Impact of data analysis methods for maximal fat oxidation estimation during exercise in sedentary adults     

《European Journal of Sport Science》2013,13(9):1230-1239

Abstract

The maximal fat oxidation (MFO), and the exercise intensity that elicits MFO (Fat_max), are considered excellent markers of fat metabolism during exercise. Besides individual’s biological characteristics (e.g. fed state, physical fitness level, sex, or age), data selection and analysis can affect MFO and Fatmax estimations, yet the effect is unknown. We investigated (i) the impact of using a pre-defined time interval on MFO and Fat_max estimation, and (ii) the impact of applying 2 different data analysis approaches (measured-values vs. polynomial-curve) on MFO and Fat_max estimations in sedentary adults. A total of 151 (97 women) sedentary adults aged 29.2?±?13.2 years old participated in the study. We assessed MFO and Fatmax through a walking graded exercise test using indirect calorimetry. We pre-defined 13 different time intervals for data analysis, and the estimation of MFO and Fat_max were performed through the measured-values and the polynomial-curve data analysis approaches. There were significant differences in MFO across pre-defined time intervals methods (P?<?0.001) applying measured-values data analysis approach, while no statistical differences were observed when using polynomial-curve data analysis approach (P?=?0.077). There were no differences in Fat_max across pre-defined time intervals independently of the data analysis approach (P?≥?0.7). We observed significant differences in MFO between measured-values and the polynomial-curve data analysis approaches across the time intervals methods selected (all P?≤?0.05), and no differences were observed in Fat_max (all P?≥?0.2). In conclusion, our results revealed that there are no differences in MFO and Fat_max across different time intervals methods selected using the polynomial-curve data analysis approach. We observed significant differences in MFO between measured-values vs. polynomial-curve data analysis approaches in all the study time intervals, whereas no differences were detected in Fatmax. Therefore, the use of polynomial-curve data analysis approach allows to compare MFO and Fat_max using different time intervals in sedentary adults.  相似文献   

Caffeine supplementation and peak anaerobic power output     

《European Journal of Sport Science》2013,13(5):400-406

Abstract

The aim of this study was to investigate the effects of caffeine supplementation on peak anaerobic power output (W_max). Using a counterbalanced, randomised, double-blind, placebo-controlled design, 14 well-trained men completed three trials of a protocol consisting of a series of 6-s cycle ergometer sprints, separated by 5-min passive recovery periods. Sprints were performed at progressively increasing torque factors to determine the peak power/torque relationship and W_max. Apart from Trial 1 (familiarisation), participants ingested a capsule containing 5 mg·kg^?1 of caffeine or placebo, one hour before each trial. The effects of caffeine on blood lactate were investigated using capillary samples taken after each sprint. The torque factor which produced W_max was not significantly different (p ≥ 0.05) between the caffeine (1.15 ± 0.08 N·m·kg^?1) and placebo (1.13 ± 0.10 N·m·kg^?1) trials. There was, however, a significant effect (p < 0.05) of supplementation on W_max, with caffeine producing a higher value (1885 ± 303 W) than placebo (1835 ± 290 W). Analysis of the blood lactate data revealed a significant (p < 0.05) torque factor × supplement interaction with values being significantly higher from the sixth sprint (torque factor 1.0 N·m·kg^?1) onwards following caffeine supplementation. The results of this study confirm previous reports that caffeine supplementation significantly increases blood lactate and W_max. These findings may explain why the majority of previous studies, which have used fixed-torque factors of around 0.75 N·m·kg^?1 and thereby failing to elicit W_max, have failed to find an effect of caffeine on sprinting performance.  相似文献   

Directionally compensated mechanical work provided by the shoulder leads to similar racket velocities during open and square stance forehand groundstrokes in tennis*     

《European Journal of Sport Science》2013,13(7):902-912

Abstract

The differences between the racket-arm acceleration mechanisms during open and square stance forehand groundstrokes in tennis were examined by quantifying the mechanical work done on the racket arm. We studied 13 advanced tennis players as they performed these strokes at maximum effort and calculated the work using inverse dynamics. The racket head speed was similar between the open and square stances. In the open stance, the lack of weight shifting towards the hitting direction resulted in a lower velocity for the shoulder joint centre in the hitting direction than in the square stance, and less work was done by the shoulder joint force in the hitting direction in the open stance than in the square stance (0.30?±?0.11?J·kg-1 vs. 0.38?±?0.16?J·kg-1; p?=?0.005). However, in the open stance, the torso rotated more towards the hitting direction and had more upward acceleration, which resulted in more work done by the sideways and upward shoulder joint forces than in the square stance (sideways: 0.07?±?0.09?J·kg-1 vs. 0.05?±?0.09?J·kg-1, p?=?0.046; upward: 0.08?±?0.09?J·kg-1 vs. 0.04?±?0.07?J·kg-1, p?=?0.002). Thus, the greater work done by the sideways and upward shoulder joint forces compensated for the lesser work done by the shoulder joint force in the hitting direction in the open stance. In both stances, mainly the horizontal flexion torque and internal rotation torque at the shoulder increased the energy of the racket arm.  相似文献   

