To our knowledge, this study could be regarded as the first randomized controlled trial (RCT) comparing the effects of different modes of exercise modalities on novel cardiovascular risk factors among women with diabetes type 2. The major novel finding from the this study was that 10 weeks of SIT in previously inactive women with diabetes type 2 improved WC, HbA1c, MetS, FRS, LAP, VAI, TyG index, TyG-BMI, eGDR to the same extent as and combined resistance and endurance, despite a 10-fold lower exercise time commitment.
This study demonstrated that sprint interval training was a more potent stimulus than combined aerobic and resistance training in improving some cardiovascular factors (LAP, VAI, FRS, TyG, TyG-WC and eGDR), though it failed to significantly improve Mets, TyG-BMI and AIP, as compared with combined training. Additionally, SIT and combined training did not lead to more powerful significant changes in body composition in terms of body mass, BMI, WHR, and body fat percentage in women suffering from diabetes.
In the present study, the LAP index was significantly improved after two exercise interventions. The association between exercise training and LAP index has not been studied before. The LAP index is an accurate index for predicting the risk of developing diabetes type 2 [31]; SIT and combined training in our study could contribute to reducing LAP in women with diabetes type 2. The improvement of LAP index after two exercise interventions reflected the possible reduction of ectopic fat deposition which could be responsible for the improvement of insulin resistance (HOMA-IR) in diabetes type 2 [38], as seen in our study. However, as observed, women' body composition did not change in this study. There have been no similar studies testing the effects of exercise modalities on the LAP index in patients with diabetes mellitus. A previous study, however, had shown that isocaloric diet lowered the LAP index in healthy non-obese non-diabetic subjects [39].
The different improvements of interventions on VAI, a reliable marker of visceral fat distribution, can be gender dependent, reflecting that fat distribution associated with cardiovascular risk in this study was independent of body composition changes. Furthermore, the independence of body composition change from -improvement in VAI could be associated with the increased physical activity volume and also, the improvement of physical fitness parameters [40], as seen in this study (data not shown). Thus, exercise training led to a significant reduction in VAI, which pointed out the potential additive effect of exercise training on WC in T2D women. It seems that exercise program that is aerobic, in contrast to resistance training and/or combined interventions, could alter adipose tissue metabolism and regional visceral adipose tissue depot loss, possibly by mobilizing free fatty acids from visceral adipose tissue at different abdominal regions [41]. Several inconsistent findings have been found regarding how interval training can reduce abdominal fat mass in T2D men [42, 43]. Comparison with our results in women participating in this shows that there are some gender differences in the effects of exercise modalities on some biomarkers of CVD risk factors. For examples, women had greater reductions in body fat than men; women could decrease hsCRP level more than men by following exercise intervention through sex differences in body fat distribution and sex hormones [44]; women could also reduce sympathetic nervous activity more than men, showing that there are greater changes in arterial stiffness and endothelial function in women than in men [44].No differences were found in MetS Z-score changes between SIT and combined training. In addition, there were also no significant changes in MetS Z-score from the baseline to post-exercise training in all groups. Furthermore, the beneficial effects of exercise on the MetS Z-score were achieved without concomitantly altering body composition. It has been shown that fat mass changes are not correlated to MetS Z-score [45]. Interestingly, we did not see any significant reduction in body composition in all groups. It seems that exercise-dependent changes in body composition or more precisely, changes in body mass, body fat percentage and WHR are not important factors in reducing the cardiovascular risk score [45].
In this study, we showed that no significant change in the MetS Z-score would be possible in the absence of change in body composition. The strengths of present study were the use of the novel Mets Z-score to evaluate the effects of different exercise modalities. Confirming the present results, Gates illustrated that 16 weeks of aerobic training did not change the Mets Z-score [35]. In addition, Johnson et al. did not show the superiority of SIT, as compared with moderate intensity training, in overweight/obese subjects [46]. Furthermore, Earnest et al. [54] showed similar reductions in the MetS Z-score in high intensity training and moderate training in overweight males [47]. Because of methodological differences across studies, such as differences in gender, age, health, weight and physical fitness status, medication, mode and intensity of exercise and duration of the training program [48], drawing general conclusions is difficult [49]. It could be speculated that both trainings might not induce improvements in the metabolism, metabolic capacity, and body composition [49, 50]. The hypothesis of the study was that the regular SIT and combined training could reduce the risk of CVD in type 2 diabetes. It has also been proven that both exercise modalities could be recommended for type2 diabetes patients. This finding is consistent with the results obtained by Ramos et al, who found that low-volume HIIT could be as effective as moderate-intensity continuous training in the reduction of the MetS Z-score [51]. In addition, Fisher and colleague demonstrated that both high intensity interval training and continuous moderate intensity training are associated with improvements in cardiovascular risk factors (body fat percent, cholesterol, VLDL, HDL, triglycerides and VO2peak) in overweight men [52]. Furthermore, the results of the present study showed that applying regular SIT and combined training could reduce risks of CVD for 10 years. This improvement may result from the decreased systolic and diastolic blood pressure and improvements of lipid profile [53], as shown in our study. Significant improvements in systolic and diastolic blood pressure and lipid profile might be because of these reductions in FRS [53]. The FRS reduction results were in agreement with those obtained by Amin-Shokravi et al., [53] and Tulley et al., [54]. It seems that the severity of applied exercise training in this study was sufficient to bring about changes in FRS.
