Stroke volume does not plateau during graded exercise in elite male distance runners

Stroke volume (SV) responses during graded treadmill exercise were studied in 1) elite male distance runners (N=5), 2) male university distance runner s (N=10), and 3) male untrained university students (N=10). Methods: Cardia c output (Q)over dot and SV were determined by a modified acetylene rebreat hing procedure. Results: There were no differences in SV responses among th e three groups during the transition from rest to light exercise (P>0.05). However, the rates of change of SV during light to maximal exercise in untr ained subjects (slope = -0.1544 mL.beat(-1)) and university distance runner s (slope = 0.1041) did not change, whereas it dramatically increased (P<0.0 01) in elite distant runners (slope=0.6734). Moreover, the elite distance r unners showed a further slope increase in SV when heart rate was above 160 bpm, which resulted in an average maximal SV of 187<plus/minus>14 mL.beat(- 1) compared with 145 +/-8 and 128 +/- 14 mL.beat(-1) in the university runn ers and untrained students, respectively (P<0.001). Similarly, max (Q)over dot reached 33.8<plus/minus>2.3, 26.3 +/-1.7, and 21.3 +/-1.5 L.min(-1) in the three groups, respectively (P<0.001). On the other hand, there was a no nsignificant tendency for maximal arteriovenous oxygen content difference t o be lower in the elite athletes compared with the other groups. Conclusion : Results from university distance runners and untrained university student s support the classic observation that SV plateaus at about 40% of maximal oxygen consumption despite increasing intensity of exercise. In contrast, s troke volume in the elite athletes does not plateau but increases continuou sly with increasing intensity of exercise over the full range of the increm ental exercise test.