Endocrinology · Medical Literature
Perceived Exertion Is Associated with Cardiovascular Strain but Not Glycemic Response to Gym-Based Exercise in Adults with Type 1 Diabetes: An Exploratory Randomized Crossover Trial.
Abstract
Adults with type 1 diabetes mellitus (T1DM) face elevated cardiovascular risk, and regular exercise is a key non-pharmacological mitigation strategy. However, safe prescription requires cardiovascular and glycemic monitoring, often unfeasible in real-world gyms. Low-cost psychophysiological tools (ratings of perceived exertion-RPE and enjoyment) may offer practical alternatives. This exploratory randomized crossover trial examined whether post-session RPE and enjoyment are associated with acute heart rate (HR) and capillary blood glucose (BG) responses to gym-based aerobic and resistance training. Twelve adults with T1DM (29.8 ± 7.8 years; HbA1c 7.7 ± 1.6%; LDL-c 119.5 ± 24.4 mg/dL) completed three ~30 min sessions: aerobic interval training (AE) and two resistance protocols (STA, STB). HR and BG were measured pre-, immediately post-, and 20 min post-exercise; RPE and enjoyment, post-session. Multiple linear regression, controlling for exercise session type, examined associations of RPE and enjoyment with resting HR, BG, and percentage of heart rate reserve (%HR). RPE was higher after STA and STB than AE (p 0.05). Controlling for exercise session type, RPE was a significant positive predictor of %HR (β = 0.44, p = 0.044), whereas enjoyment was not (β = -0.06, p = 0.719); however, the overall %HR model did not reach statistical significance (adjusted R2 =0.119; F(4,31) = 2.183; p = 0.094). These exploratory findings suggest that RPE, but not enjoyment, may serve as a low-cost adjunct intensity marker to inform exercise prescription in adults with T1DM at elevated cardiovascular risk; however, replication in larger samples is needed before clinical recommendations can be drawn. Direct BG monitoring remains essential for safety.
Clinical relevance
In adults with type 1 diabetes mellitus (T1DM), are post-session ratings of perceived exertion (RPE) and exercise enjoyment associated with acute cardiovascular strain (percentage of heart rate reserve, %HRR) and/or capillary blood glucose responses following gym-based aerobic interval training and two resistance training protocols? __SNAPSHOT__ {"studyDesign":"Exploratory randomized crossover trial","setting":"Gym-based setting; country not reported in abstract; institutional affiliation includes University of Pernambuco (Brazil), based on author profiles","sampleSize":"n=12 adults with T1DM (single group, crossover; three conditions per participant)","population":"Adults with T1DM; mean age 29.8 ± 7.8 years; HbA1c 7.7 ± 1.6%; LDL-c 119.5 ± 24.4 mg/dL. Additional inclusion/exclusion criteria not reported in abstract.","intervention":"Three approximately 30-minute gym-based exercise sessions completed by each participant: (1) aerobic interval training (AE); (2) resistance training protocol A (STA); (3) resistance training protocol B (STB). Post-session RPE and enjoyment were assessed as psychophysiological exposure variables.","comparator":"Within-participant crossover across three session types (AE, STA, STB); no separate external control group","primaryOutcome":"Associations of post-session RPE and enjoyment with (a) resting heart rate, (b) capillary blood glucose (BG), and (c) percentage of heart rate reserve (%HRR), examined via multiple linear regression controlling for exercise session type. Heart rate and BG were measured pre-exercise, immediately post-exercise, and 20 minutes post-exercise.","followUp":"Acute (single-session; measurements at pre-, immediately post-, and 20 minutes post-exercise). Inter-session washout duration not reported in abstract.","fundingSource":"Not reported in abstract"}
Key findings
RPE was significantly higher after resistance protocols STA and STB than after aerobic interval training AE (p 0.05). RPE was a statistically significant positive predictor of %HRR (β = 0.44, p = 0.044), whereas enjoyment was not (β = −0.06, p = 0.719). However, the overall regression model for %HRR did not reach statistical significance (adjusted R² = 0.119; F(4,31) = 2.183; p = 0.094), meaning the model as a whole failed to explain a statistically significant proportion of the variance in cardiovascular strain. The adjusted R² of 0.119 indicates that the full model accounted for approximately 11.9% of the variance in %HRR. NNT/NNH are not applicable to this regression-based association study. No adverse events (e.g., hypoglycemia episodes) were specifically reported in the abstract.
Practice implications
This exploratory study suggests that post-session RPE may carry a weak but statistically detectable signal related to relative cardiovascular strain (%HRR) in adults with T1DM exercising in gym settings, provided that exercise session type is taken into account. However, the overall regression model for %HRR was not statistically significant (p = 0.094), and the explained variance was modest (adjusted R² = 0.119), substantially limiting the strength of this inference. Critically, neither RPE nor enjoyment was associated with acute capillary blood glucose responses, establishing that these subjective tools cannot substitute for direct glycemic monitoring. The study did not establish that RPE can reliably replace objective cardiovascular monitoring tools; the association observed is exploratory and hypothesis-generating only. Findings apply specifically to young adults with T1DM (mean age ~30 years, near-target glycemic control with HbA1c ~7.7%), and generalizability to older patients, those with higher HbA1c, longer diabetes duration, cardiovascular complications, or those on beta-blockers or CGM is not established. The enjoyment measure was not independently associated with cardiovascular strain, though its potential relevance to adherence was not assessed in this study. Practice should not change on the basis of this single small exploratory trial. Only an abstract was available for review; full methodology, washout periods, session order randomization details, participant medications, insulin regimens, and pre-exercise glycemic management protocols could not be evaluated. __LIMITATIONS__ Very small sample size (n=12) with only 36 total session observations, severely limiting statistical power and precision of regression estimates.,Exploratory design with no a priori power calculation reported in abstract; risk of type I error inflation from multiple comparisons is not addressed.,The primary regression model for %HRR did not reach overall statistical significance (p = 0.094), yet the RPE beta coefficient is highlighted; this is a statistically borderline finding requiring cautious interpretation.,Crossover design without reported washout duration raises concerns about carryover effects on glycemia and cardiovascular parameters.,Post-session (global, single-timepoint) RPE may not capture within-session cardiovascular variation; this is a significant construct-validity limitation.,Capillary blood glucose, while clinically accessible, is a less precise glycemic surrogate than continuous glucose monitoring (CGM), which may have underestimated glycemic associations.,Insulin type, doses, and timing relative to exercise were not described in the abstract, which are critical confounders of glycemic response in T1DM.,Participant characteristics (young adults, near-target HbA1c ~7.7%) limit generalizability to older, less-controlled, or more comorbid T1DM populations.,Enjoyment was assessed using a visual analog scale, with its validity specifically in this T1DM exercise context not established in this study.,Funding source and potential conflicts of interest are not reported, precluding assessment of sponsorship bias.,Only abstract available; full methods, blinding procedures, and complete results cannot be critically appraised. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ This small (n=12) exploratory crossover trial found that post-session RPE was a marginally significant predictor of cardiovascular strain (%HRR) in adults with T1DM when exercise type was controlled, but the overall model was not statistically significant and explained only ~12% of variance. Crucially, neither RPE nor enjoyment predicted acute blood glucose responses, confirming that direct glycemic monitoring remains mandatory for exercise safety in T1DM. These hypothesis-generating findings require replication in larger, adequately powered trials before informing clinical or public health exercise prescribing guidance.