Extension du modèle puissance–temps limite pour estimer la production d’énergie aérobie et anaérobie lors de l’exercice intense

Aim

Examine how the modelling of the relation between power and time to exhaustion can provide an estimation of the production of aerobic and anaerobic energy during intense exercise.

Current knowledge

The hyperbolic model made it possible to define the critical power corresponding to the maximal rate of energy renewed by aerobic metabolism. A new model distinguishing the critical power from the maximal aerobic power has been built to estimate more precisely the anaerobic contribution. Data from middle distance runners and subjects tested on cycle ergometer showed a relative contribution of anaerobic metabolism arising from critical power and increasing until around 10 % of total power when aerobic energy production reaches its maximum.

Prospects

Considering the slow component of oxygen uptake would provide a more precise analysis of energy production and transformation during exercise at high intensity.     

Estimated aerobic power, muscular strength and flexibility in elite Brazilian Jiu-Jitsu athletes

Objective

This study was designed to estimate the maximum oxygen uptake, muscular strength and flexibility of elite Brazilian Jiu-Jitsu athletes.

Methods

The sample consisted of eleven Brazilian Jiu-Jitsu athletes (25.8 ± 3.3 years old) who were medallists at national and/or international competitions. The aerobic power was estimated by a treadmill test, according to the Bruce Protocol. The maximal isometric strength (hand, leg and back) was measured by specific dynamometric tests. We used sit-ups and push-ups to evaluate abdominal and upper limb strength endurance, respectively. We applied the sit-and-reach test to determine hip, back and posterior flexibility of the muscles of the lower limbs.

Results

We observed a VO_2max of 49.4 ± 3.6 mL/kg per minute for the treadmill test. We observed measures of 43.7 ± 4.8 kgf for the right maximal isometric handgrip strength, 40.1 ± 3.8 kgf for the left maximal isometric handgrip strength, 185.5 ± 36.0 kgf for the maximal isometric back strength and 154.3 ± 41.9 kgf for the maximal isometric leg strength. In the strength endurance test, the athletes performed 52 ± 7 repetitions in a 1-min sit-up test, and 40 ± 8 repetitions in the push-up test. In the sit-and-reach test, the athletes had an average score of 36 ± 9 cm.

Conclusions

The elite Brazilian Jiu-Jitsu athletes had medium aerobic power and flexibility, excellent abdominal and upper body strength endurance and maximal isometric back strength. However, these athletes did not have high maximal isometric handgrip or leg strength.     

Maximal endurance time at VO2max

INTRODUCTION: There has been significant recent interest in the minimal running velocity which elicits VO2max. There also exists a maximal velocity, beyond which the subject becomes exhausted before VO2max is reached. Between these limits, there must be some velocity that permits maximum endurance at VO2max, and this parameter has also been of recent interest. This study was undertaken to model the system and investigate these parameters. METHODS: We model the bioenergetic process based on a two-component (aerobic and anaerobic) energy system, a two-component (fast and slow) oxygen uptake system, and a linear control system for maximal attainable velocity resulting from declining anaerobic reserves as exercise proceeds. Ten male subjects each undertook four trials in random order, running until exhaustion at velocities corresponding to 90, 100, 120, and 140% of the minimum velocity estimated as being required to elicit their individual VO2max. RESULTS: The model development produces a skewed curve for endurance time at VO2max, with a single maximum. This curve has been successfully fitted to endurance data collected from all 10 subjects (R2 = 0.821, P < 0.001). For this group of subjects, the maximal endurance time at VO2max can be achieved running at a pace corresponding to 88% of the minimal velocity, which elicits VO2max as measured in an incremental running test. Average maximal endurance at VO2max is predicted to be 603 s in a total endurance time of 1024 s at this velocity. CONCLUSION: Endurance time at VO2max can be realistically modeled by a curve, which permits estimation of several parameters of interest; such as the minimal running velocity sufficient to elicit VO2max, and that velocity for which endurance at VO2max is the longest.     

