Lactate and ventilatory thresholds in type 2 diabetic women

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Abstract

Anaerobic threshold (AT) has been considered the optimal exercise intensity for type 2 diabetes mellitus (DM 2) patients, but there is little information about the comparison between lactate (LT) and ventilatory (VT) thresholds in this population, particularly during treadmill exercise. Therefore, we evaluated DM 2 women in order to compare and analyze the relationships between VT and LT intensities. Fifteen women with DM 2 without complications and comorbidities (50.7 ± 8.0 years; 71.3 ± 8.6 kg; 154 ± 5 cm; 37.8 ± 3.9% fat; 4.7 ± 3.2 years of disease diagnose and 138 ± 45 mg/dl fasting glucose) were subjected to a graded treadmill test—initial velocity and increments of 1 km/h every 2 min until voluntary exhaustion. VT was determined from VE/VO2 and VEVCO2 ratios and LT was defined as the point at which a first increase in blood lactate occurs during incremental test. Our results showed no significant differences (p > 0.05) and significant correlations between VT and LT expressed in velocity (4.7 ± 0.7 versus 4.6 ± 0.7 km/h, r = 0.62), absolute VO2 (1.27 ± 0.33 versus 1.24 ± 0.28 l min−1, r = 0.93); relative VO2 (18.3 ± 5.7 versus 17.6 ± 4.6 ml kg−1 min−1, r = 0.84) and %VO2max (80 ± 12 versus 78 ± 10%, r = 0.82). These results suggest that both VT and LT can be used to access AT in DM 2 women during graded treadmill exercise.

Introduction

For years epidemiologists have observed a strong association between the occurrence of type 2 diabetes mellitus (DM 2) and a sedentary lifestyle. In this context, physical training has established an important prevention strategy and treatment against this pathology [1], improving glycemic control, decreasing the atherogenic lipidic profile, reducing weight, abdominal obesity and cardiovascular complication risks, as well as improving the mood and self-esteem and relieving emotional stress in these patients [2], [3], [4].

Among the parameters to be considered in the exercise program for this population, intensity has received special attention. Kawaji et al. [5], Fujita et al. [6] and Fujita et al. [7] showed that anaerobic threshold (AT) determination is a direct, simple and useful procedure to prescribe optimal exercise intensity for DM 2 patients. AT is defined as the level of oxygen consumption (VO2) just below the exercise intensity at which metabolic acidosis and associated changes in gas exchange occur [8], or else, it demarcates the transition of predominantly aerobic steady state to anaerobic non-steady state exercise. AT represents, in DM 2 patients, an intensity that minimizes cardiac accident risk, allowing an accurate evaluation of the exercise effects and reducing plasma glucose without increasing plasma glucagon concentrations [5].

In recent years, maximal lactate steady state (MLSS) has been increasingly accepted as the gold standard evaluation in AT assessment [9], [10]. However, direct MLSS determination is a lengthy evaluation, requiring various prolonged exercise sessions in different days, which in turn lead several authors to continue employing more practical tests for AT assessment, like lactate (LT) and ventilatory (VT) thresholds [11]. Although criticized for its subjectivity [12], LT is an individual, valid and reliable procedure for AT determination [13], [14]. In spite of this, VT is the most used method for this purpose [8], [15], [16], [17], given its non-invasive nature.

Although LT and VT are considered to indicate the same physiological transition zone during exercise, some authors [18], [19], [20] have questioned VT use, emphasizing that these thresholds do not always occur together in healthy individuals [21]. Other studies found similarity when comparing them in different populations (sedentary and healthy subjects, cystic fibrosis patients and athletes) [22], [23], [24], [25]. In the only two studies that addressed LT and VT in DM 2 patients, no significant differences between these methods were found [26], [27]. However, this comparison was not the main purpose of these authors, and few data were presented to support their results. In addition, in both studies subjects were evaluated during cycle ergometer exercise, which may not be the most common exercise among DM 2 patients. It is also important to note that altered energetic properties of skeletal muscle have been reported in DM 2 patients [28]. This metabolic abnormality may have some influence in both aerobic capacity and AT in this population.

Therefore, due to the lack of satisfactory descriptions in the literature concerning LT and VT to represent the same exercise intensity during treadmill exercise in DM 2 patients, the purpose of this study was to compare and analyze the relationship between these thresholds in DM 2 women during a graded treadmill test.

Section snippets

Subjects

After approval by the São Carlos Federal University Ethics Committee for Human Experiments and Research (no. 034/04), 15 sedentary women (housewives not engaged in regular exercise practice for at least 2 years, with current physical activity <1 h/week) with DM 2 diagnosis [29], signed an informed consent and agreed to participate in this investigation. Absence of comorbidities was confirmed by clinical history analysis, clinical examination and laboratory tests. Subjects with any complication,

Results

Maximal RER values observed in the treadmill exercise test was 1.10 ± 0.09, suggesting that maximal efforts were attained. Table 2 shows maximal values of velocity, absolute and relative VO2, blood lactate and duration observed in graded test.

Blood lactate concentration at LT was 1.51 ± 0.55 mM. VT and LT values are expressed in Table 3. No significant differences (p > 0.05) and significant relationships (p < 0.05) were found between these variables whatever they are expressed as velocity, relative or

Discussion

Although several authors point that VT and LT occur at very similar exercise intensities in different populations [22], [23], [24], [25], which in turn leads to both thresholds utilization in AT identification, their cause-effect relationship is seriously questioned in the literature by those that found disparity between them [18], [19], [20], [21]. In a recent review, Péronnet and Aguilaniu [31] present important evidences against the hypothesis that hyperventilation and disproportional

Acknowledgments

This study was supported by the CNPq and CAPES. We thank DM 2 patients, Exercise Physiology Laboratory and Exercise Physiology Research Group—São Carlos Federal University, Descalvado Town Hall—Carlos Roberto Bianchi, Via Saúde Gym—Fabiano and Regilene for their contribution to this study.

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    Grant support—CAPES/Brazil.

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