The main findings of this study were the possibility of identifying the LT and GT in resistance exercise for individuals with DM-2 as well as the similarity between [Gluc] and [Lac] responses after the LT was attained during ITs on the LP and BP (Figures 3A and 4A). Moreover, the polynomial adjustment also enabled the LT identification in both exercise types, from the responses of QLac (i.e., [Lac]/% 1RM ratio) using a second-order polynomial function (Figures 3B and 4B) with no differences to the thresholds determined by other methods (Table 2). Significant correlations occurred between the thresholds identified by different methods in both resistance exercises as well as between these methods to the aerobic capacity (i.e., LT) identified on the cycle ergometer (i.e., LTc) and to the 1RM previously tested (i.e., 1RMLP and 1RMBP). The results also demonstrated the agreement between the LTLP and LTBP, considered a gold standard, with other methods used for threshold identification (Table 3; Figure 5), suggesting the validity of these protocols in the functional evaluation of individuals with DM-2.
In the current study, the intensities corresponding to the LT and GT in resistance exercise were between 30% and 32% 1RM for the LP and the BP. These results are in agreement with the results from Barros et al. (4) in a sample of healthy young individuals, in whom the LT occurred around 28% and 32% 1RM for the biceps curl and LP, respectively, as well as the thresholds identified from blood lactate and glucose in a study by Oliveira et al. (22), which occurred around 30% 1RM, also for healthy young individuals. Petrofsky et al. (23) demonstrated in an animal model that in static contractions above 20% 1RM, there is an increase in the intramuscular pressure, according to the exercise intensity, which elicits a small arterial blood flow, whereas for dynamic contractions, the literature suggests that in intensities above 30% 1RM, this reduction in blood flow would occur (35). In both conditions, the anaerobic glycolysis activity would be increased and allow for the identification of a metabolic transition of the energetic pathways. It is speculated that this phenomenon (i.e., LT) should be mainly marked by a hemodynamic factor, as evidenced in the literature (23,35) in which the higher % 1RM promotes an intramuscular pressure that increases muscular tension and that is higher than the capillary pressure, causing them to be blocked. This blockage thus leads to muscular hypoxia and diminishes oxygen availability, increasing both the activity of the glycolytic pathway and the blood lactate levels, enabling the identification of the LT.
The use of the thresholds proposed in the current study to prescribe resistance exercise intensities becomes important to individuals with DM-2, as hyperglycemia is the main sign of this disease and incremental exercises performed below these thresholds (e.g., GT) result in the reduction of [Gluc] (Figures 3A and 4A). This suggests that an acute exercise performed at intensities related to GT and LT would contribute to better blood glucose control for these patients, as demonstrated in the laboratory during exercise (21) and until 75 minutes of recovery after resistance exercise performed at 23% 1RM (20).
An important aspect related to the benefits of resistance exercise for individuals with DM-2, who may present with cardiovascular complications, is the increase in strength and muscular resistance (1,2,5). Takarada et al. (29) showed that resistance training performed at lower intensities results in an increase of muscle mass and strength in middle-aged women. Therefore, this effect would include an increased absolute load (kg) corresponding to the GT and/or LT in resistance exercise for DM-2. Possibly the benefits associated to this would include a smaller number of motor units being recruited in parallel to a decreased cardiac overload during sub-maximal activities of daily living which, in turn, would reduce the risk for cardiovascular events for DM-2 (8,24).
The results demonstrated the possibility of identifying the LT and GT in the LP and BP as well as the LTp through QLac for both exercises in individuals with DM-2. New studies are necessary to elucidate the meaning of these thresholds and their possible clinical applications in the evaluation and prescription of resistance exercises based on glycemic and hemodynamic control of these patients.
Based on the results, it can be concluded that it was possible to identify the LT and GT in resistance exercise performed by individuals with DM-2, through the presented methods, and that [Gluc] responses above LT were similar to those of [Lac] for the LP and BP. The meaning of these thresholds still needs to be established, and additional studies are being developed in order to analyze their clinical applications in exercise prescription and evaluation for the glycemic and hemodynamic control of individuals with DM-2.
Both the LT and the GT seem to delimit an exercise intensity above which the blood glucose production may be higher than blood glucose uptake, eliciting an increase in blood glucose levels. In the current study, the LT and GT intensities were beyond 30% and 32% 1RM for the individuals with DM-2. In addition, the intensities (kg) corresponding to these thresholds were between 46% and 60% of the body weight on the LP and between 18% and 26% of the body weight on the BP.
Exercise prescription would be done in 3 sets of 20 to 30 repetitions each, with 1 minute of rest and alternating the muscle groups. These suggestions would have practical applications for blood glucose control for individuals with DM-2 with characteristics similar to the participants and mainly individuals with DM-2 who present with unbalanced blood glucose, because these exercise intensities are low to moderate and thus secure in terms of cardiovascular and endocrine stress.
Alternatively, individuals with DM-2 who present with well-controlled blood glucose may be able to perform high-intensity resistance exercise training (e.g., above LT until 80% 1RM or more). However, the relative risks and benefits for patients while performing a high-intensity resistance exercise should be done on an individual basis. The training control would also be done by using the RPE with the 15-point Borg scale. The data showed that the optimal resistance exercise intensity for blood glucose diminution is an RPE around 11 to 14, while exercise performed above on RPE of 15 may elicit the blood glucose to increase for the patients and thus should be used with caution.
We are grateful to CNPq (475575/2004-0) and SIGEP/UCB for the financial support. Also, our acknowledgments extend to LAFIT/UCB, LABEF/UCB, Micromed-DF, and SalvaPé-SP for technical assistance.
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