Scapular kinematics during scaption in competitive swimmers.

This study aimed (1) to describe and compare scapular kinematics between three groups of swimmers of different levels and a group of non-swimmers, and (2) to assess whether swimming practice alters the asymmetries in scapular kinematics between the dominant and non-dominant sides, both during unilateral arm raising and lowering in the scapular plane. Scapular kinematics were assessed bilaterally during arm raising and lowering in the scapular plane using an electromagnetic system in 42 healthy males, which were split into four groups: control (n = 11), adolescent elite swimmers (n = 11), adult elite swimmers (n = 10), and club-level adult swimmers (n = 10). One-Way ANOVA SPM(t) on two repeated measures showed that the three groups of swimmers had more protracted shoulder between 30° and 90° of arm raising and lowering (p < .001). The three groups of swimmers presented no bilateral difference in scapular upward rotation, while the dominant scapula was more upwardly rotated than the non-dominant one between 74° and 104° of arm elevation in the control group (p < .001). The scapula of adult elite swimmers was more internally rotated between 67° and 116° of humeral elevation during arm raising, and between 81° and 54° during arm lowering in comparison to the other swimming and control groups (p ≤ .02), who presented similar scapular positioning in internal rotation. In conclusion, the findings of the study pointed out that swimming practice generated protracted shoulders and removed bilateral differences in scapular upward rotation during scaption, while accumulation of swimming practice at elite level enlarged scapular internal rotation.

Effect of object width on precision grip force and finger posture.

This study aimed to define the effect of object width on spontaneous grasp. Participants held objects of various masses (0.75 to 2.25 kg) and widths (3.5 to 9.5 cm) between thumb and index finger. Grip force, maximal grip force and corresponding finger postures were recorded using an embedded force sensor and an optoelectronic system, respectively. Results showed that index finger joints varied to accommodate the object width, whereas thumb posture remained constant across conditions. For a given object mass, grip force increased as a function of object width, although this result is not dictated by the laws of mechanics. Because maximal grip force also increased with object width, we hypothesise that participants maintain a constant ratio between grip force and their maximal grip force at each given width. Altogether we conclude that when the task consists in manipulating objects/tools, the optimal width is different than when maximal force exertions are required.