Physiological responses during intermittent running exercise differ between outdoor and treadmill running

The aim of this study was to compare the physiological responses during 15 min of intermittent running consisting of 30 s of high-intensity running exercise at maximal aerobic velocity (MAV) interspersed with 30 s of passive recovery (30-30) performed outdoor versus on a motorized treadmill. Fifteen collegiate physically active males (age, 22 +/- 1 years old; body mass, 66 +/- 7 kg; stature, 176 +/- 06 cm; weekly training volume, 5 +/- 2 h.week(-1)), performed the Fitness Intermittent Test 45-15 to determine maximal oxygen uptake ((V)over dotO(2max)) and MAV and then completed in random order 3 different training sessions consisting of a 30-s run/30-s rest on an outdoor athletic track (30-30 Track) at MAV; a 30-s run/30-s rest on a treadmill (30-30 Treadmill) at MAV; a 30-s run/30-s rest at MAV+15% (30-30 + 15% MAV Treadmill). Oxygen uptake ((V)over dotO(2)), time above 90%(V)over dotO(2max) (t90%(V)over dotO(2max)), and rating of perceived exertion (RPE) were measured during each training session. We observed a statistical significant underestimation of (V)over dotO(2) (53.1 +/- 5.4 mL.kg(-1).min(-1) vs 49.8 +/- 6.7 mL.kg(-1).min(-1), -6.3%, P = 0.012), t90%(V)over dotO(2max) (8.6% +/- 11.5% vs 38.7% +/- 32.5%, -77.8%, P = 0.008), RPE (11.4 +/- 1.4 vs 16.5 +/- 1.7, -31%, P < 0.0001) during the 30-30 Treadmill compared with the same training session performed on track. No statistical differences between 30-30 + 15 % MAV Treadmill and 30-30 Track were observed. The present study demonstrates that a 15% increase in running velocity during a high-intensity intermittent treadmill training session is the optimal solution to reach the same physiological responses than an outdoor training session.