Heritability estimates of endurance‐related phenotypes: A systematic review and meta‐analysis

The aim of this study was to clarify heritability estimates for endurance‐related phenotypes and the underlying factors affecting these estimates. A systematic literature search was conducted for studies reporting heritability estimates of endurance‐related phenotypes using the PubMed database (up to 30 September 2016). Studies that estimated the heritability of maximal oxygen uptake (), submaximal endurance phenotypes, and endurance performance were selected. The weighted mean heritability for endurance‐related phenotypes was calculated using a random‐effects model. A total of 15 studies were selected via a systematic review. Meta‐analysis revealed that the weighted means of the heritability of absolute values and those adjusted for body weight and for fat‐free mass were 0.68 (95% CI : 0.59‐0.77), 0.56 (95% CI : 0.47‐0.65), and 0.44 (95% CI : 0.13‐0.75), respectively. There was a significant difference in the weighted means of the heritability of across these different adjustment methods (P  < .05). Moreover, there was evidence of statistical heterogeneity in the heritability estimates among studies. Meta‐regression analysis revealed that sex could partially explain the heterogeneity in the heritability estimates adjusted by body weight. For submaximal endurance phenotypes and endurance performance, the weighted mean heritabilities were 0.49 (95% CI : 0.33‐0.65) and 0.53 (95% CI : 0.27‐0.78), respectively. There was statistically significant heterogeneity in the heritability estimates reported among the studies, and we could not identify the specific factors explaining the heterogeneity. Although existing studies indicate that genetic factors account for 44%‐68% of the variability in endurance‐related phenotypes, further studies are necessary to clarify these values.     

Effect of prolonged exercise on arterial oxygen saturation in athletes susceptible to exercise-induced hypoxemia

This study examined the effect of prolonged endurance exercise on the development of exercise-induced hypoxemia (EIH) in athletes who had previously displayed EIH during an incremental maximal exercise test. Five male and three female endurance-trained athletes participated. Susceptibility to EIH was confirmed through a maximal incremental exercise test and defined as a reduction in the saturation of arterial oxygen (SpO(2)) of >/=4% from rest. Sixty minutes of running was conducted, on a separate day, at an oxygen consumption corresponding to 95% of ventilatory threshold. Immediately following the 60 min exercise bout, athletes commenced a time trial to exhaustion at 95% maximal oxygen consumption (VO(2max)). The reduction in SpO(2) was significantly greater during the maximal incremental test, than during the 60 min, or time trial to exhaustion (-8.8+/-1.4%, -3.3+/-1.1%, and -4.1+/-2.3%, P<0.05, respectively). The degree of desaturation during the 60 min was significantly related to the relative intensity of exercise at 95% ventilatory threshold (adjusted r(2)=0.54, P=0.02). In conclusion, athletes who did not exercise at greater than 73% VO(2max) during 60 min of endurance exercise did not display EIH, despite being previously susceptible during an incremental maximal test.     

Correction de l’hypoxémie d’exercice chez le BPCO : variabilité des réponses, enjeux et problèmes posés dans le cadre de la réhabilitation respiratoire

Aim

To define in chronic obstructive pulmonary disease patients (COPD) moderately hypoxemic in resting conditions, if controlled acute oxygen supplementation was always able to increase exercise tolerance when partial oxygen saturation SpO₂ was corrected.

Results

In hyperoxia, endurance time (T_LIM) was significantly and consistently increased in 14 COPD (+68%) and decreased in seven others (–36%). These two subgroups exhibited no difference in resting values or in their disease severity. COPD with a decreased T_LIM under hyperoxic conditions had an abnormal response to O₂: unchanged cardiac output and ventilation, increased breathing frequency.

Conclusion

This work shows that acute O₂ supplementation responses in COPD are not univocal, either on exercise tolerance or cardio-respiratory variables typically affected by hyperoxia.     

Muscle-specific creatine kinase gene polymorphism and running economy responses to an 18-week 5000-m training programme

Objective

To investigate the association between muscle‐specific creatine kinase (CKMM) gene polymorphism and the effects of endurance training on running economy.

Methods

102 biologically unrelated male volunteers from northern China performed a 5000‐m running programme, with an intensity of 95–105% ventilatory threshold. The protocol was undertaken three times per week and lasted for 18 weeks. Running economy indexes were determined by making the participants run on a treadmill before and after the protocol, and the A/G polymorphism in the 3′ untranslated region of CKMM was detected by polymerase chain reaction‐restricted fragment length polymorphism (NcoI restriction enzyme).

