جستجوی مقالات مرتبط با کلیدواژه « نقطه شکست ضربان قلب » در نشریات گروه « تربیت بدنی »

The purpose of the present study was to review the various methods, invasive and non-invasive, used to determine the anaerobic threshold (AT).  AT is the highest training intensity at which energy requirements of exercise are mainly provided by aerobic energy system, and the rate of lactate appearance in the blood is equal to the rate of its disappearance.  Since AT occurrence is associated with aerobic to anaerobic transition, it has a significant contribution to precise exercise prescription, determination of exercise intensity domains, and prediction of performance especially in endurance athletes. Direct measurement of blood lactate is the most accurate method to determine AT, but it has an invasive, expensive nature, and exposes the subject to the risk of blood sampling. As a result, other non-invasive methods that mainly use heart rate and workload relationship or changes in respiratory indexes such as oxygen and carbon dioxide equivalent, have been considered to determine AT. Meanwhile, the traditional method of AT determination usually uses two-phase models (one turn point). While recent researches prefer three-phase models (two turn points) which provide better estimation of training domains compared to those offered by two-phase models. Therefore, the present study intends to review the most common methods of AT determination and their pros and cons in the form of two- and three-phase models.

Increasing the anaerobic threshold reduces lactate accumulation, postpones fatigue and improves exercise performance. Therefore, the aim of this study was to investigate the effect of acute L-carnitine supplementation on the anaerobic threshold during maximum activity in collegiate runners. For this purpose, 12 trained collegiate runners participated voluntarily in this study (exercise experience: at least 3 years, mean age: 23.33 ± 2.93 years, weight: 66.00 ± 7.21 kg, height: 176.00 ± 6.49 cm, body mass index 21.27 ± 1.35 kg/m2). The subjects were divided randomly into two groups: placebo and supplement. The study design was crossover and double-blind. Subjects in supplement group received 2g of L-carnitine while the control group received placebo 90 minutes before the exercise protocol. Blood samples were collected before and after the CONCONI protocol to measure blood lactate changes. The gas analyzer was used to estimate the respiratory exchange ratio (RER) and heart rate deflection point. After a 7-day period, the position of the two groups changed, and the previous steps were repeated again. One-way ANOVA and LSD post hoc test were used to analyze the data at a significance level less than 0.05. The results of this study showed that L-carnitine supplementation significantly improved the running time (P=0.001), the distance traveled until the anaerobic threshold (P=0.001), respiratory exchange ratio (P=0.001), and lactate accumulation (P=0.001) compared with the placebo group. But, it had no significant effect on delaying the heart rate deflection point at higher speeds (P=0.173). According to these results, it can be concluded that acute L-carnitine supplementation delays fatigue and improves the performance of runners.

  The aim of this study was to survey the validity of the modified Conconi running test for determining of the maximal lactate steady state in young male athletes. 11 young wrestler men were selected (Mean ± SD Age 19.01 ± 1.3 yrs., Height 176.64 ± 3.54 cm, BMI: 23.7 ± 4.0 kg/m2, VO2max: 51.08 ± 3.67 ml/kg/min) and incremental exercise tests in two sessions with an interval of 48 hours {1- accordance to conconi modified protocol (slope:1.5%, began speed: 3 km/h, increasing the speed of one Km per 60 sec) 2. criterion test: Increasing up MLSS }performed on a treadmill. The HRDP was determined by the S.Dmax model. Bland-Altman graphical model and Interclass Correlation Coefficient (ICC) statistical tests were used to evaluate the absolute agreement of the methods. The results indicated high agreement between HRDP and HR of the criterion method (HRMLSS) (±1.96; 95% CI= -2.4 to +7.7 b/min; ICC= 0.81). Moreover, high agreement was observed between speed at HRDP (SpeedHRDP) and speed of the criterion method (SpeedMLSS) (±1.96; 95% CI= -0.57 to +0.95 km/h; ICC= 0.83). The HR and velocity at the deflection point determined by the modified Conconi running test could predict the HRMLSS and speedMLSS. It seems that this test could be a good alternative to more invasive method to determine the anaerobic threshold test as a simple, noninvasive short for the prescribed exercise intensity in athletes used.

