INTRODUCTION

Diabetes mellitus (DM) is advancing rapidly and silently worldwide. Recent estimates indicate that approximately 589 million people live with the disease, which exerts significant pressure on health and social security systems globally, with costs exceeding US$ 1 trillion¹.

Among the types of DM, type 1 (T1DM) is less prevalent than type 2. However, the glycemic disorder resulting from this condition can lead to serious complications, such as diabetic retinopathy, amputations related to diabetic vasculopathy, and diabetic nephropathy^2,3 earlier than in other types of DM. In the United Kingdom, individuals with T1DM have a life expectancy reduced by 11 to 13 years compared with non-diabetics individuals⁴.

The main objective in the treatment of individuals with T1DM is to maintain blood glucose within the established target in order to prevent complications associated with the disease. Insulin therapy remains the main therapeutic strategy⁵. However, some patients have difficulty achieving glycemic targets and require complementary therapies⁶.

In this context, physical exercise emerges as an important adjuvant due to its multiple health benefits. According to Reddy et al., resistance exercise (RE) can improve glycemic control in adults with T1DM, regardless of adjustments in insulin dosage or diet⁷.

On the other hand, other studies question the effectiveness of RE in promoting glycemic reduction. McCarthy et al. highlight that impaired glucoregulation becomes more evident in individuals with T1DM when exercise is performed in the postprandial period, increasing the risk of hypoglycemia⁸.

In addition to this divergence, meta-analyses investigating the impact of RE on glycemic control in individuals with T1DM do not adequately delimit the study population, including individuals ranging from adolescents to adults^9,10. Study designs such as these do not take into account that the intervention may present conflicting responses due to the greater physiological reserve in a younger individual, or that it may present a different magnitude of effect with limited clinical relevance.

In light of this, the aim of this review is to determine whether RE can improve blood glucose in adult individuals diagnosed with T1DM based on revision of the current evidence.

METHODOLOGY

RESULTS

A total of 3,766 records were identified in the databases, of which 645 were excluded due to duplication. After screening the titles and abstracts of 3,131 articles, 22 studies were selected for full-text reading. Subsequently, 8 studies were excluded due to inappropriate study design, 7 due to irrelevant outcomes, and 3 because the population did not meet the predefined eligibility criteria.

Ultimately, 4 studies were included in this review, as shown in the PRISMA flow diagram in Figure 1.

Figure 1PRISMA flow diagram of the study identification, screening, eligibility, and inclusion process. 

The synoptic table (Table 1) was constructed based on information extracted from the included studies. The total sample comprised 88 individuals with medical clearance to engage in physical activity. There were no sex-based restrictions, and the mean age of participants was 29.9 years. None of the studies excluded physically active individuals. Regarding common exclusion criteria, the studies generally excluded underage individuals and those with chronic complications resulting from T1DM. With respect to the resistance exercise programs evaluated, Jimenez et al. implemented a high-intensity protocol (80% of 1RM), consisting of five sets of six repetitions for the quadriceps and hamstring muscles, with 4-minute rest intervals between sets ¹⁴. In the study by Carvalho et al., intensity was moderate (60% of 1RM), and two distinct programs were applied, both using three sets of 10 to 12 repetitions with rest intervals of 50 to 60 seconds and an approximate cadence of three seconds. The difference between them consisted in the exercise selection. Program A included bench press, leg press, biceps curl, leg extension, shoulder press, hip adduction, and floor abdominal curls, whereas Program B involved lat pulldown, seated leg curl, triceps cable pushdown, horizontal leg curl, upright row, hip abduction, and isometric plank¹⁵. Moreover, in the study by Sigal et al., the program was performed three times per week over 26 weeks, with intensity determined by the 8RM method. Two programs were carried out on alternating days: the first included 8 repetitions of abdominal crunches, leg extensions, shoulder press, seated row, and seated biceps curl, as well as 15 repetitions of leg press and supine bench press; the second included 8 repetitions of abdominal crunches, leg curls, upright row, lat pulldown, and triceps pushdown, as well as 15 repetitions of leg press and seated chest press¹⁶.

