Biomechanical analysis of the “running” vs. “conventional” diagonal stride uphill techniques as performed by elite cross-country skiers

PURPOSE: This study aimed to compare biomechanical aspects of a novel “running” diagonal stride (DS(RUN)) with “conventional” diagonal stride (DS(CONV)) skiing techniques performed at high speed. METHODS: Ten elite Italian male junior cross-country skiers skied on a treadmill at 10 km/h and at a 10° incline utilizing both variants of the diagonal stride technique. The 3-dimensional kinematics of the body, poles, and roller skis; the force exerted through the poles and foot plantar surfaces; and the angular motion of the leg joints were determined. RESULTS: Compared to DS(CONV), DS(RUN) demonstrated shorter cycle times (1.05 ± 0.05 s vs. 0.75 ± 0.03 s (mean ± SD), p < 0.001) due to a shorter rolling phase (0.40 ± 0.04 s vs. 0.09 ± 0.04 s, p < 0.001); greater force applied perpendicularly to the roller skis when they had stopped rolling forward (413 ± 190 N vs. 890 ± 170 N, p < 0.001), with peak force being attained earlier; prolonged knee extension, with a greater range of motion during the roller ski-stop phase (28° ± 4° vs. 16° ± 3°, p = 0.00014); and more pronounced hip and knee flexion during most of the forward leg swing. The mechanical work performed against friction during rolling was significantly less with DS(RUN) than with DS(CONV) (0.04 ± 0.01 J/m/kg vs. 0.10 ± 0.02 J/m/kg, p < 0.001). CONCLUSION: Our findings demonstrate that DS(RUN) is characterize by more rapid propulsion, earlier leg extension, and a greater range of motion of knee joint extension than DS(CONV). Further investigations, preferably on snow, should reveal whether DS(RUN) results in higher acceleration and/or higher peak speed.