Obesity and its subsequent disease states are major health problems in the United States. In many ways, obesity can be considered a “disease state” itself due to the changes it causes on the body. High-intensity exercise also places acute stress the body, putting humans in recovery from exercise in a state that may be analogous to a temporary disease state. The purpose of this study was to examine biomarkers associated with obesity (CRP and Leptin) before and after continuous and intermittent bouts of exercise in an obese but otherwise healthy sample vs. a healthy, non-obese sample. This investigation focused on examining the obese sample’s biomarkers at rest compared to those of the healthy group immediately and 1 hour-post exercise. Eighteen male subjects participated, with nine in each group. Each subject performed a VO2 max test and a series of three anaerobic Wingate tests at least one week apart in a cross-over study design. Blood was taken at baseline, immediately-post, and 1-hour post for each exercise mode. A significant difference was noted between groups for CRP at baseline on the VO2 testing day. A significant difference between groups existed in leptin levels at baseline on both testing days. The only significant change was the decrease in leptin from post to 1- hour post for during the VO2 in the obese group. However, both exercise protocols demonstrated various effects on the subjects and groups. Healthy participants were examined individually, and two of them showed possible signs of being at risk for obesity and its subsequent disease states based on post exercise “spikes” in CRP and leptin that caused the levels of the biomarkers to be closer to those in the obese group at rest. Another three subjects saw at least two spikes. Thus, a total of five subjects could potentially be “at-risk” based on the assumptions of the present study. These results suggest CRP and Leptin could potentially hold the ability to classify someone in a “preobesity state.” Further investigations are warranted based on these initial results and should focus on biomarkers more specific to obesity.

Background: The maximum rate of oxygen consumption (V̇O2max) can be measured through numerous tests, either directly or indirectly, where direct methods are considered more accurate, whereas indirect methods are more of an estimation with various degrees of reliability. Cooper's Test is one example of an indirect method considered reliable in estimating V̇O2max, with reliability coefficients ranging between 0.897-0.960. Cooper's Test is thus a test that is often used when estimating V̇O2max. However, there is a lack of test-retest research done utilising Cooper's Test on a younger population, which is the reasoning behind this study focusing on adolescents. Aim: The aim of the study was to study the test-retest reliability of Cooper's Test, in adolescents aged 16-19 years. Methods: Twelve healthy adolescents, aged 16-19 years, attending a sports high school participated in a test-retest study (test 1 and test 2) of Cooper's Test. The tests were performed on the short sides of a synthetic grass field, with 66 metres between the two sides, were the participants were instructed to cover as much distance as possible, with high motivation and intensity, for the whole 12 minutes of the Cooper's Test. Each individual participant's data was measured, recorded and later analysed. The total distance covered was then translated into miles and compared to Cooper's original estimated maximal oxygen consumption table for an estimation of each participant's V̇O2max value in ml*kg-1*min-1 from test 1 and test 2. The data from the test-retest and its variance was then analysed by a two-way mixed model of intraclass correlation coefficient (ICC) with an absolute agreement type. Results: The analysed data from test 1 and test 2 of Cooper's Test showed the results of an ICC (95% CI) of 0.06 (-0.353 to 0.544), indicating a substantial error variance between the two separate Cooper's Tests. Conclusion: The data and analysis from this study implied that Cooper's Test was not reliable in the study population, consisting of adolescents. Possible factors influencing the result however were lack of participant motivation and the level of intensity variance during the test-retest of Cooper's Test. Further researchers and amateur and professional users should keep these factors in mind when utilising Cooper's Test to predict V̇O2max. More research is needed within this study's age population to draw any definite conclusions on the reliability of Cooper's test on adolescents.

