Gereç ve Yöntem: Yirmi beş erkek denek şiddeti düzenli olarak artan yüke karşı yapılan egzersiz (15 W/dak) testine yorulana kadar devam ettirdiler. Egzersiz sırasında, solunum ve gaz değişim parametreleri solunumdan solunuma hesaplanmıştır. Kalp atım hızı her atımdan atıma kaydedildi. AE iş gücü ile kalp atım oranı, iş gücünün kalp atım hızı ilişkisi (Conconi metodu) ve V-slope metodu ile hesaplandı.

Bulgular: Kalp atım oranındaki kırılma sadece 6 denekte gözlendi. Diğer 19 denek kalp atım hızı iş gücü ilişkisinde lineer bir artış gösterdi. İş gücünün kalp atım hızı oranında tüm deneklerde gözlenen kırılma noktası V-slope kırılma noktası ile benzerlik gösterdi: 1.91±0.04 L/dk, ve 1.89±0.03 L/dk. Kırılma noktasının eksikliği (%76) ve çok düşük oranda eşleşen Conconi ve V-slope AE tespiti (%16), Conconi testinin güvenilirliğini azaltmaktadır.

Sonuç: Araştırmacılar hasta ve sporcular için özellikle önemli kararlar verirken dikkat etmelidirler. Fakat iş gücünün kalp atım hızı oranı kolayca güvenilir bir yöntem olarak AE hesaplanmasını sağlayabilir.

In the last few decades, several invasive and non-invasive methods have been introduced to determine or estimate the AT. The most accurate and reliable method to determine AT is the direct testing of arterial blood lactate accumulation during incremental exercise test⁷. However, this is not often applicable to most performers. The various non-invasive methods mainly based on metabolic and ventilatory gas exchange parameters, have been developed to estimate AT^1,8,9.

The V-slope method during incremental exercise has been shown as the most effective way to estimate AT non-invasively^8,10,11. This method based on detecting increased CO₂ output (VCO₂) as a function of O₂ uptake (VO₂) where extra CO₂ comes from lactate-bicarbonate buffer system during anaerobic metabolism^1,8.

The techniques that based on respiratory and pulmonary gas exchange dynamics can be easily used in laboratory conditions, but may not be possible to apply some sports in the field. To solve this problem, heart rate-work rate relationships during exercise have been introduced as a non-invasive AT estimation outside the laboratory conditions¹².

It has been proposed that AT can be validly estimated simply by establishing the point at which heart rate linearity changes during exercise¹². However, there is no general agreement among the reports concerning the heart rate work rate-work rate deflection point (HRDP) and its relation with the actual AT^13-19. The vital disappointment in this technique is the observation of a linear increase in heart rate-work rate relationships during exercise performance in most subjects^13,20,21.

Due to wide application of AT in clinical and sports medicine for important decision, the methods used to estimate AT are of great importance. In this study, validity of AT estimation comparatively examined by using the HRDP and V-slope method. In addition, during an incremental exercise test, efficiency of the work rate divided to heart rate ratio on AT estimation was also examined.

Before the test, the subject's height and body mass were measured (Tanita, TBF 300 M, Japan). The exercise tests were performed in a climatically controlled laboratory where temperature was kept at around 22ºC. The subjects familiarized with the laboratory environment and the experimental protocol that they would undergo. On the day of the test, they were instructed that taking no alcohol and stimulant drinks including coffee and tea, and had done no extenuating physical activity. All testing was performed between 08:00 and 10:00 AM.

General Procedures: All subjects performed an incremental exercise in the upright position on an electromagnetically braked ergometer (VIA sprint TM150/200P) that was completely adjustable to the physical dimensions of the subject. After a 4-min warm-up at 20 W, each subject performed a 1-min stage incremental exercise test to exhaustion with 15-W work increment²². Then, the work load decreased to 20 W for 4 min as a recovery period. The pedalling frequency was between 50 and 70 rpm (average 60 rpm). Seat and handlebar heights were set for each subject.

During incremental exercise test, pulmonary gas exchange parameters were estimated breath-by-breath. Ventilatory parameters evaluated using a light weight low resistance turbine volume transducer (Triple V-Volume Sensor) and gas exchange parameters evaluated using a gas analyser system (MasterScreen CPX). The system was calibrated be for each test for temperature, barometric pressure, O₂ and CO₂ concentrations according to the manufacturer's specifications. Cardiac parameters (including heart rate, ST, T, QT) were followed continuously using 12 lead ECG. The heart rate was recorded as beat-by-beat throughout the study.

Estimation of AT: V-slope⁸ other conventional methods, i.e. increase in end tidal PO₂ without decrease end tidal PCO₂; and increase in ventilatory equivalent for O₂ without increase in ventilatory equivalent for CO₂^9, used in AT estimation.

The break point in heart rate versus work rate plot was used to estimate AT¹². In addition, the work rate divided to heart rate ratio was also used to estimate AT (Figure 1).

