Effects of 24-week Polarized Training vs. Threshold Training in Obese Male Adults.

The combination of high volume of moderate-intensity continuous training with a low volume of high-intensity interval training improved body composition and physical capacities in individuals with obesity. However, polarized training (POL) has never been used in adult men with obesity. Thus, the purpose of this study was to investigate changes in body composition and physical capacities induced by a 24-week POL or threshold (THR) program in obese male adults. Twenty male patients (mean age 39.8±6.3 yrs; mean body mass index [BMI] 31.6±2.7 kg∙m-2) participated in this study (n: 10 POL, n: 10 THR). After 24-week, body mass (BM) and fat mass (FM) decreased by -3.20±3.10 kg (P<0.05) and -3.80±2.80 kg (P<0.05), respectively, similarly in both groups. Maximal oxygen uptake ( ̇VO2max) and ̇VO2 at respiratory compensation point (RCP) increased in the POL group (+8.5±12.2 and+9.0±17.0%, P<0.05) and in the THR group (+4.24±8.64 and+4.0±6.70%, P<0.05), as well ̇VO2 at gas exchange threshold (GET) increased similarly in both groups (+12.8±12.0%, P<0.05). POL and THR were equally effective in improving body composition and physical capacities in obese subjects. Future studies are needed to determine whether adherence to the training program can be improved by adding a running competition compared with a group without competition at the end of the training program.

A Pilot Study Using Entropy for Optimizing Self-Pacing during a Marathon.

A new group of marathon participants with minimal prior experience encounters the phenomenon known as "hitting the wall," characterized by a notable decline in velocity accompanied by the heightened perception of fatigue (rate of perceived exertion, RPE). Previous research has suggested that successfully completing a marathon requires self-pacing according to RPE rather than attempting to maintain a constant speed or heart rate. However, it remains unclear how runners can self-pace their races based on the signals received from their physiological and mechanical running parameters. This study aims to investigate the relationship between the amount of information conveyed in a message or signal, RPE, and performance. It is hypothesized that a reduction in physiological or mechanical information (quantified by Shannon Entropy) affects performance. The entropy of heart rate, speed, and stride length was calculated for each kilometer of the race. The results showed that stride length had the highest entropy among the variables, and a reduction in its entropy to less than 50% of its maximum value (H = 3.3) was strongly associated with the distance (between 22 and 40) at which participants reported "hard exertion" (as indicated by an RPE of 15) and their performance (p < 0.001). These findings suggest that integrating stride length's Entropy feedback into new cardioGPS watches could improve marathon runners' performance.

Improvement of adiponectin in relation to physical performance and body composition in young obese males subjected to twenty-four weeks of training programs.

Obesity and related metabolic diseases represent a worldwide health problem. The main factor predisposing to obesity is an unhealthy lifestyle including the lack of physical activity. A pivotal role in the etio-pathogenesis of obesity is carried out by adipose tissue, an endocrine organ secreting several adipokines involved in numerous metabolic and inflammatory processes. Among these, of particular importance is adiponectin, an adipokine involved in the regulation of insulin sensibility and in anti-inflammatory processes. The aim of the study was to determine the effects of 24 weeks of two different training programs polarized (POL) and threshold training (THR) on body composition, physical capacities and adiponectin expression. Thirteen male obese subjects (BMI: 32.0 ± 3.0 kg m-2) followed 24 weeks of two different training programs, POL and THR, consisting of walking or running (or a combination of the two methods) in their normal living conditions. Before (T0) and after the end of the program (T1), the assessment of body composition was assessed by bioelectrical impedance and the concentration of salivary and serum adiponectin was analyzed by enzyme-linked immunosorbent assay and western blotting. Although the results obtained did not show significant differences between the two training programs, body mass and body mass index decreased by a mean of -4.46 ± 2.90 kg and 1.43 ± 0.92 kg m-2 (P < 0.05). Fat mass decreased by -4.47 ± 2.78 kg (P < 0.05). V'O2max increased by a mean of 0.20 ± 0.26 L min-1 (P < 0.05) Also, we observed an increase in saliva and in serum of adiponectin concentrations at T1 compared to T0 by 4.72 ± 3.52 µg mL-1 and 5.22 ± 4.74 ng mL-1 (P < 0.05) respectively. Finally, we found significant correlations between Δ serum adiponectin and Δ Hip (R = -0.686, P = 0.001) and between Δ salivary adiponectin and ΔWaist (R = -0.678, P = 0.011). Our results suggest that a 24 weeks training program, independently from intensity and volume, induces an amelioration of body composition and fitness performance. These improvements are associated with an increase in total and HMW adiponectin expression in both saliva and in serum.