Aim The overall aim of this study was to develop a broader understanding on how to optimize the organization of aerobic endurance training programs, and especially how to better organize high-intensity training (HIT) and low intensity training (LIT) to give an optimum endurance performance progress. Method This study compared the effects of two different training organization methods in trained cross-country (XC) skiers and biathletes. During a 5 week intervention period, one group of athletes (n = 10, 7 men and 3 women, age 23 ± 9 years) performed block periodization (BP) training with 5-1-3-1-1 HIT sessions in the respective weeks. The other group of athletes(n = 9, 7 men and 2 women, age 22 ± 5) followed a more traditional periodization (TRAD) method performing 2-2-3-2-2 HIT sessions. LIT was interspersed between the HIT sessions so that both groups performed similar total volumes of HIT and LIT during the intervention period. Results The BP group increased relative and absolute VO2max (2.6 ± 3.6% and 2.0 ± 2.5%, P < 0.05) and time to exhaustion (6.1 ± 6.4%, P < 0.01). No changes were seen in the TRAD group on relative or absolute VO2max (0.8 ± 3.5% and -0.1 ± 3.0%) or time to exhaustion (-2.0 ± 7.7%). Mean effects size (ES) of the relative and absolute improvement in VO2max and time to exhaustion revealed small to moderate effects of performing BP training vs. TRAD training (ES range from 0.51 to 1.14). Conclusions This study indicates that organizing endurance training in XC skiers with block periodization training give better adaptations compared to performing traditional periodization training during a 5 week training period when performing similar volumes of high-intensity and low intensity training.

Sammanfattning Syfte och frågeställningar. Syftet med denna studie var att på äldre personer studera olika fysiologiska parametrar före och efter en period på åtta veckor med styrketräning som utförs tre gånger i veckan. Frågeställningarna var: Hur påverkas statisk och dynamisk maximal styrka i främre lårmuskulaturen av styrketräning? Är det någon skillnad i resultat mellan koncentrisk och excentrisk styrka i lårmuskulaturen före och efter styrketräningsperioden? Är det någon skillnad i förändring mellan benstyrka uppmätt med isokinetisk teknik jämfört med uthållighetsstyrka och ett kort funktionellt benstyrketest? Hur påverkas maximal syreupptagningsförmåga registrerad via submaximalt cykeltest respektive vid pyramidtestet av träningsperioden? Metod. I studien deltog 20 generellt ej påtagligt aktiva män och kvinnor i åldrarna 66-79 år. Av dessa var 11 individer slumpvis indelade i en styrketräningsgrupp och övriga nio utgjorde en inaktiv kontrollgrupp. Ett flertal olika fysiologiska tester, som bl.a. prövade testpersonernas styrka samt kondition, utfördes innan och efter träningsperioden. De deltagare som utgjorde träningsgruppen tränades i relativt tung styrketräning i åtta veckor. Resultat. Undersökningen resulterade i en signifikant ökad koncentrisk-, excentrisk- samt statisk momentan benstyrka för träningsgruppen efter de åtta veckorna med relativt tung styrketräning. Vidare kunde även utläsas för dem en signifikant förbättring av uthållighetsstyrka i benen (hastighet vid 50 uppresningar från stol, med 16,9 %) samt vid ett kort funktionellt test (5 uppresningar från stol, med 12,8 %). De träningsgenererade signifikanta ökningarna för träningsgruppen tyder inte på några stora procentuella skillnader mellan statisk (10,4 %) och dynamisk excentrisk (7,8 %) eller koncentrisk maximal styrka (9,5 %). Vid testerna cykelergometertest (kondition), effekt i 5-minuterspyramidtest (ett modifierat steptest) samt distans vid 6-minuters gångtest framkom inga signifikanta förbättringar för träningsgruppen. Ingen i kontrollgruppen visade en signifikant förbättring i någon av de nämnda testerna. Slutsats. Studien visar att interventioner, med åtta veckors intensiv styrketräning, tre gånger per vecka för äldre kvinnor och män, påtagligt kan förbättra resultaten vid styrkemätningar såväl momentant som uthållighetsmässigt och vid ett kort funktionellt test, medan tester av maximal syreupptagningsförmåga (VO2max) inte förbättras. Emellertid framkom i cykelergometertestet en tendens till förbättring för träningsgruppen.

