## 4 Discussion  
This pilot study evaluated the influence of HIIT exercise with elastic bands on glycemic control by means of isCGM in adult patients with T1D. Twenty-four-hour isCGM data obtained from FSL showed a gradual improvement in glucose control from the first two weeks (_first stage_) until the end of the study (last two weeks, _last stage_), with only minimal changes for the 6 and 12 h post-exercise observation windows. In addition, time in hypoglycemia did not increase significantly in either stage compared to _baseline_. Moreover, CBGs were reduced shortly after exercising (only statistically significant in _first stage_), and a tendency for HbA1c improvement was observed after HIIT intervention. To our knowledge, this study was the first to examine the impact of a HIIT strength program with elastic bands on glycemic control in T1D. The main advantage of using elastic bands is that this training methodology is cheap and can be easily done at home. Before a widespread recommendation for people with T1D, we considered that evaluating safety and efficacy of such a training program was relevant. In addition, since this exercise program is new, comparisons with other types of HIIT on glycemic control in T1D are limited. In one study, TIR 24 h after performing HIIT on a treadmill showed similar results to ours (around 60%), with no differences in TIR at rest [8]. In contrast, minor differences were observed in time below range (TbR) that was 7.5%, as compared with 10.0% (_first stage_) and 14.9% (_last stage_) in our study. Similar disparities were observed in TaR, which was 34.2% versus 21.9% and 17.3% (_first_ and _last stage_, respectively) in our study [8]. These differences may be due to different protocols (HIIT with elastic bands may induce more hypoglycemia), different technology of CGM (Dexcom G4 Platinum), or different insulin strategies and populations. In relation to short time effects on glucose metabolism (six hours post-exercise), an increase in TaR was observed in the _last stage_ as compared with _baseline_ and _first stage_ (19.3% versus 12.3% and 14.1%, respectively). These observations have been also found in previous studies that showed gradual increases in glucose values after HIIT sessions [11]. Hormonal changes after exercising, particularly increased production of catecholamines, have been suggested as the main cause of increase of blood glucose levels [11]. In our study, it is noteworthy that this increment on glucose values was only observed in the _last stage_ period, and not at the beginning of the intervention. Although catecholamines' levels were not measured in this study, one possible explanation may be that the greater workloads per session after week 5 resulted in an increased catecholamines secretion rate. This point needs to be verified in future research. Regarding changes in CBGs during exercise, previous studies of isolated HIIT sessions have shown a reduction of glucose levels within the normal range [11]. In long-term HIIT interventions, the lowering blood glucose effect of HIIT diminished over time (weeks) [10]. Our findings were consistent with these studies, by observing an early significant decrease in CBG values for _first stage_. This finding suggested a possible metabolic adaptation to exercising over several weeks, preserving normoglycemia and reducing the potential impact of HIIT in inducing hypoglycemia. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Pre-Session** & **Immediately Post-Session** & **1 h after Session** \\ \hline _First stage_ & 148.42 (131.69–165.14) & 140.25 (122.81–157.69) & 126.72 (108.86–144.58) * \\ _Last stage_ & 158.17 (137.19–179.14) & 141.44 (127.98–154.91) & 139.17 (120.94–157.39) \\ \hline \hline \end{tabular} Mean values and 95% CL * Significant difference respect to pre-session (\(p<0.05\)). * Significant difference respect to immediately post-session (\(p<0.05\)).  
\end{table} 
Table 3: Capillary blood glucose (CBG) comparison on the first and last week of exercise visits.