Postural constraints modify the organization of grasping movements

Reaching and grasping movements have been studied mostly in seated contexts. There are several tasks, however, that also impose speci®c postural constraints that may a€ect the organization of these movements. For example, in rock climbing, a successful grasp is conditional of an accurate static and dynamic postural control. The purpose of our study was to analyze if postural constraints, imposed by rock climbing, would mask speed±accuracy tradeo€ normally observed in pointing and grasping movements. More speci®cally, it was predicted that climbers, in order to reduce the duration of the presumably less stable tripodal phase, would shorten the duration of their reachings whatever the size of the hold. This time reduction would be incongruous with the longer end-phase control observed in seated conditions when precision requirements increase. Seven expert rock climbers performed grasping movements in two di€erent postural conditions (easy and complex) towards holds of various depths (0.8, 2 and 5 cm). As expected, the hold depth (precision requirements) did not in ̄uence the organization of movements until contact with the hold. More speci®cally, movement duration and velocity±time pro®les of the reachings were not a€ected by the accuracy requirements but were shortened by an increased postural diculty. The duration of Human Movement Science 18 (1999) 87±102 * Corresponding author. Address: UMR CNRS ``Mouvement & Perception'', Faculte des Sciences du Sport, Universite de la Mediterranee, CP 910, 163 avenue de Luminy, F-13288 Marseille Cedex 09 France. Tel.: +33 4 91 17 22 78; fax: +33 4 91 17 22 52; e-mail: [email protected] 0167-9457/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 9 4 5 7 ( 9 8 ) 0 0 0 3 6 0 force adjustments once a contact with the hold was established increased with a decreased target size and were not a€ected by the postural complexity. The present ®ndings suggest a hierarchical processing of postural constraints and precision constraints. Ó 1999 Elsevier Science B.V. All rights reserved. PsycINFO classi®cation: 2300; 2560