Aging and diabetes are associated with decreased aerobic fitness, an independent predictor of mortality. Aerobic exercise is prescribed to improve aerobic fitness; however, middle-aged/older diabetic patients often suffer from mobility limitations which restrict walking. Non-weight-bearing/low-impact exercise is recommended but the optimal exercise prescription is uncertain. The goal of this randomized controlled trial was twofold: 1) to test if high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT), implemented on a non-weight-bearing all-extremity ergometer, are feasible, well-tolerated and safe in middle-aged/older adults with type 2 diabetes; and 2) to test whether all-extremity HIIT is more effective in improving aerobic fitness than MICT. A total of 58 sedentary individuals with type 2 diabetes (46 to 78 years; 63 ± 1) were randomized to all-extremity HIIT (n = 23), MICT (n = 19) or non-exercise control (CONT; n = 16). All-extremity HIIT and MICT, performed 4×/week for 8 weeks under supervision, resulted in no adverse events requiring hospitalization or medical treatment. Aerobic fitness (VO2peak) improved by 10% in HIIT and 8% in MICT and maximal exercise tolerance increased by 1.8 and 1.3 min, respectively (P ≤ 0.002 vs. baseline; P ≥ 0.9 for HIIT vs. MICT). In conclusion, all-extremity HIIT and MICT are feasible, well-tolerated and safe and result in similar improvements in aerobic fitness in middle-aged/older individuals with type 2 diabetes. These findings have important implications for exercise prescription for diabetic patients; they indicate that all-extremity exercise is a feasible alternative to weight-bearing exercise and those who are unable or unwilling to engage in HIIT may receive similar benefits from MICT.