Le but cette thèse était d’explorer l’influence du niveau d’activité physique et du niveau de performance physique sur la densité minérale osseuse, la géométrie osseuse de la hanche et le score de l’os trabéculaire chez de jeunes hommes en surpoids et obèses. Trois principales études ont été menées. Une première étude a montré que la pratique d’activités physiques a un effet positif sur le CMO, la DMO et la section transversale du col fémoral chez les hommes en surcharge pondérale. Une deuxième étude a suggéré que le niveau d’activité physique influence positivement les paramètres osseux chez les hommes en surpoids et obèses et que l’optimisation de la masse maigre, de la VO2 max (L/min) et de la force maximale des membres inférieurs peut aider à prévenir l’ostéoporose chez les hommes en surpoids et obèses. Enfin, une dernière étude, a été la première à démontrer une relation positive entre la VO2 max (ml/mn/kg) et les indices de résistance osseuse du col fémoral (le CSI, le BSI et l’ISI) chez les jeunes hommes en surpoids et obèses et a donc suggéré que l’augmentation de la VO2 max chez les hommes en surpoids et obèses pourrait aider à réduire les fractures stéoporotiques. Ces différents résultats suggèrent une adaptation ostéogénique significative des jeunes hommes en surpoids et obèses en réponse à l’entrainement physique. / The aim of this thesis was to explore the influence of physical activity level and physical performance on bone mineral density, hip geometry and trabecular bone score in young overweight and obese men. Three main studies have been conducted. The first study has shown that physical activity practice has a positive effect on BMC, BMD and femoral neck crosssectional area in overweight men. The second study has shown that physical activity level positively affects bone variables in overweight/obese men and that increasing lean mass, VO2 max (L/min) and muscular strength of the lower limbs can help to prevent osteoporosis in overweight and obese men. Finally, the last study, was the first to show positive associations between maximal oxygen consumption (milliliter per minute per kilogram) and composite indices of FN strength (CSI, BSI and ISI) in young overweight and obese men and therefore suggested that enhancing VO2 max in overweight and obese men may help to reduce osteoporotic fractures. These different results suggest a significant osteogenic adaptation in young overweight and obese men in response to physical training.

The aim of this thesis was to investigate the extent of peripheral and central components in the development of fatigue during maximal exercise. Fatigue during maximal and supramaximal exercise has traditionally been modelled from the peripheral context of an inadequate capacity to supply metabolic substrate to the contracting muscles to meet the increased energy demand. However, there are a number of observations that are not compatible with the peripheral fatigue model but which support a reduced central drive during exercise acting to prevent organ failure that might occur should the work be continued at the same intensity. Candidates for the role of “exercise stopper” have been identified as mechanical forces, teleoanticipation, cardiovascular capacity and dyspnoea. We explored these various possibilities in order to determine the most likely cause of exercise cessation during high intensity exercise.The development of a plateau in oxygen consumption during maximal incremental exercise has traditionally been used as evidence that an oxygen deficiency in the exercising muscles causes the termination of exercise. However, the incidence of this “plateau phenomenon” depends largely on mode of exercise, testing protocol and sampling frequency. The aim of this study was to examine whether the development of the “plateau phenomenon” is an artefact of pedalling cadence. In the first study nine healthy individuals performed in random order a maximal incremental ramp test (0.5 W.s-1) on four occasions at a fixed cadence of 60, 80 or 100 rpm and at a self-selected cadence. Oxygen consumption (VO2), CO2 production (VCO2), minute ventilation (VE) and heart rate were measured throughout each trial and averaged over 30 s. Cadence was recorded every second. Neither VO2max nor peak power output were different between trials. Submaximum VO2, VCO2 and VE were not influenced by cadence. A plateau in oxygen consumption was observed in 14% of the trials. Cadence declined significantly towards the end of the self-selected cadence trial (p < 0.05). This ramp protocol produces a low incidence of the “plateau phenomenon” and the measured physiological variables are unaffected by cadence. Furthermore, only one subject displayed this phenomenon on more than one occasion. This confirms that the “plateau phenomenon” is an artefact of the testing protocol. The significant fall in cadence in anticipation of exercise termination during the self-selected cadence trial indicates the presence of a neural regulation, which would lead to a “plateau phenomenon” in those cycle tests in which the work rate is cadence-dependent.The purpose of the second study was to assess whether pacing strategies are adopted during supramaximal exercise bouts lasting longer than 30 s. Eight healthy males performed six Wingate Anaerobic Tests (WAnT). Subjects were informed that they were performing four 30 s WAnT and a 33 s and 36 s WAnT. However, they actually completed two trials of 30, 33 and 36 s each. Temporal feedback in the deception trials was manipulated so that subjects were unaware of the time discrepancy. Power output (PO) was determined from the angular displacement of the flywheel and averaged over 3 s. The peak power (PPI), mean power (MPI) and fatigue (FI) indices