Hamstring rate of torque development is more affected than maximal voluntary contraction after a professional soccer match     

《European Journal of Sport Science》2013,13(10):1336-1341

Abstract

Match-induced fatigue of knee muscle strength and agonist-antagonist strength-ratios may affect both performance and risk of injury in soccer players. Once explosive tasks are imperative in soccer as well as hamstring strain injuries occur during high-velocity moments, rapid force capacity of this muscle group is especially important. This study evaluated the effect of match-induced fatigue on knee muscle strength and strength-ratio parameters after a single professional soccer match. Male professional soccer players (n?=?16; 24.2?±?3.9 years) were tested before and after a soccer match (56.2?±?22.6?min of playing) for knee flexors (hamstring) and extensors (quadriceps) isometric peak torque (MVC) and rate of torque development (RTD) – as well as the hamstring-to-quadriceps ratio (H:Q) – at 30° of knee flexion. Knee injuries often occur at this joint angle, which is common in sprinting, pivoting, sidecutting, and jumping. Match-induced fatigue caused a left shift in the knee extensors torque-time curve with no significant change in both early (i.e. 0–50?ms) and late (i.e. 0–200?ms) RTD, and a right shift in the knee flexors torque-time curve with a decrease in early RTD (～16%, p?=?.029) and late RTD (～11%, p?=?.011). Knee extensors and knee flexors peak torque remained unchanged (p?>?.05). Early RTD H:Q decreased by～24% (p?=?.027), while late RTD H:Q and MVC H:Q remained unchanged (p?>?.05). In conclusion, match-induced fatigue impaired the ability to rapidly produce force at an angle where injuries are most susceptible to occur. Important information is missed if only the traditional H:Q is considered.  相似文献   

Comparison of different theoretical models estimating peak power output and maximal oxygen uptake in trained and elite triathletes and endurance cyclists in the velodrome     

Carlos González-Haro  Pedro A. Galilea  Jesús F. Escanero 《Journal of sports sciences》2013,31(6):591-601

Abstract

The primary objective of this study was to examine the relationship between heart rate intensity and pedometer step counts in adolescents. To determine cardiorespiratory fitness, 106 participants (47 boys, 59 girls, mean age 14.2 years, s = 0.8) completed the Queen's College Step Test and were classified as having low, moderate or high cardiorespiratory fitness. Adolescents also completed a 10-min treadmill trial while wearing a pedometer and heart rate monitor. The participants were instructed to maintain their heart rate between 65 and 75% of their maximum heart rate while running or walking on a treadmill. A heart rate of 65–75% maximum was associated with 146 steps per minute (s = 22) in boys and 137 steps per minute (s = 22) in girls. Results of analysis of variance indicated that there was a main effect for level of fitness (F _2,102 = 9.36, P < 0.001). The correlation between mean steps per minute and estimated maximum oxygen consumption was statistically significant (r = 0.44, P < 0.001). The results from this study suggest that a step rate of 130 steps per minute is equal to 65–75% maximum heart rate in low-fit adolescents and achieving 130 steps per minute could be used as an initial goal to improve fitness.  相似文献   

Hip extension during the come-out of multiple forward and inward pike somersaulting dives is controlled by eccentric contraction of the hip flexors     

Pui W. Kong 《Journal of sports sciences》2013,31(5):537-543

Abstract

A modelling approach was used in the present study to investigate the role of the hip muscles during the come-out of forward and inward multiple somersaulting dives in a pike position. A planar two-segment model was used to simulate the somersault and come-out of three commonly performed dives from a 3-m springboard: forward two-and-one-half somersault pike dive (105B), forward three-and-one-half somersault pike dive (107B), and inward two-and-one-half somersault pike dive (405B). Three simulations were run for each dive: (1) hip angle was constrained to be constant, (2) hip torque was removed after 0.1 s, and (3) hip angle was constrained to a typical come-out time history used by elite divers. Simulation results indicated that hip flexion torque was required both to maintain a rigid pike position during somersault (range = 205.5–282.3 Nm) and to control the hip extension movement during the come-out (peak torque range = 355.8–548.1 Nm) in forward and inward multiple somersaulting dives. Coaches and divers should be aware that dry-land exercise drills producing hip extension movement by concentric actions of the hip extensor muscles do not replicate the neuromuscular control during the come-out of fast rotating dives.  相似文献   

