Effect on training on myocardial oxygen supply/demand balance.

In five well-trained and five sedentary control subjects potential subendocardial blood supply was estimated from the diastolic pressure time index (DPTI) and myocardial oxygen demands from the tension time index (TII) during a progressive near-maximal treadmill test. DPTI/TTi was used to assess the effects of training on myocardial oxygen supply/demand balance. DPTI/TTI was significantly higher in trained subjects at rest and comparable workloads. At 6.4 km/hr, 18% grade (maximum for the controls), TTI was significantly lower (4300 +/- 76 vs 4495 +/- 99 mm Hg-sec/min) and DPTI significantly higher (2534 +/- 86 vs 2295 +/- 91 mm Hg-sec/min) in the trained subjects; DPTI/TTI was significantly higher (0.59 +/- .02 vs 0.50 vs .03). At near-maximal heart rates both groups achieved the same supply/demand balance (0.50); however, the trained subjects were working at higher workloads. We conclude that endurance conditioning increases work capacity, reduces myocardial O2 demands, increases potential O2 supply and improves the supply/demand balance at any given submaximal workload which reduces the risk of ischemia.