were calculated for each trial. Power output was similar for all trials up to 30 s. However, at 36 s the PO was significantly lower in the 36 s deception trial compared to the 36 s informed trial (392 ± 32 W vs 470 ± 88 W) (p < 0.001). The MPI was significantly lower in the 36 s trials (714 ± 76 W and 713 ± 78 W) compared to the 30 s trials (745 ± 65 W and 764 ± 82 W) although they were not different at 30 s (764 ± 83 W and 755 ± 79 W). The significant reduction in FI was greatest in the 36 s deception trial. In conclusion, the significant reduction in PO in the last six seconds of the 36 second deception trial, but not in the 36 second informed trial, indicates the presence of a pre-programmed 30 second “end point” based on the anticipated exercise duration from previous experience. Furthermore the similarity in pacing strategy in all informed trials suggests that the pacing strategy is centrally regulated and is independent of the total work to be performed.Athletes adopt a pacing strategy to delay fatigue and optimise athletic performance. However, many current theories of the regulation of muscle function during exercise do not adequately explain all observed features of such pacing strategies. We studied power output, oxygen consumption and muscle recruitment strategies during successive 4km cycling time trials to determine whether alterations in muscle recruitment by the central nervous system could explain the observed pacing strategies. Seven, highly trained cyclists performed three consecutive 4 km time trial intervals, each separated by 17 minutes. Subjects were instructed to perform each trial in the fastest time possible, but were given no feedback other than distance covered. Integrated electromyographic (iEMG) readings were measured at peak power output and for 90 s before the end of each trial. Subjects reach a VO2max in each interval. Time taken to complete the first and third intervals was similar. Peak power output was highest in the first interval but average power output, oxygen consumption, heart rate and postexercise plasma lactate concentrations were not different between intervals. Power output and iEMG activity rose similarly during the final 60 s in all intervals but were not different between trials. The similar pacing strategies in successive intervals and the parallel increase in iEMG and power output towards the end of each interval suggests that these pacing strategies could not have been controlled by peripheral mechanisms. Rather, these findings are compatible with the action of a centrally regulated that are recruited and de-recruited during exercise. The extent to which peripheral feedback influences recruitment patterns could not be determined from these experiments.The fourth study examined whether the supplementation of inspired air with a hyperoxic mixture results in a dose-dependent increase in peak work rate and maximal oxygen consumption (VO2max) during a ramp test to volitional exhaustion. To avoid the methodological disadvantages associated with breathing the gas mixtures from mixing bags, the trials were performed in a sealed chamber in which the oxygen fraction (FIO2) in the ambient air was altered and subjects were able to inhale directly from the environment. The three oxygen fractions in which the subjects exercised were 21% (room air), 35 or 60%. Arterial blood sampling occurred at rest and every 3 min during the trial. The blood was analysed for the partial pressure of oxygen (pO2), and carbon dioxide (pCO2); pH; oxygen saturation (sO2); haemoglobin saturation (O2Hb); and lactate concentrations. Expired gas and heart rate were measured continuously. Arterial sO2 and O2Hb were elevated in both hyperoxic conditions and did not fall throughout either trial. However in the normoxic trial sO2 and O2Hb declined over the duration of the trial. Lactate concentrations and pH were similar between all trials. VO2max was significantly higher with an FIO2 of 35 and 60% but was not different between hyperoxic conditions. Maximal ventilation (VEmax), carbon dioxide production (VCO2max) and heart rate were similar for all trials. Peak power output was increased in the trained athletes in the 60% FIO2 trial. Since the plateau phenomenon occurred infrequently in all trial (~9%) and the effect of hyperoxia on performance was less than the changes in blood oxygen carrying capacity, we conclude that hyperoxia improved exercise performance not solely by increasing oxygen delivery to the exercising muscles.In order to be able to directly compare the results from studies using different equipment it is important to know the interchangeability of the results from the machines. The fifth study tested the reliability and interchangeability of the two automated metabolic gas analyser systems that would be used in this series of studies at a range of submaximal workloads. Eight highly trained cyclists performed two incremental submaximal cycle ergometer tests. For each session either a Schiller CS-200 or a Vmax Series 229 automated gas analyser was used for expired gas analysis. Data for oxygen consumption (VO2), CO2 production (VCO2), minute ventilation (VE) and respiratory exchange ration (RER) were averaged for each of the five stages (200, 250, 275, 300 and 325 W). The VO2, VE and RER were similar between trials at all workloads. However, VCO2 was significantly lower in the Schiller trial at workloads above 200 W (p < 0.05). Although there was a significant correlation between the two automated systems for the measured parameters (VO2 = 0.78; VCO2 = 0.80; VE = 0.82; RER = 0.72) (p < 0.05), a Bland-Altman plot revealed that the limits of agreement between the two systems were unacceptably large (VO2 = 0.53 to 1.30 L.min-1; VCO2 = 0.55 to 0.64 L.min-1; VE = -22.3 to 30.3 L.min-1; RER = - 0.03 to 0.13). The co-efficient of variation within the analysers was insignificant for both systems. Both the systems provide reliable measures of expired gas parameters. However, care should be taken in directly comparing studies that have used the two different systems due to the poor agreement between the systems.The factors causing the termination of maximal exercise at sea level are unknown. A widely held view is that skeletal muscle anaerobiosis consequent to an inadequate oxygen delivery to the exercising muscles limits exercise. However, there is also evidence that respiratory muscle fatigue at the high ventilatory volumes achieved during maximal exercise delivery and respiratory muscle work on maximal exercise performance, we exercised 8 highly trained cyclists in a pressure-sealed chamber in which O2 concentrations were manipulated and helium (He) was substituted for nitrogen in the ambient air in order to reduce the work of breathing during exercise. This system ensured that external inspiratory and expiratory resistance was minimised and identical in all experimental conditions and approximated conditions present during usual exercise. During trials with O2 enriched ambient air the peak work rate increased (451 ± 58 W vs. 429 ± 59 W). Neither maximum nor submaximal oxygen consumption was altered in FIO2 of 35% (5.0 ± 0.6 l.min-1) compared to 21% (4.9 ± 0.7 l.min- 1). Substituting helium for nitrogen had no additional effect on work (453 ± 56 W) or VO2max (4.9 ± 0.7 l.min-1) beyond those observed for the hyperoxic conditions. Although submaximum VE was reduced with helium, VEmax was unchanged. Since exercise was terminated at the same peak work rate (± 5 W) in the two hyperoxic conditions we postulate that the actual work rate may be the sensed variable that determines maximal exercise performance. The findings from these studies suggest that the maintenance of physiological homeostasis and the avoidance of organ and cellular damage are of fundamental importance during maximal exercise. This is achieved through central regulation of work output based, possibly, on afferent information from the mechanoreceptors in the exercising skeletal muscles or alternatively, the extent of motor unit recruitment during maximal exercise may be hardwired in the central nervous system in a system of feed-forward control.

ABSTRACT Male subjects are invariably used to study the physiological determinants of middle distance running performance. Studies that do include females have examined only the aerobic contribution to middle distance running performance. The aim of the present study was to investigate aerobic, anaerobic and muscle function factors that could be used to predict middle distance running performance in female runners. This study was performed at an altitude of 1800m. Eleven middle distance female runners aged 18-20 were selected for the study. Aerobic capacity was assessed by measuring the maximal oxygen consumption (VO2max), running velocity at maximal oxygen consumption (vVO2max), running economy (RE) and onset of blood lactate accumulation (OBLA). The blood lactate curve of each subject was constructed by relating the oxygen consumption, to the plasma lactate concentrations. Anaerobic capacity was determined by measuring the maximum accumulated oxygen deficit (MAOD) on a treadmill. Muscle function was assessed by having the subjects cycle as fast as possible against changing brake weights ranging from heavy to light using a Monark cycle ergometer. The brake force (kg) was related to velocity (rpm).

Highly-trained athletes are accustomed to varied and high-volume based exercise stimuli and eliciting adaptation in individuals already possessing the necessary physiology to compete at the highest level is difficult. Therefore, identifying novel, potent and time efficient methods of achieving cumulative training stress is a continual quest for coaches and exercise scientists. This thesis examined the acute and chronic effects of manipulating exercise and recovery during brief all-out sprint cycling on adaptive responses favouring enhanced endurance capacity. Chapter 3 highlighted that low-volume non-work matched all-out sprint cycling, whether it be interval- (4 x 30 s bouts) or continuous based (1 x 2 min bout) provides a similarly potent stimulus for the acute induction of cell signalling pathways and key growth factors associated with mitochondrial biogenesis and angiogenesis in trained individuals. In line with manipulating recovery and in attempting to identify a novel and potent exercise intervention capable of giving athletes more return on their training investment, Chapters 4-6 investigated the efficacy of combining sprint interval training with post-exercise blood flow restriction (BFR). Firstly, it was demonstrated that BFR potentiates HIF-1α mRNA expression in response to SIT, tentatively suggesting an enhanced stimulus for hypoxia- and/or metabolic-mediated cell signalling associated with mitochondrial biogenesis and angiogenesis over SIT alone. Secondly, four weeks of SIT combined with post-exercise BFR provides a greater training stimulus over SIT alone in trained individuals to enhance VO2max (4.7 v 1.1 % change) and MAP (3.8 v 0.2 % change), but not 15-km TT performance. Finally, in response to four weeks of SIT combined with post-exercise BFR, an international female track sprint cyclist increased her CP and W by 7 and 2 % and VO2max and absolute MAP by 3 and 4 %, respectively. Through a combination of an acute in vivo molecular experiment, a training study and an athlete case study, this thesis has introduced a potentially potent and novel training concept that appears capable of augmenting aerobic capacity.