Perhaps the most striking and novel finding form the present work was the similar improvements in TyG, TyG-BMI and TyG-WC indices. Although few studies have investigated the relationships between TyG indices and CVD risk [10, 55], none of them has yet explored the effects of different exercise modalities on TyG indices. It has been shown that TyG index is a reliable predictor to identify insulin resistance and diabetes type 2 [9, 56]. One major advantage of the TyG index is the use of fasting glucose and triglyceride parameters. It seems that the TyG index predominantly shows muscle insulin resistance, while HOMA-IR mainly reflects liver insulin resistance [57]. Several candidate mechanisms have been suggested to explain the effect of exercise training on TyG indices in patients with diabetes type 2. It might be postulated that improvement in insulin resistance, as seen in our study, may explain improvements of TyG-indices in women with diabetes type 2 [9]. Our results demonstrate that a surprisingly small amount of SIT can be as effective as a large volume of moderate combined training for improving TyG, TyG-BMI and TyG-WC indices.
As shown by the previous studies, exercise training is an effective anti-atherosclerosis intervention [58, 59] . Some novel findings from the present study were the similar improvements in atherogenic index of plasma in SIT and combined training. Both training protocols were capable of reducing AIP in women with diabetes type 2. As AIP was calculated based on TG and HDL-C levels, it was expected that any changes in TG and HDL-C following exercise training would result in the change in AIP. But, the findings also showed that vigorous intensity interval training and combined aerobic plus resistance training did not significantly change the levels of HDL and TG. The present study showed that even without changes in HDL and TG levels, both modalities could serve as an appropriate stimulus to reduce the atherogenic risk. It could be speculated that LDL particle size may explain the exercise training related mechanisms involved in the reduction of the atherogenic risk [58, 59].
Several studies recently have shown that SIT appears to be a very time-efficient exercise regime that shares many of the metabolic adaptations as traditional endurance exercise training does [60-62].
However, combined exercise training had a more considerable total duration of exercise and calorie consumption, as compared with the time when each type of training was done alone [63]. Despite the fact that such patients tolerate this exercise mode, it seems that by following this exercise prescription, more calories could be consumed.
It has been shown that lower eGDR score was associated with the prevalence of T2D and increased diabetes-related vascular complications (the use of the Estimated Glucose Disposal Rate as a Measure of Insulin Resistance in an Urban Multiethnic Population with Type 1 Diabetes). This study showed that eGDR was decreased by following two exercise modalities in 2DM patients. This effect of exercise intervention on eGDR has not been described previously. It seems that the decrease of eGDR by following exercise training could be caused by the reduction of HbA1C. Decline in HbA1C reflects an adaptation in glucose hemostasis. The novel aspect of our study was that we investigated the utility of eGDR in the assessment of exercise-induced training effects on insulin sensitivity in the patients with T2DM. The results of this study showed that both protocols had a positive effect on eGDR in the patients with type 2 diabetes, and the change in HbA1c levels at the exercise program. MThe most important was the fact that subjects receiving the SIT training program showed significantly greater improvement in eGDR levels over the 10 week period, as compared to the control group. One limitation of the present RCT was that SIT protocols had also to be evaluated in terms of safety in women living with T2D though exercise training, though it was generally quite safe [64].
Study limitations:
The randomized controlled trial design, the inclusion of two different training programs in the same study, the direct personalized exercise training for all training sessions, and the use of a novel cardiovascular risk score to evaluate the effects of different exercise modalities on the risk of cardiovascular diseases, which provided an increased level of accuracy and sensitivity, were amongst the strengths of the present study. As for the limitations of this study, the small size, significant dropout rate, and supervised exercise only in the experimental groups can be mentioned. Moreover, the non-significant reductions of body composition parameters, which can be attributed to the lack of diet control could be taken one other limitation. This study could yield some insight in selecting the type of exercises that can be more helpful for cardiovascular risk reduction. However, this exercise schedule may not be suitable for real-life setting as adequacy of exercise cannot be quantified and many patients with type 2 diabetes may not be having the facilities for such exercises. This is also is another limitation of this study.