Lauenstein, S, Wehrlin, JP, and Marti, B. Differences in horizontal vs. uphill running performance in male and female Swiss world-class orienteers. J Strength Cond Res 27(11): 2952–2958, 2013—In orienteering, athletes must choose the quickest route from point to point, considering if they want to run a longer flat distance rather than a shorter distance with an incline to reach the next point. Our aim was therefore, to determine an athlete's equivalence factor (EF, ratio between horizontal and uphill running performance) enabling coaches to provide individual route choice recommendations during orienteering competition. Ten male and 8 female orienteers performed 1 horizontal (MSThorizontal; 0% incline) and 1 uphill (MSTuphill; 22% incline) maximal running stage test to exhaustion on a treadmill in randomized order. The EFs were calculated based on maximal speeds achieved in both tests (MRVhorizontal/uphill). In addition, V̇o2peak was measured. MRVhorizontal was 20.4 ± 0.6 and17.3 ± 0.8 km·h−1, and MRVuphill was 8.8 ± 0.7 and 7.2 ± 0.5 km·h−1 (men and women). The EF was 6.3 ± 0.7 and ranged between 5.2 and 7.4. Relative V̇o2peakuphill was 69.2 ± 5.7 and 59.1 ± 3.7 ml·kg−1·min−1, whereas V̇o2peakhorizontal was lower 66.4 ± 3.5 (p < 0.05) and 55.7 ± 3.1 ml·kg−1·min−1 (p < 0.01) than in V̇o2peakuphill. Relative V̇o2peakuphill correlated strongly with MRVuphill (men: r = 0.85, p < 0.01; women: r = 0.84, p < 0.01), whereas relative V̇o2peakhorizontal showed no strong correlation with MRVhorizontal (men: r = 0.51, p = 0.12; women: r = 0.41, p = 0.32). These data show that there are relevant differences in the relation between uphill and horizontal running capacity in these athletes. Tailoring the route selection to the athletes' advantage based on the relation between their uphill and horizontal running performance and individual EF may positively impact on overall performance in orienteering competition.