Results

Three expected genotypes for CKMM‐NcoI (AA, AG and GG) were observed in the participants. After training, all running economy indexes declined markedly. Change in steady‐state consumption of oxygen, change in steady‐state consumption of oxygen by mean body weight, change in steady‐state consumption of oxygen by mean lean body weight and change in ventilatory volume in AG groups were larger than those in AA and GG groups.

Conclusions

The findings indicate that the CKMM gene polymorphism may contribute to individual running economy responses to endurance training.The muscle‐specific creatine kinase (CKMM) enzyme is bound specifically to the M line of the myofibril subfragment,¹ one of the heavy meromyosin in the vicinity of the myosin ATPase and to the outer membrane and vesicles of the sarcoplasmic reticulum,² which might change the Ca²⁺ uptake³ and power of muscle. Type I (slow‐twitch) skeletal muscle fibres and type II (fast‐twitch) fibres have been shown to differ in their CKMM activities, with type I fibres showing at least a twofold lower CKMM activity.⁴ Skeletal muscles of athletes involved in endurance sports are characterised by a high proportion of type I fibres, as well as by high activity levels of marker enzymes of aerobic oxidative metabolism.⁵ Therefore, the lower activity of CKMM might be essential to endurance athletes.Running economy is typically defined as the energy demand for a given velocity of submaximal running, and is determined by measuring the steady‐state consumption of oxygen (VO₂) and the respiratory exchange ratio.⁶ Taking body mass into consideration, runners with good running economy use less energy and therefore less oxygen than runners with poor running economy at the same velocity.⁷ There is a strong association between running economy and distance running performance.^8,9,10The CKMM gene has been mapped to the q13.2–q13.3 region of chromosome 19.¹¹ Now, several lines of evidence suggest that the CKMM‐NcoI polymorphism in the 3′ untranslated region might contribute to the individual differences in VO₂max responses to endurance training.^12,13 Lucia et al,¹⁴ however, detected CKMM‐NcoI polymorphisms in 50 top‐level Spanish professional cyclists and 119 sedentary controls and found no significant differences for CKMM‐NcoI polymorphisms between athletes and controls. Recently, we found that the CKMM‐Nco polymorphism in the 3′ untranslated region was A/G variant by sequencing, and there were considerable differences in the allelic frequencies and genotypic frequencies between the Chinese Han population and those in Europe and America.¹⁵ Moreover, less is known about the association between CKMM‐NcoI polymorphism and individual running economy responses to endurance training. The purpose of this study, therefore, was to explore the potential relationship between the CKMM gene A/G polymorphism in Chinese and running economy responses to an 18‐week 5000‐m training programme.     

Application du concept de puissance critique à différentes populations

Aim

The aim of this review was to state the use of critical power concept at different populations and to summarize studies reported data in order to highlight its interest for the aerobic abilities assessement.

Conclusion

The critical power determination is based on times to exhaustion at different exercise intensities. The synthesis of several studies showed that this concept allows to discriminate populations relatively to their aerobic abilities. This is confirmed by its correlation to maximal oxygen uptake and ventilatory threshold in age and fitness different populations.     

Comparaison des données bioénergétiques observées lors d''un exercice musculaire sur bicyclettes équipées de plateaux rond ou «Harmonic

Introduction

In order to “harmonise” the constraints of pedalling (attenuate top dead centre and bottom dead centre), a non circular chain ring called “Harmonic” has been put on the market. The purpose of this study is to understand bioenergetic repercussions of this type of non circular chain ring during muscular exercise upon a bicycle.

Method

Thirteen regional level cyclists took part in this study. Each subject performed two maximal oxygen uptake exercise tests, one with a circular chain ring, the other with a “Harmonic” chain ring with the same cogwheel (52 tooth). They were performed on a cyclo-simulator. Speeds (km·h^t-1) and/or simulated slopes (%) increased every 2 min 30 s. They were, respectively: 28-2, 30-2, 35-2, 37.5-2, 40-2, 40-3, 42.5-3. O₂ uptake (VO₂), pulmonary ventilation and heart rate were measured continuously; and blood lactate concentration was measured during the last 30 s of each level.

Results

Regardless of speeds and slopes, there was no significant difference for VO₂, pulmonary ventilation, heart rate and blood lactate concentration between the two chain rings.

Conclusion

If the chain ring in question is supposed to attenuate top dead centre and bottom dead centre pedalling, it does not present any lessened energy expenditure during muscular exercise.     