Finally, in the study by Soltani et al., the resistance exercise protocol was performed at 60% of 1RM and included bench press, leg press, biceps curl, knee extension, shoulder press, hip adduction, and floor abdominal exercises, characterizing a typical strength-training routine commonly used in fitness centers. The program was implemented twice per week, with three sets of 10 to 12 repetitions per exercise and rest intervals of 50 to 60 seconds between sets. As the original study compared three interventions —body-weight functional exercise (BWFE), interval aerobic exercise (IAE), and RE— we opted in this review to analyze only the outcomes related to RE and IAE, since the BWFE protocol shared several characteristics with the RE program¹⁷.

Among the included studies, only the study by Jimenez et al., was classified as having low methodological quality (Table 2). This classification resulted from the absence of a description of the randomization method and lack of blinding¹⁴.

Regarding risk of bias, the selected studies generally showed a low risk of bias (Figure 2). The maximum score was not reached because, in the study by Jimenez et al., the randomization process was not described¹⁴. Nevertheless, the study was retained in the analysis because the remaining methodological domains were adequately reported in the publication.

Figure 2Risk of bias assessment of the included studies using the Cochrane RoB 2.0 tool. 

Figure 3 presents the analysis of mean reductions in blood glucose immediately after the interventions. The results indicated that RE did not produce a significant improvement in glycemic control in individuals with T1DM (mean difference: 7.91 mg/dL; 95% CI = 5.62–10.20). High heterogeneity was also observed among the studies (I² = 95%), possibly influenced by higher baseline glycemic levels in the intervention group in the study by Carvalho et al.¹⁵.

Figure 3Meta-analysis of the immediate post-exercise effects of resistance training on blood glucose levels in adults with type 1 diabetes. 

Additionally, RE did not show a significant effect on long-term outcomes (Figure 4). In the study by Sigal et al.¹⁶, no significant differences were observed in HbA1c levels between groups (p = 0.32; 95% CI = −0.06–0.02).

Figure 4Meta-analysis of the effects of resistance training on glycated hemoglobin (HbA1c) levels in adults with type 1 diabetes. 

DISCUSSION

The primary objective of this review was to evaluate whether RE reduces blood glucose levels in adult individuals with T1DM. The results obtained from the analysis of the studies indicate that RE does not significantly reduce glycemia. Except for the study by Sigal et al., the remaining trials focused on the acute effects of moderate-intensity RE on blood glucose. Acute effects of exercise are understood as adaptive responses observed within the first 24 hours following the activity^18,19.

The currently available evidence indicates that RE, when applied in isolation, is not sufficient to produce significant reductions in blood glucose levels in adults with T1DM⁹. This finding is supported by studies such as that of Zinman et al., who did not observe improvements in glycemic control as a result of regular exercise²⁰. Similarly, Laaksonen et al. reported no reduction in glycemic levels even after 12 weeks of a structured training program²¹. However, these findings should be interpreted with caution, given relevant methodological limitations, such as the small sample sizes of the included trials and the wide confidence intervals reported.

Regarding the high heterogeneity observed in the analysis of RE effects on glycemia (Figure 3), this methodological variability, including differences in intervention protocols, follow-up duration, and control strategies, compromises the robustness of the conclusions and hinders direct comparisons across trials. Similar evidence has been reported in studies involving individuals with type 2 diabetes mellitus (T2DM)^22,23 and leave-one-out sensitivity analyses indicate that the sequential exclusion of studies with lower methodological quality does not substantially alter the overall result²². Therefore, it is essential to develop research involving individuals with T1DM that adopts more standardized methodologies and rigorous control of confounding variables²⁴.

