Aerobic training effects on glucose tolerance in prediabetic and normoglycemic humans

It is generally accepted that if prediabetic individuals adopt healthy lifestyle habits, the progression to type 2 diabetes mellitus can be prevented or delayed. However, the role of exercise training independent of other lifestyle factors has not been determined. Furthermore, patients with type 2 diabetes mellitus have been shown to experience greater training-induced changes in glucose and insulin metabolism compared with healthy subjects, but the adaptations of prediabetic individuals have not been adequately examined. We hypothesized that (i) prediabetic subjects would have greater endurance training-induced changes in plasma glucose and insulin responses to an oral glucose challenge compared with age- and body mass index-matched normoglycemic subjects and (ii) training would completely reverse the abnormal glucose metabolism of prediabetic subjects.

Plasma glucose and insulin responses to oral glucose tolerance tests (OGTTs) were examined in normoglycemic (n = 119) and prediabetic (n = 47) older men and women before and after a 6-month standardized endurance exercise training program.

Prediabetic subjects had greater glucose and insulin OGTT responses than normoglycemic subjects both before and after training (P < 0.05). Prediabetic subjects had greater training-induced changes in glucose and insulin areas under the glucose tolerance curve, as well as greater changes in glucose and insulin concentrations at several points of the OGTT. However, these changes did not eliminate the baseline differences in glucose tolerance between normoglycemic and prediabetic subjects. The between-group differences in changes in glucose and insulin variables were largely independent of changes in body weight or composition.

Our data indicate that prediabetes is associated with greater training-induced changes in glucose tolerance. However, 6 months of endurance training alone was not sufficient to completely reverse prediabetes.