Maximal strength training improves running economy in distance runners

PURPOSE: The present study investigated the effect of maximal strength training on running economy (RE) at 70% of maximal oxygen consumption [formula: see text] and time to exhaustion at maximal aerobic speed (MAS). Responses in one repetition maximum (1RM) and rate of force development (RFD) in half-squats, maximal oxygen consumption, RE, and time to exhaustion at MAS were examined. METHODS: Seventeen well-trained (nine male and eight female) runners were randomly assigned into either an intervention or a control group. The intervention group (four males and four females) performed half-squats, four sets of four repetitions maximum, three times per week for 8 wk, as a supplement to their normal endurance training. The control group continued their normal endurance training during the same period. RESULTS: The intervention manifested significant improvements in 1RM (33.2%), RFD (26.0%), RE (5.0%), and time to exhaustion at MAS (21.3%). No changes were found in [formula: see text] or body weight. The control group exhibited no changes from pre to post values in any of the parameters. CONCLUSION: Maximal strength training for 8 wk improved RE and increased time to exhaustion at MAS among well-trained, long-distance runners, without change in maximal oxygen uptake or body weight.     

Puissance critique : passé, présent et futur d’un concept

Current knowledge

The critical power concept was proposed in the studies carried out by Scherrer from 1954 to 1960. These studies found a linear relationship between the time to exhaustion and the total work performed during a local exercise. The slope of this relationship has the meaning of a critical power, i.e. a power output sustainable during a long time. Y intercept of this relationship has the dimension of an energy store. In 1958, Scherrer proposed the application of the critical power concept to athlete testing in running and swimming. In fact, the time limit–work limit is not perfectly linear as noted by Scherrer. The main consequence of this linear approximation is an overestimation of the true critical power and of the prediction of exhaustion times around critical power. The results of studies rediscovering the application of critical power to general exercises are presented, especially those carried out in Monod's Laboratory showing that critical power is close to a steady state of several physiological parameters, provided that this power if computed with exhaustion times ranging from 4 up to 30 min. The corollary of the unaccuracy of the prediction of exhaustion times is that the computation of critical power is insensitive to large differences in exhaustion times.

Prospects

Critical power will stay an interesting index of the aptitude to long lasting exercises, especially local exercises. On the other hand, it is unlikely that Y intercept will be used as an index of anaerobic capacity.     

Acute downhill running does not induce fat oxidation

Objectives

Eccentric exercise has been suggested for its potential to increase several health outcomes, including exercise-induced fat oxidation. Comparison of exercise intensity rather than exercise workload is required.

Methods

Thirteen moderately active young men (mean age, 24.6 ± 5.6 years; body mass index, 23.76 ± 3.24 kg/m²; maximal oxygen consumption (VO_2max), 49.00 ± 3.19 ml/kg/min) performed two counterbalanced running sessions for 40 min at 60% VO_2max, either running flat (Con-Exe) or running downhill at a gradient of ? 12% (Ecc-Exe). The volumes of oxygen and carbon dioxide (VO₂ and VCO₂) were collected during exercise sessions, and fat oxidation was calculated.

Results

There was no significant interaction between exercise condition and exercise duration (p > 0.05), and individual variations in fat oxidation during Con-Exe and Ecc-Exe were large and inconsistent.

Conclusion

Downhill running at 60% VO_2max and inclination of ? 12% does not induce fat oxidation.

     

Effects of high-intense stimuli on continuous running exercise at the ventilatory threshold

Aims

To verify the effects of previous interval training session on physiological and kinematic parameters during continuous running at ventilatory threshold.

Methods

Ten healthy male performed initially an incremental running test, in order to determine ventilatory threshold and maximal aerobic capacity. In another session, subjects performed three tasks as follows: (1) previous five-minute run at ventilatory threshold. After ten minutes rest: (2) interval training session (8 × 1-min at maximal velocity, alternated to one-minute at 50% maximal velocity). After 15 minutes rest: (3) posterior five-minute run at ventilatory threshold. Heart rate, ventilation, blood glucose and lactate concentrations, perceived exertion, stride frequency, stance period and swing period were compared before and after the interval training session.

Results

Significant increases were found in heart rate (∼12%), ventilation (∼23%), blood glucose (∼28%), blood lactate (230%), perceived exertion (∼25%) and stride frequency (∼5%) after interval training.