Which of the Physiological vs. Critical Speed Is a Determinant of Modern Pentathlon 200 m Front Crawl Swimming Performance: The Influence of Protocol and Ergometer vs. Swimming Pool Conditions.

BACKGROUND: Modern pentathlon includes horse riding, fencing, swimming, shooting and cross-country running. Events can last many hours during which the athletes face almost maximal energy and physiological demands, and fatigue. Early recognition and prevention of injuries and overuse syndromes can be achieved by refining the individual training loads. The purpose of the study was to determine which parameter could be the most accurate predictor of swimming working capacity determinants in pentathletes. METHODS: Fourteen male pentathletes performed a continuous maximal incremental test in the swimming flume ergometer to measure peak oxygen uptake (VO2peak), and five swimming tests in a 50 m swimming pool to detect critical velocity (CV); velocity at 2 and 4 mM·L-1 of blood lactate (v2, v4) and energy cost (EC). RESULTS: The 200 m swimming time was 2:18-2:32 m:s (340 FINA points). CV was 1.21 ± 0.04 m·s-1, v2 was 1.14 ± 0.09 and v4 1.23 ± 0.08 m·s-1. VO2peak was 3540.1 ± 306.2 mL·min-1 or 48.8 ± 4.6 mL·kg-1·min-1. EC at 1.24 m·s-1 was 45.7 ± 2.4 mL·kg-1·min-1. Our main finding was the large correlation of CV with 200 m swimming performance; Conclusions: Among all the protocols analysed, CV is the most predictive and discriminative of individual swimming performance in this group of pentathletes. It appears as the most suitable test to constantly refine their swimming training loads for both performance enhancement and health promotion.

Heart Rate Does Not Reflect the %VO2max in Recreational Runners during the Marathon.

Exercise physiologists and coaches prescribe heart rate zones (between 65 and 80% of maximal heart rate, HRmax) during a marathon because it supposedly represents specific metabolic zones and the percentage of V˙O2max below the lactate threshold. The present study tested the hypothesis that the heart rate does not reflect the oxygen uptake of recreational runners during a marathon and that this dissociation would be more pronounced in the lower performers' group (>4 h). While wearing a portable gas exchange system, ten male endurance runners performed an incremental test on the road to determine V˙O2max, HRmax, and anaerobic threshold. Two weeks later, the same subjects ran a marathon with the same device for measuring the gas exchanges and HR continuously. The %HRmax remained stable after the 5th km (between 88% and 91%, p = 0.27), which was not significantly different from the %HRmax at the ventilatory threshold (89 ± 4% vs. 93 ± 6%, p = 0.12). However, the %V˙O2max and percentage of the speed associated with V˙O2max decreased during the marathon (81 ± 5 to 74 ± 5 %V˙O2max and 72 ± 9 to 58 ± 14 %vV˙O2max, p < 0.0001). Hence, the ratio between %HRmax and %V˙O2max increased significantly between the 5th and the 42nd km (from 1.01 to 1.19, p = < 0.001). In conclusion, pacing during a marathon according to heart rate zones is not recommended. Rather, learning about the relationship between running sensations during training and racing using RPE is optimal.

Oxygen Uptake Measurements and Rate of Perceived Exertion during a Marathon.

Although the marathon race has been democratized, it remains complex due to the famous "hitting the wall" phenomenon after the 25th km. To characterize this "wall" from a physiological and Rate of Perceived Exertion (RPE) perspective in recreational marathon runners, we report first continuous breath-by-breath gas exchange measurements during an actual marathon race. In order to test the hypothesis that RPE could be a candidate for controlling the marathon pace, this study examined the relationship between RPE and the physiological variables time course throughout a marathon. Only the respiratory frequency and heart rate increased progressively during the race in all the runners, while the oxygen uptake and ventilatory rate followed different kinetics according the individuals. However, the indexation of the physiological parameters and speed by RPE showed the same decreased tendency for all the runners. In conclusion, these results suggest that running a marathon must be self-paced with the RPE.

