Improved running economy following intensified training correlates with reduced ventilatory demands

Purpose: To compare the effects of three types of intensive run training on running economy (RE) during exhaustive running and to establish possible relationships with changes in ventilatory function and/or muscle fiber type distribution. Methods: Thirty-six male recreational runners were divided into three groups and assigned to either exhaustive distance training (DT), long- interval training (LIT), or short-interval training (SIT) three times 20-30 min · wk^-1 for 6 wk. V̇O(2max) and RE were measured during treadmill running before and after training. Muscle fiber type distribution of the vastus lateralis muscle was established from biopsy material. Results: V̇O(2max) (L · min^-1) increased by 5.9% (P < 0.0001), 6.0% (P < 0.0001), and 3.6% (P < 0.01) in DT, LIT, and SIT, respectively, and running speed at V̇O(2max) by 9% (P < 0.0001), 10% (P < 0.0001), and 4% (P < 0.05), respectively. Time-to-exhaustion at 87% of pretraining V̇O(2max) (mean 3.83 m · s^-1) increased by 94% in DT (P < 0.0001), 67% in LIT (P < 0.0001), and 65% in SIT (P < 0.001). Running economy improved by 3.1% in DT (P < 0.05), 3.0% in LIT (P < 0.01), and 0.9% in SIT (NS); pulmonary ventilation (V̇E) was on average 11 L · min^-1 lower following training (P < 0.0001). The individual decrements in V̇E correlated with improvements in RE (r = 0.77; P < 0.0001) and may account for 25-70% of the decrease in aerobic demand. Muscle fiber composition, and respiratory exchange ratio, stride length, and stride frequency during running were unaltered with training. Conclusion: Recreational runners can improve RE and aerobic run performance by exchanging parts of their conventional aerobic distance training with intensive distance or long-interval running, whereas short-interval running is less efficient. The improvement in RE may relate to reduced ventilatory demands. Muscle fiber type distribution was unaltered with training and showed no association with RE.