  The aim of this study was to survey of the relationship between heart rate deflection point (HRDP) by the short distance maximum (S.Dmax) and second ventilatory threshold (VT2). Twenty-one sedentary men volunteers (mean age 19.9±1.31 years; height 173.4±5.3 cm; weight 67.9±8.9 kg; maximum oxygen uptake 3.08±0.52 L.min-1) performed an incremental treadmill exercise test to exhaustion. To determine the HRDP, each subject heart rate was recorded by using a polar monitor and analyzed by a designed computer program. Respiratory gases during the exercise test was measured with a gas analyzing system. Data were analyzed using depended t-test, Bland and Altman plots and intraclass correlation coefficient. The HRDP was noticed in all subjects. No significant difference (p > 0.05) between the heart rate, oxygen uptake, ventilation, tidal volume and respiratory rate corresponding to HRDP and VT2. Also, results of ICC and Bland-Altman plots showed a good agreement between HR and VO2 measured at the HRDP and VT2. It could be concluded that S.Dmax method is an accurate and reliable alternative to the expensive and time-consuming invasive methods. Therefore, the S.Dmax method can be used for the determination of anaerobic threshold in healthy young men.

Recently Sentija et al. have validated and introduced a fast running exhaustive test (Tfast) for determination of heart rate deflection point (HRDP). However, the proposed test is not according to the recommended standards in the literature. Therefore, the present study aimed to examine the agreement between the HRDP determined by the Tfast and the maximal lactate steady state model (MLSS).

Eleven young wrestler men underwent on subsequent occasions of a series of constant-velocity treadmill runs to determine MLSS. Heart rate data was obtained during the Tfast [speed increments of 1 km/h every 30 s] by using telemetry and HRDP was determined by using the S.Dmax model. Inter-observer reliability was analyzed using Bland-Altman plots and by determination of the Intraclass Correlation Coefficient (ICC).

The results indicated poor agreement between HRDP and HR of the criterion method (HRMLSS) (±1.96; 95% CI= -9.7 to +18.8 b/min; ICC= -0.09). Furthermore, poor agreement was observed between speed at HRDP (SpeedHRDP) and speed of the criterion method (SpeedMLSS) (±1.96; 95% CI= -2.3 to +3.9 km/h; ICC= 0.40).

According to the results it is concluded that the proposed protocol (Tfast) by Sentija et al cannot be used as a reliable method instead criterion method (MLSS). Therefore the Tfast is not recommended for efficient running intensity prescription.

The heart rate deflection point (HRDP) is a downward or upward change from the linear HR-work relationship which is considered as a criterion for planning of the aerobic exercise intensity. The aim of this study was to evaluate the agreement of the time vs. distance dependent protocols for determination of Heart Rate Deflection Point (HRDP) in sedentary young girls. Twenty sedentary young girls selected as subjects and divided randomly to the time dependent (group A; mean± SD Age of 19.8±1.02 years, Weight of 57.8± 7.74 kg, Height of 163.11±7.14 cm, and Vo2max of 32.89 ml/kg/min) and distant dependent (group B; mean± SD Age of 20 ±1.15 years, Weight of 57.30± 12.14 kg, Height of 162.80±7.91 cm, and Vo2max of 33.21 ml/kg/min) groups. Subjects performed the time and distance dependent incremental exhaustive exercise tests in two separate sessions with 72 h rest intervals. Determined HRDP by the gas analysis system was considered as criterion method. Polar Vantage Sport Tester XL was used to monitor heart rate performance throughout the protocols. Data were analyzed by the means of the graphical Bland-Altman as well as the Intraclass Correlation Coefficient (ICC) statistical methods. Results revealed that the time dependent protocol has no agreement with the criterion method (ICC= -0.0191; ±1.96; 95% CI = -8.9 to +26.5 b/min); However, we showed moderate agreement between the distance dependent protocol and the criterion method (ICC= 0.4002; ±1.96; 95% CI = -5.1 to +35.5 b/min). According to this study results, it can be concluded that the distance dependent protocol in comparing with the time dependent protocol have higher agreement with the criterion method; However, use of this protocol for determination of HRDP is doubtful.