Marathon Performance Depends on Pacing Oscillations between Non Symmetric Extreme Values.

A marathon was recently run in less than 2 h by a man who ran the three fastest marathons ever recorded in a span of three years-Eliud Kipchoge-in the Tokyo Olympic games. Here, we demonstrate that the best marathons were run according to a pace distribution that is statistically not constant and with negative asymmetry. The concept of mirror race enables us to show that the sign of asymmetry is not due to sampling fluctuations. We show that marathon performance depends on pacing oscillations between extreme values, and that even the best marathons ever run differ and can be improved upon. The utilization of extreme values and oscillations allows for recovery and optimization of the complementary aerobic and anaerobic metabolisms. Our findings suggest new ways to approach the pacing for optimizing endurance performance.

Pace Controlled by a Steady-State Physiological Variable Is Associated with Better Performance in a 3000 M Run.

This paper aims to test the hypothesis whereby freely chosen running pace is less effective than pace controlled by a steady-state physiological variable. Methods Eight runners performed four maximum-effort 3000 m time trials on a running track. The first time trial (TT1) was freely paced. In the following 3000 m time trials, the pace was controlled so that the average speed (TT2), average V˙O2 (TT3) or average HR (TT4) recorded in TT1 was maintained throughout the time trial. Results: Physiologically controlled pace was associated with a faster time (mean ± standard deviation: 740 ± 34 s for TT3 and 748 ± 33 s for TT4, vs. 854 ± 53 s for TT1; p < 0.01), a lower oxygen cost of running (200 ± 5 and 220 ± 3 vs. 310 ± 5 mLO2·kg-1·km-1, respectively; p < 0.02), a lower cardiac cost (0.69 ± 0.08 and 0.69 ± 0.04 vs. 0.86 ± 0.09 beat·m-1, respectively; p < 0.01), and a more positively skewed speed distribution (skewness: 1.7 ± 0.9 and 1.3 ± 0.6 vs. 0.2 ± 0.4, p < 0.05). Conclusion: Physiologically controlled pace (at the average V˙O2 or HR recorded in a freely paced run) was associated with a faster time, a more favorable speed distribution and lower levels of physiological strain, relative to freely chosen pace. This finding suggests that non-elite runners do not spontaneously choose the best pace strategy.

Marathon-Induced Cardiac Fatigue: A Review over the Last Decade for the Preservation of the Athletes' Health.

AIM: To provide a state-of-the-art review of the last 10 years focusing on cardiac fatigue following a marathon. METHODS: The PubMed, Bookshelf and Medline databases were queried during a time span of 10 years to identify studies that met the inclusion criteria. Twenty-four studies focusing only on the impact of marathons on the cardiac function and factors involved in cardiac fatigue were included in this review. RESULTS: Sixteen studies focused on the impact of marathons on several biomarkers (e.g., C-reactive protein, cardiac troponin T). Seven studies focused on the left (LV) or right (RV) ventricular function following a marathon and employed cardiac magnetic resonance, echocardiography, myocardial speckle tracking and heart rate variability to analyze global and regional LV or RV mechanics and the impact of the autonomic nervous system on cardiac function. One study focused on serum profiling and its association with cardiac changes after a marathon. CONCLUSIONS: This review reported a negligible impact of marathons on LV and RV systolic and contractile function but a negative impact on LV diastolic function in recreational runners. These impairments are often associated with acute damage to the myocardium. Thus, the advice of the present review to athletes is to adapt their training and have a regular medical monitoring to continue to run marathons while preserving their cardiac health.

The Carbon Footprint of Marathon Runners: Training and Racing.

