Type I diabetes in rats causes structural, functional, and metabolic changes in skeletal muscle which impair contractile function and alter the balance between oxygen delivery (QO2) and oxygen consumption (VO2), as reflected by changes in interstitial PO2 (PiO2). Exercise improves the QO2 to VO2 balance and muscle function. The diaphragm is also affected by diabetes however the impact of exercise training on QO2 to VO2 balance and contractile function in diabetic rats is not well described. PURPOSE: To determine the effect of low intensity exercise training on PiO2 at the onset of contractions compared to sedentary diabetic rats, and to determine whether exercise training will attenuate the diabetes-induced deficits in contractile function. METHODS: Female Sprague-Dawley rats (n=33, 257 ± 2 g) were randomly assigned to control (C, 10), diabetic (D, 9), or exercise trained diabetic groups (DET, 14). Diabetes (streptozotocin, 50 mg/kg) was confirmed by urine glucose (>2000 mg/dl). After the onset of diabetes, the DET rats began an 8 wk low intensity treadmill training program. Rats were anesthetized (pentobarbital sodium, 50 mg/kg) and the abdominal surface of the costal diaphragm was exposed. The phrenic nerves were transected and electrodes were placed in the ventral and dorsal costal diaphragm to elicit contractions at 1 and 4 Hz (6V). PiO2 (phosphorescence quenching) and contractile function were measured simultaneously in the medial costal diaphragm. RESULTS: The D group had reduced body (C, 297 ± 9; D, 254 ± 9 g; P≤.05) and diaphragm weight (C, 148 ± 10; D, 113 ± 6 mg; P≤.05). Absolute twitch tension (g) and rate of tension change (dT/dt, g/s) were reduced in D compared to C (P≤0.05). Twitch tension normalized per gram of tissue (N/g) was not different in C and D, while dT/dt (N/g.s) was lower in the D group. Training did not improve body, diaphragm weight, (262 ± 6 g; 131 ± 8 mg) or contractile function. Baseline PiO2 (C, 62 ± 5; D, 61 ± 3; DET, 62 ± 5 mmHg) and mean response time (C, 19 ± 2; D, 16 ± 3; DET, 15 ± 2 s) were similar in the three groups. CONCLUSIONS: The decreases in body and diaphragm weights are characteristic of insulin-dependent diabetes. The D diaphragm produced less absolute tension, and training did not improve contractile function. PiO2 kinetics was similar in all three groups, suggesting that chronic diaphragm activity may be sufficient to maintain the normal QO2 to VO2 balance. (Supported by the Graduate Program Committee, KCOM-ATSU)