Lateral kinetic proficiency and asymmetry in backstroke start performed with horizontal and vertical handgrips.

We aimed to compare preferred, non-preferred, hand, foot kinetics and their asymmetry in two backstroke start variants. Complementarily, asymmetries were correlated to the resultant take-off velocity. Nine swimmers completed four 15 m backstroke starts with horizontal handgrips and four with vertical handgrips on an instrumented block (right, left hand, foot forces and impulse, normalised to swimmers' weight and time). We applied handedness and footedness questionnaires. Preferred hand and foot depicted a very and most likely moderate to large increase on horizontal force before hands-off (-0.51 ± 0.10; -0.47 ± 0.10; 0.87 ± 0.15; 0.90 ± 0.18 (N/N)) and a very and most likely large to very large increase on horizontal impulse (-0.28 ± 0.05; -0.26 ± 0.04; 0.50 ± 0.03; 0.51 ± 0.04 (N/N)*(s/s)) in both variants. Non-preferred hand and foot showed a very likely large to moderate increase (95% to 99%) on vertical and lateral impulse (0.30 ± 0.03; 0.31 ± 0.03; 0.07 ± 0.04; 0.05 ± 0.03 (N/N)*(s/s)) in both variants. The horizontal handgrip demonstrated likely moderate greater horizontal forces asymmetry on hands in the starting signal (-20.39 ± 7.16 (N/N), 92%), before hands-off (-71.46 ± 24.48 (N/N), 90%) and impulse asymmetry (-21.13 ± 5.80 (N/N), 94%). Asymmetry and resultant take-off velocity in both variants were strongly associated (r = -0.733 and -0.833 for feet horizontal impulse). Kinetics lateralisation was noticed in backstroke start and asymmetry hampers desirable performance.