This phenomenon likely stems from the heterogeneity of the population included in the studies. Due to the difficulty in recruiting volunteers for research, many authors perform population subdivisions predominantly based on age, without adequately considering the clinical stage in which the individuals find themselves. Therefore, outcomes with distinct magnitudes are produced, which substantially contributes to the increased variability across the studies.

From a physiological standpoint, RE may promote peripheral glucose uptake through the translocation of GLUT-4 transporters to the cell membrane, independently of insulin action^25,26.

However, recent evidence suggests that the hyperglycemic state may induce downregulation of these pathways in certain tissues, as demonstrated in tenocytes and glomerular epithelial cells^27,28. This factor may, in part, explain the absence of significant changes in glycemic levels observed in the studies analyzed.

Despite the lack of statistical significance, it is plausible that RE may exert indirect beneficial clinical effects, such as improved body composition, increased muscle mass, and potential reduction in insulin resistance. These factors are well-recognized as relevant in the comprehensive therapeutic management of T1DM, although they were not directly measured in the studies included in this review²⁹.

When compared with the literature on RE in individuals with T2DM, it appears that positive glycemic effects tend to be more pronounced in this latter population. This discrepancy may be explained by pathophysiological differences between the two forms of the disease, particularly the presence of residual endogenous insulin in T2DM, which enhances the effects of exercise on carbohydrate metabolism³⁰.

The metaanalysis of 12 randomized trials comprising 452 adults with T1DM found that neither aerobic nor resistance exercise produced a statistically significant reduction in HbA1c³¹ (Figure 4). The authors reported a roughly linear doseresponse relationship between exercise exposure and glycemic improvement, suggesting that interventions of longer duration (~25 weeks) might achieve an HbA1c decrement of approximately 0.5 %³¹. Implementing such prolonged protocols in clinical trials, however, poses considerable logistical and methodological challenges, including maintaining participant adherence, controlling confounding variables, and minimizing attrition. Moreover, from a clinical perspective, a 0.5 % reduction is modest relative to the effort required to attain it, and the durability of the effect—i.e., the time patients remain within their daily target glucose range—remains uncertain. Consequently, future investigations should prioritize adequately powered, longterm designs that can clarify both the magnitude and the sustainability of exerciseinduced glycemic benefits in T1DM.

The present review has several limitations that should be considered when interpreting the results. First, the limited number of included randomized clinical trials (n = 4) restricts the statistical power of the analyses and increases the imprecision of effect estimates. Additionally, substantial heterogeneity was observed among the studies, particularly regarding intervention protocols and adopted control strategies. This methodological variability hinders direct comparisons and may influence conclusions.

Another relevant aspect is that the majority of studies primarily assessed the acute effects of resistance exercise on blood glucose, with only one trial investigating long-term outcomes, such as HbA1c. Consequently, it is not possible to confidently assert whether chronic and more prolonged resistance exercise interventions could yield more consistent metabolic benefits in adults with T1DM.

Finally, the generalizability of the results should be approached with caution. The included samples consisted of adults with T1DM whose clinical characteristics and baseline glycemic control levels were not always clearly described or homogeneous, which complicates the extrapolation of findings to other patient profiles, such as individuals with long disease duration, advanced chronic complications, or varying levels of physical fitness. Therefore, future clinical trials should be conducted with larger samples, more clearly defined inclusion criteria, and more standardized intervention protocols to reduce heterogeneity and enhance the quality of available evidence.

CONCLUSION

This review did not find consistent evidence that RE promotes a significant reduction in blood glucose levels in adults with T1DM. The analysis of the included studies revealed substantial heterogeneity among intervention protocols, as well as methodological limitations, particularly related to sample size. Although RE has well-recognized physiological benefits, the available data do not support its efficacy for glycemic control in this population. In light of this, randomized clinical trials with greater methodological rigor, more representative samples, and standardized interventions are recommended to clarify the role of resistance exercise in the integrated management of T1DM in adults.