Conclusion

High-intense running stimuli affect physiological, perceptual and kinematics of a constant moderate intensity running, which could influence training session programmes, considering the impairment overall running performance.     

Intérêt d’un réentraînement à l’effort intermittent individualisé chez l’adolescent obèse

Introduction

To assess in six obese teenagers, the effects of 30 sessions (three days/week) of 50-minute individualised interval training on cardiorespiratory and metabolic parameters at rest and during exercise.

Synthesis

After this programme, fat mass decreases (10.8%) while BMI did not change. The expiratory reserve volume improved (44.6%). Maximal aerobic power, oxygen pulse and maximal ventilation are higher (12.4%; 16.9%; 17.2% respectively). First and second ventilatory threshold are increased (26.1% and 17.3%).

Conclusion

This study demonstrates the efficiency of this individualised training programme for obese teenagers. Such a programme may therefore provides additional benefits in weight management of obesity.     

Exercice physique, carence estrogénique, monoxyde d'azote et remodelage osseux

Summary

Objectives

The aim of this paper is to emphasize the possible relationships established between estrogens and physical exercise and concerning bone metabolism. Nitric oxide (NO) might play an important role in such relationships.

Topics

Cellular metabolism of NO, as well as NO effects upon osteoblasts and osteoclasts have been summarized. Several studies indicate that NO deficiency might be implicated in various vascular diseases observed in post-menopausal women. Other works also indicate that NO deficiency induced by cessation of ovarian activity might be responsible for osteopenia associated with this condition. Thus, decreased production of NO would be responsible both for post-menopausal osteoporosis as well as for osteopenia sometimes observed in amenorrheic athletes. Moreover osteoblastic response to mechanical stimulation might implicate estrogenic receptor(s). The role of these receptors in the regulation of NO synthesis is still unknown.     

Effects of branched-chain amino acid (BCAA) supplementation on endurance exercise performance of pregnant rats

Aims

The present study evaluated the effects of BCAA supplementation on exercise performance of pregnant rats.

Methods

In order to assess these effects, Wistar rats were divided into four groups: sedentary not-supplemented (SNS, n = 8); sedentary supplemented (SS, n = 8); trained not-supplemented (TNS, n = 8) and trained supplemented (TS, n = 8). All groups were submitted to the endurance test until exhaustion (ET) and post-effort lactate (PEL) determination before pregnancy (ET-B and PEL-B) and at the 19th day of pregnancy (ET-19 and PEL-19).

Results

The endurance training significantly increased the ET time to exhaustion (p < 0.05). Regardless of BCAA supplementation, both endurance trained groups (TS and TNS) showed a longer time to exhaustion, assessed by ET, compared with the sedentary groups (SS and SNS) (p < 0.05). In the TNS, ET-19 time to exhaustion decreased when compared with the period before pregnancy. On the other hand, ET-19 time to exhaustion was not affected in the TS at the end of the pregnancy period. In addition, TS showed a marked PEL-19 reduction when compared with PEL-B. The data presented herein suggest that BCAA supplementation plays an ergogenic role in the maintenance of exercise performance during pregnancy in rats.     

Game analysis and energy requirements of paddle tennis competition

Objective

To determine the physiological demands as well as the structural characteristics of the competitive practice of paddle tennis.

Equipment and methods

A total of 12 top level male players (age, mean ± standard deviation: 16.57 ± 1.51 years) participated in the study. Twenty-four hours before paddle tennis competition, subjects performed a graded exercise test on a treadmill to determine maximal oxygen uptake, second ventilatory threshold, and maximal heart rate. Total time of game, in-play-time, and out-of-play-time were registered in 12 simulated paddle tennis matches, recording also the frequency and typology of the strokes performed by the analyzed subjects. In addition, oxygen uptake and heart rate values were continuously obtained during the competitive effort.

Results

Mean oxygen uptake values measured during paddle tennis competition reached values below 50% of maximal oxygen uptake assessed in treadmill test, whereas the mean value for heart rate during the matches represented approximately a 74% maximal heart rate reached in the same laboratory test. On the other hand, in-play-time:out-of-play-time ratio was 1:1 s, being the direct strokes, and especially the volley, those which showed higher frequency scores.