Run-walk marathon pacing: the energy cost of frequent walk breaks

Despite the widespread adoption of run-walk pacing in the marathon as an energy conserving strategy, the law of inertia stipulates that a runner must use more energy while frequently changing speeds than while running at a constant pace. This study examined the energy cost of the run-walk method. Thirty recreational runners (16 males and 14 females) each ran and walked at fixed, self-selected paces on a level treadmill under three conditions in a randomised and counterbalanced order: 6 min continuous running, 6 min continuous walking, and 12 min of alternating 2-min bouts of running and walking. Energy expenditure per kilometre and metres traversed per litre of absolute oxygen were assessed via indirect calorimetry. Ratings of perceived exertion were taken at 2-min intervals. Compared to continuous running, continuous walking required 8.90 fewer kilocalories per kilometres (P = 0.001). However, when alternating gaits, athletes required 3.98 kilocalories more to traverse one kilometre than when running continuously (P = 0.01). There was no difference in the distance traversed per litre of oxygen, but continuous running was faster. When runners in this study alternated gaits, they paid a 6% energy tax while benefiting from only a very slight reduction in average perceived exertion.