Marathon running leaves a significant carbon footprint regarding CO2 emissions; for example, 37 percent of New York Marathon participants travel internationally to New York. The aim of this study is to estimate the CO2 footprint of a person training and competing in a marathon; we will also propose methods to minimize the CO2 footprint because of transportation. In addition, we also examine the influence of food practices and hygiene on training and racing a marathon. METHODS: We estimated the annual carbon footprint of one person taking part in a marathon. We considered all training, racing, and travelling (local and international) for one person (we are going to give him the first name of "Henri"), and then compared his CO2 footprint with his colleagues playing tennis and soccer. The excess CO2 footprint whilst running and for shoes, clothing, books, magazines, insurance, travel, hygiene, laundry, and resources for electronics and additional food consumed were calculated. For competitions, we estimated and compared the CO2 emission from transportation to national vs. international marathon (New York). RESULTS: We estimated that our runner emitted 4.3 tons of CO2 equivalent (CO2e), including all greenhouse gases. A transatlantic flight to New York corresponded to 3.5 tons CO2, which is 83% of the annual carbon footprint of an average French citizen which is about 11 tons CO2e/year. This leads to a sudden 40% increase in Henri's annual carbon footprint. CONCLUSIONS: By focusing on the additional carbon footprint from one year of marathon training and racing, and traveling locally versus internationally, this sport still has a potentially significant carbon footprint that runners and race organizers ought to consider. We wanted to answer a growing question of marathon runners who are wondering about the carbon footprint of their sports practice in following with a new environmentalist trend that considers not traveling anymore to participate in marathons and to stay local. However, the representativeness in the selection of calculation objectives is very low. There is no need for statistics since this study is a theoretical simulation of traditional training and competition practices of marathon runners.

Maximal Time Spent at VO2max from Sprint to the Marathon.

Until recently, it was thought that maximal oxygen uptake (VO2max) was elicited only in middle-distance events and not the sprint or marathon distances. We tested the hypothesis that VO2max can be elicited in both the sprint and marathon distances and that the fraction of time spent at VO2max is not significantly different between distances. METHODS: Seventy-eight well-trained males (mean [SD] age: 32 [13]; weight: 73 [9] kg; height: 1.80 [0.8] m) performed the University of Montreal Track Test using a portable respiratory gas sampling system to measure a baseline VO2max. Each participant ran one or two different distances (100 m, 200 m, 800 m, 1500 m, 3000 m, 10 km or marathon) in which they are specialists. RESULTS: VO2max was elicited and sustained in all distances tested. The time limit (Tlim) at VO2max on a relative scale of the total time (Tlim at VO2max%Ttot) during the sprint, middle-distance, and 1500 m was not significantly different (p > 0.05). The relevant time spent at VO2max was only a factor for performance in the 3000 m group, where the Tlim at VO2max%Ttot was the highest (51.4 [18.3], r = 0.86, p = 0.003). CONCLUSIONS: By focusing on the solicitation of VO2max, we demonstrated that the maintenance of VO2max is possible in the sprint, middle, and marathon distances.

Horse-Riding Competitions Pre and Post COVID-19: Effect of Anxiety, sRPE and HR on Performance in Eventing.

The aim of the present study was to quantify the impact of training restrictions, due to COVID-19 sanitary emergency, on physical and emotional strain of horse-riding Eventing competitions before and after eight weeks of lockdown. Performance was assessed by the penalty points attained, anxiety by the Competitive State Anxiety Inventory-2, strain by the Rating of Perceived Exertion (RPE) method. Moreover, Heart Rate was continuously monitored for fifty-four female national level Eventing horse-riders. Lockdown decreased performance outcome of horse-riders in Eventing competitions up to six weeks, with the Dressage test being the most affected discipline. Performance in Dressage was strongly related to both anxiety and session-RPE. After lockdown, Show-Jumping and Cross-Country courses were shorter allowing RPE to remain stable, session-RPE to significantly decline and cardiovascular strain not to exceed pre-lockdown values. In conclusion, emotional stress in Dressage and workload in Cross-Country should be carefully managed by equestrian Eventing stakeholders when planning training and competitions after a period of lockdown. Moreover, sRPE appears to offer a practical method of monitoring riders load during training and competition and could also be of use for home-based training during any future sport activities restrictions.

Determination of Submaximal and Maximal Training Zones From a 3-Stage, Variable-Duration, Perceptually Regulated Track Test.