Büyütmek İçin Tıklayın

Figure 1: Local control rates in two treatment arms

Statistical Analysis: Values were expressed as mean and standard error (±SE). A paired t-test was used to evaluate values observed from the V-slope method and the heart rate versus work rate plot. During exercise, estimated AT values obtained both the work rate divided to heart rate ratio and the V-slope relationship were evaluated using linear regression analysis. Significance was set at P<0.05 for all statistical analyses.

During incremental exercise test, the heart rate-work rate relationship were observed in three different ways: linear increases in 19 subjects (76%), left side deflection in 4 subjects (16%) and right side deflection in 2 subjects (8%) (Table 1).

Büyütmek İçin Tıklayın

Table 1: Maximal exercise capacity (Wmax), work rate at the anaerobic threshold estimated from V-slope method and heart rate vs work rate relationship.

Interestingly, the left deflection point in heart rate-work rate relationship associated with the AT estimated from the V-slope break point. However, the right side deflection point, did not associated with the AT estimated from the V-slope break point (Table 1). In these 2 subjects, the HRDP occurred above the AT (Table 1).

However, while the heart rate–work rate relationships occurred in linear manner, the work rate to heart rate ratio response to incremental exercise test showed a clear break point in all subjects (Figures 1) (Table). The break point obtained from the work rate to heart rate ratio was closely associated with the break point obtained in V-slope method (R=0.889, P<0.0001) (Figure 2).

Büyütmek İçin Tıklayın

Figure 2: Linear regression analysis of AT estimated from using VO2 at the WR/HR break point and VO2 at the V-slope point (n: 25).

In consistent with results of several previous studies, we have observed linear increases heart rate in response to the incremental exercise test in extremely high number of subjects (19 out of 25 subjects, 76%)^20,21,29,30. Naturally, it is not possible to estimate AT under the condition of linear increase in heart rate. An observation of high percentage (86%) break point in heart rate to work rate relationship was reported in young healthy male subjects¹⁷.

The physiological mechanisms behind the 3 different heart rate response, (i.e. linear increase, left side deflection and right side deflection) during incremental exercise test have still not been fully explained. It seems logical to believe that the break point in heart rate work rate relation is related with the myocardial function of heart rather than the change in metabolism from aerobic to anaerobic. The observation of absent of break point and also dissociation of AT and HRDP in most subjects excludes the direct and strong relationship between anaerobic metabolic end productions and heart rate deflection. It has been proposed that deflection in heart rate during muscular exercise is caused by activation of the anaerobic lactic acid mechanisms of ATP production³¹. There are various suggestions concerning the occurrence of HRDP, including increased potassium and catecholamine levels and their effects on myocardial functions^32,33, neural systems and sympathetic–para sympathetic systems activities and change in beta-1 adrenoceptors^33,34. A different behaviour of left ventricular ejection fraction was suggested as a possible reason for the different behaviour of HRDP³⁵. It is also suggested that the deflection in heart rate may occur predominantly in subjects with thicker heart walls and does not seem to bear any relation to heart volüme³⁶.

In this study, HRDP occurred in only 6 subjects (24%). However, it should be emphasized that correlation between HRDP and AT estimated with V-slope method occurred in only four subjects (16%) (Table). However, in 2 of the subjects, HRDP was not associated with the AT, and it occurred markedly above the AT. This overestimation of AT using HRDP was in consistent with some previously reported studies^27,29. A deflection point in heart rate work rate relationship does not often occur, and, when it does, it does not coincide with AT, either in pre-training or post-training conditions³⁷. Despite the marked decrease in maximal exercise capacity and anaerobic threshold, the heart rate and work rate relationships did not affected during incremental exercise with breathing low level of O₂²¹.

It is suggested that exercise test protocol may have an important role on heart rate work rate deflection point during exercise^32,38. During incremental exercise tests with various work rate increments have been shown no significant effects on heart rate work rate relationships³⁹.

In this study, while the heart rate increased linearly with increasing work rate, there was a clear break point at the transition from aerobic to anaerobic metabolism in work rate divided to heart rate ratio (Figure 1). The estimated AT from the V-slope break point significantly correlated to a deflection point in work rate divided to heart rate ratio during an incremental exercise test (Figure 2). It is well known that the V-slope method has been shown as the gold standard non-invasive method used to estimate AT. This method based only detecting the metabolic changes¹⁸.

In conclusion, absent of break point in heart rate work rate relation and extremely low percent of association in AT estimation between HRDP and pulmonary gas exchange indices may reduce reliability of the Conconi test. Therefore, caution should be taken by investigators especially making important decision for patients and sports training. However, work rate to heart rate ratio could provide easy and reliable AT estimation, and importantly it may be incorporated to set exercise intensity parameters for patient's rehabilitation in clinical medicine.

Funding:
No funding.
Conflicts of interest:
There is no conflicts of interest.

Acknowledgements
Each author has participated sufficiently, intellectually or practically, in the work to take public responsibility for the content of the article, including the conception, design, and conduct of the experiment and for data interpretation.

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