, although a large variation in response between twin pairs was observed. Moreover, training reduced (P less than 0.05) basal and postprandial insulin response, plasma thyroid hormones triiodothyronine (T3), thyroxine (T4), and FT4 (P less than 0.05). Absolute changes in RMR and TEM exhibited significant within-pair resemblance in response, with intraclass correlations reaching r = 0.81 (P less than 0.05) and r = 0.72 (P less than 0.05), respectively. Changes in T4 and FT4 also exhibited moderate within-pair resemblance (0.42 less than or equal to r less than or equal to 0.71). These results suggest that short-term exercise training does not modify RMR and TEM but can significantly decrease plasma levels of insulin and thyroid hormones. Moreover, the similarity of response within twin pairs suggests that heredity plays a role in determining RMR, TEM, and thyroid hormone adaptation to exercise training generating a negative energy balance.

Relationships between skeletal muscle characteristics and aerobic performance in sedentary and active subjects

Forty-eight sedentary and 39 quite active or well-trained men participated in this study. Muscle biopsy samples were taken from the vastus lateralis for the determination of fiber type composition (I, IIa, IIb), fiber type area, and assay of the following enzymes: malate dehydrogenase (MDH), 3-hydroxyacyl CoA dehydrogenase (HADH) and oxoglutarate dehydrogenase (OGDH). Maximal oxygen uptake (VO2max) was determined with a progressive cycle ergometer test, while endurance performance or maximal aerobic capacity (MAC) was defined as the total work output during a 90-min cycle ergometer test. Correlation analysis revealed no evidence of association between fiber type composition and VO2max kg-1 or MAC kg-1 in sedentary subjects, while active men exhibited significant correlation between % type I (r = 0.52), % type IIb (r = 0.31) and VO2max kg-1. Enzyme activities were not significantly correlated with MAC kg-1 and VO2max kg-1 in sedentary men while active men exhibited significant correlation for the three enzymes (0.37 less than or equal to r less than or equal to 0.51) with VO2max kg-1. These results show that the contribution of muscle fiber type and enzyme activities to aerobic performance may be inflated from a statistical point of view by the training status heterogeneity of subjects. They also suggest that variation in these muscle characteristics does not account for the individual differences in aerobic performance of subjects who have never trained before. Therefore, the assessment of muscle characteristics is not as useful as originally thought for the detection of individuals with a high potential for endurance performance among untrained subjects.

Human skeletal muscle fiber type alteration with high-intensity intermittent training

The response of muscle fiber type proportions and fiber areas to 15 weeks of strenuous high-intensity intermittent training was investigated in twenty-four carefully ascertained sedentary (14 women and 10 men) and 10 control (4 women and 6 men) subjects. The supervised training program consisted mainly of series of supramaximal exercise lasting 15 s to 90 s on a cycle ergometer. Proportions of muscle fiber type and areas of the fibers were determined from a biopsy of the vastus lateralis before and after the training program. No significant change was observed for any of the histochemical characteristics in the control group. Training significantly increased the proportion of type I and decreased type IIb fibers, the proportion of type IIa remained unchanged. Areas of type I and IIb fibers increased significantly with training. These results suggest that high-intensity intermittent training in humans may alter the proportion of type I and the area of type I and IIb fibers and in consequence that fiber type composition in human vastus lateralis muscle is not determined solely by genetic factors.