Impact of Different Ground Surfaces and Gradient Conditions on the Spatio-Temporal Characteristics of the Bobsleigh Push Phase

<title>Abstract</title> <p>Background This study investigated whether ground surface and slope influence the push technique in bobsleigh on land versus ice. Methods Spatio‑temporal parameters were collected from active national team bobsleigh athletes during land‑based and ice‑based pushing across the start, acceleration, and high‑velocity phases using a markerless three‑dimensional motion capture system. Bayesian independent‑samples t‑tests and paired‑samples t‑tests were used to compare parameters across positions and phases. Results The results showed that, in spatio‑temporal gait parameters, the main differences across the pilot, pusher, and brakeman were a higher step frequency and shorter stride duration, stance time, swing time, and flight time on ice, with the start phase showing the largest proportion of differences across all positions. For centre‑of‑mass (COM) motion, vertical COM displacement (both maximum and mean) was smaller on ice across all positions. Mean and maximum horizontal COM velocities were generally greater on ice than on land. Mean acceleration was greater on ice during the start and acceleration phases but smaller during the high‑velocity phase. Maximum acceleration was greater on ice during the start phase but generally smaller during the acceleration and high‑velocity phases. The unique ice surface altered the athletes' spatio‑temporal push performance, with the lower‑limb push pattern adapting accordingly on ice. Conclusions Land‑based training for the start and acceleration phases may carry a risk of negative transfer to ice pushing, while high‑velocity phase training on land may fail to provide the sport‑specific stimulus required for ice pushing. Based on these findings, it is recommended that land‑based push training emphasise horizontal force application, moderately increase load to enhance step frequency and propulsive force, incorporate overspeed running and downhill push drills to strengthen neuromuscular control during the high‑velocity phase, and include additional lower‑limb eccentric and plyometric training.</p>