PURPOSE: To validate a new perceptually regulated, self-paced maximal oxygen consumption field test (the Running Advisor Billat Training [RABIT] test) that can be used by recreational runners to define personalized training zones. DESIGN: In a cross-sectional study, male and female recreational runners (N = 12; mean [SD] age = 43 [8] y) completed 3 maximal exercise tests (2 RABIT tests and a University of Montreal Track Test), with a 48-hour interval between tests. METHODS: The University of Montreal Track Test was a continuous, incremental track test with a 0.5-km·h-1 increment every minute until exhaustion. The RABIT tests were conducted at intensities of 11, 14, and 17 on the rating of perceived exertion (RPE) scale for 10, 5, and 3 minutes, respectively, with a 1-minute rest between efforts. RESULTS: The 2 RABIT tests and the University of Montreal Track Test gave similar mean (SD) maximal oxygen consumption values (53.9 [6.4], 56.4 [9.1], and 55.4 [7.6] mL·kg-1·min-1, respectively, P = .722). The cardiorespiratory and speed responses were reliable as a function of the running intensity (RPE: 11, 14, and 17) and the relative time point for each RPE stage. Indeed, the oxygen consumption, heart rate, ventilation, and speed values did not differ significantly when the running time was expressed as a relative duration of 30%, 60%, or 90% (ie, at 3, 6, and 9 min of a 10-min effort at RPE 11; P = .997). CONCLUSIONS: The results demonstrate that the RABIT test is a valid method for defining submaximal and maximal training zones in recreational runners.

Race Analysis of the World's Best Female and Male Marathon Runners.

Background: Beyond the difference in marathon performance when comparing female and male runners, we tested the hypothesis that running strategy does not different according to sex. The goal of the present study is to compare the running strategy between the best female and male marathon performances achieved in the last two years. Methods: Two aspects of the races were analyzed: (i) average speed relative to runner critical speed (CS) with its coefficient of variation and (ii) asymmetry and global tendency of race speed (i.e., the race's Kendall τ ) . Results: The females' best marathons were run at 97.6% ± 3% of CS for the new record (Brigid Kosgei, 2019) and at 96.1% ± 4.4% for the previous record (Paula Radcliffe, 2003). The best male performances (Eliud Kipchoge, 2018 and 2019) were achieved at a lower fraction of CS (94.7% ± 1.7% and 94.1% ± 2.3% in 2018 and 2019, respectively). Eliud Kipchoge (EK) achieved a significant negative split race considering the positive Kendall's τ of pacing (i.e., time over 1 km) ( τ = 0.30; p = 0.007). Furthermore, EK ran more of the average distance below average speed (54% and 55% in 2018 and 2019, respectively), while female runners ran only at 46% below their average speed. Conclusions: The best female and male marathon performances were run differently considering speed time course (i.e., tendency and asymmetry), and fractional use of CS. In addition, this study shows a robust running strategy (or signature) used by EK in two different marathons. Improvement in marathon performance might depend on negative split and asymmetry for female runners, and on higher fractional utilization of CS for male runners.

A new field test to estimate the aerobic and anaerobic thresholds and maximum parameters.

Evaluation of cardiorespiratory parameters is important in athletic population in order to monitor the training status and define training intensities. The aim of this study was to validate an easy-to-perform running test called RABIT® (Running Advisor Billat Training) for detecting aerobic (AerT) and anaerobic (AnT) threshold and maximum parameters. Fifteen trained runners completed a graded (GRAD) and RABIT test (four self-selected pace steps: (i) 10 minutes at free warm-up pace, (ii) 5 minutes at medium pace, (iii) 3 minutes at hard pace, (iv) 10 minutes at easy pace). We compared the cardiorespiratory parameters and running speed of the RABIT with those corresponding to AerT, AnT or maximum parameters obtained by the GRAD. The ⩒O2max, HRmax, RERmax and running speed max measured during the 3-minute hard pace of the RABIT were not statistically different from the maximum parameters measured during GRAD (p > 0.05). The ⩒O2, HR and RER measured during the medium and easy pace of the RABIT were not significantly different from the AnT and AerT parameters measured during GRAD. In conclusion, RABIT was validated for all the maximum parameters and for most of Ant- and AerT-related parameters and then it might be used for detecting training zones in athletes.

