In conclusion, in the cited trials, it is important to note that only interventions lasting more than 2 months resulted in improvements in insulin secretion, and that all training regimens led to benefits regarding insulin secretion. This emphasizes that significant results can only be achieved following an appropriate exercise program, whereas random exercise sessions might not result in significant improvements in glucose metabolism or cardiovascular outcomes.

Despite the well-recognized positive impact of PA on β-cell function and insulin secretion, individuals with different secretory functions at baseline may show different responses to interventions, and a variable proportion of patients have been described as exercise resistant in several studies. Dela et al. [9] stratified patients with T2DM into “moderate” and “low” secretors according to individual C-peptide responses to an intravenous glucagon test. They found that only moderate secretors obtained positive responses from an aerobic training program, thus highlighting that a residual β-cell secretory capacity is required in order to maximize the beneficial effect of aerobic exercise on glycemic control. In addition, to further investigate how baseline β-cell function may influence training-induced changes in glycemic control, the HERITAGE study [34] assessed insulin secretion patterns during an IVGTT in a large heterogenic population to detect possible differences in β-cell functional effects in response to a 20-week endurance training program (cycle ergometers 3 days/week for 60 sessions). Participants with better glucose tolerance at baseline showed reduced insulin secretion following regular exercise, while those with poorer glucose tolerance at baseline showed an increase in insulin secretion after exercise. These results suggest that intersubject variability in baseline β-cell function could partially explain the different effects of exercise on glucose homeostasis. In this context, intersubject variability in basal insulin secretion could provide an effective explanation for the different secretory responses to exercise and should be considered when prescribing tailored and individualized treatments. Consistently, another study confirmed this variability by demonstrating that long-term exposure to hyperglycemia –leading to reduced β-cell function [48] and low insulin secretory function—before the introduction of PA predict a poorer training-induced outcome. Thus, aerobic exercise may be less effective in improving glucose control in patients with poorly controlled long-term T2DM. Accordingly, another study [36] confirmed that the response to exercise in prediabetic and diabetic subjects largely depends on basal β-cell function: in particular, basal HbA1c, BMI, and β-cell function were all predictors of exercise response in elderly patients with prediabetes; by contrast, the type of PA did not predict the effectiveness of the response. In this context, residual β-cell function should be restored through appropriate pharmacological treatment by eliminating the noxious effects of gluco- and lipotoxicity before therapeutic aerobic exercise can provide effective improvements in glucose homeostasis. Collectively, these data strongly support the need for individualized treatments in order to maximize the benefit of exercise.

A recent study [18] investigated the effectiveness of a 12- or 24-month intensive lifestyle program in inducing partial or complete T2DM remission compared to standard of care, demonstrating that 23% of participants in the lifestyle intervention group met the criteria for any T2DM remission compared to 7% in the standard care group. Further, the highest remission rate was obtained in participants with well-controlled short-duration T2DM.

5. Exercise Regimens for T2DM

As shown in Table 2, many types of PA can improve glycemic control and lead to overall benefits in people with T2DM. To date, aerobic and resistance training, and the combination of both, have formed the cornerstone of lifestyle intervention for T2DM patients, as previously mentioned. Aerobic training, like running and cycling for about 1 h, is a moderate-intensity type of PA and represents the best activity to reduce body fat mass when required. Moreover, it leads to improvements in oxygen transport and metabolism in the skeletal and heart muscle [50]. Resistance training, on the other hand, is strength-building, as it increases lean body mass, and is characterized by short-term exercise repetitions performed by using, for example, external resistance tools like dumbbells, kettlebells, and barbells, or using body weight, weight machines, or elastic resistance bands.

Type of Exercise	Description	Intensity	Frequency	Duration	Proven Benefits	Additional Specification
Aerobic Training	Rhythmic and repetitive PA that uses large muscle groups, e.g., running, cycling, swimming, dancing, jogging	Moderate (55–74% HRmax) or Vigorous (75–95% HRmax)	5–7 d/week with no more than two consecutive days between bouts	At least 30′/session for ≥150′/week of moderate activity or ≥75′/week of vigorous activity (or an equivalent combination of moderate- and vigorous-intensity, preferably spread throughout the week).	↓ Glycemia with fewer daily hyperglycemic excursions ↓ HbA1c ↑ Insulin sensitivity ↓ Blood lipids ↓ BP ↑ Fitness levels, even without weight loss	-
Resistance Training	Short-term repetition exercises performed using external resistance tools like dumbbells, kettlebells, and barbells, or using body weight, weight machines, or elastic resistance bands	Moderate (50–69% of 1-RM) or Vigorous (70–85% of 1-RM)	2–3 d/week on non-consecutive days	10–15 repetitions/set with 1–3 sets per type of specific exercise	↑ Strength ↑ Bone mineral density ↑ Lean mass ↓ BP ↓ Blood lipids ↑ Insulin sensitivity ↓ HbA1c	-
Pilates	Specific targeted exercises to improve strength, flexibility, and posture, with particular focus on the core	Light	≥2–3 d/week	-	↑ Blood glucose management ↑ Functional capacity	For patients with low levels of fitness and insufficient balance
Yoga	Breath, movement, and meditation to unite mind, body, and spirit	Light	≥2–3 d/week	-	↓ HbA1c ↓ Blood lipids ↑ Improvement body composition	For patients with low levels of fitness and insufficient balance
Balance	Focuses on the ability to maintain proper posture and refers to exercises that are designed to improve and maintain balance	Light	≥2–3 d/week	-	-	↓Risk of falls by improving balance and gait, even in adults with peripheral neuropathy
Flexibility	Stretching and moving a joint through its range of motion	Light	≥2–3 d/week	10″–30″ per stretch (static or dynamic) group; 2–4 repetitions of each	-	↑ Joint range-of-motion; facilitates participation in activities that require flexibility
HIIT F-HIT	HIIT: repetitions of short intervals of vigorous aerobic training (running or cycling) alternating with a short period of active or passive recovery. F-HIT: based on real-world situational exercises at a high intensity by combining resistance training, gymnastics (body weight), and aerobic exercise	Vigorous (75–95% HRmax) follow by active or passive recovery	3 d/week	Repetitions of 10″–4′ of vigorous activity with 12″–5′ of active or passive recovery	↑ Insulin sensitivity ↑ β-cell function in T2DM with preserved residual β-cell secretory capacity ↑ Fitness levels ↓ HbA1c ↓ BMI ↑ CGM	-