Joint action modulates motor system involvement during action observation in 3-year-olds

When we are engaged in a joint action, we need to integrate our partner’s actions with our own actions. Previous research has shown that in adults the involvement of one’s own motor system is enhanced during observation of an action partner as compared to during observation of an individual actor. The aim of this study was to investigate whether similar motor system involvement is present at early stages of joint action development and whether it is related to joint action performance. In an EEG experiment with 3-year-old children, we assessed the children’s brain activity and performance during a joint game with an adult experimenter. We used a simple button-pressing game in which the two players acted in turns. Power in the mu- and beta-frequency bands was compared when children were not actively moving but observing the experimenter’s actions when (1) they were engaged in the joint action game and (2) when they were not engaged. Enhanced motor involvement during action observation as indicated by attenuated sensorimotor mu- and beta-power was found when the 3-year-olds were engaged in the joint action. This enhanced motor activation during action observation was associated with better joint action performance. The findings suggest that already in early childhood the motor system is differentially activated during action observation depending on the involvement in a joint action. This motor system involvement might play an important role for children’s joint action performance

Grip strength measurements at two different wrist extension positions in chronic lateral epicondylitis-comparison of involved vs. uninvolved side in athletes and non athletes: a case-control study

Abstract Background Lateral epicondylitis is a common sports injury of the elbow caused due to altered muscle activation during repetitive wrist extension in many athletic and non-athletic endeavours. The amount of muscle activity and timing of contraction eventually is directly dependent upon joint position during the activity. The purpose of our study was to compare the grip strength in athletes with lateral epicondylalgia in two different wrist extension positions and compare them between involved and uninvolved sides of athletes and non-athletes. Methods An assessor-blinded case-control study of eight athletes and twenty-two non-athletes was done. The grip strength was measured using JAMAR® hand dynamometer in kilograms-force at 15 degrees (slightly extended) and 35 degrees (moderately extended) wrist extension positions (maintained by wrist splints) on both involved and uninvolved sides of athletes and non-athletes with unilateral lateral epicondylitis of atleast 3 months duration. Their pain was to be elicited with local tenderness and two of three tests being positive- Cozen's, Mill's manoeuvre, resisted middle finger extension tests. For comparisons of grip strength, Wilcoxon signed rank test was used for within-group comparison (between 15 and 35 degrees wrist extension positions) and Mann-Whitney U test was used for between-group (athletes vs. non-athletes) comparisons at 95% confidence interval and were done using SPSS 11.5 for Windows. Results Statistically significant greater grip strength was found in 15 degrees (27.75 ± 4.2 kgms in athletes; 16.45 ± 4.2 kgms in non-athletes) wrist extension than at 35 degrees (25.25 ± 3.53 kgm in athletes and 14.18 ± 3.53 kgm in non-athletes). The athletes had greater grip strength than non-athletes in each of test positions (11.3 kgm at 15 degrees and 11.07 kgm at 35 degrees) measured. There was also a significant difference between involved and uninvolved sides' grip strength at both wrist positions (4.44 ± .95 kgm at 15 degrees and 4.44 ± .86 kgm in 35 degrees) which was significant (p Conclusion The grip strength was greater in 15 degrees wrist extension position and this position could then be used in athletes with lateral epicondylalgia for grip strength assessment and designing wrist splint in this population.</p