Pacing Strategy Affects the Sub-Elite Marathoner's Cardiac Drift and Performance.

The question of cardiac strain arises when considering the emerging class of recreational runners whose running strategy could be a non-optimal running pace. Heart rate (HR) monitoring, which reflects exercise intensity and environmental factors, is often used for running strategies in marathons. However, it is difficult to obtain appropriate feedback for only the HR value since the cardiovascular drift (CV drift) occurs during prolonged exercise. The cardiac cost (CC: HR divided by running velocity) has been shown to be a potential index for evaluation of CV drift during the marathon race. We sought to establish the relationship between recreational marathoners' racing strategy, cardiac drift, and performance. We started with looking for a trend in the speed time series (by Kendall's non-parametric rank correlation coefficient) in 280 (2 h30-3 h40) marathoners. We distinguished two groups, with the one gathering the large majority of runners (n = 215, 77%), who had a significant decrease in their speed during the race that appeared at the 26th km. We therefore named this group of runners the "fallers." Furthermore, the fallers had significantly lower performance (p = 0.006) and higher cardiac drift (p < 0.0001) than the non-fallers. The asymmetry indicator of the faller group runners' speed is negative, meaning that the average speed of this category of riders is below the median, indicating that they ran more than the half marathon distance (56%) above their average speed before they "hit the wall" at the 26th km. Furthermore, we showed that marathon performance was correlated with the amplitude of the cardiac drift (r = 0.18, p = 0.0018) but not with those of the increase in HR (r = 0.01, p = 0.80). In conclusion, for addressing the question of the cardiac drift in marathon, which is very sensitive to the running strategy, we recommend to utilize the cardiac cost, which takes into account the running speed and that could be implemented in the future, on mobile phone applications.

Acceleration-based training: A new mode of training in senescent rats improving performance and left ventricular and muscle functions.

High intensity training (HIT) has been shown to improve maximal aerobic capacity and muscle protein synthesis but has not yet been investigated in senescent rats. We hypothesized that the change of speed (acceleration) during each bout of HIT acts as a stimulus responsible for the adaptations of the organism to exercise. Twenty two month-old (mo) rats (n=13) were subjected to a short acceleration protocol (20-30min) of exercise, comprising 3 independent bouts of acceleration and compared to an age-matched sedentary group (n=14). The protocol was repeated twice a week for two months. Following the protocol, performance, cardiac function, muscle mechanics, and the cellular and molecular pathways that are implicated in exercise adaptations were investigated. This new training, comprising only 16 sessions, improved maximal oxygen uptake (⩒O2peak; +6.6%, p<0.05), running distance (+95.2%; p<0.001), speed (+29.7%; p<0.01) and muscle function of 24mo rats in only 8weeks. This new training protocol induced cardiac hypertrophy and improved fractional shortening (47.3% vs. 41.1% in the control group, p<0.01) and ejection fraction. Moreover, it also improved the mechanics of skeletal muscle by increasing developed force (+31% vs. the control group, p<0.05) and maximal mechanical efficiency, activated the IGF1/mTOR/Akt pathway, and reduced the Smad2/3 pathway. Our results clearly show that the change in speed is a stimulus to control cardiac and skeletal muscle mass. This acceleration-based training is not time-consuming and may be adaptable for athletes, the elderly or chronic disease patients in order to improve strength, oxidative capacity, and quality of life.

Case Studies in Physiology: Maximal oxygen consumption and performance in a centenarian cyclist.

