University of Jyväskylä

About: University of Jyväskylä is a education organization based out in Jyvaskyla, Finland. It is known for research contribution in the topics: Population & Context (language use). The organization has 8066 authors who have published 25168 publications receiving 725033 citations. The organization is also known as: Jyväskylän yliopisto & Kasvatusopillinen korkeakoulu.

Neuromuscular function and mechanical efficiency of human leg extensor muscles during jumping exercises.

Abstract: The influence of prestretch amplitude on the mechanical efficiency was examined with 5 subjects, who performed 5 different series of vertical jumps, each of which differed with respect to the mechanics of the knee joint action during the prestretch (eccentric) phase of the contact on the floor. Electromyographic activity was recorded from the major extensor muscles during the entire work period of 1 min per series. In addition, expired air was collected during the test and recovery for determination of energy expenditure. Mechanical work was calculated from the vertical displacement of the body during the jumps. The results indicated that high net efficiency of 38.7% was observed in condition where amplitude of knee bending in eccentric phase was small. In large range motion the corresponding net efficiency was 30.1%. In jumps where no prestretching of extensor muscles occurred the net efficiency was 19.7%. The high efficiency of small amplitude jumps was characterized by low myoelectrical activity of the leg extensor muscles during the positive (concentric) work phase. In addition, the small amplitude jumps had shorter transition time in the stretch-shortening cycle, high average eccentric force and high stretching speed. Therefore the results suggest that the restitution of elastic energy, which was also related to the length change and stiffness of the muscles during stretch, plays an important role in regulating the mechanical efficiency of work.

Friendship moderates prospective associations between social isolation and adjustment problems in young children

Abstract: This longitudinal study investigated prospective links between social isolation and adjustment problems among 166 (77 girls, 89 boys) Finnish children ages 7 to 9 Peer nominations for social engagement and self-reports of internalizing and externalizing problems were collected in the spring of the 1st and 2nd grade Friendship moderated prospective associations between peer and adjustment variables Among friended children, there were no prospective associations between social isolation and either internalizing or externalizing problems Among unfriended children, initial social isolation was positively linked to subsequent increases in internalizing and externalizing problems, and initial internalizing and externalizing problems predicted subsequent increases in social isolation The findings suggest that friendship buffers against the adverse consequences associated with being isolated and presenting adjustment difficulties