Metabolic Effects of Exercise Training Among Fitness-Nonresponsive Patients With Type 2 Diabetes: The HART-D Study

Abstract

Objective: To evaluate the impact of exercise training (ET) on metabolic parameters among participants with type 2 diabetes mellitus (T2DM) who do not improve their cardiorespiratory fitness (CRF) with training.

Research design and methods: We studied participants with T2DM participating in the Health Benefits of Aerobic and Resistance Training in Individuals With Type 2 Diabetes (HART-D) trial who were randomized to a control group or one of three supervised ET groups for 9 months. Fitness response to ET was defined as a change in measured peak absolute oxygen uptake (ΔVO(2peak), in liters per minute) from baseline to follow-up. ET participants were classified based on ΔVO(2peak) into fitness responders (ΔVO(2peak) ≥5%) and nonresponders (ΔVO(2peak) <5%), and changes in metabolic profiles were compared across control, fitness responder, and fitness nonresponder groups.

Results: A total of 202 participants (mean age 57.1 ± 7.9 years, 63% women) were included. Among the exercise groups (n = 161), there was substantial heterogeneity in ΔVO(2peak); 57% had some improvement in CRF (ΔVO(2peak) >0), with only 36.6% having a ≥5% increase in VO(2peak). Both fitness responders and nonresponders (respectively) had significant improvements in hemoglobin A1c and measures of adiposity (ΔHbA(1c): -0.26% [95% CI -0.5 to -0.01] and -0.26% [-0.45 to -0.08]; Δwaist circumference: -2.6 cm [-3.7 to -1.5] and -1.8 cm [-2.6 to -1.0]; Δbody fat: -1.07% [-1.5 to -0.62] and -0.75% [-1.09 to -0.41]). No significant differences were observed in the degree of change of these metabolic parameters between fitness responders and nonresponders. Control group participants had no significant changes in any of these metabolic parameters.

Conclusions: ET is associated with significant improvements in metabolic parameters irrespective of improvement in cardiorespiratory fitness.

Trial registration: ClinicalTrials.gov NCT00458133.

Figure 1

Patient selection for the current study. All control participants and exercise-training participants with available baseline and follow-up peak oxygen uptake (in liters per minute) data and >70% adherence to exercise prescription were included in the current study.

Figure 2

Monthly mean HbA_1c levels across the study groups. The data are represented as fitted means derived from a linear mixed model that included the covariables age, sex, race/ethnicity, diabetes duration, and baseline HbA_1c level. The error bars represent SEs. The group effect was significant for comparison of trends in monthly mean HbA_1c levels between control vs. responder (P = 0.014), as well as control vs. nonresponder groups (P = 0.0026), but not for responder vs. nonresponder (P = 0.254).

Figure 3

Comparisons of change in VO_2peak, HbA_1c level, and anthropometric measures from baseline to trial completion among control, fitness responder, and fitness nonresponder groups. The values are expressed as fitted means, and all are adjusted for baseline value, age, sex, duration of diabetes, and race/ethnicity. *P < 0.05 for change from baseline to end of trial within a particular study group. Circum., circumference.