Title: Comparison of universal and specific functional stress tests of ski-mountaineerers. Objectives: The aim of the thesis is to compare maximal functional parameters of ski-mountaineerers measured during three functional laboratory stress tests. The functional stress tests were set on a treadmill, bicycle ergometer, and on a ski-mountaineer trainer. Consecutively, there is evaluated the meaning of testing of the functional parameters on the ski-mountaineer trainer. Methods: Interindividual and intraindividual descriptive study of 10 ski-mountaineerers of middle and high level performance. Results: The respondents reached the average value of VO2max 63,3 ml.kg-1 .min-1 on the ski-mountaineer trainer, 67,5 ml.kg-1 .min-1 on a treadmill and 66,5 ml.kg-1 .min-1 on a bicycle ergometer. The average measured HR on the ski-mountaineer trainer was 179 heartbeats/min, on the treadmill 185 heartbeats/min and on the bycicle ergometer 183 heartbeats/min. The average value of R reached the value of 1,09 on the ski-mountaineer trainer, 1,18 on the treadmill and 1, 19 on the bycicle ergometer. The highest measured value of VO2max reached on the treadmill was 79,3 ml.kg-1 .min-1 , the bycicle ergometer enabled to reach maximum 76,5 ml.kg-1 .min-1 and the highest value reached on the ski-mountaineer trainer was...

O objetivo do presente estudo foi investigar a existência de associação entre os diferentes genótipos do polimorfismo R577X do gene ACTN3 e variáveis fisiológicas e neuromusculares associadas à aptidão aeróbia e ao desempenho em provas de longa duração. Cento e cinquenta indivíduos fisicamente ativos foram submetidos aos seguintes testes: a) teste incremental máximo para determinação do consumo máximo de oxigênio, velocidade de pico, limiar ventilatório (LV) e ponto de compensação respiratória (PCR); b) dois testes de cargas constantes nas velocidades de 10 km.h-1 e 12 km.h-1 para determinação da economia de corrida; c) teste de uma repetição máxima no exercício leg press para determinação da força máxima de membros inferiores; d) teste de salto vertical para determinação da potência máxima de membros inferiores e; e) genotipagem para determinação do genótipo do gene ACTN3. Os principais resultados foram a maior representação do genótipo XX entre os indivíduos com maiores velocidades associadas ao LV e ao PCR. Além disso, entre os indivíduos mais econômicos, foi observada uma maior representação de pelo menos uma cópia do alelo X (genótipos RX e XX). Esses resultados sugerem que o genótipo XX do gene ACTN3 parece ser favorável às variáveis fisiológicas associadas à aptidão aeróbia, sobretudo aquelas determinadas em intensidades submáximas / The aim of the present study was to investigate the relationship among the genotypes of the ACTN3 gene and physiological and neuromuscular parameters related to aerobic fitness and endurance performance. One hundred and fifty male physically active subjects performed the following tests: a) a maximal incremental test to determine maximal oxygen consumption, peak velocity, ventilatory threshold and respiratory compensation point; b) two constant speed tests at 10 km.h-1 and 12 km.h-1 to determine running economy; c) one repetition maximum in the leg press to determine the maximal dynamic strength of the lower limbs; d) vertical jump test to determine the maximum power of the lower limbs and; e) genotyping for the ACTN3 gene polymorphism. Our main results were a higher frequency of the XX genotypes among the individuals with the highest speeds associated to ventilatory threshold and to the respiratory compensation point. It was observed a higher frequency of at least one copy of the X allele (RX and XX genotypes) among the more economical individuals. These results suggest that the XX genotype of the ACTN3 gene seems to be associated with physiological variables related with the aerobic fitness, mainly those determined in submaximal intensities