The purpose of this study was to examine the physiological characteristics of an elite centenarian cyclist who, at 101 yr old, established the 1-h cycling record for individuals ≥100 yr old (24.25 km) and to determine the physiological factors associated with his performance improvement 2 yr later at 103 yr old (26.92 km; +11%). Before each record, he performed an incremental test on a cycling ergometer. For 2 yr, he trained 5,000 km/yr with a polarized training that involved cycling 80% of mileage at "light" rate of perceived exertion (RPE) ≤12 and 20% at "hard" RPE ≥15 at a cadence between 50 and 70 rpm. His body weight and lean body mass did not change, while his maximal oxygen consumption (V̇o2max) increased (31-35 ml·kg-1·min-1; +13%). Peak power output increased from 90 to 125 W (+39%), mainly because of increasing the maximal pedaling frequency (69-90 rpm; +30%). Maximal heart rate did not change (134-137 beats/min) in contrast to the maximal ventilation (57-70 l/min, +23%), increasing with both the respiratory frequency (38-41 cycles/min; +8%) and the tidal volume (1.5-1.7 liters; +13%). Respiratory exchange ratio increased (1.03-1.14) to the same extent as tolerance to V̇co2 In conclusion, it is possible to increase performance and V̇o2max with polarized training focusing on a high pedaling cadence even after turning 100 yr old.NEW & NOTEWORTHY This study shows, for the first time, that maximal oxygen consumption (+13%) and performance (+11%) can still be increased between 101 and 103 yr old with 2 yr of training and that a centenarian is able, at 103 yr old, to cover 26.9 km/h in 1 h.

Validation of a Ramp Running Protocol for Determination of the True VO2max in Mice.

In the field of comparative physiology, it remains to be established whether the concept of VO2max is valid in the mouse and, if so, how this value can be accurately determined. In humans, VO2max is generally considered to correspond to the plateau observed when VO2 no longer rises with an increase in workload. In contrast, the concept of VO2peak tends to be used in murine studies. The objectives of the present study were to determine whether (i) a continuous ramp protocol yielded a higher VO2peak than a stepwise, incremental protocol, and (ii) the VO2peak measured in the ramp protocol corresponded to VO2max. The three protocols (based on intensity-controlled treadmill running until exhaustion with eight female FVB/N mice) were performed in random order: (a) an incremental protocol that begins at 10 m.min(-1) speed and increases by 3 m.min(-1) every 3 min. (b) a ramp protocol with slow acceleration (3 m.min(-2)), and (c) a ramp protocol with fast acceleration (12 m.min(-2)). Each protocol was performed with two slopes (0 and 25°). Hence, each mouse performed six exercise tests. We found that the value of VO2peak was protocol-dependent (p < 0.05) and was highest (59.0 ml.kg (0.75).min(-1)) for the 3 m.min(-2) 0° ramp protocol. In the latter, the presence of a VO2max plateau was associated with the fulfillment of two secondary criteria (a blood lactate concentration >8 mmol.l(-1) and a respiratory exchange ratio >1). The total duration of the 3 m.min(-2) 0° ramp protocol was shorter than that of the incremental protocol. Taken as a whole, our results suggest that VO2max in the mouse is best determined by applying a ramp exercise protocol with slow acceleration and no treadmill slope.

Myostatin is a key mediator between energy metabolism and endurance capacity of skeletal muscle.

Myostatin (Mstn) participates in the regulation of skeletal muscle size and has emerged as a regulator of muscle metabolism. Here, we hypothesized that lack of myostatin profoundly depresses oxidative phosphorylation-dependent muscle function. Toward this end, we explored Mstn(-/-) mice as a model for the constitutive absence of myostatin and AAV-mediated overexpression of myostatin propeptide as a model of myostatin blockade in adult wild-type mice. We show that muscles from Mstn(-/-) mice, although larger and stronger, fatigue extremely rapidly. Myostatin deficiency shifts muscle from aerobic toward anaerobic energy metabolism, as evidenced by decreased mitochondrial respiration, reduced expression of PPAR transcriptional regulators, increased enolase activity, and exercise-induced lactic acidosis. As a consequence, constitutively reduced myostatin signaling diminishes exercise capacity, while the hypermuscular state of Mstn(-/-) mice increases oxygen consumption and the energy cost of running. We wondered whether these results are the mere consequence of the congenital fiber-type switch toward a glycolytic phenotype of constitutive Mstn(-/-) mice. Hence, we overexpressed myostatin propeptide in adult mice, which did not affect fiber-type distribution, while nonetheless causing increased muscle fatigability, diminished exercise capacity, and decreased Pparb/d and Pgc1a expression. In conclusion, our results suggest that myostatin endows skeletal muscle with high oxidative capacity and low fatigability, thus regulating the delicate balance between muscle mass, muscle force, energy metabolism, and endurance capacity.