The influence of variable resistance moment arm on knee extensor performance     

G. Dalleau  B. Baron  B. Bonazzi  P. Leroyer  T. Verstraete  C. Verkindt 《Journal of sports sciences》2013,31(6):657-665

Abstract

To enhance muscular strength, resistance training machines with a cam, incorporating a variable resistance moment arm, are widely used. However, little information is available about the influence of the variable resistance moment arm on torque, velocity, and power during muscle contraction. To address this, a knee extensor machine was equipped with a cam or with a semi-circular pulley that imposed a variable or a constant resistance moment arm, respectively. Fourteen physically active men performed two full knee extensions against loads of 40–80 kg in both conditions. Participants developed significantly higher torque with the pulley than with the cam (P < 0.001). The relative differences between pulley and cam conditions across all loads ranged from 8.72% to 19.87% (P < 0.001). Average knee extension velocity was significantly higher in the cam condition than in the pulley condition. No differences were observed in average and peak power, except at 50 and 55 kg. Torque–velocity and power–velocity relationships were modified when the resistance moment arm was changed. In conclusion, whatever the link, namely cam or pulley, the participants produced similar power at each load. However, the torque–velocity and power–velocity relationships were different in the cam and pulley conditions. The results further suggest that the influence of the machine's mechanism on muscular performance has to be known when prescribing resistance exercises.  相似文献   

Reliability and stability of anthropometric and performance measures in highly-trained young soccer players: effect of age and maturation     

Martin Buchheit  Alberto Mendez-Villanueva 《Journal of sports sciences》2013,31(12):1332-1343

Abstract

The purpose of this study was to assess both short-term reliability and long-term stability of anthropometric and physical performance measures in highly-trained young soccer players in relation to age and maturation. Data were collected on 80 players from an academy (U13–U18, pre- (n = 14), circum- (n = 32) and post- (n = 34) estimated peak height velocity, PHV). For the reliability analysis, anthropometric and performance tests were repeated twice within a month. For the stability analysis, these tests were repeated 12 times over a 4-year period in 10 players. Absolute reliability was assessed with the typical error of measurement, expressed as a coefficient of variation (CV). Relative reliability and long-term stability were assessed using the intraclass correlation coefficient (ICC). There was no clear age or maturation effect on either the CVs or ICCs: e.g., Post-PHV vs. Pre-PHV: effect size = –0.37 (90% confidence limits (CL):-1.6;0.9), with chances of greater/similar/lower values of 20/20/60%. For the long-term stability analysis, ICCs varied from 0.66 (0.50;0.80) to 0.96 (0.93;0.98) for 10-m sprint time and body mass, respectively. The short-term reliability of anthropometry and physical performance measures is unlikely to be affected by age or maturation. However, some of these measures are unstable throughout adolescence, which questions their usefulness in a talent identification perspective.  相似文献   

Age-Related Differences in Muscular Strength and Muscular Endurance among Female Masters Swimmers     

Gail M. Dummer  David H. Clarke  Paul Vaccaro  Lee Vander Velden  Allan H. Goldfarb  James M. Sockler 《Research quarterly for exercise and sport》2013,84(2):97-102

Abstract

The purpose of this study was to examine age-related differences in muscular strength and muscular endurance among 73 female masters swimmers aged 24 to 71 years. Each subject was assessed on measures of body size, grip strength, peak isokinetic torque of shoulder and knee flexion and extension, and endurance of shoulder and knee movements. Although swim training appears to have resulted in higher strength values for these swimmers than for less active women, an age-related decline in muscular strength values was nevertheless apparent. The results fail to reveal a similar age-related trend for muscular endurance, suggesting that swim training influences muscular endurance more than muscular strength among adult women.  相似文献   

Properties of Isokinetic Fatigue at Various Movement Speeds in Adult Males     

David H. Clarke  James M. Manning 《Research quarterly for exercise and sport》2013,84(3):221-226

Abstract

Eighteen male subjects, ages 20–28 years, engaged in three fatigue bouts using an isokinetic dynamometer (Cybex II). Maximum knee extension contractions were given for 100 s at a rate of 30 per minute. The three contraction speeds chosen were 120° · s ^–1 160° · s ^–1 and 200° · s ^–1.Peak torque at 120° · s ^–1 was significantly greater (p <.05) than at 200° · s ^–1 for the first 60 s, and 160° · s ^–1 for the first 50 s. Thereafter, no significant differences existed among conditions. All three curves were found to follow two-component exponential functions as shown by the equation y_t =a ₂ e^k2^t – a ₁ e^k1^t + c. The three curves possessed similar rate constants for both components. Time to peak torque was achieved at similar times for testing at 160 and 200° · s ^–1 (p <.05). It is concluded that peak torque varies inversely with movement speed, and that the pattern of decrement is independent of movement speed. Time to peak torque does not appear to change significantly across trials in isokinetic fatigue.  相似文献