Purpose This study aims to analyze swimmers' oxygen uptake kinetics ( VO 2 K) and bioenergetic profiles in 50, 100, and 200 m simulated swimming events and determine which physiological variables relate with performance. Methods Twenty-eight well-trained swimmers completed an incremental test for maximal oxygen uptake (Peak-VO 2 ) and maximal aerobic velocity (MAV) assessment. Maximal trials (MT) of 50, 100, and 200-m in front crawl swimming were performed for VO 2 K and bioenergetic profile. VO 2 K parameters were calculated through monoexponential modeling and by a new growth rate method. The recovery phase was used along with the blood lactate concentration for bioenergetics profiling. Results Peak-VO 2 (57.47 ± 5.7 ml kg −1 min −1 for male and 53.53 ± 4.21 ml kg −1 min −1 for female) did not differ from VO 2 peak attained at the 200-MT for female and at the 100 and 200-MT for male. From the 50-MT to 100-MT and to the 200-MT the VO 2 K presented slower time constants (8.6 ± 2.3 s, 11.5 ± 2.4 s and 16.7 ± 5.5 s, respectively), the aerobic contribution increased (~ 34%, 54% and 71%, respectively) and the anaerobic decreased (~ 66%, 46% and 29%, respectively), presenting a cross-over in the 100-MT. Both energy systems, MAV, Peak-VO 2 , and VO 2 peak of the MT's were correlated with swimming performance. Discussion The aerobic energy contribution is an important factor for performance in 50, 100, and 200-m, regardless of the time taken to adjust the absolute oxidative response, when considering the effect on a mixed-group regarding sex. VO 2 K speeding could be explained by a faster initial pacing strategy used in the shorter distances, that contributed for a more rapid increase of the oxidative contribution to the energy turnover. Keywords Oxygen uptake kinetics• Maximal trials • Swimming • Energy system contribution • Rate of adjustment of VO 2 Abbreviations % Percentage %MAV Percentage velocity to the MAV %Peak-VO 2 Percentage to the Peak-VO 2 τ Time constant [La − ] Blood lactate concentration ∆[La − ] Difference between rest and maximal [La − ] ∆ VO 2 /t VO 2 Growth rate A Amplitude Aer Aerobic AnaAlac Anaerobic alactic AnaLac Anaerobic lactic ANOVA Analysis of variance b Heart beats HR Heart rate ISD Individual snorkel delay K4b 2 Portable breath-by-breath gas analyzer kg Kilogram Communicated by I. Mark Olfert.

The relationship between muscle strength and bone mineral content (BMC) and bone mineral density (BMD) is supposed from the assumption of the mechanical stress influence on bone tissue metabolism. However, the direct relationship is not well established in younger men, since the enhancement of force able to produce effective changes in bone health, still needs to be further studied. This study aimed to analyze the influence of muscle strength on BMC and BMD in undergraduate students. Thirty six men (24.9 ± 8.6 y/o) were evaluated for regional and whole-body composition by dual energy X-ray absorptiometry (DXA). One repetition maximum tests (1RM) were assessed on flat bench-press (BP), lat-pull down (LPD), leg-curl (LC), knee extension (KE), and leg-press 45° (LP45) exercises. Linear regression modelled the relationships of BMD and BMC to the regional body composition and 1RM values. Measurements of dispersion and error (R2adj and standard error of estimate (SEE)) were tested, setting ρ at ≤0.05. The BMD mean value for whole-body was 1.12±0.09 g/cm2 and BMC attained 2477.9 ± 379.2 g. The regional lean mass (LM) in upper-limbs (UL) (= 6.80±1.21 kg) was related to BMC and BMD for UL (R2adj = 0.74, p<0.01, SEE = 31.0 g and R2adj = 0.63, SEE = 0.08 g/cm2), and LM in lower-limbs (LL) (= 19.13±2.50 kg) related to BMC and BMD for LL (R2adj = 0.68, p<0,01, SEE = 99.3 g and R2adj = 0.50, SEE = 0.20 g/cm2). The 1RM in BP was related to BMD (R2adj = 0.51, SEE = 0.09 g/cm2), which was the strongest relationship among values of 1RM for men; but, 1RM on LPD was related to BMC (R2adj = 0.47, p<0.01, SEE = 44.6 g), and LC was related to both BMC (R2adj = 0.36, p<0.01, SEE = 142.0 g) and BMD (R2adj = 0.29, p<0.01, SEE = 0.23 g/cm2). Hence, 1RM for multi-joint exercises is relevant to BMC and BMD in young men, strengthening the relationship between force and LM, and suggesting both to parametrizes bone mineral health.

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The purpose of this study was to investigate whether a tethered-swimming incremental test comprising small increases in resistive force applied every 60 seconds could delineate the isocapnic region during rapidly-incremented exercise. Sixteen competitive swimmers (male, n = 11; female, n = 5) performed: (a) a test to determine highest force during 30 seconds of all-out tethered swimming (Favg) and the ΔF, which represented the difference between Favg and the force required to maintain body alignment (Fbase), and (b) an incremental test beginning with 60 seconds of tethered swimming against a load that exceeded Fbase by 30% of ΔF followed by increments of 5% of ΔF every 60 seconds. This incremental test was continued until the limit of tolerance with pulmonary gas exchange (rates of oxygen uptake and carbon dioxide production) and ventilatory (rate of minute ventilation) data collected breath by breath. These data were subsequently analyzed to determine whether two breakpoints defining the isocapnic region (i.e., gas exchange threshold and respiratory compensation point) were present. We also determined the peak rate of O2 uptake and exercise economy during the incremental test. The gas exchange threshold and respiratory compensation point were observed for each test such that the associated metabolic rates, which bound the heavy-intensity domain during constant-work-rate exercise, could be determined. Significant correlations (Spearman’s) were observed for exercise economy along with (a) peak rate of oxygen uptake (ρ = .562; p < 0.025), and (b) metabolic rate at gas exchange threshold (ρ = −.759; p < 0.005). A rapidly-incremented tethered-swimming test allows for determination of the metabolic rates that define zones for domain-specific constant-work-rate training.

RESUMOIntrodução: Poucos estudos analisaram a contribuição da composição regional de nadadores para o perfil aeróbio, anaeróbio e o desempenho de nado. Objetivo: Verificar a influência da composição corporal regional e total sobre índices da aptidão aeróbia e anaeróbia em nado atado e livre, bem como sobre o desempenho de curta e média duração. Métodos: Onze nadadores (18,0 ± 4,0 anos) foram submetidos a: (1) teste incremental em nado atado, com coleta de gases respiração-a-respiração (K4b 2 associado ao novo-AquaTrainer  ); e (2) tempo limite nos desempenhos de 200, 400 e 800 metros de nado livre. A regressão linear entre distância e tempo (d-t Lim ) empregou o método dos quadrados mínimos. O coeficiente de Pearson (r) averiguou as correlações da composição corporal regional e total com índices da aptidão aeróbica e anaeróbica em nado atado e livre. Resultados: Os valores da massa isenta de gordura (MIG) foram: 61,7 ± 7,4 kg; 7,5 ± 1,1 kg; 28,3 ± 3,7 kg; 22,1 ± 2,5 kg, respectivamente para corpo todo, membros superiores (MS), tronco (T) e membros inferiores (MI). O consumo máximo de oxigênio (VO 2max ) foi 52,1 ± 5,3 ml×kg Descritores: aptidão física; absorciometria de fóton; desempenho atlético; natação. ABSTRACT